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Development of a continuous wood surface densification process: the roller pressing technique
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0002-1489-0839
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0001-8404-7356
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0002-4526-9391
Swerea MEFOS AB.
2016 (English)In: Proceedings of the 59th International Convention of Society of Wood Science and Technology.: Forest Resource and Products: Moving Toward a Sustainable Future. / [ed] Susan LeVan-Green, Monona, WI: Society of Wood Science and Technology , 2016, p. 17-24Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Monona, WI: Society of Wood Science and Technology , 2016. p. 17-24
Keywords [en]
Forestry, agricultural sciences and landscape planning - Wood fibre and forest products
Keywords [sv]
Skogs- och jordbruksvetenskap samt landskapsplanering - Träfiber- och virkeslära
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-30743Local ID: 4a861bab-bce6-4ee8-8387-7f46dd34ccedISBN: 978-0-9817876-6-4 (electronic)OAI: oai:DiVA.org:ltu-30743DiVA, id: diva2:1003972
Conference
International Convention of Society of Wood Science and Technology : Forest Resource and Products: Moving Toward a Sustainable Future 06/03/2016 - 10/03/2016
Note

Godkänd; 2016; 20160309 (dicsan)

Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2019-09-12Bibliographically approved
In thesis
1. Surface-Densified Wood: From Laboratory-Scale Research Towards a Competitive Product
Open this publication in new window or tab >>Surface-Densified Wood: From Laboratory-Scale Research Towards a Competitive Product
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

For many decades, humans have been consuming more resources than the world has to offer in the long run. Increasing the use of renewable materials, such as wood, is essential if we are to achieve a sustainable use of the resources available to us. Densification of wood in general, and surface densification in particular, has the potential to improve the properties of widely available low-density wood species, opening up new fields of application, and fostering the use of wood products in general.

The objective of this thesis is to put past research within the field of surface densification of solid wood and advancements within the present project into a context, and to suggest a path towards a performance-driven and cost-effective type of product. A prevalent research gap has been identified and this thesis summarizes how this gap can be filled by already conducted and future studies. Important aspects that need be handled in order to fulfill the overall vision of the large-scale commercialization of surface-densified wood products are considered.

Past studies were successful in gaining a good understanding of different approaches to the densification of solid wood, such as using a hot press or a friction welding machine. Problems, such as the moisture-induced recovery of the densified wood cells could be solved from a technological perspective. However, those studies did not take into account industrial implementation. Existing methods are time- and/or energy-consuming. The use of roller-pressing equipment showed promising results, but also highlighted certain limitations. Solid wooden boards have been successfully surface-densified at speeds of up to 80 m/min. However, problems arose regarding the plasticization and stabilization of the densified wood cells, indicating that a continuous belt-press approach might be more viable with regard to the objective of industrial implementation.

In parallel, a structured method to identify the most suitable wood species for surface densification has been presented, with the aim of propagating the use of surface-densified wood products and widening their fields of application. This method has confirmed the suitability of previously used wood species, and has also suggested alternatives not considered thus far.

Previous studies into the surface densification of wood have provided a rather sound understanding of the densification process and have provided a useful foundation for the current project. The work done, thus far, has shown the viability of a continuous densification process and has indicated a sensible path towards the widespread establishment of surface-densified wood products on the market. 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2016. p. 60
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-60282 (URN)978-91-7583-757-4 (ISBN)978-91-7583-758-1 (ISBN)
Presentation
2016-12-15, Hörsal A, Hus A, Luleå tekniska universitet, Skellefteå, 10:00 (English)
Supervisors
Available from: 2016-11-14 Created: 2016-11-10 Last updated: 2017-11-24Bibliographically approved
2. Surface Densification of Solid Wood: Paving the Way Towards Industrial Implementation
Open this publication in new window or tab >>Surface Densification of Solid Wood: Paving the Way Towards Industrial Implementation
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface densification of a piece of solid wood results in an increase in density and in hardness in the whole or a part of the densified material, and is one of the ways of improving the properties and value of low-density wood species. Despite efforts for many years, mass commercialisation of either bulk- or surface-densified wood products has not yet been achieved. Most of the previously tested densification methods have limitations in terms of processing speed and integration into the largely continuous wood processing chain, which leads to high production costs. Established methods to eliminate the set-recovery rely either on technologically complex close-system methods or on open-system methods that require relatively long periods of high energy input. For this reason, impregnation with adhesives is used in almost all commercially available densified wood products, and none of them have risen above their status of being niche products.

Based on this background, three objectives for this project were formulated: (1) the development of a method for selecting the most suitable wood species for surface densification, (2) showing that surface densification can be carried out in a continuous manner at high process speeds, (3) and researching a fast open-system method to reduce the set- recovery.

The method developed for selecting the most suitable wood species for surface densification was based on Lean principles, and it confirmed the suitability of previously studied wood species, such as Scots pine, spruce and poplar. In addition, several suitable alternatives from different parts of the world and from different types of forest were identified. This suggests a high potential for establishing such wood products on a global market level.

Two studies using a continuous roller press showed that solid wood can be successfully surface-densified at process speeds of up to 80 m min-1, and that some defects, such as knots, are acceptable in the raw material, but the problem of set-recovery could not however be solved.

A screening experiment testing different open-system approaches to reduce the set-recovery highlighted the potential of a novel method using ionic liquids as a plasticiser prior to the surface densification of solid Scots pine. The set-recovery could be reduced to 10%, with the time of high energy input being less than 10 minutes. The Brinell hardness was increased by a factor of 2.7 over that of undensified wood. A study with thermo-gravimetric analysis and digital image correlation showed that the set-recovery almost exclusively happens in the transition zone between the densified and undensified wood cells, where there is less penetration of the ionic liquids.

The work accomplished in this project has successfully addressed several gaps in the field of wood densification, firstly, by employing a continuous surface densification process using a roller press, and secondly, by developing and studying a fast open-system pre-treatment with ionic liquids, which greatly reduces the set-recovery. Research will continue on a new band press, facilitating a swift transfer of knowledge between small- scale studies and the continuous surface densification of production-size wooden boards.

Place, publisher, year, edition, pages
Luleå University of Technology, 2019. p. 123
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-75794 (URN)978-91-7790-435-9 (ISBN)978-91-7790-436-6 (ISBN)
Public defence
2019-10-08, Auditorium A, Skellefteå, 09:00 (English)
Opponent
Supervisors
Available from: 2019-09-02 Created: 2019-09-02 Last updated: 2019-09-12Bibliographically approved

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Neyses, BenediktHagman, OlleSandberg, Dick

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