Thermal reversibility of crystal surface structure and its contribution to degree of crystallinity in natural rubber and trans-polyisoprene

Abstract

The small-angle X-ray and electron microscopy results of the reversible phenomena of long period and/or crystal and amorphous fold thicknesses with temperature in natural rubber and trans-polyisoprene are presented and discussed in detail. The results cannot be accounted for satisfactorily by either the premelting theory or the solid-state refolding mechanism, but can best be explained by a recrystallization by refolding from a transient liquid-crystalline state. A substantial portion of the long period reversibility is seen to arise from the changes in amorphous surface thickness with temperature. This explains to a large extent the reversibility of crystallinity with temperature and the limiting crystallinity in natural rubber and trans-polyisoprene, and probably in other materials as well.