The biggest threat, with the introduction of degradable plastics, is they will not be clearly identifable. This could lead to the contamination of successful recycling methods that are in place now for other types of plastics. It is therefore paramount that a code of practice is developed to manage this.

There are five different kinds of degradable plastic:

Biodegradable, Compostable, Hydo-Biodegradable, Photo-degradable and Bioerodable.  These can be either organically based from renewable resources or synthetic with a petroleum base. 

To make sure the public is well informed about the issues surrounding these materials Plastics New Zealand hopes to develop a Code of Practice for the use of degradable plastics in New Zealand.   This will provide the plastics industry and consumers with a simple framework for making purchasing decisions.  The Code of Practice will be released to provide:

• Simple definitions of degradable plastics

• Recommended International Standards

• Best Practice Guidelines for selection, use and disposal, and

• Guidelines for Labelling

In the mean time, if you are purchasing a degradable plastics product make sure you consider:

•   How it is labelled

•   The disposal route

•   What recovery systems are in place eg. landfill, recycling, or composting

•   The infrastructure required and

•   Most importantly ensure that the product has been tested against internationally agreed standards that ensure your disposal options are appropriate and  environmentally sustainable.

Biodegradable plastics:

Biodegradable plastic bags and packaging aren't an end solution to replacing non-degradable plastic bags in supermarkets and retails stores for the following reasons:

•   They do not decompose in properly managed landfills

•   They support the throwaway mindset and the use of landfills as an acceptable disposal method

•   They do not discourage over-use in the first place.

Definitions of bioplastics:

• Compostable plastic: A plastic that undergoes biological degradation during the composting process (up to 2-3 months in a windrow) to yield carbon dioxide, water, inorganic compounds and biomass at a rate consistent with other known compostable materials and leaves no visually distinguishable or toxic residues.

• Biodegradable plastic: A degradable plastic in which the degradation must result from the action of naturally occurring microorganisms over a period of time (up to 2-3 years in a landfill).

• Degradable plastic: An oil based plastic containing a chemical additive that undergoes significant change in its chemical structure causing it to break down into smaller particles. The degradation process is triggered only when material is exposed to specific environmental conditions (such as UV, heat and moisture). Residues are not food matter for microorganisms and are not biodegradable or compostable

The range of degradable plastics now available includes (Nolan ITU, 2002):

• Starch-based products including thermoplastic starch, starch and synthetic aliphatic polyester blends, and starch and PVOH blends.

• Naturally produced polyesters including PVB, PHB and PHBH.

• Renewable resource polyesters such as PLA.

• Synthetic aliphatic polyesters including PCL and PBS.

• Aliphatic-aromatic (AAC) copolyesters.

• Hydro-biodegradable polyester such as modified PET.

• Water soluble polymer such as polyvinyl alcohol and ethylene vinyl alcohol.

• Photo-degradable plastics.

• Controlled degradation additive master batches.

For More information:

See Biodegradable Plastics - Developments and Environmental Impacts Environment Australia Report, Nolan ITU, October 2002

Australian document on ‘Biodegradable Plastics – Developments and Environmental Impacts’ published in 2002 by Nolan-ITU.

Other associated links:
http://www.deh.gov.au/settlements/waste/degradables/index.html

http://www.deh.gov.au/settlements/waste/degradables/newsletter.html