Process of manufacturing ultrahigh molecular weight linear polyethylene shaped articles
AssigneeE. I. Du Pont de Nemours and Company
InventorsStephen Li, Edward G. Howard, Jr.
Life of this patent
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Abstract
A process for preparing an ultrahigh molecular weight linear polyethylene (UHMWLPE) exhibiting a combination of properties including a creep resistance of less than 1% demonstrated under exposure to a temperature of 23.degree. C. (+ or -1.degree. C.) and a relative humidity of 50 (+ or -2% for 24 hours under a compression of 1000 psi) without sacrificing excellent tensile and flexural properties. The invention includes the use of an inert gas and a prescribed pattern of heating and cooling including a further heat and cooling treatment to create the superior properties of the UHMWLPE. Also included is the product of the process invention.
Claims26
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.degree. 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.degree. C., the reduction in said melting point upon remelting being greater than 11.degree. 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.degree. C.-300.degree. C.;
- (d) maintaining the temperature from 190.degree. C.-300.degree. C. and the pressure of at least 280 MPa for at least 0.5 hour;
- (e) reducing the temperature to below 160.degree. C.-170.degree. 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;
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- (f) cooling to a temperature of about 130.degree. C. or below and releasing the pressure to approximately 100 kPa in a manner such that remelting of said article is prevented.
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, 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.degree. 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.degree. C., the reduction in said melting point upon remelting being greater than 11.degree. C. and an infrared crystallinity index of at least about 0.45 formed by the process consisting essentially of the following steps:
- (a) forming an 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.degree. C.-300.degree. C.;
- (d) maintaining the temperature from 190.degree. C.-300.degree. C. and the pressure of at least 280 MPa for at least 0.5 hour;
- (e) reducing the temperature to below 160.degree. C.-170.degree. 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.degree. C. or below and releasing the pressure to approximately 100 kPa in a manner such that remelting of said article is prevented.
Dependencies are inferred from the claim text.