Wood bonding by vibrational welding

Abstract

Mechanically-induced wood welding, without any adhesive, is shown here to rapidly yield wood joints satisfying the relevent requirements for structural application. The mechanism of mechanically-induced vibrational wood fusion welding is shown to be due mostly to the melting and owing of some amorphous, cells-interconnecting polymer material in the structure of wood, mainly lignin, but also hemicelluloses. This causes partial detachment, the 'unglueing' of long wood cells, wood bres, and the formation of a bre entanglement network in the matrix of molten material which then solidi es. Thus, a wood cells/ bre entanglement network composite having a molten lignin polymer matrix is formed. During the welding period some of the detached wood bres which are no longer held by the interconnecting material are pushed out of the joint as excess bres. Crosslinking chemical reactions also have shown to occur. The most likely one of these identi ed by NMR appears to be a cross-linking reaction of lignin with carbohydrate-derived furfural. The presence of these reactions has been identi ed by CP-MAS 13 C-NMR. These reactions, however, are relatively minor contributors during the very short welding period. Their contribution increases after welding has nished, which explains why long holding times under pressure after the end of welding contribute strongly to obtaining a good bond.

Wood products and green chemistry

“…The same mechanically induced friction welding techniques which are widely used in the plastic and car industries have recently been applied also to joining wood, without the use of any adhesive (Gfeller et al 2003;Pizzi et al 2004;Leban et al 2004;Kanazawa et al 2005;Ganne-Chedeville et al 2005;Mansouri et al 2009a, b;Omrani et al 2009c). These work by melting some wood components and forming at the interface between the two wood surfaces to be joined a composite of entangled wood fibers drowned into a matrix of melted wood intercellular material, such as lignin and hemicelluloses.…”

“…These work by melting some wood components and forming at the interface between the two wood surfaces to be joined a composite of entangled wood fibers drowned into a matrix of melted wood intercellular material, such as lignin and hemicelluloses. Linear mechanical friction vibration has been used to yield wood joints satisfying the relevant requirements for structural applications by welding at a very rapid rate (Gfeller et al 2003;Leban et al 2004;Mansouri et al 2009a). Cross-linking chemical reactions also have shown to occur by CP-MAS 13 C NMR.…”

Influence of Welding Time on Tensile-Shear Strength of Linear Friction Welded Birch (Betula pendula L.) Wood

“…In early studies, a WT of 3 to 6 s, WF of 100 Hz, amplitude of 3 mm, and WP of 1.3 to 2 MPa have been found to give the highest and least variable tensile-shear strength (Gfeller et al 2003;Ganne-Chédeville et al 2005). Welded joints produced by Gfeller et al (2003Gfeller et al ( , 2004) yielded a tensile-shear strength of more than 10 MPa in beech (Fagus sylvatica L.) and 2 MPa in spruce (Picea abies L.…”

“…After reaching the maximum temperature, the steady state conditions of constant temperature and coefficient of friction are attained momentarily. At the end of the process, pressure is maintained on the welded wood joint for a certain holding time, allowing the interfacial film forming the connection to cool down and solidify (Gfeller et al 2003;Stamm et al 2005).…”

“…Welded joints produced by Gfeller et al (2003Gfeller et al ( , 2004) yielded a tensile-shear strength of more than 10 MPa in beech (Fagus sylvatica L.) and 2 MPa in spruce (Picea abies L. Karst.)…”