Storage Bags

A Plastic bag is a bag made of thin, flexible, plastic sheet. Plastic bags are used for containing waste for disposal, and for storing and transporting non-waste. more...

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Composition

There are four main types of plastic bags in widespread use:

High density polyethylene (HDPE); Low density polyethylene (LDPE); degradable; compostable;

Polyethylene is an economical plastic so it is commonly used for disposable bags. Plastic bags can be made having various colours, including translucent or even transparent in some cases.

Bags made of HDPE (High Density Polyethylene) are typically translucent, but not fully transparent. Bags made out of LDPE (Low Density Polyethylene) can be quite clear, but are still usually not as totally transparent as other plastics.

HDPE and LDPE bags are manufactured from a waste product of the petroleum industry.

Shapes and sizes

Many plastic bags are shaped like two identically-sized rectangular plastic sheets fused together on three of the sides, with one side open. This type of shape allows for simple, economic manufacturing and compact storage of the bags before use. Sizes vary from a few centimeters on a side, for containing small items for sale such as buttons and small electronic components, to several meters on a side for large items.

Bags are also made with carrying handles, and in other shapes. Some bags have provision for resealable hermetic or non-hermetic closing; others are sealed, often by heating the open edge, once filled, and can only be opened by destroying the packaging.

The thickness of the material used for rubbish bags, for example, varies from about 0.02mm for a very light-duty bag to ??? (this paragraph on the thickness of the material used for plastic bags, is a stub which needs expanding)

Environmental issues

Plastic bags have advantages and disadvantages when compared to alternatives such as paper bags and cardboard boxes. The durability, strength, lesser energy requirements in manufacture and light weight are advantages of plastic bags. However, non-biodegradable bags fill landfill sites and make for long-lasting litter, which in particular is dangerous to wildlife away from centers of human population.

Many studies comparing plastic versus paper for shopping bags show that plastic bags have less net environmental effect than paper bags, requiring less energy to produce and recycle; however these studies also note that recycling rates for plastic are significantly lower than for paper. Paper is also made from a renewable resource (trees), whereas plastic is non-renewable (petroleum-based). Additives have been developed that allow plastic to degrade and biodegrade within a few months in landfill (as opposed to an estimated 500-1000 years for non-degradable plastic). Plastics made with these additives are called oxobiodegradable, and have been adopted by many 'ethical' retailers, e.g., the Co-op in the UK. However, some argue that oxo-biodegradable plastics contribute more to global warming as they release their carbon as carbon dioxide and methane far more quickly than plastics in landfill. In April 2002, the Marine Conservation Society reported that a dead Minke whale that had washed up on the coast of Normandy was found to have had 800 kg of plastic bags and packaging (including two U.K supermarket bags) inside its stomach.

Read more at Wikipedia.org