Self-Healing Rubber

A new rubber material has been developed that repairs itself when torn or punctured – a discovery that could someday lead to self-repairing shoes, toys and even electronics. The material can be quickly manufactured using 3D printing methods and a process known as photopolymerization, which utilizes light to solidify a liquid resin to form a desired shape.

Photopolymerization relies on chemicals called thiols to form the cross-linked bonds that cause the resin to harden. Another group of chemicals called disulfides enable these bonds to reform when broken, and can be formed from thiols by adding an oxidizer to the polymer. But the two chemicals compete with each other, i.e., when photopolymerization factors are strong, self-healing behaviors are weak, and vice versa. The key was to find the optimum ratio between thiols and disulfides that would deliver both.

The material was tested in several forms – as a shoe pad, soft robot, multiphase composite and electronic sensor. The 3D printed samples were cut in half, and after just two hours at 60 degrees Celsius had repaired completely to regain their original strength and function. Changing the temperature (over a range of 40 to 60 degrees Celsius) impacts the speed of the reaction, but the material will heal even at room temperature.

The next step will be to apply these methods to create materials of varying stiffness, from soft rubbers to harder plastics. Applications could include everything from vehicle parts to body armor.