Development of Synthetic Resin Adhesives

Abstract

THE development of synthetic resin adhesives has proceeded very fast since about 1937 when the first urea formaldehyde wood glues were being produced on a pilot scale. The excellent resistance of these materials to weathering conditions has enabled very considerable advances in structural design both in wooden structures and rather more recently in metal aircraft. These synthetic resin adhesives are basically ‘thermosetting’, that is to say, they harden by the addition of catalysts or by the application of heat, the chemical process which takes place being irreversible and not dependent upon the evaporation of solvents. This concept leads not only to good weather resistance, but also to the practicality of sticking together non‐porous materials such as metal. The first use of bonding of mstal in aircraft structures was in the de Havilland Hornet in 1943,1 and since then bonding has proved its advantages over other methods of joining for both primary and secondary structures. Other new methods of fabrication have appeared since that time and the requirements for structures in terms of loading and environment have changed considerably; but both mctal‐to‐metal bonding and its newer partner honeycomb sandwich show signs of much more extensive use in the future. These two most important applications of synthetic resin adhesives in modern aircraft will now be considered.