The backbone structure, fabrication processing, and mechanical property relationships of ethylene and propylene-based homo and copolymers and their blends were developed by in-situ wide-angle (WAXD) and small-angle (SAXS) synchrotron X-ray diffraction and scattering examination of these polyolefins under flow and deformation.  A parallel-plate shear stage was used to investigate the shear-induced crystallization, a custom-made cross-slot flow cell device was employed to study the extension flow-induced crystallization, and a designed symmetrical-stretching tensile tester was applied to probe the structural change during mechanical deformation.<br/> <br/>It was found that the crystalline morphology from flow-induced crystallization in polyolefins is dictated by the crystallization precursor structures established under flow. In particular, results from in-situ rheo-X-ray studies and ex-situ microscopic examinations indicated the presence of shish-kebabs and that the shish entity consists of stretched chains (or chain segments) that can be amorphous, mesomorphic or crystalline, where the kebab entity mainly arises from the crystallization of coiled chains (or chain segments) with a diffusion-control growth process.  In solid-state deformation studies, it was found that, at room temperature, the interlamellar entanglement network can cause lamellar fragmentation during deformation leading to the formation of oriented mesomorphic phase. However, during stretching at high temperatures, chains disentangle resulting in the tie-chain relaxation and the formation of additional folded-chain lamellae.

Crystallization of polyolefins under flow and deformation

249th National Meeting (2015)

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