Plastic—A Familiar Product. A polymer is both complex and simple. A polymer is one molecule but is constructed of replicated sub-components. Its physical structure makes it tough and somewhat elastic. Amber, cellulose, rubber, shellac, silk, etc. are “natural” polymers. Bakelite, neoprene, nylon, polyethylene, polystyrene, polyvinyl chloride, silicone, synthetic rubber, etc. are “synthetic” polymers.
Natural Plastics—An Ancient Product. American Indians were using natural rubber 3600 years ago. Many cultures were using horn from cattle in art and tools from very ancient times. Casein has been employed in paint and glues for millennia. These and other natural polymers have a long history.
Synthetic Plastics—A “Recent” Development. Synthetic polymers have a much shorter history. Alexander Parkes took cellulose and added nitric answer about 150 years ago. The result was “Parkesine,” a synthetic that could be altered in color by pigments and molded with heat. Two decades later Eugen Baumann developed vinyl chloride without commercial application. Three decades later, “Bakelite” was developed by Leo Baekeland using formaldehyde and phenol. B.F. Goodrich Company (PVC, 1926), Imperial Chemical Industries (polyethylene, 1933), BASF (polystyrene, c. 1935), Dow Chemical (expanded polystyrene, 1954), and a myriad of others developed the diverse plastics used today.
Plastics—Materials, Forms, Molds, Extrusions
Plastics vary with materials in the polymer, its mixing and curing requirements, and its shaping requirements. “Thermoset plastics” (e.g., polyurethanes, polyesters, epoxies, etc.) are mixed, shaped, cooled, and allowed to set. They maintain rigidity. “Thermoplastics” (e.g., polyethylene, polyvinyl chloride, etc.) are similar, but can be softened and altered in shape with heat present. They return to their original shape when cooled.
Polyethyolene terephthalate (e.g., Dacron, Mylar, etc.) is a hard plastic able to maintain shape as in furniture or utensils. Its aerated “Styrofoam” form maintains its shape and also becomes an insulator. Polyvinyl chloride (PVC) is brittle, but can be softened and molded with a plasticizer for use in plumbing. Polytetrafluoroethylene (Teflon) is recognized for its nonstick surface applied to cookware, bearings, etc. Polyvinylidine chloride (Saran) is a polymer used in films and wraps to package foods. Polyethylene (LDPE and HDPE) is used in items requiring flexibility. Polypropylene has a variety of forms and hardnesses, ideal for a variety of applications.
The components of each plastic are mixed and “cured.” The consistency of the plastic is dependent on temperature and time. The given polymer may be extruded producing items like plastic films. Films can be processed into wraps or into items like corrugated plastic sheets, suitable for signage or packaging. The polymer may be injected resulting in tubs for butter, margarine, and the like. The plastic may be extruded or injected and blown with heat and compression at the same time, making a resin cylinder or tube, birthing the “plastic bottle.” If rotation is added to the polymer material in a given mold, the plastic ends up lining the mold, providing anything from a child’s toy to a plastic boat.