Showing papers in "Wood Science and Technology in 1990"

Lignin biochemistry: Biosynthesis and biodegradation *

Abstract: Lignin biosynthesis via shikimate-cinnamate pathways in plants, and the biosynthetic differences of guaiacyl-and syringyl lignins between gymnosperms and angiosperms have been elucidated by tracer experiments using 14C labeled precursors and the following enzyme reactions. The formation of guaiacyl lignin but not syringyl lignin in gymnosperms was attributed to the following factors; absence of ferulate-5-hydroxylase, poor affinity of O-methyltransferase toward 5-hydroxyferulate, and lack of activation and/or reduction of sinapatc. A mechanism of lignin-carbohydrate complexes formation in wood cell walls was elucidated based on the reaction of the quinone methide of guaiacylglycerol-β-guaiacyl ether with sugars, and the analysis of DHP-polysaccharide complexes. The main cleavage mechanisms of side chains and aromatic rings of lignin model compounds and synthetic lignin (DHP) by white-rot fungi and their enzymes, lignin peroxidase and laccase have been elucidated using 2H, 13C and 18O-labeled lignin substructure dimcrs with 18O2 and H2 18O. Side chains and aromatic rings of these substrates were cleaved via aryl cation radical and phenoxy radical intermediates, in reaction mediated only by lignin peroxidase/H2O2 and laccase/O2.

Biotechnology in the pulp and paper industry

Abstract: Biotechnology implies the technical exploitation of biological processes. One of nature's most important biological processes is the degradation of wood and other lignocellulosic materials to carbon dioxide, water, and humic substances. Consequently, there should be possibilities to apply biotechnology to wood conversion. This article summarizes briefly the knowledge relating to the enzymic degradation of cellulose, hemicelluloses, and lignin. However, it is mainly focused upon biotechnological processes in commercial use or in various stages of development for the pulp and paper industry. Areas covered are ethanol and protein production, water purification, development of new bleaching techniques, microbial delignification (biopulping), and development of “biosensors” for analysis of pulp fiber surfaces.

A new technique to classify the compatibility of wood with cement

Abstract: Wood-cement panels have commanded renewed interest during the last decade because of their potential application in the building industry. Several methods to classify wood of various species regarding its compatibility with cement have been established in the literature based on hydration measurements in Dewar flasks. These ranking methods lack consistency in the classification of species because the hydration conditions vary among laboratories. Three techniques for evaluating wood-cement compatibility were established and compared. The best technique is based on a wood-cement compatibility factor which is the ratio of the area under the wood-cement hydration heat rate curve to that of neat cement. The area is calculated on 24-h basis starting from the initial cement set time. This area ratio method ranks species over a 100% scale and accounts well for species that are totally incompatible.

Condensation of lignin during heating of wood

Abstract: The structural change of lignin during heating of wood was investigated quantitatively by a method combining nucleus exchange and nitrobenzene oxidation. Lignin modification during heating was mainly a diphenylmethane type condensation. About 40 and 75% of noncondensed units in protolignins were converted to diphenylmethane type units by heating of dry and wet wood meals up to 220 °C, respectively. On the other hand, during heating of modified lignin (dioxane lignin) various types of modifications in addition to diphenylmethane type condensation occurred. Lignin modification via the diphenylmethane type condensation was proposed as a new route for its utilization.

Effect of pre-steaming on drying rate, wood anatomy and shrinkage of regrowth Eucalyptus pilularis Sm.

Abstract: The influence of pre-steaming on the drying rate, wood anatomy and shrinkage of regrowth Eucalyptus pilularis (blackbutt) was determined. Pre-steaming increased the drying rate by 7–16%. This resulted from a mobilisation and partial removal of heartwood extractives, probably allowing greater access of water molecules to cell walls, and therefore increased radial and tangential diffusion. Longitudinal permeability is unlikely to be significantly increased by pre-steaming, as tyloses appeared unaltered. Volumetric shrinkage was unchanged.

Growth stress patterns in tree stems. A model assuming evolution with the tree age of maturation strains

Abstract: Growth stresses originate in maturation strains, induced in cambial layers during the differentiation and the maturation of new cells, impeded by the mass of the whole trunk. To predict stresses in a stem, one must add successive incremental stresses at successively created points of the growing trunk. Usual measurements of released strains at the surface of a stem do not give the evolution of maturation strains with growth. As the assumption that states that maturation strains are constant since the beginning of secondary growth leads to singularities near the pith, an empiric pattern of variation of maturation strains along the radius is proposed, using observations about relationships between released longitudinal strain and microfibril angle. Furthermore, assuming an elastic, orthotropic behavior law and a cylindrical, sufficiently long stem, residual stresses are computed and discussed.

Influence of rotatory inertia, shear deformation and support condition on natural frequencies of wooden beams

Abstract: The degree of influence of rotatory inertia and shear deformation on natural frequency determinations is discussed. It is found that for material such as wood, which has a relatively high ratio of bending modulus to shear modulus, these effects need to be taken into account even for supposedly ‘slender’ beams. The discussion covers the four most common types of support condition, namely simply supported, free-free, clamped-free and clamped-clamped ends. As a perfectly rigid clamped condition can never be achieved in practice, especially for relatively ‘soft’ material like wood, consideration is extended to also include partially-clamped beams.

Increase in the content of nitrogenous compounds at lumber surfaces during drying and possible biological effects

Abstract: Nitrogen contents have been determined at different depths from the surface of dried pine (Pinus sylvestris) and spruce (Picea abies) lumber. The effects of factors such as time of felling, storage of the timber, and drying process for the lumber, have been studied. Part of the selected lumber was characterized by surfaces which were yellowish after drying. At such surfaces, to a depth of about 2 mm, a high accumulation of nitrogen was always found. Yellowing is enhanced in lumber from wet-stored timber but also occurs in other lumber. Some possible contributive factors are suggested. More research in this field is proposed. The nitrogen gradients in outer sapwood without a yellow surface and in inner sapwood and in heartwood were much weaker. The effect which enrichment of nitrogenous compounds at surfaces may have on timber with regard to its disposition towards moulding is discussed. Although attention is drawn to the fact that strong nutrient gradients may occur, it must be emphasised that in most lumber nutrient gradients are weak and probably without practical consequence for its susceptibility towards fungal attack.

Structural variability of vascular bundles and cell wall in rattan stem

Abstract: Anatomical investigations on six species ofCalamus demonstrate that fibre wall thickness and fibre percentage within the vascular bundles vary more than the vascular bundle size and number per unit area. Both fibre wall thickness and fibre percentage decrease consistently from the basal (order) to the top (younger) internodes of the stem and from the periphery to the centre at a given internode. The increase of wall thickness with age is more pronounced in fibres than in cortical and ground parenchyma. The thickening of the fibre wall with increasing stem density results from the deposition of additional lamellae. This appears to impart stiffness and determines the breaking behaviour of rattan both within the stem and among the species. The fracture mode of the fibres depends on the fibrillar orientation, which differs between broad and narrow lamellae.

Creep in chipboard

Abstract: 4- and 5-parameter rheological models were used to pedict deflections at from 7 to 10 years from 24 weeks data. Comparison with actual deflection confirmed the unsuitability of the 4-parameter model as a predictive tool, while the range in prediction errors over 20 specimens for the 5-parameter model was +23% to -26%. The standard error, though not the mean prediction error was reduced by approximately one half by extending the data accumulation period to 39 weeks. Thus the 95% confidence limits in predicting deflections at 2,555 days (7 years) from 39 weeks data was +13% to -20% for all data, and +6% to -19% for data at 20 °C, 65% r.h.

Mineralization of the methoxyl carbon of isolated lignin by brown-rot fungi under solid substrate conditions.

Abstract: The objectives of this work were to begin developing an experimental system for studying the demethylation of lignin by brown-rot fungi and to examine the influence of selected culture parameters. As substrate for demethylation, we used partially 3-O-demethylated lignin that had been isolated earlier from brown-rotted spruce wood; we remethylated with14CH3I, giving a lignin with both [3-14C]methoxyl and [4-14C]methoxyl groups. This lignin was added to pine wood flakes, which were incubated with selected brown-rot fungi, and the evolved14CO2 was trapped and measured. Of eight fungi examined,Gloeophyllum trabeum andWolfiporia cocos gave the highest rates of mineralization of the14C-methoxyl carbons. With the former but not the latter fungus, methoxyl mineralization was over twice as fast in an atmosphere of O2 than in air. Amending the cultures with ammonium tartrate suppressed mineralization to some extent. Further studies withG. trabeum showed that glutamate lowered the rate of mineralization and that glucose and glycerol sharply suppressed it. Addition of Fe2+ and Mn2+ slightly increased the rate of mineralization. Our results suggest that in unsupplemented cultures the rate-limiting step in methoxyl mineralization is the initial demethylation. Thus the two likely initial C1 products, methanol and formaldehyde (as14C compounds), were mineralized much more rapidly than the methoxyl carbon of the lignin (as was formic acid), and no low molecular weight labeled intermediates from the [14C]-methoxyl lignin accumulated in the cultures. Our results also provide evidence that the spruce lignin was partially polymerized byG. trabeum. Mineralization of the methoxyl carbon of a synthetic [3-14C]-methoxyl lignin was slower than that of the spruce lignin, suggesting either that the synthetic lignin was more recalcitrant or that the [4-14C]methoxyl group in the [3,4-14C]-methoxyl spruce lignin was attacked more readily.

FGRG: Fibreglass reinforced gluelam — A new composite

Abstract: Beams of a composite made from wood and fibreglass layers glued with a phenolic adhesive were tested in three point bending. Experimental results indicate an increase in mechanical properties in comparison with equivalent beams without fibreglass. An interesting modification is obtained in the mode of fracture. Values of the modulus of elasticity for the adhesive, fibreglass and wood were obtained in separate loading tests and used to derive the modulus of the composite using a general relationship for layered systems. Good agreement was found between theoretical and experimental values of modulus.

Relationship between wood colour, silvicultural treatment and rate of growth in Eucalyptus grandis Hill (Maiden)

Abstract: Wood of 9.5 year old plantation grown Eucalyptus grandis Hill (Maiden) was removed at stump-height (10–25 cm above ground level) from two groups of trees — one receiving no silvicultural treatment, the other being ploughed, thinned and treated with fertilizer, weeding and insecticide. Silviculturally treated samples had higher u1 and v1 chromaticity coordinates and a lower total reflectance (i.e. colour was redder, more saturated and darker). Although perceivable mean colour differences occurred between outer and inner heartwood, chromaticity coordinates and total reflectance were not significantly different. In the outer heartwood a redder, more saturated wood colour was produced in trees having faster growth rates.

Vibration control of band saws: theory and experiment.

Abstract: Active vibration control is a key to the improvement of the cutting performance and productivity of band saws. In this paper a new method is presented for active control of band saw vibration. The transfer function of a closed-loop system consisting of the band saw, a feedback control law and the dynamics of the sensing and force actuation devices is derived. Analysis of the root loci of the closed-loop system gives two stability criteria. Stabilizing controller design is carried out for both collocation and dislocation of the sensors and actuators. It is found that vibration in all the modes can be damped through use of only one sensor and one actuator and that the control algorithms presented are realizable in practice. The theory presented is experimentally verified.

Pretreatment of poplar by acid and alkali for enzymatic hydrolysis

Abstract: The dilute acid pretreatment in a plug flow reactor and alkali pretreatments with caustic solutions at different conditions followed by enzymatic hydrolysis resulted in drastically improved glucose yields for aspen and hybrid poplar. The acid pretreatment conditions must be carefully chosen to open the cellulosic structure allowing rapid diffusion of enzyme. The effectiveness of pretreatment is chiefly based on the enlargement of the pore size suitable for enzyme molecules.

Effect of brief presteaming on shrinkage, collapse and other wood-water relationships in Eucalyptus regnans F. Muell.

Abstract: Brief presteaming of green, increment-core segments of mountain ash (E. regnans F. Muell) produced small but significant changes in a number of moisture-shrinkage parameters. Both total volumetric shrinkage and recoverable collapse were significantly greater in presteamed samples, the increase in collapse being largely attributable to an increase in moisture content after reconditioning (Mr). The change in shrinkage after reconditioning also was significantly related to changes in Mr. The change in Mr was interpreted as reflecting altered permeability in presteamed material and was shown to be negatively related to estimated residual collapse. Initial moisture content and per cent saturation showed a highly significant decrease after presteaming, while green volume showed a small but significant increase. Neither the estimated intersection point, unit shrinkage nor the R-ratio were significantly different after presteaming. However, the unit shrinkage-specific gravity relationship was changed by presteaming such that it more closely complied with Stamm's approximation.

Characterization of depolymerized cellulosic residues - Part 2: Residues derived from ethylene glycol solvolysis of cellulose

Abstract: On caracterise les residus cellulosiques obtenus par depolymerisation solvolytique en continu ou en discontinu, a l'aide d'ethyleneglycol comme solvant

Production of particleboard with steam-injection. Part 2: Computer simulation of temperature behaviour in particle mat during hotpressing and steam-injection pressing.

Abstract: On a analyse la distribution des temperatures dans les mats de particules lors du pressage a l'aide de la methode des elements finis. Les resultats calcules sont en bon accord avec les resultats experimentaux aussi bien pour le pressage chaud que pour le pressage avec injection de vapeur. On presente les courbes montrant l'influence de la temperature de pressage, de la pression de vapeur et de l'epaisseur du mat sur la temperature au cœur du panneau

Acoustic emission patterns from the surfaces of red oak wafers under transverse bending stress

Abstract: One of the applications of acoustic emission (AE) technology in the forest products field is likely to be in monitoring and/or controlling the drying of wood. This report describes experiments designed to monitor the acoustic emission patterns from the lower surfaces of small red oak test beams which were undergoing failure in tension perpendicular to the grain. Similar patterns are likely to develop in wood which surface checks during drying. When the wood was green, the emission patterns from beams under test were well defined and could be used to predict the onset of cracking before the surfaces under tension were visibly cracked. These patterns were quite similar to the acoustic response of brittle, glassy polymers under stress. Additional experiments on partially dried test beams showed that the clearly predictable emission patterns disappeared and the general level of acoustic emissions increased. This increase in emissions may correspond to shrinkage, at the cell level, of the partially dried beams.

Effect of moisture and mechanical loading on wooden materials

Abstract: In a previous paper (Martensson 1988 a), results of tests performed on hardboard in tension under cyclic humidity were presented and comparison with a suggested constitutive model was made. This paper presents the result of further work that has been carried out concerning modelling of the behaviour of tempered hardboard subjected to moisture loading combined with mechanical loading. Tests were made both in compression and bending. The tests in compression were of two types, conventional creep tests during moisture cycling and quasi-relaxation tests during moisture cycling. The model was quantified on the basis of the previous tension tests and the compression tests, in both cases creep tests, and was then checked independently against the other types of test. Interaction between moisture change and mechanical loading was found to be significant during the first moisture cycle but much smaller during subsequent cycles. Experimental and numerical analysis of composite structural elements was also performed, showing that internal stresses of significant magnitude are developed as a result of variations in moisture. Such stresses can be predicted with reasonable accuracy using the proposed model. This can be of great value in design and development of wood products and wooden structural elements. (Less)

Sticker stain formation in hardwoods: Isolation of scopoletin from sugar maple ( Acer saccharum Marsh.)

Abstract: The extractives of clear and sticker stained sapwood from sugar maple (Acer saccharum Marsh.) were isolated and screened for low molecular-weight phenols, which could be involved in the formation of sticker stain. Scopoletin (7-hydroxy-6-methoxycoumarin) was identified as the major low molecular-weight free phenol in the samples studied. This compound, which has not previously been reported in extractives from maple wood, was quantified in stained and clear samples. Additionally, the two major fatty acids present were identified as palmitic acid and linolenic acid, and the two major sterols as stigmasterol and sitosterol.

Effect of pre-steaming on moisture gradients, dryinag stresses and sets, and face checking in regrowth Eucalyptus pilularis Sm.

Abstract: The effect of pre-steaming on moisture gradients, drying stresses and sets, and face checking was determined for Eucalyptus pilularis Sm. The effect of reconditioning on drying stresses and sets was also observed. Pre-steaming reduced moisture gradients from centre to surface by 12.2 percentage units during the first eight days drying, and by 5.2 percentage units over the full duration of the run. Face checking occurred during presteaming, but total length of checks at the end of drying was only 53% that of unsteamed boards. The decrease in moisture gradients and face checking implied that stress and set gradients were also reduced, although this could not be statistically confirmed. Reconditioning relieved drying stresses and sets.

Vessel length distribution in the stems of three New Zealand species of Nothofagus

Abstract: A modification of the Zimmermann and Jeje (1981) latex paint infusion technique was utilized to determine vessel length distributions in N. fusca (Hook.f.) Oerst., N. menziesii (Hook.f.) Oerst. and N. solandri var. cliffortioides (Hock.f.) Poole. In all thirty trees examined, the majority of vessels were less than 2 cm long; with 97% of the vessels shorter than 6 cm in N. menziesii and N. solandri, with the same percentage being shorter than 8 cm in N. fusca. The longest individual vessels recorded were 24 cm for N. menziesii, 22 cm for N. solandri and 33 cm for N. fusca. The longest vessels in all three species occurred in the earlywood and also exhibited the largest diameters.

Determination of cations and anions in the ashes of some medicinally used tropical woods

Abstract: The ashes of some medicinally used tropical woods were characterised. These were Afzelia africana, Alstonia congensis, Antiaris africana, Terminalia ivorensis, Azadirachta indica, Ricinodendron heudelotti, Chlorophora excelsa and Daniellia ogea. The ashes were obtained by treating wood in a muffle furnace, after which the ashes dissolved in distilled water. The very alkaline solutions obtained were analysed for Na+, K+, Ca2+, Mg2+, Mn2+, Fe2+, Cu2+, Cl-, SO 4 2- and PO 4 3- . Due to wide medicinal application of these wood species experiments were made to determine the cations and anions which may be active ingredients in the compounds (drugs) used in the treatment of differet ailments.

HTST hydrolysis of wood: modelling of the kinetics and projections on reactor configuration.

Abstract: We present experimental data on hydrolysis of wood in high temperature short residence time (HTST) and low acid concentration conditions. Effects of temperature, acid concentration, particle size and liquid/solid ratio are discussed. A kinetic model is proposed which accounts for effects of temperature and acid concentration. This kinetic model is used to predict performance of a twin-screw extruder as a hydrolyser which consists of ideal mixed flow or plug flow reactor units in series.

Effects of atropellis canker and stalactiform blister rust on the bending strength and stiffness of lodgepole pine lumber

Abstract: This study investigated the effect of Atropellis canker,Atropellis piniphila (Weir) Lohman and Cash, and stalactiform blister rust,Cronartium coleosporioides Arth., on the bending strength and stiffness of lumber from lodgepole pine,Pinus contorta Dougl. var.latifolia Engelm. The modulus of rupture, was unaffected by either disease. However, the modulus of elasticity (MOE) of lumber from infected trees, as determined by the Cook Bolinders and static bending tests, was significantly reduced from those of healthy trees. This impact should affect the use of lumber from infected trees when serviceability criteria govern the design of a structure. Should MOE-based, machine stress-rating of lumber become standard in the future, there may be an adverse, stress-related impact of these diseases on lumber value.

Wood science improves the quality of life

Abstract: Quality of life for most citizens of industrialized countries (ICs) means an abundance of consumer goods and enjoyment of culture; for the underprivileged citizen of a developing country (DC) it means food, shelter and health care for immediate survival. Development aid to help the latter has become big business and much care is required to ensure that assistance really reaches the deserving recipients. Wood science in contributing to the wise utilization of the forest can help both. The urban and rural poor of DCs may benefit through improved access to affordable and salubrious wooden homes, furniture and other utensils, combined with sound forest management to maintain their ecological environment. Well-to-do members of ICs provide the stimulus and market support for research leading to innovations. They will reap the reward of living in homes and public buildings made of and furnished with a natural material, wood, which will acquire increasing emotional value in the coming crowded centuries. Wood, if it can meet the challenge of providing competitive goods of acceptable quality, is well placed to become a preferred material. In this sense, wood science is capable of enhancing the quality of life of many members of the human family.

Corrosive properties of “stringybark” eucalypts

Abstract: While assessing the corrosive properties of some eucalypts, it has been observed that timbers belonging to the “stringybark” group appear to be more corrosive than others. Research has been carried out therefore on the main stringybark species and major commercial brands of steel which are used for the manufacture of bandsaw blades. This study demonstrated that stringybark wood is considerably more corrosive than expected. The average corrosiveness of stringybarks is shown to be some 126% greater than that of other eucalypts. Such high corrosiveness is detrimental in woodworking, papermaking and building industries and can generally create serious problems in many wood-metal situations.

Dynamic behavior of nonuniform lumber in stress-grading machines

Abstract: A finite element model is developed to predict the dynamic behavior of nonuniform lumber in stress-grading machines of the constant deflection type. Simulations carried out with the model showed that speed largely effects the accuracy with which grading machines can identify low-point modulus of elasticity (E) oflumber. Tests conducted at 15 and 315 m/min on lumber members containing a low E zone confirmed model predictions. However, as demonstrated in this study, machine ability to detect low-point E at high speed can greatly be improved from filtering the load signal measured by the machine.