How does it work and why is landfill biodegradable the best choice?

When it comes to biodegradable plastics, the three main choices are Oxo-Degradable (sometimes just called ‘degradable’), Compostable, and now Landfill-Biodegradable (which is our choice).

The table below summarises these technologies.

Plastic Property Landfill-Biodegradable  Home Compostable Compostable Oxo-Degradable
100% biodegradable in landfills? Yes Yes No No
100% recyclable with other mainstream plastics? Yes No No No
Special storage conditions required? No Yes Yes Yes
Shelf life / has expiration dates? No Yes Yes Yes
Will degrade over a few months when exposed to sunlight No Marginally Marginally Yes
Fragments into small pieces in ambient air No No No Yes
Biodegradation begins at time of disposal; not before Yes Yes Yes, in Commercial
compost facility only
No
Will biodegrade in commercial and home composts Yes Yes No, Commercial Only No
Needs oxygen in order to biodegrade No No Yes Yes

Landfill-Biodegradable

Biogone Plastics uses a patented additive to make our disposable products landfill-biodegradable. This means that the plastics will decompose under typical landfill environmental conditions much faster than traditional plastics which have an indefinite life span.  Biodegradation of plastic is achieved by enabling microorganisms to metabolize (i.e. break down) the molecular structure of the plastic, which produces an humus-like material (organic matter that cannot break down any further) which is a natural plant fertilizer.
Landfill-Biodegradable Plastics are made by combining traditional plastic with an organic additive.  The biodegradation only begins when the plastic is exposed to a microbe rich environment such as in a landfill.   The additive attracts microbes to the plastic and they start to digest it.   As they do this, the enzymes the microbes secrete cause the plastic polymer molecules to break down into shorter chains, which the microbes can then begin to digest them too. The biodegradability of a plastic can be confirmed by comparing biodegradation results from an independent laboratory with ASTM D5526 or D5511 tests on like materials.

Advantages of Landfill-Biodegradable Plastics:

  • Currently approximately 90% of plastic waste goes to a landfill.  This then is where the product should be designed to biodegrade.
  • No change of consumer’s disposal habits is required, which has been shown to be a big problem in the past.
  • Products made with a landfill-biodegradable additive are mainstream recyclable.
  • There are no shelf life issues as the plastic will only biodegrade when disposed to a landfill

Degradable (Oxy-Degradable)

Confusion also exists over the term ‘Degradable’ plastics.  A degradable plastic is a plastic with a metallic additive that sets off a slow chemical reaction and over 12-24 months will cause the plastic to fragment into little pieces.  This has nothing to do with biodegradation and microorganisms, and so instead of 1 piece of plastic we end up with hundreds or thousands of little pieces of plastic, which is a worse result for the environment.

Also, the reaction will only work in the presence of oxygen and sunlight.  So if a degradable plastic is buried in a landfill where there is no sunlight and very little oxygen, it will stay there like a conventional plastic not degrading.  Therefore for a degradable plastic to fragment down into little pieces it has to be up on top of the ground and there those little pieces will blow around and disperse into the environment. Biogone does not use degradable additives.

Compostable

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
  • Starch-based
  • Cellulose-based

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.

Commercial 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.

Home Compostable:
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.

Biodegradable Plastic Facts and Fallacies
Biodegradable Plastic Facts and Fallacies