Plastic bag
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A Plastic bag is a bag flexible packaging made of thin, flexible, blown poly film. Plastic bags are used for containing waste for packaging, disposal, and for storing and transporting foods, produce, powders, ice, chemicals, etc.
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[edit] Composition
There are 4 main types of poly bags in widespread use:
- High density polyethylene (HDPE)
- Low density polyethylene (LDPE)
- Oriented Polypropylene (OPP)
- Complex structure (two or more plastics bonded together for better mechanical or barrier properties as Nylon and LDPE for vacuum packaging for example)
Polyethylene is an economical and versatile plastic so it is commonly used for disposable and general use bags. Poly bags are made melting the resin in a blown machine. Plastic bags were first introduced in 1977 and now account for four out of every five bags handed out at grocery stores. <references/http://www.epa.gov/region1/communities/shopbags.html>
Bags made of HDPE (High Density Polyethylene) range from 0.941 to 0.965 g/cm3 density, typically haze, typical application in supermarket and grocery stores, due to his strength even in low thickness, compared to other films. Bags made out of LDPE (Low Density Polyethylene) range from 0.910 to 0.925 g/cm3 density, can be clearer than HDPE and are used worldwide in general applications, usually for its cheap and versatile advantages, from sugar, grains, bread to ice, oranges, apples and carrot bags.
HDPE and LDPE bags are manufactured from resin pellets, from ethylene gas, a by-product of the oil industry.
OPP bags are made from Polypropylene film, usually are preferred when you look for transparency, bright, water vapour barrier and gift-look and sound, as in candies, confectionery, pasta and flour products, imported wine packaging, recordable media, etc. When a usually white OPP film is woven, the bag is a woven sack.
[edit] Shapes and sizes
Many plastic bags are shaped like two identically-sized rectangular plastic sheets welded or folded together on 1, 2 or 3 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, to several meters on a side, depending the need. Typical properties manufacturers look for when determine the bag material are impact strength, flexibility, low or high temperature properties, cristallinity, resistance to environmental stress cracking, lower melting points and wide processing ranges.
Bags are also made with carrying handles, hanging holes, tape attachments, security features, paper and other laminations, heavy sacks, pouch and standup pouch and 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 or gauge of the film is expressed in Mil - A unit of measurement in thousandths of an inch, (i.e., .001 = one thousandth of an inch or 1.0 mil), generally used to designate the thickness of LDPE products; or Mic - Short for micron, one thousandth of a millimeter, generally used to designate the thickness of HDPE products.
[edit] Environmental issues
Plastic bags have advantages and disadvantages when compared to alternatives such as paper bags and cardboard boxes. The durability, strength, low cost, water and chemicals resistance, welding properties, lesser energy and heavy chemicals requirements in manufacture, fewer atmosphere emissions and light weight are advantages of plastic bags. Plastic polymers including poly bags, bottles, foam cups, pipes, toys, TV and PC cases and more, account for about 20 percent (by volume) of landfill space. 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, due mostly to virgin resin cheap price when compared to other flexible packagings and this low price tend to be under-enthusiastic to recyclers. As the global climate crisis deepens consumers are starting to take responsibility for their actions and to use resusable cloth bags and other bags like backpacks etc in place of the proverbial one time use plastic shopping bag.
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, transport and recycle; however these studies also note that recycling rates for plastic are significantly lower than for paper[citation needed]. 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. In the other hand, bags are made from Polylactic acid (PLA) a biodegradable polymer derived from lactic acid. It is a highly versatile material and is made from 100% renewable resources like corn, sugar beets, wheat and other starch-rich products. [1] Polylactic acid exhibits many properties that are equivalent to or better than many petroleum-based plastics, which makes it suitable for a variety of applications, emits fewer greenhouse gases, and contains no toxins.
Each year, an estimated 500 billion to 1 trillion plastic bags are consumed worldwide. The United States Environmental Protection Agency (EPA) estimates that U.S. consumers throw away 100 billion plastic bags a year.[2]
Up-to-date international news regarding regional and country-wide bans of plastic bags can be found here:[3].
[edit] Reduction
At present the most widely implemented solution to these problems is to reduce the use of plastic bags. Plastic bags were outlawed in South Africa in 2003, they are banned in Bangladesh (where they were blamed for causing flooding during monsoons by clogging drains) and Taiwan. [4] A plastic bag tax was introduced in Ireland in 2002, after which plastic bag usage decreased by almost 90%. [5] The government levy on plastic bags was €0.15 as of 2006. Many retailers in Ireland switched to supplying (untaxed) paper bags, or simply stopped supplying bags. Most supermarkets continued to supply plastic bags, subject to the tax.
Plastic bags are banned in at least 30 villages and towns in Alaska, including the towns of Emmonak, Galena, and Kotlik. And a ban on the plastic sacks goes into effect towards the end of 2007 in Paris; they are outlawed in all of France starting Jan. 1, 2010. [6] As of March 28, 2007, the city of San Francisco in the US has decided to implement a ban on plastic bags in supermarkets and chain pharmacies. [7] Starting July 2007, all large supermarkets in the state of California will be required, by law, to takeback and recycle plastic shopping bags. [8]
Ikea, the home furnishings retailer, imposes its own tax on plastic bags in the US — charging a nickel to any customer who wants a plastic sack. [9] A similar charge has been in place since spring 2006 at Ikea stores in the UK, and the company says it has reduced use of bags in UK stores by 95 percent.[10] Ikea hopes the 5-cent fee in the U.S. cuts bag use in half, from 70 million bags a year to 35 million.
[edit] Biodegradability and recycling
Recycling of plastics after final use is possible, but plastic bags, in particular, are rarely recycled. According to the UK-based Ban the Bag campaigning group, 0.5% of plastic bags are recycled [11].
Standard plastic bags may take between 500 and 1000 years to decompose [12]. However, such figures are only ever estimates because plastics have not existed for long enough for the precise decomposition time to be measured [13].
According to the UK government department DEFRA, there are several problems with recycling plastics, and in particular plastic bags: [14]
- the high volume to weight ratio of plastic means that the collection and transport of this waste is difficult and expensive
- there are often high levels of contamination in plastic making the recyclate less usable, especially where food products are involved
- there is a very wide range of plastics in use and segregation is difficult
- the market for using recycled plastic is underdeveloped
When one ton of paper bags is reused or recycled, three cubic meters of landfill space is saved (the area needed for 13-17 trees). In 1997, 955,000 tons of paper bags were used in the United States.
When one ton of plastic bags is reused or recycled, the energy equivalent of 11 barrels of oil are saved.[15]
[edit] Oxo-biodegradable plastic bags
Oxo-biodegradable and other degradable plastic bags have certain useful applications when used as rubbish bags. Organic waste can be put into oxo-biodegradable plastic sacks and put straight into the composting plant, unopened, thus reducing smells, disease transmission by insects, and handling hazards. The resulting compost may be used by farmers and growers. Since oxo-biodegradable plastic (unlike the starch-based alternative) releases its carbon slowly, it produces high quality compost. Oxo-biodegradable plastic does not degrade quickly in low temperature "windrow" composting, but it is suitable for "in-vessel" composting at the higher temperatures required by new animal by-products regulations. Oxo-biodegradable plastics become peroxidised and embrittled, and behave like natural waste. It is bio-assimilated by the same bacteria and fungi, which transform the degraded plastic products to cell biomass, like lignocellulosic materials. Oxo-biodegradable plastic is designed to fragment by a process which includes both photo-oxidation and thermo-oxidation, so it can degrade in the dark.
[edit] Bag types
[edit] Shopping bags
Open bags with carrying handles are used in large numbers worldwide. A common size for general shopping is about 35 x 40cm, but sizes range from a bag to hold a couple of greeting cards, to bags which can hold large appliances. Bags are often supplied without charge by retail outlets, and usually printed with the store's identity, to serve as mobile advertising. Shopping bags may be reused for their original purpose, although there is little incentive to do so as new ones are usually supplied without charge. Used shopping bags are used for a multitude of other purposes, from reuse as rubbish bags, to manufacture of craft items, but ultimately the overwhelming majority are discarded. Taxes on bags are being introduced and discussed in several countries; once there is a cost, albeit small, associated with bags, the number used drops drastically.
[edit] Point-of-sale packaging
Many products are packaged for sale in plastic bags which are usually sealed in some way. This packaging is usually discarded without any reuse or recycling because of shipping costs.
[edit] Rubbish bags
Plastic bags are a convenient and sanitary way of handling rubbish, and are widely used. Plastic rubbish bags are fairly lightweight and are particularly useful for messy or wet rubbish, as is commonly the case with food waste, and are also useful for wrapping up rubbish to minimize odor. Plastic bags are often used for lining litter or waste containers or bins. This serves to keep the container sanitary by avoiding container contact with the rubbish. After the bag in the container is filled with litter, the bag can be pulled out by its edges, closed, and tied with minimal contact with the waste matter.
Plastic bags for rubbish or litter are sold in a number of sizes at many other stores in packets or rolls of a few tens of bags. Wire twist ties are sometimes supplied for closing the bag once full. In the mid-1990s rubbish bags with draw strings for closure were introduced. Some bags have handles which may be tied, or holes through which the neck of the bag can be pulled. Most commonly, the rather soft, flexible plastic used to make rubbish bags is LDPE (Low Density Polyethylene) or, for strength, LLDPE (Linear Low Density Polyethylene). HDPE (High Density Polyethylene) is sometimes used.
Rubbish bags are supplied in a range of sizes, from wastebasket size to lawn and leaf bags for garden waste. Some localities require the use of biodegradable plastic bags or large paper bags for disposal of garden waste.
[edit] See also
- Box wine
- Bag-In-Box
- Bigbag
