Mode III fracture energy of wood composites in comparison to solid wood

A simple experimental setup for mode III and mixed mode (I?+?III) fracture tests with anisotropic materials under steady state crack propagation has been developed. Load-displacement curves can be recorded up to the complete separation of the specimen. From the load-displacement curves several mechanical material parameters can be derived. The tests have been performed for solid wood and different wood composites, being PARALLAM^® PSL in different orientations, particleboard and INTRALLAM^® LSL, and the fracture behaviour is characterised by the specific fracture energy.     

Pilodyn在桉树活立木材性质评估中的应用

测定了建立在广西22个4年生桉树无性系的Pilodyn值、木材基本密度、边材木材密度、心材木材密度和弹性模量。结果表明：Pilodyn值为9．44—15．41mm、木材密度为0．3514-0．4913g·cm^-3、弹性模量在3．94GPa到7．53GPa之间;Pilodyn值在不同处理、不同方向及不同参试无性系间均存在极显著差异。Pilodyn值与各材性指标间的相关系数在-0．433到-0．755之间,呈显著到极显著负相关。研究表明,Pilodyn方法可以预测桉树活立木的木材密度和弹性模量。     

Impregnation of Bombax ceiba and Bombax insigne wood with a N-methylol melamine compound

Methylated N-methylol melamine (NMM) is known for its ability to enhance physico-mechanical properties, anti-fungal ability, and hydrophobicity and was therefore used to impregnate two less used and non-durable wood species from Myanmar, Bombax ceiba and Bombax insigne. Solution uptake, weight percent gain and nitrogen content were increased by increasing melamine concentrations with B. ceiba always achieving higher values compared with B. insigne. According to the leaching results, a higher degree of condensation after curing as well as a better crosslinking of NMM could be obtained at higher temperatures. However, both curing temperatures used (90 and 120 °C) resulted in almost the same amount of nitrogen fixed in the cell wall. UV microspectrophotometry confirmed the penetration of the NMM into different morphological regions of wood tissues, which was again supported by the analysis of point measurement spectra of treated and untreated specimens.     

Detection of incipient decay in tree stems with sonic tomography after wounding and fungal inoculation

Picus^® acoustic tomography was used to map incipient stages of fungal decay in the sapwood of standing Douglas fir, beech, oak, and sycamore trees 2, 16, and 27 months after wounding and artificial inoculation with brown-, soft-, and white-rot decay fungi. Some wood properties were additionally measured before (velocity of sound) and after (moisture content, weight loss, and density of sound, discoloured and/or decayed wood) tree felling (28 months). With the exception of Trametes versicolor in sycamore, wood decay was not evident from the tomograms in any host-fungus combination. In comparison to measurements after two months, the device recorded a reduction in sound velocity in some host-fungus combinations after 16 and 27 months. In beech, there was a significant reduction in sound velocity after inoculation with Ganoderma applanatum, Kretzschmaria deusta, and Trametes versicolor. Similarly, a reduction in sound velocity was recorded in sycamore inoculated with Kretzschmaria deusta and Trametes versicolor. In all these combinations, losses in wood weight and wood density were also found. Results showed that the detection of incipient fungal decay at the periphery of tree stems needs to be improved such that tomograms of the Picus^® acoustic tomograph are capable of identifying decay progressing from the sapwood inwards.     

Moisture content profiles and uptake kinetics in wood cladding materials evaluated by a portable nuclear magnetic resonance spectrometer

Abstract

This study evaluated the capability of nuclear magnetic resonance (NMR) technology based on small portable magnets for in situ studies of the local moisture content in wood. Low-field and low-resolution [¹H]NMR with a unilateral permanent magnet was used to monitor and map the moisture content of wood cladding materials of various types in a spatially resolved manner. The results show that portable NMR equipment based on small open-access permanent magnets can be successfully used for non-invasive monitoring of the moisture content in various extended wood specimens. The moisture content was measured with a depth resolution of 0.2 mm and a maximum penetration depth of 3 mm. This makes the technique suitable for in situ local moisture content measurements beneath a coating layer in the cladding, for example, and it is also possible to relate the moisture level to specific properties of the wood material.     

Application areas of synchrotron radiation tomographic microscopy for wood research

Possible applications for synchrotron radiation tomographic microscopy in the field of wood research were tested and evaluated at the TOMCAT beamline (TOmographic Microscopy and Coherent rAdiology experimenTs) at the Swiss Light Source (SLS) at the Paul Scherrer Institute (Villigen, Switzerland). For this study, small cylindrical samples (∅ 1 and 3 mm) were examined with different experimental setups resulting in a nominal voxel size of approximately 1.48 × 1.48 × 1.48 and 3.7 × 3.7 × 3.7 μm³, respectively. Suitability of the TOMCAT microscope for 3D investigations of wood anatomy was tested on several softwood and hardwood species revealing microscopic features (e.g. tyloses, wall thickenings or pits) down to the nominal pixel size. The results suggest that even features in the sub-voxel range can be made visible. Tomographic microscopy was also tested for wood technological applications, i.e. penetration behaviour of a wood preservative and also of three wood adhesives (poly-urethane resins) with different viscosities. Although the experiments with the preservative yielded no clear results, the method seems suitable for examining the penetration of the different adhesives. The adhesive penetrates the wood mainly by the vessels where it can be easily discerned from the wood structure.     

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.     

Moisture movement and thickness swelling in oriented strandboard. Part 2: Analysis using a nuclear magnetic resonance imaging body scanner

The previous paper in this series demonstrates the use of a nuclear magnetic resonance (NMR) micro-imaging system to observe the movement of liquid water through small specimens (11 × 16 mm² cross-section) of oriented strandboard (OSB) and solid wood. In the present paper, a NMR body scanner is utilized to obtain images of moisture penetration into ASTM D 1037–99 standard sized (152 × 152 mm²) thickness swelling specimens at different intervals during water soaking. As with the micro-imaging study, silicone was applied to the surfaces and edges of some of the specimens in order to observe the directional characteristics of moisture movement through OSB. Specimens with commercially applied edge sealant were also included in the study in order to observe the effectiveness of the sealant of reducing moisture penetration and thickness swelling. The presence of voids and areas of low density were shown to contribute significantly to moisture penetration into the specimens.     

Electromagnetic interference shielding material from electroless copper plating on birch veneer

Copper coating on birch veneer substrate was conducted by electroless deposition to prepare electromagnetic interference shielding material. In the process, Pd²⁺ ions were chemically adsorbed on the wood surface modified with chitosan. Then, they were reduced and dipped into a plating bath where copper film was successfully initiated. The coatings were characterized by SEM–EDS, XPS, and XRD. The metal deposition, surface resistivity, and electromagnetic shielding effectiveness were measured. The morphology of the coating observed by SEM is uniform, compact, and continuous. EDS, XPS, and XRD results showed that the coating consists of Cu⁰ with crystalline structure. Moreover, the copper films firmly adhere to the wood surface. Birch veneers plated with crystalline copper film exhibit high electro-conductivity with surface resistivity of 119.1?mΩ?cm^?2 and good electromagnetic shielding effectiveness of over 60?dB in frequencies ranging from 10?MHz to 1.5?GHz.     

Coating/wood substrate behaviour in Dacrydium cupressinum,Podocarpus dacrydioides and Pinus radiata weatherboards

Summary An electron microscope study of the behaviour of Dacrydium cupressinum Lamb. (rimu), Podocarpus dacrydioides A. Rich, (kahikatea) and Pinus radiata D. Don. (radiata pine); two endemic timbers of New Zealand and one exotic timber coated with a specially formulated TiO₂ tagged long soya oil alkyd coating was made using both the scanning and transmission electron microscopes. The key elements present in the coating were detected by energy dispersive X-ray analysis and used to qualitatively trace coating penetration into wood. Quantitative information on the nature of the coating penetration was obtained by photographing the entire cross-sectional length of each weatherboard under the scanning electron microscope and counting the number of filled cells inwards from the coating interface. The performance of the coating and the three weatherboard taxa were tested using accelerated weathering techniques involving the Xenon-arc Weather-Ometer. Coated and uncoated boards were weathered for up to three thousand hours. Coating durability and substrate behaviour were qualitatively assessed microscopically. Fourier transform infrared and attenuated total reflectance methods were used to obtain quantitative information on coating performance and particular reference is made to these latter techniques.The author gratefully acknowledges Dr. B. G. Butterfield, Dr. L. M. H. Middleton, and the University Grants Committee for awarding the U.G.C. scholarship to carry out the research     

The use of the green fluorescent protein as a biomarker for sapstain fungi

To understand wood colonization by sapstain fungi and their potential biocontrol agents, it is necessary to differentiate these organisms directly on their natural substrates. In the present study the feasibility of transforming with the green fluorescent protein (GFP), the sapstain fungus Ophiostoma piceae and a potential biocontrol agent Cartapip^®, an Ophiostoma piliferum albino strain was assessed. Transformants of the two fungal species were screened by polymerase chain reaction and Southern blot analyses. The GFP was expressed in spores, synnemata and mycelia of the transformants grown in artificial media or wood. The growth, pigmentation and wood colonization of the transformants were similar to that of the non‐transformants, suggesting that the presence of the gfp gene had no negative effect on the biology of the transformants. Using fluorescence and confocal microscopy, the GFP‐expressing fungi were easily differentiated from the wild‐type strains and other fungal species in wood, even 4 months after inoculation. The results show that the use of the GFP system is feasible to monitor Ophiostoma fungi in wood.     

Multifunctional sol-gel coatings for protection of wood

Abstract

Organic–inorganic hybrid sol-gel coatings derived from sols synthesized using two organically modified precursors were generated on wood specimens using dip and spray coating techniques. One of the sols was synthesized using methacryloxypropyltrimethoxysilane (MPTMS) and nanoscaled boehmite particles and the other was synthesized using dimethyldiethoxysilane (DMDEOS) and tetraethoxysilane (TEOS). The coatings were generated on the wood specimens by dipping into the sols for specific time periods and by using spray coating method. The coatings were cured at different temperatures for varying soaking times. The dipping times, curing temperature, and soaking times were varied between 24–96 h, 130–200°C and 1–5 h, respectively. The coated samples were characterized for their water contact angles, microstructure, and resistance to water uptake. The coatings derived from MPTMS+boehmite sol were seen to exhibit better performance than DMDEOS+TEOS sol by forming a good barrier on the wood surface, thereby providing superior resistance to water and weather. Dipping of wood into the sol was seen to provide better protection when compared to spray coating. Dipping into the MPTMS+boehmite sol for 24 h and curing at 130°C for 2 h were found to be the optimal processing parameters yielding the best properties.     

Effects of carbonization temperatures on microstructure of carbon fiber precursors prepared from liquefied wood

In order to enlarge the utilization field of wood and decrease the costs of carbon fibers, carbon fiber precursors from liquefied wood were prepared by soaking liquefied wood in a solution containing hydrochloric acid and formaldehyde, after melt-spinning by adding hexamethylenetetramine. The microstructure evolution of the precursor during carbonization was studied by FTIR, X-ray analysis and Raman spectroscopy. The results show that precursors from liquefied wood above 400°C had diffraction peaks corresponding to the (100) crystal plane. When the carbonization temperature reached 500°C, Raman spectroscopy showed the D peak at wave number of 1360 cm–1 and the G peak at 1595 cm–1. By increasing the carbonization temperature, the microstructure of the precursors became more ordered. Although the structure of the precursor changed at 500 and 800°C, the peaks at 1632 and 1454 cm–1 corresponding to the characteristic vibrations of aromatic rings, remained during carbonization. This implies that the precursor from liquefied wood cannot be easily formed into graphite.     

Influence of coating system on the moisture buffering capacity of panels of Pinus sylvestris L.

Abstract

The indoor relative humidity in dwellings and offices is an important factor in building physics. The ability of hygroscopic materials and especially wood materials to store and release moisture helps to regulate the indoor climate naturally and to avoid extremes of humidity. In the present study, cyclic sorption experiments with coated Scots pine were performed. Materials with different coating compositions were exposed to day-to-day relative humidity changes. The moisture buffering capacity was estimated by a gravimetric method and the moisture buffer value was computed. The results show that the coating has a significant impact on the moisture buffering capacity of the underlying Scots pine. The moisture distribution in the wood sample was appraised for each coating system using a proton magnetic resonance imaging technique. This study confirmed that the dynamics of moisture exchange between the indoor environment and the wooden material during typical daily moisture fluctuations is confined to a few millimetres behind the air–wood interface.     

Mould-resistance of bamboo treated with the compound of chitosan-copper complex and organic fungicides

Bamboo has received increasing attention as an alternative raw material for wood in the late twentieth century for its fast growing nature and good mechanical properties. But bamboo is readily discolored by mould fungi, which greatly limits the applications of bamboo. In this paper, mould-resistance of moso bamboo treated with chitosan-copper complex (CCC^®), propiconazole (PPA), tebuconazole (TBA), the compound of CCC^® and PPA or TBA was reported. Results showed that CCC^® or PPA used alone as bamboo-mould inhibiter could defer or restrain the growth of Penicillium citrinum Thom (P. citrinum), while not being effective against Trichoderma viride Pers. ex Fr (T. viride) and Aspergillus niger V. Tiegh (A. niger). However, the compound of CCC^® and PPA could inhibit all mould fungi in the test, showing a good synergetic effect. Additionally, TBA had better resisting effect against P. citrinum and T. viride than against A. niger, but showed no synergetic effect with CCC^®.     

Mid-infrared absorption properties of green wood

There is a lack of quantitative data on the penetration depth and the amount of energy absorbed by green wood under infrared (IR) radiation. This lack of knowledge is a potential barrier to the development of IR heating as an alternative to soaking as a means of warming logs prior to peeling in the manufacture of plywood. Experimental measurements of normal hemispherical spectral reflectance and transmittance over the range 550–5,500 cm^?1 wavenumbers on four wood species, beech, birch, Douglas-fir and spruce have brought new knowledge on mid-infrared absorption properties of green wood and removed some uncertainties. For instance, it is not possible to deliver energy deeper than up to 0.3 mm below the wood surface because 70–90 % of all incident IR radiation on the wood surface is absorbed in this layer. Some wood features, such as surface quality, the presence of knots and of free water in wood (the latter two having a more significant effect) influence the amount of energy absorbed. These results illustrate that IR radiation can heat the surface layers, but then heat penetrates deeper into the inside layers of wood by conduction.     

Biological performance,water absorption,and swelling of wood treated with nano-particles combined with the application of Paraloid B72<Superscript>®</Superscript>

We evaluated fungal decay and mold resistance, leaching, and water absorption of nano-compounds and Paraloid B72^® (PB72) in treated wood specimens to develop new methods of consolidation by combining nano-particles and consolidants. Scots pine wood specimens were treated with dispersions of nano-CuO, nano-ZnO, nano-B₂O₃, nano-TiO₂, and nano-CeO₂. PB72 treatments of nano-particle-treated wood specimens were then carried out by either vacuum or immersion for 24 h. Previously, decayed wood specimens were also consolidated with the nano-compounds and PB72. PB72 treatments reduced element release from treated wood specimens. Nearly all nano-compounds + PB72 treatments increased the biological performance of treated wood specimens against decay fungi tested. PB72-only treated wood specimens had the highest weight losses in decay tests. No improvements were obtained in mold resistance tests when the nano-compounds and PB72 were combined. In nano-compound-only treatments, unleached specimens showed slightly lower water absorption values compared to untreated control specimens. Incorporation of PB72 into nano-compound-treated wood specimens resulted in considerably lower water absorption and volumetric swell. In previously decayed specimens treated with the nano-compounds and PB72 solution, water absorption after 2-h immersion declined compared to control specimens.     

Automated image processing for quantification of blue-stain discolouration of Norway spruce wood

Bioincising is a promising method for enhancing liquid uptake (e.g. preservatives or wood-modification agents) in refractory wood. Incubation with the white-rot fungus, Physisporinus vitreus, which selectively degrades pit membranes, results in deeper and more homogeneous penetration of liquids. Conventional methods of assessing the degree of fungal discolouration of wood after treatment with preservatives (e.g. European standard EN 152) are partly based on a subjective rating scale, which gives a rough value of the surface colonisation by blue-stain fungi. Hence, an automated image processing (AIP) procedure was developed for standardised quantification of the segmentation thresholds of discolouration and tested against manual segmentation analysis. Using the red filter in the AIP method revealed high correlation (R ² 0.95) and allowed for more user friendly and objective determination of blue staining of wood.     

Comparative study between full cell and passive impregnation method of wood preservation for laser incised Douglas fir lumber

In this study, the ability of passive impregnation of Douglas fir (Pseudotsuga menziesii Franco) lumber was compared with a conventional full cell method. With an incising density of 10,000 holes/m² carried out by CO₂ laser, square Douglas fir lumber was treated by both passive impregnation and full cell method for 6 h and 50 min. Different incising densities were also used in passive impregnation to examine the optimum incising density. It was observed that there was no significant difference between these two methods regarding absorption of liquid, moisture content after dipping and penetrated area both at cross and longitudinal sections. However, the value was higher in case of full cell method. Regarding different incising densities, absorption and penetration of liquid was similar for 10,000 and 7,500 holes/m² but it was low for 5,000 holes/m². Therefore, it can be concluded that an incising density of 7,500 holes/m² is the optimum for passive impregnation. The absorption of liquid and its distribution in wood indicates that this non-pressure passive impregnation method can be a good preservation method for impermeable lumber and can be an alternative to full cell method.     

Comparative analysis of a wood: adhesive bondline

The wood–adhesive interface was analyzed using five methods with the objective of quantitatively assessing penetration of adhesive into the porous wood network. Methods included fluorescence microscopy, scanning electron microscopy, backscatter electron imaging, wavelength dispersive spectroscopy, and X-ray microtomography (XMT). Each method provided a visual inspection, and all of the analysis methods were applied to the same field of view. XMT was the primary technique of interest. Rubidium hydroxide was used in place of sodium hydroxide in the formulation of phenol–formaldehyde adhesive. Rubidium was found to increase the X-ray attenuation of the adhesive. However, rubidium migrated beyond the adhesive interphase during specimen preparation, thus reducing its effectiveness for image contrast enhancement. The wood species studied included red oak (Quercus rubra), Douglas-fir (Pseudotsuga menziesii), and hybrid poplar (Populus deltoides × Populus trichocarpa). All techniques used for this study were useful, but each presented some limitations for bondline analysis. Despite the problem with rubidium migration, XMT for this application was promising.