Preliminary study on polyisoprene-modified natural rubber via in-situ polymerization of isoprene in deproteinized natural rubber latex

Abstract

Modification of natural rubber (NR) using vinyl monomers, particularly styrene, has been widely studied. Compared to unmodified NR, the resulting graft copolymer is stronger and stiffer but sacrificed on NR elasticity. This is because of the higher glass transition temperature (Tg) of styrene as compared to NR. Therefore, the modification of NR via isoprene monomer was investigated as isoprene will have the same Tg as NR. The focus of this research is to study the effect of in-situ polymerization of isoprene in deproteinized natural rubber (DPNR) latex with unmodified DPNR latex. The success of the modification was evidenced by the degree of conversion and Fourier Transform Infrared (FTIR). The average degree conversion of polyisoprene modified natural rubber (I-DPNR) obtained was 81.42%. Comparing the FTIR of I-DPNR and DPNR, the presence of trans-1,4 polyisoprene peaks and lower transmission of cis-1,4 polyisoprene was observed. The dynamic mechanical analysis (DMA) showed that I-DPNR and DPNR has a similar Tg. Stress–strain curves obtained from the tensile test of both the unvulcanized and vulcanized rubbers revealed that I-DPNR is more elastic as compared to the DPNR. These results obtained are consistent with the hypothesis that modification of NR with the isoprene monomer can result in similar properties as the DPNR. Higher elasticity reported for I-DPNR is a result of its higher entanglement as compared to unmodified NR.