Back in the late 1950s, there was a game-show on TV in the U.S. that was so long ago that I forget the title. However, I well remember the show's premise. The contestant would have to guess the identity of an object that was hidden behind a curtain. He or she could ask questions of the master of ceremonies, but the idea was to ask the least amount of questions as possible and still identify the object. Invariably, the first question was: "Animal, Vegetable, or Mineral?"
This may also be the first question that end-users ask of adhesive developers in the future. Adhesives that are based on naturally occurring substances (animal, vegetable, and mineral) are likely to increase in popularity in the future for a variety of reasons. Adhesives based on natural products are generally:
- Lower in cost and not subject to the price volatility showed by their synthetic (petroleum based) counterparts
- Viewed as environmentally friendly since many are based on renewable products and are considered to be biodegradable
- Finding renewed interest and research funding for development in applications such as adhesives and in formulations with other products (building materials, urethane foam, etc.).
Although animal glues are probably the oldest adhesives known to man, they no longer enjoy widespread use having been replaced by synthetic adhesives with superior properties.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.
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.
Minerals, such as sodium silicate, have also been widely used in certain adhesive applications. Sodium silicate was once a primary source of corrugation adhesives for packaging. It has since been replaced by another natural adhesive, starch. Mineral based adhesives, however, are still seeing application in certain products requiring extremely high temperatures (e.g. fasteners to light bulbs) or where the substrate is ceramic.
The most interesting natural adhesive and one that provides the greatest opportunity in the future are those of vegetable origin. These materials have also been around for centuries. Today they are generally called "biopolymers". They are similar to their conventional counterparts that are derived from petroleum, except that their origin is agricultural crops.
Producing these kinds of biopolymers may also reduce the amount of petroleum consumptions that is used to produce chemicals including polymers. Although much of the attention has been focused on high commodity products such as packaging and building insulation, efforts are underway in the adhesives and sealants community to investigate and possibly exploit the use of base polymers and additives that can be manufactured from non-petroleum feedstock.
Most of the recent development efforts toward biopolymer adhesives have been in two areas: soybean derivatives and polylactic acid. Adhesive products derived directly from soy have been around for some time. They are primarily used in the wood working industries. However, the oil from soy (as well as other agricultural products) can also be refined into polymers and additives that are appropriate for adhesives and sealants. Excellent examples of this effort are polyols that are produced from soybean oil. Similarly, polylactic acid (PLA) is synthesized from bio-derived monomers to produce renewable polymers. For more information on these biopolymer adhesives, the reader is directed to a recent SpecialChem article.
It is unlikely that the biopolymers will replace petrochemical adhesives in the future. However, they are certainly expected to complement other products in the industry, and "biopolymers" may provide the first comeback to - "Animal, Vegetable, or Mineral?"