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...     

Evaluation of the photo stabilising efficiency of clear coatings comprising organic UV absorbers and mineral UV screeners on wood surfaces

A study of the surface discolouration of clear coated wood during artificial and outdoor weathering and its prevention using clear coatings comprising organic UV absorbers (UVA) and mineral UV screeners was carried out. It was shown that the use of UVA and UV screeners in clear coatings was very effective in reducing photodegradation of the wood surface. Preliminary irradiation trials with Xenon arc light showed that the UV screener TiO₂ led to the least discolouration of the coated wood surface, closely followed by UVA of the hydroxyphenyl-s-triazine class (HPT). The artificial and outdoor weathering trials indicated that UVA of the HPT class stabilised the colour of the wood surface better than UVA of the 2-(2-hydroxyphenyl)-benzotriazole class (BTZ). Comparison of different artificial weathering methods indicated that Xenon arc light weathering showed the best match to the proceeding discolouration of the clear coated wood panels during outdoor weathering.     

协同改性对水性UV木器涂料性能的影响

采用SiO2和CaCO3对水性紫外光(UV)固化木器涂料进行协同改性,通过优化工艺参数制备了水性UV固化木器涂层,并对涂层的力学性能和光泽度进行了测试.发现当水性UV固化木器涂料中CaCO3的含量控制在5.0％,SiO2含量在2.0％ ～3.0％时,先将水性UV固化木器涂料在40℃烘箱中干燥10 min,然后在UV灯下照射1min,得到的水性UV固化木器涂层具有良好的硬度、附着力和抗冲击强度;但是当SiO2含量高于3.0％时,水性UV固化木器涂层的力学性能反而下降.光泽度测试表明,当CaCO3含量控制在5.0％,水性UV固化木器涂层的光泽度随SiO2含量的升高而下降,当SiO2含量超过1.0％时,水性UV固化木器涂层呈现亚光光泽度.     

The effects of elevated temperature on certain wood cells

Summary From the microscopic evidence, the modifications observed certainly indicate that the structures viewed are temperature-sensitive, although the critical temperature is still to the determined. This sensitivity may be linked only to a change from a solid to a liquid state, and visual indications support such a tenet. This does not perclude, however, the possibility of thermo-chemical changes occurring at the elevated temperatures used.It is interesting to note that lignin has been found to soften under elevated temperature in the presence of moisture and pressure [Goring 1963], and it is very tempting to speculate along this avenue. The results thus far, however, indicate that much further work is needed before their significance can be fully established.

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Zusammenfassung Bei der mikroskopischen Untersuchung von Teilen des Holz-Feingefüges zeigten sich Veränderungen, die darauf hinweisen, daß die beobachteten Gefügeteile temperaturempfindlich sind. Die kritische Temperatur muß jedoch noch genauer festgestellt werden. Die Temperaturempfindlichkeit hängt wohl hauptsächlich mit dem Übergang vom festen zum flüssigen Aggregatzustand zusammen, eine Annahme, die durch visuell beobachtbare Vorgänge gestützt wird. Dies schließt jedoch nicht die Möglichkeit thermisch-chemischer Veränderungen aus, die bei den angewendeten höheren Temperaturen eintreten.Aufschlußreich ist die Feststellung, daß Lignin bei erhöhter Temperatur, unter Feuchtigkeit und Druck erweicht. Überlegungen in dieser Richtung erscheinen erfolgversprechend. Die bisherigen Ergebnisse zeigen aber, daß weitere umfangreiche Untersuchungen erforderlich sind, bevor die Bedeutsamkeit der bislang beobachteten Vorgänge als erwiesen betrachtet werden kann.

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Visiting scientist at the Institut für Holzforschung und Holztechnik der Universität München.

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Maintained at Madison, Wis., in cooperation with the University of Wisconsin.     

Changes in surface properties of tropical wood species exposed to the Indonesian climate in relation to mold colonies

Changes in mold populations and genera on the exposed surfaces of tropical hardwoods — albizia (Paraserianthes falcata), kapur (Dryobalanop lanceolata), mahoni (Switenia macrophylla), nangka (Artocarpus heterophyllus), puspa (Schima wallchii) — were investigated. The wood specimens were exposed to the Indonesian climate for 32 weeks. Properties including mass loss, wettability, mold growth (colony-forming units), and mold genera were evaluated. The change in properties after exposure was significantly affected by the wood species, but there was no clear relation between mass loss and the initial chemical components or between wettability and wood density. The number of mold populations was different by exposure period and wood species, but there was no significant effect of climate conditions, such as rainfall and ultraviolet radiation. Of the genera identified,Aureobasidium, Cladosporium, andPenicillium were dominant molds on the exposed wood surfaces.     

The influence of surface-treated nano-TiO2 (rutile) incorporation in water-based acrylic coatings on wood protection

The aim of this research was to synthesize surface-treated nano-titanium dioxide (TiO₂) particles and incorporate them into water-based acrylic systems, which could offer long-term protection for UV-sensible wood substrates. To suppress the photocatalytic activity, the surface of TiO₂ nanoparticles in rutile crystal structure was coated with amorphous silica (SiO₂) layer. The amounts of SiO₂ were 5 and 10 wt%, respectively. Formation of SiO₂ layer on TiO₂ surface was analyzed using scanning and transmission electron microscopy. SiO₂ layer thickness increases as a function of precursor loading. In addition, the influence of SiO₂ loading on rutile UV-protective properties was determined. Transparent UV-protective coatings were developed by incorporating surface-treated nano-TiO₂ into water-based acrylic stain. The particle size distribution was determined using dynamic light-scattering measurements, which indicate that the suspension of surface-treated rutile is stable against agglomeration. Furthermore, the color change and ability of protection against UV light of coatings after nanoparticles incorporation were determined. TiO₂, surface treated with 10 wt% of SiO_2, yielded coatings of higher transparency; however, TiO_2, surface treated with 5 wt% of SiO_2, improved UV protection.     

The effects of cell wall swelling on the permeability of grand fir wood

Summary The longitudinal permeability of Abies grandis wood swollen to varying degree by water vapour sorption has been measured using a non-swelling liquid. The results obtained show that cell wall swelling causes a reversible decrease in permeability in both air dried and solvent exchange dried specimens.Direct microscopic measurements have shown that change in lumen diameter cannot explain the observed effect.Mathematical analysis of the data suggests that the permeability decrease may be due to increase in thickness of bordered pit membrane fibrils resulting from sorption of water.     

The effects of flooding on several hybrid poplar clones in Northern China

The ecophysiological, morphological, and growth characteristics of 14 poplar clones were studied during 37 days of flooding and a 13-day recovery period. Cuttings were subjected to three soil water regimes, viz. drained (control), shallow flooding to 10 cm above the soil, and deep flooding to a depth of 120 cm. All hybrids modified their ecophysiological and morphological patterns to decrease carbon loss and maintain water balance. In response to flooding, all 14 hybrids reduced their expansion and initiation of new leaves, reduced height and root collar growth, and reduced the number of leaves. For shallowly flooded plants, adventitious roots developed by day 14, and their number increased with flooding duration; net photosynthesis, stomatal conductance, and growth decreased significantly compared with the control; dry weights of roots, leaves, and total biomass decreased and the allocation of growth to shoots and roots changed. After flooding ended, net photosynthesis recovered, but stomatal conductance recovered before net CO₂ assimilation since photosynthesis was limited by stomatal factor at the initial stage of stress and it was limited by non-stomatal factors over relatively long periods of stress. Transpiration and the amount of water obtained from the roots both decreased. In the deeply flooded plants, similar but often more severe changes were observed. Based on our results, we classified the hybrids into three types using hierarchical cluster analysis. Clones 15-29, 196-522, 184-411, 306-45, 59-289, DN-2, DN-182, DN-17, DN-14274, NE-222, DTAC-7, and R-270 were flood-tolerant, clone NM-6 was flood-susceptible, and clone 328-162 was moderately flood-tolerant.     

The effects of drying on the structure and permeability of the wood of Abies grandis

Summary The effects of air-drying and solvent-drying on the sapwood of Abies grandis have been investigated by a new method for the determination of the size and number of conducting tracheid lumina and pit membrane pores which involves the measurement of gaseous permeability at various mean pressures. Both earlywood and latewood tracheids (83% of the total) were found to be conducting in solvent-dried wood, but in air-dried wood only latewood tracheids (32% of the total) were conducting. In solvent-dried wood there were on average 27,000 pit membrane pores per conducting tracheid compared with only 600 in air-dried wood. In both, the average pit membrane pore radius was about 0.1 m.Liquid permeabilities have been predicted from the calculated radii and numbers. The liquid permeability of solvent-dried wood was 31 times greater than that of air-dried wood in which the lumina were responsible for 13% of the total resistance to flow. The lumina were responsible for 39% of the resistance in solvent-dried wood and it is suggested that in first-formed earlywood the lumina may cause more than half the total resistance.A new method is described for the cleaning of direct carbon replicas of wood. In this the cellulose is removed by cellulase instead of sulphuric acid, and no wax backing is required. This provides much cleaner replicas. Electron micrographs have been obtained of both earlywood and latewood dried by the two methods.The authors wish to thank Mr. A. R. Sayers for preparing the computer programme used in this work, Dr. R. Ph. C. Johnson for his help and advice regarding the electron microscopy and Professors Matthews and Weatherley for their advice and encouragement.     

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.     

Volatile organic compounds from wood and their influences on museum artifact materials I. Differences in wood species and analyses of causal substances of deterioration

Wood is generally used as the interior material in museum storage rooms. Recently, however, the effects of volatile organic compounds (VOCs) from wood on artifacts has become a topic of great concern. The VOCs from four species of wood (western red cedar, spruce, kiri, and sugi) and their effects on artifact materials (two types of metal, seven types of pigment) were investigated using a deterioration-accelerating test, gas chromatography-mass spectrometry, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The results suggested that the influences on artifact materials varied greatly with wood species, and depended on specific components such as hinokitiol or acetic acid rather than the amount of total volatile organic compounds (TVOCs). It is a very serious problem that of the four species of wood, western red cedar (rich in hinokitiol), which has been recommended as an interior material for museum storage rooms, showed the heaviest deterioration on metal samples, and only this type of wood discolored enpaku (white lead) and rokushou (malachite, verdigris). In such storage rooms, museum artifacts should be carefully monitored. When selecting an interior material for a storage room or studying methods of preventing deterioration, it is very important to consider fully the characteristics of wood VOCs, not only the amount of TVOC.Part of this paper was presented at the 24th (Tokyo, June 2002) and 25th (Kyoto, June 2003) Annual Meeting of the Japan Society for the Conservation of Cultural Property     

The effects on operational planning of changes in energy content of stored wood fuels

The supplier of wood fuels has a large number of interrelated activities to coordinate on the way from raw material source to consumer. Transports, storing and intermediate processing should be decided on for a number of assortments. Storing is a prominent feature of this network flow problem since consumer demand is high when small amounts of raw material become available and vice versa. Storing may, however, change the energy content of the material. This paper presents the effects of these changes on operational planning, procurement and storing policies for a wood fuel supplier. Under the assumptions of the application, it is shown that if these changes are taken fully into account, the efficiency of fuel production can be increased by about seven percent.     

Distribution of stem decay in the beech trees of the Azerbaijan and its impact on the output of commercial wood

To determine the distribution of stem decay in the beech stands of Azerbaijan, we sought to identify the species, number, and height of attachment of fruiting bodies;the extent of decay in tree trunks growing under different conditions;and its influence on the trees’ commercial wood. The research was conducted on three farms representing the most common forest types of the Greater Caucasus within Azerbaijan. Examination of the presence of fruiting bodies in the tree trunk revealed that stem decay is the most common infection in beech (Fagus orientalis) stands, especially in fresh, moist areas, with less infection under dry growing conditions. In this work, the length, diameter, and volume of decay were studied by infecting the trunks of 93 model trees affected with mushrooms in 1–4 m cuttings. Our results showed that as the age of the stand increased, extent, diameter, and volume of decay increased significantly: the extent of decay from 1.47 to 6.43 m;the diameter of the decay from 8.15 to 32.7 cm;and the volume of decay from 2.5 to 13.2%. The relationship between age and the specified indicators is presented graphically. Using data obtained from the same sample of trees, we determined the expected and actual yield of commercial wood by age class. We determined that stem decay in beech stands leads to a decrease in the yield of commercial wood on average from 25.1% in the middle-aged to 14.8% in overmature plantations, respectively, with an estimated yield of 40.8–62.7%. Here we present mathematical models of the output of commercial wood from the infected part of the stands by age classes with the use of average data on the extent of decay in model trees.     

Modeling of simultaneous three-dimensional leaching and chemical reaction of CCA components in unfixed wood exposed to water

The leaching of chromated copper arsenate (CCA) components from unfixed wood immersed in water is modeled in three dimensions using an analytical model of simultaneous diffusion and reaction. Parameters for the model were determined by laboratory leaching experiments with small uncoated wood samples, departing from previous approaches where diffusion coefficients are measured in one dimension at a time. The diffusion coefficients and reaction rate constants of Cr⁶⁺, total Cr, Cu, and As in unfixed CCA-treated red pine (Pinus resinosa Ait.) and southern pine (Pinus sp.) were estimated, assuming first-order reaction rate equations and independent Fickian diffusion for all components. Estimated reaction rate constants and diffusion coefficients were not significantly affected by sample dimensions except for very severe longitudinal leaching from short samples. The predictive ability of the model using diffusion coefficients determined from immersion of small lab samples was evaluated by leaching experiments in a spray booth of southern pine lumber at 21 and 60°C, and red pine pole sections at 21°C. The predictive ability of the model was mixed, but in all cases represents a significant improvement over small-block leaching models which do not account for the diffusive nature of the leaching process.     

Magnetic resonance imaging used for the evaluation of water presence in wood plastic composite boards exposed to exterior conditions

Abstract

Two wood plastic composite (WPC) boards, one experimental and one commercial, were exposed to exterior conditions and evaluated non-destructively using a clinical magnetic resonance imaging (MRI) unit for moisture content (MC) and distribution. The experimental board was exposed in Vancouver, British Columbia, for more than 8 years, and the commercial board was exposed near Hilo, Hawaii, for 2 years. Both boards were characterized in terms of wood content, density, water uptake properties and voids content. The experimental board was additionally destructively analysed for water absorption of the WPC and MC calculated based on the wood content for verification of MRI results. MRI detected the presence of free water and its distribution in both of the WPC boards. Fibre saturation in the experimental board was found to be about 22–24%, in comparison to 25–30% present in most wood species. There was good correlation between the detection of free water by MRI and by destructive testing. Magnetic resonance images showed various major points of water entry in the WPC boards such as the support area, the cut ends, the dripping edge and the sides of the boards. For the experimental board, significant water entry also occurred at the upper exposed surface.     

几种生物农药对茶梢蛾的毒力测定及林间防治试验

为了筛选出最适合防治茶梢蛾的农药,选用6种生物农药和1种化学农药对茶梢蛾幼虫的毒杀力进行了室内测定,并用筛选出的20%乐果乳油、2%阿维.苏可湿性粉剂和3%阿维.氟铃脲乳油这3种毒力较强的农药进行了林间幼虫防治试验。结果表明:使用阿维.苏、阿维.氟铃脲和乐果的2 000倍液进行喷雾防治的效果较为理想,可达到74%～84%的杀虫效果;而用阿维.苏、阿维.氟铃脲和乐果以注干施药法进行防治的杀虫效果并不明显。     

The stress-displacement relation of wood perpendicular to the grain

Summary A non-linear fracture mechanics model, the Fictitious Crack Model (FCM), is utilised for a theoretical study of the Compact Tension (CT) specimen. The complete stress-displacement curve for the material is used in the FCM, even the descending branch after maximum stress. The analysis shows that the computed load-displacement curve is sensitive to modulus of elasticity perpendicular to the grain, tensile strength and fracture energy. The theoretically obtained results agree well with experimentally determined curves.     

The stress-displacement relation of wood perpendicular to the grain

Summary A method for measuring the complete stress-displacement relation in both tension and shear and some experimental results on Nordic redwood (Pinus sylvestris) are presented. The complete stress-displacement relation also includes the post-peak behaviour, i.e. the descending branch of the curve. The influence of annual ring orientation and moisture content on the form of the stress-displacement curve for the fracture process zone has been examined, and the results show that the normalised curve in tension is independent of annual ring orientation and moisture content.