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Finger jointing of green Scots pine
Växjö universitet, Fakulteten för matematik/naturvetenskap/teknik, Institutionen för teknik och design. (Byggteknik)
2005 (Engelska)Ingår i: Green gluing of wood- process – products – market : International conference / workshop, Borås, April 7-8, 2005 / [ed] Björn Källander, Borås, 2005, s. 55-65Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Finger jointing of green timber enables the wood industry to produce value-added products by using a new efficient process. Green finger jointing has gradually accelerated in New Zealand, USAand Canada, but is still relatively unknown in Europe. This study evaluates three green adhesive systems used with green Scots Pine timber: 1) a modified Phenol Resorcinol Formaldehyde (PRF) known as Greenweld®, 2) a one-component polyurethane adhesive and 3) a soy protein and PRF (soy/PRF) adhesive. Green adhesives have been compared with a conventional exterior PRF-Reference adhesive used with kiln-dried timber. The evaluation of mechanical performance was carried out with 4-point bending, according to EN 408. The warp of dried finger-jointed timber was measured in the form of bow, spring and twist and microscopy studies of glue lines were performed. The moisture durability of the adhesives was tested according to ASTM-D 4688-95. The tensile strength, WFP (Wood Failure Percentage) and failure modes were determined. Results showed that bending strength did not differ either between green adhesive systems and PRF-Reference dry system, or among green adhesives themselves. The warp of dried timber was on the same level for green glued finger joints and for conventional finger joints. The durability test showed that the PUR adhesive used in the green process had highest dry tensile strength compared to the other tested adhesives. The wet tensile strength after accelerated aging of all four adhesives did not differ significantly. The dry WFP without any treatment was high for all three adhesives used for green gluing and did not differ from the PRF-Reference. However, the wet WFP after cyclic boiling treatment of the green adhesive systems turned out to be lower than the wet WFP of the PRF-Reference adhesive. The results of the failure mode also illustrate that the green adhesives glue line of the wet specimens failed more often in the interface between wood and the adhesive than those with the PRF-Reference adhesive. Additionally, microscopy studies of the glue lines revealed that the penetration of polyurethane adhesive was deepest, Greenweld’s penetration was similar to PRF-Reference and sapwood glue lines of green adhesives had more cavities than heartwood glue lines.

Ort, förlag, år, upplaga, sidor
Borås, 2005. s. 55-65
Nyckelord [en]
finger jointing, green gluing, durability
Nationell ämneskategori
Teknik och teknologier
Forskningsämne
Teknik, Byggteknik
Identifikatorer
URN: urn:nbn:se:lnu:diva-18593ISBN: 91-85533-31-9 (tryckt)OAI: oai:DiVA.org:lnu-18593DiVA, id: diva2:525516
Konferens
International conference / workshop Green gluing of wood- process – products – market. Borås, April 7-8 2005COST Action E34 Bonding of Wood in cooperation with SP Swedish National Testing and Research Institute
Tillgänglig från: 2012-05-08 Skapad: 2012-05-08 Senast uppdaterad: 2025-06-19Bibliografiskt granskad
Ingår i avhandling
1. Characterisation of green-glued wood adhesive bonds
Öppna denna publikation i ny flik eller fönster >>Characterisation of green-glued wood adhesive bonds
2012 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Växjö, Kalmar: Linnaeus University Press, 2012. s. 67
Serie
Linnaeus University Dissertations ; 85
Nyckelord
green gluing, finger jointing, durability, shear strength, wood failure percentage, fracture energy, tensile strength, PUR adhesive
Nationell ämneskategori
Materialteknik
Forskningsämne
Teknik, Byggteknik
Identifikatorer
urn:nbn:se:lnu:diva-18606 (URN)9789186983574 (ISBN)
Disputation
2012-06-01, Myrdal, Hus K, Växjö, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2012-05-09 Skapad: 2012-05-08 Senast uppdaterad: 2024-12-17Bibliografiskt granskad

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Sterley, Magdalena

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