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HDPE - High-density polyethylene.
High density polyethylene (HDPE) is a thermoplastic made from oil. It takes 1.75 kg of oil (in terms of energy and raw materials) to make 1 kg of HDPE. HDPE is resistant to many different solvents and is often used in food containers (ie certain tupperwares, containers for milk, liquid laundry detergent, etc.), some plastic bags, containment of certain chemicals, chemical resistant piping systems, and geothermal heat transfer piping systems.
HDPE has little branching and thus stronger intermolecular forces and tensile strength. The lack of branching is ensured by an appropriate choice of catalyst (e.g. Ziegler-Natta catalysts) and reaction conditions. |
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LDPE - Low density polyethylene
Low density polyethylene (LDPE) is a thermoplastic made from oil. It is non-reactive at room temperatures, except by strong oxidizing agents (and some solvents cause it swelling). It can withstand temperatures of 80oC continuously and 95 oC for a short time. It is translucent or opaque, quite flexible, and tough to the degree of being almost unbreakable.
It is used predominantly in film applications due to its toughness, flexibility and relative transparency. Its most common use is in plastic bags. It is also widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, and various molded laboratory equipment.
LDPE has a low melting point, making it popular for use in applications where heat sealing is necessary. Typically, LDPE is used to manufacture flexible films such as those used for plastic retail bags and garment dry cleaning and grocery bags.
LDPE has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced-dipole attraction) are weaker, its tensile strength is lower, its ductility is higher, and as its molecules are less tightly packed and less crystalline because of the side branches, its density is lower. It is manufactured by free radical polymerization.
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LLDPE - Linear low density polyethylene
Linear low density polyethylene (LLDPE) is a substantially linear polymer, with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins.
LLDPE has higher tensile strength and higher impact and puncture resistance than LDPE. It is very flexible and elongates under stress. It can be used to make thinner films, with better environmental stress cracking resistance. It has good resistance to chemicals and to ultraviolet radiation. It has good electrical properties. However it is not as easy to process as LDPE, has lower gloss, and narrower range for heat sealing.
It is used for plastic bags and sheets (where it allows using lower thickness than comparable LDPE), plastic wrap, toys, lids, pipes, buckets and containers, covering of cables, geomembranes, and mainly for flexible tubing |
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PP - Polypropylene
Polypropylene (PP) is a thermoplastic polymer, used in a wide variety of applications, including food packaging, textiles, laboratory equipment, and polymer banknotes. An addition polymer made from the monomer propylene, it is unusually resistant to many chemical solvents, bases and acids.
Most commercial polypropylene has a level of crystallinity intermediate between that of low density polyethylene (LDPE) and high density polyethylene (HDPE); its Young's modulus is also intermediate. Although it is less tough than LDPE, it is much less brittle than HDPE. Polypropylene has very good resistance to fatigue, so that most plastic living hinges, such as those on flip-top bottles, are made from this material.
Polypropylene has a melting point of 320 degrees Fahrenheit (160 degrees Celsius). Food containers made from it will not melt in the dishwasher, and do not melt during industrial hot filling processes. For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminium foil (both heat-resistant materials). After the product has cooled, the tubs are often given lids of a cheaper (and less heat-resistant) material, such as LDPE or polystyrene. Such containers provide a good hands-on example of the difference in modulus, since the rubbery feeling of LDPE with respect to PP of the same thickness is readily apparent
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ABS - Acrylonitrile butadiene styrene
Monomers in ABS polymerAcrylonitrile butadiene styrene, or ABS, (chemical formula ) is a common thermoplastic used to make light, rigid, moulded products such as pipes, golf club heads (used for its good shock absorbance), enclosures and toys including LEGO Bricks. It is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15% to 35% acrylonitrile, 5% to 30% butadiene and 40% to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly(styrene-co-acrylonitrile). The nitrile groups from neighbouring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures. ABS can be used between -25oC and +60oC.
Production of 1 kg of ABS requires the equivalent of about 2 kg of oil for raw materials and energy.
Today, ABS is produced through a special process called grafting, rather than the copolymerization of acrylonitrile, styrene, and butadiene. In grafting, butadiene is polymerized first, then the cyanide and phenyl groups are added through a special chemical reaction. |
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PVC - Polyvinyl chloride
Vinyl siding Polyvinyl chloride (PVC) is a widely-used plastic. In terms of revenue generated, it is one of the most valuable products of the chemical industry. Globally, over 50% of PVC manufactured is used in construction. As a building material PVC is cheap, and easy to assemble. In recent years, PVC has been replacing traditional building materials such as wood, concrete and clay in many areas. Despite appearing to be an ideal building material, concerns have been raised about the environmental and human health costs of PVC.
Polyvinyl chloride is produced from its monomer, vinyl chloride (chemical formula CH2=CHCl). PVC is a hard plastic that is made softer and more flexible by the addition of plasticizers, the most widely used being phthalates.
There are many uses for PVC including vinyl siding, window profiles, gramophone records (hence the ones made of this material are sometimes called vinyl records) pipe/plumbing/conduit fixtures, bean bags; and, in its soft form, for clothing, upholstery (car seats), flooring, roofing membranes, electrical cables, etc.
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PET - Polyethylene terephthalate
Polyethylene terephthalate (aka. PET, PETE, PETP) is a thermoplastic resin of the polyester family that is used to make beverage, food and other liquid containers, synthetic fibers, as well as for some other thermoforming applications. It is also one of the most important raw materials used in man-made fibers. Depending on its processing and thermal history, it may exist both as an amorphous (transparent) and as a semi-crystalline (opaque and white) material. It can be synthesized by a transesterification reaction between ethylene glycol and dimethyl terephthalate. It is manufactured under trade names Arnite, Impet and Rynite, Hostaphan, Melinar and Mylar foils, and Dacron, Terylene and Trevira fibers.
The main virtue of PET is that it is fully recyclable. Unlike other plastics, its polymer chains can be recovered for additional use. PETE has a resin code of 1
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