The relation between the foamability of PVC pastes and the quality of a PVC polymer

Abstract

The mechanical foaming of poly(vinylchloride) (PVC) pastes is made possible by the presence of surfactants, which secure the formation of a PVC foam and its stability at the next processing. The efficiency of the surfactants that are employed in this technology may be evaluated on the basis of viscosity difference between the descending and rising part of the viscosity curve for the PVC pastes in the region of low shear rates. This criterion, the validity of which has been proven by a correlation with the rate of degradation of the foam structure, is based on the hypothesis of the formation of a spatial network of molecular and supermolecular clusters of the soap surfactant, which is insoluble in the nonaqueous medium of the PVC paste. The criterion of the viscosity difference serves to assess the pastes of different types of PVC such as Vestolit B 7021, Pevikon D 61, AST 66, and Slovinyl K 72. In connection with the foamability of PVC pastes, it is the effect of a residual emulsifier and the character of particles in terms of their average size and distribution that are discussed.