Enhanced water resistance of welded wood joints

A multidisciplinary research team has recently developed an original method for assembling pieces of lignocellulosic materials. This method requires to apply a specific welding compound, inexpensive, non toxic, natural, abundant and environmentally friendly, on one or both faces of the materials to be joined, and then to apply a mechanically-induced friction welding. Wood industry such as construction of frames, barrels, coffins are targeted for non-exclusive licences for commercial agreement.

The mechanical junction of wood materials is performed by various physical processes (junction pieces) or chemical processes (adhesive), the latter being limited by the use of petroleum-derived compounds and/or compounds with a certain toxicity, generating pollution. Moreover, these processes have some limitations, particularly in terms of waterproofing of the joint obtained.
It is therefore important to develop new processes that are easy to implement, low-cost, and environmentally friendly for applications concerning the wood Industry (wood or lignocellulosic materials (chipboard, pressed, laminated, etc.), especially for companies working on the assembling of materials in contact with the outside, water, wet, or solvents.
In terms of strength, the joint obtained after application of the welding composition is comparable to the one obtained by a sole mechanical friction welding. Moreover, it has been shown that immersion in water of these novel assemblies does not alter the waterproof property of the welded joint, an original feature of this invention. In other words, welding of wood pieces by mechanical friction including a prior step of coating of the contact surface of at least one of the wood pieces with a specific welding composition is significantly enhancing the water resistance of welded joints of the wood assembly. The method of the invention particularly improves the water resistance properties of the rotational dowel welding joints, which are already much higher than that of linear vibration welding joints thanks to the geometry of welding joint itself.
Afterwards, X-ray micro-densitometry analysis was performed to measure the density of assembling samples obtained by linear mechanical friction welding according to increased welding time. It was observed that the area of greater density around the weldline is broader than the one observed when the linear vibration welding is performed without prior coating of the contact surfaces of the wood pieces with the welding composition.
Moreover, analysis by solid-phase CP-MAS (Cross Polarization – Magic Angle Spinning) 13C-NMR of the interfaces welded with the welding composition also showed an accumulation of lignin in the welding area.

Advantages of this novel method are :
- a 100% wood-based welding method
- are robustness, waterproof, rapidity of welding (few seconds only!),
- the low cost and environmental impact.
The compound used is inexpensive, non toxic, bio-sourced, abundant, environmentally friendly, and not a binder.

Source: Enterprise Europe Network – consortium Sud-Ouest France (11 FR 32j3 3NCM)

Opportunities

• Going international
• Technology transfer
• Seeking technical partners

Scientific typology

- Type of partner sought: Industrial - Specific area of activity of the partner: Wood and lignocellulosic industry, especially construction, civil engineering, furniture, etc. (e.g. construction of frames, framing, barrels, coffins, etc.). - Task to be performed by the partner sought: Industrial implementation of the proposed technology

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