Toughness improvement of polylactic acid blown films by adding carboxylated epoxidised natural rubber

Abstract

Polylactic acid (PLA) is one of the most interesting biodegradable polymers and commercially-produced thermoplastic that is derived from renewable resources. However, the limitation of PLA is the stiffness and brittleness. In this research, the authors had tried to improve the toughness of PLA blown film by adding carboxylated epoxidised natural rubber (ENR-COOH) as toughening agent. Epoxidised natural rubber (ENR) samples of various epoxidation level were synthesized and modified with thioglycolic acid (TGA) to yield ENR-COOH with 1, 4, 8 and 37% conversion of its initial NR, respectively, confirmed by Fourier Transforms Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (1H NMR). Then, blown films of ENRs-COOH/PLA compared with neat PLA film were studied to find the optimum type and rubber content. The results from Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) showed that thermal and thermomechanical properties dropped with increasing of polarity of ENRs-COOH. Compared with neat PLA film, 3 wt% ENR6-COOH/PLA films exhibited the highest elongation at break (which was approximately 9.98 times in Machine Direction (MD). Later, ENR6-COOH was selected to blend with PLA and 0.5 wt% magnesium stearate (MgSt) by varying rubber content at 1, 3, 4 and 5 wt%. The results showed that 4 wt% ENR6-COOH/PLA_MgSt film provided the highest elongation at break by increasing 35 times in MD compared with PLA_MgSt film.