Degradation and lifetime prediction of thermoplastic polyurethane encapsulants in seawater for underwater acoustic sensor applications

EY Choi and CK Kim, POLYMER DEGRADATION AND STABILITY, 209, 110281 (2023).

DOI: 10.1016/j.polymdegradstab.2023.110281

Degradation of thermoplastic polyurethane (TPU) encapsulants used in an underwater acoustic sensor (UAS) was examined by aging in seawater, and the lifetime of TPU encapsulants was estimated using an empirical approach based on accelerated lifetime test (ALT). The TPU encapsulants were placed in seawater and aged at temperatures of 85, 100 and 110 degrees C. TPU encapsulants underwent a hydrolysis reaction during aging in seawater, changing the chemical structure and molecular weight of TPU. Molecular dynamic (MD) simulation results described the hydrolysis degradation of TPU results in the decrease in tensile strength. Tensile tests were conducted on the aged TPU encapsulants, and then failure times for each of the accelerated conditions were estimated from the changes in tensile strength over aging time. The accelerated failure times were used for the lifetime prediction of TPU encapsulants at a use-stress level by using ReliaSoft's ALTA software. An empirical prediction model based on Arrhenius equation and Weibull distribution was determined for the lifetime prediction of the TPU encapsulant, facilitating lifetime estimations of TPU encapsulant at various failure criteria. A decrease in the tensile strength to 50% of the initial value was established as the failure criterion for lifetime prediction, indicating that half of TPU encapsulants will fail after aging about 20 years. Therefore, this result helps to determine the appropriate time for replacement of TPU encapsulant before failure.

Return to Publications page