dokladna studia http://www.env.dtu.dk/ pre danske ministerstvo zp o dopade roznych typov nakupnych sackov a tasiek
https://www2.mst.dk/Udgiv/publications/2018/02/978-87-93614-73-4.pdf

shocker: platene bavlnene tasky su otrasne.

8. Conclusions
This study identified the best disposal option for each of the carrier bags available in Danish supermarkets in 2017. In general, 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 wetted, incineration is the most preferable solution from an environmental point of view.
In general, LDPE carrier bags, which are the bags that are always available for purchase in Danish supermarkets, are the carriers providing the overall lowest environmental impacts when not considering reuse. In particular, between the types of available carrier bags, LDPE carrier bags with rigid handle are the most preferable. Effects of littering for this type of bag were considered negligible for Denmark. Carrier bags alternatives that can provide a similar performance are unbleached paper and biopolymer bags, but for a lower number of environmental indicators. Heavier carrier bags, such as PP, PET, polyester, bleached paper and textile bags need to be reused multiple times in order to lower their environmental production cost. Between the same bag types, woven PP carrier bags provided lower impacts than nonwoven PP bags, unbleached paper resulted more preferable than bleached paper, and conventional cotton over organic cotton.

For all carrier bags, reuse as many times as possible before disposal is strongly encouraged. This study also calculated how many times each bag would need to be reused in order 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 following9
:
 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, reuse as waste bin bag if possible, otherwise incinerate.
 Unbleached paper bags: Can be directly reused as waste bin bags for climate change, should be reused and up to 43 times considering all other indicators. Finally, reuse as waste bin bag if possible, otherwise incinerate.
 Bleached paper bags: Reuse for grocery shopping at least 1 time for climate change, and up to 43 times considering all indicators; reuse as waste bin bag if possible, otherwise incinerate.
 Organic cotton bags: Reuse for grocery shopping at least 149 times for climate change, and up to 20000 times considering all indicators; reuse as waste bin bag if possible, otherwise incinerate.
 Conventional cotton bags: Reuse for grocery shopping at least 52 times for climate change, and up to 7100 times considering all indicators; reuse as waste bin bag if possible, otherwise incinerate.
 Composite bags: Reuse for grocery shopping at least 23 times for climate change, and up to 870 times considering all indicators; reuse as waste bin bag if possible, otherwise incinerate.

This study focused on identifying the number of reuse times based on the environmental performance of the carrier bags. The results obtained on the minimum number of reuse times are intended to raise the discussion among the stakeholders on the effective expected lifetime of each carrier bag. While the calculated number of reuse times might be compliant with the functional lifetime of PP, PET and polyester carrier bags, but might surpass the lifetime of bleached paper, composite and cotton carriers, especially considering all environmental indicators.
In addition it should be kept in mind that the reuse times calculated are held up against a use of a reference bag a single time. If the reference bag is reused, it would mean that the reuse time of the other bags would increase proportionally.
In particular, the results of the present assessment have highlighted the importance of the design of the carrier bag and its functionality, especially for cotton carriers. In order to lower the number of reuse times, designs with light fabric and large volumes should be preferred.
These design differences can largely lower the impacts. However, the required number of reuse times for all impact categories may still be unfeasible and more than the lifetime of the bag.