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Wettability and liquid sorption of wood investigated by Wilhelmy plate method
SP Tech Res Inst Sweden, S-11486 Stockholm, Sweden.ORCID iD: 0000-0003-0016-3398
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.ORCID iD: 0000-0002-9156-3161
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
2014 (English)In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 48, no 1, 161-176 p.Article in journal (Refereed) Published
Abstract [en]

The wettability of Scots pine veneers was investigated with different approaches using the Wilhelmy plate method. The probe liquids were water and octane, which differ; in that, water is able to swell the wood sample, whereas octane does not. Novel approaches based on the Wilhelmy plate method to study wettability, liquid penetration, and swelling behavior of wood veneers are introduced. First, immersion to constant depth was performed, and liquid uptake with time was evaluated. Different kinetic regimes, the fastest one associated with contact angle changes and the slowest regime associated with liquid sorption by capillary and diffusion, were observed. Two other approaches, imbibition at constant depth (with initial deeper immersion) and full immersion, were utilized in order to keep the contact angle constant during measurements. Dynamic wettability studies were done by a multi-cycle (10-20 cycles) Wilhelmy method. Based on this, the time-dependent swelling of wood and changes in sample perimeter could be obtained. Generally, water showed higher absorption than octane. In all wettability studies, and for both probe liquids, the penetration process starts with a fast initial sorption, which is followed by swelling in the case of water.

Place, publisher, year, edition, pages
2014. Vol. 48, no 1, 161-176 p.
Keyword [en]
Acid-Base Properties, Surface Wettability, Dynamic Wettability, Heat-Treatment, Part 1, Angle, Adhesion, Fibers, Energy, Panels
National Category
Wood Science
URN: urn:nbn:se:kth:diva-142522DOI: 10.1007/s00226-013-0592-1ISI: 000330626100015ScopusID: 2-s2.0-84893668704OAI: diva2:703348

QC 20140306

Available from: 2014-03-06 Created: 2014-03-06 Last updated: 2015-10-29Bibliographically approved
In thesis
1. Wettability of modified wood
Open this publication in new window or tab >>Wettability of modified wood
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Despite many excellent properties of wood which make it suitable for many applications, it suffers from a number of disadvantages limiting its use. For instance, modification is needed to reduce water sorption and to improve decay resistance, dimensional stability and weathering performance. In addition, wood/liquid interaction such as water wettability on wood plays an important role in design and characteristics of many processes and phenomena such as adhesion, coating, waterproofing, wood chemical modification, and weathering. This thesis focuses on enhancing the understanding of wetting of wood, with emphasis on modified wood. The influence of surface chemical composition of wood and its microstructural characteristics on wetting and swelling properties has also been studied.

A multicycle Wilhelmy plate technique has been developed to evaluate wetting properties of porous materials, such as wood, in which the samples were subjected to repeated immersions and withdrawals in a swelling liquid (water) and in a non-swelling liquid (octane). This method was utilized to dynamically investigate contact angle, sorption and swelling properties, as well as dimensional stability of unmodified, chemically and surface modified wood samples. Scots pine sapwood and heartwood samples were utilized to establish the principles of the technique. Acetylated and furfurylated wood samples with different level of modification were thereafter examined utilizing the developed technique for wetting measurements. A perimeter model based on a linear combination of the measured force and final change in sample perimeter was suggested to evaluate the dynamic dimensional stability of wood veneers. The feasibility of this method for studying dynamic wettability was investigated by measuring the changes of advancing and receding contact angles over repeated cycles on surface modified wood samples, created by combining liquid flame spray and plasma polymerisation methods. X-ray photoelectron spectroscopy (XPS) and X-ray computed tomography (XCT) were employed to study the surface chemical composition and microstructural properties of the samples, respectively.

Three different kinetic regimes were observed in the wetting measurements: i) fast wetting and spreading of the liquid on the wood surface, ii) void filling and wicking and iii) swelling, which was the slowest of the three. The multicycle Wilhelmy plate method was found to be suitable for studying liquid penetration, sorption, and dimensional stability of swelling materials. The results demonstrate that the wetting properties of wood are highly affected by surface chemistry and microstructure. It was shown that using both swelling and non-swelling liquids in wetting measurements allow to distinguish between capillary liquid uptake and swelling. Based on this, for chemically modified samples, it was demonstrated that acetylation mostly reduces swelling, while furfurylation reduces both swelling and capillary uptake. This is in line with the microstructural study with X-ray computed tomography where a significant change in the porosity was found as a result of furfurylation, conversely acetylation left the total porosity values unchanged. Wetting results for hydrophobised wood samples demonstrate that the multi-scale roughness obtained by combination of nanoparticle coating and plasma polymerization increased both the hydrophobicity and the forced wetting durability compared to the micro-scale roughness found on wood modified with plasma polymerisation alone.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 89 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:56
Wood, dimensional stability, dynamic wettability, surface chemistry, microstructure, swelling, multicycle Wilhelmy plate method, contact angle, sorption, acetylation, furfurylation, surface modification
National Category
Materials Chemistry
Research subject
urn:nbn:se:kth:diva-175875 (URN)978-91-7595-707-4 (ISBN)
Public defence
2015-11-20, Konferencerummet nr 3, SP AB, Drottning Kristinasväg 45, Stockholm, 10:00 (English)
Sustainable wood modification

QC 20151029

Available from: 2015-10-29 Created: 2015-10-23 Last updated: 2015-11-18Bibliographically approved

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