In brief

A*STAR researchers have developed sturdier and longer-lasting coatings with not one, not two, but three different healing mechanisms.

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A three-in-one sustainable, self-healing coating

11 Nov 2021

Next-generation self-healing polymers use eco-friendly building blocks and manufacturing processes, providing superior durability and longevity to the materials they coat.

When we get a scratch or cut, our skin’s healing mechanisms repair the damage, quickly restoring the barrier against environmental threats. But what if everyday objects had the same restorative capabilities? From a sustainability perspective, such self-healing materials would be transformative—not only would objects last longer, but they would need to be replaced less frequently, staying out of landfills.

Thanks to innovations in materials science, this is already a possibility. Scientists have designed an array of polymer-based surface coatings with molecular properties that enable them to repair themselves after wear and tear. However, a major drawback is that the process of creating such self-healing surfaces is far from eco-friendly. These coatings use fossil fuels as raw materials and require the use of toxic chemicals during production.

In search of greener surface coating alternatives, a team of researchers led by Satyasankar Jana and Jayasree Seayad at A*STAR’s Institute of Chemical and Engineering Sciences (ICES) explored the possibility of using an emerging class of polymers called non-isocyanate polyurethanes, or NIPUs. Unlike traditional polyurethane coatings, NIPUs are made from sustainable, bio-derived building blocks, and can be manufactured efficiently using non-toxic chemicals, explained Jana.

In their study, the team investigated the self-healing properties of four novel NIPU formulations that they created. These NIPUs contained furan rings in their main polymer chain, which allowed them to crosslink to compounds called bismalemides, a reaction that gave them their intrinsic healing capabilities.

A closer look at the regenerative capacity of these NIPU-based surface coatings revealed a remarkable discovery. Existing self-healing surfaces modifications typically display a single mechanism of action, with their healing properties triggered by exposure to either heat or moisture—a feature that has limited the widespread application of these coatings. However, the next-generation NIPU coatings developed by the researchers possess not one but three different healing sites, giving them the unprecedented potential to self-repair even at room temperature.

A unique cross-linked structure between furan rings and bismalemides gives NIPU coatings their intrinsic healing capabilities.

© A*STAR Research

“Coatings with multiple healing mechanisms, especially room-temperature healing are really interesting as they will not require the inspection of healing sites or the application of special treatments like heat or moisture,” commented Jana, who added that this would substantially extend the service life of the coated substrates.

The team sees a niche for NIPU-based coatings in several commercial settings, including the automotive industry. As the next steps, there are plans to develop colorless NIPUs that can be used as clear glass coatings, given that current iterations of NIPU formulations are lightly colored. “We would also like to investigate the self-healing property of NIPU-based pigmented coatings as the pigments and other coating additives may influence their healing performance,” added Jana.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Chemical and Engineering Sciences (ICES).

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Choong, P.S., Chong, N.X., Tam, E.K.W., Seayad, A.M., Seayad, J., et al. Biobased Nonisocyanate polyurethanes as recyclable and intrinsic self-healing coating with triple healing sites, ACS Macro Letters 10, 635−641 (2021). | article

About the Researchers

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Satyasankar Jana

Senior Scientist and Team Leader

Institute of Chemical and Engineering Sciences
Satyasankar Jana is a Scientist in the A*STAR Institute of Chemical and Engineering Sciences’ Polymer Engineering and Characterization Division. His research interests include: Cool/NIR-reflective Coatings, No/Low VOC Waterborne Coatings and Coating additives, Biobased Non-Isocyanate Polyurethane, Antifouling/ Anti-dirt Coatings, ATRP/RAFT Polymerization, Smart/Responsive Polymers, Zwitterionic/ Ion-Pair Polymers, Polyoxazolines etc.
Jayasree Seayad is a senior scientist at the A*STAR Institute of Chemical and Engineering Sciences’ Functional molecules and polymers division. Her research interests are in green and sustainable methodologies for organic synthesis, organo- and transition metal catalysis, biomass valorization to specialty chemicals, bio-based polymers and plastic recycling.

This article was made for A*STAR Research by Wildtype Media Group