Liquid Rubbers—General Rubber Products Technology

Mixing and processing methods used in the rubber industry have been designed to use the only form of raw rubber hitherto available—that of a high molecular weight solid. But rubber in high molecular weight form is essential only in the finished product; in principle, similar final properties could be obtained from a low molecular weight raw material provided this could be chain extended before or during the final shaping and vulcanizing operation. This approach has been employed for some time in the rather specialized field of castable polyurethane rubber manufacture. Its exploitation for more general rubber manufacture has become more than just a theoretical possibility with the recent availability of “liquid rubbers” whose molecules have reactive end groups. Those available at present may well prove not fully acceptable, either economically or technically, but it is most unlikely that they represent the best that can be achieved. Material developments will be encouraged if means have been worked out for exploiting liquid rubbers' potential advantages (such as the ability to be processed on lighter and less powerful equipment), and the shortcomings of existing examples have been identified. These considerations led RAPRA to start a processing and compounding study—a decision which seems further justified by the very recent American announcements of development work on a tire manufacturing process using liquid rubber, and of full commerical scale production of several hydroxyl terminated liquid butadiene polymers. This report summarizes the study to date.