Investigating the Compatibility Mechanism of Bitumen Modified with Photo-Oxidative Aging of Polyethylene Using Molecular Dynamics Simulation

Oxidation degrees of recycled polyethylene (RPE) particles affect the compatibility between RPE and bitumen, resulting in the low properties of RPE-modified bitumen and uncontrolled production technology. In this study, polyethylene (PE) samples were subjected to photo-oxidative aging for 0, 8, 32, 64, and 128 days using a fluorescent ultraviolet (UV) lamp test chamber, labeled as PE-D0, PE-D1, PE-D2, PE-D3, and PE-D4. The changes in molecular functional groups at each aging condition were obtained by Fourier transform infrared spectroscopy (FTIR). Based on the FTIR result, the interaction mechanism between virgin bitumen and PE with different photo-oxidative aging degrees was studied using molecular dynamics (MD). The compatibility of the two-phase structures was characterized by the fluorescence microscope (FM). The rheological properties were evaluated by dynamic shear rheometer (DSR). The MD result showed that the binding energy of PE-D1 saturates, and PE-D1 aromatics were the largest, increasing by 26.31 and 64.07 kcal/mol, respectively. The diffusion coefficients decreased with the interaction strength. The DSR result showed that PE with slight photo-oxidative aging improved the rutting resistance of the modified bitumen. The FM indicated that PE-D1 was dispersed more uniformly in the bitumen phase and also had a better compatibility performance. The results showed that PE with slight oxidation benefits the compatibility between PE and bitumen components. The mechanisms in this study provide new insights for a better comprehension of the compatibility of bitumen and PE and the creation of high-performance modified bitumen from recycled waste plastics.