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Flat wise green gluing of Norway spruce for structural application
Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. (Byggteknik)
Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.ORCID iD: 0000-0002-5333-0682
Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
2009 (English)In: International Conference on Wood Adhesives 2009 / [ed] Charles Frihart, Madison: Forest Products Society, 2009, 325-334 p.Conference paper, (Refereed)
Abstract [en]

Unseasoned (green) Spruce timber planks with dimensions25 x 150 x 5400 mm3 were flat-wise glued with a one-componentPUR adhesive, forming laminated beams with 150 x 300 mm2 crosssection.After curing, each beam was divided in two halves and subsequentlydried. The final cross-section of the beams was thus 50 x 300mm2. The evaluation of the beams included bending stiffness andbending strength in 4-point bending and the mechanical properties ofthe adhesive bonds. The adhesive bonds were tested according toEuropean standards for glued-laminated timber (EN 392, EN 391) andaccording to ASTM D 905, but also with a special small-scale specimenfor testing the fracture properties of the adhesive bond in Mode I.The complete force vs. deformation curve, including both the ascendingand the descending parts could be obtained. The deformationswere measured with a contact-free technique, based on two camerasand white light. The equipment made it possible to register the strainin the bond line and in the adjacent wood with a high spatial resolution(0,2 mm). The strength of the bond line and the fracture energywas calculated. Results show that both the stiffness and the strength ofthe beams can comply with the requirements for glued-laminated timberclass L40. The adhesive bonds fulfill the requirements of glulam instandard EN 386. The tensile strength and fracture energy measuredwith the small specimens of green-glued bond lines is on the samelevel as of conventionally glued bond lines.

Place, publisher, year, edition, pages
Madison: Forest Products Society, 2009. 325-334 p.
Keyword [en]
green gluing, tensite strength, fracture energy
National Category
Materials Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
URN: urn:nbn:se:lnu:diva-18600ISBN: 9781892529572 (print)ISBN: 9781617389863 (print)OAI: oai:DiVA.org:lnu-18600DiVA: diva2:525532
Conference
International Conference on Wood Adhesives, Lake Tahoe, Nevada, 28-30 sept.,2009
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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