Plastic wars

C&I Issue 7, 2014

The European Union (EU) has decided that plastic shopping bags are the new scourge of society – they clog landfill sites, pollute rivers and litter town centres – so it is on a mission to start weaning its citizens off them. And with good reason: the EU estimates that almost 100bn plastics bags were used in Europe in 2010. ‘Every year, more than 8bn plastic bags end up as litter in Europe, causing enormous environmental damage,’ says EU environment commissioner Janez Potočnik. ‘Some member states have already achieved great results in reducing their use of plastic bags. If others followed suit, we could reduce consumption by as much as 80%,’ he adds.

The European Parliament has come up with draft legislation, which is described in the Auken report, after its author Margrete Auken, a Danish MEP who represents the Green party.

In the report are several recommendations. For example, by 2017, the number of plastic bags used should be halved, and cut by 80% by 2019. The legislation is expected to target the very thin bags – thinner than 50µm – that make up the bulk of the volume. These bags are seen as the main source of the problem because they are generally used only once – unlike thicker shopping bags. If the draft becomes law, member states will be free to choose their own way of tackling the problem, which can include everything from adding a tax to outlawing use of the bags altogether.

Another recommendation – already widely adopted across the world – is to switch production from conventional to biodegradable plastics. It is this recommendation that is causing controversy within the plastics industry.

In April 2014, members of the European Parliament (MEPs) voted in favour of the legislation.

The bioplastics barney

It might appear to be a simple case of ‘traditional versus biodegradable’ plastic, but it’s more complicated. The ‘biodegradable’ camp is split because there are two types of degr
adable plastic.

One is ‘biodegradable’ or ‘compostable’, and includes polymers derived from crops like corn starch or sugar; an example is polylactic acid (PLA). These polymers are broken down in soil either by microbes (biodegradable) or by the heat of the composting process (compostable) into water, carbon dioxide and biomass under certain conditions.

The other is ‘oxo-biodegradable’; these are conventional plastics that incorporate an additive to encourage the plastics to degrade into fragments, which are then consumed by microbes in the soil. These plastics are also referred to as ‘oxo-degradable’ or ‘oxo-fragmentable’.

But neither of the camps – the traditional or biodegradable plastics producers – can agree with one another in terms of the effects each has on the waste stream used to make recycled plastic bags.

This mutual antagonism stepped up a notch at the end of 2013 when European Plastics Converters (EuPC), which represents producers of ‘traditional’ plastic bags, said that both types of degradable plastics should be banned from the waste stream. The professional body favours a ‘collection and recycling’ approach for plastic bags – schemes that are already well-established in countries such as Germany and Austria.

In 2013, EuPC commissioned the Transfer Centre for Polymer Technology (TCKT) in Austria to investigate the ‘impact of degradable and oxo-fragmentable plastic carrier bags on mechanical recycling’. The work was done by Birgit Hornitschek over six months. Hornitschek’s final report was peer-reviewed by Wolfgang Stadlbauer, a retired professor of organic chemistry at the University of Graz in Austria, and published in November 2013.

Hornitschek analysed how ‘impurities’ of degradable plastic affect the recycling of plastic bags. She prepared a number of plastic mixtures containing differing levels – 2, 5, 10 and 50% by weight – and different types of degradable plastics. The base polymer was low density polyethylene (LDPE), derived from bags that are already available on the market.

These mixtures were then used to make new plastic bags by the standard industry method: blown film extrusion. Parameters such as ease of processing and the physical appearance of the final product were recorded. Samples were also tested for mechanical strength.

Over the course of the research, Hornitschek processed nearly 10t of material and made more than 3700 measurements.

The report found that a 2% ‘impurity’ of degradable plastics in the recycling stream is enough to affect mechanical and visual properties of recycled plastics. While the material processed perfectly normally on standard equipment, it had a ‘fish eye’ appearance, according to Hornitschek. At the same time, all of the formulations showed a general reduction in mechanical properties, in comparison with 100% LDPE, although occasionally the properties were improved. The report also found that higher percentages of degradable plastics in the mix reduced properties still further. ‘Whatever degradable or oxo-fragmentable material enters the recycling stream, these tests show that these materials are conflicting with the recycling process of conventional material,’ says Hornitschek.

For its part, EuPC, convinced of the detrimental effect, has called for degradable plastics to be collected separately from other materials – and sees no place for oxo-biodegradables in the recycling stream. ‘Oxo-fragmentable additives have no positive environmental impact on the existing waste streams and should be forbidden in Europe,’ it concludes.

In response

Unsurprisingly, the two degradable plastics camps have taken issue with the results.

The Oxo-Biodegradable Plastics Association (OPA) commissioned Roediger Agencies, a South African analytical laboratory that specialises in polymer analysis, to review the claims made by the TCKT report. The review, by Andy Roediger, accuses TCKT’s report of ‘serious failings from a scientific point of view’.

‘In general, the TCKT report is confused,’ he wrote. ‘The results measured are inconsistent and show few or no trends that could indicate that the presence of oxo-biodegradable recycled material weakens the physical properties of recycled film.’

Earlier, in 2012, Roediger had carried out a study for OPA, which concluded that oxo-biodegradable plastics had no significant effect on the recycling of conventional plastics. ‘We have no reason to change that opinion,’ said Roediger.

However, Roediger did agree with the TCKT report on one point: that a mixture of bio-based and conventional plastics ‘would cause a significant detriment to the newly formed recycled product’.

Canada-based EPI, which produces oxo-biodegradable additives, also tore into TCKT’s claims, saying the study contained ‘scientific inconsistencies’ and four ‘methodological flaws’ that undermined its credibility. According to EPI, the sample was too small, and concentrated on only one type of degradable plastic. This, it said, meant it could not be extrapolated to make general conclusions about oxo-biodegradable plastics. Further, EPI said that no statistical analysis was performed; and the key claims were based on subjective observations such as visual inspection. Finally, EPI claimed that data were presented in a ‘selective and biased manner’.

EPI cited an earlier study, commissioned by Recyc-Quebec in Canada, which it said verified that ‘oxo-biodegradable plastics are recyclable and are compatible with the post-consumer plastic waste recycling stream’.

Biodegradable plastics producers have also taken issue with the TCKT report. European Bioplastics, which represents producers of biodegradable plastics, says that a level of 10% degradable plastic in the waste stream has little effect on the physical properties of the resultant recycled LDPE. The association cites three separate studies to support its view: these studies were carried out by the Italian National Packaging Consortium (Conai); the Institute for Bioplastics and Biocomposites at the University of Hanover, Germany; and bioplastics company Biotec. ‘Studies have demonstrated that a small fraction of compostable plastics do not negatively impact the quality of the recycling stream,’ says François de Bie, chairman of European Bioplastics, adding that compostable materials in the PE [polyethylene] stream were easier to handle than other plastics, such as polystyrene (PS) or polypropylene (PP).

The Conai study looked at two commonly used biodegradable packaging materials: Novamont’s Mater-Bi, made from starch, and Natureworks’ Ingeo – polylactic acid that is made from corn. The testing included analysis of polyethylene with increasing amounts of Mater-Bi. ‘It is possible to recycle mixtures with up to 10% concentrations of Mater-Bi shopping bags with conventional plastic shoppers,’ the report concluded. ‘At higher concentrations – up to 20% – problems could arise that must be investigated.’

The Hanover research examined the influence of different compostable plastics on LDPE, with a contamination level up to 10%. The researchers found no reduction in viscosity, elasticity or tensile strength, in comparison with pure LDPE. At the same time, there was no noticeable change in visual appearance. The compostable plastics used in the study included a PLA/ polybutyrate adipate terephthalate (PBAT) blend, pure PBAT, and a starch blend. The Biotec study concluded that its Bioplast material (a starch/PBAT blend) had a similar effect to contamination by polystyrene or polypropylene. It also found that a 2% contamination by PET – used to make soft drinks bottles, and commonly recycled – led to material that was impossible to process by blown film extrusion.

Worldwide war on bags

The move by the European Union to curb the use of plastic shopping bags is just the latest skirmish in the global ‘war on bags’.

Countries on most continents have banned – or at least restricted – the use of plastic bags. Some bans are countrywide – such as those adopted by the United Arab Emirates in 2012 and Bangladesh in 2002. Others are restricted to particular regions: US cities such as Los Angeles and Chicago have imposed restrictions on the distribution of bags, while Himachal Pradesh – a state in northern India – recently outlawed the use of the bags for ‘non-essential’ foods such as crisps and snacks.

In most of these cases, the legislation accepts that the bags can be made from degradable plastics in place of conventional plastics. European Bioplastics supports a levy or tax on oil-based plastic shopping bags, or even banning them under certain conditions – but says that bags containing at least 50% bio-based content should be exempted. ‘Bioplastic bags will become a symbol of a resource efficient and circular economy,’ says de Bie. Such bags would ensure a lower carbon footprint than oil-based bags and reduce CO2 emissions, he says.

EuPC disagrees with de Bie – and questions whether bio-based shopping bags are really more sustainable than their oil-derived equivalents. ‘When considering sustainability, we need to look at resources used in their production, including land-use, water consumption and – in the case of bio-based plastics – the sustainability of biomass used,’ it says, adding: ‘Any EU policy related to bioplastics needs to take account of lessons learned from the biofuels sector.’

EuPC does, however, take issue with some of the wording of the Auken report – the draft legislation that MEPs have just voted to support. The final legislative resolution maintains that biodegradable and compostable materials are ‘less harmful to the environment than conventional plastic carrier bags’. ‘This statement is untrue and is not supported by any credible scientific evidence,’ says EuPC. ‘As mentioned by Commisioner Potočnik, more scientific evidence is needed on biodegradable materials to see whether they really make sense from a sustainability point of view.’

So while plastic bag consumption in Europe may have peaked at 100bn – and the European Union takes action to reduce their effect on the environment – the material debate is likely to rage on.

Lou Reade is a science writer based in Kent, UK

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