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Finger jointing of freshly sawn Norway Spruce side boards: a comparative study of fracture properties of joints glued with phenol-resorcinol and one-component polyurethane adhesive
SP Technical Research Institute of Sweden, Stockholm. (Byggteknik)
Linnaeus University, Faculty of Technology, Department of Building Technology. SP Technical Research Institute of Sweden, Stockholm.ORCID iD: 0000-0002-5333-0682
Linnaeus University, Faculty of Technology, Department of Building Technology.
Innventia AB, Stockholm.
2014 (English)In: Materials and Joints in Timber Structures: Recent Developments of Technology, Springer, 2014, 325-339 p.Conference paper, (Other academic)
Abstract [en]

Finger jointing of unseasoned Norway Spruce was studied with respect to tensile strength, adhesive penetration and durability. Finger joints were manufactured with 1) unseasoned wood and one component polyurethane (PUR) adhesive, 2) dried wood and PUR adhesive and 3) dried wood and phenol resorcinol formaldehyde (PRF) adhesive. Two levels of wood density were used. The tensile strength of the finger joints was determined and the deformations within the joint were studied with an optical measurement system (ARAMIS). The penetration of the adhesive was studied with x-ray microtomography. The durability of the joints was determined according to the standard ASTM D 4688. The results show that the tensile strength and the durability of green glued finger joints are on the same level as that of dry glued PUR joints. The penetration of the PUR adhesive is high in the unseasoned wood and cavities within the bonds seem to be smaller than in dry glued PUR joints. The tensile strength of the finger joints is dependent on density, independent on the adhesive system used. The strength of the green glued PUR adhesive bonds in finger joints measured with small scale specimens did not differ from the strength of the dry glued PUR bonds.

Place, publisher, year, edition, pages
Springer, 2014. 325-339 p.
Series
RILEM Bookseries, ISSN 2211-0844 ; 9
Keyword [en]
finger joint, bond line, fracture, green gluing, digital image correlation, x-ray tomography
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
URN: urn:nbn:se:lnu:diva-18603DOI: 10.1007/978-94-007-7811-5_30ISBN: 978-94-007-7810-8 (print)OAI: oai:DiVA.org:lnu-18603DiVA: diva2:525538
Conference
RILEM International Symposium on Materials and Joints in Timber Structures, Stuttgart, GERMANY, OCT 08-10, 2013
Available from: 2012-05-08 Created: 2012-05-08 Last updated: 2015-09-28Bibliographically approved
In thesis
1. Characterisation of green-glued wood adhesive bonds
Open this publication in new window or tab >>Characterisation of green-glued wood adhesive bonds
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The gluing of unseasoned wood, called green gluing, is a relatively new sawmill process, implying a radically changed order of material flow in the production of value-added wood-based products. It facilitates the enhancement of raw material recovery and value yield by integrating defect elimination and gluing already before kiln drying. The present study evaluates green glued adhesive bonds in flatwise glued beams and finger joints. The main part of this work deals with green gluing using a moisture curing polyurethane adhesive (PUR). Standardised test methods and specially designed, small scale, specimens were used for the determination of the strength, fracture energy and the ductility of both dry- and green glued bonds in tension and in shear. Using the small scale specimens it was possible to capture the complete stress versus deformation curves, including also their unloading part. An optical system for deformation measurement was used for the analysis of bond behaviour. The influence of moisture content during curing and temperature after curing on the adhesive chemical composition and on the mechanical properties was investigated. Furthermore, the moisture transport through the adhesive bond during curing was tested. Finally, microscopy studies were performed for analysis of bond morphology and fracture. The results show that two significant factors influence the shear strength of green glued bonds: wood density and adhesive spread rate. Bonds which fulfil the requirements according to EN 386 could be obtained within a wide range of process parameters. The small specimen tests showed that green glued PUR bonds can reach the same strength and fracture energy, both in shear and in tension, as dry glued bonds with the same adhesive amount. The local material properties of the bonds could be determined, thanks to the failure in the tests taking place within the adhesive bond itself and not in the wood. Following process factors were shown to cause lower bond strength: a) a low adhesive spread rate, b) high pressure and c) short pressing time in combination with low wood density and high moisture content. Moreover, the heat treatment of the cured PUR adhesive during drying influenced the chemical composition of the adhesive, providing for higher strength, stiffness and Tg of the adhesive, caused by an increased amount of highly ordered bidentate urea.

Place, publisher, year, edition, pages
Växjö, Kalmar: Linnaeus University Press, 2012. 67 p.
Series
Linnaeus University Dissertations, 85/2012
Keyword
green gluing, finger jointing, durability, shear strength, wood failure percentage, fracture energy, tensile strength, PUR adhesive
National Category
Materials Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-18606 (URN)978-91-86983-57-4 (ISBN)
Public defence
2012-06-01, Myrdal, Hus K, Växjö, 09:00 (English)
Opponent
Supervisors
Available from: 2012-05-09 Created: 2012-05-08 Last updated: 2012-06-15Bibliographically approved

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CiteExportLink to record
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Citation style
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