Although adhesives have been known at least from the time of the early Egyptians and are familiar to all the civilized world as useful means to hold things together, their use in industry is only now being fully realized. Adhesives have many advantages over other methods of fastenings and some important limitations. They open the door to many new combinations of materials with unusual properties unattainable in materials of one component. They can be engineered to produce structural components of unusual properties, such as prefabricated building components or high-speed aircraft, as well as such prosaic uses as holding labels on cans, paper on a wall, or sealing envelopes.
Use of adhesives is still largely an art, but a science of adhesion and adhesives applications is developing. Adhesives are formulated from many components—both natural and synthetic—and are further modified with other selected additives. Their complex molecular composition makes basic studies of interfacial phenomena in bonding difficult. However, significant strides are being made to understand the fundamental nature of adhesion to various substrates, cohesive properties of the adhesive film, and interactions between adherends and adhesives in joints as related to joint design and bonding conditions.
One of the most valuable contributions to adhesives technology in recent years has been the introduction of new man-made polymers, which, when properly formulated into adhesives, can produce strong and durable joints that can be used with confidence as primary fastenings in structures where service requirements are severe over long periods of time.
The wide variety of adhesives now available, together with the many new adhesives to be developed in the near future, challenge the engineer and fabricator. Standardized methods for evaluating and specifying adhesives for new uses are an important phase of current and future ASTM activities.