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How much energy is used to make a plastic bag?

The plastic carry bag is an established part of Australian shopping. The nation consumes approximately 6.9 billion plastic bags, or 36,850 tonnes of plastic, each year - this equates to just under one bag per person per day. About 53% of plastic bags are distributed from supermarkets, while 47% come from other retail outlets such as fast food shops, liquor stores, and general merchandising. One of the main methods of managing the use and disposal of plastic bags is the voluntary National Code of Practice for the Management of Plastic Retail Carry Bags (Australian Retailers Association 2002).

Plastic bags are popular with consumers and retailers because they are a functional, lightweight, strong, cheap, and hygienic way of transporting food and goods. Additionally, the manufacture of plastic bags uses little energy. However, research has shown that energy use and greenhouse gas emissions can be reduced by switching from the commonly used bags to larger, reusable bags, by expanding the Code, and introducing a levy. These options are discussed briefly below.

The two main types of plastic bags used in Australia are the 'singlet' bag made of high density polyethylene (HDPE) and the 'boutique' bag made of low density polyethylene (LDPE). The HDPE bags are mainly used in supermarkets and take-away food shops, whereas the LDPE are commonly used in department and fashion stores. In 2001-02, 66% (or four billion) of all HDPE bags and 25% (or 225 million) of all LDPE bags used in Australia were imported.

Around 0.48 megajoules (MJ) of energy is consumed to make one HDPE singlet bag including the energy content of the bag (the embodied energy). Another way of considering this is that the energy consumed by driving a car one kilometre is the equivalent of manufacturing 8.7 plastic bags (Nolan-ITU 2002).

By comparison, it is estimated that the making of a plastic bag uses up to 70% less energy and produces around half the greenhouse gas emissions than a paper bag (National Plastic Shopping Bags Working Group 2002). However, the amount of energy used and greenhouse gases emitted in the manufacture of plastic bags does not compare favourably to other alternatives, as shown in table S17.1. Over one year, using woven HDPE bags consumes 9% of the energy and produces 10% of the greenhouse gas emissions compared with using standard HDPE bags (Nolan-ITU 2002).

Further, modelling has shown that significant energy savings are possible with the introduction of a plastic bag levy. Under the current Code, plastic bag manufacturing uses 2,540 gigajoules (GJ) of energy per year. If the Code is expanded and a legislated levy of, say, 15 cents per bag is introduced, energy use could be cut by 54.9% (to 1,160 GJ a year). If a 25 cent levy was introduced, energy use could be reduced by over 60% (to 940 GJ per year; Nolan-ITU 2002).

S17.1 ASSESSMENT OF PLASTIC BAG ALTERNATIVES(a)
	Expected life	Bags per year	Annual greenhouse gas emissions	Annual primary energy use
Alternative	Shopping trips	no.	kg CO2-e(b)	MJ
Singlet HDPE	1	520	6.1	210
50% recycled HDPE	1	520	4.8	117
Boutique LDPE	1	650	29.8	957
Calico	52	9	2.5	160
Woven HDPE swag	104	1.65	0.6	19
Kraft paper - handled	1	520	11.8	721
(a) Based on a household carrying about 70 grocery items home from a supermarket each week for 52 weeks. (b) Kilograms of carbon dioxide equivalent (CO2-e).
Source: Nolan-ITU 2002.