Recent advances in structural characterization of natural rubber

Abstract

Structural characterization of rubber from Hevea brasiliensis (NR) has been carried out to elucidate the biosynthesis mechanism of rubber molecule as well as to find the relationship between physical properties characteristic of NR and its structure. Recent advances of structural studies have provided a series of new information on the structure of long-chain branching based on the result of selective decomposition of branch-points by chemical and enzymatic treatments as well as physical treatment such as polar solvent treatments and washing of NR latex by centrifugation in the presence of a surfactant. The measurement of the resulting rubber with NMR, FTIR, SEC and dilute solution viscosity provided confirming evidence that the initiating terminal (ω-terminal) with an unidentified functional group and phosphate terminal (α-terminal) form branch-points by hydrogen bond, ionic bond or micelle formation of phospholipids linked to both terminal groups. Based on these results, the origin of green properties characteristic of NR has been explained and a new mechanism of storage hardening has been proposed. The purification method by saponification of NR latex developed for the structural characterization has been applied to produce purified NR latex free from Type I allergic reaction. Instantaneous coagulation of saponified latex by the use of a flocculant and formic acid has provided solid saponified NR having good green and cured rubber properties.