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Micromorphological studies of modified wood using a surface preparation technique based on ultraviolet laser ablation
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.ORCID iD: 0000-0002-9156-3161
Gorgan University, Gorgan, Iran. (Agricultural Sciences and Natural Resources)
SP Technical Research Institute of Sweden. (Wood Technology)
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.ORCID iD: 0000-0001-7014-6230
2009 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, Vol. 4, no 1-2, 46-51 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this paper is to demonstrate an ultraviolet (UV) laser ablation technique as a tool for sample preparation in microscopy studies of modified wood. Improved techniques for studying the microstructure of modified wood are crucial for a deeper understanding of many of their physical, mechanical and durability properties. The surface preparation technique is described in this paper. An illustration of micrographs of the micromorphology and polymer distribution in some examples of modified wood is also presented. It is clearly demonstrated that in contrast to conventional surface preparation techniques used for light microscopy and scanning electron microscopy, i.e. razor blade and microtome cutting techniques, UV laser ablation does not introduce any mechanically induced microcracks and redistribution of polymers or other mobile substances in the prepared surface. Results also show that, in particular, this technique seems to be suitable for studying polymer distribution in resin-impregnated wood, as well as detection of microcracks in modified wood cell walls.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2009. Vol. 4, no 1-2, 46-51 p.
Keyword [en]
Cell wall damage, Micromorphology, Modified wood, SEM, UV laser
National Category
Composite Science and Engineering
URN: urn:nbn:se:kth:diva-76712DOI: 10.1080/17480270903151233ScopusID: 2-s2.0-70449372641OAI: diva2:491398
QC 20120207Available from: 2012-02-06 Created: 2012-02-06 Last updated: 2012-11-19Bibliographically approved
In thesis
1. Characteristics of wood plastic composites based on modified wood: Moisture properties, biological performance and micromorphology
Open this publication in new window or tab >>Characteristics of wood plastic composites based on modified wood: Moisture properties, biological performance and micromorphology
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biobased materials made from renewable resources, such as wood, play an important role in the sustainable development of society. One main challenge of biobased building materials is their inherent moisture sensitivity, a major cause for fungal decay, mold growth and dimensional instability, resulting in decreased service life as well as costly maintenance. A new building material known as wood-plastic composites (WPCs) has emerged. WPCs are a combination of a thermoplastic matrix and a wood component, the former is usually recycled polyethylene or polypropylene, and the latter a wood processing residual, e.g. sawdust and wood shavings.

The objective of this thesis was to gain more insight about characteristics of WPCs containing a modified wood component. The hypothesis was that a modified wood component in WPCs would increase the moisture resistance and durability in outdoor applications. The study comprises both injection molded and extruded WPC samples made with an unmodified, acetylated, thermally modified or furfurylated wood component in a polypropylene (PP), high density polyethylene (HDPE), cellulose ester (CAP, a cellulose ester containing both acetate and propionate substituents) or polylactate (PLA) matrix. The WPCs were prepared with 50-70 weight-% wood. The emphasis was on studying the moisture sorption, fungal resistance and micromorphological features of these new types of composites. Water sorption in both liquid and vapor phases was studied, and the biological performance was studied both in laboratory and in long term outdoor field tests. Micromorphological features were assessed by analyzing of the wood component prior to and after processing, and by studying the composite microstructure by means of a new sample preparation technique based on UV excimer laser ablation combined with scanning electron microscopy (SEM).

Results showed that the WPCs with a modified wood component had a distinctly lower hygroscopicity than the WPCs with unmodified wood, which resulted in less wood-plastic interfacial cracks when subjected to a moisture soaking-drying cycle. Durability assessments in field and marine tests showed that WPCs with PP or CAP as a matrix and 70 weight-% unmodified wood degraded severely within a few years, whereas the corresponding WPCs with a modified wood component were sound after 7 years in field tests and 6 years in marine tests. Accelerated durability tests of WPCs with PLA as a matrix showed only low mass losses due to decay. However, strength losses due to moisture sorption suggest that the compatibility between the PLA and the different wood components must be improved. The micromorphological studies showed that WPC processing distinctly reduces the size and changes the shape of the wood component. The change was most pronounced in the thermally modified wood component which became significantly reduced in size. The disintegration of the modified wood components during processing also creates a more homogeneous micromorphology of the WPCs, which may be beneficial from a mechanical performance perspective. Future studies are suggested to include analyses of the surface composition, the surface energy and the surface energy heterogeneity of both wood and polymer components in order to tailor new compatible wood-polymer combinations in WPCs and biocomposites.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xvii, 46 p.
Trita-BYMA, ISSN 0349-5752 ; 2012:2
Wood plastic composites, WPC, acetylation, thermal modification, furfurylation, moisture sorption, biological durability, UV excimer laser, micromorphology
National Category
Composite Science and Engineering
urn:nbn:se:kth:diva-105217 (URN)978-91-7501-554-5 (ISBN)
Public defence
2012-12-07, B2, Brinellvägen 23, KTH, Stockholm, 13:00 (English)

QC 20121119

Available from: 2012-11-19 Created: 2012-11-19 Last updated: 2012-11-19Bibliographically approved

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