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MUSHE Report Summary

Project ID: 623379
Funded under: FP7-PEOPLE
Country: Netherlands


Elastomers are used in a variety of applications such as seals, bladders or tires. While these materials can sustain large deflections with little or no permanent deformation, elastomers can still fail through fracture and fatigue processes. In existing elastomers, the development of deformation induced damage is cumulative and damage once formed will not disappear at later stages. Self-healing materials seek to enhance the long term durability of a structure by effectively removing any local micro-, meso- or sometimes even macro- damage which occurs throughout its service life, either through autonomous damage activated processes or by an external trigger.

The aim of MUSHE was to develop, for the first time, Natural Rubber (NR) compounds with self-healing properties, following the intrinsic self-healing approach based on reversible bonding and by the inclusion of conductive nanoparticles. In this sense, both mechanical and electrical functionalities could be restored. Special attention was paid to the overall molecular dynamics of these materials. It is believed that a systematic research on the relaxation behavior of these elastomers will help to elucidate the role of the key healing parameters (healing time and temperature). The new insight into the character of both the network structure and the crosslinking system by means of dielectric processes will be useful in controlling self-healing properties of all elastomeric self-healing systems yet to be developed.

The first challenge of MUSHE was to take advantage of the unique properties and dynamic character of the di- and poly-sulfide bonds naturally present in sulfur-vulcanized rubbers to develop tailor-made self-healing sulfur vulcanized NR compounds. In this sense, NR compounds based on different vulcanization systems were prepared and their healing potential was evaluated. The mechanical behaviour of the pristine and healed rubber compounds was also determined as function of sulfur content and crosslinking degree. Different mechanical testing protocols were established depending on the type of measurement (tensile, cyclic, fracture).

Integrating graphene to a NR matrix might generate some novel self-healing materials, which not only will have enhanced mechanical properties, but also can be healed via multi-channels with conductivity (thermal and electrical) restored. Thus, the second challenge of MUSHE was to develop self-healing elastomer composites using conducting particles such as graphene, in order to obtain multi-functional self-healing compounds. NR/graphene nanocomposites were prepared accordingly. All of the composites were physically and chemically characterized and their crosslinking density was calculated based on swelling measurements. The effect of graphene loading on mechanical healing performance was also analyzed. Thermal and electrical conductivity measurements were followed for NR/graphene composites under pristine, damaged and healed conditions. The evaluation of the multi-functionality of selected composites was performed.

Finally, the molecular dynamics of all systems was properly studied as function of sulfur content, graphene content, as well as of the curing degree of the compounds. Broadband dielectric spectroscopy was used for the first time to follow the molecular dynamics evolution during healing of internal and macroscopic damage in sulfur-cured NR compounds.

MUSHE has produced novel research results of high quality and subsequently published them in high ranking journals and results were also presented at international conferences and to representatives of companies in the field.

A new sulfur-cured NR compound with self-healing capability has successfully been developed. A compromise between mechanical performance and healing capability has been found; such compromise can be potentially tailored depending on the amount of sulfur in the rubber compound, the crosslinking density and the time of initial contact between damaged surfaces. Further work to combine the attractive healing efficiency with increased storage stability of these non-fully cured rubbers has to be done.

A systematic study on the relaxation behavior of these self-healing elastomers has also been accomplished. These results provide fundamental background information to help understanding the role of the key healing parameters (healing time and temperature) and for demonstrating that healing seemingly occurs, while the polymer architecture in the healed material differs from that in the original state.

NR/graphene nanocomposites were successfully prepared. The expected improvement on mechanical properties with graphene loading was not obtained; nonetheless, recovery of mechanical performance, as well as restoration of other functionalities such as thermal and electrical conductivity were achieved. A correlation of the molecular dynamics with the restored functionalities was made. These results will serve as basis for the development of new multi-functional self-healing elastomers.

MUSHE exceeded the intentions of current research projects on self-healing elastomers in its ambition to restore two (rather than one) functionalities after damage, as well as to monitor the healing process at a scale close to the relevant molecular processes. It is expected that the next decade of research may lead to a range of new commercial applications, and that new concepts covering also properties other than mechanical will emerge.

The overall results of MUSHE will be of interest to a large number of international researchers who are actively seeking new elastomeric self-healing products across a broad cross section of industries including transportation and electronics within a period of 10 years. In fact, the implementation of the main objectives of MUSHE have created a soundbasis for developing new EU research networks and programs focused on self-healing elastomers. Moreover, the successful research on self-healing rubber concepts can bring them to a level where the industry can make a comparative assessment on how to deal with the development for large scale application, hopefully leading to new industrial activities in Europe.

The summary and results of the research can be found at

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