Moisture content and its influence on the roughness and noise emission during wood machining

Numerous factors influencing the surface quality of wood after machining, among them we highlight the machining parameters and the properties of the wood. In the analysis of the influence of these factors on machining and in determining the quality measurement systems are used to obtain surface characteristics, these systems are divided into methods of contact and non-contact. The method for mechanical contact performed with the aid of the surface roughness tester is the most valued in the measurement of roughness of wood, however, aiming at a greater agility in these measurements, there is a need to seek alternatives for evaluation of surface quality, and one of these options is to use the forms of indirect measurements of this quality, as for example, the use of noise emission during the machining process. With this, the aim was to analyze the influence of the moisture content of the wood, at different levels, on surface quality of the species Pinus elliottii, determined by the method of mechanical probing move and relate this roughness with the sound emission issued for each class of humidity, during machining. The planning of experiments and statistical analyses were performed with the help of Taguchi method. The specimens were conditioned in greenhouses climatizadoras automatics for obtaining three classes of humidity. Machining tests of wooden pieces were performed on a machining center specific for this type of material. The roughness values were measured by a roughness verifier and the noise emission values were measured by for a measurer sound pressure level. Statistically significant differences were observed, the significance level of 10 %, on roughness and noise emission between the three levels of moisture. It was observed that with the increase in the moisture content occurred an increase of roughness and a reduction in noise emission. Monitoring of surface quality through noise level is an interesting alternative to the method of mechanical contact.

Storage as a tool to improve wood fuel quality

This work analysed the influence of storage in the quality of forest biomass for energy generation in the region of Lages, Brazil. Logs of Pinus taeda L. and Eucalyptus dunnii Maiden were harvested and piled during the four different seasons: spring, summer, fall and winter. The analyses were performed immediately after harvesting (without being stored), after two, four and six months of storage. The evaluated properties were: moisture content, gross and net calorific value, ash content and solubility in cold water, hot water and sodium hydroxide. The species composition, storage span, harvesting season and storage season influenced the forest biomass characteristics. In general, eucalyptus presented better results than pine, losing moisture faster, having less alteration in the chemical composition and producing greater energetic gain over storage time. For both species, the ideal storage time was four months. Furthermore, spring and summer were the best harvesting seasons. Thus, if the forest biomass is harvested at the end of winter or beginning of spring with subsequent storage during the summer, this biomass will have the best performance for energy production. (C) 2011 Elsevier Ltd. All rights reserved.

Changes in wood-water relationship due to heat treatment assessed on micro-samples of three Eucalyptus species

Wood-water relationship of untreated and heat-treated wood was studied. Specimens of Eucalyptus grandis, E saligna, and E citriodora were submitted to five conditions of heat treatment: 180 degrees C and 220 degrees C with air; 220 degrees C, 250 degrees C, and 280 degrees C with N(2). The wood-water relationships were accurately studied in a special device, in which the moisture content (MC) of the sample was measured with a highly sensitive electronic microbalance placed in a climatic chamber. The dimensions of the sample were collected continuously without contact by means of two high-speed laser scan micrometers. Sorption curves and shrinkage-MC relationships were observed. To study the effects of heat treatment, the following parameters were also determined: fiber saturation point (FPS), wood anisotropy (T/R ratio), shrinkage slope, reduction in hygroscopicity, and anti-shrink efficiency (ASE). The physical properties were significantly affected only at 220 degrees C and above. At heat temperature levels higher than 220 degrees C, the reduction in hygroscopicity and ASE are higher than 40% and continue to be reduced with increasing temperature level. This work also demonstrates that heat treatment does not change the slope of the curves shrinkage vs. MC, proving that heat treatment affects the domain of alterations in wood properties, but not the behavior within this domain.

Consolidating preservative-treated wood: Combined mechanical performance of boron and polymeric products in wood degraded by Coniophora puteana

When timber elements in heritage buildings are moderately degraded by fungi and assuming underlying moisture problems have been solved, two actions can be taken: i) use a biocide to stop fungal activity; ii) consolidate the degraded elements so that the timber keeps on fulfilling its structural and decorative functions. The aim of this work is to investigate the mechanical performance of maritime pine wood degraded by fungi after being treated with a biocide followed by impregnation with a polymer product. Three commercially available products were used: a boron water-based biocide, an acrylic consolidant and an epoxy-based consolidant. Treated and consolidated specimens were subjected to mechanical tests: axial compression test (NP 618), static surface hardness (ISO 3350) and bending test (NP 619). Sets of replicates were subjected to an evaporation ageing test (EN 73) after application of the products and also tested for mechanical behaviour. An increase in mechanical strength was observed for both consolidants with no significant influence from the previous use of biocide product. The specimens subjected to ageing showed a slightly better general mechanical performance.

Propagation of the Ignition Front against Airflow in Packed Beds of Wood Particles

Combustion of wood is increasing because of the needs of decreasing the emissions of carbon dioxide and the amount of waste going to landfills. Wood based fuels are often scattered on a large area. The transport distances should be short enough to prevent too high costs, and so the size of heating and power plants using wood fuels is often rather small. Combustion technologies of small-size units have to be developed to reach efficient and environmentally friendly energy production. Furnaces that use different packed bed combustion or gasification techniques areoften most economic in small-scale energy production. Ignition front propagation rate affects the stability, heat release rate and emissions of packed bed combustion. Ignition front propagation against airflow in packed beds of wood fuels has been studied. The research has been carried out mainly experimentally. Theoretical aspects have been considered to draw conclusions about the experimental results. The effects of airflow rate, moisture content of the fuel, size, shape and density of particles, and porosity of the bed on the propagation rate of the ignition front have been studied. The experiments were carried out in a pot furnace. The fuels used in the experiments were mainly real wood fuels that are often burned in the production of energy. The fuel types were thin wood chips, saw dust, shavings, wood chips, and pellets with different sizes. Also a few mixturesof the above were tested. Increase in the moisture content of the fuel decreases the propagation rates of the ignition front and makes the range of possible airflow rates narrower because of the energy needed for the evaporation of water and the dilution of volatile gases due to evaporated steam. Increase in the airflow rate increases the ignition rate until a maximum rate of propagation is reached after which it decreases. The maximum flame propagation rate is not always reached in stoichiometric combustion conditions. Increase in particle size and density transfers the optimum airflow rate towards fuel lean conditions. Mixing of small and large particles is often advantageous, because small particles make itpossible to reach the maximum ignition rate in fuel rich conditions, and large particles widen the range of possible airflow rates. A correlation was found forthe maximum rate of ignition front propagation in different wood fuels. According to the correlation, the maximum ignition mass flux is increased when the sphericity of the particles and the porosity of the bed are increased and the moisture content of the fuel is decreased. Another fit was found between sphericity and porosity. Increase in sphericity decreases the porosity of the bed. The reasons of the observed results are discussed.

The effect of microfibrillated cellulose addition on drying shrinkage and dimensional stability of wood-free paper

Microfibrillated cellulose (MFC) is known to enhance strength properties of paper. Improved strength usually means increased bonding which is strongly connected to dimensional instability of paper. Dimensional instability is due to changes in moisture content of paper; when paper is moistened it expands and when dried, it shrinks. Hygroexpansion is linked to end-use problems and excessive drying shrinkage consumes strength potential. Effective use of materials requires controlling of these phenomena. There isn’t yet data concerning dimensional stability of papers containing MFC which restricts wider use of MFC. Main objective of the work was to evaluate dimensional stability of wood-free paper containing different amounts of MFC. Sheets were dried with different methods to see how drying strains effected on drying shrinkage and hygroexpansion. Also tensile strength was measured to find out the effect of MFC. Results were compared to sheets containing kraft fines and in some test points cationic starch was used alongside with MFC. MFC increased the dimensional instability of freely dried sheets. As the amounts of MFC increased the effects on dimensional stability became more severe. However the fineness of MFC didn’t play any important role. Both hygroexpansion and drying shrinkage were decreased with cationic starch addition. Prevention of drying shrinkage over powered the effects of additives on hygroexpansion. Tensile strength improved up till 7 % addition amount which could be set as the upper limit of MFC addition when paper preparation and tensile strength are concerned.

Factors affecting the usability of aspen (Populus tremula) wood dried at different temperature levels

In this dissertation the main aim was to study the usability of aspen wood in the mechanical wood processes, especially the factors that affect the usability of aspen wood, which is dried at different temperature levels. The problematic of varying temperatures from level to another seem to have significant effects on distortions. According to the studies conducted, many practical solutions for drying of aspen timber can be made. European aspen sawn timber should be dried in relatively narrow widths, short lengths, edged and sawn pith free. The results achieved give an interesting view for the distortions of aspen wood between HT drying and heat treatment. The most significant result is that cupping seems to decrease when increasing temperature level from HT drying to heat treatment phase. The difference is significant. Other very obvious result is that bow and crook are increasing between these two temperature levels, bow significantly. Also the modelling gives a good background for this result since cupping is reduced by higher temperatures. It can also be assumed that these distortions can be affected for example by sorting out the timber used to different moisture levels before drying. This could be a very simple solution for practical purposes. From practical point of view, it was also noted during the drying tests performed that the discoloration seem to be no problem for aspen boards dried in temperatures under 150 °C. Altogether, this dissertation covers many interesting points of view of factors affecting distortions of wood in different temperature stages. Aspen as species in use of mechanical wood industries seems to be a species suitable for component production. According to the results, the best yield from aspen timber can be achieved in industry that can utilize relatively short components of sawn wood. Results achieved give a significant indication about the factors affecting distortions of wood at different temperature stages of drying, especially considering European aspen.

Effects of Surface Properties and Wood Modification into Direct Printing on Wood

Building industry is a high volume branch which could provide prominent markets for wood based interior decoration solutions. Competition in interior decoration markets requires versatility in appearance. Versatility in wood appearance and added value could be achieved by printing grain patterns of different species or images directly onto wood. The problem when planning wood printing’s implementing into durable applications is basically how to transfer a high quality image or print sustainably onto wood, which is porous, heterogeneous, dimensionally unstable, non-white and rough. Wood preservation or treating, and modification can provide durability against degradation but also effect to the surface properties of wood which will effect on printability. Optimal adhesion is essential into print quality, as too high ink absorbance can cause spreading and too low ink absorbance cause pale prints. Different printing techniques have different requirements on materials and production. The direct printing on wood means, that intermedias are not used. Printing techniques with flexible printing plates or in fact non-impact techniques provide the best basis for wood printing. Inkjet printing of wood with different mechanical or chemical surface treatments, and wood plastic composite material gave good results that encourage further studies of the subject. Sanding the wood surface anti-parallel to the grain gave the best overall printing quality. Spreading parallel to the grain could not be avoided totally, except in cases where wood was treated hydrophobic so adhesion of the ink was not sufficient. Grain pattern of the underlying wood stays clearly visible in the printed images. Further studies should be made to fine tune the methods that already gave good results. Also effects of moisture content of wood, different inks, and long-term exposure to UV-radiation should be tested.

COMPARISON BETWEEN WOOD DRYING DEFECT SCORES: SPECIMEN TESTING X ANALYSIS OF KILN-DRIED BOARDS

It is important to develop drying technologies for Eucalyptus grandis lumber, which is one of the most planted species of this genus in Brazil and plays an important role as raw material for the wood industry. The general aim of this work was to assess the conventional kiln drying of juvenile wood of three clones of Eucalyptus grandis. The specific aims were to compare the behavior between: i) drying defects indicated by tests with wood specimens and conventional kiln-dried boards; and ii) physical properties and the drying quality. Five 11-year-old trees of each clone were felled, and only flatsawn boards of the first log were used. Basic density and total shrinkage were determined, and the drying test with wood specimens at 100 °C was carried out. Kiln drying of boards was performed, and initial and final moisture content, moisture gradient in thickness, drying stresses and drying defects were assessed. The defect scoring method was used to verify the behavior between the defects detected by specimen testing and the defects detected in kiln-dried boards. As main results, the drying schedule was too severe for the wood, resulting in a high level of boards with defects. The behavior between the defects in the drying test with specimens and the defects of kiln-dried boards was different, there was no correspondence, according to the defect scoring method.

Impact of mineral fillers on the properties of extruded wood-polypropylene composites

The main aim of this thesis is to study the effect of mineral fillers on the properties of extruded wood-polypropylene composites (WPC). The studied minerals are Talc, Calcite (CaCO3), two quantities of Wollastonite and Soapstone, and the level of mineral addition is 20 w-%. The study shows that mineral fillers can be used to modify and improve the properties of woodplastic composites. Especially the moisture-related properties of WPCs were found to be improved significantly by mineral addition. As the WPCs of the studied type are commonly used in outdoor applications, this is of importance in terms of usability. In machining, the addition of two minerals retained the surface roughness at same level throughout the test, indicating a favorable effect on machinability. The use of hard minerals shortened the tool life in machining. In general, a modest increase in density was observed. In many of the studied properties, no apparent influence of mineral addition was found, indicating that the properties were not weakened. An overall result was that talc showed the best overall performance, indicating that it can be used as an active filler improving most of the studied properties, especially moisture resistance. Calcite was found to have nearly similar performance. According to the findings, mineral addition to wood-plastic composites appears to be beneficial; especially moisture resistance can be enhanced without diminishing the other properties or usability in general.

Surface characterization of chemically modified fiber, wood and paper

Inorganic-organic sol-gel hybrid coatings can be used for improving and modifying properties of wood-based materials. By selecting a proper precursor, wood can be made water repellent, decay-, moisture- or UV-resistant. However, to control the barrier properties of sol-gel coatings on wood substrates against moisture uptake and weathering, an understanding of the surface morphology and chemistry of the deposited sol-gel coatings on wood substrates is needed. Mechanical pulp is used in production of wood-containing printing papers. The physical and chemical fiber surface characteristics, as created in the chosen mechanical pulp manufacturing process, play a key role in controlling the properties of the end-use product. A detailed understanding of how process parameters influence fiber surfaces can help improving cost-effectiveness of pulp and paper production. The current work focuses on physico-chemical characterization of modified wood-based materials with surface sensitive analytical tools. The overall objectives were, through advanced microscopy and chemical analysis techniques, (i) to collect versatile information about the surface structures of Norway spruce thermomechanical pulp fiber walls and understand how they are influenced by the selected chemical treatments, and (ii) to clarify the effect of various sol-gel coatings on surface structural and chemical properties of wood-based substrates. A special emphasis was on understanding the effect of sol-gel coatings on the water repellency of modified wood and paper surfaces. In the first part of the work, effects of chemical treatment on micro- and nano-scale surface structure of 1st stage TMP latewood fibers from Norway spruce were investigated. The chemicals applied were buffered sodium oxalate and hydrochloric acid. The outer and the inner fiber wall layers of the untreated and chemically treated fibers were separately analyzed by light microscopy, atomic force microscopy and field-emission scanning electron microscopy. The selected characterization methods enabled the demonstration of the effect of different treatments on the fiber surface structure, both visually and quantitatively. The outer fiber wall areas appeared as intact bands surrounding the fiber and they were clearly rougher than areas of exposed inner fiber wall. The roughness of the outer fiber wall areas increased most in the sodium oxalate treatment. The results indicated formation of more surface pores on the exposed inner fiber wall areas than on the corresponding outer fiber wall areas as a result of the chemical treatments. The hydrochloric acid treatment seemed to increase the surface porosity of the inner wall areas. In the second part of the work, three silane-based sol-gel hybrid coatings were selected in order to improve moisture resistance of wood and paper substrates. The coatings differed from each other in terms of having different alkyl (CH3–, CH3-(CH2)7–) and fluorocarbon (CF3–) chains attached to the trialkoxysilane sol-gel precursor. The sol-gel coatings were deposited by a wet coating method, i.e. spraying or spreading by brush. The effect of solgel coatings on surface structural and chemical properties of wood-based substrates was studied by using advanced surface analyzing tools: atomic force microscopy, X-ray photoelectron spectroscopy and time-of-flight secondary ion spectroscopy. The results show that the applied sol-gel coatings, deposited as thin films or particulate coatings, have different effects on surface characteristics of wood and wood-based materials. The coating which has a long hydrocarbon chain (CH3-(CH2)7–) attached to the silane backbone (octyltriethoxysilane) produced the highest hydrophobicity for wood and wood-based materials.

Ultraviolet light protection and weathering properties of wood-polypropylene composites

The main aim of this thesis is to study the effect of pigments on the weathering properties of wood-polypropylene composites (WPC). The studied properties are color change, water absorption, thickness swelling and Charpy impact strength. The impact of weathering and UV exposure on WPCs was studied by using pigments and minerals as protective agents. The study shows that the pigments and/or mineral fillers can be used to improve the weathering properties of WPCs. The effect of pigments was found to vary with the type of pigment and the method of weathering. The black pigment, an inorganic carbon black master-batch, was found to be the most effective one in reduction of the discoloration of WPCs. By preventing discoloration, and further reducing the degradation of the surface of the WPC, the pigments were found to reduce the decrease in the impact strength after weathering. As well as UV protection, the moisture resistance is a significant factor affecting the durability of WPCs. The addition of mineral fillers was found to improve the moisture-related properties, such as water absorption and thickness swelling, of WPC significantly. According to the findings, addition of pigments and mineral fillers to wood-polypropylene composites appears to be beneficial: color stability and moisture resistance can be enhanced especially in outdoor weathering. The combined effect of black pigment (carbon black master-batch) and wollastonite as a mineral filler was found to bring about the most effective properties against weathering.

Utilization of recycled mineral wool as filler in wood plastic composites

The impact of a recycled mineral wool filler on the various properties of wood plastic composites was studied and the critical factors affecting the formation of the properties were determined. An estimation of the volume of mineral wool fiber waste generated in the European Union between the years 2010-2020 was presented. Furthermore, the effect of fiber pre-treatment on the properties of the wood plastic composites were studied, and the environmental performance of a wood plastic composite containing recycled mineral fibers was assessed. The results showed that the volumes of construction and demolition waste and new mineral wool produced in the European Union are growing annually, and therefore also the volumes of recycled mineral wool waste generated are increasing. The study showed that the addition of recycled mineral wool into composites can enhance some of the mechanical properties and increase the moisture resistance properties of the composites notably. Recycled mineral wool as a filler in wood plastic composites can also improve the fire resistance properties of composites, but it does not protect the polymer matrix from pyrolysis. Fiber pre-treatment with silane solution improved some of the mechanical properties, but generally the use of maleated polypropylene as the coupling agent led to better mechanical and moisture resistance properties. The environmental performance of recycled mineral wool as the filler in wood plastic composites was superior compared to glass fibers. According to the findings, recycled mineral wool fibers can provide a technically and environmentally viable alternative to the traditional inorganic filler materials used in wood plastic composites.

The feasibility of torrefaction for the co-firing of wood in pulverised-fuel boilers

Torrefaction is the partial pyrolysis of wood characterised by thermal degradation of predominantly hemicellulose under inert atmosphere. Torrefaction can be likened to coffee roasting but with wood in place of beans. This relatively new process concept makes wood more like coal. Torrefaction has attracted interest because it potentially enables higher rates of co-firing in existing pulverised-coal power plants and hence greater net CO2 emission reductions. Academic and entrepreneurial interest in torrefaction has sky rocketed in the last decade. Research output has focused on the many aspects of torrefaction – from detailed chemical changes in feedstock to globally-optimised production and supply scenarios with which to sustain EU emission-cutting directives. However, despite its seemingly simple concept, torrefaction has retained a somewhat mysterious standing. Why hasn’t torrefied pellet production become fully commercialised? The question is one of feasibility. This thesis addresses this question. Herein, the feasibility of torrefaction in co-firing applications is approached from three directions. Firstly, the natural limitations imposed by the structure of wood are assessed. Secondly, the environmental impact of production and use of torrefied fuel is evaluated and thirdly, economic feasibility is assessed based on the state of the art of pellet making. The conclusions reached in these domains are as follows. Modification of wood’s chemical structure is limited by its naturally existing constituents. Consequently, key properties of wood with regards to its potential as a co-firing fuel have a finite range. The most ideal benefits gained from wood torrefaction cannot all be realised simultaneously in a single process or product. Although torrefaction at elevated pressure may enhance some properties of torrefied wood, high-energy torrefaction yields are achieved at the expense of other key properties such as heating value, grindability, equilibrium moisture content and the ability to pelletise torrefied wood. Moreover, pelletisation of even moderately torrefied fuels is challenging and achieving a standard level of pellet durability, as required by international standards, is not trivial. Despite a reduced moisture content, brief exposure of torrefied pellets to water from rainfall or emersion results in a high level of moisture retention. Based on the above findings, torrefied pellets are an optimised product. Assessment of energy and CO2-equivalent emission balance indicates that there is no environmental barrier to production and use of torrefied pellets in co-firing. A long product transport distance, however, is necessary in order for emission benefits to exceed those of conventional pellets. Substantial CO2 emission reductions appear possible with this fuel if laboratory milling results carry over to industrial scales for direct co-firing. From demonstrated state-of-the-art pellet properties, however, the economic feasibility of torrefied pellet production falls short of conventional pellets primarily due to the larger capital investment required for production. If the capital investment for torrefied pellet production can be reduced significantly or if the pellet-making issues can be resolved, the two production processes could be economically comparable. In this scenario, however, transatlantic shipping distances and a dry fuel are likely necessary for production to be viable. Based on demonstrated pellet properties to date, environmental aspects and production economics, it is concluded that torrefied pellets do not warrant investment at this time. However, from the presented results, the course of future research in this field is clear.