Optimization of Processing Conditions for Rice Bran-based Bioplastics Through Extrusion and Injection Molding

ORIGINAL ARTICLE Jou nal o Polyme s and he En i onmen (2025) 33:512–527 h ps://doi.o g/10.1007/s10924-024-03377-4 F om he con amina ion o oceans wi h pe sis en plas ic was es o he ha m ul e ec s o mic oplas ic inges ion by wildli e, he de imen al e ec s o con en ional plas ics on biodi e si y and ecosys em heal h a e becoming inc eas- ingly e iden [2]. Bioplas ics a e a p omising and sus ain- able al e na i e p oposed by he scien i ic communi y o deal wi h his en i onmen al c isis. De i ed om enewable esou ces such as plan s a ches, ag icul u al byp oduc s, o mic obial e men a ion, bioplas- ics p esen a compelling solu ion o mi iga e he ecologi- cal oo p in associa ed wi h con en ional plas ics [3]. The use o biobased and biodeg adable plas ics (pa icula ly de i ed om was e and byp oduc s o he ag o- ood indus- y) eme ges as a cu ing-edge s a egy o add ess he en i- onmen al challenges associa ed wi h con en ional plas ics [4]. In con as o o he ypes o bioplas ics, hose based on ag icul u al aw ma e ials o e signi ican ad an ages. Fi s ly, ha nessing was e and byp oduc s om his sou ce In oduc ion Con en ional plas ics ha e eme ged as a signi ican h ea o he delica e balance o ou ecosys ems in oday’s en i on- men al landscape [1]. The ubiqui ous use o adi ional plas- ics in a ious indus ies has led o widesp ead pollu ion, ad e sely impac ing land and aqua ic en i onmen s alike. Ma ía Alonso-González [email p o ec ed] 1 Depa amen o de Ingenie ía Química, Escuela Poli écnica Supe io , Uni e sidad de Se illa, Se illa 41011, Spain 2 Depa amen o de Ingenie ía Química, Facul ad de Química, Uni e sidad de Se illa, Se illa 41012, Spain 3 Depa men o Chemical Enginee ing Ma e ials En i onmen , Uni e si y o Rome La Sapienza and UdR INSTM, Via Eudossiana 18, Rome 00184, I aly Abs ac Con en ional plas ics pose en i onmen al h ea s due o hei non-biodeg adable na u e and hei eliabili y on ossil esou ces, leading o he explo a ion o sus ainable al e na i es. In his sense, biodeg adable bioplas ics de i ed om enewable esou ces o e a p omising solu ion o mi iga e ecological impac s. This s udy ocuses on he combina ion o ex usion and injec ion molding o he de elopmen o ice b an-based bioplas ics. Being a by-p oduc om he ice indus y ich in s a ches and p o eins, ice b an is an abundan and non-expensi e esou ce ha con ibu es o an enhanced was e managemen and ep esen s a s ep o wa d in in eg a ing he p inciples o a ci cula economy. This s udy del es in o he op imiza ion o p ocessing condi ions h ough a Design o Expe imen app oach. Fo his pu pose, he numbe o ex usion s eps, cylinde and mold empe a u es, and injec ion p essu e we e in es iga ed. The esul s showed ha wo ex usion s eps led o a signi ican inc ease o app oxima ely 22.8% in Young’s modulus and 37.5% in ensile s eng h compa ed o a single ex usion cycle. This enhancemen was a ibu ed o he acili a ion o s a ch gela iniza ion and biopolyme -plas icize in e ac ions (achie ing he moplas ic s a ch and p o ein plas iciza ion). Simila ly, manipula ion o injec ion empe a u es and p essu e had no able e ec s on ensile p ope ies, highligh ing he complex in e play be ween p ocessing pa ame e s. In pa icula , when using cylinde and mold empe a u es o 110 °C and 180 °C, espec i ely, along wi h 800 ba , i was possible o achie e a u he enhancemen in ensile p ope ies, wi h an inc ease o 97.1% in Young’s modulus and o e 100% in ensile s eng h. O e all, his esea ch unde sco es he impo ance o unde s anding he ela ionship be ween p ocessing condi ions and biopolyme in e ac ions o bioplas ic p oduc ion. Keywo ds Rice b an · Ci cula Economy · Bioplas ics · Ex usion · Injec ion Molding · Design o Expe imen Accep ed: 1 Augus 2024 / Published online: 3 Augus 2024 © The Au ho (s) 2024 Op imiza ion o P ocessing Condi ions o Rice B an-based Bioplas ics Th ough Ex usion and Injec ion Molding Ma íaAlonso-González1,2,3· ManuelFelix1· Albe oRome o2· ClaudiaSe gi3· I eneBa asso3· Fab izioSa asini3 1 3 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 no only educes eliance on non- enewable esou ces bu also ackles he issue o ag icul u al was e managemen by ans o ming hem in o aluable aw ma e ials wi h speci ic applica ions [5]. Fu he mo e, hei e ec i e biodeg ada- ion in speci ic en i onmen s, such as compos ing, p o ides an addi ional solu ion o he long- e m plas ic was e accu- mula ion p oblem. In his ega d, bioplas ics de i ed om ag icul u al was e no only ep esen a mo e sus ainable al e na i e bu also cons i u e a c ucial s ep owa ds build- ing a mo e en i onmen ally espec ul u u e [6]. The selec ion o ice b an as a p ima y aw ma e ial o bioplas ic p oduc ion is suppo ed by i s nume ous ad an- ages based on i s chemical composi ion and a ailabili y. Rice b an is an abundan byp oduc o ice milling p o- cesses, mo e han 60 million me ic ons we e p oduced in 2017 [7], p o iding a sus ainable sou ce ha simul aneously add esses he issue o ag icul u al was e disposal [8] and i is aligned wi h he p inciples o ci cula economy, u ning an o he wise unde u ilized byp oduc in o a aluable esou ce o sus ainable ma e ials [9]. In his sense, ice b an p es- en s a no ewo hy eposi o y o p o eins and s a ches, bo h o which se e as biopolyme s wi h immense po en ial o bioplas ic de elopmen [10, 11]. Th ough app op ia e p o- cessing echniques, such as he momechanical ea men s, hese p o eins and s a ches can be e ec i ely ans o med in o e sa ile bioplas ic ma e ials [12, 13]. Among he many p ocessing echniques, ex usion and injec ion molding play key oles. Ex usion is a widely employed me hod ha allows he e icien and con inuous p oduc ion o bioplas ics, making i e sa ile o a ange o applica ions [14, 15]. On he o he hand, injec ion mold- ing is pa icula ly ad an ageous o p oducing in ica e and cus omized bioplas ic p oduc s [16, 17]. Bo h ex u- sion and injec ion molding echniques o e scalabili y and ep oducibili y, making hem in eg al o he indus ial-scale manu ac u ing o bioplas ics. By ha nessing hese ech- niques, he mechanical p ope ies and geome ical p ecision o bioplas ics can be op imized, pa ing he way o hei widesp ead adop ion as eco- iendly al e na i es in di e se applica ions. Howe e , cu en bioplas ics o en ace signi - ican limi a ions, including na ow p ocessing windows and poo mechanical p ope ies, such as lowe ensile s eng h and duc ili y compa ed o con en ional plas ics. Addi ion- ally, hey exhibi lowe ba ie p ope ies, which can a ec hei e ec i eness in p o ec ing agains mois u e and gases. Fu he mo e, al hough egula ions could bene i hem, he highe p oduc ion cos s and limi ed scalabili y o bioplas- ics p esen challenges o widesp ead adop ion and com- pe i i eness in he ma ke [18]. Fo hese easons, in-dep h esea ch is equi ed o o e come po en ial disad an ages. P e ious in es iga ions we e ocused on he op imiza- ion o he ice b an and plas icize s o be employed [19–22] and he in luence o some injec ion molding pa ame e s has been al eady add essed [23, 24]. This s udy aims o op i- mize he p ocessing condi ions o he de elopmen o ice b an-based bioplas ics by combining ex usion and injec- ion molding. P ocessing pa ame e s such as he numbe o ex usion cycles, he empe a u e o he cylinde , he empe a u e o he mold and he injec ion p essu e we e e alua ed and in es iga ed h ough a Design o Expe i- men (DoE) app oach o es ablish a ela ionship be ween he p ocessing condi ions and he inal p ope ies and o ailo hose ega ding speci ic applica ions. To his end, a comp ehensi e cha ac e iza ion encompassing mechani- cal, he mal and chemical and mic os uc u al analysis was conduc ed on he sys ems, using mechanical p ope ies as he main pa ame e s o sys em op imiza ion. The no el y o his s udy lies in he use o a whole by-p oduc om he ag o- ood indus y, speci ically ice b an, ins ead o isola ed p o eins o s a ches. By employing only a de a ing ea - men , his esea ch add esses he complexi y a ising om he in e ac ions be ween he a ious phases p esen in ice b an. The e o e, an in es iga ion in o op imizing p ocess- ing condi ions ia ex usion and injec ion molding, using a design o expe imen s app oach, is c ucial o unde s and how his complex ma e ial beha es. Expe imen al Ma e ials Rice b an (RB) om indica ice, p o ided by He ba Ricemi- lls (San José de la Rinconada, Se ille, Spain), was used as he aw ma e ial o his s udy. The composi ion o he ice b an, as de e mined by A.O.A.C. me hods [22], was ound o be 16 w % mois u e, 13 w % ashes, 2 w % lipids, 17 w % p o eins, 28 w % ibe (comp ising cellulose and hemicel- lulose), and 24 w % s a ch. I is impo an o no e ha he ice b an unde wen a s eaming he mal ea men , a p ocess also ca ied ou by He ba Ricemills. Glyce ol (Gly), used as he plas icize , was sou ced om Sigma-Ald ich (USA). Dis illed wa e (W) was used as needed in he expe imen al p ocedu es. De a ed Rice B an (DRB) Upon ini ial ecep ion, he lipid con en in he ice b an exceeded 20 w %. Howe e , o achie e a educed lipid con en o less han 2 w %, a de a ing p ocedu e was implemen ed using he same me hodology de ailed in p io s udies [22]. B ie ly, ice b an (< 500 μm) was mixed wi h hexane in a p opo ion o 1:10 w/ . The esul ing suspen- sion unde wen magne ic s i ing a 25 ºC o 24 h, ollowed 1 3 513 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 by cen i uga ion a 5,000 pm o 10 min. The solid ac- ion was hen sepa a ed om he supe na an , con aining he hexane phase and he ex ac ed lipids. The sepa a ed solid ac ion was subsequen ly d ied in a ume hood. This de a - ing p ocess was epea ed wice. A e de a ing, he ice b an was g ound and sie ed o a size smalle han 200 μm (70 mesh) o he balanced p ope ies o his ac ion [20], esul ing in he de elopmen o he DRB sys em. Bioplas ics P epa a ion D y-blend P epa a ion The samples we e p oduced h ough a wo-s ep p oce- du e, beginning wi h he o mula ion o a d y-blend by combining DRB, Gly, and W. This p elimina y d y-blend app oach, achie ed h ough di e en d ying s eps along wi h he addi ion o he plas icize s, acili a es subsequen ex usion, esul ing in a inal ma e ial wi h minimal exuda- ion phenomenon, ha is, mig a ion o he plas icize o e ime. This a ou able ou come is p ima ily a ibu ed o he compa ibili y o p o ein and polysaccha ide chains and he polyols used as plas icize s (Gly in his case), as epo ed by Chi ac e al. [25]. To his end, he DRB unde wen o e nigh d ying a 70 ºC in an o en AG-Sys em om F a elli Galli (I aly) o elimina e ee wa e (app oxima ely 9 w %, depending on ambien condi ions). Subsequen ly, he d ied powde was subjec ed o mechanical s i ing a 100 pm using an A go Lab AM20-D s i e (I aly), inco po a ing Gly g adually un il a uni o m mix u e was achie ed. The blend was hen d ied a 110 ºC in he o en o 1 h, acili a ing he ola- iliza ion o bound wa e h ough di usion exchange wi h Gly molecules in e ac ing wi h p o ein and s a ch mac o- molecules. A e cooling, wa e was added o he d y-blend ollowing he same p ocedu e, slowly in oducing i in o he mix u e unde mechanical s i ing. This esul ed in a o mu- la ion comp ising 60 w % DRB, 30 w % Gly, and 10 w % W, ensu ing an op imal mois u e con en (d y-blends). Ex usion The d y-blends we e in oduced in o he hoppe o a pa allel co- o a ing win-sc ew ex ude (The mo Scien i ic P ocess 11, The mo Fishe Scien i ic, Wal ham, MA, USA), wi h 11 mm ully segmen ed sc ews and a L/D a io o 40. This ex ude was equipped wi h 8 hea ing zones and a s anda d sc ew con igu a ion wi h con eying elemen s (helix pi ch o 1 L/D) in e spaced among h ee mixing sec ions ob ain- ing al e na ing elemen s wi h 0º and 90º (leng h ¼ L/D). The sc ew speed (15 pm) and empe a u e p o ile we e se based on p e iously op imized condi ions ( esul s no pub- lished ye ), main aining a cons an eeding a e. The em- pe a u e p o ile was ailo ed o an ex ude wi h 8 hea ing zones, wi h empe a u es se a 90–100–110–120–120–110– 105–100 °C, om hoppe o die. The ex usion p ocess was conduc ed once and wice o e alua e he po en ial bene i s o a second un, p o iding an ex ended esidence ime o biopolyme plas i ica ion. Injec ion Molding Following ex usion, he pelle s unde wen injec ion molding (Haake MiniJe II P o, The mo Fishe Scien i ic, Wal ham, MA, USA) unde a ying p ocessing condi ions, including adjus men s o he cylinde empe a u e (Tc), mold empe a u e (Tm) and applied p essu e (P), whe e all he specimens emained in he mold o 200 s. By hese means, ensile dogbone specimens we e ob ained. In o de o op imize he injec ion molding phase and o maximize he mechanical p ope ies o he esul ing bioplas ics, he a o emen ioned pa ame e s we e selec ed, exploi ing he DoE echnique and changing hem on wo le els, low (–) and high (+), o ob ain a 23 ull ac o ial design. Figu e S1 shows an image o he inal bioplas ics, while Table 1 de ails he low and high le els o he h ee pa ame e s ha we e used in he ull ac o ial design as well as he designa- ion o he di e en ob ained sys ems. In his way, 110 ºC and 140 ºC we e chosen as low and high le els o he em- pe a u e o he cylinde a e obse ing ha inc easing he empe a u e o he cylinde om 50 ºC o 110 ºC esul ed in imp o ed mechanical p ope ies. This imp o emen is likely asc ibed o he o e s epping o he bioplas ic glass ansi ion empe a u e, a c i ical poin a which he ma e ial unde goes a ansi ion om a igid o a mo e lexible s a e. The ole o his ansi ion in enhancing mechanical p ope - ies has been es ablished in p e ious wo ks, p o iding sup- po ing e idence o ou obse ed empe a u e-dependen e ec s. Fo he empe a u e o he mold, 150 ºC and 180 ºC we e selec ed as low and high le els, based on a p e ious s udy ha demons a ed he bene icial e ec o inc easing he empe a u e o he mold on he mechanical p ope ies Table 1 Designa ion o he di e en p ocessed biopolyme s Sys em Ex usion Injec ion molding S eps Tc (ºC) Tm (ºC) P (ba ) E1 150 150 500 E2 250 150 500 E2I1 2110 (–) 150 (–) 500 (–) E2I2 2110 (–) 150 (–) 800 (+) E2I3 2140 (+)150 (–) 500 (–) E2I4 2140 (+)150 (–) 800 (+) E2I5 2110 (–) 180 (+)500 (–) E2I6 2110 (–) 180 (+) 800 (+) E2I7 2140 (+) 180 (+)500 (–) E2I8 2140 (+) 180 (+) 800 (+) 1 3 514 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 es s we e conduc ed using a DSC 214 Polyma ins umen (Ne zsch, Selb, Ge many) in a ni ogen a mosphe e (40 mL/ min), employing a hea ing/cooling a e o 10 ºC/min. The calo ime ic es s in ol ed hea ing/cooling amps anging om − 40 ºC o 300 ºC. Key empe a u es, such as he glass ansi ion empe a u e (Tg) and mel ing empe a u e (T′m) we e ob ained om he DSC cu es. To assess he he mal s abili y o he samples, he mo- g a ime ic analysis (TGA) was pe o med. The specimens we e placed in alumina c ucibles and subjec ed o hea - ing om 25 ºC o 800 ºC a a hea ing a e o 10 ºC/min in an ine ni ogen a mosphe e (40 mL/min). All expe i- men s we e conduc ed using a TG209 F1 Lib a ins umen (Ne zsch, Selb, Ge many). Fou ie T ans o m In a ed Spec oscopy (FTIR) The FTIR analysis was conduc ed on he aw ma e ial, namely, he un ea ed DRB, and on one o he samples p ocessed a 150 °C and ano he a 180 °C as Tm (sys ems E2I1 and E2I5, espec i ely). The equipmen used was an In enio X spec ome e (B uke ) o ob ain abso bance spec- a be ween 4000 and 750 cm−1. Scanning Elec on Mic oscopy (SEM) Mic og aphs o he bioplas ics ac u e su ace we e aken by SEM o assess he mic os uc u e o he di e en speci- mens and he ailu e mechanism. To his end, a ield-emis- sion scanning elec on mic oscope (FE-SEM) MIRA 3 by Tescan (B no, Czech Republic) was used. The samples we e coa ed wi h a hin laye o gold by spu e ing o p e en cha ging and hey we e hen obse ed a 10 kV accele a ion ol age. S a is ical Analyses S a is ical analysis was used o disclose he ela ionship be ween he injec ion molding pa ame e s selec ed and he esul ing mechanical p ope ies and i was di ided in wo di e en s eps. A i s , in e en ial s a is ic was used o de e - mine whe he he injec ion molding pa ame e s selec ed as independen a iables, i.e., Tc, Tm and P, ha e an ac ual e ec on he dependen a iable, i.e., ensile modulus, en- sile s eng h and elonga ion a b eak, by mee ing he c i e ia o s a is ical signi icance. The analysis was pe o med by applying he F- es (ANOVA) and selec ing a p- alue < 0.05 as a s a is ically signi ican limi . This means ha a p- alue lowe han 0.05 con i ms ha he pa ame e unde con- side a ion had an ac ual e ec on he dependen a iable. The analysis was pe o med wi h he R-s udio pla o m, o ice b an-based bioplas ics [23]. Ne e heless, he em- pe a u e was no inc eased beyond 180 ºC because u he inc emen s led o samples ha we e comple ely bu n , eas- ily b eaking upon demolding, as can be seen in Figu e S2. Finally, 500 ba and 800 ba we e selec ed as low and high le els o injec ion p essu e o es ablish a compa ison wi h p e ious s udies and add ess he sui abili y o bioplas ics o ma ion d i en by high injec ion p essu e [26]. Rega ding he ex usion p ocedu e, designa ion o he sys ems is based on E1 o 1 s ep and E2 o 2 s eps. Since E2 was selec ed based on he mechanical p ope ies o he esul ing samples (injec ed a Tc = 50 ºC, Tm = 150 ºC and P = 500 ba ), he es o he sys ems whe e he injec- ion molding condi ions we e changed a e designa ed as E2I1-E2I8. Cha ac e iza ions Tensile Tes s Tensile es s we e ca ied ou on he samples using a Zwick/ Roell Z010 uni e sal es ing machine. Measu emen s we e pe o med a oom empe a u e based on he ISO 527-2 s anda d [27] using a s ain a e o 1 mm/min, a load cell o 1 kN, a g ip- o-g ip sepa a ion o 53 mm and an ex en- some e wi h a 30 mm gauge leng h. S ess-s ain cu es we e ob ained, which we e used o calcula e he alues o Young’s modulus (E), ensile s eng h (σmax) and s ain a b eak (εmax) o he di e en sys ems de eloped. A leas h ee specimens we e es ed o each sys em. Dynamic Mechanical The mal Analysis (DMTA) DMTA es s we e pe o med on a DMA850 heome e (TA ins umen s, USA) wi h ec angula p obes measu ing 10 mm × 8 mm × 1.5 mm using he ilm clamp in ension mode. Fi s ly, he linea iscoelas ic ange was de e mined by s ain sweep es s a a cons an equency o 1 Hz wi hin a de o ma ion ange om 0.01–1%. F om his es , he c i ical de o ma ion was de e mined, and a sui able de o ma ion was selec ed wi hin he linea iscoelas ic ange (LVR) o ca y ou he ollowing es s. F equency sweep es s be ween 0.5 Hz and 20 Hz a oom empe a u e and empe a u e amps be ween − 10 ºC and 160 ºC a a cons an equency o 1 Hz we e ca ied ou . F om hese es s, he alues o he s o age modulus (E′), he loss modulus (E″) and he an δ = E″/E′ we e ob ained as a unc ion o equency and empe a u e. The mal Cha ac e iza ion Di e en ial Scanning Calo ime y (DSC) was employed o examine he he mal cha ac e is ics o he sys ems. The 1 3 515 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 an inc ease o 22.8% in s i ness and 37.5% in s eng h was obse ed. Fo his eason, wo ex usion s eps we e selec ed o he es o he es s used o op imize he injec ion molding condi ions. The longe p ocessing ime unde empe a u e, shea o ces and he p esence o plas icize s could imp o e s a ch gela iniza ion and he c ea ion o mo e biopolyme - plas icize in e ac ions [28, 29] wi h bo h he s a ch and p o ein ac ions, esul ing in a ma e ial mo e sui able o be manu ac u ed by he mo-mechanical me hods. On he o he hand, he e ec s o inc easing he cylinde ’s empe a u e we e es ed while keeping he o he wo pa am- e e s, Tm and P, cons an . In his way, he Tc was inc eased om 50 ºC (E2) o 110 ºC (E2I1) and o 140 ºC (E2I3) o Tm = 150 ºC and P = 500 ba . In his case, he inc easing Tc om 50 ºC esul ed in enhancemen s in bo h σmax and εmax, imp o ing om 1.1 o 1.6 MPa and om 4.0 o 6.9%, espec i ely when using Tc = 110 ºC, he Young’s modulus emaining a 70 MPa. The bene icial e ec was no obse ed when u he inc easing he Tc o 140 ºC, e ealing simila alues o σmax (1.8 MPa) and εmax (7.0%). As E dec eased o 42 MPa, no u he inc eases o he Tc we e p oposed. Simila endencies we e obse ed when inc easing he Tc o bo h Tm = 150 and 180 ºC and P = 800 ba (compa ing E2I2 o E2I4 and E2I6 o E2I8), wi h highe εmax bu lowe E and σmax. A highe empe a u es he e is mo e mobili y o he biopolyme chains because he glass ansi ion has ully de eloped so i is easie o hem o low and comple ely ill he mold ca i y, leading o mo e compac bioplas ics wi h enhanced mechanical p ope ies [30]. Indeed, he empe a- u e inc ease is bene icial only o some ex en because oo high empe a u es will accele a e c osslinking be o e illing he mold ca i y and e en plas icize e apo a ion dec eases he p ocessabili y o he ma e ial. Fo hese easons, inc eas- ing he empe a u e o he cylinde om 110 ºC o 140 ºC does no lead o clea imp o emen s when balancing he 3 pa ame e s unde s udy. The only imp o emen wi h Tc = 140 ºC is obse ed when using Tm = 180 ºC and P = 500 ba (E2I5 o E2I7) whe e he high empe a u e combined wi h he lowe P led o plas icize e apo a ion, esul ing in s i e bioplas ics wi h highe load capaci y bu educed lexibili y. When s udying he e ec o P, i is possible o obse e ha when he cylinde is se a 140 ºC, c osslinking begins o ake place wi hin he ma e ial be o e en e ing he mold and he p ocessabili y dec eases, making i mo e di icul o uni o mly ill he mold ca i y ega dless o he applied P. The e o e, no signi ican ad an ages a e obse ed be ween he sys ems p ocessed a 500 ba (E2I3 and E2I7) and hose p ocessed a 800 ba (E2I4 and E2I8). On he o he hand, when Tc = 110 ºC, a bene icial e ec o P can be obse ed bu only o high mold empe a u es, i.e., 180 ºC. Wi h good p ocessabili y, he aw ma e ial will low easily om he cyl- inde o he mold, whe e P will be a de e mining ac o when applying a linea model (lm), which also accoun ed o he in e ac ions o injec ion molding pa ame e s. The second s ep o he analysis en ailed he implemen- a ion o he esponse su ace echnique h ough he so - wa e Ma lab® e sion 2020a o iden i y he manu ac u ing pa ame e s ha maximize he mechanical p ope ies o he bioplas ic. Conside ing ha he ull ac o ial design was se only on wo le els, i.e., an uppe and a lowe one, a linea app oxima ion unc ion was used o desc ibe he esponse su ace. Based upon he esul s ob ained om in e en ial s a is ics also, some o he in e ac ions o he injec ion molding pa ame e s we e conside ed in he app oxima ion unc ions leading o he Eq. (1): Y(T c ,T m ,P)=a+b×T c +c×T m +d×P+e×T c ×P+ ×Tm×P+g×Tc×Tm×P (1) whe e Y is he mechanical p ope y unde conside a ion, Tc he cylinde empe a u e, Tm he molding empe a u e and P he injec ion p essu e. Resul s and Discussion Tensile Tes s and S a is ical Analysis Tensile p ope ies o he di e en s udied sys ems a e ga h- e ed in Table 2. A i s , he e ec o ex usion s ep numbe was in es iga ed (E1 and E2 sys ems o one pass o wo passes h ough he ex ude , espec i ely) and i was ound ha he longe esidence ime gi en by he second ex usion esul ed in imp o ed Young’s modulus and ensile s eng h wi hou any de imen al e ec upon elonga ion a b eak. In his way, unde he same injec ion molding condi ions, he samples submi ed o wo ex usion s eps e ealed a e age alues o E and σmax o 70 MPa and 1.1 MPa compa ed o he 57 MPa and 0.8 MPa exhibi ed by he sys em submi ed o only a single ex usion s ep, wi h an almos cons an elon- ga ion a b eak (4.0% o E2 and 3.9% o E1). The e o e, Table 2 Mechanical p ope ies (Young’s modulus (E), ensile s eng h (σmax) and s ain a b eak (εmax)) o he di e en biopolyme s Sys em E (MPa) σmax (MPa) εmax (%) E1 57 ± 4 0.8 ± 0.1 3.9 ± 0.6 E2 70 ± 4 1.1 ± 0.1 4.0 ± 0.2 E2I1 70 ± 4 1.6 ± 0.1 6.9 ± 0.6 E2I2 65 ± 2 1.5 ± 0.1 6.0 ± 0.3 E2I3 42 ± 6 1.8 ± 0.3 7.0 ± 2.0 E2I4 30 ± 7 1.6 ± 0.1 7.2 ± 0.9 E2I5 56 ± 5 1.2 ± 0.1 6.8 ± 0.8 E2I6 138 ± 18 2.5 ± 0.2 5.7 ± 0.6 E2I7 95 ± 8 1.9 ± 0.1 6.1 ± 0.3 E2I8 67 ± 1 1.9 ± 0.1 6.6 ± 0.5 1 3 516 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 op imiza ion o he injec ion molding p ocess depends on a complex balancing o phenomena and mechanisms. Fo example, bioplas ic low is helped by empe a u es highe han glass ansi ion, bu i is also hinde ed by excessi ely high empe a u es, p omo ing c osslinking and os e ing plas icize emo al be o e injec ion. O he wise, oid con- en mus be minimized and educed by be e mold illing bu hinde ed by plas icize e apo a ion, i.e., phenomena ha mus be balanced as a unc ion o he applied empe a u es. In e es ingly, nei he he p ocessing pa ame e s selec ed no hei in e ac ions ha e any e ec on he elonga ion a b eak. This can be likely asc ibed o he ashes inside he eeds ock whose chemical composi ion and mo phology a e no a ec ed by any o he injec ion molding pa ame e s and ac ing as s ess in ensi ie s always de e mine a b i le esponse o he bioplas ic. Based on he esul s ob ained, he su ace esponse analy- sis was used o op imize he manu ac u ing pa ame e s o maximize bo h ensile modulus and s eng h by applying a linea unc ion ha accoun ed o he e na y in e ac ion o he h ee pa ame e s and he bina y in e ac ion o P wi h he mold is se a 180 ºC (E2I5 and E2I6). A hese em- pe a u es, plas icize s e apo a e apidly, bu aided by high P, he ma e ial con inues o low and dis ibu e h oughou he ca i y, elimina ing possible de ec s in he inal piece and leading o highe E and σmax. Al hough his phenomenon can occu a 150 ºC (E2I1 and E2I2), his lowe empe a- u e leads o a lowe numbe o biopolyme ic in e ac ions and less plas icize e apo a ion. Thus, ega dless o he P, he e will be a lowe deg ee o compac ion du ing injec ion. Addi ionally, in bo h cases, he εmax dec eases as a conse- quence o he plas icize losses. The e ec o Tm, as happened wi h Tc and P, will be explained in e ms o he o he wo pa ame e s ha will ha e a di ec in luence. Thus, inc easing he mold empe a- u e om 150 °C o 180 °C a a lowe P (500 ba ) does no show a clea bene i in he mechanical p ope ies o bioplas ics due o he highe plas icize losses. Fo Tc = 110 °C, he e a e no imp o emen s in E o εmax, while σmax dec eases (E2I1 and E2I5). Fo Tc = 140 °C, al hough he e is a ce ain imp o emen in E, σmax emains unchanged, and εmax dec eases (E2I3 and E2I7). On he o he hand, he use o highe P (800 ba ) p o ides a much clea e end. An imp o emen in he s i ness and load-bea ing capaci y o he specimens (E and σmax) is obse ed, accompanied by a loss o duc ili y (εmax). This ep esen s a be e comp o- mise o p ope ies, especially well-balanced when using Tc = 110 °C (E2I2 and E2I6), esul ing in a sys em wi h he bes alues o E and σmax, wi h a sligh ly lowe εmax s ill close o hose o he o he sys ems. This is achie ed h ough a combina ion o an app op ia e empe a u e in he cylinde , su icien ly high o p ope low bu no oo high o ini ia e c osslinking, as well as a high Tm and P o allow p ope mold illing wi h good compac ion and empe a u e-induced he mo o ming [30]. All hese conclusions we e u he co obo a ed by in e - en ial s a is ics, whose esul s a e summa ized in Tables 3, 4 and 5. Bo h Tm and P display s ong s a is ical signi icance on bo h ensile s i ness and s eng h, as well as hei in e - ac ion. This is cohe en wi h he di e en deg ees o hea - induced p o ein and s a ch c osslinking achie ed by he bioplas ics depending on he mold empe a u e and on i s abili y o ill he mold as a unc ion o he applied P. On he con a y, Tc p o ed o be de e minan only o ensile modu- lus, while i s in e ac ion wi h P is undamen al o bo h s i - ness and s eng h. Indeed, he capabili y o he bioplas ic o low in o he mold does no depend only on he applied P, bu also on i s iscosi y, which is s ic ly co ela ed o he cylinde empe a u e, hus explaining he s ong impo ance o he in e ac ion o hese wo pa ame e s. Finally, he e na y in e ac ion be ween he h ee p o- cessing pa ame e s displays a high s a is ical signi icance o bo h ensile s i ness and s eng h, hus p o ing ha he Table 3 S a is ical signi icance o he e ec s o he injec ion molding pa ame e s and hei in e ac ions on bioplas ic Young’s modulus Pa ame e F alue P (> F) Tc12.12 0.003 Tm65.36 4.83·10−07 P 5.51 0.032 Tc × Tm1.31 0.268 Tc × P 39.71 1.05·10−05 Tm× P 16.58 8.87·10−04 Tc × Tm× P 15.24 0.001 Table 4 S a is ical signi icance o he e ec s o he injec ion molding pa ame e s and hei in e ac ions on bioplas ic ensile s eng h Pa ame e F alue P (> F) Tc1.90 0.186 Tm13.10 0.002 P 14.86 0.001 Tc × Tm0.36 0.557 Tc × P 28.78 6.32·10−05 Tm× P 38.41 1.28·10−05 Tc × Tm× P 17.79 6.52·10−04 Table 5 S a is ical signi icance o he e ec s o he injec ion molding pa ame e s and hei in e ac ions on bioplas ic elonga ion a b eak Pa ame e F alue P (> F) Tc2.33 0.15 Tm2.79 0.11 P 1.69 0.21 Tc × Tm1.42 0.25 Tc × P 1.46 0.24 Tm× P 0.33 0.57 Tc × Tm× P 0.45 0.50 1 3 517 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 imp o ing ma e ial lowabili y; a he same ime, he highe he cylinde empe a u e, he highe he p og essi e c oss- linking o he bioplas ics, which ac s in he opposi e di ec- ion in e ms o iscosi y. In ligh o his, a highe injec ion P ensu es a be e lowabili y o he ma e ial al eady a lowe Tc, hus allowing he p e en ion o bioplas ic c osslinking in he cylinde , while a lowe P, he highe iscosi y de i ing om he highe p oximi y o he glass ansi ion empe a- u e makes he highe Tc a p e e ed choice. In his way, he highes P and he lowes cylinde empe a u e a e he bes choices among he wo a o emen ioned con igu a ions. Dynamic Mechanical The mal Analysis (DMA) Figu e 3 depic s he equency sweep es s conduc ed on he E1 and E2 sys ems ( esul ing om changing he num- be o passes h ough he ex ude ). I is wo h men ioning ha he es o he sys ems displayed simila alues o he bo h Tm and Tc. The esul s ob ained a e shown in Figs. 1 and 2 o ensile modulus and s eng h, espec i ely. The main ou come is ha a P o 800 ba , a cylinde empe a u e o 110 °C and a mold empe a u e o 180 °C allow o he maximum ensile s i ness and s eng h, bu some u he conclusions can be d awn. To begin wi h, he bes mechanical pe o mance is achie ed nea ly always o he highes alue o mold em- pe a u e, i.e., 180 °C, ega dless o P and Tc and his can be likely asc ibed o he highe c osslinking deg ee induced in he bioplas ic [31]. Ano he impo an ou come is ela ed o he in e ac ion o wo pa ame e s, namely, he injec ion P and he cylinde empe a u e. When wo king wi h highe P, he bes esul s a e achie ed wi h he lowes cylinde empe a u e, while a highe Tc is necessa y when wo king wi h lowe P. This can likely be asc ibed o wo compe ing phenomena. The highe he cylinde empe a u e, he a - he he bioplas ic om i s glass ansi ion empe a u e, hus Fig. 1 Su aces esponse o ensile modulus 1 3 518 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 The iscoelas ic moduli as a unc ion o empe a u e o he sys ems ob ained o di e en injec ion molding condi- ions a e p esen ed in Fig. 4A. In his igu e, only he sys- ems whe e he injec ion condi ions (Tc, Tm and P) we e modi ied a e ep esen ed, as he iscoelas ic moduli o he E1 and E2 sys ems ollowed he same end as he es o he sys ems. Thus, hei beha io wi h empe a u e is ep e- sen ed by hese sys ems, while he change induced by using wo ex usion s eps ins ead o one is ha discussed in Fig. 3, wi h he E2 sys em exhibi ing sligh ly highe E′ and E″ han he E1 sys em. Once again, i is possible o obse e ha E′ is abo e E″ o all he s udied samples, ega dless o he empe a u e, implying ha he bioplas ics ha e a p edominan ly elas ic cha ac e (Fig. 4A). In his s udy, all sys ems exhibi simi- la beha io , wi h hei moduli emaining closely aligned and e en o e laid h oughou he en i e empe a u e ange, equency ange s udied, indica ing no disce nible di e - ences in iscoelas ic moduli (E′ and E″) o he di e en injec ion condi ions e alua ed. The e o e, E1 and E2 sys- ems a e chosen as ep esen a i es o elucida e he e ec o a second ex usion s ep on he bioplas ics de eloped. Fi s ly, all sys ems exhibi a p edominan elas ic cha - ac e , wi h highe s o age (E′) han loss modulus (E″), a ypical beha io o polyme ic ma e ials [32]. Fu he mo e, bo h iscoelas ic moduli inc ease wi h inc easing equency, showing a ce ain dependency on his pa ame e . Al hough he ensile p ope ies o he bioplas ics we e no ably al e ed by he second ex usion s ep, he e is only a small enhance- men o he heological p ope ies. This is e iden om he sligh ly highe iscoelas ic moduli o he E2 sys em com- pa ed o he E1 one. Such enhancemen could be a ibu ed o he longe esidence ime in he ex ude du ing he sec- ond s ep, acili a ing s a ch gela iniza ion and p omo ing inc eased p o ein chain in e ac ions [28, 29]. Fig. 2 Su aces esponse o ensile s eng h 1 3 519 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 he mose ing po en ial (i.e., he e is no eco e y o he is- coelas ic alues a ele a ed empe a u es), indica ing, on he one hand, ha i is no possible o achie e u he enhance- men in heological p ope ies wi h highe injec ion mold- ing empe a u es and, on he o he hand, ha he bioplas ics de eloped beha e as he mose s [34]. The abili y o hese ma e ials o main ain hei iscoelas ic moduli a ele a ed empe a u es, coupled wi h hei high E′ and E″ alues, sug- ges s po en ial sui abili y o subs i u ing con en ional poly- me s in speci ic applica ions [35]. suppo ing he s a emen ha signi ican di e ences among samples canno be iden i ied. In e ms o he e olu ion o he iscoelas ic moduli wi h empe a u e, i is no iceable ha he iscoelas ic moduli dec ease in all cases as he empe a u e ises om − 10 ºC o app oxima ely 100–120 ºC due o inc eased polyme chain mobili y p omo ed by ce ain s uc u al elaxa ion [33]. Subsequen ly, o u he empe a u e inc ease, he iscoelas ic moduli emain s able up o 160 ºC, eaching a pla eau. In his sense, none o he sys ems exhibi ed u he Fig. 4 (A) Viscoelas ic moduli and (B) loss angen a ia ions du ing he empe a u e amp es s be ween − 10 and 160 ºC a 1 Hz o he E2I1, E2I2, E2I3, E2I4, E2I5, E2I6, E2I7 and E2I8 sys ems Fig. 3 F equency sweep es s pe - o med be ween 0.5 and 20 Hz a oom empe a u e o he E1 and E2 sys ems 1 3 520 Jou nal o Polyme s and he En i onmen (2025) 33:512–527 55. Xu YX, Kim KM, Hanna MA, Nag D (2005) Chi osan–s a ch composi e ilm: p epa a ion and cha ac e iza ion. Ind C ops P od 21:185–192. h ps://doi.o g/10.1016/J.INDCROP.2004.03.002 56. Liu H, Adhika i R, Guo Q, Adhika i B (2013) P epa a ion and cha ac e iza ion o glyce ol plas icized (high-amylose) s a ch–chi osan ilms. J Food Eng 116:588–597. h ps://doi. o g/10.1016/J.JFOODENG.2012.12.037 57. Be i S, Jagus RJ, Flo es SK (2021) E ec o Rice B an Addi- ion on Physical p ope ies o An imic obial Biocomposi e ilms based on S a ch. Food Biop oc Tech 14:1700–1711. h ps://doi. o g/10.1007/S11947-021-02669-0/FIGURES/5 Publishe ’s No e Sp inge Na u e emains neu al wi h ega d o ju is- dic ional claims in published maps and ins i u ional a ilia ions. 51. Ceylan Z, Unal Sengo GF, Yilmaz MT (2018) Nanoencapsula- ion o liquid smoke/ hymol combina ion in chi osan nano ibe s o delay mic obiological spoilage o sea bass (Dicen a chus lab ax) ille s. J Food Eng 229:43–49. h ps://doi.o g/10.1016/J. JFOODENG.2017.11.038 52. E ü k B, Me al R (2019) The impac o s abiliza ion on unc- ional, molecula and he mal p ope ies o ice b an. J Ce eal Sci 88:71–78. h ps://doi.o g/10.1016/J.JCS.2019.05.011 53. Yin YJ, Yao KD, Cheng GX, Ma JB (1999) P ope ies o polyelec- oly e complex ilms o chi osan and gela in. Polym In 48:429– 432. h ps://doi.o g/10.1002/(SICI)1097-0126(199906)48:6 54. Meenakshi P, Noo jahan SE, Rajini R e al (2002) Mechanical and mic os uc u e s udies on he modi ica ion o CA ilm by blend- ing wi h PS. Bull Ma e Sci 25:25–29. h ps://doi.o g/10.1007/ BF02704590/METRICS 1 3 527