Compostable versus Biodegradable
To be termed `compostable’ packaging has to meet specific criteria in terms of:
- The time it takes to break down
- The environmental conditions it will break down in; and
- The quality and non-toxicity of the compost produced.
The American Society for Testing and Measurement (ASTM) defines compostable plastics as: “Capable of undergoing biological decomposition in a compost site as part of an available program, such that the plastic is not visually distinguishable and breaks down to carbon dioxide, water, inorganic compounds, and biomass, at a rate consistent with known compostable materials (e.g. cellulose), and leaves no toxic residue.”
According to the ASTM standards D6400 and D6868 (and the European equivalent EN13432), compostable plastics must meet the following three criteria:
- Biodegradability – Determined by measuring the amount of CO2 produced over a certain time period by the biodegrading plastic. The standards require 60% (90% in Europe) conversion of carbon into carbon dioxide within 180 days for resins made from single polymer and 90% conversion of carbon into carbon dioxide for co-polymers or polymer mixes.
- Disintegration – Measured by sieving the material to determine the biodegraded size and that less than 10% remains on a 2mm screen within 120 days.
- Eco-Toxicity – Measured by testing the concentrations of heavy metals to ensure that they are below the limits set by the standards and by testing plant growth by mixing the compost with soil in different concentrations and comparing plant growth in test and controlled compost samples.
Biodegradable means that a product will degrade from the action of naturally occurring microorganisms, such as bacteria and fungi, over a period of time. However – unlike compostable products – there is no requirement for products labelled `biodegradable’ to meet any eco-toxicity or break-down timeframe requirements.