biofibres biodegradable polymers and biocomposites an overview

Macromol.Mater. Eng.276/277,1–24(2000) 1

Biofibres,biodegradablepolymersandbiocomposites:An overview

A. K. Mohantya,b, M. Misraa,b, G. Hinrichsen*

TechnicalUniversity of Berlin, Instituteof NonmetallicMaterials,PolymerPhysics,EnglischeStr. 20,D-10587Berlin,Germany

(Received:September27,1999;revised:March2, 2000)

Summary of contents1. Introduction2. Reinforcing biofibres2.1 Chemical constituents andstructuralaspects2.2 Propertiesof biofibres2.3 Degradationpropertiesof biofibres2.4 Costaspects,availability andsustainable develop-

mentof biofibres

3. Biodegradable polymers3.1 Definition3.2 Classification

Review: Recentlythecritical discussionaboutthepreser-vation of natural resourcesand recycling has led to therenewedinterestconcerning biomaterialswith the focuson renewableraw materials.Becauseof increasingenvir-onmentalconsciousnessanddemandsof legislativeautho-rities, useandremovalof traditionalcompositestructures,usuallymadeof glass,carbonor aramidfibersbeingrein-forcedwith epoxy, unsaturatedpolyester, or phenolics,areconsideredcritically. Recent advancesin natural fiberdevelopment,geneticengineeringand compositescienceoffer significant opportunities for improved materialsfrom renewableresourceswith enhancedsupportfor glo-bal sustainability. The important feature of compositematerialsis that theycanbedesignedandtailoredto meetdifferentrequirements.Sincenaturalfibers arecheapandbiodegradable,the biodegradablecompositesfrom biofi-bersand biodegradablepolymerswill rendera contribu-tion in the 21st centurydueto seriousenvironmentalpro-blem. Biodegradablepolymershave offered scientistsapossiblesolution to waste-disposalproblemsassociatedwith traditional petroleum-derivedplastics.For scientiststherealchallengelies in finding applicationswhich wouldconsumesufficiently large quantitiesof thesematerialstoleadprice reduction,allowing biodegradablepolymerstocompeteeconomicallyin themarket.Today’s muchbetterperformanceof traditional plastics are the outcome ofcontinuedR&D efforts of last severalyears;howevertheexistingbiodegradablepolymerscameto public only fewyears back. Prices of biodegradablepolymers can bereducedon massscaleproduction;and such massscaleproductionwill be feasiblethroughconstantR&D effortsof scientiststo improvetheperformanceof biodegradableplastics.Manufactureof biodegradablecompositesfromsuchbiodegradableplasticswill enhancethe demandof

such materials.The structuralaspectsand propertiesofseveral biofibers and biodegradablepolymers, recentdevelopments of different biodegradablepolymers andbiocompositesarediscussedin this review article. Colla-borativeR&D efforts amongmaterialscientistsandengi-neersaswell as intensiveco-operationandco-ordinationamong industries,researchinstitutions and governmentare essentialto find various commercialapplicationsofbiocompositesevenbeyondto our imagination.

Macromol. Mater. Eng.276/277 i WILEY-VCH VerlagGmbH,D-69451 Weinheim2000 1438-7492/2000/0103–0001$17.50+.50/0

a Presentaddress: Composite Materials andStructuresCenter,MichiganStateUniversity, 2100EngineeringBuilding, EastLansing,MI 48824-1226,USA.

b Home address: Polymer & Composites Laboratory, Depart-mentof Chemistry, RavenshawCollege (Autonomous), Cut-tack – 753003,Orissa, India.

Life cycle of compostable, biodegradablepolymers (afterref.78))

2 A. K. Mohanty, M. Misra, G. Hinrichsen

3.3 Importance of biodegradable polymers fromrenewable resources

3.4 Structure, synthesis and properties of biodegrad-ablepolymers

3.4.1 Aliphatic polyesters3.4.2 Polyesteramides3.4.3 Starchplastics3.4.4 Celluloseacetate3.4.5 Soyplastic3.5 Biodegradableplasticsvs. traditionalplastics4. Biocomposites4.1 Cellulosefibre basedbiocomposites4.2 Flax, hemp,andramiebasedbiocomposites4.3 Jutebasedbiocomposites4.4 Miscellaneousbiocomposites4.5 Applicationof biocomposites5. ConclusionAcknowledgement

1. Intr oductionFibre-reinforcedplastic composites beganwith cellulosefibre in phenolics in 1908, later extending to urea andmelamine, and reachingcommodity status in the 1940swith glassfibre in unsaturated polyesters. From guitars,tennisracquetsandcarsto microlight aircrafts, electroniccomponentsand artificial joints, composites are findingusein diversefields. Becauseof increasing environmen-tal consciousnessanddemandsof legislative authorities,the manufacture, useand removal of traditional compo-site structures,usually made of glass,carbonor aramidfibres beingreinforced with epoxy, unsaturatedpolyesterresins,polyurethanes,or phenolics, are considered criti-cally. The most importantdisadvantageof suchcompo-site materials is the problem of convenient removal afterthe endof life time, asthe components areclosely inter-connected, relatively stable and therefore difficult toseparateandrecycle1). In themodern polymer technologyit is a greatdemandthat everymaterialshouldespeciallybe adapted to the environment. In order to successfullymeettheenvironmentalandrecyclingproblems,theDLR(Deutsches Zentrum fur Luft- und Raumfart e.V.) Insti-tuteof Structural Mechanics,applying their knowledgeincomposite technology in a new broadenedway2), devel-opedaninnovativeideain 1989.

By embedding natural reinforcing fibres, e.g. flax,hemp,ramie, etc. into biopolymeric matrix madeof deri-vativesfrom cellulose,starch,lactic acid, etc; new fibrereinforced materials called biocompositeswere createdandarestill being developed2–8). Biocompositesconsistofbiodegradable polymer as matrix material and usuallybiofibre as reinforcing element. Since both componentsare biodegradable, the composite as the integral part isalsoexpectedto bebiodegradable. Biofibres, i. e., naturalpolymers, are generally biodegradable but they do not

possessthe necessary thermalandmechanical propertiesdesirablefor engineeringplastics. On the otherhand, thebest engineering plastics are obtained from syntheticpolymers,but they arenon-biodegradable.A lot of R&Dwork hasbeencarriedoutonbiofibre reinforcedsyntheticpolymers.The compositesof naturalfibres andnon-bio-degradable synthetic polymers may offer a new classofmaterials but arenot completely biodegradable.Govern-ment regulations and growing environmental awarenessthroughout the world have triggered a paradigm shifttowardsdesigning materials compatible with theenviron-ment9). The biofibres derived from annually renewableresources,asreinforcing fibres in both thermoplasticandthermoset matrix composites provide positive environ-mentalbenefitswith respect to ultimate disposability andraw material utilization10). Auto makers now seestrongpromisein natural fiber reinforcements11). We find a num-ber of publications on natural fiber compositesin auto-motive applications12–14). Literature also shows somereviews on cellulosic as well as ligno-cellulosic fiberbasedcomposites15–18). Advantagesof biofibres over tra-ditional reinforcing materials such as glass fibres, talcand mica are9): low cost, low density, high toughness,acceptablespecificstrengthproperties,reducedtool wear,reduceddermal and respiratory irrit ation, good thermalproperties,ease of separation, enhancedenergy recoveryand biodegradability. The main drawbackof biofibres istheir hydrophilic naturewhich lowers the compatibilitywith hydrophobic polymeric matrix during compositefabrications. The other disadvantageis the relatively lowprocessing temperaturerequired dueto the possibility offibre degradation and/orthe possibility of volatile emis-sionsthat could affect composite properties.The proces-sing temperaturesfor mostof the biofibres are thus lim-ited to about2008C, althoughit is possible to usehighertemperaturesfor shortperiods19).

The annual disposalof over 10 milli on tons of plasticsin both the US and EC countrieshasraised the demandfor means of managing this non-biodegradable wastestream.The synthetic polymers have displacedmetals,glasses,ceramicsandwood in many products,especiallyin the areaof packaging. The commodity plastics, the socalled “big four” polyethylene (PE), poly(propylene)(PP),polystyrene(PS)andpoly(vinyl chloride)(PVC) ina variety of forms suchas films, flexible bagsand rigidcontainershave revolutionized the packaging industry.However, oncethesematerials arediscarded,theypersistin the environment without being degraded thus givingrise to a multitude of ecological andenvironmentalcon-cerns.The important feature of composite materials isthat they can be designed and tailored to meetdifferentrequirements. Since biofibres are cheapand biodegrad-able, the biocompositesfrom biofibre reinforccedbiode-gradablepolymerswill rendera contribution in 21st cen-tury due to seriousenvironmental problem. Now it is a

Biofibres,biodegradablepolymersandbiocomposites: An overview 3

challengefor scientists to examine the properties of dif-ferentbiodegradable polymersavailable in the markettomakesurewhetheror not they aresuitedto be usedasamatrix systemfor biocomposites. Keeping above factsinto consideration the presentreview article dealswiththe current developmentof biocompositeswith a broadoutline of discussion on structuralparts of some impor-tantbiofibres,thecurrentdevelopment of differentbiode-gradablepolymerssoasto giveabroadideafor thefutureR&D activities in this challenging field of work.

2. Reinforcing biofibr esIn biocomposites the biofibres serve as a reinforcementby enhancingthe strengthand stiffnessto the resultingcomposite structures.Source, origin, nature as well asphysical and chemical composition of different naturalfibers have beenreviewed20,21). The conventional fibreslike glass,carbon,aramid,etc., can be produced with adefinite range of properties, whereasthe characteristicproperties of natural fibres vary considerably22). Thisdependson whether the fibres are taken from plant stemor leafs23), thequality of theplantslocations24), theageofthe plant25) and the preconditioning26,27). Depending ontheir origin, the natural fibres may be groupedinto: leaf,bast,seed,andfruit origin. Thebestknownexamplesare:(i) Leaf: Sisal, pineappleleaf fibre (PALF), and hene-quen;(ii) Bast:Flax, ramie,kenaf/mesta, hempandjute;(iii) Seed:Cotton; (iv) Fruit: Coconuthusk, i. e.,coir. Thenaturalfibres are lignocellulosic in nature.Lignocellulo-sic materials are the mostabundantrenewablebiomater-ial of photosynthesison earth.In termsof massunits, thenet primary production per year is estimated to be261011 tons28) as compared to synthetic polymers by1.56108 tons.Lignocellulosic materials are widely dis-tributed in the biospherein the form of trees (wood),plantsandcrops.Cellulose,in its variousforms, constitu-tes approximately half of all polymer utilized in theindustryworldwide29).

2.1 Chemicalconstituentsandstructuralaspects

The major constituentsof biofibres (lignocelluloses) arecellulose,hemicelluloseandlignin. The amount of cellu-lose, in lignocellulosic systems,can vary depending onthe speciesand age of the plant/species. Cellulose is ahydrophilic glucan polymer consisting of a linear chainof 1,4-b-bonded anhydroglucose units30) which containsalcoholic hydroxyl groups.Thesehydroxyl groups formintramolecularhydrogenbondsinsidethemacromoleculeitself andamongothercellulosemacromoleculesaswellaswith hydroxyl groupsfrom theair. Therefore,all of thenatural fibres are hydrophilic in nature; their moisturecontentreaches8–12.6%22). Althoughthechemical struc-tureof cellulosefrom differentnaturalfibresis thesame,

the degreeof polymerization (DP) varies. The mechani-cal properties of a fibre are significantly relatedto DP.Bast fibres commonly show the highest DP amongapproximately10000differentnatural fibres31).

Lignin is a phenolic compound,generallyresistant tomicrobial degradation, but the pretreatmentof fibre ren-ders it susceptible to thecelluloseenzyme32,33). Theexactchemical natureof the principal component of biofibre,the lignin, still remains obscure16,34). The main difficultyin lignin chemistry is that no method has so far beenestablishedby which it is possible to isolatethe lignin inthe nativestatefrom the fibre. Although the exactstruc-tural formula of lignin in natural fibre hasyet not beenestablished, most of the functional groups and unitswhich make up the molecule havebeenidentified. Thehigh carbonand low hydrogencontentof lignin suggestthat it is highly unsaturatedor aromatic in character. Lig-nin is characterizedby its associated hydroxyl andmeth-oxy groups. Ethylenic andsulfur-containinggroups havealsobeenfound in lignins28). The chemical natureof lig-nin in lignocellulosic materials has been an importantsubject of studies35,36). Lignin is a biochemical polymerwhich functionsasa structural support material in plants.During synthesis of plant cell walls,polysaccharidessuchas cellulose and hemicellulose are laid down first, andlignin fills the spacesbetweenthe polysaccharide fibres,cementing them together. This lignification processcausesa stiffening of cell walls, and the carbohydrateisprotectedfrom chemical andphysicaldamage.Thetopol-ogy of lignin from differentsourcesmay be differentbuthasthesamebasiccomposition.

Although the exact mode of linkagesin biofibre16) isnot well known, lignin is believedto be linked with thecarbohydrate moiety through two types of linkages,onealkali sensitive and the other alkali resistant. The alkalisensitive linkage forms an ester-type combinationbetweenlignin hydroxyls andcarboxylsof hemicelluloseuronic acid. The ether-type linkage occurs through thelignin hydroxylscombining with the hydroxyls of cellu-lose.The lignin, being polyfunctional, existsin combina-tion with morethanoneneighbouringchainmoleculeofcellulose and/or hemicellulose, making a crosslinkedstructure. The lignocellulosic material possessesmanyactive functional groups28) like primary and secondaryhydroxyls, carbonyls, carboxyls(esters), carbon-carbon,ether andacetallinkages.

The chemical compositions and structuralparametersof some important biofibresarerepresentedin Tab.1. Asit is found from Tab.1 the various chemical constituentsof a specific natural fibre also vary considerably. Suchvariation may be dueto the origin, age,retting (modeofextraction of fibre from the source)processadopted,etc.Among all the natural fibres listed, coir is observedtocontain leastamount of cellulosebut highestpercentoflignin.


2.2 Propertiesof biofibres

The natural fibres exhibit considerable variation in dia-meteralongwith thelength of individualfilaments.Qual-ity as well as most of the properties dependon factorslike size,maturityaswell asprocessing methodsadoptedfor the extraction of fibres. The modulus of fibredecreaseswith increasein diameter. The propertiessuchasdensity, electrical resistivity, ultimate tensilestrength,initial modulus,etc., are relatedto the internal structureand chemical composition of fibres. A comparison ofproperties of somenaturalfibreswith conventional man-madefibres can be obtained from Tab.2. The strengthand stiffness correlate with the angle betweenaxis andfibril of the fibre, i. e., the smaller this angle,the higherthe mechanicalproperties;the chemicalconstituents andcomplex chemical structureof natural fibres also affectthe properties considerably. Coir shows least tensile

strengthamong all the natural fibres as listed in Tab.2which is attributed to low cellulosecontentandconsider-ably high microfibrillar angleas evidencedfrom Tab.1.Again high tensilestrengthof flax maybeattributedto itshigh cellulosecontentandcomparatively low microfibril-lar angle.However, it is not possible to correlatethefiberstrengthexactlywith cellulosecontent andmicrofibrillarangle becauseof the very complex structure of naturalfibres. Filament and individual fibre propertiescan varywidely depending on the source,age,separatingtechni-que,moisturecontent,speedof testing, history of fibre,etc. The lignin content of the fibres influencesits struc-ture31), properties31,37–49) and morphology50). The waxysubstances of natural fibres, generally influence thefibre’swettability andadhesioncharateristics51,52).

In termsof specific strength, natural fibres canbecom-paredwith well-known glassfibres. The breakinglength

Tab.1. Chemical composition andstructuralparametersof somenaturalfibres

Typeoffibre

Cellulose————

wt.-%

Lignin———wt.-%

Hemicellulose——————

wt.-%

Pectin———wt.-%

Wax——wt.-%

Micro-fibrillar/spiral

angle(Deg.)

Moisturecontent

————wt.-%

References

BastJuteFlaxHempRamieKenaf

61–71.571

70.2–74.468.6–76.2

31–39

12–132.2

3.7–5.70.6–0.715–19

13.6–20.418.6–20.617.9–22.413.1–16.7

21.5

0.22.30.91.9–

0.51.70.80.3–

8.010.06.27.5–

12.610.010.88.0–

22,28,37,3822,28,37,3822,28,37,3822,28,37,39

28,40

LeafSisalPALFHenequen

67–7870–8277.6

8.0–11.05–1213.1

10.0–14.2–

4–8

10.0––

2.0––

20.014.0

–

11.011.8

–

22,28,37,414228

SeedCotton 82.7 – 5.7 – 0.6 – – 43

FruitCoir 36–43 41–45 0.15–0.25 3–4 – 41–45 8.0 37,41,44

Tab.2. Comparativepropertiesof somenatural fibreswith conventionalmanmadefibres

Fibre Density———g/cm3

Diameter———

lm

Tensilestrength——————

MPa

Young’smodulus———————

GPa

Elongationat break

————%

References

Cotton 1.5–1.6 – 287–800 5.5–12.6 7.0–8.0 45,49Jute 1.3–1.45 25–200 393–773 13–26.5 1.16–1.5 22,23,37,45,49Flax 1.50 – 345–1100 27.6 2.7–3.2 22,23,37,49Hemp – – 690 – 1.6 22,37Ramie 1.50 – 400–938 61.4–128 1.2–3.8 22,37,46,49Sisal 1.45 50–200 468–640 9.4–22.0 3–7 22,23,37,45,49PALF – 20–80 413–1627 34.5–82.51 1.6 45Coir 1.15 100–450 131–175 4–6 15–40 22,45E-glass 2.5 – 2000–3500 70 2.5 22,47S-glass 2.5 – 4570 86 2.8 22,23,47Aramid 1.4 – 3000–3150 63–67 3.3–3.7 22,47Carbon 1.7 – 4000 230–240 1.4–1.8 22,47


versuselongationof somenatural fibres is represented inFig. 1. As observed, the stiffnessof hemp is evenhigherthan that of E-glass.The natural fibres showing bestmechanical properties are to be selected53–56) for compo-site fabrication. On the otherhandthe low thermal resis-tanceof naturalfibres doesnot allow an arbitrary choiceof polymersasmatrix materials.For manufactureof com-positeswith suitablematrix systems, it is very importantto know the degradation of mechanical properties whenthe fibres areexposed to composite processing tempera-ture between180–2008C for certain time. The tempera-tureresistanceof coir andof differentmodified jute fibreshasbeeninvestigated44,57,58). The surfacemodification ofnatural fibre improvesthe mechanical properties of thefibre59). The studieson degradation of tensile strengthofelementaryramie fibres dueto the influenceof tempera-ture and time of exposure reveal4,5,8) that manufacturingconditionsat about2008C lasting for a period of 10 minmake the fibres lose nearly 10% of their strength.Thesaid testswere performed on pure fibres. As fibres areusually surroundedand protected by the matrix whenexposedto heat during the composite fabrication, theactualdecreaseof mechanical propertiesis expectedto belessthanreported.

2.3 Degradationpropertiesof biofibres

The lignocellulosic natural fibres are degraded biologi-cally becauseorganismsrecognisethecarbohydratepoly-mers, mainly hemicellulosesin the cell wall and havevery specific enzyme systems capable of hydrolysingthese polymers into digestible units40). Fig. 2 demon-strateshow thecomponentsof lignocellulosics interactinvarious ways. Biodegradation of the high molecularweight cellulose weakens the lignocellulosic cell wallbecausecrystalline cellulose is primarily responsible forthe strengthof the lignocellulosics60). Due to degradationof cellulose,the strength getslost. Photochemicaldegra-dation by ultraviolet light occurs when lignocellulosicsare exposedto outside.This degradation primarily takesplace in the lignin component,which is responsible for

the characteristic colour changes61). The surfacebecomesricher in cellulosecontentasthe lignin degrades.In com-parison to lignin, cellulose is much less susceptable toUV degradation. After the lignin is degraded, the poorlybonded carbohydrate-rich fibres erode easily from thesurface,which exposes new lignin to further degradativereactions. It is important to note that hemicellulose andcellulose of lignocellulosic fibres are degradedby heatmuch before the lignin61). The lignin componentcontri-butes to char formation, and the charredlayer helps toinsulate the lignocellulosics from further thermal degra-dation. Biofibres changetheir dimensions with varyingmoisture content becausethe cell wall polymerscontainhydroxyl and other oxygen-containing groups whichattractmoisture throughhydrogenbonding62). The hemi-cellulosesare mainly responsible for moisture sorption,but the accessible cellulose,noncrystallinecellulose,lig-nin, and surface of crystalline cellulosealso play majorroles.Lignocellulosicsshrinkastheylosemoisture.

2.4 Costaspects,availability andsustainabledevelopment of biofibres

Theworld’s supplyof naturalresources is beingdepleted,the demandfor sustainable and renewableraw materialscontinues to rise. In 1997, approximately 25 millionmetric tonsof man-madefibres (about45 million metrictons of man-madeand natural fibres) were producedworldwide63). So responsible use of available naturalfibres has becomean inevitable task for scientists. Inorder to ensurea reasonable return to the farmers,non-traditional outlets haveto be exploredfor biofibres. Onesuchavenueis in theareaof fibre reinforcedcomposites.Now we cannot only useour natural renewableresourcesfor applicationslike for makingtwines,ropes,cords,etc.,where cheapand synthetic PP fibres can be used.Theprice for biofibres which are feasible for different appli-cationsvariesa lot dependingon thechangedeconomy ofthecountrieswheresuchfibresarewidely available.Jute

Fig. 1. Breaking length versus elongation of some naturalfibers(afterref.2))

Fig. 2. Cell wall polymersresponsible for lignocellulosic prop-erties(afterref.40))


is the so-called golden fibre from India and Bangla-desh34); coir is produced in the tropical countriesof theworld and India accounts20% of total world productionof coir64); sisalplantthoughnative to tropical andsub-tro-pical North andSouthAmerica, is alsowidely grown intropical countries of Africa, the West Indies and FarEast23), Tanzania andBrazil being now the two mainpro-ducingcountries65); Kenaf is a crop grown commerciallyin theU.S66); flax is mostlyplantedin EC althoughnow itis grown in many diverseagricultural systems andenvir-onments throughout the world, as far apart as Canada,Argentina, India and Russia,and flax fibre accountsforlessthan2% of world consumptionof apparelandindus-trial textiles, despite the fact that it has a number ofunique and beneficial properties67); hemp is originatedfrom CentralAsia, from which it spreadto China,andisnow cultivated in many countries of the temperaturezone67); ramiefibres arethe longestandoneof the stron-gest fine textile fibres and mostly availableand usedinChina,Japanand Malaysia67). For comparison, pricesofsome natural and synthetic fibres are representedinTab.3a andb. From Tab.3a it is observedthat the priceof natural fibre is very low as compared to syntheticfibres.For specificprice (modulusper unit price), jute isthebest.In recentyears,pricesof naturalfibreswere notstable,especially for flax fibres43), beingabout30%moreexpensive thanglassfibres (Tab.3b). For theseeconom-ical reasons,asubstitution of glassfibresby natural fibresseemsnot to be easily realized. Howeverbiofibres offerseveraladvantages,the most importantbeingbiodegrad-ibility . Geethammaet al.69) havereportedthecostratio ofsome natural fibres as coir:sisal:PALF : jute =1:1.5:1.5:2. From the abovediscussionit is found thatcostof natural fibres variesa lot dependingon the placeof origin andchangedeconomy of thatplace.

3. BiodegradablepolymersThe rising oil priceshelped to stimulate early interest inbiodegradables back in the 1970sand concernsover thedwindling availability of landfill sitesare reviving inter-ests in biodegradable materials today. Tab.4 illustratessome typical prices for composting, incineration andlandfilling in threeEuropean countries70). The differencein cost between the various countries can be partlyexplainedby somereasonssuch as a different level oftechnology required,environmental regulations, scaleofinstallation, etc. Biodegradable polymers have offeredscientistsa possible solution to waste-disposal problemsassociatedwith traditional petroleum-derived plastics.First introducedin the 1980s,biodegradable plastics andpolymersas usedin films, molded articles,sheets,etc.,comprisea market that is still in its infancy.

3.1 Definition

According to Albertssonand Karlsson71) biodegradationis defined as an event which takes place through theaction of enzymesand/orchemical decompositionasso-ciated with liv ing organisms (bacteria,fungi, etc.) andtheir secretionproducts. It is also necessary to considerabiotic reactions like photodegradation, oxidation andhydrolysiswhich may alsoalter the polymer before, dur-ing or instead of biodegradation becauseof environmen-tal factors.Internationalorganizations,suchastheAmer-ican Society for Testingand Materials (ASTM) in con-nectionwith the Institute for StandardsResearch(ISR),the European Standardisation Committee (CEN), theInternational Standardisation Organisation (ISO), theGermanInstitute for Standardisation (DIN), the ItalianStandardizationAgency(UNI), the OrganicReclamationand Composting Association (ORCA) are all activelyinvolved in developing definitions and tests for biode-gradability in different environments and compostabil-ity72,73). A standard world-wide definition for biodegrad-able polymersalthoughhasnot yet beenestablished,allthe definitions alreadyin place, correlatethe degradabil-ity of a materialto a specific disposal environmentandtoa specific test methodwhich simulates this environmentin a time period which determines its classification74).Thebasicrequirementsfor a material to bedeclaredcom-postableare basedon: 1. Complete biodegradability of

Tab. 3. (a) Comparison of the price of synthetic and naturalfibres(cf. ref.23))

Fibre Carbon Steel Glass Sisal Jute Coir

Cost(US$/kg)

200 30 3.25 0.36 0.30 0.25

Modulus/cost(GPakg/$)

2.0 6.7 21.5 41.7 43.3 20.0

Tab. 3. (b) Production of plant fibres in comparison to glassfibres(1993)(cf. ref.43,68))

Fibre Pricein comparisonto glassfibres(%)

Production(1000t)

Jute 18 3600E-glass 100 1200Flax 130 800Sisal 21 500Banana 40 100Coir 17 100

Tab. 4. Costsof wastemanagement optionsin Germany, Bel-gium andTheNetherlands(in US$ perton) (cf. ref.70))

Option Germany Belgium TheNetherland

Composting 151 80 60Incineration 486 110 135Landfilling 402 75 105


the material, measuredby respirometric testslike ASTMD5338-92, ISO/CD 14855 andcorresponding CEN draftor themodifiedSturmtestASTM D5209,in a time periodcompatible with the composting technology (somemonths);2. No adverseeffectson compostquality andinparticular no toxic effects of the compostand leachateson the aquaticandterrestial organisms;3. Disintegrationof the material during the fermentation phase;4. Control

of laboratory-scale results on pilot scale compostingplants.

3.2 Classification

Theclassificationof biodegradablepolymerson thebasisof materialclassis represented in Tab.5. Biodegradablepolymersmaybeclassifiedas:biosynthetic,semi-biosyn-

Tab.5. Classification of biodegradable polymerson thebasisof materialclass(cf. ref.75))a)

Materialclass Manufacturer Productname

Celluloseacetate MazzucchelliPlanetPolymer

BIOCETAmEnviroPlasticm-Z

Copolyester BASFEastman

EcoflexEasterBioTM

Polycaprolactone(PCL) BirminghamPolymersPlanetPolymerSolvayUnion Carbide

Poly(e-caprolactone)Enviroplasticm-CCAPAmTONEm

Poly(esteramide) Bayer BAK 1095BAK 2195

Poly(ethyleneterepthalate)(PET)-modified

DuPont Biomaxm

Polyglycolide(PGA) AlkermesBirminghamPolymersBoehringerIngelheimPURAC

MedisorbmPoly(glycolide)ResomermPURASORBm PG

Polyhydroxyalkanoates(PHA) MetabolixBiomerMonsanto

PHABiomerTM

BiopolmPoly(lacticacid)(PLA) Alkemers

BirminghamPolymersBoehringerIngelheimCargill Dow PolymersChronopolHygailNestePURAC

MedisorbmPoly(L-lactide) & Poly(DL-lactide)ResomermEcoPLAmHeplonTM

PLAPoly(L-lactide)PURASORBm PL/PD/PDL

Poly(vinyl alcohol)(PVOH) IdroplastNovonPlanetPolymerTexasPolymer

HydrolenemAqua-NOVONmAquadroTM

VinexTM

Starch& starchblends AVEBEBioPlastic(Michigan)BIOTECBunaSowLeunaEarthShellMidwestGrainNovamontNovonStarchTech

ParagonTM

EnvarTM

Bioplastm, Bioflexm, BiopurmSconacellmStarch-basedcompositePolytriticumTM 2000Mater-BiTM

Poly-NOVONmST1,ST2,ST3

Otherblends AlkermersBio Plastic (Colorado)BirminghamPolymers

BoehringerPlanetPolymerPURAC

MedisorbmBiocompositematerialPoly(DL-lactide-co-caprolactone)& Poly(DL-lactide-co-glycolide)ResomermEnviroPlasticm-UPURASORBm PLG,PURASORBm PDLG

a) Reproducedwith permissionfrom Mar Tech,USA (Website:http://www.Mar Tech-Reports.com).


thetic, and chemosynthetic type. Steinbuchel76) hasstud-ied the useof biosynthetic, biodegradablethermoplasticsandelastomersfrom renewableresources.Almost all bio-synthetic polymers which are readily available fromrenewable resources are biodegradable within a reason-able time scale.Many semibiosyntheticand chemosyn-thetic polymers are also biodegradable if they containchemical bondswhich occur in naturalcompounds.Thusbiodegradability is not only a function of origin but alsoof chemicalstructureanddegradingenvironments.

3.3 Importanceof biodegradablepolymersfromrenewableresources

When a biodegradable material (neat polymer, blendedproduct, or composite) is obtained completely fromrenewable resourceswe may call it a green polymericmaterial. Biopolymers from renewable resources haveattractedmuch attention in recent years77). Renewablesourcesof polymeric materials offer an answerto main-taining sustainable development of economically andecologically attractive technology. The innovations in thedevelopmentof materials from biopolymers, the preser-vation of fossil-basedraw materials,complete biologicaldegradability , the reduction in thevolumeof garbage andcompostability in the naturalcycle, protection of the cli-matethroughthereductionof carbondioxidereleased,aswell as the application possibilities of agriculturalresources for the production of bio/greenmaterials aresomeof thereasonswhy suchmaterialshaveattractedthepublic interest78). The life cycle of compostablebiode-gradable polymers is represented in Fig. 3. The use of

agricultural materials andbiomasshasbeenreviewedbyMulhaupt79) who hasconcluded that, although Germanyis at the forefront of greentechnology anda wide rangeof biodegradable pharmaceutical and novel surfactantmaterials can be made from renewable materials, it isonly as components of packaging and as natural fibrecomposites that thesematerials are currently viable interms of price and performance.The effect on the USeconomyof substituting production of corn-basedpoly-mer resins for petroleum-based polymers hasbeenana-lysedby Beachet al.80)

3.4 Structure,synthesisandpropertiesofbiodegradablepolymers

The beststartingpoint for a correctapproachto the pro-ductionof biocompositesis to know thestructure,proper-ties, and function of biodegradable polymers very well,andalsohow they intercombineor interactwith differentnatural fibres in the formation of biocomposites.Struc-tural aspectsand properties of somenatural fibres havealreadydiscussedin Section 2. In this section the struc-ture, synthesis,and properties of some biodegradablepolymersaresummarized.

3.4.1 Aliphatic polyesters

Structural effects on the biodegradation of aliphaticpolyesters havebeenreported81). Aliphatic polyesters asbiodegradable structuralmaterials areclassified into twotypes regarding the mode of bonding of constituentmonomers, i. e., polyhydroxyalkanoates,which are poly-mersof hydroxy acids,HO-R-COOH,as repeatingunitsandpoly(alkylenedicarboxylate)swhich aresynthesizedby polycondensation reaction of diols and dicarboxylicacids.Again hydroxy acidsareclassifiedinto a-, b- andx-hydroxy acidsin respectof bondingposition of theOHgroupfrom theCOOH endgroup. All suchstructuresarerepresentedin Fig. 4.

i. Poly(a-hydroxy acid) such as poly(glycolic acid),PGA, or poly(lactic acid), PLA, arecrystallinepolymerswith relatively high melting point. Although recentlymicroorganismsor enzymesthat can degradePLA havebeenreported,thenumber of carbon atomsbetweenesterbondsin themain chainmayberesponsible for themajornonenzymatic hydrolytic degradation of poly(a-hydroxyacid). Recently PLA hasbeenhighlighted becauseof itsavailability from renewable resourceslike corn.PLA is ahydrophobic polymerbecauseof the incorporationof the1CH3 side groups when compared to PGA. PLA issynthesized by the condensation polymerization of D- orL-lactic acid or ring opening polymerization of the lac-tide. Advanced industrial technologiesof polymerizationhave been developed to obtain high molecular weightpurePLA which leadsto a potential for structuralmateri-

Fig. 3. Life cycle of compostable, biodegradablepolymers(afterref.78))


als with enoughlifetime to maintainmechanical proper-ties without rapid hydrolysis evenunderhumid environ-ment,aswell asgood compostability. The physical prop-erties and biodegradibility of PLA can be regulatedbyemployinga comonomer component of hydroxy acidsorracemization of D- or L- isomer, whereasPLA homopoly-mer suchas poly(L-lactic acid) (PLLA) is a hard, trans-parentandcrystallinepolymerhavinga melting point of170–1808C and a glasstransition temperature of about538C81). PLLA, a highly crystalline polymer, is moreresistantthanPGA to hydrolysis dueto themethyl substi-tuent’s steric shielding effect of the estergroup.PLA isprimarily usedfor medical applicationsincludingsutures,drugdelivery, vascular grafts,artificial skin, andorthope-dic implants82). Synthetic biodegradable PLA, PGA, andcopolymers of these,have been manufactured for bio-medicalapplicationssincethe1970s.

A new rangeof PLA biodegradablepolymersis beingoffered by Cargill Dow Polymers83). All PLA resinsaremanufactured using renewable agricultural resources,suchascorn or sugarbeets.Theyarecomposedof chainsof lactic acid that areproducedby converting starchintosugarwhich is thenfermented. By removal of water lac-tide is formed which is then converted into PLA resinsthroughsolvent-free polymerization.Cargill Dow is con-fident that the new PLA polymerswill competesuccess-fully on a cost-performancebasiswith certainpolymers,like polyethylene, poly(propylene)andpolyester. Currentcommercial applicationsinclude compostablefood andlawn wastebags,yoghurtcartons,seedingmats andnon-wovenmulchto prevent weedgrowth.

DuPont’s biodegradable Biomax copolyester resin, amodified form of PET, waslaunchedin 1997. Its proper-ties, according to DuPont,are diverseand customisable,but they aregenerally formulatedto mimic polyethyleneor poly(propylene)83). Becauseit is basedonPETtechnol-ogy, and can be produced on commercial lines, DuPontbelievesthat Biomax is only marginally more expensiveto producethan PET itself, and significantly cheaper toproducethanotherbiodegradable polymers.Biomax hasa relatively high melting point for a biodegradableresin,of around 2008C, which accountsfor its wide rangeofprocessing options.As a modifiedPETit canalsobepro-cessedon equipmentsdesignedfor the standardpolymer.It canbe made into films, fibre andnon-wovens,aswellas being thermoformed and injection moulded.Biomaxhasa broadrange of potential applicationsincluding sin-gle-useproductssuch as geotextiles, agricultural mulchfilms, seedmats,plant potsandbagsfor covering ripen-ing fruits, disposableplates and cups, waste bags,etc.Biomaxcanberecycled,incinerated,or land-filled, but itis intendedmainly for disposal by composting andin-soildegradation. It is hydro/biodegradableasit mustundergohydrolysisfirst beforebecoming biodegradable.Thelargemolecules are split by moisture into smaller molecules

which areconsumedandconvertedto carbondioxide andwater by naturallyoccurring microbes.

ii. Poly(b-hydroxyalkanoate)s (PHAs), which aresynthesizedbiochemically by microbial fermentationandwhich maybeproduced in thefutureby transgenic plants,representnaturalpolyesters. Bacteriacamefirst and arestill the only real sourceof thesepolyesters;it wil l stillrequire somemore years research until transgenic plantswil l beavailable for production.Poly(b-hydroxybutyrate)(PHB) (commercial name Biopolm) is a biotechnologi-cally produced polyesterthat constitutesa carbonreservein a wide variety of bacteria84) and has attractedmuchattention asa biodegradable thermoplasticpolyester85–87).It can be degraded to water and carbondioxide underenvironmental conditionsby a varietyof bacteriaandhasmuch potential for applications of environmentallydegradableplastics88). However, it suffers from somedis-advantages compared with conventional plastics, forexample, brittlenessand a narrow processability win-dow89). To improve theseproperties, various copolymerscontaining hydroxyalkanoateunits other than3-hydroxy-butyrate(3HB) havebeenbiosynthesized90). PHB andthecopolymer, poly(3-hydroxybutyrate-co-3-hydroxyvale-rate) (PHBV), areproducedby Monsantoandsold underthetradenameBiopolm. PHBV polymers were first manu-factured88) by ICI in 1983andwereoriginally intendedasbiodegradable substitutes for oil-based polyolefins infilms, bottles and plastic containers91). The actual andpotential usesof PHB and PHBV for motor oil contain-ers,film formation andpaper-coating materialshavebeenreviewed92). In 1990 the manufacture of blow-mouldedbottles usingBiopolm for packaging shampoowasstartedin Germanyby Wella AG, Darmstadt.Therangeof possi-ble usesof Biopolm polymershavebeensummarized byAmasset al.93) PHBVs are highly crystalline polymerswith meltingpointsandglasstransition temperaturesimi-lar to poly(propylene) (PP)84). Due to characteristics ofbiodegradability through non-toxic intermediates andeasy processability, PHBV polymersarebeingdevelopedand commercialized as ideal candidatesfor the substitu-tion of non-biodegradablepolymeric materials in com-modity application94,95). However, the prohibitive cost,the small difference betweenthermal degradation andmelting temperature andespecially the low impact resis-tance around the room temperature and below, due tohigh crystallinity and relatively high glass transition,havepreventedits largercommercialapplication.

With all melt-processedpolymersthereis thepossibilityof thermaldegradation at temperaturesin theregionof themelting point (in caseof PHB,melting point ascalculatedis 1808C)96). PHB is known97–100)to besusceptible to ther-mal degradationat temperaturecloseto its melting point.This degradation occursalmostexclusively via a randomchain scissionmechanisminvolving a six-memberedringtransitionstate99,100). LehrleandWilli ams101) havereported


that under certainconditionsrandom chain scissioncannot be responsible exclusively for the formation of theobserveddegradationproducts.In particular, it wasshownthatprimaryproductsareinvolvedin anumberof second-aryreactionsandisomerizationsand,indeed,thattetrameris formedprincipally asa result of suchsecondary reac-tions102). Thetwo monomerunitsi. e.,3-hydroxypentanoicacid (trivially known as 3-hydroxyvaleric acid or 3HV)and3-hydroxybutyricacid(3HB) of PHBV copolymerareshownin Fig. 4. Thecopolymercanbeproduced by add-ing propionicacidto thenutrient feedstocksuppliedto thebacteria.Thecopolymercompositionscontainingupto 30mol-% of 3HV canbe produced by controlling the feed-stockand the conditions. Biopolm is alsoproducedcom-mercially byafermentationprocessusingglucoseandpro-pionicacidascarbonsourcesfor themicroorganisms.Themolepercentageof valerate in thepolymersampleis lim-itedby thetoxicity of thepropionicacidto themicroorgan-ismsused, Alcaligenes eutrophus101). However, polymerswith compositions up to 95 mol-% 3HV have beenobtainedby adding controlledmixture of pentanoic acidandbutyric acid to the feedstock103,104). The copolymer isbelievedto possessanalmostcompletely randomdistribu-tion105–107). The comonomerreducesthe crystallinity andalso the melting point of the homopolymer. The meltingpoint (Tm) of thecopolymerdecreases from thecalculated1808C with increasing 3-hydroxyvalerate content andreaches a minimum value of 758C at approximately 40mol-% 3HV. Again,asthe3HV contentincreasestowardspure3PHV, themeltingpoint increases; thus at 95 mol-%3HV the melting point increasesto 1088C88,106,108). Theimpactstrength88), flexural modulus109), melting tempera-ture106), andtherate of crystallization110) of PHBV copoly-mershavebeenshown to be regulatedby the contentof3HVunits.

There are not only poly(b-hydroxybutyrate) and thecopolymerof 3-hydroxybutyratewith 3-hydroxyvaleratethat are produced by bacteria, other bacterialpolyestersare also available. Steinbuchel and Valentin111) havereviewedthe diversity of bacterial polyhydroxyalkanoicacidsin which an overview is provided on the diversityof biosynthetic polyhydroxyalkanoic acids, and allhitherto known constituents of thesemicrobial storagecompounds.The occurrenceof 91 differenthydroxyalka-noic acidsreflects thelow substrate specificity of polyhy-droxyalkanoic acid syntheseswhich arethe key enzymesof polyhydroxyalkanoic acid biosynthesis.Inspite of theexcitement of morethan90 differentconstituentsof bio-syntheticPHA, the commercial exploitation of this vari-ety remainslimited, sinceonly very few PHA areavail-able in sufficient amounts to allow the evaluation of thephysical,chemical and biological material propertiesofthesepolyesters. Microbiologists can contribute signifi-cantly in thenearfutureto solvethis dilemma.

iii. A Poly(x-hydroxyalkanoate) such as poly(e-caprolactone),PCL, is a partially crystalline linear poly-esterwith a low Tg of –608C anda low Tm of 608C. It isproduced by several manufacturers,includingUnion Car-bide, Solvay, and Daicel. PCL is preparedfrom cyclicestermonomer, lactone,by a ring-opening reaction with acatalyst like stannousoctanoate in the presenceof aninitiator that containsan active hydrogenatom81). PCL isa toughandsemi-rigid material at roomtemperaturehav-ing a modulusbetweenthoseof low-density and high-density polyethylene. It has been shown that PCL isdegradedby enzymes,lipases,secretedfrom microorgan-isms112,113). Currently, most of its applications are notrelated to its biodegradability. PCL is compatible withmanyorganicmaterials andpolymersandthus it is usedin manypolymerformulationsascompatibilizers. Its lowTg (high chain flexibility) leadsto its useas soft blocksfor segmentedpolyurethanes.Recent findings showingthatPCL canprovidewaterresistancein starch-basedfor-mulationsmay leadto future application of large quanti-tiesof this polymer in thisarea114).

iv. Poly(alkylene dicarboxylate) type of biodegrad-able aliphatic polyesters has beendeveloped by ShowaHighpolymer under the tradename ‘‘Bi onolle”. Dif ferentgrades(Fig. 4) of Bionolle are: polybutylene succinate,PBS(#1000 series),poly(butylene succinate-co-butyleneadipate),PBSA (#3000 series)and poly(ethylenesucci-nate),PES(#6000 series).Bionolle polymers with highmolecular weight ranging from several tens to severalhundreads of thousands were inventedin 1990 and pro-ducedthrough polycondensationreactionof glycols(suchas ethylene glycol and butanediol-1,4) with aliphaticdicarboxylic acids(suchassuccinic acid andadipic acidand others)115–117). In case of need of higher molecularweight, coupling reaction is carried out with a smallamountof coupling agentsas chain extenders118,119). As

Fig. 4. Unit structuresof typical typesof biodegradablealipha-tic polyesters


reportedby Fujimaki115), Bionolle is a white crystallinethermoplastic with melting point of about 90–1208C(similar to LDPE), glasstransitiontemperatureof about–45 to –108C (between PE and PP), density of about1.25g/cm3 (similar to PET), tensile strengthbetweenPEand PP, stiffnessbetweenLDPE and HDPE and heatofcombustion below 6 kcal/g, i. e., aboutonehalf of poly-olefins. Bionolle hasexcellent processability andcan beprocessedon polyolefin processing machinesat tempera-ture of 160–2008C, into various products such asinjected, extruded and blown ones120–125). A new gradeBionolle (coded#1900 series), which has a long chainbranch,and high recrystallization rate, has beendevel-oped, to enableto preparestretched blown bottles andhighly expandedbottlesaswell as foams126). The biode-gradability of Bionolle polymers dependsupon theirstructuresand also the environment in which they areplaced. Biodegradability of different gradesof Bionolleburied in activated sludges,soils and composthasbeenstudied127). As per the findings, Bionolle #3000 showedthe best biodegradability in soils and a compost, whileBionolle #6000showedbestbiodegradability in activatedsludges119). Fujikami126) has reported the potential andnear-futureapplicationsof Bionolle.

3.4.2 Polyesteramides

Aliphatic polyester amides have been suggested andrecently investigated as a potential family of polymerswith good mechanicaland thermal properties,aswell asprocessing faciliti es and susceptibility to degrada-tion128,129). A series of biodegradable aliphatic polyesteramidesderivedfrom 1,6-hexanediol, glycine,anddiacidswith a variablenumberof methylenegroups(from 2 to 8)hasbeensynthesized andcharacterized130). The synthesisandsomephysicochemicalpropertiesof polyesteramidesderivedfrom 1,6-hexanediol, sebacicacidandana-aminoacid suchasglycine,alanineor phenylalaninehavebeenreported131). Saotomeet al.132) havesynthesizeda seriesofpolyesteramidesbasedon1,2-ethanediol,adipic acid, andan amino acid asglycine, leucine,or phenylalanine.Thedegradation studieswith proteolitic enzymes(chymiotrip-sine and elastase) indicatedthat only the polymers con-taining glycine were not degradedby any of the testedenzymes.They alsoreported133) that inclusionof phenyl-alaninein the glycine-derived polyesteramidesenhancestheir degradability with chymiotripsine. As reported byParedesetal.130) thepolyester amidesderivedfrom diacidswith ahighnumberof methylenegroupspossessadequatemolecular weightsto give film- andfibre-formingproper-ties.Again thedecompositiontemperaturesof suchpoly-esteramideswere always higher than the correspondingmelting temperaturessuggestingthat thesepolymers canbe processedfrom the melt. Enzymatic incubation withpapaindemonstrated thebiodegradability of all thepoly-

ester amides of the series. In all cases, the polymersshowedahigh susceptibility to enzymatic degradation.

On a call from the Government of Germany forresearch and developmenton biodegradable thermoplas-tics with good performanceand processing behavior, in1990134), Bayer presentedits first grade of polyesteramide(BAK 1095) to thepublic, five yearslater135). Dur-ing 1997 Bayer, launchedanothergradei. e. BAK 2195.BAK 1095is basedon caprolactam(Nylon 6), butanediolandadipic acid, whereasBAK 2195 is synthesized fromadipic acid and hexamethylene diamine (Nylon 6,6) andadipic acidwith butanediol anddiethyleneglycol asestercomponents.Sincetheproduction processof BAK is sol-vent- and halogen-free, the polymer is free of halogens,aromatic compounds and toxic heavy metals. Althoughtheprocessing conditionsaresimilar to polyolefins136,137),thebiggestdifferencebeing theshapeof thegranules,thegranulationtechnique is under constant developmentbyBayer to reachat easily processiblegranules.BAK 1095has mechanical and thermal properties resembling tothose of polyethylene138). The resin is also noted for itshigh toughnessandtensilestrain at break.It canbe pro-cessedinto film andalsointo extruded or blow-mouldedparts. It is suitablefor thermoforming andcanbecolored,printed, hot-sealed and welded.The crystallisation tem-perature of BAK 1095 is 668C and it crystallisesrela-tively slowly andsoit is not ideal for injectionmoulding.BAK 2195 resin is ananinjection-moulding gradebiode-gradablethermoplasticthatexhibitsgreaterstiffness.Thisresin hashigher melting point (1758C) than BAK 1095(m.p. 1258C) andalsohighercrystallisation temperature,i. e., 1308C. The propertyprofile of BAK 2195can alsobeextendedthroughtheaddition of fillers andreinforcingsubstances,suchasstarch,natural fibres,woodflour, andminerals83). The combined performance of both BAKgradesandthe compoundsopena wide rangeof applica-tions like disposable plant pots, agricultural films, bio-waste bags, plant clips, cemetery decoration, one-waydishes and others. BAK 1095 breaksdown into water,carbon dioxide, and biomassunder aerobic conditions.The degradation rate is comparable to that of otherorganic materials that are composted138). All the biode-gradability tests139,140) demonstratethe completebiode-gradability of BAK 1095 andsimilar testsfor BAK 2195arein process135).

3.4.3 Starchplastics

Starch is produced in plants and is a mixture of linearamylose (poly-a-1,4-D-glucopyranoside) and branchedamylo-pectin (poly-a-1,4-D-glucopyranosideanda-1,6-D-glucopyranoside).Theamount of amyloseandamylopec-tin varieswith thesource.Thechemicalstructureof amy-loseandamylopectin is shown in Fig. 5. Theexactstruc-ture of starch granules is not yet fully understood. Amy-


loseis theminor componentof starchrangingfrom 20 to30%141). Theamylopectins areresponsible for thecrystal-line properties of starches. The relative amounts, struc-tures and molar massesof amyloseand amylopectin instarchesaredeterminedby means of genetic andenviron-mentalcontrolduring biosynthesis, andhencewide varia-tion occurs among plant raw materials. Corn is the pri-mary sourceof starch, although potato, wheat and ricestarchalso have markets in Europe and USA142). Up toUS$ 1.861010 worth of corn is producedin the USAannually114). Starchis one of the least expensive biode-gradable materials availablein theworld markettoday. Itis a versatilebiopolymer with immensepotential for usein the non-food industries. Of the 6.8 million tons ofstarchproducedin Europe annually, approximately 20%is usedin non-food industries141). Howeverfrom a recentreport78) it is found that, starchis industrially processedwith a volume of almost7 million tons/yearin Europe,and nearly 50% of the starchproduced is usedfor non-food applications.

Starchconvertedto thermoplasticmaterial (starchplas-tics) offers an interesting alternative for synthetic poly-

merswherelong-term durability is not neededandrapiddegradation is an advantage. The properties andapplica-tions of starch and starch plastics have been reviewedrecentlyby Shogren143). Starch canbemade thermoplasticthroughdestructurizationin presenceof specificamountsof plasticisers (water and/or poly-alcohols) in specificextrusion conditions74). Thermoplastic starch productswith different viscosity, water solubility and waterabsorption have beenprepared by altering the moisturecontent,amylose/amylopectin ratio of raw product andthe temperature or the pressure in the extruder144–148).Thermoplastic starch alone can be processedas a tradi-tional plastic; however, its sensitivity to humidity, makesit unsuitable for many applications. The thermoplasticstarchalone is mainly usedin solublecompostablefoams,suchasloose-fillers,expandedtrays,shapemouldedpartsand expanded layers,as a replacement for polystyrene.BIOTEC of Germany hasconducted promisingresearchanddevelopmentalong the lines of starch-basedthermo-plastic materials.The company‘s threeproduct lines areBioplastm granulesfor injection moulding, Bioflexm film,and Biopurm foamed starch. Starch-based biopolymerthermoplastics include, in particular, thermoplasticstarches(TPSm)149) and the group of polymer blends ofthermoplastic starcheswith additional polymer compo-nents like aliphatic polyesters e.g. polycaprolacton andbionolle, poly vinyl alcohol, polylactic acid, copolymerfrom aliphatic diolin and aliphatic as well as aromaticdicarbon acids together with especially biodegradablepolyesteramides78). Theresearchresultsfor TPSm bioplas-tics andtheir production processesareprotected by inter-nationalpatents or havepatentspending150–153). Under theMater-Bi trademark,Novamontof Italy today producesfour classesof biodegradablemateriasZ, Y, V, andA, allcontaining starch and differing in synthetic compo-nents74). Eachclassis available in severalgradesandhasbeendevelopedto meet theneedsof specificapplications.The current production capacity of Novamont is 8000tons/year. Mater-Bi canbe processedusingconventionalplastic technologies such as injection moulding, blowmoulding, film blowing, foaming, thermoforming andextrusion. The physical-mechanical propertiesof Mater-Bi aresimilar to thoseof conventional plastics like poly-ethyleneandpolystyrene. Mater-Bi is not only recyclablebut also as biodegradableas pure cellulose. The biode-gradability of Mater-Bi products has been measuredaccording to standard testmethodsapprovedby Interna-tional Organizations(ISO, CEN, ASTM). The compost-ability of someMater-Bi gradeshasbeencertified by the“Ok Compost” label. Mater-Bi can be used in a widerange of applicationssuch as disposable items (plates,cutlery, cup lids etc.),packaging(wrapping film, film fordry food packaging, board lamination etc.), stationery(pens,cartridges, pencil sharpeners etc.), personalcareand hygine (sanitary napkins, solublecotton swabs etc.)

Fig. 5. Chemical structureof some biodegradable polymers:amylose,amylopectin andcellulosediacetate


anda lot otherslike toys,shopping bags, mulch film etc.Variousstarch plastics with differenttradenames(Tab.5)arenow availablein the market. BunaSow Leuna(BSL)of Germany hasdevelopeda line of biodegradablepoly-mersbasedon esterified starchwith thetradenamesSco-nacell S, Sconacell A, and SconacellAF. Compared tocommon thermoplastics, however, biodegradable pro-ducts basedon starch still reveal many disadvantageswhich are mainly attributed to the highly hydrophiliccharacter of starch polymers. Inspite of many positiveresults,thermoplastic starch-basedmaterials arestill at anearly stageof development andthemarkets for suchpro-ductsareexpected to increasein future as the propertiesaremoreimproved, pricesstill decline,andan infrastruc-turefor compostingbecomesmore established.

3.4.4 Celluloseacetate

Celluloseesters,e.g., celluloseacetate(CA) are consid-ered as potentially useful polymers in biodegradableapplications154–160). CA is a modified polysaccharidesynthesized by the reaction of acetic anhydride with cot-ton lintersor woodpulp.Thestructureof cellulosediace-tate is represented in Fig. 5. The production of celluloseestersfrom recycledpaperandsugarcanehasalsobeendemonstrated161). Historically, therehasbeenconsiderableconfusionregardingthe biodegradation potentialof CA.It was generally accepted that cellulose esterswith adegreeof substitution (DS) less than 1.0 wil l degradefrom the attack of microorganisms at the unsubstitutedresiduesof the polymers,and that the ether linkages inthe cellulose backboneare generallyresistantto micro-bial attack162,163). It is alsoreportedthatCA is a poor sub-strate for microbial attack164). Early evidenceas to thebiodegradation potential of CA is reportedby CantorandMechales165) who demonstrated that reverse-osmosismembranesprepared from CA with DS = 2.5 sufferslossesin semipermeability dueto microbial attack. Gard-neret al.156) showed, basingon film disintegrationandonweight loss, that celluloseacetates,having DS lessthanapproximately 2.20,compostat 538C and60% moistureat ratescomparable to that of PHBV. Komarek et al.155)

providedvia aerobicbiodegradationof radiolabeledCA,that in CA with a DSof 1.85 morethan80%of theorigi-nal 14C-polymeric carbon wasbiodegradedto 14CO2. Thestudies on biodegradation of CA although have beengivenmuch attentionin recent times;scarceattention hasbeenpaid to thebiodegradation of formulatedresinscon-sisting of cellulose acetateand diluents. This shouldbetakeninto accountseriously, asthe melt processing tem-perature of the cellulose acetatesexceedsthat of itsdecomposition temperature,which implies that mostcel-luloseacetatesmustbe plasticized if they are to be usedin thermoplasticapplications166). Effect of plasticizeronbiodegradation of CA films hasbeenreported by Jiang

andHinrichsen167). In thatwork, biodegradationof plasti-cized celluloseacetate (PCA) film wasevaluatedby theways of percent conversionof carbon to CO2. A stronglossof 20%in weightoccuredwithin the first two weeksof degradation. It was concluded that the fractions oflower molecular weight or lower substitution portion ofPCA were biodegradedand removed preferentially fromthe film. CA of various DSarenow being widely usedasfilms andcoatings.Commercially available CA hasa DSbetween1.7 and 3.0. CA films have a tensile strengthcomparableto polystyrene,which makesthepolymer sui-table for injection moulding82). CA is used to produceclearadhesivetape,tool handles,eyeglassframes,textilesand related materials. Mazzucchelli of Italy and Planetpolymer of USA manufacture biodegradable plasticsbasedoncelluloseacetateunder thetradenames,BIOCE-TAm andEnviroPlasticm Z respectively. BIOCETAm is tar-geted for the manufactures of biodegradable packagingfilms, retractable films, tubes, and containers for oils,powders,and other products.EnviroPlasticm Z materialsarealsoaimedat usein products in thepackaging andtheindustrialmarkets.

3.4.5 Soyplastic

The production, structure, and composition, physico-chemical properties,processing for plastics, industrialapplicationsandbiodegradablenature of soyprotein bio-polymerhave beenreviewed168). In US, soybeansprovideover 60%of thefatsandoils usedfor food andthemajor-ity of the feedprotein.Soybeanstypically containsabout20% oil and40% protein. Proteinlevels ashigh as55%have beenobservedin soybeans.Soybeansconsist of dis-crete groupsof proteins(polypeptides)that spana broadrange of molecular sizesand are comprised of approxi-mately 38% of non-polar, non-reactive amino acid resi-dues, while 58% are polar and reactive. Modificationsthat takeadvantageof watersolubility andreactivity areexploited in improving soyprotein for usein plastics andother biomaterials169, 170). Soy protein plastics of differentcompositions have been preparedby injection mould-ing171). Compressionmoulding is alsousedfor soyplasticprocessing.Lessthan0.5%of theavailable soyprotein isused for industrial products172, 173). Soy protein has un-usual adhesive properties.Soy plastics havebeenusedformanufacturing automobile parts by Ford company168).Dried soy plastics display an extremely high modulus,50%higherthanthatof currently usedepoxyengineeringplastics174). Sowith propermoisture-barrier, soyprotein isa potential starting material for engineering plastics.Blending thebiodegradable soyprotein plastic with poly-phosphate filler greatly reduced its water sensitivity,allowing new usesin moist and load-bearing environ-ments where the unfill ed plastic was not useable175).Development of affordable soy-basedplastics, resins, and


adhesivesis reviewedrecently176). The reaction productof soybean,a carbohydratefiller, a reducing agent, waterandadditivesresultedin animproved biodegradableplas-tic177)havinghigh degreeof flowability for processing byextrusion andinjection mouldinginto solid articleswith ahigh degreeof tensilestrengthandwaterresistance.

3.5 Biodegradableplasticsvs.traditional plastics

The growing environmental concernhasmade plastics atargetof criticism dueto their lack of degradability . Of allthepackaging wastes discardedin theUnitedStates,plas-tics accountfor about20% by volume178). Annual expen-diture on packaging increasedby more than 4% to US$111 billion between 1994 and 1996, according to areport179) from Pira, the UK packagingconsultancy. Plas-tic‘s shareof the total packagingexpenditureremainedconstantoverthesameperiod,at 29%, secondin termsofsector importance behind paper and board, whichaccountedfor 41% of the market in 1996. So therehasbeena lot of interestin researchcommitted to the designof biodegradable plastics180). Theconceptof environmen-tally consciousmaterials (ecomaterials) is being rapidlyaccepted by countriesall over the world181). Biodegrad-ablepolymersareconsideredasanenvironmentalwaste-managementoption182). They constitute a loosely definedfamily of polymersthat aredesignedto degrade throughactionof living organismsandoffer a possible alternativeto traditional non-biodegradable polymers where recy-cling is unpracticalor not economical. Thetwo mainrea-sonsfor the interestin biodegradablematerials are: thegrowing problem of waste thereby resulting generalshortageof landfill availability andtheneedfor theenvir-onmentally responsibleuseof resourcestogetherwith theCO2 neutrality aspect183). Interestin biodegradable plas-tics is being revived by new technologiesdevelopedbymajor companies,suchasBayer, DuPont,andDow Car-gill 83). Demandsfor biodegradables are forecastto grownearly 16% per annum184). Performancelimitations andhigh costshaverestricted theadoption of suchplastics tovery small nichesup to now. For scientists, the real chal-lengelies in finding applications which would consumesufficiently large quantities of thesematerials to lead toprice reduction, allowing biodegradable polymers tocompeteeconomically in the market. The challenge inreplacing conventional plastics by biodegradable materi-als is to designmaterialsthat exhibit structuralandfunc-tional stability during storageanduse,yet aresusceptibleto microbial and environmental degradation upondispo-sal, without any adverse environmental impact. Thedesignof appropriatebiodegradablematerialswill requirea clear understanding of factors influencing materialproperties and performance as well as biodegradability,so that appropriate trade-off canbe made. The balancingof degradability andperformanceof biodegradablemate-

rials is reviewed82). The performance of biodegradablematerials must be maintainedduring processing,storageand use in order to ensure that they can carry out theirintendedfunctions.

Theblending of biodegradable polymers is a methodofreducing the overall cost of the material and offers amethod of modifying both properties and degradationrates.However a blend, particularly with a non-biode-gradablepolymer, can even reduce or even inhibit thedegradation of the biodegradable component93). In recentyears,thebiodegradable polymershaveofferedscientistsa possiblesolution to the waste-disposalproblemsasso-ciated with traditional petroleum-derived plastics. Mostof the biodegradable polymerswere intendedto be usedin packaging industries,in farmingandalsoin specializedbio-medical applications.A lot of researchwork hasbeendoneon blendingof biodegradable polymers.

The main constraint on the useof biodegradable poly-mersis thedifferencein thepriceof thesepolymerscom-paredto bulk produced oil-basedplastics93). The cost ofBiopolm is approximately 8000 UK pounds per ton(1000kg), comparedwith the UK pricesof commoditypolymersof between500 pound/ton (PVC and PP) and600pound/ton(HDPEandhigh-impactPS).According toa recent report185), Monsantosaysit wil l cease productionandresearch,asit cannot sustainthemoney-losingbusi-ness.According to Mar Techreportof July 1998, a largermarket for biodegradable plastics and polymers is notexpectedto open up until prices drop below US$ 2/lb;which is not likely to occur until products can be massmarketed.The prices in US$/lb of somebiodegradableand traditional plastics are representedin Tab.6. As canbe observedfrom the table, biodegradable plastics cancostup to tentimesmorethancommodity plastics.Mayerand Kaplan82) have also reviewed the cost (US$/lb) ofpolymers such as, starch (0.15–0.8), cellulose acetate(1.70),PHBV (6–8), PVOH (1.5–2.5), polycaprolactone(2.7) and PLA (1–3). According to thesevalues PHBVcosting6.00–8.00US$/lb is aboutfour to ten timesmoreexpensivethanstarch which costsonly 0.15–0.8 US$/lb.First prices of BAK of 7.00 DM/kg (ca. 2 US$/lb) aresubject of further quantities per delivery and annualdemand187). The productcostsof differentgradesof Sco-nacellwil l dependon the production scale andasspecu-latedby theproducer BSL, Germany188), thecostswil l bein the range 0.6–1.1 US$/lb. Starch-basedand PLA-basedpolymershaveoccupiedthemajormarket of biode-gradableplastics today. Cargill Dow officials say thatPLA will initial ly be priced in the 50 cts – $ 1/lb range,but thatwill comedownasgreaterscaleandprocesseffi-ciencies areachieved189). The marketpotential for biode-gradableproducts in the next five years canbe estimatedat approximately 30000–40000 tons/year74) in Europe.American and Japanesemarketsare of great potential,but arestill at a very early stageof development,with the


exception of starch-basedloose-fillers. The demandsofcertainbiodegradable productsare at the rising level. Apilot plant of Bionolle by ShowaHighpolymer115) with acapacity of 10 tons/yearwas built in 1991, whereasaplant with a capacity of 3000 tons/yearwasconstructedonly after three years, i. e., in 1993. Cargill’ s existingPLA facility nearMinneapolis, in US, having 3600 tons/yearcapacityduring the beginning of 1998, expandedto7200 tons/year towards the end of the year. A new140000 tons/yearcommercial plant83) is alsoplannedfor2001.The production capacity of starch-basedmaterialsby Novamont74) is 8000 tons/year. The market potentialfor bioplasticshasbeenstudied by EC Commission GDXII 190). 1.1 million tons/year of bioplastics with anincreasein economic value andjob potential of four bil-lion DM and 20000 new jobs respectively is predicted.This optimistic forecastappearsto be unbelievably highwhen the current production amounts of bioplastics aretaken into account78); however, in comparisonwith thecurrentproduction datafrom plastic industry: 32 milliontons/yearin Europeand120million tons/yearworldwidedisplaysrealistic estimatesfor the future technology. Upto the year2000an averageincreasein the consumptionof plastics of about 5% per annum is expected191). InUSA, peopleprimarily userecycling and landfill to dis-pose the plastic materials; composting is also beingdebated, especially in Europe for disposing of plasticsand in Japan,wherethe land is expensiveandnot avail-able for landfilling, combustion to carbon dioxide andwaterandreuseof theenergy seemsto beonly choice192).Today’s much better performanceof traditional plasticsare the continuedR&D efforts of severalyears. Most ofthe biodegradable polymers came to public only fewyearsback and from around 1990 onwards the marketandproduction for biodegradable materials havetakenamarchingform. Pricesof biodegradablescanbe reducedonly on massscale production; andsuchmassscalepro-duction by companies will be feasiblethrough constant

R&D efforts of scientiststo improve the performanceofbiodegradable plastics.In any case,the potential marketfor biodegradableplastics is significant,evenif theyonlymanage to capture a small segmentof the commodityplastics market.Over the next severalyears,demandforbiodegradable plastics is expectedto grow fastestin Eur-ope, dueto Europeandirectivesthatencouragetheuseofbiodegradable polymersfor compostablepackaging. TheGermanFederalGovernment andtheGermanParliamenthave agreed on an amendmentto the Packaging Regula-tion with a rule for compostableplastic packaging. Thisspecial provision is valid for compostable packagingmaterials that contain mainly biodegradable materialsbasedon renewable resources78). In nearfuturebecauseofseriousenvironmentalthreatwhole world will takea ser-ious look towardsuse of biodegradable polymers. Themarket for biodegradable plastics in North America andEuropefrom 1997to 2006(Fig. 6) is quiteencouraging.

Tab.6. Biodegradablevs. traditionalplastics– costcomparison(cf. ref.186))a)

Material Averagecost————–

$//lb.

Biodegradableplastics PLA (Cargill Dow Polymers)Starch-basedresins(Novon/Novamont)PHA (BIOTEC/Monsanto)

1.50–3.001.60–2.904.00–6.30

Commoditypetrochemical plastics PPLDPEHDPEPSPVCPolyesterPVOHPolycarbonate

0.330.410.370.390.280.521.401.60

a) Reproducedwith permissionfrom Mar Tech,USA (Website:http://www.Mar Tech-Reports.com).

Fig. 6. Market for biodegradable plasticsin North America&Europe(1997 – 2006)(after ref.75), reproducedwith permissionfrom MarTech,http://www.Mar Tech-Reports.com)


4. BiocompositesThe literature surveyreveals that only litt le work hasyetbeendone on biocomposites.The developmentsof bio-compositesstarted in the late 1980s,andmostof thebio-degradable polymersas discussedin Section3, not yetsatisfying eachof therequirementsfor biocomposites,arenow available in themarket.Thebiodegradable polymerslike Biopolm, polycaprolacton,Bioceta,Mater Bi, Scona-cell, etc.8,193) have beentested,in order to examine theirpropertieswith special emphasison thesuitability of suchpolymers for useasmatrix materialfor the fabrication ofbiocomposites.The low viscosity of thesematrix poly-mers at the processingtemperature, good mechanicalproperties of both the matrix and reinforceing fibre aswell asgoodfibre-matrix adhesionarerequiredto obtainhigh-quality biocomposites.

4.1 Cellulosefibre basedbiocomposites

The study of polymer compositesthat contain cellulosicmaterials has been recognised as an important area ofresearchfor over a decade.Cellulosic materials areusedin the polymer industry for a wide rangeof applications,including: laminates, fillers and panelproducts,compo-sites,alloys andblends,andcellulosederivatives29). Inter-estis growing in the field of cellulose-reinforcedthermo-plastics194–197). Graft co-polymers of the matrix materialandtheadditionof a polargrouphavebeenusedsuccess-fully to improve the mechanical properties of cellulose-polymer composites198,199). Cellulosic fibresarealsofind-ing applicationsas reinforcement in most commonther-moset polymers200–202) like polyester, epoxy, amino andphenolic resins. Short cellulosic fibre-reinforced elasto-mer composites have gained practical and economicinterest in the rubber industry203,204). However, all theabovementionedcellulose-basedcompositesarenot fullybiodegradable because of non-degradable syntheticmatrix components.

The structure and physical properties of bacteriallysynthesized polyesters have beenreviewed205). The pro-cessingand properties of biodegradable compositesofbacteria-produced polyesters(Biopolm) reinforced withwoodcellulosehavebeenreportedby Gatenholm et al.206)

Although cellulosefibres improvedthestrength andstiff-nessof the polyhydroxybutyrate(PHB), the compositeswerevery brittle. At a high proportionof HV, the tensilemodulus is reducedup to 30%, whereaselongation atbreak increasesto about60%. The effect on the tensilemodulus (TM) by the incorporation of cellulose fibresinto three different thermoplasticslike PP, PS (polysty-rene), and PHB has also been investigated, whichrevealed that thetensilemodulusincreasedfor eachcom-positewith increasing fibre content.The stiffening effectof cellulosefibre in PHB wasin thesameorderasin PS.

From the studies of dynamic mechanical propertiesofPHB copolymers of varying composition and of cellu-lose-filled compositesit wasobservedthat the introduc-tion of cellulose resultedin a decreasedmechanical lossfactorowing to restrictionsof chain mobility in theamor-phousphase,while an improvement in thedynamicmod-ulus wasnoticed.An excellentdispersibility of cellulosefibres wasachievedin the PHB matrix ascomparedwithsyntheticmatricessuchasPPor PS.Thedegreeof disper-sibility wasstrongly dependent on processing conditionsandrelatedto thefibre-lengthreduction.Themicroscopicinvestigations on the fibres extracted from compositeshoweddefibrillation characteristics, suggestinga possi-ble hydrolysisof celluloseby crotonic acidformedin situasa resultof thermal decompositionof the PHB matrix.The synergistic effectsduring the processing of cellulosewith Biopolm have been reported207). Lignocellulosicstraw fibre-reinforced PHB generally leads to expectgood mechanical properties of such composites asreportedby Avella et al.208)

4.2 Flax, hemp,andramiebasedbiocomposites

As discussedunder Section2, flax, hemp and ramie arethemostinteresting biofibres to beusedasreinforcementin compositestructures.Flax fibre-reinforcedPPcompo-siteshaveattractedmuchattention209–211). The resultsof aresearchproject of a German company(Daimler-BenzA.G.) suggests212) that flax andsisalbasedcompositesareusedfor making vehicle interior parts.Thereinforcementof polyisocyanate-bondedparticleboardswith flax fibresled to products comparable to thoseof carbon andglassfibre-reinforcedparticleboards213).

As far as biocompositesare concerned, Herrmann etal.2) havereportedthe tensile strength andstiffness214,215)

of unidirectional-laminatesfrom hemp, ramie and flaxeachcombined with a matrix of Sconacell A and ramieembeddedin a shellac basedresin193). The stiffness oframie/SconacellA andflax/SconacellA wereabout50%,whereastensile strengthswere about60%ascomparedtoE-glass-epoxy composites (GFRP). The stiffness oframie/shellac laminates was quite comparable withGFRP, while the tensile strength was only 43%. Hemp/Sconacellbiocomposite showed 143% of the stiffnessand60%of tensile strengthascompared to GFRP. Thesevaluesof mechanicalproperties revealthatbiocompositescan in many cases replaceGFRP in structuralapplica-tions.Several publications4–7,216,217) report aboutthe com-parabilityof mechanicalpropertiesof biocompositeswithwell-known glassfibre reinforcdplastics. Testswith dif-ferent flax fibre-reinforced biodegradable matrix poly-mersby Hanselka et al.4) showed that the tensile strengthandYoung’smodulusof thesebiocompositeswereclearlyinfluenced by particular matrix and adhesion betweenfibre and matrix. The mechanical properties of extruded


flax fibre-reinforcedthermoplasticstarch(structuredwithwateror glycerin)showedincreasedvalues,especially fortensilestrengthandYoung’s modulusbecauseof additionof green-flaxfibre rovings.The literature on this subjectsuggests that from the point of view of the mechanicalproperties,suchbiocompositesare suitableconstructionmaterials; however, limit ations must be seen whereexcessiveenvironmental conditions exist. Major pro-spectsfor thesematerial systems are, therefore, liningelementswith support functionin theautomobile, rail car,and furniture industries4). The tensile strengthand stiff-nessof biocompositesmainly meant for useaspanellingsi. e. non-woven fabrics from flax reinforced with Scona-cell A, Bioceta, shellac and some newly investigatedmatrix systems (yet confidential) and also from Lyocell(a man made cellulosic fibre), embedded in Sconacellhavebeenreported2). The fibre volumecontent was30%with the exception of an additional flax/shellac samplecontaining 45% fibres by volume. As reported, flax/newly developed matrix system and flax/shellac com-poundsgave good valuesof tensilestrengthwhich werein the rangefrom 80 to 93 MPa or even109 MPa withincreasedfibre volumecontentof flax/shellaccompositesfrom 30 to 45%. A considerableimprovement in tensilestrengthwas achieved by using Lyocell insteadof flaxfibres eachembedded in SconacellA; the correspondingvaluesbeing 57 and80 MPa, respectively. Strucural bio-compositesarereinforcedby multilayer or wovenfabrics,mainly from yarns or slivers for strengthand stiffnessrequirements, whereaspanellings areusually madefromnon-woven fabricsfrom relatively shortfibresfor a betterdraping.Biocompositescontainingnatural fibresandbio-degradable matricesare patented218) for applications asbuilding materials. The title materials contain naturalfibres, e.g., flax, hemp,ramie,sisal or jute and a biode-gradablematrix such as cellulose diacetate,or a starchderivative.While reviewing the chancesand limitationsof biodegradablepolymersbasedon renewable raw mate-rials,Fritz et al.219) havereportedthatsomedestructurizedpolysaccharides can form the polymer matrix of flaxfibre-reinforcedcomposites.

4.3 Jutebasedbiocomposites

Juteis oneof the mostcommon agro-fibreshaving hightensilemodulus and low elongation at break. If the lowdensity(1.45g/cm3) of this fibre is takeninto considera-tion, thenits specificstiffnessandstrengtharecomparableto therespectivequantitiesof glassfibre220–223). Thespeci-fic modulusof jute is superiorto glassfibre,andonamod-ulus per cost basis, jute is far superior. The specificstrengthperunit costof juteapproachesthatof glassfibre.Therearemanyreportsabouttheuseof juteasreinforcingfibres for thermosets224–229) and thermoplastics223,230–232).MohantyandMisra16) havereviewed jute reinforced ther-

mosets,thermoplastic,and rubberbasedcomposites. Toreducethemoisture regain property of jute, it is essentialto pretreatjute so that the moistureabsorptionwould bereducedand wettability of the matrix polymer would beimproved.Recently, Mitra et al.233) havereportedthe stu-dies on jute-reinforcedcomposites, their limitations andsome solutions through chemicalmodificationsof fibres.Flexural strength, flexural modulus and the dynamicstrength of chemically modified jute-PP compositesincreased by 40,90 and40%respectivelyascomparedtounmodified jute-PP composites234) due to the chemicalmodification of jute with maleic anhydride graftedpoly-propylene.The reinforcementof jute with biodegradablematrix hasnotbeenstudiedto agreatextent.Theeffect ofdifferent additives on performanceof biodegradable jutefabric-Biopolm composites has been reported235). Inabsence of any additive, both tensile strength (TS) andbending strength (BS) of composites were found toincreasearound50%whereaselongationat break reducedonly 1% ascomparedto pure Biopolm sheet.In order tostudy theeffectsof additives, thejute fabricswere soakedwith several additive solutionsof different concentrations.During suchtreatmentsdicumyl peroxide(DCP)wasusedas the initiator. The effects of varioussurface modifica-tions of jute on performance of biodegradablejute-Bio-polm compositesaspreparedby hot-presstechnique, havebeenreportedvery recently236,237). The surfacemodifica-tions of jute, involving dewaxing, alkali treatment, cya-noethylation and grafting are made with the aim toimprove the hydrophobicity of the fibre so as to obtaingood fibre-matrix adhesion in the resulting composites.Dif ferently chemically modified jute yarn-Biopolm com-posites236) showedmaximum enhancement of mechanicalpropertieslike tensile strength(TS), bendingstrength (BS),impactstrength(IS) andbending-modulus(Bmf) by 194,79,166and162% respectively in comparisonto pureBio-polm. With 10% acrylonitile (AN) graftedyarn, the TSofcompositeenhancedby 102%, whereaswith 25%graftedyarn, TSenhancedby 84%in comparisonto pureBiopolm.Thus with increaseof grafting percent the mechanicalpropertieswere found to decrease.The compositesmadefrom alkali treatedyarnsproduced bettermechanical prop-ertiesthandewaxedandgrafted yarns.Orientationof juteyarn played an important role on the properties. Theenhancementof mechanicalpropertiesof compositesarenoticedonly whenthepropertiesof compositesweremea-suredalongtheyarn wrappingdirection.

Unlike jute yarn,theenhancementof mechanicalprop-erties of jute fabric-Biopolm compositesdo not showanyvariation with the direction of measurement of proper-ties237). More than 50% enhancement of TS, 30% of BSand 90% of IS of resulting composites as compared topureBiopolm sheets were observedunder the experimen-tal conditionsused.Scanning electronmicroscopy(SEM)showedthatthesurfacemodificationsimprovedthefibre-


matrix adhesion.The superiorstrength of alkali treatedjute may be attributed to the fact that alkali treatmentimprovesthe adhesivecharacteristics of jute surfacebyremovingnaturalandartificial impurities therebyprodu-cing a rough surfacetopography238). In addition, alkalitreatment leadsto fibre fibri llation, i. e.,breaking downoffabricsfibre bundle into smaller fibres.This increasestheeffective surfaceareaavailable for contactwith matrixpolymer. An effective method of natural fibre chemicalmodification is graft copolymerization34,239–241). It isobservedthat the composite preparedfrom 10% ANgraftedjute fabric shows superiorpropertiesascomparedto untreatedfabric237). AN-grafting exhibited compara-tively better properties of the composites than methylmethacrylate (MMA) grafting. Similar results havealsobeen reported in the literature221). From the compostdegradation studies it was observed that about 34%weight loss occurred for neat Biopolm, while dewaxed,alkali treated,19%AN-grafted,and30%AN-graftedjutefabric-Biopolm composites decreased their weights byabout 56, 42, 37 and 34% after 150 d of degradation.Higher percent weight loss of dewaxedsample as com-paredto alkali treatedsamplewas attributed to the factthat therewasa weekfibre-matrix adhesionwhich mighthaveboosted the degradation. A lower degradation rateof AN-grafted basedcompositeswasnoticedbecauseofthenon-biodegradabilitybehaviorof polyacrylonitrile.

Keeping in view thebroaderapplicationsof commercialbiodegradable polyesteramide (BAK), different surfacemodified jute fabrics were usedasreinforcing componentin biodegradable composites242) based on BAK 1095.Amongthechemically modified jute (dewaxed,bleached,alkali treated,cyanoethylatedandgrafted),thealkali trea-ted,cyanoethylated andlow percentgrafted samplesbasedcompositesproducedcomparativelybetterpropertiesthantheir untreated and dewaxedcounterparts.The effect ofdifferenttypesof surfacemodificationsof jute fabricsonthemechanicalpropertiesof compositesarerepresentedinFig. 7. More than40%improvement in TS of BAK 1095occurred asaresultof thereinforcementwith alkali treatedjute. Jutecontent also affectedthe properties of compo-sitesandabout30 wt.-% jute gaveoptimum mechanicalproperties. Among MMA and AN grafted samples, thelow percent,i. e., 10% AN-graftedjute showed compara-tively betterimprovementof mechanicalpropertiesof thecomposites than high percent grafted counterparts.SEMinvestigationsdemonstratedthat fibre pull out from com-positesamplewasreducedasa result of the fibre surfacemodification. From degradationstudiesit wasfound thatabout5–10%weightlossandabout11 to 45%decreaseofbendingstrengthof differently surfacemodifiedjute-BAKcompositestook placeafter 15 d of compostdegradation.The loss of weight as well as the decreaseof BS ofdegradedcompositesweremoreor lessdirectly relatedtoeachother.

4.4 Miscellaneousbiocomposites

A nonwoven fabric sheetand a film both from Bionolle1030werelaminatedandbondedto give composite sheetmaterials243) showing good water resistance, flexibility ,anddecomposition in soil after 6 months.The first sheet,i. e., nonwoven fabrics of melt-spun continuous longfibres from polyesterscomprisingglycolsandderivativesof dicarboxylic acids,werebondedwith thesecondsheetcomprising films (obtained from samepolyester)on oneside to give the titl e products useful for disposabledia-pers,etc. It hasbeenshownthat aliphatic polyesters likepolycaprolactone(PCL) andPHBV can be usedto formbiodegradable composites with polysaccharides reinfor-cing materials244). Thenaturally occuring polysaccharideshave relatively high strength in the dry state,however,their physical propertiesweaken whenplasticizedand/orswollen by water. When usedas reinforcing materials,they are protected by hydrophobic polyester matrices.The polarity and hydrophilicity of polysaccharidespro-vide gasbarrier propertiesto the composites.Cross-link-ing was necessary to provide dimensional stability andcreepresistance to the compositesand it was observedthatsuchcross-linkingdid not affect thebiodegradabilityof thecompositematerial. It is alsoreportedthatcompati-bilizers and reactive oligomerscan be usedto providebetter bonding of the PCL and polysaccharide compo-

Fig. 7. Effect of differentsurfacemodificationsof jute fabricson tensilepropertiesof thecomposites: (A) bleached;(B) deter-gent washed;(C) dewaxed; (D) alkali treated;(E) cyanoethy-lated(afterref.242))


nents,thereby increasing the strength and rigidity of thecomposites, and the use of oligomerscan also increasetheeaseof processing of thecomposites.

Relatively water-resistant biodegradable soy-proteincomposite is resulted245) through blending of specialbioabsorbable polyphosphate filler s, biodegradable soyprotein isolate, plasticizer, and adhesion promoter in ahigh-shearmixer followed by compressionmoulding. Todevelopaffordable,stiff, strong bioabsorbable polyphos-phatefiller/soy protein polymer composites, along withmethodsfor making practicalshapesfrom theseproductsare under current investigations245–248). The degradablecomposite films composedof soy protein isolate (SPI)andfatty acids249) aswell asSPIandpropyleneglycolalgi-nate(PGA)250) havebeenprepared.Incorporation of fattyacidsinto SPI resultedin films which werethicker, morewhitish, and less susceptible to shrinkage upon dryingthan the control SPI films. The composite films withmorethan20%of fatty acidswereheatsealableandalsoshowedimproved tensile strength.The incorporation ofPGA into SPI also resulted in compositefilms of modi-fied physical properties. Suo and Netravali251) havereportedthe mechanical and thermal propertiesof bio/green composites obtained from pineapple leaf fibers(with fiber content up to 28%) and Biopolm, i. e., PHBVresin.The tensile strengthandmodulusof thebiocompo-sites increasedsignificantly as comparedto pure PHBVresin, in the longitudinal direction but decreasedin thetransverse direction with increaseof fiber content. Theflexural strength andmodulusof thebiocompositesalongthe longitudinal direction increasedwith increaseof fibercontentwhereastheflexural strengthalong thetransversedirectiondecreasedandtheflexural modulusin thetrans-versedirection showed little changewith the increaseoffiber content.The interfacial and mechanical propertiesof PALF-PHBV green composites with 20 to 30 wt.-%contentof fibers placedin a 08/908/08 fiber arrangementhavealsobeenreported252). Thetensile andflexural prop-ertiesof thosegreencompositesin comparisonwith dif-ferenttypesof woodspecimens showedthatalthoughthetensile and flexural strength and moduli of the formerspecimenswerelower along thegraindirectionof testing,they were significantly higher perpendicular to graindirection than the corresponding wood specimens. SEMphotographs of the fracture surfaceof the biocompositesshowedfiber pull-out indicating weekfiber-matrix adhe-sion. More investigations on such biocomposites areneededto improvefiber-matrix interactions.

4.4 Applicationsof biocomposites

Recentwork on biocompositesrevealsthat in mostcasesthe specific mechanical properties of biocomposites arecomparable to widely usedglassfibre reinforcedplastics.Variouscomplexstructures,i. e., tubes,sandwichplates,

car door interior panellings, etc; havebeenmadeof bio-composites2,4–7). A newverticaldrainage product madeofcoconut and jute fibres is being introducedin EuropebyHorman252). Vertical drainageis neededto acceleratecon-solidation of soft compressibleclay soils. With the rightpreservationof the fibre the product hasa predicted life-time,andaftertheconsolidationprocessthis environmen-tally friendly product will decomposeas claimedby thecompany. A resinmadeout of soy beanoil on reinforce-ment with glass-fibre produceda new productdevelopedat the University of Delaware as to be usedin parts ofnewest tractors producedby JohnDeere253). The replace-ment of GFRP by biocomposites in many applicationshas been proved from the results of several investiga-tions3–8,193). Apart from satisfactory mechanical proper-ties, there are very often applications demanding addi-tional features. Sincebiocomposites are organic materi-als, they arecombustible. So, oneof the most importantrequirementsfor biocompositesas to be usedfor panel-lings in railways or aircraft is a certain degreeof flameresistance.In the modernpolymer industry the differenttypesof polymer flame retardantsbasedon halogens(Cl,Br), heavy andtransitionmetals(Zn, V, Pb, Sb),or phos-phorus organic compoundsmay reducerisk during poly-mer combustionand pyrolysis, yet may presentecologi-cal issues.Theuseof halogenatedflameretardantsis stillshowing an up-ward trend, and the environmental con-cerns havestarted a definite search for environmentallyfriendly polymer additives. The new aspectsof ecologi-cally friendly polymerflameretardantsystems havebeenreported254). Whenregardingthelatestresultsof examina-tionson naturalfibre andmatrix combinationsandenvir-onmentally compatible flame retardants,biocompositescanreplaceglassfibre reinforcedplastics in manycases2).The newconstructionmaterials arewell suitedfor aniso-tropic and specially tailored lightweight structural partsas well as for panelling elementsin cars.The potentialapplicationsof biocompositesin railways, aircraft, irriga-tion system, furniture industries, sportsandleisureitemsareunder current reseachactivities2).

5. ConclusionThe persistenceof plastics in the environment,the short-age of landfill space,concernsover emissions duringincineration,andentrapmentand ingestion hazardsfromthesematerialshavespurredefforts to developbiodegrad-ablematerials. In order to be competitive, biodegradableplastics must have the same desirable properties asobtainedin conventional plastics.Existing biodegradableproduct lines needto be broadenedto meetspecific end-usephysicalpropertyrequirementsandpolymer formula-tions must be further researched and modified so thatdegradationtiming canbe easily manipulatedto accountfor climate differencesand performance requirements.


Thereis broadagreementin the industry that thereis theroom,andthe needfor differentbiodegradabletechnolo-gies,but thereis still muchwork to be done if the useofbiodegradablesis to accelerate.The most importantfac-tors to the formation of a successful biodegradable poly-mer industry includecostreductionaswell aspublic andpolitical acceptance.Government should encourage theuseof biodegradable materialsby tax reduction.Germanyis fore-runnerin the field of green technology. The mar-ket although is increasing significantly in Europe, butlagsbehindUSA.

Existing biodegradable polymers are mainly blendedwith differentmaterials with anaim to reducecostandtotailor theproduct for some specific applications.Applica-tion of biodegradable polymersin natural fibre-reinforcedcompositeswill brodentheir uses.The world‘s supplyofnaturalresourcesis beingdepleted.The demandfor sus-tainableand renewable materials continuesto rise. Nat-ural resourcedevelopmentand agriculture will continueto be key sectors for the developing countries butresearchhasbecomeso globalizedandcomplexthroughtrade,finance,andelectronic developmentthat no coun-try can escape globalization’s embarce.As alreadydis-cussed,biodegradable polymers may be obtained fromrenewable resourcesor by syntheticroutes.Sincecertainbiocompositeshaveprovento be a very interestingalter-nativeto traditionalGFRP, thenewor existingbiodegrad-able polymersshouldbe continuously developedwith aclose co-operation with such polymers producers tosatisfy the special demandof biocomposites.Becauseofthe very complex structureof biofibres, more data onproperties of biocompositesarerequiredto establishcon-fidencein their uses.Trainingmust havepriority to accel-eratethe acceptanceof biocompositesfor variousappli-cations.The structural aspectsand properties of variousbiofibres and biodegradable polymers, recent develop-mentof differentbiodegradable polymersandbiocompo-sites as discussedin this review article and appropriateknowledgemight be usedwith properR&D efforts, forthecommercialization of biocompositesproductsfor var-ious applications. An intensive co-operation amongindustries, researchinstitutesand governmentsis essen-tial for achieving this.

Acknowledgement:One of the authors, A. K. Mohanty, isthankful to the Alexander von Humboldt Foundation, Germany,for an AvH fellowship.The helpsrenderedby Prof. R. P. Wool,University of Delaware,USA; Prof. Anil N. Netravali, CornellUniversity, USA; Dr. C. Bastioli, NovamontSpA, Italy; Dr. R.Kakuschke, BSL, Germany;Mr. J. Hierschmann, Bayer Corp.USA; Mrs. H. Schmidt, Mrs. Erhardt and Dr. H. Springer, ofTechnicalUniversityof Berlin, Germanyaregratefullyacknowl-edged.

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