The molecular mechanisms of plasticizers in rejuvenating oxidized asphalt: A preliminary study

Plasticizers are common additives used to enhance the flexibility and workability of polymer materials. Recent findings suggest a great potential for typical plasticizers being used as rejuvenators to recycle oxi-dized paving asphalts. This study investigated the rejuvenating effectiveness of two plasticizers via rhe-ological evaluation and explored the underlying mechanism by analytical characterizations and molecular dynamics (MD) simulations. A conventional plasticizer dibutyl phthalate (DBP) and an envi-ronmentally friendly tributyl citrate (TBC) were selected given the discrepancies in their molecular struc-tures. Both plasticizers were effective in restoring the rheological performance of the aged asphalt; TBC was relatively more efficient which was attributed to its higher molecular polarity and the formation of hydrogen bonds with the oxidized asphalt molecules. Analyses based on the gel permeation chromatog-raphy and differential scanning calorimetry suggested the capability of the plasticizers in dissociating the oxidized asphalt molecules and improving the molecular mobility. The improved molecular mobility was considered responsible for the reversing effect of the plasticizers, as compared to aging, in terms of widening the relaxation spectrum and broadening the glass transition region. The plasticizers' dissociat-ing effect was confirmed and visualized in the simulations by inspecting their impacts on the spatial arrangement and distribution of the asphaltenes.(c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigates the rejuvenating effectiveness of two plasticizers in restoring the rheological performance of aged asphalt. The results show that both dibutyl phthalate (DBP) and tributyl citrate (TBC) are effective, with TBC being more efficient due to its higher molecular polarity and ability to form hydrogen bonds with oxidized asphalt molecules. The plasticizers also improve the molecular mobility of the asphalt, widening the relaxation spectrum and broadening the glass transition region. These effects are confirmed by gel permeation chromatography, differential scanning calorimetry, and molecular dynamics simulations.