With so many end-of-life solutions for plastics, it has grown harder for design engineers and the public to fully understand the differences between them. Even within one specific category, such as biodegradable plastics, there is a vast array of options, from compostable to hydrodegradable.
A study by McKinsey & Company found that only 16 per cent of plastic waste is recycled to make new plastics, whereas 40 per cent is sent to landfills, and 19 per cent is unmanaged dumps. This suggests the need for plastics that can biodegrade into benign components in landfills or natural environments. However, according to a European Bioplastics study in 2020, only about one per cent of plastics and plastic products on the market are considered bio-based. Therefore, the need for greater awareness around these bio-based plastics is essential for the environment to survive.
Biodegradable plastics are defined by their ability to break down in a specific setting, for example, water. However, there is no set time limit on when the product can break down, meaning the plastics that take years to degrade still get counted as biodegradable.
More importantly, many biodegradable plastics can leave behind a toxic residue when they degrade. This is because of the constituent parts of the biodegradable polymer itself, which do not necessarily come from biological feedstock. Oftentimes, the polymer can break down into smaller pieces of plastic, making it harder to remove the damaging product from the environment. This is why alternatives that will break down without harming the environment are essential to produce.
Compostable plastics are one such answer to the problems with just simply labelling a plastic as biodegradable. Compostable plastics will break down at the same rate as cellulose into biomass, carbon dioxide and water. Not only that but they are not allowed to leave any toxic materials behind and must become identical to the compost.
One example of compostable materials is the carrier bags rolled out to all stores of UK supermarket chain Co-Op in 2021. Novamont, who helped create the compostable plastic used in this bag, found that this bag will fully break down with no toxic by-products in the sea over the course of four to twelve months.
Although compostable plastics have the benefits of breaking down and leaving no toxic residue, there are some complications. First is the environment in which the compostable plastics are left. Industrially compostable plastic products can only be broken down in an industrial composting plant, as carefully controlled environmental conditions must be maintained for the plastic to break down. They do not always fully compost in home composters or out in the environment, which is a problem if people do not dispose of them correctly.
The public not sorting compostable plastics correctly is a recurring problem. One German survey found that 58 per cent of participants thought all bioplastics were compostable, which is not necessarily the case. People also often mistakenly put compostable plastics in recycling bins, which forces the recycling plants to sort through them.
These problems can be circumvented by using compostable plastics in applications where they do break down. For instance, they can be used in food caddy liners, as that becomes compost. Another example is using the plastic as agricultural mulch film, which would allow it to break down into the mulch without damaging the soil. That would overcome the challenge of traditional plastics, which are difficult for farmers to remove from the farmland. As it is mulch film, it will also be in the right conditions to compost rather than at the bottom of a landfill, where it does not get enough sunlight or oxygen to decompose.