| 1. |
- 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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| 2. |
- 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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| 3. |
- 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
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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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