A Fully Bio‐Based Elastomer with Ultrahigh Lignin Content and Performance Rivaling Nitrile Rubber

Achieving renewable, high‐performance elastomers remains a key goal of green materials science. Here, we report a high‐performance and recyclable elastomer produced directly from industrial Kraft lignin through a one‐pot in situ graft copolymerization strategy. A deep eutectic solvent composed of oxalic acid and 1,6‐hexanediol simultaneously dissolves lignin, provides flexible chains, and drives catalyst‐free esterification at 110°C, constructing an interpenetrating rigid–flexible network that incorporates 50–75 wt.% lignin. The optimal elastomer delivers a tensile strength of 12.0 MPa, 878% elongation, and 85.1 MJ m − 3 fracture energy, rivaling or exceeding petroleum‐derived nitrile butadiene rubber (3.1 MPa, 750% elongation and 11.0 MJ m − 3 ). It also offers a low dielectric constant, high electrical insulation, superior oil and abrasion resistance, efficient photothermal conversion, and infrared‐induced self‐healing. The material can be repeatedly reprocessed, enabling closed‐loop recycling. Converting an abundant lignin by‐product into a value‐added elastomer thus provides a scalable route to eco‐materials with broad application potential.