From the most commonplace tasks to our most unusual needs, plastics increasingly have provided the performance in products that consumers want. That’s because, in just a few decades, consumers have come to consider the extraordinary properties of plastics as nothing out of the ordinary.

      Plastics’ popularity and wide usage can be attributed to one basic fact: Because of their range of properties and design technologies, plastics offer consumer benefits unsurpassed by other materials.

      Plastics generally are organic high polymers (i.e., they consist of large chainlike molecules containing carbon) that are formed in a plastic state either during or after their transition from a small-molecule chemical to a solid material. Stated very simply, the large chainlike molecules are formed by hooking together short-chain molecules of chemicals in a reaction known as polymerization. When units of a single monomer are hooked together, the resulting plastic is a homopolymer, such as polyethylene, which is made from the ethylene monomer. When more than one monomer is included in the process, for example, ethylene and propylene, the resulting plastic is a copolymer.

      Let’s look at the different types of plastics, usually referred to as resins, and see how they are made and used:

Thermosets and thermoplastics

      Thermoplastic resins consist of long molecules, each of which may have side chains or groups that are not attached to other molecules (i.e., are not cross linked). Thus, they can be repeatedly melted and solidified by heating and cooling so that any scrap generated in processing can be reused. No chemical change generally takes place during forming. Usually, thermoplastic polymers are supplied in the form of pellets, which often contain additives to enhance processing or to provide necessary characteristics in the finished product (e.g., color, conductivity, etc.). The temperature service range of thermoplastics is limited by their loss of physical strength and eventual melting at elevated temperatures.

      Thermoset plastics react during processing to form crosslinked structures that cannot be re-melted and reprocessed. Thermoset scrap must be either discarded or used as low-cost filler in other products. In some cases, it may be pyrolyzed to recover inorganic fillers such as glass reinforcements, which can be reused. Thermosets may be supplied in liquid form or as a partially polymerized solid molding powder. In their uncured condition, they can be formed to the finished product shape with or without pressure and polymerized by using chemicals or heat.

      The distinction between thermoplastics and thermosets is not always clearly drawn. For example, thermoplastic polyethylene can be extruded as a coating for wire and subsequently crosslinked (either chemically or by irradiation) to form a thermoset material that no longer will melt when heated. Some plastic materials even have members in both families; there are, for instance, both thermoset and thermoplastic polyester resins.

Acetal

      Acetal is an engineering thermoplastic introduced in 1956 as a potential replacement for die-cast metals. Acetal resins are produced by the polymerization of purified formaldehyde into both homopolymer and copolymer types. Industrial end-users are familiar with the acetals in the form of gears, bearings, bushings, cams, housings, conveyors and any number of moving parts in appliances, business machines, etc., they have a high melting point, high strength, good frictional properties and resistance to fatigue.

Acrylics

      Acrylics were introduced in 1936 in the form of hard, rigid and transparent materials. Acrylics were used in World War II as aircraft canopies. Other applications include: lighting diffusers; outdoor signs; automobile tail lights; washbasins and sinks; safety shields; furniture (e.g., tables); skylights, and large-area enclosures for shopping centers, swimming pools, restaurants, etc., and as room dividers. The outstanding resistance to long-term exposure to sunlight and weathering is one of the important characteristics of acrylic. Also notable is the exceptional clarity and good light transmission (cast acrylic sheet transmits about 92 percent total light).

Acrylonitrile-Butadiene-Styrene (ABS)

      Chemically, this family of thermoplastics is called terpolymers, because it is made of three different monomers: acrylonitrile, butadiene and styrene, to create a single material that draws on the best properties of all three. ABS was introduced in 1948, primarily as a result of activities that had taken place during the war years in the development of synthetic rubbers. ABS possesses outstanding impact strength and high mechanical strength, which makes it suitable for use in tough consumer and industrial products, including: appli-ances, automotive parts, pipe, business machines and telephone components. In the 1960s, ABS found wide outlet as a substrate for metallizing (i.e., applying a chrome-like metallic finish to the plastic) and appeared in such products as shower heads, door handles, faucet handles and automotive front grilles.

Alkyds

      This plastic was developed in 1926 and was promptly put to work in liquid form as enamels, paints, lacquers, and similar coatings for automobiles, refrigerators, stoves and similar products — still the largest use for alkyds. In 1948, however, an alkyd compound was introduced as a molding material for compression molding electrical applications like circuit breaker insulation, coal forms, capacitor and resistor encapsulation, cases, housings, and switchgear components. Major properties are in the electrical area where alkyd molding materials offer excellent dielectric strength. Alkyds also have excellent heat resistance and are dimensionally stable under high temperatures. Typical applications are electrical uses, automotive parts, and as coatings.

Cellulosics

      Cellulosics date to the start of the plastics industry when John Wesley Hyatt created the first commercial U.S. plastic, cellulose nitrate, in 1868. Several other important members of the cellulosics family, each with its distinct properties, were introduced in the 1900s. Since then, cellulosics have been used to make knobs, appliance housings, handles, toys, packaging, consumer products, and automotive parts, among many other products.

Coumarone-Indene

      These resins have no commercial applications when used alone. They are used primarily as processing aids, extenders and plasticizers with other resins in asphalt floor tile.

Diallyl Phthalate (DAP)

      The term DAP is used both for the monomeric and polymeric forms. The monomer is used as a cross-linking agent in unsaturated polyester resins. As a polymer, it is used in the production of thermosetting molding powders, casting resins and laminates.

Epoxy

      Epoxies are used by the plastics industry in several ways. One is in combination with glass fibers (i.e., impregnating fibers with liquid epoxy resins) to produce high-strength composites or reinforced plastics that provide heightened strength, electrical and chemical properties, and heat resistance. Typical uses for epoxy-glass reinforced plastics are in aircraft components, filament wound rocket motor casings for missiles, pipes, tanks, pressure vessels and tooling jigs and fixtures. Epoxies are also used in the encapsulation or casting of various electrical and electronic components and in the powder coating of metal substrates. Major outlets for epoxies also include adhesives, protective coatings in appliances, industrial equipment, gymnasium floors, etc., and sealants.

Fluoropolymer

      Fluoropolymers are known for their inertness to most chemicals, resistance to high temperatures, extremely low coefficients of friction and excellent dielectric properties which are relatively insensitive to temperature and power frequency. Typical applications for fluoropolymers are electrical/ electronic uses and pipe and chemical processing equipment and non-stick coatings for cookware and other applications. Fluoropolymers make up a family of thermoplastic resins analogous to polyethylene in which some of the hydrogen atoms attached to the carbon chain are replaced by fluorine or fluorinated alkyl groups. In some cases, other halogens such as chlorine are also part of the molecule.

Melamine-Formaldehyde

      This plastic is a member of the amino family (which also includes urea) and is probably best known to the public as colorful, rugged dinnerware. However, it also finds use in many household goods, in various electrical applications, and in bonding, adhesives and coatings. Melamines offer extreme hardness, excellent colorability and arc-resistant non-tracking characteristics.

Nitrile Resins

      This family of resins started to appear in the late 1960s and early 1970s. They are called barrier resins since one of their prime attributes is their resistance to the transmission of gas, aroma or flavor, making them useful in packaging applications.

Nylon

      The nylon fiber industry was born in 1939 when 64 million pairs of nylon stockings were sold—and to this day, most people still associate nylon with fibers. However, in the 1940s and 1950s work continued on developing nylon compounds that could be molded and extruded or otherwise processed like plastics. Typical applications for nylons are in automotive parts, electrical/electronic uses, and packaging. Nylon is a generic name for a family of long-chain polyamide engineering thermoplastics which have recurring amide groups as an integral part of the main polymer chain. Nylons are synthesized from intermediates such as dicarboxylic acids, diamines, amino acids and lactams.

Petroleum Resins

      Thermoplastic resins obtained from a variable mixture unsaturated monomers recovered as byproduct from cracked and distilled petroleum streams. They also contain indene, which is copolymerized with a variety of other monomers including styrene, vinyl toluene, and methyl indene. Typical applications are adhesives, printing inks, rubber compounding, and surface coatings.

Phenolic

      These thermosetting resins are credited with being the first commercialized wholly synthetic polymer or plastic, and the second major plastic (the first being cellulosics cellulose nitrate). The basic raw materials are formaldehyde and phenol, although almost any reactive phenol or aldehyde can be used. In the uncured and semi- cured condition, phenolic resins are used as adhesives, casting resins, potting compounds, and laminating resins. As molding powders, phenolic resins can be found in electrical uses. They are also used in such applications as: automotive distributor caps, fuse blocks and connectors and appliance handles, knobs and bases. Phenolic is the most popular binder for holding the various plies of wood together in plywood.

Polyamide-Imide

      Engineering thermoplastic resins produced by the condensation reaction of trimellitic anhydride and various aromatic diamines. Typical applications are in the aerospace, automotive and heavy equipment industries.

Polyarylates

      These can be used for automotive, appliance and electrical applications requiring outstanding heat resistance. The major use of polyarylates is in outdoor lighting.

Polybutylene

      Thermoplastic resins offering high flexibility, resistance to creep, cracking and most chemicals. Typical applications are pipe and packaging film.

Polycarbonate

      Polycarbonates were developed commercially in 1957 and are one of the pioneering members of the family of engineering thermoplastics created to compete with die-cast metals. They are strong, tough and rigid, while having the ductility normally associated with softer, lower-modulus thermoplastics. They also have excellent electrical insulating characteristics, maintained over a wide range of temperatures and loading rates. Polycarbonates are transparent and can be processed in a variety of ways, including  injection molding,  extrusion, blow molding and rotational molding. Typical applications are glazing, appliances, water bottles and electrical uses.

Polyethylene

      This plastic came to the fore during the World War II years, first as an underwater cable coating, then as a critical insulating material for such vital military applications as radar cable. Its rise in popularity for both consumer and industrial uses was so spectacular that polyethylene became the first plastic in the U.S. to sell more than 1 billion pounds a year. Today, it is still the largest volume plastic in the United States; in fact, it is the largest in the world. Applications for polyethylenes are many and varied, including: packaging films; trash, garment, grocery and shopping bags; molded housewares; toys; containers; pipe; drums; gasoline tanks; coatings and many others. Polyethylenes are thermoplastic resins obtained by polymerizing the gas ethylene. Low molecular weight polymers of ethylene are fluids used as lubricants; medium weight polymers are waxes miscible with paraffin; and the high molecular weight polymers (i.e., over 6000) are the materials used in the plastics industry. Polymers with densities ranging from about .910 to .925 are called low density; those of densities from .926 to .940 are called medium density; and those from .941 to .965 and over are called high density. The low density types are polymerized at very high pressures and temperatures, and the high density types at relatively low temperatures and pressures. A relatively new type called linear low density polyethylene is manufactured through a variety of processes: gas phase, solution, slurry, or high pressure conversion. A high efficiency catalyst system aids in the polymerization of ethylene and allows for lower temperatures and pressures than those required in making conventional low density polyethylene.

Polyimides

      Thermoset polyimides were introduced in the 1960s, followed in the early 1970s by thermoplastic polyimides. They are used in wire enamels, laminates, adhesives, gears, covers, bushings, piston rings, valve seats, and in solution form as a laminating varnish. Polyimides are characterized by repeating imide linkages. Thermoset polyimides are produced in condensation polymers that possess reactive terminal groups capable of subsequent cross-linking through an addition reaction.

Polyphenylene Oxide, Modified

      Engineering thermoplastic resins produced by the oxidative coupling of 2, 6-dimethylphenol (xylenol), then blended with impact polystyrene. Typical applications are electrical/electronic uses, business machine parts, appliances, and automotive parts.

Polyphenylene Sulfide

      Engineering thermoplastic resins produced by the reaction of p-dichlorobenzene with sodium sulfide. A thermoplastic, PPS exhibits excellent heat resistance, as well as outstanding chemical resistance, high stiffness and good retention of mechanical properties at elevated temperatures. The major use for polyphenylene sulfide is in electrical/ electronic parts and automotive parts.

Polypropylene

      Polypropylene was developed out of the Nobel award-winning work of Karl Ziegler and Professor Natta in Europe, and came to the United States in 1957. It belongs to the olefins family, which also includes the polyethylenes, but it is quite different in its properties. It has a low density, is fairly rigid, has a heat distortion temperature of 150 to 200 degrees F (making it suitable for hot-fill packaging applications), and excellent chemical resistance and electrical properties. Polypropylenes are also very easy to process in all conventional systems. Major applications of commercial PP are packaging, automotive, appliances and carpeting.

Polystyrene

      It wasn’t until after World War II when monomer capacity could be diverted from its essential wartime use for styrene-butadiene synthetic rubber that polystyrene became an important plastic. Today, polystyrene is among the most heavily used commodity thermoplastics. Foamed polystyrene is familiar to consumers as foam cups and containers, protective packaging and building insulation. Polystyrene is also widely used in other packaging and foodservice products, such as trays, disposable plates, cutlery and tumblers. Other applications include: automotive parts, toys, housewares, appliance parts, wall tiles, radio and TV housings, furniture, floats, luggage and many more.

Polyurethanes

      They are extremely versatile plastics in terms of the forms in which they are available: flexible or rigid foams, solid elastomers (or rubbers), coatings, adhesives and sealants. Their versatility also extends to chemical structure in that, although the urethanes are generally considered to be thermosets, there are grades of urethane elastomers that are thermoplastic in nature and are supplied in pellet form for molding, calendering and extrusion. Polyurethane’s major and best known form, however, is a foamed or cellular material. Like all urethanes, the foams are prepared by first reacting two liquid components — polyols and isocyanates — together. In the presence of a blowing agent, this reaction will produce a foamed material having excellent thermal insulating properties, and, in fact, polyurethane foam is widely used in building insulation. The foams can either be soft and flexible or tough, and rigid, with all the possible variations in-between. Flexible foams have outstanding cushioning characteristics, excellent energy-absorbing properties and long life. They are used in furniture, cushioning, carpet underlay, bedding, packaging, textiles and automotive seating and safety padding. Rigid foams offer outstanding insulating values, excellent compressive strength, good dimensional stability and buoyancy. Besides building insulation, they are also found in refrigerators, trucks, boats (for flotation), and in the construction of furniture components. As coatings, polyurethanes impart excellent protective and decorative effects to wood, metals, rubber, textiles, concrete, paper, leather, other plastics and many other materials. In the form of elastomers, polyurethanes offer superior abrasion resistance and toughness, and are used in applications in which good performance and long service life are important: printing rolls, gaskets and seals, cable insulation, drive and conveyor belts, solid tires and automotive applications. Elastomers can also be processed by reaction injection molding, an important technique for producing automotive panels, front ends and bumpers.

Polyvinyl Acetate (PVAc) & Other Vinyls

      Polyvinyl acetate is a thermoplastic resin produced by the polymerization of vinyl acetate monomer in water producing an emulsion with a solids content of 50-55 percent. Polymerization of vinyl acetate with ethylene also can be used to produce solid vinyl acetate/ethylene copolymers with more than 50 percent vinyl acetate content. Co-polymers of replaced acetate groupings and other monomers such as ethylene and acrylate esters are commercially important. Typical applications are adhesives, paints, coatings and finishes, and packaging.

Polyvinyl Chloride

      The birth of polyvinyl chloride, or PVC or vinyl as it is better know to the public, dates to a German patent in the 1910s, but it was not until the late 1920s that a technically useful product was introduced in the U.S. By the start of World War II, the significance of plasticizing PVC (that is, adding a chemical known as a plasticizer to make PVC flexible and processible) was fully realized. It was during the war that the real importance of this polymer became apparent when, due to the acute shortage of rubber, many companies turned to PVC and began to realize its advantages. Because of its wide use in applications that are close to consumers, such as upholstery, flooring, wall coverings, pipe, siding, apparel and accessories, vinyl is one of the better-known plastics. Vinyls are used mainly for their chemical and weathering resistance, high dielectric properties, or abrasion resistance. Vinyl is also dip molded into gloves, slush molded into boots and foamed to make calendered flooring, leather-like upholstery, shoe fabrics and carpet backing. Vinyls are thermoplastic resins produced by the polymerization of the gas vinyl chloride. Under pressure, vinyl chloride becomes liquefied and is polymerized by one of four basic processes: suspension, emulsion, bulk, or solution polymerization. The pure polymer is hard, brittle and difficult to process, but it becomes flexible when plasticizers are added. A special class of PVC resin of fine particle size, often called dispersion grade resin, can be dispersed in liquid plasticizers to form plastisols. The addition of a volatile diluent or a solvent to the plastisol produces an organosol.

Styrene Acrylonitrile

      These are thermoplastic copolymers of styrene and acrylonitrile. SAN resins are random, amorphous copolymers produced by emulsion, suspension, or continuous mass polymerization. Typical uses include automobile instrument panels and interior trim and housewares.

Sulfone Polymers

      A family of engineering thermoplastic resins characterized by the sulfone group. Typical applications for sulfone polymers are electrical/electronic uses and automotive parts.

Thermoplastic Polyester (Saturated)

      As molding and extrusion thermoplastic polyester compounds were introduced in the early 1970s, they quickly became important new members of the family of engineering thermoplastics. These linear polyesters are highly crystalline, hard, strong and extremely tough. The most familiar uses are soda bottles and textiles, but they are also used in X-ray film, magnetic tape (audio, video and computer); packaging; metallized film, strapping and labels. They form a family of polyesters in which the polyester backbones are saturated and hence unreactive. The most common commercial types are: PET (polyethylene terephthalate) produced by polycondensation of ethylene glycol with either dimethyl terephthalate or terephthalic acid and PBT (polybutylene terephthalate) produced by the reaction of DMT with 1,4 butanediol.

Unsaturated Polyester

      While this family of plastics goes under the name of polyesters, they are distinct from the polyesters described above. In fact, they are thermosets, and are probably most familiar to the public for their role in fiberglass reinforced plastics. These materials were introduced to military use (i.e., naval craft) in 1942. After World War II, their characteristics proved extremely appealing to such non-military markets as automotive, marine, corrosion-resistant structures, building, electrical applications, and consumer goods such as luggage, fishing poles and cases and housings of every type and description. These thermosetting resins are made by the condensation reaction between difunctional acids and glycols. The resulting polymer is then dissolved in styrene or other vinyl unsaturated monomer.

Urea-Formaldehyde

      This plastic is another member of the amino family (as is melamine) and was developed in 1929. Like melamine, it is a very hard, scratch-resistant material with good chemical resistance, good electrical qualities and heat resistance up to 170 degrees F. These thermoset resins are clear water-white syrups or white powered materials which can be dispersed in water to form colorless syrups. They cure at elevated temperatures with appropriate catalysts. Molding powders are made by adding fillers to the uncured syrups, forming a consistency suitable for compression and transfer molding. The liquid and dried resins find extensive uses in laminates and chemically resistant coatings. The molding compounds are formed into rigid electrical and decorative products.