Oxygen barrier films of scCO2-assisted thermoplastic starch/poly (vinyl alcohol) blends.

Renewable thermoplastic starch (TPS) was modified by poly (vinyl alcohol) (PVA) with varying degrees of polymerization (DPs) or scCO2-assisted processing to prepare TPSxPVAyz or scCO2TPSxPVAyz fully biodegradable blends. The TPSxPVAyz (or scCO2TPSxPVAyz) films showed the smallest free volume characteristics and oxygen transmission rates (OTRs), as their PVA loadings approached an optimum value. The smallest free volume characteristics and OTRs evaluated for each optimal TPSxPVAyz (or scCO2TPSxPVAyz) films reduced noticeably as their DPs reduced from 2400 to 300. Considerably smaller OTRs and free volume characteristics were acquired for scCO2TPSxPVAyz films than those of corresponding TPSxPVAyz films prepared without the assistance of scCO2. An essential result is that the OTR of the optimal scCO2TPSxPVAyz film with a moisture content of 4wt% was merely 4.6 cm3/m2∙day∙atm. This OTR is as good as that of the polyvinylidene chloride oxygen barrier packaging. Dynamic mechanical relaxations and WAXD characterizations revealed that TPS and PVA are miscible, as PVA loadings were ≤ the optimum values. The enhanced oxygen barrier resistance and reduced free volume characteristics for optimal TPSxPVAyz and scCO2TPSxPVAyz films are partly ascribed to the strengthened molecular interactions between O–H groups of TPS and PVA, as they were processed with the assistance of scCO2, optimum PVA loadings or diminished DPs. [ABSTRACT FROM AUTHOR]