Another type of biodegradable plastic often mentioned is known as ‘Compostable’. These are a type of bioplastic made from plant based material. Compostable plastics are subset of bioplastics that will biodegrade under composting conditions. Not all bioplastics are compostable and confusion exists over the term. Some people think that a bioplastic is automatically biodegradable. This is not the case. A bioplastic is a plastic made from plant materials. There is no inference about its biodegradability. Polyethylene plastic can be made from sugar cane, but it is no more biodegradable than polyethylene made from petroleum.
The more common types of bioplastics are:
- Polylactic acid (PLA) produced from cane sugar or glucose
Although the manufacturing of bioplastic materials is reliant upon petroleum as an energy and materials source, it is generally regarded as a more sustainable activity (due to carbon sequestration) when compared to petroleum-based plastics.
There are two types of compostable plastics they can biodegrade relatively fast in their respective locations. Commercial Compostable and Home Compostable.
These are bioplastics that biodegrade under commercial composting conditions as per AS736
At the present time there are several limitations for commercial compostable plastics that make them not a suitable choice for controlling plastic waste.
- For a compostable plastic to biodegrade it must be in a commercial compost facility with temperatures of 60 deg C, plenty of oxygen and good moisture levels. If those conditions are not met, the compostable plastic will not biodegrade as the microorganisms need those conditions to live.
- Due to their different composition, compostable plastics cannot be recycled in the mainstream. Their materials have different properties and would contaminate other conventional plastics if they were mixed together. If they cannot be delivered to a commercial compost facility, they need to go to landfill.
- There is no separate recycle facilities that will sort out the compostable plastic from other plastic waste. Which means by default a compostable plastic will generally go to a landfill where it will not biodegrade.
- There are very few commercial compost facilities in Australia, making it very unlikely that a commercial compostable plastic will ever be transported there.
- When a compostable plastic biodegrades its gaseous by-product is CO2, which cannot be used for energy capture methods to generate green electricity (as opposed to the CH4 generated from landfill-biodegradable plastics).
*Biogone does not supply commercial compostable plastics.
Though similar to commercial compostable plastics, they have an extra component in them, PBAT* which is a highly degradable material. This allows home compostable products to biodegrade in the cooler temperatures of home compost bins or landfills. Their biodegradation rates are longer than commercial compost facilities but still relatively fast being several months to 1-2 years. Biogone’s home compostable products will biodegrade in the anaerobic conditions of a landfill too. This makes them especially appealing to the general consumer who disposes their plastic waste to a rubbish bin. They come with an AS5810 standard certification to guarantee their biodegradability.
Benefits of Home Compostable Products:
- Can be disposed to a rubbish bin or home compost pile. They can also be disposed to some green council bins where permitted. Inquire with your local council.
- Will biodegrade in aerobic or anaerobic conditions in a landfill. The latter condition allowing their internal energy to be captured and used to generate electricity.
Note neither compostable nor home compostable plastics are recyclable. Their material will not mix with conventional plastics.
*PBAT (polybutyrate adipate terephthalate) is a biodegradable random copolymer . The co-polymer is available commercially as resin and as compound with PLA or starch. Today, the building blocks are made from petrochemicals. As a “drop-in” polymer, PBAT resembles LDPE in its properties. The flexibility and toughness of this polymer makes it ideal for blending with another biodegradable polymer that is strong and rigid.
*Note: In all the types of plastic mentioned above, none will biodegrade in the ocean or waterways as there are no suitable microorganism there to digest the material. So every attempt should be made to ensure they do not end up there by disposing of them correctly. i.e. landfill or home compost bin where suitable.