Compostable Plastics are a new generation of plastics which are biodegradable and compostable. They are derived generally from renewable raw materials like starch (e.g. corn, potato, tapioca etc), cellulose, soy protein, lactic acid etc., are not hazardous/toxic in production and decompose back into carbon dioxide, water, biomass etc. when composted. Some compostable plastics may not be derived from renewable materials, but instead derived made from petroleum or made by bacteria through a process of microbial fermentation.
Currently, there are a number of different compostable plastics resins available in the market and the number is growing every day. The most commonly used raw material for making the compostable plastics is corn starch, which is converted into a polymer with similar properties as normal plastic products. Other compostable resins are available made from potato starch, soybean protein, cellulose and as well from petroleum and petroleum by products. It is counter intuitive to think that compostable resins could be derived from petroleum, when all normal plastic products are derived from petroleum and are non compostable. However, there are certified compostable resins available in the market, derived from petroleum and the field of compostable plastics is constantly evolving with new materials and technologies being worked on and being brought to market. There is even research underway to make compostable plastics from carbon dioxide.
Properties: The compostable resins for the most part mimic plastic properties, and different resins have different properties related to heat resistance, tensile strength, impact resistance, MVTR, oxygen barrier etc. One of the main compostable resin PLA, for example has a heat resistance of only 110F, while other compostable resins can have a much higher heat resistance.
Biodegradability and 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.