The development of poly(lactic acid) packaging films with natural rubber

Abstract

The main objective of this study is to improve toughness of poly(lactic acid) (PLA) blown films with natural rubber (NR). PLA is high in strength and modulus (62 MPa and 3.1 GPa, respectively); however, it exhibits poor toughness (elongation at break 3.3%) while NR is elastic and tough. In this work, NR, NR-Powder and NR-Commercial with various rubber contents (0-7 wt%) were blended with PLA. Crystallization of the PLA component, phase morphology, mechanical properties, and toughening mechanism of the blends were investigated. DSC showed that the obtained blends were immiscible. The NR component might accelerate the crystallization rate of PLA but had little effect on its final degree of crystallinity. With the increase in NR content (3-5 wt%), the blend showed the decrease of tensile strength and Young’s modulus. On the contrary, elongation at break, impact strength and tensile toughness were dramatically increased. DMA results exhibited that storage modulus and glass transition temperature of PLA did not significantly change after adding NR. Morphology of PLA and PLA/NR, examined by SEM, showed voids due to debonding of NR domains from PLA and induced large plastic deformation in PLA matrix ligaments. With the addition of NR, the failure mode changed from brittle fracture of the neat PLA to ductile fracture of the blend as demonstrated by tensile test and SEM micrographs. In addition, the obtained results indicated that NR-Powder and NR-Commercial did not improve the toughness of PLA. The oxygen permeation of PLA blended with NR and NR-Commercial increased with increasing NR contents. While the water vapor permeation decreased when ≤ 3 wt% NR were used. At > 3 wt%, the water vapor permeation increased due to large free volume of rubber within PLA matrix.