18. One of the peer-reviewers commented “Postconsumer shopping bags are printed, and probably often contain some unwanted materials; this would make it very difficult to use shopping bags as a high value plastic.”
19. The Report does not give starch-based plastics any credit for recycling, but it does not factor in the adverse effects of starch-based polymers in the recycling stream. It is well known that those plastics cannot be recycled with normal oil-based plastics and will compromise such a recycling stream.
20. Report says “Any environmental impacts associated with storage activities at the bag importers and supermarkets have been excluded.” If they had been included oxobio and conventional bags would have scored even higher, because they are half the weight and thickness of the starch-polyester bags and take up half as much space in warehouses and trucks. The other types of bags considered in the Report are even thicker and heavier.
21. Report says “The impacts for the [oxobio] bag are very similar to the [ordinary] HDPE bag. The percentage contribution of each lifecycle stage on each impact category is almost identical to the HDPE bag because of their similarity in material content, production, transportation, secondary reuse and end-of-life. However, in general, the material-extraction and production lifecycle stage has a larger impact because the HDPE prodegradant bag is heavier.”
22. The bag selected for the study had a 4% loading of catalyst containing cobalt stearate, but a Symphony d2w bag with a much lower loading of a manganese catalyst would not be measurably heavier than a normal HDPE bag. The Report includes the weight of titanium dioxide but does point out that this is not used in clear bags, and that “the impact of some HDPE bags would therefore be overstated in terms of freshwater ecotoxicity.”
23. Credit for composting has been given to starch-polyester bags, and this of course assumes that the starch-polyester shopper-bag would find its way into a composting plant. This is highly unlikely except as part of a dedicated scheme, and its most likely destination would be landfill where it could emit methane. Moreover, industrial composters do not generally accept post-consumer plastic waste because it is not economic to separate compostable plastic from ordinary plastic.
Even if compostable plastic did get into an industrial composting unit it would be of little or no value for the compost because EN13432 requires it to convert to CO2 gas within 180 days - contributing to global warming but doing nothing for the value of the compost to the plants. This cannot be honestly described as “organic recycling” or “recovery.”
