life cycle assessment of paper bag

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  Introduction  Plastic bags have become one of the most ubiqitous consumer items on the planet today. Eachday shoppers everywhere use the bags to bring home their groceries and newly purchased items only to discard the bags after one use. Plastic bags litter the sidewalks of our cities and line the banks of rivers and creeks that run through our towns. Not only are the collections of discarded bags unattractive, but they can be deadly as well. Each year millions of marine animals die from ingesting or becoming tangled in plastic bags [1. !ince the plastic is made from petroleum it can be argued that the bags create a comparable level of environmental impacts as harvesting fossil fuels. ne study also found that many of the inks used to producelogos on bags contained lead and are not even suitable for carrying food. #oday plastic bags have become a widely debated topic in society. $any cities and companies have gone as far as to ban the distribution of the items. Even so, billions of plastic bags find their way to consumers each year. #his page will look at the life cycle of the plastic bag and provide an overview of the composition, production and usage as well as outline the energy inputs and outputs during the cycle. Material Culture/Usage  Plastic bags have become a pervasive icon of convenence and symboli%e the emphasis on fastand easy solutions in many societies today. &lthough the first plastic bag was invented in 1'(), it was in the 1')*+s that retailers began distributing the bags to consumers [. #oday it is estimated that every minute, humans use about 1 million plastic bags[-. &lthough many  people today are choosing to bring their own reusable shopping bags, total yearly consumption is still a staggering number estimated in the billions [.Part of the issue is not that plastic is necessarily preferred over other materials/ it0s that many societies place a value on the most accessible and fastest option. !ince it is easier to use plastic bags from the store,  instead of making it a habit to bring reusable cloth bags, the plastic bag is prevailing despite the debates. owever as the accessibility of studies and information on environmental impacts are becoming more readily available, more people each day are reali%ing the impacts of their choices. !ome consumers have begun to eliminate plastic bags from their shopping routines or have found ways to slightly e2tend the life of their bags by reusing them. &lthough it is a good start to the solution, even with reuse the bags are generally used only one more time as a garbage can liner or to pick up after a pet. !o although many consumers are choosing to reuse their bag in some way, the detrimental effect of a plastic bag+s entire lifecycle greatly outweighs the generally short lived purpose it serves. #he issue at hand is not  3ust how to reduce the use of plastic bags, but how to actuali%e the change in a society dependent on their culture of convenience. Energy Usage  Energy is the driving force behind every stage in the life cycle of plastic bags. #his energy is usually produced from non4renewable resources, such as fossil fuels. Even the building  blocks of a polyethylene bag are made from these non4renewable resources. 5eedstock energy is the energy embodied within a physical material. 6n the case of plastic  bags, the feedstock energy is the energy that was consumed in order to produce the igh 7ensity Polyethylene 87PE9.6t is usually a combination of the energy required to e2tract,  process, and transport the raw materials. Process energy is the energy used in production of a physical material. 5or plastic bags, this may include the polymeri%ation and e2trusion processes. 6n one estimate, a single plastic bag uses ':k; of natural gas, 1* k; of petroleum, and <* k;of coal[:. &nother found that 1:** plastic bags use 1:' $; in fuel production, 1)1 $; in fuel use, 1( $; in transportation, and 1< $; in feedstock, for a total of )(- $;. Per bag, thisequates to :*< k; in total energy use [(. 6t should be noted that estimates are vulnerable to variability, due to the numerous assumptions that must be made to come up with these values. #hese estimations include assumptions such as= ã !ources of oil, gas, and electricity ã >ocation of manufacturing and processing ã Efficiency of manufacturing and processing ã >ocation of usage ã End use of product 8how many times it is reused, etc9 ã 7isposal method 8landfill, incineration, etc9  #he following table is the amount of energy in mega 3oules 8$;9 which goes into 1***  polyethylene bags. [)  Transportation  & ma3or contributor to the environmental impact of the plastic bag is the transportation that it takes to get the bag to its final consumer. #he production of the bags require the raw materialsto first be transported to the different levels of manufacturers and once created, are transported out to retailers everywhere. #he carbon emissions e2pelled by the transportation during the life cycle of the plastic bag have a harmful effect on the environment. !ince retailers cannot store all the bags that they will require throughout the year, they receive shipments often. #his means that the carbon footprint created by the transporting of bags is anongoing process, with more bags being create and shipped each day. #he cost of the transportation and bags, estimated at ? billion dollars annually to &merican retailers alone, is then passed on to consumers in the form of higher product prices [<. !ince the bags are generally a one4time use item, they are then transported to the landfills. 6n effect, each time a new plastic bag is used and discarded, the entire production cycle has to begin again and the raw materials are once again transported to first stage of the manufacturing process. #he frequency of carbon emissions during the different transportation stages, illustrates one of themany harming effects that plastic bags have on the environment. Raw Materials  #he main components of polyethylene are natural gas and petroleum. E2traction of both  products is energy intensive. #his is increasingly true as tapped wells become less productive,and supplementary methods are required to continue e2traction 8e2 +fracking+ or hydraulic fracturing9. &fter e2traction, the raw materials must be refined, adding to the energy consumed. E2tracted natural gas is often referred to as +sour,+ a term used for gas containing large amounts of sulphuric acid. @efore it can be efficiently used, the gas must be turned +sweet+ by removing the sulphuric acid. #hese processes add to the embodied energy of the raw materials of plastic bags, before production has even begun. Production    nce transported to a processing facility, the raw materials are treated to create monomers 8mers9, like ethylene and propylene. #hese mers are the basis of many plastics like  polypropylene 4or in the case of plastic bags4 polyethylene. #hey can be further processed to create the various other types of plastic monomers. $ers undergo further manipulation, called polymeri%ation, to form long chains, which are essentially the backbone of the plastic  polymer. 5or the production of plastic bags, the raw polyethylene is shipped in granule form. &t the production facility, the granules are loaded into a hopper, along with recycled  polyethylene chips, if available. #hey are then carried to a heated chamber, called an e2truder.#he granules are mi2ed and worked, and then thinned into a film through a tool called a die. &t the output of the e2truder, the polyethylene is thin enough to form into plastic bags. 6n the Anited !tates, polyethylene is the most consumed polymer, nearly doubling the nearestcontender, polystyrene. Bonsumption of Polyethylene is estimated at ' million tonnes per year ['. & large portion of polyethylene is turned into consumer products and packaging, such as bottles, plastic film, and shopping bags. $any of the ob3ects created out of  polyethylene are designated as non4durables= their useful life is designed to be less than three years. 5urthermore, most of these polyethylene ob3ects will skip the recycling stage and go straight to disposal. Recycling  6t is estimated that only one percent of plastic bags are recycled worldwide[1*&fter primary use however, polyethylene bags can be recycled in numerous ways. Even without reprocessing, plastic grocery bags can be re4used as garbage bags or shopping bags. therwise, the polyethylene can be reprocessed and create new plastic bags, or other goods such as clothing and containers. @y some estimates, (* percent of the Anited !tates population have access to recycling  programs. #hese are often in the form of curbside collection and drop4off centers. @ut &mericans only recycle *.( percent of the 1** billion plastic bags taken home. #he remainder usually ends up as litter or at a landfill [11. #he recycling rate of plastic bags has influence on the embodied energy within them. #hrough recycling, feedstock energy can be reduced. &dditionally, the amount of petroleum and natural gas required for raw materials can be cut  by up to :C and :*C, respectively[1 Each type of plastic requires a different processing technique. &s such, when sent to recyclingfacilities, they are sorted by polymer type. Plastic bags are sorted into a 7PE collection, where they are compressed and baled. #hen they are shipped to a reclaimer. ere, the bags and other assorted 7PE are cut into small flakes, washed, and sold to container or bag manufacturers[1-. Dhen making bags out of recycled material, the strength and appearance significantly deteriorate[1. &lso, due to the possibility of contamination, the recycled  polyethylene may be unhygienic. #herefore, many recycledF plastic bags are not made out of 1**C recyclable materials. 6n some cases, the energy and costs of recycling plastic bags e2ceeds the energy usage and cost of creating new ones[1:.
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