LDPE carrier bags come out tops in Danish LCA

n---life-cycle-assessment-of-plastic-carrier-bags

A RESEARCH study released earlier this year, “Life Cycle Assessment of grocery carrier bags”, a project by the Danish Ministry of Environment and Food’s Environmental Protection Agency, state that the results of their research assessment highlighted the importance of the design of the carrier bag and its functionality.

The research showed that in general, LDPE carrier bags, which are always available for sale in Danish supermarkets, are the carriers providing the overall lowest environmental impact.

Since 1993, Denmark has taken action against single-use plastic carrier bags by introducing a tax on retailers. Currently, Danish supermarkets provide multiple-use carrier bags of different materials (such as recyclable and non-recyclable plastic, paper and cotton) which can be bought by customers at the cash register.

The study provides the life cycle environmental impacts of the production, use and disposal of grocery carrier bags available for purchase in Danish supermarkets in 2017.  In general, it was found that reusing the carrier bag as a waste bin bag is better than simply throwing away the bag in the residual waste and it is better than recycling.

Recycling can potentially offer more benefits in the case of heavy plastic bags, such as PP, and PET. Reuse as a waste bin bag is most beneficial for light carrier bags, such as LDPE, paper and biopolymer. When reuse as a waste bin bag is not feasible, for example when the bag can easily be punctured, torn or wet, incineration is the most preferable solution from an environmental point of view.

Three end-of-life options were taken into account for the disposal. In particular, the study wishes to:

  1. Identify the best disposal option for each carrier bag type within the identified end-of-life options;
  2. Identify the multiple-use carrier bag alternative with the best environmental performance for each of the investigated impact categories;
  3. Define the number of times a multiple-use carrier bag would need to be reused in order to provide a better environmental performance than another carrier bag alternative, for a range of environmental indicators.

 

The project also took into account that reuse of the carrier bag could occur both as primary reuse (where the carrier bag is reused for the same function for which it was produced, i.e. for carrying grocery shopping from the supermarket to the home), or replacing other products as waste bin liners (secondary reuse).

In particular, LDPE carrier bags with rigid handle are the most preferable. Effects of littering for this type of bag were considered negligible for Denmark. Heavier carrier bags, such as PP, PET, polyester, bleached paper and textile bags need to be reused multiple times to lower their environmental production cost. Between the same bag types, woven PP carrier bags provided lower impacts than non-woven PP bags.

For all carrier bags, reuse as many times as possible before disposal is strongly encouraged. The study also calculated how many times each bag would need to be reused to lower its associated environmental impacts to the levels of the LDPE carrier bag. The number of calculated reuse times varies if only one environmental indicator is observed, or if all environmental indicators are taken into account.

The results are the following:

  • Simple LDPE bags: Can be directly reused as waste bin bags for climate change, should be reused at least 1 time for grocery shopping considering all other indicators; finally reuse as waste bin bag.
  • LDPE bags with rigid handle: Can be directly reused as waste bin bags considering all indicators; finally reuse as waste bin bag.
  • Recycled LDPE bags: Reuse for grocery shopping at least 1 time for climate change, at least 2 times considering all indicators; finally reuse as waste bin bag.
  • PP bags, non-woven: Reuse for grocery shopping at least 6 times for climate change, and up to 52 times considering all indicators; finally dispose with recyclables, otherwise reuse as waste bin bag if possible, lastly incinerate.
  • PP bags, woven: Reuse for grocery shopping at least 5 times for climate change, at least 45 times considering all indicators; finally dispose with recyclables, otherwise reuse as waste bin bag if possible, lastly incinerate.
  • PET bags: Reuse for grocery shopping at least 8 times for climate change, and up to 84 times considering all indicators; finally dispose with recyclables, otherwise reuse as waste bin bag if possible, lastly incinerate.
  • Polyester bags: Reuse for grocery shopping at least 2 times for climate change, and up to 35 times considering all indicators; finally dispose with recyclables, otherwise reuse as waste bin bag if possible, lastly incinerate.
  • Biopolymer bags: Can be directly reused as waste bin bags for climate change, should be reused and up to 42 times for grocery shopping considering all other indicators. Finally, re-use as waste bin bag if possible, otherwise incinerate.