This week's editorial looks at the animal world as a source of adhesives. These early bioadhesives have contributed substantially to the growth of the adhesive industry and to the growth of society in general. Tomorrow, animal adhesives could well provide the key to the future.

Glues that are derived from animal parts have been in existence since very early times. An early American Indian culture called the Yakutat Timgit made a waterproof paste out of burned clamshells, salmon eggs, seal brains or seal blood, and fish skins. They often used this for caulking boxes. A passage from a book on this culture reveals the formulation for this glue.

"They used dried fish, tear the meat off. Scrape the outside off, throw the scales away. Heat the skin up in warm water. It gets nice and soft. Then put it between two pieces of wood and tie them together, and it holds them when it gets dry." ¹

"They used dried fish, tear the meat off. Scrape the outside off, throw the scales away. Heat the skin up in warm water. It gets nice and soft. Then put it between two pieces of wood and tie them together, and it holds them when it gets dry."

Although animal glues are probably the oldest adhesives known to man, they no longer enjoy widespread use having been replaced by synthetic adhesives with superior properties. However, some animal glues are sill preferred by craftsmen and are being used in high-end kitchen wood cabinetry and furniture.

Animal glues are of three main types: (1) those made from hide and bone, (2) those made from fish skins, and (3) those made from dried beef blood. Animal glues are made from the collagen-based protein extracted from skin, bone, and muscle. When treated with hot water the collagen slowly becomes soluble and the end result is either gelatin or glue. The extract can be reliquified by heating giving it fast setting properties. The major source for this type of glue is byproducts from meat processing and it is the basis of the joke about the old horse being past its prime and headed for the "glue factory".

Not much is known about animal based glues until the 1500s when they were used extensively in the building of furniture. However, in addition to the Yakutat Timgit, there are many hints in the historical archives to the importance of these adhesives.

Today, most animal adhesives are sold in a solid form and have to be dispersed in water and then heated in a jacketed kettle at 38-60°C. They are applied to the substrate as a hot liquid and generally posses good wet tack - a property that is highly valued by craftsman. The adhesive sets hard on cooling, much like a hot melt adhesive.

The hardened adhesive gives a strong dry bond. The bondline will weaken, however, if exposed to temperatures over 38°C, high moisture conditions, or water immersion. Animal glues are susceptible to mold growth and attack by vermin in the package and in bonded joints. Consequently animal glues are confined to interior applications where normal ambient temperature and normal relative humidities are encountered. The primary applications are for assembling kitchen units, edge-bonding lumber, edge banding (veneer), and laminating small lumber parts for furniture use.

Adhesives made from fish skin are weaker than those made from hide and bone. However, it adheres well to glass, ceramics, metal, wood, leather, and many other common household substrates. Unlike hide and bone glues, fish glues do not require heat for solubility. It is primarily used as cold glue for woodworking.

Blood glues are made from soluble dried beef blood, a by-product of the meat packaging operation. Glues based on blood albumen are light colored powders that can be dissolved in water at the time of use. They have good adhesion to porous substrates, and good water resistance compared to hide or bone glues. Blood glues have been used in food packaging, as the bonds are odorless, nontoxic, and tasteless. A typical use was the bonding of cork disks in metal bottle caps. In some countries, blood glues are used for interior grade plywood manufacture.

The adhesive industry has focused on animal glues throughout its history. Rather than grinding-up and making glues from animals, modern day scientists have taken a more humane approach. They are working to synthesize the outstanding adhesive excreted by mollusks (mussels and barnacles) and trying to understand the principles of the gecko's adhesion to vertical ceilings. Understanding how the animal-world utilizes adhesives may provide for an entirely new class of bioadhesives in the human-world.

References

Should you have any comments or feedback, please contact me.

Edward M. Petrie