By Professor Gerald Scott DSc, FRSC, C.Chem, FIMMM

Chairman of the British Standards Institute Committee on Biodegradability of Plastics,and of the Oxobiodegradable Plastics Association’s Scientific Advisory
Board.

There is increasing public concern about plastic waste in the environment. All plastics will degrade and biodegrade, but they take much too long. In an ideal world all the plastic would be collected and re-used or ecycled, or incinerated with energy-recovery.  However, for the foreseeable future much of this plastic will be accidentally or deliberately released into the open environment, where it will lie or loat around for many decades.

An effective solution is to use oxo-biodegradable technology, which is designed to shorten the life of the plastic so that it will degrade at the end of a service life which is pre-programmed into it.  It degrades by a process of oxidation in the presence of oxygen, and then by the same biodegradation process as nature’s wastes (See: www.biodeg.org). Like ordinary plastic, it is made from a by-product of oil refining which used to be wasted, so nobody is importing extra oil to make it.

How ‘oxo-bio’ plastic works

A small percentage of an additive formulation is included in the plastic at the extrusion stage. The formulation breaks the molecular chains within the polymer and makes it degrade then biodegrade more quickly than twigs and leaves, and much more quickly than ordinary plastic.  Formulations approved by the OPA are certified non-toxic and fit for food-contact. They do not contain heavy metals

In the marine environment toxins are no more likely to attach themselves to pieces of plastic than to pieces of dead seaweed or to the trillions of other particles already present in the sea.

Oxo-biodegradation is effective on land or water and in all climatic conditions, in the light or the dark, in heat or cold, in whatever timescale is appropriate for the product.  It leaves no methane and no toxic dust nor any other harmful residues.  It does not leave any fragments and will self-destruct automatically, even if dropped as litter. There is no evidence that degradable plastics (whether oxo or compostable) have encouraged littering.

As ‘oxo-bio’ is designed to address the problem of plastic waste in the open environment, it is not designed to degrade in landfill.  It is not in fact desirable for anything to decompose deep in landfill unless the landfill is designed to collect the methane gas.  

Deep in landfill oxobio plastic becomes inert, like ordinary plastic, but compostable plastic can emit methane - a powerful greenhouse gas.

Recyclability

If collected during its useful life, oxobio plastic can be recycled (see www.biodeg.org/recycling.htm).  Banning plastic bags has an emotional appeal but it is not a good idea (see http://www.biodeg.org/Plasticbagbans.htm).

In June 2009 Germany’s Institute for Energy and Environmental Research concluded that oil-based plastics, especially if recycled, have a better Life-cycle Analysis than compostable plastics.

It is sometimes claimed by the lobbyists for the compostable plastics industry (“European Bioplastics” and “Biodegradable Products Institute”) that a plastic product is not “biodegradable” unless it can comply with EN13432 (and similar standards such as ISO 17088, ASTM D6400, ASTM D6868, and Australian 4736-2006).  This is not correct.  These standards are appropriate for compostable plastics but not for products designed to biodegrade if they get into the evironment.  EN13432 itself says that is not appropriate for plastic waste which may end up in the environment through uncontrolled means.

Industrial composting is not the same as biodegradation in the environment, as it is an artificial process operated according to a much shorter timescale than the processes of nature.  The requirement in EN13432 and similar standards for 90% conversion to CO2 gas within 180 days is not useful even for composting, because it contributes to climate change instead of contributing to the fertility of the soil.  “compostable” plastic, 90% of which has been converted to CO2 gas, is therefore virtually useless in compost. Nature's lignocellulosic wastes do not behave in this way.

Compliance with international standards

Oxo-biodegradable plastic products are normally tested according to ASTM D6954-04 “Standard Guide for Exposing and Testing Plastics that Degrade in the Environment by a Combination of Oxidation and Biodegradation.”  There are two types of Standards – Standard Guides and Standard Specifications  ASTM 6954 is an acknowledged and respected Standard Guide for performing laboratory tests on oxo-biodegradable plastic, and the second Tier of ASTM D6954-04 is directed specifically to proving biodegradation.

The tests performed according to ASTM D6954-04 tell industry and consumers what they need to know – namely whether the plastic is (a) degradable (b) biodegradable and (c) non eco-toxic.

It is not necessary to refer to a Standard Specification unless the material is intended for a particular purpose. ASTM D6954-04 provides that if composting is intended, ASTM D6400 should be used.

Conditions in the laboratory are designed to simulate so far as possible conditions in the real world, but have to be accelerated in order that tests may be done in a reasonable time.  Pre-treatment does not invalidate the results as extrapolated to real-world conditions.

ASTM D6954-04 not only provides detailed test methods but it also provides pass/fail criteria.  For example, para. 6.6.1 requires that 60% of the organic carbon must be converted to carbon dioxide during the test.  It is not necessary to continue the laboratory test until
100% has been achieved, because it is possible, by applying the Arrhenius relationship, to predict the time at which complete biodegradation is likely to occur.

Tests on oxo-biodegradable plastic products are usually conducted according to the test methods prescribed by ASTM D6954-04 by independent laboratories.  I have seen many laboratory test reports and am satisfied that oxo-bio products will totally biodegrade.

If the plastic currently polluting much of our land and marine environment had been made of oxo-biodegradable plastic, most of it would by now have completely degraded, and there would be no Great Pacific Garbage Patch.