Morphology of peroxide-prevulcanised natural rubber latex: effect of reaction time and deproteinisation

A non-uniform mesh structure, i.e. a dense network near the surface of peroxide-prevulcanised natural rubber latex particles, was observed under transmission electron microscopy. In the initial period of prevulcanisation, the swelling ratio of the latex sheet decreased with longer reaction time while an increase in crosslink density of rubber particles containing polystyrene, prepared using the phase transfer/bulk polymerisation process, was noticed. The modulus of the rubber sheet increased up to maximum crosslinking and thereafter decreased. After removal of proteins from the latex membrane layer, derived from protein-lipid originally existing at the rubber particle surface, could not be detected. The absence of proteins, which act as free radical scavengers, resulted in a rapid diffusion of alkoxy radicals into the rubber phase of deproteinised latex and, therefore, a uniform crosslink distribution inside each particle was obtained.     

Morphology of natural rubber latex particles prevulcanised by sulphur and peroxide systems

Transmission electron microscopy provided direct evidence of the morphology of sulphur- and peroxide-prevulcanised natural rubber latex particles. A mesh structure of all cross-linked rubber particles containing polystyrene, prepared using the phase-transfer/bulk polymerisation process, was found. Each peroxide-prevulcanised particle had a nonuniform network structure, whereas the rubber network in sulphur-prevulcanised particles was homogeneous, irrespective of size. The effects of maturation and sodium dodecyl sulphate on the swelling ratio of the sulphur-prevulcanised latex film were investigated.