Boron fixation in wood: studies of fixation mechanisms using model compounds and maritime pine

The purpose of the research work reported in this paper was to study the kinetics and thermodynamics of reactions of some boron compounds with some simple wood model compounds and with maritime pine (Pinus pinaster Ait.). The wood model compounds were selected in order to reproduce in a simple way the possible reactions boron may undergo with wood. Two boron compounds were tested with the wood: sodium tetraborate decahydrate (borax) and boric acid. Boron containing solutions applied to wood and model compounds were tested in such a way that they could lead to the insolubilization of boron or to its chemical fixation. Thermodynamics of boric acid fixation on the wood surface was studied. Results suggest that, even though boron reacts faster with polysaccharides than with lignin, all reactions are very slow at 20 °C. Adsorption should be the preferential mechanism for the bonding of boric acid to wood. This weak bond explains why boron tends to leach out from wood in wet conditions after conventional preservative treatments.     

Effects of N′-N-(1, 8-Naphthalyl) hydroxylamine (NHA-Na) and hydroxynaphthalimide (NHA-H) on boron leachability and biological degradation of wood

Although boron wood preservatives have many advantages, boron itself does not adequately protect wood in ground contact and exterior applications because its susceptibility to leaching. As a result of previous studies to limit or decrease boron leaching, several fixation systems have been developed. In this study, we evaluated the effects of N′-N-(1, 8-Naphthalyl) hydroxylamine (NHA-Na) and hydroxynaphthalimide (NHA-H) on boron leaching and decay and termite resistance via possible boron precipitation in wood after NHA treatments at varying concentrations. Results showed that treatment of wood blocks with disodium octaborate tetrahydrate (DOT), boric acid (BA), or calcium tetraborate (CaB) incorporation with 1.0% NHA-Na solutions in sequential processes appears to somewhat reduce the susceptibility of boron to leaching. Blocks treated sequentially with boron compounds and then 1.0% NHA-Na solutions showed about 30% less boron leaching compared to boron only treated blocks. In addition, the existence of boron and NHA-Na in wood together showed a synergistic effect against brown-rot fungus, Fomitopsis palustris. We conclude that the relationship between boron and NHA-Na concentration in wood as regards precipitation possibilities appears to be predictive for reducing boron leachability.     

Leachability and termite resistance of wood treated with a new preservative: ammonium borate oleate

Synthesis of a new chemical compound combining water-repellence of oleic acid and biocidal effect of boric acid linked by ammonia have been followed and validated by fourier transformed infra red (FTIR). This compound named ammonium borate oleate (ABO) has then been studied as a wood preservative. Different molar ratios of oleic acid have been involved in the synthesis of ABO and leachability of those mixes from wood observed according to Japanese industrial standard. The formulation one mole of boric acid and one of ammonia (1:1:4) for four moles of oleic acid has shown the best efficiency compared to formulations 1:1:1, 1:1:2 and 1:1:3 with about 52% of boron remaining after weathering when other formulations retained respectively 10%, 29% and 46% of boron in the case of an impregnation of Cryptomeria japonica. Seven solutions of 1:1:4 ABO in ethanol of different concentrations were then produced and sapwood blocks of C. japonica and Fagus crenata were impregnated. A toxicity threshold of around 2.0 kg/m³ for both species was determined in a termite resistance test to Coptotermes formosanus indicating the positive effect of combining water repellent and biocide. Termite mortality recording and microscopic observations complete this study indicating that the action mechanism of ABO is providing a water resistant inner coating.     

Protein impact on the capability of the protein-borate preservative penetration and distribution into pine and aspen wood

The aim of the research project was to determine the capability of the protein-borate preservative to penetrate into the wood of Scots pine (Pinus sylvestris L.) and aspen poplar (Populus tremula L.). This capability was assessed by the preservative retention and the measurement of the penetration depth of the treatment solution. The scope of the performed experiments comprised two methods of treatment. The treatability of the two wood species with the examined formulations was compared with their treatability with the solution of the boric acid alone or with protein. The performed quantitative analysis of the boric acid and protein in individual wood layers allowed to characterise the distribution of the formulation ingredients on the cross-section of the treated elements. Significant differences were shown to occur in the degree of wood treatment with the formulation containing globular protein using the vacuum and vacuum-pressure methods. In addition, the impact of the protein presence on the way of boric acid penetration into wood was also determined.     

An economical treatment schedule for boron impregnation of Eucalyptus grandis wood: Commercial trial of partially dried material

Being non-durable, Eucalyptus grandis wood needs treatment with preservative chemicals. As vacuum-pressure impregnation treatment being more suitable for commercial applications, and boron chemicals being environment-friendly for indoor uses, an economical treatment schedule (15 minutes initial vacuum of -85 kPa followed by a pressure of 1300 kPa for 15 minutes and a final vacuum of -85 kPa for 5 minutes) developed at the Kerala Forest Research Institute was tested for its commercial suitability for treating E. grandis wood with boron chemicals. A pooled mean dry salt retention (DSR) of 7.7 kg m ^-3 was achieved for wood in partially dried condition with average moisture content of around 32%, using a 6% boric acid equivalent (BAE) solution. This confirms the success of the schedule for commercial application, as the DSR achieved is much higher than the standard specification of many countries.     

Investigation of modified water glass as adhesive for wood and particleboard: mechanical,thermal and flame retardant properties

Water glass (WG) is an inorganic binder with excellent fire resistance in porous materials but has limited application to wood bonding. In this work, modified WG adhesive was developed and the effect of modification on the properties of adhesive and particleboard bonded with it was investigated. The bonding strength of WG adhesives increased by the modification with boric acid and aminofunctional silane. Stable siloxane linkage can lead to enhanced bonding. Particleboards with modified WG were manufactured with a target density of 750 kg m^?3. The silane was selected as the best modifier; it was the only one to meet the requirements of EN 312 (Type 2). The reaction of amino groups onto the surface of wood was confirmed by Fourier-transform infrared spectrum. All particleboards produced with WG adhesives showed resistance to fire comparable to those with urea formaldehyde in the combustion test for 30 min. As a result of this investigation, WG modified with silane could be a desirable alternative to current synthetic adhesives for wood composites and fire resistance application.     

MUF复配硼系化合物处理柳杉木材的热分析

通过热重(TG)和差热分析(DTA),考察经不同浓度的MUF及其与硼酸、硼砂复配的改性液处理后柳杉木材的热分解过程,结果表明:MUF对木材具有一定的催化成炭作用,复配硼酸、硼砂后其催化成炭作用得到进一步的加强;MUF促进了木材燃烧时的氧化分解,但复配硼酸、硼砂后,氧化分解反应得到明显抑制,放热量降低,剩炭率提高。     

Effect of hot air post-treatments on copper leaching resistance in ACQ-D treated Chinese fir

Chinese fir (Cunninghamia lanceolata Hook.) wood cubes (19?×?19?×?19 mm³) were treated with amine copper quat-type D (ACQ-D) solution and fixed with different hot air post-treatments. The effects of temperature, relative humidity, duration, air circulation of post-treatment as well as the copper retention in the treated wood on copper leaching were investigated. With the help of ultraviolet or visible spectroscopy (UV/VIS), the valence conversion of copper in treated wood post-treated with optimal post-treatment conditions was investigated, and its relation with copper leaching was also discussed. The results showed that besides temperature and relative humidity, air circulation during hot air post-treatments also had a significant effect on accelerating copper fixation in ACQ-D treated wood. 70 °C, 80% R.H. with good air circulation provided a suitable condition for complete fixation of copper in a short period. After the applied post-treatments, up to 11.3% cupric copper reduced to cuprous form. A higher copper conversion rate usually corresponds to lower copper leaching, which is consistent with the contribution of lower water solubility cuprous copper.     

Evaluation of new quaternary ammonium compound, didecyldimethylammonium tetrafluoroborate (DBF) in comparison with DDAC: Leachability and termite resistance tests

Modifications in the structure of wood preserving quaternary ammonium compounds (QACs) may result in improvements in leaching of components and biological resistance of treated wood. In this study, we evaluated the leaching characteristics and termite resistance of wood treated with a newly developed QAC compound didecyldimethylammonium tetrafluoroborate (DBF) in comparison with commercial DDAC, another QAC compound. Laboratory leaching tests showed that amount of DBF released from treated wood specimens was less than that of DDAC. However there was no difference between DBF and DDAC in the resistance of treated wood specimens against termite attack. Retention level at about 3 kg/m³ of DBF and DDAC seems to be enough to protect wood against termite attack, however, no comparative data are available for resistance of DBF and DDAC-treated wood against wood degrading fungi. Field tests are also needed to determine the performance of DBF-treated wood in ground contact in comparison with DDAC.     

Process related copper leaching during a combined wood preservation process

A combined wood impregnation process including impregnation with a chromium-free wood preservative and oil treatment was evaluated with regard to leaching of copper during the oil process. Two different experimental setups make up the balance of copper content in oil, wood samples and condensate water, also taking different fixation times and process durations into account. Copper is sufficiently fixed after 24 hours, and leaching of copper into the oil is low. Increasing the oil process time does not lead to increased leaching. The hot oil treatment of impregnated wood under vacuum atmosphere is a fast drying method without major negative consequences for the impregnated copper.     

Influence of dipping time on uptake of preservative solution, adsorption, penetration and fixation of copper-ethanolamine based wood preservatives

Copper-ethanolamine based wood preservatives are the most important products for protection of wood in use class III and IV applications. These preservatives can be applied using different procedures. One of them is dipping, a method which is predominantly used in less industrialised countries. The most important parameter, that influences the quality of this treatment, is dipping time. Influence of various dipping times on copper retention, adsorption, penetration, colour of the specimens and copper fixation was examined. In this paper copper-ethanolamine solutions of two different concentrations were utilised (c_Cu=0.05% or 0.25%). The results showed that longer dipping treatments resulted in higher uptakes of preservative solution, better penetrations and lower leaching of copper-ethanolamine based wood preservatives from Norway spruce wood. After one week of dipping, samples retained on average 275 kg/m³ of preservative solution, copper active ingredients penetrated on average 3 mm into the specimens, and only 2.3% of copper was emitted from wood impregnated with aqueous solution of the higher concentration, when subjected to ENV 1250 leaching procedure.     

Commercial scale trial of an economical schedule for boron impregnation treatment of green rubber wood

An economical treatment schedule, developed at the Kerala Forest Research Institute for boron impregnation of rubber wood, was tested in a commercial wood treatment plant. A pooled mean dry salt retention (DSR) of 12.4 kg/m³ was achieved for rubber wood in green condition with average moisture content of around 70%, using a 6% boric acid equivalent solution. This confirms the success of the schedule for commercial application, as the DSR achieved is much higher than the standard specification of many countries.     

Arsenic speciation of solvent-extracted leachate from new and weathered CCA-treated wood

For the past 60 yr, chromate-copper-arsenate (CCA) has been used to pressure-treat millions of cubic meters of wood in the United States for the construction of many outdoor structures. Leaching of arsenic from these structures is a possible health concern as there exists the potential for soil and groundwater contamination. While previous studies have focused on total arsenic concentrations leaching from CCA-treated wood, information pertaining to the speciation of arsenic leached is limited. Since arsenic toxicity is dependent upon speciation, the objective of this study was to identify and quantify arsenic species leaching from new and weathered CCA-treated wood and CCA-treated wood ash. Solvent-extraction experiments were carried out by subjecting the treated wood and the ash to solvents of varying pH values, solvents defined in the EPA's Synthetic Precipitation Leaching Procedure (SPLP) and Toxicity Characteristic Leaching Procedure (TCLP), rainwater, deionized water, and seawater. The generated leachates were analyzed for inorganic As(III) and As(V) and the organoarsenic species, monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), using high-performance liquid chromatography followed by hydride generation and atomic fluorescence spectrometry (HPLC-HG-AFS). Only the inorganic species were detected in any of the wood leachates; no organoarsenic species were found. Inorganic As(V) was the major detectable species leaching from both new and weathered wood. The weathered wood leached relatively more overall arsenic and was attributed to increased inorganic As(III) leaching. The greater presence of As(III) in the weathered wood samples as compared to the new wood samples may be due to natural chemical and biological transformations during the weathering process. CCA-treated wood ash leached more arsenic than unburned wood using the SPLP and TCLP, and ash samples leached more inorganic As(III) than the unburned counterparts. Increased leaching was due to higher concentrations of arsenic within the ash and to the conversion of some As(V) to As(III) during combustion.     

Feasibility study of utilization of commercially available polyurethane resins to develop non-biocidal wood preservation treatments

Evaluation of commercially available polyurethane resins used up to now for coating applications to develop non-biocidal wood preservation treatments has been conducted. A simple method of vacuum impregnation of these resins into beech wood (Fagus sylvatica L.) and pine wood (Pinus sylvestris L.) samples followed by varied curing processes at ambient temperature, 103, and 200 °C has been performed. Based on the analysis of weight percent gain before and after leaching, treatment resistance to leaching, anti-swelling efficiency, wettability and decay durability measured for treated and untreated blocks after leaching with the white-rot fungus Coriolus versicolor for both wood species and the brown-rot fungi Poria placenta and Gloeophyllum trabeum for pine wood, it can be concluded that such treatment can be considered as potential valuable non-biocidal treatments.     

Boron effect on decay resistance of some fire-retardant coatings applied on plywood surface

Boron effect on decay resistance of some fire-retardant coatings applied on plywood surface was studied. Boric acid (B) was mixed into aqueous trimethylol melamine (TM) solution to increase the fixation in wood. To reveal the decay resistance of boric acid-added formulations, coatings were applied over radiata pine plywood surface as 100 g/m² amounts. Phosphoric acid (P) and dicyandiamide (D) were also used alone or in mixtures as reference coatings for comparison. Coated specimens were exposed to weathering according to Japanese Industrial Standard JIS A 9201 (1991) as severe leaching for 10 cycles, prior to decay-test. Non-leached and leached specimens, then, were inoculated with a brown-rot fungus Tyromyces palustris and a white-rot fungus Coriolus versicolor. Extent of the fungal attack was determined by mass loss of the specimens after 12 weeks incubation and microscopic examinations by 6 × magnification. Results indicated that TMB and TMDB coatings imparted the panels complete decay resistance despite severe weathering conditions and were proved superior over all other alone and mixture coatings. Although other combinations and alone treatments used in the study were also effective to inhibit the fungal damage before weathering, leaching greatly reduced their protective efficacy. Surface characteristics of decayed specimens were consistent with the determined values of mass losses caused by fungal attack. TMB and TMDB coatings were remarkably effective in maintaining sound surface properties after exposure to weathering and decay fungi.     

Fungal and termite resistance of wood treated with 4-methoxytrityl tetrafluoroborate

This study evaluates the decay and termite resistance of Scots pine (Pinus sylvestris L.) treated with 4-methoxytrityl tetrafluoroborate (MTFB). Decay resistance tests of unleached samples showed that 2%, 1.5% and 1% concentrations of MTFB (15.4 kg/m³, 11.1 kg/m³, and 7.4 kg/m³, retention levels, respectively) gave less than 2% decay of Postia placenta and concentrations of 2% and 1.5% less than 2% decay of Coniophora puteana. Wood specimens treated with 4-methoxytrityl tetrafluoroborate solutions were not protected against the brown rot fungi after a 14-day severe leaching process, suggesting excessive leaching of the chemical from wood. Treatment with 2% concentration protected against subterranean termites, Coptotermes formosanus Shiraki based on mass losses in both leached and unleached wood specimens in comparison with lower concentration levels. These results suggest that 4-methoxytrityl tetrafluoroborate might be promising to protect wood being used outdoors against termite attack. However, 4-methoxytrityl tetrafluoroborate did not protect wood against fungal decay. Field tests are needed to observe the performance of 4-methoxytrityl tetrafluoroborate treated wood in ground contact.     

A pilot plant investigation of boron treatment of rubber wood: Arriving at an economical treatment schedule

An economical treatment schedule (15 minutes initial vacuum of 85kPa; 15 minutes pressure of 1000 kPa; 5 minutes final vacuum of 85kPa; was arrived at for treating air-dried rubber wood in a pilot plant cylinder. Treating with 3% BAE (boric acid equivalent) solution resulted in a dry salt retention of 13.1 kg/m³. Also, the study showed that green rubber wood can be treated to required chemical retention level by employing the above treatment schedule and by increasing the concentration of the treatment solution to 6% BAE.     

Re-evaluation of fungicidal properties of boric acid

Minimal inhibitory fungicidal concentrations of one of the most important biocides were determined in nutrient medium and on impregnated wood specimens. The results showed, that brown rot fungi are more sensitive to boric acid than white rot ones. To inhibit growth of wood decay fungi, lower minimal effective retentions have been determined than reported in previous publications.     

Release of arsenic to the environment from CCA-treated wood. 2. Leaching and speciation during disposal

Wood treated with chromated copper arsenate (CCA) is primarily disposed within construction and demolition (C&D) debris landfills, with wood monofills and municipal solid waste (MSW) landfills as alternative disposal options. This study evaluated the extent and speciation of arsenic leaching from landfills containing CCA-treated wood. In control lysimeters where untreated wood was used, dimethylarsinic acid (DMAA) represented the major arsenic species. The dominant arsenic species differed in the lysimeters containing CCA-treated wood, with As(V) greatest in the monofill and C&D lysimeters and As(III) greatest in the MSW lysimeters. In CCA-containing lysimeters, the organoarsenic species monomethylarsonic acid (MMAA) and DMAAwere virtually absent in the monofill lysimeter and observed in the C&D and MSW lysimeters. Overall arsenic leaching rate varied for the wood monofill (0.69% per meter of water added), C&D (0.36% per m), and MSW (0.84% per m) lysimeters. Utilizing these rates with annual disposal data, a mathematical model was developed to quantify arsenic leaching from CCA-treated wood disposed to Florida landfills. Model findings showed between 20 and 50 t of arsenic (depending on lysimeter type) had leached prior to 2000 with an expected increase between 350 and 830 t by 2040. Groundwater analysis from 21 Florida C&D landfills suspected of accepting CCA-treated wood showed that groundwater at 3 landfills was characterized by elevated arsenic concentrations with only 1 showing impacts from the C&D waste. The slow release of arsenic from disposed treated wood may account for the lack of significant impact to groundwater near most C&D facilities at this time. However, greater impacts are anticipated in the future given that the maximum releases of arsenic are expected by the year 2100.     

Fire resistance of wood treated with a cationic silica sol

Wood was treated with the cationic silica sol (CSS) Levasil 200S and dried at various temperatures (room temperature, 40, 60, 80 and 103 °C). A water leaching test revealed fixation of the silica in wood even after drying at room temperature. Maximum cross sectional swelling of the specimens decreased from 15.6 % (untreated control) to 13.0 %, when treated wood was dried at 103 °C; cell wall bulking values were also negative (?2.3 %), indicating a thermal degradation of the cell wall polymers catalyzed by the CSS. Penetration of the CSS into the cell wall did not occur. A simple flammability test revealed increased fire resistance of the treated wood. Mass loss and velocity of mass loss as well as burning time were reduced; glowing of the formed charcoal was completely prevented. The effectiveness increased with increasing weight percent gain of the CSS in the wood. Thermo gravimetric analysis under nitrogen atmosphere displayed only minor reduction in the initial temperature of thermal decomposition for wood treated with CSS as compared to the control. In the presence of oxygen the resulting charcoal showed comparable thermal behaviour to the control. The yield of charcoal after pyrolysis was increased to a minor extent (from 19.9 to 23.0 %), indicating that the release of combustible gases was hardly reduced. The mode of action of enhanced fire resistance due to CSS-treatment is discussed.