Preparation of Dried Latex Films

Abstract

Abstract Various technical applications of latex call for the formation of a latex film and its drying by evaporation of the water in which the rubber is dispersed. The same problem is encountered also in the preparation of dried latex films, both uncompounded and compounded, for film testing for tensile, elongation, and other properties. Very frequently the preparation of such films is complicated by the development of surface cracks and ridges in the drying films, which mar the appearance of the films, detract from their strength, and make testing difficult and uncertain. These imperfections in the films generally arise from the formation of impervious surface skins on the drying latex. Such impervious skins lead to shrinkage and subsequent cracking of the films on the one hand, and to bubble formation on the other. The result is that the preparation of dried latex films by this method becomes a very slow process, which yields as a rule films of inferior appearance and quality. It was found in this laboratory that many of the difficulties encountered in the preparation of latex films by evaporation can be overcome by appropriate control of humidity in the initial drying stages, and the use of an agent which prevents formation of the impervious surface skins on the drying latex. The agent found to be most suitable with alkaline latexes for the latter purpose is carbon dioxide gas. By utilizing moisture and carbon dioxide in a definite technique, films can be prepared from various latexes which are smooth and uniform in thickness and possess improved appearance and properties. The purpose of this paper is to describe the technique developed for preparation of dried latex films by casting, and to give some results for tensile and elongation obtained on GR-S, Hycar, Neoprene, and natural latexes.