Optimization of synthesis technology to improve the design of asphalt self-healing microcapsules

Microcapsules are considered as a potential method to enhance self-healing capability in asphalt materials. This study aims to investigate the optimization of self-healing microcapsule synthesis technology. According to prepolymer synthesis test results, the melamine-urea-formaldehyde (MUF) terpolymer, which contains 20 wt% urea, is selected as shell material. Fluorescence Microscope (FM) is employed to observe the rejuvenator emulsion and prepared microcapsules. The result reveals that Sodium Dodecyl Sulfate (SDS) has the best emulsion performance and can be determined as emulsifier of core material. By means of FM and microcapsule size calculation, sixteen sets of microcapsules prepared under different conditions are investigated to determine the optimization of reaction condition. The optimal MUF microcapsule is synthesized under core/shell ratio as 2:1, end point reaction temperature as 65 °C, emulsifying speed as 1500 r/min, emulsifier content as 0.7% and end point pH as 3. Scanning Electronic Microscope (SEM) result shows that the microcapsules are spherical and intact without damage. Fourier Transform Infrared Spectroscopy (FTIR) result indicates that with the increase of core/shell ratio, shell material in microcapsules becomes less. Thermo-gravimetric analysis (TGA) result shows that the mass loss of microcapsules is not distinct after maintained at 180 °C for 1 h, indicating that the optimal microcapsules can meet the temperature requirement of asphalt mixing and compaction. Finally, the self-healing process of microcapsules in asphalt binder is observed to prove the healing efficiency.