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Källbom, S., Lillqvist, K., Spoljaric, S., Seppala, J., Segerholm, K., Rautkari, L., . . . Wålinder, M. (2020). Effects of water soaking-drying cycles on thermally modified spruce wood-plastic composites. Wood and Fiber Science, 52(1), 2-12
Open this publication in new window or tab >>Effects of water soaking-drying cycles on thermally modified spruce wood-plastic composites
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2020 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 52, no 1, p. 2-12Article in journal (Refereed) Published
Abstract [en]

The overall aim of this work was to gain more insight on the potential of modified wood (TMW) components for use in wood-thermoplastic composites (WPCs). Laboratory-scale TMWPCs were produced, and the effects of severe water soaking-drying cycles on the samples were studied. Water sorption behavior and resulting dimensional and micromorphological changes were also studied, and the results were compared with those of unmodified wood-plastic composites (UWPCs) used as control. The TMW was prepared by cutting a spruce board into half and subjecting one-half to an atmosphere of superheated steam at atmospheric pressure with a peak temperature of 210 degrees C, with the other unmodified wood (UW) half as a control. The TMW and UW components were then prepared by a Wiley mill and thereafter sifted into smaller (mesh 0.20-0.40 mm) and larger (mesh 0.40-0.63 mm) size fractions. A portion of the wood components were also subjected to hydrothermal extraction (HE). Composite samples with these different wood components, polypropylene (PP) matrix, and maleated PP (MAPP) as coupling agent (50/48/2 wood/PP/MAPP ratio by weight) were then prepared by using a Brabender mixer followed by hot pressing. The matching micromorphology of the composites before and after the soaking-drying cycles was analyzed using a surface preparation technique based on ultraviolet-laser ablation combined with scanning electron microscopy. The results of the water absorption tests showed, as hypothesized, a significantly reduced water absorption and resulting thickness swelling at the end of a soaking cycle for the TMWPCs compared with the controls (UWPCs). The water absorption was reduced with about 50-70% for TMWPC and 60-75% for HE-TMWPC. The thickness swelling for TMWPCs was reduced with about 40-70% compared with the controls. Similarly, the WPCs with HE-UW components absorbed about 20-45% less moisture and showed a reduced thickness swelling of about 25-40% compared with the controls. These observations also were in agreement with the micromorphology analysis of the composites before and after the moisture cycling which showed a more pronounced wood-plastic interfacial cracking (de-bonding) as well as other microstructure changes in the controls compared with those prepared with TMW and HE-UW components. Based on these observations, it is suggested that these potential bio-based building materials show increased potential durability for applications in harsh outdoor environments, in particular TMWPCs with a well-defined and comparably small size fractions of TMW components.

Place, publisher, year, edition, pages
SOC WOOD SCI TECHNOL, 2020
Keywords
thermally modified wood (TMW), wood-plastic composite (WPC), water absorption, dimensional stability, dynamic mechanical analysis (DMA), micromorphology, scanning electron microscopy (SEM), UV-laser ablation
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-273529 (URN)10.22382/wfs-2020-002 (DOI)000529410400010 ()2-s2.0-85083033453 (Scopus ID)
Note

QC 20200519

Available from: 2020-05-19 Created: 2020-05-19 Last updated: 2020-05-19Bibliographically approved
Lillqvist, K., Källbom, S., Altgen, M., Belt, T. & Rautkari, L. (2019). Water vapour sorption properties of thermally modified and pressurised hot-water-extracted wood powder. Holzforschung, 73(12), 1059-1068
Open this publication in new window or tab >>Water vapour sorption properties of thermally modified and pressurised hot-water-extracted wood powder
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2019 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 73, no 12, p. 1059-1068Article in journal (Refereed) Published
Abstract [en]

The objective of the study was to investigate the water vapour sorption behaviour of thermally modified (TM) wood powder, e.g. ground wood prepared from waste streams of TM solid wood, and wood powder that was extracted in pressurised hot water. Solid spruce wood was TM in steam conditions (210°C for 3 h), milled and hot-water-extracted (HWE) at elevated pressure (140°C for 1 h). The results evidence that the hot-water extraction reduced the water sorption and the accessible hydroxyl group concentration by the removal of amorphous carbohydrates. In contrast, the enhanced cross-linking of the cell wall matrix and the annealing of amorphous matrix polymers during thermal modification reduced the sorption behaviour of wood additionally, without further reducing the hydroxyl accessibility. These additional effects of thermal modification were at least partially cancelled by hot-water extraction. The results bring novel insights into the mechanisms that reduce the water vapour sorption of wood by compositional and structural changes induced by heating.

Place, publisher, year, edition, pages
De Gruyter, 2019
Keywords
carbohydrate analysis, deuterium exchange, dynamic vapour sorption, hot-water extraction, thermal modification, Carbohydrates, Crosslinking, Sorption, Water vapor, Wood, Dynamic vapour sorptions, Hot water extraction, Extraction
National Category
Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-263273 (URN)10.1515/hf-2018-0301 (DOI)000497967800002 ()2-s2.0-85069753584 (Scopus ID)
Note

QC 20191105

Available from: 2019-11-05 Created: 2019-11-05 Last updated: 2019-12-12Bibliographically approved
Källbom, S. (2018). Characterisation of thermally modified wood for use as component in biobased building materials. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Characterisation of thermally modified wood for use as component in biobased building materials
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. iii, 50
Series
TRITA-ABE-DLT ; 1818
Keywords
Thermally modified wood (TMW) components, surface properties, inverse gas chromatography (IGC), water sorption, dynamic vapour sorption (DVS)
National Category
Materials Chemistry
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-233569 (URN)978-91-7729-860-1 (ISBN)
Public defence
2018-09-19, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
EnWoBio - Engineered Wood and Biobased Building Materials Laboratory
Funder
Swedish Research Council Formas, EnWoBio 2014-172
Note

QC 20180824

Available from: 2018-08-24 Created: 2018-08-24 Last updated: 2018-08-24Bibliographically approved
Källbom, S., Moghaddam, M. S. & Wålinder, M. (2018). Liquid sorption, swelling and surface energy properties of unmodified and thermally modified Scots pine heartwood after extraction. Holzforschung, 72(3), 251-258
Open this publication in new window or tab >>Liquid sorption, swelling and surface energy properties of unmodified and thermally modified Scots pine heartwood after extraction
2018 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 3, p. 251-258Article in journal (Refereed) Published
Abstract [en]

The effect of extractives removal on liquid sorption, swelling and surface energy properties of unmodified wood (UW) and thermally modified Scots pine heartwood (hW) (TMW) was studied. The extraction was performed by a Soxtec procedure with a series of solvents and the results were observed by the multicycle Wilhelmy plate method, inverse gas chromatography (IGC) and Fourier transform infrared (FTIR) spectroscopy. A significantly lower rate of water uptake was found for the extracted UW, compared with the unextracted one. This is due to a contamination effect in the latter case from water-soluble extractives increasing the capillary flow into the wood voids, proven by the decreased water surface tension. The swelling in water increased after extraction 1.7 and 3 times in the cases of UW and TMW, respectively. The dispersive part of the surface energy was lower for the extracted TMW compared to the other sample groups, indicating an almost complete removal of the extractives. The FTIR spectra of the extracts showed the presence of phenolic compounds but also resin acids and aliphatic compounds.

Place, publisher, year, edition, pages
Walter de Gruyter, 2018
Keywords
extractives, FTIR, inverse gas chromatography (IGC), liquid sorption, multicycle Wilhelmy plate method, Scots pine, surface energy, swelling, thermally modified wood
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-224686 (URN)10.1515/hf-2017-0064 (DOI)000426254900009 ()2-s2.0-85037846034 (Scopus ID)
Funder
Swedish Research Council Formas, EnWoBio 2014-172
Note

QC 20180326

Available from: 2018-03-26 Created: 2018-03-26 Last updated: 2020-03-10Bibliographically approved
Källbom, S., Altgen, M., Militz, H. & Wålinder, M. (2018). Sorption and surface energy properties of thermally modified spruce wood components. Wood and Fiber Science, 50(3), 346-357
Open this publication in new window or tab >>Sorption and surface energy properties of thermally modified spruce wood components
2018 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 50, no 3, p. 346-357Article in journal (Refereed) Published
Abstract [en]

The objective of this work is to study the water vapor sorption and surface energy properties of thermally modified wood (TMW) components, ie wood processing residuals in the form of sawdust. The thermal modification was performed on spruce wood components using a steam-pressurized laboratoryscale reactor at two different temperature (T) and relative humidity (RH) conditions, T = 150 degrees C and RH = 100% (TMW150), and T = 180 degrees C and RH = 46% (TMW180). A dynamic vapor sorption (DVS) technique was used to determine water vapor sorption isotherms of the samples for three adsorption-desorption cycles at varying RH between 0% and 95%. Inverse gas chromatography (IGC) was used to study the surface energy properties of the samples, including dispersive and polar characteristics. The DVS results showed that the EMC was reduced by 30-50% for the TMW samples compared with control samples of unmodified wood (UW) components. A lower reduction was, however, observed for the second and third adsorption cycles compared with that of the first cycle. Ratios between EMC of TMW and that of UW samples were lower for the TMW180 compared with the TMW150 samples, and an overall decrease in such EMC ratios was observed at higher RH for both TMW samples. The IGC results showed that the dispersive contribution to the surface energy was higher at lower surface coverages, ie representing the higher energy sites, for the TMW compared with the UW samples. In addition, an analysis of the acid-base properties indicated a higher KB than KA number, ie a higher basic than acidic contribution to the surface energy, for all the samples. A higher KB number was also observed for the TMW compared with the UW samples, suggested to relate to the presence of ether bonds from increased lignin and/or extractives content at the surface. The KB was lower for TMW180 compared with TMW150, as a result of higher modification temperature of the first, leading to cleavage of these ether bonds.

Place, publisher, year, edition, pages
Society of Wood Science and Technology, 2018
Keywords
Thermally modified wood, dynamic vapor sorption (DVS), inverse gas chromatography (IGC), Norway spruce, surface energy, acid-base properties
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-232780 (URN)000439305600010 ()2-s2.0-85050353079 (Scopus ID)
Funder
Swedish Research Council Formas, EnWoBio 2014-172
Note

QC 20180803

Available from: 2018-08-03 Created: 2018-08-03 Last updated: 2018-08-24Bibliographically approved
Lillqvist, K., Rohumaa, A., Källbom, S., Rautkari, L. & Wålinder, M. (2017). THE INFLUENCE OF THERMAL MODIFICATION ON VENEER BOND STRENGTH. In: Engelund Thybring, E. (Ed.), Proceedings of the 13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29: . Paper presented at 13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29 (pp. 56).
Open this publication in new window or tab >>THE INFLUENCE OF THERMAL MODIFICATION ON VENEER BOND STRENGTH
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2017 (English)In: Proceedings of the 13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29 / [ed] Engelund Thybring, E., 2017, p. 56-Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

The purpose of this study was to investigate the effect of thermal modification on birchveneer properties relevant in plywood manufacture. The wood material used in thisstudy was a birch (Betula pendula Roth) stem sectioned into small logs nominally 1.2 min length. The logs were completely immersed in a water tank heated to either 70 °C or20 °C. The soaked logs were rotary cut on an industrial scale lathe (Model 3HV66;Raute Oyj, Lahti, Finland) into veneer with a nominal thickness of 0.8 mm.Veneer specimens (150x150 mm2) were cut and thermally modified at 200°C in steamconditions for 2, 4 and 8 h. Mass loss and equilibrium moisture content (EMC) weremeasured after modification. The bond strength of the veneers was measured withautomated bonding evaluation system (ABES- Adhesive Evaluation Systems, Inc.,Corvallis, Oregon, USA) using phenol formaldehyde (PF) resin (Prefere 14J021, PrefereResins Finland Oy, Hamina, Finland). Specimens (20 x 117 mm2), were cut from theconditioned veneer sheets. A liquid PF resin was applied to an area of 5 x 20 mm2 atone end of the veneer specimens (approx. spread rate 100 g m-2). After adhesiveapplication, the veneer-resin assembly was placed into the ABES and after 180 s ofpressing (130 °C and 2.0 MPa) the shear strength of adhesive bond was measured.As expected from previous studies, the mass loss increased and EMC reduced withlonger thermal modification time. No significant difference in mass loss or EMCbetween log soaking temperatures was recorded in this study. The thermal modificationslightly reduced the bond strength; however, longer treatment time did not furtherreduce the bond strength. Therefore, based on this study, thermally modified veneerscould be successfully bonded and

National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-271598 (URN)
Conference
13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29
Projects
EnWoBio
Funder
Swedish Research Council Formas
Note

QC 20200331

Available from: 2020-03-30 Created: 2020-03-30 Last updated: 2020-03-31Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7250-8693

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