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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.
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.
In adhesive joints this contact is attained by intermolecular or valence forces exerted by molecules in the surface layers of the adhesive and adherend.
In addition to adsorption, four other mechanisms of adhesion have been proposed.
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.
Though the demand for natural products has declined since the mid-20th century, certain of them continue to be used with wood and paper products, particularly in corrugated board, envelopes, bottle labels, book bindings, cartons, furniture, and laminated film and foils.
In addition, owing to various environmental regulations, natural adhesives derived from renewable resources are receiving renewed attention.
“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.These tests are carried out over a wide range of temperatures and under various environmental conditions.An alternate method of characterizing an adhesive joint is by determining the energy expended in cleaving apart a unit area of the interphase.In the formation of an adhesive bond, a transitional zone arises in the interface between adherend and adhesive.In this zone, called the interphase, the chemical and physical properties of the adhesive may be considerably different from those in the noncontact portions.