plastic of the future

The Ultimate Guide to Plastics of the Future Part 5 – Biodegradable and Compostable Plastics

Single-use plastics are definitely one of the many key contributors to the current solid waste crisis. While they may be used for a short time, they cause a lot of harm because of how quickly they pile up in landfills. 

While the useful life of a durable toy such as Lego blocks or a reusable water bottle can be many years, the time span for other materials such as candy bar wrappers and plastic cups could be merely minutes.

End-of-life plastics are amassing in landfills resulting in both management issues and environmental harm. Today, plastics occupy up to 25% of the total waste in landfills, and a lot of that plastic will take decades or more to decompose.

There’s a lot of talk about greener, more environmentally-friendly plastics these days and between bioplastics, bio-materials and bio-based additives, it can get quite confusing. Judging by the names, you would think all would be biodegradable (which really everything is, it’s just a matter of how easily that is accomplished). 

Some materials degrade in hours, some take centuries. What we are focusing on here are plastics that are designed to be compostable and degradable.

What is the Difference Between Compostable Plastics and Biodegradable Plastics?

All compostable plastics are biodegradable, but not all biodegradable plastics are compostable. Let us explain.

While biodegradable items refer to just any material which breaks down and decomposes in the environment, compostable items are composed of specific organic matter which breaks down and is returned to the ecosystem.

Compostable plastics are made from natural materials that can be decomposed by microorganisms in a tightly controlled, and typically a containerized environment. Under these controlled conditions, heat, composting time, and enzyme combinations are standardized and tightly regulated.

Biodegradable plastics are made from natural materials such as corn, potatoes, cellulose or sugarcane, and these materials are then processed into polymers that can be used to produce plastic products that will biodegrade in an estimated time span of the product’s life cycle. They can be decomposed by bacteria and other common methods in a variety of mediums (soil, marine and even airborne).

Composting is merely one possible biodegradation medium. We included Compostable Plastics in this article because research shows that composting (and more specifically, industrial composting) is the most efficient and complete method of returning the engineered bioplastics back into our ecosystem.

To make it even more confusing, the term “biodegradable” is often a bit ambiguous. Biodegradation is a subset of degradation involving mineralization by microorganisms primarily back the original molecules of CO2, H2O, and CH4, which are the final products of aerobic or anaerobic degradation. 

In some cases, the degradation conditions are often harsh (high temperatures, extreme pH values) or not environmentally realistic (isolated and enriched microorganism/enzymes). The gap between the lab and the actual environment that biodegradation is taking place is sometimes vast. Replication of the microbial ecology, population, diversity, and dynamics from the field to the lab is a monumental task.

Now let’s be clear, compostable plastics are certainly more environmentally friendly than regular plastic. Mostly because they create less toxic substances when they decompose and they don’t use up as many non-renewable resources to make them. They also have a lower carbon footprint than regular plastic because the production process is typically less energy intensive.

As for biodegradable plastics, as the name suggests, they ensure the safe return of carbon to ecosystems by complete assimilation of the degraded product as a food source for soil or aquatic microorganisms.

However, despite more than a decade of commercial presence, these plastics are still far from replacing the demand for fossil-fuel-based commodity plastics.

What are the  Benefits and Drawbacks of Composting Plastic?

Compostable and biodegradable plastics certainly have a place in the future of plastic. Still, unanswered critical issues have hampered the progress of biodegradable plastics. They have been commercially available for several decades; however, this niche market is challenged with a variety of headwinds such as high prices, poor performance, lack of industrial infrastructure, and inconsistent quality standards.

Biodegradable plastics are designed to mineralize in a controlled waste management environment. However, littering is an uncontrolled event without a perfect way to predict the amounts or types of materials discarded improperly. Also, there’s the concern over the increasing amounts of microplastics in the environment. Some studies show that biodegradable plastics may produce microplastics at a faster rate. 

Larger plastic litter, including everyday items such as drink bottles and other types of plastic packaging, as well as synthetic textiles, migrate to our oceans from land-based sources. Regardless of any improvement in our collection systems, leakage of plastics into the environment is unavoidable.

The current biodegradable products may not meet their goals to totally return to the ecosystem, if they leak into the environment or if they are disposed of in an non-ideal manner (such as in a landfill where greenhouse gas emissions will not be controlled). 

This is a huge issue with biodegradable plastics, as standards lay out a specific protocol to follow that ensures they degrade in a safe manner for the environment. This means the composting processes need to be strictly controlled.

What are the Standards and Tests for Biodegradability?

Standards are being created for plastics biodegradability, but as you can imagine, landing on harmonized certification processes when dealing with so many variables can be like trying to hone in on a moving target!

The ASTM D6400 (the North American equivalent of the European EN 13432) requires that biodegradable/compostable products completely decompose in a composting setting in a specific time frame, leaving no harmful residues behind. 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). 

ASTM D6400 also requires that the labeling of these plastics carefully spell out that they are designed to be aerobically composted in municipal or industrial facilities, and certification depends on adherence to these rules.

An important aspect is the necessity to specify the testing environment. Because, both the level and the rate of biodegradation can be different from one environment to another. For example, poly(lactic acid) (PLA), a commonly known industrially compostable plastic, exhibits very limited degradation in anaerobic landfill or soil medium, and is best composted in an industrial environment. 

Several insights can further be drawn from the detailed analysis of these products:

  1. Out of all possible biodegradation media, the industrial compost environment is the most prevalent among brand owners because it can easily be introduced into the current organic waste management systems, and it is the most aggressive medium for plastic degradation. 
  2. In general, in terms of microbial diversity and the rate of biodegradation: industrial composting > home composting > soil > water > marine. The number of certified products for each media type indirectly confirms this observation.
  3. The size of an item (e.g. – a bottle’s thickness) is a critical factor in determining the certification. Unsurprisingly, the greater the thickness of the article, the longer it takes to disintegrate and biodegrade in the environment.
  4. Polylactic Acid or PLA is certified only in an industrial composting environment.
  5. Poly Hydroxyalkanoates or PHAs, starch, and cellulose or cellulose derivatives are certified for a significantly broader range of environments such as soil.
  6. No acceptable test standards for any biodegradable plastics exist for the marine medium, making this the least likely method to be widely adopted anytime soon, even though a large portion of plastic waste is living in our oceans.

Application development of a biodegradable plastic is a challenging task where the performance requirements of the application need to be balanced with the end-of-life degradability requirements. Primary challenges include the expectation of the formulators to utilize the new materials in their existing equipment and processes and lack of understanding of the certification requirements across the value chain.

Biodegradable plastics can benefit waste management only if efficient collection and sorting systems are implemented. Without a dedicated place for containment, biodegradable plastics may adversely impact the current waste management practices. 

For example, due to their physically indistinguishable nature, biodegradable plastics may end up in the current recycling scheme with the nondegradable counterpart, initiating degradation and cross-contamination issues.

Another challenge is the natural cycle of degradation of these plastics. Depending on the formulation, time, heat, PH level, and type of enzymes required can vary, but a standard cycle looks like this:

1. Mesophilic phase (25−50 °C, pH 7−8): lasts for 2−3 days with mesophilic bacteria and fungi as the dominant microbial species.

2. Thermophilic phase (temperature 60−70 °C, pH 8−10): lasts for 10−15 days, where the thermophilic bacteria, actinomycetes, and heat-tolerant fungi survive.

3. Second mesophilic phase (25−50 °C, pH 7−8): lasts for a couple of months, dominated by mesophilic bacteria, actinomycetes, and fungi.

An important fact here is that the 90-day disintegration criteria imposed by standard test methods (ASTM D6400 or EN 13432) are not always aligned to commercial composting goals. Many industrial composting plants operate at cycles of 8 weeks (and even as low as 3 weeks!) to maximize the feedstock and minimize operational costs.

Finally, the ecological formulation demands end-of-life knowledge for each ingredient and that can greatly alter the product design and ability to decompose. Plastics are a formulated final product where individual polymers are usually mixed with additives such as strengtheners (e.g., carbon or silica), thermal stabilizers, plasticizers, fire retardants, UV stabilizers, colorants, matting agents, opacifiers, or luster additives. These additives can introduce the possibility of adverse degradation processes/cycles.

Where does Packaging fit into this Process?

Packaging is one of the most important aspects in the supply chain. It’s not just about protecting the products, but also about protecting the environment. That’s why sustainable packaging is becoming more popular, and biodegradable plastics could be a good fit here.

The future of sustainable packaging will be about a combination of biodegradable materials, recyclable materials, bio-based additives and minimizing plastic usage. The use of bio-plastics will increase in the coming years and what’s more, companies will start to use less paperboard and instead use plastics or cardboard for their boxes.

Tesco, for example, is implementing controls for vendors who want to put packaged goods on their store shelves. Both Tessco-branded and name brand items will need to comply with sustainable packaging standards. In the UK, there are labeling formats that tell a consumer how sustainable the packaging is. They range from Red (not so sustainable or recyclable), Amber (no substitution or functional alternative available) to Green (preferred for ease of recyclability and/or sustainable materials). As of 2020, all Tesco-branded packaging had to be reusable or recyclable, and name brands will eventually be held to the same standards. 

Some other countries are turning to regulations to advance biomaterials for packaging. For example, bans or taxes on the use of nonbiodegradable shopping bags in Italy and France have led to a substantial surge in the consumption of biodegradable plastics. In contrast, the growth of biodegradable polymers is slower in places that lack these types of  mandates. 

Risk and Impact of Littered Plastics 

Like their nondegradable counterparts, biodegradable plastics may share the same end-of-life fate if they are not a part of controlled waste management systems. However, some of the lingering questions remain. Why do the compostable plastics end up in landfills? Are biodegradable plastics promoting an alternative to sound waste management practices?

In order to reduce the amount of plastic in the environment, we need to find a way to make it degrade more easily. This will help the companies steer away from negative connotations about their plastics use. In a twist of fate, corporations who tend to use a lot of plastic in their packaging, also tend to face more public scrutiny. Many of the top organizations leading the sustainability charge, are still considered the top plastics polluters. 

We also need to find substitutes for plastic packaging so that we can reduce our dependence on this material, and with 40% of the global plastics market dominated by packaging, biodegradation polymers have substantial room to grow. However, as we have attempted to convey, broader implementation of biodegradable plastics in the marketplace faces tremendous, intertwined challenges.

The Future of Compostable & Biodegradables Plastics

There are many different types of biodegradable materials in R&D today, and our choices of which materials to incorporate are not just tied to end-use performance, but after-life disposal and the industrial composting methods we standardize on. Biodegradable plastics are not commonplace today, and the methods of manufacturing may be years away from reaching large-scale operations.

In addition, biodegradable polymers are often derived from feedstocks considered inferior to their petroleum-based counterparts in several aspects, so end-use performance is crucial to the type of biodegradable plastics that manufacturers will adopt. 

Most every manufacturer wants to do their part towards the goals of sustainability, but guaranteed is the fact that the materials chosen will have to live up to the necessary functionality that they rely upon today.

With the continuous increase in pollution, we need to find a solution that can reduce our collective carbon footprint. Compostable and biodegradable plastics may certainly be one of the answers to this problem. 

Join us in making a world out of hemp.

Heartland Team