Synthesis and characteristics of α-carboxyl, ω-hydroxyl natural rubber toughened poly(lactic acid)

Abstract

This work presented the synthesis of α-carboxyl, ω-hydroxyl natural rubber (CHNR) for use as an alternative toughening agent for poly(lactic acid) (PLA). The proton nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FTIR) analyses verified the chemical structure of CHNR consisting of the hydroxyl and carboxyl end groups. The molecular weights of CHNR were set from 5000 to 15 000 g·mol–1 which were determined by gel permeation chromatography (GPC) and1H-NMR. The PLA and CHNR were prepared by reactive blending using a twin-screw extruder. It was found that the reaction between PLA and CHNR proceeded through transesterification without a catalyst. The formation of copolymer (PLA-co-CHNR) at the interface of PLA and CHNR increased the interfacial adhesion between the two phases. Differential scanning calorimetry (DSC) analysis revealed that CHNR was more compatible with PLA than natural rubber (NR). The compatibilization affected the blend morphology by reducing the interfacial tension. It resulted in a reduction of rubber particle size. The CHNR with a molecular weight of 5000 g·mol–1 showed the greatest improvement in the toughness and ductility of PLA.