Termite resistance and wood-penetrability of chemically modified tannin and tannin-copper complexes as wood preservatives

We examined the ability of chemically modified tannin and tannin-copper complexes to penetrate wood and the ability of the treated wood to resist termites. Only the tannin-treated wood retained the agents after treatment. Wood with untreated mimosa tannin (MT) retained the least amount, followed by wood with resorcinolated tannin (RMT) and that with catecholated tannin (CMT). When RMT or CMT was mixed with ammonia-copper, the wood retained twice as much of these solutions as the MT -ammonia-copper solution. The degree of retention of RMT-NH₃-Cu and CMT-NH₃-Cu ranged from 268 to 326kg/m³. The solutions penetrated 2–13 mm from the tangential sections of the logs. We also measured the termite resistance conferred by these solutions. Most of the tannin-NH₃-Cu solutions showed contact lethality for termites in the contact toxicity test. However, the termites were fed cellulose treated with those solutions and most survived the oral toxicity test (14 days). Moreover, these solutions reduced the amount of damage to the wood by termites. However, the mortality rate of the termites during the eating-damage test (>21 days) did not reach 100% for any of the solutions except for RMT. As a result of the field stake test with the same log's used for the penetrability test, the mass loss of wood treated with RMT or CMT alone or with RMT + NH₃ + CuCl₂, was about one-third to one-half that of the controls. Because these solutions have good wood penetrability and good termite resistance, they have potential use as low-toxicity wood preservatives.     

Tannin-caprolactam and Tannin-PEG formulations as outdoor wood preservatives: weathering properties

Key message

This article presents the leaching, fire and weathering resistance improvements of samples treated with tannin-based wood preservatives added of caprolactam. PEG-added formulations show limited applicability. The FT-IR and ¹³ C-NMR analyses of the caprolactam-added formulations show some evidences of copolymerization.

Context

Tannin-boron wood preservatives are known for their high resistance against leaching, biological attacks, fire as well as for the good mechanical properties that they impart to wood. These properties promoted these formulations for being a candidate for the protection of green buildings. However, the low elasticity of these polymers and their dark colour implied limited weathering resistances.

Aims

The aim of the study is to find suitable additives for tannin-based formulations to overcome their limited weathering resistances, without compromising the other properties.

Methods

Treatment, leaching and fire tests, dimensional stability as well as artificial and natural weathering of the timber treated with caprolactam-added and PEG-added formulations were performed. FT-IR and ¹³C-NMR of the formulations were presented.

Results

The presence of caprolactam improved the properties of the formulation with particularly significant results in terms of resistance against leaching and dimensional stability. These enhancements were imparted also to the weathering resistance of the tannin-caprolactam formulations. Indeed, the colour changes during the artificial and natural exposures were stable for longer periods. FT-IR and ¹³C-NMR investigations of the advanced formulations were led, and covalent copolymerization of the caprolactam with the tannin-hexamine polymer was observed.

Conclusion

The tannin formulations with caprolactam improved the durability of the wood specimens, while the PEG-tannin presented strong application drawbacks.

     

Tannin-caprolactam and Tannin-PEG formulations as outdoor wood preservatives: biological properties

Key Message

This article presents the enhancement in boron fixation as well as the improved biological resistance against fungi and termites for wood samples treated with tannin-caprolactam and tannin-PEG formulations.

Context

Although the recently developed tannin-boron wood preservatives have shown high biological protection, they presented also average resistance against weathering. The tannin-caprolactam formulations have shown improved weathering resistances and dimensional stability.

Aims

For this reason, more detailed biological tests were performed to evaluate the influence of the caprolactam and PEG on the biological resistance.

Methods

In this paper, the boron leaching of the tannin-caprolactam and tannin-PEG impregnated Scots pine specimens was observed and the biocidal effect against fungi (Antrodia spp. and Coniophora puteana) and insects (Reticulitermes flavipes and Hylotrupes bajulus) were determined according to the guidelines of EN 113, EN 117, and EN 47.

Results

The advanced formulations containing PEG have shown interesting resistance against fungal decay, but very low penetration and weak resistance against larvae while the tannin-caprolactam preservatives have shown overall improved biological performances and higher boron fixations.

Conclusion

The biocidal activity of the caprolactam-added formulations was overall enhanced and therefore these formulations are confirmed to be an interesting alternative for the wood preservation in outdoor environment.

     

心材提取物和专用木材防腐剂作为木材保护剂的相对功效

本文调查了三种耐用木材(Afzelia africana J.E. Smith; Erythrophleum suaveolens (Guill & Perr.) Brenam. Syn. E guinensis G.Don. or Milicia excelsa (Welw) C.C. Berg. Syn. Chlorophora excelsa (Welw) Benth.)的心材提取物（在60%的甲醇中风干提取）和两种专用木材防腐剂（CCA和Penta）在暴露的土壤区组设计条件下，抑制三种木材腐朽菌(Coridopsis Polyzona Klotzch; Lenzites trabea; or Trametes cingulata Fr.)对见血封喉边材的侵袭的相对潜能，并测定其阈值。提取物和防腐剂的剂量分别是8.009、24.778、48.056、96.111、144.167 kg·m-3 ，样品的暴露处理时间与ASTM D1413-72规定的一致分别是14周和18周。结果显示：在阈值范围内，任何一种心材提取物或木材防腐剂在研究中对木材腐朽菌的抑制能力在0.01的显著水平下，差异显著。这些生物杀灭剂的相对功效是取决于真菌的种类。没有任何一种心材提取物或木材防腐剂（除在用最高的存留水平处理被侵袭的非洲毒箭木的条件下）对于被处理的木材能够授予"非常持久"等级。本土树种的心材提取物相对持久力的减少的可能原因是复杂的。在最高的存留量（144.167 kg·m-3）水平下，在0.05显著水平下每种心材提取物和任一种专用木材防腐剂（CCA和Penta）之间的功效差异不显著.     

Chemical mechanism of fire retardance of boric acid on wood

It is commonly accepted that the fire retardant mechanism of boric acid is a physical mechanism achieved by the formation of a coating or protective layer on the wood surface at high temperature. Although a char-forming catalytic mechanism has been proposed by some researchers, little direct experimental support has been provided for such a chemical mechanism. In this paper, new experimental results using thermal analysis, cone calorimetry (CONE), and gas chromatography–Fourier transform infrared spectroscopy (GC–FTIR) analysis are presented and the fire retardant mechanism of boric acid on wood is discussed. Basswood was treated with boric acid, guanylurea phosphate (GUP), and GUP–boric acid. Treated wood was then analyzed by thermogravimetry (TG/DTG), differential thermal analysis (DTA), CONE, and GC–FTIR analysis. Thermogravimetry showed that the weight loss of basswood treated with boric acid was about three times that of untreated or GUP-treated wood at 165°C, a temperature at which GUP is stable. The DTA curve showed that boric acid treated basswood has an exothermal peak at 420°C, indicating the exothermal polymerization reaction of charring. CONE results showed that boric acid and GUP had a considerable synergistic fire retardant effect on wood. The GC–FTIR spectra indicated that compounds generated by boric acid treated wood are different than those generated by untreated wood. We conclude that boric acid catalyzes the dehydration and other oxygen-eliminating reactions of wood at a relatively low temperature (approximately 100–300°C) and may catalyze the isomerization of the newly formed polymeric materials by forming aromatic structures. This contributes partly to the effects of boric acid on promoting the charring and fire retardation of wood. The mechanism of the strong fire retardant synergism between boric acid and GUP is due to the different fire retardant mechanisms of boric acid and GUP and the different activation temperatures of these two chemicals.The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright. The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. Department of Agriculture of any product or service.     

Comparative effectiveness of two alkylammonium compounds as wood preservatives

This study describes a laboratory evaluation of the efficacy of two alkylammonium compounds [didecyldimethylammonium tetrafluoroborate (DBF) and didecyldimethylammonium chloride (DDAC)] when applied via vacuum impregnation or superficial treatment. Treated wood specimens were tested for their termite and microbial resistance under controlled laboratory conditions. The higher chemical retentions were needed to suppress the feeding by Coptotermes formosanus ≦3% mass loss in the multichoice test than in the no-choice test. The DBF and DDAC retention levels necessary to meet the performance requirement ≦3% mass loss after 12-week fungal exposure varied with wood species. The retention level of 3 kg/m³ for DBF and DDAC was generally high to keep the nondurable wood species free of decay. Although there was no difference between DBF and DDAC in the efficacy against decay and termite attack, the former slightly outperformed the latter as an antimold and antisapstain agent.     

Raman spectroscopic study on the behavior of boric acid in wood

 Raman spectra of Japanese cedar (Cryptomeria japonica D. Don) treated by vacuum impregnation with aqueous boric acid solutions (8.1 × 10⁻² to 7.29 × 10⁻¹ mol dm⁻³) were recorded using a near-infrared laser as an excitation source. Raman spectroscopic measurements were carried out on treated wood blocks of two sizes: 20(T) × 20(R) × 5(L) mm (A-type) and 15(T) × 15(R) × 50(L) mm (B-type). Our attention was focused on a prominent band (ν ₁) assigned to a symmetrical stretching vibration of the BO₃ group because no Raman band due to boron species was observed except bands of B(OH)₃. We observed a change in ν ₁ band intensity with increasing boric acid concentration in the aqueous solution used to treat the A-type wood blocks and investigated the correlation between the intensity and the peak-top wavenumber. Raman line maps in the longitudinal direction of the treated B-type wood blocks revealed that B(OH)₃ is concentrated near the cut ends. These results suggested that two groups of B(OH)₃ exist in wood in terms of the chemical species in the nearest neighbor sphere. Received: March 11, 2002 / Accepted: June 26, 2002     

新型木材防腐剂的研究

本研究通过对国内外现有木材防腐剂的筛选和改良,得到了两个比较理想的配方ACB(暂定名)和CCB-M,并测定了它们的抗腐力、抗流失性、防蚁、防霉和防变色性能、耐燃性、对动物毒性、对木材强度的影响、对金属的腐蚀性等各项指标。ACB适合于橡胶木和建筑材的防腐,CCB-M可用于对处理材颜色要求不高的场合。是有推广价值的木材防腐剂。     

Comparison of chitosans with different molecular weights as possible wood preservatives

Fungi cause serious problems in wood utilization, and environmentally benign wood protection is required as an alternative to traditional chemicals. Chitosan has shown promising antimicrobial properties against several microorganisms. In this study, we present the characterization of and antifungal properties of a commercial chitosan formulation developed for impregnation of wood. A broad range of chemical and mycological methods were used to evaluate the uptake, fixation, and antifungal properties of chitosan for wood preservation. The results show that the higher the uptake of chitosan the lower the relative recovery of chitosan in wood after leaching, and the higher the molecular weight of chitosan the higher the recovery. Chitosan with high molecular weight proved to be more efficient against decay fungi than chitosan with low molecular weight. The fungi tested on chitosan-amended nutrient agar medium were totally inhibited at 1% (w/v) concentration. In decay studies using small wood blocks, 4.8% (w/v) chitosan concentration gave the best protection against brown rot fungi.     

Distribution of boron in wood treated with aqueous and methanolic boric acid solutions

The distributions of boron in Japanese cedar (Cryptomeria japonica D. Don) sapwood blocks treated with aqueous or methanolic boric acid [B(OH)₃] solutions were explored through Raman spectroscopy and prompt gamma-ray analysis (PGA). B(OH)₃ was the sole boron species observed in Raman spectra of the wood blocks treated with either solution. Plots of weight gain of the treated wood blocks versus boron concentration in treatment solutions were found to be linear. The results indicated that the methanolic solution makes it possible to impregnate wood with much larger amounts of boron than the aqueous solution. PGA confirmed that B(OH)₃ was highly enriched near the end grains of the treated wood blocks. Raman measurements suggested that boron content in the bulk of the wood block is not as large as expected from the weight gain of the treated wood blocks when an ordinary air-drying method is used. It was concluded that the aqueous solution impregnates the cell walls of wood with boron more easily than the methanolic solution. Part of this report was presented at the 55th (Kyoto, March 2005) and 56th (Akita, August 2006) Annual Meetings of the Japan Wood Research Society. This article follows the previous rapid communication “Analysis of boron in wood treated with boric acid solutions using Doppler broadening method of prompt gamma-rays.” J Wood Sci (2006) 52:279–281     

A new boron impregnation technique of wood by vapor boron of boric acid to reduce leaching boron from wood

This study was designed to reveal impregnation ability and to enhance leaching resistance of boron from borate-treated wood. Vapor boron treatment was applied in compressed and uncompressed states at high temperatures such as 180 and 200°C for 6, 8 and 15 min. Following ten-cycle leaching periods, amounts of boron leached from vapor boron treated wood was measured by ion chromatography. According to the results, boric acid can be vaporized under heat and can be impregnated into wood. Success of the technique can be increased by increasing vapor pressure in a closed chamber. Leachability results proved the boron vaporization along with water vapor at various ratios depends on the process variables. These results have importance on dry wood treatment under heat by boron vapor with a little water presence which does not necessitate a further drying process.     

EFFECT OF TIMBER DENSITY ON RETENTION OF WOOD PRESERVATIVES

The amount of CCA fixed in the southern pine treated with CCA have been eval-uated.The conclusions from these experiments are:with the timber density increases,the reten-tion based on weight/weight will decrease,but the retention based on weight/volume will bealmost constant.Retention by weight would be more influential than by volume.     

Serial exposure technique for assessing performance of wood preservatives

Summary The performance of copper-chrome-arsenate (CCA) and two quaternary ammonium compounds as wood preservatives was compared using a serial exposure technique, involving successive 10-week exposures in conventional soil jars. All preservative treatments were successful in preventing decay of Pinus radiata sapwood after the first exposure, but successive 10-week exposures clearly distinguished those treatments likely to offer long-term protection. The progressively increasing times of exposure with test fungi overcame the time lag for decay initiation in wood treated to preservative retentions above the toxic threshold established by conventional laboratory methods. Consequently, an additional and higher toxic threshold could be calculated. Examination of data from field stake tests suggested that a series of toxic thresholds established by a serial exposure technique could be related to preservative retentions which protect wood in the field from decay for increasing periods of time. Results of all tests are discussed in relation to the development of a laboratory procedure which may predict field performance of wood preservatives.     

Effect of an oil heat treatment on the teachability and biological resistance of boric acid impregnated wood

Vegetable oils provide boron retention of about 30% of initial amount depending on oil drying properties. Linseed oil is the most efficient, followed by soybean oil and rapeseed oil. Durability of C. japonica and F. crenata wood specimens has been enhanced by application of linseed oil alone but not enough to reduce termite’s attack of Coptotermes formosanus. Treating wood with a 1.0% w/w boric acid solution prior to oil treatment protects C. japonica from termite and fungi degradations. Efficiency against termites is mainly due to boron retention by oil but hydrophobic oil also forms a barrier decreasing fungi penetration. Boron efficacy threshold around 0.7 kg/m³BAE, lower than classical boron treatments thresholds indicates that oil water-repellence reinforces boron biostatic effect.     

Evolution of CO2 during the fixation of chromium containing wood preservatives on wood

Summary A titration procedure was used to confirm carbon dioxide evolution from wood treated with solutions containing chromic acid and to quantify the effects of species (red pine vs soft maple), solution concentration and reaction temperature on the rate and amount of CO₂ evolved. Small blocks or chips were vacuum treated with either chromated copper arsenate (CCA) wood preservative or chromic acid solutions and the release of CO₂ monitored until the reaction was complete. Significant volumes of CO₂ were measured. This is attributed to the oxidation and subsequent decarboxylation of primary hydroxyl groups on wood constituents. The ratio of moles of CO₂ produced to moles of chromium added to the wood ranged from about 0.07 to 0.24 depending on the wood species, solution properties and fixation conditions. This accounted for from 9 to 32% of the total oxidation potential of the hexavalent chromium applied. The relative amounts of CO₂ produced were higher for maple than for red pine. The rate of CO₂ evolution was also higher in the maple samples, consistent with the higher rate of chromium reduction in soft maple compared to red pine. The amount of C0₂ produced was approximately proportional to the amount of hexavalent chromium in the CCA treating solution although the ratio of CO₂ produced to chromium added to the wood increased slightly with increasing solution concentration. The relative amounts of CO₂ produced increased with increasing fixation temperature over the 50–90 °C range in both species. The rate of CO₂ evolution was accelerated as the fixation temperature was increased. The rates and amounts of CO₂ produced were similar for CCA and Cr0₃ treatments containing the same concentration of chromic acid. Copper and arsenic components of the CCA solution did not appear to have any effect on the decarboxylation reaction.We gratefully acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada, Natural Resources Canada;, LPB Poles Inc., Masson Quebec, Timber Specialties Ltd., Campbellville Ontario and Guelph Utility Pole Co. Ltd., Guelph Ont. for this study.     

Copper complexes grafted to functionalized silica gel as wood preservatives against the brown rot fungus <Emphasis Type="Italic">Coniophora puteana</Emphasis>

Wood modification with siloxanes bearing amino groups with copper-linking function was carried out by a sol–gel process. Tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) were the main components. Two different procedures were followed: a two-step process (impregnation with the TEOS/APTES mixture followed by dipping into a copper sulphate solution) and a one-step process (impregnation with a homogeneous sol mixture of TEOS, APTES and copper (II) chloride). The obtained materials were characterized by infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis. The determination of copper content before and after leaching was performed by atomic absorption spectroscopy. The efficacy against the brown rot fungus Coniophora puteana was tested by an accelerated procedure. SEM analyses showed that silicon penetrated into wood, while copper is effectively drawn into wood only in the one-step treatment. Copper fixation to the silica gel proved to be adequately strong. Both sol–gel treatments gave good protection against Coniophora puteana.     

房屋建筑材用防腐剂的毒性试验

通过对十八种药剂配方(其中水溶性配方15种、油溶性配方3种)对木腐菌的毒性试验及对初筛后的配方进行流失后毒性试验,结果表明,水溶性配方中的铜铬砷即CCA_3、CCA_4、CCA_5,铜铬硼即CCB_5配方,以及油溶性配方中的P—B剂的毒性较大。     

Efficacy of wood preservatives formulated from okara with copper and/or boron salts

As a substitute for high-cost copper azole (CuAz) and alkaline copper quaternary (ACQ) wood preservatives, alternative wood preservatives were formulated with okara, which is an organic waste from the production of tofu, and copper chloride and/or borax. Each preservative was used in treatment of wood blocks in a reduced-pressure method to measure its treatability. The treated wood blocks were placed in hot water for 3 days to examine the stability of the preservatives against hot-water leaching. The preservatives successfully penetrated into wood blocks, probably due to the use of ammonium hydroxide as a dissociating agent. However, the stability of okara-based preservatives dropped as the concentration of acid in the solutions used for hydrolysis of okara increased. The treatability and leachability of the preservatives were not affected by hydrolysis temperature but were negatively affected by the addition of borax. Leached wood blocks treated with okara-based preservatives and exposed to decay fungi Gloeophyllum trabeum and Postia placenta over 12 weeks showed good decay resistance. Okara-based wood preservatives can protect wood against fungal attack as effectively as CuAz, and have potential for use as environmentally friendly wood preservatives.