Effect of thermal-oxidative aging on the microstructure of thermoplastic poly(ether-urethane)

Thermodynamic incompatibility between the hard and soft segments in thermoplastic polyurethanes (TPUs) leads to a two-phase microstructure, which is usually demonstrated by the characterizations of fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The effect of thermal-oxidative aging durations (up to 300 days) and temperatures (40, 50, 55, 70°C) on the microstructure of TPUs were investigated by FTIR, DSC, specific surface energy and dynamic mechanical analysis (DMA) in this work. The TPUs were synthesized by 4,4'-methylenediphenyl diisocyanate and 1,4-butanediol as hard segments and poly(tetramethylene glycol) as soft segments. The result demonstrates that the degree of the phase separation value in virgin TPUs is about 0.332. The specific surface energies of hard and soft segments are 56.9 and 35.7 mJ/cm², respectively. Furthermore, the degree of microphase separation and damping property achieved by the aid of the Gauss method and DMA, respectively, of the TPUs show an obvious decrease during the durations. Moreover, the change of glass transition temperature T _g of the TPUs was also investigated by the DMA. The result indicates that the T _g of the TPUs is almost unchanged with the aging temperatures and durations.