Degradable and Biodegradable Plastics

Degradable plastics

Plastic bags labelled as ‘degradable’ are generally made of the same material as lightweight, checkout-style plastic bags but include an additive that causes the plastic to breakdown more quickly into small pieces when exposed to light, oxygen and heat. However, the ultimate breakdown to an environmentally benign endpoint is slow. Lightweight ‘degradable’ plastic bags are banned under the Tasmanian legislation.

Compostable biodegradable plastics

Retailers can continue to supply compostable biodegradable plastic bags that demonstrate compliance with the Australian Standard AS 4736 ‘Biodegradable Plastics Suitable for Composting and Other Microbial Treatment’.

Plastics complying with this standard are made of materials that under suitable conditions in commercial composting facilities, and in a relatively short time frame, can degrade to the point where microorganisms can completely metabolize them to carbon dioxide, water, biomass & mineral salts.

The AS 4736 standard has been chosen for inclusion in the legislation because it is a widely accepted standard with reliable testing procedures to confirm the legitimacy of any claims. Australian commercial composting facilities can accept plastics that comply with this standard and process them into compost.

At the end of their life, compostable biodegradable plastics should be placed in kerbside food and green garden organics A number of Tasmanian Councils have undertaken kerbside food and green garden organics collection trials and a local Tasmanian company now provides household and business kerbside collections of food and green garden organics (including AS4736 compliant plastics), in some areas. The ‘wastes’ are processed into premium compost at a Tasmanian commercial composting facility and then sold throughout Tasmania.

Under the proposed legislation, if requested, retailers providing these bags must be able to validate their compliance with the standard by providing certification from the supplier/manufacturer.

What is the AS 4736 – 2006 standard for biodegradable plastics?

A description of the AS 4736 by the Australasian Bioplastics Association (ABA) is given below.

If a plastic material claims to be biodegradable and compostable in Australia, it must comply with Australian Standard AS 4736 ‘Biodegradable Plastics Suitable for Composting and Other Microbial Treatment’. This Standard provides assessment criteria for plastic materials that are to be biodegraded in municipal and industrial aerobic composting facilities. This Australian Standard is similar to the widely known European EN 13432 standard, but has an additional requirement of a worm test. In order to comply with the AS 4736-2006, plastic materials need to meet the following requirements:

  • minimum of 90 percent biodegradation of plastic materials within 180 days in compost;
  • minimum of 90 percent of plastic materials should disintegrate into less than 2mm pieces in compost within 12 weeks;
  • no toxic effect of the resulting compost on plants and earthworms;
  • hazardous substances such as heavy metals should not be present above the maximum allowed levels; and
  • plastic materials should contain more than 50 percent organic materials.

This Standard was prepared by Standards Australia to assist authorities regulate polymeric materials entering into the Australian market.

The ABA manages a certification system for biodegradable plastics. A seedling logo is used to clearly identify certified compostable packaging materials. To be certified compostable and carry the seedling logo, suitable biopolymer materials must undergo a stringent test regime outlined by AS 4736 and carried out by recognised independent accredited laboratories to the AS 4736 standard.

Use of the seedling logo is available by both packaging material producers and their customers. The seedling logo can be printed on the finished product (e.g. films, injection mouldings and bags) to market the product’s compliance to AS 4736. Use of the seedling logo will ultimately help the end consumer, customers and/or municipal authorities to recognise compostable packaging and dispose of it accordingly. Importantly, the seedling logo will communicate the authenticity and independent verification of claims of compliance to AS 4736.

Other similar standards include the American Standard ASTM D6400 by the Biodegradable Products Institute (BPI), and the European standard EN 13432-2000 by Organic Waste Systems (OWS) in Belgium.

What is the AS 5810 standard for biodegradable plastics?

The AS5810 standard specifies requirements and procedures to determine whether a plastic material is biodegradable in home composting conditions and provides the basis to allow labelling of materials or products made from plastic as 'home compostable', for use in home composting systems.

Home composting systems vary considerably in their design, construction and operation; hence their performance also varies considerably compared to commercial composting facilities. Consequently, this Standard, in comparison to AS 4736, uses lower temperatures in test environments and a longer test duration, to account for such variations in home composting performance.

Interestingly, many AS 4736 complaint bags manufactured by Australian companies also meet the AS 5810 standard, so can be put in your home compost bin. Contact the manufacturer of the bags to confirm.