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Lillqvist, KristiinaORCID iD iconorcid.org/0000-0001-8514-5409
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Publications (4 of 4) Show all publications
Lillqvist, K., Källbom, S., Altgen, M., Belt, T. & Rautkari, L. (2019). Water vapour sorption properties of thermally modified and pressurised hot-water-extracted wood powder. Holzforschung, 73(12), 1059-1068
Open this publication in new window or tab >>Water vapour sorption properties of thermally modified and pressurised hot-water-extracted wood powder
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2019 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 73, no 12, p. 1059-1068Article in journal (Refereed) Published
Abstract [en]

The objective of the study was to investigate the water vapour sorption behaviour of thermally modified (TM) wood powder, e.g. ground wood prepared from waste streams of TM solid wood, and wood powder that was extracted in pressurised hot water. Solid spruce wood was TM in steam conditions (210°C for 3 h), milled and hot-water-extracted (HWE) at elevated pressure (140°C for 1 h). The results evidence that the hot-water extraction reduced the water sorption and the accessible hydroxyl group concentration by the removal of amorphous carbohydrates. In contrast, the enhanced cross-linking of the cell wall matrix and the annealing of amorphous matrix polymers during thermal modification reduced the sorption behaviour of wood additionally, without further reducing the hydroxyl accessibility. These additional effects of thermal modification were at least partially cancelled by hot-water extraction. The results bring novel insights into the mechanisms that reduce the water vapour sorption of wood by compositional and structural changes induced by heating.

Place, publisher, year, edition, pages
De Gruyter, 2019
Keywords
carbohydrate analysis, deuterium exchange, dynamic vapour sorption, hot-water extraction, thermal modification, Carbohydrates, Crosslinking, Sorption, Water vapor, Wood, Dynamic vapour sorptions, Hot water extraction, Extraction
National Category
Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-263273 (URN)10.1515/hf-2018-0301 (DOI)000497967800002 ()2-s2.0-85069753584 (Scopus ID)
Note

QC 20191105

Available from: 2019-11-05 Created: 2019-11-05 Last updated: 2019-12-12Bibliographically approved
Lillqvist, K., Rohumaa, A., Källbom, S., Rautkari, L. & Wålinder, M. (2017). THE INFLUENCE OF THERMAL MODIFICATION ON VENEER BOND STRENGTH. In: Engelund Thybring, E. (Ed.), Proceedings of the 13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29: . Paper presented at 13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29 (pp. 56).
Open this publication in new window or tab >>THE INFLUENCE OF THERMAL MODIFICATION ON VENEER BOND STRENGTH
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2017 (English)In: Proceedings of the 13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29 / [ed] Engelund Thybring, E., 2017, p. 56-Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

The purpose of this study was to investigate the effect of thermal modification on birchveneer properties relevant in plywood manufacture. The wood material used in thisstudy was a birch (Betula pendula Roth) stem sectioned into small logs nominally 1.2 min length. The logs were completely immersed in a water tank heated to either 70 °C or20 °C. The soaked logs were rotary cut on an industrial scale lathe (Model 3HV66;Raute Oyj, Lahti, Finland) into veneer with a nominal thickness of 0.8 mm.Veneer specimens (150x150 mm2) were cut and thermally modified at 200°C in steamconditions for 2, 4 and 8 h. Mass loss and equilibrium moisture content (EMC) weremeasured after modification. The bond strength of the veneers was measured withautomated bonding evaluation system (ABES- Adhesive Evaluation Systems, Inc.,Corvallis, Oregon, USA) using phenol formaldehyde (PF) resin (Prefere 14J021, PrefereResins Finland Oy, Hamina, Finland). Specimens (20 x 117 mm2), were cut from theconditioned veneer sheets. A liquid PF resin was applied to an area of 5 x 20 mm2 atone end of the veneer specimens (approx. spread rate 100 g m-2). After adhesiveapplication, the veneer-resin assembly was placed into the ABES and after 180 s ofpressing (130 °C and 2.0 MPa) the shear strength of adhesive bond was measured.As expected from previous studies, the mass loss increased and EMC reduced withlonger thermal modification time. No significant difference in mass loss or EMCbetween log soaking temperatures was recorded in this study. The thermal modificationslightly reduced the bond strength; however, longer treatment time did not furtherreduce the bond strength. Therefore, based on this study, thermally modified veneerscould be successfully bonded and

National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-271598 (URN)
Conference
13th annual meeting of the Northern European Network for Wood Science and Engineering, September 28-29
Projects
EnWoBio
Funder
Swedish Research Council Formas
Note

QC 20200331

Available from: 2020-03-30 Created: 2020-03-30 Last updated: 2020-03-31Bibliographically approved
Laine, K., Segerholm, K., Wålinder, M., Rautkari, L., Hughes, M. & Lankveld, C. (2016). Surface densification of acetylated wood. European Journal of Wood and Wood Products, 74(6), 829-835
Open this publication in new window or tab >>Surface densification of acetylated wood
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2016 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 74, no 6, p. 829-835Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Springer, 2016
Keywords
Acetylation, Densification, Hardness, Recovery, Acetylated wood, Densified wood, Mechanical properties of wood, Porous structures, Process parameters, Property improvement, Surface densification, Surface region, Wood
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-195233 (URN)10.1007/s00107-016-1077-3 (DOI)000385208400005 ()2-s2.0-84976477767 (Scopus ID)
Note

QC 20161117

Available from: 2016-11-17 Created: 2016-11-02 Last updated: 2017-11-29Bibliographically approved
Laine, K., Segerholm, K., Wålinder, M., Rautkari, L. & Hughes, M. (2016). Wood densification and thermal modification: hardness, set-recovery and micromorphology. Wood Science and Technology, 50(5), 883-894
Open this publication in new window or tab >>Wood densification and thermal modification: hardness, set-recovery and micromorphology
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2016 (English)In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 50, no 5, p. 883-894Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Springer, 2016
National Category
Wood Science
Identifiers
urn:nbn:se:kth:diva-196446 (URN)10.1007/s00226-016-0835-z (DOI)000385253100002 ()2-s2.0-84969895593 (Scopus ID)
Note

QC 20161129

Available from: 2016-11-29 Created: 2016-11-14 Last updated: 2017-11-29Bibliographically approved
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