Purified Natural Rubbers. Mechanical Aging, Hygroscopic, and Electrical Properties of the Vulcanizate

Abstract

Abstract The fact that the nonrubber components of crude rubber, especially those of a hygroscopic nature, impair the electrical properties of the vulcanizate has long been known, and the preparation of deproteinized or otherwise purified rubbers for use in electrical insulation had reached the commercial stage before the 1939–1945 war. With the rehabilitation of the plantation industry, the question of what special types of natural rubber should be prepared and marketed has become important, and purified rubbers represent one type that merits careful consideration. Published data on the electrical properties of purified rubbers, both before and after vulcanization, relate entirely to types prepared from solid rubber (crepe or sheet) or ammonia-preserved latex in the consuming country, and there is no published record of experiments on rubber purified during its preparation on the plantation. In 1935 the R.A.B.R.M. began investigations on the use of purified rubbers of the latter type in making electrical ebonite; the results will shortly be published. Examination of soft vulcanizates was began in 1937, but war conditions made it necessary to discontinue the work, for which reason the electrical results are less complete and conclusive than could have been wished. Nevertheless, it is hoped that the results obtained will be of value to the rubber manufacturing and plantation industries. Another use of purified rubbers is in the manufacture of transparent articles that come in contact with water or aqueous solutions. Transparent vulcanizates made from ordinary raw rubber quickly become white and opaque owing to absorption of water, but it would be expected that the use of purified rubber would remove or lessen this defect. This point has accordingly been examined. The thanks of this Association are due to the London Advisory Committee for Rubber Research (Ceylon and Malaya) for arranging for the preparation of special purified rubbers, in Ceylon and Malaya, and for examining the water absorption of the unvulcanized rubbers.