Grantee Research Project Results

Final Report: Environmentally Friendly Borate-Based Wood Preservative

EPA Contract Number: EPD13033
Title: Environmentally Friendly Borate-Based Wood Preservative
Investigators: McIntyre, Craig
Small Business: Liquid Lignin Company
EPA Contact: Richards, April
Phase: I
Project Period: May 15, 2013 through November 14, 2013
Project Amount: $80,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2013) RFA Text | Recipients Lists
Research Category: SBIR - Innovation in Manufacturing , Small Business Innovation Research (SBIR)

Description:

The goal of this Phase I project was to determine the feasibility of using a lignin-based additive to impede the leaching of borates from pressure-treated wood. Currently, borates can be used only in interior under-roof applications that are protected from rain, due to the tendency of borates to leach readily from wood. The lignin-based additive uses a stream available from lignin-recovery processes being implemented by the paper industry to remove lignin from their black liquor, unloading their Recovery Boilers, and increasing the throughput of their pulp mills. Liquid Lignin Company team has experience regarding chemistry and manufacture of lignin and has developed a strong network within the paper industry while developing their innovative SLRP^® Process to recover lignin, which was funded initially by a U.S. Department of Energy SBIR in 2009.

Summary/Accomplishments (Outputs/Outcomes):

In Phase I experiments, the lignin-based protectorant (LBP) was shown to impede leaching significantly, retaining as much as 50 percent of the initial borate in small wooden blocks in an accelerated test regimen that for unprotected samples leached almost all of the borate from the blocks. The working hypothesis is that the LBP forms ionic complexes within the microscopic volumes of wood. These complexes are soluble at the working pH 10 in the treating solutions used by wood-treatment processes. These complexes then become insoluble when pushed into the wood in pressure treatment and exposed to the lower pH 5 within the wood matrix. During drying, these macro-complexes are withdrawn into the innermost volumes within the wood matrix, and upon rewetting, the disodium octaborate tetrahydrate diffuses very little—if at all—to the outer surface of the wood where it could be washed away. This novel concept is the basis of a patent application filed in early 2014.

Initially in Phase I, a set of statistically designed experiments (Plackett-Burman design) tested a variety of control variables. Small blocks of wood were pressure-treated with test formulations and then immersed in water. Effectiveness was measured by the leaching rate of borate into water; the lower the rate, the more effective the additive. These experiments identified the critical control variables which then were tested using a statisticallydesigned factorial design. The factorial design identified the formulation concentrations that had the best combination of cost and effectiveness. The cost of the proposed system was shown to be financially attractive relative to competitive systems that are based on micronized copper and quaternary compounds. These levels will be the starting point for the Phase II experiments.

Two deficiencies were observed during the course of the Phase I experiments—dark (black) color and a strongly negative odor of the treated wood, both resulting from the crude LBP system used in Phase I. Simple experiments identified two unit operations that could correct these deficiencies. Phase II experiments will better define the operating conditions of these unit operations that produce the best and most cost-effective LBP.

Conclusions:

Test formulations demonstrated significant reduction in borate leaching from wood blocks during testing.

There continues to be interest in the market for products that will enable the broader use of borates for wood preservation. Several treated wood companies have written letters of support for Liquid Lignin Company’s pursuit of a natural protectorant system which impedes the leaching of borates. These letters are indicative of the market pull that exists within the marketplace for this product concept. A strong project team has been assembled to support Liquid Lignin Company to pursue commercialization of the LBP product, including key wood treatment partners and process and project engineering support.

Supplemental Keywords:

wood preservatives, borate, lignin

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