Structure and properties of crazes in polycarbonate and other glassy polymers

Abstract

Crazes in glassy polymers are now known not to be true cracks at all but rather regions containing polymer interconnecting the craze walls, which regions have lower refractive indices than the bulk polymer. Refractive indices of suitable crazes may be determined from the critical angle for total reflection at the craze/bulk polymer interface. From the indices craze compositions may be calculated. Such calculations show polycarbonate crazes to be roughly 50 per cent polymer: 50 per cent void. From electron micrographs of silver-doped crazes the void content appears to be distributed in the form of holes most of which have dimensions in the range 20–200Å. Crazing is seen in essence to be a process of polymer rarefaction involving the conversion of strain energy to surface free energy.