MACROMOLECULAR CHEMISTRY AND POLYMERIC MATERIALS Softeners for Rubber Based on Shale Thermal Dissolution Products

The source of raw materials for manufacturing softeners for rubber is extended through applying a nonwaste process of thermal dissolution of ordinary or enriched shale in crude producer-gas tar. The result- ing products are less expensive than the conventional high-melting oil asphalts and oils. Progress in the rubber industry is determined to a considerable extent by extension of the source of raw materials, i.e., by broadening of the spectrum of the products used. In production of elastomers, the weak point is a limited spectrum of softeners. Among the commonly used products of this type are asphaltic tar softeners, specialty bitumens, etc. Their introduc- tion into rubber stocks allows control of the most important performance characteristics of rubber stocks and finished articles such as rubber-to-cord adhesion, ozone resistance, and abradability. These products serve also as dispersants for rubber stock components and as reinforcing agents. Virtually the only source of softeners of this type is deep processing of oil. The rubber and tire industries are large-scale consumers of high-molecular-weight petroleum products such as PN-5 oil, black oils, tars, Rubraxes, and other asphaltic tar products. These softeners (plasticizers) demonstrate wide action spec- trum: they reduce the shrinkage in calendering and extrusion molding of rubber stocks, improve the strength and heat resistance of rubber, and impart moisture resistance and solidity to finished articles (1, 2). It was suggested that such products could be obtained from sapropelic coals, among them shales, whose reserves are huge. In this study we examined the possibility of pre- paration of shale-oil bitumens by thermal dissolution of ordinary or enriched shales in shale-oil producer- gas tar and also of their use as softeners for rubber. Since bituminous softeners are used to improve per- formance characteristics of heavily extended elas- tomers and rubber stocks with a polymer body from rubber reclaim and SKD butadiene rubber, an asso- ciated task was to improve performance of the com- posites by introducing the indicated softeners, thus extending their application range. Low branching of the macrochains and only slight temperature dependence of the viscosity of SKD cause its high cold flow in storage and transportation (3). The processibility of SKD is characterized by its mil- lability, estimated from the critical roll opening (mm). The millability of SKD ranges from 0.5 to 2 mm, depending on the molecular-weight distribution and polydispersity.