Facile preparation of cellulose nanocrystal/alumina oxide composite flame retardant with corn-like structure, superhigh heat insulation, and synergistic smoke suppression ability

It is necessary and urgent to develop high-performance flame retardants (FRs) with heat insulation and smoke suppression functions for public security. In this work, cellulose nanocrystal/alumina oxide (CNC/Al2O3) composites with corn-like structure were designed and synthesized by a facile sulphate half-esterification and chemical precipitation strategy. The hydrolyzed CNCs with rich sulfonate groups (SO3-) acted as carriers to anchor the Al2O3 nanoparticles. As the concentrations of Al3+ increased, denser Al2O3 nanoparticles were adsorbed on the surface of CNCs to form the protective layer, which significantly enhanced the thermal stability, heat resistance, and heat insulation of CNCs. Compared to CNCs, the maximum decomposition temperature (Tmax) of the CNC/Al2O3-2 composite was increased by 85.0 °C, and the heat insulation efficiency was as high as 40.5%. More importantly, the formation of dense carbon layer on the surfaces significantly improved the flame retardancy and smoke suppression of CNC/Al2O3-2 composite under the synergistic protection of the Al2O3 nanoparticles layer.