Compatibility and degradation of low density polyethylene/poly(lactic acid) blends

Abstract

Blends off LDPE and PLA with two molecular weights of LDPEs (125 kg/mol and 240 kg/mol) were prepared by a twin screw extruder with PLA content from 5-20%. LLDPE-g-MA was used as a coupling agent because of natural incompatibilization of polyolefin and polyester. The blend morphology was investigated by SEM from which a better distribution of the PLA dispersed phase was found in LDPE (240 kg/mol) blends. The effect of LLDPE-g-MA compatibilizer was observed in both types of LDPE as that the size distributions of dispersed PLA were reduced. MFI of blends was decreased and showed poor interfacial adhesion between the two phases. DSC thermograms could not detect a significant effect of the compatibilizer LLDPE-g-MA. Tensile and Young’s modulus of the compatibilized blends were improved but Ized impact and elongation at break were dropped. They were improved by the LLDPE-g-MA addition. The blends of LDPE with 240 kg/mol degraded faster in Proteinase K than those of 125 kg/mol, due to the better and denser distribution of PLA in the LDPE matrix leading to a better enzymatic degradation. Upon adding the compatibilizer, the enzymatic degradation efficiency was reduced especially in the blends with a better PLA dispersion. After the enzymatic degradation pores were widely distributed on the surface of the films. The blends were destroyed at the PLA dispersed phase.