Plastic means pliable or impressionable. It is defined as the capability of being deformed continuously in any direction without breaking apart, Following this definition , plastics could include glass, metals, and wax. Thus, it is evident that the name plastics is misleading and not exactly correct. Today, however, the name plastics is identified with the products which are derived from synthetic resins, The synthetic resins are made by various chemical processes.Plastics manufacturing is of comparatively recent date. The discovery of ebonite, or hard rubber by Charles Goodyear in 1839 , and the development of celluloid ( cellulose nitrate ) by Hyatt in1869 marked the beginning of plastic products. It was not until 1909, however,  phenol formaldehyde resin, was developed by Dr. L. H. Baekeland and his associates.Today plastics are commonly found in homes, automobiles, numerous other products, and machines. Some machines which utilize electricity require plastic parts with electrical insulating properties. One of the largest plastic products ever built is a 2600-pound 28-foot-longboat hull which is made of fiber-glass matting impregnated with polyester resin and low-pressure laminated. The unusual properties of some plastic materials are used in many interesting applications. Advantage should be taken of these unusual properties wherever possible.Thermosetting or Thermoplastic, Plastic materials, commonly called plastics, are know neither as thermosetting or as thermoplastic. Upon the application of initial heat the thermosetting plastics soften and melt, and under pressure they will fill every crevice of a mold cavity. Upon continued application of heat they polymerize , or undergo a chemical change , which hardens them into a permanently hard , infusible , and insoluble state. After this they cannot again be softened or melted by further heating. The thermoplastic materials are those which soften with heating and solidify and harden with cooling. They can be remelted and cooled time after time without

undergoing any appreciable chemical change.

Fillers. Plastics often contain other added materials called fillers. Fillers are employed to increase bulk and to help impart desired properties, Plastics containing fillers will cure faster and hold closer to established finished dimensions, since the plastic shrinkage will be reduced. Wood flour is the general-purpose and  commonly used filler, Cotton frock, produced from cotton linters , increases mechanical strength, For higher strength and resistance to impact, cotton cloth

fibers, silicon, cellulose, clay, or nutshell flour may also be used. Nutshell flour is used instead of wood flour where a better finish is desired plastic parts using short fiber fillers will result in lower costs, while those with long fiber filler shaving greater impact strengths are more expensive. Other materials, not defined as fillers , such us dyes , pigments , lubricants , accelerators , and plasticizers may also be added. Plasticizers are added to soften and improve the mold ability of plastics. Filler and modifying agents are added and mixed with the raw plastic before it is molded or formed.Properties. Numerous plastics have already been discovered and developed by the chemist and chemical engineer , and research on the synthetic resins is one of the  prominent fields inorganic chemistry today. The mechanical properties are considerably lower than those for metals with the tensile strengths usually ranging from 5, 000 to 15, 000 psi.Some of the plastics listed, such as phenol formaldehyde resin, consist of several different varieties and mixtures included under the one family. Numerous other plastics with special properties are available. However, the ones listed should serve as a brief introduction.