Effects of Additives on Weather-Resistance Properties of Polyurethane Films Exposed to Ultraviolet Radiation and Ozone Atmosphere

Three polyurethane films were prepared by adding the antioxidant-1010 and the composite stabilizer to the polyurethane matrix, respectively. The accelerated weathering tests were performed by using self-designed UV/ozone aging test device. The color difference, yellowness index, UV-Vis spectrum, and infrared spectrum were recorded with colorimeter apparatus, UV-Vis spectroscopy, and FT-IR spectroscopy, respectively. The results show that, for the polyurethane film, the composite stabilizer can remarkably decrease UV transmission, the antioxidant-1010 and the composite stabilizer can markedly decrease the photooxidation index and the carbonyl index, respectively, and the antioxidant-1010 can significantly improve the antiyellowing properties after 60？h exposure. With incremental exposure time for the three films, UV-Vis transmission decreases, the photooxidation index, the carbonyl index, color difference, and yellowness index increase gradually. Under current experimental conditions, the order of UV/O3 aging resistance from highness to lowness is as follows: the polyurethane film modified by the antioxidant-1010, the polyurethane film modified by composite stabilizer, and the pure polyurethane film. 1. Introduction Polyurethane (PU), a polymer containing repeated group (–NHCOO–) on the main chain, is well-known coating materials in a large variety of commercial and technical applications, including adhesives, sealants, coatings, fibers, thermoplastic parts, elastomers, and both rigid and flexible foams [1, 2]. PU is available in many formulations and possesses an excellent balance of properties [3]. As an alternative material for the weathering layer of the high-altitude balloon or airship, thermoplastic PU has recently attracted more and more attention, because it has outstanding overall toughness, high tensile strength, tear strength, abrasion resistance properties requiring much less coating weight, low temperature flexibility, fair gas permeability, good handling properties, and good weatherability and ozone resistance properties. Thermoplastic polyurethane can be heat-sealed, adhesively bonded, and laminated to other substrates [4]. However, similar to other polymer materials, exposure of thermoplastic PU to aggressive environments (i.e., UV radiation, thermal exposure, and oxidative atmosphere) causes changes in their physical, chemical, and mechanical characteristics and even loss of use value [5]. Hence, in order to suppress degradation and prolong the service life, the antiaging agent should be added to the polymer. The suitable antiaging