A Branched Polyelectrolyte Complex Enables Efficient Flame Retardant and Excellent Robustness for Wood/Polymer Composites.

Wood/thermoplastic composites (WPCs) have been restricted in some fields of building construction and electrical equipment because of their inherent high flammability and lower toughness. In this work, a branched crosslinking network polyelectrolyte complex (PEC) has been designed by incorporation of polyethyleneimine (PEI), a cation polyelectrolyte end capped amine groups, into cellulose nanocrystals (CNC), and ammonium polyphosphate (APP) via self-assembling. The hydrogen bonding interactions, penetration, and mechanical interlock provided by PEC effectively enhance the interfacial bonding within matrix, wood fibers, and flame retardant. Interestingly, it generates abundant micropores on the inner structure of WPC. The excellent interfacial bonding performance and easy-to-move molecular chain successfully transfer the stress and induce energy dissipation, simultaneously giving rise to higher strength and toughness for WPC. As well as the PEC endows WPC with a promotion in both smoke suppression and UL-94 V-0 rate. Additionally, the peak heat release rate and total smoke release for WPC obviously reduce by 36.9% and 50.0% respectively in presence of 25% PEC. A simple, eco-friendly, and concise strategy exhibits prospects for fiber-reinforced polymer composites with effective flame retardancy and mechanical robust properties.