Dynamic Polyimine Resin Enables a Formaldehyde-Free, Remoldable, Degradable, and Closed-Loop Recyclable Wood-Based Composite

Abstract

Conventional wood-based composites (WCs) were mainly manufactured by gluing woody biomass with formaldehyde-containing resin adhesives that have permanent covalent cross-links, making them harmful to human health and giving them poor remoldability, degradability, and recyclability. Herein, a formaldehyde-free and dynamic adaptive polyimine (PI) resin linked by reversible imine bonds was synthesized using a Schiff-base polymerization reaction. Then, a novel and formaldehyde-free wood-based composite film (WCF) was developed by gluing wood fibers (WFs) using PI resin. The resulting WCF exhibited a tensile strength of 32.5 MPa, a Young’s modulus of 1.4 GPa, a flexural strength of 59.1 MPa, and a flexural modulus of 4.5 GPa. The heat-induced exchangeability of dynamic imine bonds facilitated the WCF could be easily reshaped, rehealed, and remolded at moderate temperature (70 °C). The chemical reversibility of imine bonds enabled the WCF to rapidly (3 h) degrade. The degraded WFs and chemicals could be fully recycled to prepare a new batch of WCF. This work opened a vast space to develop high-performance and environmentally friendly WCs.