Elastomers (elastic polymers) are used in numerous applications, including seals and tyres. Although the materials bounce back from deformation, the cumulative result over time is damage and eventual breakdown. The EU-funded MUSHE (Multifunctional self healing elastomers) project developed self-repairing elastomers based on NR. The team’s novel approach was based on reversible bonding combined with the inclusion of conductive nanoparticles. The project concept was intended to restore both mechanical and electrical function to the fatigued elastomer. The team investigated the role of elastomer-repair variables, including time and temperature. Using dielectric processes, the group worked to gain new insights into the elastomer network structure and the cross-linking system. Such outcomes will improve the development of self-repair properties in future elastomers. First, the team developed tailor-made, self-repairing, sulfur-vulcanised NR compounds. The compounds take advantage of the unique properties of di- and polysulfide bonds naturally present in such rubbers. They prepared and tested the self-repair properties of various NR compounds, each based on different vulcanisation systems. Researchers also determined the mechanical properties of both pristine and repaired rubber compounds, in relation to sulfur content and degree of cross-linking. The consortium also developed self-repairing elastomers that use conducting particles such as graphene. The team physically and chemically characterised the composites, and calculated the respective cross-linking densities based on swelling measurements. Investigators detailed the effect of graphene loading on mechanical self-repair, and evaluated the multifunctionality of selected composites. Consequently, MUSHE developed a new sulfur-cured NR compound with self-repair capability. The new material trades off mechanical performance and repair capacity, a balance that can be tailored depending on need. Mechanisms for tailoring the performance include varying the amount of sulfur in the rubber compound, cross-linking density and time of initial contact between damaged surfaces. Having developed the new compound, researchers also studied its relaxation behaviour. The team additionally developed NR-graphene composites. Although the compounds did not show the expected improvement on mechanical properties, the team did demonstrate recovery of mechanical performance and also thermal and electrical conductivity. MUSHE results represent a step towards the ubiquitous industrial usage of such compounds and the creation of new European industries.
Self-repairing elastomers, natural rubber, graphene, mechanical performance, MUSHE