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Critical Reviews in Biotechnology, 25:243–250, 2005Copyright ©c Taylor & Francis Inc.ISSN: 0738-8551 print / 1549-7801 onlineDOI: 10.1080/07388550500346359
A Review of Plastic Waste BiodegradationYing Zheng andErnest K. YanfulDepartment of Civil andEnvironmental Engineering
Amarjeet S. BassiDepartment of Chemical andBiochemical EngineeringThe University of WesternOntario, London, Ontario,Canada
ABSTRACT With more and more plastics being employed in human livesand increasing pressure being placed on capacities available for plastic wastedisposal, the need for biodegradable plastics and biodegradation of plasticwastes has assumed increasing importance in the last few years. This reviewlooks at the technological advancement made in the development of more eas-ily biodegradable plastics and the biodegradation of conventional plastics bymicroorganisms. Additives, such as pro-oxidants and starch, are applied in syn-thetic materials to modify and make plastics biodegradable. Recent research hasshown that thermoplastics derived from polyolefins, traditionally consideredresistant to biodegradation in ambient environment, are biodegraded follow-ing photo-degradation and chemical degradation. Thermoset plastics, such asaliphatic polyester and polyester polyurethane, are easily attacked by microor-ganisms directly because of the potential hydrolytic cleavage of ester or urethanebonds in their structures. Some microorganisms have been isolated to utilizepolyurethane as a sole source of carbon and nitrogen source. Aliphatic-aromaticcopolyesters have active commercial applications because of their good mechan-ical properties and biodegradability. Reviewing published and ongoing studieson plastic biodegradation, this paper attempts to make conclusions on poten-tially viable methods to reduce impacts of plastic waste on the environment.
KEYWORDS thermoplastics, polyolefins, additive, thermoset plastics, polyester,polyurethane.
1. INTRODUCTIONPlastics are man-made long chain polymeric molecules.30 They are widely
used, economical materials characterized by excellent all-round properties, easymolding and manufacturing. Traditionally plastics are very stable and not read-ily degraded in the ambient environment. As a result, environmental pollutionfrom synthetic plastics has been recognized as a large problem. For instance,statistics published by the United States Environmental Protection Agency in2003 indicated that, before recycling, approximately 236 million tons of mu-nicipal solid waste (MSW) was generated in the United States in that year, ofwhich 11.3% was composed of plastics.32 Only a small fraction of this plasticwaste (mostly soft drink and other bottles) was recovered.32 Thus the remain-ing quantity of plastic waste was required to be disposed. Most of this plasticwaste has been accumulating in landfills. Therefore, in order to save capacityfor plastic waste disposal, there is a growing interest both in the development
Address correspondence to AmarjeetS. Bassi, Department of Chemical andBiochemical Engineering. TheUniversity of Western Ontario,London, Ontario N6A 5B9, Canada.E-mail: [email protected]
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of newer, readily biodegradable plastics and in thebiodegradation of conventional plastic waste. Thepresent study reviews current research in these areas.
2. TYPES OF PLASTICS AND USAGE2.1. Types of Plastics and Properties
for DegradationPlastics are synthetic polymers. There are two main
processes in the manufacture of synthetic polymers.The first involves breaking the double bond in theoriginal olefin by additional polymerization to formnew carbon-carbon bonds, the carbon-chain polymers.For example, the fabrication of polyolefins, such aspolyethylene and polypropylene, is based on this gen-eral reaction. The second process is the elimination ofwater (or condensation) between a carboxylic acid andan alcohol or amine to form polyester or polyamide.Polyurethane is also made by this general reaction.30
Plastics are divided into two groups: thermoplasticsand thermoset plastics.2 Thermoplastics are the prod-ucts of the first kind of general reaction mentionedabove. Thermoplastics can be repeatedly softened andhardened by heating and cooling. In thermoplastics, theatoms and molecules are joined end-to-end into a seriesof long, sole carbon chains. These long carbon chainsare independent of the others.3 This structure in whichthe backbone is solely built of carbon atoms makes ther-moplastics resistant to degradation or hydrolytic cleav-age of chemical bonds. Consequently, thermoplasticsare considered non-biodegradable plastics. Thermosetplastics are synthesized from the second kind of gen-eral reaction stated above. They are solidified after beingmelted by heating. The process of changing from the liq-uid state to the solid state is irreversible.2 Distinguishedfrom the linear structure of thermoplastics, thermosetplastics have a highly cross-linked structure.2,30 Sincethe main chain of thermoset plastics is made of hetero-atoms, it is possible that they are potentially susceptibleto be degraded by the hydrolytic cleavage of chemicalbonds such as ester bonds or amide bonds.23
2.2. Application of PlasticsThermoplastics are widely used in packaging and
fabrication of bottles and films (Table 1). The ma-jor types of thermoplastic material include linear, low-density polyethylene (LLDPE), high density polyethy-lene (HDPE), polyvinyl chloride (PVC), low density
TABLE 1 Main plastics and their applications (the list is notexhaustive).
Plastics Applications
Low density polyethylene(LDPE), linear low densitypolyethylene (LLDPE),polyvinylchloride (PVC)
Films and packaging
Polyethylene terephthalate(PET), PVC, high densitypolyethylene (HDPE)
Bottles, tubes, pipes,insulation molding
Polystyrene (PS),polypropylene (PP), PVC
Tanks, jugs, containers
LDPE, LLDPE BagsPolyurethane (PUR) Coating, insulation, paints,
packing
polyethylene (LDPE), polypropylene (PP), polystyrene(PS) and other resins. The major classes of thermosettingplastics include polyester, one of which is polyethyleneterephthalate (PET), and polyurethane (PUR).6
Table 2 shows percentage distribution of plastic resinsin terms of sales and use in 2004 in the United States,Canada and Mexico, published by The American Plas-tics Association.5 It is notable that 92% of plasticsemployed are non-biodegradable thermoplastics. Asa consequence, the environmental impact caused bythermoplastics, the main packaging materials, is a ma-jor concern. To deal with this environmental prob-lem related to non-biodegradable thermoplastics, re-search to modify non-biodegradable thermoplastics tobiodegradable materials is of great interest. Althoughthermoset plastics comprise only 8% of the totalamount of plastics,5 their susceptibility to biodegrada-tion also raises attention. Several investigations have
TABLE 2 Percentage distribution of plastic resins: sales andcaptive use in North America (2004) (5adapted from AmericanPlastics Council Year End Statistics 2004).
Type of plastic resin Percentage distribution
Polypropylene (PP) 18.4%Polyvinyl chloride (PVC) 15.8%Polystyrene (PS) 6.7%High density polyethylene
(HDPE)17.4%
Low density polyethylene (LDPE) 8.2%Linear low density polyethylene
(LLDPE)12.1%
Other thermoplastics 12.5%Thermoplastics total 92.0%Thermosets and other plastics 8.0%Total 100%
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been carried out on the biodegradation of thermo-setplastics such as polyurethane and are discussed later.
2.3. BiodegradablePlastics—Limitations and Obstacles
for UseTable 3 shows some of the different types of
biodegradable plastics being considered. New applica-tions based on synthetic polyester–based biodegradableresins have been commercialized, especially in the pack-aging industry, paper coating and garbage bags. Thesepolyesters are made using modified polyethylene poly-merization processes and as blends. A second–class ofbiodegradable polyesters include polylactic acid andthermoplastic starch-based polymers. These polyestersenvironmentally degrade to water and carbon dioxidewhen exposed to microorganisms and water in com-posting piles. A third type of biodegradable plastics in-cludes aliphatic co-polyesters such as polyhydroxyalka-noates or PHAs produced by bacteria. Potato, corn andwheat starch are renewable raw materials for starch–based plastics. While a number of alternatives haveemerged, one of the main limitations for syntheticbiodegradable polymers such as polyesters and starch–based blends is higher cost compared to synthetic poly-mers such as LDPE, PP, PS, and PET. Another seriousobstacle is a lack of suitable infrastructure for sorting,recycling and composting solid wastes.
3. DEGRADATION OFTHERMOPLASTIC POLYOLEFINS
Generally speaking, synthetic polyolefins are inertmaterials whose backbones consist of only long car-bon chains.36 This characteristic structure makes poly-olefins non-susceptible to degradation by microorgan-isms. However, a comprehensive study of polyolefinbiodegradation has shown that some microorganismscould utilize polyolefins with low molecular weight.36
This biodegradation always follows photo-degradationand chemical degradation. Although traditional poly-olefins are non-biodegradable, their biodegradabilityis enhanced when blending with starch or otherpolyesters. Zuchowska et al.38 investigated the degra-dation of blends of low density polyethylene (PE) orisotactic polypropylene (PP) with glycerol plasticizedstarch (GS). Glycerol mono-ethers, fatty alcohols or
epoxidized rubber were required as compatibilizers. Theresults showed that the blends were subject to differentkinds of degradation. However, the degree of degrada-tion was a function of the type of polymer and theblend composition. The biodegradation of the poly-olefin chain was clearly observed. Therefore, with thedevelopment of starch-plastic as well as the discovery ofother additives added to synthetic plastics, biodegrad-able polyolefins provide an attractive option for reduc-ing plastic waste in the environment.4 The followingsection reviews biodegradable polyolefins and specifi-cally examines the degradation of polyethylene (PP).
3.1. Biodegradable PolyolefinsTraditionally, polyolefins are considered to be non-
biodegradable for three reasons. First, the hydropho-bic character of polyolefins makes this material resis-tant to hydrolysis. Secondly, the use of anti-oxidantsand stabilizers during manufacture keeps polyolefinsfrom oxidation and biodegradation.17 Thirdly, poly-olefins have high molecular weights36 of 4000 to 28,000.Therefore, to make polyolefins biodegradable, these fac-tors have to be considered. The study of Bonhommeet al.7 indicated that the molecular weight of biodegrad-able polyolefins must be less than 500. Accordingly,the principle of making biodegradable polyolefins in-volves adding special additives to the synthetic poly-olefins so that the modified structures are suscepti-ble to photo-degradation and chemical degradation.As a result, the long carbon chains are broken toshorter segments and their molecular weights are re-duced below 500. Microorganisms can then assimilatethe polyolefins monomeric and oligomeric breakdownproducts previously derived from photo and chemicaldegradations.7,36,39
As commercial products, synthetic polyolefins resistoxidation and biodegradation because of the presenceof anti-oxidants and stabilizers. The use of pro-oxidantadditives makes polyolefins oxo-bio-degradable. First,pro-oxidant activities can change the polyolefins’surface from hydrophobic character to hydrophilic.Secondly, pro-oxidants can catalyze the breakdown thelong chain of polyolefins and produce lower molecularweight products either during photolysis or thermoly-sis. Jakubowicz17 studied the thermo-oxidative degra-dation of polyethylene films during composting condi-tions and in the presence of pro-oxidant additives. Hefound that metal combinations were the most active
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TABLE 3 Biodegradable plastics (21adapted from Leaversuch).
Type of Names ofbiodegradable plastic Applications some manufacturers Limitations for use
Synthetic polyester blends(Amorphous)
Flexible films and tubing.Properties similar to LDPE
Dupont 1. Higher cost2. Lack of infrastructure for
disposal such as compostingand recycling
Semi-crystalline polyesters Rigid Containers, packing Dupont 3. May require blending withAromatic-Aliphatic General purpose and Eastman, other polyesters or polymers
Copolyesters films, lawn and garden BASF to obtain desired propertiesbags, netting, food wraps 4. Bacterial derived
Polylactic acid Coatings Cargill-Dow biopolymers such asStarch based blends Films, packing, packaging Novamont PHAs will requirePolyhydroxyalkanoates Film, sheets, elastomers Proctor and more experimental
(PHAs) Gamble testing and evaluationPolycaprolactone Films, sheets, packaging, Union Carbide,
coatings Dow PerformanceChemicals
pro-oxidants. To be active as catalysts, it is necessarythat two metal ions of similar stability be involved inthe metal combinations, and also when the two metalions are oxidized by oxidants, the oxidation number ofthe metal ion must be only one unit different from theone before oxidation. For example, Mn (manganese)is a suitable metal participating in metal combinationfor pro-oxidant activity. As an oxidation-reduction cat-alyst, two Mn2+ ions with similar stability can formand would be oxidized to Mn3+ and then later reducedto Mn2+. Thus, when polyolefins are exposed to theenvironment, a free radical chain in the material canreact with oxygen from the atmosphere and producehydro-peroxides that can, in turn, be hydrolyzed andphotolyzed. Also the pro-oxidant catalyzes the reactionof chain scission in the polymer, producing low molec-ular mass oxidation products, such as carboxylic acids,alcohols and ketones. Furthermore, peroxidation modi-fies the material surface character from hydrophobic tohydrophilic. Consequently, microorganisms can accessthe material surface, bio-assimilate the low molecularmass, hydrophilic oxidant products and facilitate thebiodegradation process.
Starch can also be blended into the polymers forproducing biodegradable polyolefins.27,28,38 However,as mentioned earlier, without the addition of a suitablepro-oxidant system, biodegradation will simply causethe removal of starch and leave behind shorter chainsof unmodified polyolefin.
The amount of starch required to be added to syn-thetic polyolefins needs to be optimized. If the amount
of starch is too high, the mechanical properties of thematerial may be adversely affected. On the contrary, ifthe amount of starch is too low, the material may notbiodegrade.9,38 For instance, an experiment was con-ducted by Zuchowska et al.38 to examine propertiesof starch blends containing 40% polyolefin and 60%plasticized starch (40 PE-SG) or 50% polyolefin and50% plasticized starch (50 PP-SG). The results showedthat after aging in soil for four months, both sampleshad a very large weight loss (ca. 55 or 43%), indicat-ing the degradation of materials. The 40 PE-SG, withhigher starch content, lost more weight, implying morematerial was degraded. Relative changes in mechani-cal properties showed that the tensile strength of bothblends did not change significantly, whereas elongationat break changed considerably, especially in the blendcontaining higher amounts of starch. The addition ofstarch to polyolefins modifies their structure. Therefore,in starch blends, there is a continuous starch phase thatis favorable to microorganisms and is easily attackedby microorganisms under the catalytic action of α- andβ- amylase enzymes. Under the effect of this reaction,the continuous starch phase is removed, resulting inporous polyolefin starch blends. If pro-oxidants are alsopresent, an accelerated degradation of polyolefins ma-trix will occur.38
3.2. Biodegradation of PolyethyleneSince polyethylene (PE) is widely used as pack-
aging material (Table 2), considerable research not
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only on biodegradable polyethylene but also onbiodegradation of polyethylene has been recentlyconducted.7,8,11,12,17,34 The results of these studiesindicated that polyethylene was biodegraded follow-ing photo-degradation and/or chemical degradation.Biodegradation of polyethylene is known to occurby two mechanisms: hydro-biodegradation and oxo-biodegradation.7 These two mechanisms agree withthe modifications due to the two additives, starchand pro-oxidant, used in the synthesis of biodegrad-able polyethylene. Starch blend polyethylene has acontinuous starch phase that makes the material hy-drophilic and, therefore, catalyzed by amylase en-zymes. Microorganisms can easily access, attack andremove this part. Thus the hydrophilic polyethylenewith the matrix continues to be hydro-biodegraded. Forthe biodegradable polyethylene synthesized by addingpro-oxidant additive, biodegradation occurs followingphoto-degradation and chemical degradation. As men-tioned in section 3.1, the pro-oxidant is a metal com-bination. After transition metal catalyzed thermal per-oxidation, biodegradation of the low molecular weightoxidation products occurs sequentially.7,11,36 Ei-Shafeiet al.11 investigated the ability of fungi and Streptomycesstrains to attack degradable polyethylene consistingof disposed polyethylene bags containing 6% starch.Microorganisms employed in the investigation wereeight different isolated Streptomyces strains and two fungiMucor rouxii NRRL 1835 and Aspergillus flavus. Afterten days of heat treatment, polyethylene films wereincubated and shaken at 125 rpm at 30◦C in 0.6%yeast extract medium (pH 7.5) for Streptomyces spp.and in 3% yeast extract medium (pH 5.5) for fungi.Active enzymes were detected and biodegradation ofpolyethylene was confirmed by testing changes in me-chanical properties, such as tensile strength and percentelongation. Yamada-Onodera et al.36 isolated a strainof the fungus Penicillium simplicissimum YK to biode-grade polyethylene. They also discussed pretreatment ofpolyethylene before fungus cultivation to make degra-dation more complete. In contrast to the research doneby Ei-Shafei et al.11 that used polyethylene-containingstarch as a carbon source to help microorganisms grow,Yamada-Onodera et al.36 investigated biodegradation ofpolyethylene without additives. UV light or oxidizingagents, such as a UV sensitizer, were used at the be-ginning of the process to activate an inert material,polyethylene. Polyethylene was also treated with ni-tric acid at 80◦C for 6 days before cultivation with
inserted functional groups that were susceptible to mi-croorganisms. The experimental result showed that withthe fungus activity, polyethylene with a starting molec-ular weight in the range of 4000 to 28,000 was de-graded to units with a lower molecular weight of 500after three months of liquid cultivation, which indi-cated the biodegradation of this polyethylene. Over-all, polyethylene degradation is a combined photo- andbio-degradation process. First, either by abiotic oxida-tion (UV light exposure) or heat treatment, essentialabiotic precursors are obtained. Secondly, selected ther-mophilic microorganisms degrade the low molar massoxidation products to complete the biodegradation.7
4. DEGRADATION OF THERMOSETPLASTICS, POLYESTER AND
POLYURETHANEThermoset plastics, such as polyester and
polyurethane, have recently become materials ofconsiderable interest because of their potentialbiodegradability. It was found that due to their hy-drolysable ester bonds, polyester and polyurethane arebiodegradable.3,14,23,24,33
4.1. Degradation of PolyestersThere are two kinds of polyesters: aliphatic and aro-
matic. Their biodegradability is completely different.Muller et al.23 concluded that pure aromatic polyestersare quite insensitive to any hydrolytic degradation. Itwas observed that direct microbial or enzymatic at-tack of pure aromatic polyester was not significant.22,31
However, other research has recently claimed that aro-matic polyester could be disintegrated by microbialstrains of Trichosporum and Arthrobacter in a time scale ofweeks. Some growth of Aspergillus niger was found onthe surface of aromatic polyesters.15 Because no con-trol samples were tested and the degradation test meth-ods used were very basic, the results were considerednot completely convincing. On the contrary, aliphaticpolyester is considered to be susceptible to microbialattack. Aliphatic polyester degradation is seen as a two-step process: the first is depolymerization, or surfaceerosion. The second is enzymatic hydrolysis, which pro-duces water-soluble intermediates that can be assimi-lated by microbial cells.23
In order to solve the problem of aromatic polyes-ter non-degradability, aliphatic-aromatic co-polyesters
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were made. The idea was that by introducing aliphaticcomponents into aromatic polyester, its hydrolytic sus-ceptibility should be increased.19 Raw materials consist-ing of copolyesters of 1,4-butanediol, terephthalic acidand adipic acid (BTA-copolyesters) are preferentiallyused for commercial biodegradable copolyesters. Thegreater the fraction of terephthalic acid, the lower therate of biodegradation of the copolyesters. In biodegra-dation assaying of copolyesters, Thermomonospora fuscaDSM43793 was used. Copolyester has been observedto be degraded in mineral media within days,20 andfilms, approximately 90-µ m thick, were totally disinte-grated within 7 days on agar plates at 55◦C. A detailedanalysis of the intermediate and final products fromthe degradation of the commercial, aliphatic-aromaticcopolyester, Ecoflex, was undertaken by Witt et al.35
using GC-MS measurements. Similar to the process ofaliphatic polyester degradation from depolymerization,aromatic and aliphatic oligomers are intermediates thatare, at least, slightly water-soluble and can be metab-olized by microorganisms. However, final degradationof longer aromatic oligomers has not been achieved sig-nificantly. This aspect needs further study.
4.2. Degradation of PolyurethanePolyurethane (PUR) is commonly utilized as a con-
stituent material in many products including furni-ture, coating, construction materials, fibers, and paints.Structurally, PUR is the condensation product ofpolyisocyanate and polyol having intramolecular ure-thane bonds (carbonate ester bond, -NHCOO-).29
The urethane bond in PUR has been reported to besusceptible to microbial attack.25 The hydrolysis ofester bonds in PUR is postulated to be the mecha-nism of PUR biodegradation. The breakdown productsof the biodegradation are derived from polyester seg-ment in PUR when ester bonds are hydrolyzed andcleaved.25
Three types of PUR degradation have been identifiedin literature: fungal biodegradation, bacterial biodegra-dation and degradation by polyurethanase enzymes.13
For example, four species of fungi, Curvularia sene-galensis, Fusarium solani, Aureobasidium pullulans andCladosporium sp, were obtained from soil and found todegrade ester-based polyurethane.10 Kay et al.18 isolatedand investigated 16 different bacteria in their abilityto degrade PUR. In another comprehensive study inJapan, PUR was biodegraded as a sole carbon and ni-
trogen source by Comamonas acidovorans.1,24 To purifyand characterize polyurethanase enzymes, the growthof Pseudomonas chlororaphis, Comamonas acidovorans, andPseudomonas fluorescens on polyurethane has been pre-viously studied Two kinds of PUase enzyme were iso-lated and characterized by Howard et al.14 Allen et al.3
and Vega et al.33 These were shown to be a cell-associatedmembrane bound PU-esterase and an extra-cellular PU-esterase. An investigation of the action of these two en-zymes during the polyurethane biodegrading is quitehelpful for an increased understanding of the mecha-nism of polyurethane biodegradation. These two en-zymes play different roles in polyurethane biodegra-dation. The membrane bound PU-esterase providescell-mediated access to the hydrophobic polyurethanesurface. Then the extracellular PU-esterase sticks onthe surface of the polyurethane. Under these enzy-matic actions, bacteria could adhere to the surface ofpolyurethane and hydrolyze PU substrate to metabo-lites. Results obtained by Nakajima-Kambe et al.24
and Howard et al.14 indicate that the polyurethanebiodegradation was due to the hydrolysis of esterbonds.
In an experimental study conducted by the authorsof this review to obtain a simple culture medium for en-gineering application, the effects of YES (Yeast extractsalts) medium components on polyurethane (ImpranilDLN) biodegradation by Pseudomonas chlororaphis wereinvestigated.37 The results showed that Pseudomonaschlororaphis could grow and degrade Impranil DLN as asole carbon and nitrogen source in the modified YESmedium with no additional carbon and nitrogen source,yeast extract, NH4Cl and gelatin. However, the bacte-ria grew much better and degraded more Impranil DLNin the YES medium with the addition of gelatin thanin the one without gelatin, indicating some inductioneffects may have occurred as a result of the presenceof the gelatin. After 10 days of incubation, the amountof polyurethane degraded was about 50%, and bacterialconcentration reached the maximum of 1010 cfu/mL.Additionally, FTIR spectroscopy was used to confirmthat the mechanism of polyurethane biodegradationwas the hydrolysis of the ester bond in polyurethane.The decrease of the ratio of ester bond over etherbond was also approximately 50%, which agreed withthe measured amount of polyurethane degraded. Thesefindings have potential benefits in future studies onPUR biodegradation in landfills or in other plastic wastetreatment processes.
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4.3. Degradation ofPolyhydroxyalkanoates
Bacteria produce polyhydroalkanoates as energy stor-age materials. A good example of this is polyhy-droxybutyrate (PHB), which is made by numerousmicroorganisms.26 PHAs are easily metabolized. Theenzymes responsible for the biodegradation, PHA de-polymerases, have a wide substrate specificity.16 PHAsand PHBs are recently finding commercial interest.They may also find applications as blends and additivessimilar to starch based plastics.
CONCLUSIONSThis paper reviewed recent research on plastic waste
biodegradation. To reduce the impact of plastic wasteon the environment, two main efforts have gener-ally been pursued: one is to synthesize biodegradableplastics, and the other to isolate selected microorgan-isms to biodegrade plastic wastes. Thermoplastics arewidely used as packaging materials. Traditionally, thesepolyolefins are non-biodegradable. With the develop-ment of biodegradable polyolefins synthesis, activeadditives such as pro-oxidants and starch, a naturalbiodegradable polymer, are added to synthetic plas-tics to make them biodegradable. By photo or heatdegradation, high molecular mass materials are bro-ken down to low molecular mass intermediates thatcan be continuously biodegraded by microorganisms.With more and more research on polyolefins’ biodegra-dation, environmental pollution caused by packag-ing non-biodegradable plastics could be reduced. Re-search on thermoset plastics, such as polyester andpolyurethane, shows that they are biodegradable dueto ester bonds or amide bonds that are potentiallysusceptible to hydrolytic cleavage. However, aromaticpolyester is resistant to microbial attack because of itslong aromatic oligomers. In order to achieve both goodmechanical properties and biodegradability, aliphatic-aromatic copolyesters are synthesized. It has also beendiscovered that another widely employed biodegrad-able thermoset plastic, polyurethane, can be utilizedas a sole source of carbon and nitrogen by microor-ganisms. With more and more research on plasticwaste biodegradation, practical solutions to environ-mental problems caused by plastic waste will soonemerge.
ACKNOWLEDGEMENTSFunding for the research was provided by Individ-
ual Discovery Grants from the Natural Sciences andEngineering Research Council of Canada awarded toDr. Ernest Yanful and to Dr. Amarjeet Bassi.
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