Sorting out Biodegradable Plastics

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.

 


Although there are three main categories of degradable plastics each category has its own nuances and particulars which need to be understood.  For example: biodegradable plastics can happen in either aerobic (with oxygen) or anaerobic (without oxygen) environments.  Compostable plastics such as PLA do not degrade in backyard composting but require “professional composting facilities” in order to maintain the constant temperature requirements for the bioplastics to degrade and the infrastructure for proper disposal is not present at this time.  Degradable plastics are those which break down from environmental conditions such as oxygen and ultra-violet light.  This degradation or fragmentation leaves small particles of plastic around until microbes are able to digest them (if ever).

 

Bioplastics/Bioresins — these are really the same terms in that bioresins are manufactured into bioplastics.  Bioplastics are a form of plastics derived from biomass sources which come from plants.  There are a number of various bioplastics solutions on the market today, however, based on the market size there are really two main bioplastics categories PLAs (Polylactic Acid) and PHAs (Polyhydroxyalkanoates)  .  PLA being derived from plant starches i.e. corn, potato, etc and PHA being derived from plant sugars i.e. sugarcane, molasses, etc.  Within both bioplastics category technologies there are literally dozens of different kind of polymers which can be created.  Currently both of these solutions require the use of the part of the plant which is also used as a human or animal food source.  In the bigger picture of things we as a human race need to decide which is more important to feed those in the world who are starving or to use our food resources to make plastics?

 

There is currently a lot of research happing in the area of bioplastics to develop new sources which are more environmentally friendly.  Moving away from fossil fuels as the feedstock for traditional plastics is definitely a better solution for the environment, however, we should move to bioplastics which are more environmentally sound, today there are no bioplastics on the market which have a better environmental footprint than that of traditional fossil fuel based plastics.

 

A very important aspect to keep in mind with the issue of biodegradable plastics is the entire lifespan of the biodegradable plastic (raw materials, development of those raw materials, manufacturing, product use and lifecycle, product end of life and disposal) and the environmental impact each segment has.