COMPATIBILIZATION OF POLY(LACTIC ACID)/NATURAL RUBBER BLENDS USING NATURAL RUBBER-GRAFT-POLY(LACTIC ACID)

Abstract

Poly(lactic acid) (PLA) or polylactide is bioplastics produced from agricultural products, which are renewed and also bio-degraded by enzyme. PLA has high strength, but it has the brittleness and low impact strength, which limit its applications. Thus, several previous research works studied the properties improvement of PLA by blending with elastomers such as natural rubber (NR) with excellent elastic property to reduce PLA’s brittleness and to increase its impact strength. However, the direct blending of PLA, which is the polyester and NR with low polarity leads the incompatible blend resulting in its poor mechanical properties. Thus, the aim of this research was to use the NR grafted with PLA (NR-g-PLA, NR-PLA) as the compatibilizer for PLA/NR blends. There were 2 steps to prepare NR-PLA compatibilizer. Firstly, NR was functionalized by maleic anhydride (MAH) (NR-MAH) to increase the polarity of NR. Then, NR-MAH was grafted with PLA via esterification. The effects of grafting parameters in the esterification step on the %grafting PLA were investigated. The result showed that the increase in the MAH contents (5-20 phr) led the higher %grafted PLA content in NR-MAH from 27.5 to 46.4 wt%. The suitable condition to increase the %grafted PLA was 1/1 (w/w) NR-MAH/PLA and 0.05 M 4-dimethylaminopyridine (DMAP) at 140 oC for 16 h. Moreover, the addition of 5 wt% NR-PLA (%grafted PLA = 2.66) on the PLA/NR blends (80/20 (w/w)) increased the Izod impact strength to 62.7 J/m higher than neat PLA (22.8 J/m). The compatibility of PLA/NR blends with NR-PLA compatibilizer was also improved by morphology and thermal properties. For the bio-degradation of the blends via hydrolysis and enzyme proteinase K, it was shown that the degradation rate of PLA/NR blends with/without addition of NR-PLA compatibilizer was slightly decreased from the neat PLA.