Low Glass Transition Temperature (Tg) Rubber Latex Film Formation Studied by Atomic Force Microscopy

Abstract

Latex with very low glass transition temperature (Tg) polymers forms a continuous film on drying. The physical and mechanical properties of the film are dependent on the extent the latex particles are able to coalesce and fuse into each other. Any hindrance to the film formation process would result in a poorly formed film and a drop in performance. The film formation process of natural rubber (Tg ∼ −65 °C) latexes and synthetic latexes with low Tg are monitored as a function of time using atomic force microscopy (AFM). The influence of the leaching method of the film, the presence of additives (some added after preparation) and nonrubber materials [specific for natural rubber (NR) latex only], and gel content on film morphology and flattening of the particles in the film is studied. The influence of the leaching procedure on the effectiveness of nonrubber removal from NR latex films and their effect on film formation is highlighted. The effects of nonrubbers and high gel content of NR latex in slowing down the NR film formation is discussed and contrasted with the synthetic polyisoprene and chloroprene latexes. The change of the surface mean roughness, Ra, with time provides a convenient means of comparing the rate of flattening of the polydisperse particles in these films.