路用聚氨酯胶结料的抗紫外老化性能

Polyurethane (PU) binders are inevitably affected by ultraviolet (UV) irradiation in engineering applications. Given this, the tensile properties and viscoelasticity (dynamic thermomechanical performance based on temperature and frequency scanning) that affect road performance were considered as the evaluation indexes. This was done to study the evolution law relating to the performance of PU binders used in roads under UV aging, using a UV aging chamber to simulate the natural aging process. The aging mechanism was revealed via scanning electron microscopy (SEM) and the infrared (IR) spectrum. Additionally, the influence law and mechanism of different isocyanate contents relating to the UV aging performance of PU was revealed by adjusting the ratio of the components of PU (the mass ratios of polyol/isocyanate are 100/80 and 100/65 and are denoted as PU-Ⅰ and PU-Ⅱ, respectively). The tests show that UV aging has the most significant impact on the tensile strength and elongation at the break of the PU in the early stage of aging, followed by a relatively stable impact on its performance in the middle and later stages of aging. For example, the residual strength of PU-Ⅰ recovered to 98.8% after a 28-day aging process. The UV aging did not significantly reduce the tensile modulus of the PU. However, it increased the tensile modulus, given that the tensile modulus of PU-Ⅰ nearly doubled after 28 days of aging. The UV aging enhanced the storage modulus and glass transition temperature (T_g) of the PU, increased the complex modulus and viscoelastic ratio in the low-frequency region, and decreased their value in the middle and high-frequency regions, particularly for PU-Ⅰ. The above evolution mechanisms of the performance of PU mainly include plasticization, molecular chain fracture, and physicochemical crosslinking. Moreover, the physiochemical crosslinking primarily includes physical crosslinking resulting from the formation of strong hydrogen bonds, and chemical crosslinking resulting from the post-curing and the reaction between water molecules and the unreacted -N=C=O functional groups. The study findings indicate that increasing the isocyanate content enhances the physicochemical crosslinking effect, which improves the aging resistance of the PU. Therefore, the research results have laid the foundation for the application of PU-binders in road engineering.