Will It Compost?

A longer story about compostable polymers

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When I started graduate school oil prices were over 100 dollars a barrel, biofuels were hot, and plastic waste was a problem that was being noticed on a global scale. I had just read Cradle to Cradle. I felt I needed to do something of importance or impact with my life, but aligned within my interest in polymer chemistry. Thus, my thesis was focused on trying to make the world a more sustainable place through making new polymers from biomass and understanding how structure influenced properties. 

“There isn’t a problem in the world that cannot be solved through a new polymer.” 

-A synthetic polymer chemist somewhere being semi-serious

The problem that compostable or biodegradable polymers have tried to solve is one of plastic waste in the environment. If the plastic can biodegrade or compost naturally, then there is no plastic waste...eventually. The idea is one of designing for the worst case scenario, if even all of our containment measures fail to keep plastic waste out of the environment then that plastic will not persist for decades. Maybe a few years instead. It takes years for a dead tree to biodegrade.

I’ve been a big proponent of compostable or biodegradable plastics only being viable if the world has access to industrial composting (not your backyard compost pile). Industrial composting’s advantage is higher heat and humidity than what is possible through backyard composting and this heat and humidity speeds up biodegradation of all biodegradable matter. 

Recently, I was surprised to learn that Oregon based composting companies wanted a ban on compostable plastics. I’ve written previously about how access to industrial composting is necessary to see a compostable plastics revolution, but this pushback from composters was something I had never considered. This challenged my previous beliefs on the value of biodegradable plastics and I asked myself the question: will these polymers actually compost?

I knew that industrial compostable polymers like poly(lactide) or poly(hydroxyalkanoates) can take longer to degrade under home composting conditions and degrade faster under industrial composting conditions where temperatures need to be as high as 131 Fahrenheit with high humidity. The companies that make compostable polymers do not put their biodegradation studies on their websites either, which I felt was a little bit odd. If the whole value proposition of the biodegradable plastic is its ability to biodegrade then why not use this as a marketing tool? 

I wanted to investigate what actually happens to these compostable polymers when they get to a composter. So, I did what I suppose anyone with a question about composting would do. I went on LinkedIn and tried to find someone that knew more about composting than myself.

Source

The Composter

I spoke to Jorge Montezuma, a professional engineer and Director of Engineering at Atlas Organics, about the state of composting capacity in the United States. Jorge’s background is impressive. He has been a trainer for the US Composting Council since 2013 and was part of the Peace Corps, Americorps, and USAID. Jorge gave me a crash course in the different types of composting and what help he would like from the upstream producers of compostable packaging. 

Atlas Organics was named one of Inc’s 5000 fastest growing companies in America. His colleague Leslie Rodgers, VP of Sales at Atlas Organics, joined the board of directors for the Biodegradable Products Institute (BPI) in January 2021 as the first composter. BPI is the non-profit that advocates for biodegradable polymers and was formed in 1999. It has taken 22 years for a composter to join the board of directors (crazy right?).

No time like the present.

According to Jorge, there is a lack of infrastructure in composting and there is a lot of space for growth, which is why Atlas Organics is growing so fast. 

There is not enough capacity in the United States to compost all of our compostable materials  and individual states are incentivizing diversion of materials away from landfills. In the future we might see municipalities that were once only equipped to compost leaves and grass clippings become able to process food scraps and solid waste from water treatment facilities. Expansion of composting capacity and infrastructure could transform our current linear consumption model to one that is more circular.

Jorge also described what industrial composting actually looks like because in my mind there was a giant vessel that maintained a specific temperature and humidity. 

Jorge said, “There are always going to be piles in industrial composting. These piles might be under a roof, behind walls, under pressure, exposed to the elements, or in a warehouse, but there will always be piles of compost.” 

Jorge explained that there are three primary methods of composting such as windrows, aerated static piles (ASPs), and in-vessel (what I pictured in my mind), but they all primarily function on similar principles. During industrial composting the compost needs to hit 131 Fahrenheit for at least three days for ASPs and in-vessel composting.  Windrow composting (think long tall lines) requires 15 days at 131 Fahrenheit plus 5 turns (literally turning it over). Then, the compost pile needs to off-gas ammonia and cool. Hotter for longer isn’t necessarily better because this can cause microbes to die. Atlas Organics can typically produce finished compost in 2 months.

There are challenges with compostable plastics for composters, even commercial composters like Atlas Organics. The American Society for Testing and Materials (ASTM) standards state that compostability means greater than 90% of the product breaks down in a “reasonable short period of time”. This standard deems 84 days as reasonable, but the test is typically for longer. Atlas’s aerated static pile composting process typically takes 45-60 days, as do their competitors.

This means that a compostable polymer might take at least two or three cycles to reach 90% biodegradation. Putting materials through the process multiple times takes time and space at a composting facility. Another problem Jorge outlined was that the ASTM has test methods that do not accurately represent real world composting conditions and durations that are representative of determining if something is truly compostable at commercial composting facilities.

Jorge told me that as a composter he would love it if more guidance was given to composters from the producers of the compostable materials on how to better process the biodegradable plastic. 

“Does it need layering or a lot of surface area within a pile? How long does it take and under what conditions?” Jorge asked me with some mild frustration. I didn’t have any good answers for him.

There is also the problem of misidentification. Without globally unified visible labeling, the compost companies cannot always properly identify the compostable item if it resembles what might look like typical plastic such as PET. There is a project called Holy Grail that is seeking to fix this problem with digital watermarks.It is still being developed and it has serious industry backing from companies like BASF and P&G. 

In closing, Jorge told me that composters should be included in product development by the producers of compostable packaging and compostable single use plastics. Composters need to be included for running field trials and developing guidelines on how to best process these new compostable plastics. As the demand increases for compostable plastic, the need increases for more communication between the producers of compostable plastic and the industrial composters. Atlas is the first composter to be on the board of BPI. I hope they will not be alone for too long. 

The Marketer

In an effort to understand things from the packaging perspective, I reached out to numerous scientists and marketing professionals around food packaging. The first to get back to me was Bob Lilienfeld, a marketing and management professional with over 25 years of experience in food packaging. Bob runs a newly launched consortium of academics and professionals called the Sustainable Packaging Research, Information, and Networking Group (SPRING). When I asked him about compostable food packaging, the value proposition of an environmentally degradable plastic, and plastic waste pollution, he led off with, “the majority of plastic waste in the ocean comes from developing countries in South East Asia.”

The big value proposition of biodegradable plastics is that in a worst case scenario these plastics will naturally degrade in the environment as opposed to staying around forever. Bob elaborated that people want to spend money on prevention, taxing, and banning of plastics, but if they were really serious about mitigating plastic pollution they would spend money on solid waste remediation in Thailand, Indonesia, and The Philippines. 

This Reuter’s article from 2019 discusses much of the same issues that Bob was talking about in terms of plastic waste. Thailand is planning on banning seven types of plastic most commonly found in the ocean. Investing in waste mitigation might yield a better return than bans on plastic for Thailand.

Bob doesn’t think that banning is the solution to our problems. He gave the example of the age old question at the grocery store checkout: plastic or paper? He told me that, “It takes ten truckloads of paper bags to equal one truckload of plastic bags in terms of volume. The cost and emissions from the additional transportation of paper should be factored into sustainability considerations.”

Bob believes that performing a life cycle analysis (LCA) is critical before making any sort of big long term decision for anyone seeking to transition to a new material or new process. He gave an example of a workplace cafeteria supplying reusable flatware as opposed to single use. The energy required to clean and sanitize reusable flatware by that workplace needs to be factored into the decision. “But what about compostable single use flatware?” I asked.

Bob answered by saying that it sounds great on paper, but there isn’t really a good framework right now when labeling something as compostable. There are no guarantees that it will actually compost despite a label that might say, “compostable.” Further, there are good chances consumers just put the plastic into a mixed use recycling stream, which further complicates our ability to recycle the plastics we have now. Claims of compostability he told me don’t mean much because the measurements of how these claims are determined are not indicative of actual compost conditions. 

This confirms what Jorge was telling me earlier. 

Further, these methods do not help make a determination on compostability, but rather only how much of the plastic weight has been removed (notice a trend?). A method by which plastics are measured for compostability is ASTM D6400-19: 

The requirement for a material to pass ASTM D6400 and be considered “compostable'' is that the material must reach or exceed 90% conversion of the carbon within the material into carbon dioxide (CO2). In other words, 90% or more of the material would need to be turned into CO2 (converted by micro-organisms) during the time-frame of the test – 180 days.

Curious about the last 10%? I am guessing that is what remains as “soil,” but no one I spoke to was able to give me a good answer. Also, another thing to point out is that most composters cannot wait 180 days for a plastic fork to degrade. They are looking to cycle in and out of a composting process every 45-60 days and their capacity is limited. This limited capacity to compost materials means that composters want to be producing as much viable and usable compost as possible.This immediately translates to cash flow, a healthy company, stable jobs, and alternatives to traditional synthetic fertilizers. What are the economic incentives for them to wait an additional 3-4 months to compost a pile full of compostable forks and even if they did wait would those forks actually compost? 

As I wrapped up my conversation with Bob, he left me with one thing to think about. Even if we got our compostable polymers to compost into the soil, what value are these compostable polymers providing to the farmer or gardener who is going to use it? The oligomers and carbon dioxide that these polymers break down into are not especially nutrient dense nor would they function as humectants. The real value is that to us they break down and we feel good about ourselves for not contributing to landfills.

The Polymer Chemists

I reached out to a lot of chemists working in the compostable plastics space to interview them. I was a bit underwhelmed by the responses. Most scientists don’t want to talk to anyone or even publish our own thoughts with our own names because we are afraid of the consequences (I’ll dive into that later this year), but I did get a chance to speak to Bruno Pereira from BiologiQ and their new product (which is also kind of old) NuPlastiQ--a thermoplastic starch. 

Bruno confirmed much of what I had already found, many companies want to be able to put a recyclable or compostable label on their products just to check the box in a product scorecard. They are not as concerned if it actually gets recycled or composted. Bruno told me that NuPlastiQ is a new thermoplastic starch that is more easily processed than previous thermoplastic starches and it is very compatible with the existing plastics out there. It can be blended with polyolefins to help improve biodegradation and biomass content. This one slide stood out in particular to me:

Essentially, blending  25% NuPlastiQ with 75% linear low density polyethylene (LLDPE) enabled biodegradation of polyethylene under ideal conditions, such as ASTM D5338-15 performed by Eden Labs, which is composting at thermophilic temperatures of 50-55 C for a very long time. So, if you read the chart it takes just under a year to hit 75% biodegradation, which is a long time. This means it wouldn’t biodegrade significantly under ASTM D6400 conditions and is not certifiable as compostable. This is significantly longer than cellulose (paper), but shorter than pure polyethylene. 

Bruno told me they are not really sure how or why this phenomena occurs, but they are investigating. They suspect that certain enzymes from microorganisms that help biodegrade NuPlastiQ are also able to biodegrade polyethylene. While I understand that the starch portion would biodegrade, which in itself is an improvement over current plastics, I am inherently skeptical of the data showing full biodegradation because it’s hard for me to believe from a chemical mechanism aspect.  But, if it is true, then it could be something significant to explore due to a potential enzyme that could degrade polyethylene. 

I don’t think that incorporating NuPlastiQ into polyethylene will solve our plastic pollution problem and if you want you can check out BioloigQ’s technology here. The plastic that makes its way to the ocean could be mitigated with better investment into waste infrastructure and oceans won’t present ideal conditions like ASTM D5338 either. I do think that increased levels of biodegradation could reduce the total amount of persistent microplastics accumulating year over year in the environment, but there are plenty of other sources of microplastics entering into the environment outside of food packaging such as shoes, tires, paint, and roads. Ever wonder where the tread on your tires or the outsoles of your Nikes go after a lot of use?

Bruno closed out our conversation with the expectation that certified compostable packaging’s only play is one of niche applications and he doesn’t expect this technology to replace significant amounts of PE, PET, PP or PS. Compostable plastics are all going to be small volume applications such as compostable fruit labels, hot and cold paper cup linings, or some sort of high food contact single use applications where the packaging is expected to be composted. 

I spoke to a lot of other polymer chemists, scientists, and engineers out there when it comes to sustainable or compostable packaging. One of them was Mario Grimau and the others didn’t necessarily want to be named. We all agreed that there is opportunity for new packaging alternatives, but they will have to be in very niche applications and consumers will need education on how to use new packaging. 

The problem that new commercialized polymers represent is increased complexity in the recycling and composting waste streams. If we make these polymers from corn, petroleum, or plastic waste and if they are degradable or nondegradable, then the consumer ultimately needs to know what to do with them when those polymers have served their purpose. Life cycle assessments are critical to understand if we are headed in the right direction and honest feedback through the value chain from producer to composter or from producer to recycler is necessary. If a polymer chemist wants to design compostable plastics, they not only have to design for their primary customer and the customer’s customer, but they also need to design for the composters like Jorge and Leslie.

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My Conclusion

There are a lot of reasons to not pursue this area of research and product development. The first being cost and the second is that the value of traditional plastic packaging and compostable plastic packaging are in opposition to each other. Ultimately though, I think if you’ve got a good idea you should go for it.

Our packaging needs to protect the stuff it surrounds. Traditional plastics are often used to protect against water and to keep gases and other liquids from moving through the packaging. In terms of value for protection, traditional plastics are really efficient, there is a growing capacity for recycling of these plastics, and the consumer is relatively well educated about them. The problem is when plastic packaging is not recycled and then becomes a liability if it escapes the path to a recycling facility or landfill. Canada has declared plastic waste as hazardous waste.

A compostable polymer like cellulose is natural, but it’s a terrible barrier to water. Try to make a cup out of printer paper and see how long it holds water. Cellulose is great at composting, but awful at water protection. We don’t make rain jackets out of paper.

A compostable plastic that is useful for packaging or single use applications should do the following:

1. Degrade into “not plastic” within 60 days of being introduced into a composting pile. The not plastic could be carbon dioxide, a humectant, or ideally something of value in the soil.

2. Be efficient at stopping liquid water and water vapor for extended time periods perhaps up to a day or more, but the longer the better.

3. Be shelf stable so that it doesn’t degrade under warehouse storage conditions.

4. Be fit for use for consumer applications, such as eating soup or protecting a sandwich.

The attributes that make a biodegradable plastic compostable can also compromise its longer term protection capability. If it’s easily degraded by microbes then what is going to stop it from biodegrading on the shelf? 

There is a “degrade on command” need here that is currently not being met by any of the compostable polymers on the market. Whoever synthesizes a polymer or figures out how to use a biopolymer that solves for these properties could be unlocking the next generation of sustainable packaging. I suspect that enzymatic degradation will be important here.

Ultimately, if you are going to enter the compostable polymers space please run trials with an actual composter before you go to market. If it doesn’t actually compost what is the point? Synthetic polymer chemists want to solve the problems of the world by making a new polymer, but what if really simple natural materials can already do it?

Here is a good example of some leaf plates. There is irony here. They are packaged in plastic. 

Tony