Penetration of urea–formaldehyde resins with different formaldehyde/urea mole ratios into softwood tissues

In order to understand the impact of formaldehyde/urea (F/U) mole ratio on penetration characteristics of urea–formaldehyde (UF) resin into softwood tissues, a quantitative measurement of UF resin penetration into radiata pine (Pinus radiata) tissues from the bond-line was undertaken. Four different F/U mole ratios (1.6, 1.4, 1.2, and 1.0) of UF resins with different viscosities and two levels of hardener (NH₄Cl) for two extreme F/U mole ratios (1.6 and 1.0) were studied. Firstly, field emission scanning electron microscope and confocal laser scanning microscopy were used to localize UF resins in the bond-line for the qualitative evaluation of resin penetration. Then light microscopy was employed to quantitatively measure the resin penetration and bond-line thickness. A decrease in the F/U mole ratio of UF resin that proportionately decreased the resin viscosity resulted in an increase in the average resin penetration and a decrease in the bond-line thickness. Higher hardener level provided a greater resin penetration with all F/U mole ratio UF resins. These results demonstrated that F/U mole ratio had an impact on the penetration and bond-line thickness of UF resins, owing to differences in the reactivity of resins, with higher F/U mole ratio resins being more reactive.     

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.     

Preparation and adsorption properties of macroporous tannin resins

1 Introduction Plant polyphenols are a large and diverse class of poly-atomic phenols which occur naturally in some parts of plants. Their molecular weight ranges from 500 to 3,000 g·mol–1. Plant polyphenols are abundant in nature and their production capacity is only second to that of cellulose, hemicellulose and lignin (Sun, 1988). Polyphenols can be divided into two kinds given their chemical constitution: hydrolysable tannin and condensed tannin (Song and Di, 2000). Benzene rings in th…     

Shear strength development of the phenol–formaldehyde adhesive bond during cure

The development of the shear strength of the phenol–formaldehyde (PF) adhesive bond during curing was investigated. Five different PF adhesive mixtures and 1.1 mm thick peeled beech (Fagus sylvatica L.) veneer were used to produce lap-shear specimens, which were cured at a pressing temperature of 160°C. Dielectric analysis (DEA) and modified ABES (automated bonding evaluation system) were used to evaluate the physical–chemical and mechanical aspects of PF adhesive cure in a miniature hot-press. The degree of cure, which was calculated from conductivity data, was dependent on pressing time and the composition of the PF adhesive. An addition of rye flour to the PF adhesive significantly postponed the curing process as determined by DEA. It was found that the adhesive bond started to develop in the last stage of the curing (vitrification), by which time most of the physical–chemical conversion of the adhesive had been completed.     

The effect of the G‐layer on the viscoelastic properties of tropical hardwoods

Context and aim

This study aimed to examine the effect of the tension wood G‐layer on the viscoelastic properties of wood.

Methods

Tension wood and opposite wood samples were obtained from six French Guianese tropical rainforest species (Sextonia rubra, Ocotea guyanensis, Inga alba, Tachigali melinoni, Iyranthera sagotiana and Virola michelii); the tension wood of the former three of these species had a G‐layer, whilst the tension wood from the latter three had no G‐layer. Tensile dynamic mechanical analysis (DMA) was performed on green never dried wood samples in the longitudinal direction with samples submerged in a water bath at a temperature (30°C) and frequency (1 Hz) representative of the conditions experienced by wood within a living tree. Then, DMA was repeated with samples conditioned to an air-dried state. Finally, samples were oven-dried to measure longitudinal shrinkage.

Results

Tension wood did not always have a higher longitudinal storage (elastic) modulus than opposite wood from the same tree regardless of the presence or absence of a G‐layer. For the species containing a G‐layer, tension wood had a higher damping coefficient and experienced a greater longitudinal shrinkage upon drying than opposite wood from the same species. No difference was found in damping coefficients between tension wood and opposite wood for the species that had no G‐layer.

Conclusion

It is proposed that the different molecular composition of the G-layer matrix has an influence on the viscoelasticity of wood, even if a biomechanical gain is not yet clear. This study shows that rheological properties and longitudinal shrinkage can be used to detect the presence of a G‐layer in tension wood.

     

Effect of organoclay platelets on the mechanical properties of wood–plastic composites formulated with virgin and recycled polypropylene

Abstract

This study investigated the effects of organoclay platelet contents (0, 3 and 5 wt%) and polypropylene type (virgin and recycled) on the mechanical properties of polypropylene/wood flour composites. Composite samples were made by melt compounding and consequent injection moulding. The tensile, flexural and impact properties of resultant composites were determined. X-ray diffraction (XRD) analysis of composites with 3 and 5% nanoclay content was also conducted. The results indicated that tensile and flexural properties of the composites increased with the addition of nanoclay particles up to 3 wt% and decreased thereafter. The impact strength of the composites, however, decreased with the incorporation of nanoclay. The mechanical properties of the recycled polypropylene-based nanocomposites were statistically comparable with those based on virgin polypropylene. XRD analysis revealed that the degree of intercalation in the nanocomposites containing 3% nanoclay was higher than in those containing 5%. Based on these results, it can be concluded that recycled polypropylene could be used instead of virgin polypropylene in the production of value-added products with no significant adverse effects on the mechanical properties.     

Reduction of formaldehyde emission from plywood using composite resin composed of resorcinol–formaldehyde and urea-modified scallop shell nanoparticles

More than 200,000 tons of scallop shells are disposed annually alone in Japan. Nanoparticles derived from scallop shells have the potential to adsorb gaseous formaldehyde; therefore, such discarded shells have now been tested as additive filler in plywood adhesive by mixing high specific surface area, urea-modified shell nanoparticles with a resorcinol–formaldehyde resin. With this procedure, it was found that the emission of formaldehyde from the resulting plywood could be substantially reduced. The urea-modified scallop shell nanoparticles were prepared by two different methods: (1) a dry method where the shells were treated by planetary ball-grinding under ambient conditions—a completely dried powder was obtained after addition of the surface-modifying urea solution; (2) a moist method by treating dry ground shell particles in a wet grinding process with the urea solution, followed by centrifugation to obtain a paste. The specific surface area of the nanoparticles obtained by both treatments was 42 ± 3 m²/g. Measurement of the subsequent formaldehyde emission showed that the addition of the modified scallop shell nanoparticles substantially reduced the formaldehyde emission from plywood. The reduction of the specific mass uptake of urea depends on the nanoparticles which especially was the case when resins containing nanoparticles processed by the moist method were used.     

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.     

Mechanical properties of kenaf fiber–cement composites containing kenaf gamma-ray grafted with acrylamide

Kenaf fibers have excellent properties and possess the potential to be outstanding reinforcing fillers in cement. The grafting of acrylamide to kenaf fibers is important in improving the compatibility between the fibers and the cement. Acrylamide was grafted onto kenaf fibers using gamma-ray radiation. The radiation dose ranged from 20 to 100 kGy, and the dose rate was 10 kGy/h. The degree of grafting increased with increased radiation doses. FT-IR analysis revealed an increase in amide content after gamma-ray-radiation-induced grafting, further evincing the attachment of acrylamide to the kenaf fibers. SEM images showed evidence of acrylamide grafting to the fiber surface. Contact angle measurements on individual fibers taken before and after grafting demonstrated changes in wettability. The mechanical properties of the gamma-ray-grafted kenaf fiber–cement composites were superior to those of the ungrafted kenaf fiber–cement specimens.     

The tree/crop interface — or simplifying the biological/environmental study of mixed cropping agroforestry systems

A key to understanding the biological potentials and restraints of agroforestry systems, and the environmental responses of plant components within them, is the tree/crop interface. All agroforestry systems can be studied by separating the growth and yield characteristics of the three basic sets of variables (a) the sole agricultural crop (b) the effects of the tree/crop interface on the crop and tree and (c) the growth of the tree as a whole crop.The interface can be studied wherever it occurs in natural situations, or conventional or systematic experimental layouts, but very simple forms of geometric layouts can be very space efficient.

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Resumer La interfase arbol/cultivo, o como simplificar los estodios biologicoambientales de sistemas mixtos de cultivos agrogorestales.La interface arbol/cultivo es la clave para entender el potencial y las limitaciones biologicas de los sistemas agroforestales, y de la respuesta ambiental de las plantas dentro de los mismos. Todos los sistemas agroforestales pueden ser estudiados separando las caracteristicas de crecimiento y rendimiento de los tres conjuntos basicos de variables: (a) el cultivo agricola solo; (b) los efectos de la interfase arbol/cultivo sobre el cultivo y los arboles; y (c) la plantation forestal sola.La interfase puede ser estudiada cuando ella ocurre en situaciones naturales, o en arreglos experimentales convencionales o sistematicos, pero formas simples de arreglos geometricos pueden ser muy eficientes en el uso del espacio.

     

Maximum size–density relationships for mixed softwoods in the northeastern USA

The maximum size–density relationships or self-thinning lines were developed for three mixed-softwood climax forest habitats (hemlock-red spruce, spruce-fir, and cedar-black spruce) in the northeastern USA. The plot data were collected from an extensive data base used in growth studies from 1950 to 1970, and represented a wide range of species compositions, sites, management options, and densities. Plots having late successional species compositions with relative density index higher than 0.7 were selected as the most fully-stocked plots for model development. Reduced major axis regression was used to fit the self-thinning lines to the data. The differences between the three forest habitats were tested using the 95% confidence intervals of the coefficients of the self-thinning lines. The results indicated that there were no differences between the hemlock-red spruce and spruce-fir habitats for both relationships of the mean tree volume versus number of trees, and the quadratic mean tree diameter versus number of trees. Thus, these two habitats were combined to develop a single self-thinning line. However, the cedar-black spruce forest habitat required a separate self-thinning line. These maximum size–density relationships can be readily used to construct stand density management diagrams.     

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.     

Effect of the addition of <Emphasis Type="Italic">Acacia mangium</Emphasis> bark on thermosetting of phenol–formaldehyde resin

The effect of addition of Acacia mangium bark powder on the thermosetting processes of two commercial phenol resins, PF-A and PF-B, was examined by bond strength test, torsional braid analysis, and differential scanning calorimetry. When the bark powder was added to PF-A, the bond strength of plywood pressed at 110°C increased and was comparable to that of plywood pressed at 120 and 130°C. However, when the bark powder was added to PF-B, the bond strength of plywood pressed at 110°C was still lower than that of plywood pressed at 120 and 130°C. The relative rigidity and loss tangent of PF-A cured with the bark powder obtained by heating at 100°C were comparable to those at 120 and 140°C, and the reaction enthalpy was increased by bark powder addition. In contrast, chemical reactions for cured PF-B were not enhanced by bark powder addition.     

Effects of wet–dry cycling on the mechanical properties of Arundo donax L. used for the vibrating reed in woodwind instruments

Wood Science and Technology - The effects of wet–dry and moist–dry cycling on the mechanical properties of reed (Arundo donax L.) were investigated. Because water-soluble extractives...     

The optimum temperature–humidity combination for the feeding activities of Japanese subterranean termites

Two species of Japanese subterranean termite, Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe), were used in an investigation of the optimum temperature–relative humidity (RH) combination for their feeding activities. Daily wood consumption per worker and survivals were measured, and the protozoan fauna in the hindgut were observed under 15 temperature–RH combinations for 1 week. Five temperatures (20°, 25°, 30°, 35°, and 40°C) and three RH conditions (50%, 70%, and 90% RH) were examined. The activities of the workers were highest at around 30°C for both species, and workers died at 40°C within 5 days and 2 days for C. formosanus and R. speratus, respectively. The optimum RH condition for feeding activity was 90% RH for C. formosanus and 70%–90% RH for R. speratus. The optimum temperature–RH combinations for feeding activities were 30°C at 90% RH for C. formosanus and 30°C at 70%–90% RH for R. speratus.     

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.     

Nondestructive determination of paper properties of Populus × euramericana with near infrared spectroscopy

Five Populus x euramericana wood samples representing three different sites were selected and nearinfrared （NIR） spectra were obtained. For these sections, basis weight, brightness and three mechanical properties （tensile index, tearing index and bursting index） were determined by standard analytical methods. Calibrations were developed for each paper property using the NIR spectra, data on paper properties, using partial least squares （PLS） regression. The results show that the coefficients of correlation of calibration and validation for basis weight were 0.8824 and 0.8299, respectively; the standard error of calibration （SEC） and prediction （SEP） were 1.150 and 1.170, respectively. In testing for brightness, the correlation coefficient of calibration was 0.9621 and for validation 0.9612, while the SEC and SEP were 0.997 and 1.300, respectively; paper brightness and NIR spectroscopy were highly correlated. NIR spectroscopy can be used to predict tensile, tearing and bursting indices of paper samples rapidly. We found that the paper properties fitted by NIR and GB methods were highly correlated. The coefficients of correlation of calibration and validation for basis weight exceeded 0.8000, while the SEC and SEP were very small. These results reveal that the five paper properties of Populus x euramericana and those predicted by the NIR model were highly correlated. We conclude that the NIR models can be used for the prediction of paper properties.     

The tree species matrix,influence on the level of herbivore browsing in mixed forest stands in southwest Sweden†

Herbivory pressure on a forest stand and each plant individual may be affected by the spatial distribution of conspecific and allospecific plants on the site; whether the plants are standing in solitary or groupwise settings; or by the differences in the preference of plants in relation to each other. The study was conducted in southwest Sweden, where 120 plots (1508?m²) were visited and 1280 individual woody plants evaluated and measured. We tested the hypothesis that preferred woody plants can protect unpreferred conspecific and allospecific woody species against herbivory in a system with one dominant, generalist herbivore, the fallow deer (Dama L.), and that the effectiveness of this protection varies depending on the relative preference of the neighboring conspecific and allospecific woody species placed in conspecific groups or standing solitary. Our results support the hypothesis that preferred woody plants can protect unpreferred conspecific and allospecific woody species against herbivory in the case of Picea abies dominating stands.