Hypothesis of Voids in Semicrystalline Polymers

Abstract

The expression V=xV_c+(1−x)V_a, for the specific volume of a semicrystalline polymer, is a highly successful approximation; here x is the degree of crystallinity, V_c is the specific volume for the crystalline regions, and V_a is the specific volume for the amorphous regions. In specimens for which x is near unity, however, this equation demands values for the parameters which are inconsistent with other experimental evaluations. We suggest that the discrepancy arises because of the presence of voids. Thus in addition to crystalline and noncrystalline regions we propose regions of zero density. The average volume of such voids is not known, but their existence can be inferred from the significant, permanent density enhancement which can be brought about by pressure‐induced crystallization.