Environmental effects of silicone oil on mechanical properties of low and high molecular weight PMMA

Abstract

The influence of a silicone oil environment on deformation modes and tensile behaviour of poly(methylmethacrylate) were investigated. Tests were made on samples coated with oils of varying viscosity, ranging from 5 to 1000 cSt. To investigate the effects of polymer molecular weight on environmentally induced craze growth and stability, tests were conducted on an extruded grade of relatively low molecular weight and on a cast grade of high molecular weight. All of the silicone oils acted as crazing agents and tensile strength and ductility were reduced in value as the viscosity of the oil was lowered. The low molecular weight polymer failed in a brittle manner in all environments but developed earlier and more intensive crazing as the liquid viscosity was reduced. The high molecular weight material underwent a ductile-brittle transition when the environment was changed from air to low viscosity silicone oils. The flow of the oil into existing flaws and crazes was sufficiently impeded at 1000 cSt viscosity so that both necking and surface crazing were observed under these conditions. To illustrate the various deformation and fracture modes that were observed, micrographs of free and fracture surfaces are presented and discussed.