Adhesiveless bonding of wood - a review with a focus on wood welding

Most industrially used synthetic wood adhesives release formaldehyde, which is carcinogenic for humans. Adhesiveless bonding of wood can be achieved using heat treatment by either hot-pressing method, suitable mainly for wood particles and fibres or by wood welding. Welding of wood, which relies on the heat generated via friction, can be used for bonding two or more solid wood pieces together. The process can be carried out either by linear or rotational wood welding. This review first considers the manufacturing of binderless wood-based panels by hot-pressing. Then this is followed by an in-depth outlook of wood welding and its application in the wood industry. The effects of varying wood welding parameters, such as applied pressure, vibrational frequency and amplitude, holding pressure, holding time, welding time in linear wood welding, and relative diameter difference between the substrate and the dowel in rotational wood welding to obtain joints with optimal mechanical and physical properties is reviewed and discussed. Wood products made by heat treatment (hot-pressing and wood welding) are environmentally friendly, and the brief curing times needed for their manufacture represent a great advantage compared with the usage of wood adhesives to bind pieces of wood.