Adhesive

Adhesives bond two or more materials at their surface, and may be classified as structural or nonstructural. Structural adhesives can support heavy loads, while nonstructural adhesives cannot. Most adhesives exist in liquid, paste, or granular form, although film and fabric-backed tape varieties are also commercially available.

Adhesives have been used since ancient times. The first adhesives were probably made from boiled-down animal products such as hides or bones. Organic, i.e., carbon-based, adhesives have also been derived from plant products for use with paper products. While many of these organic glues have proven effective in the adhesion of furniture and other indoor products, they have not been effective in outdoor use where they are exposed to harsher environmental conditions.

Although inorganic adhesives, which are based on materials not containing carbon, such as the sodium silicates (water glasses) for bonding paper board, are sold commercially, most adhesives in common use are made of synthetic, organic materials. By far, the most widely used adhesives today are synthetic, polymer-based adhesives.

Synthetic adhesives may be made of amorphous thermoplastics above their glass transition temperatures; thermosetting monomers as in the case of epoxy glues and cyanoacrylates; low molecular weight reactive species as in the case of urethane adhesives; or block copolymers, suspensions, or latexes.

Adhesives are characterized by their shelf life, which is defined as the time that an adhesive can be stored after manufacture and still remain usable, and by their working life, defined as the time between mixing or making the adhesive and when the adhesive is no longer usable. The best choice of adhesive depends on the materials to be bonded.

General purpose adhesives including rubber cements and epoxies are capable of bonding fabrics together, as well as fabrics to other materials. When coated fabrics must be joined, the base adhesive material must be the same as the fabric coating. Rubber cements, gum mucilages, wheat pastes, and wood rosin adhesives can be used to join paper or fabric assemblies.