Environmental crazing and cracking in poly(methyl methacrylate) under diametral compression

Abstract

The diametral compression test was performed on poly(methyl methacrylate) in six kinds of alcohols, i.e., methanol, ethanol, 2-propanol, 1-butanol, 2-ethyl-1-butanol, and 1-octanol. The load-displacement relation was maintained as almost linear until fracture in all these alcohols except for octanol. The fracture load generally increases with increasing molar volume of the alcohol, but here the lowest value was not measured in methanol but in ethanol. Fracture surfaces have in common two regions of comparatively smooth surface and of rough pleats called usually hackle or rib marks correlated with fast crack growth. In the former, a characteristic ‘sprig-like’ branched pattern was always found except in octanol. Scanning electron microscopy revealed that in the sprig-like pattern there are numerous patch marks peculiar to craze fracture. Thus this pattern may be interpreted as evidence of a perturbed crack front where the polymer is plasticized and then crazed with the aid of diffusing alcohol.