Dr Chaoying Wan, Reader (Associate Professor) of Functional Polymers and Nanocomposites at the Institute for Nanocomposites Manufacturing (IINM), WMG, University of Warwick, provides an insight into the importance of sustainability and a circular economy in rubber production. Dr Wan highlights how considered changes to production processes could play a huge part in global efforts to enable the transition to sustainable advanced rubber products.
As the UK continues its support of global decarbonisation efforts, the implementation of new innovative manufacturing decisions around principles of sustainability has never been more important. This is particularly valid when we reflect on the manufacturing processes and usage patterns of materials across the world as a means of fulfilling business and consumer demands across a plethora of industries.
Rubber is one of the most diversely used materials in the world, with widespread applications in products such as vehicle tyres, cabling, damping systems, adhesives and medical devices. Currently, rubbers are primarily made by vulcanisation processes, which permanently cross-links the polymer chains into a three dimensional network. This gives added strength, robustness and stability to the materials, but also means that they are not able to be reprocessed, reshaped or recycled.
Striving to achieve sustainable synthetic rubber production
Manufacturing processes applied to produce sustainable rubber products are conducted in a fully controllable laboratory environment at the International Institute for Nanocomposites Manufacturing (IINM), WMG. This allows innovative solutions and new methods to flourish. The level of flexibility offered by the facilities at the IINM has resulted in advances across polymer-based manufacturing, particularly when establishing ways to increase the durability and sustainability of polymer-based materials, such as vulcanised rubbers.
A significant amount of progress has been made in extending the lifespan of rubber materials in order to reduce the replacement and increase the reliability. ‘Preserving materials for longer means reducing the frequency at which they need to be replaced, which has knock-on effects on decarbonisation’, says Dr Alan Wemyss, Research Fellow at IINM, WMG at the University of Warwick.
For example, in the automotive industry around one billion tyres are produced each year to meet current demand, with each tyre requiring in the region of seven gallons of oil to make. Therefore, extending the service life of tyres by even a small amount would significantly reduce global oil usage. Working alongside Dr Alan Wemyss, we have been collaborating with the Bridgestone Corporation on developing advanced automotive tyres that have the ability of self-healing, and could be potentially responsive and recyclable.
The importance of self-healing
Inspired by natural biological systems, self-healing is a key approach to extending the stability and service life of materials, whilst improving their operational safety. Self-healing means that the material can heal its molecular structure and recover its functional properties autonomously or upon the application of an external stimulus, such as heat or light. Producing a self-healing material involves substituting the permanent cross-links between polymer chains with non-permanent analogues, such as supramolecular interactions or dynamic covalent bonds. Under the right conditions, this gives the polymers the freedom to diffuse across a damage boundary and entangle with the chains opposite, before the non-permanent bonds reform to once again restrict chain movement.
Self-healing polymers have found wide-ranging applications in areas such as flexible sensors, wearable electronics and biomedical devices. Such materials are also in particularly high demand for applications that are remote to access or in hostile or extreme environments. For example, this could include the outer components of deep sea submersibles or the functional parts of satellites orbiting the Earth. Ensuring the efficiency of self-healing polymers across a range of different extreme conditions is one of the biggest challenges with this work, as high salinity, high pressure, and low temperatures are all factors that can affect the mobility of polymer chains and, consequently, the ability of these materials to self-heal.
Increasing recyclability through self-healing polymers
In addition to the work around integrating self-healing properties within polymer-based materials, thereby improving the safety and extending the lifespan of products, we also need to consider the long term implications and what happens to the material when it does inevitably reach that end of useful life. Investigating how self-healing polymers can help make rubber more recyclable as a material is a key part of this, linking to the importance of implementing sustainable processes mentioned at the start of this piece.
At WMG, we are working on both synthetic chemistry and processing approaches to construct non-permanent networks in elastomers. Moving away from solvent-based and lab-scale methods for the fabrication of self-healing polymers, which are currently multistep, high cost, environmentally unfriendly and small scale, the self-healing rubbers are manufactured using standard industrial solid-state compounding processes. These processes are highly energy-efficient, scalable and environmentally friendly, requiring only the solid-mixing of compounds at moderate temperatures. This technology is applicable for producing self-healing flexible sensors, stretchable electronics, soft robots and tyres. By invitation, our perspective was recently published in the top journal Angewandte Chemie International Edition.
With the effective combination of self-healing polymers and sustainable production methods, enabling an extended lifespan and recyclability on a mass scale for rubber products throughout the world, we can help support widespread efforts to tackle climate change through decarbonisation.