What are compostable plastics


The vast majority of our unwanted materials are buried in Tasmanian landfills, including compostable plastics. As the clip above shows, landfills are designed to hold these materials rather than to create a place where materials can decompose. As the movement towards food and greenwaste collection services increases momentum, people are now looking to compostable plastics as a way to improve the end of life options for many of our unwanted goods. 

If you are interested in compostable plastics, information can be found on the Australasian Bioplastics Association website (including the certification processes and who is certified). Below is a short summary: 

All (bio- and petroleum-based) plastics are technically biodegradable, meaning they can be degraded by microbes under suitable conditions. However, many degrade at such slow rates as to be considered non-biodegradable in practical terms.

Bioplastics are a form of plastics derived from renewable biomass sources, such as vegetable fats and oils, corn starch, pea starch or microbiota. Common plastics, such as fossil-fuel plastics, are derived from petroleum. Some, but not all, bioplastics are designed to biodegrade. Bioplastics which are designed to biodegrade can break down in either anaerobic or aerobic environments, depending on how they are manufactured.

The degree of biodegradation varies with temperature, polymer stability, and available oxygen content. Consequently, most bioplastics will only degrade in the tightly controlled conditions of industrial composting units. In compost piles or simply in the soil/water, most bioplastics will not degrade, starch-based bioplastics will. The Australian Standard AS4736 defines how quickly and to what extent a plastic must be degraded under industrial composting conditions for it to be called compostable. It is designed for the aggressive conditions of industrial composting units at or above 55 degrees Celsius.

Traditional plastics such as polyethylene are degraded by ultra-violet (UV) light and oxygen. To prevent this, process manufacturers add stabilising chemicals. However, with the addition of a degradation initiator to the plastic, it is possible to achieve a controlled UV/oxidation disintegration process. This type of plastic may be referred to as degradable plastic or oxy-degradable plastic or photodegradable plastic because the process is not initiated by microbial action. While some degradable plastics manufacturers argue that degraded plastic residue will be attacked by microbes, these degradable materials do not meet the requirements of the AS4736 commercial composting standard. The bioplastics industry has widely criticized oxo-biodegradable plastics, which the industry association says do not meet its requirements. Oxo-biodegradable plastics – known as "oxos" – are conventional petroleum-based products with some additives that initiate degradation. There is currently no proven evidence that bio-organisms are really able to consume and biodegrade oxo plastics.

Biodegradability is defined in the AS4736 as ‘the ability of organic substances to be broken down by micro-organisms in the presence of oxygen (aerobic) to carbon dioxide, water, biomass and mineral salts or any other elements that are present (mineralisation). Alternatively, the breakdown of organic substances by micro-organisms without the presence of oxygen (anaerobic) to carbon dioxide, methane, water and biomass.

Composting is defined in the AS4736 as ‘the aerobic and thermophilic degradation of organic matter to make compost.

Biodegradability standards

Australian Standards have been developed to provide reference for Australian government, regulators and industry so that compostable, home compostable and biodegradable can be defined, in this way minimising the likelihood of misrepresentation and preventing harmful products being introduced. Times and conditions are specified in the performance standards to give meaning to the words. The product must disintegrate and biodegrade within the stipulated times under the stipulated conditions with the stipulated results including toxicity of the residue to meet the requirements of the performance standard and be so certified.
When asked about other standards the Australasian Bioplastics Association (ABA) gave this reply:

To the best of our knowledge, there are no American, Australian or International performance standards addressing biodegradability of plastics for the reason that exposure conditions vary so much that it has proven impossible to arrive at acceptable test conditions that will cater for all environments. In all jurisdictions, biodegradability is covered within the compostability performance standards where the test duration and conditions are defined. An industry in-soil biodegradability test method and performance process exists in Europe, but to date it has not been adopted as an ISO standard. Much work has been done in Australia and elsewhere in the expectation of developing biodegradability standards covering terrestrial and aquatic conditions, but no Australian Standard is likely for some time. In summary, AS4736 - 2006 addressing industrial compostability and AS 5810 - 2010 addressing home compostability are the referenced performance standards for biodegradability because duration and conditions are defined.

Australian Standard AS 4736

The Australian Standard AS 4736 was prepared by Standards Australia to assist authorities regulate polymeric materials entering into the Australian market.

In order to comply with the AS 4736‐2006, plastic materials must meet the requirements specified in the standard and summarized below:

• 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
• plastic materials should contain more than 50 percent organic materials.

Plastics complying with the AS 4736‐2006 can be accepted at the commercial composting facilities in Tasmania. The plastics disintegrate sufficiently (and commence biodegradation) within the time that it takes to complete one compost cycle.

The majority of biodegradable plastics sold in Australia are certified to AS 4736‐2006 and made from starch-based bioplastics or polylactic acid (PLA) bioplastics. PLA is produced from cane sugar or glucose. It not only resembles conventional petrochemical mass plastics in its characteristics, but it can also be processed easily, albeit more expensively, on standard equipment that already exists for the production of conventional plastics.

Environmental claims

The AS 4736‐2006 is not a mandatory requirement for biodegradable plastics in Australia, however, the environmental benefits claimed by any product must be substantiated and cannot contravene the principles outlined in the Australian Competition & Consumer Commission’s publication Green marketing and the Australian Consumer Law. So, if a product claims to be biodegradable in Australia, in accordance with the Australian Consumer Law, it must comply with the AS 4736‐2006. The same applies to ‘compostable’ claims. To not meet this standard would be misleading.

However, according to the ABA:

Products certified to the requirements of another region’s compostable plastic standard (e.g. the similar European standard EN13432) can be sold in Australia and may carry the seedling logo, but cannot be assumed to meet the requirements of the Australian standard. They may disintegrate and biodegrade within acceptable time frames and conditions, but the resulting compost may fail the worm toxicity test. Interestingly many commercial composting facilities will accept compostable plastic products that are certified to other regions’ standards.

One would presume that products certified to the requirements of another region’s compostable plastic standard (e.g. (the European standard EN 13432 is similar to AS4736 ) and being sold in Australia would need to be clearly labelled to explain what standard they comply with.

BioPak, suppliers of take away deli containers, amongst other biodegradable plastic products, interestingly, at one point stopped declaring (on the packaging itself) that their products are biodegradable and compostable because, according to advice that they were given from the ABA, the ACCC believes that until 60% of the population have the ability to get their biodegradable wastes to a commercial composting facility, the wastes are not in fact biodegradable or compostable, hence the public are being misled.

The collection of food and green waste for commercial composting is expected to grow over the coming years, so we hope compostable biodegradable plastics will have an end destination soon.

Compostable biodegradable plastics seedling logo

Compostable biodegradable plastics can, if certified, carry the seedling logo. The seedling logo is used around the world to clearly identify certified compostable packaging materials. The Australasian Bioplastics Association (ABA) manages the certification system for biodegradable plastics in Australia. To be certified compostable in Australia 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.

Australian home composting standard AS 5810

There is an Australian Standard for biodegradable plastics suitable for home composting (AS 5810-2010). As there are very few ways for compostable plastics to get to commercial composting facilities in Tasmania, this is perhaps a better standard to aim for. The time frames specified in this standard are longer and so plastics meeting this standard could potentially not compost within one compost cycle at a commercial composting facility, however according to the ABA most, if not all, bioplastics meeting the AS 5810 also meet the AS 4736.