Surface morphology of prevulcanized natural rubber latex films by atomic force microscopy: New insight into the prevulcanization mechanism

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.