Definition :

Plastic is an organic material with the ability to flow into a desired shape when heat and pressure are applied to it and to retain the shape when they are withdrawn.

Plastic is the general term for a wide range of synthetic or semisynthetic polymerization products. They are composed of organic condensation or addition polymers and may contain other substances to improve performance or economics. There are few natural polymers generally considered to be "plastics". Plastics can be formed into objects or films or fibers. Their name is derived from the fact that many are malleable, having the property of plasticity.

Plastic can be classified in many ways, but most commonly by their polymer backbone (polyvinyl chloride, polyethylene, polymethyl methacrylate and other acrylics, silicones, polyurethanes, etc.). Other classifications include thermoplastic, thermoset, elastomer, engineering plastic, addition or condensation or polyaddition (depending on polymerization method used), and glass transition temperature or Tg.

Some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures above which the extent of localized molecular is substantially increased). So-called semi-crystalline plastics include polyethylene, polypropylene, poly(vinyl chloride), polyamides (nylons), polyesters and some polyurethanes. Many plastics are completely amorphous, such as polystyrene and its copolymers, poly(methyl methacrylate), and all thermosets.

People experimented with plastics based on natural polymers for centuries. In the nineteenth century a plastic material based on chemically modified natural polymers was discovered: Charles Goodyear discovered vulcanization of rubber (1839) and Alexander Parkes, English inventor (1813—1890) created the earliest form of plastic in 1855. He mixed pyroxylin, a partially nitrated form of cellulose (cellulose is the major component of plant cell walls), with alcohol and camphor. This produced a hard but flexible transparent material, which he called "Parkesine." The first plastic based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented by Leo Hendrik Baekeland in 1909, the product being known as Bakelite. Subsequently poly(vinyl chloride), polystyrene, polyethylene (polyethene), polypropylene (polypropene), polyamides (nylons), polyesters, acrylics, silicones, polyurethanes were amongst the many varieties of plastics developed and have great commercial success.

The development of plastics has come from the use of natural materials (e.g., chewing gum, shellac) to the use of chemically modified natural materials (e.g., natural rubber, nitrocellulose, collagen) and finally to completely synthetic molecules (e.g., epoxy, polyvinyl chloride, polyethylene).

In 1959, Koppers Company in Pittsburgh, PA had a team that developed the expandable polystyrene foam cup. On this team was Edward J. Stoves who made the first commercial foam cup. The experimental cups were made of puffed rice glued together to form a cup to show how it would feel and look. The chemistry was then developed to make the cups commercial. Today, the cup is used throughout the world in countries desiring fast food, namely, the United States, Japan, Australia,and New Zealand. Freon was never used in the cups. As Stoves said, "We didn't know freon was bad for the ozone, but we knew it was not good for people so the cup never used freon to expand the beads."

The foam cup can be buried, and it is totally stable such as is concrete and brick. No plastic film is required to protect the air and underground water. If it is burned with sufficient oxygen, the only chemicals generated are water and carbon dioxide. Burning a ton of cups results in less than 600 grams of ash. It can be recycled to make park benches, flower pots and toys.

Biodegradable plastics :

Research has been done on biodegradable plastics that break down with exposure to sunlight (e.g. ultra-violet radiation), water (or humidity), bacteria, enzymes, wind abrasion and some instances rodent pest or insect attack are also included as forms of biodegradation or environmental degradation. It is clear some of these modes of degradation will only work if the plastic is exposed at the surface, while other modes will only be effective if certain conditions are found in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically engineered bacteria that synthesize a completely biodegradable plastic, but this material is expensive at present e.g. BP's Biopol. BASF make Ecoflex, a fully biodegradable polyester for food packaging applications. A potential disadvantage of biodegradable plastics is that the carbon that is locked up in them is released into the atmosphere as a greenhouse gas carbon dioxide when they degrade, though if they are made from natural materials, such a vegetable crop derivatives or animal products, there is no net gain in carbon dioxide emissions, although concern will be for a worse greenhouse gas, methane release.

So far, these plastics have proven too costly and limited for general use, and critics have pointed out that the only real problem they address is roadside litter, which is regarded as a secondary issue. When such plastic materials are dumped into landfills, they can become "mummified" and persist for decades even if they are supposed to be biodegradable.

Different Use of Plastic :

• Wide range of inexpensive uses including supermarket bags, plastic bottles.
  
• Food containers, appliances, car fenders (bumpers).
  
• Packaging foam, food containers, disposable cups, plates, cutlery, CD and cassette boxes.
  
• fridge liners, food packaging, vending cups.
  
• Electronic equipment cases (e.g., computer monitors, printers, keyboards).
  
• carbonated drinks bottles, jars, plastic film, microwavable packaging.
  
• Fibers, textiles.
  
• Fibers, toothbrush bristles, fishing line, under-the-hood car engine mouldings.
  
• Plumbing pipes and guttering, shower curtains, window frames,flooring, erotic clothing.
  
• cushioning foams, thermal insulation foams, surface coatings, printing rollers. (Currently 6th or 7th most commonly used plastic material, for instance the most commonly used plastic found in cars).
  
• Compact discs, eyeglasses, riot shields, security windows, traffic lights, lenses.
  
• Food packaging.
  
• A blend of PC and ABS that creates a stronger plastic. :Car Interior and exterior parts.
  
• contact lenses, glazing (best known in this form by its various trade names around the world, eg, Perspex, Oroglas, Plexiglas, fluorescent light diffusers, rear light covers for vehicles.
  
• Heat-resistant, low-friction coatings, used in things like non-stick surfaces for frying pans, plumber's tape and water slides.
  
• Strong, chemical- and heat-resistant thermoplastic, biocompatibility allows for use in medical implant applications, aerospace mouldings. One of the most expensive commercial polymers.
  
• High modulus, relatively heat resistant, and excellent fire resistant polymer. Used for insulating parts in electrical fixtures, paper laminated products (e.g. "Formica"), thermally insulation foams. It is a thermosetting plastic, with the familiar trade name Bakelite, that can be moulded by heat and pressure when mixed with a filler-like wood flour or can be cast in its unfilled liquid form or cast as foam, e.g. "Oasis". Problems include the probability of mouldings naturally being dark colours (red, green, brown), and as thermoset difficult to recycle.