| 摘要 |
Isotactic polypropylene is melt-spun to yield filaments having number average molecular weight in excess of 20,000 and birefringence less than 10 X 10-3 and the filaments are then drawn at a ratio of at least 2 : 1, preferably at elevated temperatures. Isotactic polypropylene, which may contain small amounts of atactic polypropylene or of polyethylene, may be spun at from 285 DEG -305 DEG C. and filaments of number average molecular weight between 50,000 and 60,000 wound up at a speed imparting a bire-fringence not exceeding 3 X 10-3, (e.g. at about 1,000 ft./min.), before being drawn to at least 4,5 times their original length, preferably from 4,5-10 times. Before the extrusion of filaments, the isotactic polypropylene may be subjected to thermal degradation, desirably such that the drop in polymer intrinsic viscosity, measured in tetralin at 135 DEG C., is at least 1. In a preferred method, isotactic polypropylene is melted and compressed at about 200 DEG -320 DEG C., preferably in a screw extruder. Specifications 810,023 and 818,100 are referred to and Specification 828,735 is referred to in the Provisional Specification. |
