Glues and adhesives - Features and types

Bonding techniques have developed considerably over the last fifty years, for a number of reasons. On the one hand, polymer chemistry has made it possible to formulate glues and adhesives that are much more efficient, more durable, with higher bond strengths and predictable, reliable results. Examples include :

• the development of adhesives based on neoprene or polychloroprene rubber during the Second World War, which enabled powerful, long-lasting bonds to be made by simple contact under short pressing times;

• epoxy structural adhesives, also discovered at the same time by the Swiss company Castan, which for the first time produced high-strength bonds (up to 15 MPa in shear) on metals, and were therefore rapidly and widely used in aeronautical and then automotive construction. Since 1960, these epoxy adhesives have also been used to bond prefabricated voussoirs in prestressed concrete bridge construction, with excellent durability and compressive and shear strength;

• followed by the emergence of water-based glues, vinyl glues for wood and acrylic glues for plastics;

• more recently, polyurethane adhesives and sealants with their wide range of possibilities.

On the other hand, bonding has made it possible, in some cases, to do away with mechanical assemblies, by replacing sewing, screwing, welding, crimping, stapling and so on. It has also made it possible to reduce stresses and design different parts or assemblies, by assembling parts over their entire surface or over larger areas. In addition, gluing, which is easy to automate on production lines, has made it possible to reduce labor costs in certain industries, and has been widely used for the prefabrication of building components (sandwich panels, doors, etc.).

In the building and civil engineering sectors, adhesive bonding has found many important applications, accounting for the largest tonnages in the glues, adhesives and sealants industry.

Bonding techniques require a detailed study of the problem to be solved, in order to be able to select the bonding method to be used in comparison with other assembly techniques, an understanding of the physico-chemical and mechanical phenomena involved, and a good knowledge of the different characteristics of glues and adhesives, so as to be able to select, design, test and control a bonded assembly.

A distinction is made between :

• conventional adhesives for bonding decorative coverings that do not require very high performance (e.g. water-based vinyl and acrylic adhesives, Neoprene adhesives);

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