Effect of non-rubber components on basic characteristics and physical properties on natural rubber form hevea brasiliensis

The effect of climate on the properties of natural rubber (NR) latex from the Hevea rubber tree was investigated by collecting fresh NR latex frequently over a period of two years. A high rubber content of NR latex exploiting in the cold season was observed, whereas a dilution effect was found in rainy season. There was a considerably higher amount of non-rubber materials in the rainy season. The effect of metal ions on prevulcanization of concentrated NR latex was characterized by extraadding metal ions into the concentrated NR latex prior to the vulcanization process. The presence of metal ions caused a delay in the maturation time required to obtain a desirable prevulcanized level. The metal ions strongly affected the stability of concentrated NR latex by means of the divalent effect on the formation of branching and gel, involving the adsorption on NR particles leading to the reduction of latex stability. The structure of branch-points in NR was analyzed by physical decomposition of branch-points using surfactant washing by high-speed centrifugation of NR latex. The diminution of nitrogen content is consistent with the disintegration of gel fraction. This suggests that the branching formation at w-terminal derives from proteins via supramolecular bond. Based on the result of the evaluation of the performance of deproteinized reaction by SDS-PAGE, enzymatic deproteinization was proposed to cleave the proteins so that the retained proteins would be oligopeptides or short-chain proteins. Surfactant washing with high-speed centrifugation denatured the proteins without degradation, whereas saponification reaction decomposed both proteins and fatty acids, although NaOH treatment of latex was not identified. Gel formation in the storage deproteinized NR latex could not be as fully accomplished as in the normal NR due to the lack of proteins leading to the deterioration in physical properties. Accelerated storage hardening test disclosed that both residual proteins and fatty acids play a role in the formation of gel fractions including the change of physical properties in the deproteinized NR. Proteins and lipids on surface of NR particle were characterized in nano-scale by Atomic Force Microscopy (AFM) and Confocal fluorescence Microscopy. Different phase contrasts from the proteins and lipids monolayer on NR particle were discovered. The fluorescence technique provided evidence showing that proteins and lipids are tenaciously bound at the exterior layer of NR particles as a core-shell, in which lipid materials were disclosed to be amine functionalized molecules such as phosphatidyl choline and phosphatidyl ethanolamine. The film formation of NR was unveiled to reach the inter-diffusion step by spontaneous fragmentation of the protein-lipid membrane leading to the formation of a homogenous matrix of NR, which particularly corresponds to the increase of Young's modulus of NR surface measured by nanoindentation with AFM probe.