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Wood Plastic Composites made from Modified Wood: Aspects on Moisture Sorption, Micromorphology and Durability
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.ORCID iD: 0000-0001-7014-6230
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Wood plastic composite (WPC) materials have seen a continuous market growth worldwide in the last decade. So-called extruded WPC profiles are today mainly used in outdoor applications, e.g. decking, railing and fencing. In outdoor conditions, moisture sorption in the wood component combined with temperature induced movements of the polymer matrix causes deformations of such composites. On the macroscopic scale this may lead to unacceptable warp, cup and bow of the WPC products, but on a microscopic scale, the movements will cause interfacial cracks between the particles and the matrix, resulting in little or no ability to transfer and re-distribute loads throughout the material. Moisture within the composite will also allow fungi and micro organisms to attack the wood particles.

The conceptual idea of this work is to use a chemically modified wood component in WPCs to enhance their long term performance. These chemically modified wood particles exhibit reduced susceptibility to moisture, resulting in better dimensional stability and a higher resistance to biological degradation as compared to that of unmodified wood. The objective of this thesis is to study the effects of using modified wood in WPCs on their moisture sorption behaviour, micromorphology and microbiological durability. The modification methods used were acetylation, heat treatment and furfurylation.

Equilibrium moisture content (EMC) and sorption behaviour of WPCs were determined by water vapour sorption experiments. The use of thin sections of the composites enabled EMC to be reached within a comparably short time span. The micromorphology was studied by LV-SEM (low vacuum-scanning electron microscope) using a specially designed sample preparation technique based on UV laser. The biological durability was evaluated by laboratory fungal test methods.

The moisture sorption experiments showed lower moisture levels for all the composites when modified wood particles were used. This was also reflected in the micromorphological studies where pronounced wood-plastic interfacial cracks were formed due to moisture movement in the composites with unmodified wood particles. The sample preparation technique by UV laser proved to be a powerful tool for preparing surfaces for micromorphological studies without adding mechanical defects caused by the sample preparation technique itself. Results from the durability test showed that WPCs with modified wood particles are highly resistant to decay by fungi.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , xi, 23 p.
Series
Trita-BYMA, ISSN 0349-5752 ; 2007:3
Keyword [en]
Wood plastic composites, WPC, acetylation, heat treatment, furfurylation, moisture sorption, micromorphology, decay, UV laser, soil test
National Category
Biomaterials Science
Identifiers
URN: urn:nbn:se:kth:diva-4582ISBN: 978-91-7178-823-8 (print)OAI: oai:DiVA.org:kth-4582DiVA: diva2:12979
Presentation
2007-12-18, Fysiklabbet, Byggvetenskap, Brinellvägen 34, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101116Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2010-11-16Bibliographically approved
List of papers
1. Wood plastic composites made from acetylated wood: Effects on water vapour sorption behaviour and durability
Open this publication in new window or tab >>Wood plastic composites made from acetylated wood: Effects on water vapour sorption behaviour and durability
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2005 (English)In: Proceedings of the 9th European Panel Products Symposium, 2005, 233-242 p.Conference paper, Published paper (Refereed)
National Category
Dentistry
Identifiers
urn:nbn:se:kth:diva-7837 (URN)
Conference
The 9th European Panel Products Symposium, Lladudno, Wales, 2005, October 5-7,
Note
QC 20101116Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2010-11-16Bibliographically approved
2. Micromorphology, moisture sorption and mechanical properties of a biocomposite based on acetylated wood particles and cellulose ester
Open this publication in new window or tab >>Micromorphology, moisture sorption and mechanical properties of a biocomposite based on acetylated wood particles and cellulose ester
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2007 (English)In: Wood Material Science and Engineering, ISSN 1748-0272, Vol. 3-4, no 2, 106-117 p.Article in journal (Refereed) Published
Abstract [en]

One of the major issues in a long-term perspective for the use of wood-plastic composites (WPCs) in outdoor applications is the moisture sensitivity of the wood component and the consequent dimensional instability and susceptibility to biological degradation of the composite. In this work, the effects of using an acetylated wood component and a cellulose ester as matrix on the micromorphology, mechanical performance and moisture uptake of injection-moulded WPCs have been studied. Composites based on unmodified and acetylated wood particles, specially designed with a length-to-width ratio of about 5-7, combined with both cellulose acetate propionate (CAP) and polypropylene (PP) matrices were studied. The size and shape of the wood particles were studied before and after the processing using light microscopy, and the micromorphology of the composites was studied using a newly developed surface preparation technique based on ultraviolet laser irradiation combined with low-vacuum scanning electron microscopy (LV-SEM). The water vapour sorption in the composites and the effect of accelerated weathering were measured using thin samples which were allowed to reach equilibrium moisture content (EMC). The length-to-diameter ratio was only slightly decreased for the acetylated particles after compounding and injection moulding, although both the unmodified and the acetylated particles were smaller in size after the processing steps. The tensile strength was about 40% higher for the composite based on acetylated wood than for the composite with unmodified wood using either CAP or PP as matrix, whereas the notched impact strength of the composite based on acetylated wood was about 20% lower than those of the corresponding unmodified composites. The sorption experiments showed that the EMC was 50% lower in the composites with an acetylated wood component than in the composites with an unmodified wood component. The choice of matrix material strongly affected the moisture absorptivity of the WPC. The composites with CAP as matrix gained moisture more rapidly than the composites with PP as matrix. It was also found that accelerated ageing in a Weather-Ometer® significantly increased the moisture sensitivity of the PP-based composites.

Keyword
Acetylation, Cellulose acetate propionate, Mechanical performance, Micromorphology, Moisture sorption, UV excimer laser, Wood-plastic composite
National Category
Dentistry
Identifiers
urn:nbn:se:kth:diva-7838 (URN)10.1080/17480270801906175 (DOI)2-s2.0-49549093826 (Scopus ID)
Note

Uppdaterad från submitted till published(20101116) QC 20150716

Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2015-10-13Bibliographically approved
3. Improved Durability and Moisture Sorption Characteristics of Extruded WPCs made from Chemically Modified Wood
Open this publication in new window or tab >>Improved Durability and Moisture Sorption Characteristics of Extruded WPCs made from Chemically Modified Wood
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2007 (English)In: Proceedings of the 9th International Conference on Wood & Biofiber Plastic Composites., 2007, 251-256 p.Conference paper, Published paper (Refereed)
National Category
Dentistry
Identifiers
urn:nbn:se:kth:diva-7839 (URN)
Conference
the 9th International Conference on Wood & Biofiber Plastic Composites, Madison, WI, USA, 2007, May 21-23
Note

QC 20101116

Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2014-09-24Bibliographically approved

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