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Microstructure of chemically modified wood using X-ray computedtomography scanning in relation to wetting properties
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.ORCID iD: 0000-0003-0016-3398
(UGCT - Laboratory of Wood Technology, Department of Forest and Water Management, Faculty of Bioscience)
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.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

X-ray computed tomography was utilized to visualize and quantify the 2D and 3D microstructure of acetylated and furfurylated southern yellow pine (SYP) and maple samples. The total porosity and the porosity of different anatomical components, the cell wall thickness and the maximum opening of tracheid lumens were evaluated. The wetting properties (swelling and capillary uptake) were related to these microstructural characteristics. Our data show significant changes in the wood structure for furfurylated sapwood samples, including a change in tracheid shape and filling of tracheids by furan polymer. In contrast, no such changes were noted for acetylated samples at the resolution of the measurement (0.8 μm). The images obtained for furfurylated maple samples demonstrated that all ray cells and some vessel elements were filled with furan polymer while the fibres largely remained unchanged. Furfurylation significantly decreased the porosity of the sample, and this was observed in both earlywood and latewood regions in southern yellow pine softwood samples. In contrast, the total porosity of this softwood sample was hardly affected by acetylation. These findings are in line with wetting results demonstrating that furfurylation reduces both swelling and capillary uptake in contrast to acetylation which reduces mostly swelling. Cell wall thickness measurements revealed a significant increase after chemical modification especially at higher levels of furfurylation.

Keyword [en]
acetylation, cell wall thickness, furfurylation, hardwood, microstructure, porosity, softwood, tracheid, wettability, sub-micron X-ray Computed Tomography
National Category
Wood Science
Research subject
URN: urn:nbn:se:kth:diva-175874OAI: diva2:863047

QS 2015

Available from: 2015-10-23 Created: 2015-10-23 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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Sedighi Moghaddam, MaziarWålinder, E.P. MagnusCalessson, M. PerSwerin, Agne
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