BIO-DEGRADABLE VS. COMPOSTABLE PLASTICS
Over the last few years, a number of bioplastic products have emerged. They are sometimes labeled “biobased,” “biodegradable,” and/or “compostable.” Bioplastics, according to the Society of the Plastics Industry (SPI) Bioplastics Council, are defined as a plastic that is biodegradable, has biobased content, or both. For biodegradable bioplastics, products are typically intended for short-life applications such as single-use packaging, food waste collection bags, or food service ware (e.g. utensils, cups, plates), and are promoted for composting at the end-of-life. Compostable products have the potential to streamline the collection of food scraps and yard trimmings for composting, helping to divert it from disposal in landfills and incinerators.
To make the right choice to recycle, compost, or dispose of these products at their end-of-life, consumers need to know the differences and be able to identify these products from traditional plastics. Labeling can be confusing. And, if products are improperly sorted at their end-of-life, they can cause problems with traditional plastic recycling, contaminate compost, and cause more products to end up in landfills.
WHAT IS BIOPLASTIC?
A biobased plastic is made from renewable resources instead of fossil fuels. Examples of renewable carbon resources include corn, potatoes, rice, soy, sugarcane, wheat, and vegetable oil. A biobased plastic can be partly or entirely biobased.
Note that just because a plastic product is biobased does not necessarily mean the product is biodegradable or compostable.
WHAT IS BIO-DEGRADABLE PLASTIC?
A biodegradable plastic can degrade by naturally occurring microorganisms such as bacteria, fungi, and algae to yield water (H2O), carbon dioxide (CO2) and/or methane (CH4), biomass, and inorganic compounds. However, the environment and timeframe must be specified in which biodegradation is expected to occur, otherwise, the claim is meaningless. For example, a yard waste collection bag may be biodegradable in a composting environment; agricultural mulch film may be soil biodegradable. Without these qualifications, the term “biodegradable” can be problematic, since it may lack clearly definable information about recycling or composting facility process requirements and timeframe for biodegradation.
“Biodegradable” does not mean a material is compostable or recyclable.
WHAT IS COMPOSTABLE Plastic?
Compostable plastic is biodegradable in a composting environment, yielding H2O, CO2, biomass, and inorganic compounds. The biodegradation during composting should be at a rate similar to other known compostable materials, and should not leave a visual or toxic residue.In order for a plastic to be labeled compostable, it must meet scientific standards, such as:
Disintegration: No more than 10 percent of the original dry weight of a product must remain after 84 days in a controlled composting test.
Biodegradation: 90 percent of the organic carbon in the test materials must be converted to carbon dioxide within 180 days.
Nontoxic to plants: The product must have less than 50 percent of the maximum allowable concentrations of certain heavy metals regulated by biosolids. Compost must also be able to support the germination of two different plant species at a rate of at least 90 percent of that in a “control” sample.
Bioplastics can be biobased and/or compostable. USDA’s BioPreferred Program only refers to the biobased content, and does not mean an item is biodegradable or compostable. Other bioplastics are completely biodegradable/compostable, but are made with fossil materials. Whether a material can biodegrade or be accepted at a compost facility does not depend on its origin (renewable or fossil). It depends on its chemical structure, if it can be a food source for bacteria, fungi, and algae in a set environment and timeframe, and if a composter will accept them.
The terms “biodegradable” and “compostable” are often used interchangeably, but they are not the same. Composting is one environment where biodegradation occurs. The term “biodegradable” must be qualified by the environment and timeframe. Compostable plastics are those that biodegrade in industrial composting operations at the rate of other compostable materials.
The standard for compostability (ASTM 6400) is based on complete biodegradation within 180 days under active composting conditions. However, many industrial composters finish their active composting process between 60 and 90 days, or less. This may not allow enough time for some products to completely biodegrade in those operations. Incompletely degraded fragments must then be screened out of the finished compost, leading some facilities to not accept compostable plastics with incoming feedstocks.
Bioplastics have certain benefits, depending on the desired attributes. For instance, biobased plastics use renewable materials things like plants, replacing the use of limited fossil materials. Biodegradable and compostable plastics can help reduce the amount of waste sent to landfills and incinerators, such as diverting organics to composting. However, bioplastics are not always a solution, and must be linked to specific environmental goals.
Modern landfills are designed to reduce oxygen and moisture, limiting biodegradation. The Federal Trade Commission cautions that items destined for landfills, incinerators, or recycling facilities will not degrade within a year, so marketers should not make unqualified degradable claims for these items.