Symphony Environmental Technologies : Intertek Report to European Chemicals Agency

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Oxo-Biodegradable plastics and the micro-plastics issue: towards a logical approach Report to the European Chemicals Agency May 2018

1. lntertek has carried out a wide range of (LCAs) and other environmental studies. biodegradable plastics. The second one, biodegradable plastics and litter (1).

work on polymers, including various life Cycle Assessments lntertek produced two LCAs on plastic bags and oxo­ carried out in 2012, included an assessment of oxo­

1. Oxo-degradableplastics are conventional plastics which degrade by oxidation but do not become biodegradable for a long period of time. By contrast, oxo-biodegradable plastics are plastics which are designed to become biodegradable in a shorter time. Oxo-biodegradation is defined in CEN/TR 15351 as "degradation identified as resulting from oxidative and cell-mediated phenomena, either simultaneously or successively." It is not clear whether the reference to ECHA includes oxo­ biodegradable plastics, but this document is concerned with oxo-biodegradable plastics.
2. Oxo-biodegradableplastics are conventional plastics that contain a metal-based catalyst or catalysts that are designed to speed up the breakdown of polymer molecules until they are reduced to a size that is able to be biodegraded. Polymers comprise long molecular chains in the region of 250,000 Daltons in mass (one Dalton is the mass of one hydrogen atom). Polymers need to be broken down into the region of 5000 Oaltons before organisms can feed on them and achieve biodegradation. Conventional plastics eventually break down to this size, but oxo-biodegradable plastics are designed to achieve it much faster. Conventional plastics and oxo-biodegradable plastics are the same (apart from the addition of a small amount of catalyst in the case of oxo-biodegradable plastics), and the mechanisms of biodegradation are the same; oxo-biodegradable plastics are simply designed to achieve biodegradability sooner. Conventional plastics may take up to a century to be reduced in size to 5000 Daltons (the rate is highly variable depending on environmental conditions and other factors), whereas oxo-biodegradable plastics are likely to reach 5000 Daltons significantly sooner (again, the rate is variable, but is designed to be faster than conventional plastics).
3. Oxo-biodegradableplastics are made with a plastic masterbatch containing a catalyst that promotes degradation by oxidation in the presence of oxygen, and which reduces molecular weight to the point where biodegradation can occur. The masterbatch typically makes up 1% of the plastic it is used in. The masterbatch is itself mostly polymer, with the catalyst (or catalysts) making up only a small portion of the 1%. Therefore, the amount of catalyst in the plastic product is low-typically lower than other additives.in conventional plastic such as colourants, UV inhibitors, stabilisers,-extenders and so on.
4. The catalysts used in oxo-biodegradable plastics are metallic catalysts, often based on manganese, iron or cobalt, that are considered safe. They are not on any known toxic lists; for example, they are not among the hazardous substances listed in Art 11 of the Packaging Waste Directive 94/62/EC or in EN13432 AnnexA.1.2 (which is the European standard for plastics intended for composting in food­ production). Also, oxo-biodegradable plastics are tested according to the same eco-toxicity tests prescribed by EN13432 Annex E for plastics intended for composting (even though oxo-biodegradable plastics are not intended for composting). They are shown to be non-toxic by OECD standard testing. Plastics (whether oxo-biodegradable or not) may contain other less desirable substances-for which there may be evidence of harm, such as Bisphenol A - and authorities are taking appropriate steps to restrict the use of these substances.

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6. Various stakeholders offer differing opinions about how much faster degradation of oxo­ biodegradable plastics occurs compared to conventional plastics. The somewhat limited research [2) that has been carried out to date shows that the speed range of degradation may be from marginally faster than normal plastics, to very significantly faster, depending on such factors as the formulation of the masterbatch and the extent to which the plastic is exposed to UV light and heat (3).

1. "Polyethylenes containing pro-oxidant substances degrade by exposure to the environment, resulting in decreased molar mass and incorporated oxygen in the chain in the form of carboxylic groups.

   This exposure to natural weathering for a period of 3-4 months decreased the mechanical properties of polyethylene (containing about 80 mg kg-1 of cobalt), causing disintegration of the material. Saturated humidity increased abiotic oxidative degradation and biodegradation, as compared to natural humidity. The polyethylene bags mineralized about 12% of the original carbon in compost at 58 degrees C for three months after being exposed for one year to natural weathering. Exposure periods longer than three months and environmental moisture exert little influence on the degradability of cobalt-activated PE. There was low biodegradation of conventional PE films exposed to natural weathering for one month or longer, and fungi belonging to the genera Aspergillus and Penicillium grew on oxo-biodegradable PE films in environments with saturated humidity." [3)

   "........Oxo-biodegradable plastics are conventional plastics, such as High Density Polyethylene (HOPE), commonly used in carrier bags, which also include additives which are designed to promote the oxidation of the material to the point where it embrittles and fragments. This may then be followed by biodegradation by bacteria and fungi at varying rates depending upon the environment." (4)

   "Extrapolations from a laboratory study on a particular LOPE film engineered with a short service life suggest that almost complete degradation in soil can be achieved within two years." [4)

   "The debate around the biodegradability of PAC plastic is not finalised, but should move forward from the assertion that PAC plastics merely fragment, towards confirming whether the timeframes observed for total biodegradation are acceptable from an environmental point of view and whether this is likely to take place in natural environments." (4)

   "From the information studied, the authors of this Report can believe that it is possible for an OBP plastic to fully mineralise in an open environment, with the prodegradant additives encouraging this action, and thus the polymers and entrained substances can be assimilated into the natural environment." (4)

2. In ideal conditions for degradation, such as where the plastic has been exposed to UVB light [SJ, heat, humidity, and mechanical stress, there is no doubt that the rate of degradation is significantly faster than that of conventional plastics.
   "While all biomaterials, including plastics, will invariably biodegrade in the marine environment, the rate of this process, even in the benthic sediment, is several orders of magnitude slower compared to light-induced oxidative degradation of plastics." [6)
3. In non-ideal conditions, the degradation rate may be only marginally faster than that of normal plastics. (Oxo-biodegradable plastics are designed this way, so that they do not degrade in storage or use, only after use.) This is why the research shows a wide range of degradation rates. The key point is that the rate is faster. How much faster, and under what scenarios, is a matter of debate.

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