PURPOSE AND TARGET OF THE DEVELOPMENT OF CARBON

FIBER REINFORCED THERMOPLASTICS

Daisuke Suzuki, Jun Takahashi, Kazuro Kageyama, Kiyoshi Uzawa and Isamu Ohsawa

Department of Environmental and Ocean Engineering, The University of Tokyo

7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

d-suzuki@sunshine.naoe.t.u-tokyo.ac.jp

ABSTRACT

Energy consumption of the running stage of automobiles can be dramatically reduced by

lightening their weight by using CFRP (carbon fiber reinforced plastics). And, in order to

widely apply such environmental friendly performance of CFRP to general industry fields, it

is necessary to use thermoplastics as matrix resins to not only reduce cost but improve

processability and recyclability. In this paper, the advantage and development goal of CFRTP

(carbon fiber reinforced thermoplastics) are made clear from viewpoints of LCA and micro

mechanics, in particular, the interfacial adhesiveness between fiber and resin.

KEY WORDS: CFRP, Thermoplastics, Surface treatment

1. INTRODUCTION

People become to pay more attention to CFRP as structural material from a viewpoint of

energy saving of vehicles and hence economical efficiency in transportation, such as airplane,

train, passenger automobile, truck and bus. However, current CFRP has problems, such as

cost, manufacturing time, processability, recyclability, etc., when we apply it to mass

production since most of it is made by thermosetting resin like epoxy [1]. To solve these

problems, CFRTP (carbon fiber reinforced thermoplastics) is promising although CFRTP also

has some other unsolved technical problems. One of the most severe problems of CFRTP is

poor adhesiveness between carbon fiber and thermoplastics. This topic has been investigated

mainly between glass fiber and thermoplastics, but sufficient technical solutions concerning

carbon fiber is not established yet. Another severe problem is poor impregnation of

thermoplastics into carbon fiber bundle. In this paper, CFRTP is compared with competitive

materials from viewpoints of mechanical properties and LCA. Then, some trial to confirm the

effect of carbon fiber surface treatment is introduced.

2. CHARACTERISTICS OF CFRTP

First of all, a comparison with competitive materials is shown in fig.1. This figure shows

specific tensile strength and specific flexural rigidity of typical structural materials, where

specific tensile strength indicates weight-lightening potential of strength member, and specific

flexural rigidity indicates weight-lightening potential of rigid member. Compared with

metallic materials, CFRTS (carbon fiber reinforced thermosetting resin) is excellent in both

10th Japan International SAMPE Symposium & Exhibition (JISSE-10)November 27-30, 2007, Tokyo Big Sight, Tokyo, Japan

Copyright © 2007 by SAMPE(Poster Session-11)-1

specific tensile strength and specific flexural rigidity, and CFRTP is excellent in specific

flexural rigidity even if fiber volume fraction is small. Then, CFRTS is good at

weight-lightening of strength member such as chassis and frame of automobile, pressure

vessel, etc. On the other hand, CFRTP is good at weight-lightening of rigid member such as

roof and door of automobile, wall, etc. Considering that most of the weight of structures,

except for pressure vessel and airplane, is the weight of rigid member, technical development

of CFRTP will contribute well to reduce structural weight drastically.

Fig.1 Specific tensile strength and specific flexural rigidity

As shown in fig.1, mechanical properties of CFRTS are outstanding. However, following

problems are pointed out to apply this material to general industrial field.

1. The cost of CFRTS is too expensive. Even if carbon fiber will depreciate,

thermosetting resin is still expensive. Then, the pay back time becomes longer than

lifetime of structures, except for airplane.

2. Processability is very bad. For example, secondary processing by bending or

pressing machine is impossible and adhesion by welding is also impossible. The hole

opening for bolted joint brings decrease of strength, then reinforcement is necessary,

which kills the lightweight feature.

3. Hence near net shape molding is necessary, then large-scale molding equipment,

such as autoclave, is required.

4. Molding speed is too slow to apply to mass production.

5. Repair and recycling is difficult, since original properties are very high.

CFRTP is promising material to solve these problems at once. Furthermore, fig.2 shows

the comparison of energy consumption to make structural member [2]. This figure shows that

0000

10101010

20202020

30303030

40404040

50505050

60606060

0000 0.050.050.050.05 0.10.10.10.1 0.150.150.150.15 0.20.20.20.2 0.250.250.250.25 0.30.30.30.3

Specific rigidity（（（（3√√√√E/ρ））））

Specific strength

（（ （（σ/ρ

）） ））

Steel CFRTP

(Vf=0.1~0.2)

CFRTS (Vf=0.6)

GFRP

Aluminium

Titanium

Magnesium

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recycling of CFRTS and CFRTP are extremely effective for energy saving, this is because

energy consumption in carbon fiber production is too large.

All these things make it clear that CFRTP is very attractive material. Then, it follows

from this that challenging to the unsolved problems of CFRTP is quite valuable. In the next

section, influence of the surface treatment on the mechanical properties of CFRTP is

discussed.

0 50 100 150 200 250

Recycle CFRTP

Fresh CFRTP

Recycle CFRTS

Fresh CFRTS

Recycled Steel

Fresh Steel

Energy intensity [MJ/kg]

assembly, molding steel or matrix resin production

CF production materials recoverly

Fig.2 Comparison of energy consumption to make structural member.

3. INFLUENCE OF THE SURFACE TREATMENT ON THE MECHANICAL

PROPERTIES OF CFRTP

Composite material is composed of more than two different materials. Especially in

CFRP, difference of mechanical properties between matrix resin and filler is quite large, so

that influence of interfacial adhesiveness on the properties of CFRP is large [3, 4]. To

understand this interfacial feature, following experiment was performed.

3.1 Test piece making

Polypropylene (PP: J3000GP), produced by Idemitsu Co. Ltd., Japan, was used as

matrix resin (Fig.3). And, the following two types of carbon fiber were examined.

i) NST : carbon fiber without surface treatment (very weak adhesiveness)

ii) ST : carbon fiber with surface treatment (relatively stronger adhesiveness)

First of all, fibers and resin were dried well, and each fiber was cut into 6 mm length and

mixed with PP to make fiber volume fraction be 15%. Laboprastomil (Toyo Seiki

Seisaku-Sho, Ltd., 10C100 R60) was used for the mixing. The mixing condition was 200

degree Celsius, 10 rpm and 5 minutes. Next, the press molding was done by using hot press

machine (Toyo Seiki Seisaku-Sho, Ltd., MP-S). The molding temperature was 200 degree

Celsius, and the size of the molded plate was 100mm × 130mm × 4mm. Finally, the molded

plates were cut out for test pieces with a diamond cutter. The size of the test pieces were

80mm ×10mm ×4mm.

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Fig.3 PP pellet

3.2 Experimental result

Three points bending test was performed under the condition that load cell was 50kgf

and cross head speed was 2mm/min. The support span was 64mm. The test was done 5 times

for “NST” and “ST” respectively.

The result is summarized in Table 1. Vf was calculated from the specific gravity. Fig.4

shows the flexural load-deflection curves. Figs. 5 to 7 show the flexural modulus, the flexural

strength and Izod impact energy absorption of each material respectively. Figs. 8 and 9 show

SEM image of the fracture surface of three points bending test pieces.

Table1 Experimental results.

notation carbon fiber

volume fraction

flexural

modulus

flexural

strength

failure

strain

Izod impact

Energy absorption

(%) (GPa) (MPa) (%) (kJ/m2)

NST 6.9 8.60 103 1.44 20.1

ST 7.6 10.46 125 1.46 28.2

0

5

10

15

20

0 1 2 3

Deflection(mm)

Load

(kg)

NST ST

Fig.4 Flexural load to deflection curves.

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0

2

4

6

8

10

12

14

NST ST

Young's

Modulu

s(G

Pa)

Fig.5 Flexural modulus.

0

20

40

60

80

100

120

140

160

NST ST

Str

ength

(MP

a)

Fig.6 Flexural strength

05

101520253035

NST ST

IZO

D im

pact

energ

yab

sorp

tion(k

J/m

2)

Fig.7 Izod impact energy absorption.

Fig.8 SEM image of NST

Fig.9 SEM image of ST

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3.3 Discussion

As shown in figs.5 and 6, both flexural modulus and strength were increased about

twenty percent by surface treatment. And, Izod impact energy absorption was also increased

about 1.4 times by surface treatment as shown in fig.7. Figs.8 and 9 show that an attached

resin on the surface of carbon fiber is increased by surface treatment. All these things make it

clear that surface treatment of carbon fiber induces stronger adhesiveness with thermoplastics

hence better mechanical properties.

4. CONCLUSIONS

In this paper, characteristics of CFRTP were discussed first. Then it was clarified that

CFRTP is actually promising material to solve the problems which are the restriction of the

application of CFRTS to general industrial fields, such as cost, processability, recyclability,

etc. Therefore challenge to the unsolved problem of CFRTP is very valuable to reduce energy

consumption of vehicles globally. Next we showed that better adhesiveness between fiber and

matrix induces better mechanical properties of CFRTP. More advanced research on surface

treatment and comprehensive understanding between interfacial bonding and mechanical

properties of CFRTP are expected.

REFERENCES

1. Next generation fiber technological strategy council, “Research about next generation

fiber technological strategy”, 2007

2. T. Suzuki and J. Takahashi, Prediction of energy intensity of carbon fiber reinforced

plastics for mass-produced passenger cars, Proceedings of 9th Japan International SAMPE

Symposium, pp.14-19, (2005-11).

3. D. Hull, T. W. Clyne, translated by Kimpara, et. al., An Introduction to Composite

Materials (First edition), Bayfu-Kan, pp.8-32 (1983).

4. Research institute of material Technology, Composite material and interface, 1988, pp.37.

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