The effects of pH on copper leaching from wood treated with copper amine-based preservatives

As pH of leaching medium is an important factor in the leaching of wood preservative components, its effects on leaching should be quantified to ensure environmentally safe use of treated wood. In this study, the effects of pH on leaching of copper from wood treated with copper amine-based preservatives [alkaline copper quat (ACQ)-2, bis-(N-cyclohexyldiazeniumdioxy)-copper (CuHDO)-3, and copper azole (CUAZ)-3] were evaluated in comparison with wood treated with chromated copper arsenate (CCA)-3. Radiata pine sapwood blocks treated with these preservatives were leached at five pH levels (3.0, 3.5, 4.0, 4.5, and 6.5). The leached blocks were subjected to laboratory-scale decay tests using two brown-rot fungi. The blocks treated with copper amine-based preservatives leached significant amounts of copper at pH levels below 4.0. At all pH levels, the CuHDO-3-treated samples generally leached the most copper, followed by the samples treated with ACQ-2, CUAZ-3, and CCA-3. When the treated blocks were leached at pH 3.0, the degradation of hemicelluloses, which can chemically adsorb copper, was confirmed through Fourier transform infrared attenuated total reflectance (FTIR-ATR) analysis. Moreover, X-ray photoelectron spectroscopy (XPS) analysis indicated that the ratio of precipitates of the remaining copper in the treated wood severely decreased after leaching at pH levels below 4.0. Subsequent reduction in the biological effectiveness of wood treated with copper amine-based preservatives was not hardly observed after leaching at pH levels 4.0 or above. These results indicate that copper loss at pH levels 4.0 or above is not great enough to cause public concern about environmental problems and reduction of biological efficacy in practical applications.

Mold resistance of bamboo treated with copper complexes-grafted silica gel and its microdistribution in treated bamboo

Bamboo is readily discolored by mold fungi, which greatly limits its applications. An effective antifungal agent, copper(II) chloride (CuCl2)-grafted silica gel, was prepared by a sol–gel process using tetraethoxysilane (TEOS)/3-aminopropyltriethoxysilane (APTES) mixtures. The elemental composition and the chemical combinations of homogeneous sol mixture (HSM) and bamboo were determined via Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectrometry (SEM–EDS). The mold resistance of bamboo treated with HSM, alkaline copper quat (ACQ), chromated copper arsenate (CCA), and purified water was characterized by an indoor mold test. The micro-morphology of bamboo treated with HSM was investigated using scanning electron microscopy (SEM). HSM penetrated into the bamboo vessels, and formed xerogels, which was able to coordinate copper(II) cations. SEM–EDS investigations suggest that Si–O–Cu linkages may be formed through an exchange reaction between silanol groups and copper complexes. The bamboo samples treated with HSM showed highly efficient mold resistance due to a good penetration of HSM. Furthermore, no fungal hyphae were found in the structure of HSM-treated bamboo after a 5-week mold test. The copper complexes grafted to silica gel developed in this work provide an efficient antifungal agent for a wide range of potential applications in bamboo protection.

Relationship between copper species in solution and leaching from alkaline copper quat (ACQ) treated wood

The effects of pH and Cu:Mea ratio in alkaline copper quat (ACQ) solution formulation on the distribution of copper-monoethanolamine (Cu-Mea) complex species and Cu precipitation, and its influence on copper leaching from treated southern pine samples were investigated. Distribution of Cu in ACQ solution was studied by means of an equilibrium speciation model for aqueous systems (MINTEQA2). Conditions that favored a higher proportion of monovalent cationic complex, [Cu(Mea)2-H]1+, and precipitated copper as CuCO3(s), resulted in higher leach resistance in treated wood compared to conditions that favored the neutral copper complexes, [Cu(Mea)2-2H]0, and higher ligand copper complexes, [Cu(Mea)3]2+, [Cu(Mea)4]2+. Monovalent cationic Cu complex is maximized at a pH close to 9 with a Cu:Mea molar ratio of 1:4. Amounts of Cu leached at pH 9 were low compared to those at pH 12, where most of the Cu is present as neutral complex. Reduction of pH from 9 to 8 did not reduce Cu leaching, because of the lower cation exchange capacity of wood at the lower pH. Changing the Cu:Mea molar ratio to 1:3 at pH 9 significantly reduced the higher ligand complexes in the formulation and resulted in the majority of the copper being distributed as monovalent cationic complexes and some CuCO3(s) precipitation. These changes in 1:3 formulation significantly reduced copper leaching compared to Cu:Mea ratios of 1:4 and 1:10.

Effects of ionic strength, monoethanolamine, copper, and pH on adsorption of alkyl dimethyl benzyl ammonium chloride in wood

Various factors were investigated that could affect the adsorption of alkyl dimethyl benzyl ammonium chloride (ADBAC) on red pine wood. An increase in ionic strength of ADBAC solution had little effect on ion exchange (chemisorption) but allowed higher hydrophobic uptake (physisorption) of ADBAC in wood. ADBAC solution containing high amounts of monoethanolamine (MEA) and Cu decreased the chemisorption of ADBAC; free MEA and Cu appear to compete with ADBAC cations for the same bonding sites in wood. When ADBAC in MEA solution was adsorbed on wood under different pH conditions, ADBAC adsorption increased with increasing pH, but was considerably lower than the cation exchange capacity of red pine. Red pine blocks were treated radially and longitudinally with alkaline copper quat solution to verify how the micelle form of ADBAC penetrates into wood. Copper penetrated evenly into 50 mm thick wood samples with little gradient with depth; however, high amounts of ADBAC were concentrated on the surface creating a steep gradient with depth. After accelerated leaching, considerable amounts of physically adsorbed ADBAC leached out, especially from the surface.