Crack healing in poly(methyl methacrylate) induced by co-solvent of methanol and ethanol

The crack healing of poly(methyl methacrylate)(PMMA) treated with a solvent mixture of methanol and ethanol was studied. The mass transport of the solvent mixture in PMMA is anomalous; it is mixed Case I and Case II transport. The data of mass transport can be analyzed by Harmon's model. It was found that the activation energies of Case I and Case II transport of mixture are equal to the summation of the corresponding quantities for methanol and ethanol with each weight factor based on the respective volume fraction. The solubility of the mixture is equal to the summation of solubilities of methanol and ethanol with weighting factor based on their molecular weight. The solvent healing including wetting and diffusion stages was analyzed based on the morphology and mechanical strength. The crack closure rate is constant during the wetting stage. Comparing the activation energies of both mass transport and crack closure rate, the crack tip recession is controlled by Case II transport. Crack tip recession was observed from both lateral and top views. The mechanical strength of the healed specimen increases with decreasing volume fraction of ethanol. Fractography was provided as evidence of recovery of mechanical strength. (C) 2000 Elsevier Science Ltd. All rights reserved.