Are Bioplastics Compostable? Part 1

Bioplastics are rolling to market fast, with biobased resin makers touting their wares as compost-facility ready.  But is it a given that these alternatives to conventional plastics will break down well and quickly under composters’ operating conditions?  Part 1 of this two-part series broaches this question and others.

In Part 2, Emily McGill, manager of Research and Communications for BSIbio Packaging Solutions and founding partner of the Compostable Field Testing Program, discusses limitations of lab testing on bioplastics and other “compostables.” She describes how a program to test these products in real-world facilities is working with composters; what they are learning; who they’ll be sharing the data with; and when.

The term “bioplastics” is heating up conversations in the industrial compost community. These materials, made wholly or partly from renewable plant-based sources, are often pegged as contaminants because they typically degrade much slower than leaves, grass, and food scraps, throwing a monkey wrench into composters’ established processes. By reports from the ground, even polylactic acid (PLA), often touted as 100% compostable, rarely breaks down in the timeframe processors need to run an efficient business.

Tim O’Neill, president Engineered Compost Systems, says he sees and hears this often.

“While bio-based plastics are considered better for the environment than petroleum-based plastics, the degradation time scales don’t match process conditions in most commercial-scale compost facilities. When we talk to clients they consistently say, ‘We screen bioplastics out with all the other plastics,’” he says.

Pulling out contaminants takes time and money, and it means having to let some of the good material go too, since mechanical separation doesn’t allow for selection of what’s ideal feedstock.  

Meanwhile, composters are getting hammered with way more food scraps and packaging coming into their streams, pressuring them to turn products around faster, and to move a lot more material. As they try and pick up their pace, they can expect to see more biopolymers; over 2.8 million metric tons will be produced in 2025 alone, projects Markets and Markets.

Those in the industry looking to be problem solvers are trying to optimize process conditions to better degrade bioplastic packaging and products.

“Moisture, weather, and elevated temperatures all impact degradation rates, and that’s what we are homing in on through our process testing. How fast can it break down in a given set of conditions that hopefully can be controlled in the field?” O’Neill says.

But the industry is also beginning to call on biopolymer makers to produce what will break down faster under those conditions.  Academia and private companies have actually begun working on creating what composters want while meeting the performance standards of the food industry. Clemson University is working on a plant-based film purported to biodegrade in three to four weeks. The University of Washington says it’s developed a bioplastic that degrades in the same times as a banana peel. And Grow Plastics, a packaging manufacturer, makes lightweight rigids, proven at a compost facility (not just in a lab) to degrade in 20 days.

What does ASTM testing tell you? It confirms a certified compostable plastic, exposed to conditions required for composting, can fully break down without releasing toxins into the soil. But these lab tests are done with controls in place preventing researchers from concisely mirroring what goes on in the field, explains Emily McGill, program director of the Compostable Field Testing Program (CFTP) and manager of Research & Communications for BSIbio Packaging Solutions. The CFTP is a non-profit platform, administered by the Compost Research and Education Foundation (CREF) and BSIbio Packaging Solutions, to help facilitate field testing across North American compost sites.

In the lab, the feedstock has to be consistent, whereas the mix that lands in real-world facilities has a range of maturity levels. Temperature and moisture are not the same as in the field. And because products are size reduced in the lab, there’s no way to accurately capture how materials break down in a large compost pile. 

At least as much of an issue is that ASTM standards are based on a substantially longer processing timeframe, evaluating disintegration at 84 days and biodegradation at 180 days. O’Neill believes materials have to degrade in 20 days to work with composters’ economic model.

“That’s what we will need [so bioplastics] do not add to the contamination problem,” he says. Though producing a mature, finished product takes longer, typically at least six weeks.

McGill and her colleagues will collect real-world data from a range of facilities to better understand what would be ideal composting conditions for certified compostable food ware and packaging.

“Each facility's operations are as different as a fingerprint, and having results across many facilities gives us a better picture of how a product will disintegrate in real-world situations than any single facility test,” McGill says.

There’s work happening on the policy front too, in order to regulate materials claimed to be compostable. The fast emergence of bioplastics and confusing messaging around their biodegradability and compostability is driving some of these evolving rules.

The term “biodegradable” has been used to misrepresent the compostability of items. It simply means a material will break down through microbial activity. Unlike the term “compostable,” “biodegradable” does not infer a timeframe or specific conditions for a material to break down. This is leading some jurisdictions to explicitly ban the use of the term biodegradable for marketing.

In the face of confusion, many composters have stopped taking bioplastic, says Neil Edgar, executive director California Compost Coalition.

Legislation in California, Washington State, Colorado, Maryland, and Minnesota set label requirements to better inform composters, enabling them to identify incoming materials—bioplastics and other— that will work in their processes. They are setting other requirements such as mandating third-party certification and requiring products to meet ASTM standards in order to be deemed compostable.

“California does not accept bioplastics at all for use in organic production, as many composters there were getting pressure from growers to sell products that meet National Organic Program standards If they include bioplastics they are in violation, so composters have removed them and sent them to landfill,” Edgar says.

Even many of the skeptical folks in the compost world like O’Neill are not giving up on bioplastics.

“If they are fully degradable, they don’t end up producing microplastics that release into the environment that distribute around the globe. So if they degrade to CO2 that’s fantastic,” he says.

“Hopefully through the combination of optimizing processes to degrade bioplastics plus biopolymer producers making materials more degradable we will reach a point where bioplastics work better in commercial composting facilities than they do today.”