A team of scientists has developed a 3D printed self-repairing rubber. Rather than throw away your punctured tires and broken boots, why not let them fix themselves?
Assistant Professor Qiming Wang has been researching printed materials for years. He has created new functions for a range of purposes, from sound control to flexible electronics.
Now, Prof. Wang and colleagues have created a new material that they can manufacture rapidly. This new material is self-repairing. In other words, it fixes itself if it becomes punctured or fractured.
The researchers believe their material could be a game-changer for industries like tires, soft robotics, and shoes. It could also be game-changing for electronics. The self-repairing rubber not only reduces manufacturing time but also increases product durability and longevity.
The researchers wrote about their work in the journal NPG Asia Materials (citation below). The authors were Kunhao Yu, Qiming Wang, An Xin, Haixu Du (all from the University of Southern California); and Ying Li (University of Connecticut).
Self-repairing rubber 3D printed using photopolymerization
The scientists used a 3D method that uses photopolymerization to manufacture the material. The process uses light to turn a liquid resin into a solid in a desired geometry or shape.
To make the rubber self-healing, they had to dig slightly deeper into the material’s chemistry.
Photopolymerization is achieved through a reaction with thiols. Thiols, organic compounds, are sulfur (UK: sulphur) analogues of alcohols. With the addition of an oxidizer, thiols transform into disulfides (UK: disulphides). Disulfides belong to a functional group with the structure R−S−S−R′.
It is the disulfide group that gives the new material its self-healing quality. The key to unlocking the unique properties of the materials lay in finding the right ratio between the two groups.
Prof. Wang explained:
“When we gradually increase the oxidant, the self-healing behavior becomes stronger, but the photopolymerization behavior becomes weaker.”
“There is competition between these two behaviors. And eventually, we found the ratio that can enable both high self-healing and relatively rapid photopolymerization.”
Self-repairing within hours
The researchers say they can print a 17.5-millimeter square in just five seconds. Whole objects take approximately twenty minutes. They are self-repairing within just a few hours.
The scientists demonstrated their material’s ability on a variety of products, including a soft robot and a shoe pad. They also demonstrated its ability on an electronic sensor and a multiphase composite.
According to a University of Southern California press release:
“After being cut in half, in just two hours at 60 degrees Celsius (four for the electronics due to the carbon used to transmit electricity) they healed completely, retaining their strength and function. The repair time can be decreased just by raising the temperature.”
First author, Mr. Yu, a PhD (structural engineering) student, said:
“We actually show that under different temperatures – from 40 degrees Celsius to 60 degrees Celsius – the material can heal to almost 100 percent.”
“By changing the temperature, we can manipulate the healing speed, even under room temperature the material can still self-heal.”
The researchers are now trying to develop self-repairing materials along a range of stiffness, from hard plastics to the current soft rubber.
They believe that their self-healing rubber could be used for composite materials, vehicle parts, and even body armor.
3D printing contrasts with subtractive manufacturing, where you remove material until you have your product. You might, for example, start with a block of wood and chip away at it until you have your product.
“Additive manufacturing of self-healing elastomers,” Kunhao Yu, An Xin, Haixu Du, Ying Li, and Qiming Wang. NPG Asia Materials, Volume 11, Article number: 7 (2019). DOI: https://doi.org/10.1038/s41427-019-0109-y.