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Plastic

Plastic


Plastics are a subspecies of a class of materials known as polymers. These are composed of large molecules , formed by joining many, often thousands, of smaller molecules (monomers) together. Other kinds of polymers are fibers, films, elastomers (rubbers), and biopolymers (i.e., cellulose, proteins, and nucleic acids). Plastics are made from low-molecular-weight monomer precursors, organic materials, which are mostly derived from petroleum, that are joined together by a process called "polymerization." Plastics owe their name to their most important property, the ability to be shaped to almost any form to produce articles of practical value. Plastics can be stiff and hard or flexible and soft. Because of their light weight, low cost, and desirable properties, their use has rapidly increased and they have replaced other materials such as metals and glass. They are used in millions of items, including cars, bullet-proof vests, toys, hospital equipment, and food containers. More than a hundred billion pounds of plastic were produced in 2000. Their increased use has resulted in concern with (1) the consumption of natural resources such as oil, (2) the toxicity associated with their manufacture and use, and (3) the environmental impact arising from discarded plastics.


Pollution Problems

Industrial practices in plastic manufacture can lead to polluting effluents and the use of toxic intermediates, the exposure to which can be hazardous. Better industrial practices have led to minimizing exposure of plant workers to harmful fumes; for example, there have been problems in the past resulting from workers being exposed to toxic vinyl chloride vapor during the production of polyvinyl chloride. Much progress has been made in developing "green processes" that avoid the use of detrimental substances. For example, phosgene, a toxic "war gas," was formerly used in the manufacture of polycarbonates. New processes, now almost universally employed, eliminate its use. Also, the "just in time" approach to manufacture has been made possible by computer-controlled processes, whereby no significant amounts of intermediates are stored, but just generated as needed. In addition, efforts are ongoing to employ "friendly" processes involving enzyme-catalyzed low-temperature methods akin to biological reactions to replace more polluting high-temperature processes involving operations like distillation.

Spillage of plastic pellets that find their way into sewage systems, and eventually to the sea, has hurt wildlife that may mistake the pellets for food. Better "housekeeping" of plastic molding facilities is being enforced in an attempt to address this problem. Most plastics are relatively inert biologically, and they have been employed in medical devices such as prosthetics, artery replacements, and "soft" and interocular lenses. Problems with their use largely result from the presence of trace amounts of nonplastic components such as monomers and plasticizers. This has led to restrictions on the use of some plastics for food applications, but improved technology has led to a reduction in the content of such undesirable components. For example, the use of polyacrylonitrile for beverage bottles was banned at one time because the traces of its monomer, acrylonitrile, were a possible carcinogen. However, current practices render it acceptable today. There has been concern about endocrine disruption from phthalate-containing plasticizers used for plastics such as polyvinyl chloride (PVC). The subject of this possible side effect is controversial, but caution in use is warranted pending further study. Plastics may also result in problems resulting from their improper use, and there is need of better education concerning limitations of use, for example, precautions that should be taken with items such as frying pan coatings and microwavable containers. When exposed to high temperatures, some plastics decompose or oxidize and produce low molecular weight products that may be toxic.



Reduced Use and Recycling

There is growing concern about the excess use of plastics, particularly in packaging. This has been done, in part, to avoid the theft of small objects. The use of plastics can be reduced through a better choice of container sizes and through the distribution of liquid products in more concentrated form. A concern is the proper disposal of waste plastics. Litter results from careless disposal, and decomposition rates in landfills can be extremely long. Consumers should be persuaded or required to divert these for recycling or other environmentally acceptable procedures. Marine pollution arising from disposal of plastics from ships or flow from storm sewers must be avoided. Disposal at sea is prohibited by federal regulation.

Recycling of plastics is desirable because it avoids their accumulation in landfills. While plastics constitute only about 8 percent by weight or 20 percent by volume of municipal solid waste, their low density and slowness to decompose makes them a visible pollutant of public concern. It is evident that the success of recycling is limited by the development of successful strategies for collection and separation. Recycling of scrap plastics by manufacturers has been highly successful and has proven economical, but recovering discarded plastics from consumers is more difficult. It is well recognized that separated plastics can be recycled to yield more superior products than possible for mixed ones.

Labeling plastic items with symbols has been employed, which enables consumers to identify them easily for placement in separate containers for curbside pickup. However, success depends on how conscientious consumers are in employing such standards and the ability of collectors to keep various types of plastic separate. Even a small amount of a foreign plastic in recycling feedstock can lead to the appreciable deterioration of properties, and it is difficult to achieve a high degree of purity. Manual sorting at recycling centers helps, but even trained sorters have difficulty identifying recyclables. Furthermore, manual sorting is an unattractive task and retaining labor willing to be trained for this is problematic. Automatic sorting techniques have been developed that depend on various physical, optical, or electronic properties of plastics for identification. Such methods prove difficult because of the variety of sizes, shapes, and colors of plastic objects that are encountered. Although in principle it is possible to create devices that can separate plastics with varying degrees of success, the equipment generally becomes more expensive with increasing efficiency. Technology for this continues to improve, and it is becoming possible to successfully separate mixed plastics derived from curbside pickup using such equipment.

To separate plastics, it is first necessary to identify the different types as indicated in the table. One must also distinguish between thermoplastics and thermosets. The latter, as found in tires and melamine dishes, has molecules that are interconnected by "crosslinks" and cannot be readily melted for recycling unless they are chemically reduced to low-molecular-weight species. For tires, recycling has not proved economical so disposal has involved grinding them up as asphalt additives for roads or burning in cement kilns.

Over 1.5 million pounds of plastic bottles were recycled in 2000, representing a four-fold increase in the amount of plastic recycled the previous decade. Nonetheless, the capacity to recycle bottles appreciably exceeds their supply by about 40 percent, so local governments and environmental groups need to encourage greater participation in this practice among consumers.

Profitable operations are currently in place for recycling polyethylene terephthalate (PET) from bottle sources and converting it into products such as fibers. One persistent problem, though, is obtaining clean enough feedstock to avoid the clogging of orifices in spinnerets by foreign particles. This has limited the ability to produce fine denier fibers from such sources. PET recycling is also constrained by regulations limiting its use to produce items in contact with food because there had been concern about contamination in consideration of improved recycling techniques.

A leading candidate for recycle feedstock is carpets because replacement carpets are usually installed by professionals able to identify recyclables and who serve as a ready source for recycling operations. They face the problem, however, of separating the recyclable carpet components from other parts such as jute backing and dirt. Such recycling operations have been only marginally profitable.

Polystyrene (PS) is another potentially recyclable polymer, but identifying a readily collectable source is problematic. One had been the Styrofoam "clamshells" fast-food chains use to package hamburgers. Recyclers were able to profitably collect polystyrene from such sources and produce salable products. However, largely because of public pressure, this use of polystyrene has declined, so related recycling practices have largely disappeared too. Cafeteria items from school lunchrooms are another potential, but the collection of such objects involves the development of an infrastructure, often not in place. In these cases, it is necessary to separate the polystyrene from paper and food waste, but washing and flotation techniques have been developed for this purpose.

Increasing amounts of plastic components appear in automobiles, and their recovery from junked cars is a possibility. Its success depends on the ability of a prospective "junker" to identify and separate the plastic items. Three efforts may aid in this accomplishment:

  1. The establishment of databases to enable junkers to learn what kinds of plastic are used in what parts of what model cars.
  2. A reduction in the number of different plastics used for car construction.
  3. The design of cars such that plastic parts may be removed easily (this would require special types of fasteners).

This illustrates a general needthe design of plastic-containing products with the ability to recycle in mind. As a consequence of public concern about the environmental problems arising from plastic use, industry is responding to these needs. The effort continues to use fewer different kinds of plastics and to adopt designs that allow for easier recycling but still retain desirable properties.

There are, however, some worthwhile products that can be produced from mixed plastic, such as "plastic lumber" used for picnic benches and marine applications such as docks and bulkheads that successfully replace wooden lumber which often contains toxic preservatives and arsenic. But, the market for such a product is limited, so efforts to obtain separated plastics are preferred.


Degradable Plastics

Discarded plastics are hard to eliminate from the environment because they do not degrade and have been designed to last a long time. It is possible to design polymers containing monomer species that may be attacked by chemical, biological, or photochemical action so that degradation by such means will occur over a predetermined period of time. Such polymers can be made by chemical synthesis (as with polylactic acid) or through bacterial or agricultural processes (as with the polyalkonates). Although such processes are often more expensive than conventional ones, cost would undoubtedly drop with increased production volume. One success story was the introduction of carbonyl groups into polyethylene by mixing carbon monoxide with ethylene during synthesis. These carbonyl groups are chomophores that lead to chain breaking upon the absorption of ultraviolet light. The polymer is then broken down into small enough units that are subject to bacterial attack. This approach has been successful, for example, in promoting the disappearance of rings from beverage cans, which are potentially harmful to wildlife.

A problem with the degradation of plastics is that it is probably undesirable in landfills because of the leachants produced that may contaminate water supplies. It is better in these instances to ship the plastics to composting facilities. This requires the separation of degradable plastics from other materials and the availability of such facilities. In most cases, the infrastructure needed for such an approach is not in place. This has discouraged its use for disposable diapers that are said to constitute 1 to 2 percent of landfill volume.

Degradable polymers may have limited use in the reduction of litter and production of flushable plastics, for example, feminine hygiene products, but it seems unlikely that the use of such materials will be a viable means of disposal for large amounts of plastic products. Degradation leads to the loss of most of the potential energy content of plastics that might be recovered by trash-to-energy procedures.


Trash to Energy

A method of plastic disposal with more positive environmental implications is burning and recovering the energy for power generation or heating. Plastics contain much of the energy potential of the petroleum from which they are made, and they, in a sense, are just borrowing this energy that may be recovered when the plastic is burned. Environmentalists and the public have objected to this procedure, leading to legislative restrictions. This has arisen, in part, because of the image of "old-fashioned" incinerators polluting the air with toxic fumes and ash. However, it is possible to construct a "high-tech" incinerator designed to operate at appropriate temperatures and with sufficient air supply that these problems are minimized. Remaining toxic substances in fumes may be removed by scrubbing, and studies have shown that no significant air pollution results. Toxic ash, for the most part, does not arise from the polymer components of the feedstock, but rather from other materials mixed with the polymers as well as from fillers, catalyst content, and pigments associated with the polymers. Proper design of the polymers and crude separation of the incinerator feedstock can reduce this problem. Furthermore, if the feedstock was not incinerated but placed in landfills, contaminants would ultimately enter the environment in an uncontrolled way. Incineration reduces the volume, so that the ash, which may contain them, can be disposed of under more controlled conditions. Also, it is possible to insolublize the ash by converting it into a cementlike material that will not readily dissolve.

Facilities for converting trash to energy in an environmentally acceptable way are expensive and at present not cost-effective when considering short-range funding. However, in the long run, they are environmentally desirable and reduce the need for alternative means for plastic waste disposal. It is imperative that legislators and taxpayers soon adopt this long-range perspective.

see also Endocrine Disruption; Recycling; Solid Waste; Waste.

Bibliography

American Plastics Council. (2001). "2000 National Post Consumer Plastics Recycling Report." Arlington, VA: Author.

Gerngross, T.U., and Slater, S.C. (2000). "How Green Are Green Plastics." Scientific American August.

Hocking, M.B. (1991). "Paper vs. Polystyrene, a Complex Choice." Science 251.

Limbach, B.M. (1990). Plastics and the Environment, Progress and Commitment. Washington, D.C.: Society of the Plastics Industry.

Piaecki, B.; Rainry, D.; and Fletcher, K. (1998). "Is Combustion of Plastics Desirable?" American Scientist 86: 364.

Stein, R.S. (1992). "Polymer Recycling: Opportunities and Limitations." Proceedings of the National Academy of Sciences of the United States of America 89: 835.

Stein, R.S. (2002). "Plastics Can Be Good for the Environment." NEACT Journal 21: 1012.

Vesilind, P.A. (1997). Introduction to Environmental Engineering. Boston, MA: PWS Publishing.

Richard S. Stein

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Plastics

PLASTICS

PLASTICS. Perhaps the most prevalent manufactured material in society today is plastics. About 200 billion pounds of plastics are produced annually in the world, 90 billion pounds in the United States alone. In the 1967 movie The Graduate, the title character, played by Dustin Hoffman, was offered one word of advice for future success: "plastics." It is difficult to imagine society without plastics. Plastics come in innumerable forms, types, and items. They can take the form of adhesives, casting resins, coating compounds, laminates, or molded plastics. They are formed through extrusion, injection, compression, blowing, transfer (fusing), or by a vacuum. There are thermoplastics of nylon, polyester, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and many other substances. There are also thermoset plastics, made of phenols, urea-formaldehydes, melamines, or epoxies. A single object may involve many different types of plastics. For example, the plastics in a car include phenolic and glass (fiberglass), acetal, nylon, polypropylene, fluorocarbon, polyethylene, acrylic, butyrate, and melamine. Plastic can be a natural substance or a synthetic one. In other words, "plastics" can mean any number of different substances and products.

History

Resin is the key to plastics. Until the mid-nineteenth century, societies used natural plastic materials such as amber, sealing wax, shellac, or animal horns. These materials could be softened and molded. When cooled, they retained the new shape. Sealing wax was used to close documents with a personal mark. Items made from animal horns included buttons, cups, hornbooks, and lantern windows. Shellac (a gutta-percha molded plastic) was often

used for lamination and for phonograph records (until vinyl was introduced).

In the mid-nineteenth century, the organic chemical industry began, which led to a study of the chemical makeup of materials and many man-made products. Early plastics were created from cellulose wood fibers treated with nitrate. A German, Christian Friedrich Schönbein, was one of the first to develop cellulose nitrate plastics in 1846. Later, in England, Alexander Parkes developed Parkesine, a pressure-molded collodoin (cellulose nitrate in ethanol). He displayed many Parkesine objects at the 1862 London International Exhibition. However, as happened with so many inventions from Europe, it was the Americans who developed them as commercial successes. John Wesley Hyatt and his brother created the Celluloid Manufacturing Company in Newark, New Jersey, in 1872; this company became the renowned Celanese Corporation of America, renamed CelaneseAG in 1999. Hyatt used camphor as a plasticizer with cellulose, which proved safer and, therefore, more commercially viable. Camphor is still used as a natural plasticizer. Hyatt also introduced injection molding, extrusion molding (forcing molten plastics through an opening), and blow molding (like glass blowing). His work in celluloid made possible motion picture film for Thomas Edison, photographic film for George Eastman, and other products such as collars, eyeglass frames, and side curtains for automobiles. The great disadvantage of celluloid nitrate was its flammability. However, by World War I (1914–1918) the Tennessee Eastman Corporation had developed cellulose fibers mixed with acetate, which proved much less flammable and was used widely on airplane wings.

Leo Baekeland, a Belgian who came to the United States in 1889, developed the first commercial synthetic resin and the first thermoset resin in the early 1900s. He created a substance from phenolics (found in coal tar) and formaldehyde to impregnate fibrous sheets. His new synthetic was called Bakelite, which became the foremost name in plastics.

The work of Hermann Staudinger in Zurich in the 1920s was critical in explaining how the plastic molecules, polymers, were created. Once his work was accepted in the 1930s, the plastics industry developed rapidly with diversified products for commercial uses. In the 1930s the new plastics materials included urea resins, acrylics, and polyethylene in 1931; vinyl resins in 1933; melamine, fiberglass, and styrene in 1937; Teflon and epoxy in 1938; and nylon in 1939. After World War II (1939–1945), society entered the "Plastics Age."

What Are Plastics?

Plastics are inexpensive substances that are soft and malleable during manufacturing and are fabricated into lightweight, tough, rigid or flexible, clear or opaque, corrosive-resistant objects. There are some inorganic substances that conform to this definition—concrete, mortar, and plaster of Paris for example. However, as we think of them, plastics are organic substances made up of huge molecules called polymers. The organic material generally used is coal, oil, natural gas, or wood. Plastics have a high molecular weight; for instance, the molecular weight of oxygen is 32, and that of a polymer is between 10,000 and 500,000. Chemicals are used to distill and modify the organic substance. Chemicals found in plastics include carbon, hydrogen, oxygen, and nitrogen. Chlorine, fluorine, sulfur, or silicon may also be present. To make the polymers more flexible or tougher, a plasticizer is added. There are many different plasticizers, and it is important to use the right one in the right amount for the particular substance or object desired. If the wrong plasticizer is used, the polymer loses its plasticity in a short time. In the early days of the plastics industry, this happened often with raincoats, handbags, curtains, and other objects, which soon became brittle and cracked.

There are two types of plastics—thermoplastics and thermoset plastics. Thermoplastics are formed from long linear chains of molecules (polymers). These polymers can be softened and when cooled regain a solid state. These plastics can be first formed as sheets, pellets, films, tubes, rods, or fibers. These forms can then be reheated and molded into other shapes. For example, nylon thread can be made into fabric. The various chemical and molecular properties of thermoplastics determine whether they are called nylon, polyester, polypropylene, polystyrene, polyethylene, polyvinyl chloride (PVC), or other names.

Thermoset plastics are different. These polymers are formed from two directions and produce three-dimensional networks of molecules, not linear chains. Such substances cannot be remelted. They are formed through compression molding or casting. Thermoset plastics include phenolic laminates (the original Bakelite), urethane, melamine, epoxy, acrylic, silicone, fluorocarbons, and others.

Uses of Plastics

Plastics are prolific and have many advantages over other heavier, easily corroded, breakable, or more expensive materials. A home provides a good example of the ubiquity and versatility of plastics. The house may use vinyl concrete, vinyl siding, vinyl window frames, vinyl wallpaper, and vinyl venetian blinds. These are long lasting and require little upkeep. The wiring in the house could be polyethylene with epoxy coating. The insulation may be silicone or polystyrene. The house will also have polyvinyl chloride pipes. The outdoor furniture is likely to be molded PVC. Windows may be acrylic and so, too, the sofa. Seat cushions and pillows will likely be made with urea-formaldehyde foam; the carpets, nylon. The tables and cabinets may be polyurethane. Dishes may be melamine, which is easily dyed, durable, and very scratch resistant. The family car is also likely to be melamine coated. Pots and pans often use Teflon, a fluorocarbon invented in 1943. Serving dishes may be the acrylic Lucite,

and small windows may be of another acrylic, Plexiglas. Clothing may also be of plastics, including nylon stockings and nylon underwear. In the late 1960s, clothing often was all polyester; today, polyester fibers are often mixed with natural fibers such as wool or cotton for a more natural look. The home's air ducts are also likely to be polyester, and if there is a boat, it is most likely fiberglass, made from polyester and glass fiber mix. The glass fibers reinforce the plastics and allow for repairs. Foods in a home, especially meats, are packaged in Styrofoam, made from polystyrene, as are some carry-out containers. Polystyrenes are thermoplastics that are easily molded, rigid, and good insulators.


The five most prevalent plastics are all thermoplastics and account for 90 percent of the plastics of the early twenty-first century. These include polyethylene, used in all types of bags, diaper liners, agricultural covers, and milk and juice jugs; polyethylene terephthalate (PET), used principally for soda bottles and videotapes; polystyrene, used as clear packaging, as a foam (Styrofoam), or for furniture, toys, utensils, and dishes; polypropylene, used for battery cases, crates, film, molded car parts, appliances, fish nets, and wire coating; and polyvinyl chloride, used as a flexible substance in film, hoses, rainwear, and wall coverings, or as a rigid substance in pipes, buildings, and credit cards. The most prevalent thermoset plastics are phenolics, used with formaldehyde and fillers in plywood, fiberglass, and circuit boards; and urea resins, used in polyurethane foam fillers.

The uses of plastics are always expanding and new polymers are being created. One example of thermoset plastics whose uses are expanding is silicone. It is an oxygen-based, and not the usual carbon-based, substance. Because it is highly resistant to ozone, chemicals, sunlight, and aging, it has a wide variety of uses, such as polishes, insulation, waterproofing, adhesives, and implants. Two very versatile thermoplastics are polyethylene and polycarbonate. Polyethylene is used for toys, electronic devices, wires, and milk carton coatings. Polyethylene is also now used widely in medical procedures, for example, to replace aortas or as prosthetic devices. Polycarbonates are fairly new polymers that are formed from bonding oxygen and silicon. Polycarbonates are easy to use yet highly rigid and very corrosive resistant. They have replaced phenol laminates in spacecraft, automobiles, and ships.

Disadvantages of Plastics

Though plastics are ubiquitous and versatile, they also have several disadvantages. The original plastic, cellulose nitrate, was highly flammable; celluloid acetate lessened that danger. Later plastics have included flame retardants, which delay the outbreak of flames but not the decomposition before reaching flammable temperatures. Because of the flame retardants, plastics produce thick, dense smoke that is acrid from the chemicals, especially carbon monoxide. In some of the most disastrous fires, more people suffocated from the plastics smoke and soot than died from the flames. Also, once plastic does flame, it burns faster and hotter than natural substances.

Decomposition is another issue. Because plastics are made from long chains of molecules that receive high heat to set or mold them, decomposition can emerge as weaknesses in the chain. When thermoplastics are remolded, weaknesses can increase. Some plastics also decompose more rapidly than others, especially the less expensive plastics such as PVC and urethane foam. Some critics claim that the phthalate plasticizers used in PVC create low-level toxicity. The urethane foam cushions begin to break down fairly quickly, leaving bits of foam and dust. Leaving plastics exposed to sunlight and heat also causes decomposition and cracking. As plastics decompose, they release chemicals such as carbon monoxide, chlorine, and benzene into the air. For example, the "office worker's illness" is caused by decomposing polymers of the air ducts, furniture, and equipment, and too little fresh air.

Future

Another problem with plastics is waste disposal. In the United States alone, some 60 billion pounds of plastics

are discarded annually and over 90 percent of the waste is not yet recycled. Thermoset plastics cannot be reused; neither can some thermoplastics because of impurities (including disposable diapers, food packaging, and trash bags). Nevertheless, in the United States and Europe plastics recycling has become a major industry, tripling in the United States since 1990. Recycled bottles alone have grown from 411 million pounds in 1990 to 1,511 million pounds in 2000. There are over 1,400 products made from recycled plastics, most of the same items as new synthetic plastics—furniture, packaging, household items—but also new items such as lumber and posts.

Composting is a principal method of recycling plastics. Synthetic plastics may decompose through photo-degradation, oxidation, or hydrolysis—naturally or chemically. Success in composting depends on the environment and the chemicals used in the plastics. Some, such as the polyolefins, are hydrophobic (water-resistant) and thus highly resistant to biodegradation.

The newest research and development in plastics is in bioplastics, biodegradable plastics whose components are principally derived from renewable raw materials. This often means a return to many of the natural polymers used in the nineteenth century, with late-twentieth or twenty-first-century technology added. In 1941 Henry Ford produced a prototype Ford made of soybean plastics. Due to war needs and the rise of synthetic plastics, the work was abandoned, but such innovation is typical of today's research and development. Bioplastics are already used in a wide variety of products including all types of bags, packaging, fishnet and lines, pet toys, wall coverings, razors, and golf tees.

Starch is a prolific raw material that makes a good plastic. It is now used in many fast-food containers and for the "peanuts" used in shipping. The water solubility of starch is both an advantage for decomposition and a limitation, which technology may overcome. For example, some eating utensils are now made of 55 percent cornstarch and 45 percent poly(lactic acid), which is insoluble in water but biodegradable in seawater. Poly(lactic acid) is a polyester synthesized from lactic acid. It shows solid commercial production growth and is used, for example, in compost bags, agricultural films, fibers, and bone repair. Cellulose is another bioplastic from the past. It is contained in 40 percent of organic matter and thus is renewable. Its limitation is that it is not thermoplastic, though it can be made into films.

Though bioplastics have limitations such as tensile strength, solubility, and cost, they produce less toxicity to humans and the environment and are based on renewable resources. Improved technology may overcome the limitations.

BIBLIOGRAPHY

Hooper, Rodney. Plastics for the Home Craftsman. London: Evans Brothers, 1953.

Simonds, Herbert R., and James M. Church. A Concise Guide to Plastics. New York: Reinhold Publishing Company, 1963.

Stevens, E. S. Green Plastics: An Introduction to the New Science of Biodegradable Plastics. Princeton, N.J.: Princeton University Press, 2002.

Wallace, Deborah. In the Mouth of the Dragon. Garden City Park, N.Y.: Avery Publishing Group, 1990.

Diane NagelPalmer

See alsoBuilding Materials ; Carpet Manufacture ; Industrial Research ; Manufacturing ; Textiles .

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Plastics

Plastics


The term "plastic" can be broadly defined as any inherently formless material that can be molded or modeled under heat and/or pressure. It is derived from the Greek word plastikos, meaning a shaped or molded substance.

The term "plastics" first included only natural polymersusually animal proteins (horn and tortoise shell), tree resins, or insect secretions called shellacthat were subsequently mixed with fillers such as wood flour to yield substances having better molding properties. (A polymer, from the Greek word poly, meaning "many," and mer meaning "unit," is a molecule with an extremely high molecular weight.)

The use of natural polymers to make plastic products started as early as 1760, when Enoch Noyes opened a business making combs out of keratin and albuminoid organic proteins derived from animal horns and horse hoofs. However, the first commercially successful plastic material, celluloid, would not come about for another hundred years.

In the 1840s German chemist Christian Schönbein developed cellulose nitrate from a mixture of cotton, nitric acid, and sulfuric acid. Cellulose nitrate is a highly flammable doughlike substance primarily used in the manufacture of explosives. Schönbein's innovation represents the beginning of the modification of natural polymers by chemists so as to increase their processibility and functionality. Cellulose nitrate's properties as a molding substance interested other scientists of the time, and in 1855 an Englishman named Alexander Parkes developed a form of cellulose nitrate he named Parkesine. From this material, Parkes manufactured a number of buttons, pens, medallions, and combs. In 1862 he displayed this material officially at the Great International Exhibit in London. Parkes made small commercial gains with Parkesine and eventually sold the rights to Daniel Spill, who subsequently began production of the substance under the names Xylonite and Ivoride, around 1865. Spill received British patents for Xylonite and Ivoride in 1867 and 1869, respectively.

At around the same time in the United States, a billiard ball company advertised a $10,000 reward for the discovery of an alternate material to ivory. John Wesley Hyatt developed collodion, a mixture of cellulose nitrate and alcohol. Like cellulose nitrate, collodion was highly flammable and would produce a small explosion upon agitation. Hyatt reported: "[W]e had a letter from a billiard saloon proprietor in Colorado mentioning this fact saying he did not care so much about it, but that instantly every man in the room pulled a gun." To avoid melee, camphor, a derivative of the laurel tree, was added, and in 1870 Hyatt received a U.S. patent for celluloid. In 1871 Hyatt and his brother Isaiah formed the American Celluloid Company, which is today the Plastics Division of the Celanese Corporation.

HERMAN MARK (18951992)

The influence of Herman Mark, the so-called father of polymer science, on the plastics industry still echoes today in a legacy of education and research. His work in the 1920s on the structure of cellulose opened the door for the development of synthetic fibers such as acrylic, nylon, polyester, polystyrene, and PVC.

Valerie Borek

A more common perception of plastic is that it is a synthetic or man-made material, with highly engineered properties and product designs. Dr. Leo Baekeland engineered the first totally synthetic plastic in 1907. Patented in 1909 and named Bakelite after its inventor, the material was the first thermoset plastic. The term "thermoset" refers to a plastic that under initial heat and pressure can be molded into form. After cooling, the material sets and cannot be remelted or re-formed. This setting is due to the cross-linking of polymer chains, wherein strong covalent bonds form between separate oligomers, short chains of polymer units called monomers. The most common thermoset resin is vulcanized rubber, created by Charles Goodyear in the United States in 1839. Vulcanized rubber utilizes natural hevea rubber made from the gutta percha tree, and therefore is not totally synthetic (like Bakelite). Ironically, the first use of Bakelite was as a replacement for natural rubber in electrical insulations. Bakelite is formed via the reaction of phenol and formaldehyde under high heat. Initially, formaldehyde is added to the reaction mixture in small amounts (forming a resin); the mixture is then poured into a mold, into which more formaldehyde is added; and pressure is applied to create the final product.

Over the next several decades, many varieties of synthetic thermoplastic materials would be developed in Germany, England, and the United States. Thermoplastic materials such as vinyls, nylons, and acrylics are polymers that can be molded or formed under heat and pressure, and if necessary can be reheated and re-formed (and will retain most of their original mechanical properties).

Eugen Baumann created today's most common vinyl, polyvinyl chloride (PVC), in 1872. However, Friedrich Heinrich August Klatte did not patent it until 1913. At that time PVC was not well received, as illustrated by Waldo Semon's comment, "People thought of PVC as worthless back then; they would throw it in the trash." Semon was responsible for creating plasticized PVC. He had been attempting to dehydrohalogenate PVC in a high boiling solvent when he realized that the molten material was exhibiting greater flexibility and elasticity. The exposure of PVC to a boiling solvent introduced a plasticizer, or low molecular weight molecule, to the PVC matrix. Today plasticizers are commonly added to polymers (especially PVC) to enhance flexibility, prevent stress cracking, and enhance processability. This has enabled the use of PVC in diverse commercial applications, including the manufacture of rigid tubing and flexible car seats.

In 1920 German scientist Hermann Staudinger published his theories on polyaddition polymerization, the formation of long-chain molecules. (Previously, the manner in which long-chain molecules were formed was unexplained.) Nine years later, in a publication that detailed the polymerization of styrene, this method of chain formation would be laid out. During this time period Staudinger developed polystyrene into a commercial product. A division of the German chemical company IG Farben, known as Badische Anilin-und Soda-Fabrik, or BASF, produced polystyrene in 1930. The Dow Chemical Company introduced the American public to polystyrene in 1937.

In 1928 directors at E. I. du Pont de Nemours & Company (Du Pont) placed Dr. Wallace H. Carothers in charge of fundamental research into what are now classic studies on the formation of polymer chains. During his years at Du Pont, Carothers published his theory on polycondensation, and discovered both neoprene and nylon.

Nylon, not publicly announced until 1938, was first used for bristles on combs, but made headlines in 1939 when nylon stockings debuted at the World's Fair in New York City. Nylon is known by its chemical name, poly(hexamethylene) adipamide, but more often simply as nylon. The first nylon manufacturing plant went into production at Seaford, Delaware, in 1940. Commercial production of nylon 6 by IG Farben in Germany began in 1941. These two plants would go on to produce millions of pounds of nylon annually. This mass production was essential to the World War II effort, as nylon was used for everything from belts, ropes, and straps to tents and parachutes.

Another polymer that came into use during World War II was polytetrafluoroethylene (PTFE), which received the trademark Teflon. Dr. Roy J. Plunkett and his assistant Jack Rebock at Du Pont discovered PTFE accidentally on April 6, 1938. They had been conducting research on alternate refrigeration methods when they discovered the polymerization of tetrafluoroethylene. Plunkett received a patent for PTFE in 1941. It was found that the material was resistant to corrosion by all the solvents, acids, and bases that were available for testing at that time. This led to the U.S. military's interest in PTFE, and its subsequent use as a cover for proximity fuses on the nose cones of artillery shells. It was not until the material was declassified in 1946 that the public learned of the material Du Pont had named Teflon two years earlier. Teflon has since become a household name; its best-known use being its contribution to nonstick surfaces on pots and pans.

Today's most widely produced and perhaps most versatile plastic, polyethylene, was discovered at the Imperial Chemical Industries (ICI) in England in 1933. E. W. Fawcett and R. O. Gibson set off a reaction between ethylene and benzaldehyde under 2,000 atmospheres of pressure, resulting in the polymerization of ethylene and the birth of polyethylene. By 1936, ICI had developed a larger volume compressor that made the production of useful quantities of polyethylene possible. Among polyethylene's first applications were its uses as underwater cable coatings and as insulation for radar during World War II.

In 1943, Karl Ziegler began work that would drastically alter the production of polyethylene. Ziegler used organometallic compounds, which have both metallic and organic components, as catalysts. At very modest pressures, these catalysts generated a linear, more rigid, high molecular weight polyethylene, and the innovation increased the number of the polymer's applications. Today polyethylene is used in the production of detergent bottles and children's toys, and is even replacing Kevlar as a bulletproof material.

In 1957, at the Montecatini Laboratories in Italy, Giulio Natta continued the work of Ziegler and used what is now termed ZieglerNatta polymerization to create polypropylene. When Natta reported the polymerization of ethylene with a titanocene catalyst, it became clear that polymer chains with specific tacticities, or specific ordered structures, were possible. Polypropylene rose to become a substitute for polyethylene in products in which slightly higher temperature stability was necessary, for example, dishwasher-safe cups and plates.

Polycarbonate, a popular plastic used originally to make eyeglass lenses, was first discovered by A. Einhorn in 1898. But it would be more than fifty years before further research was performed on the material. In the 1950s Dr. Herman Schnell, working at Bayer, a division of IG Farben, along with Daniel Fox of General Electric's Corporate Laboratory in Schenectady, New York, conducted concurrent research on the synthesis of polycarbonate. Schnell and Fox each achieved a polymerization that produced polycarbonate via different methods, and received patents in 1954 and 1955, respectively. Upon his achievement of polymerization, Fox described his attempts to remove the newly formed polymer from the reaction vessel: "The remnants of the glass were broken away to yield a hemispherical, glass fragment embedded, glob of plastic on the end of a steel stirrer shaft. The glob was pounded on the cement floor and struck with a hammer in abortive attempts to remove the remaining glass, and/or, shatter the plastic. The pseudo plastic mallet was even used to drive nails into wood." That glob would eventually be developed into bulletproof glass and provide General Electric and Bayer with billions of dollars in revenue.

Means to improve the material properties of plastics have been sought for decades. Improvement has sometimes come in the form of compounds such as mineral fillers, antioxidants, and flame-retardants. One of the first searches for an improved material was centered on cellulose nitrate. Cellulose nitrate is colorless and transparent, which enabled it to be used as photographic film. However, it is extremely flammable, and its early use in motion picture film and concomitant exposure to hot lights led to numerous fires. In 1900, Henri Dreyfus substituted acetic acid for nitric acid in the synthesis of cellulose nitrate, and created instead a less flammable material, cellulose acetate. Today, polymers are often halogenated in order to achieve flame-retardation.

Plastics have been designed to be chemically resistant, stable compounds, and have been extremely successful in these regards. In fact, they have been so successful that an environmental problem has been created. Plastic products discarded in landfills decay slowly. They sometimes contain heavy metal additives. In addition, the millions of pounds of plastic discarded annually have engendered a crisis over landfill space. In the early 1980s plastic recycling programs began to spring up across the United States in response to the large number of polyethylene terephthalate (PET or PETE) bottles being discarded. In 1989, 235 million pounds of PET bottles were recycled. The number rose to 1.5 billion pounds in 1999.

Most plastics can be recycled. Even mixed plastic waste can be recycled into artificial lumber or particleboard. Plastic "wood" is easy to saw, and it has better resistance to adverse weather and insects than real wood.

see also Baekeland, Leo; Carothers, Wallace; Goodyear, Charles; Staudinger, Hermann; Nylon; Polymers, Synthetic.

Paul E. Koch

Bibliography

DiNoto, Andrea (1984). Art Plastic Designed for Living. New York: Abbeville Press.

Morawetz, Herbert (1985). Polymers: The Origins and Growth of a Science. New York: John Wiley.

Seymour, Raymond B. (1986). High Performance Polymers: Their Origin and Development. New York: Elsevier Science.

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Koch, Paul E.. "Plastics." Chemistry: Foundations and Applications. 2004. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

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Koch, Paul E.. "Plastics." Chemistry: Foundations and Applications. 2004. Retrieved May 24, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3400900394.html

plastic

plastic, any organic material with the ability to flow into a desired shape when heat and pressure are applied to it and to retain the shape when they are withdrawn.

Composition and Types of Plastic

A plastic is made up principally of a binder together with plasticizers, fillers, pigments, and other additives. The binder gives a plastic its main characteristics and usually its name. Thus, polyvinyl chloride is both the name of a binder and the name of a plastic into which it is made. Binders may be natural materials, e.g., cellulose derivatives, casein, or milk protein, but are more commonly synthetic resins. In either case, the binder materials consist of very long chainlike molecules called polymers. Cellulose derivatives are made from cellulose, a naturally occurring polymer; casein is also a naturally occurring polymer. Synthetic resins are polymerized, or built up, from small simple molecules called monomers. Plasticizers are added to a binder to increase flexibility and toughness. Fillers are added to improve particular properties, e.g., hardness or resistance to shock. Pigments are used to impart various colors. Virtually any desired color or shape and many combinations of the properties of hardness, durability, elasticity, and resistance to heat, cold, and acid can be obtained in a plastic.

There are two basic types of plastic: thermosetting, which cannot be resoftened after being subjected to heat and pressure; and thermoplastic, which can be repeatedly softened and remolded by heat and pressure. When heat and pressure are applied to a thermoplastic binder, the chainlike polymers slide past each other, giving the material "plasticity." However, when heat and pressure are initially applied to a thermosetting binder, the molecular chains become cross-linked, thus preventing any slippage if heat and pressure are reapplied.

See epoxy resins; polyacrylics; polycarbonates; polyethylene; polyolefins; polypropylene; polystyrene; polyurethanes; polyvinyl chloride; vinyl plastics.

Molding of Plastic

Plastics are available in the form of bars, tubes, sheets, coils, and blocks, and these can be fabricated to specification. However, plastic articles are commonly manufactured from plastic powders in which desired shapes are fashioned by compression, transfer, injection, or extrusion molding. In compression molding, materials are generally placed immediately in mold cavities, where the application of heat and pressure makes them first plastic, then hard. The transfer method, in which the compound is plasticized by outside heating and then poured into a mold to harden, is used for designs with intricate shapes and great variations in wall thickness. Injection-molding machinery dissolves the plastic powder in a heating chamber and by plunger action forces it into cold molds, where the product sets. The operations take place at rigidly controlled temperatures and intervals. Extrusion molding employs a heating cylinder, pressure, and an extrusion die through which the molten plastic is sent and from which it exits in continuous form to be cut in lengths or coiled.

Environmental Considerations

Plastics are so durable that they will not rot or decay as do natural products such as those made of wood. As a result great amounts of discarded plastic products accumulate in the environment as waste. It has been suggested that plastics could be made to decompose slowly when exposed to sunlight by adding certain chemicals to them. Plastics present the additional problem of being difficult to burn. When placed in an incinerator, they tend to melt quickly and flow downward, clogging the incinerator's grate. They also emit harmful fumes; e.g., burning polyvinyl chloride gives off hydrogen chloride gas.

Development of Plastics

The first important plastic, celluloid, was discovered (c.1869) by the American inventor John W. Hyatt and manufactured by him in 1872; it is a mixture of cellulose nitrate, camphor, and alcohol and is thermoplastic. However, plastics did not come into modern industrial use until after the production (1909) of Bakelite by the American chemist L. H. Baekeland. Bakelite, made by the polymerization of phenol and formaldehyde, is thermosetting. New uses for plastics are continually being discovered. Following World War II optical lenses, artificial eyes, and dentures of acrylic plastics, splints that X rays may pierce, nylon fibers, machine gears, fabric coatings, wall surfacing, and plastic lamination were developed. More recently a hydrophilic, or water-attracting, plastic suitable for use in non-irritating contact lenses has been developed. Among the trade names by which many plastic products are widely known are Plexiglas, Lucite, Polaroid, Cellophane, Vinylite, and Koroseal. Plastics reinforced with fiberglass are used for boats, automobile bodies, furniture, and building panels.

Bibliography

See L. K. Arnold, Introduction to Plastics (1968); J. H. DuBois, Plastics History, U.S.A. (1972); H. D. Junge, Dictionary of Plastics Technology (1987); A. W. Birley et al., Plastics Materials: Properties and Applications (1988).

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plastic

plastic. Any of a large and varied class of artificial substances which are usually carbon-based polymers (i.e. with molecular structures made up largely or wholly from a great number of similar polyatomic bonded units) derived from synthetic resins or modified natural polymers, and with added substances giving colour and improved performance. They may be obtained in permanent or rigid form after moulding under pressure, extrusion. etc., when they are mouldable or liquid. Although discovered in C19 they were developed from the 1930s, and after the 1939–45 war (when they were employed for numerous purposes, notably in aircraft) were used in buildings for cladding, mouldings, pipes, gutters, etc. Plastics in building are of two general types: thermosets (incapable of being softened or melted by heat) and thermoplastics (which become soft when heated and rigid when cool, and can be repeatedly reheated and reshaped without any loss of their essential properties). In C20 certain plastics were used to create tensile structures (e.g. the work of Otto) and transparent polycarbonates for use in e.g. Fuller's geodesic domes, roofing, etc. Although capable of being formed into curved shapes (e.g. the tubes for the external escalators at the Centre Pompidou, Paris, by Piano and Rogers), transparent plastics, though tough, can be scratched, and can look very unsightly after a time. Plastics cause pollution during manufacture, so they are not favoured by advocates of Environmentally Responsible Architecture (they cannot be recycled and are difficult to dispose of), nor do those who argue in favour of traditional building methods approve of them (their appearance (not universally admired even when new) often deteriorates, and, in many cases, they have not lived up to expectations, have discoloured, or failed). However, plastics are widely used in protective coatings (e.g. paints), for electrical and plumbing systems, for insulation, and as waterproof sealants, gaskets, and membranes. Moulded plastic panels reinforced with glass-fibre (GRP) are used for walls and roofs. Whole buildings can be made from moulds on which liquid plastics are sprayed, and the material is being further researched as offering potential in architecture.

Bibliography

M. Foster (ed.) (1982);
T. Newman (1972);
Skeist (ed.) (1996);
Jane Turner (1996)

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JAMES STEVENS CURL. "plastic." A Dictionary of Architecture and Landscape Architecture. 2000. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

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plastic

plas·tic / ˈplastik/ • n. a synthetic material made from a wide range of organic polymers such as polyethylene, PVC, nylon, etc., that can be molded into shape while soft and then set into a rigid or slightly elastic form. ∎  inf. credit cards or other types of plastic card that can be used as money: he pays with cash instead of with plastic. • adj. 1. made of plastic: plastic bags. ∎  looking or tasting artificial: long-distance flights with their plastic food she smiled a little plastic smile. 2. (of substances or materials) easily shaped or molded: rendering the material more plastic. ∎  (in art) of or relating to molding or modeling in three dimensions, or producing three-dimensional effects. ∎  (in science and technology) of or relating to the permanent deformation of a solid without fracture by the temporary application of force. ∎  offering scope for creativity: the writer is drawn to words as a plastic medium. ∎  Biol. exhibiting adaptability to change or variety in the environment. DERIVATIVES: plas·ti·cal·ly / -(ə)lē/ adv.

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"plastic." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

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plastic

plastic Synthetic material composed of organic molecules, often in long chains called polymers, that can be shaped and then hardened. The weight and structure of the molecules determine the physical and chemical properties of a given compound. Plastics are synthesized from common materials, mostly from petroleum. Cellulose comes from cotton or wood pulp, casein from skimmed milk, others from chemicals derived from plants. Thermoset plastics, such as Bakelite, stay hard once set, while thermoplastics, such as polyethene, can be resoftened by heat. New, biodegradable plastics are more expensive to produce but are environmentally friendly because they eventually decompose. US inventor John Hyatt (1837–1920) created the first plastic, which was celluloid in 1869. In 1908, US chemist Leo Baekeland produced the first mouldable industrial plastic.

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"plastic." World Encyclopedia. 2005. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

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plastic

plastic characterized by moulding or modelling, causing growth or development XVII; capable of being moulded XVIII; of synthetic material XX. As sb., art of modelling figures XVI; plastic substance XX. — F. plastique or L. plasticus — Gr. plastikós, f. plastós, ppl. adj. f. plássein; see PLASMA, -IC.

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T. F. HOAD. "plastic." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 24 May. 2016 <http://www.encyclopedia.com>.

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plastic

plasticachromatic, acrobatic, Adriatic, aerobatic, anagrammatic, aquatic, aristocratic, aromatic, Asiatic, asthmatic, athematic, attic, autocratic, automatic, axiomatic, bureaucratic, charismatic, chromatic, cinematic, climatic, dalmatic, democratic, diagrammatic, diaphragmatic, diplomatic, dogmatic, dramatic, ecstatic, emblematic, emphatic, enigmatic, epigrammatic, erratic, fanatic, hepatic, hieratic, hydrostatic, hypostatic, idiomatic, idiosyncratic, isochromatic, lymphatic, melodramatic, meritocratic, miasmatic, monochromatic, monocratic, monogrammatic, numismatic, operatic, panchromatic, pancreatic, paradigmatic, phlegmatic, photostatic, piratic, plutocratic, pneumatic, polychromatic, pragmatic, prelatic, prismatic, problematic, programmatic, psychosomatic, quadratic, rheumatic, schematic, schismatic, sciatic, semi-automatic, Socratic, somatic, static, stigmatic, sub-aquatic, sylvatic, symptomatic, systematic, technocratic, thematic, theocratic, thermostatic, traumatic •anaphylactic, ataractic, autodidactic, chiropractic, climactic, didactic, galactic, lactic, prophylactic, syntactic, tactic •asphaltic •antic, Atlantic, corybantic, frantic, geomantic, gigantic, mantic, necromantic, pedantic, romantic, semantic, sycophantic, transatlantic •synaptic •bombastic, drastic, dynastic, ecclesiastic, elastic, encomiastic, enthusiastic, fantastic, gymnastic, iconoclastic, mastic, monastic, neoplastic, orgastic, orgiastic, pederastic, periphrastic, plastic, pleonastic, sarcastic, scholastic, scholiastic, spastic •matchstick • candlestick • panstick •slapstick • cathartic •Antarctic, arctic, subantarctic, subarctic •Vedantic • yardstick •aesthetic (US esthetic), alphabetic, anaesthetic (US anesthetic), antithetic, apathetic, apologetic, arithmetic, ascetic, athletic, balletic, bathetic, cosmetic, cybernetic, diabetic, dietetic, diuretic, electromagnetic, emetic, energetic, exegetic, frenetic, genetic, Helvetic, hermetic, homiletic, kinetic, magnetic, metic, mimetic, parenthetic, pathetic, peripatetic, phonetic, photosynthetic, poetic, prophetic, prothetic, psychokinetic, splenetic, sympathetic, syncretic, syndetic, synthetic, telekinetic, theoretic, zetetic •apoplectic, catalectic, dialectic, eclectic, hectic •Celtic •authentic, crescentic •aseptic, dyspeptic, epileptic, nympholeptic, peptic, proleptic, sceptic (US skeptic), septic •domestic, majestic •cretic •analytic, anchoritic, anthracitic, arthritic, bauxitic, calcitic, catalytic, critic, cryptanalytic, Cushitic, dendritic, diacritic, dioritic, dolomitic, enclitic, eremitic, hermitic, lignitic, mephitic, paralytic, parasitic, psychoanalytic, pyritic, Sanskritic, saprophytic, Semitic, sybaritic, syenitic, syphilitic, troglodytic •apocalyptic, cryptic, diptych, elliptic, glyptic, styptic, triptych •aoristic, artistic, autistic, cystic, deistic, distich, egoistic, fistic, holistic, juristic, logistic, monistic, mystic, puristic, sadistic, Taoistic, theistic, truistic, veristic •fiddlestick •dipstick, lipstick •impolitic, politic •polyptych • hemistich • heretic •nightstick •abiotic, amniotic, antibiotic, autoerotic, chaotic, demotic, despotic, erotic, exotic, homoerotic, hypnotic, idiotic, macrobiotic, meiotic, narcotic, neurotic, osmotic, patriotic, psychotic, quixotic, robotic, sclerotic, semiotic, symbiotic, zygotic, zymotic •Coptic, optic, panoptic, synoptic •acrostic, agnostic, diagnostic, gnostic, prognostic •knobstick • chopstick • aeronautic •Baltic, basaltic, cobaltic •caustic • swordstick • photic • joystick •psychotherapeutic, therapeutic •acoustic • broomstick • cultic •fustic, rustic •drumstick • gearstick • lunatic

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