The two main types of single use plastic bags used in the world are the "singlet’ bag made of high density polyethylene (HDPE) and the "boutique’ bag, made of low density polyethylene (LDPE). The HDPE bag is the common plastic bag used in supermarkets and other retail outlets. The LDPE boutique bags are generally branded and used by department stores and clothing stores.
Environmental Costs of Shopping Bags Over Their Entire Life Cycle
To assess the full environmental impact of the various shopping bag materials we need to determine the resource consumption and environmental consequences of each stage of a bag's life cycle. This commences with the raw material extraction and processing, followed by the manufacture, distribution, use and reuse of the bag, and finally, the eventual disposal of the bag in the environment.
Biodegradable Shopping Bags
Another option is the use of biodegradable bags made from starch based plastics or various other bio-plastics. The environmental breakdown of these various compounds is very variable though many may have adverse environmental consequences, both before and after breaking down. Aggravating this problem is the practice of adding chemicals to bio-plastics to accelerate breakdown. Furthermore, the crop starch or petroleum origin of biodegradable plastics is more wasteful of resources than is the production of conventional plastic bags. The perception that littering of biodegradable plastic bags poses no environmental problems may also increase bag consumption and consumption of associated resources. Another problem with bio-plastics is the possible contamination of recycled plastic with litter comprised of biodegradable plastics. This could threaten the viability of the plastic recycling industry.
According to the Nolan-ITU Report into Plastic Shopping Bags - Analysis of Levies and Environmental Impacts in 2002 in regard to the use of biodegradable plastics (1) : "widespread use as an alternative to plastic shopping bags may not deliver overall environmental gains." Or, in the words of Sustainability Victoria (3): "Degradable bags require energy, water and materials in their production and are still used only once, so substituting billions of shopping bags with billions of degradable bags isn't a great environmental outcome."
Paper Shopping Bags
Comparing single use plastic shopping bags with paper bags reveals that more than four times as much energy is used to manufacture a paper bag as compared to manufacture of a plastic bag, and, over their complete life cycles, a plastic bag uses about 40 per cent the amount of energy of a paper bag. Transportation of plastic bags also uses 11 times less fuel as compared to the more bulky paper bags. Recycling of paper is also much more demanding of energy resources than recycling of plastic. However, the persistence of plastic litter in the environment poses far more problems than does paper.
Calico or Cotton Bags
Cotton bags have definite advantages because they are both reusable as well as being biodegradable and cotton is a natural renewable resource. However, conventional cotton farming, as distinct from organic cotton farming, is extremely wasteful of resources and detrimental to the environment, requiring huge quantities of water, chemical fertilisers, and pesticides. Although only 2.4% of the world’s arable land is devoted to conventional cotton farming, cotton producers use an amazing 25% of all insecticides and 11% of all pesticides used each year. These facts make the advantages of organic cotton farming quite clear.
Non Woven Polypropylene Bags or "Green Bags"
Various studies have found that durable reusable bags offer definite environmental advantages and have a much lower life cycle impact than any single-use bag, largely because they address the vitally important issue of consumption. With their expected 2 year life span, with the use of these bags the average consumer could be expected to reduce their consumption of shopping bags by more than 98% when compared to single use bags. Non woven polypropylene bags are strong and durable, and can hold much more than conventional single use HDPE shopping bags. These bags are also recyclable through supermarket plastic bag recycling bins. Especially considering the expected 2 year life of non woven polypropylene bags, these bags create less litter and use significantly less material resources and energy resources than biodegradable bags, paper bags, cotton bags, or single use plastic bags and do not require the huge water resources and agricultural chemicals required by cotton. On the downside, non-woven plastic polypropylene bags are manufactured from polypropylene gas, a by-product of oil refining and are therefore made from non renewable resources. Additionally, non woven polypropylene is not biodegradable or compostable. In the environment these bags will degrade into tiny less visible pieces of plastic so they would be expected to add to accumulation of plastic in the eco system.Notwithstanding these facts, according to Sustainability Victoria (3 ) "The reusable, non-woven plastic (polypropylene) "Green Bag’ was found to achieve the greatest environmental benefits."
Since jute or hessian bags share the durability strength and long life of non woven bags they also share the environmental advantages of the latter. However, jute bags are environmentally superior to non woven bags in many ways. Firstly, unlike petrochemical industry derived polypropylene plastic, jute is a totally natural renewable resource which is biodegradable and compostable. Environmental breakdown of jute therefore ultimately contributes to soil structure unlike polypropylene which adds to environmental plastic accumulation. Jute plants also clean the air by consuming large quantities of greenhouse causing CO2. One hectare of jute plants can consume about 15 tons of CO2 and release about 11 tons of oxygen during the jute growing season.
From an environmental perspective jute also compares very favourably to cotton or calico. Although jute crops have a high water requirement jute is normally grown in areas of high rainfall where this is not a problem. Additionally, compared to cotton, jute crops require minimal use of pesticides, fertilisers, and agricultural chemicals. Jute farming is also a labour intensive process which contributes to the livelihood of 4 million farming families, and nearly half a million additional processing workers in India alone.
On the downside, although 100% natural jute bags are readily available, in practice most jute bags are lined with a plastic material to improve the rigidity and shape, increase the water resistance of the bag, and to improve the cleanability of the bag. This plastic lining or lamination is usually either polypropylene (PP) or low density polyethylene (LDPE) which typically constitutes 10% of the bag, making the final product 90% biodegradable and 10% degradable. Biodegradable linings for jute bags are available but are expensive and not commonly used.
Even though a jute bag lined with LDPE plastic may contain a plastic content equivalent to 2-3 single use plastic bags, in the case of the jute bag these plastic bags continue to be used for the duration of the life of the jute bag, perhaps 2 years or more. Over the same period a single consumer may use more than 1000 single use plastic bags.
The coarse knit nature of jute bags is also not so conducive to printing as non woven polypropylene and therefore for elaborate detailed printing for promotional bags non woven bags are clearly superior. The biggest disadvantage of jute bags however, is their greater cost as compared to other reusable bags such as non woven polypropylene and cotton. The Ipswich City Council in Queensland, Australia, (4) has described jute bags as "the logical 'next step' for socially-concerned shoppers and retailers":
"Jute bags are biodegradable alternatives to the green polypropylene bag. They are naturally recyclable and are the logical 'next step' for socially-concerned shoppers and retailers. The bag can be recycled by composting them or using as mulch in the garden. Jute is a long, soft shiny plant fibre that can spun into coarse, strong threads. Jute is one of the most abundant natural fibres and is second only to cotton in the amount produced and variety of uses".
In view of the undisputed environmental advantages of natural plant fibres such as jute and hemp it is disappointing that the option of shopping bags made from these natural fibres has often been omitted from recent Australian enquiries into the problems of plastic shopping bags and the possible alternatives.For a more detailed account of the environmental advantages of jute, especially as compared to polypropylene, see our in depth article entitled Natural Jute Shopping Bags or Synthetic Polypropylene Plastic?
From an environmental perspective most experts agree that the best shopping bags are durable reusable bags such as those made from non woven polypropylene, jute or cotton. Of these three, jute bags and non woven bags are generally considered more environmentally desirable than cotton bags because of the excessive water resources and agricultural chemicals required during the growing of cotton crops, unless of course the bags are made from organic cotton.
The biodegradability of jute bags and the fact that jute is a renewable natural resource makes these bags a much better environmental choice than those manufactured from non woven polypropylene plastic. Non woven polypropylene is only superior to jute in regard to its lower cost and ability to more readily accept complex print designs.