Fracture mechanisms of poly(methyl methacrylate) under static torsion in alcohol environments

Abstract

Static torsion tests of poly(methyl methacrylate) were conducted in several alcohol environments at room temperature. The critical torsional stress for crazing and/or cracking increased with increasing molar volume of alcohol, and was not correlated with the solubility parameter, nor with equilibrium solubility as reported in previous results on n-alkanes. Crazing stresses in alcohols were generally lower than those in alkanes. According to Fourier transform-infrared microscopy of the surface scratch made in several environments, both in ethanol and in 1 -butanol, some absorptions were detected at 3450–3650 cm−1, probably due to the hydroxyl group of these alcohols caught by hydrogen bonding to oxygen of the carbonyl group in the side chain, whereas in other environments (1 -octanol, n-hexane, and air) there were no absorptions in this region of wave number. These results suggest that at a flaw tip strained under stress, penetrating alcohol molecules are chemically adsorbed in a cluster, which breaks a weak bond (e.g. dipole interaction) between the polymer chains and, as a result, facilitates craze formation and breakdown leading to brittle fracture.