Title Investigation of natural adhesive composed of tannin...

Title Investigation of natural adhesive composed of tannin andsucrose for particleboard( Dissertation_全文 )

Author(s) Zhao, Zhongyuan

Citation Kyoto University (京都大学)

Issue Date 2016-03-23

URL https://doi.org/10.14989/doctor.k19776

Right

Type Thesis or Dissertation

Textversion ETD

Kyoto University

Investigation of natural adhesive composed of tannin

and sucrose for particleboard

2016

Zhao Zhongyuan

Ⅰ

Contents

Chapter 1 General Introduction ----------------------------------------------- 1

1.1 Development of synthetic resins on the wood-based materials ------------------------1

1.2 Development of natural adhesives on wood-based materials----------------- 5

1.2.1 Tannin based adhesives-------------------------------------------------------- 5

1.2.2 Protein based adhesives ------------------------------------------------------- 9

1.2.3 Polysaccharide based adhesives ----------------------------------------------10

1.2.4 Lignin based adhesives ------------------------------------------------------ 12

1.3 Objectives----------------------------------------------------------------------- 13

1.4 References ---------------------------------------------------------------------- 14

Chapter 2-------------------------------------------------------------------------- 20

Effects of pre-drying treatment, mixture ratio and resin content on

physical properties of the particleboard bonded by tannin and sucrose

2.1 Introduction ---------------------------------------------------------------------20

2.2 Exploratory experiments---------------------------------------------------------21

2.2.1 Materials and Methods--------------------------------------------------------21

2.2.1.1Materials-------------------------------------------------------------------21

2.2.1.2 Manufacture of the particleboards-----------------------------------------22

2.2.1.3 Evaluation of board properties---------------------------------------------23

2.2.1.4 Fourier transform infrared spectroscopy (FT-IR) --------------------------24

2.2.1 Results and discussion--------------------------------------------------------24

Ⅱ

2.2.2.1 Effects of tannin/sucrose mixture ratio without drying treatment before

hot-pressing ---------------------------------------------------------------24

2.2.2.2 Effects of tannin/sucrose mixture ratio with drying treatment before

hot-pressing ---------------------------------------------------------------27

2.2.2.3 Effects of resin content ----------------------------------------------------32

2.2.2.4 Curing mechanism---------------------------------------------------------36

2.3 Summary-------------------------------------------------------------------------38

2.4 Reference------------------------------------------------------------------------38

Chapter 3---------------------------------------------------------------------------42

Effects of pressing temperature and time on particleboard properties,

and characterization of tannin-sucrose adhesive

3.1 Introduction----------------------------------------------------------------------42

3.2 Effects of hot pressing temperature and time on board properties ----------------43

3.2.1 Materials and Methods--------------------------------------------------------43

3.2.1.1 Materials------------------------------------------------------------------ 43

3.2.1.2 Manufacture of the particleboards ---------------------------------------- 43

3.2.1.3 Evaluation of board properties-------------------------------------------- 44

3.2.2 Results and discussion ------------------------------------------------------- 45

3.2.2.1 Effects of hot pressing temperature --------------------------------------- 45

3.2.2.2 Effects of hot pressing time------------------------------------------------51

3.3 Characterization of tannin and sucrose adhesive---------------------------------57

3.3.1 Materials and Methods------------------------------------------------------- 57

3.3.1.1 Materials------------------------------------------------------------------ 57

3.3.1.2 Thermal analysis---------------------------------------------------------- 57

Ⅲ

3.3.1.3 Insoluble matter and FT-IR ----------------------------------------------- 57

3.3.2 Results and Discussion------------------------------------------------------- 58

3.3.2.1 Thermal analysis ------------------------------------------------------- 58

3.3.2.2 Insoluble matter and FT-IR--------------------------------------------- 60

3.4 Summary------------------------------------------------------------------------ 64

3.5 Reference ----------------------------------------------------------------------- 64

Chapter 4-------------------------------------------------------------------------- 67

Effects of addition of citric acid on physical properties of particleboard

using tannin-sucrose adhesive

4.1 Introduction--------------------------------------------------------------------- 67

4.2 Effects of the addition of citric acid on thermal and chemical properties of

tannin-sucrose adhesive-------------------------------------------------------- 68


4.2.1.1 Materials------------------------------------------------------------------ 68

4.2.1.2 pH adjustment of adhesive solution by adding citric acid ----------------- 68


4.2.1.4 Insoluble matter and FT-IR ----------------------------------------------- 70

4.2.4 Results and discussion ------------------------------------------------------- 70


4.2.2.2 Insoluble matter----------------------------------------------------------- 73

4.2.2.3 FT-IR --------------------------------------------------------------------- 75

4.3 Effects of the addition of citric acid on the properties of the particleboard------- 78


Ⅳ

4.3.1.1 Materials------------------------------------------------------------------ 78

4.3.1.2 Manufacture of the particleboard ----------------------------------------- 78

4.3.1.3 Evaluation of the board properties ---------------------------------------- 79

4.3.2 Results and Discussion------------------------------------------------------- 80

4.3.2.1 Bending properties ----------------------------------------------------- 80

4.3.2.2 IB properties ----------------------------------------------------------- 82

4.3.2.3 Water resistance properties--------------------------------------------- 84

4.4 Summary ----------------------------------------------------------------------- 87

4.5 Reference ----------------------------------------------------------------------- 88

Conclusion ------------------------------------------------------------------------ 91

Acknowledgments --------------------------------------------------------------- 95

1

Chapter1

General Introduction

1.1 Development of synthetic resins on the wood-based

materials

Wood-based materials are generally used in housing construction and furniture

manufacture, and they are frequently present in living environments (Sellers, 2000;

Zheng et al., 2007). In the wood industry, wood adhesives are necessary to obtain

satisfactory physical properties of the wood-based materials. Usually, the synthetic

resins are used during the manufacture of the wood-based materials, such as

formaldehyde-based, polyvinyl acetate (PVAc), isocyanate based resin and so on.

These synthetic resins are mostly based on the chemical substances which derived

from fossil resources; however, it is believed that the use of the current wood

adhesives will be unavoidably restricted in the future due to decreases in the reserves

of fossil resources.

In addition, the most of the wood-based materials bonded by these synthetic

resins release amount of volatile organic compounds (VOCs) (Edmone, 2006; Kim et

al., 2006). Many wood-based materials were bonded by formaldehyde based resins,

which emitted formaldehyde vapor and lead to consumer dissatisfaction and health

related complaints. The emission of formaldehyde have caused various symptoms, the

most common of which are irritation in the eyes and the upper respiratory tract (Kim

and Kim, 2004, 2005; Edmone, 2006; Kelly et al., 1999). When the human body is

exposed to formaldehyde in high doses there is a risk of serious poisoning, and

prolonged exposure can lead to chronic toxicity and even cancer (IARC, 2006; Tang

et al., 2009).

2

Recently, as decreasing of the fossil resources and the increasing of

environmental awareness from public, the current development of the synthetic resin

focuses on the replacing the chemical substances derived from fossil resources with

non-fossil resources and reducing of harmful substances emission from the resins. The

development of synthetic resins on wood-based materials is reviewed as follows.

Urea-formaldehyde (UF) resin is still the most commonly wood adhesives in the

manufacture of wood-based materials; it is produced in amounts exceeding 5million

metric tons annually in the world (Maminski et al., 2007). UF resins have advantages

of high reactivity, fast curing, water solubility, and low price. However, the cured UF

resins have poor water resistance and emit formaldehyde, which have stimulated lots

of researches on the development of UF resins. The recent research about UF resin

focused on addition of the substances derived from non-fossil resources to improve

the mechanical properties of the wood-based materials and reducing the using of the

toxic substances derived from fossil resources. Boran et al. modified the

urea-formaldehyde resin by adding amine compounds, and manufactured the medium

density fiberboard (MDF). This research used the resin with 1:1.17 molar ratio of

formaldehyde to urea, and 2% ammonium chloride (NH4Cl) was added as a hardener.

Amine solution was added with different ratio, and the effects on the mechanical

properties of MDF were investigated. The results showed that MOR of the MDF

bonded by 16 wt% UF resin added 0.8 wt% ethylanmine, propylamine, methylamine,

and cyclopentylamine solution increased 2.08, 16.07, 7.04, and 7.85%, respectively. It

was also determined that the IB values of the MDF increased 40.91% by adding 0.8

wt% propylamine in 16 wt% UF resin. The water resistance of the MDF improved

slightly after adding amine compounds in the UF resin. In addition, the formaldehyde

emission of MDF panels decreased 16.5% by using a 16 wt% of UF resin and 0.8 wt%

of urea and ethylamine solution. (Boran et al., 2011). Younsei-Kordkheili et al.

incorporated the glyoxalated soda bagasse lignin into the urea formaldehyde resin to

improve the mechanical properties and water resistance of the plywood. The results

stated that when the plywood manufactured at 120℃ with 1MPa pressure for 10min

conditions, it is possible to partially (10-20 mass%) replace urea in the UF resin by

3

glyoxalated soda bagasse lignin without reducing the physical and mechanical

properties of the UF resin. The maximum shear strength was 1.78MPa at 65% wood

failure percentage, which obtained from the plywood bonded by UF resin mixed with

10 mass% glyoxalated lignin. The lowest water absorption was 28% obtained from

the plywood bonded by UF resin modified by 20 mass% glyoxalated lignin, which

lower than the plywood bonded by UF resin only (48%). Zhang et al. used the

nanocrystalline cellulose (NCC) modified the UF resin to increase the bonding

strength and reduce the formaldehyde emission. Due to the lack of compatibility with

UF resin, the surface of NCC was modified by 3-aminpropyltriethoxysilane (APTES)

and 3-methacryloxypropyltrimethoxysilane (MPS). As a result, the bonding strength

of the plywood bonded with UF resin with NCC modified by APTES showed a 23.6%

improvement, and the formaldehyde emission of the board boned by UF resin with

1.5% NCC decreased by 53.2% (Zhang et al., 2011).

Phenol-formaldehyde (PF) resin is widely used due to its high water resistance,

which makes it suitable for exterior applications (Danielson and Simonson, 1998;

Oilvares et al., 1988; Khan et al., 2004). However, the rapidly decreasing of fossil

resources will be a restriction on the applications of PF resin. Therefore, in the current

development of PF resin, phenol are usually be replaced by lignin or tannin based on

the structural similarity. Qiao et al. added the enzymatic hydrolysis lignin (EHL) to

replace phenol for preparing the PF resin. The results showed that the EHL could

substitute 60wt% phenol, and the adhesive strength did not deteriorate (Qiao et al.,

2015). Tabarsa et al. used tannin to modify the PF resin and manufacture the

particleboard. The optimal weight ratio of tannin was 10wt%, hot pressing

temperature is 180℃, and the hot pressing time is 12min. When the particleboard

manufactured at optimal conditions, the physical properties equal to or better than the

board bonded by the pure PF resin. Therefore, it is possible to replace parts of the

phenol in the PF resin by tannin (Tabarsa et al., 2011). Zhang et al. modified the

phenol-formaldehyde resin by adding lignocellulosic ethanol residue. The optimized

conditions for preparation lignocellulosic ethanol residue-phenol-formaldehyde resin

were phenol substitution at 50 wt%, F/P molar ratio at 3/0 and catalyst concentration

4

at 20%. The mechanical properties of the plywood bonded by the modified PF resin

satisfied the Chinese national standard (GB/T 9846.3-2004). Furthermore, the

formaldehyde emission of the plywood was 0.1 mg/L, which was lower than the

board manufactured by the pure PF resin (Zhang et al. 2013).

Melamine-urea-formaldehyde (MUF) resin is also widely used in the wood

industry. The benefit of the MUF resin is the acquired improved resistance to

humidity (Amirou et al., 2015). In case of the current research of MUF resin, the

researchers carried out the experiments on the addition of natural substance to replace

part of the chemical substances derived from fossil resources. Kunaver et al. studied

the possibility to partially replace MUF by liquefied wood to manufacture the wood

panels. The research concluded that, it would be possible to replace up to 50 wt% of

the MUF resin by liquefied wood to manufacture the particleboard (Kunaver et al.,

2010). Zhou et al. modified the MUF resin by Na+-montmorillonite (Na-MMT) and

organic modified-montmorillonite (O-MMT) nanoclay to improve the mechanical

properties of the particleboard. The results showed that, small percentages of

Na-MMT and O-MMT improved the internal bond strength of the particleboard both

under dry and wet conditions. The increase in water resistance of the MUF-bonded

panel was particularly noticeable. Furthermore, the addition of Na-MMT was shown

to increase considerably the resistance of the MUF resin to abrasion, which was

important from a wood surface finish point of view (Zhou et al. 2012).

Besides the formaldehyde-based resin, other kinds of the synthetic resins also

have been developed focused on the replacing the chemical substances derived from

fossil resources by natural substances. Fiorelli et al. develop the castor oil-based

polyurethane adhesive for the manufacture of particleboards. The research aimed at

demonstrating the feasibility of producing panels made of coconut fiber particles with

fiber lengths of 7mm and 2 different densities (0.8 and 1.0 g/cm3) and evaluating the

efficiency of producing boards with castor oil polyurethane adhesive compared with

panel made with UF resin. As a result, the bending property and water resistance of

the particleboard bonded by the castor oil-based polyurethane adhesive higher than

the board bonded by UF resin (Fiorlli et al., 1992). Kaboorani and Riedl added used

5

two types of the hydrophilic nano-clay mixed with PVAc at different ratios (1%, 2%

and 4%), and the results showed that the shear strength of wood joints increased in all

states by adding nano-clay to PVAc. In addition, the addition of nano-clay also

improved the thermal stability of PVAc resin (Kaboorani and Riedl, 2011).

The current development of synthetic resin in wood industry showed that, under

the pressure of decreasing of fossil resources and the requirement of human health,

the research about synthetic resin focus on the modification or partly replace by the

natural substances, which could reduce the utilization of fossil resources.

1.2 Development of natural adhesives on the wood-based

materials

Wood adhesives derived from natural substances have been a topic of

considerable interest for many years. This interest, already present in the 1940s,

became more intense with the first oil crisis in the early 1970s but subsided as the cost

of oil decreased (Pizzi, 2006). Recently, as the sustained decreasing of the fossil

resources and the increasing of environmental awareness from public, the researchers

turned to the development of natural adhesives, such as tannin-based, protein-based,

polysaccharide-based and lignin-based adhesives. However, the mechanical properties

and water resistance of the wood-based materials bonded by these natural substances

could not satisfied the requirement of the standards, therefore, in the current

development of the natural adhesives, some modification treatments or the addition of

the chemical substance were needed.

1.2.1 Tannin based adhesives

Tannin contains two kinds of the phenolic chemical compounds, hydrolyzable

tannin and condensed tannin. Hydrolyzable tannin is mixtures of simple phenols,

6

which with low nucleophilicity and low level of phenol substitution (Pizzi, 2006).

Therefore, the hydrolysable tannin is hardly to be used as adhesive.

Condensed tannin was 90% of the total world production of commercial tannins

(200 000 tons per year). Condensed tannin is wide distributed in nature, especially in

the wood and bark of various trees, such as Acacia (wattle or mimosa bark extract),

Schinopsis (quebracho wood extract), Tsuga (hemlock bark extract) and Rhus (sumach

extract) (Pizzi, 2006). Figure 1.1 shows the chemical structure of wattle tannin and

pine tannin. The wattle tannin composed of resorcinol A-rings and pine tannin

composed of phloroglucinol A-rings with catechol or pyrogallol B-rings (Kim and

Kim, 2003). The free C6 or C8 sites on the A-ring could react with active substance to

form the adhesive, due to their strong nucleophilicity.

Fig. 1.1 Chemical structures of wattle and pine tannins. (Pizzi, 1983)

Condensed tannins are well known to react with formaldehyde, and result in a

three-dimensional network polymer. Therefore, tannins could be used as a raw

material for adhesives. Condensed tannin-based wood adhesive has been used in

several countries for quite a long time (Trosa and Pizzi, 1997; Kim and Kim, 2003).

The research about tannin-based wood adhesives started at 1950’s, Dalton produced

the adhesives with the extracts from Acacia mearnsii, Callitris calcarata, Callitris

glauca, and Ecrebra, and the adhesives exhibited strong water-resistant. However, the

tannins extracted from Eucalyptus redunca and Eucalyptus consideniana could not

7

produce satisfactory adhesives, which is due to the difference of the major

components contained in these tannin extracts (Dalton, 1950 a). In the further work of

Dalton, he researched on viscosity control of tannin, and reported that tannin solutions

after heating with sulphites have low viscosities and are suitable for the preparation of

adhesives to be spread by mechanical rolls. The conditions for treatment with sulphite

were determined for extracts from Eucalyptus crebra and Pinus radiate and for

commercial wattle tannin extract. The sulphited tannin solutions, mixed with

paraformaldehyde and filler, were examined as adhesives for plywood (Dalton, 1950

b).The research of Plomley et al. showed that, a strong bond could be obtained with

pine veneers and mangrove tannin adhesive formulations containing 70% mangrove

tannin and 30% phenol-formaldehyde resin ( Plomely et al., 1957, 1964) . In the

further research of Plomely, the effect of soluble salts on gelation wattle tannin

adhesives was investigated. Various salts were shown to be capable of reducing

gelation times, and the bonding quality could be improved such as the addition of 5%

magnesium (Plomely, 1959). Based on the fundamental research, Plomley established

the basic principles for the use of wattle tannin as adhesives for reconstituted wood

products, and then, the subsequent production technology for wattle tannin based

adhesives was commercialized in the late 1960’s in Australia. Phenol-formaldehyde

fortified wattle tannin adhesives have been in continuous use for plywood since 1966

and for particleboard since 1968 in Australia (Plomley, 1966; Yazaki, 1998).

In addition, tannin also could be used as adhesives based on the

autocondensation reaction by the catalyst of lignocellulosic substrate or weak Lewis

acid such as alkali dissolved silica. Pizzi et al. manufactured the particleboard by the

autocondensation reaction of tannin, the results showed that more alkaline the tannin

extract solution the higher ceiling internal bond strength of the particleboard.

Furthermore, the differences of autocondensation reactions of four commercial

tannins are discussed. Pecan nut tannin and pine tannin need only lignocellulosic

indued autocondensation to give excellent interior grade particleboard (Pizzi et al.,

1995). Yano et al. produced plastic-like by using tannin and wood flour. The

moulded was manufactured by hot pressing the mixture of tannin and wood flour

8

( tannin:wood flour=1:1 w/w) at 190℃ at 100 MPa for 10min. The Plastic-like

moulded products having mechanical properties comparable to those of PF resin

moulded products and good water resistance were obtained without the addition of

any formaldehyde. The MOE and MOR of the moulded products were 9-10 GPa and

60-70 MPa, respectively (Yano, 2001).

In the recent research about tannin-based adhesives, due to the chemical

properties of tannin are very similar to phenol, tannin usually was used as substitute

of phenol in the phenol-formaldehyde resin (Tabarsa et al., 2011; Moubarik et al.,

2009), and this also could reduce the utilization of chemical substances derived from

fossil resources. Pizzi et al. have done a lot of work on the development of the

tannin-hexamethylenetetramine (hexamine) adhesive, which yield extremely low

formaldehyde emission in bonded wood-based materials (Pizzi et al., 1994; Pizzi et

al., 1997; Heinrich et al., 1996; Pizzi, 2006). When the particleboard bonded by

tannin-hexamine adhesives, both the mechanical properties and water resistance

increased compare with the particleboard bonded by PF resin. Valenzuela et al.

investigated the properties of the particleboard bonded by pine tannin with a small

percentage of pMDI. The results showed that, when the particleboard bonded by pine

tannin with 5% pMDI at 186℃ conditions, the MOR was 27.1MPa, IB strength was

0.92MPa, and 2h boil thickness swelling was 7%, all the physical properties satisfied

the standard ( EN 312 1995) (Valenzuela et al., 2012). Moubarik et al. developed the

corn flour-mimosa tannin-based adhesives to manufacture the particleboard. In this

research, the mimosa tannin solution in water was prepared at 45% concentration, and

its pH vas adjusted to 10 with NaOH (33% aqueous solution). Hexamine was used as

hardener with 5 % by the weight on tannin extract solids content. Particleboards were

manufactured at 195℃ for 2.6min. The results showed that, the MOR, MOE and IB

of the particleboard bonded by tannin-NaOH-hexamine adhesive are 18MPa, 2.84GPa

and 0.5 MPa, respectively. The mechanical properties are higher than the

particleboard bonded by UF under the same manufacture conditions (Moubarik et al.,

2013).

9

1.2.2 Protein based adhesives

Protein based adhesives derived from soy, blood and casein reached their peak

use in early 1960s. However, they were subsequently supplanted by synthetic resins

(Yang et al., 2006). An intense research stimulated by the sponsorship of the

American United Soybean Board has revived interest in protein adhesives. (Pizzi,

2006).

Soy protein based adhesive is the most representative protein based adhesive, it

is derived from soybean, which is abundant, inexpensive, and environmentally

friendly (Luo et al., 2015). Soy protein consists mainly of the acidic amino acids

(aspartic and glutamic acids) and their corresponding amides (asparagine and

glutamine), non-polar amino acids (lysine and arginine), uncharged polar amino acid

(lysine and arginine), uncharged polar amino acid (glycine) and approximately 1% of

cystin (Berk, 1992). These amino acid composition leads to the functional properties

of soy protein, which could be used as adhesives (Hettiarachchy et al., 1995).

However, the low bond strength and water resistance of the soy protein based

adhesives limit their application. Therefore, some modification treatments on the soy

protein are needed to obtain satisfactory bond performance. Hettiarachchy et al.

modified the soy protein by alkali and trypsin, and the effects of the bondability on

wood-based materials were investigated. The results showed that, modifying soy

protein by alkali (pH 10.0 at 50℃) and trypsin, enhanced adhesive strengths (730 and

743N, respectively) compared with unmodified soy protein (340N). In addition, the

water resistance of the modified soy protein also improved (Hettiarachchy et al.,

1995). Huang and Sun modified the soy protein by sodium dodecyl sulfate (SDS) and

sodium dodecylbenzene sulfonate (SDBS). The results showed that, 1% SDS

modification and 1% SDBS modification had the highest shear strength within each

wood type tested. Compared to the unmodified protein, the modified proteins also

exhibited higher shear strengths after incubation with two cycles of alternating

relative humidity and zero delamination rate and higher remaining shear strengths

10

after three cycles of water soaking and drying. These results indicated that, soy

proteins modified with SDS and SDBS have enhanced water resistance as well as

adhesive strength (Huang and Sun, 2000).

Recently, a new protein based adhesive which got the inspirations from mussel is

developed. Some marine organisms such as mussels, oysters, barnacles, and

sandcastle worms all use specialized adhesives in order to affix themselves to wet

surfaces. Most synthetic glues, by contrast, fail at wet bonding, perhaps the most well

studied bio-adhesive is that produced by marine mussels (Jenkins et al., 2013).

This adhesive is comprised of several proteins, each containing the

3,4-dihydroxyphenylalanine (DOPA) amino acid for cross-linking and cuing (Wilker,

2010). However, any given synthetic polymer mimic may be called upon to

reproduced the function of the six different proteins produced by mussels with a wide

range of molecular weights found for mussel adhesive proteins, it is difficult to

predict which single polymer chain length will yield the strongest adhesion.

According to the studied on the mussel adhesive mimics, Jenkins et al. researched the

adhesion system based on the poly[(3,4-dihydroxystyrene)-co-styrene]. The results

showed that, the strongest bonding for cross-linked polymers was observed at

molecular weights roughly corresponding to the middle range of protein molecular

weights used by mussels (Jenkins et al., 2013).

1.2.3 Polysaccharide based adhesives

Polysaccharides are polymeric carbohydrate molecules composed of long chains

of monosaccharide units bound together by glycosidic linkages. The polysaccharides

form a class of materials which have generally been underutilized in the biomaterials

field, and also be widely used in the natural adhesive research, such as starch-based

and chitosan based adhesives.

Starch is a renewable polymer derived from a commodity crop produced in

surplus, and the low cost and versatility for chemical manipulation makes it an

https://en.wikipedia.org/wiki/Polymeric

https://en.wikipedia.org/wiki/Carbohydrate

https://en.wikipedia.org/wiki/Monosaccharide

https://en.wikipedia.org/wiki/Glycosidic_bond

11

attractive material for use as a substitute for synthetic polymers (Imam et al., 2001).

Starch molecular chain is formed by the condensation of D-glucose monomer, with the

molecule weight of 106-10

7. Every glucose unit has a hydroxyl group on C2, C3, and

C6 each (Nie et al., 2013).

Imam et al. developed the starch-based wood adhesives by adding polyvinyl

alcohol and hexamethoxymethylmelamine. The results showed that, optimal viscosity

of the adhesive was obtained at 27% solid content, the optimal cure temperature and

time were 175℃ and 15min. In the shear strength experiments, wood samples

conditioned at 93% RH for two months exhibited >95% failure in wood but little in

adhesive joints (Imam et al., 2001). Nie et al. modified the corn starch by

starch-g-poly-vinyl acetate (Starch-g-PVAc) and epoxy. The results showed that,

addition of the poly vinyl acetate could increase the dry shear strength of starch

adhesive, and the addition of epoxy, which could easily crosslink with the oxidized

starch, is used as water-resistant component to improve the wet shear strength. When

the weight ratio between starch, starch-g-PVAc, and epoxy at 30:47:23, the highest

bond strength was obtained (Nie et al., 2013).

Chitosan is a linear polysaccharide composed of randomly distributedβ-(1,4)

linked D-glucosamine and N-acetyl-D-glucosamine residues (Serrero et al., 2011).

Chitosan has drawn a lot of attention, particularly in the biomedical field, because of

its biocompatibility, bioresorbability, and bioactivity as well as its bacteriostatic and

fungistatic properties (Suh and Matthew, 2000).

Patel et al. develop the chitosan based adhesive for wood-based materials by

adding glycerol and trisodium citrate dehydrate. The optimal bond strength was obtain

when the adhesive composed of 6% chitosan, 1% of glycerol, and 5 mmol/L of

trisodium citrate dehydrate. The best shear strength from this adhesive was found to

be equal to 6.0 MPa in dried conditions and 1.6 MPa in wet conditions ( specimens

immersed for 3h at 30℃ in water) (Patel et al., 2013). Umemura et al. manufactured

the plywood by chitosan and estimated the water resistance of chitosan on plywood

adherends after 24 h water soaking. The bond strength was 2.13 MPa for dried

specimens with 20% wood failure whereas the bonded resistance was 1.4 MPa for wet

12

specimens with 0% wood failure. The bond strength after water immersion treatment

was inferior to that of UF resin adhesive (2.1 MPa, 30% wood failure). However,

compared to natural adhesive (the casein and soybean glues), chitosan developed

excellent bonding properties (Umemura et al., 2003).

1.2.4 Lignin based adhesives

Lignin can be defined as an amorphous, polyphenolic material arising from the

copolymerization of three phenylpropanoid monomers, namely, p-coumaryl alcohol,

coniferyl, and sinapyl. These structures are linked by a multitude of interunit bonds

that include several types of ether and carbon-carbon linkages (Mansouri and Salvado,

2006).

The literature on the use of lignins to prepare wood adhesives is very extensive,

and most of the researchers focus on adding lignin into phenol-formaldehyde (PF)

resins, or urea-formaldehyde resins (Qiao et al., 2015; Zhang et al., 2013; Danielson

and Simonson, 1998). Mansouri et al. developed the lignin-based wood panel

adhesives without formaldehyde. The glyoxalation of lignin treatment were carried

out before the utilization of lignin, and then the glyoxalated lignin was thoroughly

mixed with a phenolic resin with a solid content around 60%, finally, the diisocyanate

raw polymeric MDI was added. Particleboards were manufactured bonded by this

glyoxalated lignin-phenolic resin-pMDI resin. The results of the evaluation of the

particleboard showed that, the IB strength enough to comfortable pass relevant

international standard specifications for exterior-grade panels. The adhesives also

showed sufficient reactivity to yield panels in press times comparable to those of

formaldehyde-based commercial adhesives (Mansouri et al., 2007). Kadla and Kubo

investigated the blend properties of lignin with four synthetic polymers, namely, poly

(ethylene oxide) (PEO), poly (vinyl alcohol) (PVA), poly (ethylene terephthalate)

(PET) and poly (propylene) (PP). The results of thermal analysis exhibited that, the

glass transition (Tg) of the lignin/PEO and lignin/PET blends showed a negative

13

deviation from a linear mixing rule, indicative of specific intermolecular interactions.

DRFT-IR analysis revealed the formation of a strong intermolecular hydrogen bond

between lignin and PEO (Kadla and Kubo,2003).

1.3 Objectives

As the decreasing of fossil resources and the toxic pollution around human

beings in interior space, it is necessary to develop the wood adhesive based on the

natural substances. According the study on the current development of wood

adhesives above, developing of the natural adhesive has been a trend all over the

world. However, both of synthetic resins and natural adhesives, the chemical

substances derived from fossil resources are need, which indicated that current

research could not solve the problem of the fossil resource shortage radically.

Therefore, it is needed and necessary to develop the natural adhesive without any

chemical substances which derived from fossil resources.

The main purpose of present study is to develop a natural adhesive composed

with natural substances only, and this adhesive could be used to manufacture the

particleboard with good physical properties. Wattle tannin has a poly-hydroxylphenol

structure, and the chemical properties close to the phenol. Sucrose is a common

disaccharide, and under the heating treatment 5-hydroxymhthylfurfural (5-HMF) was

generated, which has the active chemical properties. Therefore, tannin and sucrose

were chosen as the adhesive component. In the first place, the weight ratio of adhesive

compounds, mat moisture content, the effects of hot pressing temperature, hot

pressing time and resin content on the physical properties of the particleboard bonded

by tannin and sucrose, based on the results, the optimal manufacture conditions were

obtained. Second, the thermal analysis, insoluble matter and FT-IR analysis were

carried out to study the curing behavior of tannin and sucrose. Finally, based on the

results of reaction mechanism of tannin and sucrose, citric acid was added to reduce

the reaction temperature of tannin and sucrose.

14

This thesis is organized as follows:

In Chapter 1, the general introduction about the development and utilization of

synthetic resins and natural adhesive on the wood-based materials were studied.

In Chapter 2, the effects of the weight ratio between tannin and sucrose, mat

moisture content, and resin content on the physical properties of the particleboard

bonded by tannin and sucrose were investigated, and the optimal manufacture

conditions of these factors were decided. The reaction mechanism was studied by

FT-IR.

In Chapter 3, in the first place, the effects of the hot pressing temperature and hot

pressing time on the physical properties of the particleboard bonded by tannin and

sucrose were investigated, and the optimal hot pressing temperature and hot pressing

time were decided. In the second place, tannin and sucrose adhesive was characterized

by thermal analysis, insoluble matter and FT-IR analysis.

In Chapter 4, in the first place, the effects of the addition of citric acid on the

curing behavior of tannin and sucrose adhesive were investigated by thermal analysis,

insoluble matter and FT-IR analysis. In the second place, the effects of the addition of

citric acid on the hot pressing temperature of the particleboard bonded by tannin and

sucrose were investigate by the evaluation of the physical properties of the

particleboard.

1.4 Reference

Amirou, S., Zhang, J., Essawy, H., Pizzi, A., Zerizer, A., Li, J., Delmotte, L. (2015)

Utilization of hydrophilic/hydrophobic hyperbranched poly(amidoamine)s as

additives for melamine urea formaldehyde adhesives Polymer composites.124,

2255-2264.

Berk, Z. (1992) Technology of production of edible flours and protein products from

soybeans. FAO Agric. Serv. Bull. 97,1-10.

Boran, S., Usta, M., Gumuskaya, E. (2011) Decreasing formaldehyde emission from

medium density fiberboard panels produced by adding different amine

15

compounds to urea formaldehyde resin. Int J Adhes Adhes.31, 674-678.

Dalton, L.K. (1950 a) Tannin formaldehyde resins as adhesives for wood. Aust. J.

Appl. Sci. 1, 54-70.

Dalton, L.K. (1950 b) Resins from sulphited tannins as adhesives for wood. Aust. J.

Appl. Sci. 4, 136-154.

Danielson, B., Simonson, R. (1998) Kraft lignin in pheonol formaldehyde resin. Part 2

Evaluation of a industrial trial. J Adhes Sci Technol. 12(9) 941-946.

Edomone, R. (2006) Volatile organic compounds and formaldehyde in nature, wood

and wood based panels. Holz als Roh-und Werkstoff. 64, 144-149.

Heinrich, H., Pichelin, F., Pizzi, A. (1996) Lower temperature tannin/hexamine-onded

particleboard of improved performance. Roh-und Werkstoff. 54(4), 262.

Hettiarachchy, NS., Kalapathy, U., Myers, DJ. (1995) Alkali-modified soy protein

with improved adhesive and hydrophobic properties. J Am Oil Chem Soc. 72,

1461-1464.

Huang, W., Sun, X. (2000) Adhesive properties of soy proteins modified by sodium

dodecyl sulfate and sodium, dodecylbenzene sulfonate. J Am Oil Chem Soc. 77,

705-708.

IARC. (2006) Formaldehyde, 2-butoxyethanol and 1-tert-butoxypropan-2-0l.

Monographs on the evaluation of carcinogenic risk to humans, Vol, 88.

Imam, S., Gordon, S., Mao, L., Chen, L. (2001) Environmentally friendly wood

adhesive from a renewable plant polymer: characteristics and optimization.

Polym Degrad Stabil. 73, 529-533.

Kaboorani, A., Riedl, B. (2011) Effects of adding nano-clay on performance of

polyvinyl acetate (PVA) as a wood adhesive. Composites: Part A. 42, 1031-1039.

Kadla, J., Kubo, S. (2003) Lignin-based polymer blends: analysis of intermolecular

interactions in lignin-synthetic polymer blends. Composites: Part A. 35,

395-400.

Kelly, T., Smith, D., Satola, J. (1999) Emission rates of formaldehyde from materials

and consumer products found in California homes. Environ Sci Technol. 33, 81.

Khan, MA., Ashraf, SM., Malhotra, VP. (2004) Eucalyptus bark lignin substituted

phenol formaldehyde adhesives: a study on optimization of reaction parameters

and characterization. J Appl Polym Sci. 92, 3514-3523.

Kim, S., Kim, H. (2004) Evaluation of formaldehyde emission of pine and wattle

16

tannin-based adhesives by gas chromatography. Holz als Roh-und Werkstoff. 62,

101-106.

Kim, S., Kim, H. (2005) Comparison of standard methods and gas chromatography

method in determination of formaldehyde emission from MDF bonded with

formaldehyde-based resins. Bioresour Technol. 96, 1457.

Kim, S., Kim, J., Kim, H., Kim, S.(2006) Determination of formaldehyde and TVOC

emission factor from wood-based composites by small chamber method.

Polymer Testing. 25, 605-614.

Kim. S., Kim. H. (2003) Curing behavior and viscoelastic properties of pine and

wattle tannin-based adhesives stydied by dynamic mechanical thermal analysis

and FT-IR-ATR spectroscopy. J Adhesion Sci Technol, 17: 1369-1383.

Kohlmayr, M., Zuckerstatter, G., Kandelbauer, A. (2011) Modification of

melamine-formaldehyde resins by substances from renewable resources. J Appl

Polym Sci.124, 4416-4423.

Kunaver, M., Medved, S., Cuk, N. (2010) Application of liquefied wood as a new

particleboard adhesive system. Bioresource Technology. 101(4), 1361-1368.

Luo, J., Luo, JL., Yuan, C., Zhang, W., Li, J., Gao, Q., Chen, H. (2015) An

eco-friendly wood adhesive from soy protein and lignin: performance properties.

RSC Adv. 100849-100855

Maminski, ML., Pawlicki, J., Zado, A., Parzuchowski, P. (2007) Hyperbranched

polyether as a modifying agent for urea-formaldehyde resins—hardness and

strength control tool. Int J Polym Mater.56(4),1–8.

Mansouri, N., Pizzi, A., Salvado, J. (2007) Lignin-based wood panel adhesives

without formaldehyde. Holz Roh Werkst. 65, 65-70.

Mansouri, N., Salvado, J. (2006) Structural characterization of technical lignins for

the production of adhesives: application to lignosulfonate, kraft,

soda-anthraquinone, organosolv and ethanol process lignins. Ind Crop Prod. 24,

8-16.

Moubarik, A., Mansouri, H., Pizzi, A., Charrier, F., Allal, A., Charrier, B. (2013) Corn

flour mimosa tannin based adhesives without formaldehyde for interior

particleboard production. Wood Sci Technol. 47, 675-683.

Moubarik, A., Pizzi, A., Allal, A., Charrier, F., Charrier, B. (2009) Cornstarch and

tannin in phenol-formaldehyde resins for plywood production. Ind Crop Prod.

http://www.medsci.cn/sci/submit.do?id=89c43092


17

30, 188-193.

Nie,Y., Tian, X., Liu, Y., Wu, K., Wang, J. (2013) Research on starch-g-polyvinyl

acetate and epoxy resin-modified corn starch adhesive. Polym composite. 10,

77-87.

Oilvares, M., Guzman, JA., Natho, A., Saavedra, A., Santiago, C. (1988) Kraft lignin

utilization in adhesives. Wood Sci Technol. 22, 157-165.

Patel, A. (2015) Chitosan: emergence as potent candidate for green adhesive market.

Biochemical Engineering Journal. 102, 74-81.

Patel, A., Michaud, P., Petit, E., Baynast, H., Grediac, M., Mathias, J. (2013)

Development of a chitosan-based adhesive. Application to wood bonding. J Appl

Polym. 127(6), 5014-5021.

Ping, L., Pizzi, A., Guo, Z., Brosse, N. (2012) Condensed tannins from grape pomace:

Characterization by FTIR and MALDI TOF and production of environment

friendly wood adhesive. Ind Crop Prod. 40, 13-20.

Pizzi, A. (1983) Wood adhesives chemistry and technology. Aarcel Dekker, New York,

NY.

Pizzi, A. (2006) Recent developments in eco-efficient bio-based adhesives for wood

bonding: opportunities and issues. J Adhesion Sci Technol. 8 (20), 829-846.

Pizzi, A., Meikleham, N., Dombo, B., Roll, W. (1995) Autocondensation-based,

zero-emission, tannin-adhesives. Holz als h-und Werkstoff. 53, 201-204.

Pizzi, A., Stracke, P., Trosa, A. (1997) Industrial tannin/hexamine low-emission

exterior particleboards. Roh-und Werkstoff. 55(2), 168.

Pizzi, A., Valenezuela, J., Westermeyer, C. (1994) Low formaldehyde emission, fast

pressing, pine an pecan tannin adhesives for exterior particleboard. Holz als

Roh-und Werkstoff. 52(5) 311-315.

Plomely, K.F.(1966) Tannin-formaldehyde adhesives for wood. Division of Forest

Products Technological Paper. 39, 1-16.

Plomely, K.F., Gottstein, J.W., Hillis, W.E. (1957) Tannin formaldehyde adhesives.

Csiro for. Prod. Newslett. 234, 6-8.

Plomely, K.F., Gottstein, J.W., Hillis, W.E. (1964) Tannin-formaldehyde adhesives for

wood. 1. Mangrove tannin adhesives. Aust. J. Appl. Sci. 15, 171-182.

Qiao, W., Li, S., Guo, G., Han, S., Ren, S., Ma, Y. (2015) Synthesis and

characterization of phenol-formaldehyde resin using enzymatic hydrolysis lignin.


18

J Ind Eng Chem. 21, 1417-1422.

Sellers, T. (2001) Wood adhesive innovations and applications in North American.

Forest Prod J. 51(6),12-22.

Serrero, A., Trombotto, S., Bayon, Y., Gravagna, P., Montanari, S., David, L. (2011)

Polysaccharide-based adhesive for biomedical applications: correlation between

rheological behavior and adhesion. J Am Chem Soc. 12, 1556-1566.

Suh, J., Matthew, H. (2000) Application of chitosan-based polysaccharide

biomaterials in cartilage tissue engineering: a review. Biomaterials. 20,

2589-2598.

Tabarsa, T., Jahanshahi, S., Ashori, Alireza. (2011) Mechanical and physical

properties of wheat straw boards bonded with a tannin modified

phenol-formaldehyde adhesive. Composites: Part B. 42, 176-180.

Tang, X., Bai, Y., Duong, A., Smith, MT., Li L., Zhang, L. (2009) Formadehyde in

Chian: production, consumption, exposure levels, and health effects. Environ Int.

35(8), 1210-1224.

Trosa. A., Pizzi. A.(1997) Stability and performance of tannin-accelerated PF resins

for plywood. J Holz Roh- Werkst, 55:306.

Umemura, K., Inoue, A., Kawai, S. (2003) Development of new natural

polymer-based wood adhesive 1: dry bond strength and water resistance of

konjac glucomannan, chitosan, and their composites. J Wood Sci. 49, 221-226.

Valenzuela, J., Leyser, E., Pizzi, A., Westermeyer, C., Gorrini, B.(2012) Industrial

production of pine tannin-bonded particleboard and MDF. Eur J Wood Prod. 70,

735-740.

Wilker, J.J. (2010) Marine bioinorganic materials:mussels pumping iron. Curr Opin

Chem Biol.14(2), 276-283.

Yang, I., Kuo, M., Myers, D., Pu, A. Comparison of protein-based adhesive resins for

wood composites. J Wood Sci. 52, 503-508.

Yano, H., Collins, P.J., Yazaki, Y. (2001) Plastic-like moulded products made from

renewable forest resources. J. Materials Sci. 36, 1-4.

Yazaki, Y. (1998) Research on utilization of Acacia bark in Australia. Proceedings of

the ACACIA’98 Conference. 16-18, 1-19.

Younesi-Kordkheili, H., Kazemi-Najafi, S., Eshkiki, R., Pizzi, A. (2015) Improving

urea formaldehyde resin properties by glyoxalated soda bagasse lignin. J. Wood

19

Prod. 73, 77-85.

Zhang, H., Zhang, J., Song, S., Wu, G., Pu, J. (2011) Modified nanocrystalline

cellulose from two kinds of modifiers used for improving formaldehyde emission

and bonding strength of urea-formaldehyde resin adhesive. Bioresources. 6(4),

4430-4438.

Zhang, W., Ma, Y., Xu, Y., Wang, C., Chu, F. (2013) Lignocellulosic ethanol

residue-based lignin-phenol-formaldehyde resin adhesive. Int J Adhes Adhes. 40,

11-18.

Zheng, Y., Pan, ZL., Zhang, RH., Jenkins, BM., Blunk, S. (2007) Particleboard quality

characteristics of saline jose tall wheatgrass and chemical treatment effect.

Bioresour Technol. 98, 1304-1310.

Zhou, X., Pizzi, A., Du, G . (2012) The effect of nanoclay on melamine urea

formaldehyde wood adhesives. J Adhes Sci Technol. 26, 1341-1348.

20

Chapter2

Effects of pre-drying treatment, mixture ratio and resin

content on physical properties of the particleboard bonded

by tannin and sucrose

2.1 Introduction

In the woo industry, adhesives play an important role. At present, resin adhesives

derived from fossil resources, such as formaldehyde-based resins, vinyl acetate resins

and isocyanate-based resins are widely used (Li et al., 2004). However, as the

availability of the fossil resources continues to decrease, it will become necessary to

develop wood adhesives based on alternative, renewable resources. Some studies have

reported research about wood adhesives made by bio-resources, such as protein-based,

tannin-based and lignin-based natural adhesives (Pizzi, 2006; Yonghwa et al., 2011;

Lei and Pizzi, 2008; Trosa and Pizzi, 1997). Due to its polyphenol chemical

construction, tannin has been seen as a replacement for phenol in

phenol-formaldehyde resin (PF). Generally, formaldehyde, hexamine and pMDI are

used in tannin-based adhesives to obtain satisfactory bond performance (Valenzuela et

al., 2012; Pichelin et al., 2006), but these chemical substances can be harmful to

human health. Thus, both the perspective of environmental sustainability and the

consumer demand for nonhazardous materials contribute to the imperative for

alternative materials manufacturing processes.

Recently, it was found that the mixture of tannin and sucrose had adhesiveness

for wood (Umemura, 2013). However, the detailed manufacture conditions and

bonding properties for wood-based materials bonded with tannin-sucrose resin were

not investigated. Wattle tannin has a poly-hydroxylphenol structure and a molecular

21

weight ranging from 500 to 10000 Da, and it is widely used in the tanning and

adhesive industries (Yao, 2006), and has also been researched in the context of wine

manufacture (Mcrae et al., 2013) and medicine (Piwowarski et al., 2011). Sucrose is a

common disaccharide used as a condiment and food ingredient, whose chemical

characteristics have been well researched, and under the heating treatment

5-hydroxymhthylfurfural (5-HMF) was generated (Jeong et al., 2013; Lee et al.,

2011). The adhesive with phenol and 5-HMF was already researched (Koch and Pein,

1985). In addition, the reactivity of the reaction between tannin and formaldehyde was

10 to 50 times higher rate of the reaction between phenol and formaldehyde (Kim and

Kim, 2003), therefore, tannin was considered as a suited substitute of phenol. Baseded

on chemical properties of tannin and sucrose, there is a possibility to use tannin and

sucrose as an adhesive for wood-based materials. In this chapter, tannin and sucrose

were used as an adhesive component for particleboard, and fundamental manufacture

conditions were studied. The effects of the different mixture ratios of tannin and

sucrose, drying treatment after spraying and different resin contents on the physical

properties of the resulting particleboard were investigated. The reaction mechanism

between tannin and sucrose was studied by Fourier transform infrared spectroscopy

(FT-IR).

2.2 Exploratory experiments

2.2.1 Materials and Methods

2.2.1.1 Materials

Recycled wood particles consisting mainly of softwood were obtained from a

particleboard company in Japan. The wood particles were screened by a sieving

machine, and particles screened between the aperture sizes of 5.9 and 0.9 mm were

used as the starting materials. The particles (original moisture content, 3‒4%) were

dried in an oen at 80°C for 12 h. Wattle tannin (commercial name: tannic acid ME)

was purchased from Fuji Chemical Industry Co. (Wakayama, Japan), and the tannin

22

content was 88.1%, which measured by methanol method (Soto et al. 2001). Sucrose

(guaranteed reagent) was purchased from Nacalai Tesque, Inc. (Kyoto,Japan), and

used without further purification. Both tannin and sucrose were dried in a vacuum

oven at 60°C for 15 h.

2.2.1.2 Manufacture of the particleboards

Tannin and sucrose were dissolved in distilled water at various proportions, and

the concentration of the solution was adjusted to 40 wt%. The viscosity and pH of the

solution were measured by a rotational viscometer (Viscolead One, Fungilab S.A.,

Barcelona, Spain) at 20 °C and a pH meter (D-51, Horiba Scientific, Kyoto, Japan),

respectively, and the results are shown in Table 2.1.

Table 2.1 Viscosity and pH of mixture solutions of tannin and sucrose

Mixture ratio of

tannin and sucrose

(wt%)

Concentration (wt%) Viscosity at 20 °C

(mPa·s) pH

100:0 265.9 4.51

75:25 177.4 4.62

50:50 40 78.0 4.71

25:75 51.3 4.76

0:100 35.7 5.52

As Table 2.2 shows, we tested tannin/sucrose mixture ratios of 100/0, 75/25,

50/50, 25/75, and 0/100. The solution was used as an adhesive and sprayed onto

particles in a blender at 20wt% resin content based on the weight of the oven-dried

particles. In Group 1, the sprayed particles were not dried in an oven, while Group 2

sprayed particles were dried at 80°C for 12h. In the case of Group 3, the

tannin/sucrose ratio was 25/75, and resin contents of 10, 20, 30 and 40wt% (based on

the weight of the oven-dried particles) were tested, and then the sprayed particles

were dried at 80°C for 12h. The mat moisture content of Group 1 was 38‒42%, while

that of Groups 2 and 3 was 3‒6%. The particles were mat-formed using a forming box

23

of 300×300 mm, after that, the mat was hot-pressed at 200°C for 10 min with a

distance bar of 9 mm to control the thickness. The size of the manufactured board was

300 × 300 × 9 mm, and the target density was 0.8 g/cm3. For comparison,

particleboard bonded with pMDI (polymeric 4,4-diphenyl methane diisocyanate) was

manufactured at a resin content of 8 wt%, and the press method and target density

were the same as those described above.

Table 2.2 Manufacture condition of particleboards

Groups

Mixture

ratio of

tannin

and

sucrose

(wt%)

Resin

content

(wt%)

Pressing

temperatur

e(°C)

Pressing

time(min)

Target

density

(g/cm3)

Drying

treatment

after

spraying

100:0

25:75

Group1 50:50 20 200 10 0.8 No

75:25

0:100

100:0

25:75

Group2 50:50 20 200 10 0.8 Yes

75:25

0:100

10

15

Group3 25:75 20 200 10 0.8 Yes

30

40

2.2.1.3 Evaluation of board properties

The boards obtained were conditioned for 1 week at 20 °C and 60% relative

humidity (RH), and then evaluated according to the Japanese Industrial Standard for

particleboard (JIS A 5908, 2003). The static 3-point bending test was carried out on a

200 mm × 30 mm × 9 mm specimen from each board, and the effective span and

24

loading speed were 150 mm and 10 mm/min, respectively. The modulus of rupture

(MOR) and the modulus of elasticity (MOE) were calculated from the bending test.

The internal bond strength (IB) test was performed on a 50 mm×50 mm specimen

with a loading speed of 2 mm/min, and thickness swelling (TS) after water immersion

for 24 h at 20 °C was measured in specimens of the same size. Following the TS test,

thickness changes and weight changes under a cyclic accelerated aging treatment

(drying at 105°C for 10 h, warm water immersion at 70°C for 24 h, drying at 105°C

for 10 h, boiling water immersion for 4 h, and drying at 105°C for 10 h) were

measured. Each experiment was performed five times, and the average values and

standard deviations were calculated. Statistical significance was considered for p

values < 0.05.

2.2.1.4 Fourier transform infrared spectroscopy (FT-IR)

Tannin and sucrose were dissolved in distilled water with the ratio of tannin to

sucrose at 25/75, and the concentration of the solution was adjusted to 40 wt%. The

adhesive solution was heated at 80°C for 12h to remove water. The adhesive was

pulverized into less than 250-μm mesh size, after that, one part of the powder was

heat at 200°C for 10min, another part of the powder was reserved as the comparation.

Both the two parts of the powder were dried in a vacuum oven at 60°C for 15 h. Two

infrared spectra were obtained with a Fourier transform infrared spectrophotometer

(FT/IR-4200, JAS-CO Corporation) using the KBr disk method and were recorded

with an average of 32 scans at a resolution of 4 cm-1

.

2.2.2 Results and discussion

2.2.2.1 Effects of tannin/sucrose mixture ratio without drying treatment

before hot-pressing

The particleboards were manufactured with various mixture ratios of tannin and

25

sucrose without drying treatment before hot-pressing. Figure 2.1 shows the bending

properties of the particleboards. The bending properties were promoted as the sucrose

ratio increasing. For MOR values, the board bonded with tannin only (100/0) was 8

MPa. At a tannin/sucrose ratio of 25/75, the MOR increased to 11.9 MPa, an increase

of 49% compared to tannin only. For MOE values, the board bonded with tannin only

(100/0) was 2.3 GPa. At a tannin/sucrose ratio of 25/75, the value increased to 3.0

GPa, an increase of 43%.

Fig. 2.1 Effect of tannin/sucrose ratio on bending properties without drying treatment

before hot-pressing. Error bars indicate standard deviations.

Figure 2.2 shows the IB strength of the particleboard. The value decreased

slightly as increasing of sucrose ratio. When the particleboard was bonded with tannin

only, the IB value was 0.3 MPa, equivalent to the minimum 18 type of JIS A 5908

standard. At tannin/sucrose ratios of 75/25, 50/50 and 25/75 conditions, the IB

strength were 0.24 MPa, 0.3 MPa and 0.1 MPa, respectively, the addition of sucrose

ratio decreased the IB strength. Figures 2.1 and 2.2 demonstrate how the bending

0

1

2

3

4

5

6

0

5

10

15

20

25

30

100/0 75/25 50/50 25/75 0/100M

OE

(G

Pa

)

MO

R (

MP

a)

Tannin/Sucrose (wt%)

MOR

MOE

26

properties and IB strength had opposite trends. This is perhaps because during the

hot-pressing process, water moved from the surface to the core and then steam moved

out from the core of the board; this movement took out the heat, and so affected the

bonding properties. When the ratio of tannin decreased, the effect of tannin on the

bonding property was reduced, which lead to the reduction of IB strength. Bending

properties are more affected by the surface of the boards, and because the temperature

on the surface was high during the hot-pressing process, more sucrose led to better

mechanical properties. Overall, both bending properties and IB strength showed

mediocre properties of the particleboard without drying treatment before hot pressing.

This indicated that when the moisture content was high, irreversible thickness

swelling was caused when the particles’ recovery forces exceeded the restraining

action of the adhesive. The internal failures of the particleboard were attributed to

stress release and signified adhesive damage among the particles. This is because

swelling stress and particle deterioration accompanied the moisture change (Lin et al.,

2002).

Fig. 2.2 Effect of tannin/sucrose ratio on IB strength without drying treatment before

hot-pressing. Error bars indicate standard deviations.

0.0

0.5

1.0

1.5

2.0

2.5

100/0 75/25 50/50 25/75 0/100

IB (

MP

a)


27

Figure 2.3 shows the results for the TS of the boards. The value was fairly

constant regardless of the sucrose ratio. At a tannin/sucrose ratio of 25/75, the TS was

43%, far exceeding the JIS A 5908 standard upper limit of 12%. The boards bonded

with tannin only had a TS value of 44%; ANOVA analysis showed no significant

difference in water resistance between boards with tannin/sucrose ratios of 100/0 and

25/75. Additionally, all the samples were very weak after the immersion treatment

(20 °C for 24 h), such that cyclic accelerated aging treatment could not be carried out.

Consequently, increasing the sucrose ratio did not obviously change the properties of

the particleboards. Former research has indicated that heat treatment before

hot-pressing is the one of the most effective ways to increase water resistance of wood

and wood-based composites (Sar et al., 2013). Thus, investigations of the effects of

drying treatment before hot pressing on the properties of the particleboard bonded by

tannin and sucrose were investigated.

Fig. 2.3 Effect of tannin/sucrose ratio on TS without drying treatment before hot

pressing. Error bars indicate standard deviations.

2.2.2.2 Effects of tannin/sucrose ratio with drying treatment before

0

20

40

60

80

100

100/0 75/25 50/50 25/75 0/100

TS

(%

)


28

hot-pressing

Particleboards were manufactured at various mixture ratios of tannin and sucrose

by a drying treatment before hot-pressing. Figure 2.4 shows the bending properties of

the resultant particleboards. The bending properties increased obviously as the

sucrose ratio increased. The maximum values of MOR was 18.7 MPa, when the ratio

of tannin to sucrose at 25/75. The MOR was 2.4 MPa when the particleboard was

bonded with tannin only, and 15.2 MPa with sucrose only. The maximum value of the

MOE was 4.1 GPa at tannin-to-sucrose ratios of 25/75 and 0/100. By contrast, the

MOE was 0.7 GPa for tannin only. The result of the bending test indicated that

sucrose offered improved bond performance in the adhesion system. According to the

type 18 of JIS A 5908 standard, which is for construction use, an MOR of 18 MPa and

MOE of 3 GPa or more is required. We found that the bending properties of board

using a tannin/sucrose ratio of 25/75 were comparable to the standard. The

improvements in MOR and MOE in Group 2 samples compared to Group 1 were 57%

and 28%, respectively. These results confirmed that low moisture content leads to

improved bending properties of particleboard bonded with tannin and sucrose.

0

1

2

3

4

5

6

0

5

10

15

20

25

30

100/0 75/25 50/50 25/75 0/100

MO

E (

GP

a)

MO

R (

MP

a)


MOR

MOE

29

Fig. 2.4 Effect of tannin/sucrose ratio on bending properties with drying treatment


Figure 2.5 shows the IB strength of the particleboards bonded with tannin and

sucrose. The value increased with increasing sucrose ratios, and a value of 1.0 MPa

was recorded at the tannin/sucrose ratio of 25/75. This was 20 times higher than that

using only tannin. The addition of sucrose brought marked improvement in the bond

strength between particles; moreover, the strength of the board bonded at a

tannin/sucrose ratio of 25/75 greatly exceeded the type 18 of JIS A 5908 minimum

requirement of 0.3 MPa. Compared with the best value obtained from Group 1 (0.3

MPa), the IB strength was improved 206%. Judging from the results summarized in

Figs. 2.1, 2.2, 2.4 and 2.5, the mechanical properties were greatly affected both by the

tannin/sucrose ratio and by the moisture content before hot-pressing.

Fig. 2.5 Effect of tannin/sucrose ratio on IB strength with drying treatment before

hot-pressing. Error bars indicate standard deviations.

Figure 2.6 shows the thickness change of cyclic accelerated aging treatment. As

0.0

0.5

1.0

1.5

2.0

2.5

100/0 75/25 50/50 25/75 0/100

IB(M

Pa

)

Tannin/Sucrose(wt%)

30

the sucrose ratio increased, the TS value decreased (except the sucrose only condition).

In the case of a tannin/sucrose ratio of 25/75, the value of TS was 28%. When the

boards were bonded with tannin only, immersion in water led to decomposition while

the TS of boards bonded with sucrose only was 49%, indicating that the dimensional

stability of the boards bonded with tannin or sucrose only were extremely low. This

result indicated that tannin kept it hydroscopicity after hot-pressing at 200°C for 10

min. The subsequent cyclic accelerated aging treatment brought a stepwise increase in

the thickness of specimens. In the second immersion treatment (immersion at 70°C

for 24 h), the range of thickness increased from 46 to 87%, and in the third immersion

treatment (immersion at 100°C for 4 h), the thickness range increased from 51 to

103%. When the board was bonded with tannin only, the specimens decomposed after

the first immersion treatment at 20°C for 24 h. As the sucrose ratio increased, the

thickness change of the cyclic accelerated aging treatment was restrained. The results

of thickness change in immersion treatments indicate that higher sucrose content

possibly promoted the adhesiveness, and thereby markedly improved water resistance

properties.

31

Fig. 2.6 Thickness change in a cyclic accelerated aging treatment with drying

treatment before hot-pressing. Error bars indicate standard deviations.

Figure 2.7 shows the weight changes during the cyclic accelerated aging

treatment. In the first immersion treatment (immersion at 20°C for 24h), the weight

increase range decreased as the sucrose ratio increased. The lowest weight increase

value was 60% at a tannin/sucrose ratio of 25/75. The boards bonded with tannin only

decomposed, and the value of board bonded with sucrose only was 90%. In the first

drying treatment (drying at 105°C for 10 h), boards with higher sucrose ratios lost less

water weight. The lowest decrease value was 3% for the boards bonded with the

tannin/sucrose ratio of 25/75. The weight decrease range on other tannin/sucrose

ratios were from 4% to 11%, which indicated that maybe there was some unreacted

adhesive dissolved in the water after the immersion treatment, however, at the

tannin/sucrose ratio of 25/75, the amount of unreacted tannin and sucrose would be

least. In the second immersion treatment (immersion at 70°C for 24 h), the weight

increase dropped as the sucrose ratio increased. The lowest weight increase was 80%

when the board was bonded with a tannin/sucrose ratio of 25/75. The same tendency

0

20

40

60

80

100

120

Th

ickness c

hange (

%)

75/25

50/50

25/75

0/100

Tannin/Sucrose(wt%)

32

was recognized in the third immersion treatment (boiling for 4h); namely, the value

decreased with increasing sucrose ratio, and the best value was 80% when the board

bonded with tannin/sucrose ratio at 25/75. The weight change value between second

immersion treatment and third treatment was almost the same. The final weight

decrease when dried at 105°C for 10 h showed a range from 19% to 9%, and a higher

sucrose proportion brought less weight decrease. According to the results shown in

Figs. 2.6 and 2.7, increasing the proportion of sucrose enhanced the water resistance

of the adhesion system. Some researchers have shown that sucrose can yield

5-hydroxymethyl-2-furfural (HMF) under heating or acidic conditions (Jeong et al.,

2013; Lee et al., 2011; Kitts et al., 2006). The subsequent reaction of HMF with

tannin may be the process that leads to the polymerization between sucrose and tannin

(Wu and Fu, 2006; Sotoudehnia et al., 2012). Our results indicated that a

tannin/sucrose ratio of 25/75 yielded excellent mechanical properties for

particleboard.

Fig. 2.7 Weight change in a cyclic accelerated aging treatment with drying treatment


-20

0

20

40

60

80

100

120

140

We

ight c

ha

nge

(%

)

75/25

50/50

25/75

0/100


33

2.2.2.3 Effects of resin content

The effects of resin content on the physical properties of particleboard bonded at

the tannin/sucrose ratio of 25/75 were investigated. Figure 2.8 shows the bending

properties of particleboard bonded with different resin contents. Both MOR and MOE

were slightly enhanced with the increase of resin content. The maximum average

values of MOR and MOE were 21.2 MPa and 5.0 GPa, respectively, obtained at

40wt% resin content. Our results indicated that the boards bonded with 15wt% resin

content or more were comparable to the requirements of the type 18 of JIS A 5908

standard. When the board was bonded with isocyanate (8wt% resin content), the

MOR and MOE were 25.3 MPa and 4.0 GPa, respectively.

Fig. 2.8 Effect of resin content of tannin/sucrose on bending properties. Error bars

indicate standard deviations.

Figure 2.9 shows the IB strengths of the particleboards bonded with different

resin contents. The IB strength performance did not change obviously with changes in

resin content. The maximum average value was 1.3 MPa at resin content of 30wt%.

All the specimens satisfied the requirement of the type 18 of JIS A 5908 (more than

34

0.3 MPa); this result indicated that resin content as low as 10 wt% provided

satisfactory internal bonded strength. The IB strengths of particleboards bonded with

tannin and sucrose were about half of those bonded with isocyanate. Based on the

results of bending test and IB test, the bending properties increased with the

increasing of resin content, but the IB strength did not change obviously. This

phenomenon perhaps was due to the decrease of wood particles when the resin

content increased and the density remain unchanged; the decrease of wood particles

led to more void areas in the particleboard, and the percentage of void areas had a

negative effect on IB strength (Arabi et al., 2011).

Fig. 2.9 Effect of resin content of tannin/sucrose on IB strength properties. Error bars


35

Fig. 2.10 Thickness change in a cyclic accelerated aging treatment. Error bars


Figure 2.10 shows the thickness changes of the particleboards with different

resin contents in the cyclic accelerated aging treatment. In the first immersion

treatment (immersion at 20°C for 24 h), the TS value decreased as the resin content

increased. The lowest value of TS was 20% with 40wt% resin content, which

indicated that the increase of resin content enhanced the water resistance of the

particleboard. Ordinarily, tannin and sucrose are water-soluble substances. However,

the reaction of tannin and sucrose may result in insoluble materials. After boiling

water treatment for 4 h, the value for 40wt% particleboard was 34%, exceeding the

value of particleboard bonded with isocyanate at 32%.

0

20

40

60

80

100

120

Th

ickn

ess c

ha

ng

e (%

)10

15

20

30

40

Isocyanate

Resin content (wt%)

36

Fig. 2.11 Weight change in a cyclic accelerated aging treatment. Error bars indicate

standard deviations.

Figure 2.11 shows the weight changes of the particleboards in a cyclic

accelerated aging treatment. There was less of a change in weight as the resin content

increased, indicating that the resin inhibited the absorption of water. Compared with

the weight increase in the first immersion, the weight increase of warm immersion

and boiling treatment were higher, due to the lowering of the water resistance of the

adhesive and the penetration of water into the wood (Umemura et al., 2013). The

range of the weight decrease was -3 to -6 % after the first drying treatment and -8 to

-15% after the last drying treatment; these values gradually increased with increasing

resin content. This result indicated that as the resin content increased, the

decomposition and elution of the adhesive increased.

2.2.2.4 Curing mechanism

-20

0

20

40

60

80

100

120

140W

eig

ht c

ha

ng

e (

%)

10

15

20

30

40

Isocyanate

Resin content (wt%)

37

Fig. 2.12 Infrared spectra of the cured and uncured tannin and sucrose adhesive.

The FT-IR curves of the mixture of tannin and sucrose before and after heating

were shown in Figure 2.12. The absorption bands at around 1705, 1509, 1200 and 780

cm-1

increased clearly in the heat treatment. The peak at around 1705 cm-1

attributed

to C=O stretching derived from the carbonyl group (Vaz and Ribeiro, 2003). The

peaks at around 1509 and 780 cm-1

are characteristic of C=C stretching vibration and

unsubstituted CH=CH of 5-HMF, respectively (Chuntanapum and Matsumura, 2009;

Zhang et al., 2012; Alakhras and Holze; 2007). The peak located around 1200 cm-1

was associated with the -CO stretching of the benzene nucleus and/or the dimethylene

ether bridges (-CH2OCH2-) (Kim and Kim, 2003; Choi et al., 2002). In addition,

disappearance of two absorption peaks at around 1130 cm-1

and 920 cm-1

was

observed. The peak at 1130 cm-1

was dominated by the glycosidic linkage (C-O-C)

contribution (Kacurakova et al., 2000), and the absorption bond at around 920 cm-1

was attributed to pyranose ring of sucrose (Seino et al., 1984). This indicated the

decomposition of sucrose. Judging from these spectra changes, 5-HMF is formed by

decomposition of sucrose during heating. Furthermore, 5-HMF seems to react with

tannin and form dimethylene ether bridges. The possible reaction equation between

80012001600200024002800320036004000

Wavenumber(cm-1)

Ab

sorb

an

ce

Mixture without heat

treatment

200℃ ,10min

17

05

15

09

12

00

11

30

78

09

20

400

38

tannin and sucrose was shown in Figure 2.13.

Fig. 2.13 Possible reaction equation between tannin and sucrose.

2.3 Summary

The results of this chapter showed that tannin and sucrose, natural substances

derived from readily available bio-resources, can be used to manufacture

particleboard that meets industrial standards. This chapter investigated the

tannin/sucrose ratio, effects of the drying treatment after spraying and resin content on

particleboard properties. The properties were enhanced when the drying treatment was

carried out after the spraying, and when the sucrose ratio increased. Based on the

results obtained, the optimum proportion of tannin to sucrose was 25/75, and the

optimum resin content was between 30 wt% and 40 wt%. When the particleboards

were manufactured under the optimum conditions, they showed excellent mechanical

Sucrose

5-HMF

Wattle tannin

39

properties, higher than those required for JIS A5908 type 18. Based on the results of

FT-IR, 5-HMF was formed from the decomposition of sucrose during the heating

treatment. In addition, as one kind of the possible reaction mechanism between tannin

and sucrose, the dimethylene ether bridges seems to be formed.

2.4 Reference

Alakhras. F., Holze. R. (2007) In situ UV-vis-and FT-IR-spectroscopy of

electrochemically synthesized furan-thiophene copolymers. Synthetic metals. 157,

109-119.

Arabi. M., Faezipour. M., Layeghi. M., Enayati. AA. (2011) Interaction analysis

between slenderness ratio and resin content on mechanical properties of

particleboard. J For Res. 23, 461-464.

Choi. MH., Byun. HY., Chung. IJ. (2002) The effect of chain length of flexible diacid

on morphology and mechanical property of modified phenolic resin. J Polymer.

43, 4437-4444.

Chuntanapum. A., Matsumura. Y. (2009) Formation of tarry material from 5-HMF in

subcritical and supercritical water. Ind Eng Chem Res. 48, 9837-9846.

Jeong. J., Antonyraj. C., Shin. S., Kim. S., Kim. B., Lee. KY., Cho. JK. (2013)

Commercially attractive process for production of 5-hydroxymethyl-2-furfural

from high fructose corn syrup. J Ind Eng Chem. 19, 1106-1111.

JIS A 5908(2003) Particleboard (in Japanese). Japanese Standards Association, Tokyo,

Japan.

Kacurakova. M., Capek. P., Sasinkova. V., Wellner. N., Ebringerova. A. (2000) FT-IR

study of plant cell wall model compounds: pectic polysaccharides and

hemicelluloses. Carbohyd Polym. 43, 196-203.

Kim. S., Kim. H. (2003) Curing behavior and viscoelastic properties of pine and

wattle tannin-based adhesives stydied by dynamic mechanical thermal analysis

and FT-IR-ATR spectroscopy. J Adhesion Sci Technol. 17, 1369-1383.

http://admin-apps.webofknowledge.com/JCR/JCR?RQ=RECORD&rank=2&journal=CARBOHYD+POLYM

40

Kitts. DD., Wu. CH., Kopec. A., Nagasawa. T. (2006) Chemistry and genotoxicity of

caramelized sucrose. Mol Nutr Food Res. 50, 1180-1190.

Koch. H., Pein. J. (1985) Condensation reactions between phenol, formaldehyde and

5-hydroxymethylfurfural, formed as intermediate in the acid catalyzed

dehydration of starchy products. Polym Bull. 13, 525-532.

Lee. JW., Thomas. L., Jerrell. J., Feng. H., Cadwallader. K., Schmidt. S. (2011)

Investigation of thermal decomposition as the kinetic process that causes the loss

of crystalline structure in sucrose using a chemical analysis approach. J Agric

Food Chem. 59, 702-712.

Lei. H., Pizzi. A., Du. GB. (2008) Environmentally friendly mixed tannin/lignin wood

resins. J Appl Polym Sci. 107, 203-209.

Li. K., Geng. X., Simonsen. J., Karchesy. J. (2004) Novel wood adhesives from

condensed tannins and polyethylenimine. Int J Adhes Adhes. 24, 327-333.

Lin. HC., Fujimoto. Y., Murase. Y. (2002) Behavior of acoustic emission generation

during tensile tests perpendicular to the plan of particleboard: effects of particle

sizes and moisture content of boards. J Wood Sci. 48, 374-379.

McRae. J., Schulkin. A., Kassara. S., Holt. H., Smith. P. (2013) Sensory properties of

wine tannin fractions: implications for in-mouth sensory properties. J Agric Food

Chem. 61, 719-727.

Pichelin. F., Nakatani. M., Pizzi. A. (2006) Structural beams from thick wood panels

bonded industrially with formaldehyde-free tannin adhesives. J Forest Prod. 56,

31-36.

Piwowarski. JP. , Kiss. AK., Kozłowska-Wojciechowska. M. (2011)

Anti-hyaluronidase and anti-elastase activity screening of tannin-rich plant

materials used in traditional Polish medicine for external treatment of diseases

with inflammatory background. J Ethnopharmacology. 137, 937-941.

Pizzi. A.(2006) Recent development in eco-efficient bio-based adhesives for wood

bonding: opportunities and isues. J Adhes Sci Technol. 20, 829-846.

Sar. B. , Nemli. G., Ayrilmis. N., Baharoğlu. M., Bardak. M. (2013) The influences of

drying temperature of wood particles on the quality properties of particleboard

http://www.scopus.com/authid/detail.url?authorId=38862661600&eid=2-s2.0-80052036647

mailto:[email protected]



41

composite. J Drying Technol. 31, 17-23.

Seino. H., Uchibori. T., Nishitani. T., Inamasu. S. (1984) Enzymatic synthesis of

carbohydrate esters of fatty acid (I) esterification of sucrose, glucose, fructose

and sorbitol. JAOCS. 61(11), 1761-1765.

Soto, R., Freer, J., Reues, N., Baeza, J. (2001) Extraction of folyflavonoids from pinus

radiate D. Don bark evaluation of effects of solvent composition and of the

height of tree bark . Bol. Soc. Chil. Qui. 46, 14-19.

Sotoudehnia. MM., Soltani. AK., Jam. JE., Moztarzadeh. F. (2012) The effect of

modified processing on the densification efficiency and microstructure of

phenol–furfural-based carbon composite. J Anal Appl Pyrol. 96, 2-5.

Trosa. A., Pizzi. A. (1997) Stability and performance of tannin-accelerated PF resins

for plywood. J Holz Roh- Werkst. 55, 306.

Umemura, K. (2013). Condensed tannin-containing composition which is cured by

application of heat and pressure. WO2013018707 A1.

Umemura. K., Sugihara. O., Kawai. S. (2013) Investigation of a new natural adhesive

composed of citric acid and sucrose for particleboard. J Wood Sci. 59, 203-208.

Valenzuela. J., Von. Leyser. E., Pizzi. A. (2012) Industrial production of pine

tannin-bonded particleboard and MDF. Eur J Wood Prod. 70, 735-740.

Vaz. PD., Ribeiro-Claro. PJA. (2003) C-H…O hydrogen bonds in liquid

cyclohexanone revealed by the vC=O splitting and the vC-H blue shift. J. Raman

Spectrosc. 34, 863-867.

Wu. DC., Fu. RW. (2006) Synthesis of organic and carbon aerols from phenol-furfural

by two-step polymerization. Micropor Mesopor Mat. 96, 115-120.

Yao. K., He. Q., Jia. DY., Shi. B. (2006) The potential of wattle tannin extracts for

fine use. J Nat Prod Res. 20, 271-278.

Yonghwa. J., Jian. H., Kaichang. L. (2011) A new formaldehyde-free wood adhesive

from renewable materials. Int J Adhes Adhes. 31, 754-759.

Zhang. M., Yang. H., Liu. Y., Sun. X., Zhang. D., Xue. D. (2012) Hydrophobic

precipitation of carbonaceous spheres from fructose by a hydrothermal process.

Carbon. 50, 2155-2161.

42

Chapter3

Effects of pressing temperature and time on particleboard

properties, and characterization of tannin-sucrose adhesive

3.1 Introduction

In a previous study in Chapter2, particleboard was manufacture bonded by tannin

and sucrose. The mechanical properties of particleboard produced with tannin to

sucrose ratio of 25/75 and a resin content of 30 to 40 wt% satisfied the requirement of

the JIS A 5908 type 18 standard (2003). However, the water resistance of the

particleboard bonded by tannin and sucrose at optimal manufacture conditions in

Chapter 2 still lower than the standard. The reaction mechanism was studied by FT-IR,

and the results showed the dimethylene ether bridges seems to be formed. The results

obtained from chapter 2 indicated that, it is possible to manufacture the particleboard

bonded by tannin and sucrose. Therefore, more information of the manufacture

conditions and the curing behavior of tannin and sucrose adhesive are needed.

In the Chapter 3, the effects of the hot pressing temperature and hot pressing

time on the physical properties of the particleboard were investigated. The

relationship between curing process and temperature was also studied by

thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The

insoluble matter of the cured adhesives was measured, and the change of the chemical

structure of adhesives cured for different heating times was studied by Fourier

transform infrared spectroscopy (FT-IR).

43

3.2 Effects of hot pressing temperature and time on board

properties


3.2.1.1 Materials

Recycled wood particles obtained from a particleboard company were used as

raw materials, and the particles were screened using a sieving device to collect

particles in the range between 5.9 and 0.9 mm. The moisture content of the original

particles was 3 to 4 wt%. Before the manufacturing of the particleboards, the particles

were dried in an oven at 80 °C for 12 h until the moisture content at 2 wt%.

Wattle tannin (Commercial name: tannic acid ME) was purchased from Fuji

Chemical Industry Co. (Wakayama, Japan), and the tannin content was 88.1%, which

measured by methanol method (Soto et al. 2001). Sucrose (guaranteed reagent) was

purchased from Nacalai Tesque, Inc. (Kyoto, Japan). Those materials were used

without further purification and dried in a vacuum oven at 60 °C for 15 h before using.

Based on the previous paper (Zhao and Umemura, 2014), tannin and sucrose were

mixed with a ratio of 25/75, and then the mixture was dissolved in distilled water with

a concentration of the solution at 40 wt%. The solution was used as an adhesive, and

the viscosity and pH of the solution at 20 °C were 51.3 mPa·s and 4.76, respectively.

3.2.1.2 Manufacture of the particleboard

The adhesive solution was sprayed onto particles in a blender. The resin contents

were 30 and 40 wt% based on the weight of the oven-dried particles. The sprayed

particles were dried at 80 °C for 12 h, and the moisture content after drying was 3 to 6

wt%. Then the particles were mat-formed using a forming box of 300×300 mm. The

particleboards were manufactured in two Groups. In Group 1, hot pressing

temperatures of 160, 180, 200, and 220 °C were used, and the hot pressing time was

10 min. In Group 2, the hot pressing temperature was 220 °C, and hot pressing times

44

of 5, 7, 10, and 15 min were used. Both in Groups 1 and 2, one board was

manufactured for every condition. The thickness was controlled using a distance bar

of 9 mm thickness. The size of the manufactured board was 300 × 300 × 9 mm, and

the target density was 0.8 g cm-3. The obtained boards were conditioned for 1 week at

20 °C and 60% relative humidity (RH). The details of the manufacturing conditions

are shown in Table 3.1.

Table 3.1 Manufacturing Conditions of Particleboard

Groups

Mixture ratio

of tannin and

sucrose (wt%)

Resin content

(wt%)

Pressing

temperature (°C)

Pressing

time (min)

Target density

(g cm-3)

Group1 25:75

30 160

10 0.8

40

30 180

40

30 200

40

30 220

40

Group2 25:75

30

220

5

0.8

40

30 7

40

30 10

40

30 15

40

3.2.1.3 Evaluation of Board Properties

The boards were evaluated according to the Japanese Industrial Standard for

particleboard (JIS A 5908. 2003). The static three-point bending test was carried out

under dry condition on a 200 × 30 × 9 mm sample from each board, and the effective

span and loading speed were 150 mm and 10 mm/min, respectively. The modulus of

rupture (MOR) and the modulus of elasticity (MOE) were calculated. The internal

bond strength (IB) test was performed on a 50×50×9 mm sample with a loading speed

45

of 2 mm/min, and thickness swelling (TS) after water immersion for 24 h at 20 °C

was measured in samples of the same size. Following the TS test, thickness and

weight changes under a cyclic accelerated aging treatment (drying at 105 °C for 10 h,

warm water immersion at 70 °C for 24 h, drying at 105 °C for 10 h, boiling water

immersion for 4 h, and drying at 105 °C for 10 h) were measured. Each experiment

was performed in quintuplicate, and the average value and standard deviation were

calculated. Statistical significance was considered for p values < 0.5. The MOR, MOE,

and IB of the boards shown in the figures are values corrected for target density based

on each regression line between actual values and sample densities of the mechanical

properties.


3.2.2.1 Effect of hot pressing temperature

Fig. 3.1 Effect of hot pressing temperature on MOR in bending test. Error bars

0

5

10

15

20

25

30

160 180 200 220

MO

R (

MP

a)

Hot pressing temperature (°C)

30wt%

40wt%

Resin content

46


Fig. 3.2 Effect of hot pressing temperature on MOE in bending test. Error bars


The particleboard was manufactured at different hot pressing temperatures with

resin contents of 30 and 40 wt%. Figures 3.1 and 3.2 show the influence of hot

pressing temperature on MOR and MOE. As the hot pressing temperature was

increased, the values of MOR and MOE were enhanced irrespective of the resin

content, and the values obtained at a 40 wt% resin content were a little higher than

those of the 30 wt% resin content at the same hot pressing temperature. The

maximum average values of MOR and MOE were 21.9 MPa (40 wt%-220 °C) and

5.0 GPa (40 wt%-200 °C), respectively. Analysis of variance (ANOVA) showed no

significant difference in MOR and MOE among the three particleboards bonded with

resin content at hot pressing temperature levels of 40-200, 30-220, and 40-220. In

0.0

1.0

2.0

3.0

4.0

5.0

6.0

160 180 200 220

MO

E(G

pa

)

Hot pressing temperature(°C)

30wt%

40wt%

Resin content

47

addition, those bending properties were comparable to the requirement of the type 18

JIS A 5908 standard (MOR>18MPa) (JIS A 5908. 2003). The results indicated that

when the hot pressing temperature was higher than 200 °C, the influence of hot

pressing temperature on the bending properties was small, and a temperature that is

200 °C or higher is required to obtain satisfactory bending properties of the

particleboard bonded with tannin and sucrose.

Fig. 3.2 Effect of hot pressing temperature on IB strength. Error bars indicate


Figure 3.3 shows the IB strength of the particleboard. Under both of the 30 and

40 wt% resin content conditions, the IB strength was obviously enhanced as the hot

pressing temperature increased, and the maximum average value was 1.6 MPa,

0.0

0.5

1.0

1.5

2.0

160 180 200 220

IB (

MP

a)

Hot pressing temperature (°C)

30wt%

40wt%

Resin content

48

obtained from the board with a 40 wt% resin content at 220 °C. When the hot pressing

temperature was higher than 200 °C, the IB strength of all the samples satisfied the

requirement of the type 18 JIS A 5908 (IB>0.3MPa) (JIS A 5908. 2003).

It is worth noting that, if the hot pressing temperature was less than or equal to

200 °C, the IB strength of the board with 30 wt% was higher than that of the 40 wt%

board. This phenomenon was perhaps due to the decrease in wood particles when the

resin content was increased under the same board density. This means that the

decrease in wood particles led to more void areas in the particleboard, and the

increase in void areas had a negative effect on IB strength (Arabi et al., 2011).

However, the opposite results were obtained when the hot pressing temperature was

220 °C, as the IB strength at a 40 wt% resin content was a little higher than that at 30

wt%. This would be due to the promotion of adhesiveness at 220 °C.

Figure 3.4 shows the thickness changes of the particleboard. In the first

immersion treatment (immersion at 20 °C for 24 h), the samples manufactured at 160

and 180 °C were decomposed, which indicated that the water resistance of those

boards was very weak. Comparing with the results obtained from the board hot

pressed at 200 and 220 °C, the TS values decreased greatly when the board was hot

pressed at 220 °C. The TS values of 30 and 40 wt% resin content at 220 °C were 10

and 7%, respectively, which satisfied the requirement of the type 18 JIS A 5908

(TS<12%) (JIS A 5908. 2003). The subsequent cyclic accelerated aging treatment

brought a stepwise increase in the thickness of the samples, and the boards pressed at

220 °C showed lower thickness swelling values than the boards pressed at 200 °C in

each immersion treatment. This indicated that increasing the hot pressing temperature

to 220 °C greatly promoted the water resistance of the particleboard bonded with

tannin and sucrose.

49

Fig. 3.4 Effect of hot pressing temperature on thickness change in a cyclic accelerated

aging treatment. Error bars indicate standard deviations.

Figure 3.5 shows the weight changes during the cyclic accelerated aging

treatment. In the first immersion treatment, the weight increase of the boards pressed

at 220 °C was obviously lower than those of the boards pressed at 200 °C. This

indicated that the water absorption was inhibited by increasing the hot pressing

temperature. Weight decreases ranging from 1.9 to 4.5% were observed after the first

drying treatment, indicating that some elution from the samples occurred. The weight

increases of 70 °C water immersion and boiling treatment were higher than the first

treatment. This phenomenon was possible due to the decreasing of water resistance of

0

10

20

30

40

50

60

Th

ickness c

hange (

%)

30-200

40-200

30-220

40-220

Resin content (wt%)-Hot pressing temperature(°C)

50

adhesive and the penetration of water into the wood. (Umemura et al., 2013). In the

last drying treatment, the weight decreases of the boards pressed at 200 and 220 °C

ranged from 11.8 to 14.7% and 4.7 to 5.4%, respectively. There was a smaller weight

decrease when the hot pressing temperature was 220 °C, which means that less

elution occurred during the cyclic accelerated aging treatment. This indicated that the

curing of tannin and sucrose adhesive at 220 °C led to a more complete

insolubilization than curing at 200 °C.

Fig. 3.5 Effect of hot pressing temperature on weight change in a cyclic accelerated

aging treatment. Error bars indicate standard deviations.

-20

0

20

40

60

80

100

We

igh

t c

ha

ng

e (

%)

30-200

40-200

30-220

40-220

Resin content (wt%)-Hot pressing temperature(°C)

51

3.2.2.2 Effect of hot pressing time

Fig. 3.6 Effect of hot pressing time on MOR in bending test. Error bars indicate


Based on the results obtained, the effects of hot pressing time on the physical

properties of particleboard bonded with 30 and 40 wt% resin content were

investigated at 220 °C. Figures 3.6 and 3.7 show the influence of hot pressing time on

MOR and MOE. The results show that the bending properties of all the samples

satisfied the requirement of the type 18 JIS A 5908 standard (JIS A 5908. 2003). The

0

5

10

15

20

25

30

0 5 10 15

MO

R (

MP

a)

Hot pressing time (min)

30wt%

40wt%

Resin content

7

52

maximum values of MOR and MOE were 23.5 MPa and 5.3 GPa, respectively, with a

hot pressing time of 7 min and 40 wt% resin content. Based on the ANOVA analysis,

there were no significant differences of MOR among all samples. In terms of MOE,

the values were increased in the hot pressing time range of 5 to 7 min, and decreased

from 7 to 15 min. This means that prolonging hot pressing time would not promote

the bending properties of the particleboard.

Fig. 3.7 Effect of hot pressing time on MOE in bending test. Error bars indicate


Figure 3.8 shows the effect of hot pressing time on IB strength. Both the 30 and

40 wt% resin contents showed the same trend in IB values with increasing hot

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 5 10 15

MO

E(G

Pa

)


30wt%

40wt%

Resin content

7

53

pressing time. A significant increase was observed as the hot pressing time was

prolonged from 5 to 10 min. This phenomenon would be due to a more efficient

curing in the core layer. A slight decrease was observed in 15 min. The maximum

value was 1.6 MPa in the case of a 40 wt% resin content and 10 min, and the IB

values of all the samples except for the boards pressed for 5 min with a 30 wt% resin

content were comparable to the requirement of the type 18 JIS A 5908 standard (JIS A

5908.2003).

Fig. 3.8 Effect of hot pressing time on IB strength. Error bars indicate standard

deviations.

Judging from the results of the bending and IB tests, when the hot pressing time

0.0

0.5

1.0

1.5

2.0

0 5 10 15

IB(M

Pa

)


30wt%

40wt%

Resin content

7

54

was in the range of 5 to 7 min, the bending properties of the boards were good;

however, the IB strength was weak. This phenomenon was explained as follows: the

short hot pressing time led to sufficient curing at the surface but insufficient curing in

the core of the particleboard, and the bending properties and IB properties of the

particleboard were more strongly affected by the surface and core layers, respectively.

Figure 3.9 shows the thickness changes of the particleboard samples bonded with

different hot pressing times and resin contents in the cyclic accelerated aging

treatment.

Fig. 3.9 Effect of hot pressing time on thickness change in a cyclic accelerated aging

treatment. Error bars indicate standard deviations.

0

10

20

30

40

50

60

Th

ickn

ess c

ha

ng

e (

%)

30-5

40-5

30-740-7

30-10

40-10

30-15

40-15

Resin content (wt%)- Hot pressing time(min)

55

In the first immersion treatment, the TS values under the same resin content

decreased in the time range of 5 to 10 min, and then they remained the same at 10 min

and 15 min. In addition, the TS values of the boards bonded with a 40 wt% resin

content were lower than those with a 30 wt% resin content at every hot pressing time.

The minimum TS value was 7%, obtained from the boards bonded with a 40 wt% for

10 and 15 min. When the particleboard were manufactured with a 40 wt% resin

content for 7 min, and 30 or 40 wt% resin content for 10 or 15 min, the TS values

were comparable to the requirement of the type 18 JIS A 5908 standard (JIS A 5908.

2003). The subsequent cyclic accelerated aging treatment brought a stepwise increase

in the thickness of the samples, and the least thickness changes were obtained in

samples bonded with a 40 wt% resin content with 10 or 15 min. This indicated that

the prolonging of hot pressing time contributed to the inhibition of the thickness

change of the boards.

Figure 3.10 shows the weight changes of the particleboard bonded with different

hot pressing times in the cyclic accelerated aging treatment. In the first immersion

treatment, the weight increase between the boards hot-pressed for 10 and 15 min was

lower than the boards hot-pressed for 5 and 7 min, meaning that water absorption was

inhibited by prolonging the hot pressing time. The weight change range after the first

drying treatment was -1.2 to -7.8%, indicating that some elution including adhesive

occurred. In the 70 °C immersion treatment, the weight increase ranged from about 58

to 79% and dropped as the hot pressing time increased. The overall weight change

between 70 °C immersion treatment and boiling treatment were almost the same, and

the values were higher than the first immersion treatment. The final weight decrease

with drying at 105 °C ranged from 4.7 to 14.8%, and a long hot pressing time

corresponded to a slight weight decrease. Based on the results shown in Figs. 3.9 and

3.10, prolonging the hot pressing time brought good water resistance of the board.

56

Fig. 3.10 Effect of hot pressing time on weight change in a cyclic accelerated aging

treatment. Error bars indicate standard deviations.

Judging from the results obtained from Figs. 3.9 and 3.10, the optimal hot

pressing time of the particleboard bonded with tannin and sucrose was 10 min. In

terms of resin content, the best physical properties were obtained from the boards

bonded with 40 wt% resin content, although the physical properties of the boards

bonded with 30 wt% resin content also satisfied the requirement of the type 18 JIS A

5908 standard (JIS A 5908. 2003).

-20

0

20

40

60

80

100

We

igh

t c

ha

nge (

%)

30-5 40-5 30-7 40-7

30-10 40-10 30-15 40-15

Resin content (wt%)- Hot pressing time(min)

57

3.3 Characterization of tannin and sucrose adhesive


3.3.1.1 Materials

Wattle tannin (Commercial name: tannic acid ME) was purchased from Fuji

Chemical Industry Co. (Wakayama, Japan), and the tannin content was %, which

measured by methanol method (Soto et al. 2001). Sucrose (guaranteed reagent) was

purchased from Nacalai Tesque, Inc. (Kyoto, Japan). Those materials were used

without further purification and dried in a vacuum oven at 60 °C for 15 h before using.

Based on the previous paper (Zhao and Umemura, 2014), tannin and sucrose were

mixed with a ratio of 25/75, and then the mixture was dissolved in distilled water with

a concentration of the solution at 40 wt%. The solution was used as an adhesive, and

the viscosity and pH of the solution at 20 °C were 51.3 mPa·s and 4.76, respectively.

3.3.1.2 Thermal analysis

Tannin and sucrose were dissolved in distilled water with the ratio of tannin to

sucrose at 100/0, 25/75, and 0/100. The concentration of each solution was adjusted to

40 wt%. From every kind of the solution, 20 g solution was taken out and divided in

10 aluminum cups and dried in an oven at 80 °C for 12 h. After that, the samples were

pulverized into less than 250-μm mesh size to obtain uncured adhesive powder. TGA

was carried out using a TGA 2050 (TA Instruments Japan). The samples were scanned

from room temperature to 400 °C at a rate of 10 °C /min under nitrogen purging. The

DSC measurement was conducted using a DSC 2910 (TA Instruments, Japan). The

samples were encapsulated in an aluminum pan and scanned from room temperature

to 400 °C at a rate of 10 °C /min under nitrogen purging.

3.3.1.3 Insoluble matter and FT-IR

58

Tannin and sucrose were dissolved in distilled water with a ratio of tannin to

sucrose of 25/75, and uncured adhesive powder was obtained, in the same manner as

was done for the thermal analysis. The uncured adhesive powder was divided into 7

parts. The powder was heated in an oven at 220 °C for 1, 3, 5, 7, 10, 15, and 20 min,

respectively. Then 2 g samples were sampled from every part of the cured adhesives,

and the samples were then boiled in distilled water for 4 h to obtain the insoluble

matter. The boiling treatment for every sample was carried out in triplicate. All of the

samples that were obtained from the heat treatments and boiling treatments were

vacuum-dried at 60 °C for 15 h.

Infrared spectra were obtained with a Fourier transform infrared

spectrophotometer (FT/IR-4200, JAS-CO Corporation) using the KBr disk method

and were recorded with an average of 32 scans at a resolution of 4 cm-1

.

3.3.2 Results and Discussion


Figure 3.11 shows the thermogravimetric (TG) and derivative TG (DTG) curves

of the tannin, adhesive, and sucrose. Tannin (100/0) showed two-step degradation

from the DTG curve, with the first stage at around 193 °C and the second stage at

around 240 °C. In the first stage, 10% weight loss was observed from the TG curve.

Judging from a previous study (Gaugler and Grigsby, 2009), the first and the second

stages can be attributed to the decomposition of polysaccharide from tannin and the

decomposition of tannin, respectively. Sucrose (0/100) showed two-step degradation

from the DTG curve. The first step at around 220 °C relates to the caramelization

phase of sucrose (Gintner et al., 1989; Eggleston et al., 1996). The second step at

around 270 °C was due to the production of a black aerated char-like solid (Eggleston

et al. 1996). The adhesive (25/75) had a significant weight decrease at around 204 °C

according to the DTG. Considering the results of tannin and sucrose, some reaction

must occur between tannin and sucrose.

59

Fig. 3.11 TG and DTG curves of wattle tannin, adhesive and sucrose

Figure 3.12 shows the DSC curves of tannin, adhesive, and sucrose. The results

for tannin (100/0) show an exothermic peak at around 255 °C. In research on the

thermal degradation of pine tannin, an exothermic peak at around 255 °C was

observed, and this was attributed to the charring of tannin (Gaugler and Grigsby,

2009). Therefore, the peak observed in the present study was likewise attributed to the

charring of tannin. In the case of sucrose (0/100), two sharp endotherms were

observed at 180 and 226 °C. Considering the results of TG analysis of sucrose above,

there was no peak at 180 °C; therefore, the endotherm peak at 180 °C was attributed

to the melting of sucrose. The previous research also reported that the peaks at 180

and 226 °C were attributable to the melting and caramelization, respectively

(Eggleston et al., 1996). When testing a mixed adhesive (25/75), two endothermic

peaks were observed. The first endotherm at around 180 °C, given what was shown in

the sucrose-only condition, was due to the melting of sucrose. The second endotherm

appeared at around 215 °C, which was lower than the second peak of the sucrose;

therefore, this endotherm may be due to the caramelization of sucrose and the reaction

between the products from caramelization and tannin.

0.0

0.5

1.0

1.5

-40

-20

0

20

40

60

80

100

0 100 200 300 400

De

riva

tive

(%/°

C)

We

ight(

%)

Temperature (°C)

100/0

25/75

0/100

Tannin/Sucrose ratio

60

Fig. 3.12 DSC curves of wattle tannin, adhesive, and sucrose

Based on the results obtained from Figs. 11 and 12, the reaction of the mixture

composed of tannin and sucrose at a ratio of 25/75 occurred at a temperature higher

than 200 °C. These results were consistent with the good physical properties of

particleboard manufactured at 220 °C.


The adhesive (25/75) was heated at 220 °C for different heating times, and

insoluble matter after boiling treatment were observed. The results are shown in Fig.

3.13. As the heating time was increased from 1 to 5 min, the value of insoluble matter

was small, but when the heating time was longer than 5 min, the value of insoluble

matter increased obviously. This phenomenon indicated that the curing of adhesive

progressed significantly. When the heating time was longer than 10 min, the

0 100 200 300 400

Temperature (°C)

Tannin/Sucrose

100/0

25/75

0/100

En

do

the

rmE

xo

the

rm

0.5 W/g

61

insoluble matter was higher than 70 wt% and changed slightly.

Fig. 3.13 Insoluble matter of the adhesive heated for different heating time

The effect of heating time on the chemical structure of the adhesive heated at

220 °C is shown in Fig. 3.14. Compared with the peaks obtained from the adhesive

that had not undergone heat treatment, the absorption bands at around 1705, 1667,

1509, 1200, and 780 cm-1

appeared clearly. The peak at around 1705 cm-1

can be

attributed to C=O stretching derived from the carbonyl group (Vaz and Ribeiro-Claro,

2003). The peaks near 1509 and 780 cm-1

are characteristic of the C=C stretching

vibration and the unsubstituted CH=CH of the furan ring, respectively (Chuntanapum

and Matsumura., 2009; Zhang et al., 2012; Alakhras and Holze, 2007). The peak

located around 1200 cm-1

was associated with the the dimethylene ether bridges

and/or -CO stretching of the benzene nucleus (-CH2OCH2-) (Kim and Kim, 2003;

Choi et al., 2002). A new peak located at 1667 cm-1

was ascribed to the C=O

stretching of 5-HMF (Chuntanapum and Matsumura, 2009). Disappearance of two

absorption peaks at around 1130 cm-1

and 920 cm-1

were observed. Those peaks were

0

30

60

90

0 5 10 15 20

Inso

luble

ma

tter

(%)

Heating time (min)

1 3 7

62

attributed to the glycosidic linkage (C-O-C) contribution (Kacurakova et al., 2000)

and pyranose ring of sucrose (Seino et al., 1984). This indicated the decomposition of

sucrose.

Fig. 3.14 FT-IR curves of the curing adhesives

Heat time

20 min

15 min

10 min

7 min

5 min

3 min

1 min

No heat

17

05

15

09

12

00

11

30

92

0

78

0

16

67

70010001300160019002200250028003100340037004000

Ab

so

rban

ce

Wavenumber (cm-1)

63

Fig. 3.15 FT-IR curves of the residue after the boiling treatment of the curing

adhesives

To observe the chemical structure change of cured adhesives, FT-IR spectra of

the insoluble residue after boiling treatment were obtained, and the results are shown

in Fig. 15. No results of the heating of the adhesives for 1 and 3 min were obtained

because very little residue remained, as shown in Fig. 13. The absorption band at

around 1667 cm-1

was not observed in any samples due to the solubility of 5-HMF.

The absorption bands at around 1705, 1509, 1200, and 780 cm-1

were observed,

indicating that the functional groups mentioned above existed in the cured adhesive.

The FT-IR spectra of the adhesives heated for 10, 15, and 20 min were almost the

same, which means that the chemical structures of the adhesives heated for more than

Heat time

20 min

15 min

10 min

7 min

5 min

No heat

78

017

05

15

09

12

00

70010001300160019002200250028003100340037004000

Ab

so

rban

ce

Wavenumber (cm-1)

64

10 min were almost the same. Judging from these results, the cured adhesive had a

furan ring structure and dimethylene ether bridges, and the water resistance was high.

When the heating time was 10 min, higher values of insoluble substances were

obtained, and the chemical structure of the adhesion system seemed to be stable.

Therefore, a heating time of 10 min is needed to cure the adhesive sufficiently.

3.4 Summary

Particleboards using tannin and sucrose as an adhesive were manufactured to

investigate the effects of hot pressing temperature and hot pressing time on the

physical properties of the boards. The mechanical properties and water resistance

increased as the hot pressing temperature and time increased. The optimum hot

pressing temperature was 220°C, and the optimum hot pressing time was 10min. The

MOR, MOE, IB and TS of the board manufactured under the optimum condition were

higher than the requirement of the 18 type of JIS A 5908. Thermal analysis showed

that the endothermic reaction of the adhesive composed with tannin and sucrose (only

the ratio at 25/75) were happened at more than 200°C, this explaining the promotion

of the particleboard properties when the hot pressing temperature was increased to

220°C. When the heating time was longer than 10min, insoluble matter was higher

than 70wt%. The FT-IR results showed the existence of the furan ring, carbonyl group

and dimethylene ether bridges. Comparing The FT-IR spectra of the adhesives heated

in different heating time, there was not obviously change of chemical structure in the

hot pressing time range of 10-20min.

3.5 Reference

Alakhras, F., and Holze, R. (2007) In situ UV-vis-and FT-IR-spectroscopy of

electrochemically synthesized furan-thiophene copolymers. J Synthetic Metals 157.

109-119.

http://www.sciencedirect.com/science/article/pii/S0379677907000070


65

Arabi, M., Faezipour, M., Layeghi, M., and Enayati, A. A. (2011) Interaction analysis

between slenderness ratio and resin content on mechanical properties of

particleboard. J For Res. 23, 461-464.

Choi, M. H., Byun, H. Y., and Chung, I. J. (2002) The effect of chain length of

flexible acid on morphology and mechanical property of modified phenolic resin.

J Polymer. 43, 4437-4444.

Chuntanapum, A., and Matsumura, Y. (2009) Formation of tarry material from 5-HMF

in subcritical and supercritical water. Ind Eng Chem Res. 48, 9837-9846.

Eggleston, G., Trask-Morrell, B. J., and Vercellotti, J. R. (1996) Use of differential

scanning calorimetry and thermogravimetric analysis to characterize the thermal

degradation of crystalline sucrose and dried sucrose-salt residues. J Agric Food

Chem. 44, 3319-3325.

Gaugler, M., and Grigsby, W. J. (2009) Thermal degradation of condensed tannins

from radiata pine bark. J Wood Chem Technol. 29, 305-321.

Gintner, Z., Vegh, A., and Ritlop, B. (1989) Determination of sucrose content of

cariogenic diets by thermal analysis. J Thermal Analysis. 35, 1399-1404.

Japanese Industrial Standards (JIS) (2003) JIS A 5908.Particleboard.

Jeong, J. A., Antonyraj, C., Shin, S., Kim, S., Kim, B., Lee, K. Y., and Cho, J. K.

(2013) Commercially attractive process for production of

5-hydroxymethyl-2-furfural from high fructose corn syrup. J Ind Eng Chem. 19,

1106-1111.

Kacurakova, M., Capek, P., Sasinkova, V., Wellner, N., and Ebringerova, A. (2000)

FT-IR study of plant cell wall model compounds: Pectic polysaccharides and

hemicelluloses. Carbohyd Polym. 43, 196-203.

Kim, S., and Kim, H. (2003) Curing behavior and viscoelastic properties of pine and

wattle tannin-based adhesives studied by dynamic mechanical thermal analysis

and FT-IR-ATR spectroscopy. J Adhesion Sci Technol. 17, 1369-1383.

Lee, J. W., Thomas, L. C., Jerrell, J., Feng, H., Cadwallader, K. J., and Schmidt, S. J.

(2011) Investigation of thermal decomposition as the kinetic process that causes

the loss of crystalline structure in sucrose using a chemical analysis approach. J



http://pubs.acs.org/action/doSearch?ContribStored=Chuntanapum%2C+A

http://pubs.acs.org/action/doSearch?ContribStored=Matsumura%2C+Y

http://pubs.acs.org/action/doSearch?ContribStored=Eggleston%2C+G

http://pubs.acs.org/doi/abs/10.1021/jf950836z#jf950836zAF1

http://pubs.acs.org/action/doSearch?ContribStored=Trask-Morrell%2C+B+J

http://pubs.acs.org/action/doSearch?ContribStored=Vercellotti%2C+J+R

http://admin-apps.webofknowledge.com/JCR/JCR?RQ=RECORD&rank=2&journal=CARBOHYD+POLYM

66

Agric Food Chem. 59, 702-712.

Seino, H., Uchibori, T., Nishitani, T., and Inamasu, S. (1984) Enzymatic synthesis of

carbohydrate esters of fatty acid (I) esterification of sucrose, glucose, fructose and

sorbitol. JAOCS. 61(11), 1761-1765.




Umemura, K. (2013) Condensed tannin-containing composition which is cured by

application of heat and pressure. WO2013018707 A1.

Umemura, K., Sugihara, O., and Kawai, S. (2013) Investigation of a new natural

adhesive composed of citric acid and sucrose for particleboard. J Wood Sci. 59,

203-208.

Vaz, P. D., and Ribeiro-Claro, P. J. A. (2003) C-H…O hydrogen bonds in liquid

cyclohexanone revealed by the v C=O splitting and the v C-H blue shift. J Raman

Spectrosc. 34, 863-867.

Zhang, M., Yang, H., Liu, Y., Sun, X., Zhang, D., Xue, D. (2012) Hydrophobic

precipitation of carbonaceous spheres from fructose by a hydrothermal process. J

Carbon. 50, 2155-2161.

Zhao, Z., and Umemura, K. (2014) Investigation of a new natural particleboard

adhesive composed of tannin and sucrose. J Wood Sci. 60, 269-277.







67

Chapter4

Effects of addition of citric acid on physical properties of

particleboard using tannin sucrose adhesive

4.1 Introduction

Based on the previous research in Chapter 2 and Chapter 3, wattle tannin and

sucrose can be combined to make an adhesive for particleboard manufacturing. The

mechanical properties of the particleboard produced with a tannin-sucrose ratio of

25/75, resin content of 30 to 40wt%, hot pressing temperature of 220 °C, and hot

pressing time of 10 min satisfied the requirements of the Japanese Industrial

Standards A 5908 (2003) type 18. However, the hot pressing temperature, time, and

resin content were much higher than that of particleboard produced using commercial

synthetic resins. During the reaction between tannin and sucrose,

5-hydroxymethyl-2-furfural (5-HMF) forms from the decomposition of sucrose, and

then 5-HMF reacts with tannin. Methods or substances that accelerate sucrose

decomposition to 5-HMF seems to improve the manufacturing conditions of

particleboard bonded with tannin and sucrose.

Acid compounds catalyze the decomposition of sucrose, thus increasing the yield

of 5-HMF (Locas and Yaylayan, 2008; Sievers et al., 2009). In addition, acid

compounds reduce the temperature of 5-HMF formation (Haworth and Jones, 1944;

Asghari and Yoshida, 2006). Citric acid is effective in forming 5-HMF from

saccharides (Asghari and Yoshida, 2006). Citric acid

(2-hydroxy-1,2,3-propanetricarboxylic acid) has a certain acidity (Grudpan et al.,

1998). It is an organic polycarboxylic acid containing three carboxyl groups, and it is

68

mainly produced by the fermentation of sucrose (Shu and Johnson, 1948). As a safe

natural substance, citric acid is widely used in food, beverages, and pharmaceuticals

(Černáa et al., 2003; Summers and Enever, 2006). In addition, citric acid can be used

as a natural adhesive to manufacture wood-based materials (Umemura et al., 2012),

and it reacts with sucrose (Umemura et al., 2013, 2015). Therefore, the addition of

citric acid is expected to promote the curing reaction of the adhesive and reduce the

hot pressing temperature. In this Chapter, citric acid was incorporated into a tannin

and sucrose adhesive, and the effect of this addition on the hot pressing temperature

of particleboard was investigated.

4.2 Effects of the addition of citric acid on thermal and

chemical properties of tannin-sucrose adhesive


4.2.1.1 Materials

Wattle tannin (commercial name: tannic acid ME) was purchased from the Fuji

Chemical Industry Co. (Wakayama, Japan), and the tannin content was 88.1%, which

measured by methanol method (Soto et al. 2001).. Sucrose (guaranteed reagent) and

citric acid (extra pure reagent) were purchased from Nacalai Tesque, Inc. (Kyoto,

Japan). These materials were used without further purification and were dried in a

vacuum oven at 60 °C for 15 h before use.

4.2.1.2 pH adjustment of adhesive solution by adding citric acid

The citric acid content in tannin-sucrose adhesive was determined by the

adjustment of pH values. The optimal ratio of tannin to sucrose is 25:75 (Zhao and

Umemura 2014). In this study, 25 g of tannin and 75 g of sucrose were mixed in a

beaker, and 150 g of distilled water was added to the mixture to blend a

http://www.sciencedirect.com/science/article/pii/S014486170200259X


69

tannin-sucrose adhesive solution at a concentration of 40 wt%. Citric acid was also

dissolved in distilled water at a 40 wt% concentration. Subsequently, 0.5 g of the

citric acid solution was added stepwise to the tannin-sucrose solution. The viscosity

and pH of the solution at 20 °C was measured by a rotational viscometer (Viscolead

One, Fungilab S.A., Barcelona, Spain) and a pH meter (D-51, Horiba Scientific,

Kyoto, Japan), respectively. This process was repeated several times until the

tannin-sucrose solution reached pH 1.5. Basic information regarding the

tannin-sucrose-citric acid adhesives is presented in Table 4.1.

Table 4.1 Formulation of Tannin-Sucrose-Citric Acid Adhesives

The ratio of

tannin:sucrose:citric acid

Addition

of citric

acid

solution

(g)

Citric acid

content in

adhesive

(wt%)

Concentration

(wt%)

Viscosity at

20 °C

(mPa·s)

pH

25:75:0.0 0.0 0.0

40

51.3 4.8

25:75:0.4 1.0 0.4 50.5 3.8

25:75:1.8 4.5 1.8 48.7 3.0

25:75:4.8 12.0 4.6 43.5 2.5

25:75:16 40.0 13.8 42.7 2.0

25:75:25 62.5 20.0 40.4 1.8

25:75:50 125.0 33.3 36.5 1.5


After pH adjustments, 100 g of adhesive was prepared for each variation in citric

acid content. In each version of the adhesive solution, 20 g of the solution was divided

into 10 aluminum cups and dried in an oven at 80 °C for 12 h. The samples were then

pulverized to smaller than 250-μm mesh size to obtain the uncured adhesive powder.

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were

carried out using a TGA 2050 (TA Instruments, Tokyo, Japan) and DSC 2910 (TA

Instruments, Tokyo, Japan), respectively, and the samples were scanned from room

temperature to 400 °C at a rate of 10°C/min under nitrogen purging with the flow rate

70

at 100 mL/min and 40 mL/min, respectively.


As shown in Table 4.1, 100 g adhesive solutions with of 4.6%, 13.8%, 20.0%,

and 33.3% citric acid were prepared. Uncured adhesive powder was obtained in the

same manner as in the thermal analysis. Each of the uncured adhesive powders was

divided into four parts, and these were heated in an oven at 160, 180, 200, or 220 °C

for 10 min. Next, 2-g samples of each cured adhesive were boiled in distilled water

for 4 h to obtain the insoluble matter. The boiling treatment was carried out in

triplicate. All samples obtained from heating treatments and boiling treatments were

vacuum-dried at 60 °C for 15 h. Infrared spectra were obtained with a Fourier

transform infrared spectrophotometer (FT/IR-4200, JASCO Corporation, MD, USA)

using the KBr disk method; they were recorded with an average of 32 scans at a

resolution of 4 cm-1

.



0

20

40

60

80

100

0 100 200 300 400

We

ight (

% )

Temperature ( ﾟC ）

0.0

0.4

1.8

4.6

13.8

20.0

33.3

Citric acid content

of adhesive (wt%)

71

Fig.4.1 TG curves of the adhesives with different citric acid contents.

Fig.4.2 DTG curves of the adhesives with different citric acid contents.

In the derivative TG (DTG) curves (Fig. 4.2), tannin-sucrose adhesive (0 wt%

citric acid content) had a noticeably weight loss at 204 °C; this result was attributed to

the reaction between tannin and sucrose (Zhao and Umemura, 2015). In the

tannin-sucrose-citric acid adhesives, the temperatures of significant weight loss in

adhesives with 0.4, 1.8, 4.6, 13.8, 20.0, and 33.3 wt% citric acid content were 202,

200, 176, 162, 159, and 151 °C, respectively. As the citric acid content increased, the

temperature of significant weight loss decreased. Because acid compounds catalyze

sucrose decomposition at lower temperatures (Haworth and Jones, 1944; Asghari and

Yoshida, 2006), the observed results reflected the decomposition of sucrose or another

reaction between tannin, sucrose, and citric acid. A shoulder at 200 °C in the 20.0 and

33.3 wt% citric acid adhesive curves reflected an apparent degradation of citric acid

(Umemura et al., 2012). Another shoulder located at 300 °C was observed in the

curves produced from all tannin-sucrose-citric acid adhesives, and this decline was

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 100 200 300 400

De

rivative (

%/ﾟ

C )

Temperature ( ﾟC )

0.0

0.4

1.8

4.6

13.8

20.0

33.3

Citric acid content

of adhesive (wt%)

72

possibly caused by decomposition of the cured adhesives.

Fig. 4.3 DSC curves of the adhesives with different citric acid contents

DSC curves of the adhesives showed that tannin-sucrose adhesive (0 wt% citric

acid content) had two endothermic peaks (Fig. 4.3). The peak located at 180 °C was

0 100 200 300 400

Temperature ( °C )

En

doth

erm

Exo

therm

1.0 W/g

33.3

20.0

13.8

4.6

1.8

0.4

0.0

Citric acid content

of adhesive (wt%)

73

due to the melting of sucrose (Eggleston et al., 1996), and the peak located at 215 °C

was attributed to the caramelization of sucrose or polymerization (Eggleston et al.,

1996; Zhao and Umemura, 2015). In tannin-sucrose-citric acid adhesives with 0.4 and

1.8 wt% citric acid, a shoulder was detected at 157 °C, and endothermic peaks were

observed at 210 and 194 °C. TG analysis of these two adhesives indicated that the

weight loss at 157 °C was not noticeable. Therefore, the shoulder must have been due

to the melting of some substance, which could have been citric acid (Barbooti and

Al-Sammerrai, 1986). The endothermic peak located at 210 °C was due to

caramelization or polymerization reactions.

When the citric acid content was equal to or greater than 4.6 wt%, a broad

endothermic peak was observed at 155 °C in all adhesives. In accordance with the TG

analysis, this peak was probably due to the loss of sucrose or some reaction between

tannin, sucrose, and citric acid. In adhesives with 20.0 and 33.3 wt% citric acid, a

small endothermic shoulder was observed at 212 °C, which was due to the loss of

citric acid (Barbooti and Al-Sammerrai, 1986).

In sum, increasing citric acid content decreased the temperature of weight loss

and endothermic reactions from 220 to 155 °C, demonstrating that citric acid

effectively reduced the reaction temperature of the adhesive. When the citric acid

content was equal to or greater than 4.6 wt%, the reaction temperature was noticeably

reduced. Therefore, in the next set of experiments, tannin-sucrose-citric acid

adhesives with 4.6, 13.8, 20.0, and 33.3 wt% citric acid contents were tested, and

tannin-sucrose adhesive with 0 wt% citric acid content was used as a reference.

4.2.2.2 Insoluble matter

The adhesives were heated at 160, 180, 200, and 220 °C for 10 min, and the

insoluble matter after boiling was measured (Fig. 3). As the heating temperature

increased, the insoluble matter also increased considerably. In each heating

temperature condition, the insoluble matter increased with increasing citric acid

content, indicating that the addition of citric acid improved adhesive curing. Analysis

74

of variance (ANOVA) showed no significant (p>0.05) difference between the

adhesives with 20.0 and 33.3 wt% citric acid in all heating temperature conditions.

Notably, when the heating temperature was 160 or 180 °C, there was no insoluble

matter in 0 wt% citric acid tannin-sucrose adhesive, but some insoluble matter was

present in adhesives containing citric acid. Judging from the thermal analysis, this

result reflects the reaction of adhesives with citric acid at a lower temperature than in

the tannin-sucrose adhesive. When the heating temperature was 200 °C, adhesives

with 20.0 and 33.3 wt% citric acid contained 60% insoluble matter, nearly two times

higher than the 0 wt% citric acid tannin-sucrose adhesive.

Fig. 4.4 Insoluble matter of the adhesives with different citric acid contents.

0

20

40

60

80

100

160 180 200 220

Inso

luble

ma

tter

( %

)

Heating temperature ( ﾟC )

0.0

4.6

13.8

20.0

33.3

Citric acid content of

adhesive ( wt% )

75

4.2.2.3 FT-IR

Fig. 4.5 Infrared spectra of the adhesives heated at 200 °C for 10 min before boiling.

700125018002350290034504000

Wavenumber ( cm-1 )

Ab

so

rban

ce

33.3

20.0

13.8

4.6

0.0

17

31

11

90

78

0

26

30

17

05

12

00

Citric acid content

of adhesive ( wt% )

76

Fig. 4.6 Infrared spectra of the adhesives heated at 200 °C for 10 min after boiling.

The effect of citric acid on the chemical structure of the adhesives cured at

200 °C for 10 min before boiling treatment was investigated by FT-IR, and the results

were shown in Fig. 4.5. Compared with the peaks obtained from tannin-sucrose

adhesive (0 wt% citric acid content), the absorption bands of the tannin-sucrose-citric

acid adhesives appeared at 2630 and 1731 cm-1

, and these two peaks located at 1190

to 1200 cm-1

and 780 cm-1

increased as citric acid content increased. The broad

absorption band at 2630 cm-1

belongs to the vibration of H-bonded carboxylic OH

groups (Zagar and Grdadolnik, 2003). The peak at 1731 cm-1

can be attributed to C=O

700125018002350290034504000

Wavenumber ( cm-1 )

Ab

so

rban

ce

17

31

11

90

78

0

17

05

12

00

33.3

20.0

13.8

4.6

0.0

Citric acid content

of adhesive ( wt% )

77

stretching derived from the carboxyl group and/or ester group (Yang and Wang, 1996;

Zagar and Grdadolnik, 2003). The peak located at 1190 cm-1

is due to C-O stretching

from the carboxyl group and/or dimethylene ether bridges (Mawhinney and Yates,

2001; Kunnambath and Thirumalaisamy, 2015). Meanwhile, the peak located at 780

cm-1

is derived from the unsubstituted CH=CH of the furan ring (Cimino et al., 1972).

In the tannin-sucrose adhesive (0 wt% citric acid content), the peak located at 1705

cm-1

is derived from the C=O carbonyl group (Sellitti et al., 1990). The peak located

at 1200 cm-1

can be attributed to C-O-C dimethylene ether bridges in the phenolic

resin and wattle tannin adhesives (Choi et al., 2002; Kim and Kim, 2003); therefore,

the peak located at 1200 cm-1

derived from tannin-sucrose adhesive (0 wt% citric acid

content) was possibly due to the dimethylene ether bridges.

The peaks derived from citric acid appeared strongly when the citric acid content

of the adhesives was high, and some water-soluble substances were contained in the

samples. The chemical structure of the insoluble matter in cured adhesives was

observed by FT-IR measurements after the cured adhesives were boiled (Fig. 4.6).

The absorption band at 2630 cm-1

was barely recognizable in all spectra, indicating

that carboxyl groups did not exist in the insoluble matter. The peaks located at 1731

and 1190 cm-1

were only observed in the insoluble matter of the adhesives with 20.0

and 33.3 wt% citric acid. The peaks increased with increasing citric acid content,

implying that the ester linkage and dimethylene ether bridges were more abundant as

the citric acid increased. The peaks at 1705 and 1200 cm-1

were observed in the

insoluble matter of the adhesives with 0, 4.6, and 13.8 wt% citric acid, indicating that

the chemical structure of the insoluble matter of these adhesives was very similar. The

peak at 780 cm-1

increased slightly as citric acid increased, suggesting that the furan

ring content in the insoluble matter increased. In sum, when the citric acid content of

adhesive was adjusted to 20.0 and 33.3%, ester linkages and dimethylene ether

bridges were formed. With increased citric acid content, the furan ring content

increased, and more chemical bonds derived from tannin participated in the reaction.

78

4.3 Effects of the addition of citric acid on the properties of

the particleboard


4.3.1.1 Materials

Wattle tannin (commercial name: tannic acid ME) was purchased from the Fuji

Chemical Industry Co. (Wakayama, Japan). Sucrose (guaranteed reagent) and citric

acid (extra pure reagent) were purchased from Nacalai Tesque, Inc. (Kyoto, Japan).

These materials were used without further purification and were dried in a vacuum

oven at 60 °C for 15 h before use.

Recycled wood particles were obtained from a particleboard company, and they

were screened using a sieving device to collect particles between 0.9 mm and 5.9 mm.

The moisture content of the original particles was 3 to 4 wt%. Before particleboard

manufacturing, particles were dried in an oven at 80 °C for 12 h to a final moisture

content of 2 wt%.

4.3.1.2 Manufacture of the particleboard

Tannin, sucrose, and citric acid were dissolved in distilled water with 4.6%,

13.8%, 20.0%, and 33.3% citric acid contents and a solution concentration of 40 wt%

(Table 4.1). The adhesive solution was sprayed onto particles in a blender at 30 wt%

resin content based on the weight of the oven-dried particles. After spraying, the

particles were dried at 80 °C for 12 h until the moisture content was 3 to 6 wt%. The

particles were mat-formed using a 300 × 300 mm forming box. For every variation in

citric acid content, particleboards were manufactured with hot pressing temperatures

of 160, 180, 200, and 220 °C; the hot pressing time was 10 min. The thickness was

controlled using a 9-mm distance bar during pressing. The size of the manufactured

board was 300 × 300 × 9 mm, and the target density was 0.8 g/cm3.

79

4.3.1.3 Evaluation of the board properties

The boards were conditioned for 1 week at 20 °C and 60% relative humidity (RH)

and then evaluated according to the Japanese Industrial Standard for particleboard

(JIS A 5908 2003). The average density of the particleboards after conditioning was

calculated by measuring the dimension and weight of all the samples obtained from

each particleboard. The mechanical properties of the particleboards were investigated

with a universal testing machine (Model 4411, Instron Corp., PA, USA). The static

three-point bending test was carried out on a 200 × 30 × 9 mm specimen from each

board, and the effective span and loading speed were 150 mm and 10 mm/min,

respectively. The modulus of rupture (MOR) and the modulus of elasticity (MOE)

were obtained. The internal bond strength (IB) test was performed on a 50 × 50 mm

specimen with a loading speed of 2 mm/min, and thickness swelling (TS) after water

immersion for 24 h at 20 °C was measured in specimens of the same size. Following

the TS test, thickness and weight changes under a cyclic accelerated aging treatment

(drying at 105 °C for 10 h, warm water immersion at 70 °C for 24 h, drying at 105 °C

for 10 h, boiling water immersion for 4 h, and drying at 105 °C for 10 h) were

measured to investigate the water resistance in severe conditions. Each experiment

was performed in quintuplicate, and the average value and standard deviation were

calculated. Statistical significance of ANOVA analysis was considered for p values <

0.05. The MOR, MOE, and IB values were corrected for target density based on each

regression line between actual values and sample densities of the mechanical

properties.

80


4.3.2.1 Bending properties

Fig. 4.7 Effects of the citric content of adhesive and hot pressing temperature on

MOR in bending properties. Error bars indicate standard deviations.

0

5

10

15

20

25

160 180 200 220

MO

R (

MP

a )

Hot pressing temperature ( °C )

0.0

4.6

13.8

20.0

33.3

Citric acid content

of adhesive ( wt% )

81

Fig. 4.8 Effects of the citric content of adhesive and hot pressing temperature on

MOE in bending properties. Error bars indicate standard deviations.

Particleboards bonded using adhesives with various citric acid contents were

manufactured at different hot pressing temperatures, and MOR and MOE were

evaluated (Figs. 4.7 and 4.8). As the hot pressing temperature increased, both MOR

and MOE were enhanced in all particleboards. When the pressing temperature was

equal to or higher than 200 °C, the bending properties of the particleboards satisfied

the requirements of the 18 type JIS A 5908 standard (MOR > 18 MPa, MOE > 3 GPa)

0

1

2

3

4

5

160 180 200 220

MO

E (

GP

a )


0.0

4.6

13.8

20.0

33.3

Citric acid content

of adhesive ( wt% )

82

(JIS A 5908 2003). With hot pressing temperatures of 160, 180, and 200 °C, the MOR

and MOE values of the boards bonded with adhesives containing citric acid were

higher than those bonded with tannin-sucrose adhesive, as the curing temperature of

the tannin-sucrose-citric acid adhesives was lower. The maximum average MOR and

MOE values were 21.5 MPa and 4.9 GPa, respectively, which were obtained from the

board bonded with 33.3% citric acid adhesive at 200 °C. Analysis of variance

(ANOVA) showed no significant difference (p>0.05) in MOR or MOE in boards

bonded with 20.0 and 33.3% citric acid adhesives at 200 °C, and there was no

significant (p>0.05)difference in any boards hot-pressed at 220 °C.

4.3.2.2 IB properties

The IB of the particleboards was evaluate, and the results were shown in Fig. 4.9.

The strength increased with increasing hot pressing temperature, irrespective of the

citric acid content. The IB of the boards bonded with tannin-sucrose-citric acid

adhesives at all hot pressing temperatures satisfied the requirements of the 18 type JIS

A 5908 standard (IB > 0.3 MPa) (JIS A 5908 2003). However, the maximum value

obtained from the board bonded with tannin-sucrose (0 wt% citric acid content)

adhesive at 220 °C was 1.45 MPa. Analysis of variance (ANOVA) showed no

significant difference (p>0.05) between the boards bonded with 20.0 and 33.3% citric

acid adhesives at all hot pressing temperatures. When the hot pressing temperature

was equal to or lower than 180 °C, the IB of the board bonded with tannin-sucrose

adhesive was very low; however, the particleboard bonded with the adhesives with

citric acid exhibited superior IB because of the curing of citric acid-containing

adhesives at 160 and 180 °C. As the hot pressing temperature increased to 200 and

220 °C, the opposite result was obtained, with IB increasing with the decreasing citric

acid content. This phenomenon requires further clarification.

83

Fig. 4.9 Effects of adhesive citric acid content and hot pressing temperature on IB.

Error bars indicate standard deviations.

Overall, when the hot pressing temperature was 160 or 180 °C, the mechanical

properties of the particleboard increased with increasing citric acid (Fig. 5, 6).

However, citric acid did not enhance particleboard mechanical properties when the

hot pressing temperature was 200 or 220 °C.

0.0

0.5

1.0

1.5

160 180 200 220

IB (

MP

a )


0.0

4.6

13.8

20.0

33.3

Citric acid content

of adhesive ( wt% )

84

4.3.2.3 Water resistance properties

Fig. 4.10 Effects of citric content and hot pressing temperature on TS. Error bars


Figure 4.10 shows the TS analysis of the particleboards. When the particleboards

were bonded with tannin-sucrose (0 wt% citric acid content) adhesive at 160 or

180 °C, the boards decomposed during the immersion treatment, showing very low

water resistance. As the hot pressing temperature increased, the TS values of the

particleboards decreased irrespective of the citric acid content of the adhesive. At each

hot pressing temperature, the TS values decreased with increasing citric acid,

0

10

20

30

40

50

60

70

80

90

160 180 200 220

TS

( %

)


0.0

4.6

13.8

20.0

33.3

Citric acid content

of adhesive ( wt% )

85

indicating that citric acid improved particleboard TS properties. The best value was

5%, obtained from the board bonded with 33.3% citric acid adhesive at 220 °C. For

the particleboards bonded with 20.0 and 33.3% citric acid adhesives at 200 °C and for

all boards manufactured at 220 °C, the TS values satisfied the requirements of the 18

type JIS A 5908 standard (TS < 12%) (JIS A 5908 2003).

To further clarify the effect of citric acid on water resistance, a cyclic accelerated

aging treatment was performed, and the thickness changes of the particleboards

bonded at 200 °C were measured (Fig. 4.11). The results for immersion at 20 °C for

24 h were similar to those shown in Fig. 4.10. Generally, a stepwise increase in the

thickness of the boards was observed. For boards bonded with tannin-sucrose

adhesive at 200 °C, the final thickness change was 17.9%, whereas the board

manufactured with 33.3% citric acid adhesive showed a 6.1% change. When the

particleboards were bonded at 220°C, the thickness changes were similar to the results

shown in Fig. 8a; however, the thickness changes after every treatment were lower

than the changes in the boards manufactured at 200 °C. The least final thickness

change was 2.1%, which was obtained from the board manufactured with 33.3% citric

acid adhesive at 220 °C.

The weight changes of the particleboards bonded at 200 °C in a cyclic

accelerated aging treatment were measured (Fig. 4.12). In the first water immersion

treatment, water absorption was similar to the TS data. This result indicated that the

addition of citric acid to the adhesives inhibited water absorption by the particleboards.

The weight decrease in the subsequent drying treatment of all boards ranged from -4.5%

to -1.6%, suggesting that a slight elution of the adhesive components occurred. The

overall weight increase in the 70 °C immersion treatment was higher than in the first

treatment. This effect could be due to the lowering of the water resistance of the

adhesive and the penetration of water into the wood (Umemura et al., 2013). The

weight change of each board after boiling treatment was almost the same as in the

warm water treatment, indicating that the boards exhibited excellent stability during

boiling. The least final weight change of the board manufactured at 200 °C was -8.0%,

which was obtained from particleboards bonded with 20.0 and 33.3% citric acid

86

adhesives. The boards bonded with adhesives containing citric acid showed smaller

final weight changes than those manufactured with the tannin-sucrose adhesive. The

particleboards bonded at 220 °C showed the same trend of weight changes in the

cyclic accelerated aging treatment. The final weight change of the board

manufactured using tannin-sucrose adhesive at 220 °C was -4.7%, whereas the board

manufactured with 33.3% citric acid adhesive showed a relatively small value at

-3.8%. Thus, the addition of citric acid enhanced water resistance in the

particleboards.

Fig. 4.11 Effects of the citric acid content of adhesive on thickness changes in

particleboards bonded at 200 °C in a cyclic accelerated aging treatment. Error bars


0

5

10

15

20

25

30

35

40

Th

ickness c

ha

ng

e (

% )

0.0

4.6

13.8

20.0

33.3

Citric acid content

of adhesive ( wt% )

87

Fig. 4.12 Effects of the citric acid content of adhesive on weight changes in

particleboards bonded at 200 °C in a cyclic accelerated aging treatment. Error bars


4.4 Summary

The effects of adding citric acid to tannin-sucrose adhesive were investigated by

the analysis of adhesives and evaluation of particleboard properties. The results

showed that the addition of citric acid was effective in reducing reaction temperature,

and the insoluble matter remaining from 20.0 and 33.3 % citric acid contents

0.0

4.6

13.8

20.0

33.3

Citric acid content

of adhesive ( wt% )

-20

0

20

40

60

80

100W

eig

ht c

ha

ng

e (

% )

88

adhesives at 200 °C was 2 times higher than for the tannin-sucrose adhesive. In

addition, ester linkage and dimethylene ether bridges were recognized by FT-IR. The

physical properties of the particleboards bonded with tannin-sucrose-citric acid

adhesive with 20.0 and 33.3 % citric acid contents at more than 200 °C satisfied the

requirements of the type 18 standard of JIS A 5908 (2003). Consequently, the addition

of citric acid promoted the reaction between tannin and sucrose at a lower temperature,

and decreased the hot pressing temperature to 200 °C, while enhancing the bending

properties and water resistance of the particleboards.

4.5 Reference

Asghari, F., and Yoshida, H. (2006) Acid-catalyzed production of 5-hydroxymethyl

furfural from D-fructose in subcritical water. Ind Eng Chem Res . 45(7),

2163-2173.

Barbooti, M., and Al-Sammerrai, D. (1986) Thermal decomposition of citric acid.

Thermochim Acta. 98(1), 119-126.

Černá, M., Barros, A., Nunes, A., Rocha, S., Delgadillo, I., Čopı́ková, J., and Coimbra,

M. (2003) Use of FT-IR spectroscopy as a tool for the analysis of polysaccharide

food additives. Carbohyd Polym. 51(4), 383-389.

Choi, M. H., Byun, H. Y., and Chung, I. J. (2002) The effect of chain length of

flexible diacid on morphology and mechanical property of modified phenolic resin.

Polym. 43(16), 4437-4444.

Cimino, G., De Stefano, S., and Minale, L. (1972) Minor C-21 furanoterpenes from

the sponges Spongia officinalisand Hippospongia communis. Tetrahedron. 28(2),

267-273.

Eggleston, G., Trask-Morrell, B. J., and Vercellotti, J. R. (1996) Use of differential

scanning calorimetry and thermogravimetric analysis to characterize the thermal

degradation of crystalline sucrose and dried sucrose-salt residues. J Agr Food

Chem. 44(10), 3319-3325.










http://pubs.acs.org/action/doSearch?ContribStored=Eggleston%2C+G

http://pubs.acs.org/doi/abs/10.1021/jf950836z#jf950836zAF1

http://pubs.acs.org/action/doSearch?ContribStored=Trask-Morrell%2C+B+J

http://pubs.acs.org/action/doSearch?ContribStored=Vercellotti%2C+J+R

89

Grudpan, K., Sritharathikhun, P., and Jakmunee, J. (1998) Flow injection

conductimetric or spectrophotometric analysis for acidity in fruit juice. Anal Chim

Acta. 363(2-3), 199-202.

Haworth, W., and Jones, W. (1944) The conversion of sucrose into furan compounds.

Part I. 5-Hydroxymethylfurfuraldehyde and some derivatives. J Chem Soc. 1944,

667-670.

JIS A 5908 (2003) Particleboards, Japanese Standards Association, Tokyo, Japan.

Kim, S., and Kim, H. (2003) Curing behavior and viscoelastic properties of pine and

wattle tannin-based adhesives studied by dynamic mechanical thermal analysis

and FT-IR-ATR spectroscopy. J Adhes Sci Technol. 17(10), 1369-1383.

Locas, C., and Yaylayan, V. (2008) Isotope labeling studies on the formation of

5-(hydroxymethyl)-2-furaldehyde (HMF) from sucrose by pyrolysis-GC/MS. Agr

Food Chem. 56(15), 6717-6723.

Mawhinney, D. B., and Yates Jr., J. T. (2001) FTIR study of the oxidation of

amorphous carbon by ozone at 300K - Direct COOH formation. Carbon. 39(8),

1167-1173..

Sellitti, C., Koenig, J., and Ishida, H. (1990) Surface characterization of graphitized

carbon fibers by attenuated total reflection Fourier transform infrared

spectroscopy. Carbon. 28(1), 221-228.

Shu, P., and Johnson, M. (1948) Citric acid. Ind Eng Chem. 40(7), 1202-1205.

Sievers, C., Musin, I., Marzialetti, T., Olarte, M., Agrawal, P., and Jones, C. (2009)

Acid-catalyzed conversion of sugars and furfurals in an ionic-liquid phase.

ChemSusChem. 2(7), 665-671.




Summers, M., and Enever, R. (2006) Preparation and properties of solid dispersion

system containing citric acid and primidone. J Pharm Sci. 65(11), 1613-1617.


adhesive composed of citric acid and sucrose for particleboard. J Wood Sci. 59(3),



90

203-208.


adhesive composed of citric acid and sucrose for particleboard II: Effects of board

density and pressing temperature. J Wood Sci. 61(3), 40-44.

Umemura, K., Ueda, T., and Kawai, S. (2012) Characterization of wood-based

molding bonded with citric acid. J Wood Sci. 58(1), 38-45.

Wang, Z., Gu, Z., Hong, Y., Cheng, L., and Li, Z. (2011) Bonding strength and water

resistance of starch-based wood adhesive improved by silica nanoparticles.

Carbohyd Polym. 83(1), 72-76.

Yang, C., and Wang, X. (1996) Formation of cyclic anhydride intermediates and

esterification of cotton cellulose by multifunctional carboxylic acids: an infrared

spectroscopy study. Text Res J. 66(9), 595-603.

Zagar, E., and Grdadolnik, J. (2003) An infrared spectroscopic study of H-bond

network in hyperbranched polyester polyol. J Mol Struct. 658(3), 143-152.


adhesive composed of tannin and sucrose. J Wood Sci. 60(4), 269-277.


adhesive composed of tannin and sucrose 2: Effect of pressing temperature and

time on board properties, and characterization of adhesive. BioResources. 10(2),

2444-2460.

91

Conclusion

This thesis consists of four chapters: Chapter1, General introduction; Chapter 2,

Exploratory experiments of tannin and sucrose for particleboard; Chapter 3, Effects of

hot pressing temperature and time on board properties, and characterization of

adhesive; Chapter 4, Effects of the addition of citric acid on the curing of tannin and

sucrose adhesive and bond performance of particleboard. The results of each chapter

are summarized as follows:

In Chapter1, the current development of synthetic resin and natural adhesive

were studied. The current development of synthetic resin showed that, under the

pressure of decreasing of fossil resources and the requirement of human health, the

research about synthetic resin focus on the modification or partly replace by the

natural substances, which could reduce the utilization of fossil resources and reduce

the toxic emission from some of the synthetic resin. The current development of

natural adhesive showed that, due to the low bond ability of natural substances, some

modification by chemical substances derived from the fossil resources are needed, the

natural substance only seems hardly to use as adhesive. Therefore, it is necessary to

develop the adhesive composed of natural substances only.

In Chapter 2, the exploratory experiments of tannin and sucrose adhesive for

particleboard were carried out. By the experiments, the effects of the drying treatment

before hot pressing, weight ratio between tannin and sucrose, and resin content on the

physical properties were investigated. All the particleboards in this chapter were

manufactured at 200℃ for 10min. The results of the particleboard bonded by tannin

and sucrose without drying treatment before hot pressing showed that, the physical

properties of the particleboards are very low in all the weight ratio of tannin and

sucrose conditions, indicated that the high moisture content of the mat negative affect

the physical properties of the particleboard bonded with tannin and sucrose. For

92

certifying this conclusion, the particleboards were manufactured with drying

treatment before hot pressing, the results showed the physical properties improved

significantly irrelevant the weight ratio between tannin and sucrose. The results of

effects of weight ratio between tannin and sucrose on the properties of the

particleboard showed that, as the increasing of the sucrose content, the physical

properties of the particleboard were improved, the optimal weight ratio between

tannin and sucrose was 25/75. The results of the effects of resin content on the

properties of the particleboard exhibited that, as the increasing of the resin content,

the physical properties increased. When the resin content was higher than 30wt%, the

mechanical properties satisfied the JIS 18 type standard. Therefore, the optimal

manufacture conditions of the with/without drying treatment before hot pressing,

weight ratio between tannin and sucrose, and resin content of the particleboard

bonded by tannin and sucrose were with drying treatment, 25/75, and 30-40wt%,

respectively. The reaction mechanism between tannin and sucrose was studied by

FT-IR analysis, and the spectra obtained from uncured and cured adhesives were

compared. The results showed that, after the heating treatment, the peak located at

1130 and 920cm-1

derived from glycosidic linkage and pyranose ring disappeared,

indicated the decomposition of the sucrose during the heating treatment. The

increased peak located around 1705, 1509, 1200 and 780cm-1 derived from carbonyl

group, furan, dimethylene ether bridges, and furan, respectively, this indicated the

formation of the 5-HMF from the decomposition of sucrose, and 5-HMF reacted with

tannin and form the dimethylene ether bridges.

In Chapter 3, the effect of the hot pressing temperature and hot pressing time on

the properties of the particleboard bonded by tannin and sucrose were investigated.

Based on the results obtained from Chapter 2, all the particleboards manufactured in

this chapter with the optimal weight ratio between tannin and sucrose was 25/75, resin

content was 30 and 40wt%, and did the drying treatment at 80℃ for 12h before hot

pressing. The results of the effects of hot pressing temperature on the particleboard

properties showed that, as the increasing of the hot pressing temperature, both the

mechanical properties and the water resistance increased. When the hot pressing

93

temperature at 220℃, the TS values of the particleboards both bonded with 30 and

40wt% resin content are satisfied the JIS 18 type standard. The results of the effects of

hot pressing time on the board properties exhibited that, in the time range from 5 to

10min, as the increasing of the hot pressing time, the mechanical properties of the

particleboard increased, however, a slightly decrease happened when the hot pressing

time longer than 10min. Therefore, the optimal hot pressing temperature and hot

pressing time of the particleboard bonded by tannin and sucrose were 220℃and

10min, respectively. The tannin and sucrose adhesive was characterized by thermal

analysis, insoluble matter and FT-IR analysis. Thermal analysis showed that the

endothermic reaction of the adhesive composed with tannin and sucrose (only the

ratio at 25/75) were happened at more than 200°C, this explaining the promotion of

the particleboard properties when the hot pressing temperature was increased to

220°C. When the heating time was longer than 10min, the maximum insoluble matter

at more than 70% was obtained, indicated the heating time at 10min for the curing of

tannin and sucrose adhesive is needed. The FT-IR results showed the existence of the

furan ring, carbonyl group and dimethylene ether bridges in the adhesives cured at

220℃. Comparing The FT-IR spectra of the adhesives heated in different heating time,

there was not obviously change of chemical structure in the hot pressing time range of

10-20min.

In Chapter 4, the effects of adding citric acid to tannin-sucrose adhesive were

investigated by the analysis of adhesives and evaluation of particleboard properties.

The results of the thermal analysis showed that, as the increasing of the citric acid

content, both the weight loss and endothermic reaction temperatures decreased,

indicated that the addition of citric acid was effective in reducing reaction temperature

of tannin and sucrose. The results of the insoluble matter showed that, the insoluble

matter from 20.0 and 33.3% citric acid contents adhesives at 200℃ was 2 times

higher than that from tannin-sucrose adhesives, means that the addition of citric acid

effective on the curing of tannin and sucrose adhesive. The results of FT-IR analysis

showed that, when the citric acid content of adhesive was adjusted to 20.0 and 33.3%,

ester linkages and dimethylene ether bridges were formed. With increased citric acid

94

content, the furan ring content increased, and more chemical bonds derived from

tannin participated in the reaction, this also indicated that the addition of citric acid

improve the curing of tannin and sucrose. The effects of the addition of citric acid on

the hot pressing temperature and properties of the particleboard bonded by tannin and

sucrose adhesive were investigated. The results showed that, physical properties of

the particleboards bonded with tannin-sucrose-citric acid adhesive with 20.0 and 33.3 %

citric acid contents at more than 200 °C satisfied the requirements of the type 18

standard of JIS A 5908 (2003). Consequently, the addition of citric acid promoted the

reaction between tannin and sucrose at a lower temperature, and decreased the hot

pressing temperature to 200 °C, while enhancing the bending properties and water

resistance of the particleboards.

95

Acknowledgments

My deepest gratitude goes first and foremost to Professor Kozo Kanayama , my

supervisor, for his constant encouragement and guidance on my research, and he

taught me how to open the mind during the research. I learned a lot from him, not

only in the research area but also the attitude of life, these gains will influence my life

in the future.

I also must be deeply grateful to Associate Professor Kenji Umemura, he taught

me a lot of the research and experiment methods, which help me to finish the

experiments showed in this thesis. In addition, the conscientious work attitude from

him is very worth me to learn.

I also want to thank Professor Hiroshi Isoda, Professor Hiroyuki Yano, Professor

Tsuyoshi Yoshimura, and Professor Junji Sugiyama for your help on my research, and

I also learn a lot of the knowledge of wood and wood composites from your research.

Last my thanks would go to my beloved family for their loving considerations

and great confidence in me all through these years. I also owe my sincere gratitude to

my friends and my fellow classmates who gave me their help and time in listening to

me and helping me work out my problems during the difficult course of the thesis.

Thanks to all the member in the Lab. Sustainable Materials and my friends in

other Labs. You give me a lot of pleasant memories in Kyoto, Japan, and I think this

friendship will be continued wherever where we are.

I would like to thank Associate Professor Tomoya Imai, Associate Professor

Kentaro Abe, Aya Yanagawa, Takuro Mori, Akihisa Kitamori for helping me to carry

out my experiments and kindly comments on my research.

Finally, I am deeply indebted to Ms. Shijing Sun for her continuing support and

encouragement.

Title Investigation of natural adhesive composed of tannin...

Documents

Transcript of Title Investigation of natural adhesive composed of tannin...