| 1. |
- Olsson, Anders, 1973-, et al.
(författare)
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Relationships between stiffness of material, lamellas and CLT elements with respect to out of plane bending and rolling shear
- 2023
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Ingår i: European Journal of Wood and Wood Products. - : Springer Nature. - 0018-3768 .- 1436-736X. ; 81, s. 871-886
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Tidskriftsartikel (refereegranskat)abstract
- The use of cross laminated timber (CLT) for construction has increased greatly in recent years and the large volumes ofwood used for CLT means that it is important to optimize the use of the material. This requires relevant grading of lamellasand knowledge of relationships between lamella and CLT properties. In the present study, the relationship between dynamicaxial modulus of elasticity (MoE) of lamellas and the quasi-static out of plane bending stiffness of CLT is investigated. Bymeans of four-point bending test, it is shown that the effective quasi-static MoE of lamellas in CLT is only 2–6% lower thanthe average axial dynamic MoE of the individual lamellas. With this knowledge, producers of CLT can easily predict andcontrol the important out of plane bending stiffness of the produced CLT. Moreover, it is shown that effective rolling shearstiffness of layers in CLT can be accurately determined by means of digital image correlation performed in connection tofour-point bending of CLT, even for long test spans. For layers of lamellas of Scots pine of size 40 × 190 mm2the averageapparent or effective rolling shear modulus was determined to be 159 MPa. The average rolling shear modulus of the samematerial was determined to be 56 MPa.
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| 2. |
- Clemons, Craig M., et al.
(författare)
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Chapter 13 : Wood/nonwood thermoplastic composites
- 2012. - 2
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Ingår i: Handbook of wood chemistry and wood composites, second edition. - Boca Racon, FL : CRC Press. - 9781439853801 ; , s. 473-508
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Bokkapitel (refereegranskat)
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| 3. |
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| 4. |
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| 5. |
- Källbom, Susanna
(författare)
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Characterisation of thermally modified wood for use as component in biobased building materials
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The building sector shows growing interest in biobased building materials. Wood components, here defined as ground or milled wood, i.e. by-products (residuals/residues) from wood processing, such as sawdust or shavings, are valuable raw materials for new types of durable biocomposites suitable for outdoor building applications. An important research question related to such composites is how to characterise and enhance molecular interactions, i.e. adhesion properties, between wood and binder components. Another challenge is the hygroscopicity of the wood component, which can lead to dimensional changes and interfacial cracks during exposure to varying moisture conditions. Thermal modification of wood reduces its hygroscopicity, thereby, increasing its durability, e.g. its dimensional stability and resistance to biodeterioration. The hypothesis is that the use of thermally modified wood (TMW) components in biocomposites can enhance their durability properties and, at the same time, increase the value of residues from TMW processing. The main objective of this thesis is to study and analyse the surface and sorption properties of TMW components using inverse gas chromatography (IGC), dynamic vapour sorption (DVS), X-ray photoelectron spectroscopy (XPS), and the multicycle Wilhelmy plate method. The aim is to gain a better understanding of the surface and sorption characteristics of TMW components to enable the design of optimal adhesion properties and material combinations (compatibility) for use in biocomposites, especially suitable for outdoor and moist building material applications. Samples of TMW and unmodified wood (UW) components of Norway spruce (Picea abies Karst.) and Scots pine (Pinus sylvestris L.) heartwood were prepared and analysed with respect to surface energetics, hygroscopicity, liquid sorption and resulting swelling. The work also included analysis of surface chemical composition, as well as influences of extractives and moisture sorption history. The effect of using TMW components in a wood plastic composite (WPC) exposed to a series of soaking-drying cycles in water was studied with a focus on water sorption, swelling and micromorphological changes. The IGC analyses indicate that TMW components of spruce have a more heterogeneous surface energy character, i.e. a distinctly higher dispersive part of surface energy for low surface coverages, than do UW components. This is suggested to be due to the higher percentage of hydrophobic extractives present in TMW samples. Lewis acid-base analysis indicates that both UW and TMW components from spruce have a predominantly basic character and an enhanced basicity for the latter ones. Results show that both the hygroscopicity and water liquid uptake are lower for TMW than for UW samples. Unexpectedly, a significantly lower rate of water uptake was found for the extracted UW of pine heartwood than for non-extracted samples. In the former case, this is presumably due to contamination effects from water-soluble extractives, which increase capillary flow into wood voids, as proven by a decrease in water surface tension. Water uptake as well as swelling was significantly reduced for the WPCs with TMW and hot-water extracted UW components compared with the WPCs with UW components. This reduction also resulted in fewer wood component-polymer interfacial cracks in the WPCs with the modified wood components.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Popescu, Carmen-Mihaela, et al.
(författare)
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Structural characterization and mechanical properties of wet-processed fibreboard based on chemo-thermomechanical pulp, furanic resin and cellulose nanocrystals
- 2020
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Ingår i: International Journal of Biological Macromolecules. - : Elsevier. - 0141-8130 .- 1879-0003. ; 145, s. 586-593
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Tidskriftsartikel (refereegranskat)abstract
- Fibreboards are made of lignocellulosic fibres and synthetic adhesive which connect them. These synthetic adhesives, while relatively low-cost, are usually non-biodegradable and may cause health and environmental issues. Therefore, in recent years, there has been an increased demand for replacing these adhesives with bio-derived adhesives. The present study aims to develop fibreboards from chemo-thermomechanical pulp (CTMP) and a furanic resin based on prepolymers of furfuryl alcohol via wet-processing. To improve the bonding properties, maleic acid, aluminium sulphate, and cellulose nanocrystals (CNCs) were added. The resulting fibreboards were evaluated for their structural features and mechanical properties. The bending strength was improved when CNCs were added into the fibre's suspension, and the morphology indicated a more compact structure. The combination of the CTMP with CNC and Biorez resulted in the same mechanical behaviours as those noted for CTMP alone, the best performance being observed for the boards in which Al2(SO4)3 was added. Infrared spectroscopy and X-ray diffraction also proved the presence of cellulose nanocrystals and resin in the boards by increased specific bands intensity and crystallinity index, respectively.
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| 10. |
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| 11. |
- Ruponen, J., et al.
(författare)
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Tensile-shear strength studies on self-bonded 2-ply birch veneer joint manufactured and tested by applying Automated Bonding Evaluation System (ABES) hot press
- 2016
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Ingår i: WCTE 2016 - World Conference on Timber Engineering. - : Vienna University of Technology. - 9783903039001
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Konferensbidrag (refereegranskat)abstract
- An Automatic Bond Evaluation System (ABES) hot press was employed to manufacture a self-bonded joint between two veneers of rotary-cut birch (Betula pendula Roth). The hot-pressing conditions were 220 °C and 5.0 MPa, with press times ranging from 180 s to 600 s with 60 s intervals. Additionally, the log-soaking temperature (20 °C and 70 °C) and the veneer initial MC (6% and 11%) were varied to study the effect on the tensile-shear strength of the joints. For one set, the surface properties were altered by acetone extraction. The samples were tested at 11% MC. However, one set was partly duplicated and tested at 6% MC, to study how the testing conditions influenced the bond strength. The maximum average tensile-shear strength was 3.3 MPa, observed after 600 s hot pressing. The studies also included bond-line micromorphology analysis by applying SEM combined with a micromachining surface preparation technique based on UV excimer laser ablation. It was also indicated that longer hot-pressing times, lower veneer initial MC and a lower testing MC resulted in increased tensile-shear strength. Acetone extraction decreased the bond strength with increased standard deviation. Finally, the highest single and average strengths were observed for veneers from higher soaking temperature.
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| 12. |
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| 13. |
- Segerholm, Kristoffer, 1979-, et al.
(författare)
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Adhesion studies of scots pine-polypropylene bond using ABES
- 2010
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Ingår i: In Proceedings of the 6th meeting of the Nordic-Baltic Network in Wood Material Science and Engineering, WSE. - : Tallinn University of Technology.
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Konferensbidrag (refereegranskat)
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| 14. |
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| 15. |
- Segerholm, Kristoffer, 1979-
(författare)
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Characteristics of wood plastic composites based on modified wood : Moisture properties, biological performance and micromorphology
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biobased materials made from renewable resources, such as wood, play an important role in the sustainable development of society. One main challenge of biobased building materials is their inherent moisture sensitivity, a major cause for fungal decay, mold growth and dimensional instability, resulting in decreased service life as well as costly maintenance. A new building material known as wood-plastic composites (WPCs) has emerged. WPCs are a combination of a thermoplastic matrix and a wood component, the former is usually recycled polyethylene or polypropylene, and the latter a wood processing residual, e.g. sawdust and wood shavings.The objective of this thesis was to gain more insight about characteristics of WPCs containing a modified wood component. The hypothesis was that a modified wood component in WPCs would increase the moisture resistance and durability in outdoor applications. The study comprises both injection molded and extruded WPC samples made with an unmodified, acetylated, thermally modified or furfurylated wood component in a polypropylene (PP), high density polyethylene (HDPE), cellulose ester (CAP, a cellulose ester containing both acetate and propionate substituents) or polylactate (PLA) matrix. The WPCs were prepared with 50-70 weight-% wood. The emphasis was on studying the moisture sorption, fungal resistance and micromorphological features of these new types of composites. Water sorption in both liquid and vapor phases was studied, and the biological performance was studied both in laboratory and in long term outdoor field tests. Micromorphological features were assessed by analyzing of the wood component prior to and after processing, and by studying the composite microstructure by means of a new sample preparation technique based on UV excimer laser ablation combined with scanning electron microscopy (SEM).Results showed that the WPCs with a modified wood component had a distinctly lower hygroscopicity than the WPCs with unmodified wood, which resulted in less wood-plastic interfacial cracks when subjected to a moisture soaking-drying cycle. Durability assessments in field and marine tests showed that WPCs with PP or CAP as a matrix and 70 weight-% unmodified wood degraded severely within a few years, whereas the corresponding WPCs with a modified wood component were sound after 7 years in field tests and 6 years in marine tests. Accelerated durability tests of WPCs with PLA as a matrix showed only low mass losses due to decay. However, strength losses due to moisture sorption suggest that the compatibility between the PLA and the different wood components must be improved. The micromorphological studies showed that WPC processing distinctly reduces the size and changes the shape of the wood component. The change was most pronounced in the thermally modified wood component which became significantly reduced in size. The disintegration of the modified wood components during processing also creates a more homogeneous micromorphology of the WPCs, which may be beneficial from a mechanical performance perspective. Future studies are suggested to include analyses of the surface composition, the surface energy and the surface energy heterogeneity of both wood and polymer components in order to tailor new compatible wood-polymer combinations in WPCs and biocomposites.
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| 16. |
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| 17. |
- Segerholm, Kristoffer, 1979-, et al.
(författare)
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Durability of PLA - Modified Wood Composites
- 2011
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Ingår i: Proceedings of the 11th International Conference on Wood & Biofiber Plastic Composites.
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Konferensbidrag (refereegranskat)
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| 18. |
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| 19. |
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| 20. |
- Segerholm, Kristoffer, 1979-, et al.
(författare)
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Moisture and Fungal Durability of Wood-Plastic Composites Made With Chemically Modified and Treated Wood Flour
- 2013
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Ingår i: Proceedings IRG Annual Meeting. ; , s. IRG/WP 13-40648-
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Konferensbidrag (refereegranskat)abstract
- Evaluating the fungal durability of wood-plastic composites (WPCs) is complicated by the influence of slow moisture sorption. Recently, the American Wood Protection Association (AWPA) Standard Method E10, Testing Wood Preservatives by Laboratory Soil-Block Cultures, was modified to incorporate not only solid wood, but also wood-based composites and WPCs. To simulate long term WPC performance, conditioning of the specimens is now required prior to fungal exposure to increase the moisture content of the specimens. The moisture and fungal durability, as well as the mechanical properties, of two different WPCs were investigated in the laboratory following this new AWPA E10-12 Standard. Wood flour was modified with acetic anhydride and then extruded with high density polyethylene (HDPE). Wood flour was treated with an isothiazolone-based solution and then injected molded with polypropylene (PP). WPCs were conditioned by water soaking either 2 weeks at 22 ˚C or 5 days at 70 ˚C. Weight and moisture content of the WPCs were monitored. Results showed that the acetylation decreased the moisture sorption of the WPCs and showed no mass losses due to decay. The WPC with an isothiazolone-based solution did not show any mass losses due to fungal decay.
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| 21. |
- Segerholm, Kristoffer, 1979-, et al.
(författare)
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Moisture sorption, biological durability, and mechanical performance of WPC containing modified wood and polylactates
- 2012
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 7:4, s. 4575-4585
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Tidskriftsartikel (refereegranskat)abstract
- Biological durability is an important feature for wood-plastic composites (WPC) intended for outdoor applications. One route to achieving WPC products with increased biological durability is to use wood preservative agents in the formulation of the WPC. Another option could be to use a chemically modified wood component that already exhibits increased resistance to biological degradation. There is also a need to use biobased thermoplastics made from renewable resources, which would decrease the dependency on petrochemically-produced thermoplastics in the future. The objective of this study was to examine moisture sorption properties, biological durability, and mechanical performance of injection-molded WPC samples based on acetylated or thermally modified wood components and a polylactate matrix. The biological durability was evaluated in a terrestrial microcosm (TMC) test according to ENV 807, followed by mechanical evaluation in a center point bending test. The moisture sorption properties were investigated via both water soaking and exposure in a high-humidity climate. Low or negligible mass losses were observed in the TMC test for all WPC samples. However, the mechanical evaluation after exposure in the TMC test showed 35-40% losses in both strength and stiffness for the WPC containing an unmodified wood component.
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| 22. |
- Segerholm, Kristoffer, 1979-, et al.
(författare)
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Moisture sorption in artificially aged wood-plastic composites
- 2012
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Ingår i: BioResources. - 1930-2126. ; 7:1, s. 1283-1293
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Tidskriftsartikel (refereegranskat)abstract
- Moisture sorption in wood-plastic composites (WPCs) affects their durability and dimensional stability. In certain outdoor exposures, the moisture properties of WPCs are altered due to e. g. cracks induced by swelling and shrinkage of the components, as well as UV degradation or biological attack. The aim of this work was to study the effect of different artificial ageing routes on the moisture sorption properties of WPCs. Extruded WPCs were prepared with either unmodified or acetylated wood and recycled high-density polyethylene (HDPE). The WPC samples were artificially aged involving water soaking, artificial weathering, and white-or brown-rot decay in different combinations. After the ageing, the samples were conditioned in either 65% or 90% relative humidity (RH) until equilibrium moisture content was reached. A dynamic moisture sorption analyzer was used to monitor the sorption rate of samples subjected to a climate change from 65% to 90% RH. Scanning electron microscopy was used to study the surface morphology of the aged composites. Results showed that the artificial weathering caused cracking of the HDPE matrix at the composite surface, as well as a wood-matrix debonding, resulting in an increased moisture sorption rate. The WPC samples subjected to white-rot decay showed the highest moisture sorption rate.
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| 23. |
- Segerholm, Kristoffer, 1979-, et al.
(författare)
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Mould growth resistance of fungicide-containing WPC
- 2011
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Ingår i: Proceedings of the 7th meeting of the Nordic-Baltic Network in Wood Material Science & Engineering (WSE). - : Norsk institutt for skog og landskap. ; , s. 25-30
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Konferensbidrag (refereegranskat)
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| 24. |
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| 25. |
- Segerholm, Kristoffer, 1979-
(författare)
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Wood Plastic Composites made from Modified Wood : Aspects on Moisture Sorption, Micromorphology and Durability
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood plastic composite (WPC) materials have seen a continuous market growth worldwide in the last decade. So-called extruded WPC profiles are today mainly used in outdoor applications, e.g. decking, railing and fencing. In outdoor conditions, moisture sorption in the wood component combined with temperature induced movements of the polymer matrix causes deformations of such composites. On the macroscopic scale this may lead to unacceptable warp, cup and bow of the WPC products, but on a microscopic scale, the movements will cause interfacial cracks between the particles and the matrix, resulting in little or no ability to transfer and re-distribute loads throughout the material. Moisture within the composite will also allow fungi and micro organisms to attack the wood particles. The conceptual idea of this work is to use a chemically modified wood component in WPCs to enhance their long term performance. These chemically modified wood particles exhibit reduced susceptibility to moisture, resulting in better dimensional stability and a higher resistance to biological degradation as compared to that of unmodified wood. The objective of this thesis is to study the effects of using modified wood in WPCs on their moisture sorption behaviour, micromorphology and microbiological durability. The modification methods used were acetylation, heat treatment and furfurylation. Equilibrium moisture content (EMC) and sorption behaviour of WPCs were determined by water vapour sorption experiments. The use of thin sections of the composites enabled EMC to be reached within a comparably short time span. The micromorphology was studied by LV-SEM (low vacuum-scanning electron microscope) using a specially designed sample preparation technique based on UV laser. The biological durability was evaluated by laboratory fungal test methods. The moisture sorption experiments showed lower moisture levels for all the composites when modified wood particles were used. This was also reflected in the micromorphological studies where pronounced wood-plastic interfacial cracks were formed due to moisture movement in the composites with unmodified wood particles. The sample preparation technique by UV laser proved to be a powerful tool for preparing surfaces for micromorphological studies without adding mechanical defects caused by the sample preparation technique itself. Results from the durability test showed that WPCs with modified wood particles are highly resistant to decay by fungi.
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| 26. |
- Westin, Mats, et al.
(författare)
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Wood Plastic Composites from Modified Wood : Part 3. Durability of WPCs with bioderived matrix
- 2008
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Ingår i: The 39th Annual Meeting of the International Research Group on Wood Preservation.
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Konferensbidrag (refereegranskat)abstract
- The decay resistance of fully bio-derived wood plastic composites, WPCs, was tested in bothlaboratory and field tests. The laboratory tests were performed according to modified versionsof AWPA E10 (soil-block test) and ENV 807 (tests in three un-sterile soils) and the field testsaccording to EN 252 (stakes in ground) and EN 275 (resistance to marine borers). The WPCmaterials for laboratory tests were injection molded test specimens with 50% modified woodparticles and 50% cellulose ester (CAP) or poly-lactic acid (PLA) content. The field testspecimens were taken from larger extruded decking board profiles with 60% wood contentand 40% CAP. 60/40-mix (wt/wt) for CAP corresponds to the same volumetric compositionas 70/30-mix (wt/wt) with polypropylene as matrix that was presented in Part 1 and 2.In all laboratory tests the control WPCs performed much better than the pine sapwood controlblocks. The WPCs from modified wood performed better than the control WPC and WPCsfrom acetylated wood performed best with no detectable decay whatsoever.In the field stake test, the WPC from unmodified wood were slightly decayed whereas theWPCs from modified wood were sound. In the marine field test the WPC from unmodifiedwood were severely attacked by shipworm (Teredo navalis), whereas the WPCs frommodified wood were sound.
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| 27. |
- Wålinder, Magnus, 1965-, et al.
(författare)
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Durability of high wood content WPCs
- 2010
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Ingår i: Proceedings of the International Convention of Society of Wood Science and Technology andUnited Nations Economic Commission for Europe – Timber Committee.
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Konferensbidrag (refereegranskat)abstract
- One increasing market segment of building materials is so-called biocomposites, or wood-thermoplastic composites (WPCs). Chiefly, these products are partly made from renewable resources such as wood residuals or agro fibres, functioning as reinforcement, and partly from recyclable thermoplastics or biopolymers, functioning as matrix. In general, WPC products are marketed as a low maintenance building material with a high outdoor durability. The intrinsic high moisture sensitivity of the wood component in combination with a low compatibility between the hydrophilic wood and hydrophobic thermoplastic may, however, result in poor long-term performance and outdoor durability. The objective of this paper is to recapitulate some of our research group’s observations and experience during recent years with respect to both field and laboratory tests related to the durability of WPCs. Of particular interest is one type of extruded WPCs with a comparable high wood content, i.e. ca 70 weight-%, prepared with either a heat treated, acetylated, or unmodified wood component. Observations from outdoor field trials, laboratory fungal decay tests, moisture sorption properties and effects on micromorphology, show that the use of a modified wood component in these WPCs considerably increases their long-term outdoor durability. One reason for this is related to the reduction of the moisture sensitivity of the wood component. Such durable biocomposite-type of building materials with a high wood-content level have the potential to fulfill the criteria for being eco-efficient, that is being both a sustainable and a cost-efficient “green” material.
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| 28. |
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| 29. |
- Wålinder, Magnus, 1965-, et al.
(författare)
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Micromorphological studies of modified wood using a surface preparation technique based on ultraviolet laser ablation
- 2009
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280. ; 4:1-2, s. 46-51
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to demonstrate an ultraviolet (UV) laser ablation technique as a tool for sample preparation in microscopy studies of modified wood. Improved techniques for studying the microstructure of modified wood are crucial for a deeper understanding of many of their physical, mechanical and durability properties. The surface preparation technique is described in this paper. An illustration of micrographs of the micromorphology and polymer distribution in some examples of modified wood is also presented. It is clearly demonstrated that in contrast to conventional surface preparation techniques used for light microscopy and scanning electron microscopy, i.e. razor blade and microtome cutting techniques, UV laser ablation does not introduce any mechanically induced microcracks and redistribution of polymers or other mobile substances in the prepared surface. Results also show that, in particular, this technique seems to be suitable for studying polymer distribution in resin-impregnated wood, as well as detection of microcracks in modified wood cell walls.
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| 30. |
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| 31. |
- Wålinder, Magnus, 1965-, et al.
(författare)
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Water sorption properties and dimensional changes of high wood-content WPC
- 2009
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Ingår i: Proceedings of the 5th meeting of the Nordic Baltic Network in Wood Material Science and Engineering. ; , s. 153-160
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Konferensbidrag (refereegranskat)abstract
- The increased use of wood plastic composites (WPCs) for outdoor building applicationsis accompanied by an increased need for research about their durability properties. Oneparticularly important feature is their water sorption behaviour which relates to e.g. theirdimensional stability, mechanical properties and decay resistance. In this study, we haveinvestigated the water sorption ability and resulting dimensional changes of WPCs witha comparable high wood content, i.e. ca 70 weight-%, prepared with either a heattreated, acetylated or unmodified wood component. The experiments involve immersionof thin veneers of the composites in water with registration of their weight anddimensional changes until they have reached saturation. The results show that the WPCscontaining a modified wood component show the lowest level of water sorption anddimensional changes after saturation compared with the WPCs containing unmodifiedwood. A notably lower degree of a supposedly algae growth is also observed for thesamples with acetylated wood. One question that was generated during thisinvestigation relates to the density of the wood cell-wall and its relation to the appliedwood modification route and moisture uptake. The general conclusion regarding this isthat further studies are necessary to encompass such a topic, e.g. by more precisemeasurements of the wood cell-wall density in both dry and wet state.
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| 32. |
- Wålinder, Magnus, 1965-, et al.
(författare)
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Wettability of acetylated Southern yellow pine
- 2013
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Ingår i: International Wood Products Journal. - 2042-6445 .- 2042-6453. ; 4:3, s. 197-203
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to achieve a better understanding of the wettability, i.e. liquids wetting and sorption characteristics (or penetrability), of acetylated Southern yellow pine (SYP) including probable differences in such characteristics between early- or latewood. Matched samples of acetylated and untreated SYP boards were prepared. The wettability of the samples were measured by the Wilhelmy technique using standard probe liquids as well as two different sample coatings, a cationic knot sealer and an acrylic based dye. The results showed that latewood regions of the acetylated wood had a noticeably lower uptake of the non-polar low surface tension liquid octane as well as the polar high surface tension liquid water compared with latewood of the untreated controls. Contact angle analysis based on the Lewis acid-base concept indicated that the acetylated wood is predominantly Lewis basic. A preferential wetting of the knot sealer was observed on the acetylated wood.
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