Self-Healable, Recyclable, and Strengthened Epoxidized Natural Rubber/Carboxymethyl Chitosan Biobased Composites with Hydrogen Bonding Supramolecular Hybrid Networks

Self-healing based on noncovalent bonds and mechanical strengthening based on fillers are contradictions for commercial rubbers. To solve this problem, in this paper, we constructed a hydrogen bonding supramolecular hybrid network by incorporating carboxymethyl chitosan (CMCS) into epoxidized natural rubber (ENR) through a solution-mixing method. The regenerated CMCS with multiple hydrophilic groups formed hydrogen bonding interactions with ENR chains, which served as multifunctional linkages to construct the supramolecular hybrid network. In this way, the regenerated CMCS belonged to the hydrogen bonding healing system and simultaneously improved the mechanical properties of the ENR/CMCS composites. The dispersion, structure of regenerated CMCS, and formation of the hydrogen bonding supramolecular hybrid network in the ENR/CMCS composites were studied and confirmed by Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry, X-ray diffraction, dynamic mechanical analysis, and equilibrium swelling experiment. It was found that the ENR with 5 and 10 wt % CMCS possessed improved tensile strengths of 1.40 and 1.92 MPa, respectively, and simultaneously exhibited considerable self-healing efficiency of about 90% (room temperature, healing 12 h). When the CMCS content exceeded 10 wt %, although the mechanical property increased continuously, the self-healing effect decreased significantly because of the unavoidable negative effect of filler restriction. The dynamic nature of hydrogen bonding interactions facilitated the rearrangement of the supramolecular hybrid network, which endowed ENR/CMCS composites with derived recycling capacity. However, the mechanical properties are reduced after multi-recycling.