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Single-crystal mats of ultrahigh molecular weight polyethylene were successfully prepared from p-xylene solution for studies of the influence of chain entanglement on the drawability of these mats. In the microscopic levels observed for small-angle X-ray scattering and scanning electron microscopy, films prepared from the mats had a morphology similar to that of dried gel films that were prepared by the usual procedure. The maximum attainable draw ratio was well in excess of 200 if the specimen was annealed at 130-140 °C and stretched at the same temperature. But it was only about 10 when the specimen annealed at 140 °C, slightly above the melting point, was stretched at 20 °C. This draw ratio at 20 °C was one-third of the annealed gel films prepared from solutions with their optimum concentration. On the other hand, single-crystal mats prepared by a new procedure to minimize the number of entanglement meshes showed a wide variation in the drawability, ranging from 0 to 150 depending on the temperature at which the specimens were stretched. However, the compressed mats could not be elongated at room temperature without the annealing at 140 °C. These results support the hypothesis that the suitable number of chain entanglements plays an important role in transmitting the tensile force effectively during the drawing.

ABSTRACT:Polyethylene-polypropylene blends were produced by gelation/crystallization from semidilute solutions by using ultrahigh molecular weight polyethylene (UHMWPE) (3 x 10 6 ) and low molecular weight polypropylene (LMWPP) (2.2 x 10 5 ). The polyethylene/polypropylene (PE/PP) compositions were 80/20, 60/40, 40/60, 25/75, and 20/80. The blend gels except the 20/80 composition formed films. The maximum drawability was affected by composition. This phenomenon is discussed in terms of the morphology of blend films as studied by wide-angle X-ray diffraction, small-angle X-ray scattering, small-angle light scattering, optical microscopy, and birefringence. It turned out that the facile drawability of the blend films with draw ratio of 230 is due to the existence of a suitable level of entanglement meshes between UHMWPE and LMWPP chains in spite of their incompatibility in solution.