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.

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The potential of linear vibration friction as an innovative means of producing increases in both surface density and surface hardness was explored. The influence of processing pressure and time on the degree of surface densification, surface hardness and surface elasticity was investigated. It was found that surface hardness (measured as Brinell hardness) was positively correlated with densification ratio. Furthermore, surface elasticity, that is the ability of the surface to recover elastically after indentation during the Brinell hardness test, could be increased by up to 33% depending on the degree of surface densification. The temperature rise due to friction was also studied. During processing, it was found that the temperature rise on both the radial and tangential surfaces was positively correlated with the processing pressure and time.