Synthesis Of Boron Compounds And The Leachability And Durability Of Treated Wood

Inorganic borates are effective and environmental friendly as wood preservatives and offer good protection to timber in indoor applications. But these compounds can not be used in exterior circumstance for they are likely to leach out from treated wood. For finding new boron preservatives of leach resistance, some kinds of borates were synthesized and laboratory leaching performance, fungicidal activity and termite resistance of these borates were conducted in this paper.Insoluble inorganic borates, quaternary ammonium tetrafluoroborate, quaternary ammonium tetraphenylborate and quaternary ammonium bis(salicylato)borate were synthesized by the metathesis reaction in water. Each of those resulting compounds has been confirmed by micro-elemental analysis and melting point. The results of the elemental analysis are consistent with the theoretical calculation of the same chemical formula.The boron leaching rates of wood treated by different formulations and post-treatment were determined according to AWPA standard E11-06. The results show that: The boron leaching rates of treated samples are decreased significantly by two-step method, wood treated by borax firstly, and then by calcium chloride, polyvinyl alcohol(PVA P1763) or hydrophobic materials. The boron leaching rates are as low as 39.6% to 55.5%. The leaching rates of water insoluble inorganic borate prepared by metathesis reaction are between 83.2% ~ 96.8%. The boron leaching rate of wood samples treated by organic solvent-based ZB (oleic acid) is as low as 2.7%. The boron leaching rates of wood treated by quaternary ammonium tetrafluoroborate compounds increase with the number of carbon atoms of the compounds decrease. When the numbers of carbon atoms of the compounds are more than 19, the boron leaching rates by the compounds decrease significantly, the minimum up to 19.8%. The leaching rates of boron treated by quaternary ammonium tetraphenylborates are 2.1% ~ 24.7%, and 11.3% ~ 16.5% by didecyl dimethyl ammonium bis(salicylato) borates, and from 33.2% to 38.4% by dodecyl dimethyl benzyl ammonium bis(salicylato) borates.The inhibition zone test of quaternary ammonium tetrafluoroborate, quaternary ammonium tetraphenylborate and quaternary ammonium bis(salicylato) borate compounds were conducted, test fungus included white rot fungi, brown rot fungi and mold, etc. The results show that quaternary ammonium tetrafluoroborate have the best inhibitory effect, the best of them containing C8 ~ C12 alkyl groups. Termite test results show that, didecyl dimethyl ammonium tetrafluoroborate(DBF) and benzyl dodecyl dimethyl ammonium tetrafluoroborate (BBF) are effective against termites.The anti-fungi performance of DBF and BBF was evaluated by laboratory sand block test and field stake test. Different formulations of preservatives based on DBF and BBF were tested. In laboratory accelerated test, the brown rot fungi Gloeophyllum trabeum (G.T) and white rot fungi Coriolus versicolor (C.V) were used. The result shows that there is no significant difference of anti-fungi performance between DBF and BBF. DBF is just a little better than BBF, the weight loss of specimens by the two fungi were both less than 4% at the retention about 7.0 Kg/m3 of the two compounds. After field trial test for about 10 months, the stakes of DBF at the retention of 11.1Kg/m3, perform a good resistance to decay. Termite resistance of treated stakes by both DBF and BBF were poor and could be efficiently improved by adding pyrethroid in treating solution.An analytical method for determining boron-containing quaternary ammonium compounds in preservative or treated wood by HPLC is established. The apparatus and reagents: Elite P230 pump with 20μL loop injector; the column is Venusil SCX (100 mm×4.6 mm, 5μm) strong cation exchange column; UV detector with a measuring wavelength of 262 nm; EC2000 workstation; HPLC mobile phase is the mixture of acetonitrile, methanol and water in a volume ratio of 1:1:1, within appropriate amount of ammonium chloride; the flow rate is kept at 1.5 mL per minute. The linear correlation of this method is 0.9989 at concentration of the activities from 10 mg/L to 500 mg/L. The average recovery of spiked samples is 100.44%, and relative standard deviation is 0.397%. The detection limit of method was 2.0 mg/L.For quaternary ammonium borate compounds, the leaching rates of boron and quaternary ammonium are uncoordinate, the leaching rate of boron is much higher than the leaching rate of quaternary ammonium. The leaching rate of boron-containing quaternary ammonium compounds in treated wood have a relationship with their solubility in water. The higher solubility in water, the higher leaching rate of boron. When the concentration of saturated aqueous solution of boron-containing quaternary ammonium compound is less than 0.036%, the leaching rates of boron of its treated wood could be reduced to less than 40%.