Experimental Investigation on the Performance Degradation of TPO Waterproofing Membranes Under Coupled Thermo-Oxidative Aging and Freeze–Thaw Cycles

Thermoplastic polyolefin (TPO) waterproofing membranes are widely used in building roofs and underground waterproofing systems, and their durability under complex service environments is critical to long-term waterproofing reliability. Self-adhesive TPO membranes from one production batch were evaluated in the unaged condition (C0) and after 5, 7, 14, and 28 complete coupled aging cycles (C5, C7, C14, and C28, respectively). Each complete cycle lasted 48 h; thus, C5, C7, C14, and C28 corresponded to total elapsed times of 10, 14, 28, and 56 d. Mass variation, Fourier-transform infrared spectroscopy (FTIR), peel, tensile, and scanning electron microscopy (SEM) measurements were integrated to evaluate physical, near-surface chemical, interfacial, and mechanical changes. The reported mass-loss ratios varied only slightly from 0.25% to 0.35%, indicating limited sensitivity of mass variation under the adopted conditions. FTIR band-depth indices near 1021, 876, 1462, and 719 cm−1 changed non-monotonically with cycle number, whereas SEM images showed a visually more heterogeneous exposed TPO surface after aging. At C28, the mean peak peel resistance decreased from 94.2 ± 3.1 to 28.5 ± 0.6 N/50 mm (69.8%), while the mean nominal tensile stress at 250 mm crosshead extension decreased from 2.59 ± 0.14 to 2.06 ± 0.05 MPa (20.7%). No tensile specimen ruptured within the investigated extension range. These descriptive results indicate that the self-adhesive joint response was more sensitive to the adopted coupled aging protocol than the fixed-extension tensile response of the membrane.