On the morphology of polyethylene crystallised from a sheared melt

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Description/Abstract

The morphology of linear polyethylene, crystallized from a sheared melt in the form of shish-kebabs, has been investigated by transmission electron microscopy following permanganic etching. The microstructure of lamellae crystallized transversely on a central linear thread changes systematically with crystallization temperature and shear rate. Higher strain rate produces more and longer filaments and aligns lamellar normals along their rows. At lower strain rate, lamellar habits resemble, but differ from, those characteristic of quiescent growth. Fold surfaces that are inclined to the chain axis c at lower shear rates become normal to c with higher shear, thereby adopting a state of higher energy. It is inferred from this and the high crystallization temperatures that their crystallization was not strain-free. The separation of adjacent lamellae and its decrease at higher strain rate are consistent with pressure from molecular cilia emerging from fold surfaces, in a similar way to the basic cause of lamellar divergence in spherulites.