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Water vapour sorption characteristics and surface chemical composition of thermally modified spruce (Picea abies karst)
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
Department of Forest Products Technology, Aalto University.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.ORCID iD: 0000-0002-9156-3161
Aalto University, Finland.
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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. Vol. 7, no 3, p. 116-123
Keywords [en]
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: urn:nbn:se:kth:diva-188633DOI: 10.1080/20426445.2016.1160590ISI: 000382319700002Scopus ID: 2-s2.0-84981554847OAI: oai:DiVA.org:kth-188633DiVA, id: diva2:937648
Note

QC 20160711

Available from: 2016-06-15 Created: 2016-06-15 Last updated: 2018-08-29Bibliographically approved
In thesis
1. Characterisation of thermally modified wood for use as component in biobased building materials
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

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