Bioplastics are plastic materials that are derived from biological materials. Currently, petrochemical-based plastics make up 99% of the plastics market. However, production of bioplastics is increasing as the world looks for more sustainable options to petrochemical-based plastics.
Plastics: a versatile material
The term ‘plastic’ refers to material that is capable of being moulded. Historically, this included plastic materials from natural sources, such as animal horn, amber and shellac. However, with the rapid expansion of petrochemical-based plastics after World War II, plastics made from natural resources declined, and the term ‘plastic’ now generally refers to synthetic plastics.
With scientific and technological advances, plastics rapidly gained popularity during the 20th century. Plastics are easy to mould into complex shapes and are lightweight, flexible, durable, long lasting and cost-effective to produce. These properties make plastics very versatile and often better suited for many products than traditional materials such as metal, wood and glass. Consequently, their use is increasing all the time.
The problem with conventional plastics
Increasing use of conventional plastics is becoming unsustainable due to their reliance on petrochemicals – a finite and depleting resource. The durability of plastic products is also creating serious environmental issues because of the amount that we use and discard every day and the fact that they take hundreds of years to break down. For example, in New Zealand, approximately 252,000 tonnes of plastic waste is disposed of in landfills annually – enough to fill approximately 200 Olympic-sized swimming pools! This takes up approximately 20% of all landfill space. These concerns are leading to a greater interest in bioplastics.
Growth of bioplastics
The predicted growth in the production of bioplastics is being driven by a number of factors, including:
- the fluctuating cost of petroleum and the drive for independence from fossil fuels
- increasing availability of bioplastics and decreasing cost as greater volumes are produced
- environmental and social impacts of petrochemical-based plastics including carbon footprint, sustainability, pollution involved in end-of-life disposal and health concerns such as leaching of chemicals from plastic packaging into food products
- branding and product differentiation as manufacturers perceive a marketing advantage
- waste minimisation regulations
- the fact that plastic products are useful and we’ve become used to using them.
In June 2021, the government announced a three-stage plan to phase out plastics that are hard to recycle in New Zealand. As part of this plan, a new Plastics Innovation Fund was launched to help support projects that reimagine how we make, use and dispose of plastics. It is anticipated that this fund will further drive the increase and production of bioplastic alternatives.
Properties of bioplastics
Bioplastics is a broad term used to describe a range of plastic materials that are derived from renewable resources. Some bioplastics are biodegradable.
We can generally group bioplastic materials according to their properties:
- Bio-based and biodegradable bioplastics: These are made using renewable resources, such as plant biomass, and will biodegrade under certain environmental conditions. These materials are suitable for disposable items, such as packaging, drink bottles, single-use food containers and cutlery. They are more sustainable because they save fossil fuel resources and, if disposed of appropriately, support further plant growth.
- Bio-based and durable (non-biodegradable) bioplastics:These are made using renewable resources but are designed to have a longer life span (for example, carpet fibres and interior car panels). Using renewable resources makes these materials more sustainable. Also, using them to replace metal components in vehicles has the advantage of reducing vehicle weight, which increases fuel efficiency.
- Petrochemical-based and biodegradable bioplastics: There are some petrochemical-based plastics that can be biodegraded by the microbes in the soil, compost or oceans.
The Rethinking Plastics in Aotearoa New Zealand report by the Office of the Prime Minister’s Chief Science Advisor reported on general confusion about how plastics are made and classified.
...not all biobased plastics are biodegradable and not all biodegradable plastics are biobased.Rethinking Plastics in Aotearoa New Zealand – Key Messages
A bioplastic is not necessarily good for the environment or sustainable. Some problematic examples are oxo-degradable plastics. These plastics can be bio-based or petrochemical-based. They all contain additives known as ‘pro-oxidants’ that speed up degradation of the plastics into smaller fragments. If fragmentation occurs, some biodegradation may occur in the right environment. However oxo-degradable plastics typically result in a large number of micro-fragments or microplastics that do not break down further.
In New Zealand, there have been claims by two manufacturers of oxo-degradable bags that the bags were environmentally friendly. Both companies were prosecuted for making misleading claims.
Oxo-degradable plastics are one of the types of plastics that the government is phasing out.
Disposal options for bioplastics
With the expected increase in bioplastic products, it’s important we understand the different categories of bioplastic and how best to dispose of each type – otherwise, they can contaminate waste systems.
- Recycling: Many plastics can be successfully recycled into new plastic materials at the end of their life. However, if plastics are not sorted into different categories, mixing some degradable plastics with other recycled plastics can reduce the performance and life span of the recycled product.
- Composting: Not all biodegradable products are suitable for composting. Products labelled ‘compostable’ must meet recognised international standards, which specify the composting conditions such as time, temperature and the environmental effects of the final compost. Also, industrial and home composting conditions are different. Where industrial facilities are not locally available, which is generally the case in New Zealand, compostable products are likely to contaminate other waste streams.
- Landfill: Biodegradable and compostable plastics take a long time to degrade in the anaerobic environment of a landfill. Anaerobic digestion of organic materials also produces methane gas that, if not captured, adds to greenhouse gases in the atmosphere.
Where would you place composting of bioplastics on the hierarchy?
Overall, the most sustainable option for all plastics – whether petroleum-based or bio-based – is to reduce our use of them!
Plastic alternatives from biomass residues
Scion is leading a lot of research around converting biomass residues into new materials to replace plastic. An example in production is the Zespri biospife – a compostable tool for eating kiwifruit made from kiwifruit residues.
Scion developed biodegradable clips for vineyard nets using marc – the skins and seeds left after the grapes have been crushed. Marc is a significant biomass residue from the wine industry.
One research focus at Scion at present is around using polymers from bark to create polyhydroxyalkanoate (PHA) bioplastics from microbes. This is particularly exciting as the PHAs can then be broken down by the same microbes at the end of their useful life.
Earthpac (previoulsy Potatopak) is an innovative New Zealand company that makes disposable food ware from recycled potato starch. The products are designed to compost in a domestic compost system within 30 days. Find out more about these products and their environmental benefits.
Plastic is a wicked problem. It’s incredibly useful, but it’s also a huge environmental issue. A helpful resource is Thinking about plastic – planning pathways which includes our interactive planning pathway – use this to begin a cross-curricular look at plastics.
Microplastics – small particles of plastic – are polluting land and water environments. These small particles are very difficult to clean up and are another impetus for alternatives to traditional plastics.
Try this experiment to explore the degradability of different materials with your students.
Lou Sherman is the Packaging Research Leader at Scion, read his Sciblogs article on 'why we need plastic' and what biodegradable plastic really means in Compostable Packaging.
Listen to this Radio NZ programme, Bio-plastic fantastic, featuring Dr Florian Graichen, Scion's science leader for biopolymers and green chemicals, and their work on incorporating horticultural waste and aquaculture waste into bio-plastics.
Watch this video from Rural Delivery on the work at Scion to create biodegradable vine clips from grape skin and seed biomass.
Some of the text around oxo-degradable plastics was taken from the website for the Parliamentary Commissioner for the Environment – see Biodegradable and compostable plastics in the environment.