Evaluation of Physical and Physicochemical Properties of Bitumen with Lignin from Bio-ethanol Residue

The objective of the present study is to evaluate the potential of lignin-containing by-products obtained from the bio-ethanol industry as a partial substitution for bitumen. The study investigated how the chemical composition of lignin, derived from rice straw biomass, impacts the physical and physicochemical properties of bitumen. Specifically, the paper explored the effect of incorporating the fermentation residue (FRL) and isolated lignin (IL) at varying concentrations (5, 10, and 15%) into VG40 grade base bitumen. To characterize the chemical structure of IL and FRL, the study employed elemental analysis (CHNS analyzer and X-ray fluorescence spectrometer (XRF)) and Fourier transform infrared (FTIR) spectroscopy. The study then evaluated the physical properties such as softening point, viscosity, storage stability, complex shear modulus master curves, and physicochemical properties (surface free energy (SFE)) of the IL and FRL partially substituted bitumen. The chemical analysis of lignin-containing by-products revealed the structural similarity between lignin and bitumen. The addition of IL and FRL increased the softening point, viscosity, and complex shear modulus of the base bitumen. However, the storage stability tests revealed a higher degree of separation for bitumen with FRL. Therefore, if storage stability is a critical criterion, it is advisable to limit the use of FRL to 10%, while IL can be employed up to 15% or even higher concentrations. Furthermore, the SFE of the IL partially substituted bitumen increases with higher lignin content, signifying enhanced cohesive properties. In contrast, the addition of FRL reduces the SFE of the bitumen.