Phenol–formaldehyde impregnation of densified wood for improved dimensional stability

To produce a highly stable wood-based product with increased mechanical properties, phenol formaldehyde (PF) resin impregnation was combined with the viscoelastic thermal compression (VTC) process. Dimensional stability and bending stiffness were evaluated. Two PF resins with weight average molecular weights of 172 and 780 were studied at three different concentrations, 5, 10 and 20%. After 24-h room temperature water soak and 2-h boil, both PF treatments at all concentration levels showed high levels of dimensional stability compared to non-impregnated VTC processed controls. The higher molecular weight PF provided greater stability with an average thickness swell value of 12% compared to 20 and 37% for the lower molecular weight PF resin treatment and control, respectively. High anti-swelling efficiency values were recorded for both low and high molecular weight resins, implying these modifications were effective at reducing the volumetric swelling which occurred in the unmodified control. PF treatments were also extremely effective at reducing irreversible swelling. The low and high molecular weight resin treatments had 1/5th and 1/7th the irreversible swelling than the unmodified VTC processed controls, respectively. All dimensional stability values improved as resin concentrations increased. Both resin types at all concentration levels reduced Young’s modulus.     

A model of supplying poplar wood for Iranian paper ＆ wood factories

The objective of this research is to design a method for an appropriate alternative to supply poplar wood as raw material for wood and paper factories in Iran.Due to the destruction of the forests and lack of proper plantation,replacement of the forest wood by the fast growing wood is vital to satisfy all requirements of these factories.A hierarchy was used to prioritize benefits,opportunities,costs and risks (BOCR) using the Analytic Hierarchy Process (AHP) ratings approach.To evaluate the "control criteria" of the system,a control hierarchy was also created and prioritized by applying the Analytic Network Process (ANP).A total of four major control criteria in the system are prioritized where each one controls a network structure evaluated by using ANP.The final synthesis results of the system showed that internal poplar tree farming supplied by the forest product factories was the best choice among three potential alternatives (factory procurement,external procurement and mix procurement).     

Sound absorption property of wood for five eucalypt species

The sound absorption coefficients of wood and wood boards for five eucalypt species (Eucalyptus urophylla, Eucalyptus urophylla x E. grandis, Eucalyptus urophylla x E. tereticornis, Eucalyptus urophylla x E. camaldulensis and Eucalyptus cloeziana) that were collected from plantation in Dongmen Forestry Center of Guangxi Province, China were tested with standing wave method and their sound absorption properties were also compared. The results showed that the sound absorption coefficients of the five eucalypt wood species did not change evidently below 1000 Hz, but above 1000 Hz their sound absorption coefficients increased with the increasing frequency. The difference in sound absorption coefficient among five species of eucalypt wood is not evident at the tested frequency range (200–2000 Hz), but the sound absorption property ofEucalyptus urophylla at low frequency is better than that of other four species. The sound absorption coefficient of the tangential-sawn board is higher than that of the radial-sawn board. The sound absorption property of eucalypt wood of 0.5 cm in thickness is much better than that of 1.0 cm in thickness. It is concluded that wood sound absorption properties of eucalypts are affected by their board thickness and the type of sawn timber within the testing frequency, but the variance of wood sound absorption property among the five tested species is not significant. Fundation item This study is Part of 2000-4-13 in “948” Project from the State Forestry Administration of P.R. China Biography: JIANG Ze-hui (1939-), female, Professor in Research Institute of Wood Industry in Chinese Academy of Forestry. Responsible editor: Chai Ruihai     

Fracture characteristics of PARALLAM® PSL in comparison to solid wood and particleboard

Summary Typical fracture characteristic values like load-displacement curve and specific fracture energy of the new wood laminate compound PARALLAM® PSL were determined by using the wedge splitting technique. Comparison with the values of solid wood and particleboard showed the superiority of this wood composite in both weak transverse orientations. This result is explained by the favourably oriented wood strands in PARALLAM® PSL with a length up to 2.6 m, which give rise to crack arresting mechanisms. In addition the influence of specimen geometry on the critical load and corresponding loadpoint-displacement at crack initiation was calculated for both isotropic and orthotropic materials using linear elastic FE-models.The authors thank Trus Joist McMillan for supplying the testing material and especially Dir. Donald Sharp for his helpful cooperation. Financial support by the Austrian National Bank (project no. 4917) is gratefully acknowledged.     

A critical discussion of the physics of wood–water interactions

This paper reviews recent findings on wood–water interaction and puts them into context of established knowledge in the field. Several new findings challenge prevalent theories and are critically discussed in an attempt to advance current knowledge and highlight gaps. The focus of this review is put on water in the broadest concept of wood products, that is, the living tree is not considered. Moreover, the review covers the basic wood–water relation, states and transitions. Secondary effects such as the ability of water to alter physical properties of wood are only discussed in cases where there is an influence on state and/or transition.     

Proton spin–lattice relaxation time measurements of solid wood and its constituents as a function of pH: Part I*

Summary  By measuring the proton spin–lattice relaxation times (T_1H) in the solid-state for black spruce softwood, the molecular mobilities of carbohydrates and lignin have been evaluated as a function of pH. These studies have shown that the mobility of the polymeric constituents of wood is affected by the ionization of the different functional groups at different pH's. The analyses of the proton-spin–lattice relaxation time data at constant humidity revealed that the maximum T_1H for both carbohydrates and lignin occurs at about neutrality, while it was found to be depressed at the two extremes of the pH range. By treating a wood sample with propylene oxide, the esterification of the acid groups was affected, thus deactivating the ionization process and their contribution to T_1H. The experimental T_1H values for cellulose and lignin after the esterification were significantly decreased at pH 6 confirming that their ionization plays a very significant role in determining chain mobility. Received 1 December 1998     

Application of micromechanical models to tensile properties of wood–plastic composites

Wood–plastic composites (WPC) were produced with white birch pulp fibers of different aspect ratios (length-to-diameter), high-density polyethylene, and using two common processes: extrusion or injection molding. Three additive levels were also used: no additive, compatibility agent, and process lubricant. Fiber size was measured with an optical fiber quality analyzer. Tensile properties of WPC were measured and modeled as a function of fiber aspect ratio. Models were fitted to experimental values using the minimum sum of squared error method. A shift from the oriented fiber case (injection molding) to the randomly oriented fiber case (extrusion) was achieved using a fiber orientation factor. Fiber/matrix stress transfer increased with increasing fiber aspect ratio. Stress transfer was reduced with the use of process lubricant. Unexpectedly, the compatibility agent had the same effect. Fiber strength and stiffness contributions to the composite were lower than those of intrinsic fiber properties.     

Manufacture and properties of Miscanthus–wood particle composite boards

Miscanthus sacchariflorus straw was used as a raw material for the manufacture of Miscanthus–wood particle composite board with Douglas-fir particles in ratios of 100/0, 80/20, 60/40, 40/60, 20/80, and 0/100. A commercial phenol–formaldehyde resin was used as a binder at 9 and 11 % for target densities of 0.50 and 0.65 g/cm³, respectively. The effects of the Miscanthus/wood particle ratio on the composite board properties were investigated. In addition, the density profile was also examined to improve the understanding of the composite board manufacturing process. Results indicate that the internal bonding value increased drastically in the board containing up to 50 % wood particles, providing a valuable parameter for subsequent research. The board properties were greatly improved with increasing density and binder addition level.     

Colorimetric and vibrational spectroscopic characterization of weathered surfaces of wood and rigid polyvinyl chloride–wood flour composite lumber

Rigid polyvinyl chloride–wood flour composite lumber containing either pine or maple wood flour and pine and maple lumber was subjected to accelerated weathering according to the ASTM Standard G 53 protocol. Non-weathered and weathered surfaces of all specimens were analyzed using colorimetric methods, reflectance infrared Fourier transform and Raman spectroscopic techniques. In the FT-IR spectra, conjugated ketones (1,744 cm^?1) of lignin as evidenced by their skeletal vibrations (1,560–1,500 cm^?1) and stretching (1,440–1,500 cm^?1) were reduced in weathered specimens. Cellulose was largely unaffected by weathering. C–O bending vibrations at 1,040 cm^?1 from holocellulose in pine specimens and intensity bands at 1,125–1,090 and 1,360 cm^?1 (C–O stretching and O–H bending from cellulose) in the maple and wood–plastic composite (WPC)-maple specimens were unaffected. A band at 1,650 cm^?1 became prominent after weathering of both pine and maple WPC specimens which is due to C=C–C=C stretching vibration of weathered PVC portion of the specimen. Raman shifts at 530 and 840–900 cm^?1 are attributed to C–O and C–C–O stretching in cellulose (remain unchanged). The role of extractives in weathering of pine is shown by the disappearance of Raman shifts at 392 and 434 cm^?1 (C=C deformations in pine extractives) in weathered pine. One-Way ANOVA, between-group designs showed significant effect on brightness (L*), redness (a*) and yellowness (b*) for all treatments.     

Curing kinetics study of melamine–urea–formaldehyde resin/liquefied wood

The objective of this research was to investigate the effect of liquefied wood (LW) on the cure kinetics and network properties of melamine–urea–formaldehyde (MUF) resins by differential scanning calorimetry. The MUF/LW compounds exhibited two distinct cross-linking processes. It can be assumed that there did not appear to be a coreaction of the MUF with the LW. The overall apparent activation energies (E _a) of the curing reactions were calculated using the Kissinger equation. An nth-order kinetic model was used to describe the cross-linking of MUF/LW compounds, of various compositions, cured at different heating rates. The E _a values for the cross-linking process of the MUF/LW compounds predominantly tended to be approximately 80 and 71 kJ mol^?1 for MUF and LW, respectively. The apparent reaction orders of the MUF cross-linking process of the MUF/LW compounds were in the range 1–2, whereas the n values of the LW were approximately unity or less, which hints to there being a more complex mechanism of this process.     

Isolation of lignin–carbohydrate bonds in wood. Model experiments and preliminary application to pine wood

A novel method for analysis of benzylic ether type lignin–carbohydrate bonds has been developed by using model compounds. Four diastereomers of model compound 3-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-3-(methyl -d-glucopyranoside-6-O-yl)-1-propanol (GGMGP), were ozonized in acetic acid/water/methanol 16:3:1 for 1h at 0°C. The product from ozonation of each diastereomer was saponified and the corresponding -etherified tetronic acid (TAMGP) was isolated using ion exchange chromatography. Minor amounts of methyl -d-glucopyranoside (MGP) and small amounts of a gluconic acid etherified with tetronic acid (TAGLCA), tetronic acid, gluconic acid, and glyceric acid were detected in the product mixture of ozonated benzylic ether type model compounds. The results suggest that a benzyl ether bond between lignin and carbohydrate is rather stable during the ozone treatment. Acid treatments with sulfuric acid or trifluoroacetic acid of the derived TAMGP led to cleavage of the glucosidic bond but only a small amount of products (tetronic acid and glucose) resulting from cleavage of the -ether bond were formed. The successful chemical treatments were used for studies of benzylic ether bonds in Japanese red pine. The results suggest the presence of benzylic ether bonds to polysaccharides in the wood.Part of this paper was presented at the 10th International Symposium of Wood and Pulping Chemistry (ISWPC), Yokohama, 1999; the 11th ISWPC, Nice, 2001; and as a rapid comunication in J Wood Sci (2000) 46:263–265     

Flavonoid tannins — structural wood components for drought-resistance mechanisms of plants

Summary Myrothamnus flabellifolia Welw., Eragrostis nindensis Fic. and Hiern, Xerophyta villosa, Th. Dur and Schinz, and Sporobolus stapfianus Gand, present a so-called resuscitation behaviour when subjected to drought and subsequent rehydration. Absence of cell wall cracking is one, if not the main cause of this behaviour. Polyflavonoid tannins content of Myrothamnus flabellifolia is high and increases under drought-induced stress. It does not increase in the other plants where a surge of the content of the amino acid proline occurs instead. The authors now present the hypothesis and circumstantial evidence that the helicoidal tridimensional structures of these tannins function as the springs disallowing cracking of the cell walls and rendering possible the resuscitation characteristics of Myrothamnus flabellifolia and of the other plants through two slightly different mechanisms. This explains why many trees originally of Southern Africa, a drought area, are high producers of tannins. It infers that tannins are structural wood components just as much as cellulose, hemicelluloses and lignin.     

Formation of carbon–carbon composite using wood as a precursor

Abstract

The use of wood as structure-giving material may be an effective approach to reduce some barriers for producing high temperature ceramic especially carbon composites. The objective of this study was to develop a simple process for producing carbon–carbon (C–C) composite through porous template result from pyrolysing of wood. Walnut, known to be relatively permeable, was being heat treated under controlled atmosphere. The carbon-template formed was infiltrated with coal tar pitch. Morphological characterization of the resulting composite was carried out by scanning electron microscopy morphology and physical properties of sample were evaluated with determination of bulk density and open porosity. In addition mechanical properties of products were analysed with three-point bending test and Vickers micro hardness. Results showed that bulk density had an uprising trend with increasing the number of densification cycles and subsequently open porosity decreased. Moreover, from mechanical property's point of view, results had a good compatibility with increase in the densification cycles.     

Determination of 2-thiocyanomethylthiobenzothiazole (TCMTB) in treated wood and wood preservative using Ultraviolet–visible spectrophotometer

Ultraviolet–visible Spectrophotometer method for the determination of 2-thiocyanomethylthiobenzothiazole (TCMTB) in treated wood and wood preservative was developed. The determination was done after conversion of TCMTB to 2-mercaptobenzothiazole (2-MBT). This conversion was obtained by reaction with 0.1?M cystein alkaline condition (pH 10). The extraction of 2-MBT was carried out with ethyl acetate containing 0.2% of ?-mercaptoethanol after acidification with 2?M phosphoric acid (pH 2.5). The sample absorbance was measured at 324?nm wavelength with a calibration curve range from 10 to 90?ppm of TCMTB. The Regression value, R ², achieved was 0.9998, while the precision, RSD, was <10% (n?=?6). The recovery was in the range of 90.7–103.2% (n?=?6). The result obtained with this colorimetric procedure is comparable to the HPLC–PDA method.     

A simple process for electroless plating nickel–phosphorus film on wood veneer

A facile electroless Ni–P plating process for preparing EMI shielding wood-based composite was studied. In the process, the activation was combined with electroless deposition in the plating bath. By a simple and environmentally friendly method, Ni–P film was easily deposited on the surface of birch veneer. The plated specimens were observed by SEM, and it was found that the film is uniform, compact, and continuous. EDS results show that the coating contains 3.32 wt% phosphorus and 96.68 wt% nickel. It is indicated by XRD analysis that the film on birch veneer is crystalline. It is considered that the crystalline structure is related to the lower phosphorus content of the film. It was found that the birch veneer plated with crystalline Ni–P coating has better electrical conductivity and electromagnetic shielding performance.