Properties of Hard Rubber. XVII. Influence of Rubber-Sulfur Ratio and Vulcanization Time on the Properties of Pure Rubber-Sulfur Compositions. (3) Swelling, Water Absorption, Aging, and a General Discussion of Results

Abstract

Abstract (a) Method of Test.—The materials selected were A, 5 hours, and C, 3.75 hours. It was not possible to include sufficient samples to show the separate effects of varying vulcanization time and rubber-sulfur ratio, but the samples show the effect of a considerable difference in combined sulfur, having vulcanization coefficients of 49.5 and 38.7, respectively. To show the dependence of swelling on the nature of the liquid, tests were carried out in twenty different liquids selected to represent various chemical types. Each piece of hard rubber, measuring 20 × 19 × 5.5 mm., was placed in a stoppered bottle with about 40 cc. of the liquid under examination. The bottle was kept in a thermostat at 34° C and shielded from light. The test-piece was then weighed after various periods of immersion ranging from 4 to 4000 hours. The absorption of liquid after each period was calculated from the increase in weight and expressed by the volume of liquid absorbed as a percentage of the initial volume of the test-piece. (b) Results.—No sign of solution of the rubber-sulfur compound was observed, but in certain cases, where swelling was rapid, cracking occurred. In three cases this took place before the first weighing could be made. Full-time swelling curves were obtained, but as most of the liquids are not likely to come into regular contact with hard rubber in electrical service, figures are given in Table 19 for one long and one short period only. In this table, swelling less than 1 per cent is shown as zero. Closer readings for certain liquids of very low absorption are shown in Table 20.