Common Synthetic Plastics full report
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COMMON SYNTHETIC PLASTICS
Plastic molecules are made of long chains of repeating units called monomers. The atoms that make up a plasticâ„¢s monomers and the arrangement of the monomers within the molecule both determine many of the plasticâ„¢s properties. Plastics are one of the classification of polymers .If a polymer is shaped into hard and tough utility articles by the application of heat and pressure ,it is used as plastic.
Synthetic polymers are often referred to as "plastics", such as the well-known polyethylene and nylon. However, most of them can be classified in at least three main categories: thermoplastics, thermosets and elastomers.
Man-made polymers are used in a bewildering array of applications: food packaging, films, fibers, tubing, pipes, etc. The personal care industry also uses polymers to aid in texture of products, binding etc.
A non-exhaustive list of these ubiquitous materials includes:
acrylonitrile butadiene styrene (ABS)
poly(butylene terephthalate) (PBT)
poly(ether sulphone) (PES, PES/PEES)
poly(ethylene glycol) (PEG)
poly(ethylene terephthalate) (PET)
polypropylene (PP )
styrene acrylonitrile (SAN)
SOME COMMONLY USED SYNTHETIC PLASTICS
After the First World War, improvements in chemical technology led to an explosion in new forms of plastics. Among the earliest examples in the wave of new plastics were "polystyrene" (PS) and "polyvinyl chloride" (PVC), developed by the I.G. Farben company of Germany.
POLYVINYL CHLORIDE (PVC
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, PVC has high environmental and human health costs.
PVC has side chains incorporating chlorine atoms, which form strong bonds. PVC in its normal form is stiff, strong, heat and weather resistant, and is now used for making plumbing, gutters, house siding, enclosures for computers and other electronics gear, and compact-disk media. PVC can also be softened with chemical processing, and in this form it is now used for food packaging, and raingear.
Polyvinyl chloride was accidentally discovered on at least two occasions in the 19th century, first in 1838 by Henri Victor Regnault and in 1872 by Eugen Baumann. On both occasions, the polymer appeared as a white solid inside flasks of vinyl chloride that had been left exposed to sunlight. In the early 20th century, the Russian chemist Ivan Ostromislensky and Fritz Klatte of the German chemical company Griesheim-Elektron both attempted to use PVC in commercial products, but difficulties in processing the rigid, sometimes brittle polymer blocked their efforts.
In 1926, Waldo Semon of B.F. Goodrich developed a method to plasticize PVC by blending it with various additives. The result was a more flexible and more easily processed material that soon achieved widespread commercial use.
Dangers of PVC
Most vinyl products are believed to be generally harmless when used properly. However, some of the additives and softeners leach out of certain vinyl products. Even though soft PVC toys have been made for babies for years, studies find that these additives leach out of soft toys into the mouths of the children chewing on them.. In Europe, phthalate additives in PVC toys for children under the age of three have been banned and in the USA, most companies have voluntarily stopped manufacturing PVC toys for this age group or have eliminated the phthalates. However, alternative softeners have not been properly tested to determine whether they are safe. Other vinyl products like brand new car interiors, shower curtains, and flooring, to name a few, initially release chemical gases into the air. Some studies indicate that this outgassing of additives may contribute to health complications, but the information on this is preliminary and needs further study.
PREPARATION OF PVC
It is obtained by heating a water â€œemulsion of vinyl chloride in presence of small amount hydrogen peroxide under pressure.
H H H H H H
\\ / | | | |
C == C ----------------- - - -> -- C -- C -- C -- C --
/ \\ | | | |
H Cl H Cl H Cl
vinyl chloride monomer polyvinyl chloride polymer
ÃƒËœ Most widely used synthetic plastic
ÃƒËœ Chemically inert
ÃƒËœResistant to light,atmospheric oxygen
ÃƒËœ It has greater stiffness compared to polyethylene , but is brittle
1.Rigid PVC or unplasticized PVC
It is used for making
ÃƒÂ¼ Light fittings
ÃƒÂ¼ Safety helmets
ÃƒÂ¼ Cycle and motorcycle mudguards
2. Plasticized PVC
It is used for
ÃƒÂ¼ Packing rain coats ,tablecloths, curtains etc
ÃƒÂ¼ Injection moulding of toys, tool handles, radio components etc
ÃƒÂ¼Making chemical containers, conveyor belts etc
Polystyrene is a rigid, brittle plastic that is now used to make plastic model kits, disposable eating utensils, and similar knicknacks.It is a Thermoplastic; transparent; nontoxic substance having optical and electrical properties; easy to color; resistant to X rays, oils, and grease
v By polymerization of styrene in presence of catalyst like benzoyl peroxide.
ÃƒËœ Optical and electrical properties;
ÃƒËœ Easy to color;
ÃƒËœ Resistant to X rays, oils, and grease
ÃƒËœ Excellent moisture resistant
ÃƒÂ¼ Plastic wrap,
ÃƒÂ¼ Kitchen utensils
ÃƒÂ¼ Furniture covers
ÃƒÂ¼ Toys, office supplies, disposable razors
POLYMETHYL METHACRYLATE (PMMA)
It is also called lucite or plexiglass.It is a rigid and hard material .It has out standing shape- forming properties.It is amorphous by nature..
Optical clarity is the main feature of this material.Hence it is an excellent substitute for glass.It can be thermally depolymerised to yield back entire quantity of monomer..
v by polymerisation of methyl methacrylate in presence of hydrogen peroxide
ÃƒËœIt is a fairly rigid material with high softening point of about 130 - 140 degree Celsius
ÃƒËœ It has high optical â€œtransparency, high resistance to sunlight and ability of transmitting light accurately even in curved sections .
ÃƒËœ Low chemical resistance..
ÃƒËœ Low scratch resistance.
It is used for making
ÃƒÂ¼ Aircraft light fixtures
ÃƒÂ¼ Artificial eyes
ÃƒÂ¼ Wind screens
Another important plastic, "polyethylene" (PE), sometimes known as "polythene", was discovered in 1933 by the Reginald Gibson and Eric Fawcett at the British industrial giant Imperial Chemical Industries (ICI). This material evolved into two forms, "low density polyethylene" (LDPE), and "high density polyethylene" (HDPE).
vBy polymerization of ethylene as shown below
H H H H H
\\ / | | |
C == C ------------- -> -- C -- C -- C --
/ \\ | | |
H H H H H
ethylene monomer polyethylene polymer
ÃƒËœWaxy and white
ÃƒËœ It is a good insulator of electricity
ÃƒÂ¼ Making high frequency insulator parts
ÃƒÂ¼ Making bottle caps
ÃƒÂ¼ Toys, sheets for packing etc
ÃƒÂ¼ LDPE is used to make films and packaging materials, while HDPE is used for containers, plumbing, and automotive fittings.
ÃƒÂ¼ Whenever high tensile strength and stiffness are required, high density polyethylene finds better use..
PTFE also known as TEFLON in trade may be visualised as polyethylene with all its hydrogen atoms substituted by fluorine. PTFE molecule has a highly regular structure .It is also a linear polymer with practically no branches .. Chemically inert, antiadhesive, impermeable to water and grease, heat and corrosion resistant
vIt is obtained by polymerization of tetrafluoro ethylene, under pressure
in presence of catalyst like benzoyl peroxide.
v The polymerisation is associated with release of large quantities of heat and if
sufficient precautions are not taken this can result in violent explosions ..
1. Processes and Materials of Manufacture by R.A. LINDBERG
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