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AdvancedProcessing, Properties,and ApplicationsofStarch
andOtherBio-Based
Polymers
Editedby
FARISM.AL-OQLA
DepartmentofMechanicalEngineering
FacultyofEngineering
TheHashemiteUniversity
Zarqa,Jordan
S.M.SAPUAN
AdvancedEngineeringMaterialsandComposites
ResearchCentre(AEMC)
DepartmentofMechanicalandManufacturingEngineering
UniversitiPutraMalaysia
Serdang,Selangor,Malaysia
LaboratoryofBiocompositeTechnology
InstituteofTropicalForestryandForestProducts
UniversitiPutraMalaysia
Serdang,Selangor,Malaysia
Elsevier
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ListofContributors
HairulAbral DepartmentofMechanicalEngineering AndalasUniversity Padang,SumateraBarat,Indonesia
H.A.Aisyah LaboratoryofBiocompositeTechnology InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
AmaniM.Al-Ghraibah Al-AhliyyaAmmanUniversity Amman,Jordan
FarisM.AL-Oqla DepartmentofMechanicalEngineering FacultyofEngineering TheHashemiteUniversity Zarqa,Jordan
MahaAl-Qudah PrimaryHealthCareCorporation(PHCC) Doha,Qatar
MochamadAsrofi LaboratoryofMaterialTesting DepartmentofMechanicalEngineering UniversityofJember Jember,EastJava,Indonesia
M.R.M.Asyraf DepartmentofAerospaceEngineering UniversitiPutraMalaysia Serdang,Selangor,Malaysia
M.S.N.Atikah DepartmentofChemicalandEnvironmental Engineering UniversitiPutraMalaysia Serdang,Selangor,Malaysia
M.N.M.Azlin InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia SchoolofIndustrialTechnology DepartmentofTextileTechnology UniversitiTeknologi MARANegeriSembilan KualaPilahCampus KualaPilah,NegeriSembilan,Malaysia
ManikChandraBiswas DoctoralFellow FiberandPolymerScience TextileEngineering ChemistryandScience NCStateUniversity Raleigh,NC,UnitedStates
AhmedEdhirej AdvancedEngineeringMaterialsandComposites ResearchCentre DepartmentofMechanicalandManufacturing Engineering UniversitiPutraMalaysia Serdang,Selangor,Malaysia DepartmentofMechanicalandManufacturing Engineering SabhaUniversity Sabha,Libya MohdNorFaizNorrrahim ResearchCentreforChemicalDefence(CHEMDEF) UniversitiPertahananNasionalMalaysia KualaLumpur,Malaysia
OsamaO.Fares ElectricalEngineeringDepartment IsraUniversity Amman,Jordan
M.D.Hazrol
AdvancedEngineeringMaterialsandComposites ResearchCentre(AEMC) DepartmentofMechanicalandManufacturing Engineering, UniversitiPutraMalaysia Serdang,Selangor,Malaysia
MdEnamulHoque DepartmentofBiomedicalEngineering MilitaryInstituteofScienceandTechnology(MIST), MirpurCantonment,Dhaka,Bangladesh
M.R.M.Huzaifah
LaboratoryofBiocompositeTechnology InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
M.I.J.Ibrahim
AdvancedEngineeringMaterialsandComposites ResearchCentre DepartmentofMechanicalandManufacturing Engineering
UniversitiPutraMalaysia Serdang,Selangor,Malaysia DepartmentofMechanicalandManufacturing Engineering SabhaUniversity Sabha,Libya
LaboratoryofBiocompositeTechnology InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
RushdanIbrahim PulpandPaperBranch ForestResearchInstituteMalaysia Kepong,Selangor,Malaysia
R.A.Ilyas
BiocompositeTechnology & Design AdvancedEngineeringMaterialsandComposites ResearchCentre(AEMC) DepartmentofMechanicalandManufacturing Engineering UniversitiPutraMalaysia(UPM) Serdang,Selangor,Malaysia LaboratoryofBiocompositeTechnology InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
LatifahJasmani PulpandPaperBranch ForestResearchInstituteMalaysia Kepong,Selangor,Malaysia
RidhwanJumaidin FakultiTeknologiKejuruteraanMekanikaldan Pembuatan UniversitiTeknikalMalaysiaMelaka DurianTunggal,Melaka,Malaysia
AbudukeremuKadier
DepartmentofChemicalandProcessEngineering FacultyofEngineeringandBuiltEnvironment NationalUniversityofMalaysia(UKM) Bangi,Selangor,Malaysia ResearchCentreforSustainableProcessTechnology (CESPRO) FacultyofEngineeringandBuiltEnvironment NationalUniversityofMalaysia(UKM) Bangi,Selangor,Malaysia
MohdSahaidKalil DepartmentofChemicalandProcessEngineering FacultyofEngineeringandBuiltEnvironment NationalUniversityofMalaysia(UKM) Bangi,Selangor,Malaysia ResearchCentreforSustainableProcessTechnology (CESPRO) FacultyofEngineeringandBuiltEnvironment NationalUniversityofMalaysia(UKM) Bangi,Selangor,Malaysia
A.Khalina InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
SanthanaKrishnan CentreofEnvironmentalSustainabilityandWater Security(IPASA) ResearchInstituteofSustainableEnvironment(RISE) SchoolofCivilEngineering FacultyofEngineering UniversitiTeknologiMalaysia(UTM) JohorBahru,Johor,Malaysia
C.H.Lee
InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia INTROP UniversitiPutraMalaysia Serdang,Selangor,Malaysia
S.H.Lee
InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
TariqMahbub DepartmentofMechanicalEngineering MilitaryInstituteofScienceandTechnology(MIST), MirpurCantonment,Dhaka,Bangladesh
SushmitaMajumder DepartmentofMaterialsandMetallurgical Engineering
BangladeshUniversityofEngineeringandTechnology (BUET),MirpurCantonment,Dhaka,Bangladesh
S.Misri
LaboratoryofBiocompositeTechnology InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
N.MohdNurazzi
BoardofTechnologists(MBOT) Futurise
PersiaranAPEC Cyberjaya,Selangor,Malaysia
SitiNuraishahMohdZainel FakultiTeknologiKejuruteraanMekanikaldan Pembuatan UniversitiTeknikalMalaysiaMelaka DurianTunggal,Melaka,Malaysia
A.Nazrin LaboratoryofBiocompositeTechnology InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
M.N.F.Norrahim ResearchCentreforChemicalDefence(CHEMDEF) UniversitiPertahananNasionalMalaysia SungaiBesi,KualaLumpur,Malaysia
MahmoudM.Rababah
DepartmentofMechanicalEngineering TheHashemiteUniversity
Zarqa,Jordan
TilottomaSaha DepartmentofMaterialsandMetallurgicalEngineering BangladeshUniversityofEngineeringandTechnology (BUET)
Dhaka,Bangladesh
S.M.Sapuan
AdvancedEngineeringMaterialsandComposites ResearchCentre(AEMC) DepartmentofMechanicalandManufacturing Engineering
UniversitiPutraMalaysia Serdang,Selangor,Malaysia LaboratoryofBiocompositeTechnology InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
NasmiHerlinaSari
DepartmentofMechanicalEngineering MataramUniversity Mataram,WestNusaTenggara,Indonesia
AhmedSharif
DepartmentofMaterialsandMetallurgicalEngineering BangladeshUniversityofEngineeringandTechnology (BUET)
Dhaka,Bangladesh
R.Syafiq LaboratoryofBiocompositeTechnology InstituteofTropicalForestryandForestProducts UniversitiPutraMalaysia Serdang,Selangor,Malaysia
EdiSyafri DepartmentofAgriculturalTechnology PoliteknikPertanian Payakumbuh,Sumatra,Indonesia
JarinTusnim
DepartmentofMaterialsandMetallurgicalEngineering BangladeshUniversityofEngineeringandTechnology (BUET)
Dhaka,Bangladesh
TengkuArisyahTengkuYasim-Anuar DepartmentofBioprocessTechnology FacultyofBiotechnologyandBiomolecularSciences UniversitiPutraMalaysia Serdang,Selangor,Malaysia
E.S.Zainudin
AdvancedEngineeringMaterialsandComposites ResearchCentre(AEMC) DepartmentofMechanicalandManufacturing Engineering FacultyofEngineering UniversitiPutraMalaysia Serdang,Selangor,Malaysia
M.Y.M.Zuhri
AdvancedEngineeringMaterialsandComposites ResearchCentre(AEMC) DepartmentofMechanicalandManufacturing Engineering FacultyofEngineering UniversitiPutraMalaysia Serdang,Selangor,Malaysia
BiopolymerCompositesand Sustainability
MAHMOUDM.RABABAH • FARISM.AL-OQLA
1 INTRODUCTION
Itisveryobviousthatplasticpollutionhasnegative impactontheenvironmentaswellastheclimate change.Unfortunately,thepollutionoccurredalong thewholeproductioncycleoftheplasticfromitsproductionusingthefossilfuelsuntilitsdisposalby burning.Besidetheplasticpollution,deforestation, greenhouseeffect,industrialpollution,andmanyother factorsareresponsibleincausingthenegativeimpact ontheenvironmentbyblowingmoregasestoairascarbondioxide,methane,SO2,nitrousoxide,andmany others(AL-Oqlaetal.,2016;Alaaeddinetal.,2019b).
Greenerplasticcompositescanbeobtainedof renewableresourcesinamoreecologicalresponsible manner.Thisisachievedusingthebiotechnology andwasimprovedusingthenanotechnology,which isapromisingapproachthatwouldgreatlyaffectthe valuechainsoftheplasticindustryworldwide.Some stepsarealreadyachievedindevelopingsustainable plastics.Infact,photodegradableplasticswitha balanceamountofbothantioxidantsandcatalysts aredeveloped.Thecatalystsinitiateacontrolleddegradationwhilemaintainingtheperformanceproperties oftheplastics.Thesephotodegradableplasticsarepossessingsimilarperformancepropertiestoconventional plasticsatclosecosts.However,atthemoment,they stillusefossilfuelsandtheyarenotabletofully degradetoH2OandCO2 inthesoil(Khabbazetal., 1999).Besides,photofragmentationmayoccurifno controlisperformedcausingalitterincrease. Degradablepolymersaredevelopedwithoutusing antioxidantorwithprooxidantsthathelpinaslow degradation.Comparingtophotodegradable polymers,degradablepolymerspossesssimilarperformanceproperties,coststructure,andproductionof otherdegradationproductsthanH2 OandCO2,such asalcohols,alkenes,esters,andketones(Jakubowicz, 2003).Therefore,developingsustainableplastics
frombiodegradableandrenewableresourcesisa demandinggoal.
Anamountof260billionboundsofplasticwere annuallyproducedintheworldattheendofthelast century,withanindustryvalueof1trilliondollars (HalleyandDorgan,2011).Thisamountissubjected toamassiveincreasebecauseofthehighdemanding duetothepopulationincreaseandthenewdeveloped consumers ’ habits.Greatamountofpetroleumis consumedforplasticproduction.However,asitis finite supply,itspriceswillincreasemoreandmore.Inaddition,theenvironmentalpollutioncausedfromproducing,using,anddisposingofplasticmaterialsisofagreat concernduetogreenhousegasesandtheglobal warmingeffects.Thedecayingofworldreservefrompetroleumandtheincreasingdemandsfromdeveloping countriessuchasChinaandIndiaarebothcausethe pricesofoiltoreachunprecedentedlevels.Thesehigh pricesdriveasimilarincreaseinpetroleum-basedplastics.Thisleadsforminingoflower-gradecrudeoilsuch astheCanadianheavyoil(Deffeyes,2008).Theheavy oilislesseconomicalandmoreenvironmentallyharmfulthanthelightoil.However,plasticscanbeofagreat assisttohumanitybyincreasingtheagricultural production,decreasingthefoodloses,reducingthe fuelconsumption,offeringlighterandcheaperalternativesformanyproducts,improvingthehealthcare,etc. Inotherwords,plasticmaterialsareessentialinour modernsocieties.Unfortunately,theenergyissues directlyimpacttheplasticsindustries.Whatwillbe theimpactonourdailylives,ourhealth,ourenvironment,andontheplasticindustryitself(morethan1 millionemployeesintheUnitedStatesalone)ifthesustainabletechnologiesdonotreachmaturitysosoonor iftheyarenotwidelyadopted?Developingappropriate methodsandapproachesforproducinggreencompositeshasbeenademandingpriorityforsometime. However,theevolvingeconomicalandtechnical
problemlimitspursuingsuchapproachesonlarge scales(AL-OqlaandSapuan,2014a,c).Eventhough theneedofdevelopingbioplasticandbiocomposite materialsisdemanding,suchmaterialsmust firstbe costcompetitive.
2 PLASTIC
2.1 OriginofPlastics
Thepolyethylenepolymerusedinplasticbagsproductionisderivedfrompetroleum.Petroleumisacomplex mixtureofcarbonandhydrogencompoundswith heavymetalsasnickelandvanadiumandothercomponentsassulfur.Aspetroleumcontainshighconcentrationofchlorinatedhydrocarbonsaswellasheavy metals,itistoxictoanimalsandplants.
Theprocessofextractionpetroleumiscomposedof fourstages: first,crudeoilisobtainedbydeepdrilling fromnaturalreservoirsbelowtheseaoroffshore.This crudeoilisshippedtotherefineries.Inthesecondstage, thecrudeoilisseparatedbyevaporation/condensation processatdifferenttemperatures.Inthethirdstage,the compoundsareyieldedtoconversionprocessinthe presenceofheat,pressure,andcatalyst(forinstance, platinum).Inthisprocess,theshapeofthecompounds anditsmolecularweightarechanged.Thecompounds obtainedfromtheprocessservesasfueltoautomobiles, factories,etc.Someofthesecompoundscanbedeliveredtofactoriesforupgrading(laststage)toproduce fertilizersanddifferentplasticproducts.Forinstance, ethyleneisupgradedfromtheserefinedcompounds andusedforplasticproducts.Ethyleneisexplosive, inflammable,toxic,andcarcinogenic.
Extractionpetroleumstages:Drilling / Separation / Conversion / Upgrading
Duringtherefiningstagesofthecrudeoiltobeconvertedtofuel,plastics,andotherpetro-basedproducts, manytypesofgasesareemittedtoair.Thesegasesare carryingharmfulcomponentslikecarbonmonoxide, hydrocarbons,sulfurdioxide,andnitrousoxide. Unfortunately,thesecomponentsremaininthe final petroleumcompoundsaftertheseparationprocess. Theireffectsonourenvironmentandontheecosystems arecatastrophicandcanleadtoacidrains,andunfortunately,theseeffectsareirreversible.
2.2 ApplicationsofPlastics
Plasticsbecomemoreandmoreveryessentialinour modernsocieties.Itisusedinawidevarietyofapplications,suchasinpackaging,automobileindustry,aerospace,agriculture,andhouseholdproducts,etc.Its availability, flexibility,durability,lightweight,and
mostimportantitscheappriceshelpplasticstodominateagreatportionofthecurrentproductionmarkets. Plasticsaremainlycategorizedintotwomaingroups: thermoplasticsandthermosets.Thermoplasticscanin generalbemeltedandrecycled,someexamplesofthermoplasticmaterialsarePE,PP,PS,polyethyleneterephthalate(PET),andpolyamide.Ontheotherside, thermosetshavecanneitherbemeltednorberecycled. Thisisbecausethepolymerchainsfortheseplasticsare connectedinstrongcross-linkbondsasthecasein epoxyresin,polyurethane,andunsaturatedpolyester. Asthepetro-basedplasticsdonotdegrade,theycause pollution.Thesolutiontothisistodevelopanduse biodegradablebioplasticsasalternativestotheconventionalplastics.Thesebioplasticswillrequireshorter timetodecomposeafterbeendisposed.Also,theycan fertilizethesoilinthecompostingprocess,wherethey canbemixwithsoilinordertodegradebythehelp ofbacteria.Thelifeofthebiodegradablebioplasticsbeginsfromrenewableresource,suchascelluloseand starch,andendseco-friendlycomparingwithpetrobasedplastics.
2.3 ChemicalPollutionfromPlastics
Greatportionofthechemicalpollutionoccursduring energygeneration;suchenergyisusedforgenerating electricity,miningindustry,transportation,etc.The pollutionstrikesourenvironmentthroughglobal warming,acidrains,andthroughproducingcarcinogenicsubstancesinairandallaround.Tonsofharmful gasesareblownintheatmosphereinmostoftheindustrialsectorsascoalmining,uraniumprocessing, petrochemicalindustry,etc.Thepollutionisexpected toincreasewiththeincreasepopulation,thedeveloped consumptionhabitsofpeople,andthegrowingandthe spreadingoftechnology.Directburningofplasticsin airspreadsveryharmfulandtoxicgasesintotheatmosphere.Someofthesegasesarealkanes,alkenes,and chlorinatedandaromatichydrocarbons(PAHs, PCDDs,andPCDFs).Infact,hugeamountofgases areaccumulatedinecosystem.Gaseslikecarbonmonoxide,nitrogenoxide,andvolatileparticulateswhen accumulatedinatmosphereformdarksmog.Inthe extrusionprocesseswherethemeltingtemperatureis reached(between150and300 ),manygasesareleaked totheecosystemduetotheattractionbetweenpolymersandtheadditives,longthermalexposure,oraging.
2.4 InitiativesAgainstPlasticsPollution
Somepeoplewhoareawareabouttheharmfulimpact ofusingconventionalplasticsinourdailylifearetrying toraisetheawarenessoftheirsocietiesbydistributing
eco-friendlybagsfabricatedfromnatural fibers(ALOqlaandSalit,2017;AL-OqlaandSapuan,2018a; Alaaeddinetal.,2019c).UnitedKingdomtooka pioneerstepandpreventedusingmicroplasticsinpersonalcareproductsaswellasincosmetics.Thisstep istaken,accordingtotheDepartmentofEnvironment, FoodandRuralAffairs,sincethemicroplasticsaremore harmfulthanthelarge-sizeplastics.Asthemicroplastics areinfinitesimal,theycannotberemovedorseparated fromtheecosystemeasily,andthus,theycaneasily reachthefoodchain.AstudentnamedJonssonfrom Icelandintroducednewbottlesbymixingpowdered agarwithwater.Thesebottleshelpindevelopingsustainableenvironmentandreplacetheconventionalbottlesmadenormallyfromplastics.Somecountriessuch asSriLankastartedtoenforcetheplasticmanufacturers toproducetheirproductswithcertainstandards.Some citiesfromallovertheworldarehappilydeclaringthat theircitiesareplastic-freezones.Mostofthesecities startedbybanningtheuseofplasticbagsand announcedadeadlinefortheiruse.
3 RENEWABLE-BASEDPLASTICS
Inthepast,renewable-basedplasticswerelackingthe sufficientpropertiesformanyapplicationsbesidetheir highcosts.Nowadays,greatsuccessesarebeing achievedinnewbioplasticmartialscommercially. Theseachievementsaredirectlyreflectedfromthesuccessfulapplicationsoftheindustrialbiotechnology.ExamplesincludeMirel(polyhydroxyalkanoates polymers)forinjection-moldedproducts,polylactides for flexible films,andcompostbags(AL-Oqlaetal., 2018a;AL-Oqlaetal.,2015c;AL-OqlaandSapuan, 2014b).Otherexamplesarethesoyoil-basedmaterials thatareproducedoncommercialscalebynumberof companiesinordertobeusedinurethanesindustries (AL-Oqlaetal.,2018b;Faresetal.,2019).
Moreover,manyglobalcompaniesareworkingon commercializingfurtherrenewable-basedplasticsas PBS(polybutylenesuccinate)foruseas flexible films inagriculturalandpackagingapplications.Besides, manyofthesoftdrinkmanufacturershaveconverted toutilizePETfromrenewableresources.Allthesecumulativesuccessesstronglyencourageinreplacingthe petroleumplasticsproducedinbillionsofpounds annually.Fortunately,generatingrenewable-based plasticsarebecomingmoreandmorepossible.Better understandingoftheimpactsofplasticsontheenvironmentalisnowpossiblethroughthelifecyclelife-cycle analysis(LCA)oftheseplastics.Inotherwords,the LCAstudiestheoverallimpactofthematerialalong
itslife(Blacketal.,2011).Improvementstrategiesfor theprocessesarealsointroducedandanalyzedfortheir impacts.Forexample,plantingcropswithlowwater andfertilizerneedsinmarginalregionscanreduce deforestationaswellasthepressuresonfoodsupplies. Similarly,thefastandwidedevelopingstepsinthe biotechnologicalindustryarefacilitatingtheconversion ofthebiomassintofuelorusefulchemicalsandare makingitveryfeasible.Finally,nanotechnologyis contributinginenhancingthematerialsperformance properties.
Bioplasticsareobtainedbymanystagesasdescribed intheschemeshownin Fig.1.1.Thenumberofthe chemicaltransformationsrequiredtoconvertfromthe rawbiomasstothe finalpolymeriscalledastage.For example,polylactidesisconsideredasthree-stagebioplastics:plantisconvertedintosugar,thenthesugar isfermentedtolacticacid,and finallythelacticacidis polymerized.Inatwo-stageprocess,theplantisdirectly fermentedandpolymerizedasthecasewithpolyhydroxybutyrates/polyhydroxyalkanoates.Another exampleoftwo-stagebioplasticsisthepolyaminoundecanoicacidknownasNylon-11:castoroilis first extractedandthenchemicallyconvertedtopolymers. Finally,inone-stagebioplastics,thebiomassitselfcontainsthetargetedpolymer.Mostofthecommonbiopolymers,suchasthenaturalrubber,starch,and cellulose,areobtainedinone-stage.
Thegeneticengineeringcontributestotheadvances inbiotechnologybymovinggenesoverspecies,for example,movingsomegenesfromthebacteriathat producePHAsintosugarcane.Directproductionof desiredpolymersfromsunlightandCO2 hasmany attractivebenefits.However,theLCAshould firstbeperformed.Besides,suchgeneticengineeringfacesmany ethical,social,environmental,andregulatoryissues.
4 STARCH-BASEDBIOPLASTICS
Starch-basedplasticshavemanyindustrialapplications infoodpackaging,injectionmolding,andas flexible films.Theyarecomposedofstarch,plasticizeragents, andadditives.Starch-basedplasticsareconsidered veryattractivechoicesintermsofeconomicalandsustainableaspectsduetothelowcost,theinherentbiodegradability,andthelargecontentoftherenewable resourcesinitscomposition.However,theyarewater sensitive,andtheyrevealpoorperformanceproperties insevereenvironmentalconditions(Iannottietal., 2018).Recentlydevelopedresearchesimprovedthewaterresistivityofthestarch-basedplasticswhilemaintainingtheirbiodegradability,andhence,their
Bioplasticsfeaturesbaseduponthenumberofbiochemicaltransformationsrequiredtoachievethe finalpolymer.
applicationswereextendedtonewaspects.Somegrades oftheseplasticsarecommerciallyproducedasshownin Fig.1.2
Blendingstarchwithsyntheticpolymerssuchas polyethyleneorethylenevinylacetatehasbeen extensivelyinvestigated.Theadvantagesoftheobtained plasticsarethelowcost,thegoodmechanicalproperties,thegoodpackagingproperties,andtheabilityto manufactureusingconventionalmachines.The disadvantagesoftheseplasticsarethenonrenewable syntheticcomponentsandthepartialdegradability (Alaaeddinetal.,2019a,d).
5 BIOPOLYESTERS
Regardlessofwhetherthepolyestersarecomposedof renewableresourcesorfromfossilresources,theyare oftendegradableastheesterbondscanbeeasilyhydrolyzed.PolyestersfromrenewablesourcesasPLAsand PHBsarenowcommerciallyavailable.Ontheother side,polyestersfromfossilresourcesarealsocommerciallyavailableasPBS.Itisnoteworthythatsignificant effortsarecurrentlypushingtoproducecommercial PBSfromrenewableresources.Therearewideand extensiveinvestigationsintheliteratureonincorporatingbiopolyesters,petroplastics,andotherbioplastics inpolymerblends(AL-OqlaandEl-Shekeil,2019; Alaaeddinetal.,2019c;Valerioetal.,2016).
6 BIOCOMPOSITESANDBIONANOCOMPOSITES
Significantattentionisalsoraisedfornatural fiberreinforcedcompositeslately.The fibersareobtainedfrom abaca, flax,jute,hemp,palm,kenaf,andmanymore plants(AL-Oqla,2017;AL-OqlaandSapuan,2018b; AL-Oqlaetal.,2015b).These fibersareusedtoproduce biocompositeswithmatricesofbioplasticorpetroplasticmaterials.Amongthese fibers,kenafisconsidered oneofthemostpromisingnatural fibersformanyreasons,includingthelowemissionofodor.Untilnow, biocompositesaremainlydevotedforsheetapplications,morespecificallyasinteriorpartsinautomobiles (AL-Oqlaetal.,2015a).Ontheotherside,nanocompositesarethepromisingkeytoovercomemanyofthe drawbacksofthebiocomposites.However,thereare stillmanychallengesintheirdevelopment(AL-Oqla andOmari,2017;AL-OqlaandSalit,2017;AL-Oqla etal.,2014;Sadrmaneshetal.,2019).Massiveresearch hasbeenconductedonnanoclayreinforcedbioplastics. Addingnanocelluloseorcarbonnanotubestobiopolymerscanimproveasetofthermalproperties.An increasingattentionispaidtousingnanocellulosein bio-basedmaterialsasitscostislessexpensivethan manyconventionalpetroplastics($0.20 $0.25/lb). Renewable-basedpolymersarepreferredoverpetroplastics.However,formanyapplicationssuchasin automobileindustry,andinbuildingconstructions,
FIG.1.1
theyareundesirableastheypossessfastdegradability (AL-Oqlaetal.,2018a;Aridietal.,2016a,b;Fares etal.,2019).Furthermore,asthepetroleumpricesare continuallyvibrating,andlately,theyarereachingunprecedentedlevels.Thereisastrongeconomicneedto searchforotheralternativestothetraditionalmaterials available(AL-OqlaandSapuan,2018a).
Extensiveeffortshavebeenspentinthelastfew yearsindevelopingsuchalternativesfromrenewable resources.TheUnitedStatesisleadingtheworldin this fi eldasitisthelargestproducerofethanolfrom biomass.Ethanol,inturn,isusedinproducingtwo importantnondegradablebioplastics:thesearethe biopolyethyleneandbio-PET.Theproduction pathwayofthebiopolyethyleneisusuallyachieved byseveralstepsas fi rst,ethanolisdehydratedto ethylene,andthen,ethyleneispolymerizedusing oneofmanyavailablemechanismswiththehelpof catalysts.Anotherexampleofdevelopingalternative productsfromrenewableresourcesisthebutylrubber (acopolymerofisopreneandisobutylene)thatwill soonbecommercialized.First,isobutanolisfermentedfromcellulosesugarorfromstarch.Then,isobutanolisconvertedintoisobutylene.Combiningthe derivedisobutyleneandtherenewableisopreneproducesthebutylrubber,whichiscalledthenatural/syntheticrubber.Onemoreexampleofdeveloping alternativeproductsfromrenewableresourcesisthe 3-hydroxypropionicacid(3-HP).Thismonomercan
bedehydratedtoproducerenewableacrylicacid (usedinpaintsandinsuperabsorbants),oritcanbe polymerizedtoproducebiopolyesterpoly(3-HP).Nylons,ontheotherhand,havedesirablepropertiesbesidetheirtoughness.However,theyshowrelatively highprices.Inthepast,Nylon-11hasbeenderived fromcastoroil.Nowadays,manyresearchersaretrying todevelopothergradesofNylonfromrenewableresources.Asanexample,Nylon-4cannowbederived frommonosodiumglutamate.Thebiotechnological industryiscon fi denttorevealneworganismswith engineeredmetabolismtoinnovatenewpathways forotherpolyamideprecursors.
7 SUSTAINABILITY
Inordertoenhancethepropertiesofplastics,chemical additivesarecommonlyused.unfortunately,theseadditiveshaveharmfulimpactontheenvironment.The microparticlesinplasticsusuallyreachtheecosystem bywind,water,animals,andorganisms.Hence,they combinewiththefoodchaincausinghazardoushealth problemsthatmayleadtoinjuriesorevendeathofthe organisms.Inordertolimitthebadeffectofplastics, newawaretrendsshouldbedevelopedinsocietiesaccordingthesustainableenvironment.Anexampleto thisisbyreplacingtheplasticbagscommonlyusedby bagsmadeofnatural fibers.Theharmfulcomponents intheplasticproductscancausemanycomplex
FIG.1.2 Starchchemicalstructureofbothamyloseandamylopectin.
problemsasreducingthequalityofair,water,andthe wholesurrounding.Foraproducttobeclaimedthat itissustainable,itshouldfulfillalltherequirements ofhealthyenvironmentwithoutharmingthe ecosystem. Fig.1.3 highlightstheclosingloopofend lifeofbioplastics(PLAasanexample)toenhancethe sustainability.Forbioplastics,theplantsaregrownin farms,then,theyarepolymerizedandconvertedto theintendedproducts,andthen,theyaretransported tomarketsuntiltheyreachtheconsumers.Attheend ofthesebioplastics’ life,theyarecompostedorrecycled (degradationoccursfordegradablepolymers)without leavinganyharmfulortoxiccomponentsinthe environment.
Butunfortunately,fossilfuelisrequiredduringthe manufacturingstepsofthebioplastic,aswellasduring transportingtheplantstothemanufacturersorthe final productstotheretailers.However,apartialsolutionto thisissuecomesfromthefactthatmanymanufacturers aremovingtowardusingcleanrenewableenergyin theirfactories.Bioplasticsarecategorizedaccordingto manyparameters:origin,composition,synthesisprocess,andapplication. Fig.1.4 demonstratestheclassificationsofbiodegradablepolymers,and Fig.1.5 illustratesthebioplasticsandthethreedistinct biopolymergroupswithrespecttodegradabilityand renewabilityaspects.
7.1 TypesofBioplasticstoDevelop SustainableIndustry
7.1.1 Starch-basedplastics
Starch-basedplasticsarethemostcommonlyused amongallotherbioplastics.Itisdominatingabout 50%ofthebioplasticmarket.Simplestarch-based plasticscanbeproducedathomewithsimpletools. Starchisgoodinabsorbinghumidity,andthus,it wasasuitablechoicefordrugcapsulesaswellas medicalapplications. Fig.1.6 isanillustrativediagramfortheapplicationsofbiopolymersinnerve repairing.
Additiveslikeglycerineandsorbitolcanworkas plasticiserand fl exibilizerwhenaddedtostarchto enhanceitsthermalcharacteristics.Thesethermal characteristicscanbetailoredtotherequiredneeds bycontrollingtheamountoftheadditivesinthe starch-basedplastic(calledthermoplasticalstarch). Starchiscommonlymixedwithbiodegradablepolyestersinordertoproducevarietiesofcompounds,such asstarch/polylacticacid,starch/Eco fl ex,orstarch/polycaprolactone.Thesecompoundsarecompostable,and theyareusedformanyapplications.Othercompoundsarealsodevelopedasstarch/polyole fi nblends. Theyarenotbiodegradable,buttheyreveallowercarbonfootprintcomparingtopetro-basedplasticsfor sameapplications.Starchischeap,renewable,and
FIG.1.3 Endoflifeofbioplasticstoenhancesustainability.
FIG.1.4 Biodegradablepolymers.
FIG.1.5 Illustrationofthebioplasticsandthethreedistinctbiopolymergroups.
availableinplentyamounts.Starch-basedplasticsare composedofcomplexblendswithcompostable plasticsaspolycaprolactone,polylacticacid,PBS, polyhydroxyalkanoates,andpolybutyleneadipate terephthalate.Thiscombinationwillenhancetheperformancepropertiesoftheplastic,aswellasimprove itswaterresistivity.Bioplastic fi lmsareproduced mainlyfromblendingstarchwithbiodegradablepolyesters;hence,these fi lmsarebiodegradableandcompostable.Theirapplicationsaremainlyinpackaging: foodpackagingasinbakeryorfruitandvegetable bagsandgoodspackagingwherebubble fi lmsare commonlyused.Newlydevelopedstarch-based fi lms bytheAgriculturalResearchServicescientistshave thepotentialtobeusedaspapers.
7.1.2 Cellulose-basedplastics
Thecellulose-basedbioplasticscommonlyusedarethe celluloseesters(includingcelluloseacetateandnitrocelluloseandtheirderivatives).Celluloseacetateis commonlyusedinpackagingblisters.Itispossibleto modifythecellulose-basedplasticstobecomethermoplasticmaterialssuchasthecelluloseacetate.However, thecelluloseacetateisexpensiverelativetoother plastics,aswellasitrequiresextensivemodi fications. Therefore,itsuseinpackagingisnotcommon.Onthe otherside,addingcellulosic fiberstostarchcanenhance itscharacteristicsasthemechanicalproperties,thewater resistance,andthegaspermeability.
7.1.3 Protein-basedplastics
Proteinsderivedfromdifferentsourceshavebeen alreadyusedinplasticstoformbiodegradablebioplastics.Forexample,soyproteinshavebeenusedin bioplasticssinceearly1900s.Fordcompanyhadused soy-basedplasticsintheirautomobileslongtimeago.
Therearesomechallengesinusingsoy-basedplastics duetotheircostandtheirwatersensitivity.However, thiscanbeovercomebyblendingsoyproteinwith someexistingbiodegradablepolyestersinorderto decreasethecostandimprovethewatersensitivity. Otherproteinsarebeinginvestigatedforpotential blending.Forexample,wheatglutenandcasein revealedverypotentialpropertiestobeusedasrawmaterialsforvarietiesofbioplastics.
7.2 EnvironmentalImpact
Cellulose,starch,sugar,wood,andmanyotherrenewableresourcescanbeusedassustainablealternatives tothefossilfuelresourcesintheplasticproduction. Thebioplasticsproducedfromtheserenewable resourcesaresustainableincomparisontotheconventionalplastics.However,theenvironmentalimpactof bioplasticsshouldbeinvestigated.Thisisconductedusingmanymetricssuchasthewaterandenergyusage, thebiodegradation,thedeforestation,etc.Theenvironmentalimpactsofbioplasticsarecategorizedasthe nonrenewableenergyusage,theeutrophication,the acidification,andtheclimatechange.Thenonrenewableenergyusageinbioplasticproductionislower thantherequiredenergyfortheconventionalplastics forthesameapplications.Theemissionofthegreenhousegasesissignificantlyreducedinbioplasticproduction.Hence,governmentsandorganizationscan increasethesustainabilityoftheenvironmentbyadoptingthebioplasticsinsteadoftheconventionalplastics, andbyapplyingsuitableregulationstoachievethis goal.Althoughtheenvironmentalimpactmetrics regardingenergyandgreenhousegasesencourageusing bioplasticsinsteadofconventionalplastics,othermetricsshouldalsobeinvestigated.Bioplasticshavehigher potentialsofeutrophicationthanconventionalplastics.
FIG.1.6 Illustrativediagramfortheapplicationsofbiopolymers-basedmaterialsfornerverepairing.
Eutrophicationisthewaterrichnessofnutrients.Itis consideredaseriousthreattowaterresourcesasit endsthelifeoftheaquaticorganisms,harmsthefreshwater,andcausesharmfulalgalblooms.Thereasonof theeutrophicationisthatduringproductionofthe biomass,phosphate,andnitrate filtrateintothefreshwaterreservoirs.Anothermetricistheacidi fication.In fact,thisenvironmentalimpactisnegativeinbioplasticsastheyincreasetheacidi fication.Thehigh harmfulincreasesofbothmetrics(acidificationand eutrophication)arenotonlyduringthebioplasticproductionbutalsoduringplantingandgrowingtheraw materialswherethechemicalfertilizersareused.
7.3 BiodegradationofBioplastics
Thebiodegradationinbioplasticsisoccurredbydepolymerizingthepolymericmaterialsusinginherentenzymes.Thebiodegradationstartsatthesolid/liquid interfacewheretheenzymesareincontactwiththe solidpolymers.Someconventionalplasticscanalso bebiodegradableiftheycontainbiodegradableadditives.Bioplasticsareabletobiodegradeunderextreme conditionsofheatandhydration.Thebiodegradation speedoftheseplasticsisalteredbytheenvironmental conditions,whereinthepresenceofsoilandcompost, thebiodegradationbecomesfasterandmoreefficientas richmicrobialdiversitywillexist.Theefficiencyofthe biodegradabilityincompostenvironmentscanbe increasedmorebyincreasingthetemperatureandby addingsolublesugar.Besideincreasingthebiodegradationefficiency,compostingisabletoincrediblyreduce theemissionofgreenhousegases.Ontheotherside, biodegradationinsoilenvironmentswillprovide higherdiversityofmicrobes;makingiteasierfor biodegradationtotakeplace.However,soilenvironmentstakelongertimetobiodegradethebioplastics andrequirehighertemperatures.Otherenvironments canincreasetheefficientlyofthebiodegradationas theaquaticenvironment.However,usingtheaquatic environmentsinordertobiodegradethebioplasticsis riskyandnotrecommended;itshouldbeavoidedas itharmsthefreshwaterandtheecosystemsandends thelifeoftheaquaticorganisms.Lastparameters affectingthebiodegradationspeedarethecomposition andthestructureofthebioplastics,andindeveloping thebioplastics,theresearchersputgreateffortstooptimizethebiodegradationspeedratetomeettheapplicationsneeds.
8 CONCLUSIONS
Thesocialandtheenvironmentaldemandsinone hand,aswellthelateachievementsofthebiotechnologyandthenanotechnologyontheother,are
dramaticallyaffectingourviewforplasticsandhow theyshouldbeproduced.Thesereasonsarepushingresearcherstoaccelerateinenhancingthebioplasticmaterialstohigherlevelsofperformanceandin commercializingtheirprocesses.Starch-basedplastics arethemostcommonlyusedamongallotherbioplastics.Theemissionofthegreenhousegasesissignificantlyreducedinbioplasticproduction.Hence, governmentsandorganizationscanincreasethesustainabilityoftheenvironmentbyadoptingthebioplasticsinsteadoftheconventionalplastics,andby applyingsuitableregulationstoachievethisgoal. Nowadays,greatsuccessesarebeingachievedinnew bioplasticmaterialscommercially.Theseachievements aredirectlyreflectedfromthesuccessfulapplications oftheindustrialbiotechnology.
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ProcessingofThermoplasticStarch
RIDHWANJUMAIDIN • SITINURAISHAHMOHDZAINEL • S.M.SAPUAN
1 INTRODUCTION
Duetoenvironmentandmanageabilityissues,thiscenturyhasseenexceptionalaccomplishmentsingreen innovationinthematerialscience fieldthroughthe improvementofbiocomposites(Joshietal.,2004). Society’sexpandingfamiliarityonthesignificanceof ecologicalsafeguardinghasdriventremendous measuresforexploringdevelopmentsofmorenatural materials.Theadvancementofelitematerialproduce usingnormalassetsispresentaroundtheworld.The improvementofregular fibercompositesisbecoming amoregenuineconsiderationduetotheirpromising properties.Abundantagriculturalwastemakesthem aneasysourceformaterialenhancement.Theenhancementofbio-basedpolymersasalternativematricesfor petroleum-derivedpolymersfurtherprovidesanother greenperspectiveforcomposites.Adaptingnatural fiber asthereinforcementappearasapracticalsolution, particularlyinautomotive,foodpackaging,infrastructure,andbuildingitemapplications(Scholtenetal., 2014).Amongbiopolymers,starchstandsoutasthe mostencouragingsinceitiseasilyaccessible,simple, abundant,sustainable,andbiodegradable.
2 BIOPOLYMERS
Biopolymersarepolymersthatoccurinnature.Starches andproteins,forinstance,arebiopolymers.Numerous biopolymersarenow financiallydeliveredatavast scale,despitethefactthattheywillnotbeusedoften forthecreationofplastics.Onlyasmallportionof deliveredbiopolymersareemployedinthecreationof plastics.Byutilizingthemmore,itwouldfundamentallydiminishourrelianceonfabricated,nonsustainableassets.Otherthanbeingaccessible,biopolymers haveafewmonetaryandecologicalpointsofinterest. Biopolymersdemonstrateanadvantageforhandling waste.Forinstance,replacingpolyethylenebya biopolymercouldhelpremoveplasticpiecesfoundin compost.Coalitionbetweensyntheticpolymers,
commonpolymers,andbiodegradablepolymerscan formnovelmaterialssincetheycanconsolidatethe processcapacitywithbiodegradationandutilization ofsustainablecrudematerials.Inanycase,customary polymerstypicallydisplayabnormalamountsofrecyclabilityandtherecyclingprocedurecanbeinfluenced bythepresentationofasystemcontainingcommon polymers(Peresetal.,2016).
2.1 CategorizationofBiopolymers
Biopolymerscanbeobtainedfrommicrobialframeworksextractedfromhigherlifeformssuchasplants orintegratedsyntheticallyfromessentialbiological buildings.Biopolymersaredevelopedforvariousapplicationsrangingfrompackaging,medical,pharmaceutical,etc.Apreviousstudy(Scholtenetal.,2014)had investigatedtheroleofbiopolymercompositesforemulsionsandgelsinfoodengineering.Biopolymersare furtherdevelopedforuseinclothingtextures,watertreatmentchemicals,modernplastics,sponges,biosensors, andeveninformationstockpilingcomponents.Thecategorizationofbiopolymersisprovidedin Table2.1.
Biopolymershavetheirownproperties.Theyareinexhaustible,maintainable,biodegradable,safe,nonimmunogenic,non-cancer-causing,nonthrombogenic,and carbon;forexample,chitin/chitosan.Chitinexistsinthe skeletalsystemofcreaturesandhasawhiteappearance (Asgharietal.,2017).Inexhaustibleresourcesareutilized progressivelyinthecreationofpolymers(specifically, monomers).Forexample,carbondioxide,terpenes, vegetableoils,andsugarscanbeappliedasfeedstocks forthefabricationofavarietyofmanageablematerials andproducts,includingelastomers,plastics,hydrogels, adaptablegadgets,resins,engineeringpolymers,and composites(Zhuetal.,2016).Biodegradablematerials areemployedaspartofbundling,farming,prescription, anddistinguishedareas.Asoflate,theenthusiasmfor biodegradablepolymersisrising.Therearetwoclasses ofbiodegradablepolymerspresent:engineeredandcharacteristicpolymers.Thesearepolymersmadefromstocks
TABLE2.1
CategorizationofBiopolymers.
Polyesters
Polysaccharides(lant/ Algal)
PolyhydroxyalkanoatesStarch(amylose/ amylopectin)
PolylacticacidCellulose
Proteins Agar
SilksAlginate
Collagen/GelatinCarrageenan
ElastinPectin
ResilinKonjac
AdhesivesVariousgums(e.g.,guar)
Polyaminoacids
Soy,zein,wheatgluten, casein
Polysaccharides(animal)
Chitin/chitosan
SerumalbuminHyaluronicacid
Polysaccharides (bacterial)
Lipids/Surfactants
XanthanAcetoglycerides,waxes, surfactants
DextranEmulsan
Gellan Polyphenols
LevanLignin
CurdlanTannin
PolygalactosamineHumicacid
Cellulose(bacterial) Specialtypolymers
Polysaccharides (fungal)
Shellac
PullulanPoly-g-glutamicacid
ElsinanNaturalrubber
YeastglucansSyntheticpolymersfrom naturalfatsandoils;nylon fromcastoroil
predominantresourceofcarbohydratesdevouredby humans,providingaround66%oftherequireddayto-daycalories.Itassumesacrucialpartinourregular dailyexistenceandisavitalplant-derivedmaterial generallyusedasfood(Riyajan,2015),inpackaging products,andinthemanufacturingofnonnourishment products.Itisnotonlyamajordietarycarbohydratebut isalsoemployedtomanufacturehouseholdproducts suchaspharmaceuticals,paper,andtextiles(Seung etal.,2015).Starchisthesecondlargestsourcefor biomass(inexhaustible)onthisplanet,providingan eco-friendlyapproachtoproduceenormousassortmentsofmaterialswhenmixedwithotherbiodegradablepolymers.Moreover,itisafamiliarpolymer accessibleinlargeamountsfromvarioussources(Pasquinietal.,2010).Thedegradationofstarchatnight distributescarbohydratestofuelrespirationandgrowth whenphotosynthesisisnonviable.
Starch,initslocalgranularshape,issometimesutilizedasnourishment.Initslocalstate,starchcomprises ofsemicrystallinegranulesthatareinsolubleinwater (Pasquinietal.,2010).Starch,forthemostpart,ispreparedbyheatwhichpromptsgelatinizationandsubsequentlycrumblesintoessentialsugarsegments, amylose,andamylopectin(Pasquinietal.,2010).Other refinementsofstarchincludetheutilizationofenzymatic orchemicaltreatments.High-control,low-frequencyultrasoundhandlinghastheadditionalcapabilityofhydrolyzingstarchparticles,withthebenefitofbeinga physicaltechnique(Kangetal.,2016).Todate,starch isgenerallyemployedasnourishment(Riyajan,2015), inbuildingmaterials(Teodoroetal.,2015),andinthe creationofpaper(Petersenetal.,2013).Itisaneasy, inexhaustibleasset(Riyajan,2015).
acquiredfromeitheroilassets(noninexhaustibleassets) ororganicassets(sustainableassets).
3 STARCH
Starchishydrophilicinnature(Zhangetal.,2014).Asa completelybiodegradablepolysaccharidethatisbiosynthesizedbynumerousplants,starchisoneofthe mostabundantrenewableresourcesknowntoman (MohammadiNafchietal.,2013).Starchisthe
Starchfundamentallyexistsasefficientgranulesin whichamylopectinexhibitsnonrandomappropriation oflinerchainsandacongregatearrangementofbranch linkages,givingrisetoahighdegreeofstructuralorganization.Starchisasemicrystallinepolymermadefrom directpolysaccharidemolecules(amylose)and stretchedparticles(amylopectin).Itisadistinctivepolymercharacterizedasaccessiblegranulematerial(Peres etal.,2016).Thepreserveddesignofamylopectinis inchargeofthesemicrystalline,water-insolublestarch granules.Starchgranulesarethemostimportantenergy reserveinplantsandcanbefoundintubers,cereals, roots,sorghum,andstemofaplant,i.e.,barley,wheat, oat,corn,sago,greenpea,cassava,sugarpalm,andpotato(Saharietal.,2014).
Starchgranulesconsistoftwomajortypesofpolysaccharides:amyloseandamylopectin.Eachdiffersin atomicmass,levelofexpansion,andchemicalproperties
(Baietal.,2017).Theminorcomponentssuchaslipid, protein,andphospholipidsarefoundatthestarch’ ssurfaceorconnectedwithpolysaccharidechains.
Forpotatostarch,theshapechangesfromovaltocircularasthewidthofthegranulesdiminishes.Potatoisa tuberousharvestthatcontainsahighmeasureofstarch andgenerallyutilizedaspartofthefoodindustry, materialindustry,adhesives,andpaperindustry.In addition,thestateofpotatostarchgranulesistypically representedaslenticularandtheirnormalsizecan changebetween5and100 mm(Baietal.,2017).Other thanthat,itcanbeappliedasthickeners,coating,gelling,bonding,anduniquecasingsfordrugrelease.In variousmechanicalapplications,potatostarchisused fornourishmentsolutions,operatorsforpaperandmaterials,biodegradableplastics,andpharmaceuticals. Fig.2.1 displaysthepotatostarchgranules.
Thegranulesizeofstarchcouldreflectthebiosyntheticage.Smallsizedgranulesareconsideredasprepubescentgranulesthatcannotdevelopintofull-estimate granules,whileextensivegranulesarecompletelydevelopedgranules(Wangetal.,2016).
3.1 ApplicationofStarch
Ingeneral,starchisacommonsourceofcarbohydrates forthehumandiet.Itisconsumedintheformofstaple foodssuchasrice,pasta,breads,cereals,andvegetables. Starchisalsousedinfoodpreparationprocessessuchas athickeningagentforgravy,puddings,etc(Jumaidin etal.,2018).Inthepharmaceuticalindustry,starchis employedasadrugexcipientthatexhibitstheslow releasecharacteristics(LeBailetal.,1999).Itisreported thathighamylosestarchdisplaysgoodswellingand drugreleasebehaviorwhenformedasatablet.Inpapermaking,starchisappliedtoenhancethestrengthofpaper.Itisalsousedforadhesivematerialsinthe manufacturingofglueandothertypesofadhesives. Starchisfurtherusedincosmetics,petfood,aquatic food,andclothing.
3.2 ThermoplasticStarch
Starchhasuniquecharacteristicswhereitcanbetransformedintothermoplasticswhensubjectedtohightemperature,shear,andwiththepresenceofaplasticizer.In general,theroleoftheplasticizeristodisruptstarch granulesbybreakingitsintermolecularandintramolecularhydrogenbonds.Thestarch-plasticizerinteractionis formedbyeliminatingthestarch-starchinteraction. Thisprocessisaccompaniedbypartialdepolymerization ofthestarchbackboneandadecreaseinthemeltingtemperatureofstarch(Stepto,2003).Theintroductionofa plasticizerandheatwithrawstarchistermedasplasticization.Theroleoftheplasticizeristoreducethe
brittlenessofstarchandincrease flexibilityforfutureapplications.Theuniquecharacteristicsofthermoplastic starchallowthisbiomaterialtomeltandhardenrepeatedly,makingitsuitableforvariousfabricationprocesses forconventionalplastics.Hence,thisfeaturecanbe includedinthepositiveattributesofthematerial,apart frombeingbiodegradableandrenewable.
3.3 ProcessingofThermoplasticStarch
Aspreviouslymentioned,starchrequiresthepresence ofheat,shear,andplasticizertotransformintothermoplasticstarch.Ingeneral,thereareseveraltypesofplasticizers:glycerol,sorbitol,fructose,urea,water,etc.Two mainprocessescanbeappliedtoproducethisgreen material.Hotpressandsolutioncastingarethemost commonmethodsemployedinreportedstudieson thermoplasticstarchdevelopment.
3.3.1 Hotpress
Thehotpressmethodreferstoaprocesswherethe starchmixtureispressedatacertaintemperature;the
(A) ThenativelargepotatostarchgranulesbySEM and (B) thenativesmallpotatostarchgranulesbySEM (Sandhuetal.,2015).
FIG.2.1
pressureisappliedbyusinghydraulicpressequipped withaheatingelement.Toemploythehotpress method,severalstagesmustbeaccomplished.Firstly, nativestarchshouldbemixedwithaplasticizeratapredeterminedratio,i.e.,20to30wt%.Apreviousstudy hadreportedthatmixingcanbeconductedinaplastic baguntilahomogeneousmixtureisattained(Lomelí Ramírezetal.,2011).Anotherstudyreportedthata mechanicalstirrercanbeusedtocompletethisprocess (Saharietal.,2013).Itwasalsomentionedthatahighspeedmixercanbeemployedtoensuregoodmixingis achievedatthisstage(Jumaidinetal.,2016).Thehomogenousstarch/plasticizermixturecanbehotpressed atcertaintemperatureranges,from130to180 Cwith pressurerangingbetween10and20tons.However, somestudiesdidreportusingthemelt-mixingprocess withapolymermelt-mixerbeforethehotpressing process(Lopezetal.,2014;Lópezetal.,2015;Salaberriaetal.,2014;TaghizadehandFavis,2013).The melt-mixingprocessisaccomplishedtoobtainearly plasticizationofthestarch,whileacquiringahomogeneousstarch/plasticizermixture.Thiscanbeachieved moreeasilyduringthemeltcondition.Theproduct frommelt-mixingwillbecrushedintosmallpellets beforeplacedontoasteelmoldforthehotpressingprocess.Here,thethermoplasticstarchwillpossesssimilar characteristicstoconventionalpolymer,i.e.,polypropyleneorpolyethylene.ThepressingofcrushedTPS pelletsmaybeconductedattemperaturesbetween 130and180 Cwithapressureof10 30tons,dependingonthestudy.Removalagentshouldbeappliedonto themold’ssurfaceinordertofacilitatetheremovalof samplesafterhotpressing.Sincethermoplasticstarch isknowntobemoisturesensitive,thesamplesobtained fromhotpressingshouldbecooleddowninadesiccatortoavoidmoistureabsorption,whichwillaffect themechanicalpropertiesofthematerial.Theadvantageofthehotpressingmethodistheabilitytoproduce arigidmaterialandproductthatisnotpossiblefor solutioncasting.Thelimitationofthisprocessisthe variationinthephysicalpropertiesoftheproductdue toanonhomogeneousstructure,void,cracks,etc., formedwhensamplesaresubjectedtohighpressure. Anaccurateamountoftherawmixtureisquitedifficult toobtainsincelowamountswillresultinunmelted samplesatthecorner,whileexcessiveamountswill resultinincreasinglythicksamples.Toaccomplish thisprocess,multipletrialsshouldbeconductedinordertoobtaintheidealtemperature,pressure,time,and amountofrawmaterialstobeplacedontothemold. Theseparametersarehighlydependentonthetypes ofstarch,plasticizer,anddimensionofthemold.
3.3.2 Solutioncasting
Solutioncastingisaprocessofproducingthermoplastic starchbyusingwatersolution,plasticizer,heat,andstirring.Ingeneral,thismethodisalsousedforothertypes ofbiopolymerssuchasagar,alginate,carrageenan,chitosan,chitin,etc.(Haciuetal.,2013;Pereiraetal.,2003; Wuetal.,2009).Theprocessofproducingthermoplasticstarchusingsolutioncastingisrelativelyeasier thanthehotpressingmethod.Ingeneral,ahotplate orwaterbath,aswellasdistilledwaterandmechanical/magneticstirrer,isrequired.Film-formingsolution thatconsistsofstarch,plasticizer,anddistilledwater shouldbepreparedforthisprocess.Priortoheating, theamountofstarchandplasticizershouldbeweighed accordingtothedesiredratiotoobtainthe film-forming solution.Edhirejetal.employeda film-formingsolutioncontaining5gofcassavastarch/100mLdistilled water(Edhirejetal.,2016).Fructosewasthenusedas theplasticizer,atconcentrationsof0.30g/gofdry starch.The film-formingsolutioncontainingallnecessarymaterialsisthenheatedto80 Cinathermal bathandkeptatthistemperaturefor20minunder constantstirring.Duringstirring,bubblestendto formwithinthesolution;however,accordingtoEdhirej etal.itcanberemovedbyplacingthe film-formingsolutionintoadesiccatorunderavacuum.Thesolution shouldbekeptinthevacuumdesiccatoruntilnobubblesarevisible.Theremovalofbubblesfromthesolutioniscrucialinordertoensureahomogeneous structureofthethermoplasticstarch.Theexistenceof bubblesmayleadtotheformationofavoidinthe final filmthatcouldinterferewiththemechanicalproperties oftheresultant film.
Thebubble-freesolutionwasthenpouredontocircularglassplateswith10cmdiameters.Next,the film-formingsolutionwasdriedat50 Cinanaircirculatingoven.Thedried filmswereslowlyremovedby peelingthe filmofffromtheplates.Theresultant film isthenkeptinazip-lockedplasticbagpriortocharacterization(Edhirejetal.,2016).
Solutioncastingisasimplemethodthatproduces thermoplasticstarchthatdoesnotrequireheavyequipment,i.e.,heatedhydraulicpress(hotpressmethod). Theadvantagesofthismethodisthatonlyminimum amountsof film-formingmaterialarerequiredto producethe film.Hence,multipleproductionscanbe carriedout,especiallyformaterialsthataredifficultto extractorhighincost(suchasnanoscalematerials). Sincethereisnopressureappliedduringthefabrication ofthe film,thestructureofanyadditionalmaterials (suchasnatural fiber)isnotsusceptibletodamageas inthehotpressmethod.However,thelimitationof
thismethodisthattheresultantproductisonlyinthe formofathin film.Hence,fabricationofothershapes isnotpossible,andthesamplescanonlyundergo tensiletestingforthecharacterizationofmechanical properties.Thermoplasticstarchproducedfromthehot pressmethodcanundergo flexuralandimpacttesting. The filmformedfromsolutioncastingisonlysuitable forexperimentalpurposesandisnotreadyforactual productionprocesses.Thehotpressmethodismuch moresimilartotheactualproductionprocessforconventionalplasticsandsimilardatacanbeappliedfor productionusingextrusionorinjectionmolding.
3.3.3 Injectionmolding
Injectionmoldingisatypeofmanufacturingprocess commonlyemployedforcreatingthermoplasticmaterialsinrapidproduction.Thismethodincludesinjectingmoltenmaterialsintoamold,whicharethen cooledandhardenedinsidethemoldcavity.Apart fromplastic,thismethodisemployedforglass,metals (knownasdie-casting),andelastomers.
Rosaetal.fabricatedthermoplasticcornstarchby usinginjectionmolding(RosaandAndrade,2004). Priortoinjectionmolding,thepreparationofaplasticizedmixtureisakeystepforthisprocess.Toobtain ahomogeneousmixture,Rosaetal.preparedaconstant weightofstarch,glycerol(15wt%),andwater(15wt %).ThismixturewasinjectionmoldedintoASTM D638-72TypeIspecimens,approximately2mmthick, usingaPicBoy15/42PetersenIrmaosMachine(Sao Paulo,Brazil).Thiswasprovidedwiththreeelectrically heatedzones,maintainedat130and145 Cfromthe feedzonetothedieend.Themixturesweremanually fedintothemachine,andtheinjectionpressurewas keptat113bar.Theinjectionmoldwascooledat 30 40 Cbyarefrigerationsystemandkeptclosedat 1275bar.
Injectionmoldingisthemostcommonprocessused fortheproductionofconventionalplastics.However, therearesomelimitationstothisprocessascompared withothers.Intermsofcost,injectionmoldingrequires high-endequipmentinorderfortheprocesstobecarriedout.Thisprocesswillrequirehugeamountsofmaterialstobeused,whichcanbeunlikelydependingon thematerialinvolved.
4 PROCESSINGOFTHERMOPLASTIC STARCHCOMPOSITES
Eventhoughthermoplasticstarchseemstobeapromisingmaterialforreplacingconventionalpetroleumbasedpolymers,therearesomelimitationspresentfor thismaterial,i.e.,poormechanicalproperties,low thermalstability,highmoisturesensitivity,andlow dimensionalstability.Theselimitationsrestrictthematerial’spotentialofbeingusedasanalternativeto conventionalplastics.Hence,variousstudieshave beencarriedouttoimprovethepropertiesofthermoplasticstarch.Thismodi ficationincludestheincorporationofnatural fibersatthemacro,micro,andnano levelsaswellasblendingTPSwithotherpolymers thathavebetterphysicalproperties.
Ibrahimetal.investigatedtheeffectofdatepalmand flax fiberonthebehaviorofthermoplasticstarchcomposites(Ibrahimetal.,2014),wherethermoplasticstarch compositeswerefabricatedusingthehotpressmethod. Priortothat,nativecornstarchwasmixedwith30wt %glycerinand20wt%distilledwateratatemperature between60and80 C.Itwasreportedthatthegelatinizationprocessofstarchcanbeenhancedwiththepresence ofwater,whichcouldimprovethetensilestrainofsampleswithoutsignificanteffectontensilestrength.Adding glycerinmayenhancetheprocessabilitywhilereducing
Anotherstudy(Avérous,2004)usedextrusionand injectionmoldingtofabricatethermoplasticwheat starch.Theauthorsfabricatedtwotypesofplasticized starchmatrix:TPS1andTPS2.TPS1waspreparedwith acombinationof70wt%starch,18wt%glycerol,and 12wt%water;whileTPS2waspreparedwith65wt% starchand35wt%glycerol.TheprocessingofTPS beganbyweighingthestarchandglycerol,followed bymixingathighspeed(2000rpm).Next,thestarch washeatedat170 Cfor45mininaventedovento allowglyceroldiffusionintothestarchgranulesas wellaswatervolatilizationfromthemixture.The mixturewasthencooledandbecameadryblend.The dryblendwasaddedwithwateratacertainformulation thatwasnotmentionedspecificallybytheauthors.The mixturewassubjectedtodispersioninamixer.Itthen underwenthigh-speedmixing(2500rpm)toobtain the finalmixture.Thepowderwasextrudedwithasinglescrewextruderandgranulated.Thepelletswere extrudedforthesecondtimeinordertoimprovedispersion.The finalpelletswereequilibratedat50%RHfor 8dayspriortotheinjectionmoldingprocess.Next,the injectionmoldingmachinewithaclampingforceof 50tonswasusedtomoldstandarddumbbells.The parametersfortheinjectionmoldingprocessareasfollows:screwbarreltemperature(100 130 C), moldtemperature(20 25 C),holdingpressure (1000bars),holdingtime(20s),andcoolingtime (10s).Theresultantdumbbell-shapedproductwas conditionedatatemperatureandhumidity-controlled room(23 C,54%RH)during2,4,or6weeks.
embrittlementbyinhibitingtheretrogradationprocedureafterprocessing.Thepreparationofcompositeswas accomplishedbyusingapositivetypemoldcoated withstericacidasthereleasingagent.Natural fiber (i.e.,datepalmand flax fiber)waschoppedanddistributedinthemold.Next,thermoplasticstarchwasemulsifiedinwaterwithTPS:waterratioof1:1,1:2,1:3,1:4, and1:8for0,20,40,50,60,and80wt% fibercontents, respectively.Thesampleswerepreheatedat140 3 C for30mininahydraulicpresstoremoveexcesswater fromtheemulsion.Thiswasfollowedbyhotpressing at5MPaand160 3 Cfor30minandthencooled atarateofabout2 C/min.The findingsindicatethat theincorporationofbothdatepalmand flax fiberdid improvethemechanicalpropertiesandthermalstability, whilereducingthewateruptake. Fig.2.2 showsthe treatedanduntreateddatepalm fiberandtheSEM micrographofstarchandthethermoplasticstarch.
Jumaidinetal.investigatedtheeffectofagaronthe thermal,mechanical,andmoistureabsorptionbehaviorsofthermoplasticsugarpalmstarch(Jumaidin
etal.,2016).Thecompositesweredevelopedbyusing acombinationofmelt-mixingandhotpressing methods.Priortotheirfabrication,sugarpalmstarch wasmanuallyextractedfromthesugarpalmtreebyusingextraction,washing,sedimentation,anddryingprocesses.TheTPSmatrixwaspreparedbyusing30wt% glycerolastheplasticizer.Themixturewasthenmixed usingahigh-speedmixerat3000rpmfor5min.The well-mixedsampleunderwentamelt-mixingprocess usingBrabenderplastographat140 Candrotorspeed of20rpmfor10min.Theresultantproductfromthe melt-mixingapproachwasgranulatedbyusingablade millwith2mmmeshtoproducesmallpellets.Lastly, thepelletswerepressedinamoldat140 Cfor 10minundertheloadof10tons.Thesameprocess wasadoptedforthecompositepreparationofagar (10,20,30,and40wt%)introducedduringthehighspeedmixingprocess.Theauthorsreportedthatthe incorporationofagardidimprovethethermalstability andmechanicalproperties,whileincreasingthemoistureuptakeandthicknessswellingofthecomposites.
FIG.2.2 Datepalm fibersandstarchSEMinvestigation: (A) rawdatepalm fibersarecoveredwithmuch lignin; (B) NaOH-treateddatepalm fiberswithcleansurfaceandprotruded fibrils; (C) overnight-stored plasticizedcornstarch;and (D) compressionmoldedthermoplasticstarchbyemulsiontechnique(Ibrahim etal.,2014).
Fig.2.3 showstheSEMmicrographoffracturesurfaceof thermoplasticSPSblendedwithdifferentratioofagar (A)0wt%,(B)10wt%,(C)20wt%,(D)30wt%,and (E)40wt%.
Anotherrecentstudyhadreportedthedevelopment ofthermoplasticstarch/naturalkeratin fibercomposites for flame-retardantapplication(Rabeetal.,2019).In thisstudy,theauthorsusedthermoplasticstarch (namely,Mater-BiEF05B)procuredfromNovamont S.p.A(Novara,Italy).Thekeratin fiberswereobtained aswastefromthebeamhousestageofaMexicantannery, whilethecoconut fiberswereobtainedfromthehuskof coconutfruits.Thenatural fibersunderwentseveralprocedurespriortothemixingprocesswithTPS.TheTPS compositeswerepreparedbytheextrusionofTPSand fibermixtureinatwinscrewextruderL/D ¼ 32witha diameterof27.0mmandeightheatingzonesusinga counterrotatingintermeshingmode.Thetemperature profileforthecompoundingprocess(fromfeedtodie)
wereasfollows:130/135/135/140/145/150/145/ 140 C.Therotationalspeedofthetwinscrewswasset at120rpm.Theauthorsadoptedthedoubleextrusion method(repeated)inordertoensurebetterdispersion of fibersand flame-retardantproperties.Forthesecond extrusion,theTPSandcompositesweredriedat105 C inmodel30lowpressuredryerwith80psi (0.5516MPa)maintainedduringheating.Aftereach extrusionstep,thecompositesweregranulatedina7.5 HPgranulatorusingascreenwitha5mmmesh.The findingsindicatethattheincorporationof fiberdid improvethe flame-retardantpropertiesofthecomposites.Thiswasindicatedbythelowerheatreleaserate andtotalheatevolvedfromtheTPScomposites.
5 CONCLUSIONS
Ingeneral,thischapterhasshownthatthermoplastic starchisaversatilematerialthatcanbeprocessedusing
FIG.2.3 SEMmicrographoffracturesurfaceofthermoplasticSPSblendedwithdifferentratioofagar (A) 0wt%, (B) 10wt%, (C) 20wt%, (D) 30wt%,and (E) 40wt%.
variousmethods.TPScanbefabricatedusingexisting equipmentforthemanufacturingofcommercialplastic productsintheplasticindustry.Hence,thepromising characteristicsofTPSprovidegreatopportunitiesfor thismaterialtobecomeasustainablealternativetosyntheticnonbiodegradablepolymers.Morestudies regardingthefeasibilityofTPSforvariousapplications, especiallyforhighmoistureenvironment,mustbe exploredbyresearcherstofurtherenhancethereadiness ofTPSforwidercommercialapplications.
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