Plastic shopping bag
Plastic shopping bags, carrier bags, or plastic grocery bags are a type of plastic bag used as shopping bags and made from various kinds of plastic. In use by consumers worldwide since the 1960s, these bags are sometimes called single-use bags, referring to carrying items from a store to a home. However, reuse for storage or trash is common, and modern plastic shopping bags are increasingly recyclable or biodegradable. In recent decades, numerous countries have introduced legislation restricting the sale of plastic bags, in a bid to reduce littering and plastic pollution.
American and European patent applications relating to the production of plastic shopping bags can be found dating back to the early 1950's, but these refer to composite constructions with handles fixed to the bag in a secondary manufacturing process. The modern lightweight shopping bag is the invention of Swedish engineer Sten Gustaf Thulin. In the early 1960s, Thulin developed a method of forming a simple one-piece bag by folding, welding and die-cutting a flat tube of plastic for the packaging company Celloplast of Norrköping, Sweden. Thulin's design produced a simple, strong bag with a high load-carrying capacity, and was patented worldwide by Celloplast in 1965.
Celloplast was a well-established producer of cellulose film and a pioneer in plastics processing. The company's patent position gave it a virtual monopoly on plastic shopping bag production, and the company set up manufacturing plants across Europe and in the US. However, other companies saw the attraction of the bag, too, and the US petrochemicals group Mobil overturned Celloplast's US patent in 1977.
The Dixie Bag Company of College Park, Georgia, owned and operated by Jack W. McBride, was one of the first companies to exploit this new opportunity to bring convenient products to all major shopping stores. The Dixie Bag Company, along with similar firms such as Houston Poly Bag and Capitol Poly, was instrumental in the manufacturing, marketing and perfecting of plastic bags in the 1980s. Kroger, a Cincinnati-based grocery chain, began to replace its paper shopping bags with plastic bags in 1982, and was soon followed by its rival, Safeway.
Without its plastic bag monopoly, Celloplast's business went into decline, and the company was split up during the 1990s. The Norrköping site remains a plastics production site, however, and is now the headquarters of Miljösäck, a manufacturer of waste sacks manufactured from recycled polyethylene.
From the mid-1980s onwards, plastic bags became common for carrying daily groceries from the store to vehicles and homes throughout the developed world. As plastic bags increasingly replaced paper bags, and as other plastic materials and products replaced glass, metal, stone, timber and other materials, a packaging materials war erupted, with plastic shopping bags at the center of highly publicized disputes.
In 1992, Sonoco Products Company of Hartsville, SC patented the "self-opening polyethylene bag stack". The main innovation of this redesign is that the removal of a bag from the rack opens the next bag in the stack. This team was headed by Wade D Fletcher and Harry Wilfong.
Although few peer-reviewed studies or government surveys have provided estimates for global plastic bag use, environmental activists estimate that between 500 billion and 1 trillion plastic bags are used each year worldwide. In 2009, the United States International Trade Commission reported that 102 billion plastic bags are used annually in the United States alone.
Manufacture and composition
Traditional plastic bags are usually made from polyethylene, which consists of long chains of ethylene monomers. Ethylene is derived from natural gas and petroleum. The polyethylene used in most plastic shopping bags is either low-density (resin identification code 4) or, more often, high-density (resin identification code 2). Color concentrates and other additives are often used to add tint to the plastic. Plastic shopping bags are commonly manufactured by blown film extrusion.
Some modern bags are made of vegetable-based bioplastics, which can decay organically and prevent a build-up of toxic plastic bags in landfills and the natural environment. Bags can also be made from degradable polyethylene film or from polylactic acid (PLA), a biodegradable polymer derived from lactic acid. However, most degradable bags do not readily decompose in a sealed landfill, and represent a possible contaminant to plastic recycling operations. In general, biodegradable plastic bags need to be kept separate from conventional plastic recycling systems.
Biodegradable plastic carrier bags and manufacture
Biodegradable plastics are plastics that are decomposed by the action of living organisms, usually bacteria. Two basic classes of biodegradable plastics exist: Bioplastics, whose components are derived from renewable raw materials, and plastics made from petrochemicals containing biodegradable additives which enhance biodegradation.
Because plastic bags are so durable, this makes them a concern for the environment. They will not break down easily and as a result may be harmful to wildlife. Each year millions of discarded plastic shopping bags end up as plastic waste litter in the environment when improperly disposed of. The same properties that have made plastic bags so commercially successful and ubiquitous—namely their low weight and resistance to degradation—have also contributed to their proliferation in the environment. Due to their durability, plastic bags can take centuries to decompose.
On land, plastic bags are one of the most prevalent types of litter in inhabited areas. Large buildups of plastic bags can clog drainage systems and contribute to flooding, as occurred in Bangladesh in 1988 and 1998 and almost annually in Manila. Littering is often a serious problem in developing countries, where trash collection infrastructure is less developed than in wealthier nations.
Plastic bags were found to constitute a significant portion of the floating marine debris in the waters around southern Chile in a study conducted between 2002 and 2005. If washed out to sea, plastic bags can be carried long distances by ocean currents, and can strangle marine animals.
Reduction, reuse and recycling
Plastic shopping bags are in most cases not accepted by standard curbside recycling programs; though their composition is often identical to other accepted plastics, they pose problems for the single-stream recycling process, as most of the sorting equipment is designed for rigid plastics such as bottles, so plastic bags often end up clogging wheels or belts, or being confused as paper and contaminating the pulp produced later in the stream.
Heavy-duty plastic shopping bags are suitable for reuse as reusable shopping bags. Lighter weight bags are often reused as trash bags or to pick up pet feces. All types of plastic shopping bag can be recycled into new bags where effective collection schemes exist.
By the mid-1900s, the expansion of recycling infrastructure in the United States yielded a 7% annual rate of plastic bag recycling. This corresponded to more than 800,000,000 pounds (360,000 tonnes) of bags and plastic film being recycled in 2007 alone. Each ton of recycled plastic bags saves the energy equivalent of 11 barrels of oil, although most bags are produced from natural-gas-derived stock. In light of a 2002 Australian study showing that more than 60% of bags are reused as bin liners and for other purposes, the 7% recycling rate accounts for 17.5% of the plastic bags available for recycling.
According to the UK's Environment Agency, 76% of British carrier bags are reused. A survey by the American Plastics Counsel found that 90% of Americans answer yes to the question "Do you or does anyone in your household ever reuse plastic shopping bags?" UK Environment Agency published a review of supermarket carrier bags and compares energy usage of current styles of bag.
Several countries, regions, and cities have enacted legislation to ban or severely reduce the use of disposable plastic shopping bags. Outright bans have been introduced in some countries, notably China, which banned very thin plastic bags nationwide in 2008. Several other countries impose a tax at the point of sale.
- Photodegradation, the process through which chemicals decompose when exposed to light
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|Wikimedia Commons has media related to Plastic bags.|
- Selke, Susan. Packaging and the Environment, 1994, ISBN 1-56676-104-2
- Selke, Susan. Plastics Packaging, 2004, ISBN 1-56990-372-7
- Stillwell, E. J. Packaging for the Environment, A. D. Little, 1991, ISBN 0-8144-5074-1
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- Celloplast 1965 US Patent: Copy of US Patent 5669504
- Northern Ireland's new five-pence carrier bag tax