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Aspects on wettability and surface composition of modified wood
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Wood is often combined with other materials such as thermoplastics, adhesives and coatings. In general, combinations of wood and polymers especially in outdoor exposure have poor long-term durability. This behaviour can be related to an insufficient wood-polymer adhesion due to the low intrinsic compatibility between the wood substance and the polymers used. Another source for woodpolymer de-bonding is the high hygroscopicity of wood and great difference in hygro-thermal properties between the components.

The basic conceptual idea related to this work is to reduce the hygrosensitivity of wood by applying different wood modification methods, in particular, acetylation, furfurylation and heat treatment. The effects of such chemical modifications of wood, also accompanied with ageing effects, on its adhesion properties with commonly used synthetic polymers are, however, not well understood. In this context, the over-all purpose of this thesis is to achieve a better understanding of wood-polymer adhesion and interfacial forces which also may guide us to tailor the interaction between modified wood and e.g. thermoplastics and adhesives. The main focus of this thesis is therefore to apply contact angle analysis based on the Chang-Qin-Chen (CQC) Lewis acid-base model in order to estimate the work of adhesion (Wa) between the wood, modified wood and certain polymers. Contact angle measurements on wood samples were performed based on the Wilhelm plate principle. Related to this, an effort was also made to characterize the studied modified wood surfaces according to morphology and chemical composition. The methods that have been used are low vacuum scanning electron microscopy (LV-SEM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS).

Results show that so-called interaction parameters can be successfully estimated for prediction of Wa between wood and polymers using the applied CQC model. Furthermore, such wetting analysis was successfully related to spectroscopic findings of the chemical composition of the wood samples surface. Ageing effects, i.e. the time after preparation of the wood surface, play a central role for the surface characteristics. In most cases, ageing resulted in a significant decrease of Wa between wood and water and a moderate decrease between wood and thermoplastics. The surface characteristics of acetylated wood were, however, more stable over time compared to unmodified, furfurylated and heat treated wood. The predicted Wa with the adhesives for heat treated and acetylated wood was increased due to ageing. Future work is planned to involve studies in order to relate such predicted adhesion properties with the actual performance of various wood-polymer systems.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , xi, 41 p.
Series
Trita-BYMA, ISSN 0349-5752 ; 2008:1
Keyword [en]
Wettability, contact angle, work of adhesion, Lewis acid-base, modified wood
National Category
Building Technologies
Identifiers
URN: urn:nbn:se:kth:diva-4735ISBN: 978-91-7178-952-5 (print)OAI: oai:DiVA.org:kth-4735DiVA: diva2:13693
Presentation
2008-05-16, Seminarierummet, KTH, Brinellvägen 34, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20101108Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-11-08Bibliographically approved
List of papers
1. Wood adhesion mechanisms: prediction of wood-thermoplastic-water interactions
Open this publication in new window or tab >>Wood adhesion mechanisms: prediction of wood-thermoplastic-water interactions
2006 (English)In: Wood Adhesives 2005 / [ed] Charles R. Frihart, Forest Products Society , 2006, no 7230, 385-392 p.Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Forest Products Society, 2006
Series
Forest Products Societey, Proceedings No. 7230
Keyword
Wood adhesion, modified wood, acetylated, furfurylated heat treated
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-8384 (URN)1-892529-45-9 (ISBN)
Conference
Wood Adhesives 2005
Note

QC 20101108

Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2016-04-11Bibliographically approved
2. Ageing of modified wood: Part 1: Wetting properties of acetylated, furfurylated, and thermally modified
Open this publication in new window or tab >>Ageing of modified wood: Part 1: Wetting properties of acetylated, furfurylated, and thermally modified
2010 (English)In: Holzforschung, ISSN 0018-3830, Vol. 64, no 3, 295-304 p.Article in journal (Refereed) Published
Abstract [en]

The main objective of this work was to apply contact angle analysis to predict work of adhesion (W-a) between some modified wood materials and certain thermoplastics and adhesives. Wetting properties, i.e., contact angles, were measured by the Wilhelmy method on both freshly prepared and aged veneer samples of unmodified and acetylated Scots pine, furfurylated radiata pine, and heat treated Norway spruce. The sessile drop method was used to measure contact angles on a phenol resorcinol formaldehyde, an emulsion polymer isocyanate, and a one-component polyurethane adhesive. Contact angle data were also collected from the literature on polyethylene, polyvinyl chloride, polymethyl methacrylate, polystyrene, and Nylon 6. Contact angle analysis based on the Chang-Qin-Chen model was then applied to determine so-called acid-base interaction parameters and W-a between the wood samples and the selected thermoplastics and adhesives. Results show that the ageing process led to an increased hydrophobic character of unmodified, heat treated, and furfurylated wood samples. The freshly prepared acetylated wood samples had a pronounced hydrophobic character which remained approximately constant after ageing. The predicted W-a between the wood and the adhesives was considerably higher than that between the wood and the thermoplastics. Furthermore, the predicted W-a between the acetylated wood and both the thermoplastics and water was approximately unchanged when comparing the fresh and aged samples. In contrast, the ageing of all other wood samples resulted in a dramatic decrease of the wood-water W-a and a moderate decrease of the wood-thermoplastics W-a. The wood-adhesives W-a, however, was unchanged for the unmodified and furfurylated wood when comparing the fresh and aged samples and even increased for heat treated and acetylated wood samples.

Keyword
adhesives, contact angle analysis, modified wood, thermoplastics, work of adhesion
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-8385 (URN)10.1515/HF.2010.040 (DOI)000276810800004 ()2-s2.0-77951275505 (Scopus ID)
Note
QC 20101108 Uppdaterad från submitted till published (20101108). Tidigare titel: Surface characteristics and ageing effects of modified wood : Part 1 : prediction of work of adhesion and wetting propertiesAvailable from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-11-08Bibliographically approved
3. Ageing of modified wood: Part 2: Determination of surface composition of acetylated, furfurylated, and thermally modified wood by XPS and ToF-SIMS
Open this publication in new window or tab >>Ageing of modified wood: Part 2: Determination of surface composition of acetylated, furfurylated, and thermally modified wood by XPS and ToF-SIMS
Show others...
2010 (English)In: Holzforschung, ISSN 0018-3830, Vol. 64, no 3, 305-313 p.Article in journal (Refereed) Published
Abstract [en]

The main objective of this work was to study the chemical composition of surfaces and ageing effects on acetylated pine (Pinus sylvestris), heat treated spruce (Picea abies), and furfurylated radiata pine (Pinus radiata) in comparison to unmodified wood. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were the instruments of choice. Observation with a low-vacuum scanning electron microscope (LV-SEM) complemented the study. The spectroscopic information was also linked to a parallel wettability study on matched wood samples by the Wilhelmy method. The results show that XPS and ToF-SIMS are two powerful tools that in combination give complementary information, both quantitative and qualitative, and are well suited for observation of the ageing process of different wood surfaces. The hydrophobization process as a result of migration of extractives during ageing was well quantified by the XPS measurements and the results correlated well with wetting results. Several specific hydrophobic substances could be identified by ToF-SIMS measurements.

Keyword
acetylation, electron spectroscopy for chemical analysis (ESCA), furfurylation, heat treatment, modified wood, surface chemical composition, time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS)
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-8386 (URN)10.1515/HF.2010.062 (DOI)000276810800005 ()2-s2.0-77951280203 (Scopus ID)
Note
QC 20101108 Uppdaterad från submitted till published (20101108). Tidigare titel: Surface characteristics and ageing effects of modified wood : Part 2 : spectroscopic studies of surface chemical compositionAvailable from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-11-08Bibliographically approved

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