2007 Volume 56 Issue 5 Pages 472-476
A highly concentrated aqueous solution of sodium borate in the range 5.24mol/kg (20°C)-24.1mol/kg (80°C), which is more than twice more concentrated than the most soluble known borate solutions, was prepared and applied to the fireproofing agent of wood. This high concentration is due to the formation of polyborate ions. Wood specimens of Japan cedar (Cryptomeria japonica) was pressure-impregnated with the solution at 120-190°C for 1 - 24h. The most appropriate temperature was 150°C (474kPa) and the treatment for 1h. was sufficient for the impregnation. Weight percent gains (WPGs) were increased with increasing the concentration of the borate solution, and this lead to the decrease of weight loss (WL) when heated at 750°C for 20min in air. The specimens pressure-impregnated for 1h. using the solution containing 24mol/kg of boron achieved the WPG of 124% and the WL of 38%. The fireproofing procedure was greatly simplified by using the new highly concentrated borate solution. The other kinds of wood showed lower WPGs than Japan cedar because of the high density or the much resin. SEM and EDX observation indicated that the sodium polyborate enrolled wood fiber by heating and intercepted oxygen and heat conduction. The polyborate foam and carbonized layer also intercepted the heat conduction. This technique is also expected to be applied to the fireproofing of laminated wood and particle board.