The Influence of High-Activity Silica upon the Thermal Aging of Latex Vulcanizates Cured by Thiuram Compounds

Abstract

Once it had been shown that high-activity silica, even in comparatively small additions, improves the aging resistance of latex vulcanizates by many times, and that also an effect similar to that of a coactivator is set up by the interaction of high-activity silica with age resistors, ultra-accelerators and atmospheric oxygen in latex mixtures, a like effect was to be expected in sulfur-free latex vulcanizates crosslinked by thiuram compounds. In order to get comparable data it was necessary in the first place to get sulfur-free latex mixtures giving vulcanizates with starting properties in the same order of value as those of latex vulcanizates with the classical sulfur recipe. In addition it was necessary also to develop stocks from which threads could be extruded by the well-known two-stage method, since the investigations mentioned at the beginning were carried out exclusively on vulcanized threads, which lend themselves particularly well to determinations of tensile strength, elongation at break and tensile stress. Above all an attempt was made to manage with vulcanization temperatures below 100° C. To make this possible a thiuram compound active at relatively low temperatures had to be used. Here we had the opportunity of using DPTT (dipentamethylenethiuram tetrasulfide, Tetrone A), which the manufacturers (Du Pont) designate, alone among their thiuram accelerators, as “very active”, and which J. Willums referred to in a German journal as far back as 1944.