Bonding agents are called adhesives or glues. They may be made from natural substances or artificial materials. They bind together metals, wood, fabric, ceramics, plastics, composite materials, or virtually any material known. Because of the rising price of oil, scientific investigators have begun a search for natural adhesive materials. At the present time, many are known but are not commercially profitable.
Adhesives have been used by humans for thousands of years. The natural glues have varied from region to region because of the limited materials available locally. One of the simplest adhesives has been made from gluten in flour or cornstarch. Other binding materials have been made from natural resins or from animals. Glue from animals is made by boiling the connective tissues to make protein colloid glues. Horses have often been used in modern times as a source of animal glue. This type of glue is commonly used in the bottle-labeling process.
Starch glues are used to make corrugated cardboard. Huge rolls of paper are threaded though machines that precisely set the folds and use starch glues in a hot mixture to produce a flowing volume of cardboard, which is then cut to make various-sized boxes or other products. Many other products, especially paper products, use natural glues.
Bioadhesives are glues made from naturally occurring organic materials. The term also may be used to describe processed natural materials that have been converted into synthetic adhesives. The bookbinding industry has long used animal glues.
Adhesives are used by dentists to bond crowns to stumps of teeth. The temporary binding agents are adhesives, and the permanent ones are cements. These types of adhesives have to be safe for humans because they are used in the mouth of the patient. Other uses include cavity liners and dental cement.
Actors use adhesives to attach wigs, moustaches, beards, and other objects such as fake noses. These types of adhesives have to be a chemical compound that will not harm the skin or be absorbed as a toxin. Some forms of skin adhesives are an alcohol-resin mixture. Spirit gum remover is used to remove the adhesive. These types of adhesives are not likely to last very long because the body sheds skin cells constantly and the adhesive sheds off with the skin to which it is attached, most likely within a few days or a week.
Bandages with adhesive gums are very common, a variety of which are used in medical treatments and are made from natural or synthetic rubber, acrylic, silicon, or other materials.
Synthetic adhesives are made from chemicals that have been processed through the necessary chemical reactions to produce the adhesive. Adhesives made synthetically include resins, silicon, elastomeric, thermoplastics, acetate, polyvinyl, polyurethane, and others. The artificial adhesives are designed and sold to meet a vast number of needs. Some are for general use, are nontoxic, and are water-soluble. Children and the general public safely use these types of glues for simple crafts and many other projects.
Some types of synthetic glues may be used to bond ceramic materials such as the broken handle of a coffee mug. Properties have been manufactured into some glues of this type that allow the coffee mug handle to remain bonded even after repeated washings in the dishwasher. Other types or glues have such strength that it is unlikely that the materials will separate once glued together.
Large quantities or adhesive materials are used in construction, such as silicon adhesives used to seal bathtubs or the joints in a shower. Other silicon products are used as putty to seal flooring joints, around windows, other in other locations where air may be exchanged in a building with the outside. The sealing adhesive also blocks the entrance of insects into the building or house.
Adhesives are also used for a variety of flooring materials. Linoleum, vinyl, rock, or even wood products are bonded to the rough subflooring to make a floor covering that will be durable and cleanable. Many of the adhesives used in flooring are contact adhesives. Some are composed of two types of solvent glues that require some time to “set up” before bonding can occur. Some types are used to make laminated materials.
Some adhesives are formed by mixing two chemical compounds together. Many epoxy glues use this method to create the chemical adhesive that is needed for the product at hand. These are emulsion adhesives.
Drying adhesives use chemical mixtures that are dissolved in a solvent. When applied, the glue dries because the solvent evaporates. These types of adhesives usually have weaker bonds than those of other glues, so they make safer household glues.
Other adhesives bond when exposed to ultraviolet light. Emulsion adhesives are used for other purposes. Pressure-sensitive adhesives are often used as the coating of a film that protects a surface.
In addition to efforts to develop natural and more sustainable adhesive materials for commercial use, recent years have seen the emergence of a wide variety of “green adhesives.” Efforts to produce and market these have been associated not only with the use of more sustainable raw materials but also with minimizing the environmental impacts of adhesives, particularly with regard to reducing harmful compounds and solvents contained in the adhesives. A number of governments have introduced regulations or restrictions on the chemical emissions produced when using adhesives. These regulations have attempted to place limits on the amount of volatile organic compounds contained in adhesive products, as these compounds are thought to release hazardous air pollutants posing both health and environmental risks. Other products are designed to save energy and minimize waste. Low-temperature hot melt glues, for example, require less energy to melt and apply, and new cardboard and foil-based packaging has also been developed to reduce the landfill waste from plastic tube applicators. Adhesives that improve energy efficiency in the building industry (such as sealants that reduce heat leakage) have also been developed.
Environmentally Friendly, Green Consumer, Packaging and Product Containers
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