Adhesive

adhesive, any substance that is capable of holding materials together in a functional manner by surface attachment that resists separation. “Adhesive” as a general term includes cement, mucilage, glue, and paste—terms that are often used interchangeably for any organic material that forms an adhesive bond. Inorganic substances such as portland cement also can be considered adhesives, in the sense that they hold objects such as bricks and beams together through surface attachment, but this article is limited to a discussion of organic adhesives, both natural and synthetic.

Natural adhesives have been known since antiquity. Egyptian carvings dating back 3,300 years depict the gluing of a thin piece of veneer to what appears to be a plank of sycamore. Papyrus, an early nonwoven fabric, contained fibres of reedlike plants bonded together with flour paste. Bitumen, tree pitches, and beeswax were used as sealants (protective coatings) and adhesives in ancient and medieval times. The gold leaf of illuminated manuscripts was bonded to paper by egg white, and wooden objects were bonded with glues from fish, horn, and cheese. The technology of animal and fish glues advanced during the 18th century, and in the 19th century rubber- and nitrocellulose-based cements were introduced. Decisive advances in adhesives technology, however, awaited the 20th century, during which time natural adhesives were improved and many synthetics came out of the laboratory to replace natural adhesives in the marketplace. The rapid growth of the aircraft and aerospace industries during the second half of the 20th century had a profound impact on adhesives technology. The demand for adhesives that had a high degree of structural strength and were resistant to both fatigue and severe environmental conditions led to the development of high-performance materials, which eventually found their way into many industrial and domestic applications.

This article begins with a brief explanation of the principles of adhesion and then proceeds to a review of the major classes of natural and synthetic adhesives.