Formation and growth of crazes in multiphase acrylic systems

Abstract

The appearance of visible crazes and the growth of crazes during creep in tension for multiphase acrylic systems have been studied. The polymeric materials, commonly applied in bioengineering, were processed by polymerization of a mixture of liquid methacrylate monomers and poly(methyl methacrylate) (PMMA) powder. The specimens were made with various ratios of methyl methacrylate (MMA) and the crosslinking agent ethyleneglycol dimethacrylate (EGDMA) in the monomer liquid. Two different processing conditions were used, i.e. heat-polymerization at 100°C and auto-polymerization at 45°C. The critical strain value ɛc for the appearance of visible crazes under the influence of a constant tensile stress increased with increasing quantity of EGDMA in the heat-polymerized materials, and the crazes were equally distributed at the surface of the materials observed. In the cross-linked auto-polymerized materials, crazing started in the spherical polymer beads from the PMMA prepolymer powder, and ɛc was independemt of the quantity of EGDMA. In the auto-polymerized materials crazes in a necked region opened up to form diamond-shaped cavities. Fracture started with a cavity that expanded through both matrix and polymer beads. The heat-polymerized materials failed in a brittle manner, whereas the auto-polymerized materials failed in a ductile manner.