Modification of bitumen with polyether-based polyurethanes containing different hard segments

To expand the application of polyurethane (PU) modified bitumen, it is necessary to understand the influence of PU raw materials on PU modified bitumen systematically. Three polyether-based polyurethanes were used to modify the unmodified bitumen, synthesised from toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and polyaryl polyisocyanate (PAPI) by reaction with polytetrahydrofuran diol (PTMEG) respectively. And the performance of polyether-based PU modified bitumen was investigated at various contents of isocyanates. Firstly, the modification mechanism of PU modified bitumen binders was analysed by Fourier transform infrared spectroscopy (FTIR). Then, the high and low temperature properties and resistance to permanent deformation of modified bitumen binders were investigated through dynamic shear rheometer (DSR) test, bending beam rheometer (BBR) test and multiple stress creep recovery (MSCR) test. Finally, the microstructure and molecular movement were analyzed by fluorescence microscopy (FM), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). As the results show, there are significant differences in the molecular structure, cross-linking and hydrogen bonding of polyurethane modifiers synthesised from different isocyanates, which then affect the interaction between polyurethane molecules and bitumen molecules and result in different modification effects on bitumen. Concerning high-temperature properties and storage stability, PU synthesised by PAPI is the best solution for improving bitumen. PU synthesised by TDI offers the best improvement in low temperature performance. It is worth noting that the PU synthesised by MDI provides a more balanced improvement in high and low temperature performances. This study provides guidance for the development of PU modified bitumen.