Polymer shear stability

Abstract

A reduction in molecular weight frequently occurs when polymers are subjected to the action of mechanical forces. For synthetic polymers such degradation has usually been measured by the decrease in viscosity in solution, and various attempts have been made to relate the magnitude of such a change to the shear stresses involved, the molecular weight distribution of the polymer species, the molecular geometry and the type of shear and/or thermal effects. Relevant literature over the past quartercentury is reviewed in chronological order. Some initial experimental work is described with particular reference to the effect of shear stresses on high molecular weight polysiloxanes. Relationships between molecular geometry and the effects of shear are indicated. It is suggested that the determination of shear stresses in functional mechanisms may be possible.