Biomaterial-Based Cu₂O@Chitosan/Phosphorylated Cellulose Core-Shell Flame Retardant Fabricated via Layer-by-Layer...

Epoxy resins (EPs) are widely used in advanced engineering applications but suffer from inherent flammability and rapid heat release during combustion. A biomaterial-based core-shell flame retardant, Cu₂O@(CH/PT), has been fabricated using a mild layer-by-layer (LbL) assembly strategy by alternately depositing chitosan (CH) and phosphorylated cellulose (PT) onto Cu₂O particles. Scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) analyses provided complementary morphological and chemical evidence for the surface deposition and assembly of CH and PT on Cu₂O particles. The resulting Cu₂O@(CH/PT) was incorporated into epoxy resin blends to investigate its effects on thermal degradation and combustion behavior. The incorporation of 8 wt % Cu₂O@(CH/PT) increased the residual mass of the EP blends at 700 °C during thermal degradation from 7.79% to 20.62% and increased the limiting oxygen index (LOI) for combustion from 23.3% to 31.0%. Microscale combustion calorimetry results showed that the peak heat release rate (PHRR), total heat release (THR), and heat release capacity (HRC) for combustion of EP-8 were reduced by 45.1%, 33.4%, and 44.0%, respectively, compared with the corresponding values for combustion of neat EP. The enhanced flame-retardant performance may be associated with the cooperative effects of the Cu₂O catalytic core and the biomaterial-based phosphorus/nitrogen-containing CH/PT shell, where PT promotes condensed-phase charring, CH contributes to the development of protective char structures, and Cu₂O facilitates the stabilization of carbonaceous residues. A sustainable strategy for constructing biomaterial-based core-shell Cu₂O flame retardants through LbL assembly to improve the fire safety of epoxy resin blends has been developed.