The University of Reading (Reading / UK; www.reading.ac.uk) has developed materials with intrinsic “repairability” built into their design, which could play a role in increasing safety in aircraft and automobiles. Researchers in the "Reading Centre for Advanced Polymers" (ReCAP), based in the university’s department of chemistry, have designed a novel material in which the binding forces between two different plastics are designed to be quantitatively reversible. As a result, the material’s viscosity falls significantly when the temperature is raised, enabling it to flow into damaged areas and repair them. On returning to room temperature the interactions are re-established and the material is claimed to fully recover its mechanical strength.

Howard Colquhoun, professor of materials chemistry at the University of Reading, said: “Polymeric components, such as the high-performance composite materials now in widespread use for aircraft construction, are often safety-critical. They are exposed to a wide range of mechanical and thermal stresses that can result in crack formation, which is potentially an extremely serious problem. Our research shows it is possible to design intrinsic repairability into polymer systems by exploiting the concepts which have been developed over the past 30 years or so in the field of supramolecular chemistry”.

The research group has designed a pair of macromolecular structures which bind to one another through aromatic stacking and hydrogen-bonding. When blended together, these give a material whose mechanical properties can be recovered easily and quantitatively after fracture. Importantly, the material can be damaged and repaired many times at the same site without loss of performance.

Conventional polymers are often permanently cross-linked, which leads to high stiffness and thermo-mechanical stability. However, they also suffer from severe disadvantages including brittleness, lack of repairability, and poor recyclability. The new research work was inspired by the idea of using reversible cross-links between the polymer chains, which could allow the material to be strong at room temperature but readily self-repair at higher temperatures.