Some recent results on crack healing of poly(methyl methacrylate)

The solvent healing and void growth of poly(methyl methacrylate) (PMMA) at elevated temperatures were studied. In addition to entanglement between two or more broken polymeric chains, the chemical bonds between two polymeric broken chains were produced during healing in methanol or d1-methanol. Cracks in PMMA were induced either by Nd-YAG laser irradiation or by acetone immersion. The solvents occupied the voids enclosed by polymeric chains. The chemical bonds and structure were analyzed with FTIR and NMR spectroscopy. The results show that in addition to mechanical lock of broken chains, hydrogen bond increases with uptake of solvent which enhances the crack healing. The cylindrical crack in PMMA was healed at temperatures 110–160 °C and spherical void was grown at temperatures 170–190 °C. This suggests that annealing above the glass transition temperature of polymer is a necessary condition for thermal healing, but not for the sufficient condition.