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BIOPOLYMERSMany of the polysaccharides earlier studies are also biopolymers since they have repeating units

Cellulose most abundant biopolymer Biopolymers are polymers produced by living organisms.

Since they are polymers, biopolymers contain monomeric units that are covalently bonded to form larger structures.

There are three main classes of biopolymers based on the differing monomeric units used and the structure of the biopolymer formed:

polynucleotides, which are long polymers composed of 13 or more nucleotide monomers; polypeptides, which are short polymers of amino acids; andpolysaccharides, which are often linear bonded polymeric carbohydrate structures.Synthetic polymers are much simpler and random and molecular mass.This fact leads to a molecular mass distribution that is missing in biopolymers.

All biopolymers of a type (say one specific protein) are all alike: they all contain the similar sequences and numbers of monomers and thus all have the same mass.

This phenomenon is called monodispersity in contrast to the polydispersity encountered in synthetic polymers.

As a result biopolymers have a polydispersity index of 1. BIOPOLYMERS AS MATERIALS

Some biopolymers- such as polylactic acid (PLA), naturally occurring zein, and poly-3-hydroxybutyrate can be used as plastics, replacing the need for polystyrene or polyethylene based plastics.

Some plastics are now referred to as being 'degradable', 'oxy-degradable' or 'UV-degradable'. This means that they break down when exposed to light or air, but these plastics are still primarily (as much as 98 per cent) oil-based and are not currently certified as 'biodegradable' under certain international laws.

Biopolymers, however, will break down and some are suitable for domestic composting.Zein is a class of prolamine protein found in maize. It is usually manufactured as a powder from corn gluten meal.Biopolymers (also called renewable polymers) are produced from biomass for use in the packaging industry.

Biomass comes from crops such as sugar beet, potatoes or wheat: when used to produce biopolymers, these are classified as non food crops. These can be converted in the following pathways:

Sugar beet > Glyconic acid > Polyglonic acid

Starch > (fermentation) > Lactic acid > Polylactic acid (PLA)

Biomass > (fermentation) > Bioethanol > Ethene > Polyethylene

Many types of packaging can be made from biopolymers: food trays, blown starch pellets for shipping fragile goods, thin films for wrapping.

BIOPOLYMER USES

Polylactic acid (PLA)Poly(lactic acid) or polylactide (PLA) is a thermoplastic aliphatic polyester commonly made from a-hydroxy acids, derived from renewable resources, such as

corn starch (in the United States),

tapioca products (roots, chips or starch mostly in Asia) or

sugarcanes (in the rest of world).

It can biodegrade under certain conditions, such as the presence of oxygen, and is difficult to recycle.

PLA is not a polyacid (polyelectrolyte), but rather a polyesterOne of the few polymers in which the stereochemical structure can easily be modified by polymerizing a controlled mixture of L and D isomers to yield high molecular weight and amorphous or semi-crystalline polymers.

Properties can be both modified through the variation of isomers (L/D ratio) and the homo and (D, L) copolymers relative contents.

PLA can be tailored by formulation involving adding plasticizers, other biopolymers, fillers, etcPolylactic acid (PLA)Polylactic acid (PLA)Bacterial fermentation is used to produce lactic acid from corn starch or cane sugar.

Catalytic and thermolytic ring-opening polymerization of lactide (left) to polylactide (right)Stannous octonateOr tin(II) chloride Two lactic acid molecules undergo a single esterfication and then catalytically cyclized to make a cyclic lactide ester.PLA of high molecular weight is produced from the dilactate ester by ring-opening polymerization.

Polymerization of a racemic mixture of L- and D-lactides usually leads to the synthesis of poly-DL-lactide (PDLLA) which is amorphous.

poly-DL-lactide (PDLLA) Due to the chiral nature of lactic acid, several distinct forms of polylactide exist: poly-L-lactide (PLLA) is the product resulting from polymerization of L,L-lactide (also known as L-lactide). heat resistant PLA can withstand temperatures of 110C (230F)

PDLA (poly-D-lactide): optically transparent.PLA has similar mechanical properties to PETE polymer, but has a significantly lower maximum continuous use temperature.PETE: Polyethylene terephthalate, commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containersPLA is considered both as biodegradable (e.g. adapted for short-term packaging) and as biocompatible in contact with living tissues (e.g. for biomedical applications such as implants, sutures, drug encapsulation, etc.).

PLA can be degraded by abiotic degradation (i.e. simple hydrolysis of the ester bond without requiring the presence of enzymes to catalyze it). During the biodegradation process, and only in a second step, the enzymes degrade the residual oligomers till final mineralization (biotic degradation).

As long as the basic monomers (lactic acid) are produced from renewable resources (carbohydrates) by fermentation, PLA complies with the rising worldwide concept of sustainable development and is classified as an environmentally friendly material.Polylactic acid (PLA): BiodegradabilityWoven shirts (ironability), microwavable trays, hot-fill applications and even engineering plastics (in this case, the stereocomplex is blended with a rubber-like polymer such as ABS). APPLICATIONSPLA is currently used in a number of biomedical applications, such as sutures, stents, dialysis media and drug delivery devices. The total degradation time of PLA is a few years. It is also being evaluated as a material for tissue engineering.Because it is biodegradable, it can also be employed in the preparation of bioplastic, useful for producing loose-fill packaging, compost bags, food packaging, and disposable tableware. In the form of fibers and non-woven textiles, PLA also has many potential uses, for example as upholstery, disposable garments, awnings, feminine hygiene products, and diapers.PLA is more expensive than many petroleum-derived commodity plastics, but its price has been falling as production increases.

The demand for corn is growing, both due to the use of corn for bioethanol and for corn-dependent commodities, including PLA.PLA is a sustainable alternative to petrochemical-derived products, since the lactides from which it is ultimately produced can be derived from the fermentation of agricultural by-products such as corn starch or other carbohydrate-rich substances like maize, sugar or wheat.

PLA can be an alternative to high-impact polystyrene by using as much as 1 wt% non-PLA due to creating co-polymers which can strengthen PLA plastic.The Korean research center KAIST has announced that they have found a way to produce PLA using bio-engineered Escherichia coli.As of Jun 2010, NatureWorks was the primary producer of PLA (bioplastic) in the United States.Plastics are resistant to biodegradation accumulating at the rate of 25million tonnes per year. Much disposed in landfill sites. Possibility of recycling plastics is limited and incineration yields toxic compounds

Due to PLA's relatively low glass transition temperature, PLA cups cannot hold hot liquids. However, much research is devoted to developing a heat resistant PLAMulch film made of polylactic acid (PLA)-blend bio-flexBiodegradable cups at a restaurantDegradable plastics can be biodegradable or photodegradablePhotodegradable plastics can break down to small fragments and lose structure but small fragments are not degradable.Biodegradable plastics can be metabolized by MOSemidegradable plastics contain starch, cellulose and polyetheneFor complete degradation 50% mix is required which compromises structural propertiesBiodegradable plasticsPolyhydroxy alkanoates (PHAs): PHBPolyactidesAliphatic polyestersPolysaccharidesBlends of aboveBioplastics from MicroorganismsDegradable polymers that are naturally degraded by the action of microorganisms such as bacteria, fungi and algae

Several legislations enacted but demand for bioplastics have not increasedBenefits100 % biodegradableProduced from natural, renewable resourcesAble to be recycled, composted or burned without producing toxic byproducts

2003- North America107 billion pounds of synthetic plastics produced from petroleumTake >50 years to degradeImproper disposal and failure to recycle overflowing landfillsIMPORTANCECarbon Cycle of BioplasticsCO2 H2O BiodegradationCarbohydratesPlastic ProductsPlantsFermentation PHA PolymerPhotosynthesisRecyclePolyhydroxyalkanoates (PHAs)Polyesters accumulated inside microbial cells as carbon & energy source storage

Ojumu et al., 2004Polyhydroxyalkanoates (PHAs)Produced under conditions of:Low limiting nutrients (P, S, N, O)Excess carbon2 different types:Short-chain-length3-5 CarbonsMedium-chain-length6-14 Carbons~250 different bacteria have been found to produce some form of PHAsPolyhydroxybutyrate (PHB)Example of short-chain-length PHAProduced in activated sludgeFound in Alcaligenes eutrophusAccumulated intracellularly as granules (>80% cell dry weight)

Lee et al., 1996PHA Biosynthesis

Ojumu et al., 2004PHB: polyhydroxybutyrateIntracellular microbial plastic first found in Bacillus megaterium80 different types of PHAs formed from 3-hydroxyalkanoate acid monomers 3-14 carbons in length

Energy store when nutrient is limitedAlcaligenes eutrophus (Ralstnia etropha) to produce PHB

Polymer had low thermal stability and brittleAddition of propionate to culture produced P (3HB-co-3HV) and polymer was flexible and toughHB: hydroxybutyrate HV: hydroxyvalerateMarketed as BIOPOLTM used to make films, coated paper, compost bags, disposable foodwares , bottles, razors

COST is still HIGHER than chemically synthesized polymersPropylene: 1$/kgPHVB: 3-5$/kgphbC-A-B Operon in A. eutrophusStructural genes encoded in single operonPHA synthaseb-ketothiolaseNADPH-dependent acetoacetyl-CoA reductase

Lee et al., 1996Recovery of PHAs from CellsPHA producing microorganisms stained with Sudan black or Nile blueCells separated out by centrifugation or filtrationPHA is recovered using solvents (chloroform) to break cell wall & extract polymerPurification of polymerBioplastic PropertiesSome are stiff and brittleCrystalline structure rigiditySome are rubbery and moldableProperties may be manipulated by blending polymers or genetic modificationsDegrades at 185CMoisture resistant, water insoluble, optically pure, impermeable to oxygenMust maintain stability during manufacture and use but degrade rapidly when disposed of or recycledBiodegradationFastest in anaerobic sewage and slowest in seawaterDepends on temperature, light, moisture, exposed surface area, pH and microbial activityDegrading microbes colonize polymer surface & secrete PHA depolymerasesPHA CO2 + H2O (aerobically)PHA CO2 + H2O + CH4 (anaerobically)Biodegradation by PHA depolymerases

ConclusionsNeed for bioplastic optimization:Economically feasible to produceCost appealing to consumersGive our landfills a breakHow many of you would be willing to pay 2-3 times more for plastic products because they were environmentally friendly?