Plastic Carrier Bags the Sustainable Alternative to Biodegradable Plastics

An ecologically correct shopping bag from the cornfield – sounds good, doesn't it? However, it isn't as simple as it sounds. Bags and foil can nowadays be produced from renewable raw materials such as corn starch and are then biodegradable, but on closer consideration such shopping bags offer no ecological benefits compared to conventional plastic bags made of polyethylene (PE). At least these are the findings of the Heidelberg Institute for Energy and Environmental Research (ifeu) in a study carried out on behalf of the Federal Department of the Environment. Among other reasons this is because up to 70 % of fossil raw materials are added to provide the required technical properties such as tear strength and durability.

On the one hand packaging from biodegradable plastic takes a long time to decompose, which makes it unsuitable for industrial composting plants, and on the other it can't be fed into the recycling process for conventional plastics either. The reason is that the biodegradable plastic bags would 'contaminate' the other PE waste, which is mainly produced from oil, and thus have a negative effect on the recycling process. As a result these bags are separated out in advance and neither recycled nor composted but are thermally utilised in waste incineration plants. Accordingly this material, which is in principle reusable, is in practice not available for recycling at all. In addition the cultivation of crops for plastic bags is controversial, because the areas of land involved are lost to agricultural food production.

English scientists searching for a solution to this problem have developed a highly environmentally-friendly additive which is marketed under the trade name 'Enzymoplast'. This granulate consists of natural proteins and special enzymes which are added during the manufacturing process of PE bags and have the effect of actually improving the technical properties of these bags, in other words their tear strength and durability. In addition bags which are produced using this enzyme can be recycled at any time together with conventional polyethylene.

And if – as still happens much too often in global terms – the bag is simply carelessly thrown away and then comes into contact with microorganisms in the soil and with water it decomposes, depending on the prevailing environmental conditions, within several months, leaving behind only water and CO₂ – two of nature's fundamental building blocks.

In the process the additive is so effective that the bags which contain it biodegrade significantly according to EN 14855. In addition it also meets the requirements of EN 13432 certification, which specifies that the material must decompose to a level of 90% within 180 days under industrial composting conditions. In the case of this additive the hundred per cent stage is in fact reached only a little later. For purposes of comparison: a conventional polyethylene bag takes up to 500 years to decompose fully.