The effect of molecular properties on mechanical behaviour of PMMA—III. Environmental stress crazing in methanol

Abstract

The correlation between the stress-relaxation curves of methanol-equilibrated poly(methyl methacrylate) (PMMA) and environmental fracture behaviour indicates the role of molecular entanglements in determining if the fracture process of PMMA in methanol occurs via stress-cracking (Regime II) or stress-crazing (Regime I and Transition Regime). The fracture data for high molecular weight (MW) PMMA (Regime I) and medium MW PMMA (Transition Regime) were analyzed by linear, elastic fracture-mechanics (LEFM) and Williams-Marshall (WM) theory. High MW PMMA absorbed more energy and had a wider crack-opening-displacement (COD) than medium MW PMMA, due to a thicker primordial craze thickness. Craze matter in the high MW sample gave a slower crazing stress decay and a better stretching capability with time than that of medium MW sample. The craze-initiation and the craze-growth obeyed a flow-controlled mechanism and relaxation-controlled mechanism, respectively.