Structure-Property relationships in natural rubber representing several clonal varieties of Hevea Brasiliensis

In this study, the relationships between the structure of unvulcanized rubber and vulcanizate properties were investigated for the three natural rubber clones: RRIT251, PB235, and RRIM600. The highest tensile properties of rubber vulcanizates were achieved from the PB235 clone whereas the RRIM600 showed the lowest. The PB235 contained the largest average molecular weight (Mw) with the narrowest molecular mass distribution (MWD), whereas the least Mw was for RRIM600 with the broadest MWD. The highest protein contents were noticed in RRIM600 where the highest gel formation was found. In contrast, the PB235 showed the smallest amount of proteins and gel contents. Based on this finding, the results clearly suggested that the Mw represented as a key factor controlling the mechanical properties of vulcanizates. This was because the higher average Mw provide the greater active sites available for crosslinking reaction, while the protein content governed the gel formation in the unvulcanized rubber.