ULTRADRAWING BEHAVIOR OF ONE-STAGE AND 2-STAGE DRAWN GEL FILMS OF ULTRAHIGH MOLECULAR-WEIGHT POLYETHYLENE AND LOW-MOLECULAR-WEIGHT POLYETHYLENE BLENDS

The ultradrawing behavior of gel films of plain ultrahigh molecular we ight polyethylene (UHMWPE) and UHMWPE/low molecular weight polyethylen e (LMWPE) blends was investigated using one- and two-stage drawing pro cesses. The drawability of these gel films were found to depend signif icantly on the temperatures used in the one- and two-stage drawing pro cesses. The critical draw ratio (lambda(c)) of each gel film prepared near its critical concentration was found to approach a maximum value, when the gel film was drawn at an ''optimum'' temperature ranging fro m 95 to 105 degrees C. At each drawing temperature, the one-stage draw n gel films exhibited an abrupt change in their birefringence and ther mal properties as their draw ratios reached about 40. In contrast, the critical draw ratios of the two-stage drawn gel films can be further improved to be higher than those of the corresponding single-stage dra wn gel films, in which the two-stage drawn gel films were drawn at ano ther ''optimum'' temperature in the second drawing stage after they ha d been drawn at 95 degrees C to a draw ratio of 40 in the first drawin g stage. These interesting phenomena were investigated in terms of the reduced viscosities of the solutions, thermal analysis, birefringence , and tensile properties of the drawn and undrawn gel films. (C) 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 149-159, 1998.