The Mechanochemistry of High Polymers

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.

Study of Permanent Shear Thinning of VM Polymer Solutions

“…A fresh lubricant test sample of a few mm 3 was then applied to the clean rotor and stator, which were then reassembled in the USV and a test carried out. This method differs considerably from the conventional flushing cycle recommended by PCS Instruments but was found to improve viscosity measurement accuracy considerably.…”

“…However, the method is quite difficult to apply in the current study because the volume of oil sample subject to high shear rate is very small. Based on the concentric cylinder length and diameter of 16 and 12 mm, respectively, and the gap of 1.28 lm, the contained volume is only 0.77 mm 3 . Also there is a considerable additional reservoir of solution that is contained above and below the concentric cylinder geometry itself, which serves to ensure the gap is filled.…”

“…In the normal use of the USV the test solution is injected into the apparatus and this reservoir is very large. However, by applying the assembly method outlined above, this volume is much reduced to typically 7 mm 3 . The ratio of the volume within the concentric cylinders to that outside is also known and was typically 1:10.…”

“…Throughout the 1950s to 1970s, there was considerable research work on permanent shear thinning with respect to both the mastication of solid polymers and viscosity loss of polymer solutions. Three useful reviews in the 1970s summarise the state of knowledge at this time [2][3][4]. Mackenzie where viscosity has units Poise, shear rate s -1 , and MWt is the weight average molecular weight in g/mol.…”

On the similarity of macromolecular responses to high-energy processes: mechanical milling vs. irradiation

“…The time independence of solubility after 1 h indicates that crosslinking occurs quickly and that a steady state ensues wherein chain crosslinking and scission occur at nearly equal rates. This steady state is attributed to an increase in chain scission efficiency with increasing molecular weight [14,29,30]. High-energy mechanical milling of PMMA, however, results in a rapid and dramatic decrease in molecular weight [14].…”