GLOBAL - Is oxo-degradable a biodegradable plastic or not? Or is the great debate just a silly semantic squabble over which is more sustainable?
The controversy over the end-of-life options for oxo-degradable plastics hit the headlines earlier this year when the US SIP Bioplastics Council and European Bioplastics trade associations fired an opening salvo at producers of oxo-degradable plastics alleging ‘unfounded claims’ and ‘misuse of the term biodegradability’.
The second salvo came with the publication of an independent British Government-funded report from Loughborough University, which questioned the impact of oxo-degradable plastics on the natural environment when it begins to break down into smaller pieces.
The report, commissioned by the UK’s Department for Environment, Food and Rural Affairs (Defra) also suggested that oxo-degradable plastics are neither suitable for conventional recycling methods due to the chemical additives. Nor is it suitable for composting - due to the plastics not converting carbon to carbon dioxide at the level of 60 per cent and 90 per cent over a period of 180 days according to the US and EU Standards, ASTM D6400-04 and EN 13432 respectively.
However, the report does concede “That oxo-degradables do degrade when exposed to either sunlight or heat (around 60 degC)”.
According to Robert Bobroff, International Business development manager of Symphony Environmental, all of these recent controversies have been borne out of a misconception of the terminology surrounding biodegradation, composting and oxo-degradable plastics.
Symphony Environmental is a producer and supplier of d2w, an additive formulation that renders conventional polyolefins oxo-degradable in a two-step process. The purpose of this, according to Symphony, is to address the problem caused by plastics waste that gets into the environment and cannot be collected for recycling, landfill, or other methods of disposal.
When included in the basic polymer resin during the manufacturing process, a catalyst within the d2w additive causes the breakdown of the molecular structure of the plastics film.
|Biodegradability||The breakdown of an organic chemical compound by micro-organisms in the presence of oxygen to carbon dioxide, water and mineral salts of any other elements present (mineralisation) and new biomass, or in the absence of oxygen, to carbon dioxide, methane, mineral salts and new biomass (from EN13432)|
|Biodegradable plastic||A degradable plastic in which the degradation results from the action of naturally occurring micro-organisms such as bacteria, fungi and algae (ASTM D 6400-99)|
|Composting||A managed process that involves the biological decomposition and transformation of biodegradable material to produce carbon dioxide, water, minerals and organic matter (compost or humus)|
|Degradation||A change in the chemical structure of a plastic involving a deleterious change in properties|
|Disintegration (syn. fragmentation)||The physical breakdown of a material into very small fragments. (After ISO/DIS 17088)|
|EN 13432||European standard for packaging recoverable through composting and biodegradation.|
|Oxidative Degradation||A complex series of chemical reactions in which the long chains of polyethylene molecules are broken down into shorter lengths by the action of oxygen, ultra-violet light and/or heat.|
|Source: EV0422: Assessing the Environmental Impacts of Oxo-degradable Plastics across their Life Cycle – Report to Defra. Dr Noreen Thomas, Dr Jane Clarke, Dr Andrew McLauchlin and Stuart Patrick|
“The first degradation stage starts when the plastic containing the additive is exposed to oxygen, heat, UV light and stress,” explained Bobroff. “Our d2w additives act to break down the carbon-carbon molecular bonds in the plastics, leading to a lowering of the molecular weight and eventual loss of strength and other properties. By that stage it is chemically no longer a plastic.”
The second stage occurs after the molecular weight loss has occurred and the material is then able to be completely biodegraded by bacteria and micro-organisms.
Stabilisers act to ensure that a sufficiently long shelf life is provided for each specific product, between 12 and 18 months.
“The shelf life requirements can be extended, depending on the customer’s requirements and intended application; we can give a shelf life of up to five years.”
Bobroff noted that the actual degradation period is not fixed, taking anything from two to five years to degrade totally.
“It is a process that is not solely dependent on the presence of the bacteria,” he said. “For example underground, where you would normally also get the bacteria in the soil, there are different soil temperatures and that also affects the speed of degradation.”
According to Bobroff, d2w additives do not affect the performance and optical properties of the plastics product during its useful life. They are also affordable, as products made with d2w comprise more than 99.5 per cent normal polymer and can be produced using conventional machinery.
In addition, oxo-degradable plastics can be re-used and recycled in the same recycling stream as conventional plastics.
Hydro vs Oxo
Bobroff is careful in his use of the term ‘biodegradable’. What is generally referred to in the market as ‘bioplastics’ – films made from a biological source for example starch-based PLA (polylactic acid)– Bobroff consistently referred to as ‘hydro-degradable’ films.
“Hydro-degradable films don’t react to oxygen, heat or UV rays; the only way they would break down is through exposure to bacteria,” he said. “So if you have a hydro-degradable film made from one of the various starch-based products that are available in the market, it will stay intact until it comes into contact with bacteria and/or micro-organisms.
“If they go into landfill, they will emit methane gas in the absence of oxygen, and this is a powerful greenhouse gas.
“Thicker cross-section plastics will not compost even under those conditions. So if you have a hydro-degradable film made from one of the various starch-based products that are available in the market, it will stay intact until it is collected and taken to an industrial composting plant.
“In a situation where the plastic is carelessly discarded as litter, nothing is going to happen to it.”
Hydro-degradable films, according to Bobroff, are not suitable for use unless an infrastructure is in place to collect them for industrial composting; otherwise, they are useless.
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