Biomass-derived closed-loop recyclable chemically crosslinked polymer composites for green soft electronics

Developing green polymers is the key to addressing the limitations associated with the recycling and reprocessing strategies for conventional analogs. Polymers derived from α-lipoic acid (or lipoate), a bio-based molecule, are considered promising candidates for sustainable alternatives, offering the advantage of on-demand chemical degradation through disulfide reduction or depolymerization. Here, we examined the depolymerization kinetics of poly(ethyl lipoate) (PEtLp) under varying acidic and basic conditions and found that they are significantly reliant on the pKa values. Notably, PEtLp solution in chloroform or toluene (20 mg/mL) showed complete depolymerization (100 % conversion) into original EtLp under trifluoroacetic acid (TFA) within two days at 25 ˚C. In this manner, we designed a closed-loop recyclable polymer composite that can be fully decomposed into a liquid solution, including a monomer and crosslinker, and conducting filler such as carbon nanotubes (CNT), thus enabling self-sustained repetitive chemical recycling. The resulting conductive composite demonstrated minimal changes in electrical resistance (ΔR/R0 ∼ 0.15) under 100 % uniaxial stretching while maintaining consistent mechanical and electrical properties throughout repeated recycling and reuse at various tensile strains without damaging the filler. These self-sustaining recyclable polymer composites could have significant potential for recyclable conducting electrodes in green soft electronics.