The word plastic comes from the Greek word plastikos, meaning capable of being molded. The chief property of plastics is that they are deformable and easily made into almost any shape by processes such as molding or extrusion. Plastics are composed of high molecular weight organic MOLECULES, or POLYMERS, made up of repeating units chemically linked together in the form of a chain or network. Plastics can conveniently be divided into two categories: semisynthetic, in which the basic chain structure is derived from a natural product, such as cellulose; and fully synthetic, in which the chain is built up chemically from small units, or monomers. The process of forming a polymer from its constituent monomers is called POLYMERIZATION.
The first plastics to be manufactured commercially were semisynthetic, and they were derived from the CARBOHYDRATE cellulose which was usually obtained from cotton waste. In 1862 the British chemist Alexander Parkes prepared a plastic material called Parkesine which could be readily molded and shaped. It was made by reacting cotton waste with a mixture of nitric and sulfuric acids to give a nitrocellulose compound which was then mixed with castor oil, a little camphor and a coloring material.
Although Parkesine was easy to prepare on a small scale, in laboratory-sized plants it proved difficult to make in large quantities, and its industrial manufacture was not a success.
In 1870 the American chemist John W. Hyatt prepared the first commercially successful plastic, Celluloid, which was similar to Parkesine but used camphor in place of the castor oil. The new material was used to make a wide range of products, including eyeglass frames, combs, billiard balls, knife handles and photographic film. The first synthetic fiber, introduced in 1889, was an artificial silk made of nitrocellulose.
The chief drawback of these early plastics was that they were extremely flammable, because the main ingredient, nitrocellulose, is closely related to the explosive guncotton; both are forms of nitrated cellulose. For this reason, another ester of cellulose, cellulose acetate, is normally used in preference to cellulose nitrate for preparing cellulose-based plastics. These plastics are mainly used for making textiles. Regenerated cellulose, or Rayon, is a fibrous material composed of cellulose, the molecules of which have been shortened by dissolving and reprecipitation.