Synthesis and physicochemical properties of high compact microcapsules containing rejuvenator applied in asphalt

Microcapsules containing rejuvenator is a promising chemical product applied to prolong the service-lift of asphalt. The aim of this work was to synthesize and characterize the physicochemical properties of novel microcapsules containing rejuvenator by in-situ polymerization of methanol–melamine–formaldehyde (MMF) prepolymer. A two-step coacervation (TSC) was successfully applied to enhance the thermal stability and compactability of shells with the help of styrene maleic anhydride (SMA) as surfactant. The optimum usage of SMA was 1.5–2.0 wt.% of rejuvenator. FT-IR results showed that the rejuvenator had been encapsulated by MMF resin. The parameters of average size, shell thickness, shell density and encapsulation efficiency could be controlled by adjusting the emulsion stirring rate and core/shell ratio. TGA tests indicated that microcapsules had a thermal decomposing temperature higher than the melting temperature of asphalt. Compactability measurements showed that more shell material could encapsulate the core droplets even better. However, surface morphology observation showed that the optimum core/shell weight ratio is 1/3, because excess prepolymer made the microcapsules in an aggregated state. By adjusting the temperature increasing rate of 2 °C min−1, powder microcapsules were easily be fabricated without aggregation.

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► Novel microcapsules containing rejuvenator had been fabricated by in-situ polymerization.
► A two-step coacervation was applied to form methanol–melamine–formaldehyde shell.
► The microcapsules had high compact structure and thermal stability.
► The surfactant amount and core/shell ratio had been optimized.