Plastics are broadly integrated into today’s lifestyle and make a major, irreplaceable contribution to virtually all product areas. Although the plastics industry in the United States is now in its second century, the most important developments have occurred since 1910. However, the roots of these modern developments go back not only to the research of cellulose nitrate by John Wesley Hyatt in the 1860s, but also to the plastic-like compositions used by man through the centuries.

Origin of Plastics
One can go as far back as the Old Testament to find references about natural materials used as fillers, adhesives, coatings, and the like. These materials were the precursors of modern plastic materials. Historians continue to differ as to the exact year or decade that the plastics industry began because the definition of “plastic” is a matter of interpretation.

Certainly, the history of the rubber industry has a bearing on plastics. This is because ebonite, or hard rubber, discovered in 1851, was the first thermosetting material to be prepared and the first material that involved a distinct chemical modification of a natural material. But ebonite was not exploited commercially for some years after its discovery; for that reason, its historical importance has become somewhat blurred.

European Developments
While the basic processes of rubber technology were developing, other important discoveries were taking place in Europe. Following work by Pelouze, Schonbein established conditions of controlled nitration of cellulose. The product soon became of interest as an explosive and in the manufacture of collodion, a cellulose solution in an alcohol-ether mixture. In the 1850s, the English inventor Alexander Parkes observed that the solid residue left after the evaporation of the solvent of photographic collodion was a “hard, horny elastic and waterproof substance.” In 1856, he patented the process of waterproofing woven fabrics by the use of such materials.

In 1862, at the Great Exhibition in London, Parkes introduced a new material named for himself- Parkesine. Parkesine was obtained by dissolving cellulose nitrate in a minimum of solvent. The mixture was then put on a heated rolling machine from which some of the solvent was then removed. While still in the plastic state the material was then shaped by dies or pressure. In 1866, Parkes organized the Parkesine Company to manufacture products from his new material, but the company failed in 1868. This appears to be due, in part, to Parkes’ attempt to reduce production costs that resulted in the production of inferior items.

One year after the failure of the Parkesine Company, an associate of Parkes, Daniel Spill, formed the Xylonite Company to manufacture products similar to Parkesine. Once again, economic failure resulted and Spill’s company went bankrupt in 1874. Undaunted, Spill moved to a new site, established the Daniel Spill Company, and continued production of his material, Xylonite.

First Plastics in the U.S.
In the United States during the 1860s, John Wesley Hyatt experimented with cellulose nitrate. In 1865, Hyatt became involved in devising a method for producing billiard balls from materials other than ivory. Originally using mixtures of cloth, ivory dust, and shellac, he patented in 1869 the use of collodion for coating billiard balls. The patent came one year after his collodion material was introduced commercially.

In 1868 John Wesley Hyatt became the first to inject hot Celluloid into a mold, producing Billiard Balls. He and his brother Isaiah patented an injection molding machine that used a plunger in 1872, and the process remained more or less the same until 1946, when James Hendry built the first screw injection molding machine, revolutionizing the plastics industry. Roughly 95% of all molding machines now use screws to efficiently heat, mix, and inject plastic into molds.

John W. Hyatt and his brother Isaiah took out U.S. Patent 105,338 in 1870 for a process of producing a horn-like material using cellulose nitrate and camphor. Although Parkes and Spill had mentioned camphor in their work, the Hyatt brothers recognized the value of camphor as a plasticizer for cellulose nitrate. In 1872, the term “celluloid” was coined by Isaiah Hyatt to describe the Hyatts’ commercially successful product.

The validity of Hyatts’ patents was challenged by Spill, and a number of court actions took place between 1877 and 1884. In the final action, it was found that Spill had no claim on the Hyatt brothers’ patents, the judge ruling that Parkes was the true inventor of the process because he had mentioned the use of camphor in his patents. Thus, there was no restriction on the use of these processes and any company, including the Hyatts’ Celluloid Manufacturing Company, was free to use them. After that decision, the Celluloid Manufacturing Company prospered, changed its name to the American Cellulose Chemical Corporation, and eventually was absorbed by the Celanese Corporation.

Formaldehyde Resins
Next to cellulose nitrate, the most important material in the early history of plastics was formaldehyde. Around 1897 there was a demand in German schools for a white chalkboard. Efforts to obtain such a product resulted in the discovery of casein plastics, produced by reacting casein (milk protein) with formaldehyde. The material soon became established under the trade names of Galalith and Erinoid. Today, casein still is used by the button industry.

In 1899, Arthur Smith took out British Patent 16,275, the first dealing with phenol-formaldehyde resins for use as an ebonite substitute in electrical insulation. During the next decade, the phenol-formaldehyde reaction was investigated mainly for academic interest. In 1907, however, Leo Hendrik Baekeland discovered techniques to control and modify the reaction so that useful products could be made from it. Thus, phenolics were the first fully synthetic resins to become commercially successful.

Prompted by the success of phenolic moldings, research began on reacting other materials, such as urea and thiourea, with formaldehyde. These materials were used to manufacture molding powders. Unlike phenolics, they could be molded into light-colored articles and rapidly achieved commercial success. Today, these urea-based resins are used for molding powders, adhesives, and textile and paper finishing, while the related melamine-formaldehyde resins are used in decorative laminates.

Growth of Modern Plastics
Cellulose acetate, a thermoplastic, was developed about the same time as the urea-based resins. Similar in structure to cellulose nitrate, it was found to be safer to process and use. Cellulose acetate was introduced as a molding compound in 1927.

The period 1930-1940 saw the initial commercial development of today’s major thermoplastics: polyvinyl chloride, low density polyethylene, polystyrene, and polymethyl methacrylate. The advent of World War II in 1939 brought plastics into great demand, largely as substitutes for materials in short supply, such as natural rubber. In the United States, the crash program leading to large-scale production of synthetic rubbers resulted in extensive research into the chemistry of polymer formation and, eventually, to the development of more plastic materials.

The first decade after World War II saw the development of polypropylene and high density polyethylene and the growth of the new plastics in many applications. Linear low density polyethylene was introduced in 1978 and made it possible to produce polyethylenes with densities ranging from 0.90 to 0.96. Large-scale production of these materials reduced their cost dramatically. The new materials began to compete with the older plastics and even with the more traditional materials such as wood, paper, metal, glass, and leather. The introduction of alloys and blends of various polymers made it possible to tailor properties to fit certain performance requirements that a single resin could not provide. The demand for plastics has increased steadily; plastics are now accepted by designers and engineers as basic materials along with the more traditional materials. The automotive industry, for instance, relies on plastics to reduce weight and thus increase energy efficiency.

For more information on the history of plastics, including the Plastics Hall of Fame, visit the National Plastics Center and Museum

Evolution of Screw and Evaluation Vs. Plunger
The machine that the Hyatt brothers invented was primitive, but performed well for the situation they were presented. It was simple in that it acted like a large hypodermic needle and contained a basic plunger to inject the plastic through a heated cylinder into a mold. In 1946, James Hendry began marketing his recently patented screw injection machine. This auger design replaced the conventional Hyatt plunger device and revolutionized the processing of plastics. Screw machines now account for approximately 95% of all injection machines.

The auger design of the screw creates a mixing action when new material is being readied for injection. The screw is inside the heating cylinder and, when activated, mixes the plastic well, creating a homogenized blend of material. This is especially useful when colors are being molded or when regrind is being mixed with virgin material. After mixing, the screw stops turning and the entire screw pushes forward, acting like a plunger for injecting material into a mold.

Another advantage of using the screw technology is a reduction of energy requirements. The injection cylinder that holds the plastic that is being readied for the next cycle has a series of electrical heater bands around the outside. When energized, these bands heat up the cylinder to the point of softening the plastic. However, because the screw generates friction when it turns within the cylinder, heat is generated. Thus the material is also heated from the inside out which results is less heat required from the electrical heater bands to soften the plastic to the correct temperature.

Although the screw machine is the most popular, there is still a place for the plunger type machine. A plunger does not rotate. It simply pushes material ahead, then retracts for the next cycle. It, too, resides within a heated cylinder. Because there is no rotating, there is no shearing or mixing action. So, in a plunger machine the necessary heating action is provided solely by the external heater bands because there is no friction from the plunger as there is from the screw. Also, if two different colored materials are placed together in the heated cylinder they are not blended together. The plunger simply injects the materials at the same time. If the two colors are, for instance, white and black, the resultant molded part will take on a marbled appearance with definite swirls of black and white through the part. This may be a desired finish for a particular product, such as lamp bases or furniture, and the use of a plunger machine allows that finish to be molded into the product. Use of a screw machine would result in a single color (gray) product being molded because the two colors would be well mixed prior to injecting.

The injection molding industry has made a huge impact on our lives. Starting in the workshop of the two Hyatt brothers, it has become a major focus for manufacturing of products from toys to medical devices, and everything in between. The future holds only great promise for more productive, cost effective methods of producing more products using this technology. Improved methods, materials, processing, and tooling will increase the advantages for product designers and manufacturers who choose plastic injection molding as their primary method of manufacturing.