Brewer’s SpentGrainsasAlternativeLigno-Cellulosic Filler forthePreparationofBio-BasedPolymerComposites

Brewer’s spentgrains(BSGs)arelignocellulosicsourcesthatcanbeconsideredpromisingeconomicalternativestowoodas biofillers toproducewood–plastic composites(WPCs).Giventhehighproteincontent(25wt.%) ofBSGs,alkalinehydrolytic solid–liquid (S/L)extractionswerecarriedoutatdifferentpHs,withthegoalofextractingasmuchproteinaspossiblewithout altering orcompromisingthequalityofthelignocellulosicmatrix.Biocompositeswith10–50 wt.% biofiller wereproducedby blending polybutylenesuccinate(PBS)andpoly(hydroxybutyrate-co-hydroxyhexanoate)(PHBH)withnativeBSG(BSG),BSG treated atpH10.5(BSG-S2_T2)andBSGtreatedatpH12(BSG-S2_T3).Theinjection-moldedcompoundswerecharacterizedin terms ofstructural,rheological,mechanical,morphological,andthermalpropertiestoinvestigatethepotentialimpactofdifferent biofillers ontheoverallcompatibilityofthetwodifferentbiopolymermatricesasanalternativetoconventionalwood flour-based WPCs. Fouriertransforminfrared(FT-IR)spectra,thermal(differentialscanningcalorimetry[DSC]),andmorphological(scan- ning electronmicroscope[SEM])analysesrevealedonlyminorinteractions.Themelt flow rate(MFR)analysesshowedthe increased viscosityinPBS-basedbiocompositeswhenthe filler concentrationincreased.Incontrast,forPHBH-basedcomposites, an increaseinMFRvalueswasobtainedunderthesametestconditions,withamaximumpeakof97% for S2_T330wt.% filler. From amechanicalpointofview,theadditionofreinforcing fibers ledtoamoresignificant increaseinYoung’s modulus(E) in PBS-based compositesasthebiofiller contentincreased,upto98%, comparedtopurePBS.Onthecontrary,inPHBH-based composites, theadditionof fillers ledtoasignificantly lowerincrease,withvaluesbetween14% and 20% compared topurePHBH. The tensilestrength(σB) andelongationatbreak(εB) decreasedproportionallyinthetwobiopolymermatricesasthepercentageof natural filler increased,withpropertiessimilartotraditionalWPCs.Theseresultsareconsistentwiththeliteratureandsupportthe application ofPBSandPHBHbiocomposites filled withBSGasanenvironmentallyfriendlyalternativetoconventionalplastics.