Effect of Hydrothermal Aging on Mechanical Properties and Long-Term Durability of Recycled Polysulfone

The present experimental investigation aims to discover the effect of hydrothermal aging on the mechanical properties of virgin and recycled PSU, as well as the effect of hydrothermal aging on the long-term durability including stress relaxation and creep properties of virgin and recycled PSU. Virgin and recycled PSU specimens were exposed to pure hot water at temperatures of 98 °C for 1, 1.5, 3, 4.5, 6, 9, and 12 months, respectively. Mechanical test of tensile, three-point bending, impact, and fracture toughness was carried out on those aged specimens. To obtain the long-term stress relaxation and creep property, a series of short-time stress relaxation and creep tests were performed by using dynamic mechanical analysis (DMA), and the master curve of long-term stress relaxation modulus and creep compliance was drawn by shifting those short relaxation and creep curve based on the time–temperature superposition principle (TTSP). It was finally concluded that the virgin PSU exhibits excellent hydrothermal aging resistance in tensile, flexural, impact and fracture toughness, stress relaxation, and creep properties, even if it was aged in 98 °C hot water for 1 year. Although the tensile and flexural properties of the unaged recycle PSU are similar to those of virgin PSU, the hydrothermal aging resistance in tensile, flexural, stress relaxation, and creep properties of recycled PSU is worse than that of virgin PSU. In addition, the activation energy required for stress relaxation of PSU is same with that for creep.