The oxo-bio debate

Oxo-biodegradable technology is not intended for PET bottles, and the Oxo-biodegradable Plastics Association does not recognise any additive as suitable for this purpose.
Shopping bags and rubbish sacks are typically made from High-Density Polyethylene (HDPE) containing mineral fillers, which is not suitable for recycling into long-life products.

Further, post-household plastic waste consists of a variety of different polymers, usually contaminated with other materials. For these reasons it is unlikely that these plastics will find their way into products such as building films, and they are not suitable for food-contact. If recycled at all they will typically be used for low-value, short-life items for which degradability is a desirable feature.

Ordinary plastic and oxo-bio plastic are made from a by-product of oil which used to be wasted. Oil is extracted to make petrol, diesel, and aviation fuel, and the same amount of oil would be extracted if plastics did not exist. This means feedstock to make plastic is unlimited for the foreseeable future.

Oxo-bio plastics have been in commercial use since the 1970s, and are designed to address the problem of plastic waste which escapes into the open environment and cannot realistically be collected. They contain formulations (not heavy metals) that promote oxidation in the presence of oxygen, and convert the plastic into a biodegradable material. In Pakistan and eight other countries, with a combined population of more than 200 million it is now mandatory to use oxo-biodegradable technology for a wide range of short-life plastic products.

Symphony agrees with the recyclers that bio-based compostable plastic cannot be recycled with conventional plastic, and that it should not therefore be encouraged (see the Austrian TCKT report of Nov 2013 commissioned by European Plastics Converters (EuPC)).

Recycling

However, this is not the case with oxo-biodegradable plastics, for the reasons given in Roediger laboratories report of May 2012, and their supplementary report of Dec 2013, having reviewed the TCKT report. Recyclers and governments should therefore be worried about bio-based compostable plastics, because they will certainly compromise an oil-based recycling stream if added at as little as 2%. Oxo-bio plastics will not.

Oxo-bio plastics can be manufactured with the same machines as conventional plastics at little or no extra cost, and their performance during manufacture and use is indistinguishable from that of regular polyolefins.

Recycled plastics are not degradable and will, like ordinary plastics, accumulate for decades if they get into in the open environment. However, recycled plastic as well as virgin plastic can now be made oxo-biodegradable by the inclusion of a pro-degradant formulation at the extrusion stage, typically at 1%. The length of the useful life of an oxo-biodegradable plastic product is determined by antioxidants (processing stabilisers and UV stabilisers) contained within the formulation, which can be modified so that the plastic product degrades according to whatever approximate timescale is specified.

Extensive tests by Roediger laboratories of Stellenbosch South Africa were reported on May 21 2012. They concluded that Plastic products made with oxo-biodegradable technology may be recycled without any significant detriment to the newly formed recycled product. Roediger also examined the report prepared by TCKT from November 2013 on behalf of EuPC and reported that there was no reason to change their conclusion.

Testing

Symphonys experience is entirely consistent with the Roediger reports. In the last two years enough masterbatch has been sold to make more than 600,000 tons of oxo-biodegradable plastic products, and we know that oxo-bio plastic products have been successfully recycled for the past 10 years by companies around the world. In those ten years we have heard no reports of any difficulty encountered.

In its 2011 report for the UK Government, and in its 2012 supplementary report, Intertek found that oxo-biodegradable plastic bags have better environmental credentials for making shopping bags than conventional plastic, bio-based plastic, paper, or cotton.

For the reasons already given, oxo-biodegradable plastics are unlikely to be recycled into long-life products. However, since polymers lose stabilisers every time they are reprocessed, it is good practice to add new stabilisers each time, whether the feedstock contains oxo-biodegradable plastic or not. If suitably formulated, the stabilisers will neutralise any pro-oxidant which may still be effective.