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Polymer

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POLYCARBONATE

Polycarbonate is one of the most widely used engineering thermoplastic. It is commonly formed with the reaction of Bisphenol A with carbonyl chloride in an interfacial process. They are named so because they are polymers containing carbonate groups.

Brand names of Polycarbonate: PANLITE produced by Teijin Chemical Limited, MAKROLON manufactured by Bayer and LEXAN by SABIC.

Generic abbreviation: PC

Polymer description: PC stands for Polycarbonate

Polycarbonates are strong, stiff, hard, tough, and transparent and can maintain rigidity up to 140 C and toughness down to -20 C. They have excellent mechanical properties, high dimensional stability and thermal resistance up to 135 C. It is a light weight, high performance plastic that can be easily moulded and dyed in various colors. Outstanding properties include impact strength and scratch resistance.

Polycarbonate is commercially available in both pellet and sheet form.

The processing methods of Polycarbonate include Injection moulding, Structural Foam moulding, Extrusion, Vacuum Forming and Blow moulding.

Polycarbonate is used in making mobile phones, connectors, electrical household appliances, dash boards, automotive lighting, power tools, baby bottles, water dispensers, garden equipment, sporting goods and in medical applications. Despite being an ideal material for food and beverage containers, studies have found out that, Bisphenol A can leach in trace amounts from such polycarbonate containers and mix with food and beverages. Bisphenol A disrupts the hormone estrogen and affects the reproductive system raising the risk of cancer.

Polycarbonate containers should not be put in the microwave as when they get heated, the plastic may eventually break down over time.

Even though toxic chemicals are used in the production of Polycarbonate, it is recyclable. One such method comprises subjecting a polycarbonate waste component to either one or both of a trans-esterification reaction and a poly-condensation reaction. Another method comprises introducing a dihydroxy compound and a carbonate diester to a mixing tank and then directing the mixed composition for prepolymerization. This process is followed by melting the polycarbonate waste component and mixing it with the prepolymerized composition and finally extruding the polycarbonate product.

POLYETHYLENE

Polyethylene is a member of a huge family of polyolefin resins obtained by the polymerization of ethylene gas. It is the most popular commercial polymer. A molecule of polyethylene is made of a long chain of carbon atoms with two hydrogen atoms attached to each carbon atom. Polyethylene is further categorized into branched or low density polyethylene  (LDPE) where the chain of carbon atoms has chains of polyethylene  attached, linear or high density polyethylene  (HDPE) where there is no branching,  medium density polyethylene (MDPE) and linear low density polyethylene (LLDPE) which has a significant number of short branches.

Brand names of Polyethylene are: Titanex linear low – density Polyethylene and Titanlene low density polyethylene produced by Toling Corporation (M) Sdn. Bhd, GUR ultra-high molecular polyethylene produced by Ticona, Hostalen HMW developed by Ticona / Celanese and DOWLEX Polyethylene resins by DOW chemical company.

Generic abbreviation: PE

Polymer description:  PE stands for Polyethylene.

Polyethylene is a thermoplastic available in a range of flexibilities, and it has interesting engineering characteristics. Polyethylene has a crystalline structure which does not dissolve at room temperature. LDPE is semi-rigid, translucent, very tough, and weatherproof.  It has good chemical resistance and low water absorption. HDPE is flexible, translucent, weatherproof, and low cost and has good chemical resistance. Both LDPE and HDPE are easily processed by most methods.

Polyethylene can be processed by a variety of fabrication techniques like film/sheet extrusion, injection molding, blow molding, pipe extrusion and profile extrusion.

Polyethylene is used to make grocery bags, shampoo bottles, children’s toys, bullet proof vests, gas pipe pressure fittings and several other industrial applications.

Depending on the compounds it is bonded with, PE’s level of toxicity and flammability varies. Polyethylene glycol (PEG), which is found in products such as shampoo and toothpaste, can cause allergic reactions like nausea, flatulence, rashes and diarrhea in certain individuals. Harmful chemicals such as Phthalate may leach from Polyethylene-terephthalate (PET) which is widely used in a plastic bottle industry. This may cause hormonal imbalances and allergies. 

When Polyethylene is disposed and made to sit in a landfill for many years, it becomes an environmental concern as it does not biodegrade easily. However, by recycling, PE scraps can be melted down and reused. An anaerobic bacterium called Sphingomonas can be used to reduce the amount of time to break PE.

POLYIMIDE

Polyimide is available both as thermoplastic and thermoset resins. Aromatic polyimides are formed by the polycondensation of  dianhydrides such as pyromellitic anhydride with diamines. Polyimides are the most heat and fire resistant polymers known. They are incredibly strong and have astounding chemical properties. Their strength combined with heat and chemical resistance makes these materials replace glass and steel in several industrial applications.

Brand names of Polyimide: Cirlex and Kapton polyimide films manufactured by DuPont, Aurum polyimide resin manufactured by Mitsui Toatsu and VTEC Polyimide made by RBI,Inc.

Generic abbreviation: PI

Polymer description: PI stands for Polyimide

Physical properties of Polyimide include low dielectric constant, flexibility, high temperature stability, excellent machinability and mechanical strength, good dimensional and thermal stability. Typical polyimide parts are not affected by commonly used solvents and oils including hydrocarbons, esters, alcohols and freons.

Thermosetting polyimides are commercially available in many uncured forms that include stock shapes, thin sheets, laminates and machined parts.

Polyimide parts are fabricated by techniques ranging from powder-metallurgy methods to conventional injection, transfer and compression molding and extrusion.

Polyimides are used in the electronics industry for making flexible wires and cables, printed circuit boards, insulating films, bearings and various medical and industrial applications. Polyimides have poor resistance to alkalies and hydrolysis. They may undergo hydrolysis and crack in water or steam at temperatures above 100 C. It can be easily attacked by concentrated acids.

The ways of recycling polyimides are incineration, mechanical recycling techniques based on granulation and comminution, Solvolysis and chemical recycling process.

SYNTHETIC RUBBER

Synthetic rubber or man-made rubber is a compound of rubber produced by the polymerization of hydrocarbons or co-polymerization of Styrene and 1,3- Butadiene. The popular varieties of Synthetic rubber include Styrene Butadiene Rubber (SBR) and Isoprene Rubber (IR).

Brand names of Synthetic Rubber: Stereon by Firestone, Neoprene by Dupont, Viton Syntheric rubber by DuPont.

Full technical name: Synthetic Rubber

Synthetic rubbers are marketed as compressed bales and square blocks. They are also produced in the form of powder rubber, talcum-coated chips, and granules and as latex concentrates in liquid form.

Processing of rubber into finished goods include the following steps: Compounding, Mixing, Shaping which is subdivided into Extrusion, Calendering, Coating, Molding, Casting and Vulcanizing.

The properties of synthetic rubber include elasticity, water repellence, electrical, heat, and chemical and abrasion resistance.

Synthetic rubber has a wide range of applications such as in the tire industry (car, aircraft and bicycle tires), drive belts, hoses, medical equipments, conveyor belts and molded parts.

Synthetic rubber withstands temperatures of up to 30 C. When this temperature is exceeded, cold flow starts as a result of which the rubber begins to flow and ruptures the wrapping. Excessive temperatures result in rubber softening, artificial aging combined with hardening.

Rubber recovery is a difficult process. However, recovered rubber has better properties than natural rubber. Tire recycling process has been implemented in many countries.

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