Tony Ung

Rate and extent of adsorption of ACQ preservative components in wood

Abstract The adsorption of copper, [as Cu(II)], monoethanolamine (MEA) and didecyldimethyl ammonium chloride (DDAC) components of CuMEA and alkaline copper quaternary (ACQ) solutions impregnated into wood was followed by measuring the changes in solution concentrations in the wood over time. The rate and extent of copper and MEA adsorption were highly dependent on the solution strength and the conditioning temperature. Both copper and MEA were adsorbed by the wood structure with a rapid initial reaction, with higher relative amounts sorbed from lower concentration solutions. This was followed by a slower adsorption that still had not equilibrated after 7 weeks at 22°C. Generally, the adsorption pattern was similar for copper and MEA, suggesting that they were adsorbed as a copper MEA complex, with an MEA/copper molar ratio close to the theoretical maximum of 4. At a higher conditioning temperature of 50°C the reaction time was greatly reduced, with the adsorption after 1 week higher than after 7 weeks at 22°C, suggesting faster and more complete reaction at higher temperatures. DDAC was adsorbed more quickly and to a higher degree than Cu(II) for all treatment solutions and should be preferentially removed from such solutions, especially if empty-cell treatments are used. There appeared to be higher Cu adsorption from the higher concentration solutions of CuMEA than from corresponding ACQ solutions, likely due to DDAC competition with copper for the same reaction sites.

Prediction of long-term leaching potential of preservative-treated wood by diffusion modeling

Abstract An approach to modeling leaching and leaching impacts of preservative components from treated wood is presented based on three simple laboratory determinations: the amount of preservative component available for leaching (Le), equilibrium dissociation of preservative into free water in wood (Di) and diffusion coefficients for component leaching in different wood directions (D). In this study, the following inorganic wood preservative systems were investigated: chromated copper arsenate (CCA), the copper component of copper azole (CA) and alkaline copper quaternary (ACQ), and boron in disodium octaborate tetrahydrate (DOT). Aggressive leaching of finely ground wood showed that amounts of preservative compounds available for leaching were highest for borates, followed by copper in copper amine systems and arsenic in CCA, copper in CCA and chromium in CCA. The equilibrium dissociation or solubility of components in free water in the wood was much higher for borates and copper amine, followed by copper and arsenic in CCA and chromium in CCA. Use of the applicable diffusion coefficient (D) and Di or Le values in a diffusion model allows the prediction of total amount leached and emission or flux rate at different times of exposure for products with different dimensions and geometries. The approach was tested and generally validated through application of the model to results of laboratory water spray leaching of full-size lumber samples. The approach explains the rapid leaching of boron compounds (large diffusion coefficient and high initial dissociated concentration) compared to other preservative components and predicts that ACQ will have higher initial leaching rates compared to CCA and CA, but the latter preservatives will continue to leach copper at a measurable rate for a much longer time. The practical implications and limitations of the approach are discussed.

Effects of fixation temperature and environment on copper speciation in ACQ treated red pine

Abstract Red pine (Pinus resinosa Ait.) sapwood samples treated with alkaline (amine) copper quaternary (ACQ) were conditioned at different temperatures and under wet or dry conditions to evaluate the stability of copper (Cu) to leaching and conversion of divalent copper (Cu-II) to monovalent copper (Cu-I). Significant Cu-II was reduced to Cu-I during post-treatment stabilization, especially at elevated temperatures (105°C and 120°C). The percent conversion to Cu-I was higher at lower retentions; in some cases, at low retentions and high fixation temperatures, all of the cupric Cu was reduced to Cu-I, raising the possibility of reduced activity of Cu as a biocide when high temperature conditions are used to fix ACQ treated wood. However, exposure of wood to a leaching procedure (rewetting, re-drying) generally resulted in a significant component of the Cu-I in wood being oxidized back to Cu-II. Steaming of weathered ACQ treated wood at 120°C also converted significant amounts of Cu-II to Cu-I.

Surface quality sensing of trembling aspen (Populus tremuloides Michx.) veneer products by near infrared spectroscopy

Abstract The potential of near infrared spectroscopy (NIRS) to estimate wood moisture content (MC), surface energy characteristics and adhesive bond strength were evaluated on aspen (Populus tremuloides Michx.) veneer subjected to different drying times. For samples dried progressively at 103°C, the best MC prediction model was for the total MC range (0–100%) with an R2 value of 0.68. However, exposure at 180°C produced surface colour changes, and the CIE L*a*b* colour parameters measuring colour changes were better estimated using the 400–900 nm spectral data than the 1100–2400 nm spectral data. Increased exposure time at 180°C resulted in lower wettability and, hence, larger contact angles, especially when ethylene glycol was used as probe solvent. Lap shear strength tests on veneers showed that adhesion by phenol formaldehyde resins was impaired by the high temperature exposure; however, the lap shear strength test had high variability so there was not always a clear relationship between contact angle and lap shear strength test.

Prediction of Boron Content in Wood Pellet Products by Near-Infrared Spectroscopy

Abstract A rapid method assessed the potential of near-infrared spectroscopy (NIRS) to estimate boron content of wood pellet products. Based on a comparison of NIR spectra data in the 1,100- to 2,200-nm wavelength region of Eastern black spruce (Picea mariana var. mariana) wood pellets treated with preservative concentrations ranging from 0 to 2 percent and from 0 to 20 percent glycol borate–based disodium octaborate tetrahydrate (DOT), the minimum level of boric acid equivalent required to protect wood from biodegradation was revealed. Borate was indicated in the 1,700- to 1,900-nm wavelength region and the visible-NIR absorbance trended to a proportion higher for the lower borate concentrations and lower for the higher borate concentrations. These were correlated by projection to the latent structures–partial least-squares regression method and the sample-specific standard error of prediction method. Calibration sets achieved R2 values from 0.7 to 0.95, root mean square error (RMSE) ranging from 0.3 to ...

Effect of Copper to Quat Ratio on Fixation and Leaching of Preservative Components in Alkaline Copper Quat–Treated Wood

This study investigates the effect of the relative proportion of copper oxide (CuO) to didecyl dimethyl ammonium carbonate (DDACb) in an alkaline copper quat (ACQ) formulation on the rate of copper fixation or stabilization and the resistance of treated wood to leaching of copper and quat (DDACb) for different ACQ retentions in wood. Red pine, jack pine, and black spruce samples were treated with ACQ at concentrations of 0.6, 1, and 1.5 percent with CuO to DDACb ratios of 2:1 (the usual ratio for ACQ-D), 1:1, and 1:2. Red pine samples posttreated at 50°C were evaluated for rate of fixation by the expressate method. Conditioned samples of the three species were evaluated for the leaching of copper, and DDACb (red pine). At similar ACQ retentions, a decrease in proportion of copper in the formulation resulted in a substantial reduction in the time required for copper fixation. There was a significant decrease in the amount of copper leached for all three species studied with reduction of proportion of copper in the ACQ formulation. Improved fixation time and reduced copper leaching resulted from the lower copper retentions in the samples with lower relative proportions of copper in the formulations. The reduction in leaching was higher for samples treated with concentrations of 1 and 1.5 percent ACQ. The formulation having a 1:1 CuO to DDACb ratio appears to be the most promising, considering the positive effects of reduced copper ratio on copper leaching and fixation time and the minimal effect on DDAC leaching.

Protocol Comparison: Laboratory versus Natural Weathering Tests for Performance Evaluation of Coatings on Preservative-Treated Wood

Abstract Fourteen stains were tested in the laboratory to compare water uptake and leaching reduction of wood treated with chromated copper arsenate, alkaline copper quat, and copper azole. Based on results of a 2-week test, eight stains were selected to be evaluated over 3 months of accelerated weathering and five stains over 3 years of natural exposure in Toronto, Ontario, Canada. These comparisons were made in order to find a quick and reliable method for replacing natural exposure tests. Comparison of different weathering techniques showed significant correlations between leaching and water uptake results from laboratory tests and natural weathering. The cumulative percentage of inorganic elements leached from coated samples was highly correlated with the cumulative percentage leached during 3 years of natural weathering. Also, the average moisture content of treated-coated samples after 1 and 3 days of water immersion showed a relatively strong positive correlation with the average moisture content o...