Boron Leaching Control by Heat Treatment and Tannin Impregnation

This dissertation aimed to assess whether tannins were able to prevent boron leaching using heat treatment. First, to understand tannin behavior under high temperatures a pilot test was performed. Tannin powder from the Quebracho tree was dissolved into deionized water (DW). Southern yellow pine (SYP) and yellow-poplar (YP) woods were impregnated with tannins under a full cell process. Heat treatment under N2 atmosphere at 190/195/210°C was evaluated for four hours for both species. Mass loss due to heat treatment for wood and tannin as well as radial and tangential shrinkage were calculated. FT-IR spectroscopy and scanning electron microscopy were performed to understand the phenomena. Results indicated that at temperatures above 190°C there was an excessive tannin mass loss with collapse formation on SYP tannin-treated samples as well as changes in the in the spectra. The detailed study used 80 g of tannins and 12 g of DOT into 800 g of DW to attempt preventing boron leaching. SYP and YP samples were impregnated through full cell process and heat treated under N2, at 190°C for four hours. Samples were leached for 15 days. Anti-swelling efficiency was calculated. The resistance of the woods was tested against Gloeophyllum trabeum and Trametes versicolor fungi as well as the subterranean termite Reticulitermes flavipes for leached and unleached samples. The mass loss due to heat treatment was higher in YP than in SYP. The color changed for both woods, turning into much darker after tannin impregnation and heat treatment. All treatments for both species had lower volumetric shrinkage when compared to control as an effect of heat treatment, leading to improvement in dimensional stability. When mixed with tannins and heat treated, DOT remained in wood with leaching reduction of 46.5% and 34.5% for SYP and YP, respectively. After 15 days leaching HT T/DOT samples were classified as resistant (SYP) and highly resistant (YP) to the attack of decay fungi. Heat treated wood had improvement in durability against R. flavipes. HT DOT leached samples had 20.6% mass loss, whereas HT T/DOT 13.8%. Future work with amine-tannin solution should be tested to improve the leaching reduction