Photodegradation Behavior and Blocking Strategy of Waterborne Polyurethane under UV and Xenon Irradiation

Waterborne polyurethane (WPU) materials are vulnerable to be destroyed under long-term sunlight exposure, reducing their service life. Therefore, it is necessary to investigate the photodegradation behavior and blocking strategy of WPU. In general, UV and Xenon light sources are often used to accelerate photodegradation process to shorten the experimental time. In this work, the blocked and un-blocked WPU were synthesized and the difference in photodegradation behavior under UV and Xenon irradiation was preliminarily investigated. The results showed that the urethane bonds of WPU were cleaved and ether linkages were oxidized and degraded, generating some primary degradation products after UV and Xenon irradiation, the primary degradation products can continue to decompose or re-construct after UV exposure, inducing deeper yellowing and more cracks or holes on the surface of the film. Fortunately, this photodegradation behavior can be blocked by addition of composite additives according to the photodegradation mechanism. The morphology, structure and properties of the blocked WPU changed slightly after UV irradiation and kept almost unchanged after Xenon exposure. In comparison with control sample, the tensile strength retention ratio increased from 9.3% to 77.5% for UV exposure 72 h and from 12.4% to 88.4% for Xenon irradiation 72 h, which confirmed that the proposed blocking strategy was successful and effective.