Infrared spectroscopic investigations of weathering effects on the surface of tropical wood

 Two Fourier transform infrared spectroscopic techniques, photoacoustic and diffuse reflectance spectroscopy, were utilized to explore the physical and chemical changes in wood caused by weathering. Five tropical wood species (albizia, kapur, mahoni, nangka, puspa) were exposed to natural weathering for various periods. The contents of extracts, phenolics, and Klason lignin in unexposed samples of these wood species were determined by chemical analysis. Infrared spectra of the weathered surfaces were recorded by the two techniques. The photoacoustic spectra exhibited rapid decomposition and elusion of wood constituents containing benzene rings in the region closest to the exposed surface. Line maps of infrared spectra in the vertical direction obtained by diffuse reflectance infrared microspectroscopy were consistent with the view that the additive effects of water and ultraviolet irradiation play an important role in destroying the lignin-hemicellulose matrix of the cell wall. The infrared spectroscopic techniques are available for the analysis of weathered wood. Received: October 22, 2001 / Accepted: February 20, 2002 Correspondence to:S. Yamauchi     

Treatment of sugi （Cryptomeria japonica D.） sapwood with aqueous solution of acetic acid

Sugi sapwood samples were processed with aqueous solution of acetic acid in order to find the response of the weight of sugi sapwood and the treatment of aqueous solution of acetic acid. The result showed that loss of weight for the treated sugisapwood was about equal to yield of extracts from sugi sapwood, and increased with the increment of the concentration of aqueous solution of acetic acid. Fourier transform infrared spectroscopy spectra changes of the treated sugi wood and extracts from sugi sapwood were analyzed by FT-IR spectroscopic technique. Increasing tendency of absorption intensities of the stretching vibration at 3 400 cm^-1 of hydroxyl group (OH) and C=C in lignin stretching vibration at 1510 cm^-1 of benzene ring inlignin were observed from FT-IR of the treated sugi sapwood. From FT-IR spectra of extracts from sugi sapwood by aqueoussolution of acetic acid, the dissolution of lignin was observed during the treatment with 30% acetic acid solution aqueous.     

Decomposition behavior of woody biomass in water-added supercritical methanol

The chemical conversion of Japanese beech (Fagus crenata Blume) in water-added supercritical methanol was studied for a wide range of water content using a batch-type reaction vessel to obtain chemicals from lignocellulosics. It was consequently found that addition of water enhanced the decomposition of wood cell wall components; cellulose, hemicelluloses, and lignin. In cases of high water content, however, it resulted in low solubility of lignin-derived products causing an increase in the mass of the residue. The water content was thus optimized to be around 10% (v/v) for the decomposition of wood. Concomitantly, the yields and selectivity of the chemicals from wood could be regulated by the addition of water, especially for the lignin-derived products. As a result, the monomeric compounds of lignin, coniferyl alcohol and sinapyl alcohol, were recovered as their γ-methyl ethers in the presence of water in higher yields than those obtained without addition of water.     

Weathering characteristics of hardwood surfaces

Summary Four hardwoods, red oak, white oak, yellow-poplar, and sweetgum, were exposed to outdoor weathering and to artificial ultraviolet (UV) light with wavelengths of >220 and >254 nm. Discoloration and loss of brightness were observed from all specimens regardless of their exposure conditions. White oak and sweetgum changed color at a slower rate than did red oak and yellow-poplar. SEM micrographs showed that all wood species exhibited surface deterioration after 30 days exposure to sunlight or 500 hrs to UV light. Loss of middle lamella, separation of procumbent cells, and damage of pit structures were observed on transverse sections for all species. ESCA studies revealed a high oxygen content at the wood surfaces indicating severe oxidation of wood exposed either outdoors or to artificial UV light. The generation of new chromophoric groups such as carbonyls, carboxylic acids and quinones, and the loss of lignin at the oxidized surface were demonstrated experimentally by infrared studies.This study was supported by cooperative research funds provided by the U.S. Forest Products Laboratory, Madison, Wisconsin. The authors wish to acknowledge this support     

醋酸水溶液处理对杉树材影响

为了研究醋酸水溶液处理给杉树材重量带来的变化,使用醋酸水溶液对杉树材进行了处理。结果发现处理后杉树材重量的减小量大约等于抽出物的重量,而且随着醋酸水溶液浓度的增加而增加。利用傅立叶变换红外光谱法对处理后的杉树材及抽出物进行了光谱分析。从处理后杉树材的光谱图可以观察到3400cm-1附近的OH伸缩振动及1510cm-1附近的木质素中苯环C=C伸缩振动的吸收强度有增加倾向。从醋酸水溶液抽出物光谱图可以发现用浓度30%醋酸水溶液处理时木质素被溶出。图2表2参6。     

Lignification and peroxidase in tension wood ofEucalyptus viminalis seedlings

Seedlings ofEucalyptus viminalis were grown for 50 days with their stems bent so tension wood would form. Every 10 days the lignin content, monomeric composition, and peroxidase activity in the tension wood were compared with those in the lower side (opposite wood) and in vertically grown controls. The lignin content in the developing tension wood started to decrease after 10 days of bending and kept decreasing for 50 days, whereas those in control plants and opposite wood remained almost unchanged. The yields of syringaldehyde from tension wood by nitrobenzene oxidation increased, and consequently the syringyl/ guaiacyl ratio of the lignin was higher in tension wood than in opposite wood and control plants. The peroxidase ionically bound to the cell walls (IPO) catalyzed oxidation of guaiacol and syringaldazine. The syringaldazineoxidizing activity of IPO from tension wood increased, whereas the activities of IPO from opposite wood and control plants did not show any marked change. In tension wood the increase in syringaldazine-oxidizing activity of IPO was consistent with an increase in the syringaldehyde yield. This suggests that IPO contributes to syringyl lignin deposition as other enzymes involved in the monolignol biosynthesis do in tension wood formation.This study was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000     

Effects of UV light irradiation on colour stability of thermally modified, copper ethanolamine treated and non-modified wood: EPR and DRIFT spectroscopic studies

A series of experiments were carried out to investigate the colour stability of chemically treated and thermally modified wood compared to non-modified wood during long term artificial UV light irradiation. One set of wood samples was vacuum-pressure impregnated with alkaline (pH 9.8) copper (II) ethanolamine aqueous solution, while another set of samples from the same wood block was thermally modified at 210°C and −0.90 bar for 2 h. The treated and modified wood samples along with the non-modified ones were exposed to artificial UV light with the wave length in the region of UVA (315–400 nm) and UVB (280–315 nm) intermittently for 500 h. Colour measurements were carried out throughout the irradiation period at an interval of 100 h according to CIEL*a*b* system, where the results are presented in terms of ΔE, ΔL*, Δa* and Δb* values. Better photo-stability in terms of colour changes was recorded for both treated and modified woods compared to the non-modified one. By means of EPR and DRIFT spectroscopic study it was shown that some degree of colour stability of treated and modified woods, achieved during artificial UV light irradiation, resulted from lignin modifications and monomers of phenolic compounds.     

Impregnated wooden claddings and the influence of nanoparticles on the weathering performance

Abstract

This work was an investigation of the effect of nanoparticles on the durability of wood specimens exposed to artificial weathering. TiO₂ and clay nanoparticles were mixed with preservative (Wolmanit CX-8) for improving the durability of Norway spruce (Picea abies). Impregnated and untreated specimens were subjected to Atlas Solar Simulator accelerated ageing test chamber for solar radiation and water spray exposure. The effectiveness of the treatment against colour and chemical changes was investigated using CIEL*a*b* colour measurements system and Fourier transform infrared analysis. The present study showed that the wood specimens that had been treated with preservatives containing nanoparticles were slightly more stable against artificial ageing than both untreated specimens and specimens treated with preservative alone.     

Chemical changes in terpenes of sugi (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) wood during steam drying in kiln at high temperature

Sawdusts of sugi (Cryptomeria japonica) wood prepared before and after steam drying at 120°C in a kiln were extracted with n-hexane and ethyl acetate to give n-hexane extracts and ethyl acetate extracts. From gas chromatography-mass spectrometry analysis of the ethyl acetate extracts from woods before and after steam drying, the components of 4-epi-cubebol, cubebol, and 2,7(14),10-bis-abolatrien-1-ol-4-one, which existed in the raw sugi wood, were proved to disappear in the steam-dried wood. These components were also absent in the ethyl acetate extract of the steam-condensed solution of waste steam from the kiln outlet. When these three components were treated with 0.2% (v/v) acetic acid solution at 120°C, δ-cadinene was produced as a major product from both 4-epi-cubebol and cubebol by dehydration and cleavage of the cyclopropane ring, and cryptomerone from 2,7(14),10-bisabolatrien-1-ol-4-one by hydration. The chemical changes of the three components presumably occur during steam drying of the sugi wood. This study was presented in part at the 85th Spring Meeting of the Chemical Society of Japan, Kanagawa, Japan, March 26–29, 2005     

Resistance of wood from black pine (<Emphasis Type="Italic">Pinus nigra</Emphasis> var. <Emphasis Type="Italic">austriaca</Emphasis>) against weathering

At present tapped wood of black pines (Pinus nigra var. austriaca) is mainly combusted. The priority of material use over thermal recycling has led to some considerations regarding the utilization of tapped wood. The high content of extractives suggests a higher natural durability, and therefore, the suitability for outdoor applications. Tapped and not tapped wood boards from black pine (sapwood and heartwood) were subjected to weathering tests to find out its resistance against abiotic stress. Additionally tapped wood particles with a high content of resin were exposed to weathering and to composting. Weathering caused roughness to increase. Infrared spectral characteristics revealed the differences before and after tapping and weathering. Principal component analyses supported the grouping according to the chemical changes. In heartwood the lignin band at 1510 cm^??1 disappears and the typical resin band at 1688 cm^??1 decreases considerably. The lignin band of resinous parts is affected neither by weathering nor by composting. However, the resin band shows an intensity decrease and broadening due to weathering and disappears during composting.     

The effects of within-species and between-species variation in wood density on the photodegradation depth profiles of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa)

Low density wood is more rapidly eroded than denser wood when exposed to the weather, possibly because it is more susceptible to photodegradation. Fourier transform infrared microscopy was used to examine: (1) the depth of photodegradation in earlywood and latewood of sugi (Japanese cedar) and earlywood of hinoki (Japanese cypress) exposed for up to 1500 h to artificial sunlight emitted by a xenon lamp (375 W/m² within the 300 to 700 nm spectral range); and (2) the relationship between the density of wood tissues and depth of photodegradation. The depth of photodegradation varied between species (sugi and hinoki) as well as within a growth ring (sugi earlywood and latewood), and there was an inversely proportional relationship between depth of photodegradation and wood density. These findings may explain why low density earlywood is more rapidly eroded than latewood during weathering, and more generally, why there is an inverse relationship between the density of wood species and their rate of erosion during artificial and natural weathering. Part of this work was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, August 2004     

Surface checking of wood is increased by photodegradation caused by ultraviolet and visible light

The aim of this research was to test the hypothesis that exposure to solar radiation increases the checking of wood exposed to the weather, and to examine the causes and spectral dependency of such an effect. Lodgepole pine decking samples were exposed outdoors under filters, which blocked selected regions of the solar spectrum while allowing other weathering factors to act on samples. Surface checking in samples was quantified after 12, 24 and 36 weeks of exposure, and the chemical and micro-structural changes occurring at weathered wood surfaces were examined. Check numbers and dimensions were greater in samples exposed under a filter to the full solar spectrum than in samples exposed under filters that blocked the transmission of UV, visible or infrared radiation. Samples that were shielded from more energetic wavelengths developed less checking and also showed less delignification at the exposed wood surfaces. Checks developed at the margins of rays and propagated at the interface between adjacent tracheids, close to the middle lamella. We conclude that exposure to UV and visible light increases the tendency of wood to check during exterior exposure. Our findings point to a link between changes in cell micro-structure as a result of photodegradation of lignin and the development of visible checks in wood exposed outdoors.     

Depth profiling of weathered tropical wood using Fourier transform infrared photoacoustic spectroscopy

Depth profiling analysis of wood samples using Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) was carried out to obtain information on the chemical changes caused by weathering. The test samples used for PAS measurements were tropical wood species, puspa (Schima wallichii Korth) and kapur (Dryobalanop lanceolata Burck), that were exposed outdoors for periods of 2–32 weeks. FTIR-PAS spectra of the weathered surfaces were recorded at various moving-mirror velocities in the range from 0.081 to 0.56cm/s (linear-scan method) to provide the depth profiling analysis. The band intensity of vibrations attributed to phenyl groups clearly decreased as weathering proceeded and demonstrated a tendency to be reduced with a decrease in the photoacoustic probing depth during relatively short weathering periods. The bands of C=O groups also exhibited remarkable spectral changes. The PAS spectra of the tropical wood changed considerably during the 32 weeks of weathering, and their spectral contours gradually approached that of pure cellulose (microcrystalline). It was noted that FTIR-PAS is very useful for depth profiling analysis of the wood surface in the early stages of deterioration.     

真菌致泡桐材组分变化研究

用FTIR、ESCA等波谱分析方法，对真菌侵蚀的泡桐材进行了分析，结果表明：真菌侵蚀后，泡桐材的木质素含量相对比例增加、半纤维素含量降低、纤维素含量变化不明显。     

Contribution of active defense responses in the limitation of fungal spread in the sapwood of living sugi (Cryptomeria japonica) tree

The participation of active defense responses in the limitation of fungal spread in the sapwood of living sugi tree was determined. Isolates ofGuignardia cryptomeriae were inoculated to living trees, fresh logs, frozen and thawed logs and autoclaved logs, and the spread of wood discoloration and fungal hyphae was assessed. In autoclaved logs and freeze-treated logs, wood discoloration and reaction zone formation were not observed, and fungal hyphae of both of virulent and avirulent isolates grew rapidly in the wood. In fresh logs, wood discoloration and the formation of a pale reaction zone and transition zone were observed. Virulent isolates spread rapidly, but the spread of avirulent isolates was inhibited. In living trees, wood discoloration was observed and reaction zones were formed at lesion margins. These results indicated that constitutive defense mechanisms had no effect on the spread of both of virulent and avirulent isolates, and that active defense responses were important in the limitation of spread of fungal hyphae, hence in the limitation of wood discoloration. Further, it appeared that avirulent, but not virulent, races ofG. cryptomeriae were easily inhibited even by weak host responses. This study was presented at 105th and 106th Annual Meeting of the Japanese Forestry Society.     

白桦木材侵染菌侵染材的化学分析

白桦木材在自然和人工干燥过程中易受真菌类微生物的侵染产生色变,在一定程度上降低了白桦木材的加工利用价值。本文针对白桦木材侵染菌侵染试材的化学成分变化进行分析,以期为白桦木材生物变色防治提供参考。首先对白桦木材侵染菌进行分离、纯化与鉴定,确定侵染白桦试材的侵染菌的基本类型,然后进行白桦试材接菌,最后对白桦侵染菌侵染木材的化学成分进行测定。结果表明,与未侵染素材相比,侵染菌侵染试材中苯醇抽提物含量、1%NaOH抽出物含量、热水抽出物含量和多戊糖含量均较高,而纤维素及木素含量较低。这表明侵染菌在适宜的条件下会侵蚀白桦木材细胞壁组织,造成纤维素和木素等主要成分含量的降低,导致木材组分的破坏。同时,侵染菌的存在会造成白桦木材抽提物组分中的显色及助色物质的含量变化,以致木材产生不同程度的变色。     

Environmental effects on the color of sugi (Cryptomeria japonica D. Don) heartwood

Sugi (Cryptomeria japonica D. Don) is one of the most important planted trees in Taiwan. The normal heartwood of sugi has a red to pinkish rose color. Unfortunately, this pleasant appearance is susceptible to discoloration after environmental exposures. This discoloration is a serious defect that decreases the value of sugi products. The objective of this study was to investigate the effects of environmental factors such as moisture, oxygen, and lights of different wavelengths on the discoloration of sugi. The results show that under the combined effects of light and oxygen the color of heartwood changes from red (or rosepink) to bluish green. The color further darkens and eventually turns to black with the presence of moisture. As for the effect of light wavelengths on the discoloration of sugi heartwood, it was found that the red color was enhanced after being irradiated with light of wavelengths above 600 nm. Botha ^* andb ^* values increased significantly as a result of such exposure.     

Feeding activities of Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe) as affected by moisture content of wood

The relationship between the moisture content (MC) of wood blocks and the feeding activities of two Japanese subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe), was investigated with two choice tests. When three wood blocks with low MC (6%–12%), middle MC (79%–103%), and high MC (140%–182%) were exposed to workers of C. formosanus and R. speratus in a choice test, the feeding preferences were found in the middle MC blocks for C. formosanus, and the middle and high MC blocks for R. speratus, although wood blocks of low MC were also attacked. In a second choice test, wood blocks consisting of five pieces with water-impregnated (MC: 133%–191%) top, middle, or bottom piece were exposed to workers of both species. Higher consumptions were generally obtained in water-impregnated wood pieces and bottom pieces.     

Erythro/threo ratio ofβ-O-4 structures as an important structural characteristic of lignin. I: Improvement of ozonation method for the quantitative analysis of lignin side-chain structure

Ozonation as a quantitative tool to analyze the stereo structures of arylglycerol--aryl ether linkages was examined using wood meal, milled wood lignin, and a lignin model compound, 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (veratrylglycerol--guaiacyl ether, VG). The procedure was improved. When mild postreduction was conducted for ozonation products, the total yield of erythronic and threonic acids from this model compound was 74%, which is 15% higher than the yield without postreduction. A decrease in the recovery of these two acids under prolonged ozonation treatment was successfully suppressed by postreduction. Theerythro/threo ratio of VG determined by the ozonation method with postreduction is in good agreement with the ratio determined by¹H-nuclear magnetic resonance. Excellent reproducibility of the yield was obtained by adopting a procedure that included trimethylsilylation of ammonium salts of ozonation products using a dimethylsulfoxide-hexamethyldisilazane-trimethylchlorosilane mixture and subjecting it to gas chromatography analysis. It was concluded that arylglycerol--aryl ether structures comprise at least 35% of the C₃-C₆ structure in birch wood meal, with anerythro/threo ratio of 2.8.This paper was presented at the 43rd Lignin Symposium, Fuchu, Japan, October 1998; and at the 10th ISWPC, Yokohama, Japan, June 1999     

Degradation of wood surfaces during natural weathering. Effects on lignin and cellulose and on the adhesion of acrylic latex primers

Summary Radiata pine veneers and blocks were exposed to natural weathering under Australian summer conditions over a period of 30 days. Infrared spectroscopy revealed that there was perceptible surface delignification after 4 hours exposure, substantial surface delignification after 3 days exposure and almost complete surface delignification after 6 days. Rapid lignin degradation was also suggested by measurements of the acid insoluble lignin content of weathered veneers. Viscometry determinations on holocellulose samples from weathered veneers and unweathered controls indicated significant depolymerisation of cellulose after 4 days exposure. A tape test was used to assess the adhesion of acrylic latex primers to weathered blocks. The adhesion of exterior acrylic primers decreased on weathered wood surfaces and was significantly lower on specimens that were weathered for 5 to 10 days. An oil-modified acrylic primer showed greater adhesion to weathered wood surfaces. Primer adhesion was lower on weathered radial surfaces than on similarly exposed tangential surfaces. The practical implications of these findings for the coating of exterior wood with acrylic latex primers are discussed briefly.The authors wish to thank Dr. A. J. Michell for FTIR spectral determinations and the Australian Research Council small grants scheme for financially supporting part of the work