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

Abstract

SynopsisA 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 shish kebab.

Review on processing ultra high tenacity fibers from flexible polymer

“…It is obviously clear that the strengths of commercial fibers obtained from flexible polymers have rarely been in excess of about 5 percent of each ultimate polymer strength, except Kevlar from a fully extended chain polymer (37,38). There have been many considerations (39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52) provided of the reasons related to fine structure of fiber. As a consequence, the fibrous structure model as shown in Fig.…”

Flow‐induced crystallization by surface growth of polyethylene fibers

“…On the other hand, our results indicate that the interconnected network structure associated with loops on the surface adhering to the growing fiber can generate for some distance along the surface and the formation of these connections is the most likely prerequisite for continuous growth as suggested in the model in ref. 11.…”

Elastic flow instabilities and shish-kebab formation during gel-spinning of ultra-high molecular weight polyethylene

“…Again a shishkebab structure, can be seen, consisting of a central backbone overgrown with lamellar platelets. Such shish-kebab morphologies appear to be a general feature in the deformation of entangled UHMWPE solutions [58], since they were also generally observed in stirring-induced fibres [40] and "surface-growth" fibres [59].…”