Bioplastics


PLA Quick Facts

Bioplastics: PLA derived from corn-starch
Bioplastics are a new generation of biodegradable and compostable plastics. They are derived from renewable raw materials like starch (e.g. corn, potato, tapioca etc), cellulose, soy protein, lactic acid etc., not hazardous in production and decompose back into carbon dioxide, water, biomass etc. when discarded.  Corn starch is currently the main raw material being used in the manufacture of bioplastic resins. Mater-Bi  (main component corn-starch), and PolyActide (PLA) (made from corn-starch as well) are currently the 2 main resins (raw materials), being used today in the production of compostable & biodegradable plastics and are certified for compostability under standards set by international organizations.  However, other resins are coming into the market made from potato starch, soybean protein, cellulose etc.  Most of these are currently not certified for compostability, though some are for biodegradability.  The field of bioplastics is constantly evolving with new materials and technologies being worked on and being brought to market.

Heat Resistance Biodegradability & Compostability
Bioplastics can take different length of times to totally compost, based on the material and are meant to be composted in a commercial composting facility, where higher composting temperatures can be reached and is between 90-180 days. Most existing international standards  require biodegradation of 60% within 180 days along with certain other criteria for the resin or product to be called compostable. It is important to make the distinction between degradable, biodegradable and compostable. These terms are often (incorrectly) used interchangeably.

Compostable Plastic is plastic which is "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."  American Society for Testing & Materials (ASTM).  In order for a plastic to be called compostable, three criteria need to be met:

  1. Biodegrade - break down into carbon dioxide, water, biomass at the same rate as cellulose (paper).
  2. Disintegrate - the material is indistinguishable in the compost, that it is not visible and needs to be screened out
  3. Eco-toxicity - the biodegradation does not produce any toxic material and the compost can support plant growth.

Biodegradable Plastic is plastic which will degrade from the action of naturally occurring microorganism, such as bacteria,  fungi etc. over a period of time.  Note, that there is no requirement for leaving "no toxic residue", and as well as no requirement for the time it needs to take to biodegrade.

Degradable Plastic is plastic which will undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties.  Please note that there is no requirement that the plastic has to be degrade from the action of "naturally occurring microorganism" or any of the other criteria required for compostable plastics.

A plastic therefore may be degradable but not biodegradable or it may be biodegradable but not compostable (that is, it breaks down too slowly to be called compostable or leaves toxic residue).  

Estimated Composting Times


The rate of biodegration for different biocompostables is dependent upon the composition and thickness of the material as well as composting conditions. Commercial composting facilities grind the materials, turn over the piles and reach high temperatures, thus reducing the amount of time it takes to compost and, is thus, the recommended method for composting these products. Home composting rates are slower and can vary, depending on how frequently the pile is turned over, the moisture and material content and the temperature.

Standards
There are currently few international organizations which have established standards and testing methods for compostability, namely:
The ASTM, CEN and DIN standards specify the criteria for biodegradation, disintegration and eco-toxicity for a plastic to be called compostable.

In the USA, the BPI (Biodegradable Products Institute) certifies bioplastics under the ASTM-6400-99 standard for "compostable plastics" and awards their logo to products which pass this certification.

The Natureworks resin is certified by BPIWorld.Org.