Intermolecular Interactions of Isolated Bio-Oil Compounds and Their Effect on Bitumen Interfaces

Abstract

Bio-oils derived from low-value or waste biomass have been shown to be useful as low-cost, sustainable additives to improve the adhesion or moisture resistance of bituminous asphalt binder. The chemical profile of bio-oil is complex, and identifying the most active compounds in the mixture and understanding how they work to modify bitumen properties is essential for synthesizing bio-based additives with desired characteristics and performance. Hexadecanamide and hexadecanoic acid, two surfactants prevalent in both animal-and plant-derived bio-oils, are notable candidates as active compounds responsible for altering the colloidal or interfacial properties of bitumen. In this study, pure forms of these surfactants were mixed into bitumen to examine their effects on binder composition and morphology. AFM and FTIR data show that the amide strongly separated from the mixture, much of it crystallizing at the exposed surface. The DFT-based studies indicate that selfassembly of amide molecules is energetically preferred to adsorption of amides to asphaltenes or wax crystals in bitumen. The acid seemed to mix in well but induced the growth of a unique morphology at the glass interface. However, in combination, the amide and acid improve each other's solubility without strongly interacting with each other. Other molecules in bio-oil may similarly work to improve the solubility of the total mixture and make it an effective surface-modifying additive.

Surface Morphology and Chemical Mapping of UV-Aged Thin Films of Bitumen

“…We previously used AFM–IR to study the chemical composition of modified bitumen and its interface with mineral fillers or glass, showing how some compounds preferentially accumulate at the bitumen–mineral interface. − Xing et al performed AFM–IR on thermally aged samples of bitumen and styrene-butadiene-styrene-modified bitumen and showed that there are some differences in chemical composition of the surface of the bitumen and the bulk. , A recent study used AFM–IR to identify changes in bitumen surface morphology and composition with decreasing temperatures . Here, we used AFM–IR to examine the surface composition of spin-coated bitumen thin films with or without UV aging.…”

Sustainability Implications of Regenerative Sulfur Blooms in Bituminous Composites

“…Our previous work has shown that certain chemical compounds in bitumen tend to migrate toward and separate out at bitumen interfaces. For example, fatty acid compounds can accumulate at the bitumen–silica interface and increase the susceptibility of asphalt concrete to moisture damage. − We also showed that saturated wax crystallizes as lamellae at the bitumen–air surface that wrinkles under compressive strain to produce the characteristic “bee-like” structures often observed on bitumen surfaces. , …”

Effects of Elemental Sulfur on the Aging Trajectory and Adhesion Characteristics of Rubber-Modified Bitumen

“…However, many acid groups are probably hydrated, which would shift their SO and S–O absorption peaks to ranges similar to those of ionic groups ( 3d , 6c , or 7c ). Carboxylic acid compounds have previously been implicated in reducing the moisture-stripping resistance of bitumen in asphalt pavement. − Sulfoxides were found to be less susceptible to water displacement from aggregate surfaces than carboxylic acids but more susceptible than nitrogen compounds . Sulfuric and sulfonic acids are more easily ionizable than carboxylic acids and merit further observation in case they have a similarly damaging effect.…”