Sustainable castor oil and hydroxyl-terminated polyester oligomer-based polyurethane modified bitumen

Castor oil (CO) and hydroxyl-terminated polyester oligomers (HTPO) generated via alcoholysis of waste polyethylene terephthalate bottles were used to develop CO-HTPO-based polyurethane (CH-PU) modified bitumen (CH-PUMB). Optimisation of CH-PUMB composition and curing via fundamental physical properties yielded optimal values: hard-segment 20%, reactive-group ratio 1.2, CO molar ratio 2:1, and curing at 155 °C for 1 h. Softening point and 5 °C ductility increased with CH-PU content and the substitution ratio (SR) of the total amount of CO and HTPO relative to polytetramethylene ether glycol. At 30% CH-PU, increasing SR from 20% to 50% raised the softening point from 83.0 to 100.0 °C and ductility from 21.5 to 30.0 cm. Moreover, increasing CH-PU content improved the rheological properties (multiple-stress creep recovery, zero-shear viscosity, and linear amplitude sweep) of CH-PUMB, and near 30% SR achieved the best. Finally, the calculated mixing temperature and dynamic viscosity of CH-PUMB decreased with increasing SR.