Development of Hard Elastic Solids from Glassy Polymers.

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 reproduced morphologies resembling the row nucleated structures of stacked lamellar aggregates bridged by extended fibrils. Films in this form possess repeated high recovery from large extension without rapture. Stress-Strain and stress-relaxation tests performed in air and in a variety of liquids in addition to thermoelastic experiments indicate that this novel material has identical characteristics to that of hard elastic crystalline polymers. The time-independent component of elastic recovery was found to be an energy driven process which originates largely from surface forces. Our results confirm that the recovery process of elastic HIPS, like crystalline systems, is composed of an instantaneous component in addition to time-dependent healing mechanism. The first was found to be energetic in nature whereas the second remained conformational entropic. A structural model is presented which explains the observed mechanical and structural data. The model is based on the reversible extensive formation of fresh surface of the craze or interlamellar fibrillar material giving rise to the elastic restorative force. Time-dependent healing stems from the conformational character maintained by the subfibrils. Stress-induced sorption and release of liquid, a newly discovered property, is also discussed. Author