Energy Requirements of Mechanical Shear Degradation in Concentrated Polymer Solutions

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Abstract
Molecular weight decrease by mechanical shearing results when solutions of around 10% of polyisobutene having average molecular weights above 500 000 are forced through a capillary at nominal rates of shear above 10 000 sec—1. Comparison of observed plots of shear load vs duration of shearing at fixed rates of shear during this degradation process with the corresponding estimated plots which would be expected to obtain if degradation did not occur provide a means of evaluating the amount of applied shearing energy which is dissipated by the degradation process. The result is several hundred thousand kilocalories per mole of broken bonds, which is several thousand times the bond energy of carbon‐carbon bonds. This finding is consistent with the hypothesis that whenever a bond breaks the system loses much of the free energy temporarily stored in bonds and macromolecular chains located in a comparatively large volume surrounding the broken bond, these bonds and chains having been involved in concentrating the required activation energy into the ruptured bond.