A Facile Preparation of Environmentally-Benign and Flame-Retardant Coating on Wood by Comprising Polysilicate and Boric Acid

For the sake of direct use on the previously constructed wooden buildings, a green flame resistant coating comprising sodium polysilicate (SPS) and boric acid was prepared. With weight gain of only 10 wt%, the treated wood sample (SPS/B-wood) had an improved limiting oxygen index value of 40.3% and passed the V-0 rating in UL-94 test. Additionally, the total heat release, total smoke production and peak carbon monoxide production of SPS/B-wood sample were decreased by 24.5%, 36.0% and 59.4% respectively, compared with that of control wood sample. The residue of SPS/B-wood sample was increased to 54.0% from 18.4% of control wood sample at 800 °C in the thermogravimetric analysis. The flame retardant mechanism suggested that SPS and boric acid formed Si–O–B and Si–O–Si contained structures, isolating the heat and smoke transfer during wood combustion. Notably, NaOH introduced by the SPS/B coating, catalyzed the lignin to form compact and high-quality char. To conclude, this low-cost and easily-applied coating has a promising future in villages where wooden buildings are densely arranged.