Not All Bioplastics are Compostable & Vice Versa

GUEST BLOG: The Difference Between Biobased & Biodegradable Plastics

Bioplastics are often labeled as either one of, or a combination of biobased, biodegradable or compostable. Green Dot Bioplastics’ Kevin Ireland explains some of the differences and advantages of each

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Bioplastics are often labelled as either one of, or a combination of biobased, biodegradable or compostable. Green Dot Bioplastics’ Kevin Ireland explains some of the differences and advantages of each.

What are the differences between biodegradable and biobased plastics?
The demand for bioplastics has increased dramatically over the last few years, but there still tends to be a lot of confusion about the terms used in environmental claims. Bioplastics are often labelled one, or a combination, of biobased, biodegradable or compostable. What do these labels mean and how are they different from each other?

What are biobased plastics?
Biobased plastics are made from renewable resources instead of non-renewable petroleum based resources. These renewable resources can include corn, potatoes, rice, soy, sugarcane, wheat, and vegetable oil. Biobased plastics are made by creating plastic polymers from these materials, through either chemical or biological processes.

Examples of these types of plastics are polylactic acid (PLA) –  derived from starch, polyhydroxybutyrate (PHB) – derived through microbial synthesis, and biobased polyethylene (bioPE) – produced from sugar cane.

In the United States, the USDA Biopreferred Program promotes products with renewable content by certifying them as biobased. The program uses ASTM’s D6866 standard for measuring the%age of biobased content by measuring the presence of Carbon-14 in the material. This test can differentiate between renewably sourced carbon and carbon sourced from non-renewable petroleum.

Advantages:

  • Reduces reliance on non-renewable petroleum based feedstocks
  • Can help to reduce greenhouse gases by up to 35%
  • Increases the value of agricultural byproducts, helping farmers and rural economies
  • While traditionally used in single-use products, new technology and designs allow for durable goods

While biobased materials can be biodegradable or compostable, not all of them are. And, not all biodegradable plastics are biobased.

What are biodegradable plastics?
Biodegradable plastic degrades through exposure to naturally occurring microorganisms. When classifying a plastic as a biodegradable, the environment and timeframe must be specified; otherwise the claim is rendered pointless due to an array of variations.

All organic matter will eventually biodegrade. This includes traditional petroleum-based plastics. However, the rate of biodegradation of different organic materials can vary on an exponential scale.

The plastics we call “biodegradable” are designed to biodegrade in specific environments, including marine environments, sunlight, soil, industrial composting facilities and backyard home compost.

In the U.S., plastics labeled compostable are designed to degrade in an industrial composting environment at a similar rate to other known compostable materials without leaving visual or toxic residue.

To be classified as compostable, the plastic is tested according to ASTM’s D6400 test protocols. Plastic is placed in a controlled composting test and must disintegrate to no more than 10% of the original dry weight after 84 days; 90% of the organic carbon must convert to carbon dioxide within 180 days, contain less than 50

% of the maximum allowable concentrations of certain heavy metals and the compost must be able to support germination of two different plant species at a rate of 90% in a control sample. European agencies have created standards for home composting as well; however, to date these standards have not been adopted by the American Society for Testing and Materials.

It’s important to note that just because a compostable material is used for a product doesn’t mean the product will meet these standards. Rate of degradation will vary depending upon the thickness of the product.

Advantages:

  • Ideal for packaging and single-use applications
  • Increases productivity in horticultural applications
  • Reduces plastic litter in marine environments
  • Decreases organic material going to a landfill

What are the best applications for biobased materials and biodegradable plastic?
Traditionally, biobased plastics were focused on single-use items - plastic bottles, utensils, etc. Recently, companies have developed better performing biobased materials to be used in a wider range of durable applications. From automotive and furniture to construction and toys, biobased materials are gaining a lot of traction.

Compostable plastics have seen the most use in packaging, food service ware and agricultural mulch films. Plastic utensils, plates and containers using compostable plastics means the food service ware can be discarded and composted along with the food waste.

Agricultural mulch films are used to cover seedlings and decrease water, herbicide and pesticide use. The film doesn’t have to be removed or disposed since it’s soil degradable.

While biobased materials and biodegradable plastics have many differences in composition, development and usage, they can offer distinct advantages over traditional petroleum-based plastics.

With more consumers looking for greener products, biobased and biodegradable plastics are becoming an ideal solution for product designers and plastics processors seeking to lighten the environmental footprint of the products we use everyday. 

Kevin Ireland is communications manager for Green Dot Bioplastics, a Kansas-based manufacturer of bioplastics and biocomposites.

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