Academic literature on the topic 'Equilibrium moisture content of wood'

An improved knowledge of wood material behavior in hot-pressing environments can provide the benefit of an increased understanding of material properties during the manufacture of wood-based composites as well as insight into the development of new processes and products which manipulate the viscoelastic nature of wood. Two specific areas where additional knowledge is needed are: the high temperature equilibrium moisture content (EMC) behavior and the moisture dependent softening behavior. EMC data was collected and desorption isotherms were generated for mature and juvenile wood of aspen, loblolly pine and yellow-poplar at 50 and 160°C. High temperature EMC behavior was found to be distinct from that at lower temperatures, and considerable differences between the isotherms for juvenile and mature wood were detected. Substantial thermal degradation was observed during desorption at 160 °C and found to be strongly influenced by relative humidity. The thermal softening behavior of wood was evaluated using dielectric thermal analysis (DETA) at moisture levels from 0 to 20 percent. Coincident in situ relaxations of hemicellulose and amorphous cellulose in the range of 20 to 200 °C were observed and found to exhibit the characteristics of a secondary (glass) transition. The moisture dependence of this transition was characterized, and differences in the observed Tg were detected between juvenile and mature wood. Time-temperature superposition was also shown to be applicable to the wood-water system.<br>Ph. D.

This paper deals with the determination of the capillary pore-size distribution (CPSD) and equilibrium moisture content (EMC) of untreated and thermally modified (TM) Norway spruce [Picea abies (L.) Karst.] by means of the pressure plate technique (PPT). Desorption experiments were conducted at very high values of relative humidity (RH) in the range between 99.2% and 100%. The thermal modification of spruce results in an alteration of the CPSD, owing to the formation of intercellular cracks in the middle lamella, as a result of cell-wall compression. The desorption curves for both untreated and TM spruce show an extremely upward bend at 99.97% RH. This step reflects an EMC of 38.1% for untreated spruce and 33.8% for TM spruce. None of the samples shrunk during the PPT measurements. Following desorption experiments at 97.4% RH, all samples shrunk. This step reflects an EMC of 27.9% for untreated spruce and 21.7% for TM spruce.

Percent Moisture Content (MC %) of wood is defined to be the weight of the moisture in the wood divided by the weight of the dry wood times 100%. Equilibrium Moisture Content (EMC), moisture content at environmental equilibrium is a very important metric affecting the performance of wood in many applications. For best performance in many applications, the goal is to maintain this value between 6% and 8%. EMC value is a function of the temperature and the relative humidity of the surrounding air of wood. It is very important to maintain this value while processing, storing or finishing the wood. This thesis develops a special purpose sensor and processor system to be implemented as a small hand-held device used to sense, calculate and display the value of EMC of wood depending on surrounding environmental conditions. Wood processing industry personnel would use the hand-held EMC calculating and display device to prevent many potential problems that can show significant affect on the performance of wood. The design of the EMC device requires the use of sensors to obtain the required inputs of temperature and relative humidity. In this thesis various market available sensors are compared and appropriate sensor is chosen for the design. The calculation of EMC requires many arithmetic operations with stringent precision requirements. Various arithmetic algorithms and systems are compared in terms of meeting required arithmetic functionality, precision requirements, and silicon implementation area and gate count, and a suitable choice is made. The resulting processor organization and design is coded in VHDL using the Xilinx ISE 6.2.03i tool set. The design is synthesized, validated via VHDL virtual prototype simulation, and implemented to a Xilinx Spartan2E FPGA for experimental hardware prototype testing and evaluation. It is tested over various ranges of temperature and relative humidity. Comparison of experimentally calculated EMC values with the theoretical values of EMC derived for corresponding temperature and relative humidity points resulted in validation of the EMC processor architecture, functional performance and arithmetic precision requirements.

Made available in DSpace on 2016-12-23T14:37:35Z (GMT). No. of bitstreams: 1 lucelio lovatti.pdf: 1248502 bytes, checksum: c196251467613db326908ba81532337a (MD5) Previous issue date: 2008-03-26<br>This research had as general objective to obtain information regarding commercialization and physical properties of the sawn wood marketed in the South area of the Esp?rito Santo State. Seventeen wood deposits were visited and collected samples, as well as applied a questionnaire for obtaining of the information. Through the anatomy of the log forty species being marketed as sawn coming mainly of the Amazonia area were identified. Regarding the collected general information, it can highlight, there are no one use of technical specifications established by entities of normalization, so much for the dimensioning of the pieces as for the quality in relation to defects and problems with the drying of the wood, which are commonly marketed green. The behavior hygroscopic in several conditions of relative humidity of the air and the relationships between retratibility and the moisture content of the wood for the main species was studied. The wood used in the study concerning of the behavior hygroscopic and of the retratibility are deriving from the trade of the area and also of the Laborat?rio de Ci?ncias da Madeira (LCM) of the Departamento de Engenharia Florestal of the Univercidade Federal do Esp?rito Santo. For the sorption curves it was observed that each species possesses own a characteristic that means a differentiated behavior among the wood in the several conditions of relative humidity of the air. In relation to the retratibility with the variation in the moisture content of the samples the shrinkages volumetric, radial and tangential not vary exponentially with the loss of water by wood.<br>A presente pesquisa teve como objetivo geral obter informa??es referentes ? comercializa??o e propriedades f?sicas das madeiras serradas comercializadas na regi?o Sul do Estado do Esp?rito Santo. Foram visitadas dezessete madeireiras e coletadas amostras, bem como aplicado um question?rio para obten??o das informa??es. Atrav?s da anatomia do lenho, foram identificadas quarenta esp?cies sendo comercializadas na forma serrada, provenientes principalmente da regi?o Amaz?nica. Referente ?s informa??es gerais coletadas, se pode destacar, o n?o uso de especifica??es t?cnicas estabelecidas por entidades normalizadoras, tanto para o dimensionamento das pe?as quanto para a qualidade em rela??o a defeitos e problemas com a secagem das madeiras, as quais s?o comumente comercializadas verdes. Para as principais esp?cies, estudou-se o comportamento higrosc?pico em diversas condi??es de umidade relativa do ar e as rela??es entre retratibilidade e o teor de umidade da madeira. As madeiras utilizadas no estudo acerca do comportamento higrosc?pico e da retratibilidade s?o provenientes do com?rcio da regi?o e tamb?m do Laborat?rio de Ci?ncia da Madeira (LCM) do Departamento de Engenharia Florestal da Universidade Federal do Esp?rito Santo. Para as curvas de sor??o, observou-se que cada esp?cie possui caracter?sticas pr?prias, o que significa um comportamento diferenciado entre as madeiras nas diversas condi??es de umidade relativa do ar. Em rela??o ? retratibilidade com a varia??o no teor de umidade das amostras, observou-se que as contra??es volum?trica, radial e tangencial, n?o variam exponencialmente com a perda de ?gua pela madeira.

This thesis deals with the temperature-moisture assessment of members in truss with above-rafter thermal insulation. Within this system it focuses on the details of creating a roof overhang because that is where the timber elements are under the greatest amount of moisture stress. Different variations of this detail are presented including the extent to which thermo-technical requirements and requirements surrounding the built-in timber elements are satisfied. Theoretical calculations are then compared with measurements which were performed on a real building. This task of measurement involved developing a new measuring device. The development of this device is also described in this paper.

This thesis deals with massive wooden buildings especially with regard to the current approach to their design, assessment and approval. In this thesis are shown future possibilities of development of traditional wooden buildings with regard to current thermal technical requirements. Theoretical considerations are then compared with measurements which were performed on massive wooden wall samples.

In the wood industry, determination of the moisture content (mc) with a highaccuracy is of great importance. The green mc is important for optimisation of thewood drying process at sawmills, whereas the mc of dried boards is of interest for thefurther processing and final use of the boards. In the first publication in this thesis,which is a technical report written in Swedish, different measuring techniques withtheir own pros and cons are discussed. A total of 13 different measurement principlesare discussed, focusing on the ability to measure mc in the range of 7-18%. The resultsuggests that mc-meters that use electromagnetic waves in the radio- and microwaveranges have the greatest potential to become the next generation mc-meters for driedboards.The second publication, which is presented in this thesis, investigates the possibilityof measuring the green sapwood mc in pine logs by combining industrial X-rayscanners and 3D-scanners. The method is shown to be suitable for identifying batchesof logs in which the sapwood has begun to dry prior to sawing, rather than predictingthe sapwood mc with high accuracy at the level of individual logs.In a single board, one would ideally like to measure the mc profile over the entirecross section to determine the mc gradient. However, the measured result is affectedin the vicinity of the board edges. In the third publication, the existence of thisproblem is identified, and it is shown that it can be decreased by using correlationfunctions generated by finite element simulations of the measurement system.The fourth publication considers the potential to increase the measurement accuracyof the mc of single boards by combining different measurement techniques.Microwaves, X-rays and visual sorting into different wood quality classes are used. Itis shown that the measurement accuracy is increased by the addition of both the Xraymeasurements and the visual sorting. This result is interesting because visualsorting is usually already present in the final sorting of large sawmills. This is alsowhere the mc measurement preferably is to be performed.<br>Godkänd; 2012; 20120315 (tomvik); LICENTIATSEMINARIUM Ämnesområde: Träfysik/Wood Physics Examinator: Professor Tom Morén, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Teknologie licentiat Björn Källander, Stora Enso Timber AB, Falun Tid: Torsdag den 26 april 2012 kl 10.00 Plats: Hörsal A, Campus Skellefteå, Luleå tekniska universitet

<p>Timber drying is one of the most important processes whenmanufacturing sawn timber products. The drying processinfluences deformations, surface checking, discoloration andhence, the product quality and the manufacturing costs.Research in this field is of great importance for the woodindustry since the industrial drying process always needs to beimproved as market demands increases and new wood products aredeveloped.</p><p>The aim of the present thesis was to investigate themoisture transport behaviour in wood based on measurementsduring drying from fresh condition down to end use moisturecontent. The behaviour near the surface interface has beenspecifically investigated since it is of great importance forthe theoretical description of the drying process. Furthermore,studies based on measurements in the wood surface layer duringdrying are not easy to find in the literature. The reason forthat is probably that it is very difficult to make accuratemoisture measurements with high spatial or temporal resolutionwithout disturbing the drying process.</p><p>Measurements of moisture content profiles in Scots pineheartwood and sapwood during drying have been performed byusing three different methods. The first was a destructivemethod where the wood samples are sliced with a knife intoseveral smaller pieces. The moisture content in each piece wasdetermined with the dry weight method. The second method usedis non-destructive and it utilises a medical CT-scanner thathas been adapted for drying experiments. The samples are driedin-situ the scanner through the whole experiment. TheCT-scanner measures density and the moisture content arecalculated according to existing methods developed by otherscientists. The third method was also non-destructive and itutilises a Magnetic Resonance Imaging, MRI, technique. Withthis technique the amount of water in the wood sample ismeasured directly even though it has to be calibrated tomoisture content.</p><p>The surface emission factor, S, or surface resistance, 1/S,has been studied by performing sorption experiments with MDF ina narrow moisture content range. The experiment was evaluatedusing a simple diffusion model that includes a surface emissionfactor S. The experimental result was compared with resultscalculated using well established boundary layer theories.</p><p>Measurements of moisture content profiles in the wood bulkshowed an expected Fickian behaviour at moisture contents belowthe fibre saturation point. Above the fibre saturation pointalmost flat moisture profiles were observed. This behaviour wasnot expected and it is not possible to simulate this behaviourwith the existing drying models since they usually assume thatthere is a gradient in the moisture profile over the wholemoisture content range. From the moisture profiles thediffusion coefficients were determined over a moisture contentranging from 8 to 30%. The values for heartwood and sapwood areapproximately equal in radial and tangential direction tograin. Furthermore, the diffusion values in longitudinaldirection are much higher as expected.</p><p>The sorption experiments with MDF gave a greater surfaceresistance compared with the calculation that was based onboundary layer theory. The ratio was three or higher. Thisimplied that there was a greater resistance in the surfacelayer. In addition, this was not well described in theliterature even though a few recent published studiesexist.</p><p>High resolution measurements in the surface layer of woodshowed behaviour similar to that observed in the bulk wood. Theresults showed the very early development of a dry zone closeto the surface interface. In that zone or shell the moisturecontent was below the FSP even though the bulk moisture contentwas far above the FSP. At the end of the experiments themoisture content in the surface layer (0–300 µm)nearly reached the equilibrium moisture content even though thebulk moisture content still was much higher.</p><p><b>Keywords:</b>Computer tomography, Diffusion, Magneticresonance, Moisture measurements, Moisture profiles, Surfaceemission, Wood drying</p>

Thesis (PhD (Forest and Wood Science))--Stellenbosch University, 2007.<br>ENGLISH ABSTRACT: There has been a reported reduction in the durability of creosote treated, wooden utility poles in South Africa in recent years. Several factors could have been responsible for this. In this study, Eucalyptus grandis pole drying schedules currently used, methods of measurement of moisture content (MC) after drying and drying defects were investigated. Relationships involving drying defects and MC gradient before treatment which may help in the development of simple nondestructive methods of assessing defects such as surface checking, honeycomb and collapse, and MC gradient were also explored. The long term goal of this study was to increase the durability of treated poles by avoiding unacceptable drying defects and MC values before treatment. The results of this investigation are presented in the following chapters: an introduction motivating the aims of the investigations (Chapter 1); a review of literature relevant to MC and drying defects in sawn or round wood (Chapter 2); ready for press manuscripts on MC and drying defects in kiln-dried E. grandis poles (Chapters 3 to 7) and a general conclusion that links up chapters 3 to 7, and recommendations (Chapter 8). The auger drill method gave reliable MC values when samples in increments of 25 mm depths into the pole were taken. However, when single samples of 50 mm and 75 mm depths were considered, the auger drill MC measurements were unreliable. It was concluded that SABS SM 983 (2000), which specifies taking single radial auger drill samples of depth 70±5 mm at pole mid length, is not a reliable method of measuring MC in a kiln-dried E. grandis pole. Correlation results indicated that tree growth factors such as sapwood depth, green MC and heartwood percentage were related to final drying defects and may be used as criteria for pole sorting before kiln drying. Also, the number of valleys per unit length (VPUL) of the circumference at the theoretical ground line (TGL) was positively correlated with honeycomb and closed surface checks, implying that VPUL as a parameter of the pole circumference profile can be used to assess invisible, internal defects. The dry bulb temperature (Tdb) of 80oC, used to dry poles in industry, was too high and resulted into unacceptable levels of drying defects in kiln dried E. grandis poles. In addition, the drying period of 8 days was too short to attain an acceptable MC gradient in poles. It is, therefore, recommended that: To use the auger drill method to reliably determine the moisture content of a pole, samples in increments of 25 mm should be taken. MC measurements should be made at the most critical zones of a pole such as the TGL and not higher up since there is normally considerable MC variation in the longitudinal direction. It is also important to consider sampling more than one position on the pole circumference to cater for the MC variation in the tangential direction. For poles with large sapwood depths i.e. >15mm, mild drying conditions at the beginning of a drying run should be used, since such poles may be more susceptible to surface checking. Poles with large heartwood percentages should also be dried with suitable kiln schedules, i.e. with low Tdb to minimise honeycomb and collapse. In general, Tdb lower than 80oC should be considered in order to reduce the defects to acceptable levels. Poles should be dried for longer than 8 days even at Tdb as high as 80oC to reduce the MC to acceptable values and gradients. Since only three schedules were tested, more drying schedules should be investigated to make reliable conclusions about the effect of schedule on drying defects. In addition, more poles per schedule should be considered in order to obtain statistically reliable results. The relationship of pole diameter and drying defects also requires further investigation. Since a limited sample was used to test for the effect of source of poles and drying schedules on defect correlations, further studies should be done on sufficient samples to come up with more reliable conclusions. It is also necessary to further investigate the possible variation in correlation of VPUL and internal defects on a large sample of poles from specific sources and drying schedules.<br>AFRIKAANSE OPSOMMING: Die afgelope paar jaar is waargeneem dat kreosootbehandelde transmissiepale 'n afname in duursaamheid toon. Verskeie faktore kan hiervoor verantwoordelik wees. In hierdie studie is huidige Eucalyptus grandis oonddrogingskedules en voggehalte- (VG) bepalingsmetodes vóór en na droging asook drogingsdefekte ondersoek. Verwantskappe tussen drogingsdefekte en VG-gradiënt vóór behandeling wat kan meehelp om nie-destruktiewe metodes te ontwikkel om defekte soos oppervlaktekrake, interne barste en instorting en VG-gradiënt te bepaal, is ook bestudeer. Die langtermyn doelwit van hierdie studie is om die duursaamheid van behandelde pale te verbeter deur onaanvaarbare drogingsdefekte en voggehaltes vóór behandeling te vermy. Die resultate van hierdie ondersoek word in die volgende hoofstukke bespreek: 'n inleiding waarin die doelwitte van die onderskeie ondersoeke motiveer word (Hoofstuk 1); 'n oorsig van die literatuur relevant tot VG en drogingsdefekte in gesaagde en rondehout (Hoofstuk 2); persklaar manuskripte oor VG en drogingsdefekte in oondgedroogde E. grandis pale (Hoofstukke 3 tot 7) en 'n algemene gevolgtrekking wat bevindings uit hoofstukke 3 tot 7 saamvat gevolg deur aanbevelings (Hoofstuk 8). Die augerboor-metode kon betroubare VG-waardes lewer indien monsters van 25mm diepteinkremente in die paal geneem is. Augerboor-voggehaltemetings met enkel 50mm en 75mm monsters was egter onbetroubaar. Daar is bevind dat SABS SM 983 (2000), wat 'n enkel radiale augerboormonster tot op 'n diepte van 70±5 mm in die middel van die lengte van die paal spesifiseer, nie 'n betroubare VG-bepalingsmetode vir oondgedroogde E. grandis pale is nie. Die resultate het aangetoon dat boomgroeifaktore soos spinthoutdiepte, groen voggehalte en die persentasie kernhout aan drogingsdefekte verwant is en as basis vir sortering van pale vóór oonddroging gebruik kan word. Ook kon die aantal valleie per eenheidslengte (e. VPUL) van die omtrek by die teoretiese grondlyn (TGL) positief met interne barste en geslote oppervlaktekrake korreleer word wat impliseer dat VPUL as parameter van die omtrekprofiel van die paal gebruik kan word om onsigbare, interne defekte mee vas te stel. Die droëbaltemperatuur (Tdb) van 80oC wat in die industrie gebruik word, was te hoog omdat dit onaanvaarbare vlakke van drogingsdefekte in oondgedroogde E. grandis veroorsaak het. Daarbenewens was die drogingsperiode van 8 dae by 'n Tdb van 80oC te kort om 'n aanvaarbare VG-gradiënt te lewer. Die volgende word derhalwe aanbeveel: Om betroubare VG-resultate d.m.v. die augerboormetode te verkry, behoort monsters in inkremente van 25mm geneem te word. VG-metings behoort in die mees kritiese dele van 'n paal gedoen te word byv. by TGL en nie hoër nie omdat daar normaalweg beduidende VG-variasie in die longitudinale rigting is. Dis ook belangrik om op meer as een posisie op die omtrek te meet om vir die variasie in die tangensiale rigting voorsiening te maak. Ligte drogingstoestande behoort aan die begin van die drogingsproses by pale met groot spinthoutdieptes, bv. > 15mm, gebruik te word omdat sulke pale meer geneigd tot oppervlaktekrake is. Pale met hoë kernhoutpersentasies moet ook met geskikte drogingskedules, bv. met lae Tdb, gedroog word om interne barste en ineenstorting te verminder. Oor die algemeen behoort Tdb laer as 80oC oorweeg te word om die omvang van defekte by aanvaarbare vlakke te hou. Selfs by Tdb so hoog as 80oC behoort pale langer as 8 dae te droog om die VG tot by aanvaarbare waardes en 'n gradiënt te bring. Omdat slegs drie skedules evalueer is, behoort meer skedules ondersoek word om betroubare gevolgtrekkings oor die effek van skedule op drogingsdefekte te verskaf. Addisioneel behoort meer pale per skedule oorweeg word om statisties betroubare resultate te verkry. Die verwantskap tussen paaldeursnee en drogingsdefekte benodig ook verdere ondersoek. Aangesien 'n beperkte aantal pale gebruik is om die herkoms en drogingskedule met defekte te korreleer, behoort verdere studie op genoeg pale gedoen te word om meer betroubare gevolgtrekkings te kry. Dit is ook noodsaaklik om die moontlike variasie in die korrelasie tussen VPUL en interne defekte op 'n groot aantal pale van spesifieke herkoms en drogingskedules vas te stel.