Ingredients Present in Glue

Glues are either natural or synthetic, depending on their ingredients and characteristics. Let us take a look at each: Ingredients for natural glues are derived from either mineral sources or biological sources such as animals. For example casein, or from vegetable sources like natural resins, starch (dextrin), etc. There are three categories of substances that are called glues, i.e., they do not have chemical contents. These three categories are bone glue, hide or skin glue, and fish glue. Technically, other glues are called adhesives, gum, or cement, although most of us tend to use these terms with a generic meaning. Compounds with adhering properties like epoxies, caulks, or sealants are mixed with special additives to impart suitable properties according to their usage. Historically, glue was invented when ancient tribes found out that bones, hides, skin, and connective tissues of animals could be processed and collagen protein in them could be extracted. Collagen is a sticky protein and has useful adhesive properties. Even today, a huge chunk of glue made all over the world is animal glue, which is manufactured by a process similar to that was used in the past. These days, animal glue is made by soaking the hides in water to produce 'stock', which is then treated with lime to break down the hides. Lime is then separated and the residue is neutralized with a weak acid solution. At around 70ºC, the hides are heated in water. The glue liquor thus formed, is then separated and more water is added. The whole process is repeated with an increase in temperatures. The resultant glue liquor is dried into resin-like chipped pellets. Milk can also be a source from which glue is manufactured. Casein, a milk solid, and blood albumin can also be used to make glue. Dried cow blood serum has albumin, which is heated so as to coagulate it so that it becomes insoluble in water. Fish is another source of glue. Fish glue is made from heads, bones, and scales of fish, but it is too thin and is a weak adhesive. Primitive men discovered that air bladders of some fish could produce a much stronger glue that was white and odorless and was named ichtyocolle. Apart from animals, plants can also be used to produce glues. Such a type of a glue is called vegetable glue. This type of glue is water soluble and is made from starch, which is found in vegetables and grains. This segment of natural gum also includes, agar from mixtures in aquatic plants, algin which is deduced from seaweed, and gum arabic, which is nothing but an extract of the acacia tree, more commonly known as the gum tree. Cyanoacrylate is the main ingredient of synthetic glue, also known as superglue. It was discovered by Dr. Harry Coover, in 1942, when he was working for Kodak Research Laboratories towards development of an optically clear plastic for gunsights. Actually, Coover first rejected cyanoacrylate because of its highly sticky nature. But later, he realized that cyanoacrylate was useful, and in 1958, it was marketed and packaged as superglue. Synthetic glues used for industrial purpose are called epoxy adhesives. There are two basic components to which various modifying ingredients are added to enhance elasticity and improve their physical and mechanical properties. These additives usually include extenders, filling agents, curing accelerators, and diluent. Here is a sample list of the items used while manufacturing synthetic glue:

• Low Molecular Weight Epoxy Resin (Modified), Molecular Weight 500
• Aluminum powder
• Amorphous silica
• Sodium carbonate Na₂ CO₃.10H₂O
• Sodium chromate Na₂CrO₄.4H₂O
• Polyaminoamide (amine number 180-250)