What Makes a Biodegradable Trash Bag Decay?
A traditional trash bag, even when made with some recycled materials, will take hundreds of years to degrade. The plastics break down into smaller pieces and in many cases can never truly decompose. Biodegradation is the process by which organic substances are broken down by living organisms and their enzymes. While it takes hundreds of years for a regular plastic bag to break down, its more eco-friendly, biodegradable version will decompose in months or years.
The Problem with Plastic
Plastic trash bags contain plastics like polyethylene, polypropylene or polystyrene. Microorganisms do not recognize these man-made polymers as food, so when the trash bags end up in the trash, the plastics go uneaten. Some experts suggest it could take more than 500 or even 1,000 years for plastic bags to biodegrade in a landfill.
Plastic Decay
Plastic bags do photodegrade, which means they can break down when exposed to the ultraviolet radiation of the sun. The polyethylene fibers become brittle and begin to crack, breaking into microscopic granules. But because plastics in landfills are not exposed to the sun, breakdown by light isn't an option. Most statistics of the life of a plastic bag come from experiments using photodegradation, so we can't be precisely certain of just how long plastic will survive.
Aerobic versus Anaerobic Conditions
Materials biodegrade under aerobic or anaerobic conditions. Oxygen is present in aerobic conditions, and not present in anaerobic. This becomes important when considering biodegradable decay, since most trash ends up in landfills. Landfills are anaerobic environments, packed tightly and lined with clay and plastic to prevent leaks from escaping. Many bags sold as biodegradable are actually considered compostable. These bags need heat, moisture and air to break down, none of which is available in a landfill.
Oxo-Biodegradables
Because there are different definitions of biodegradable, there are different kinds of biodegradable plastic bags. In the oxo-biodegradable bag, transition metals (like manganese or iron) incorporated into the plastic encourage oxidation and work to break apart the long polymer chains that make up the plastic. Over a few months or years, the oxo-biodegradable bag fragments into smaller and smaller pieces. This kind of "biodegradable" works more efficiently in dry conditions, and when exposed to the sun.
Other Biodegradables
The other kind of biodegradable bag involves adding organic compounds during the production of plastic. These organic materials attract microorganisms, which work to metabolize and break down the molecular structure of the plastics. Biopolymers, sometimes from raw, renewable resources, can be used instead of man-made plastic polymers. This method of biodegradation can work in aerobic or, sometimes, anaerobic environments. The organic portions of the biodegradable plastic will degrade first, leaving remaining fragments to further get broken down over a longer period of time.
Definitions
The Biodegradable Products Institute is the only recognized organization for certifying plastics as biodegradable in the United States. If a biodegradable bag meets the ASTM D6400 standard, it is compostable, but it is actually only truly biodegradable if meeting ASTM D6868 standards, or EN 1342, the European standard for biodegradable plastics.
Tags: break down, anaerobic environments, biodegradable plastic, Biodegradable Trash, Biodegradable Trash Decay