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Adhesives: Their Types and Classes

6/28/2013 8:11:24 AM | by Anonymous

Adhesives

An adhesive is referred to as a substance that binds things together when it is applied to their surfaces and tries to keep them from being separated. There are many classes and types of adhesives, ranging from glue used in crafts to heavy-duty industrial uses. Adhesives can be made synthetically but there are many adhesives that can be found naturally, such as tar, resin and beeswax. Humans have been using adhesives since approximately 200 000 years ago and discoveries in the field have been gradual until the 1900s, where there have been rapid advances in the creation of synthetic adhesives.

The use of adhesives can be seen throughout the history of mankind, from the creation of new tools through different segments together to burial or religious rituals.

There are hardly any products nowadays that do not have some form of adhesives on them. Using adhesives can be advantageous compared to other ways of binding such as sewing or welding because it is much easier, more cost effective and often is more effective than other methods.

There are many types and classes of adhesives and different ways to classify them such as reactivity, origin or how the adhesion occurs.

The first kinds of adhesives are non-reactive adhesives. Non-reactive adhesives, as the name suggests, are adhesives that do not use chemical reactions in the binding process. Drying adhesives, which are adhesives that simply harden after they are applied and adhere the two surfaces together, are non-reactive. The most common example of this is white glue. Pressure sensitive adhesives (PSAs) adhere materials together when light pressure is applied. It makes use of molecular interactions such as van der Waals forces to contribute to the strength of the bond. PSAs are designed to either be temporary or permanent. Contact adhesives use very strong bonds and make the two materials very hard to separate, such as in lamination or attaching the soles of shoes. A glue gun is an example of a hot adhesive, which work on the concept of melting the solid adhesive and then allowing it to solidify and bind materials together. The adhesive is usually a thermoplastic, which forms strong bonds when it solidifies.

Reactive adhesives are adhesives that use chemical reactions to form permanent bonds between materials. The bonds formed are usually very strong and durable. Multi-component adhesives mix two or more components together. By themselves, the components are not adhesive but once mixed they react and adhere. An example of this is polyester resin. One-part adhesives work on the same concept except an outside source such as radiation, heat or moisture causes the chemical reaction. An example of this is the use of ultraviolet (UV) light adhesives, which are very widely used due to the strength and durability of the bonds.

Natural adhesives can be called bioadhesives and are organic in nature. One example of this is animal glue, which is formed through boiling the connective tissues of animals for an extended period of time. However, animal glue is now largely being replaced by synthetic glue. Another source of natural glue is vegetable matter such as starch. Natural synthetics are commonly used in fields such as woodwork, such as how casein-based glues are used to adhere labels to glass bottles.

Synthetic adhesives are man-made adhesives. They are derived from polymers and have a wide range of uses depending on the nature of the adhesives produced. The very first synthetic adhesive was produced in the 1920s. One of the more well known uses of a synthetic adhesive are the post-it notes, where a scientist, while attempting to create a super-strong adhesive accidentally created one that was weak, pressure sensitive and reusable, leading to the creation of the widely used post-it notes today.

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