OXO-biodegradation

OXO Biodegradable OXO-biodegradation is defined by CEN (the European Standards Organisation) {CEN/TR 1535–2006} as "degradation resulting from oxidative and cell-mediated phenomena, either simultaneously or successively."^[1] It is sometimes described as "OXO-degradable", but this describes only the first or oxidative phase and this description should not be used for material which degrades by the process of OXO-biodegradation defined by CEN. The correct description is "OXO-biodegradable."

Background

There are two different types of biodegradable plastic:

1. Vegetable based plastics (also loosely known as bio-plastics "bioplastics" or "compostable plastics"). These are tested in accordance with ASTM D6400 or EN13432 to biodegrade in the conditions found in industrial composting or biogas facilities. These plastics can contain up to 70% of oil derived components
2. Oxo-degradable plastic, made from polymers such as PE (polyethylene), PP (polypropylene), and PS (polystyrene) containing extra ingredients (metal salts) and tested according to ASTM D6954 or BS8472 or AFNOR Accord T51-808 to degrade and biodegrade in the open environment. These salts catalyze the degradation process to speed it up so that OXO plastic will degrade abiotically as soon as the addtives are added and oxygen is present, much more quickly than ordinary plastic.

It has then been converted into small-chain organic chemicals such as ketones, alcohols, carboxylic acids and low molecular mass hydrocarbon waxes which are no longer plastic and biodegradable by bacteria which are ubiquitous in the terrestrial and marine environments . The timescale for complete bio degradation 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^[2] and cause large scale harm.

The European Union has banned the use of oxo-degradable additives and since oxo-degradable additive containing plastics do not meet the compostability requires set out in ASTM D6400, they cannot be used in California. Some countries in the Middle East^[3] have banned plastics unless they are upgraded with oxo-biodegradable technology.

Degradation process

Degradation is a process that takes place in almost all materials. Conventional polyethylene (PE) and polypropylene (PP) plastics will typically fragment quite quickly, but will then take decades to become biodegradable. But OXO-degradable products utilize a catalyst to speed up the fragmentation.

Illustration of the OXO-Degradation: A process whereby the conventional polyolefin plastic is first oxidised to short-chain oxygenated molecules.

The first process of degradation in OXO-treated plastic is an oxidative chain scission that is catalyzed by metal salts leading to oxygenated (hydroxylated and carboxylated) shorter-chain molecules .

OXO-plastic, if discarded in the environment, will degrade to oxygenated low molecular weight chains (typically MW 5-10 000 amu) within 2–18 months depending on the material (resin, thickness, anti-oxidants, etc.) and the temperature and other factors in the environment. By contrast old-fashioned plastic will take decades to reach this stage, and in the meantime will have adsorbed toxins.

OXO plastics are designed so that they will not degrade deep in landfill and they will not therefore generate methane (a powerful greenhouse gas) in anaerobic conditions.

OXO-degradable products do not degrade immediately in an open environment because they are stabilized to give the product a useful service-life, during which they do not break down.

OXO-degradation of polymer material has been studied in depth at the Technical Research Institute of Sweden and the Swedish University of Agricultural Sciences. A peer-reviewed report of the work was published in Vol 96 of the journal of Polymer Degradation & Stability (2011) at page 919-928. It shows 91% biodegradation in a soil environment within 24 months, when tested in accordance with ISO 17556. It has been studied at the Eurofins laboratory in Spain and in many other laboratories around the world. It has been degraded in real time in seawater at the Banyul laboratory in France.

Standards applicability

OXO-biodegradable plastic degrades in the presence of oxygen, heat and UV light will accelerate the process, but they are not necessary and nor is moisture. It 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.

The standards for industrial composting (EN13432 and ASTM D6400) require the material to convert to CO2 gas within 180 days because industrial composting has a short timescale and is not the same as degradation in the open environment. A leaf is generally considered to be biodegradable but it will not pass the composting standards due to the 180-day limit. (Indeed, materials which do comply with ASTM D6400, EN13432, Australian 4736 and ISO 17088 cannot properly be described as "compostable." This is 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.

Oxo-biodegradable 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 has to comply with these standards. These standards contain contains 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 Australian 4736 and EN13432 are Standard Specifications appropriate only for the special conditions found in industrial composting.

Environmental issues

Oxo-degradable plastic, including plastic carrier bags, may degrade quicker in the open environment than conventional plastic. However, according to a report from the European Commission, there is no evidence that oxo-degradable plastic will subsequently fully biodegrade in a reasonable time in the open environment, on landfills or in the marine environment ^[4]. According to the report: "Sufficiently quick biodegradation is in particular not demonstrated for landfills and the marine environment. A wide range of scientists, international and governmental institutions, testing laboratories, trade associations of plastics manufacturers, recyclers and other experts have therefore come to the conclusion that oxo-degradable plastics are not a solution for the environment and that oxo-degradable plastic is not suited for long-term use, recycling or composting. There is a considerable risk that fragmented plastics will not fully biodegrade and a subsequent risk of an accelerated and accumulating amount of microplastics in the environment, especially the marine environment. The issue of microplastics is long acknowledged as a global problem in need of urgent action, not just in terms of clean-up of littering but also of plastic pollution prevention. ^[4]"

One major problem with testing oxo-degradable plastics for safety is that current standards and test methods can't realistically predict the biodegradability of carrier bags within natural ecosystems.^[5] Moreover, existing biodegradability standards and test methods for aquatic environments do not involve toxicity testing or account for the potentially adverse ecological impacts of carrier bags, plastic additives, polymer degradation products or small (microscopic) plastic particles that can arise via fragmentation.^[5]

Call to ban

On 6 November 2017, the Ellen MacArthur foundation issued a paper supported by 150 organisations, including M&S, PepsiCo and Unilever, backing a call to ban oxo-biodegradable plastics. The report had support from industry associations including the British Plastics Federation Recycling Group and Gulf Petrochemicals and Chemicals Association, NGOs such as the World Wildlife Fund (WWF), scientists including those based at Plymouth Marine Laboratory and ten MEPs from nine EU countries^[6].

The Oxo-Biodegradable Plastics Association (OPA) however, claimed the report was inaccurate. It argued many of the 150 organisations aggressively promoted a rival bio-plastic technology, while many of the others whose logos appeared in the document are themselves producers of the plastic items which get into the open environment as litter. 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.^[7]

European Strategy for Plastics in a Circular Economy

On 16 January 2018, the European Commission published its report on the use of oxo-degradable plastic.^[4] The document forms part of the European Strategy for Plastics in a Circular Economy,^[8] which was released the same day.

The Commission focussed on three key issues relating to oxo-degradables: the biodegradability of oxo-degradable plastics in various environments; the environmental impacts in relation to littering; and recycling.

The Commission found there was no conclusive evidence that, in the open environment, oxo-degradables fragmented to a sufficiently low molecular weight to enable biodegradation. There was no conclusive evidence about the time needed for oxo-degradable plastics to fragment in marine environments, nor about the degree of fragmentation. It said there was a considerable risk that fragmented plastics would not fully biodegrade, leading to a subsequent risk of an accelerated and accumulating amount of microplastics, especially in the marine environment. Rapid fragmentation increased the risk of microplastic ingestion by marine animals.

In relation to littering, the report found that although it appeared the oxo-degradable plastics industry could create products with minimal toxic impact on flora and fauna, it had not been conclusively proven that there were no negative effects. Marketing oxo-degradables as a solution for plastic waste in the environment may make it more likely items are discarded inappropriately and in marine environments, the fragmentation process made oxo-degradable plastic less likely to be recovered during clean-up exercises.

The report was criticised by the Oxo-Biodegradable Plastics Association (OPA) and said the European Commission had failed to understand the difference between oxo-degradable and oxo-biodegradable plastics.^[9]

It accused the Commission of not listening to evidence relating to the breakdown of oxo-plastics, which it maintained showed the plastic broke down to a molecular level that could be bioassimilated. In relation to timescales for biodegradation the OPA said it was not useful to examine how long it took for particular specimens to breakdown in particular conditions, due to the variability of environmental conditions. It said the key point was that oxo-biodegradable plastics would breakdown faster than conventional plastics in the same conditions. Regarding recycling, it said its members had been successfully recycling oxo-biodegradable plastics for more than ten years, with no adverse reports. It rejected the Commission’s view on littering and said that as oxo-degradable plastics were indistinguishable from other plastic products they were unlikely to cause any additional levels of littering.

It criticised the Commission’s use of external reports, including that of the Ellen MacArthur Foundation; the findings of which it previously disputed.

Sources

• Wiles, David M.; Scott, Gerald (2006). "Polyolefins with controlled environmental degradability". Polymer Degradation and Stability. 91: 1581–1592. doi:10.1016/j.polymdegradstab.2005.09.010.
• 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: 919–928. doi:10.1016/j.polymdegradstab.2011.01.031.CS1 maint: Explicit use of et al. (link)
• Sipinen, Alan J.; Rutherford, Denise R. (1993). "A Study of the Oxidative Degradation of Polyolefins". Journal of Environmental Polymer Degradation. 1 (3): 193–202. doi:10.1007/bf01458027.
• Taylor, Lynn J.; Tobias, John W. (1977). "Accelerated Photo-Oxidation of Polyethylene (I). Screening of Degradation-Sensitizing Additives". Journal of Applied Polymer Science. 21: 1273–1281. doi:10.1002/app.1977.070210510.
• Taylor, Lynn J.; Tobias, John W. (1981). "Accelerated Photo-Oxidation of Polyethylene (II). Further Evaluation of Selected Additives". Journal of Applied Polymer Science. 26: 2917–2926. doi:10.1002/app.1981.070260908.
• Koutny, Marek; Lemaire, Jaques; Delort, Anne-Marie (2006). "Biodegradation of polyethylene films with prooxidant additives". Chemosphere. 64: 1243–1252. Bibcode:2006Chmsp..64.1243K. doi:10.1016/j.chemosphere.2005.12.060.
• Jakubowicz, Ignacy (2003). "Evaluation of degradability of biodegradable polyethylene (PE)". Polymer Degradation and Stability. 80: 39–43. doi:10.1016/s0141-3910(02)00380-4.
• "Environmentally Degradable Plastics Based on Oxo-biodegradation of Conventional Polyolefins". Norman C. Billingham, Emo Chiellini, Andrea Corti, Radu Baciu and David M Wiles, Paper presented in Cologne (can be obtained from Authors).
• Koutny, Marek; Sancelme, Martine; Dabin, Catherine; Pichon, Nicolas; Delort, Anne-Marie; Lemaire, Jacques (2006). "Acquired biodegradability of polyethylenes containing pro-oxidant additives". Polymer Degradation and Stability. 91: 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.
• Chiellini, Emo; Cortia, Andrea; Swift, Graham (2003). "Biodegradation of thermally-oxidized, fragmented low-density polyethylenes". Polymer Degradation and Stability. 81: 341–351. doi:10.1016/s0141-3910(03)00105-8.
• Zheng, Ying; Yanful, Ernest K.; Bassi, Amarjeet S. (2005). "A Review of Plastic Waste Biodegradation". Critical Reviews in Biotechnology. 25: 243–250. doi:10.1080/07388550500346359.
• 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.
• 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.

References

External links

• Oxo Biodegradable Plastics Federation