18-03-2014, 10:57 AM
COMMON SYNTHETIC PLASTICS
[attachment=60157]
INRODUCTION
Plastic molecules are made of long chains of repeating units called monomers. The atoms that make up a plastic’s monomers and the arrangement of the monomers within the molecule both determine many of the plastic’s properties.
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.
History
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.
POLYSTYRENE
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
POLYTETRAFLUOROETHYLENE (PTFE)
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
[attachment=60157]
INRODUCTION
Plastic molecules are made of long chains of repeating units called monomers. The atoms that make up a plastic’s monomers and the arrangement of the monomers within the molecule both determine many of the plastic’s properties.
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.
History
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.
POLYSTYRENE
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
POLYTETRAFLUOROETHYLENE (PTFE)
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