Experimental studies and molecular dynamics simulation of the compatibility between thermoplastic polyurethane elastomer (TPU) and asphalt

Compatibility between polymer and asphalt is an important issue to be considered when the polymer is added to base asphalt as a modifier. It determines the stability of the modified asphalt system. The purpose of this paper is to investigate the effect of shearing temperature and the content of thermoplastic polyurethane elastomer (TPU) on the compatibility between TPU and asphalt by means of experiments and molecular dynamics simulations. Firstly, the molecular models of base asphalt, TPU chain and TPU/asphalt blends were constructed by using Materials Studio 8.0. Based on the rational construction of the model, the effect of shearing temperature on the storage stability of TPU modified asphalt was evaluated by the calculation of solubility parameter (δ) and mean square displacement (MSD). In addition, the effect of different TPU admixtures on the compatibility of TPU with asphalt was characterized by interaction energy and radial distribution function (RDF). The results of molecular dynamics calculation were compared with the results of fluorescence microscopy test (FM) and segregation test. It showed that the minimum difference in solubility parameters between TPU and asphalt occurs when the shearing temperature was 170 °C, at which the diffusion movement of TPU in asphalt was the most active. The interaction energy between TPU and asphalt reached the peak when the content of TPU in asphalt was 17 wt%. Furthermore, the RDF results also indicated that the optimum dispersion effect of TPU in asphalt is achieved at this TPU content. The molecular dynamics simulation results are in agreement with the experimental results.