Fabrication of mechanically robust, recyclable, and degradable bio-elastomer through dynamic hard domains for contact/noncontact capacitive sensors.

The rapid development of flexible electronics resulted in a surge in the generation of e-waste, which stimulated a strong demand for environmentally friendly polymer substrates. Developing mechanically robust and recyclable polymer substrates is a promising approach, but remains an ongoing challenge due to the conflict in intrinsic mechanisms of that the weak noncovalent bonds required for recyclability resulting in poor mechanical strength. Herein, we design a dynamic hard domains strategy to develop a cellulose/castor oil-derived fully bio-based thermoset elastomer with excellent mechanical robustness, recyclability, and biodegradation performance for flexible electronic substrates. The construction of the phase separated structure realizes high strength (25.6 MPa), and toughness (43.5 MJ/m), while the reconfigurability of the dynamic hard domains achieves excellent recyclability with a high mechanical strength retention rate of 88.2 %. Impressively, the bio-based thermoset elastomer can be completely degraded by being buried in the soil for 70 days. Given these features, the bio-based thermoset elastomers are employed as an environmentally friendly substrate for the preparation of printable capacitive sensors (PCSs). The PCSs exhibit robust capacitive sensing performance in both contact or non-contact modes for detecting multiple signals, including pressure, orientation, humidity, and respiration. This work promotes the development of environmentally friendly bio-based polymeric substrates for addressing the growing e-waste problem in flexible electronics.