Comparative Performance of Three Magnesium Compounds on Thermal Degradation Behavior of Red Gum Wood.

Yiqiang Wu,Chunhua Yao,Yunchu Hu,Qinglin Wu,Yan Qing,Xiaodan Zhu

doi:10.3390/ma7020637

Abstract

The effect of basic magnesium carbonate (BMC), magnesium hydroxide (MH), and magnesium chloride hydrate (MCH) on thermal degradation of red gum wood was studied using cone calorimetry, Thermogravimetric-differential scanning calorimetry (TG-DSC) analysis, and X-ray diffraction (XRD) characterization. The results showed common fire retardation actions of the three compounds by releasing incombustible gas and/or water vapor to dilute combustible gas in the flaming zone, and by converting to MgO, which had a satisfactory protective wall effect on the wood. Individually, BMC absorbed heat from the wood at the pre-decomposition stage and, thus, slowed down wood pyrolysis process. It slightly increased the char yield by charring in both the charring stage and the char calcination stage. MH lost water at about 270°C, close to the temperature at which wood thermally degraded. MH rendered wood char quickly, and the compact char layer impeded further carbonization and burning of inner wood. MCH promoted charring with Mg2+ as a Lewis acid, and increased wood char yield. MCH also released Cl· free radical and HCl at 167°C, which easily coordinated with combustion reaction radical, and slowed down, even inhibited, the combustion chain reaction.

Highlights

Inorganic chemicals are attracting more and more attention among common fire-retardants due to their low cost and environmental-friendliness
Test results showed that the three magnesium compounds were able to decrease the fire intensity and heat release of the wood during combustion, exhibiting satisfactory flame retardation effects
After treatment with magnesium compounds, the HRR values decreased by over 40%, and the treatment effects on HRR decreased in sequence of magnesium hydroxide (MH), magnesium chloride hydrate (MCH), and basic magnesium carbonate (BMC)

Summary

Introduction

Inorganic chemicals are attracting more and more attention among common fire-retardants due to their low cost and environmental-friendliness. Magnesium compounds are effective fire-retardants, and have been used for fire retardation treatment of polymers. Limited study has been reported on using these three magnesium compounds for fire retardation treatment of wood- and other cellulosic materials. Ondrej Grexa et al [8] carried out a cone calorimetric study of MH-treated plywood, and showed that MH reduced specific extinction area (SEA—a smoke generation parameter) of wood from about 50 m2/kg to 40 m2/kg, and carbon monoxide yield from about 0.009 kg/kg to 0.007 kg/kg. Sain et al [9] studied fire retarding effects of MH for sawdust filled PP composites and showed that the addition of MH reduced horizontal burning rate of the composites from about 33 mm/min to 15 mm/min, and raised their oxygen index (i.e., minimum oxygen concentration required to support combustion) from about 20% to 34%. MH had a high endothermic value of 1450 J/g during its decomposition into magnesium oxide and water at

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