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Continuous Wood Surface Densification: Chemical Treatments to Reduce the Set-Recovery
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0001-8404-7356
Swerea Mefos.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0002-4526-9391
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Number of Authors: 5
2016 (English)In: BIOCOMP 2016: The 13th Pacific Rim Bio-Based Composites Symposium - Bio-based composites for a sustainable future, Concepción: University of Concepción , 2016, 66-77 p.Conference paper (Refereed)
Abstract [en]

The hardness of the outer surface of solid wood can be improved by densification, and this opens up new fields of application for low-density species. So far, surface densification is carried out in time- and energy-consuming batch processes, and this means that potential advantages over more expensive hardwood species or non- renewable materials are lost. One of the crucial problems in all densification processes is to reduce the moisture-induced set-recovery of the densified wood cells. In a previous study, a new high-speed continuous surface densification process was introduced, where the surface of solid Scots pine boards could be densified at speeds of up to 80 m/min by a roller pressing technique. The aim of the present study was to integrate the roller pressing technique with different pre- and post-treatment methods to reduce the set- recovery. An aqueous solution of sodium hydroxide was used as a pre-treatment agent to activate the wood surface prior to densification, and a methacrylate ester monomer solution was used as an impregnation agent, both before and after densification. After densification and impregnation, the methacrylate monomers are polymerized by curing in an oven at 100°C in order to stabilize the compressed wood cells. The results show that the different treatments had no significant effect on the set-recovery, probably due to insufficient penetration into the wood material. Future work will focus on improving the treatment process and integrating all process steps into a fully continuous and automatic process. 

Place, publisher, year, edition, pages
Concepción: University of Concepción , 2016. 66-77 p.
Keyword [en]
compression, sodium hydroxide, methacrylate, impregnation, roller pressing
National Category
Other Natural Sciences Wood Science
Research subject
Wood Science and Engineering
URN: urn:nbn:se:ltu:diva-60281OAI: diva2:1045754
13th Pacific Rim Bio-Based Composites Symposium, Concepción, Chile, 13-15 November 2016
Available from: 2016-11-10 Created: 2016-11-10 Last updated: 2017-01-19Bibliographically 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. 60 p.
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Other Natural Sciences
Research subject
Wood Science and Engineering
urn:nbn:se:ltu:diva-60282 (URN)978-91-7583-757-4 (ISBN)978-91-7583-758-1 (ISBN)
2016-12-15, Hörsal A, Hus A, Luleå tekniska universitet, Skellefteå, 10:00 (English)
Available from: 2016-11-14 Created: 2016-11-10 Last updated: 2016-11-25Bibliographically approved

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