CHAPTER 1 INTRODUCTION
In the late 1970s, single-use plastic bags became prevalent in supermarkets and stores across the United States (Clapp & Swanston, 2009). Plastic bags then spread to Europe in 1980s, and by 1990s, these bags were commonplace in developing countries (Clapp & Swanston, 2009). At present, plastic bags are ubiquitous across the world. They are now provided free of charge in most countries. People make use of plastic bags daily in different ways, such as for shopping, disposal of waste, and storage of food items.
It is estimated that, globally, people use 500 billion to 1 trillion plastic bags annually (Spokas, 2008). For example, estimates of annual plastic bags used include 8 billion bags annually in the United Kingdom, 9.8 billon in Hong Kong, 6.9 billion in Australia, 100 billion in the United States, 3.3 billion in Bangladesh, and 300 billion in China (Clapp & Swanston, 2009). This widespread usage of plastic bags can be credited to the convenience in the use of the plastic bags because they are cheap and lightweight. After a single use, most of the plastic bags are thrown away to the environment as waste (Adane & Muleta, 2011).
As plastic bags began to pile up in the environment, governments and the general public began to see a downside to the widespread use of these bags. First, they are not biodegradable. Plastic bags may take up to 1,000 years to degrade by sunlight (Sutton & Turner, 2012). Second, these bags comprise one of the largest portions of solid waste in the world today. Third, they cause the death of wild and domestic animals (Adane & Muleta, 2011). Some animals’ mistake plastic bags as food, and
when consumed, this might end up killing them. Fourth, plastic bags cause environmental hazards, including toxins released from manufacturing of the bags and pollution in the form of plastic litter and waste (Nhamo, 2008). Both the manufacturing process and the use of plastic bags play a significant role in adding pollution to water, air, and soil.
Because of the effects caused by plastic bags, different countries started taking actions to control the usage of plastic bags. Some regions introduced compulsory taxes; some provided a discount for consumers who carry their own reusable bags for shopping; and some placed an outright ban on the use of plastic bags. Some of these countries have succeeded in reducing the amount of plastic bag consumption, while some failed. Ban on plastic bags has led to a drastic decrease in the consumption of plastic bags in different countries around the world. For example, a ban on plastic bags in China has led to an enormous decrease in the amount of plastic bags consumed in the country. Since the implementation of the ban, the country’s consumption on plastic bags has decreased by one third (“Plastic Bag Ban,” 2013).
Life cycle of plastic bags
The life cycle of plastic bag starts with extraction of ethylene from crude oil or natural gas and ends with the disposal of bags as waste after usage (Fig. 1). Ethylene, which is the main component of a synthetic bag, is derived from the catalytic cracking of crude oil gasoline or from modifying natural gas, such as ethane, methane, or propane mix (Ruban, 2012; Greene, 2011). Ethylene is transformed to polyethylene (a polymer of ethylene) by a process known as polymerization. After the polymerization stage, plastic bags are processed via conversion of film,
production of a vest shaped bag , and printing the plastic bag (Ruban, 2012). Plastic bags can be manufactured from low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE). Bags produced from LDPE are very soft compared to bags produced from HDPE (Ruban, 2012). LDPE and LLDPE are mainly use for department store bags, while HDPE is mainly use for single-use plastic bags (Greene, 2011). HDPE is thicker than the LDPE because the textile used in production is stronger than that of low-density polyethylene.
Table 1. Different types of polyethylene with their packaging applications (Andrady, 2003).
| Type | Co monomer | Density g/cm | Melt Index | Applications |
| LDPE | None 2–5% vinyl acetate 7% vinyl acetate None | 0.919- 0.923 0.922– 0.925 0.925– 0.930 0.927– 0.945 0.924– 0.926 | 0.2-0.8 1.5–2.0 1.5–2.0 0.2–0.4 6–10 | Heavy duty sacs Bread, bakery and general-purpose bags Frozen food Liquid packaging and extrusion coating Bottles and closures |
| LLDP | Butene Hexene, octene | 0.917– 0.922 0.912– 0.919 | 0.8–2.5 2.0–4.0 | General-purpose packaging Stretch wrap |
| HDPE | None BM | 0.960 0.940 0.960 | 0.35 0.2 30 | Containers, bottles, and pails, General purpose Food containers |
Once produced, plastic bags are transported to stores and markets where they are sold. Only a few of these plastic bags are later recycled; most of them are used once
and then disposed as waste (Greene, 2011). Some of these plastic bags are shipped from different countries. For example, 67% of the 6 billion HDPE bags used in Australia are imported (Environment Protection and Heritage Council, 2002). It was also reported that in the years 2001 to 2002, 225 million LDPE bags were imported to Australia (Environment Protection and Heritage Council, 2002).
Environmental impacts
The production of plastic bags leads to a number of environmental impacts. The drilling of crude oil and gas, for example, releases toxic contaminants to the atmosphere, which include benzene, xylene, hydrogen sulfide, toluene, sulfur dioxide, ethyl benzene, ozone, and volatile organic compounds. Most of the harmful gases released in the process of plastic bag production are greenhouse gases, which are the major causes of global warming. Some of these gases also lead to acid rain and ozone-layer depletion (Ruban, 2012).
