Is oxo-degradability the answer?

Bright Green Plastics’ technical manager, Dr. Sam Hill, looks at the big picture.

Additives that are supposedly meant to accelerate the oxo-degradability of polyolefin plastics, when they are littered or find their way into our waterways and oceans, have been under the spotlight again.

Oxo-degradable plastics are conventional plastics combined with an additive to allow the plastic to degrade quicker. However, these don’t break down much at the molecular or polymer level, in the short term, resulting in microplastics that are left in the environment for a time until they eventually fully break down.

I believe that the use of an additive, or any other means, to accelerate the degradation of a plastic material is counterintuitive in several ways, including the synthesis of biodegradable plastics.

Firstly, anaerobic digesters must remove these oxo-degradable bags from their process, as they are incompatible with their process. They cannot be composted, and recyclers cannot use them as they worsen properties of plastics. This all leads to extra separation and landfill or incineration.

Additionally, these additives simply miniaturise “the plastic problem” by producing microplastics which can accumulate in the environment. The UK government is urged to proceed with the banning of the use of plastics containing such additives, which they voted for in 2019, which will be EU-wide, as they severely disrupt the current recycling streams and actively displace easily mechanically recyclable plastics.

This would see us moving away from a circular market to a linear one.

Unless the production of the biodegradable polymer is much less energy intensive overall, it will lead to a worse environmental impact than those they displace.

Interestingly, despite the UK government’s move to ban such products containing these additives, WRAP, FERA and BEIS were part of the steering group that developed a new publicly available specification, or PAS, to measure the biodegradability of polyolefins in open air environments.

The development of the specification was sponsored by Polymateria, a technology company that develops biodegradable plastics. This standard aims to set a methodology for technology providers to demonstrate that their product offers the benefits they claim. WRAP has, however, noted that this PAS does not offer any information if the material enters waterways. Additionally, this PAS does not allow any green claims to be made as these must be made in accordance with ISO 14021. WRAP is interested, also, in understanding how plastics behave that are intended to be in the environment for an extended amount of time, such as tree guards for saplings that this PAS can inform. 

Plastics do degrade, and over a period much less than the hundreds or thousands of years that some suggest.

It is of no surprise to anyone who is involved in the manufacture of thermoplastics that they are not an infinitely stable item. They are always formulated or produced incorporating a stabiliser package to protect them from high temperature and UV stress.

There are studies showing that PP and PE can degrade severely within three years when exposed to oxygen and sunlight. Heavily stabilised PE landfill liners have been shown to begin to degrade within 14 years when exposed to the atmosphere. This degradation is not just of colour or mechanical properties, the degradation is of molecular weight and particle size, increasing surface area for oxygen attack and accelerated degradation. It is nonsensical to assume plastics just break down to smaller “pieces” and just stop there.

The answer is education and effective waste segregation – not additives.

WRAP states that its focus is still on reducing littering by Deposit Return Schemes (DRS) and awareness campaigns but feels the public will not completely halt this behaviour.

We must educate, promote, and provide a system that allows people to separate their waste simply and easily to reduce littering and mishandling of plastics (and all other recyclables). We should celebrate the versatility of this class of materials while simplifying design choices such as easily removable labels rather than heavily printed surfaces to promote recycling, reducing excessive use, thinner walls, homopolymer construction, and increased use of recycled plastic in our products – which is set to be helped along with the introduction of the plastic tax.

In summary, I feel that WRAP and local authorities must not lose focus on the standardisation of waste segregation, collections, and methodologies across the UK, as this will further drive the efficiency of the UK’s recycling infrastructure.