Water leaching resistance of fire retardant impregnation chemicals in wood

Wood is a combustible material and needs to be protected against fire. Most of fire retardants are not resistant to leaching. The aim of this study was to increase the retention of fire retardants and increase the resistance of these chemicals to leaching in order to improve the fire resistance of wood. For these purpose Scotch pine (Pinus sylvestris L.) and Chestnut (Castenea sativa Mill) wood impregnated with 2 % and 3 % aqueous solutions of boric acid, zinc chloride and aluminum chloride at various temperature (0, 20, 40, 60 oC) by using vacuum- press impregnation method according to instruction of the ASTM D1413-07 standard. Optimum impregnation conditions have been determined according to amount of retention. Leaching resistance of the samples post impregnated with sodium silicate (silica gel treatment) and esterified with propionic anhydride (propionylation treatment) were determined. Termogravimetric analysis was applied according to the ASTM E1131-03 standard in order to determine the thermal properties of these samples. The highest amount of retention was determined in samples impregnated with the solutions having 3 % concentration and 60 oC temperature. Silica gel treatment decreased the amount of leachant in all three impregnations. For propionylation treatment, amount of leachant was decreased in parallel with weight percent gain after propionylation. The highest leaching resistance was determined in chesnut and aluminum chloride. According to thermogravimetric analysis silica gel treatment improved the fire resistance property of treated wood. But propionylation treatment affected the fire resistance property of wood negatively although decreased the leaching of impregnation chemicals.