Process for strengthening a shaped article of a polyester
AssigneeE. I. Du Pont de Nemours and Company
InventorRobert R. Luise
Life of this patent
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Abstract
Heat treatment of shaped articles, larger than films or fibers, formed from anisotropic-melt-forming polymers provides an increase of at least 25% in energy to break in flexure. In at least one direction of measurement the heat treated articles are characterized by a flexural break strength of at least 10,000 psi, maximum strain to break in flexure of at least 2% and a flexural modulus of at least 500,000 psi. In many instances the heat treated articles can be further characterized by a notched Izod impact strength of at least 2 foot-pounds per inch. Since the heat-treated shaped articles have high levels of strength, stiffness and toughness, they are useful as replacements for some metals, e.g., brass.
Claims17
A process for strengthening a shaped article formed by longitudinal flow of a melt of an anisotropic-melt-forming linear condensation polymer wherein the article is larger than a fiber or a film and in which the polymer is a (co)polyester consisting essentially of recurring structural units selected from the group
- --O--R.sub.1 --O-- (I)
- --OC--R.sub.2 --CO-- (II)
- --O--R.sub.3 --CO-- (III)
- wherein units I and II, if present, are present in substantially equimolar amounts:
- R.sub.1, R.sub.2 and R.sub.3 are radicals selected from the group of (1) single and fused six-membered aromatic carbocyclic ring systems wherein the chain-extending bonds of the ring system, if attached to the same ring, are positioned 1,4- to each other, and if attached to different rings, are in positions parallel and oppositely directed, and (2) multiple six-membered aromatic carbocyclic rings systems in which the chain-extending bonds of each ring are in the 1,4-positions and in which the individual rings are joined by a chemical bond or a divalent radical containing no more than 4 acyclic in-chain atoms;
- R.sub.2 may also be ##STR6## wherein A is a divalent radical containing one or two acyclic in-chain atoms;
- and R.sub.3 may also be ##STR7## wherein the aliphatic portion is attached to the carbonyl group comprising heating said shaped article at a temperature from above 140.degree. C. to below the flow temperature of the polymer for a period of time sufficient to increase energy to break in flexure by at least 25% in at least one direction of measurement.
Dependencies are inferred from the claim text.