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Segerholm, KristofferORCID iD iconorcid.org/0000-0001-7014-6230
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Joffre, T., Segerholm, K., Persson, C., Bardage, S. L., Hendriks, C. L. L. & Isaksson, P. (2017). Characterization of interfacial stress transfer ability in acetylation-treated wood fibre composites using, X-ray microtomography. INDUSTRIAL CROPS AND PRODUCTS, 95, 43-49
Open this publication in new window or tab >>Characterization of interfacial stress transfer ability in acetylation-treated wood fibre composites using, X-ray microtomography
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2017 (English)In: INDUSTRIAL CROPS AND PRODUCTS, ISSN 0926-6690, Vol. 95, p. 43-49Article in journal (Refereed) Published
Abstract [en]

The properties of the fibre/matrix interface contribute to stiffness, strength and fracture behaviour of fibre-reinforced composites. In cellulosic composites, the limited affinity between the hydrophilic fibres and the hydrophobic thermoplastic matrix remains a challenge, and the reinforcing capability of the fibres is hence not fully utilized. A direct characterisation of the stress transfer ability through pull-out tests on single fibres is extremely cumbersome due to the small dimension of the wood fibres. Here a novel approach is proposed: the length distribution of the fibres sticking out of the matrix at the fracture surface is approximated using X-ray microtomography and is used as an estimate of the adhesion between the fibres and the matrix. When a crack grows in the material, the fibres will either break or be pulled-out of the matrix depending on their adhesion to the matrix: good adhesion between the fibres and the matrix should result in more fibre breakage and less pull-out of the fibres than poor adhesion. The effect of acetylation on the adhesion between the wood fibres and the PLA matrix was evaluated at different moisture contents using the proposed method. By using an acetylation treatment of the fibres it was possible to improve the strength of the composite samples soaked in the water by more than 30%.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
CT analysis, Wood fibres, PLA, Adhesion, Acetylation
National Category
Environmental Sciences related to Agriculture and Land-use
Identifiers
urn:nbn:se:kth:diva-200197 (URN)10.1016/j.indcrop.2016.10.009 (DOI)000390621600006 ()2-s2.0-84991689339 (Scopus ID)
Note

QC 20170202

Available from: 2017-02-02 Created: 2017-01-23 Last updated: 2022-06-27Bibliographically approved
Kymalainen, M., Hautamaki, S., Lillqvist, K., Segerholm, K. & Rautkari, L. (2017). Surface modification of solid wood by charring. Journal of Materials Science, 52(10), 6111-6119
Open this publication in new window or tab >>Surface modification of solid wood by charring
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2017 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, no 10, p. 6111-6119Article in journal (Refereed) Published
Abstract [en]

Most wooden structures for outdoor applications require repetitive maintenance operations to protect the surfaces from adverse effects of weathering. One-sided surface modification of boards with a relatively fast charring process has the potential to increase the durability and service life of wooden claddings. To assess some weathering-related effects on surface charred wood, spruce and pine sapwood were subjected to a series of long charring processes (30-120 min) at a moderate temperature of 250 A degrees C and to a short one (30 s) at a high temperature of 400 A degrees C. The wettability and contact angles of treated samples were investigated, and the heat transfer was measured along with the micromorphological changes taking place in the material. The result revealed an increased moisture resistance of charred spruce sapwood and an increased water uptake of pine sapwood. The contact angles of both wood species improved compared to references. Heat conduction measurement revealed that only a thin section of the wood was thermally modified. Some micromorphological changes were recorded, especially on the inside walls of the lumina. The results show that spruce sapwood has an improved resistance towards moisture-induced weathering, but more studies are needed to unlock the potential of surface charred wood.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-205754 (URN)10.1007/s10853-017-0850-y (DOI)000395206400058 ()2-s2.0-85011878891 (Scopus ID)
Note

QC 20170424

Available from: 2017-04-24 Created: 2017-04-24 Last updated: 2024-03-18Bibliographically approved
Laine, K., Segerholm, K., Wålinder, M., Rautkari, L., Hughes, M. & Lankveld, C. (2016). Surface densification of acetylated wood. European Journal of Wood and Wood Products, 74(6), 829-835
Open this publication in new window or tab >>Surface densification of acetylated wood
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2016 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 74, no 6, p. 829-835Article in journal (Refereed) Published
Abstract [en]

The mechanical properties of wood can be improved by compressing its porous structure between heated metal plates. By adjusting the process parameters it is possible to target the densification only in the surface region of wood where the property improvements are mostly needed in applications, such as flooring. The compressed form is, however, sensitive to moisture and will recover to some extent in high humidity. In this study, therefore, acetylated radiata pine was utilised in the surface densification process in order to both reduce the set-recovery of densified wood and to improve the hardness of the acetylated wood. Pre-acetylation was found to significantly reduce the set-recovery of surface densified wood. However, after the second cycle the increase in set-recovery of acetylated wood was relatively higher than the un-acetylated wood. The acetylated samples were compressed by only 1 mm (instead of the target 2 mm), yet, the hardness and hardness recovery of the acetylated samples significantly increased as a result of densification. It was also discovered that rough (un-planed) surfaces may be surface densified, however, even if the surface became smooth to the touch, the appearance remained uneven.

Place, publisher, year, edition, pages
Springer, 2016
Keywords
Acetylation, Densification, Hardness, Recovery, Acetylated wood, Densified wood, Mechanical properties of wood, Porous structures, Process parameters, Property improvement, Surface densification, Surface region, Wood
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-195233 (URN)10.1007/s00107-016-1077-3 (DOI)000385208400005 ()2-s2.0-84976477767 (Scopus ID)
Note

QC 20161117

Available from: 2016-11-17 Created: 2016-11-02 Last updated: 2022-06-27Bibliographically approved
Ruponen, J., Kimpimäki, S., Rohumaa, A., Laine, K., Segerholm, K., Wålinder, M., . . . Hughes, M. (2016). Tensile-shear strength studies on self-bonded 2-ply birch veneer joint manufactured and tested by applying Automated Bonding Evaluation System (ABES) hot press. In: WCTE 2016 - World Conference on Timber Engineering: . Paper presented at 2016 World Conference on Timber Engineering, WCTE 2016, 22 August 2016 through 25 August 2016. Vienna University of Technology
Open this publication in new window or tab >>Tensile-shear strength studies on self-bonded 2-ply birch veneer joint manufactured and tested by applying Automated Bonding Evaluation System (ABES) hot press
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2016 (English)In: WCTE 2016 - World Conference on Timber Engineering, Vienna University of Technology , 2016Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
Vienna University of Technology, 2016
Keywords
ABES, Birch, Laser ablation, Self-bonding, SEM, Soaking temperature, Tensile-shear strength, Veneer, Ablation, Acetone, Bond strength (materials), Excimer lasers, Extraction, Hot pressing, Presses (machine tools), Scanning electron microscopy, Shear flow, Tensile testing, Thermal logging, Timber, Veneers, Self bonding, Tensile shear strength, Tensile strength
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-207528 (URN)2-s2.0-85010960673 (Scopus ID)9783903039001 (ISBN)
Conference
2016 World Conference on Timber Engineering, WCTE 2016, 22 August 2016 through 25 August 2016
Note

Conference code: 124667; Export Date: 22 May 2017; Conference Paper. QC 20170531

Available from: 2017-05-31 Created: 2017-05-31 Last updated: 2022-11-29Bibliographically approved
Ormondroyd, G. A., Källbom, S., Curling, S. F., Stefanowski, B. K., Segerholm, K., Wålinder, M. & Jones, D. (2016). Water sorption, surface structure and surface energy characteristics of wood composite fibres refined at different pressures. Wood Material Science & Engineering, 1-8
Open this publication in new window or tab >>Water sorption, surface structure and surface energy characteristics of wood composite fibres refined at different pressures
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2016 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, p. 1-8Article in journal (Refereed) Published
Abstract [en]

During fibre processing, wood fibres are subjected to a range of physical and chemical conditions sufficient to slightly alter their chemical composition and hence their ultimate performance when used in the manufacture of wood fibre-based composites. In order to better understand the effects of refiner conditions on material performance, wood fibres were subjected to processing at different refiner pressures (4, 6, 8 and 10 bar) and subsequently dried in a flash drier. The fibres were analysed for changes in surface area, surface energy, surface structure and water vapour sorption characteristics. The methods applied were nitrogen adsorption utilising the Brunauer–Emmett–Teller theory, inverse gas chromatography, scanning electron microscopy and dynamic vapour sorption. It was found that increasing refiner pressure resulted in fibres of lower surface area, accompanied by increasing dispersive surface energies up to operating refiner pressures of 8 bar. It was found with fibres refined at different pressures that as the refiner pressure increased the equilibrium moisture content of the fibre decreased at the set relative humidities. However, it was also noted that the hysteresis was not significantly different between each of the refiner pressures. The results suggest that different refiner pressures can be used to tune the surface characteristics which may be beneficial to product development and the improvement of the environmental profile of the wood fibre composites.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
Keywords
dynamic vapour sorption, refiner pressures, surface energy, surface structure, water sorption, Wood fibre, Atmospheric humidity, Chromatography, Fibers, Gas adsorption, Gas chromatography, Interfacial energy, Nitrogen, Processing, Refining, Scanning electron microscopy, Sorption, Dynamic vapour sorptions, Energy characteristics, Equilibrium moisture contents, Inverse gas chromatography, Sorption characteristics, Surface characteristics, Wood
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-188232 (URN)10.1080/17480272.2016.1150343 (DOI)000402709800003 ()2-s2.0-84958818439 (Scopus ID)
Note

QC 20160613

Available from: 2016-06-13 Created: 2016-06-09 Last updated: 2024-03-18Bibliographically approved
Källbom, S., Rautkari, L., Wålinder, M., Johansson, L.-S., Campbell, J., Segerholm, K., . . . Laine, K. (2016). Water vapour sorption characteristics and surface chemical composition of thermally modified spruce (Picea abies karst). International Wood Products Journal, 7(3), 116-123
Open this publication in new window or tab >>Water vapour sorption characteristics and surface chemical composition of thermally modified spruce (Picea abies karst)
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2016 (English)In: International Wood Products Journal, ISSN 2042-6445, E-ISSN 2042-6453, Vol. 7, no 3, p. 116-123Article in journal (Refereed) Published
Abstract [en]

The objective of this work was to study the hygroscopicity and surface chemical composition of thermally modified (TM) spruce. An effort was also made to study if those features were influenced by a previous exposure to a significant increase in relative humidity (RH). TM and unmodified Norway spruce (Picea abies Karst) samples, both in solid and ground form, were prepared. Water vapour sorption characteristics of the ground samples were obtained by measuring sorption isotherms using a dynamic vapour sorption (DVS). The surface chemical composition of the solid samples, both acetone extracted and non-extracted, were analysed using X-ray photoelectron spectroscopy (XPS). The DVS analysis indicated that the TM wood exposed to the 75% RH revealed a decrease in isotherm hysteresis. The XPS analysis indicated a decrease of acetone extractable or volatile organic components and a relative increase of non-extractable components for the samples exposed to the increased RH condition.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
Keywords
Dynamic vapour sorption (DVS), Extractives, Norway spruce, Surface chemical composition, Thermally modified wood, X-ray photoelectron spectroscopy (XPS)
National Category
Materials Engineering Chemical Sciences Wood Science
Identifiers
urn:nbn:se:kth:diva-188633 (URN)10.1080/20426445.2016.1160590 (DOI)000382319700002 ()2-s2.0-84981554847 (Scopus ID)
Note

QC 20160711

Available from: 2016-06-15 Created: 2016-06-15 Last updated: 2024-03-18Bibliographically approved
Laine, K., Segerholm, K., Wålinder, M., Rautkari, L. & Hughes, M. (2016). Wood densification and thermal modification: hardness, set-recovery and micromorphology. Wood Science and Technology, 50(5), 883-894
Open this publication in new window or tab >>Wood densification and thermal modification: hardness, set-recovery and micromorphology
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2016 (English)In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 50, no 5, p. 883-894Article in journal (Refereed) Published
Abstract [en]

The density of wood can be increased by compressing the porous structure under suitable moisture and temperature conditions. One aim of such densification is to improve surface hardness, and therefore, densified wood might be particularly suitable for flooring products. After compression, however, the deformed wood material is sensitive to moisture, and in this case, recovered up to 60 % of the deformation in water-soaking. This phenomenon, termed set-recovery, was reduced by thermally modifying the wood after densification. This study presents the influence of compression ratio (CR = 40, 50, 60 %) and thermal modification time (TM = 2, 4, 6 h) on the hardness and set-recovery of densified wood. Previously, set-recovery has mainly been studied separately from other properties of densified wood, while in this work, set-recovery was also studied in relation to hardness. The results show that set-recovery was almost eliminated with TM 6 h in the case of CR 40 and 50 %. Hardness significantly increased due to densification and even doubled compared to non-densified samples with a CR of 50 %. Set-recovery reduced the hardness of densified (non-TM) wood back to the original level. TM maintained the hardness of densified wood at an increased level after set-recovery. However, some reduction in hardness was recorded even if set-recovery was almost eliminated.

Place, publisher, year, edition, pages
Springer, 2016
National Category
Wood Science
Identifiers
urn:nbn:se:kth:diva-196446 (URN)10.1007/s00226-016-0835-z (DOI)000385253100002 ()2-s2.0-84969895593 (Scopus ID)
Note

QC 20161129

Available from: 2016-11-29 Created: 2016-11-14 Last updated: 2022-06-27Bibliographically approved
Laine, K., Segerholm, K., Wålinder, M., Rautkari, L., Hughes, M. & Rowell, R. (2015). Acetylation and densification of wood. In: : . Paper presented at 11th Meeting of the Northern European Network for Wood Science and Engineering – WSE. 14.-15.9.2015, Poznan, Poland.
Open this publication in new window or tab >>Acetylation and densification of wood
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2015 (English)Conference paper, Published paper (Other academic)
Abstract [en]

The purpose of this study was to explore the possibility to surface densify acetylated solid wood. The aim of surface densification is to improve mechanical properties, such as hardness, at the very surface of wood where the property improvements are mostly needed (e.g. in flooring and decking). However, when subjected to moisture, surface densified wood may swell back almost to the original dimensions. Therefore, acetylated and non-acetylated wood was surface densified in order to investigate whether the dimensional stability of densified wood may be improved by pre-acetylation. Surface densification was performed by compressing the acetylated radiate pine samples between metal plates with only one side heated (150°C) in order to target the deformation to one surface only. The original thickness of the samples was 20 mm and the target thickness 18 mm which was controlled by metal stops. The recovery of the deformation (set-recovery) was measured by soaking the samples in water and measuring the oven-dry thickness before and after soaking in repeated cycles. It was found that acetylated wood may be surface densified and indeed the set-recovery of the pre-acetylated wood was significantly lower (17.4 %) compared to non-acetylated wood (72.8 %). Further studies in adjusting the process parameters might lead to even higher reduction in set-recovery.

Keywords
acetylation, densification, moisture content, set-recovery
National Category
Wood Science
Identifiers
urn:nbn:se:kth:diva-205574 (URN)
Conference
11th Meeting of the Northern European Network for Wood Science and Engineering – WSE. 14.-15.9.2015, Poznan, Poland
Note

The authors would like to acknowledge Accsys Technologies (Chiel Lankveld, Ferry Bongers and John Alexander) for providing the wood material for this study and giving comments during the writing process. QC 20170424

Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2024-03-18Bibliographically approved
Laine, K., Segerholm, K., Wålinder, M., Rautkari, L., Hughes, M., Källbom, S. & Jones, D. (2015). Hardness, set-recovery and micromorphology studies of densified and thermally modified wood. In: : . Paper presented at The 8th European Conference of Wood Modification. 26.-27.10.2015, Helsinki, Finland..
Open this publication in new window or tab >>Hardness, set-recovery and micromorphology studies of densified and thermally modified wood
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2015 (English)Conference paper, Published paper (Other academic)
Abstract [en]

The purpose of the work reported in this paper was to increase the density of Scots pine wood in order to improve its hardness. Density was increased by compressing the porous structure of wood between heated metal plates in the radial direction by 40, 50 or 60% of the thickness. The compressed state was stabilised by thermally modifying (TM) the samples at 200 °C under steam conditions for 2, 4 or 6h. Set-recovery was almost eliminated (<1%) with TM of 6h for samples compressed 40 and 50%. It was discovered that hardness of densified wood was in some cases even three times higher compared to untreated wood. However, the hardness of the densified, non-TM wood was reduced after soaking and drying back to the original untreated level, while TM of 4 and 6h maintained an increased level of hardness.

Keywords
densification, hardness, SEM, set-recovery, thermal modification, UV-laser ablation
National Category
Wood Science
Identifiers
urn:nbn:se:kth:diva-205570 (URN)
Conference
The 8th European Conference of Wood Modification. 26.-27.10.2015, Helsinki, Finland.
Note

The authors would like to thank Joachim Seltman (SP, Sweden) and Niko Tuominen (Aalto University) for technical support. The study was supported by the EcoBuild Centre, Stiftelsen Nils och Dorthi Troëdssons forskningsfond and the Finnish Cultural Foundation. QC 20170424

Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2024-03-18Bibliographically approved
Källbom, S., Wålinder, M., Segerholm, K. & Jones, D. (2015). Surface energy characterization of thermally modified spruce using inverse gas chromatography under cyclic humidity conditions. Wood and Fiber Science, 47(4), 410-420
Open this publication in new window or tab >>Surface energy characterization of thermally modified spruce using inverse gas chromatography under cyclic humidity conditions
2015 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 47, no 4, p. 410-420Article in journal (Refereed) Published
Abstract [en]

The surface energy of unmodified and thermally modified spruce wood components was researched at dry and moist conditions using inverse gas chromatography. The results indicate a more pronounced heterogeneous nature of the thermally modified wood surfaces in terms of the dispersive (nonpolar) component of the surface energy, compared with that of the unmodified wood surfaces. The dispersive component of the surface energy of the thermally modified wood ranged between 44 and 38 mJ/m(2) corresponding to an increase in surface coverage from a low level and up to about 10%. Suggested explanations for the more distinct heterogeneity of the thermally modified wood sample are related to chemical changes of the wood substance which seem to result in certain micromorphological features observed by scanning electron microscopy as alternated fracture surfaces created in the grinding process; and also possible changes or redistribution of the wood extractives. An increase of the MC, representing a change from a dry condition of approximately 0% RH to ca 75% RH, of both the unmodified and thermally modified samples seemed to have a marginal influence on the dispersive component of the surface energy. Possible implications of the results in this study can be found in the tailoring of new compatible and durable material combinations, for example, when using thermally modified wood residuals as a component in new types of biocomposites.

Place, publisher, year, edition, pages
SOC WOOD SCI TECHNOL, 2015
Keywords
Thermally modified wood, inverse gas chromatography, humidity cycling, Norway spruce, dispersive surface energy, surface energy heterogeneity, BET-specific surface area
National Category
Materials Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-172956 (URN)000363992000011 ()2-s2.0-84991704745 (Scopus ID)
Funder
Swedish Research Council Formas, EnWoBio 2014-172
Note

QC 20151202

Forskningsfinansiärer: Stiftelsen Nils och Dorthi Troëdssons forskningsfond (Projektnr 793/12 Hydro-termo-mekanisk modifiering av trä). EcoBuild Institute Excellence Centre

Available from: 2015-09-04 Created: 2015-09-03 Last updated: 2024-03-18Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-7014-6230

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