Chemical and Rheological Characterization of Polyurethane-Modified Bio-Asphalt

Abstract

Every year a huge amount of wood and forestry waste is produced, which needs to be landfilled. The bio-oil obtained from pyrolysis of the wood and forestry waste is a low-viscosity material that has a similar chemical structure to petroleum-based asphalt binder. Therefore, it has been used to partially replace the petroleum-based asphalt binder. Bio modification of asphalt binder resulted in a higher aging susceptibility and a decline in the high-temperature grade of asphalt binder. Thus, bio-oil application in asphalt pavement has been limited to low percentages. In a novel approach, and to address the challenges related to bio-asphalt, polyurethane modification (PU) of bio-asphalt was introduced. Polyurethane bonds form when isocyanate groups (-NCO) react with hydroxyl groups (-OH) in bio-oil and asphalt binder. Fourier-transform infrared (FTIR) spectroscopy was used to confirm the presence of hydroxyl groups in wood-based bio-oil, while elemental analysis was conducted to identify its chemical structure. An unmodified asphalt binder commonly used in the state of North Carolina, PG 64-22, was mixed with two different percentages (10% and 20%) of local wood-based bio-oil. Next, the prepared bio-asphalt samples were mixed with two different percentages of methylene diphenyl diisocyanate (MDI) (2% and 4%) to produce the PU-modified bio-asphalt. FTIR was used to examine the chemical reaction of MDI and bio-asphalt, and the formation of urethane and urea bonds. Results confirmed the formation of urethane after the addition of MDI. Dynamic shear rheometer (DSR) was used to evaluate the rheological properties of unmodified and modified samples. An increase was observed in the toughness and complex modulus of bio-asphalt samples when 2% MDI was added to 10% bio-asphalt.