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Plastics - Crystalline And Noncrystalline Thermoplastics

applications chains electrical consist

Thermoplastics may be classified by the structure of the polymer chains that comprise them.

In the liquid state, polymer molecules undergo entanglements that prevent them from forming regularly arranged domains. This state of disorder is preserved in the amorphous state. Thus, amorphous plastics, which include polycarbonate, polystyrene, acrylonitrile-butadiene-styrene (ABS), and polyvinyl chloride, are made up of polymer chains that form randomly organized structures.

These polymer chains may themselves have attached side chains, and the side chains may also be quite long. When the side chains are particularly bulky, molecular branching prevents the molecules from forming ordered regions, and an amorphous plastic will almost certainly result.

Under suitable conditions, however, the entangled polymer chains can disentangle themselves and pack into orderly crystals in the solid state where the chains are symmetrically packed together; these materials are known as crystalline polymers.

TABLE 2. THERMOPLASTICS
Type Chemical basis Uses
ABS plastics Derived from acrylonitrile, butadiene, and styrene Electroplated plastic parts; automotive components; business and telecommunication applications such as personal computers, terminals, keyboards, and floppy disks; medical disposables; toys; recreational applications; cosmetics packaging; luggage; housewares
Acetals Consist of repeating -CH2-O-units in a polymer backbone Rollers, bearings and other industrial products; also used in automotive, appliance, plumbing and electronics applications
Acrylics Based on polymethyl methacrylate Automobile lenses, fluorescent street lights, outdoor signs, and boat windshields; applications requiring high resistance to discoloration and good light transmission properties
Cellulosics Derived from purified cotton or special grades of wood cellulose Insulation, packaging, toothbrushes
Fluoroplastics Consist of carbon, fluorine, and or hydrogen atoms in a repeating polymer backbone Applications requiring optimal electrical and thermal properties, almost complete moisture resistance, chemical inertness; non-stick applications
Nylons Derived from the reaction of diamines and dibasic acids; characterized by the number of carbon atoms in the repeating polymeric unit Electrical and electronic components; industrial applications requiring excellent resistance to repeated impact; consumer products such as ski boots and bicycle wheels; appliances and power tool housings; food packaging; wire and cable jacketing; sheets, rods, and tubes; and filaments for brush bristles, fishing line, and sewing thread
Polyarylates Aromatic polyesters Automotive appliance, and electrical applications requiring low shrinkage, resistance to hydrolysis, and precision void-free molding



Crystalline thermoplastics consist of molecular chains packed together in regular, organized domains that are joined by regions of disordered, amorphous chains. Examples of crystalline thermoplastics include acetals, nylons, polyethylenes, polypropylenes, and polyesters.

TABLE 2. THERMOPLASTICS (cont'd)
Type Chemical basis Uses
Polyarylsulfones Consist of phenyl and biphenyl groups linked by thermally stable ether and sulfone groups Electrical and electronic applications requiring thermal stability including circuit boards, connectors, lamp housings, and motor parts
Polybutylenes Polymers based on poly(1-butene) Cold- and hot-water pipes; hot-metal adhesives and sealants
Polybutylene terephthalate (PBT) Produced by reaction of dimethyl terephthalate with butanediol Automotive applications such as exterior auto parts; electronic switches; and household applications such as parts for vacuum cleaners and coffee makers
Polycarbonates Derived from the reaction of bisphenol A and phosgene Applications requiring toughness, rigidity, and dimensional stability; high heat resistance; good electrical properties; transparency; exceptional impact strength. Used for molded products, solution-cast or extruded films, tubes and pipes, prosthetic devices, nonbreakable windows, street lights, household appliances; compact discs; optical memory disks; and for various applications in fields related to transportation, electronics sporting goods, medical equipment, and food processing
Polyesters Produced by reacting dicarboxylic acids with dihydroxy alcohols Reinforced plastics, automotive parts, foams, electrical encapsulation, structural applications, low-pressure laminates, magnetic tapes, pipes, bottles. Liquid crystal polyesters are used as replacements for metals in such applications chemical pumps, electronic components, medical components, and automotive components
Polyetherimides Consist of repeating aromatic imide and ether units Temperature sensors; electrical/electronic, medical (surgical instrument parts), industrial; appliance, packaging, and specialty applications

TABLE 2. THERMOPLASTICS (cont'd)
Type Chemical basis Uses
Polyetherketones Polymerized aromatic ketones Fine monofilaments, films, engine parts, aerospace composites, and wire and cables, and other applications requiring chemical resistance; exceptional toughness, strength, and rigidity; good radiation resistance; and good fire-safety characteristics
Polyethersulfones Consist of diaryl sulfone groups with ether linkages Electrical applications including multipin connectors, integrated circuit sockets, edge and round multipin connectors, terminal blocks, printed circuit boards
Polyethylenes, polypropylenes, and polyallomers Polyethylenes consist of chains of repeated ethylene units; polypropylenes consist of chains of repeated propylene units; polyallomers are copolymers of propylene and ethylene Low density polyethylene is used for packaging films, liners for shipping containers, wire and cable coatings, toys, plastic bags, electrical insulation. High density polyethylene is used for blow-molded items, films and sheets, containers for petroleum products. Low molecular weight Polyethylenes are used as mold release agents, coatings, polishes, and textile finishing agents. Polypropylenes are used as packaging films, molded parts, bottles, artificial turf, surgical casts, nonwoven disposable filters. Polyallomers are used as vacuum-formed, injection molded, and extruded products, films, sheets, and wire cables
Polyethylene terephthalate Prepared from ethylene glycol and either terephthalic acid or an ester of terephthalic acid Food packaging including bottles, microwave/conventional oven-proof trays; x-ray and other photographic films; magnetic tape
Polyimides and polyamide-imides Polyimides contain imide (-CONHCO-) groups in the polymer chain; polyamide-imides also contain amide (-CONH-) groups Polyimides are used as high temperature coatings, laminates, and composites for the aerospace industry; ablative materials; oil sealants; adhesive; semiconductors; bearings; cable insulation; printed circuits; magnetic tapes; flame-resistant fibers. Polyamide-imides have been used as replacements for metal parts in the aerospace industry, and as mechanical parts for business machines

TABLE 2. THERMOPLASTICS (cont'd)
Type Chemical basis Uses
Polymethylpentene Polymerized 4-methylpentene-1 Laboratory ware (beakers, graduates, etc.); electronic and hospital equipment; food packaging; light reflectors
Polyphenylene ethers, modified Consist of oxidatively coupled phenols and polystyrene Automobile instrument panels, computer keyboard bases
Polyphenylene sulfides Para-substituted benzene rings with sulfur links Microwave oven components, precision molded assemblies for disk drives
Polystyrenes Polymerized ethylene and styrene Packaging, refrigerator doors, household wares, electrical equipment; toys, cabinets; also used as foams for thermal insulations, light construction, fillers in shipping containers, furniture construction
Polysulfones Consist of complicated chains of phenylene units linked with isopropylidene, ether, and sulfone units Power tool housings, electrical equipment, extruded pipes and sheets, automobile components, electronic parts, appliances, computer components; medical instrumentation and trays to hold instruments during sterilization; food processing equipment; chemical processing equipment; water purification devices
Vinyls Polymerized vinyl monomers such as polyvinyl chloride and polyvinylidene chloride Crystal-clear food packaging, water pipes, monolayer films



Liquid crystalline plastics are polymers that form highly ordered, rodlike structures. They have good mechanical properties and are chemically unreactive, and they have melting temperatures comparable to those of crystalline plastics. But unlike crystalline and amorphous plastics, liquid crystalline plastics retain molecular ordering even as liquids. Consequently, they exhibit the lowest shrinkage and warpage of any of the thermoplastics.


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