Researchers in China have developed a self-healing epoxy resin which can be repaired by heating when cracks form. 

Epoxy resin is a tough polymer with many uses from glues to circuit boards, aerospace engineering to art restoration. Epoxy materials are often used under harsh conditions where long-term service and durability are needed. So, it would be ideal if damaged epoxy resin could self-heal, a property recently developed for other polymers.

Conventional epoxy resin is based on epoxides to which an additive (or curing agent) is added to form cross-linking between the chains strengthening the polymer. However, these cross-linked bonds are usually irreversible meaning that if cracks form, the bonds cannot be remade to repair the material. 

Min Zhi Rong and co-workers from Zhongshan University, Guangzhou, China, have solved this problem by making a new epoxy material which contains both epoxide and furan groups in the same molecule. To this they add a maleimide-based curing agent, as well as the conventional anhydride curing agent.

The anhydride forms irreversible strong bonds with the epoxide groups but the maleimide makes bonds with the furan groups which are reversible at 110 degrees centigrade. So when cracks form in the cured polymer, it is heated to 120 degrees centigrade to break the reversible bonds and then cooled to 80 degrees centigrade so the broken bonds could reform.

'The smart epoxy not only has the superior properties over conventional epoxy', claims Rong, 'but it also exhibits thermal self-healing'. Rong goes on to say that his epoxy 'may prolong the service of the products made from the resin'.

Fred Wudl, a polymer expert from University of California, Los Angeles, US, says Rong's work 'is an interesting step towards creating remendable epoxy resins, following on from previous work in the field.' 

Rong says that his group is currently working to make an epoxy resin which will be able to self-heal at lower temperatures. 

Ruth Doherty

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