Strengthened, Recyclable, Weldable, and Conducting-Controllable Biobased Rubber Film with a Continuous Water-Soluble Framework Network

At present, recycling of rubbers is the main method to achieve their sustainable development. However, it is a challenge to recycle rubbers without retaining pristine reinforcing-fillers. Herein, we report fully biobased rubber films prepared by mixing epoxidized natural rubber (ENR) latex and carboxymethyl chitosan (CMCS) solution. CMCS was regenerated and selectively located in the interstitial space between the ENR latex particles during the film-forming process, forming a CMCS framework network in the films. The special CMCS network with hydrogen bonding interactions with ENR endowed rubber films with improved mechanical properties. At the same time, the self-sticky characteristic of ENR with the assistance of chain diffusion and reversible hydrogen bonding interactions made the cut films to be welded. Because the water-soluble CMCS is a continuous phase, the ENR could be perfectly recycled by soaking films in water to remove the CMCS. Furthermore, the CMCS framework running through the whole films provided a wonderful 3D network for conducting. The ENR/CMCS films could turn into conductive films when the moisture content was higher than 1 wt %. The conductivity of the ENR/CMCS films could be tailored conveniently by controlling the moisture content or changing the concentration of the electrolyte in the absorbed water. Thus, we provide a convenient approach to prepare strengthened, recyclable, weldable, and conductive biobased rubber films that can find applications in humidity sensors.