Flame-Retardant Coating on Wood Surface by Natural Biomass Polyelectrolyte via a Layer-by-Layer Self-Assembly Approach

In this study, environmentally friendly and low-cost biomass materials were selected as wood flame retardants. Three polyelectrolyte flame-retardant coatings made from chitosan (CS), tea polyphenols (TP), soybean isolate protein (SPI), and banana peel powder (BBP) were constructed on wood surfaces by layer-by-layer (LBL) self-assembly. The results of SEM-EDS and FT-IR analyses confirmed the successful deposition of CS-TP, CS-SPI, and CS-BPP on the wood surface, and the content of N element increased. The TG results showed that the initial decomposition temperature and the maximum thermal decomposition temperature of the coated wood specimens decreased, while the char residue increased significantly. This is due to the earlier pyrolysis of CS-TP, CS-SPI, and CS-BBP. This shows that the three polyelectrolyte flame-retardant coatings can improve the thermal stability of wood. The combustion behavior of the wood specimen was observed by exposure to combustion; the coated wood could self-extinguish within a certain period of time after ignition, and the flame-retardant performance was improved to a certain extent. SEM and EDS characterization analyses of the carbon residue after combustion showed that the coated wood charcoal layer was denser, which could effectively block heat and combustible gas.