Life Cycle of Carrier Bags

The life cycles of supermarket carrier bags of different materials have been studied by the UK Environmental Agency. Their key findings are summarized here.

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Which of these materials has the least environmental impact: paper, biopolymer, cotton, conventional plastic or TDPA™ plastic?

The environmental impact of a range of bag materials (including HDPE, LDPE, biopolymer (starch-polyester), non-woven PP, paper & cotton bags) was assessed, concluding that HDPE bags have the lowest overall environmental impact.

Although alternative materials to plastics, such as paper, cotton and biopolymers, are frequently touted as being more environmentally-friendly options, they all had a greater overall environmental impact and global warming potential than conventional plastic bags. Paper, non-woven PP and cotton bags have to be re-used 4, 14 and 173 times respectively for their global warming potential to be less than that of HDPE bags (assuming only 40% of HDPE bags are re-used as bin liners). Greater re-use of HDPE bags further reduced their environmental impact.

This study did not consider the impact of inadvertent littering. As TDPA™ bags that have escaped into the open environment can degrade, whereas conventional plastic bags cannot, TDPA™ technology likely further reduces the environmental impact of carrier bags.

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What is the environmental benefit of recycling and composting of carrier bags?

The report concluded that recycling and composting of carrier bags only result in a small reduction in global warming potential and abiotic depletion. Instead, the key determinant of the environmental impact of carrier bags is the degree to which they are re-used.

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What are the main conclusions of the UK Environmental Agency’s life cycle assessment of supermarket carrier bags?

  • Amongst the different types of carrier bags studied (including HDPE, LDPE, biopolymer (starch-polyester), non-woven PP, paper & cotton bags), HDPE bags have the lowest overall environmental impact
  • For all types of carrier bags, the key determinant of their environmental impact was the degree to which they were re-used
  • Paper, non-woven PP and cotton bags have to be re-used 4, 14 and 173 times respectively for their global warming potential to be less than that of HDPE bags (assuming 40% of HDPE bags are re-used as bin liners)
  • Bio-polymer (starch-polyester) bags have greater global warming potential than conventional plastic bags due to “the increased weight of material [per] bag, higher material production impacts and a higher end-of-life impact in landfill”