Stable and Strong Lignocellulosic Polyimide Vitrimers with Good Reprocessability and Closed-Loop Recyclability

The reprocessing stability and recyclability of bio-based thermosetting materials have positive environmental and economic values. In this work, two types of lignocellulosic polyimide vitrimers were developed from two lignin-derived aldehyde monomers and a cellulose-derived diamine monomer based on a dynamic covalent adaptive network. Both polyimide vitrimers demonstrated high fracture strengths of up to 67.5 and 40.2 MPa, and the vitrimers had no obvious dissolution and weight change after soaking in ten common solvents for 30 days. Similar to other literature reports, the vitrimers still maintained more than 92% fracture strength after 5 fracture–hot-press cycles. Besides, due to the presence of large amounts of nitrogen and phosphorus elements, both vitrimers exhibited good flame-retardant properties: they could self-extinguish in 10 s while removing the flame after ignition and generated no molten droplets. More importantly, these two highly cross-linked thermoset materials were efficiently transformed back into related monomers, guaranteeing excellent monomer–polymer–monomer closed-loop recycling. The stable cycle processability and efficient closed-loop recovery of lignocellulosic thermosetting materials provided the possibility of the efficient utilization of biomass materials. Furthermore, the successful preparation of basalt fiber composites with high mechanical properties and easy recovery demonstrated the application potential of these vitrimers.