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Surface energy characterization of thermally modified spruce using inverse gas chromatography under cyclic humidity conditions
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.ORCID iD: 0000-0002-9156-3161
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. SP Technical Research Institute of Sweden.ORCID iD: 0000-0001-7014-6230
SP Technical Research Institute of Sweden.
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. Vol. 47, no 4, p. 410-420
Keywords [en]
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: urn:nbn:se:kth:diva-172956ISI: 000363992000011Scopus ID: 2-s2.0-84991704745OAI: oai:DiVA.org:kth-172956DiVA, id: diva2:851329
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: 2018-08-24Bibliographically approved
In thesis
1. Surface characterisation of thermally modified spruce wood and influence of water vapour sorption
Open this publication in new window or tab >>Surface characterisation of thermally modified spruce wood and influence of water vapour sorption
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Today there is growing interest within the construction sector to increase the proportion of biobased building materials made from renewable resources. By-products or residuals from wood processing could in this case be valuable resources for manufacturing new types of biocomposites. An important research question related to wood-based biocomposites is how to characterise molecular interactions between the different components in the composite. The hygroscopic character of wood and its water sorption properties are also crucial. Thermal modification (or heat treatment) of wood results in a number of enhanced properties such as reduced hygroscopicity and improved dimensional stability as well as increased resistance to microbiological decay.

In this thesis, surface characteristics of thermally modified wood components (often called wood fibres or particles) and influencing effects from moisture sorption have been analysed using a number of material characterisation techniques. The aim is to increase the understanding in how to design efficient material combinations for the use of such wood components in biocomposites. The specific objective was to study surface energy characteristics of thermally modified spruce (Picea abies Karst.) under influences of water vapour sorption. An effort was also made to establish a link between surface energy and surface chemical composition. The surface energy of both thermally modified and unmodified wood components were studied at different surface coverages using inverse gas chromatography (IGC), providing information about the heterogeneity of the surface energy. The water vapour sorption behaviour of the wood components was studied using the dynamic vapour sorption (DVS) method, and their surface chemical composition was studied by means of X-ray photoelectron spectroscopy (XPS). Additionally, the morphology of the wood components was studied with scanning electron microscopy (SEM).

The IGC analysis indicated a more heterogeneous surface energy character of the thermally modified wood compared with the unmodified wood. An increase of the dispersive surface energy due to exposure to an increased relative humidity (RH) from 0% to 75% RH at 30 ˚C was also indicated for the modified samples. The DVS analysis indicated an increase in equilibrium moisture content (EMC) in adsorption due to the exposure to 75% RH. Furthermore, the XPS results indicated a decrease of extractable and a relative increase of non-extractable compounds due to the exposure, valid for both the modified and the unmodified wood. The property changes due to the increased RH condition and also due to the thermal modification are suggested to be related to alterations in the amount of accessible hydroxyl groups in the wood surface. Recommendations for future work and implications of the results could be related to knowledge-based tailoring of new compatible and durable material combinations, for example when using thermally modified wood components in new types of biocomposites for outdoor applications.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. p. xiii, 36
Series
TRITA-BYMA, ISSN 0349-5752 ; 2015:4
Keywords
Thermally modified wood, Norway spruce, inverse gas chromatography (IGC), dynamic vapour sorption (DVS), X-ray photoelectron spectroscopy (XPS), surface energy, Värmebehandlat trä, gran, omvänd gaskromatografi (IGC), dynamic vapour sorption (DVS), röntgenelektronspektroskopi (XPS), ytegenskaper, ytenergi
National Category
Civil Engineering Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-172989 (URN)
Presentation
2015-09-25, B25, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas, EnWoBio 2014-172
Note

Forskningsfinansiärer och strategiska forskningsprojekt:

Nils och Dorthi Troëdssons forskningsfond (Projektnr 793/12 Hydro-termo-mekanisk modifiering av trä).

 KTH Royal Institute of Technology.

 COST Action FP0904.

 KK-Stiftelsen.

Stiftelsen för strategiskt forskning (SSF). QC 20150908

Available from: 2015-09-08 Created: 2015-09-04 Last updated: 2015-09-08Bibliographically approved
2. 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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Wålinder, MagnusSegerholm, Kristoffer

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