Crystallinity in Hydrolytically Aged Polyester Polyurethane Elastomers.

摘要

Several experimental and two commercial polyurethanes were aged in wet air. Polyester types suffered molecular weight degradation but became more crystallizable at 25 C than unaged specimens. Crystallinity contributes to modulus and hardness, and, if measured at 25 C, these properties appear to have been increased by aging. However, at 60 C, 10 C above the crystalline melting point, the moduli of the wet-aged polyester types are less than those of unaged counterparts, showing the effect of the decreased molecular weight. Earlier assessments of polyurethane stability were based on the mechanical properties of reconditioned samples at room temperature, and this probably caused an overestimate of the lifetime of polyester types. Polyether types showed little change in molecular weight on aging, and remained uncrystallizable. Consequently, aged and unaged polyether types show the same relative moduli at 25 and 60 C. The commercial polyester type underwent about ten times as many scissions as the polyether type when aged under the same conditions. (Author)