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Biodegradable Plastics from Renewable ResourcesA. Demirbas aa Sila Science , Universite Mahallesi , Trabzon, TurkeyPublished online: 01 Mar 2007.

To cite this article: A. Demirbas (2007) Biodegradable Plastics from Renewable Resources, Energy Sources, Part A: Recovery,Utilization, and Environmental Effects, 29:5, 419-424, DOI: 10.1080/009083190965820

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Energy Sources, Part A, 29:419–424, 2007Copyright © Taylor & Francis Group, LLCISSN: 1556-7036 print/1556-7230 onlineDOI: 10.1080/009083190965820

Biodegradable Plastics from Renewable Resources

A. DEMIRBAS

Sila Science, Universite MahallesiTrabzon, Turkey

Abstract Natural biodegradable plastics are based primarily on renewable resources.Biodegredation is degradation caused by biological activity, particularly by enzymeaction leading to significant changes in the material’s chemical structure. The bio-degradability of plastics is dependent on the chemical structure of the material. Thebiodegradation of plastics proceeds actively under different soil conditions accord-ing to their properties. Biodegradation of starch based polymers occurred between thesugar groups leading to a reduction in chain length and the splitting off of mono-, di-,and oligo-saccharide units by a result of enzymatic attack at the glucosidic linkages.

Keywords biodegradable plastics, biopolymer, biowaste, mechanisms, renewableresources

Introduction

Biodegradable plastics are polymer species. Biodegradable plastics that are compostablecan be treated biologically together with other bio-waste. Plastic bags are generallymade from nonrenewable petroleum resources. In general, biodegradable plastics whosecomponents are derived from renewable raw materials can be made from abundant agri-cultural/animal resources like cellulose, starch, collagen, casein, soy protein polyestersare triglycerides. Biodegradable plastics degrade over a period of time if exposed to sunand air. Use of plastics in agriculture and rural communities has extensively increased(Orhan et al., 2004). The increasing use of polymers for disposable items such as packag-ing creates problems for garbage disposal and has produced a demand for biodegradablepolymers (Rutkowska et al., 2000). Biodegradability of plastics has been proposed asa solution for the waste problem. Biodegradable plastics have an expanding range ofpotential applications, and they are environmentally friendly. Therefore, there is growinginterest in degradable plastics, which degrade more rapidly than conventional disposable.

The biodegradability of plastics is dependent on the chemical structure of the materialand on the constitution of the final product. Therefore, biodegradable plastics can bebased on natural or synthetic resins. Natural biodegradable plastics are based primarily onrenewable resources and can be either naturally produced or synthesized from renewableresources. Biodegredation is degradation caused by biological activity, particularly byenzyme action leading to significant changes in the materials chemical structure.

Non-renewable synthetic biodegradable plastics are petroleum-based. As any mar-ketable plastic product must meet the performance requirements of its intended function,

Address correspondence to Ayhan Demirbas, P. K. 216, TR-61035 Trabzon, Turkey. E-mail:ayhandemirbas@hotmail.com

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Table 1Biodegradable polyester

Polyester Abbreviation

Aliphatic-aromatic copolyesters AACPolyethylene terephthalate PETPolyhydroxyalkanoates PHAPolyhydroxybutyrate PHBPolybutylene succinate PBSPolybutylene succinate adipate PBSAPolybutylene adipate/terephthalate PBATPolymethylene adipate/terephthalate PTMATPolybutylene succinate PBSPolybutylene succinate adipate PBSAPolylactic acid PLAPolycaprolactone PCL

many natural biodegradable plastics are blended with synthetic polymers to produceplastics that meet these functional requirements.

Biodegradable polyesters are listed in Table 1. The biodegradable polyesters familyis made of 2 major groups of aliphatic (linear) polyesters and aromatic (aromatic rings)polyesters. Polyesters play a predominant role as biodegradable plastics due to theirpotentially hydrolysable ester bonds.

Figure 1 shows the schematic illustration of polymer chains. Linear polymers, suchas acrylics, nylons, polyethylene, polyvinyl chloride, and branched polymers, such aspolyethylene, are thermoplastic; that is, they soften when heated. Cross-linked poly-mers, such as rubbers or elastomers, are thermosetting; that is, they harden when heated.Network polymers, which are basically highly cross-linked examples, are thermosettingplastics, such as epoxies and phenolics. Thermoplastics make up 80% of the plasticsproduced today.

Biopolymers from Renewable Resources

Biopolymers are new materials from renewable resources. Their properties are supposedto be similar to conventional plastics, but bioplastics have to be biodegrable (Hoppenheidtand Trankler, 1995). Sugar molecules form the basis of cellulose and starch. Although

Figure 1. Schematic illustration of polymer chains: (a) linear polymer, (b) branched polymer,(c) cross-linked polymer, and (d) network polymer.

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Table 2Degrees of polymerization of celluloses of different origin

Type of celluloseDegree of

polymerization

Cellulose isolated from pulped aspen 2,550Cellulose isolated from pulped beech 3,060Cellulose isolated from pulped spruce 3,320α-Cellulose isolated from wood fibers 800–1,100Cotton linters 6,500Flax 8,000Raw cotton 7,000

starch and cellulose consist of the same basic chemical elements, they differ in theirphysicochemical properties. By chemical derivation, the functional groups of the sugarring can be exchanged and rearranged. Cellulose, with its linear molecules, is in generalmore suitable for material processing into fibers and films. The degrees of polymerizationof celluloses of different origin are given in Table 2.

All starches consist of highly branched molecules (amylopectin) and the linearmolecules of amylase at ratios that vary with the starch source. This variation providesa natural mechanism for regulating starch material properties. Starch is an inexpensive,annually renewable material derived from corn and other crops. Cellulose and starch arealso useful additives in the chemical industry: in toothpaste, detergents, or constructionmaterials. Cellulose acetate is used in many common applications, including toothbrushhandles and adhesive tape backing. Starch grains can be more easily obtained frompotatoes, corn, or peas than cellulose can from wood. Starch has a linear polysaccaridepolymeric structure made up of repeating glucose groups linked by glucosidic linkages inthe 1-4 carbon positions. The length of the starch chains will vary with plant source, butin general, the average length is between 500 and 2,000 glucose units. The biodegradationof starch products recycles atmospheric CO2 trapped by starch-producing plants.

The cellulose block polymers of defined block molecular weight, high degree ofblock substitution (Paul and Newman, 1978). Crosslinked block polymers have beensuccessfully prepared from cellulosic renewable resources (Narayan and Tsao, 1986).Mixed cellulose esters, such as cellulose acetate propionate, cellulose acetate butyrate,yield thermoplastics with properties similar to acetate. The properties of cellulose blocksdepend on the location of the blocked side chains.

Biodegradable Polymers and Degradation Mechanisms

Degradation of a plastic is to undergo a significant change in its chemical structure underspecific ambient conditions. When degradation is caused by biological activity, especiallyby enzymatic action, it is called biodegradation. Biodegradable matter is material thatcan be biodegraded. The biodegradability of plastics is dependent on the chemical struc-ture of the material. Synthetic polymers can generally be attacked either chemically ormechanically by living organisms.

Biodegradable polymers (BPs) disposed in bioactive environments degrade by theenzymatic action of microorganisms such as bacteria, fungi, and algae. The polymer

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chains of BPs may also be broken down by nonenzymatic processes such as chemicalhydrolysis (Gross and Kalra, 2002). There are mainly 7 types of degradable plastics:(1) biodegradable, (2) compostable, (3) hydro-biodegradable, (4) bioerodable, (5) photo-degradable, (6) oxo-degradable, and (7) hydro-degradable. Aliphatic polyesters have thesame disadvantage as starch. They are also expensive. Photo-degradable plastics degradeafter prolonged exposure to sunlight. The most effective and economic of the new plasticsis based on oxo-degradation and has become known as oxo-biodegradable plastic.

Some degradable plastic products are based on starch, and while non-food uses ofagriculture may seem attractive, some of these plastics perforate over time but do nottotally degrade because the starch constituent is consumed by microbial activity.

The degradation of plastics can generally occur by different molecular mechanisms;chemical-, thermal-, photo-, and bio-degradation. Some studies (Glass and Swift, 1989;Anderson et al., 1998; Lim et al., 1999; Ratto et al., 1999; Atkins, 1998; Zhang et al.,2000; Labow et al., 2002; Tang et al., 2003; Smith et al., 2003) have assessed thebiodegradability of some plastic waste materials by measuring changes in physical prop-erties or by observation of microbial growth after exposure to biological or enzymaticenvironments. The plastic residues can be harmful to the soil and to birds and insects.Most of today’s plastics and synthetic polymers are produced from petrochemicals. Asconventional plastics are persistent in the environment, improperly disposed plastic mate-rials are a significant source of environmental pollution, potentially harming life (Orhanet al., 2004).

The biodegradation of polycaprolactone (PCL) incubated in sea water for severalweeks was investigated by Rutkowska et al. (2000). The influence of different processingadditives on the biodegradation of PCL film in the compost with plant treatment activesludge has been studied. It was found that PCL without additives completely degradedafter 6 weeks in compost with activated sludge. The rate of marine biodegradation ofPCL has been studied by measuring the tensile strength and percent weight loss over timein both seawater and a buffered salt solution (Janik et al., 1988). It was found that theweight loss, as a percent of total weight, decreased more rapidly in seawater than in the

Figure 2. Plots for biodegradation of different cellulosic based products. (Source: Modified fromHoppenheidt and Trankler, 1995.)

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Figure 3. Plots for biodegradation of starch and cellulosic based products.

buffered salt solution. After 8 weeks, the PCL in seawater was completely decomposed,whereas that in salt solution had lost only 20% of its weight.

The properties of an aliphatic polyester blended with wheat starch have been studied(Lim et al., 1999). The polyester was synthesized from the poly-condensation of 1,4-butanediol and a mixture of adipic and succinic acids. The wheat starch-aliphatic polyesterblend demonstrated excellent biodegradability in soil within 8 weeks.

Biodegradation of starch based polymers occurred between the sugar groups leadingto a reduction in chain length and the splitting off of mono-, di-, and oligo-saccharideunits by a result of enzymatic attack at the glucosidic linkages.

The studies in simulated compost environments revealed that cellulose acetates withdegrees of substitution of up to 2.5 are biodegradable. A decrease in the degree ofsubstitution of cellulose acetate from 2.5 to 1.7 results in a large increase in the rate oftheir biodegradation (Gross and Kalra, 2002). Figure 2 shows the plots for biodegradationof different cellulosic based products. The plots for biodegradation of starch and cellulosicbased products are shown in Figure 3.

Conclusion

In recent years, extraordinary progress has been made in the development of practicalprocesses and products from bio-polymers such as starch, cellulose, and lactic acid.Starch is an inexpensive, annually renewable material derived from corn and other crops.Cellulose, with its linear molecules, is in general more suitable for material processinginto fibers and films. The degrees of polymerization of celluloses of different origin arebetween 2,500 and 8,000. The biodegradability of plastics is dependent on the chemicalstructure of the material and on the constitution of the final product.

Biodegradable plastics disposed in bioactive environments degrade by the enzymaticaction of microorganisms such as bacteria, fungi, and algae. The degradation of plastics

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can generally occur by different molecular mechanisms: chemical-, thermal-, photo-, andbio-degradation.

Biodegradation of starch based polymers occurred between the sugar groups leadingto a reduction in chain length and the splitting off of mono-, di-, and oligo-saccharideunits by a result of enzymatic attack at the glucosidic linkages. The studies in simulatedcompost environments revealed that cellulose acetates with degrees of substitution of upto 2.5 are biodegradable.

References

Anderson, J. M., Hiltner, A., Wiggins, M. J., Schuber, M. A., Collier, T. O., Kao, W. J., and Mathur,A. B. 1998. Recent advances in biomedical polyurethane biostability and biodegradation.Polym. Int. 46:163–171.

Atkins, T. W. 1998. Biodegradation of poly(ethylene adipate) microcapsules in physiological media.Biomaterials 19:61–67.

Glass, J. E., and Swift, G. 1989. Agricultural and Synthetic Polymers, Biodegradation and Utiliza-tion, ACS Symposium Series 433, American Chemical Society, Washington DC.

Gross, R. A., and Kalra, B. 2002. Biodegradable polymers for the environment. Gren Chem.297:803–807.

Hoppenheidt, K., and Trankler, J. 1995. Biodegrable plastics and biowaste options for a commontreatment. Proccedings of the Biowaste’95 Conference, Aalborg, Denmark, 21–24 May.

Janik, H., Justrebska, M., and Rutkawska, M. 1998. Biodegradation of polycaprolactone in seawater. Reactive Functional Polymers 38:27–30.

Labow, R. S., Meek, E., Matheson, L. A., and Santerre, J. P. 2002. Human macrophage-mediatedbiodegradation of polyurethanes: Assessment of candidate enzyme activities. Biomaterials 23:3969–3975.

Lim, S. W., Jung, I. K., Lee, K. H., and Jin, B. S. 1999. Structure and properties of biodegradablegluten/aliphatic polyester blends. Eur. Polym. J. 35:1875–1881.

Narayan, R., and Tsao, G. T. 1986. In Cellulose: Structure, Modification, and Hydrolysis, Young,R. A., and Rowell, R. M. (Eds.). New York: Wiley.

Orhan, Y., Hrenovic, J., and Buyukgungor, H. 2004. Biodegradation of plastic compost bags undercontrolled soil conditions. Acta Chim. Slov. 51:579–588.

Paul, D. R., and Newman, S. (Eds.). 1978. Polymer Blends. New York: Academic Press.Ratto, J. A., Stenhouse, P. J., Auerbach, M., Mitchell, J., and Farrell, R. 1999. Processing, per-

formance and biodegradability of a thermoplastic aliphatic polyester/starch system. Polymer40:6777–6788.

Rutkowska, M., Krasowska, K., Heimowska, A., Smiechowska, M., and Janik, H. 2000. The influ-ence of different processing additives on biodegradation of poly(epsilon-caprolactone. IranianPolymer J. 9:221–229.

Smith, R., Williams, D. F., and Oliver, C. 1987. The biodegradation of poly(ether urethanes).J. Biomed. Mater. Res. 21:1149–1166.

Tang, Y. W., Labow, R. S., and Santerre, J. P. 2003. Isolation of methylene dianiline and aqueous-soluble biodegradation products from polycarbonate-polyurethanes. Biomaterials 24:2805–2819.

Zhang, J. Y., Beckman, E. J., Piesco, N. P., and Agarwal, S. 2000. A new peptide-based urethanepolymer: synthesis, biodegradation, and potential to support cell growth in vitro. Biomaterials21:1247–1258.

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