A guide to self-healing materials
NASA has invented a self-healing polymer that can automatically heal punctures by bullets. In NASA’s case, this material will heal space craft hit by space debris at high speeds. The material is designed to locally melt upon impact. The melt elasticity of the material means it will then snap back and close the hole.
NASA is not alone in their developments. Researchers at the Vrije Universiteit Brussel (VUB) have brought self-healing properties to soft robots. These are robots constructed from flexible materials that allow them to grab delicate objects in the food industry or in minimally invasive surgery.
The Massachusetts Institute of Technology (MIT) is working with Lamborghini to build a self-healing electric sports car. The idea: the car will conduct its own health monitoring, detecting any cracks or damages in its structure. Once identified, it will begin to self-heal through micro-channels filled with healing chemistries. This will reduce the risk of small cracks propagating further in the carbon-fibre structure.
Harvard researchers have developed a tough, self-healing rubber. Imagine a car tyre repairing itself from a nail puncture. Goodyear have also developed a self-healing car tyre.
Self-healing materials are appearing in just about every industry, from construction (self-healing asphalt) to oil & gas (self-healing oil-well casings).
There are essentially three types of self-healing mechanisms:
Embedded heating agents
Encapsulated healing agents are embedded in the material matrix. Built-in microcapsules filled with a glue-like chemical repairs the damage. If the material cracks inside, the capsules break open, and the repair material is released. The crack seals up immediately, making it ideal for NASA and their astronauts in space. The drawback for other industries is repeatability. Once the microcapsules are used, that’s it.
The word ‘vascular’ is a nod to how our bodies work when damaged: our vascular system sends help to the damaged area when needed. These materials have thin tubes that, when triggered by the damage, pump healing agents, such as adhesives, to the affected area. This is the preferred method of researchers, as it can contribute to the long life of the application, such as a bridge or building. The drawback is that the healing agent has further to travel, but if we’re talking about a slow-spreading crack that needs repairing, it’s not a problem.
Intrinsic polymer-based systems
Materials with intrinsic healing properties are triggered by external stimuli, such as electrical or photo-stimuli, or the reaction of substances when introduced together. The result is the restoration of the material’s integrity. Self-healing cement sometimes uses this method.
Of course, the ideal method will depend on the final application. Right now, the most promising applications for self-healing materials are in the automotive/aerospace, building and construction, and oil and gas sectors. Their favourite material choices are polymer composites, paints and coatings, and cement and concrete.
Plastics Today points out, “The technology drivers for applications in all sectors are robustness, functional restoration (meaning that the base properties of the material are not diminished following the healing cycle), long-term reliability, ease of adoption and cost benefit to the end user.”
What about consumer electronics and wearables? Users will have to decide if they’re willing to pay a premium, says Issac Premsingh, an expert and industry analyst in computational quantam chemistry. According to Premsingh, we’re still about five years away from self-healing batteries and devices, so we don’t yet know the wide-scale commercialisation for these technologies.
That’s not stopping manufacturers. Some companies, such as LG, have already started using self-healing materials in the production of smartphones. Research by Modor Intelligence reports that the electrical & electronics sector is expected to account for the highest share in the market by 2022.
According to Premsingh, the immediate applications in sectors such oil and gas are making self-healing technology a must-have. Self-healing coatings are now being used to coat docks, ships or platforms in order to strengthen steel underneath and prevent it from corrosion. The problems self-healing technology can prevent represent a big savings in time and money, while increasing efficiency.