Efficient Flame Retardant with Ultrahigh Limiting Oxygen Index Obtained by Self-Assembly Impregnation Method

Abstract

With the increasing demand for environmentally friendly flame retardants for wood, there is a pressing need for efficient and eco-friendly flame retardants. In this study, a novel flame-retardant coating was synthesized using a simple self-assembly impregnation method. Positively charged polyethyleneimine (PEI) was coated on the wood surface via impregnation. Negatively charged ammonium polyphosphate (APP) and montmorillonite (MMT/K10) composites were attached to the PEI surface. Finally, copper sulfate (CuSO4)-sodium alginate (SA) was encapsulated on the wood surface as a protective layer. Analysis of the cone calorimetry data showed that the self-assembled treated wood (SCAKP-W) suppressed the heat release and mass loss appreciably. It was found that the peak heat release rate (pHRR) of untreated wood was 275.05 kW/m2 and the total heat release (THR) was 17.17 MJ/m2, whereas the flame retardant-treated wood (SCAKP-W) had a pHRR of 179.38 kW/m2 and a THR of 12.97 MJ/m2, a considerable reduction of 34.78% and 24.46%, respectively. In the thermogravimetry (TG) test, the SCAKP-W had a high residual carbon (34.45%) at 800 °C. Importantly, the SCAKP-W achieved a UL-94 V-0 rating and ultrahigh limiting oxygen index (LOI) of 57.3%. These results demonstrated that the flame-retardant layer (obtained by simple impregnation self-assembly) was a highly efficient flame retardant that was amenable to the environment and exhibited enormous application potential as a surface flame retardant.

Keywords: flame retardant, limiting oxygen index, self-assembly impregnation, layer-by-layer, eco-friendly