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  • 1.
    Adamopoulos, Stergios
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Lankveld, Chiel
    Accsys Group, Netherlands.
    Acoustic properties of acetylated wood under different humid conditions and its relevance for musical instruments2018In: Proceedings of the 9th European Conference on Wood Modification 2018, Arnhem, The Netherlands / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz and Brigitte Junge, The Netherlands: Practicum , 2018, p. 236-243Conference paper (Refereed)
    Abstract [en]

    In musical instrument making, less expensive wood species and materials with good characteristics and acoustical properties can provide potentials to find alternatives to the traditional exotic wood species used today. Modified wood could be such a choice if shows similar sound characteristics to wood coming from endangered and expensive tropical species with problematic commercial availability. In musical instruments, the overall functionality depends on the contribution of wood to different material performance indexes like sound radiation coefficient (R), characteristic impedance (z) and acoustic conversion efficiency (ACE). In this study, the performance indexes were measured for acetylated beech, maple and radiata pine and compared with these obtained for the reference wood materials maple, mahogany, alder and ash. A non-destructive free-free flexural vibration test method was used at constant temperature (20oC) but in different humid conditions- dry (35% RH), standard (65% RH) and wet (85% RH). Dimensional changes in the different humid conditions were also taken in account. Acetylated wood showed lower EMC with higher dimensional stability at each humidity level as compared with the reference wood materials. These properties are considered important factors for making quality musical instruments. Based on the acoustical properties, acetylated wood materials, especially radiata pine, showed good potential for use for musical instruments where specific characteristics of sound are required. However, the other types of acetylated wood can also be used for specific musical instruments.

  • 2.
    Ahmed, Sheikh Ali
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Acoustic properties of modified wood under different humid conditions and their relevance for musical instruments2018In: Applied Acoustics, ISSN 0003-682X, Vol. 140, p. 92-99Article in journal (Refereed)
    Abstract [en]

    In musical instrument making, there is a strong need to find alternatives to the traditional endangered and expensive tropical wood species used today. The present study examined whether different commercial and experimental modified wood materials have the necessary acoustic qualities under different humid conditions (dry, standard and wet) to contribute to the use of raw materials for wooden musical instruments. The materials were thermally-modified wood (ash, aspen and birch), acetylated wood (beech, maple and radiata pine), melamine- and phenol formaldehyde-treated beech and furfurylated Scots pine (Kebony Scots pine). Investigations involved physical (density ρ, Equilibrium moisture content EMC, volumetric shrinkage) and dynamic elastic testing by a free-free flexural vibration method to determine various acoustic characteristics: specific dynamic modulus (MOEdyn/ρ), damping coefficient (tanδ), speed of sound (c), specific acoustic impedance (z), sound radiation coefficient (R) and acoustic conversion efficiency (ACE). The modified materials and especially acetylated wood showed low EMC values and high dimensional stability at each humidity level, which are considered important factors for making quality musical instruments. Based on the obtained value ranges of all acoustical properties, the different modified wood materials could find uses in musical instruments where specific characteristics of sound are required. Furthermore, most of the modified materials showed an excellent acoustic performance in the three humid conditions based on a high ACE and low tanδ. Furfurylated Scots pine and phenol formaldehyde-treated beech showed an inferior acoustic quality with the lowest ACE and the highest tanδ, which is a less favourable combination for most of the musical instruments.

  • 3.
    Ahmed, Sheikh Ali
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Adamopoulos, Stergios
    Swedish university of agricultural sciences, Sweden.
    Li, Junqiu
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Kovacikova, Janka
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Prediction of mechanical performance of acetylated MDF at different humid conditions2020In: Applied Sciences, E-ISSN 2076-3417, Vol. 10, no 23, p. 1-16, article id 8712Article in journal (Refereed)
    Abstract [en]

    Change of relative humidity (RH) in surrounding environment can greatly affect the physical and mechanical properties of wood-based panels. Commercially produced acetylated medium density fiberboard (MDF), Medite Tricoya®, was used in this study to predict strength and stiffness under varying humid conditions by separating samples in parallel (//) and perpendicular (⊥) to the sanding directions. Thickness swelling, static moduli of elasticity (MOEstat) and rupture (MORstat), and internal bond (IB) strength were measured at three different humid conditions, i.e., dry (35% RH), standard (65% RH) and wet (85% RH). Internal bond (IB) strength was also measured after accelerated aging test. A resonance method was used to determine dynamic modulus of elasticity (MOEdyn) at the aforementioned humid conditions. Linear regression and finite element (FE) analyses were used to predict the MDF’s static bending behavior. Results showed that dimensional stability, MOEstat, MORstat and IB strength decreased significantly with an increase in RH. No reduction of IB strength was observed after 426 h of accelerated aging test. A multiple regression model was established using MOEdyn and RH values to predict MOEstat and MORstat. In both directions (// and ⊥), highly significant relationships were observed. The predicted and the measured values of MOEstat and MORstat were satisfactorily related to each other, which indicated that the developed model can be effectively used for evaluating the strength and stiffness of Medite Tricoya® MDF samples at any humid condition. Percent errors of two different simulation techniques (standard and extended FE method) showed highly efficient way of simulating the MDF structures with low fidelity.

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  • 4.
    Ahmed, Sheikh Ali
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Poggi, Francesco
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Walther, Thomas
    IKEA Industry AB, Sweden.
    Resonance and time-of-flight methods for evaluating the modulus of elasticity of particleboards at different humid conditions2020In: Wood research, ISSN 1336-4561, Vol. 65, no 3, p. 365-380Article in journal (Refereed)
    Abstract [en]

    Non-destructive testing of wood panels by either resonance or time-of-flight (TOF) methods provides possibilities for predicting their static bending properties. In the present study, three non-destructive devices (BING - Beam Identification by Non-destructive Grading by CIRAD, Montpellier, France, Fakopp Ultrasonic Timer and Sylvatest TRIO) were used for measuring the dynamic stiffness of different particleboard types. Fakopp Ultrasonic Timer and Sylvatest TRIO produce ultrasonic pulses to measure the sound velocity while BING uses resonance frequencies. Commercially produced particleboards with different thickness and densities were used to measure the dynamic modulus of elasticity (MOEdyn) in two directions (parallel and perpendicular to the production line) and at three different humidity levels (dry - 35%, standard - 65% and wet - 85% RH in constant temperature of 20°C ). MOEdyn of particleboards were correlated with the static moduli of elasticity (MOEstat) and rupture (MORstat). It was found that the non-destructive methods gave higher MOEdyn values in both production directions than that of MOEstat values. MOEdyn was found to decrease from dry to wet conditions. A very strong and statistically significant correlation existed between MOEdyn and static bending properties. MOEdyn correlated stronger to MOEstat than MORstat. At different humidity level, all three methods- Fakopp Ultrasonic Timer, BING and Sylvatest TRIO analyses showed good predicting capabilities to estimate MOEstat and MORstat of different particleboard types with high level of accuracy.

  • 5.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Hansson, Lars
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Distribution of preservatives in thermally modified Scots pine and Norway spruce sapwood2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 3, p. 499-513Article in journal (Refereed)
    Abstract [en]

    Studying the impregnation and distribution of oil-based preservative in dried wood is complicated as wood is a nonhomogeneous, hygroscopic and porous material, and especially of anisotropic nature. However, this study is important since it has influence on the durability of wood. To enhance the durability of thermally modified wood, a new method for preservative impregnation is introduced, avoiding the need for external pressure or vacuum. This article presents a study on preservative distribution in thermally treated Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) sapwood using computed tomography scanning, light microscopy, and scanning electron microscopy. Secondary treatment of thermally modified wood was performed on a laboratory scale by impregnation with two types of preservatives, viz. Elit Träskydd (Beckers) and pine tar (tar), to evaluate their distribution in the wood cells. Preservative solutions were impregnated in the wood using a simple and effective method. Samples were preheated to 170 °C in a drying oven and immediately submerged in preservative solutions for simultaneous impregnation and cooling. Tar penetration was found higher than Beckers, and their distribution decreased with increasing sample length. Owing to some anatomical properties, uptake of preservatives was low in spruce. Besides, dry-induced interstitial spaces, which are proven important flow paths for seasoned wood, were not observed in this species.

  • 6.
    Ahmed, Sheikh Ali
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Michigan Technological University, USA.
    Adamopoulos, Stergios
    Swedish University of Agricultural Sciences, Sweden.
    Micro-Fibrillated Cellulose in Lignin–Phenol–Formaldehyde Adhesives for Plywood Production2023In: Forests, ISSN 1999-4907, E-ISSN 1999-4907, Vol. 14, no 11, article id 2249Article in journal (Refereed)
    Abstract [en]

    Petrochemical-based phenol–formaldehyde (PF) adhesives are widely used in plywood production. To substitute phenol in the synthesis of PF adhesives, lignin can be added due to its structural similarity to phenol. Moreover, micro-fibrillated cellulose (MFC) can further enhance the bond performance, mechanical properties, and toughness of adhesive systems. Thus, the aim of this study was to evaluate the adhesion performance of lignin–PF (LPF) adhesives reinforced with MFC. In LPF formulations, three levels of MFC (0, 15, and 30 wt% based on the total solid content of adhesives) were added to the homogenous adhesive mixture. Three-layer plywood panels from birch (Betula pendula Roth.) veneers were assembled after hot pressing at 130 °C under two pressing durations, e.g., 60 and 75 s/mm. Tensile shear strength was measured at dry (20 °C and 65% RH) and wet conditions (water soaked at room temperature for 24 h). The results indicated that the addition of lignin reduced the strength of LPF adhesives in both dry and wet conditions compared to the control PF adhesive. However, MFC reinforcement enhanced the shear strength properties of the plywood. Furthermore, a longer pressing time of 75 s/mm slightly increased the shear strength.

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  • 7.
    Ahmed, Sheikh Ali
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials. Linnaeus University, The University Administration.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials. Linnaeus University, Linnaeus Knowledge Environments, Green Sustainable Development.
    Brischke, Christian
    University of Goettingen, Germany.
    Adamopoulos, Stergios
    Swedish University of Agricultural Sciences, Sweden.
    Anatomical, Physical, Chemical, and Biological Durability Properties of Two Rattan Species of Different Diameter Classes2022In: Forests, ISSN 1999-4907, E-ISSN 1999-4907, Vol. 13, no 1, article id 132Article in journal (Refereed)
    Abstract [en]

    Rattan cane is an important forest product with economic value. Its anatomical, physical, and biological properties vary with the cane height. This makes it difficult to select the appropriate cane diameter for harvesting. Understanding the material properties of rattan cane with different diameter sizes is important to enhance its utilization and performance for different end uses. Thus, the present study was performed on two rattan species, Calamus zollingeri and Calamus ornatus, at two different cane heights (bottom/mature and top/juvenile). Calamus zollingeri was studied at diameter classes of 20 mm and 30 mm, while Calamus ornatus was analyzed at a diameter class of 15 mm. The anatomical properties, basic density, volumetric swelling, dynamic moisture sorption, and biological durability of rattan samples were studied. The results showed that C. zollingeri with a 20 mm diameter exhibited the highest basic density, hydrophobicity, dimensional stability, and durability against mold and white-rot (Trametes versicolor) fungi. As confirmed by anatomical studies, this could be due to the higher vascular bundle frequency and longer thick-walled fibers that led to a denser structure than in the other categories. In addition, the lignin content might have a positive effect on the mass loss of different rattan canes caused by white-rot decay.

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  • 8.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology .
    Morén, Tom
    Luleå University of Technology .
    Förstudie: värmebehandling av trä: slutrapport2012Report (Other academic)
    Abstract [sv]

    Projektet har bedrivits som en förstudie till en större ansökan inom området Värmebehandlat trä för interiört bruk. Projektet inleds med studier av olje- och tjärupptagning i värmebehandlat trä genomen speciell impregneringsmetod som bygger på förvärmning och undertryck i materialet. Tanken är att med denna metod kunna tillföre ytterligare en egenskap som skyddar trä och gör det attraktivt för inomhusbruk genom att t ex blockera den något besvärande luft som kommer från värmebehandlat trä.

    Projektet syftar till att undersöka möjligheten att med en förenklad impregneringsmetod erhålla tillräcklig penetrering av impregneringsmedel (Becker olja och trätjära) och i samband därmed studera fördelningen av impregneringsmedel i trä.

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  • 9.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Sweden.
    Morén, Tom
    Luleå University of Technology, Sweden.
    Moisture properties of heat-treated Scots pine and Norway spruce sapwood impregnated with wood preservatives2012In: Wood and Fiber Science, ISSN 0735-6161, Vol. 44, no 1, p. 85-93Article in journal (Refereed)
    Abstract [en]

    An experiment was conducted on commercially heat-treated (HT) Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst.) sapwood collected from Ht Wood AB, Arvidsjaur, Sweden. Secondary treatment on HT wood was performed in laboratory scale by impregnating with water-repellent preservatives (a commercial one and pine tar) to evaluate their retention and different moisture-related properties. Preservative solutions were impregnated using a simple and effective method. Wood samples were heated at 170°C in a dry oven and were immediately immersed in preservative solutions. Considerable retention was observed in HT wood, particularly in pine. Moisture adsorption properties were measured after conditioning in a high-humidity environmental chamber (4°C and 84% RH). Experimental results showed that secondary treatment enhanced moisture excluding efficiencies by decreasing equilibrium moisture content, suggesting better hydrophobicity. Soaking test in water showed that antiswelling and water repellence efficiencies improved, especially in tar-treated wood. In addition, this type of treatment significantly decreased water absorption. It was also possible to decrease volumetric swellings. Thus, secondary treatment of HT wood with preservative, in particular with tar, improved dimensional stability and water repellency.

  • 10.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Hagman, Olle
    Luleå University of Technology.
    Cloutier, Alain
    Laval University, Canada.
    Fang, Chang-Hua
    Laval University, Canada.
    Elustondo, Diego
    Luleå University of Technology.
    Anatomical properties and process parameters affecting blister/blow formation in densified European aspen and downy birch sapwood boards by thermo-hygro-mechanical compression2013In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, no 24, p. 8571-8579Article in journal (Refereed)
    Abstract [en]

    Approximately, 13.5 % of the standing volume of productive forest land in Sweden is covered by birch and aspen, which provides the vast potential to produce value-added products such as densified wood. This study shows whether it is possible to densify those species with a thermo-hygro-mechanical (THM) process using heat, steam, and pressure. In this process, transverse compression on thin European aspen (Populus tremula) and downy birch (Betula pubescens) boards was performed at 200 °C with a maximum steam pressure of 550 kPa. To obtain a theoretical 50 % compression set, the press’s maximum hydraulic pressure ranged from 1.5 to 7.3 MPa. Preliminary tests showed that ~75 % of the birch boards produced defects (blisters/blows) while only 25 % of the aspen boards did. Mainly, radial delamination associated with internal checks in intrawall and transwall fractures caused small cracks (termed blisters) while blows are characterized by relatively larger areas of delamination visible as a bumpy surface on the panel. Anatomical investigations revealed that birch was more prone to those defects than aspen. However, those defects could be minimized by increasing the pre-treatment time during the THM processing.

  • 11.
    Ahmed, Sheikh Ali
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Morén, Tom
    Luleå University of Technology.
    Sehlstedt-Persson, Margot
    Luleå University of Technology.
    Blom, Åsa
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Effect of oil impregnation on water repellency, dimensional stability and mold susceptibility of thermally-modified European aspen and downy birch wood2017In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 63, no 1, p. 74-82Article in journal (Refereed)
    Abstract [en]

    Conventional chemical wood preservatives have been banned or restricted in some applications due to human and animal toxicity and their adverse impact on the surrounding environment. New, low-environmental-impact wood treatments that still provide effective protection systems are needed to protect wood. Thermal modification of wood could reduce hygroscopicity, improve dimensional stability and enhance resistance to mold attack. The aim of this study was to investigate if these properties enhanced in thermally modified (TM) wood through treatments with oils. In this study, TM European aspen (Populus tremula) and downy birch (Betula pubescens) wood were impregnated with three different types of oil: water-miscible commercial Elit Träskydd (Beckers oil with propiconazole and 3-iodo-2-propynyl butylcarbamate, IPBC), a pine tar formulation and 100% tung oil. The properties of oil-impregnated wood investigated were water repellency, dimensional stability and mold susceptibility. The treated wood, especially with pine tar and tung oil, showed an increase in water repellency and dimensional stability. However, Beckers oil which contains biocides like propiconazole and IPBC showed better protection against mold compared with pine tar and tung oil. To enhance the dimensional stability of the wood, pine tar and tung oil can be used, but these oil treatments did not significantly improve mold resistance rather sometimes enhanced the mold growth, whereas a significant anti-mold effect was observed on Beckers oil treated samples.

  • 12.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Sehlstedt-Persson, Margot
    Luleå University of Technology.
    Hansson, Lars
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Evaluation of preservative distribution in thermally modified European aspen and birch boards using computed tomography and scanning electron microscopy2013In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 59, no 1, p. 57-66Article in journal (Refereed)
    Abstract [en]

    The aim of this experiment was to impregnate thermally modified wood using an easy and cost-effective method. Industrially processed thermally modified European aspen (Populus tremula L.) and birch (Betula pubescens Ehrh.) were collected and secondarily treated at the laboratory scale with the preservatives tung oil, pine tar and Elit Träskydd (Beckers) using a simple and effective method. Preservative uptake and distribution in sample boards were evaluated using computed tomography (CT) and scanning electron microscopy (SEM) techniques. Preservative uptake and treatability in terms of void volume filled were found the highest in Beckers and the lowest in tung oil-treated samples. Thermally modified samples had lower treatability than their counterpart control samples. More structural changes after thermal modification, especially in birch, significantly reduced the preservative uptake and distribution. The differences of preservatives uptake near the end grain were high and then decreased near the mid position of the samples length as compared with similar type of wood sample. Non-destructive evaluation by CT scanning provided a very useful method to locate the preservative gradients throughout the sample length. SEM analysis enabled the visualization of the preservative deposits in wood cells at the microstructural level.

  • 13.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Sehlstedt-Persson, Margot
    Luleå University of Technology.
    Karlsson, Olov
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Uneven distribution of preservative in kiln-dried sapwood lumber of Scots pine: Impact of wood structure and resin allocation2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 251-258Article in journal (Refereed)
    Abstract [en]

    Scots pine (Pinus sylvestris L.) sapwood lumber was collected after kiln drying and preservative treatment with Celcure AC 800 (a copper-amine wood preservative). Distribution of the preservative throughout the lumber was visually examined. Not all, but some samples showed specific localized areas without any preservative distribution throughout their entire length. Those samples were assessed further for anatomical properties, specifically in impregnated and unimpregnated areas. Additional study was conducted on the morphological nature and redistribution of lipophilic extractives using three different histochemical staining methods. Intrinsic wood properties – especially the frequency of axial resin canals and the percentage of canals blocked – were found to be responsible for the irregular distribution of the preservative. Furthermore, the inability to create continuous and frequent interstitial spaces due to the collapse of thin-walled ray cells throughout the lumber resulted in un-even distribution of preservatives. Staining techniques were useful to localize places with more or less abundance of extractives (e.g., fats) in impregnated and unimpregnated wood, which varied considerably. Histochemical observations revealed information pertaining to the kiln dry specific distribution and redistribution of extractives between the areas. Moreover, resin reallocation and modification in ray parenchyma and resin canals induced by kiln drying would be another reason for the impregnation anomalies.

  • 14.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Sehlstedt-Persson, Margot
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Development of a new rapid method for mould testing in a climate chamber: preliminary tests2013In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 71, no 4, p. 451-461Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to develop fast, simple and robust solid wood mould testing methods for the use in small-scale laboratory tests. The objective was to investigate mould susceptibility of different wood materials within the batches. The proposed method is based on natural contamination of non-sterile surfaces in climates conducive to mould growth. For this purpose, a climate chamber with regulated temperature and relative humidity was used. The conditioning chamber was divided into upper and lower chamber by a thin layer of stainless steel placed horizontally above the fan to minimise air circulation to the sample in the upper compartment. Mould-infected samples from outdoor tests were used as a source of mould inocula, and test trials were conducted on Scots pine (Pinus sylvestris L.) sapwood. Samples were suspended from the top of the upper chamber, and the chamber was exposed to different temperature and humidity levels. Severe mould infestation was observed after 12–14 days of incubation. Visual mould rating was then performed. Regardless of some constraints, this test method was very simple, fast, and effective. More importantly, unlike other test methods, it closely models mould infestation as it would occur under natural condition.

  • 15.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Sehlstedt-Persson, Margot
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Mould susceptibility of Scots pine (Pinus sylvestris L.) sapwood: Impact of drying, thermal modification, and copper-based preservative2013In: International Biodeterioration & Biodegradation, ISSN 0964-8305, E-ISSN 1879-0208, Vol. 85, p. 284-288Article in journal (Refereed)
    Abstract [en]

    The development of mould on wood surfaces depends on several factors. Although mould does not affect the mechanical properties of wood, it greatly reduces the aesthetic value of wood such as the sapwood of Scots pine (Pinus sylvestris L.), which is very prone to mould. In addition, adverse health effects of mould on humans are a great concern. Different types of dried and treated wood were used to observe whether they had enhanced durability against mould following an accelerated laboratory test method in a climate chamber. Samples were green, air-dried, industrially thermally modified, treated with copper-based preservative, and kiln-dried wood, which were tested within a single test run. The test produced the following main results: The thermal modification increased the durability of the wood, and the protective effectiveness of alternative treatments was comparable to that of commercially available copper-based treatment. However, the initial moisture content of the samples during mould exposure had a great influence on the onset of mould growth. The risk of mould susceptibility of industrial kiln-dried lumber can be reduced by drying using the double-layering technique and planing off the nutrient enriched evaporation surfaces.

  • 16.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Yang, Qian
    Luleå University of Technology.
    Sehlstedt-Persson, Margot
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Accelerated Mold Test on Dried Pine Sapwood Boards: Impact of Contact Heat Treatment2013In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 33, no 3, p. 174-187Article in journal (Refereed)
    Abstract [en]

    We test the hypothesis that the combination of kiln drying of double-stacked boards and contact heat treatment will reduce the susceptibility of treated boards to colonization by mold fungi. Winter-felled Scots pine (Pinus sylvestris L.) sapwood boards were double-stacked in an industrial kiln in ''sapwood out'' and ''sapwood in'' positions. Dried samples were then contact heat-treated using a hot press at three different temperatures (140°C, 170°C, and 200°C) for three different periods (1, 3, and 10 min). An accelerated mold test was performed in a climate chamber where naturally mold-infected samples were used as a source of mold inocula. Contact heat treatment degraded the saccharides that accumulated at dried surfaces, and reduced the mold growth. The threshold temperature and time for inhibiting mold growth were 170°C for 10 min. However, for industrial application, the most feasible combination of temperature and time would be 200°C for 3 min. We concluded that double stacking/contact heat treatment used is an environmentally friendly alternative to chemicals for reducing mold on Scots pine sapwood boards.

  • 17.
    Bobadilha, Gabrielly S.
    et al.
    Mississippi State University, USA.
    Stokes, C. Elizabeth
    Mississippi State University, USA.
    Kirker, Grant
    U.S. Forest Products Laboratory, USA.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Ohno, Katie
    U.S. Forest Products Laboratory, USA.
    Lopes, Dercilio Junior Verly
    Mississippi State University, USA.
    Effect of exterior wood coatings on the durability of cross-laminated timber against mold and decay fungi2020In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 15, no 4, p. 8420-8433Article in journal (Refereed)
    Abstract [en]

    Cross-laminated timber (CLT) is increasingly used in building construction worldwide. Durability of CLT against fungal attack has yet to be fully explored. Water intrusion in mass timber can yield dimensional changes and microbial growth. This study evaluated the performance of CLT coated with various water- and solvent-based stains commercially available in the United States. Twelve coatings were tested for moisture excluding effectiveness, water repellency effectiveness, volumetric swelling, and anti-swelling efficiency. Only five coatings repelled water, limiting dimensional changes. A modified version of AWPA E10-16 (2016) was performed to evaluate decay of the coated CLT samples. Weight losses were recorded after 18 weeks' exposure to the brown-rot decay fungus Gloeophyllum trabeum. In accelerated mold testing, coated CLT samples were grown in chambers containing spores of Aspergillus sp., Rhizopus sp., and Penicillium sp. for 29 d and assessed visually for mold growth. In both tests, coating C (transparent, water-based, alkyd/acrylic resin) performed the best among the tested coatings. Mold growth was completely prevented, and weight loss caused by G. trabeum was approximately 1.33%. Although coating C prevented decay for 18 weeks, coatings are not intended to protect against decay fungi. However, they may offer short-term protection during transport, storage, and construction. 

  • 18.
    Elustondo, Diego
    et al.
    Luleå University of Technology.
    Ahmed, Sheikh Ali
    Luleå University of Technology.
    Oliveira, Luiz
    FPInnovations, Canada.
    Drying western red cedar with superheated steam2014In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 32, no 5, p. 550-556Article in journal (Refereed)
    Abstract [en]

    This exploratory study evaluated the possibility of drying 50-mm-thick western red cedar with superheated steam. Since there are no industrial facilities in Canada drying western red cedar with superheated steam, the study was designed to explore the potential of this technology in terms of lumber quality, moisture content distribution, and drying time. The experiments showed that the 50-mm-thick product can be dried in less than three days without jeopardizing lumber quality (in comparison with the two weeks that is currently required in conventional kilns), and the percentage of pieces that remained wet after drying was within the 10% to 15% range that is typically tolerated in industry.

  • 19.
    Hemmilä, Venla
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Ammonium Lignosulfonate Adhesives for Particleboards with pMDI and Furfuryl Alcohol as Crosslinkers2019In: Polymers, E-ISSN 2073-4360, Vol. 11, no 10, p. 1-17, article id 1633Article in journal (Refereed)
    Abstract [en]

    Tightening formaldehyde emission limits and the need for more sustainable materials have boosted research towards alternatives to urea-formaldehyde adhesives for wood-based panels. Lignin residues from biorefineries consist of a growing raw material source but lack reactivity. Two crosslinkers were tested for ammonium lignosulfonate (ALS)—bio-based furfuryl alcohol (FOH) and synthetic polymeric 4,4′-diphenylmethane diisocyanate (pMDI). The addition of mimosa tannin to ALS before crosslinking was also evaluated. The derived ALS adhesives were used for gluing 2-layered veneer samples and particleboards. Differential Scanning Calorimetry showed a reduction of curing temperature and heat for the samples with crosslinkers. Light microscopy showed that the FOH crosslinked samples had thicker bondlines and higher penetration, which occurred mainly through vessels. Tensile shear strength values of 2-layered veneer samples glued with crosslinked ALS adhesives were at the same level as the melamine reinforced urea-formaldehyde (UmF) reference. For particleboards, the FOH crosslinked samples showed a significant decrease in mechanical properties (internal bond (IB), modulus of elasticity (MOE), modulus of rupture (MOR)) and thickness swelling. For pMDI crosslinked samples, these properties increased compared to the UmF. Although the FOH crosslinked ALS samples can be classified as non-added-formaldehyde adhesives, their emissions were higher than what can be expected to be sourced from the particles. 

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  • 20.
    Jiang, Wen
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Biziks, Vladimirs
    Georg-August University Göettingen, Germany.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Militz, Holger
    Georg-August University Göettingen, Germany.
    Adamopoulos, Stergios
    Swedish University of Agricultural Sciences, Sweden.
    Preparation of Polyurethane Adhesives from Crude and Purified Liquefied Wood Sawdust2021In: Polymers, E-ISSN 2073-4360, Vol. 13, article id 3267Article in journal (Refereed)
    Abstract [en]

    Polyurethane (PU) adhesives were prepared with bio-polyols obtained via acid-catalyzedpolyhydric alcohol liquefaction of wood sawdust and polymeric diphenylmethane diisocyanate(pMDI). Two polyols, i.e., crude and purified liquefied wood (CLW and PLW), were obtained fromthe liquefaction process with a high yield of 99.7%. PU adhesives, namely CLWPU and PLWPU,were then prepared by reaction of CLW or PLW with pMDI at various isocyanate to hydroxyl group(NCO:OH) molar ratios of 0.5:1, 1:1, 1.5:1, and 2:1. The chemical structure and thermal behavior of thebio-polyols and the cured PU adhesives were analyzed by Fourier transform infrared spectroscopy(FTIR) and thermogravimetric analysis (TGA). Performance of the adhesives was evaluated by singlelap joint shear tests according to EN 302-1:2003, and by adhesive penetration. The highest shearstrength was found at the NCO:OH molar ratio of 1.5:1 as 4.82 ± 1.01 N/mm2 and 4.80 ± 0.49 N/mm2 for CLWPU and PLWPU, respectively. The chemical structure and thermal properties of the cured CLWPU and PLWPU adhesives were considerably influenced by the NCO:OH molar ratio. 

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  • 21.
    Kovacikova, Janka
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Kroon, Martin
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Swedish University of Agricultural Sciences, Sweden.
    Mechanical properties of fiberboard composite bonded with polymer matrixcomputed by mean-field homogenization methods2021In: 25th International Congress of Theoretical and Applied Mechanics, August 22-27, 2021: Book of Abstracts / [ed] Alberto Corigliano, Milano, Italy, 2021, p. 1984-1985Conference paper (Other academic)
    Abstract [en]

    Nowadays, the design of composite materials considering sustainability and the environmental impact of the production is conspicuous. Therefore, in this work, we focus on investigating the mechanical behaviour and structure of a new green wood-based fibrous composite material bonded with a novel polymer matrix. The constitutive prediction models employing the material and structure design approaches simultaneously are proposed here to describe the material's microstructure. The goal is speeding up trials and reducing experiments expenses by replacing tests with computer simulations. Additionally, the relationship between material behaviour and structure is established and will be later used to generate Representative Volume Elements (RVEs) for finite element analysis (FEA).

  • 22.
    Qian, Yang
    et al.
    Luleå University of Technology.
    Karlsson, Olov
    Luleå University of Technology.
    Ahmed, Sheikh Ali
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Dimensional Stability and Water Repellency of European Aspen Improved by Oxidized Carbohydrates.2013In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 8, no 1, p. 487-498Article in journal (Refereed)
    Abstract [en]

    Small samples from European aspen (Populus tremula L.) were impregnated with carbohydrates oxidized by Fenton's reagent using water in a vacuum, followed by heating in an oven at 103 °C. An antiswelling efficiency (ASE) of around 45% for wood treated with oxidized glucose and 35% for wood treated with oxidized sucrose was obtained. Samples treated with oxidized carbohydrates gave water repellent effectiveness (WRE) values over 35%. The decrease in cell wall thickness during impregnation was about 18% less in the presence of oxidized glucose than samples only treated with Fenton's reagent. An ASE of 20% for the wood samples that had been treated with oxidized glucose was obtained after 7 days of soaking in water. The reasons for the improvement in dimensional stability are discussed in this work.

  • 23.
    Sehlstedt-Persson, Margot
    et al.
    Luleå University of Technology.
    Ahmed, Sheikh Ali
    Luleå University of Technology.
    Metodutveckling för mögeltestning av trä - förstudie: Slutrapport2014Report (Other academic)
    Abstract [sv]

    Syftet med denna förstudie har varit att utveckla enkla och robusta forcerade mögeltester på trä som kan följas och utvärderas kontinuerligt i forskningsprojekt som bedrivs inom beständighetsområdet vid LTU och SP Trätek i Skellefteå. Testerna som gjorts i klimatskåp bygger på naturlig kontaminering och klimatval som gynnar mögeltillväxt.De metoder som utvecklats gör inte anspråk på att kunna erbjuda jämförelser med andra etablerade metoder utan enbart jämförelser inom batcher som ingår i de material- och processvariabler som studeras, exempelvis inom virkestorkning, värmebehandling och impregneringsmetoder.I förstudien utvärderades ett antal olika klimatval i ett klimatskåp som användes i försöken. Mögelpåväxt gynnas av stabil och hög RF, mörker och stillastående luft. Därför täcktes glasdörren till skåpet med svart plast och övre delen av klimatskåpet skärmades av med en mellanplåt eftersom en fläkt cirkulerar luften i kammaren nedre delar. I den övre delen av klimatskåpet gjordes noggranna mätningar av klimatet för att säkerställa ett jämnt och stabilt klimat i olika positioner.Mögelkontaminerat furumaterial sparat från tidigare TCN projekt användes som ”smittokälla” genom att placeras i klimatskåpets nedre del vid valt klimat under 2 dygn för att infektera kammaren med mögelsporer. Därefter placerades försöksmaterialet i klimatskåpets övre del. Smittokällan dvs. det kontaminerade materialet befann sig i skåpet under hela försöket. Inspektion av mögelpåväxtengjordes regelbundet fram tills beslut togs att avbryta försöket och utvärdera mögelpåväxten. Den utvärderingsmetod som används för att bedöma mögelpåväxt bygger på en visuell bedömningsskala översatt i ”praktisk användning” som utarbetats i tidigare TCN-projekt.Den lämpligaste metoden bedöms vara att använda klimatskåpets ”set-points” +27°C/95 % RF samt att avbryta försöket efter ca 12-14 dagar. Mögelgraderna på de undersökta proverna har då varit av samma omfattning som efter ca 100 dagars forcerat utomhustest beskrivit i tidigare TCN-projekt.Den framtagna metoden har använts i fyra ”skarpa” studier som publicerats i vetenskapliga tidskrifter. Detta får ses som att projektet varit lyckat och utgör ett viktigt vetenskapligt bidrag.Metoden beskrivs i detalj i en av dessa publikationer som finns som bilaga till denna rapport nämligen: “Development of a new rapid method for mould testing in a climate chamber: Preliminary tests.” Ahmed, S. A., Sehlstedt-Persson, M. & Morén, T. jul 2013 i :Holz als Roh- und Werkstoff .71 ,4 ,s. 451-461.11 s.Den framtagna metoden har fungerat mycket bra. Metoden har följande fördelar:* Den är enkel, robust och billig.* Mögelpåväxten kan följas på plats.* Det är möjligt att få svar redan efter två veckor på inverkan av olika variabler som undersöks.* Enkel kontaminering – ingen uppodling av speciella mögelarter.* Upp till 44 stycken prover kan ingå i en batch, beroende av dimension.Metoden har följande nackdelar:* Ingen standardiserad metod dvs. det är inte möjligt göra jämförelser mellan olika försöksomgångar utan endast möjligt att göra ”inom-batch” jämförelser.* Ingen kontroll av vilka mögelarter som angriper virket.

  • 24.
    Sehlstedt-Persson, Margot
    et al.
    Luleå University of Technology.
    Persson, Fredrik
    SP Trä.
    Karlsson, Olov
    Luleå University of Technology.
    Ahmed, Sheikh Ali
    Luleå University of Technology.
    Virkestorkningens inverkan på impregnerbarhet i furusplint – Del II: Delrapport 12013Report (Other academic)
    Abstract [sv]

    Projektets målsättning är att undersöka om och hur virkestorkning påverkar impregnerbarhet i furusplint med vattenbaserat kopparmedel, samt att ge rekommendationer om hur torkningsbetingelserna kan göras så gynnsamma som möjligt för ett bra impregneringsresultat. Det bör tydliggöras att det virke som impregnerats i denna studie inte kommer att säljas inom detaljhandeln. Virket anses inte heller vara representativt för impregnerat virke då det har impregnerats vid fuktkvoter som avsiktligt avviker från normala förhållanden och som kan antas vara ogynnsamma för inträngningen. Virket impregnerades enligt Nordiska Träskyddsföreningen (NTR) klass AB.

    I delsteg 1 som avrapporteras i denna rapport, har huvudfrågan varit att undersöka inverkan av fuktkvotsnivå och maxtemperatur under torkningen på impregneringsresultatet. Försöksmaterialet har bestått av totalt 553 hyvlade bräder och plank (28 resp. 48 mm). Både planken och bräderna sågades fram ur centrumutbyte och innehöll därför kärnved. Virket torkades industriellt vid 60°C och 80°C maxtemperatur till tre målfuktkvoter: 24 %, 18 % och 10 %. Efter impregnering har samtliga virkesstycken kapats upp var 50:e cm och impregneringsresultat har analyserats visuellt enligt NTR:s bedömningsgrunder. Vissa kemiska analyser har även utförts för att undersöka om och hur extraktiver och fetter kan förklara impregneringsmissarna i bräderna.

    Undersökningen visar att virkesdimension, fuktkvot och temperaturnivå har betydelse för impregneringsresultatet. Totalt sett fanns det fler missar i planken än i bräderna. Plank och bräder uppvisar dessutom något olika beteende: för bräder är resultatet mera tydligt vilket även framkom vid multivariat dataanalys (MVDA) på medelvärdesnivå: högre temperatur och högre fuktkvot visar minst impregneringsmissar hos brädgrupperna. För plankgrupper erhölls överhuvudtaget inga MVDA-modeller. Även för plank hade den högre temperaturen i medel bättre impregneringsresultat. Sambandet hög fuktkvot och god impregnerbarhet är inte lika tydligt för plank, möjligen att kombinationen låg temperatur och låg fuktkvot är ogynnsam.

    Densitetsvariationerna visade sig vara tämligen liten och inga låga/höga extremvärden fanns i försöksmaterialet. Vid MVDA framkom ändå tendenser att det hos bräder var gynnsamt ur impregneringssynpunkt med högre densitet.

    Kemiska analyser visar inga dramatiska omfördelningar av extraktiver under torkning som förklaring till impregneringsmissar. Detekterbara fetter och hartssyror var dock lägre i ytliga än i inre delar av splintveden troligen beroende på oxidativ förnätning av deras struktur under torkningen.

    Sammanfattningsvis blir tolkningen att torktemperatur, fuktkvotsintervall och virkesdimensioner har betydelse för impregneringsresultat men att det finns ett antal okända materialvariabler som har stor inverkan på resultatet på individnivå. Även om torkningsbetingelserna görs så gynnsamma som möjligt för impregnering förekommer individer som har allvarliga genomgående missar.

  • 25.
    Sehlstedt-Persson, Margot
    et al.
    Luleå University of Technology.
    Wamming, Thomas
    SPTrätek.
    Karlsson, Olov
    Luleå University of Technology.
    Ahmed, Sheikh Ali
    Luleå University of Technology.
    Modern torknings inverkan på impregnerbarhet i furusplint: Förstudie2011Report (Other academic)
    Abstract [sv]

    Under senare år rapporteras i Sverige för vissa impregneringsmedel en kraftig ökning av antalet underkända prov och då speciellt för kopparbaserade vattenlösliga medel. På några års sikt, när konsekvenserna av impregneringsmissar blir synliga hos slutanvändaren genom att rötskadat virke måste bytas ut, beräknas kostnaderna kunna uppgå till en halv miljard årligen. Orsakerna till inträngningsproblem diskuteras och en av många teorier är att virkestorkningen är en av huvudorsakerna. Målet med denna förstudie har varit att identifiera relevanta process- och materialvariabler som misstänks inverka på impregnerbarheten i furusplint. Resultat från impregneringsförsöken i denna förstudie visar att fuktkvotsnivån i bräder efter torkning är viktig för impregneringsresultatet. Bäst inträngning erhölls vid högre fuktkvotsnivåer än vad som vanligen används vid anläggningarna idag: i fuktkvotsintervallet 20-25 % var andelen missar lägst medan andelen missar ökade påtagligt vid sjunkande fuktkvot. En rekommendation är att inte övertorka virke som ska impregneras. Detta är vanligt speciellt vid torkning av tunna dimensioner i äldre brädkanaler.Resultat från denna förstudie sammanfattas enligt följande•Inverkan av fuktkvotsnivå vid impregnering är viktig. Bäst inträngning i bräder erhölls i fuktkvotsintervallet 20-25 %, dvs. vid högre fuktkvot än vad som vanligen görs medan missarna ökade påtagligt vid sjunkande fuktkvot. •Resultaten pekar på att splintvedsdensiteten tycks spela roll för impregnerbarheten: högre densitet tenderar att vara bättre ur impregneringssynpunkt. •Olika typer av impregneringsmissar noteras. Vissa typer har en tydlig koppling till vedanatomiska detaljer medan andra missar kopplas till process och yttre form.•Anrikning av näring mot splintvedsytor som sker vid forcerad torkning kan i vissa fall ha försvårat inträngning av träskyddsmedel.•Vedanatomiska studier visar att– axiella kådkanaler sannolikt spelar en viktig roll för inträngning av träskyddsmedel– parenkymcellers hartsinnehåll i splintved kan blockera inträngning via märgstrålar•Tomografering indikerar att hög splintvedsdensitet är gynnsamt för inträngning av träskyddsmedel. Detta överensstämmer med iakttagelsen att axiella hartskanaler är viktiga för inträngning av träskyddsmedel eftersom axiella hartskanaler främst finns i sommarved och hög densitet förknippas med hög sommarvedsandel. •Kemisk analys indikerar att lokal skillnad i extraktivämneshalt kan vara en av förklaringarna till impregneringsmiss i splintved. •I fortsatta studier är tomografering ett kraftfullt analysverktyg för att se inträngningsmissar i rått tillstånd.

  • 26.
    Sidorova, Ekaterina
    et al.
    Luleå University of Technology.
    Ahmed, Sheikh Ali
    Luleå University of Technology.
    Diego, Elustondo
    Luleå University of Technology.
    Wood thermal-modification at Luleå University of Technology2014In: Final Cost Action FP0904 Conference “Recent Advances in the Field of TH and THM Wood Treatment” May 19-21, 2014, Skellefteå, Sweden: Books of Abstracts / [ed] Mojgan Vaziri, Dick Sandberg, Skellefteå: Luleå tekniska universitet , 2014, p. 75-75Conference paper (Refereed)
    Abstract [en]

    The Wood Physics group at Luleå University of Technology (LTU) has the vision of transforming Swedish solid wood into the material of choice for the renewable economy of the future. To realize that vision, the group believes, stability and durability of local softwood species must be enhanced at a reasonable cost without jeopardizing the natural beauty of this environmentally friendly material. One of the methods for enhancing stability and durability of solid wood is thermal modification, and LTU's Wood Physics group has vast experience in developing and evaluating thermal modification process. In simple words, thermal modification involves exposing the wood to relatively high temperatures, between 160o C and 240o C depending on the products and technologies used, and in the absence of oxygen to avoid degradation of the wood by combustion. It has been proved that these relatively high temperatures modify the chemical structure of the wood polymers (cellulose, hemicellulose and lignin), and wood becomes less prone to absorb moisture from the environment and more resistance to biological degradation. There are a number of thermal modification methods that have been implemented in Europe at the commercial level, such as ThermoWood® and WTT thermo-treatment. ThermoWood® process is performed under normal atmospheric pressure with superheated steam containing as little oxygen as possible. The wood is first dried to almost 0% moisture content with steam temperatures up to 130°C, and then exposed to steam temperatures between 185°C to 212°C for a few hours. Afterward the vapor temperature is reduced to below 90°C to saturate the steam and allow the wood regain moisture. The WTT thermotreatment is performed with saturated steam under pressure up to 20 bars and temperatures between 160°C and 210°C, so the wood is not dried during the process. In the last years, LTU's Wood Physics group has performed several studies in collaboration with local wood producers interested in the evaluation and optimization of thermal modification processes. To study thermal modification in laboratory, LTU's Wood Physics has built pilot scale kiln/thermal-modification unit that fits through the field of view of a CT-scanner unit specially adapted for wood material studies. This combined equipment allowed measuring wood density profiles through entire thermal modification process, thus providing valuable information about the effect of the process conditions in the material. More recently, LTU's Wood Physics group became interested in the process of thermal modification by boiling in linseed oil for 2 to 4 hours. This technology is available in the market, but the novelty at LTU was the implementation of an additional oil impregnation cooling phase in which the wood is submerged in cool oil after thermal modification. This creates a sudden contraction of the gases inside the wood, which in turn draws considerable amounts of oil into the wood. The authors believe that this combined thermal-modification/oil-impregnation treatment offers a simple but effective methodology for simultaneously: 1) enhance the stability and durability of solid wood, 2) impregnate the wood surfaces with oil for increasing the repellency to moisture. This presentation includes an example of the combined thermal-modification/oil-impregnation treatment applied to common Swedish softwood and hardwood species. Both species were treated by using the WTT heat treatment technology and impregnated with different types of preservative oils. After impregnation, the samples were tested for water repellency, dimensional stability, and resistance to mould. Water repellency and dimensional stability were assessed for both liquid water and air relative humidity, and the resistance to oil leaching was determined by exposing the treated wood to cycles in which the samples absorbed water by immersion and then release the water under vacuum. As expected, the treatments showed a significant improvement in the water repellency and dimensional stability of the wood. Overall, untreated wood was more stable after thermal modification, and thermally modified wood was more stable after oil impregnation. The resistance to mould was evaluated by using an accelerated technique also developed by the Wood Physics group at Luleå University of Technology. The technique consists in placing the wood samples in the upper zone of a conditioning chamber in which there are other pieces of wood already infected by mould in the lower zone. Typically, the source of mould is pine sapwood infected with mould of aspergillus, rhizopus, penicillium genus along with other various species, and the test samples are exposed approximately 20 days to the infected environment. After incubation, the incidence of mould over the surfaces is graded in scale from 0 to 6 based on the visual assessment of two independent observers. The results of the study showed that some of the oil impregnation treatments did not significantly improved mould resistance, and it was still questionable whether the oil would not leach from the wood when the products are in service. Future research in wood modification would be certainly needed to find the right thermal-modification/oil-impregnation combination for the right application, as well as to realize the vision of transforming solid wood in the material of choice for the renewable economy of future.

  • 27.
    Sivrikaya, Hüseyin
    et al.
    Bartin Univ, Turkey.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials. Linnaeus University, Linnaeus Knowledge Environments, Green Sustainable Development.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Adamopoulos, Stergios
    Swedish university of agricultural sciences, Sweden.
    Vacuum-heat treatment of Scots pine (Pinus sylvestris L.) wood pretreated with propanetriol2022In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 17, no 5, p. 328-336Article in journal (Refereed)
    Abstract [en]

    Scots pine sapwood was pretreated with two levels of propanetriol (20% and 40% w/w glycerol), and then subjected to vacuum-heat treatment (VHT) at 180°C and 200°C. The treated samples were examined with respect to their weight and volumetric changes, mechanical properties, colour changes, and dynamic water vapour sorption. The weight of the samples after VHT did not change with increasing the temperature, but it was increased in glycerol pretreated samples. Combination of glycerol pretreatment and VHT decreased the maximum swelling. Total colour change was significantly higher during VHT at a higher temperature, while no obvious trend observed in the samples pretreated with glycerol. Modulus of elasticity (MOE) and modulus of rupture (MOR) were not affected by solely VHT, but strongly decreased after glycerol pretreatment. The equilibrium moisture content (EMC) of the samples decreased by VHT. The glycerol pretreatment caused a reduction in EMC values at a relative humidity (RH) below 60%, but considerably increased the moisture sorption in the RH above 75%. VHT slightly reduced the sorption hysteresis compared to untreated wood, but an apparent reduction in hysteresis observed by glycerol pretreatment. This indicates that the flexibility of the wood cell wall polymers increases due to glycerol pretreatment, which results in decreased MOE and sorption hysteresis values.

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  • 28.
    Sjökvist, Tinh
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Blom, Åsa
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Liquid water absorption in coated Norway spruce: Impact of heartwood, sapwood, density and weather exposure2020In: MADERAS: Ciencia y Tecnología, ISSN 0717-3644, E-ISSN 0718-221X, Vol. 22, no 3, p. 335-346Article in journal (Refereed)
    Abstract [en]

    Water is one of the most significant factors for the durability of wood. A common solution is to use a coating to protect and maintain low water content. However, little knowledge exists how the underlying wood substrate affects the water sorption of coated wood. Therefore, the liquid water absorption of coated and uncoated Norway spruce heartwood and sapwood with a variety of densities was measured by letting the panels float freely in the water. The effect of one year weathering of the coatings was also included. Coated heartwood and sapwood had no difference in water absorption in opposite to uncoated spruce. The influence of heartwood and sapwood seemed to have limited impact when a coating hindered the presence of free water. Wood density had a positive effect on the absorption of coated wood, i.e. low absorption for low-density samples, in opposite to uncoated samples. Low-density characteristic also contributed to a lower increase of water absorption after weather degradation, for samples with water-borne coatings. Natural weathering enhanced the effect of wood characteristics on coated samples, likely by an increase of coating permeability.

  • 29.
    van Blokland, Joran
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University, Linnaeus Knowledge Environments, Advanced Materials.
    Performance of thermally modified spruce timber in outdoor above-ground conditions: Checking, dynamic stiffness and static bending properties2020In: Applied Sciences, E-ISSN 2076-3417, Vol. 10, no 11, p. 1-25, article id 3975Article in journal (Refereed)
    Abstract [en]

    Previous studies have shown that thermally modified wood (TMW) performs well in outdoor, above‐ground conditions in terms of resistance to wood‐decaying fungi. Yet, little is known about the development of defects such as checks and the corresponding mechanical properties of TMW in this condition. This experiment focused on the effect of 30 months outdoor above‐ground exposure (weathering) on the degree of checking, dynamic stiffness and static bending properties of thermally modified timber (TMT) of Norway spruce. Two board pairs per log were cut from 190 logs; one board of each pair was thermally modified and the other used as control. Then, 90 board pairs were exposed to the weather in south Sweden. Surface checking and axial stiffness were monitored at six‐month intervals by using digital photography and non‐destructive tests (time‐of‐flight and resonance method) to monitor changes in the material upon weathering. Finally, all boards were tested destructively in a 4‐point static bending test following EN 408 standard. Results showed that weathering had no significance influence on static bending properties of TMT even though the degree of checking was considerably higher in TMT than unmodified timber after weathering. In particular, checks along growth rings were deeper, longer and more common in TMT after weathering, especially on the pith side of boards. The maximum depth of these checks did not depend on board orientation (i.e., which side was exposed) and exceeded limits given in strength grading standards for 7% of the modified boards included. Axial dynamic stiffness determined at 6‐month intervals was less influenced by fluctuations in moisture content for TMT compared to unmodified timber, but did not confirm the increase in the degree of checking of TMT. The presence of checks from weathering did influence failure modes in TMT; horizontal shear failure became more frequent and some boards failed in compression.

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  • 30.
    Wang, Xiaodong Alice
    et al.
    Luleå University of Technology.
    Björnberg, Jonathan
    Luleå University of Technology.
    Hagman, Olle
    Luleå University of Technology.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Wan, Hui
    Mississippi State University, USA.
    Niemz, Peter
    Swiss Federal Institute of Technology in Zurich, Switzerland.
    Effect of Low Temperatures on the Block Shear Strength of Norway Spruce Glulam Joints2016In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 11, no 4, p. 9638-9648Article in journal (Refereed)
    Abstract [en]

    The block shear strength of Norway spruce (Picea abies (L.) Karst.) glulam joints was tested under low temperature. Glulam samples were glued with the three of the most common outdoor structural adhesives. The cold temperatures tested were 20, −20, −30, −40, -50 and −60 °C. Within the temperature test range, the block shear strength of the glulam joints was resistant to the effect of temperature. As the temperature decreased, the joints’ block shear strength did not show any significant change. In most cases, phenol-resorcinol-formaldehyde (PRF) adhesive yielded the strongest block shear strength, while melamine-formaldehyde (MF) adhesive yielded the weakest block shear strength. Melamine-urea-formaldehyde (MUF) adhesive yielded similar results to those of MF adhesives for all temperatures tested. The block shear strengths of the glulam joints with PRF, MUF and MF adhesives were not sensitive to temperature change. The results indicated that PRF, MUF and MF adhesives are stable for outdoor structural engineered wood construction in cold climate. The results also suggest that the SS-EN 14080 (2013) standard for the block shear method may not be the proper standard for testing differences in shear strength at different temperatures. The EN 302-1 (2011) standard could be more suitable for this purpose.

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