Characterization and photodegradation mechanism of three Algerian wood species

Aging is the irreversible change of mechanical, physical, and chemical properties of materials; the main objective of this work was to study the photochemical degradation and structural changes of three major Algerian wood species. For this, we evaluated the photodegradation mechanism for Maritime Pine (Pinus pinaster), zeen oak (Quercus canariensis), and afares oak (Quercus afares) by accelerated aging in a Xenon test chamber. Degradation of the samples was established by an initial color change (after 30 h exposure), followed by roughening and cracking (120 h exposure) as translated by scanning electron microscopy and Fourier transform infrared spectroscopy. The discoloration of irradiated wood samples was primarily related to the decomposition of lignin which is the key structure in wood photodegradation. As expected, a decrease in mechanical properties was observed; for all samples, the modulus of elasticity decreased after aging, indicating that the wood specimens loss some of their stiffness.     

Effect of three tree species on UV weathering of wood flour-HDPE composites

Eucalyptus urophylla, Acacia mangium, and Pinus caribaea are the primary species for the wood industry in Vietnam. Wood residues of these species were used to reinforce high-density polyethylene(HDPE) composites. The flexural or bending property, impact strength and surface color were evaluated after exposure to accelerated ultraviolet weathering up to 2000 h. The weathered surface was characterized by scanning electron microscopy(SEM) and Fourier transform infrared(FTIR) spectroscopy. The results indicate that A. mangium/HDPE composites had the lowest color change and least fading,and remained stable after 1500 h exposure. FTIR spectroscopy showed that the oxidation of the composites increased in parallel with duration of exposure by assessing the concentration of carbonyl groups on the surfaces. SEM showed that all three species reinforced composites exhibited similar severe cracks after 1000 h;however, at the end of the weathering test, E. urophylla and P. caribaea composites were more severely cracked than A. mangium composites. A. mangium also had the highest flexural strength, impact strength and crystallinity duringweathering. A. mangium is the most preferable among the three species to reinforce HDPE.     

Light source dependence of the photodegradation of wood

The aim of this study was to determine whether artificial ultraviolet (UV) light sources are able to imitate properly the photodegradation of wood caused by sunlight. In this study, wood specimens were irradiated with a xenon lamp and a mercury lamp. The xenon light simulated sunlight only in the case of long-term irradiation. The photoinduced yellowing of wood was faster and greater in the case of short-term exposure to xenon light than that caused by sunlight. The number of UV light-generated carbonyl groups absorbing infrared light around 1700 cm⁻¹ showed good correlation with photoinduced yellowing. On the other hand, mercury light did not simulate sunlight. However, the mercury lamp, as a strong UV light emitter, can be applied to determine the valid limits of the Kubelka–Munk (K-M) equation. Our results show that the K-M equation cannot be applied to determine the absorption properties of the sample if the values of the K-M units exceed 50.     

Electromagnetic shielding efficiency of the electric field of charcoal from six wood species

Six wood species were carbonized under various carbonization temperatures and nonoxygen conditions to obtained charcoal. The effects of wood species, rate of temperature rise, and carbonization temperature on the electromagnetic shielding efficiency (ESE) of the electric field were investigated. The wood species used in this study were Japanese cedar, China fir, western hemlock, red oak, fortune paulownia, and Taiwan acacia. Tested materials were carbonized in a high-temperature oven under the following conditions: rate of temperature rise 1°–5°C/min; carbonization temperature 500°–1100°C, with temperature intervals of 100°C; maximum temperature maintained for 1h; and flow rate of nitrogen 300ml/min. The electromagnetic insulation strength system was used to detect the ESE of the electric field of charcoal. It was found that western hemlock and fortune paulownia charcoal showed maximum ESE values of of 36 and 61dB generated at a carbonization temperature of 1000°C. The charcoals derived from four other wood species showed maximum ESE values of 28dB for Japanese cedar, 23dB for China fir, 32dB for red oak, and 38dB for Taiwan acacia, respectively, at a carbonization temperature of 1100°C. The ESE value for fortune paulownia charcoal was similar to those of metal nets. The relations between ESE and logarithmic values of resistivity (log) could be represented by a negatively exponential formula.Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000     

Participation of singlet oxygen in the photodegradation of wood surfaces

Summary Photodegradation of wood surfaces in the presence of oxygen was studied. ESR studies revealed that free radicals were formed at the wood surface during photoirradiation. These wood free radicals readily interacted with oxygen molecules to form peroxide radicals. Iodometry UV absorption studies showed that hydroperoxide was formed in the photoirradiated wood. The hydroperoxide concentration increased when wood was irradiated in the presence of singlet oxygen generators such as Rose Bengal and Methylene Blue. Hydroperoxide concentration decreased when wood was irradiated in the presence of singlet oxygen quenchers such as 1,4-diazobicyclo (2,2,2) octane, -carotene and triethylamine. These findings imply the participation of singlet oxygen in the photodegradation of wood surfaces. The mechanisms of formation of singlet oxygen and hydroperoxide during photoirradiation are proposed. The consequence of hydroperoxide decomposition reactions on the discoloration and degradation of wood surface is discussed.This study was supported by cooperative research funds provided by the US Forest Products Laboratory, Madison, Wisoonsin. The authors (DNSH and STC) wish to acknowledge this support     

Comparative study on penetration characteristics of modern wood coatings

Summary The penetration characteristics of five modern wood coatings (three waterborne, one high solid and one solvent borne) into pine sapwood, spruce and dark red meranti have been systematically compared. The degree of coating penetration is mainly determined by the ability of the coating to flow into wood capillaries. Binder type, pigmentation, solid matter content and drying speed appeared to influence this ability. In softwoods the following different coating penetration routes are observed: the flow into open ends of longitudinal early-and latewood tracheids, the flow into ray cells and the transport from rays through the cross-field into longitudinal tracheids adjacent to rays. The possibility for the coating to follow the latter route is strongly influenced by the existing type of cross field pitting and to a lesser degree by the pigmentation of the paint. Clear differences between pine and spruce have been found with respect to the flow into ray parenchym and ray tracheids. The flow into open ends of longitudinal tracheids is strongly influenced by the grain angle of tracheids. Penetration into dark red meranti is mainly limited to vessels and rays. Tylose membranes can prevent the complete filling of vessels. The impact on penetration of the removal of extractives and of sanding of the surface has also been studied but appears to be of only minor importance.The authors want to thank Akzo Nobel Coatings, DSM Resins and Sigma Coatings for their technical support. This research was financed by the the Dutch Innovative Research Program on Coatings under contract number IVE 93-812. Authors also thank the University of Hamburg (BFH) for the use of their electron microscopy facilities.     

Termite feeding preference to four wood species after gamma irradiation

The effect of gamma irradiation at 100 kGy and at lower levels on termite resistance was examined in the laboratory by no-choice and choice feeding termite tests (Coptotermes formosanus Shiraki) using four wood species: sapwood of Cryptomeria japonica D. Don, and heartwoods of Pseudotsuga menziesii (Mirbel) Franco, Larix kaempferi (Lambert) Carriere, and Chamaecyparis obtusa Endl. The wood consumption rates in C. japonica and P. menziesii specimens were likely to increase with increases in gamma-irradiation levels, whereas little effect of gamma irradiation was seen in L. kaempferi and C. obtusa. Similar results were obtained in the two-choice test. The current results indicated that in the two-choice test with C. formosanus, 100-kGy-irradiated C. japonica and P. menziesii, which are not rich in antitermite substances, were eaten more than other wood samples with or without gamma irradiation. However, only C. japonica showed significant difference in termite feeding activity. The mass loss in 100-kGy-irradiated C. japonica was significantly higher in the multichoice test.     

COMPARATIVE STUDY OF WOOD PROPERTIES BETWEENWHITE WOOD OF DAHURIAN LARCH AND MONGOLIANSCOTCH PINE

DahurianlarchandMongolianscotchpinearetwomajorconunerciaIconilbroustTeesinDaxing'anlingForesnyArea.Itisob-viousthattbcwoodproPertiesandworkability'ofthetWoplantsarecompletelydifferent.Butlnrecert'years,ltlsfoundthattherearetwodiffer':nttypesinparameterofwood'scolour.phy'sicalandmechanicalproPertiesandwork-ability'inDahurianlarch,namelyredwoodandx"hite..od.l']Andthepropertiesofwhite`voodaresligl1tlyyellow-white,medianweightandhardness,goodinworkability'andLard-ness,goodinwodability'anduneas…     

Effects of moisture content and specific gravity on static bending properties and hardness of six wood species

This study was designed to investigate the effects of moisture content (MC) and specific gravity (SG) on the bending strength and hardness of six wood species including Japanese cedar (Cryptomeria japonica D. Don), China fir (Cunninghamia lanceolata), western hemlock (Tsuga heterophylla), red meranti (Shorea spp.), Selangan batu (Shorea spp.), and red oak (Quercus spp.). The experimental results are summarized as follows: Effects of MC and SG on the strength (MOR), stiffness (MOE), and hardness (H _B) could be represented by a multiregression formulas. A negative correlation existed between these properties and MC, whereas a postive correlation showed between them and the SG. The changing rate of these properties induced by 1% MC changes varied with the wood species: 2.6% change in MOR was observed in Japanese cedar, China fir, western hemlock, red meranti, and Selangan batu; and 3.9% was found in red oak. For MOE, a 0.58% change was observed in Japanese cedar, China fir, and red meranti; western hemlock and Selangan batu exhibited 1.2% and red oak 2.5%. For hardness, a 1.1% change was observed in Japanese cedar, western hemlock, and red oak; red meranti and China fir exhibited 3.3%; and Selangan batu 1.8%.A part of this report was presented at the 48th annual meeting of the Japan Wood Research Society in Shizuoka, Japan, April 3-5, 1998     

Thermal degradation modeling of flexural strength of wood after exposure to elevated temperatures

Abstract

Wood is being used heavily in single-family residential dwellings. Therefore, it is important to categorize their response when exposed to elevated temperatures for a sustained period of time. An important aspect of structural fire design is to assess postfire residual strength of existing structures. This study addresses this issue by developing models to predict strength degradation of wood after exposure to elevated temperature. The objectives were to (a) study the effect of exposure time on bending strength [Modulus of Rupture (MOR)] of wood at elevated temperatures, (b) interpret any relationships between different temperature and time of exposure using kinetics and a statistical approach, and (c) compare the two approaches. Two hundred thirty-two samples in total were tested in flexure as a function of exposure time and several temperatures. MOR of wood decreased as a function of temperature and exposure time. Rate of degradation was higher at higher temperatures. These results were fit to a simple kinetics model, based on the assumption of degradation kinetics following an Arrhenius activation energy model with apparent activation energy of 37.4 kJ/mol. A regression-based statistical model was also developed. The kinetics-based model fit the data better with one less parameter and predictions consistently matched the observed values, making the model preferred over the regression approach.     

十种树种刨花板制板工艺条件的研究

试验测定了十种树种枝桠材的密度、木材水浸提液的pH值和碱缓冲能力,及刨花堆积密度。通过对树种、板材密度、施胶量、固化剂和石蜡用量与板材性能之间关系的研究,提出了十种树种刨花板的制板工艺条件。     

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.     

尾叶桉家系木材性状的变异研究

对75个月生32个尾叶桉家系的6个与木材相关的性状进行了研究.6个木材性状在家系间存在显著或极显著差异,说明通过家系选择可以获得性状优良的家系/无性系;木材基本密度、木材含水量、纤维宽、纤维长宽比与生长、形质性状间的相关关系不显著,表明该4个研究性状能各自遗传,可以分别独立选择;纤维长与树高、胸径及单株材积相关关系达到显著或极显著水平,说明纤维长度随树龄增长而增加,材性逐渐得到改善;所有木材性状间的遗传力均在0.5左右,说明各性状受到中等水平的遗传控制;水分含量、基本密度、树皮厚度、纤维长宽比性状的遗传变异系数较高,表明尾叶桉家系在4个性状上具有较丰富的遗传变异,进行性状遗传改良可获得较高遗传增益,按25%入选率,预期遗传增益可达5.68%～17.66%.     

Bondability of tropical fast-growing tree species I: Indonesian wood species

To estimate the potential bonding performance of bonded wood products from tropical fast-growing tree species, a study on the bondability of Paraserianthes falcataria L. Nielsen, Pinus merkusii Jungh et. De. Vriese, and Acacia mangium Willd from Indonesia was conducted. Two-ply laminations were produced using polyvinyl acetate emulsion (PVAc), urea formaldehyde (UF), resorcinol formaldehyde (RF), and water-based polymer isocyanate (API) adhesives. In order to determine the bonding performance, the block-shear test was applied according to the Japanese Agricultural Standard for structural glued laminated timber under normal conditions and after accelerated-aging treatments. To support this study, the wettability of each wood species was also investigated through contact-angle measurement. The results showed that the bonding performance of low-density P. falcataria was better than that of medium-density P. merkusii and medium-density A. mangium, while the bonding performance of medium-density P. merkusii was better than that of medium-density A. mangium. Furthermore, compared with A. mangium, the small contact angle and good wettability in P. falcataria and P. merkusii result in better adhesion and more intimate contact between the wood surfaces and adhesive.     

Combined effects of UV light and elevated temperatures on wood discolouration

Wood Science and Technology - Two conifers and two deciduous wood species were irradiated by strong UV emitter mercury lamp at elevated temperatures up to 160 °C. Other series of...     

Laser-excited fluorescence spectra of eastern SPF wood species. An optical technique for identification and separation of wood species?

Summary Use of UV-laser excitation to produce fluorescence spectra for heartwood and sapwood from jack pine (Pinus banksiana), white spruce (Picea glauca) and balsam fir (Abies balsamea) was examined. Spectra were fairly broad without sharp spectral features and overlap of spectra between species was common. Sample to sample and in-sample variation of the recorded fluorescence spectra was observed. The fluorescence spectra obtained from heartwood samples of jack pine showed evidence of photochemical bleaching as a result of the multiple laser pulses needed to produce a complete spectrum. Bleaching may have obscured differences between species. For the mix of species examined no sapwood nor heartwood samples were distinguishable by this technique with the detector used. Use of an optical multichannel analyzer (OMA) could reduce the number of laser pulses needed to obtain an entire spectrum. Under these conditions it would be possible to determine whether the minor differences in spectral features observed for the different species are more pronounced in the first few laser pulses and if they are characteristic of species. Certain aspects of the data suggest that with improved analytical equipment UV-fluorescence might prove to be a useful technique for the identification of certain species.     

Comparative study of anatomy and lignin distribution in normal and tension wood of Salix gordejecii

Fibre morphology, anatomy and ultrastructure in cell wall of Salix gordejecii normal wood were examined by transmission electron microscopy (TEM). S. gordejecii tension wood can be recognized anatomically by the presence of gelatinous (G) fibres, which contain a conspicuously thickened inner cell wall layer. TEM images showed that cell wall of S. gordejecii normal wood was typically divided into three layers including the primary wall (P), the middle lamellar (ML) and the secondary wall (S₁, S₂ and S₃). Lignin distribution was determined by using confocal laser scanning microscopy (CLSM) and transmission electron microscopy with energy dispersive X-ray analysis (TEM-EDXA). Confocal images (530 nm) of S. gordejecii normal wood showed strongly lignified CCML, and weakly lignified ML and S2 layer. Weakly lignified fibres (F) and strongly lignified vessels (V) were also detected by using CLSM. Results obtained from confocal microscopy were further confirmed by using TEM-EDXA, indicating that the ratio of lignin concentration in CCML, ML and S2 is 1.72 (1321):1.31 (1006):1 (768). Lignin distribution in tension wood is similar to that in normal wood, except for the non-lignified G layer.     

Shear deflection of two species laminated wood beams

Summary In addition to the deflection due to pure bending in a beam, there is a shear force in all cases of non-uniform bending and a further deflection, due to shear stresses. This additional shear deflection usually is assumed to be negligible and is not considered in computing the total deflection of a beam. In the case of two-species laminated wood beams, due to the development of greater shear stresses, the percentage of shear deflection further increases and failure to take it into consideration may introduce errors of considerable magnitude in determining the distortion of the beam. It is shown here that the percentage of shear deflection can be considerable, approaching the amount due to pure bending. Furthermore it is shown that the magnitude of shear deflection depends on both the span to depth ratio of the beam and the elastic properties of the species involved. It increases as the effective span to depth ratio of the composite beam decreases and as the core ratio of pure modulus of elasticity to modulus of rigidity increases.

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Zusammenfassung Zu der Verformung eines Balkens unter reiner Biegung tritt bei der Einwirkung ungleichförmiger Biegekräfte eine zusätzliche Verformung, die durch eine Schubkraft und die daraus resultierenden Schubspannungen verursacht wird. Von dieser zusätzlichen Schubverformung nimmt man gewöhnlich an, daß sie vernachlässigt werden kann. Sie wird daher bei der Berechnung der Gesamtverformung eines Balkens nicht mit berücksichtigt. Im Falle von Schichtholzbalken aus zwei verschiedenen Holzarten erhöht sich der Anteil der Schubverformung, verursacht durch das Auftreten größerer Schubspannungen noch weiter, und die Vernachlässigung kann bei der Bestimmung der Gesamtformveränderung zu beträchtlichen Fehlern führen. Es wird gezeigt, daß der Anteil der Schubverformung hoch sein und sich der Größe der reinen Biegeverformung deutlich nähern kann. Es wird ferner nachgewiesen, daß die Größe der Schubverformung vom Verhältnis der Stützweite zur Dicke des Balkens und von den elastischen Eigenschaften der verwendeten Holzarten abhängt. Die Schubverformung erhöht sich, wenn das wirksame Verhältnis von Spannweite zu Dicke des Schichtholzbalkens ansteigt und wenn das Verhältnis zwischen reinem E-Modul und Schubmodul ansteigt.

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The experimental work of this study was conducted at the Yale School of Forestry in cooperation with the Office of Naval Research. Department of the Navy, under contract No. 609 (13), Project NR 330-001, Properties of Tropical Woods.