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Unit:2 Thermoplastic Materials
Introduction
Unit:2 Thermoplastic Materials
Introduction
A thermoplastic, or thermosoftening plastic, is a plastic material, a polymer, that becomes pliable or moldable above a specific temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains associate throughintermolecular forces, which weaken rapidly with increased temperature, yielding a viscous liquid. Thus, thermoplastics may be reshaped by heating and are typically used to produce parts by various polymer processing techniques such as injection molding, compression molding, calendering, and extrusion.[3][4] Thermoplastics differ fromthermosetting polymers, which form irreversible chemical bonds during the curing process. Thermosets do not melt when heated: they decompose and do not reform upon cooling.
Stress-strain graph of a thermoplastic material
Above its glass transition temperature and below its melting point, the physical properties of a thermoplastic change drastically without an associated phase change. Some thermoplastics do not fully crystallize below the glass transition temperature, retaining some or all of their amorphous characteristics. Amorphous and semi-amorphous plastics are used when highoptical clarity is necessary, as light is scattered strongly by crystallites larger than its wavelength. Amorphous and semi-amorphous plastics are less resistant to chemical attack and environmental stress cracking because they lack a crystalline structure.
Brittleness can be decreased with the addition of plasticizers, which increases the mobility of amorphous chain segments to effectively lowers the glass transition temperature. Modification of the polymer throughcopolymerization or through the addition of non-reactive side chains to monomers before polymerization can also lower it. Before these techniques were employed, plastic automobile parts would often crack when exposed to cold temperatures.These are linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling.
Thermoplastic Armor
Naval Research Laboratory developed thermoplastic armor, that can be repaired in the field by a user via tools for pressing irons.
Acrylic
Acrylic, a polymer called poly(methyl methacrylate) (PMMA), is also known by trade names such as Lucite, Perspex and Plexiglas. It serves as a sturdy substitute for glass for items such as aquariums, motorcycle helmet visors, aircraft windows, viewing ports of submersibles, and lenses of exterior lights of automobiles. It is extensively used to make signs, including lettering and logos. In medicine, it is used in bone cement and to replace eye lenses. Acrylic paint consists of PMMA particles suspended in water.
ABS
Acrylonitrile butadiene styrene (ABS) is aterpolymer synthesized from styrene andacrylonitrile in the presence of polybutadiene. ABS is a light-weight material that exhibits high impact resistance and mechanical toughness. It poses few risks to human health under normal handling. It is used in many consumer products, such as toys, appliances, and telephones.
Nylon
Nylon belongs to a class of polymers called polyamides. It has served as a substitute mainly for hemp, cotton and silk, in products such as parachutes, cords, sails, flak vests and women's clothing. Nylon fibers are useful in making fabrics, rope, carpets and musical strings, whereas in bulk form, Nylon is used for mechanical parts including machine screws, gears and power tool casings. In addition, it is used in the manufacture of heat-resistant composite materials.
PLA
Polylactic acid (polylactide) is a biodegradable thermoplastic aliphaticpolyester derived from renewable resources, such as corn starch (in the United States),tapioca roots, chips or starch (mostly in Asia), or sugarcane. It is one of the materials used for 3D printing with fused deposition modeling (FDM) techniques
Polybenzimidazole
Polybenzimidazole(PBI,short for Poly-[2,2’-(m-phenylen)-5,5’-bisbenzimidazole]) fiber is a synthetic fiber with a very high melting point. It has exceptional thermal and chemical stability and does not readily ignite. It was first discovered by American polymer chemist Carl Shipp Marvel in the pursuit of new materials with superior stability, retention of stiffness, toughness at elevated temperature. Due to its high stability, Polybenzimidazole is used to fabricate high-performance protective apparel such as firefighter’s gear, astronaut space suits, high temperature protective gloves, welders’ apparel and aircraft wall fabrics. In recent years, polybenzimidazole found its application as membrane in fuel cells.
Polycarbonate
Polycarbonate (PC) thermoplastics are known under trademarks such as Lexan, Makrolon, Makroclear, and arcoPlus. They are easily worked, molded, and thermoformed for many applications, such as electronic components, construction materials, data storage devices, automotive and aircraft parts, check sockets in prosthetics, and security glazing. Polycarbonates do not have a unique resin identification code. Items made from polycarbonate can contain the precursor monomer bisphenol A (BPA).
Polyether sulfone
Polyether sulfone (PES) is a class of specially engineered thermoplastics[6] with high thermal, oxidative, and hydrolytic stability, and good resistance to aqueous mineral acids, alkalis, salt solutions, oils and greases
Polyetherether ketone
Poly ether ether ketone (PEEK) has attractive properties like good abrasion resistance, low flammability and emission of smoke and toxic gases, resistance to ra
Polyetherimide
Polyetherimide (PEI), produced by a novel nitro displacement reaction involving bisphenol A, 4, 4’-methylenedianiline and 3-nitrophthalic anhydride, has high heat distortion temperature, tensile strength and modulus. They are generally used in high performance electrical and electronic parts, microwave appliances, and under-the-hood automotive parts
Polyethylene
Polyethylene (polyethene, polythene, PE) is a family of similar materials categorized according to their density and molecular structure. For example:
- Ultra-high molecular weight polyethylene (UHMWPE) is tough and resistant to chemicals. It is used to manufacture moving machine parts, bearings, gears, artificial joints and some bulletproof vests.
- High-density polyethylene (HDPE), recyclable plastic no. 2, is commonly used as milk jugs, liquid laundry detergent bottles, outdoor furniture, margarine tubs, portable gasoline cans, drinking water distribution systems, water drainage pipes, and grocery bags.
- Medium-density polyethylene (MDPE) is used for packaging film, sacks and gas pipes and fittings.
- Low-density polyethylene (LDPE) is flexible and is used in the manufacture of squeeze bottles, milk jug caps, retail store bags and linear low-density polyethylene (LLDPE) as stretch wrap in transporting and handling boxes of durable goods, and as the common household food covering
Commodity plastics
Commodity plastics are plastics that are used in high volume and wide range of applications, such as film for packaging, photographic and magnetic tape, clothing, beverage and trash containers and a variety of household products where mechanical properties and service environments are not critical. Such plastics exhibit relatively low mechanical properties and are of low cost. The range of products includes Plates, Cups, Carrying Trays, Medical Trays, Containers, Seeding Trays, Printed Material and other disposable items.[1]
Examples of commodity plastics arepolyethylene, polypropylene,polystyrene, polyvinyl chloride,poly(methyl methacrylate) and more
Material
|
Characteristic
|
Application
|
ABS
|
High Rigidity
High Impact
Electroplating
Flame Retardant
High Heat
|
Monitor, Telephone, Blender
Helmet, Pipe Fitting, Profile
Shower Head, Radiator Grille
Computer Peripheries, Calculator
Dashboard, Tail Lamp, etc
|
AS
|
High Clarity
Heat Resistant
|
Blender's jug, Fan's Blade
Security Seat, etc
|
PS
|
Food Grade
High Impact
High Heat
|
Food Container
CD Casing, etc
|
PMMA
|
High Strength
Medium Strength
High Flow
|
Water Filter
Sun Visor, Lens, Lighting
Screen, Sheet, etc
|
Engineering plastics
Engineering plastics are a group ofplastic materials that have better mechanical and/or thermal properties than the more widely used commodity plastics (such as polystyrene, PVC,polypropylene and polyethylene).
Engineering plastics are a group ofplastic materials that have better mechanical and/or thermal properties than the more widely used commodity plastics (such as polystyrene, PVC,polypropylene and polyethylene).
Being more expensive, engineering plastics are produced in lower quantities and tend to be used for smaller objects or low-volume applications (such as mechanical parts), rather than for bulk and high-volume ends (like containers and packaging).
The term usually refers tothermoplastic materials rather thanthermosetting ones. Examples of engineering plastics includeacrylonitrile butadiene styrene (ABS), used for car bumpers, dashboard trim and Lego bricks; polycarbonates, used in motorcycle helmets; andpolyamides (nylons), used for skis andski boots.
Engineering plastics have gradually replaced traditional engineering materials such as wood or metal in many applications. Besides equalling or surpassing them in weight/strength and other properties, engineering plastics are much easier to manufacture, especially in complicated shapes.
The global engineering plastics market is valued at $57.2 billion in 2014 and is expected to reach $91.78 billion by 2020 at a compound annual growth rate of 8.2%.[2]
Relevant properties
Each engineering plastic usually has a unique combination of properties that may make it the material of choice for some application. For example, polycarbonates are highly resistant to impact, while polyamides are highly resistant to abrasion. Other properties exhibited by various grades of engineering plastics include heat resistance, mechanical strength, rigidity, chemical stability, self lubrication (specially used in manufacturing of gears & skids) and fire safety.
List of engineering plastics
- Polyamides (PA)
- Polycarbonates (PC)
- Polyetheretherketone (PEEK)
- Polyetherketone (PEK)
- Polyoxymethylene plastic (POM / Acetal)
- Polyphenylene sulfide (PPS)
- Polyphenylene oxide (PPO)
- Polysulphone (PSU)
- Polytetrafluoroethylene (PTFE / Teflon
Pages in category "Plastics applications"
The following 28 pages are in this category, out of 28 total. This list may not reflect recent changes (learn more).
P
Z
AApplications of Engineeringťplastic.
Engineering plastics are a group of plasticmaterials that have better mechanical and/or thermal properties than the more widely used commodity plastics(such as polystyrene, PVC, polypropylene and polyethylene
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