| 1. |
- Clemons, Craig M., et al.
(författare)
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Chapter 13 : Wood/nonwood thermoplastic composites
- 2012. - 2
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Ingår i: Handbook of wood chemistry and wood composites, second edition. - Boca Racon, FL : CRC Press. - 9781439853801 ; , s. 473-508
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Bokkapitel (refereegranskat)
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| 2. |
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| 3. |
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| 4. |
- Joffre, Thomas, 1987-, et al.
(författare)
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Characterization of interfacial stress transfer ability in acetylation-treated wood fibre composites using X-ray microtomography
- 2017
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Ingår i: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 95, s. 43-49
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Tidskriftsartikel (refereegranskat)abstract
- The properties of the fibre/matrix interface contribute to stiffness, strength and fracture behaviour of fibre-reinforced composites. In cellulosic composites, the limited affinity between the hydrophilic fibres and the hydrophobic thermoplastic matrix remains a challenge, and the reinforcing capability of the fibres is hence not fully utilized. A direct characterisation of the stress transfer ability through pull-out tests on single fibres is extremely cumbersome due to the small dimension of the wood fibres. Here a novel approach is proposed: the length distribution of the fibres sticking out of the matrix at the fracture surface is approximated using X-ray microtomography and is used as an estimate of the adhesion between the fibres and the matrix. When a crack grows in the material, the fibres will either break or be pulled-out of the matrix depending on their adhesion to the matrix: good adhesion between the fibres and the matrix should result in more fibre breakage and less pull-out of the fibres than poor adhesion. The effect of acetylation on the adhesion between the wood fibres and the PLA matrix was evaluated at different moisture contents using the proposed method. By using an acetylation treatment of the fibres it was possible to improve the strength of the composite samples soaked in the water by more than 30%.
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| 5. |
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| 6. |
- Kymäläinen, Maija, et al.
(författare)
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Surface modification of solid wood by charring
- 2017
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 52:10, s. 6111-6119
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Tidskriftsartikel (refereegranskat)abstract
- Most wooden structures for outdoor applications require repetitive maintenance operations to protect the surfaces from adverse effects of weathering. One-sided surface modification of boards with a relatively fast charring process has the potential to increase the durability and service life of wooden claddings. To assess some weathering-related effects on surface charred wood, spruce and pine sapwood were subjected to a series of long charring processes (30–120 min) at a moderate temperature of 250 °C and to a short one (30 s) at a high temperature of 400 °C. The wettability and contact angles of treated samples were investigated, and the heat transfer was measured along with the micromorphological changes taking place in the material. The result revealed an increased moisture resistance of charred spruce sapwood and an increased water uptake of pine sapwood. The contact angles of both wood species improved compared to references. Heat conduction measurement revealed that only a thin section of the wood was thermally modified. Some micromorphological changes were recorded, especially on the inside walls of the lumina. The results show that spruce sapwood has an improved resistance towards moisture-induced weathering, but more studies are needed to unlock the potential of surface charred wood.
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| 7. |
- Källbom, Susanna
(författare)
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Characterisation of thermally modified wood for use as component in biobased building materials
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The building sector shows growing interest in biobased building materials. Wood components, here defined as ground or milled wood, i.e. by-products (residuals/residues) from wood processing, such as sawdust or shavings, are valuable raw materials for new types of durable biocomposites suitable for outdoor building applications. An important research question related to such composites is how to characterise and enhance molecular interactions, i.e. adhesion properties, between wood and binder components. Another challenge is the hygroscopicity of the wood component, which can lead to dimensional changes and interfacial cracks during exposure to varying moisture conditions. Thermal modification of wood reduces its hygroscopicity, thereby, increasing its durability, e.g. its dimensional stability and resistance to biodeterioration. The hypothesis is that the use of thermally modified wood (TMW) components in biocomposites can enhance their durability properties and, at the same time, increase the value of residues from TMW processing. The main objective of this thesis is to study and analyse the surface and sorption properties of TMW components using inverse gas chromatography (IGC), dynamic vapour sorption (DVS), X-ray photoelectron spectroscopy (XPS), and the multicycle Wilhelmy plate method. The aim is to gain a better understanding of the surface and sorption characteristics of TMW components to enable the design of optimal adhesion properties and material combinations (compatibility) for use in biocomposites, especially suitable for outdoor and moist building material applications. Samples of TMW and unmodified wood (UW) components of Norway spruce (Picea abies Karst.) and Scots pine (Pinus sylvestris L.) heartwood were prepared and analysed with respect to surface energetics, hygroscopicity, liquid sorption and resulting swelling. The work also included analysis of surface chemical composition, as well as influences of extractives and moisture sorption history. The effect of using TMW components in a wood plastic composite (WPC) exposed to a series of soaking-drying cycles in water was studied with a focus on water sorption, swelling and micromorphological changes. The IGC analyses indicate that TMW components of spruce have a more heterogeneous surface energy character, i.e. a distinctly higher dispersive part of surface energy for low surface coverages, than do UW components. This is suggested to be due to the higher percentage of hydrophobic extractives present in TMW samples. Lewis acid-base analysis indicates that both UW and TMW components from spruce have a predominantly basic character and an enhanced basicity for the latter ones. Results show that both the hygroscopicity and water liquid uptake are lower for TMW than for UW samples. Unexpectedly, a significantly lower rate of water uptake was found for the extracted UW of pine heartwood than for non-extracted samples. In the former case, this is presumably due to contamination effects from water-soluble extractives, which increase capillary flow into wood voids, as proven by a decrease in water surface tension. Water uptake as well as swelling was significantly reduced for the WPCs with TMW and hot-water extracted UW components compared with the WPCs with UW components. This reduction also resulted in fewer wood component-polymer interfacial cracks in the WPCs with the modified wood components.
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| 8. |
- Källbom, Susanna, et al.
(författare)
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Effects of water soaking-drying cycles on thermally modified spruce wood-plastic composites
- 2020
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Ingår i: Wood and Fiber Science. - : SOC WOOD SCI TECHNOL. - 0735-6161. ; 52:1, s. 2-12
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Tidskriftsartikel (refereegranskat)abstract
- The overall aim of this work was to gain more insight on the potential of modified wood (TMW) components for use in wood-thermoplastic composites (WPCs). Laboratory-scale TMWPCs were produced, and the effects of severe water soaking-drying cycles on the samples were studied. Water sorption behavior and resulting dimensional and micromorphological changes were also studied, and the results were compared with those of unmodified wood-plastic composites (UWPCs) used as control. The TMW was prepared by cutting a spruce board into half and subjecting one-half to an atmosphere of superheated steam at atmospheric pressure with a peak temperature of 210 degrees C, with the other unmodified wood (UW) half as a control. The TMW and UW components were then prepared by a Wiley mill and thereafter sifted into smaller (mesh 0.20-0.40 mm) and larger (mesh 0.40-0.63 mm) size fractions. A portion of the wood components were also subjected to hydrothermal extraction (HE). Composite samples with these different wood components, polypropylene (PP) matrix, and maleated PP (MAPP) as coupling agent (50/48/2 wood/PP/MAPP ratio by weight) were then prepared by using a Brabender mixer followed by hot pressing. The matching micromorphology of the composites before and after the soaking-drying cycles was analyzed using a surface preparation technique based on ultraviolet-laser ablation combined with scanning electron microscopy. The results of the water absorption tests showed, as hypothesized, a significantly reduced water absorption and resulting thickness swelling at the end of a soaking cycle for the TMWPCs compared with the controls (UWPCs). The water absorption was reduced with about 50-70% for TMWPC and 60-75% for HE-TMWPC. The thickness swelling for TMWPCs was reduced with about 40-70% compared with the controls. Similarly, the WPCs with HE-UW components absorbed about 20-45% less moisture and showed a reduced thickness swelling of about 25-40% compared with the controls. These observations also were in agreement with the micromorphology analysis of the composites before and after the moisture cycling which showed a more pronounced wood-plastic interfacial cracking (de-bonding) as well as other microstructure changes in the controls compared with those prepared with TMW and HE-UW components. Based on these observations, it is suggested that these potential bio-based building materials show increased potential durability for applications in harsh outdoor environments, in particular TMWPCs with a well-defined and comparably small size fractions of TMW components.
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| 9. |
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| 10. |
- Källbom, Susanna, 1988-
(författare)
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Surface characterisation of thermally modified spruce wood and influence of water vapour sorption
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today there is growing interest within the construction sector to increase the proportion of biobased building materials made from renewable resources. By-products or residuals from wood processing could in this case be valuable resources for manufacturing new types of biocomposites. An important research question related to wood-based biocomposites is how to characterise molecular interactions between the different components in the composite. The hygroscopic character of wood and its water sorption properties are also crucial. Thermal modification (or heat treatment) of wood results in a number of enhanced properties such as reduced hygroscopicity and improved dimensional stability as well as increased resistance to microbiological decay.In this thesis, surface characteristics of thermally modified wood components (often called wood fibres or particles) and influencing effects from moisture sorption have been analysed using a number of material characterisation techniques. The aim is to increase the understanding in how to design efficient material combinations for the use of such wood components in biocomposites. The specific objective was to study surface energy characteristics of thermally modified spruce (Picea abies Karst.) under influences of water vapour sorption. An effort was also made to establish a link between surface energy and surface chemical composition. The surface energy of both thermally modified and unmodified wood components were studied at different surface coverages using inverse gas chromatography (IGC), providing information about the heterogeneity of the surface energy. The water vapour sorption behaviour of the wood components was studied using the dynamic vapour sorption (DVS) method, and their surface chemical composition was studied by means of X-ray photoelectron spectroscopy (XPS). Additionally, the morphology of the wood components was studied with scanning electron microscopy (SEM).The IGC analysis indicated a more heterogeneous surface energy character of the thermally modified wood compared with the unmodified wood. An increase of the dispersive surface energy due to exposure to an increased relative humidity (RH) from 0% to 75% RH at 30 ˚C was also indicated for the modified samples. The DVS analysis indicated an increase in equilibrium moisture content (EMC) in adsorption due to the exposure to 75% RH. Furthermore, the XPS results indicated a decrease of extractable and a relative increase of non-extractable compounds due to the exposure, valid for both the modified and the unmodified wood. The property changes due to the increased RH condition and also due to the thermal modification are suggested to be related to alterations in the amount of accessible hydroxyl groups in the wood surface. Recommendations for future work and implications of the results could be related to knowledge-based tailoring of new compatible and durable material combinations, for example when using thermally modified wood components in new types of biocomposites for outdoor applications.
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| 11. |
- Källbom, Susanna, et al.
(författare)
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Surface chemical analysis and water vapour sorpion of thermally modified wood exposed to increased relative humidity
- 2015
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Ingår i: The Eighth European Conference on Wood Modification (ECWM8) 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The increased interest in environmentally friendly building materials is accompanied with an increased need for research on thermally modified wood. Products made from recycling or reusing of thermally modified residuals will have advantages in terms of environmental aspects. Surface characteristics of thermally modified wood play an important role for the development of applications involving bonding processes, for example when using thermally modified wood residuals in biocomposites. Surface chemistry characteristics are important in developing such materials. A technique used for surface chemical analysis of the outermost surface is X‑ray photoelectron spectroscopy (XPS). Some surface chemical analyses of wood and modified wood can be found in Nzokou and Kamdem (2005), Inari et al. (2006), Bryne et al. (2010), Johansson et al. (2012), Rautkari et al. (2012). Furthermore, the influence of water and moisture has crucial effect on the properties of wood and wood products. Water vapour sorption properties of hygroscopic materials can be studied using a dynamic vapour sorption (DVS) instrument. Previous studies on thermally modified wood exposed to several sorption cycles using DVS have shown an increase in hysteresis during the first cycle, compared with unmodified wood (Hill et al., 2012). However, during the second and the third sorption cycle a reduction in sorption hysteresis was observed. The objective of this work was to study the surface chemical composition and water vapour sorption properties of thermally modified wood. In particular, an effort was made to study any influence on such properties due to a previous exposure to a high relative humidity (RH). Interpretations of the results indicate a decrease of extractable or volatile organic components and a relative increase of non-extractable components, for the high humidity-exposed samples. This could be due to remaining extractives migrating towards or redistribution at the wood surface layer as a result of moisture diffusion. The DVS results show that the thermally modified wood samples that had been exposed to the high relative humidity condition revealed a slight decrease of the hysteresis of the sorption isotherms. The opposite trend was furthermore seen for the unmodified wood.
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| 12. |
- Källbom, Susanna, 1988-, et al.
(författare)
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Surface energy characteristics of refined fibres at different pressures
- 2014
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Ingår i: Proceedings of 10th Meeting of the Northern European Network for Wood Science & Engineering (WSE 2014). ; , s. 134-138
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Wood fibres were produced on the pilot scale refiner at the BioComposites Centre, Bangor University, from a commercially sourced mix of chipped wood. The fibres were produced at refiner pressure 4, 6, 8 and 10 bar and dried in the associated flash drier. Surface energy characterization of the refined fibres was performed using inverse gas chromatography (IGC). The dispersive part of the total surface energy was analysed for duplicates of fibre samples at the four different refiner pressures. Non-polar alkane probes were used for the dispersive surface energy analysis at different surface coverage. Results indicate that the processing pressure has an effect of the dispersive surface energy and IGC analysis could be developed as a tool both for process development and process control in refining fibres.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Källbom, Susanna, 1988-, et al.
(författare)
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Surface energy characterization of thermally modified spruce using inverse gas chromatography under cyclic humidity conditions
- 2015
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Ingår i: Wood and Fiber Science. - : SOC WOOD SCI TECHNOL. - 0735-6161. ; 47:4, s. 410-420
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Tidskriftsartikel (refereegranskat)abstract
- The surface energy of unmodified and thermally modified spruce wood components was researched at dry and moist conditions using inverse gas chromatography. The results indicate a more pronounced heterogeneous nature of the thermally modified wood surfaces in terms of the dispersive (nonpolar) component of the surface energy, compared with that of the unmodified wood surfaces. The dispersive component of the surface energy of the thermally modified wood ranged between 44 and 38 mJ/m(2) corresponding to an increase in surface coverage from a low level and up to about 10%. Suggested explanations for the more distinct heterogeneity of the thermally modified wood sample are related to chemical changes of the wood substance which seem to result in certain micromorphological features observed by scanning electron microscopy as alternated fracture surfaces created in the grinding process; and also possible changes or redistribution of the wood extractives. An increase of the MC, representing a change from a dry condition of approximately 0% RH to ca 75% RH, of both the unmodified and thermally modified samples seemed to have a marginal influence on the dispersive component of the surface energy. Possible implications of the results in this study can be found in the tailoring of new compatible and durable material combinations, for example, when using thermally modified wood residuals as a component in new types of biocomposites.
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| 17. |
- Källbom, Susanna, 1988-, et al.
(författare)
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Surface energy characterization of thermally modified wood particles exposed to humidity cycling using inverse gas chromatography
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this work was to study surface energetics of thermally modified wood particles exposed to dry-humid cycling. This information can give insight in the adhesion properties between the modified wood and composite matrices, adhesives or coatings. The surface energy characterization as well as the dry-humid cycling was performed using inverse gas chromatography (IGC). Duplicates of thermally modified and unmodified spruce particles with size 0-0.125 mm were investigated and conditioned in dry-humid cycles at 0-75 % RH and 0‑25 % RH. The BET specific surface area as well as the dispersive surface energy heterogeneity (or distribution) at different surface coverage was determined. The results showed similar trends for the different cycles in the dry and humid states, respectively. The difference in dispersive surface energy distribution between the dry and humid state was more pronounced at the lower surface coverage.
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| 18. |
- Källbom, Susanna, et al.
(författare)
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Surface energy characterization of thermally modified wood using inverse gas chromatography
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this work is to characterize surface energetics of thermally modified wood. Such information may be useful for a better understanding and predictions of adhesion properties between the modified wood and other material systems, e.g. coatings, adhesives or matrices in composites. Inverse gas chromatography (IGC) was used to study the surface energy characteristics of thermally modified spruce in particle form. Two different wood component samples were prepared, one with a larger and one with a smaller particle size distribution. Measurements of BET specific surface area and dispersive surface energy distribution of the particle samples are presented. Results indicate that a ground wood component of a finer size distribution of thermally modified wood is less energetically heterogeneous compared with a component with a larger size distribution.
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| 19. |
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| 20. |
- Källbom, Susanna, 1988-, et al.
(författare)
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The influence of log soaking temperature and thermal modification on the properties of birch veneers
- 2016
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Ingår i: IRG Annual Meeting. - : IRG Documents.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In veneer manufacture the logs are routinely soaked in heated water baths in order to soften the wood prior to peeling. The temperature of the water may vary greatly between batches; however, the influence of log soaking temperature on veneer properties has had little research attention. Uncontrolled moisture is known to cause problems in wood-based materials, while thermal modification offers a method to control the interaction between wood and water. Therefore it might be beneficial to utilise thermally modified veneers in plywood manufacture. Yet, thermal modification is expected to also change other wood properties which might influence the possibility to utilise thermally modified veneers for wood-based-panels. The purpose of this study was to investigate the influence of log soaking temperature (70 °C and 20 °C) and thermal modification (8h in steam conditions) on selected properties of birch veneers, which are relevant in plywood manufacture. The surface area and surface free energy was studied with inverse gas chromatography (IGC). The surface free energy was found to be slightly higher for the unmodified veneers, however, no major difference was found in the dispersive part of the surface free energy between the log soaking temperatures or between unmodified or thermally modified veneers. The wetting of the veneers was investigated with the Wilhelmy plate method utilising the multicycling technique. It was found that lower log soaking temperature produced veneers with more hydrophobic nature. Also, thermal modification increased the hydrophobicity of the veneers. The bond strength was measured with an automatic bond evaluation system (ABES) using phenol formaldehyde (PF) resin. In general, the lower log soaking temperature resulted in slightly higher bond strength (however, the result was statistically insignificant), while thermal modification slightly lowered the bond strength. Based on these initial results thermally modifying the veneers prior to plywood manufacture might be useful.In veneer manufacture the logs are routinely soaked in heated water baths in order to soften the wood prior to peeling. The temperature of the water may vary greatly between batches; however, the influence of log soaking temperature on veneer properties has had little research attention. Uncontrolled moisture is known to cause problems in wood-based materials, while thermal modification offers a method to control the interaction between wood and water. Therefore it might be beneficial to utilise thermally modified veneers in plywood manufacture. Yet, thermal modification is expected to also change other wood properties which might influence the possibility to utilise thermally modified veneers for wood-based-panels. The purpose of this study was to investigate the influence of log soaking temperature (70 °C and 20 °C) and thermal modification (8h in steam conditions) on selected properties of birch veneers, which are relevant in plywood manufacture. The surface area and surface free energy was studied with inverse gas chromatography (IGC). The surface free energy was found to be slightly higher for the unmodified veneers, however, no major difference was found in the dispersive part of the surface free energy between the log soaking temperatures or between unmodified or thermally modified veneers. The wetting of the veneers was investigated with the Wilhelmy plate method utilising the multicycling technique. It was found that lower log soaking temperature produced veneers with more hydrophobic nature. Also, thermal modification increased the hydrophobicity of the veneers. The bond strength was measured with an automatic bond evaluation system (ABES) using phenol formaldehyde (PF) resin. In general, the lower log soaking temperature resulted in slightly higher bond strength (however, the result was statistically insignificant), while thermal modification slightly lowered the bond strength. Based on these initial results thermally modifying the veneers prior to plywood manufacture might be useful.
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| 21. |
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| 22. |
- Källbom, Susanna, 1988-, et al.
(författare)
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Water vapour sorption characteristics and surface chemical composition of thermally modified spruce (Picea abies karst)
- 2016
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Ingår i: International Wood Products Journal. - : Taylor & Francis. - 2042-6445 .- 2042-6453. ; 7:3, s. 116-123
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work was to study the hygroscopicity and surface chemical composition of thermally modified (TM) spruce. An effort was also made to study if those features were influenced by a previous exposure to a significant increase in relative humidity (RH). TM and unmodified Norway spruce (Picea abies Karst) samples, both in solid and ground form, were prepared. Water vapour sorption characteristics of the ground samples were obtained by measuring sorption isotherms using a dynamic vapour sorption (DVS). The surface chemical composition of the solid samples, both acetone extracted and non-extracted, were analysed using X-ray photoelectron spectroscopy (XPS). The DVS analysis indicated that the TM wood exposed to the 75% RH revealed a decrease in isotherm hysteresis. The XPS analysis indicated a decrease of acetone extractable or volatile organic components and a relative increase of non-extractable components for the samples exposed to the increased RH condition.
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| 23. |
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| 24. |
- Källbom, Susanna, et al.
(författare)
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Wood-plastic composites made from thermally modified spruce wood components and effects of exposure to water-soaking-drying cycles
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The over-all aim of this work is to gain more insight on the potential to use thermally modified wood (TMW) components in wood-thermoplastic composites (WPCs), ie a new type of biobased building material, here defined as TMWPCs, assumed to have significantly increased moisture resistance and durability related to conventional WPCs. The specific objective was to prepare lab-scale TMWPCs and WPC controls with unmodified wood (UW), and to expose these samples to a series of severe water-soaking-drying cycles to study the effects on the water sorption behavior and resulting dimensional and micromorphology changes. TMW was prepared by thermal modification of a spruce board in an atmosphere of superheated steam at atmospheric pressure with a peak temperature of 210°C (also matched with an UW board as control). TMW and UW components were then prepared by a Wiley mill and thereafter sifted into a smaller (0.20-0.40 mm) and a larger (0.40-0.63 mm) size fraction. A portion of the wood components were also hot-water extracted (HE) with liquid hot-water. Composite samples with these different wood components, polypropylene (PP) matrix, and maleated PP (MAPP) as coupling agent (50/48/2 wood/PP/MAPP ratio) were then prepared by using a Brabender mixer followed by hot-pressing. The matching micromorphology of the composites before and after the soaking-drying cycles was analyzed using a surface preparation technique based on UV-laser ablation combined with scanning electron microscopy (SEM). An effort was also made to study the wood-thermoplastic interfacial behavior in the composites by dynamic mechanical analysis (DMA). The results of the water absorption tests showed, as hypothesized, a significantly reduced water absorption and resulting thickness swelling for the TMWPCs compared with the controls. Similarly, the WPCs with HE-UW components showed a significant reduction in water absorption and thickness swelling compared with the controls. In contrast, the samples with HE-TMW components resulted in only minor moisture property changes. These observations were also in agreement with the micromorphology analysis of the composites before and after the moisture cycling which showed a more pronounced wood-plastic interfacial cracking (de-bonding) as well as other microstructure changes in the controls compared with those prepared with TMW and HE-UW components. The DMA indicated better dispersion and increased interfacial interaction for the WPCs with UW components with the smaller size fraction compared with the larger size fraction. The loss modulus and storage modulus were overall reduced for samples with HE and TMW components compared with those with UW components. Based on these observations it is suggested that a potential biobased building material with increased durability for applications in harsh outdoor environments may be tailored as a TMWPC with a well-defined and comparably small size fractions of TMW components.
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| 25. |
- Laine, Kristiina, et al.
(författare)
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Acetylation and densification of wood
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this study was to explore the possibility to surface densify acetylated solid wood. The aim of surface densification is to improve mechanical properties, such as hardness, at the very surface of wood where the property improvements are mostly needed (e.g. in flooring and decking). However, when subjected to moisture, surface densified wood may swell back almost to the original dimensions. Therefore, acetylated and non-acetylated wood was surface densified in order to investigate whether the dimensional stability of densified wood may be improved by pre-acetylation. Surface densification was performed by compressing the acetylated radiate pine samples between metal plates with only one side heated (150°C) in order to target the deformation to one surface only. The original thickness of the samples was 20 mm and the target thickness 18 mm which was controlled by metal stops. The recovery of the deformation (set-recovery) was measured by soaking the samples in water and measuring the oven-dry thickness before and after soaking in repeated cycles. It was found that acetylated wood may be surface densified and indeed the set-recovery of the pre-acetylated wood was significantly lower (17.4 %) compared to non-acetylated wood (72.8 %). Further studies in adjusting the process parameters might lead to even higher reduction in set-recovery.
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| 26. |
- Laine, Kristiina, et al.
(författare)
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Hardness, set-recovery and micromorphology studies of densified and thermally modified wood
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of the work reported in this paper was to increase the density of Scots pine wood in order to improve its hardness. Density was increased by compressing the porous structure of wood between heated metal plates in the radial direction by 40, 50 or 60% of the thickness. The compressed state was stabilised by thermally modifying (TM) the samples at 200 °C under steam conditions for 2, 4 or 6h. Set-recovery was almost eliminated (<1%) with TM of 6h for samples compressed 40 and 50%. It was discovered that hardness of densified wood was in some cases even three times higher compared to untreated wood. However, the hardness of the densified, non-TM wood was reduced after soaking and drying back to the original untreated level, while TM of 4 and 6h maintained an increased level of hardness.
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| 27. |
- Laine, Kristiina, et al.
(författare)
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Micromorphological studies of surface densified wood
- 2014
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 49:5, s. 2027-2034
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Tidskriftsartikel (refereegranskat)abstract
- Scots pine (Pinus sylvestris L.) wood was surface densified in its radial direction in an open press with one heated plate to obtain a higher density on the wood surface whilst retaining the overall thickness of the sample. This study investigated the effect of temperature (100, 150 and 200 A degrees C) and press closing speed (5, 10 and 30 mm/min, giving closing times of 60, 30 and 10 s, respectively) on the micromorphology of the cell-wall, as well as changes occurring during set-recovery of the densified wood. The micromorphology was analysed using scanning electron microscopy (SEM) combined with a sample preparation technique based on ultraviolet-excimer laser ablation. Furthermore, the density profiles of the samples were measured. Low press temperature (100 A degrees C) and short closing time (10 s) resulted in more deformation through the whole thickness, whilst increasing the temperature (150 and 200 A degrees C) and prolonging the closing time (30 and 60 s) enabled more targeted deformation closer to the heated plate. The deformation occurred in the earlywood regions as curling and twisting of the radial cell-walls, however, no apparent cell-wall disruption or internal fracture was observed, even at low temperatures and fast press closing speed, nor after soaking and drying of the samples. In the SEM-analysis after soaking and drying, it was noticed that the cells did not completely recover their original form. Thus, part of the deformation was considered permanent perhaps due to viscoelastic flow and plastic deformation of the cell-wall components.
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| 28. |
- Laine, Kristiina, et al.
(författare)
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Surface densification of acetylated wood
- 2016
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Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 74:6, s. 829-835
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of wood can be improved by compressing its porous structure between heated metal plates. By adjusting the process parameters it is possible to target the densification only in the surface region of wood where the property improvements are mostly needed in applications, such as flooring. The compressed form is, however, sensitive to moisture and will recover to some extent in high humidity. In this study, therefore, acetylated radiata pine was utilised in the surface densification process in order to both reduce the set-recovery of densified wood and to improve the hardness of the acetylated wood. Pre-acetylation was found to significantly reduce the set-recovery of surface densified wood. However, after the second cycle the increase in set-recovery of acetylated wood was relatively higher than the un-acetylated wood. The acetylated samples were compressed by only 1 mm (instead of the target 2 mm), yet, the hardness and hardness recovery of the acetylated samples significantly increased as a result of densification. It was also discovered that rough (un-planed) surfaces may be surface densified, however, even if the surface became smooth to the touch, the appearance remained uneven.
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| 29. |
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| 30. |
- Laine, Kristiina, et al.
(författare)
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Wood densification and thermal modification: hardness, set-recovery and micromorphology
- 2016
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Ingår i: Wood Science and Technology. - : Springer Berlin/Heidelberg. - 0043-7719 .- 1432-5225. ; 50:5, s. 883-894
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Tidskriftsartikel (refereegranskat)abstract
- The density of wood can be increased by compressing the porous structure under suitable moisture and temperature conditions. One aim of such densification is to improve surface hardness, and therefore, densified wood might be particularly suitable for flooring products. After compression, however, the deformed wood material is sensitive to moisture, and in this case, recovered up to 60 % of the deformation in water-soaking. This phenomenon, termed set-recovery, was reduced by thermally modifying the wood after densification. This study presents the influence of compression ratio (CR = 40, 50, 60 %) and thermal modification time (TM = 2, 4, 6 h) on the hardness and set-recovery of densified wood. Previously, set-recovery has mainly been studied separately from other properties of densified wood, while in this work, set-recovery was also studied in relation to hardness. The results show that set-recovery was almost eliminated with TM 6 h in the case of CR 40 and 50 %. Hardness significantly increased due to densification and even doubled compared to non-densified samples with a CR of 50 %. Set-recovery reduced the hardness of densified (non-TM) wood back to the original level. TM maintained the hardness of densified wood at an increased level after set-recovery. However, some reduction in hardness was recorded even if set-recovery was almost eliminated.
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- Olsson, Anders, 1973-, et al.
(författare)
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Relationships between stiffness of material, lamellas and CLT elements with respect to out of plane bending and rolling shear
- 2023
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Ingår i: European Journal of Wood and Wood Products. - : Springer Nature. - 0018-3768 .- 1436-736X. ; 81, s. 871-886
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Tidskriftsartikel (refereegranskat)abstract
- The use of cross laminated timber (CLT) for construction has increased greatly in recent years and the large volumes ofwood used for CLT means that it is important to optimize the use of the material. This requires relevant grading of lamellasand knowledge of relationships between lamella and CLT properties. In the present study, the relationship between dynamicaxial modulus of elasticity (MoE) of lamellas and the quasi-static out of plane bending stiffness of CLT is investigated. Bymeans of four-point bending test, it is shown that the effective quasi-static MoE of lamellas in CLT is only 2–6% lower thanthe average axial dynamic MoE of the individual lamellas. With this knowledge, producers of CLT can easily predict andcontrol the important out of plane bending stiffness of the produced CLT. Moreover, it is shown that effective rolling shearstiffness of layers in CLT can be accurately determined by means of digital image correlation performed in connection tofour-point bending of CLT, even for long test spans. For layers of lamellas of Scots pine of size 40 × 190 mm2the averageapparent or effective rolling shear modulus was determined to be 159 MPa. The average rolling shear modulus of the samematerial was determined to be 56 MPa.
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| 35. |
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| 36. |
- Olsson, Sara, et al.
(författare)
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The use of esterified lignin for synthesis of durable composites
- 2011
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Ingår i: 7th meeting of the Nordic-Baltic Network in Wood Material Science & Engineering (WSE). - : Norsk institutt for skog og landskap.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Lignin is a natural polymer and one of the most abundant materials on earth. Despite this fact, lignin is often viewed as a by-product in chemical pulp processing and the use of lignin as a sustainable material is low. However, research and public awareness of sustainability have opened up new possibilities for using lignin as a material. In this study, Kraft softwood lignin was reacted with acetic and propionic anhydride to synthesize esterified lignin. Reactions were performed at 80 °C. The product was analyzed using IR, DSC and processability parameters, such as melt viscosity. The product was then blended with LDPE and extruded into composite films. The films were analyzed using FTIR and TGA, and the mechanical properties were determined by tensile tests. Preliminary results are positive and further studies are planned to confirm the results and establish the range of properties attainable.
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| 37. |
- Ormondroyd, G. A., et al.
(författare)
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Water sorption, surface structure and surface energy characteristics of wood composite fibres refined at different pressures
- 2016
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; , s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- During fibre processing, wood fibres are subjected to a range of physical and chemical conditions sufficient to slightly alter their chemical composition and hence their ultimate performance when used in the manufacture of wood fibre-based composites. In order to better understand the effects of refiner conditions on material performance, wood fibres were subjected to processing at different refiner pressures (4, 6, 8 and 10 bar) and subsequently dried in a flash drier. The fibres were analysed for changes in surface area, surface energy, surface structure and water vapour sorption characteristics. The methods applied were nitrogen adsorption utilising the Brunauer–Emmett–Teller theory, inverse gas chromatography, scanning electron microscopy and dynamic vapour sorption. It was found that increasing refiner pressure resulted in fibres of lower surface area, accompanied by increasing dispersive surface energies up to operating refiner pressures of 8 bar. It was found with fibres refined at different pressures that as the refiner pressure increased the equilibrium moisture content of the fibre decreased at the set relative humidities. However, it was also noted that the hysteresis was not significantly different between each of the refiner pressures. The results suggest that different refiner pressures can be used to tune the surface characteristics which may be beneficial to product development and the improvement of the environmental profile of the wood fibre composites.
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| 38. |
- Popescu, Carmen-Mihaela, et al.
(författare)
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Structural characterization and mechanical properties of wet-processed fibreboard based on chemo-thermomechanical pulp, furanic resin and cellulose nanocrystals
- 2020
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Ingår i: International Journal of Biological Macromolecules. - : Elsevier. - 0141-8130 .- 1879-0003. ; 145, s. 586-593
-
Tidskriftsartikel (refereegranskat)abstract
- Fibreboards are made of lignocellulosic fibres and synthetic adhesive which connect them. These synthetic adhesives, while relatively low-cost, are usually non-biodegradable and may cause health and environmental issues. Therefore, in recent years, there has been an increased demand for replacing these adhesives with bio-derived adhesives. The present study aims to develop fibreboards from chemo-thermomechanical pulp (CTMP) and a furanic resin based on prepolymers of furfuryl alcohol via wet-processing. To improve the bonding properties, maleic acid, aluminium sulphate, and cellulose nanocrystals (CNCs) were added. The resulting fibreboards were evaluated for their structural features and mechanical properties. The bending strength was improved when CNCs were added into the fibre's suspension, and the morphology indicated a more compact structure. The combination of the CTMP with CNC and Biorez resulted in the same mechanical behaviours as those noted for CTMP alone, the best performance being observed for the boards in which Al2(SO4)3 was added. Infrared spectroscopy and X-ray diffraction also proved the presence of cellulose nanocrystals and resin in the boards by increased specific bands intensity and crystallinity index, respectively.
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| 39. |
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| 40. |
- Ruponen, J., et al.
(författare)
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Tensile-shear strength studies on self-bonded 2-ply birch veneer joint manufactured and tested by applying Automated Bonding Evaluation System (ABES) hot press
- 2016
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Ingår i: WCTE 2016 - World Conference on Timber Engineering. - : Vienna University of Technology. - 9783903039001
-
Konferensbidrag (refereegranskat)abstract
- An Automatic Bond Evaluation System (ABES) hot press was employed to manufacture a self-bonded joint between two veneers of rotary-cut birch (Betula pendula Roth). The hot-pressing conditions were 220 °C and 5.0 MPa, with press times ranging from 180 s to 600 s with 60 s intervals. Additionally, the log-soaking temperature (20 °C and 70 °C) and the veneer initial MC (6% and 11%) were varied to study the effect on the tensile-shear strength of the joints. For one set, the surface properties were altered by acetone extraction. The samples were tested at 11% MC. However, one set was partly duplicated and tested at 6% MC, to study how the testing conditions influenced the bond strength. The maximum average tensile-shear strength was 3.3 MPa, observed after 600 s hot pressing. The studies also included bond-line micromorphology analysis by applying SEM combined with a micromachining surface preparation technique based on UV excimer laser ablation. It was also indicated that longer hot-pressing times, lower veneer initial MC and a lower testing MC resulted in increased tensile-shear strength. Acetone extraction decreased the bond strength with increased standard deviation. Finally, the highest single and average strengths were observed for veneers from higher soaking temperature.
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| 41. |
- Segerholm, B. Kristoffer, et al.
(författare)
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Process-related mechanical degradation of the wood component in high-wood-content wood-plastic composites
- 2012
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Ingår i: Wood and Fiber Science. - 0735-6161. ; 44:2, s. 145-154
-
Tidskriftsartikel (refereegranskat)abstract
- Micromorphological studies of wood plastic composites (WPC) are crucial for deeper understanding of their physical, mechanical, and durability properties. The objective of this study was to examine process-related mechanical degradation of the wood component in an extruded high-wood-content WPC. WPC with approximate to 70% wood content and three distinctly different ground wood components were manufactured by a conical extrusion technology, ie WPC were prepared with an unmodified, acetylated, or thermally modified wood component. Size and shape of wood components were determined before and after the extrusion process. Micromorphology of WPC samples was studied using a scanning electron microscope (SEM) and a surface preparation technique based on UV laser ablation. This micromachining technique was also applied to prepare that specimens for micromechanical analysis using a tensile stage mounted in a SEM. Results show that extrusion processes cause a significant mechanical degradation of the wood component. Degradation was most pronounced for the thermally modified wood component, and interestingly, this resulted in a more homogenous WPC micromorphology compared with WPC with unmodified and acetylated wood components. WPC with thermally modified wood also exhibited the highest micromechanical strength.
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| 42. |
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| 43. |
- Segerholm, Kristoffer, 1979-, et al.
(författare)
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Adhesion studies of scots pine-polypropylene bond using ABES
- 2010
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Ingår i: In Proceedings of the 6th meeting of the Nordic-Baltic Network in Wood Material Science and Engineering, WSE. - : Tallinn University of Technology.
-
Konferensbidrag (refereegranskat)
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| 44. |
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| 45. |
- Segerholm, Kristoffer, 1979-
(författare)
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Characteristics of wood plastic composites based on modified wood : Moisture properties, biological performance and micromorphology
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 46. |
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| 47. |
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| 48. |
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| 49. |
- Segerholm, Kristoffer, 1979-, et al.
(författare)
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Durability of PLA - Modified Wood Composites
- 2011
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Ingår i: Proceedings of the 11th International Conference on Wood & Biofiber Plastic Composites.
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Konferensbidrag (refereegranskat)
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| 50. |
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