This study involved the on-site evaluation of commonly employed equipment and procedures for evaluation of moisture content in solid-wood products. Specifically, a DC-resistance and two RF-based moisture meters were evaluated. The main overall objective was to identify procedures or develop information to allow more accurate final MC estimates to be determined. Lodgepole pine lumber of 25 and 40 mm thicknesses was employed for the test Material was tested at three time intervals spanning from the completion of drying to approximately 30 hours after drying. Meter readings were compared against oven-dry moisture contents. In most situations the moisture meters employed tended to underestimate final moisture content with the error varying from close to zero up to about 3 percent. The errors observed seemed to be consistent for a given test. This opens the possibility of employing site-specific correction factors to obtain better estimates of oven-dry moisture content. Problems may still arise when comparing mill results of moisture tests against those performed elsewhere by customers and end users.
Les facteurs clé à la source du gauchissement des panneaux ont été identifiés suite à une revue de littérature exhaustive. Les méthodes pour mesurer ces variables ont été soit identifiées dans la littérature soit mises au point au laboratoire de l'Est de Forintek. les méthodes de laboratoire incluent la mesure du gauchissement ainsi que celle des gradients des propriétés suivantes : densité; module d'élasticité; dilatation linéaire; teneur en humidité. Des gauchissements ont été induits en laboratoire sur des panneaux de diverses configurations et ces variables ont été mesurées. Les expériences ont permis de construire une base de données sur le comportement ds panneaux agglomérés en fonction des variations de conditions ambiantes. La base de données a ensuite été utilisée pour vérifier la comformité des phénomènes observés avec les meilleurs modèles de prédictions disponibles.
Surface deactivation of wood strands due to drying at elevated temperatures was evaluated by different techniques. The ability of resin to spread over the strands was estimated by measuring the contact angle between the resin droplet and the strand surface. Contact angles were measured by the Wilhelmy tensiometry balance and by the Sessile drop goniometer methods. Electron spectroscopy for chemical analysis (ESCA) was also used to follow chemical changes of the strand surface in terms of carbon and oxygen content and in terms of oxygen to carbon (o/c) atomic ratio as a function of the drying conditions. Three series of strands were used in this study: multiple-pass dried strands, conveyor-dried strands, and lab-made strands. The first two series of strands were industrially produced ready and dried for panel production. Drying schedules varied from freeze-drying to temperatures of 200°C. Wilhelmy advancing contact angles (2a) as measured on the mill dried strands increased with the increase of post drying temperature while the receding angle (2r) decreased with the first series of strands but increased with the second series. ESCA analysis of these same samples showed a transportation and deposition of extractives from the inner layers to the outer surface of strands. Surface oxidation due to the high temperature drying conditions could also contribute to this surface chemical composition variation.
Sessile drop results from the lab-made strands showed excellent correlation with resin viscosity, contact angles for any wood type increased in the order of the resin viscosity i.e. PF face (110 cP)< PF core (170 cP)< UF (320 cP). Contact angles also increased in the following order for any given resin: southern yellow pine
L’objectif général du projet était de développer un modèle tridimensionnel de séchage permettant de prédire l’évolution des profils de teneur en humidité, de température, de contraintes et de déformations dans le bois pour des conditions industrielles de séchage. Un tel outil fournirait l'information de base nécessaire à la rédaction de programmes de séchage optimisés, au développement de systèmes de régulation plus performants et servirait à définir des stratégies de séchage mieux adaptées aux installations de séchage en place et aux propriétés changeantes de la matière première.
Une équipe de quatre professeurs de l’Université Laval et d’un collaborateur industriel de Forintek était responsable de la réalisation de ce projet. Le projet fut divisé en trois volets. Dans un premier temps, l’équipe a procédé à la mesure des propriétés viscoélastiques du bois d’épinette en direction longitudinale dans des conditions représentatives du séchage à moyenne température. Le développement d'un modèle mathématique de prédiction des champs de déformation ou de contraintes dans le bois au cours du séchage exige la connaissance de l'évolution des propriétés viscoélastiques du bois dans des conditions hygro-thermiques représentatives du séchage.
Dans un second temps, l’équipe de recherche a consolidé le modèle 2-D existant de transfert de masse et de chaleur (basé sur le concept du potentiel hydrique) et développé un modèle 3-D en C++ prenant en compte les caractéristiques anatomiques et physiques du bois. Ainsi, les lois de conservation de mouvement furent ajoutées au modèle de base et la conductivité hydrique effective fut déterminée sous vide afin de simuler l’évolution des profils de teneur en humidité, de température et de pression en cours de séchage sous vide. Le modèle fut également appliqué au phénomène de mouvement cyclique de l’humidité dans les enveloppes de bâtiment. Cette application a permis de vérifier la performance du modèle face à l’étape du conditionnement en cours de séchage. De plus, un travail important de modélisation fut effectué afin de rendre le modèle tridimensionnel et sensible aux caractéristiques du bois telles l’orientation et le rayon de courbure des cernes, la proportion duramen/aubier et la présence de bois juvénile. Finalement, un prototype d’interface du modèle bidimensionnel de transfert de masse et de chaleur fut développé par Forintek.
Dans le cadre du troisième volet du projet, l’équipe a travaillé au développement d’un modèle numérique pour la simulation du comportement viscoélastique du béton, modèle qui devra servir de cadre au développement d’un nouveau modèle de comportement mécanique pour le bois. Ce travail a fait appel à une étroite collaboration des chercheurs du département de génie civil de l’Université Laval.
Ce projet a contribué à la formation de cinq étudiants. Cinq articles scientifiques ont été rédigés et publiés ou soumis à des revues scientifiques avec comité de lecture. Le projet a aussi conduit à la présentation de six communications et deux affiches techniques. Deux nouveaux projets ont été présentés au Comité Consultatif Technique de janvier 2000 afin d’assurer la poursuite du développement du modèle de séchage.
The aim of this project was to assess the impact of Moisture Content (MC) on the performance of black spruce fingerjointing for structural applications. Joint performance was assessed using phenol-resorcinol type adhesive with black spruce blocks of the same MC, at various MC levels, and with blocs of different MC. Black spruce blocks were face-glued at four different moisture contents (8, 12, 16, 20%) and tested in shear parallel to grain to evaluate the performance of the adhesive bond. A phenol-resorcinol adhesive curing at room temperature was used. To complement the study, mill data on quality control tensile test was observed to confirm the laboratory findings on the impact of wood moisture content on the process performance.
Although, a trend was observed in joint performance with a peak at 13,5% MC on the shear MOR, no statistically significant differences were observed between MC levels in the range of 8 to 20% on the joint performance of phenol-resorcinol glued black spruce. The bond performance appeared to be more variable though with green wood (20%). Marginal differences were found on shear strength with four groups of MC differential (0%,4%, 8% and 12%).
The work described in this report involved examination of the development of IB strength in OSB panels as a function of pressing parameters and mat moisture content. Response surface methodology (RSM) was used in the design the experimental work employing a Box-Behnken design with four (4) variables (platen temperature, pressing time, moisture content (MC) of the face layers of the mat and face/core ratio).
Results showed that the relationships between the study parameters and IB strength fit very well the form of quadratic polynomials. Within the limits studied, it was found that increasing the pressing time and/or temperature could significantly improve the IB strength in OSB panels. Also, the study showed that bonding strength is improved by reducing mat moisture content.
It recommended that the study proceed as planned, using a thermal analysis technique (DSC) to compare the chemical reactions and curing behaviour of some commercial PF resins. Also, lap-shear tests, will be employed to evaluate strength development of the adhesives as function of time, temperature and furnish moisture content. It also recommended that a bench-making will be proceeded at laboratory and mill scale to verify the model.
Forintek a effectué un essai de séchage d’aubier d’érable à sucre afin d’évaluer la performance de différents modèles de baguettes en ce qui a trait à l’élimination des taches de baguettes. Au total, sept modèles de baguettes constituées de bois, de plastique (UHMW) et d’un matériau composite bois-plastique furent testés. Les résultats ont démontré que le matériau constituant la baguette n’a aucune influence sur la formation des taches de baguettes au cours du séchage de l’aubier d’érable à sucre.
In North America studs made from short lengths of lumber connected by finger-jointing have gained popularity due to their superior straightness compared to solid wood studs. To evaluate performance in exterior applications, Forintek installed an above-ground field test of CCA-treated and untreated 2x4 spruce-pine-fir finger-jointed studs in 1980. After twenty years of exposure, the CCA-treated material was free from decay, compared to severe decay in untreated samples.
Le but de ce manuel est de présenter l’opération du séchage du bois en liant les phénomènes physiques qui y prennent place avec les éléments de commande du séchoir c’est-à-dire la température et l’humidité de l’air. Par l’utilisation de l’ensemble des équations contenues dans ce manuel, il sera possible à l’ingénieur et à l’opérateur d’estimer l’importance des phénomènes présents lors du séchage et cela à l’aide d’une calculatrice ou du chiffrier Excel que nous avons inclus.
The objective of this manual is to provide a representation of the drying operation, linking the physical processes taking place during drying and the kiln control parameters, i.e. air temperature and humidity. By using sets of equations shown in the manual, engineers and kiln operators will be able to assess the significance of events occurring during the drying process with a calculator or a simple Excel spreadsheet (included).
A reliable tool for detecting UF or MUF resin distribution in MDF fiber is essential to the study of blowline dynamics and the development of the next generation of MDF blending. Two fluorescent dyes Uvitex and fluorescein were studied as UF and MUF labeling agents. It was found in the experiments that fibers with MUF resin (containing 10% melamine) at 5% and 15% add-on levels gave results that were promising. Resin distribution patterns were easily detected and distinguishable under UV light. In contrast to MUF resin, it was found that UF resin with Uvitex or fluorescein produced no clear fluorescent images. It appeared that the fluorescent dyes did not stay completely with the resin droplets and spread everywhere in the fiber. It can be concluded that Uvitex and fluorescein are not suitable as labeling agents for UF resin distribution.
In the case of MUF resins, quantitative evaluation has not been completed although indication from the preliminary work was positive.
The Automated Bond Evaluation System (ABES) is an invaluable tool in evaluating the bonding characteristics of adhesives. The system uses minimal amounts of adhesive and wood while avoiding the difficulties associated with density variations in OSB panels manufactured in the laboratory. Since the quality and uniformity of the wood substrate can be controlled by careful selection the key factor in comparing adhesive performance is the moisture content of the wood strands used in the test. This study examines the uniformity of moisture content of strands exposed to selected conditions in environmental chambers.
Aspen strands of 0.69 mm (27 thousandths of an inch) absorb or give off moisture fairly readily and equilibrium conditions are generally established in 4 hours or less. The equilibrium moisture content of aspen strands approximates that of solid wood but is not identical to that predicted by the Wood Handbook tables. Aspen strands are more susceptible to moisture content fluctuations than solid wood and strand moisture content should be confirmed prior to use in the ABES equipment.
The Automated Bond Evaluation System (ABES) is an invaluable tool in evaluating the bonding characteristics of adhesives. The system uses minimal amounts of adhesive and wood while avoiding the difficulties associated with density variations in OSB panels manufactured in the laboratory. The quality and uniformity of the wood substrate can be carefully controlled and the optimum bond between two strands is determined. It is thus possible to evaluate the effect of particle size and resin distribution for different adhesive samples and the performance of an adhesive under very controlled conditions. GluScan is a computer imaging system, developed by Forintek Canada Corp. for evaluating resin distribution on OSB strands.
This study employed the GluScan system to evaluate the particle sizes of commercial powdered phenol formaldehyde OSB adhesive and the ABES system to evaluate the curing conditions required for the resin.
Waferboard/oriented strandboard (OSB) has been traditionally manufactured almost exclusively with trembling aspen in Canada. With the declining availability of aspen wood resource, OSB mills have begun to use alternative species in their production, usually other hardwood species. Meanwhile the mills have also begun experiencing some constraints in the use of phenol-formaldehyde (PF) resins for bonding these species, such as poor resin distribution and low retention on the surfaces of strands, particularly for a powdered form. The change of binder systems for bonding dense hardwoods can be extremely costly to OSB producers. The objective of this study is to determine the optimum adhesive and process requirements for manufacturing OSB from high-density hardwood furnish.
Study in 1997-1999 has shown that a dense wood is more difficult to bind than a less dense wood with a powder phenolic resin due to the poor resin distribution and retention. A liquid resin appears to produce stronger panels compared to a powder resin. The powder resin blending and bonding efficiency could be apparently improved by different resin application methods: (1) enhancing the wax distribution; (2) separately applying wax and resin to individual species strands and then mixing them up; (3) spraying a small amount of liquid additives after resin application; and (4) finally using small particle-size powders. A series of strandboards were constructed with aspen, birch, southern yellow pine, and sweetgum, using powder PF resins in the face and powder PF, liquid PF or diphenylmethane diisocyanate (MDI) in the core. An overall comparison showed that the aspen panels performed best followed by the southern yellow pine panel while the birch and sweetgum panels performed similarly with regard to both physical and mechanical properties.
Work in 1999-2000 focused on some fundamental studies on wood chemical and physical properties. Seven wood species were characterised for pH, base and buffering capacities, bound and soluble acids, and water and ethanol-toluene solubility. The wood species included aspen, white birch, yellow birch, red maple, sugar maple, southern yellow pine, and sweetgum. The study was also extended to the mixed wood species, included white/yellow birch, aspen/birch, southern yellow pine/sweetgum, aspen/red maple, aspen/sugar maple, and aspen/red maple/birch. This work indicated that there were significant differences in the chemical characteristics between the species investigated. These wood species were also characterised for surface roughness using a surface roughness tester. It was found that aspen strands showed significantly rougher surfaces than did southern yellow pine, sweetgum, and sugar maple. Strand surface characteristics seem to be related to the wood anatomical structure. A species (like aspen) having low density appears to yield a rougher surface than does one having high density (like sweetgum).
In the coming year, the efforts will focus on characterisation of wood/resin interaction, modification of phenolic resin, and optimization of panel manufacturing process parameters in order to more efficiently utilise various high-density hardwood furnishes for OSB production based on the information obtained in the previous studies of this project. The detailed information on project plan and milestone is illustrated in Appendixes 1 and 2.
Part 1 : Plywood press emissions as a function of panel processing parameters were evaluated by means of a laboratory caul plate press stack collection system. Panel pressing temperatures were 140, 150 and 160°C and pressing times 7, 9 and 11 minutes. Glue spreads in terms of resin solids were 0.033, 0.040 and 0.046 lbs/ft² (161.46, 193.75, 226.04 g/m², respectively). Response surface methodology (RSM) with the Box and Behnken design was used to define the minimum number of experimental points needed to fully represent a quadratic regression model. A total of 15 experimental points and 3 extra centre points was determined leading to an incomplete 33 factorial design. Results indicated that plywood press emissions are affected by processing parameters in different ways depending on the type of the volatile organic compound of interest. The quadratic RSM models in terms of the coded factors showed that formaldehyde emissions were more sensitive to pressing time while methanol and total volatile organic chemical (TVOC) emissions were more sensitive to resin content. However, an increase in any processing parameter resulted in an overall increase in press emissions. On the other hand, the amounts of formaldehyde and TVOC emitted from the resulting plywood panels were more sensitive to resin solids content than to pressing temperature or time, showing decreases with increasing resin contents. The use of an optimization procedure based on the geometric mean of each response desirability function allowed multiple solutions with minimum press emission levels with a desirability value of up to 0.97 when the imposed limits during the optimization procedure were less stringent. The ideal desirability value is 1.0.
Part 2 : A laboratory method was developed to evaluate the effects of key wood particleboard processing parameters on hot-press emissions of volatile organic compounds (VOCs). The method was based on an enclosed caul plate system that trapped the gas stream containing the VOCs emitted during board pressing. The hot gases trapped in the caul plate were cleaned through cold traps containing distilled water or organic solvent for non-water-soluble chemicals, in order to condense and trap VOCs from the air stream. Formaldehyde was quantified by the chromotropic acid method (NIOSH* modified method), while methanol and phenol were quantified by gas chromatography/flame ionisation detection (GC/FID. Other VOCs were characterised and quantified by gas chromatography/mass spectroscopy (GC/MS). Formaldehyde emissions as well as methanol, phenol and total volatile organic compound (TVOC) emissions, which consisted mainly of terpenes, increased with platen temperature, pressing time and mat resin solids content conversely, subsequent emissions from the panels themselves decreased. Inversely, panels produced showed decreasing emission levels when processing parameters such as resin content, pressing time and pressing temperature were increased. Furnish composition significantly affected press emissions in terms of both nature and amount of chemicals emitted. The surface moisture content of the mat also seems to increase press emissions but further work needs to be conducted to support this observation. This includes works on the response surface methodology in the study of plywood press emissions of volatile organic compounds; Press volatile organic compound emissions as a function of wood particleboard processing parameters
This project was started on April 1, 1999 following recommendations at the fall 1998 Structural Board Association (SBA) Technical Committee meeting in Banff, Alberta to quantify the benefits of the GluScan resin distribution analyzer for measuring resin distribution in OSB.
Resin distribution refers to how resin is dispersed on strand surfaces after the blending process. The main attributes of distribution include resin coverage and resin spot size which both can change due to blending variables. To date, it has been unclear whether or not resin distribution is sufficiently important to require monitoring by the OSB industry. To answer this question, experiments have been designed in this project to quantify how selected panel properties including Internal Bond, Modulus of Rupture, Modulus of Elasticity and Thickness Swell are affected by different resin distributions from batches blended at the Alberta Research Council (ARC). The resin distributions studied in this project were intended to simulate actual mill conditions and were measured by optically scanning strand surfaces using an image analysis system (GluScan) developed by Forintek Canada Corp.
Finally, a mill case study was carried out to determine whether the laboratory results together with GluScan could be used to measure and characterize resin distribution from a mill production line.
Laminating wood to produce clear or larger sizes is one of the easiest ways to add value to wood products. The Canadian producer is today presented with many choices in wood species, adhesives and equipment available for laminating. Success in this business environment requires that the producer have access to the skills needed to produce durable laminates with whatever wood species, adhesive or processing method requested by the customer.
Available information on properties of various Canadian wood species has usually been limited to particular species or to a specific property. The intent of this report is to fill in the information gaps on the laminating properties of Canadian wood species and, in particular, to see how these species compare to commercially prominent imports.
The eighteen Canadian species examined performed favourably in comparison to the imports while the performance of some of the species variants was not always similar. More difficulty was encountered with laminating with Phenol Resorcinol Formaldehyde (PRF) than with the other adhesives. Radio-frequency (RF) curing also showed some varied results with several species passing delamination testing but failing in the shear block wood failure criterion. Care should be taken when bonding porous woods with low viscosity adhesives.