Frequently Asked Questions
Why do we need oxo-biodegradable plastic?
Because thousands of tons of plastic waste are entering the worlds environment every day, and will remain there unless collected for incineration or composting, for hundreds of years.
How does it work?
A very small amount of pro-degradant additive is put into the manufacturing process. This breaks the molecular chains in the polymer, and at the end of its useful life the product falls apart. The plastic does not just fragment, but will be consumed by bacteria and fungi after the additive has reduced the molecular weight to a level which permits micro-organisms access to the carbon and hydrogen. It is therefore "biodegradable."
Does it really biodegrade, or does it just fragment?
The process of degradation continues until the material has biodegraded to nothing more than CO2, water, and humus, and it does not leave fragments of petro-polymers in the soil.
What types of biodegradable plastics exist?
The two main types are oxo-biodegradable and hydro-biodegradable. In both cases degradation begins with a chemical process (oxidation or hydrolysis), followed by a biological process. Both types emit CO2 as they degrade, but hydro-biodegradables (usually starch-based) can also emit methane. Both types are compostable, but only oxo-biodegradable can be economically recycled.
Surely education is the way to solve the litter problem?
Hopefully education will reduce the litter problem over several generations, but there is a lot of litter today and there will always be some litter. Action needs to be taken today to switch to oxo-biodegradable before millions more tons of plastic waste accumulate in the environment.
Isn it better to recycle than to let it biodegrade?
Yes, and one of the benefits of oxo-biodegradable plastic is that it can be recycled as part of a normal plastic waste stream. However, if the plastic is not collected it cannot be recycled, so it needs to biodegrade instead of accumulating in the environment.
Can it be composted?
oxo-biodegradable plastic does not degrade quickly in low temperature "windrow" composting, but it is ideal for "in-vessel" composting at the higher temperatures required by the new EU animal by-products regulations. Indeed it is likely that windrow composting will soon have to be phased out.
What happens to it in a landfill?
oxo-biodegradable plastics fragment and partially biodegrade to CO2 and water in the surface layers of the landfill, but the residues are completely inert deeper in the landfill in the absence of oxygen. They do not emit methane
By contrast, hydro-biodegradable (starch-based) plastics will degrade and emit CO2 in the surface layers of a landfill if there is enough microbial activity. However, in the depths of a landfill, in the absence of air, Hydro-biodegradable plastics generate copious quantities of methane, which is a powerful greenhouse gas.
Does it contain "heavy metals"?
It contains transition metal ions of Cobalt or Iron or Manganese, which are trace elements required in the human diet. They should not be confused with toxic heavy metals such as Lead, Mercury, Cadmium and Chromium, which are never used in oxo-biodegradable plastics.
Isn it made from oil?
oxo-biodegradable plastics are currently made from naptha, which is a by-product of oil refining, which would otherwise be wasted. Oil is of course a finite resource, but this by-product arises because the world needs fuels and oils for engines, and would arise whether or not the by-product were used to make plastic goods.
Unless the oil is left under the ground, carbon dioxide will inevitably be released, but until other fuels and lubricants have been developed for engines, it makes good environmental sense to use the by-product, instead of wasting it by "flare-off" at the refinery and using scarce agricultural resources to make plastics.
Recently, interest has been shown in manufacturing sugar derived polyethylene. These, like oil-derived PE, are not biodegradable, but they can be made oxo-biodegradable in the same way as the latter, by the addition of a pro-degradant additive.
But aren the hydro-biodegradable plastics renewable?
No. because the process of making them from crops is itself a significant user of fossil-fuel energy and a producer therefore of greenhouse gases. Fossil fuels are burned in the machines used to clear and cultivate the land, and in the manufacture and transport of fertilizers and pesticides and in transporting the crop itself. Energy is also used by the autoclaves used to ferment and polymerize material synthesized from biochemically produced intermediates (e.g. polylactic acid from carbohydrates etc). When the material biodegrades it emits CO2 and methane, so the total fossil fuels used and greenhouse gases emitted are more than for conventional or oxo-biodegradable plastic.
Hydro-biodegradables are sometimes described as made from "non-food" crops, but are in fact usually made from food crops, and drive up the price of human and animal food.
Does it leave any harmful residues?
No. oxo-biodegradable plastic passes all the usual ecotoxicity tests, including seed germination, plant growth and organism survival (daphnia, earthworms) tests carried out in accordance with ON S 2200 and ON S 2300 national standards.
Deliberately and totally lost?
The argument that oxo-biodegradable plastics are undesirable because their components are designed to be deliberately and totally lost is a fallacy, because if people want to incinerate with heat recovery, or mechanically recycle them, or compost them in-vessel, or re-use them, then thats OK, and they cost very little if anything more than conventional products. The key point is what happens to the plastic which is not collected, and gets into the environment as litter?
In any event, oxo-biodegradable plastics are not "deliberately and totally lost" even if they degrade in the environment, because biodegradation on land is a source of plant nutrients, just as is straw, grass, leaves etc.
More careless disposal?
Degradable plastic bags have been supplied by supermarkets for more than four years, but there is no evidence that people dispose more carelessly of them (whether oxo or hydrobiodegradable) and they have not been encouraged to do so.
But suppose for the sake of argument that 10% more were discarded. If 1,000 conventional and 1,100 oxo-biodegradable bags were left uncollected in the environment, 1,000 conventional bags would remain in the rivers, streets and fields for decades, but none of the oxo-biodegradable bags would be left at the end of the short life programmed into them at manufacture.
There will always be people who will deliberately or accidentally discard their plastic waste. What will happen to all the plastic waste that will not be recycled or will not be incinerated, and instead will litter the countryside - would it not be better if the discarded plastic were all oxo-biodegradable?
Can it be marketed as Biodegradable or Compostable?
The current EU Standard for composting (EN13432) is not appropriate for testing oxo-biodegradable plastic. However the EU Packaging Waste Directive does NOT require that when a packaging product is marketed as "degradable" or "compostable" conformity with the Directive must be assessed by reference to EN13432. The Directive provides that conformity with its essential requirements may be presumed if EN 13432 is complied with, but it does not exclude proof of conformity by other evidence, such as a report from a reputable body. Indeed Annex Z of EN13432 itself says that it provides only one means of conforming with the essential requirements.
How long does it take to completely degrade?
An important advantage of oxo-biodegradable plastic is that it can be programmed to degrade in whatever timescale is required. The average useful life of a carrier bag is about 18 months. During that time bags are often re-used for shopping or for use as bin-liners etc.
What national or international standards exist?
Until recently there was no standard designed to test oxo-biodegradable plastic.
However, In July 2007 the French Standards organisation, AFNOR, published XP T 54-980, which is a Standard for oxo-biodegradable plastics in agriculture.
A draft standard 8472 capable of measuring oxo-biodegradation was published by the British Standards Institution in 2007.
oxo-biodegradable plastic can be tested according to American Standard ASTM D6954-04 for Plastics that Degrade in the Environment by a Combination of Oxidation and Biodegradation.
European standard EN 13432 applies only to plastic packaging, and was written before oxo-biodegradable plastics became popular. It is not appropriate for testing oxo-biodegradable plastics because it is based on measuring the emission of carbon dioxide during degradation. Hydro-biodegradable plastic is compliant with EN 13432, precisely because it emits CO2 (a greenhouse gas) at a high rate.
Another unsatisfactory feature of EN 13432 is that it requires almost complete conversion of the carbon in the plastic to CO2, thus depriving the resulting compost of carbon, which is needed for plant growth, and wasting it by emission to atmosphere.
Conversion of organic materials to CO2 at a rapid rate during the composting process is not "recovery" as required by the European Directive on Packaging and Packaging Waste (94/62/EC as amended), and should not be part of a standard for composting. Natures lignocellulosic wastes do not behave in this way, and if they did the products would have little value as soil improvers and fertilizers, having lost most of their carbon.
If a leaf were subjected to the CO2 emission tests included in EN13432 it would not be considered biodegradable or compostable!
Packaging made from oxo-biodegradable plastic complies with para. 3(a), (b) and (d) of Annex II of the European Parliament and Council Directive 94/62/EC (as amended) on Packaging and Packaging Waste. This Annex specifies the essential requirements for the composition, and the reusable and recoverable, including recyclable, nature of packaging.
oxo-biodegradable plastic satisfies para. 3(a) because it can be recycled. It satisfies para. 3(b) because it can be incinerated. It satisfies para. 3(d) because it is capable of undergoing physical, chemical, thermal or biological decomposition such that most of the finished compost ultimately decomposes into carbon dioxide, biomass and water.
With what level of certainty can the timing of degradation be controlled?
As indicated elsewhere, the speed of degradability can largely be controlled by the additive package used for any particular application. The actual speed of degradation, however, is affected by the levels of uncontrollable variables – particularly heat, light and stress - to which the plastic is exposed. Higher than planned levels of these will speed up the process and lower levels will slow it down (but not stop it). For this reason, manufacturers typically build a significant safety margin into the planned degradation time so as to ensure that the properties of the plastic remain intact for the full useful life of the product in question.
Do the additives or finished products need to be stored or handled in any special way?
As indicated in the answer above, a degree of care is sensible so as to ensure that the products are not exposed to excessive heat, light or stress. For example, degradable plastics should be stored in a cool/shaded place rather than in the open air or in a hot, sunny place. Beyond this sort of ‘common sense’, no special requirements apply.
Is biodegradation the end result of degradation?
For products, the answer is yes. Oxidative degradation of polyethylene and polypropylene causes a breakdown of the molecular backbone of these plastics. The molecular chains become shorter and water ‘wettable’ permitting the formation of a bio-film on the surface of the plastics which allows microbial deterioration to take over.
Is the plastic material in a flexible packaging product (e.g. a shopping bag) after degradation reduced to zero?
Flexible plastic packaging, by its nature, has properties that are essential to provide effective packaging of products. These properties include water resistance, flexibility and strength. The long entangled molecular chains within a polymer determine these properties. With the oxidative action of the molecular ‘backbone’ collapses. The initial result is embrittlement leading to disintegration – the material can no longer be considered as a plastic. A loss of strength and then ultimately, after microbial deterioration has completed, the overall degradation process will have resulted in the creation of some H2O, some CO2, and a small amount of biomass.
How can microbes consume a plastic material?
Normally the microbes can not access the carbon or hydrogen in a plastic material because the chains are too long – indicated by the huge molecular mass of plastics, e.g. 300,000u However, it is now widely recognized that when a plastic material descends to below 40,000 molecular weight – due to oxidative degradation – the material becomes water wettable and can sustain a bio-film on its surface. This bio-film supports numerous micro-organisms that will feed off the carbon and hydrogen elements of the oxidizing plastic.
ref. Oxo-Biodegradable Plastics Association