Bulk versus fiber crystal structures of polymers and biopolymers

摘要

Processing of crystalline polymers such as injection moulding or fibre spinning produces usually the mechanically more stable crystal modification of any polymer. Also, especially in fibre spinning, the chain axis is supposed to remain parallel to the fibre axis, as crystallization takes place under stress. Exceptions to these rules do however exist, that help shed light on molecular and structural processes that take place during processing of polymers. For the most part, these effects are revealed only when resorting to polymers that display adequate crystal polymorphs or specific growth features. Also, comparison of oriented morphologies obtained by mechanical and by milder means (e.g. epitaxial crystallization) can help determine the impact of stresses during crystallization. Illustrations taken from our work with isotactic polypropylene, syndiotactic polypropylene and poly(L-lactic acid) are discussed.