Estimation of Carbon Black in Neoprene Compounds

Abstract

Abstract During a recent investigation it was necessary to determine the amount of carbon black in a sample of vulcanized Neoprene. The usual method adopted for vulcanized rubber, which consists in dissolving the rubber in nitric acid (British Standard Methods of Testing Vulcanized Rubber, B.S. 903–1940, p. 28), was tried without success, as the Neoprene did not dissolve. No methods for the analysis of Neoprene compounds appear to have been described in the literature; the following method of estimating carbon black, which has been found to work satisfactorily, may therefore prove of interest, especially as it can be used for certain other synthetic rubbers such as Buna. About 1.0 gram of the Neoprene sample is reduced to a fine crumb, such as will pass through a B.S. 10-mesh test sieve, by means of a rapidly rotating rasp. After extraction with acetone and chloroform, the extracted material is dried in a vacuum desiccator, transferred to a 400 cc. beaker, 20 cc. of nitrobenzene added, and the whole heated on a hot plate for a few minutes to allow the Neoprene to swell. 20 cc. of 25 per cent nitric acid (25 volumes of conc. nitric acid and 75 volumes of water) are then added, and the beaker is replaced on the hot plate. The Neoprene disintegrates and dissolves in the nitrobenzene in a few minutes. The beaker is then heated on a steam bath for about an hour, after which 100 cc. of xylene is added and the mixture filtered, while hot, through an alundum crucible or prepared Gooch crucible. The carbon is carefully washed with hot xylene till free from decomposed Neoprene, and finally with acetone. After drying at 150° C, the crucible is weighed, the carbon black then burnt off in a muffle furnace, and the crucible reweighed. The difference between these weights is the amount of carbon black present.