Types of plastic, qualities, uses.

Types of plastics, qualities, uses.

Types of plastics have been split into three categories, Thermoplastics(can be remolded and recycled without negatively affecting the material’s physical properties), Thermosetting plastics(irreversible curing of polymers, resulting in resistance to deformation) and Elastomers(can be either thermoplastic or thermosetting). Also see http://www.modorplastics.com/thermoset-vs-thermoplastics for Pro and Con list for Thermoplastic and Thermosetting

Thermoplastic. Plastic that becomes pliable or moldable above a specific temperature, and returns to a solid state upon cooling.

Polycarbonate (PC) PC is one of the 'engineering' thermoplastics. The optical transparency and high impact resistance of PC make it suitable for bullet-resistant or shatter-resistant glass applications, even at relatively high temperatures. It can be reinforced using glass fibres to reduce shrinkage problems on cooling and to improve the mechanical performance at high temperatures. It is readily colour. PC is usually processed by extrusion or thermoforming (techniques that impose constraints on design), although injection moulding is possible. Also used for safety shields and goggles, lenses, glazing panels, business machine housing, and instrument casings.

Polymethyl methacrylate (Acrylic, PMMA) PMMA is the thermoplastic that most closely resembles glass in transparency and resistance to weathering. It is easy to polish but sensitive to stress concentrations. It shares with glass certain fragility, something that can be overcome by blending with acrylic rubber to give a high-impact alloy. Used for lenses of all types; cockpit canopies and aircraft windows, signs, domestic baths, packaging, containers, electrical components, drafting equipment and tool handles.

Polyoxymethylene (Acetal, POM) It is similar to nylon but is stiffer, and has better fatigue and water resistance It is rarely used without modifications: most often filled with glass fibre, flame retardant additives or blended with PTFE or PU. It has good toughness. POM is used where requirements for good moldability, fatigue resistance and stiffness justify its high price relative to mass polymers, like polyethylene, which are polymerized from cheaper raw materials using lower energy input. POM is more expensive than commodity polymers such as PE, so is limited to high performance applications in which its natural lubricity is exploited. It is found in fuel-system; seat-belt components; steering columns; window-support brackets and handles; shower heads, ballcocks, faucet cartridges, and various fittings; quality toys; garden sprayers; stereo cassette parts; butane lighter bodies and zippers.

Polypropylene (PP) Produced in very large quantities can be tailored by clever catalysis, giving precise control of impact strength, and of the properties that influence molding and drawing. In its pure form polypropylene is flammable and degrades in sunlight. Fire retardants make it slow to burn and stabilizers give it extreme stability, both to UV radiation and to fresh and salt water and most aqueous solutions.

Polypropylene is widely used in household products such as ropes, garden furniture, pipes and pipe fittings, chair shells, capacitor dielectrics, cable insulation, kitchen kettles, car bumpers, shatter proof glasses, crates, artificial turf, thermal underwear.

Polyamides (Nylons, PA) Polyamides are tough, wear well and have low coefficient of friction. Nylon (PA) can be drawn to fibers as fine as silk, and was widely used as a substitute for it. Not used as much in clothes design, but nylon-fiber ropes, and nylon as reinforcement for rubber (in car tires) and other polymers (PTFE, for roofs) remains important. It is used in product design for tough casings, frames and handles, and - reinforced with glass - as bearings gears and other load-bearing parts. There are many grades (Nylon 6, Nylon 66, Nylon 11….) each with slightly different properties.

Nylon is used for light duty gears, bearings; electrical equipment housings, tubing, bicycle wheel covers, ketchup bottles, toothbrush bristles, handles, food packaging, ropes, fishing line, carpeting, car upholstery and stockings.

Polystyrene (PS)This material is an optically clear, cheap, easily moulded polymer which is a good thermal and electrical insulator.  In its simplest form it is considered to be brittle, ie a CD case. However, blending allows a drastic improvement to its mechanical properties but this involves it losing its optical transparency. A typical blended polystyrene with 10% polybutadiene, also known as High Impact PS, is much stronger, especially at low temperatures and widely used for packaging. The most common use of PS is as foam packaging. All of the main forms are FDA approved as food containers.

Polyethylene terephthalate (PET) Often used for blow moulded bottles, audio/visual tapes, ovenproof cookware, windsurfing sails and credit cards, this material has a wide range uses.  There are four grades of thermoplastic polyesters: unmodified, flame retardant, glass-fiber reinforced and mineral-filled. These all have various properties and varying strengths/weaknesses. But common PET is tough, strong, easy to shape, join and sterilize - allowing it to be reused. When its first life comes to an end, it can be recycled to give fibers and fleece materials for clothing and carpets.

Starch-based thermoplastics (TPS) Starch is a naturally occurring polysaccharide made up of glucose molecules, the bonds between the sugar molecule building blocks are different. Starch is therefore a polymer, but the problem with using it for making structural products is that it is softened by and dissolves in water. Mater-Bi is a family of biodegradable thermoplastics materials made from maize starch.  They are water resistant. They retain their properties while in use, but when composted in an environment containing bacteria, they biodegrade to carbon dioxide, water and fibrous residue.

Injection moulded: pencil sharpeners, rulers, cartridges, plant pots and other toys for pets, plastic cutlery, hair combs.

Thermo-formed: trays for fresh food packaging, especially fruit and vegetables.

Film extrusion: shopping bags, bubble film for wrapping, plastic laminates for paper cups and plates, bags for rubbish disposal, lining for baby nappies, mulching films for horticulture, wrapping for fruit, vegetables and sanitary products.

Mater-Bi polysaccharide fruit packaging trays

Cellulose Acetate. Used mainly for photography as a film base, but also for glasses frames, tooth brushes & pen bodies due to its rigidity, toughness & resistance to chemicals. The fibre is often used in the textile industry to improve a materials lustre, particularly with satin. It is highly breathable and easily dyed.

Acrylonitrile butadiene styrene (ABS) ABS is tough, resilient, and easily moulded. It is often opaque, although some grades can now be transparent, and it can be given vivid colours. It allows for detailed mouldings and is non-toxic, making it perfect for outdoor applications if stabilizers are added to make it UV resistant, which also slows loss of strength in the material. A large range of shapes can be made as ABS can be extruded, compression molded or formed to sheet that is then vacuum thermoformed. It can be joined by ultrasonic or hot-plate welding, or bonded with polyester, epoxy, isocyanate or nitrile-phenolic adhesives.

Used for automotive instrument panels and other interior components, pipe fittings, home-security devices and housings for small appliances. ABS-PVC alloys are tougher than standard ABS and are used for the casings of power tools.

Polyolefins. Very resistant to chemicals. This means they cannot be glued together by solvent welding or other solvents. If treated, the surfaces can be stuck together with adhesives (typically superglue). Thermal welding is also effective as their chemical inertness decreases as temperature increases. Polyolefins are used for blown film and heatshrink electrical insulation sleeves. Polyolefin elastomer is used as a main ingredient in the molded flexible foam technology which is used to produce Crocs.

Polyethylene (PE) Polyethylene is inert, and extremely resistant to fresh and salt water, food, and most water-based solutions. Because of this it is widely used in household products, food containers like Tupperware and chopping boards. Polyethylene is cheap,particularly easy to mold and fabricate, biologically inert and recyclable. It accepts a wide range of colors, can be transparent, translucent or opaque, has a pleasant, slightly waxy feel, can be textured or metal coated, but is difficult to print on.

Low density polyethylene (LDPE), used for film and packaging whereas Medium (MDPE) and High (HDPE) density polyethylenes are stiffer and stronger; used for containers and pipes.

Polyvinylchloride (tpPVC) Vinyl - is one of the cheapest, most versatile and - with polyethylene - the most widely used of polymers. It is rigid, and not very tough; its low price makes it a cost-effective engineering plastic where extremes of service are not encountered. Both rigid and flexible PVC can be foamed to give lightweight structural panels, and upholstery for cars and domestic use. It is less transparent than PMMA or PC, but it also costs much less, so it is widely used for transparent, disposable containers. It has excellent resistance to acids and bases and good barrier properties to atmospheric gasses, but poor resistance to some solvents. It’s compatible with many manufacturing processes such as extrusion moulding, calendering, injection moulding, thermal moulding, dipping and coating.

Polyetheretherketone (PEEK) PEEK has exceptionally high stiffness, strength and resistance to heat but it is 50 times more expensive than PP, and 10 to 20 times more than nylon. This limits it use to applications in which technical performance is paramount.

It offers high hardness and therefore abrasion resistance; it has excellent fatigue properties and good creep resistance. PEEK can be injection molded, extruded (into rod, profile, film or wire insulation) and compression molded.

It has many uses such as electrical connectors, hot water meters, F1 engine components, valve and bearing components, wire and cable coatings and bearings.

Thermosetting plastic. Plastic that changes irreversibly into an infusible insoluble polymer network by curing.  Curing can be induced by the action of heat or suitable radiation.

Epoxies. Are thermosetting polymers with excellent mechanical, electrical and adhesive properties and good resistance to heat and chemical attack. They are used for adhesives (Araldite), surface coatings and, when filled with other materials such as glass or carbon fibers, as matrix resins in composite materials. Typically, as adhesives, epoxies are used for high-strength bonding of dissimilar materials; as coatings, they are used to encapsulate electrical coils and electronic components; when filled, they are used for tooling fixtures for low-volume molding of thermoplastics. Typical uses include pure epoxy molding compounds: the encapsulation of electrical coils and electronics components; epoxy resins in laminates: pultruded rods, girder stock, special tooling fixtures, mechanical components such as gears; adhesives, often for high-strength bonding of dissimilar materials; patterns and molds for shaping thermoplastics. Tradenames: Araldite, Epikote, Epolite, Fiberite, Lytex, Stycast.

Phenolics. Bakelite is stiff, fairly strong, could (to a muted degree) be coloured, and - above all - was easy to mold. Products that, earlier, were handcrafted from woods, metals or exotics such as ivory, could now be molded quickly and cheaply. At one time the production of phenolics exceeded that of PE, PS and PVC combined. Now phenolics still have a unique value. They are stiff, chemically stable, have good electrical properties, are fire-resistant and easy to mold - and they are cheap. Typical uses Electrical parts - sockets, switches, connectors, general industrial, relays, brake pistons, brake pads, microwave cookware, handles, bottles tops, coatings, adhesives, bearings, foams and sandwich structures

Polyester. (can also be thermoplastic) Cheapest resin for making glass or carbon fiber composites.  Lower strength than epoxies.  Can be made conductive by adding 30% carbon fiber.  Good melt flow properties, low shrinkage, good resistance to oil and fuels.  Modifications can improve chemical resistance, UV resistance and heat resistance without too much change in the ease of processing. Used for laminated structures, surface gel coatings, bowling balls, boats, skylights, fishing rods.

Elastomers. Polymer having elastic properties. E.g. rubber

Polychloroprene (Neoprene, CR(chloroprene rubber) Polychloroprenes can by modified by copolymerization with sulfur, with other chloro-butadienes and by blending with other polymers to give a wide range of properties such as high chemical stability, resistance to water, oil, gasoline and UV radiation. They are also exceptionally tough, having high tear resistance.

Typical uses Brake seals, diaphragms, hoses and o-rings, tracked-vehicle pads, footwear, wetsuits.

Ethylene Vinyl Acetate. (EVA) A copolymer made up of ethylene and vinyl acetate. A plastic which shares the flexibility and softness of an elastomer, but can be processed as a thermoplastic. Its advantages are high clarity, low-temperature toughness, stress-crack resistance  and resistance to UV radiation.

Butyl Rubber (IIR)  (Isobutylene Isoprene Rubber)- Synthetic that resembles natural rubber. Good resistance to abrasion, tearing and flexing.  Low dielectric constant and loss, hence attractive for electrical applications. An excellent cheap, general purpose elastomer with large stretch capacity. Poor oil, oxidation, ozone and UV resistance.  Low hysteresis-very bouncy. Used for inner tubes, seals, pumps, electrical insulation, brake pads.

Natural rubber (NR) Latex, the sap of the rubber tree, is cross-linked (vulcanized) by heating with sulfur; the amount of the cross-linking determines the properties. It is the most widely used of all elastomers - more than 50% of all produced. Natural rubber is used in medical equipment, fashion items, tubing and tires. Gloves, Car tires, seals, belts, anti-vibration mounts, electrical insulation, tubing, rubber lining pipes and pumps.

Polyurethane Most commonly they are elastomers but, like PVC, polyurethanes have thermoplastic, elastomeric and thermosetting grades. Polyurethane elastomers are thermosets, and thus cannot be recycled. Their disposal creates an environmental problem. They are easily foamed; around forty percent of all PU is made into foam by mixing it with a blowing agent. The foams are the strongest of elastomers.

Typical uses are shoe sole, tyres, gears and bearing and car bumpers. These have exceptional strength and are very abrasion resistant, making them perfect for outdoor use. They have useful properties from -55 C to 90 C. It is also the main component in soft stretchy fabrics like Lycra.

Silicone Elastomers. Silicones are high-performance, high cost materials. Silicone and fluoro-silicone elastomers have long chains of linked O-Si-O-Si- groups (replacing the -C-C-C-C- chains in carbon-based elastomers), with methyl (CH3) or fluorine (F) side chains. They have poor strength, but can be used over an exceptional range of temperature (-100 C to + 300 C), have great chemical stability, and an unusual combination of properties (Silly Putty is a silicone elastomer - it bounces when dropped but flows if simple left on the desk).Typical uses: Wire and cable insulation, mold release agents and flexible molds, lens cleaning tissue coatings, seals, gaskets, adhesives, o-rings, insulation, encapsulation and potting of electronic circuitry, surgical and food processing equipment, baby bottle tips, breast implants.

Styrene butadiene rubber (SBR)

Is the synthetic rubber that is most widely used and has the highest production volume.  It is nearly always compounded with reinforcing fillers such as carbon black.

Strengths: When filled, its strength approaches natural rubber (NR) and polychloroprene.  Similar chemical and physical properties to NR and somewhat better abrasion resistance.

Limitations: Weaker and lower fatigue resistance than natural rubber (it does not undergo strain-induced crystallation) especially when unfilled.  Like NR: prone to oxidation, degrades in ozone, swells readily in hydrocarbon fluids with loss of properties.

Typical uses: Car and truck tires, belt, hose, footwear

Qualities of Plastics can be compared using CES, Cambridge Engineering Software available at the JWS building.  The following graph plots the plastics fracture toughness against compressive strength.

Fracture toughness against price:

Fatigue strength against price: