Kraft lignin-modified bitumen: A comprehensive analysis via rheology, FTIR and ¹H NMR spectroscopy

Abstract

The present study focuses on the characteristic, rheological and physicochemical properties as well as the short-term aging susceptibility of Kraft lignin-modified bitumen. The reference binder was a 70/100 penetration grade bitumen, from which three lignin-modified binders with different lignin content per weight (5%, 10% and 15% lignin content) were produced. The rheological characterization was conducted via a Dynamic Shear Rheometer (DSR). The sulfoxide and carbonyl functional groups of the binders were explored via Fourier Transform Infrared (FTIR) spectroscopy and the molecular structure of the binders was inspected via Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy. The aforementioned testing protocols were assessed before and after Rolling Thin Film Oven Test (RTFOT) aging to assess the impact of lignin on bitumen during short-term aging, a crucial process during the production stage. Two rheological and four physicochemical aging indexes were calculated to quantify the short-term aging susceptibility of bitumen. A notable reinforcement of bitumen’s resistance to rutting and permanent deformation was observed following bio-modification, albeit with a compromise in fatigue performance. Kraft lignin contributed to increased aging susceptibility of bitumen across all chemorheological aging metrics. Additionally, the sulfoxide FTIR region correlated significantly with the mechanical characteristics of bitumen, especially when determined via the subtraction computational approach. Finally, the two spectroscopic techniques should be applied complementarily, as each provides unique, non-redundant structural information.