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Prevulcanization of natural rubber latex was investigated as a function of maturation duration. The morphology of the film formed from these latexes was monitored using atomic force microscopy (AFM) as the film aged. The morphology is correlated with the cross-link density of the rubber molecules. Film formed from prevulcanized latex was further postvulcanized, and their film morphologies were compared. Inhomogeneous latex particles cross-linked on the surface with an unvulcanized core were obtained during prevulcanization. This gives rise to the characteristic indentation structure when these hard shell−soft core latex particles coalesce to form film. Basically the prevulcanization mechanism is controlled by the relative rates of the diffusion of vulcanizing reagents and the cross-linking reaction within the latex particles. It is clear that the partially vulcanized particles have a profound influence on the film-forming property of the prevulcanized latex.

Summary: Three different methods of deproteinization, i.e. saponification, surfactant washing and enzymatic treatment were employed to unravel the effect of deproteinized on the properties of natural rubber (NR) latex. The cleavage of proteins in NR latex was found to proceed with concomitant formation of low molecular weight polypeptides. This results in a lowering in gel formation of the enzyme‐treated latex, indicating modification of the remaining proteins at the rubber chain‐end. Washing NR latex with surfactant would efficiently reduce and remove proteins from NR latex particles through denaturation and transferring them to the serum phase. The relatively stable gel formed during storage of surfactant‐washed NR latex is an indication of the absence of branch formation of proteins at the rubber molecule terminal. Saponification by strong alkali would hydrolyze the proteins and phospholipids adsorbed on the latex particle surface. The reason of the significantly higher gel formed in saponified NR latex is still not clear. The present study shows that deproteinization treatments result in modification of the proteins at the surface of NR latex particles and also those freely‐suspended in the serum. The cleavage or the denaturation of the rubber proteins during purification by washing has a profound effect on the properties of the deproteinized NR latex upon storage, in particular the thermal oxidative aging properties of the rubber obtained.

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