Developing Rules of the Bonding and Micro Properties of Ballastless Track Sealants Under Ultraviolet Aging Environment

To study the developing rules and the micro-mechanism of the bonding properties of ballastless track sealants under ultraviolet aging, the glass transition point of sealants was measured, the developing rules of the adhesive properties of sealants were tested after various ultraviolet aging time, and the micro Derjaguin-Muller-Toporov (DMT) modulus of sealants was researched based on AFM equipment under the same aging conditions. The correlation analysis was then conducted among thermodynamic property, mechanical behavior, and micro properties. It is shown that for non-aged polyurethane sealants, isocyanate index (R value) motivates the sealants to double glass transition point material, and it has a positive relationship with the bonding strength, but a negative relationship with the tenacity and ultraviolet resistance ability. At the beginning aging period, some sealants present a lag effect of performance degradation. At the micro-level, the adhesive properties of polyurethane sealants were affected mainly by their hard phases, which were mainly affected by the ultraviolet aging. In addition, the rapid development of the properties of soft phase may lead to foaming of the micro-structure, and also loss of the adhesiveness.