Adhesives

There are hundreds of adhesive preparations on the market today, supplemented by hundreds of available formulations, which are capable of holding materials together by surface attachment. Although the basic components of the products are generally obtainable, their specific combinations are not always known to the public. Many compositions are protected by patents. In 1980 adhesive shipments were valued at nearly $2000 x 108. Modern adhesive may be classified by one of several methods, for example, their use in bonding various types of material, such as structural adhesives, or their composition, based on the principal ingredient, such as thermoplastic resin. Since the more or less general term adhesives embraces many types, they are discussed under their composition.

History of Adhesive Made

Animal glue is the oldest type of adhesive, having been known for at least 3300 years. Its manufacture began in the United States in 1808, and it has been an important article of commerce for more than 150 years, although practical application in broad industrial fields had to await progress in colloid and protein chemistry and the development of standard testing methods. Casein and starch adhesives became of commercial importance more than a generation ago, and soybean-protein adhesive in the last 50 years, synthetic resin adhesives were developed after 1940.

Animal Glues

The manufacture of glue is almost identical with the manufacture of gelatin. The procedures include grinding bones; cutting hides and scrapes into small pieces; degreasing the material by percolating a grease solvent through it; liming and plumping, washing, making several extractions by hot water, filtering liquors’ evaporating, chilling, and drying the jelly slabs in a tunnel. When dry, the slabs of glue are flaked or ground, blended, graded, and barreled or bagged for shipment.

Other Protein Adhesives

Fish glues are liquid glues made from waste materials of cod, haddock, cusk, hake, and Pollock, and have practically the same applications as other animal glues. Casein, a milk derived protein, is the basis of another large class of adhesives and can be made both water, and non water resistant. Casein adhesives are widely employed in the woodworking industry and in the manufacture of drinking cups, straws and ice cream containers. Soybean protein adhesives, although similar in properties to casein adhesives are cheaper but not so good. The two are generally employed in combination, particularly in the veneer field, thus permitting a reduction in glue costs. Albumin adhesives, from both egg and blood, find specialized uses where low film strength is unimportant, yet water resistance is. The attachment of cork pads to crown bottle caps is one of these applications. Zein, a corn protein is used to a small extent as an adhesive, particularly in combination with other bases. Peanut protein hydrates are suitable for making gummed tape and flexible glues for boxes and books.