Depending upon the material your recycled bag is made from, the amount of energy consumed during its life cycle can vary greatly. For instance, when compared with polyester, cotton proves to use less energy during its life cycle, although cotton requires more water to produce and emits more CO2. According to Sustainability Ed.org, one kilogram of cotton fabric requires less energy during a two year life cycle, including washing it 12 times, than one kilogram of polyester. This translates to about 140 mega joules (MJ) versus about 170 MJ, respectively. Since a medium weight cotton or polyester tote weighs roughly .2 to .3 kilograms, the above figures represent about four reusable totes over a two year life cycle. Obviously, polyester uses more about 22 more energy than cotton does under this scenario.
In place of any disposable bag, cotton and polyester are both good choices provided they are used regularly during the two year life cycle. The life cycle of 1500 polyethylene bags consumes approximately 763 MJ of energy. The American Chemistry Council conducted a life cycle analysis that reached these conclusions: 1) The average American uses about 660 plastic bags in a two year period, consuming about 336 MJ during that time. 2) At 140 MJ for cotton bags and 170 MJ for polyester bags, using four reusable bags will consume about 50 of the energy of the disposable bags. It is interesting to note that if eight bags are used for two years, then reusable polyester becomes less energy efficient than the disposable polyethylene bags. However, eight cotton bags will still be more energy efficient than plastic. (Bear in mind that it is possible that the reusable bags will last longer than two years in reality.) Then, if reusable bags are made from recycled or second hand materials, energy is saved on the fiber production end. Another life cycle assessment of fibers published in “Resources Conservation and Recycling” compared reused and recycled textiles versus using new materials. The assessment showed that preparing used cotton garments for reuse took only 2.6 of the energy involved in making new cotton garments. For polyester the figure is 1.8 . Seemingly, a good choice for reusable bags would be to find those made of recycled or reused materials.
There is an even starker difference in energy consumption when comparing reusable bags with paper or compostable plastic bags. Obviously, paper and compostable bags are biodegradable. However, the American Chemistry Council maintains that paper bags use 2,622 MJ during the life cycle of 1,000 bags, while they have about the same carrying capacity as 1500 plastic bags. Using the same carrying capacity of paper versus plastic, over the course of two years paper bags consume about 1155 MJ. This is about 8 times the energy of four cotton bags and 7 times the energy of four polyester bags. With regard to compostable bags, the energy figure is over 5 times the energy of polyester bags, or about 912 MJ. Compared with cotton, compostable bags use about 6.5 times the energy. Taking the figures out to eight reusable bags, polyester or cotton, these disposables will still use considerably more energy than reusable bags will. As you can see, reusable bags are the hands down winner for the environment. But you probably already knew that, even without all of the technical data, didn’t you? |
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