Environment-friendly microcapsules containing waste soybean cooking oil as an anti-aging rejuvenator for bitumen

In recent years, the use of waste cooking oils as bitumen rejuvenators has become a prominent research focus in the fields of environmental science and materials engineering. This approach not only addresses the problem of waste oil disposal but also facilitates bitumen recycling. In this study, we aimed to prepare microencapsulated waste soybean cooking oil (microWSCOs) using widely available sources in China, achieving in situ aging delay in bitumen. Optical microscopy and SEM analysis confirmed that the microWSCOs exhibited a spherical core-shell structure with no observable damage. FT-IR and EDS analyses revealed that the shell consisted of HMMM and PVA in varying proportions, where cross-linked HMMM formed the skeleton of the shell material, and PVA gel filled the pores of the HMMM skeleton, acting as permeation channels for WSCO release. TGA analysis demonstrated that the microWSCOs exhibited thermal stability capable of withstanding temperatures exceeding 200 °C while maintaining structural integrity in bitumen. Nano-XCT and SEM imaging showed uniform dispersion of microWSCOs in bitumen with intact interfacial structure. The permeation rate of WSCO through the shell was governed by the PVA content, where higher PVA content resulted in more oil permeation channels. Fluorescence microscopy confirmed the release process of WSCO in bitumen. Under high-temperature conditions, the diffusion rate decreased due to the thermal expansion of PVA gel, which obstructed the oil permeation channels. Since PVA is hydrophilic , oil molecules could not diffuse through it. At lower temperatures, PVA gel contracted upon freezing, reopening the oil permeation channels and enabling WSCO release. Mechanical property and softening point measurements of microWSCO/bitumen samples demonstrated that WSCO release significantly mitigated bitumen aging, effectively restoring bitumen performance. Morphology of dried microWSCOs, photographs: (a) 1.0 Kg dried microWSCOs (M 11 ) powder in a plastic bag, (b) dried microWSCOs (M 11 ) powder in a bottle, and (c) microWSCOs (M 11 ) powder without adhesion; SEM morphology of dried microWSCOs samples of (d) M 12 , (e) M 11 and (f) M 21 , and (g-i) single microWSCOs (M 13 ) with broken shell. • Waste soybean cooking oil was acted a rejuvenator for anti-aging bitumen. • Waste soybean cooking oil was microencapsuled by HMMM/PVA shells. • Microcapsules had a good thermal stability and dispersion in bitumen. • Waste soybean cooking oil penetrated into bitumen controlled by the PVA molecules.