The Mechanochemistry of High Polymers

Abstract

Abstract Several different schools of workers have dominated research in the field of polymer mechanochemistry. These include the Russian school with Baramboim, Berlin, Butyagin; Watson, Ceresa and others of the Natural Rubber Producers' Research Association; and a host of other European workers. Also active are the Japanese and Rumanian groups. In the U. S. the activity has centered at the National Bureau of Standards and in a number of labs including our own. The tables for the review summarize mechanochemical studies on individual polymers, multicomponent polymer systems, and on polymer solutions. For a field so important, it is surprising so few summaries have been prepared. An early review (1960), emphasizing the mechanical degradation of rubber, was prepared by Watson. The classic book on Mechanochemistry of Polymers by Baraboim was published in English in 1964. In the same year Watson also published an excellent book chapter on mechanochemical reactions. Other general volumes and reviews on polymer degradation and synthesis have been published. This review on mechanochemistry cites the majority of recent publications. The extensive patent literature authored particularly by workers at the NRPRA has not been considered. The review is not intended to constitute an exhaustive report but rather a survey of polymer reactions induced by mechanical means. Studies directed to thermal, oxidative, sonic wave, and additional degradation methods may be cited only incidently as they relate to predominantly mechanochemical reactions. The books by Jellinek and by Grassie remain an excellent source for information on all modes of polymer degradation. The mechanical degradation of polymers has emerged as a fundamental problem of major industrial importance. The effects are important in the processing and use properties of polymers. Mechanochemical reactions of polymers in solution is also an important commercial problem such as in the prediction of stability of polymers in multigrade automobile lubricating oils. Industrial necessities have required scientists to study mechanical reactions by the use of suitable laboratory equipment for the purpose of overcoming this problem. These studies have provided numerous, fundamental and interesting publications involving the chemistry, physics, and mechanics of mechanochemistry. As a prime example, the discovery of the softening of natural rubber by mechanical treatment was reported as early as 1857. This process is still used today in the rubber industry. In other major industrial processes such as extrusion and injection molding, mechanical reactions manifest themselves in the more severe cases as polymer discoloration, embrittlement, and stress cracking. The industrial necessity of grinding plastic wastes for recovery and reuse and the necessity of transferring and spreading polymer solutions are also modes for polymer mechanical degradation.