Oxo-degradation

Oxo-degradation, refers to the process by which plastics that contain additives that accelerate its breakdown into smaller fragments, called microplastics, when exposed to heat, light or oxygen. This is in contrast to biodegradable or compostable plastics, which break down at the molecular or polymer level. Oxo-degradable plastics are currently banned in the EU, but still permitted in other jurisdictions such as the UK.

The specific definitions are found in CEN (European Committee for Standardisation) Technical report CEN/TR 15351 "Oxo-degradation" is degradation identified as resulting from oxidative cleavage of macromolecules". This describes ordinary plastics which abiotically degrade by oxidation in the open environment and create microplastics, but do not become biodegradable except over a very long period of time.

By contrast oxo-degradation is degradation resulting from oxidative and cell-mediated phenomena either simultaneously or successively. This means that the plastic degrades by oxidation until its molecular weight is low enough to be accessible to bacteria and fungi, who then recycle it back into nature by cell-mediated phenomena. These plastics are marketed as "oxo-(bio)degradable."

Oxo-degradable plastics are intended to fragment if they get into the open environment as litter and should not be confused with plastics intended to biodegrade in the special conditions found in an industrial composting unit. These compostable plastics use an entirely different technology, but confusion is caused by the fact that they are so often referred to in discussions of oxo-degradable plastic.

Background, Characteristics, and Performance

"Biodegradable plastic" is a term that causes confusion and should not be used, because it could apply to two completely different types of plastic.

• Vegetable-based plastics, which are also loosely known as "bioplastics" or "compostable plastics", are tested in accordance with ASTM D6400 or EN13432 as to their ability to biodegrade under conditions found in industrial composting or biogas facilities.

• Oxo-degradable plastics—which are made from polymers such as polyethylene (PE), polypropylene (PP), contain a prodegradant catalyst—usually a salt of manganese or iron, and are tested in accordance with ASTM D6954 or BS8472, or AFNOR Accord T51-808, as to their ability to degrade and then biodegrade in the open environment. The prodegradant catalyzes the abiotic degradation process so that Oxo-degradable plastic will degrade in the presence of oxygen much more quickly than ordinary plastic. The plastic material has then been converted into small-chain organic chemicals, such as ketones, alcohols, carboxylic acids, and low molecular mass hydrocarbon waxes. The remaining chemicals are no longer plastic and are biodegradable by bacteria, which are ubiquitous in the terrestrial and marine environments. The timescale for complete biodegradation at any time or place in the open environment is much shorter than for "conventional" plastics, which in normal environments are very slow to biodegrade and cause large scale harm.

Degradation is initially prevented by the presence of polymer stabilizers in the plastic, which ensures a useful service-life for the article. Once the stabilisers have been exhausted Oxo-degradation will begin. The chemical mechanism is that of autoxidation but it is greatly accelerated by the presence of metal-catalysts, which promote the homolysis of hydroperoxides into free radicals which drive the degradation process. Access to oxygen is essential and OXO-degradable plastics will not degrade if buried deep in landfill.

Conventional polyethylene (PE) and polypropylene (PP) plastics will typically fragment quite quickly, but will then take decades to become biodegradable. Oxo-degradable plastic, if discarded in the environment, will degrade to oxygenated low-molecular-weight chains (typically MW 5–10,000 amu) within 12–18 months, depending on the material (resin, resin thickness, anti-oxidants, etc.), temperature, and other factors in the environment.

Biodegradation of up to 92.74% has been observed in a soil environment within 180 days, when tested in accordance with ASTM D6954. Oxo-degradation has been studied at the Eurofins laboratory in Spain, where on 25 July 2017 they noted 88.9% biodegradation in 121 days.

The statements about biodegradation of oxo-degradable plastics were considered in the 2016 Eunomia Report for the EU Commission.

Standards applicability

Oxo-degradable plastic degrades in the presence of oxygen. Heat and UV light will accelerate the process, but neither they nor moisture are necessary. Such plastic is not designed to be compostable in open industrial composting facilities, according to ASTM D6400 or EN13432; but it can be satisfactorily composted in an in-vessel process, and has been proved to be compostable according to ISO 14855 [Eurofins Laboratories 6.11.16].

The standards for industrial composting, ASTM D6400 and EN13432, require the plastic to convert to carbon dioxide (CO₂) gas within 180 days by industrial composting. Indeed materials that do comply with ASTMD6400, EN13432, Australian 4746, and ISO 17088 cannot properly be described as 'compostable' because those standards require them to convert substantially to CO2 gas within 180 days. you cannot therefore make them into compost - only into CO2 gas. This contributes to Climate Change but does nothing for the soil. A leaf is generally considered to be biodegradable, but it will not pass the ASTM composting standards, due to the 180-day limit.

Oxo-degradable plastic conforms to the American Standard (ASTM D6954) and a British Standard (BS8472), which specify procedures to test degradability, biodegradability, and non-toxicity, and with which a properly designed and manufactured OXO product must comply. These standards contain pass/fail criteria.

There is no need to refer to a standard specification unless a specific disposal route (e.g., composting), is envisaged. ASTM D6400, EN13432, and  Australian 4736 are standard specifications appropriate only for the special conditions found in industrial composting.

According to an EU report, the oxo-degradable plastics do not biodegrade on a landfill nor should they be regarded as compostable.

In the marine environment

The Oxomar project(9) was a four-year interdisciplinary study, sponsored by the French Government. The scientists reported that “The goal was to evaluate the biodegradation of oxo-bio in marine waters.

They concluded that “We have obtained congruent results from our multidisciplinary approach that clearly shows that [oxo-degradable] plastics biodegrade in seawater and do so with a significantly higher efficiency than conventional plastics. The oxidation level obtained due to the d2w degradant catalyst was found to be of crucial importance in the degradation process.”

See also the report from Queen Mary University London by Rose et. al 11th February 2020(10). Para 2.6 says “Before testing, samples of LDPE and oxo‐LDPE were surface‐weathered in seawater for 82 days, undergoing natural variations in sunlight and UV intensity.

Landfill: Oxo-degradable plastic is not designed to be able to degrade in a landfill. If the plastic has been taken to a landfill, it has been responsibly disposed of and there is no need for it to degrade. Also, if anything biodegrades in anaerobic conditions it will generate methane, which is undesirable unless the landfill has been designed to collect the gas. Oxo-degradable plastic will not become biodegradable in the absence of oxygen. Recycling:(11)

• Recyclers have to assess the level of degradation of any plastic sent for recycling whether it is oxo-degradable or not. They cannot recycle ordinary plastic which has started to degrade after exposure to sunlight.
• If the recyclate is to be used to make short-life products (eg food packaging) it does not matter whether it contains oxo-degradable plastic, because biodegradation is desirable.
• Stabilization is, therefore, necessary only for long-life products, and the producer of long-life products would stabilize them in the same way whether the recyclate contains oxo-degradable plastic or not. He does not need to know the proportion of oxo-degradable plastic in the feedstock. This normal stabilization would neutralize any oxo-degradable residue.
• It is not necessary to separate oxo-degradable PE or PP from conventional PE or PP before recycling, but if so desired oxo-degradable masterbatch could be made visible to automatic sorting equipment by including a marker.
• Oxo-degradable masterbatch is used in PE and PP, but NOT in PET.

Microplastics

Many of the microplastics in the environment are caused by the fragmentation of ordinary plastic when exposed to sunlight. These fragments are very persistent in the environment because their molecular weight is too high for microbes to consume them, and can remain so for decades. This is why oxo-degradable plastic was invented, for single-use plastics The plastic falls apart because the molecular chains have been dismantled and it is no longer a plastic.

The European Chemicals Agency (ECHA) was asked to study oxo-degradable plastic in December 2017. They made a Call for Evidence, and they informed the BPA on 30th October 2018 after 10 months of study, that they had not been convinced that it creates microplastics. ECHA has never provided a dossier to support any ban on oxo-degradable plastic, and there is no evidence that microplastics from oxo-degradable plastic have ever been found in the environment. It has been used for bread bags for more than ten years by the largest bread producer in the world (Bimbo bakeries) and there have been no problems with microplastics or recycling.

Controversy

The Biodegradable Plastics Association (BPA) claimed that the EMF report was inaccurate and pointed out that many of the organizations shown as endorsing the report aggressively promoted a rival bio-plastic technology. In contrast, many of the others whose logos appeared in the document produced the same plastic items that get into the open environment as litter(13). The paper's conclusions were rejected by Professor Ignacy Jacubowicz, who said the degradation process was not merely a fragmentation, but a change from a high molecular weight polymer to a material that can be bio-assimilated(14).

The evidence for and against oxo-degradable plastic was also reviewed in November 2018 by Peter Susman QC, a deputy judge of the High Court of England, who had over 25 years of experience in adjudicating cases in the technology and construction branch of the High Court, involving the evaluation of expert evidence. He declared the scientific case favouring oxo-degradable plastic "clear and compelling". Susman examined the processes of abiotic and biotic degradation of plastics and then looked specifically at degradation in air and degradation in seawater. He concluded, in a 15-page report(15) that

It is no longer tenable to conclude that there is 'no firm evidence either way' whether oxo-degradable is effective. I consider that recent research provides clear and compelling evidence that oxo-degradable plastic is indeed effective in facilitating very significantly speedier degradation than is the case when that technology is not used... [I] cannot imagine that such significantly speedier final degradation occurs later than 'within a reasonable time'; however, the expression might be defined... [I regard the idea that biodegradable plastics might encourage littering as] "fanciful and unreasonable".

Regulation

Since 2017 there has been a move towards regulating or banning the use of oxo-degradable plastics, when the Ellen MacArthur Foundation published a statement supported by more than 150 organizations calling for a ban.

European Union

Effective July 2021, oxo-degradating plastics have been banned in the EU with Directive 2019/904, also known as the Single-Use Plastics Directive. Oxo-degradable plastics were particularly targeted by this directive. The rationale behind this focus was that oxo-degradable plastics often do not break down completely but instead fragment into microplastics, which persist in the environment and contribute to pollution.

In December 2020, Symphony Environmental Technologies filed a lawsuit against the European Commission, arguing that the prohibition was arbitrary and unlawful. However, in January of 2024 the European Court of Justice dismissed the suit, ruling that none of the Commission's actions had been improper.

United States

Although oxo-degradable plastics are not illegal in the US, the FTC has taken the stance that oxo-degradable plastics cannot be called "degradable" or "biodegradable" without strong scientific evidence. In 2014 the FTC advised 14 firms to either remove their oxo-degradable claims or provide reliable scientific evidence.

United Kingdom

Oxo-degradable are still permitted in the UK, although Scotland and Wales are studying a ban.

References

• 1 Scott, Gerald “Degradable Polymers, Principles and Applications” ISBN 1-4020-0790-6
• 2 ibid
• 3 ibid
• 4 Intertek 2.12.21
• 5 https://www.biodeg.org/subjects-of-interest/composting/
• 6 https://www.biodeg.org/wp-content/uploads/2021/02/Swift-evidence-to-BEIS.pdf
• 7 https://www.biodeg.org/wp-content/uploads/2021/07/Final-report-OXOMAR-10032021.pdf
• 8 https://www.biodeg.org/wp-content/uploads/2022/10/QM-published-report-11.2.20-1.pdf
• 9 Ibid fn 7
• 10 Ibid fn8
• 11 See https://www.biodeg.org/subjects-of-interest/recycling-2/
• 12 See https://www.biodeg.org/wp-content/uploads/2019/11/emf-report-1.pdf
• 13 https://www.biodeg.org/wp-content/uploads/2019/11/emf-report-1.pdf
• 14 https://www.biodeg.org/wp-content/uploads/2020/05/Reply-to-Ellen-MacArthur-Foundation-from-Prof-Ignacy-Jakubowicz-21-8-17.pdf
• 15 https://www.biodeg.org/uk-judge-find-the-case-for-oxo-degradable-plastic-proven/
• 16 https://www.symphonyenvironmental.com/wp-content/uploads/2022/09/bpa-responds-to-european-commission-2.pdf

Sources

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• Chiellini, Emo; Cortia, Andrea; Swift, Graham (2003). "Biodegradation of thermally-oxidized, fragmented low-density polyethylenes". Polymer Degradation and Stability. 81 (2): 341–351. doi:10.1016/s0141-3910(03)00105-8.

• Report from CIPET (India) test on Renatura OxoDegraded PE Film using ASTM D5338 demonstrates 38,5% Bio-mineralization of PE in 180 days 1991; 57(3): 678–685.

• Jakubowicz, Ignacy (2003). "Evaluation of degradability of biodegradable polyethylene (PE)". Polymer Degradation and Stability. 80 (1): 39–43. doi:10.1016/s0141-3910(02)00380-4.

• Jakubowicz, Ignacy; et al. (2011). "Kinetics of abiotic and degradability of low-density polyethylene containing prodegradant additives and its effect on the growth of microbial communities". Polymer Degradation & Stability. 96 (5): 919–928. doi:10.1016/j.polymdegradstab.2011.01.031.

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• Koutny, Marek; Sancelme, Martine; Dabin, Catherine; Pichon, Nicolas; Delort, Anne-Marie; Lemaire, Jacques (2006). "Acquired biodegradability of polyethylenes containing pro-oxidant additives" (PDF). Polymer Degradation and Stability. 91 (7): 1495–1503. doi:10.1016/j.polymdegradstab.2005.10.007.

• Seneviratne, Gamini; Tennakoon, N. S.; Weerasekara, M. L. M. A. W.; Nandasena, K. A. (2006). "Polyethylene biodegradation by a developed Penicillium–Bacillus Biofilm". Current Science. 90: 1.

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• Taylor, Lynn J.; Tobias, John W. (1981). "Accelerated Photo-Oxidation of Polyethylene (II). Further Evaluation of Selected Additives". Journal of Applied Polymer Science. 26 (9): 2917–2926. doi:10.1002/app.1981.070260908.

• Ungtae Lee, Anthony L. Polmetto III; Fratzke, Alfred; Bailey Jr, Theodore B. (1991). "Biodegradation of Degradable Plastic Polyethylene by Phanerochaete and Streptomyces Species". Applied and Environmental Microbiology. 57 (3): 678–685. Bibcode:1991ApEnM..57..678L. doi:10.1128/AEM.57.3.678-685.1991. PMC 182779. PMID 16348434.

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External links

• Oxo Biodegradable Plastics Federation