Room temperature self-healing epoxy waterborne polyurethane containing microcapsules with waterborne polyurethane shells and mercaptan cores

Regardless of various strategies for preparing microcapsules to obtain self-healing materials with high efficiencies, it remains a significant challenge to use suitable shell materials to capsulate mercaptans due to their high reactivity. Herein, we report a simple method to utilize waterborne polyurethane (WPU) prepolymers which have priorities to react with diethylenetriamine (DETA) over thiol functional groups to make pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) incorporated into microcapsules successfully. Self-healing epoxy waterborne polyurethane (EWPU) was prepared by embedding this kind of microcapsule into the matrix. Once microcracks expand, microcapsules break and release PETMP to the valley of the microcrack to react with epoxy functional groups under the self-catalytic effects of triethylamine (TEA), making microcracks recover to the original state and reaching the self-healing target. The spherical morphology of microcapsules is affected by the TEA content that is determined to be 60% of the theoretical value for totally neutralizing 2-bis (hydroxymethyl) propionic acid (DMPA) in WPU prepolymers. Microcapsule components have been confirmed by FTIR spectroscopy. The core content of PETMP is about 60.66% resulting from TG analysis. The best self-healing conditions for EWPU include 8 wt% microcapsules and healing at room temperature for 2 days. The net self-healing efficiency could reach nearly 100%. In addition, the hydrophilic-lipophilic balance (HLB) values of emulsions are investigated by the droplet size test method. The HLB value of PETMP has been deduced to be 12.2, offering theoretical guidance to explore the emulsion properties. Finally, this efficient and straightforward preparation technology provides potential application values for self-healing materials in industry.

Automated summary

This article presents a simple and efficient method to encapsulate reactive mercaptans using waterborne polyurethane (WPU) prepolymers. The encapsulated mercaptans are successfully incorporated into microcapsules, which are then embedded in a self-healing epoxy waterborne polyurethane (EWPU) matrix. The self-healing efficiency of the EWPU is nearly 100%, making it a promising material for industrial applications.