Tensile Properties of Films from Low-Temperature GR-S Latex
Abstract Studies were made of the influence of a number of polymerization variables on the tensile strength of vulcanized evaporated films from low-temperature high-solids GR-S latexes. Previous reports of film tensiles on the order of 3000 pounds per square inch for latexes of 70/30 butadiene-styrene charge ratio were confirmed. The levels of accelerator necessary for optimum vulcanized properties were found to be considerably lower than those normally used, particularly for latexes shortstopped with dithiocarbamate salts. Microscopic coagulum found in some latex samples had a pronounced effect in decreasing film tensile of vulcanizates. Cured films from latexes emulsified with mixtures of fatty acid and rosin soap possessed considerably better tensile strengths than those from latexes using all fatty acid soap emulsification. Wide variations on Mooney viscosity had relatively little effect on ultimate film tensiles. Incorporation of small amounts of lignin into the latex as the ammonium or sodium salt decreased cure rates of films and aided in giving more reproducible tensile results. Both lignin and the sodium salt of cresyl monosulfide improved the aging characteristics of films.