Another type of biodegradable plastic often mentioned is known as ‘Compostable’. These are a type of plastic made from renewable sources rather than petroleum-based plastics and will quickly biodegrade in a commercial compost facility (not in a backyard compost or garden bed). 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. Compostable plastics are bioplastics that biodegrade under commercial composting conditions as per ASTM 6400*. Note that not all bioplastics are compostable. Bio-Gone Plastics does not use compostable plastics.
* To meet ASTM 6400 standards, a plastic needs to exhibit 60% biodegradation within 180 days in commercial composting conditions.
Confusion exists over the term bioplastic. 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 other question regarding bioplastics is, should we really be using good arable land for growing crops destined for bioplastics when the world has a food shortage?
Limitations to compostable plastics
At the present time there are several limitations for compostable plastics that make them not a suitable choice for controlling plastic waste.
- For a compostable plastic to biodegrade it has to 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 compostable plastic will ever be transported to one to biodegrade.
- 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).