A self-healing sulfur vulcanized natural rubber (NR) is here reported using the common ingredients in a traditional NR formulation. The dynamic character of the di- and polysulfide bonds naturally present in covalently cross-linked rubbers was found to be responsible for the healing ability and the full recovery of mechanical properties at moderate temperatures provided the material was employed in a nonfully cured starting state. Results show that a compromise between mechanical performance and healing capability can be reached by tailoring the amount of sulfur, the cross-linking density, and the disulfide/polysulfide ratio. The healing efficiency was found to depend on the postcuring storage time, the time between damage creation and re-establishment of mechanical contact, and the actual healing time. Furthermore, a dedicated electron spin resonance (ESR) test allowed establishing the underlying healing principle based on temperature-induced free sulfur radicals. The main observations presented here can serve as the basis for the design and preparation of other self-healing polymers with long-term durability based on di-/polysulfide bridges and other reversible moieties.
- Vulcanized natural rubber
- Degree of curing
- Time dependence
- Electron spin resonance
Hernández, M., Grande, A. M., Dierkes, W., Bijleveld, J., van der Zwaag, S., & García, S. J. (2016). Turning Vulcanized Natural Rubber into a Self-Healing Polymer: Effect of the disulfide/polysulfide Ratio. ACS sustainable chemistry & engineering, 4(10), 5776-5784. https://doi.org/10.1021/acssuschemeng.6b01760