Plasticization of poly(lactide) with poly(ethylene glycol): Low weight plasticizer vs triblock copolymers. Effect on free volume and barrier properties

Abstract

In order to make poly(lactide) (PLA) suitable for food packaging applications, its toughness must be improved. In this work, the plasticization effectiveness of a low-molecular-weight plasticizer and a triblock copolymer are analyzed. For this purpose, PLA is blended with poly(ethylene glycol) (PEG) and poly(lactide-ethylene glycol-lactide) (LA-EG-LA) triblock copolymer. The obtained results show that copolymers are more effective, reducing the glass transition temperature of PLA. Although PLA/PEG blends have been widely studied in the literature, the barrier character has not been analyzed, which is of paramount importance for packaging applications. Therefore, the permeability to carbon dioxide, oxygen, and water vapor of PLA/PEG blends has been characterized observing an increase with the incorporation of PEG, which is the expected behavior. However, the incorporation of LA-EG-LA copolymers leads to permeability values that are slightly higher, similar, or even lower than PLA. Furthermore, the free volume of the samples has been analyzed in order to gain a deeper insight on the factors affecting the transport properties. Overall, this works aims to provide a better understanding towards the design of biodegradable packaging with improved properties that could be also extended to other biodegradable polymers.PLA blends containing PEG have been widely analyzed in the literature. [9][10][11][12][13][14][15] Younes and Cohn 9 studied PLA blends containing PEG of different molecular weights (1500-35 000 g/mol range) at different composition observing a microphase separation. Hu et al. observed that PLA containing more than 15% PEG were not stable over time and phase separation occurs forming PLA rich and PEG rich domains. [10][11][12] The phase separation of PLA and PEG has been Additional Supporting Information may be found in the online version of this article.

Polilaktida plastifikatua elikagaien ontziratzerako: plastifikatzailearen pisu molekularraren eragina bolumen aske eta hesi-ezaugarrietan

“…Aipagarria da % 10 edo % 15 PEG daukaten nahaste batzuek bi fusio tontor erakusten dituztela: PEGari dagokiona eta PLAri dagokiona. Beraz, PEG kantitate batetik aurrera, kasu honetan % 10 PEG, sistema nahastezina da, literaturan frogatu den bezala [12,15]. Kristalinitate-mailari dagokionez, berriz, aldaketak txikiak dira, baina aipatzekoa da PEG 1500 plastifikatzaileak PLAren kristalizazioa areagotzen duela.…”

“…Lan horietan, oro har, propietate termikoak eta ezaugarri mekanikoak xeheki ikertu dira. Hala ere, material horiek ontziratzean erabili nahi badira haien hesi-ezaugarriak aztertzea premiazkoa da, baina, zoritxarrez, mota horretako lanak urriak dira bibliografian [14,15]. Hori kontuan izanda, PLA/plastifikatzaile sistemen bolumen askeak eta garraio-ezaugarriak xeheki aztertu dira gure taldean [14,15].…”

“…Hala ere, material horiek ontziratzean erabili nahi badira haien hesi-ezaugarriak aztertzea premiazkoa da, baina, zoritxarrez, mota horretako lanak urriak dira bibliografian [14,15]. Hori kontuan izanda, PLA/plastifikatzaile sistemen bolumen askeak eta garraio-ezaugarriak xeheki aztertu dira gure taldean [14,15]. Polilaktida/ tributil zitratoaren kasuan, plastifikatzaile horren gehikuntzak aldaketa txikiak eragiten ditu beira-trantsizio tenperaturan.…”

“…Bestalde, literaturan polietilenglikolak (PEG 1500) eta laktida-polietilenglikol-laktida blokezko kopolimeroek PLA plastifikatzeko daukaten eraginkortasuna ere aztertu da [15]. Beira-trantsizio tenperatura nabarmen murrizten da polietilenglikola gehitzean.…”

“…Hesi-ezaugarriei dagokienez plastifikatzailearen gehikuntzak ez du oxigenoaren eta karbono dioxidoaren iragazkortasuna nabarmen areagotzen; urarena, ordea, bai. Azkenik, kopolimeroen kasuan laktida blokeen presentziak polimeroarekin bateragarritasun hobea izatea eragiten du, eta pisu molekular baxuko plastifikatzailearekin baino emaitza hobeak lortzen dira, iragazkortasuna baxuagoa baita [15].…”