VERFAHREN ZUR HERSTELLUNG VON POLYPROPYLENFOLIE

摘要

A process for production of a monolithic article from a web of fibres of oriented polypropylene homopolymer or copolymer having a weight average molecular weight (Mw) of at least 250,000 includes the steps of subjecting the web to elevated temperature and pressure sufficient to melt a proportion of the polymer and compact it, and thereby yielding an oriented phase and a matrix phase, and effecting a heat treatment selected from (i) subjecting the compacted web to a retarded rate of cooling down to a lower temperature at or below the temperature a which the recrystallisation of the matrix is complete; and (ii) annealing the compacted web at an annealing temperature within 15° C. of the temperature at which the matrix phase is completely melted. The resultant articles have good stiffness and strength, and acceptable ductility, yet corresponding articles made with polypropylene of lower Mw are brittle.