Fabrication of montmorillonite wrapped with layered double hydroxide synergistic APP to improve the flame retardancy and mechanical properties for wood flour/polypropylene composites

Ammonium polyphosphate (APP) has been attracting considerable attention from researchers due to its favorable physicochemical properties, including excellent flame retardancy, competitive price and nontoxicity. It is widely used in flame retardancy of wood plastic composites (WPCs). The biggest challenge currently is that the extensive addition of APP often leads to the generation of smoke and a decrease in mechanical performance, which severely limits its application in the fields of building materials. Two-dimensional (2D) layered double hydroxide (LDH) containing the metal cation has excellent catalytic effects and smoke suppression during combustion. However, the agglomeration of LDH severely affects its dispersity, thus limiting its flame retardancy. Herein, a novel 2D/2D MMT/LDH nanosheet was synthetized via a self-assembly technique. Then, MMT/LDH nanosheets were subsequently used in conjunction with APP to synergistically endow WPCs with excellent flame retardancy, smoke suppression and mechanical properties. Compared with pure WPCs, the addition of flame retardant reduced the pHRR, THR, and TSP release of the WPCs by up to 35.6 %, 21.0 %, and 13.8 %. Additionally, the mechanical properties of the flame-retardant WPCs showed slightly improvement compared to pure WPCs composites. Consequently, this work proposes a synergistic strategy for preparing flame retardant WPCs by integrating phosphorus and nitrogen-containing flame retardant with 2D/2D MMT/LDH nanosheets.