Design and modification mechanism of a novel high-viscosity thermoplastic polyurethane modified asphalt

For the preventive maintenance engineering of special pavements such as ultra-thin friction courses and bridge deck pavements, the performance requirements of the utilized high-viscosity asphalt , including the resistance to permanent deformation , cracking ability, durability, and recyclability , are becoming increasingly stringent. In this study, based on the click reaction principle of carbon-carbon double (C C) bond, hydroxyl-terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI) were selected as the raw materials to synthesize thermoplastic polyurethane (TPU), and then 4,4’-disulfanediyldiphenol (DSDDP) was introduced as the chain extender to design a high-viscosity thermoplastic polyurethane modified asphalt (PUA). Subsequently, the mechanical and rheological properties of PUA under different types of chain extenders and polyurethane (PU) contents were tested, and the microstructure and modification mechanism were investigated at multiple scales. The results indicated that after the introduction of DSDDP, the basic physical properties and viscosity of PUA were greatly enhanced, the fluidity was significantly reduced, and excellent deformation and cracking resistance were achieved at various temperatures. The microscopic tests revealed that the viscosity enhancement effect mainly originated from the click reaction between the disulfide (S-S) bonds in DSDDP and the C C bonds on the soft segments of PU, which can further crosslink the linear PU molecular chain and form a dense spatial network structure to restrict the flow of macromolecules. The dynamic exchange of some S-S bonds facilitates the repetitive opening of the PUA network structure at high temperatures, so the PUA still exhibits thermoplasticity at high temperatures, which verifies the feasibility of the proposed design. Moreover, the addition of DSDDP reduced the degree of microphase separation of PUA, so the designed PUA can effectively adapt to various temperature environments. Overall, the findings of this study can boost the application of this novel PUA in the thin surface layers of high-performance pavements.