“Bio-based” or “degradable” plastics were developed as a solution to environmental concerns with conventional plastics: to help reduce litter and pollution and to conserve landfill space. And, they’ve been in circulation in various forms for years. So what are they?
“Biobased” vs. “Degradable” vs. “Biodegradable” vs. “Compostable”
“Biobased” or plant based plastics include degradable, biodegradable, compostable, bioplastic, bio-based, and oxo-degradable materials.
Biobased and plant-based refer to the raw materials – corn, soybean and wood, that are used as a substitute for petroleum based materials to manufacture the plastics. Biobased plastics can include a blend of ingredients from renewable and petroleum based sources or be 100% plant-based.
At end of life, they can be biodegradable, recyclable or compostable … or none of the above.1 In fact, some biobased ingredients can be chemically identical to the petroleum based alternative, and therefore, can be managed and recycled in traditional petroleum based resin streams (e.g. Coca Cola PET plantbottle).2
Biobased plastics generally comprise a small portion of inbound materials. It’s the variability and increase in these materials, combined with the need to reduce contamination in recycling and organics streams that’s a challenge. This is compounded by the lack of comprehensive data to quantify exactly how much of these materials is actually in waste and recycling streams.
Advantages of Biobased and Biodegradable Plastics
- Reduce reliance on petroleum based raw material feedstocks (biobased plastics)
- Increase convenience for users of organics diversion programs (e.g. acceptance of compostable plastic bags in residential green bin program)
- Reduce in plastic litter in marine environments
- Increase productivity & efficiency in specialized applications (e.g. agricultural mulch films, dissolvable medical sutures)
Disadvantages of Biobased, Degradable and Biodegradable Plastics
- Potential for contamination of traditional plastic recycling streams and organics streams
- Potential for increased environmental impact (e.g. compostable plastic decomposing in landfill, releasing methane)
- Confusion in the marketplace and opportunity for “greenwashing”
Distinguishing between degradable and biodegradable plastics
Degradable plastics break down into smaller pieces with mechanical degradation or through the addition of chemicals (e.g. with additives to make the plastic become brittle and crumble in sunlight, a.k.a. photodegradable, or additives that make it break down by oxidation, a.k.a oxo-degradable). While the plastic disintegrates into finer pieces, it hasn’t necessarily been converted to anything else, or the conversion can take years.3
Biodegradable plastics degrade into carbon dioxide, methane and water through biological action in a defined timescale and environment (composting, anaerobic digestion, marine environments and soil).4
Compostable plastics are a sub-classification of biodegradable plastics, where items biodegrade in an industrial composting environment. There are generally accepted standards and certifications that products must meet to be able to be classified as compostable. Most municipalities that accept compostable plastics (e.g. bags) in their organics programs endorse products that meet the specifications of the ASTM D6400 standard and are certified by the Biodegradable Products Institute (BPI) or equivalent.
A Growing Segment Within the Plastics Industry
According to the Plastics Industry Association, bioplastics are one of the fastest growing sectors of the plastics industry, with an anticipated 20-30% annual growth. Despite an increasing prevalence in the waste stream, waste composition results from audits across Ontario reveals that biobased and degradable plastics are not often sub-categorized apart from regular plastic items. For example:
- #7 PLA (biobased) plastic cup is generally categorized with #7 mixed rigid plastics;
- Retail PE film carry-out bag marked “degradable” is generally categorized with other PE film carry-out bags.
One common exception to this is compostable bags in the organics stream, which are often classified separately from other study categories.
For the Future
Degradable plastics currently comprise a relatively small proportion of the overall plastic mix. However, given the growth in this area and ever increasing pressures to reduce contamination in recycling and organics streams; consideration should be given to including degradable plastics as sub-categories within future waste composition specifications.
This blog was prepared by Ben Dunbar, AET Group Inc. and provided to share with CIF stakeholders via CIF Connections Blog. For more information, readers are invited to contact Ben at firstname.lastname@example.org
1 Biodegradable Products Institute, Confused by the terms Biodegradable & Biobased, January, 2015, www.bpiworld.org
3 Green Plastics: The Difference Between Degradable, Biodegradable, and Compostable, August, 2016, accessed in January 2018 from green-plastics.net.
4 SPI: The Plastics Industry Trade Association, Bioplastics Simplified: Attributes of Biobased and Biodegradable Plastics, February 2016.