Flow induced crystallization of polyethylene melts

Longitudinal velocity gradients in a flowing system are known to extend molecules appreci-ably and have been found to be responsible for the fibrous crystallization of polyethylene from solution. In this paper the preliminary optical observations are given of the effect this type of velocity gradient has on flowing crystallizable polymer melts. By flowing molten polymer into two mutually opposed orifices a longitudinal velocity gradient is generated specifically along the symmetry axis of the system. It was found that fibrous crystallization of polyethylene melt appeared to occur preferentially along this axis, implying that longi-tudinal velocity gradients play an important part in the production of this fibrous crystalliza-tion. The structural implications of the resulting extrudates and filaments obtained are discussed. Additional observations of the effect a fine gauze has on the crystallization of polymer melts is also presented. For crystalline polymers to approach their theoretical maximum stiffness two physical conditions must be satisfied. The molecular chains must crystallize in a manner such that they are highly aligned; and, equall