The microstructures of solvent-welded joints of irradiated poly(methyl methacrylate)

The microstructures of solvent-welded joints of irradiated poly(methyl meth acrylate) (PMMA) have been investigated. The morphologies of tensile, tear, and cleavage surfaces were examined and the effects of the solubility para meter, welding temperature, and gamma -ray dosage on the mechanical strengt h were studied. Three solvents - methanol, ethanol, and N,N-dimethyl formam ide (DMF) - were used with welding temperatures at 40, 50, and 60 degreesC. The gamma -ray dosages were 100, 200, and 300 kGy. The features of the ten sile fracture surfaces exhibit either long and narrow hackles on the interf ace of PM1MA with low dosage, or lamellae in the adherent near the interfac e with high dosage for methanol and ethanol. For DME the morphologies of th e tensile fracture surfaces at low and high dosages consist of many ellipti cal paraboloids and feathers, respectively. The morphology of the tear frac ture surface of PMMA shows equiaxed hackles for methanol and ethanol and po lygons for DME The cleavage surface appears to be chevron curves. The cleav age surface shows discontinuity of the chevron curves at the welded interfa ce for non-irradiated specimens and continuity on irradiated specimens. The slope of the chevron curve at the interface is continuous for ethanol and DMF but is discontinuous for methanol. A solvent-affected zone was observed and its size had no correlation with the mechanical strength of the joined PMMA.