Odour of Vulcanised Rubber

Abstract

As the rather unpleasant odour of vulcanised rubber limits its applications, the Rubber Growers Association has instituted an investigation into its causes and prevention (Bull, Rubber Growers Association, May, 1933). When rubber goods were made from inferior grades of wild rubber, their smell was due to putrefactive changes, but in these days of plantation rubber, the trouble arises mainly from the accelerator employed, although macintoshes and other proofed goods owe their smell to the low-grade petroleum and coal-tar naphtha products that are used as diluents when the rubber is manufactured. Vulcanised goods can often be temporarily freed from odour by steaming them, but permanent freedom can only be secured by removing the substances that give rise to odour, whether they be constituents of the raw rubber or added to it in the course of manufacture. The smell due to accelerators may be of the sulphide or of the amino type, according as they contain sulphur or amino-nitrogen. So far, no good accelerator that is free from these constituents has been found, but Messrs. H. P. Stevens and E. J. Parry, the chemists in charge of the investigation, have discovered that the presence of zinc carbonate in the compounding mixture reduces the smell to a minimum. The slight amino smell characteristic of the unvulcanised plantation rubber has been traced by them to the proteins, and not to the resins, present in the raw material and it can be practically eliminated if the latex is purified by such methods as digestion with dilute caustic, ceritrifuging, creaming, ultra-filtration, or dialysis. When the problem has been definitely solved, it will be possible to use vulcanised rubber for lining food-containers and brewers vats, and in the preparation or packing of foodstuffs in general.