Bioplastics are a relatively new addition to the plastics family and typically take two forms. "Hydrobiodegradables" are made from food or plant starch, yet often contain some percentage of synthetic (oil-based) polymers as well. Under certain conditions, these plastics can be broken down into water, carbon dioxide, methane, and biomass primarily through the enzymatic action of microorganisms. But for many brands, this can only occur within industrial composting conditions with their higher humidity and heat. "Oxobiodegradables", like traditional plastics, are often made exclusively from nonrenewable petroleum byproducts but have bio-additives included to help them break down faster – after a preset period of time. Exposure to such things as sunlight, heat, and mechanical stress ultimately can reduce oxobiodegradables to a mix of water, CO2, and biomass, making them suitable for composting.
Products on the market are made from a variety of natural feedstocks including corn, potatoes, rice, tapioca, palm fiber, wood cellulose, wheat fiber and bagasse. Products are available for a wide range of applications such as cups, bottles, cutlery, plates, bags, bedding, furnishings, carpets, film, textiles and packaging materials. In the US, the percentage of bio-based ingredients required for a product to be referred to as bio-based, is defined by the USDA on a product-by-product basis. The Institute for Local Self-Reliance has recommended that the USDA set a minimum threshold of 50 percent bio-based content for products to be considered bio-based.
An article Sustainability of bio-based plastics: general comparative analysis and recommendations for improvement by Clara Rosalía Álvarez-Chávez, Sally Edwards, Rafael Moure-Eraso and Kenneth Geiser was published in the Journal of Cleaner Production in 2012. While the article's abstract states:
It also states:
There are several manufacturers of plastic products that claim that their bottles or bags are "biodegradable" or "compostable." Here are some of these products and the manufacturer's claims, as reported and evaluated by The Institute for Local Self Reliance:
Most if not all these claims are unsubstantiated. The companies selling these products are taking advantage of markets that are unaware of the difference between certifiable compostable and biodegradable products and those that are not. Truly biodegradable plastics are plastics that can decompose into carbon dioxide, methane, water, inorganic compounds, or biomass via microbial assimilation (the enzymatic action of microorganism). To be considered biodegradable, this decomposition has to be measured by standardized tests, and take place within a specified time period, which vary according to the “disposal” method chosen. The American Society of Testing and Materials (ASTM) has created definitions on what constitutes biodegradability in various disposal environments.
Steve Mojo of the Biodegradable Products Institute (BPI) has repeatedly asked to see Aquamantra’s claims that its PET will fully biodegrade in landfills or marine environments. “Nothing of credible science has come back.” On oxo-degradables, Steve acknowledges these plastics can fragment within 3 months but clarifies that fragmentation is not a sign of biodegradation and that no data shows how long these plastic fragments will persist in the soil or the marine environment. According to Dr. Ramani Narayan, an international expert on biodegradability and a professor of Chemical Engineering & Materials Science at the Michigan State University, some evidence presented shows partial degradation but “the key phrase is ‘complete’ – if they are not completely utilized, then these degraded fragments, which may even be invisible to the naked eye, pose serious environmental consequences."
Oxo-degradable plastics do not meet any standards in place for biodegradability and should not be considered biodegradable. In fact, the US National Advertising Division of the Council of Better Business Bureaus has recommended that GP Plastics Corporation modify or discontinue some of its advertising claims for its oxo-degradable PolyGreen bags. In California, a study sponsored by the California Integrated Waste Management Board (CIWMB) and led by Dr. Joseph Greene at California State University showed that oxo-degradable bags on the markets showed no biodegradation. Its findings and the proliferation of unsupported biodegradability claims, led the state to pass two laws effective January 2009 that restrict use of the terms “compostable,” “biodegradable” “degradable,” and “marine degradable” on plastic bags.
Do plastic bags (or even 'biodegradable' plastic bags) degrade while in the stomachs of sea turtles? A study by Müller, et al published in December 2011 set out to test the decay characteristics of three common types of shopping bag polymers in sea turtle gastrointestinal fluids: standard and degradable plastic, and biodegradable. Degradation rates of the standard and the degradable plastic bags after 49 days across all treatments and controls were negligible. The biodegradable bags showed mass losses between 3% and 9%. This was a much slower rate than reported by the manufacturers in an industrial composting situation (100% in 49 days). The study concluded: "While the breakdown rate of biodegradable polymers in the intestinal fluids of sea turtles is greater than standard and degradable plastics, it is proposed that this is not rapid enough to prevent morbidity."
Bioplastics typically need the high heat (100 to 140 degrees F) of a composting process to truly biodegrade. These products typically act like conventional plastic and only 'photodegrade' (slowly disintegrate into ever smaller pieces while still retaining the basic polymer structure) when left in the park, on the beach or in the ocean. Proceed with caution. These products are a step in the right direction but not a full solution, it's best to reduce and reuse when possible before buying new products.
More on biodegradability claims.
Substantial efforts are underway by polymer scientists to develop viable bioplastics. However, “None of the [current] alternatives are what they should be,” Daniella Russo, the Plastic Pollution Coalition’s executive director, says. “For an alternative plastic to succeed, it should be non-toxic over its entire life cycle, fully biodegradable in all situations, and cost competitive.” Jacqueline McGlade, chief scientist at the UN Environment Programme, believes that biodegradable plastics are a 'false solution'. “It’s well-intentioned but wrong. A lot of plastics labelled biodegradable, like shopping bags, will only break down in temperatures of 50C and that is not the ocean. They are also not buoyant, so they’re going to sink, so they’re not going to be exposed to UV and break down."
Also keep in mind that although these products may be made from plant rather than petroleum raw materials, the basic chemical structure (PET, LDPE, PVC, etc.) of the plastic bag or bottle is still the same. Equally important to remember is that these bags or bottles are still single use plastics. Reusable bags, bottles or other containers are a much better alternative. Better for the ocean and better for your wallet.
About Bioplastics, Institute for Local Self-Reliance
Biodegradable Plastics: True or False? Good or Bad?, Institute for Local Self-Reliance
Facing the Dirty Truth About Recyclable Plastics, Yale University, Environment 360
A Primer on Biodegradable Plastics, Christian Science Monitor
Is New Biodegradable Plastic the Answer?, Treehugger
Bioplastics: Are They the Solution? Algalita Marine Research Institute
Biodegradable plastic 'false solution' for ocean waste problem. The Guardian. May 23, 2016.