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Most of the dynamic covalent bonds (DCBs) for self-healing rubber must be activated at relatively high temperatures due to the requirement of high energy during the exchange of dynamic bonds, which may lead to unexpected degradation or excessive crosslinking of rubber. Herein, we designed and fabricated a highly stretchable, self-healable and reprocessable rubber by introducing dynamic disulfide bonds into the crosslink network of epoxidized natural rubber (ENR). Lipoic acid (LA) was firstly uniformly dispersed into ENR via a latex film formation technique, and then underwent a dynamic covalent ring-opening self-polymerization during hot pressing process, during which the carboxyl group of poly(LA) attacked the epoxy group of ENR to form β-hydroxyl ester bond crosslinks. As a result, a revisable covalently crosslinked network without rigid steric hindrance groups was constructed, which exhibited a super self-healing efficiency of 99 % after self-healing at 80 °C for only 3 h. The elongation at break of the elastomer could reach 1115 % and the recovery rate of reprocessing was as high as 91 %., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Cellulose, as a green reinforcing agent for rubber, has excellent improvement on the tensile strength but usually accompany with a deterioration of extensibility and self-healing property. Herein, we report an efficient method to prepare robust and self-healable natural rubber/zinc dimethacrylate/carboxylated cellulose nanofibers (NR/ZDMA/CNC) composites which are constructed by a CNC participated ionic supramolecular network. Ionic supramolecular network in NR is generated by the polymerization of ZDMA during a controlled peroxide-initiated vulcanization of NR. Interestingly, NR with massive ion clusters has strong affinity with CNC, which facilitates the uniform dispersion of CNC and the compatibility between CNC and NR. Meanwhile, CNC participates into the supramolecular network via non-covalent interaction with NR chains equipped with ionic crosslinks. This greatly reduces the adverse effect of CNC on the dynamic characteristics of supramolecular network. As a result, the tensile strength of NR/ZDMA composite with 20 phr CNC could reach 4.13 MPa, while its self-healing efficiency still maintains at >80 %. Thus, NR composites with non-covalent interaction between CNC and supramolecular network display improved strength, maintained extensibility, and excellent self-healing capability. This study thus demonstrates a feasible approach to reduce the negative effect of reinforcing fillers on a self-healing rubber based on supramolecular networks., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Multifunctional and easily-controlled self-healing rubbers with high performance are booming and have great potential in a wide range of applications. In this paper, natural rubber/zinc dimethacrylate/carbon nanotube (NR/ZDMA/CNT) composites with satisfactory mechanical strength, photothermal conversion and accurate self-healing were developed. CNC is used to assist the dispersion of CNT into NR and ZDMA is generated in situ reaction of ZnO and MAA. The self-healing capacity of the composites is realized through ionic supramolecular network constructed by regulating the DCP-induced vulcanization of NR/ZDMA. The compatibility between CNT and NR matrix is enhanced by establishing non-covalent interactions through ionic clusters of the supramolecular network, thus, the mechanical properties of composites are significantly improved. As a result, the tensile strength of NR/ZDMA/CNT-7 reaches ∼7.8 MPa, and it can recover tensile strength of ∼65% at room temperature. The photothermal effect of CNT can effectively promote the self-healing process, and also endow the composites with NIR-actuated accurate self-healing. After activated by NIR laser for 60 min, the healing efficiency of NR/ZDMA/CNT-7 can reach 90%. Furthermore, the composites have great potential application in thermoelectric conversion. Therefore, this kind of high-performance self-healing rubber with photothermal conversion and accurate self-healing has broader application prospect in various scenarios. [Display omitted] • Non-covalent interaction is constructed between natural rubber and fillers. • The contradiction between mechanical properties and self-healing is reconciled. • NR composites with photothermal conversion apply in thermoelectric conversion. • The composites show accurate self-healing performance under NIR light. [ABSTRACT FROM AUTHOR]

To achieve self-healing for commercial rubbers, the current mainstream strategy is to equip rubber molecules with essential functional groups by chemical modifications. However, different structure of rubber molecules determines a disparate optimal self-healing mechanism, which turns out a consequent complex and multifarious chemical modifications for them. In other words, the same modification method cannot be applied to various rubbers, which is partly a limitation on the preparation of self-healing rubbers. Herein, we propose a concept of self-healing masterbatch which can effectively endow rubber matrix with self-healing ability via a facile processing method. We design this rubber masterbatch equipped with a mass of carboxyl groups by the grafting reaction between natural rubber and 2-methacrylic acid. Then the rubber masterbatch can be mixed with rubber matrix and simultaneously ZnO must be added to introduce Zn2+ via its neutralization reaction with the masterbatch. After a controlled peroxide-induced vulcanization, the chains of masterbatch are grafted onto the chains of rubber matrix and then a reversible Zn2+ crosslinking network is generated. Based on above method, natural rubber, styrene butadiene rubber and cis -polybutadiene rubber successfully earn considerable self-healing ability, showing a self-healing efficiency of >90%. Furthermore, based on the reversible non-covalent interactions between the carboxyl groups of the self-healing masterbatch and inorganic substrates, the self-healing masterbatch can recover its adhesion and reuse to bond the cements together, showing a "dynamic reversible adhesion". We hope this concept of self-healing masterbatch could open up a feasible and versatile avenue to prepare self-healing rubbers based on reversible non-covalent interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Covalent crosslinks were introduced into ionic supramolecular network. • Permanent covalent crosslinks effectively enhance natural rubber. • The effects of covalent crosslinks on the self-healing were studied systematiclly. • Mechanical properties and self-healing effect of natural rubber was balanced. Introducing covalent crosslinks into reversible supramolecular networks would effectively improve their mechanical strengths, but sacrificed the desired self-healing effect. So, it is a practical significance to explore the influence of irreversible covalent crosslinks on self-healing behavior to prepare self-healing rubbers with enhanced mechanical properties for further application. In this study, the trade-off of covalent crosslinks between the balanced mechanical properties and self-healing effect of a natural rubber/methacrylic acid/zinc oxide (NR/MAA/ZnO) supramolecular network system was studied. Zinc dimethacrylate (ZDMA) is in situ formed from MAA and ZnO during the mastication of NR, which introduce mass of ionic crosslinks to generate a reversible ionic supramolecular network at the initial stage of peroxide-induced vulcanization at 140℃. Then, free radicals continue to initiate covalent crosslinks to strengthen the NR matrix. The tensile strength of NR with slight covalent crosslinks could achieve 1.63 ∼ 3.86 MPa when vulcanization time keeps in 240 ∼ 360 s. At this time, primary continuous covalent crosslink network has little binding effect on rubber chains, and ionic interactions can be smoothly reorganized to ensure excellent self-healing behavior. The considerable self-healing efficiency of 67%∼95% indicates that the vulcanization time at 240 ∼ 360 s is an appropriate choice to achieve a win–win situation for the mechanical properties and self-healing efficiency of NR/MAA/ZnO composites. [ABSTRACT FROM AUTHOR]