Additional studies of morphological changes in latex films

Abstract

It was shown earlier that a further gradual coalescence and concurrent exudation of incompatible emulsifiers occurs upon aging in the surface of dry, transparent, and continuous films of styrene-butadiene copolymers. These processes are now shown to occur at about the same rate in the film-substrate interface and the interior of the film. The rate at which the emulsifier exudations appear is correlated with the rate of the coalescence. The further gradual coalescence is accelerated in oxygen and slowed in nitrogen; probably it involves oxidative softening of the styrene-butadiene copolymer. Other latex types which show further gradual coalescence are ethylacrylate-methylmethacrylate and vinylidene chloride-vinyl chloride-ethyl acrylate copolymers, as well as natural rubber. Polyvinyl acetate latexes do not undergo further gradual coalescence, probably because of a polyvinyl alcohol layer formed by surface hydrolysis of the particles.