Flexible and Tough Poly(lactic acid) Films for Packaging Applications: Property and Processability Improvement by Effective Reactive Blending

Abstract

This study demonstrates a practical means to overcome inherent brittleness problem of poly(lactic acid) (PLA) and make PLA feasible as packaging material. PLA with suitable processability is utterly required for package manufacturers, where flexible, tough PLA film is essential for packers and end users. Highly flexible PLA films with 60-fold increase in elongation at break (Eb) over that of the neat PLA were successfully produced by integrating effective reactive blending and economical film blowing process. The ‘two-step’ blending was used to prepare PLA compound; poly(butylene adipate-co-terephthalate) (PBAT – another biodegradable polymer) was first blended with 0.5–1% chain extender (epoxy-functionalized styrene acrylic copolymer) (ESA), followed by subsequent blending with PLA in twin-screw extruder. Blown films of reactive blend of PLA/PBAT/ESA (80/20/1) showed impressively high Eb of 250% versus a very low Eb of 4% for the neat PLA. Resulting blown films still possessed high modulus of 2 GPa, yield stress of 50–60 MPa and good toughness of ~100 MPa. Significant enhancement in the film's ductility was attributed to homogeneous blend with developed fine strand-like structure as a result of effective in situ compatibilization and good interfacial adhesion between the PLA and PBAT. PLA/PBAT/ESA blend also offered improved processability. Resulting films had acceptable haze of ~10% for common packaging, and clearer film close to PLA (≤2%) could be obtained by designing PLA skin layers in multilayer structure. Films of PLA/PBAT/1%ESA exhibit potential as packaging material; their mechanical and optical properties are comparable with or even exceed some existing films used in the market. Copyright © 2015 John Wiley & Sons, Ltd.