Development of hard-elastic solids from glassy polymers

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Abstract
High‐impact polystyrene (HIPS) has been processed into a specific microstructure which exhibited the hard‐elastic behavior previously restricted to crystalline polymers. Unidirectionally stacked profuse crazes formed in uniaxially elongated HIPS resembled the row nucleated structures of stacked lamellar aggregates bridged by extended fibrils. Films in this form possessed repeated high recovery from large extension without rupture. Stress‐strain and stress‐relaxation tests, performed in air and in a variety of liquids, and thermoelastic experiments indicated that this material has similar characteristics to those of hard‐elastic crystalline polymers. Our results confirmed that the recovery process of elastic HIPS, like crystalline systems, is composed of an instantaneous component and a time‐dependent healing mechanism. The first was found to be energetic in nature and the second conformational (entropic). A mechanism, based on the reversible extensive formation of fresh surface of the craze (or interlamellar) fibrils giving rise to the elastic restorative force, is proposed. Stress‐induced sorption and release of liquid, a newly discovered property, is also discussed.

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