Biodegradable versus compostable “plastics” – whats the difference?
Compostable products are biodegradable materials that break down quickly and can support plant growth. A compostable product must meet specific criteria in terms of time, environmental conditions and quality of compost produced.
An ideal composting environment is subject to certain heat, moisture, and oxygen conditions to assist the biological breakdown.
Compostable products break down to carbon dioxide, water, inorganic compounds, and biomass at a rate similar to paper. In approximately ninety days in the compost they break down into small pieces and leave no toxic residue. (WWW.Earth911.com)
ASTM International standards (www.ATSM.Org) determine the level to which ‘plastics’ are biodegradable, not all bags degrade quickly or safely according to these standards. The best bags meet their most stringent criteria, ASTM D6400, which is given to products that actually compost.
Biodegradable Plastic is a type of plastic which will eventually degrade (this could be 100 years) from the action of naturally occurring microorganisms (e.g., bacteria, fungi and enzymes).
On its own the term is to a degree obsolete as there is no time requirement for the biodegradation of biodegradable plastic. Nor is there any requirements for “eco-toxicity” (harmful residues) which may be left behind.
Degradable products are oil-based, they have an additive included to help trigger the process of degradation, they are neither compostable or biodegradable.
This type of plastic breaks down into smaller fragments and leaves behind plastic particles, they need specific UV conditions to create a chemical reaction for this to happen. If composted or buried in landfill they will not break down at all.
Marketing of “Biodegradable” waste bags can be misleading… always check your labels!
Unfortunately the process to make plastic biodegradable bags is cheaper and as it’s also more destructive for the planet. Compostable bags cost more to make and are therefore more expensive for the consumer to buy. However, the more we buy, the more will be made and eventually the process will become less expensive.
You can tell the difference between biodegradable and compostable quite easily, compostable feels very soft and not plastic like, they will also be clearly labelled as such.
Compostable bags are generally made from cornstarch, PLA and PBAT.
This type of cornstarch is usually made from corn not fit for consumption.
PLA (Polylactide) is also usually made from waste corn and other plants that are renewable.
PBAT (Polybutyrate Adipate Terephthalate) will biodegrade the fastest in home compost, it helps the two ingredients above decompose. It will not leave any toxic residues, however, it is currently partly derived from petrochemicals which are not renewable.
Around the world research is taking place in the hope of finding a resin with a higher bio-base, made from plants not derived from plants, that can then replace PBAT. So whilst compostable bags are the best option we have for now, they are not totally from renewable sources.