Structural characterization of polyurethane foam and implications of aging.

摘要

Polyurethane (PU) foam is used as a shock mitigation material in the national stockpile, which degrades over time. A replacement foam, ReCrete was shown to exhibit acceptable mechanical properties after aging, but fractured with impact testing. Previously, processing ReCrete foam at elevated temperature resulted in a decrease of the modulus (stiffness), which was believed to be related to chemical changes during processing. In this thesis, chemical and structural analysis of ReCrete processed at 25°C and 85°C were performed using photoacoustic infrared spectroscopy, IR imaging, and thermal analysis. The change in modulus was related to thermal decomposition of uretoneimine linkages in the diisocyanate starting material by monitoring the change in intensities of diisocyanate, carbodiimide, and uretoneimine bands in the IR spectra. Thermal analysis (DSC and TMA) were consistent with IR finding, where endothermic and exothermic events could be associated with chemical changes in the foam.