Mechanism and rheological characterization of MDI modified Wood-Based Bio-Oil asphalt

The application of waste wood-based bio-oil in asphalt binder has illustrated many performance advantages for the pavement. However, the introduction of bio-oil to asphalt binder has challenges associated with poor high-temperature performance. To address this matter, the liquefied 4,4′-diphenylmethane diisocyanate (MDI) was utilized as an additive to enhance the high-temperature performance of wood-based bio-oil asphalt (WBBA), while not reducing its low-temperature properties in this paper. Five ratios of MDI (0%, 0.5%, 1%, 2%, and 4%, by weight of bio-oil asphalt) were selected to prepare MDI modified wood-based bio-oil asphalt binder (MDI-WBBA). Fourier Transform Infrared Spectroscopy and Rod Thin Layer Chromatograph were conducted to explore the modification mechanism, while temperature sweep, frequency sweep and bending beam rheometer test were carried out to evaluate the rheological performance of MDI-WBBA. This study aims to correlate the observed rheological behaviors with the chemical reactions occurring during the process of MDI modification. The results indicated that the MDI modification was a chemical process, and the polyurethane and urea linkage in reaction polymers could easily lead to hydrogen bonds, which could increase the physical cross-linking density, and further enhance the strength and elasticity of the MDI-WBBA. Meanwhile, the asphaltenes significantly increased and the modified asphalt binder gradually tended to gel type. In particular, the colloidal structure remained stable when the amount of MDI reaches 2%. Furthermore, the high temperature and viscoelastic properties significantly enhanced through the black curve and master curve of G*, while the low-temperature behavior experienced a slight rise with the addition of MDI, which could provide an efficient method to alleviate the environmental problems of waste mass