Compostable packaging is packaging that biodegrades in a specific amount of time, in particular conditions. It is ideal for packaging that does not need to last long, such as single-use packaging. When you are composting, you are recycling organic material in a way that mimics nature. At Notpla, one of our core values is replicating what nature does best, so our products are 100% home compostable! But do you know what compostable means? What are the different compostable packaging materials, and are they all sustainable solutions for the planet?
What is composting, and how does it work?
Compostability is the decomposition process of organic materials into fertile soil, driven by microorganisms, mainly bacteria and fungi. Organic matters are food sources for these microorganisms — their digestion results in carbon dioxide, water, and humus.
This video shows how composting works for our Notpla takeaway boxes vs other materials. In less than two weeks, our coating made from seaweed has been entirely eaten by worms and bacteria!
What are the different composting processes?
Contrary to biodegradation, composting is a process that is human-driven. There are two types of composting methods:
Industrial composting occurs in large facilities, under high temperatures (55 - 60 °C). There are three types of industrial composting approaches:
- Windrow Composting is an open-air technique where (typically garden-based) waste is piled in long rows. This is the method often used for creating compost for landscaping and gardening applications.
- Anaerobic digestion utilises heat and a closed atmosphere to break material down, typically over about six weeks. This method is more suitable for food waste.
- 'In Vessel' Composting is similar to anaerobic digestion, but additionally, the material is churned to increase the surface area and better facilitate biodegradation.
Industrial composting involves some regulated setups, for example, controls on temperature or pH value. In this environment, It usually takes between 30 to 60 days for food waste or a product to compost.
Home compostable material can be composted at home, with lower temperatures (25 - 40 °C).
A product must undergo several tests before being certified 'as home-compostable'. These include screening the compost for microplastics and testing for heavy metals. The CO2 levels are also recorded to measure the compost quality. However, these tests do not account for 'biomass sludge' - a substance that is left over after certain materials break-down: whilst this is not necessarily toxic, it does not enrich the soil. Thus, not all composts produce a nutrient-rich fertiliser!
With home composting, the conversion of organic matter into compost may take up to two years, but manual turning can decrease this time to 3-6 months.
What are the different compostable packaging materials?
Generally speaking, we can separate packaging materials into paper, plastic, metal and glass packages.
Only paper and certain plastic materials are compostable. Whether we define a material as compostable depends on the material itself and the microorganisms in the compost.
A deep dive on compostable packaging made of synthetic polymers
First, here is a quick reminder of what polymers are. Polymers are materials made of long, repeating chains of molecules. They have unique properties, depending on the type of molecules being bonded and how they are bonded. For instance, rubber is a polymer that can stretch, while acrylic is a rigid polymer.
Synthetic polymers, most commonly referred to as plastic, are in theory not compostable because there are no microorganisms that can break down and digest them. But with specific conditions, there is a possibility to compost them! A handful of plastics can be compostable by the action of enzymes that can break it down organic content. An enzyme is a protein that accelerates chemical reactions. Also, the polymer chain needs to be flexible enough to fit into the enzyme's active site. Others have weak points in their polymer chain that can be hydrolysed by the heat in an industrial composting process.
So which plastics are compostable? Some bioplastics - plastics that are made from plants rather than fossil fuels - are compostable. The most well-known is polylactic acid (PLA). But watch out! This plastic is not home-compostable! It requires specialised industrial composting equipment to degrade because it can break down by chemical reaction with water only at elevated temperatures.
What about compostable packaging made of natural polymers?
Natural polymers made of starch, cellulose or seaweed extract can be directly consumed by microorganisms. Their polymer chains are enzymatically cleaved, meaning the residues are small enough to be transferred into the cells and consumed.
At Notpla, we are developing compostable packaging with our material made of seaweed and plant extracts. It takes less than six weeks for our food packaging to decompose in a home-compostable environment, even faster than some fruit peels! And worst-case scenario, if your Notpla packaging ends up in the wild, it will take more time to decompose, but it will also completely… disappear! Like a leaf, or a piece of seaweed.
What are the standards compostable packaging must follow?
Materials have to be certified to be regarded as compostable. Various standards set up frameworks to follow depending on the composting.
For home composting, two certification bodies offer a specific "home compostability" certification programme:
- DIN CERTCO (created in Germany)
- Vinçotte (created in Belgium, with the well-known "OK compost" logo).
Products that have passed all of the relevant criteria are permitted to display the appropriate logo.
In general, the standards require the testing material to be broken down by microorganisms in the presence of oxygen, carbon dioxide, water, new biomass and mineral salts. One of the conditions to pass the tests is that the biodegradation rate of the material shall not be less than 90% within a maximum of 6 months. Toxic substances and ecotoxicity are also investigated. However, composting standards still allow 10% of the material to contain problematic substances, given that 90% compostability is enough to pass through standards!
Watch out for materials that blend plastics with starches, as these will quickly fragment but leave micro flakes of plastic behind! However small the non-compostable fraction in a blend, it will never completely disappear. At Notpla, all components of our material are fully compostable.
For industrial composting, common standards include EN13432, ISO16929 and ASTM D 6400.
Similarly to home composting, the material should be at least 90% compostable. Put another way though, there's still an allowable 10% that doesn't need to break down.
Is compostable plastic a good solution?
Compostable packaging materials are a step towards solving the single-use plastic problem. It is a great alternative to waste being burned, ending up in landfills or the ocean.
However, the reality is that industrial composting programs are lacking in many countries. According to the last WRAP report around the composting industry market, there were only 272 permitted composting sites in 2019 in the UK and most generally refuse compostable packaging as they prefer processing food waste that is much faster and more productive to break down.
As a result, industrially compostable plastics are most likely to end up in landfills, along with many other packaging materials. And if they end up in the environment, they won't degrade and will create the same problems as fossil-based plastic! So it's a particularly inadequate solution for applications that require just a few minutes of usage and can end up littering the environment for hundreds of years.
There are many ways consumers can help make significant changes in the way we dispose of our waste. One key area is research; The Big Compost Experiment, in partnership with UCL, is currently investigating the effectiveness of home composting and public understanding. They call for the public to get involved in composting packaging at home and send the results back to them. So far, they have seen some interesting results, 68% of items are still visible in the compost after the suggested amount of time has passed, meaning that some packaging is not living up to the claims it is making.
Would you like to better understand the complex terminology surrounding sustainability? Have a look at our Notpla Glossary where we unravel the meaning of various terms related to sustainability!
This article was written with the support of Tian, R&D Chemist at Notpla