Robust, Fire-Safe, Monomer-Recovery, Highly Malleable Thermosets from Renewable Bioresources

TLDR

Conventional thermosets are derived from nonrenewable fossil resources, are difficult to reprocess or recycle, and are flammable, posing safety risks. The study aims to synthesize a novel Schiff base precursor from renewable vanillin to create malleable thermosets with high performance and outstanding fire resistance. The authors fabricated covalent adaptable networks (CANs) by reacting the Schiff base precursor, enabling rapid reprocessability, monomer recovery, and arbitrary shape changeability. The resulting CANs exhibit a glass transition temperature of ~178 °C, tensile strength of ~69 MPa, modulus of ~1925 MPa, UL‑94 V0/V1 flame retardancy, LOI of ~30 %, malleability with bond‑exchange activation energies of 49–81 kJ mol⁻¹, and can be reprocessed in 2–10 min at 180 °C, demonstrating a promising platform for advanced renewable thermosets.

Abstract

Conventional thermosets are built by nonrenewable fossil resources and are arduous to be reprocessed, recycled, and reshaped due to their permanent covalent cross-linking, and their flammability makes them unsafe during use. Here, for the first time, we synthesized a novel Schiff base precursor from abundant and renewable lignin derivative vanillin and produced malleable thermosets (Schiff base covalent adaptable networks (CANs)) combining high performance, super-rapid reprocessability, excellent monomer recovery, and arbitrary permanent shape changeability as well as outstanding fire resistance. The Schiff base CANs exhibited high glass transition temperatures of ∼178 °C, tensile strength of ∼69 MPa, tensile modulus of ∼1925 MPa, excellent flame retardancy with UL-94 V0 rating and V1 rating, and high LOI of ∼30%. Meanwhile, three Schiff base CANs showed high malleability with the activation energy of the bond exchange of 49–81 kJ mol–1 and could be reprocessed in 2–10 min at 180 °C. These Schiff base CANs provide a prime example to foster the development of advanced thermosetting materials from renewable bioresources.