Evolution of Morphological and Nanomechanical Properties of Bitumen Thin Films as a Result of Compositional Changes Due to Ultraviolet Radiation

Abstract

This paper examines morphological and nanomechanical changes as compositional evolution occurs because of ultraviolet (UV) radiation in thin films of bituminous adhesives. Such an insight is important for developing strategies to enhance sustainable applications of such adhesives for coating and composite manufacturing. However, the shallow penetration depth of UV light in bitumen complicates efforts to isolate its effects. To address this question, this study examined the effects of UV exposure on spin-coated films of bitumen that are 600 nm thick. Bitumen thin films were UV-aged in an accelerated weathering machine and were characterized by scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, UV–visible absorption spectroscopy, and nanoindentation. As UV radiation continued from 0 to 400 h, the hydrocarbon content of thin films gradually decreased, leaving behind sulfates and carbonyls and reducing bitumen solubility in organic solvents. This in turn led the bitumen thin films to become thinner and chemically and morphologically more heterogeneous. Nanoindentation showed a dramatic increase in stiffness and loss of viscoelasticity after 20 h of UV exposure. Stiffness continued to increase up to 50 h and nearly reached a plateau. The study results provide insights into the effects of UV radiation on structure–property changes in bitumen thin films, explaining how UV exposure causes rapid embrittlement and failure in bituminous adhesives, coatings, and composites. This in turn enables the design of sustainable bituminous composites with enhanced resistance to UV aging.

Inherently Functionalized Carbon from Lipid and Protein-Rich Biomass to Reduce Ultraviolet-Induced Damages in Bituminous Materials

“…The findings are in line with other studies showing the benefits of carbonaceous nanoparticles in delaying asphalt aging. 9 , 33 …”

“…The findings are in line with other studies showing the benefits of carbonaceous nanoparticles in delaying asphalt aging. 9,33 Finally, all the aging indexes calculated for different aging levels for the sample with no biochar and the sample with algal biochar (100−0) are summarized in Table 8.…”

“…The authors found that a bitumen film with a thickness of 600 nm became stiffer and lost its viscoelasticity after 20 h of UV exposure performed in an accelerated UV chamber. 9 In another study, bitumen was aged by exposure to combined oxidation and UV radiation, and the changes in the chemical and physical properties of the bitumen were measured; it was found that the aging process led to the formation of conjugated structures and increased the content of fused polyaromatic hydrocarbons. 10 There is a consistent increase of the carbonyl content and loss of saturated hydrocarbons during aging of bitumen.…”

“… 3 This is further accompanied by diffusion of oxygen and aging products deep within the bitumen layer. 9 …”

“…3 This is further accompanied by diffusion of oxygen and aging products deep within the bitumen layer. 9 While there have been several works on the merit of using biochar in asphalt, there is controversy pertaining to its efficacy. In addition, existing works mostly report on the effect of single-sourced biochar (for instance wood-based biochar) without accounting for variation among biochars based on their processing parameters, methods of conversion, and feedstock sources.…”