Study On Fire-retardant Properties Of Compound N-P Flame Retardant On Poplar

In order to reduce hygroscopicity and enhance leaching resistance of poplar treated with nitrogen-phosphorus (N-P) fire retardant, and further reduce its smoke production. Melamine and magnesium hydroxide were added during the manufacture of N-P fire retardant. Three excellent flame retardants of moisture resistant and three high-performance flame retardants and smoke suppressants were optimized by orthogonal test. A novel N-P-Al-Si water-soluble flame retardant formulated with poly (sodium silicate-aluminium dihydrogen phosphate) (Al-Si) and N-P was synthetized in this study. Poplar was treated by N-P and compound N-P fire retardants, and hydroscopic rate, leaching resistance, smoke density, cone calorimeter and thermogravimetric analysis (TGA) of untreated and treated poplar were measured. Flame retardant distribution on the wood’s inner surface was investigated by scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDAX) after cone calorimeter testing. The combustion performance of untreated and treated Poplar was discussed by thermal analysis. Ozawa-Flynn-Wall and Coats-Redfern (modified) were used to calculate the activation energies of untreated and treated specimens. The results showed as follows:(1) The moisture absorption rate of specimens treated with NP-MEL-3 was less than 28% when the drug-loading rate reached about 10%, which meet the requirement of America building code. When the drug-loading rate reached about 12%, compared with Poplar specimens treated with N-P, the oxygen index value and char residual yield of specimens treated with NP-MEL-3 respectively increased by 14.86% and 30.58%, while the first Peak Heat Release Rate, Total Heat Release, Carbon monoxide yields decreased by 40%,33.89% and 34.38%, respectively. The cost in using is low and can be used recycled.(2) The SDR of N-P modified with MH treated specimens were lower than that of N-P. And the SDR of samples treated by NP-MH-3 was lower than others. A maximum of SDR at 34.4 appeared when the drug-loading rate reached about 13%, which was 31.81% lower than N-P treated samples and well below the requirement of national standard(SDR<75). Compared with Poplar specimens treated with N-P, the first Peak Heat Release Rate, Total Heat Release, Mass loss, Total Smoke Production and Carbon monoxide yields of specimens treated with N-P modified with MH decreased in varying degrees. Among of them, the fire performance and smoke suppression of NP-MH-2 treated samples were the best. The amount of residual carbon increased by 47.65% and the Carbon monoxide yields was reduced by 74.68% than that of N-P, which greatly decreased the production of poisonous gases. From the char layer microstructure, particles of N-P modified with MH were uniformly dispersed in internal layers of timber, and a porous structure was formed on the surface of wood. And the cost of N-P modified with MH is low and can be used recycled.(3) Al-Si and N-P had favorable synergistic effects on flame retardance of Poplar. Smoke density and hygroscopicity of N-P-Al-Si-treated samples showed a significant reduction relative to that of N-P. N-P-Al-Si treated samples demonstrated higher char yield and formed higher-density carbon layers. At the same time, N-P-Al-Si flame retardant evenly distributed over the inner surface of the wood and penetrated inside the cell cavity of the poplar, which formed a smoother and more condense superficial layer of protection. In addition, the combustion performance of N-P-Al-Si-treated samples is Bl level, in line with the national standard fuel GB8624-1997 standards. The cost of N-P-Al-Si flame retardant is low and can be used recycled.(4) The main pyrolysis stage of N-P-Al-Si-treated samples was between Al-Si and N-P, both the weight loss rate and weight loss were much lower than those of Al-Si and N-P and heat release rate was also slow. There was a similar trend of weightlessness of N-P-Al-Si-treated samples under different heating rate of TG curves, and weight loss curves shifted to higher temperature section as the heating rate increased. The activation energy of the first and second phase of N-P-Al-Si-treated samples were bigger than that of N-P, which indicated that the efficiency of flame retardant was improved when Al-Si and N-P were blended.