An anionic polyelectrolyte hybrid for wood-polyethylene composites with high strength and fire safety via self-assembly

Abstract

Wood-plastic composite (WPC), as a renewable and sustainable material, has received wide attention, but its inherent flammability greatly limits its broad application in residential construction and so on. In this work, an anionic polyelectrolyte hybrid (APP-CNC) was built and applied to derive simultaneously flame-retardancy-improved and mechanically strengthened WPC. It was constructed with ammonium polyphosphate (APP) and cellulose nanocrystals (CNC) by self-assembly with ionic and hydrogen bonding. The physical crosslinking network between APP-CNC hybrid enabled the whole materials possess both high load capacity and good deformation capacity synchronously. According to the digital image correlation (DIC), the strain transferred uniformly from HDPE molecular to wood fibers via the physical crosslinking network based on hydrogen bonding, and hence an increased high deformation region occurred and distributed uniformly in WPC/APP-CNC. Compared with neat WPC, the tensile strength and Young's modulus of WPC/APP-9 wt%CNC increased by 42.69% and 75.90%, respectively. During pyrolysis, CNC promoted hybrid to pyrolyze ahead (T5% of 298 °C) and provided a carbon skeleton for char forming. Meanwhile, physical crosslinking network further caused a more compact char residue with a higher graphitization during combustion of WPC. For WPC/APP-9 wt%CNC, it had a significant decrease in average heat release and total heat release of 62.6%, and 23.8% respectively, compared with those of neat WPC. This work indicated that polyelectrolyte hybrid had a potential application prospect in preparation of high-performance, high-function and high-value-added WPC.