Intrinsically flame-retardant vanillin-based PU networks with self-healing and reprocessing performances

Conventional polyurethane (PU) networks fabricated from nonrenewable fossil resources are difficult to be recycled, reprocessed, and reshaped because of the permanent covalent cross-linked networks, and the flammability of PU networks limits their wide application. Herein, the novel polyols were synthesized from renewable vanillin and then reacted with hexamethylene diisocyanate (HDI) trimer to obtain versatile bio-based PU networks with dynamic disulfide and imine bonds for the first time. Obtain malleable PU networks that possess excellent reprocessability and self-healing performance, as well as superior fire resistance. The vanillin-based PU networks show a high T5d of ∼180 °C, high char yield of 23% at 800 °C, fast stress relaxation of ∼38 s at 80 °C, excellent scratch self-healing performance with approximately 100% healing efficiency at 120 °C for 90 min, outstanding flame retardancy with high LOI of ∼30% and UL-94 V0 rating. Additionally, the vanillin-based PU networks display excellent malleability with the activation energy (Ea) of 30.2–54.8 kJ•mol−1 due to dual dynamic bonds in the networks, which can be recycled in 60 min at 120 °C by hot pressing. Moreover, the vanillin-based PU networks with Schiff base can be degraded rapidly in the mixture of HCl and THF. Briefly, produced PU networks from abundant and renewable resources are significant examples to foster the development of versatile PU network materials.