Aging behavior of polyether polyurethane binder: Thermal-oxidative, photo-oxidative, hydrolytic aging, and microscale

Polyurethane pavements exhibit excellent toughness and weather resistance; however, as a polymer binder, polyurethane (PU) is prone to aging under the influence of natural factors such as heat, oxygen, light, and water. To investigate the microscale aging behaviors during thermal-oxidative, photo-oxidative, and hydrolytic aging, two types of one-component polyether polyurethanes were selected. Based on infrared spectroscopy test, atomic force microscope test, tensile performance test, and dynamic mechanical analysis test, the changes in micro-composition and micro-structure were comprehensively analyzed, and these changes were correlated with the macroscopic mechanical properties. The results indicate that no new functional groups were formed in the two types of PU during the aging processes, although molecular chain breakage occurred. Among them, the effect of thermal-oxidative aging on CO was obvious, while hydrolytic aging had a significant influence on C-H bond. After aging, the degree of hydrogen bonding increased, and microphase separation became more pronounced, variations of separation degree depending on the type of aging. Point aggregation of hard segments presented after the thermal-oxidative aging, while large area block or strip aggregation of hard segments was discovered after photo-oxidative aging. However, hard segments displayed fine-strip-aggregation and uniform dispersion in soft segments after the hydrolytic aging. A multidimensional radar chart composed of seven micro-factors revealed that chemical crosslinking dominated the polyurethane crosslinking, while physical crosslinking through hydrogen bonding between hard and soft segments was significantly enhanced. However, the strength of chemical crosslinking varied due to the residual isocyanate content in the original two types of PU. Correspondence analysis showed that the decline in tensile performance and the changes in DMA performance exhibited a high degree of consistency with microscale aging behaviors, indicating that the seven microscale factors can serve as systematic assessment indicators for formulating PU materials with enhanced anti-aging performance for pavement applications.