An adhesive is a substance that has the capability to hold materials together. The manner by which adhesives are able to serve this function is due to a surface attachment that is resistant to separation. A bond occurs when the adhesive molecules adsorb onto a solid surface and chemically react with it. Cement, mucilage, glue and paste are organic materials that form adhesive bonds.
Natural adhesives have been known to be in existence since ancient Egypt. Egyptian carvings dating back 3,300 years depict the gluing of a thin piece of veneer (a thin layer of fine wood used in covering the surface of cheaper wood or in making plywood) to what appears to be a plank of sycamore. Flour paste was used to bond together papyrus fibers that were then used as fabrics. Beeswax, tree pitches (a dark sticky substance made from trees) and bitumen (a natural substance that contains hydrocarbons. i.e. coal) were used as protective coatings and adhesives. Egg whites were used to bind manuscripts at one time and wooden objects were bonded with glues made from fish, horn, and cheese. During the 18th century, the technology of animal and fish glues advanced. In the 19th century rubber and nitrocellulose based cements were introduced.
Adhesive materials are made up of polymers. Polymers are huge molecules, or macromolecules, that are formed by the linking of thousands of simpler molecules known as monomers. When a polymer is formed the chemical reaction that takes place is called polymerization. Polymerization and adhesive bond formation take place at the same time creating the means to keep surfaces together.
It has recently been discovered that the oldest known adhesive in the world is a glue that dates back to around 8,200 years ago.
Early Hunting and Gathering Tools
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An assortment of prehistoric tools provides evidence of the hunting and gathering methods of early peoples. Slabs of bark were often used to gather nuts and berries and functioned as crude dishes or bowls (top left). Reproductions of fishing tackle and arrows believed to have been used around 8000 BC are displayed on the lower left. Recovered tools for digging and cutting (right) are shown with recreated wooden handles. The heads of the adzes are made from flint, as is the fire-starter shown below them. |
| Carbon-14 dating indicates that these Neolithic people who didn’t even make pottery may have been using glue thousands of years before the Egyptians. Arie Nissenbaum is a geochemist from the Weizmann Institute of Science in Israel. He recently analyzed some material found inside a Nahal Hemar cave, in a dry region southwest of the Dead Sea. The material that Arie Nessenbaum analyzed was first believed to be asphalt because of its color and the site’s proximity to the largest asphalt deposits in Israel. In fact, the material was found to be a collagen, a fibrous protein taken from animal skin, cartilage, bone and sinew. This is still the main ingredient in some types of glue. |
The people who would have made the glue lived around the time of the agricultural revolution and fossils of wild ibex and goats have been found in the region. "By Stone Age standards, these people had mastered at least one type of advanced technology. At this early period, humans had already become familiar with the use of collagen as an adhesive material." (Arie Nissenbaum, Science News, Nov 1). About 4,000 years ago, Egyptians used gelatinous collagen to glue together wooden furniture. At least 1,500 years ago some North American Indian groups used collagen adhesives to make archery bows. Even further back in evolutionary history evidence has been found that indicates glue-like materials were being used to attach handles to tools 36,000 years ago.
Two stones dating back to at least 36,000 years ago have traces of a sticky black substance that was once used to attach them to a handle. In a chemical analyses the glue-like material was identified as bitumen (defined above). "These new data suggest that Stone Age people had greater technical ability than previously thought, as they were able to use different materials to produce tools," said Eric Boeda of the University of Paris. The location of the site is in the Syrian Desert known as Umm el Tlel. The chemical consistency of the bitumen indicates that it was heated and applied to the implements as a glue.
A Northwestern North American culture called the Yakutat Tlingit made a waterproof paste out of burned clamshells, salmon eggs, seal brains or seal blood and fishskins. They often used this for caulking boxes. A nice passage from a book entitled Under Mount Saint Elias: the history and culture of the Yakutat Tlingit by Frederica de Laguna describes the following process;
"They make a nice glue out of fishskin. My uncle used to make it. 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. My uncle used salmon skin. Native glue is fishskin. Boil it till the water gets away and it gets sticky. They use it to glue things together, long time ago……They used the skin of any kind of fish, either sockey or silver is best. They give more juice."
Others believed that halibut skin was the best to use for glue because whenever you touch those skins they were always very "gooey."
Natural adhesives are primarily of animal or vegetable origin. Animal glues are prepared from mammalian collagen, the primary protein of skin, bone and muscle. When treated with hot water the collagen slowly becomes soluble and the end result is either gelatin or glue. By dissolving a protein from milk in an alkaline solvent one can make casein glue. Casein glues were often used to glue together wood. Today it is used to improve the adhering characteristics of paints and coatings.
Serum albumen, a component in blood obtainable from either fresh animal blood or dried soluble blood powder was also used as a glue when added with alkali. Today glue products made from blood are used in the plywood industry. Corn, wheat, potatoes or rice contain starch and dextrin that are considered vegetable adhesives. Starch and dextrin extracts are soluble in water and are obtainable from plant sources all over the world. Today they are used in corrugated board, packaging and as a wallpaper adhesive. Gums are another adhesive that can be extracted from trees. Usually it is extracted from a tree that has been wounded. Agar is a colloid from marine plants that can be extracted by hot water and then purified by freezing it. Algin is obtainable from seaweed.
Author: Andrea Delarosa
