Molecular degradation mechanism of segmented polyurethane and life prediction through accelerated aging test

Polyurethane (PU) has numerous applications in daily life, such as coating, cushions, and insulation materials. It is also used as an encapsulation material for sensors. In the case of PU used as an encapsulant, PU elastomer containing an ether-based polyol is generally used and has a long lifespan in a general environment. However, it is challenging to predict its lifespan when used as an encapsulation material for sonar sensors because PU is exposed to the filling liquid. It is required to accurately predict the encapsulation material's lifespan to ensure the sensor's safety. For the exact estimation of PU lifespan, an accelerated aging experiment was conducted on PU elastomer in a filling solution at various temperatures. Fourier transform infrared spectroscopy was used to track the chemical changes in the PU elastomer, and it was observed that both urethane and urea bonds were degraded. Modulated differential scanning calorimetry and thermogravimetric analysis were also used to study changes in the structure of PU elastomer by heat aging. The tensile strength, elongation, and hardness of the heat-aged elastomer at various temperatures were obtained, and the Arrhenius plots were constructed. Finally, the lifespan was considered when the tensile strength was 70% of the initial state by using the ASTM D2000 standard. Thus, the lifespan of PU at 25 °C was calculated to be 12.2 years.