Biobased plastics (also called plant-derived) are made from a renewable resource such as corn starch. Polylactic Acid or PLA, is a commonly recognized bioplastic. PLA is made by fermenting the dextrose from a hydrolysis of corn starch. The product of this fermentation process, lactic acid, becomes the basic building block for polylactide plastics which can be digested by the microorganisms found in commercial compost facilities.
Compostable plastics biodegrade in a composting environment yielding water, CO2 and biomass. They biodegrade at a similar rate to other known compostable materials. Compostable plastics can be plant based but they can be petroleum based as well. The biodegradability does not depend on the raw material but entirely on the chemical structure of the polymer chains. BASF® Ecoflex® is a good example of a compostable polymer which is partly petroleum based but is compostable at industrial compost facilities.
For both biobased and compostable plastics, the presence of microorganisms, high temperatures, humidity and oxygen at an industrial compost facility provide the ideal conditions for the plastics to break down rapidly.
At a compost facility, the microorganisms like bacteria will produce enzymes that break down the long and flexible polymer chains of compostable polymers into smaller and smaller molecules through a chemical process called hydrolysis which causes these molecules to split.
This can happen only if the polymer chains contain bonds called ester bonds that can be broken by hydrolysis. With the addition of water, hydrolysis splits these bonds into alcohol and organic acid.
Eventually, the compostable polymer molecules become so small that they can be digested by the bacteria found in commercial compost facilities.
Organix Solutions BPI® approved compostable liners contain both PLA and BASF® Ecoflex® resin. Within 45 days, our compostable bags - and the food waste they contained - have been turned into valuable nutrient rich compost.
BPI® Certification and the ASTM D6400 standard
In order to be recognized as a biobased or compostable plastic they must meet the ASTM D6400 standard which requires:
- The product must physically disintegrate to the extent that it cannot be "readily distinguishable" from the finished compost product
- The product must actually biodegrade (be consumed by microorganisms) and a rate comparable to know compostable materials
- The product cannot have adverse impacts on the ability of the compost to support plant growth.
For bioplastics to meet these requirements, they must undergo specific tests by approved laboratories. The Biodegradable Products Institute (BPI®) provides independent verification that a bioplastic product has passed the criteria outlined by the ASTM 6400 standard. The product can then carry the widely known and respected BPI® logo certifying the product as compostable.