Rapid Identification of Polyisoprene in Cured and Uncured Compounds

On account of the industrial development of synthetic elastomers the identification of the different types of rubber in artifacts became a necessity. Several methods have been tried and periodically reviewed by Bekkedhal and by Tyler and Higuchi. As far as the synthetic rubbers are concerned, the types being produced in industrial quantities have characteristic groups which permit their easy detection by chemical means. However, natural rubber, poly-cis-isoprene, presents a more difficult identification, especially if in admixture with other elastomers and compound ingredients, in vulcanizates—and the same is true for the synthetic poly-cis-isoprene, the production of which has just recently started. The use of special techniques as X-ray diffraction, infrared spectroscopy and chromatography permits the identification of the natural rubber hydrocarbon, but equipment for them is not always available for routine work. Simple techniques have been tried. Not mentioning methods which depend on experimenter interpretation, as behavior to burning, which furnishes valuable preliminary information for an experimenter, we verified that two tests in the British literature are of great utility. These consist of determining the swelling ratios in benzene, petroleum ether and aniline and the time of reaction in a mixture of concentrated nitric and sulfuric acids. As chemical reactions, characteristic of natural rubber and its reclaim, the old Weber reaction, the trichloroacetic acid reaction and the well known chromic oxidation to acetic acid are mentioned.