Mixing temperature optimization and modification mechanism of medical masks modified asphalt: Insights from computational chemistry

Abstract

Masks modified asphalt (MMA) offers a solution to pollution caused by discarded medical masks. Mixing temperature plays a crucial role in storage stability and even rheological performance of MMA. Traditional selection method overly relies on trial-and-error experiment, neglecting the convenience offered by computational chemistry. Furthermore, previous literature lacks precise elucidation of MMA’s physical modification mechanism, especially concerning the binding mode and energy composition. To address these issues, the optimal mixing temperature for MMA was recommended based on molecular dynamics. The rationality of recommended temperature was validated through laboratory tests, simultaneously investigating the impact of heating time. Fluorescence microscopy and multi-band spectroscopy were employed to acquire the microstructure. Binding modes in MMA were determined using binding sites exploration, evaluating the energy composition of each binding mode through quantum chemistry. The interaction mechanism was explained based on surface properties of isolated molecules. Results indicated that 170℃ was the recommended optimal mixing temperature derived from mixing free energy and Flory-Huggins interaction parameter. The fluctuations in softening point difference (ΔTR&B) and separation ratio (RS) concurrently tended towards stability, thereby validating the reliability of recommended temperature. Moreover, even after 72 h heating, MMA prepared at recommended temperature remained within a reasonable range concerning ΔTR&B, RS, and microscopic structure. Perpendicular, parallel, toroidal, and spherical modes emerged in MMA. Perpendicular and parallel modes exhibited the highest binding energies, while circular mode demonstrated the lowest. Binding energy is primarily governed by van der Waals interaction, attributed to the dominance of dispersion term on MMA’s molecular surface. Besides, due to the presence of polycyclic aromatic hydrocarbons in asphalt molecules, electrostatic interaction contributed to specific molecular bindings.