• What is biodegradable plastic and how does it differ from other types of plastic?
• What is the difference between biodegradable plastic and compostable plastic?
• What are biobased plastics?
• Which organizations are responsible for creating standards and enforcing correct labeling of biodegradable and compostable plastics?
• If a plastic product is labeled “compostable,” can I add it to my home compost pile?
• What if my community doesn’t have a composting recycling pick-up program. Should I dispose of compostable plastic in the plastic recycling pick-up bins?
• What do I do with plastic caps (on water bottles and other bottles)? Do I leave them on or take them off before disposing the bottle in the recycling bin?
• Should I be placing single-use, non-compostable plastic bags in the recycling bin?
• What is the purpose of plastic bag bans?

What is biodegradable plastic and how does it differ from other types of plastic?

Plastics are derived from organic products. The materials used in the production of plastics are natural products such as cellulose, coal, natural gas, salt and, of course, crude oil. Crude oil is a complex mixture of thousands of compounds. To become useful, it must be processed.

The production of plastic begins with a distillation process in an oil refinery involving the separation of heavy crude oil into lighter groups called fractions. Each fraction is a mixture of hydrocarbon chains (chemical compounds made up of carbon and hydrogen), which differ in terms of the size and structure of their molecules. One of these fractions, naphtha, is the crucial element for the production of plastics.1

Most petroleum-based plastic is not readily biodegradable; ie. it is not consumed by microorganisms and returned to compounds found in nature. What this means is that unless the petroleum-based plastic has been specifically designed to biodegrade, and although it may partially degrade, the plastic may last in the environment for tens to potentially hundreds of years, depending on the type of plastic and its disposal environment. The two major processes used to produce plastics are called polymerisation and polycondensation, and they both require specific catalysts. In a polymerisation reactor, monomers like ethylene and propylene are linked together to form long polymers chains. Each polymer has its own properties, structure and size depending on the various types of basic monomers used and that influence properties such as moldability and rigidity.

What is the difference between biodegradable plastic and compostable plastic?

Plastic that is compostable is biodegradable, but not every plastic that is biodegradable is compostable. Whereas biodegradable plastic may be engineered to biodegrade in soil or water, compostable plastic refers to biodegradation into soil conditioning material (i.e., compost) under a certain set of conditions. In order for a plastic to be labeled as commercially “compostable” it must able to be broken down by biological treatment at a commercial or industrial composting facility. Composting utilizes microorganisms, heat and humidity to yield carbon dioxide, water, inorganic compounds, and biomass that is similar in characteristic to the rest of the finished compost product. Decomposition of the plastic must occur at a rate similar to the other elements of the material being composted (within 6 months) and leave no toxic residue that would adversely impact the ability of the finished compost to support plant growth. ASTM Standards D6400 and D6868 outline the specifications that must be met in order to label a plastic as commercially “compostable”. There are currently no ASTM standard test methods in place for evaluating the ability of a plastic to compost in a home environment.

What are biobased plastics?

Biobased plastics are manufactured from plant materials instead of being made from oil or natural gas. Because they are plant based, there is a tendency to assume that this type of plastic must be biodegradable. However, biobased plastics can be designed to be structurally identical to petroleum based plastics, and if designed in this way, they can last in the environment for the same period of time as petroleum based plastic. Just as with petroleum-based plastics, biobased plastic can be engineered to be biodegradable or to be compostable.

The ability of biobased plastics to be recycled varies. Some forms of biobased plastic cannot be recycled together with petroleum-based plastics due to chemical structure incompatibility, while other biobased plastics may have compatible chemical structures that allow for recycling together with petroleum-based plastics. In order to determine what waste disposal options are available for a biobased plastic item, it is necessary to read the product’s label as to its compostability and recyclability.

Which organizations are responsible for creating standards and enforcing correct labeling of biodegradable and compostable plastics?

The American Society for Testing and Materials (ASTM International) sets definitions and standards, while the Federal Trade Commission (FTC) is responsible for enforcement against false or deceptive product labeling.

If a plastic product is labeled “compostable,” can I add it to my home compost pile?

No. Unless the label indicates that the product is okay for home composting, you should not try to compost it at home. Plastic that is labeled as compostable is generally intended to be sent to an industrial or commercial composting facility which has higher temperatures and different breakdown conditions than those found in a typical homeowner’s compost bin. If your community has a residential compost collection program, check with your local government or recycling company to find out if they will accept compostable plastic under this program.

What if my community doesn’t have a composting recycling pick-up program. Should I dispose of compostable plastic in the plastic recycling pick-up bins?

No. Compostable plastics are not intended for recycling and can contaminate and disrupt the recycling stream if intermixed with petroleum-based plastics that are non-compostable. If your community does not have a composting recycling pick-up program that accepts compostable plastic, contact your garbage/recycling company or local government to find out if there are any drop-off locations for your compostable plastic items.

What do I do with plastic caps (on water bottles and other bottles)? Do I leave them on or take them off before disposing the bottle in the recycling bin?

Until recently, many consumers were advised to take the caps off and dispose of them in the garbage can before placing the bottle in the recycling bin. However, processing technology has improved to the extent that the Association of Postconsumer Plastic Recyclers now recommends that plastic lids be left on the containers as they are placed in the recycling bins.  At facilities with newer processing technology, the bottles (with caps on) will be ground into flakes before being washed and the cap flakes separated from the bottle flakes during a water bath float/sink process and then both types of plastic can then be captured and recycled. Note, however, that due to the fact that not all recyclers may have equipment that enables processing of the bottles with caps left on, that you should check with your local recycling facility to see what their policy is with regard to disposal of the bottle caps.

Should I be placing single-use, non-compostable plastic bags in the recycling bin?

Contact your local government or recycling company to find out whether this practice is allowed, as policies on this vary. Loose plastic bags are difficult to handle in the recycling stream and can clog equipment. Some recycling companies allow recycling of single use bags if they are bundled together in a tight, tied package. Many supermarkets and “big box” stores have recycling bins for the collection of single-use plastic bags.

What is the purpose of plastic bag bans?

The Pollution Prevention Act establishes a national objective for environmental protection: “[T]hat pollution should be prevented or reduced at the source whenever feasible.” Similarly, the Resource Conservation and Recovery Act sets the order of preference for managing materials as: source reduction, reuse, recycling, and disposal.

With these objectives in mind, a number of communities are initiating bans of plastic bags that are intended for single use, such as those commonly provided in grocery stores. The rationale behind the bag bans includes the following:

• They are typically made out of petroleum-based plastic and don’t biodegrade when they are disposed of or escape into the environment;
• when plastic bags are disposed of on land they may be blown into creeks, lakes, or oceans where they can entangle marine life or the animals may mistakenly eat the plastic bags thinking that they are food;
• the light-weight plastic is not easily recyclable; and
• the bags are often used only once before being thrown away.

The various bag bans differ but typically contain many of the same elements:

• Replacement bags typically must be compostable or recyclable. That means that if the replacement bags are made of plastic, the plastic must either be compostable and labeled as such, or the bag must be heavier and thicker such that it won’t interfere with the industrial recycling process, is washable, can carry more weight, and be used multiple times (as many as 125 uses).
• Replacement paper bags are typically required to be made of 40% recycled paper and be 100% recyclable.
• Many plastic bag bans require retailers to charge a fee per replacement bag which is kept by the retailer.
• The purpose of the fee is to both to encourage customers to bring their own reusable bags (minimizing the need to manufacture new bags) and to cover the cost to the retailer of providing bags that are other than single use.

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