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Micromorphology, moisture sorption and mechanical properties of a biocomposite based on acetylated wood particles and cellulose ester
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.ORCID-id: 0000-0001-7014-6230
IFP Research, Swedish Institute for Fibre and Polymer Research.
SICOMP, Swedish Institute of Composites.
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.ORCID-id: 0000-0002-9156-3161
Vise andre og tillknytning
2007 (engelsk)Inngår i: Wood Material Science and Engineering, ISSN 1748-0272, Vol. 3-4, nr 2, s. 106-117Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
2007. Vol. 3-4, nr 2, s. 106-117
Emneord [en]
Acetylation, Cellulose acetate propionate, Mechanical performance, Micromorphology, Moisture sorption, UV excimer laser, Wood-plastic composite
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-7838DOI: 10.1080/17480270801906175ISI: 000219911000002Scopus ID: 2-s2.0-49549093826OAI: oai:DiVA.org:kth-7838DiVA, id: diva2:12977
Merknad

Uppdaterad från submitted till published(20101116) QC 20150716

Tilgjengelig fra: 2007-12-14 Laget: 2007-12-14 Sist oppdatert: 2022-06-26bibliografisk kontrollert
Inngår i avhandling
1. Wood Plastic Composites made from Modified Wood: Aspects on Moisture Sorption, Micromorphology and Durability
Åpne denne publikasjonen i ny fane eller vindu >>Wood Plastic Composites made from Modified Wood: Aspects on Moisture Sorption, Micromorphology and Durability
2007 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: KTH, 2007. s. xi, 23
Serie
Trita-BYMA, ISSN 0349-5752 ; 2007:3
Emneord
Wood plastic composites, WPC, acetylation, heat treatment, furfurylation, moisture sorption, micromorphology, decay, UV laser, soil test
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-4582 (URN)978-91-7178-823-8 (ISBN)
Presentation
2007-12-18, Fysiklabbet, Byggvetenskap, Brinellvägen 34, Stockholm, 10:00
Opponent
Veileder
Merknad
QC 20101116Tilgjengelig fra: 2007-12-14 Laget: 2007-12-14 Sist oppdatert: 2022-06-26bibliografisk kontrollert
2. Characteristics of wood plastic composites based on modified wood: Moisture properties, biological performance and micromorphology
Åpne denne publikasjonen i ny fane eller vindu >>Characteristics of wood plastic composites based on modified wood: Moisture properties, biological performance and micromorphology
2012 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2012. s. xvii, 46
Serie
Trita-BYMA, ISSN 0349-5752 ; 2012:2
Emneord
Wood plastic composites, WPC, acetylation, thermal modification, furfurylation, moisture sorption, biological durability, UV excimer laser, micromorphology
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-105217 (URN)978-91-7501-554-5 (ISBN)
Disputas
2012-12-07, B2, Brinellvägen 23, KTH, Stockholm, 13:00 (engelsk)
Opponent
Veileder
Merknad

QC 20121119

Tilgjengelig fra: 2012-11-19 Laget: 2012-11-19 Sist oppdatert: 2022-06-24bibliografisk kontrollert

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