Bioplastics

Definition

Often referred to as biobased, biodegradable or compostable plastics, bioplastics actually comprise a broad category of materials, with varied uses and properties. Bioplastics are generally defined as either made from plants or ‘biobased’ ingredients, or having the capacity to biodegrade rapidly. Many bioplastics are designed to reduce our reliance on non-renewable fossil fuels, although many are still made wholly or in part from fossil-based ingredients.

Production

Traditional plastic is economical, durable and lightweight and provides many essential applications across modern society, but these same highly functional properties result in discarded plastics taking hundreds of years to break down, contaminating ecosystems with waste, microplastics and chemical emissions – all of which impact the health and environments of living species including humans.

While bioplastics are considered to be a recent innovation to address these issues, their origins evolved alongside traditional fossil-based plastics, with early twentieth century examples such as linoleum and cellophane still in use today. An increased exploitation of oil resources in the mid-twentieth century saw a decline in research and development of bioplastics until the global energy crises of the 1970s. Then, generally credited as reviving bioplastics research, the chemicals multinational Akzo Nobel invented Biopal – a fossil-free plastic specifically conceived with biodegradable properties for use in temporary medical implants and tissue engineering, as well as slow-release capsules for medication and agriculture.

Today the most common bioplastics are formed – like their fossil-based counterparts – of polymers (or in this case, biopolymers). But rather than sourcing virgin materials from fossil-based ingredients such as oil, the polymers come from renewable plant-based sources. The most common bioplastic of this type is PLA (polylactic acid) made through the fermentation of sugars derived from staple crops such as corn and sugarcane. PLA accounts for approximately 37% of the bioplastic market,¹ and its successful uptake is most likely due to its chemical similarity to fossil-based plastics and is referred to as a ‘drop-in’ material, meaning it can be exchanged for the same sort of applications as traditional plastics. This benefits transitioning manufacturers who can use existing machinery and equipment with minimal cost or disruption. Although both biodegradable and compostable, PLA does not break down in water or landfill and requires specialised industrial composting to biodegrade.

Another common biobased plastic is PHA (polyhydroxyalkanoate), which is engineered from biodegradable polyesters produced by naturally occurring microorganisms and degrades faster than PLA, making it more attractive to existing industrial composting infrastructure. Although not biodegradable, bioPET is also an example of a biobased drop-in, and is equivalent to the common fossil-based plastic PET (polyethylene terephthalate) but made from biobased ingredients. Commercially framed as an alternative material for single-use drink containers, bioPET and its polythene counterpart bioPE have the advantage of easy integration into existing recycling streams.

Bioplastic PBAT (polybutylene adipate terephthalate) is made from fossil-based sources, but is both biodegradable and compostable, and is commonly utilised alongside PLA as a film lining or as a blended additive to enhance flexibility, while oxo-biodegradable plastics (sometimes labelled as d2w) are produced by mixing additives to conventional fossil-based plastics to induce biodegradation in the natural environment. However, oxo-biodegradable plastic has now been prohibited for use in the EU, due to concerns around its potential contribution to microplastic pollution.²

With traditional plastic production accounting for 5–7% of the global oil supply, bioplastics such as PLA are commercially promoted for their use of renewable resources and associated lower carbon impact, although estimates suggest that replacing existing fossil-based plastic production for this type of bioplastic would require almost one tenth of the planet’s arable land and around half of its existing global corn harvest for feedstock.³ Concerns have also been raised around bioplastic production competing with existing food crops and water resources, increasing soil depletion and reducing biodiversity, whilst also supplementing a continued use of fossil-based fertilisers.

Other challenger manufacturers are developing materials that are made from natural occurring biobased resources such as algae and seaweed. Unlike commercial crops that require significant amounts of land or water to cultivate, seaweed does not require fresh water or fertiliser. Many materials in this category of bioplastics are able to rapidly biodegrade in nature without the need for industrial composting – leading to some manufacturers distancing their products from the term ‘bioplastics’ altogether. For instance, regenerative packaging manufacturer Notpla uses the term ‘plastic free’.

Another approach to bioplastics takes post-industrial waste from the food industry which can be used to create epoxy resins from vegetable oils, polyurethanes from fruits, natural rubber from plant latex, polycarbonate ‘bioPC’ from lemon peel, and fungal-based mycelium – which can be added to organic waste and ‘grown’ into desired forms. Fabrics made from these methods have been popularised in the fashion industry by brands such as Pangia and Ganni.

In Use

Bioplastic production still only represents less than 1% of the global plastics market. To fully maximise their environmental accreditation, bioplastics should be manufactured to be both biobased and biodegradable, although not all biobased plastics are biodegradable and, confusingly (despite their biodegradable properties), some of the most widely encountered bioplastics are actually entirely fossil-based.

Biobased means a material is derived from biomass or organic plant matter.

Biodegradable is the capacity of a material to convert into water, carbon dioxide and biomass by breaking the material’s chemical bonds through the action of living microorganisms. The process depends on environmental conditions such as temperature and humidity as much as the material itself, while the biodegradable characteristics of a product are defined by its chemical structure rather than its raw materials. If used in isolation, the label ‘biodegradable' is insufficient when assessing the environmental accreditation of a material or product.

Compostable means a material must adhere to a regulated standard or certification and will only biodegrade under industrial composting conditions. While all compostable materials are biodegradable, not all biodegradable materials are compostable. Compostable materials will not necessarily break down effectively in landfill, marine environments or domestic compost. Although it is common to see home compostable certifications on bioplastics that indicate they can decompose more quickly at lower temperatures, these home compostability standards such as EN17427 are still in their infancy, and some testing has been critical. Indeed, a recent investigation by UCL (University College London) into home compostable materials found that many still failed to fully decompose to the expected level.⁴

End-of-life

The most significant challenge for bioplastics arises at their end of life. With the exception of home compostables (and depending on the specific type of bioplastic), bioplastics should be industrially composted or recycled – but in the UK most will be incinerated or sent to landfill.

Compostable bioplastics can only be composted in industrial conditions where temperatures are high enough to allow microbes to break the material down – which generally takes a period of 12 weeks. Without this intense heat of around 50-60° C, they will not degrade in a meaningful timeframe, especially in landfill. Compostable certification requires a material to achieve 90% biodegradation in 6 months, but many industrial composting facilities turn over batches of food and garden waste in a matter of weeks. This isn’t enough time for compostable bioplastics, so in the UK they are regularly rejected by composters and instead sent to landfill or for incineration.⁵

With so much plastic waste still making its way into our waterways and oceans, some critics argue there is little to distinguish between bioplastics and their conventional fossil-based counterparts – the UN environment programme has advised that ‘biodegradable plastics will not play a significant role in reducing marine litter’.⁶ Limited studies also suggest that public perceptions about whether an item is biodegradable can negatively influence littering behaviour, leading consumers to overestimate how easily a product or material can biodegrade – viewing the biodegradable label as a technical solution that removes responsibility from the individual or manufacturer.⁷ 

Bioplastic recycling methods and facilities remain limited as many bioplastics contaminate recycling streams and can be difficult to distinguish from fossil-based counterparts. Therefore, end of life challenges lie as much with the infrastructure to process bioplastics and a lack of consumer guidance as with the materials themselves. To realise the benefit of bioplastics, it is important that compostables are separated from fossil-based plastics and captured as a separate waste stream. For instance, enabling closed-loops systems at large events or venues offers a model for the disposal of used compostable packaging, as bioplastic and contaminating food waste can be composted together without separation, in a single stream.⁸

Inadequate infrastructure and lack of clear labelling or disposal instructions mean much more effort is still required to ensure bioplastics end up at their intended end-of-life destination. These might include EPR (Extended Producer Responsibility) schemes, clearer labelling standards, improved local and international governance of waste processing and the education of business and consumers around better plastic life-cycle thinking.

Certification

Certification and clear labelling is considered the best way to inform consumers on how to properly dispose of a biodegradable plastic – where facilities exist. The EU currently recommends that bioplastics carry both an official certification logo in combination with the relevant European standard number.

Industrially Compostable For European markets, there are two main certifications relating to compostable plastic packaging: The Seedling and OK Compost logos, and both indicate that a material has been certified compostable according to European EN 13432, achieving 90% biodegradation in less than 6 months. Similar compatible standards exist for other global regions.

Home Compostable If a material simply claims to be ‘compostable’ then this only refers to industrial compostability. The home compostability standard EN17427 has only recently been published, although the older and more familiar OK Compost Home specification includes lower composting periods and temperatures of between 20-30°C.