Dynamic Reversible Networks and Development of Self-Healing Rubbers: A Critical Review

Abstract

An intensive literature search shows that research in the field of self-healing rubbers is still in its infancy. By analyzing the various reviews and reports available, most of the results prove to be complicated; however, a few studies show promising self-healing properties of new elastomers. Most of these materials were prepared by relatively sophisticated chemical syntheses. Many of the studies on self-healing materials also deal with commercial rubbers, but the mechanical performance of these self-healing systems is very poor for practical application, perhaps because self-healing systems are usually prepared with an uncured or pseudo-crosslinked matrix structure. The poor mechanical properties are related to the highly viscous but inelastic nature of the uncured or only partially cured rubber compound. Importantly, most of the studies have been conducted on rubber systems without reinforcing fillers. For filler-reinforced rubber systems, the question is whether the working principle of reversible bonds is applicable. This literature review attempted to compile the current promising self-healing systems, describe their underlying chemical mechanisms, and discuss the self-healing concept from a thermodynamic perspective. In addition, this review is focused on the critical discussion of the principle and origin of self-healing behavior and finally draws conclusions on the applications and opportunities for further developments in this field.

Protein‐Mediated ZnO Synthesis for Self‐Healing in Natural Rubber

“…[16][17][18] Epoxidized natural rubber (ENR) stands out as a preferred substrate material because of its facile modification of epoxy groups. To establish reversible noncovalent bonds, ENR undergoes reactions involving various chemical functional groups, such as dicarboxylic acids [19] or mixed metal ions (Fe─Zn), along with diamine as a cross-linking agent. [20] Cheng et al subsequently developed a dual cross-linked self-healing ENR based on dynamic disulfide metathesis and thermoreversible hydrogen bond, exhibiting high mechanical strength (9.3 ± 0.3 MPa), exceptional self-healing efficiency (up to 98%), and excellent recyclability.…”

“…[ 16–18 ] Epoxidized natural rubber (ENR) stands out as a preferred substrate material because of its facile modification of epoxy groups. To establish reversible noncovalent bonds, ENR undergoes reactions involving various chemical functional groups, such as dicarboxylic acids [ 19 ] or mixed metal ions (Fe─Zn), along with diamine as a cross‐linking agent. [ 20 ] Cheng et al.…”

Novel disulfide-containing diols: synthesis and application in self-healing fluorescent polyurethane elastomers

“…[15][16][17] Intrinsic self-healing typically requires two prerequisites, viz., the dynamic physical and chemical bonds, which, coupled with chain mobility, ensure adequate chain diffusion and frequent bond exchange or rearrangement. [18][19][20] Disulfide bonds (-S-S-) are a relatively weak reversible covalent bond compared to carbon-carbon bonds. The interest in disulfide bonds had increased because of the ease of adjusting the conditions of the exchange reaction, the ability to impart different properties to polymers as needed, and responsiveness to various stimuli.…”

Water-triggered self-healing and reversible underwater adhesion in metalorganic polymers

“…Besides their role in the underwater adhesion of biological species such as mussels, the dynamic nature of metal-ligand coordination is responsible for the damage repair or healing of the mussel byssus. 22,23 Correspondingly, metal-coordination has been reported to be a relevant healing and recycling enabler of synthetic polymers using dopamine or histidine with Zn 2+ or Fe 2+ /Fe 3+ complexes amongst others. [24][25][26][27][28][29] Moreover, polymer architecture control has been recognized, together with the reversible chemistry used, as a key fundamental factor to balance healing and mechanical properties.…”