Process of manufacturing ultrahigh molecular weight linear polyethylene shaped articles

Claim 1

A process for obtaining a shaped article of an ultrahigh molecular weight linear polyethylene exhibiting a flexural modulus of 250,000-500,000 psi, a tensile stress at yield of 3500-4500 psi, a tensile stress at break of 4000-9000 psi, a tensile modulus of 250,000-700,000 psi, an elongation of 200-500%, a notched Izod impact resistance of 12-25 ft. lb. per inch of notch, a creep at a compression of 1000 psi of less than 1% after 24 hours at a temperature of 23° C. and a relative humidity of 50%, the polyethylene having a molecular weight of 400,000-10,000,000, a single crystalline melting point of greater than 144° C., the reduction in said melting point upon remelting being greater than 11° C. and an infrared crystallinity index of at least about 0.45 consisting essentially of the following steps: (a) forming said article of an ultrahigh molecular weight linear polyethylene having a molecular weight of 400,000-10,000,000; (b) surrounding said article with an inert material that is collapsible and impermeable; (c) subjecting said surrounded article to a gas under pressure of at least 280 MPa and a temperature of 190° C.-300° C.; (d) maintaining the temperature from 190° C.-300° C. and the pressure of at least 280 MPa for at least 0.5 hour; (e) reducing the temperature to below 160° C.-170° C., while maintaining the pressure at at least 280 MPa, the rate of reduction in temperature being such that temperature gradients in the shaped article are substantially avoided; and (f) cooling to a temperature of about 130° C. or below and releasing the pressure to approximately 100 kPa in a manner such that remelting of said article is prevented.