Published on Jan 10, 2016
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.
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.
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.
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.
By polymerisation of methyl methacrylate in presence of hydrogen peroxide.
It is a fairly rigid material with high softening point of about 130 - 140 degree Celsius .
It has high optical –transparency, high resistance to sunlight and ability of transmitting light accurately even in curved sections .
Low chemical resistance.
Low scratch resistance.
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).
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.
It is obtained by polymerization of tetrafluoro ethylene, under pressure in presence of catalyst like benzoyl peroxide.
The polymerisation is associated with release of large quantities of heat and if sufficient precautions are not taken this can result in violent explosions.