Mechanical and thermal analysis of aging in strained polymethyl methacrylate

Aging in quenched and strained polymethyl methacrylate (PMMA) has been studied using a differential scanning calorimetry (DSC) and a thermally stimulated deformation recovery measurement as well as a mechanical compression test. The aging in quenched and strained PMMA was compared with the physical aging in quenched PMMA with no strains. The PMMA samples strained in compression before the aging showed an evolution of yield stress with aging time much faster than that in quenched samples with no strains. The DSC analysis, however, showed that the endothermic peak for the quenched and strain-aged PMMA was less developed than that for the quenched PMMA with no strains. This paradox was analyzed using the deformation recovery data for quenched and strain-aged PMMA. The analysis led us to the conclusion that the evolution of yield stress in quenched and strain-aged PMMA is probably due to the structural change locking the strain energy tightly in the polymeric structure.