There are three main categories of degradable plastics: biodegradable plastics, compostable plastics and degradable plastics. One of the biggest contributions to the confusion surrounding the subject of degradable plastics is a combination of the lack of common definitions and the loose usage of these definitions.
The ASTM International, originally known as the American Society for Testing and Materials, is a standards organization, host to committee D20.96 on Environmentally Degradable Plastics and Biobased Products. The ASTM maintains a Standard Terminology Relating to Plastics under their designation: D 883 – 08. The following are the ASTM definitions for degradable plastics:
biodegradable plastics—a degradable plastic in which the degradation results from the action of naturally-occurring micro-organisms such as bacteria, fungi, and algae.
compostable plastic—a plastic that undergoes biological degradation during composting to yield carbon dioxide, water, inorganic compounds, and biomass at a rate consistent with other known compostable materials and leaves no visually distinguishable or toxic residues.
degradable plastic—a plastic designed to undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties that may vary as measured by standard test methods appropriate to the plastic and the application in a period of time that determines its classification.