Structural adhesives historical development

The use of adhesives can be traced back many centuries, while the production of adhesives, on an industrial scale, started about 300 years ago. The birth of modern structural adhesives can be dated from about 1910, with the introduction of the phenol-formaldehyde resins.Table II summarizes the historical development of structural adhesives, with the dates referring to the approximate time period during which each adhesive became commercially available. The introduction dates for the high-temperature polymers (polyimide, polybenzimidazole, and polyquinoxa-line) have been included for reference, although, as previously mentioned, there are presently few commercial products based on these polymers. 

Over the past thirty years, new analytical techniques have been developed which allow the scientific study of adhesives. Our Symposium this week concerns the science of adhesives and this session focuses on Natural and Structural Adhesives. The papers today exemplify recently developed techniques and show the high science approach being applied to the adhesive bond. These studies replace historically empirical ones and begin to elucidate and separate the adhesive and cohesive factors. 

More recently, there has been a renewed recognition of the potential of bark-derived polyphenols for adhesives as a result of improved understanding of the chemical structure of these materials (, 5), new types of formulations (5), and the fact that tannins are being commercially used in adhesives in South Africa (7), thus serving as a prototype for utilization in other parts of the world. In order to properly assess the current developments in this field, this overview will provide a historical perspective on adhesives based on tannins as well as a summary of the extraction techniques and chemical structures. Finally, areas where additional work could be fruitful will be suggested. 

In the context of a book on adhesives from renewable resources, blood- and casein-based adhesives are worthy of mention because of their great historical importance to the adhesives industry. Caseins are particularly important because they were the first adhesives recognized for forming structurally capable bonds in wood products. They have been used since 1880 and they are still the preferred materials for many types of bonding due to their excellent adhesive properties and ease of cure. Despite their animal origins, these materials are far from plentiful. This makes them quite expensive in terms of wood adhesives, which is the viewpoint of this discussion. The review of the history, nature, manufacturing, and uses of these materials that follows may help to develop a perspective on their future usefulness to the adhesives industry. 

Epoxies have historically been the major adhesive family used for the structural bonding of metals and composites in the aerospace, industrial and automotive industries. They are characterised by curing to hard infusible resins that bond to a wide range of metals and have excellent resistance to heat and the environment. Epoxies have been used since the 1940s and have an excellent track record of successful structural bonding. Two-component and heat-cured one-component versions are available and literally thousands of formulations have been developed over the years for specific applications. 

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