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Dr Merryn Haines-Gadd, Postdoctoral Research Associate looks at the development of self-healing materials and how they could be used to develop more sustainable products.13 October 2020
Since the industrial revolution, the innovation of materials has helped to shape our work and social lives, being at the heart of technological development and human endeavour. In the face of complex global challenges such as climate change and sustainable development, how materials are used and reused is critical.
Researchers in both academia and industry are working together to develop novel, smart materials that not only provide enhanced properties and uses, but also contribute towards building a more sustainable future.
Self-healing materials are one such innovation.
Inspired by biological systems, self-healing materials can repair themselves when damaged, either autonomously using inherent capabilities or through triggers such as heat, light, or pressure. There are two main classifications – intrinsic and extrinsic self-healing materials.
An example of intrinsic is self-healing poly-urethane, which if cut, the edges can be pushed backed together and the chemical bonds of the materials will reform. A good example of extrinsic is self-healing concrete, in which encapsulated bacteria is embedded into the bulk of the material, so that when damage occurs it produces calcium carbonate to repair the cracks as they appear.
At the University of Exeter, as part of ‘Manufacturing Immortality’, a multidisciplinary research collaboration between seven UK universities, our focus has been on collaborating with industry to uncover the most suitable design applications and the environmental implications of this technology.
In the course of this work, we have uncovered several opportunities as well as challenges.
Principally, self-healing materials have the potential to prolong the primary lifetime of a product. This is especially useful for situations where products necessitate a long lifespan or operate in harsh environments such as buildings and bridges, wind turbines and deep sea cabling within the energy sector; satellites for deep space exploration and even within the human body as with medical implants and prosthetics. In addition to lifetime extension, self-healing would also reduce the cost and risk that is associated with repair, which for many of these examples poses a great risk to human health.
Beyond physical durability, wear and tear is one of the key drivers for why products are prematurely replaced by consumers. Therefore, a product that can resist scratches or undergo a simple refurbishment treatment and be returned to a like new condition would mitigate this issue. Now, this is primarily being discussed within the automotive industry, but could be applied in other sectors. For example, for councils with building facias and public furniture to maintain the quality of social spaces. Perhaps the biggest mass potential is within consumer electronics enabling our mobile phones, iPads, and appliances to be in service for longer.
The disassembly and reassembly of products is vital for product longevity. However, this process often damages components to the extent that value cannot be recovered. Considering that some self-healing rubbers can repair up to 18 hours after they are cut, this extended material functionality could contribute to increasing the ease at which products are disassembled and reassembled. Imagine a product with an entirely sealed casing that can be cut and re-bonded. This would ultimately reduce the number of parts and components needed to make the product.
A current key limitation is that few materials have been tested beyond laboratory-based environments. There are handful of commercially available products such as self-healing paints and coatings, self-healing tires, and gas tanks. However, the diffusion of this innovation to the market has been slow. Overall, more case studies are required to show the true performance and reliability of these materials in situ, and in everyday use.
One barrier highlighted by our industry partners is the issue of warranties and liability. All products are subject to standards and compliance. However, measures have yet to be defined for assessing the health and safety associated with self-healing materials. It is important for producers and consumers to understand what the safety and liability issues would be if a healed product were to be kept in service.
Overall, however, the future looks very positive. The advanced functionality of self-healing materials offers many exciting opportunities for innovation within both the private and public sectors. In time, we will all be interacting with these materials daily. This will be good for us as consumers, but crucially should also contribute positively to the fight against climate change and dwindling natural resources.
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