Intercrystalline Links: Critical Evaluation

Abstract

Previous electron microscopic studies have demonstrated the presence of intercrystalline links between thin lateral edges of chain-folded lamellar crystals in spherulitic polymers. We now present evidence that links also connect broad faces of superimposed neighboring lamellae. The latter links have been observed by electron microscopy of polyethylene lamellae standing normal to the surface of uniaxially drawn Mylar on which they had been crystallized epitaxially. Links of this kind are similar to those observed in the first instance and are evidently produced by the same mechanism. We consider also, in a critical way, the formation of intercrystalline links and tie molecules, and their important influence on mechanical properties, in bulk polymers crystallized either from quiescent or flowing melts. We show that links and tie molecules are formed mostly during primary crystallization, and few additional ones are produced during later stages. We examine, finally, a variety of ways in which links and tie molecules strengthen adhesion between crystals to promote ductile, rather than brittle, response to applied stress.