Longitudinal growth of polymer crystals from flowing solutions. VIII. Mechanism of fiber formation on rotor surface

摘要

AbstractA study has been made of the mechanism of the fibrous crystallization process of high‐molecular‐weight polyethylene from dilute solution subjected to Couette flow. Fiber growth has been observed to take place in a gel layer adhering to the surface of the rotating inner cylinder. The fiber is both taper and ribbonlike shaped, which suggests that growth occurs primarily on the lateral surfaces. The crystal growth rate, as determined by measurements of the fiber cross section, is found to depend on the roughness and the chemical nature of the rotor surface, and is independent of the take‐up speed. These observations have led to the following conclusions concerning the mechanism. Long‐chain molecules adsorb onto the rotor surface. By reptation an entanglement network is formed. It has long relaxation times due to the tendency of the supercooled chains to form embryonic crystallites upon slight orientation. This network is stretched by the entanglement formation with the cilia of a seed crystal, followed by shear stresses. Stretching will lead to further crystallization. The elastically active chain parts between entanglements will lead to the extended‐chain backbone crystals. Inelastic chain parts will crystallize as folded platelets of the sh