Non-biodegradable fossil-based plastics: There are many types of conventional, non-biodegradable fossil-based plastics. These are extremely durable, often taking centuries to break down depending on where they end up.
Oxo-degradable plastics: Oxo-degradable plastics are essentially conventional plastics such as polyethylene and polypropylene that contain additives known as ‘pro-oxidants’. These additives are typically metal salts, which are intended to speed up degradation of the plastics into smaller fragments without any help from microbes.7
Fragmentation is facilitated by exposure to sunlight and air, which causes oxidation – a chemical reaction that leads to the loss of electrons and often involves oxygen – hence the name oxo-degradable. Oxo-degradable plastics typically result in a large number of micro-fragments or micro-plastic pieces. A key concern is that oxo-degradable plastics may be contributing to micro-plastic pollution in the marine environment.8
If fragmentation occurs, some biodegradation may occur in the right environment.9
Oxo-degradable plastics are sometimes marketed as biodegradable. However, they should not be unless they pass robust international standards for biodegradability. Beyond that, a 2018 report concluded that:
“The evidence suggests that oxo-degradable plastic is not suitable for any form of composting or anaerobic digestion and will not meet the current standards for packaging recoverable through composting in the EU.”10
There is a lack of conclusive evidence relating to the benefits of oxo-degradable plastics, and restrictions on their use are being considered in Europe.11
In New Zealand, two oxo-degradable bag manufacturers have been charged under the Fair Trading Act for misleading claims regarding the environmental benefits of these products.
Non-biodegradable bio-based plastics: These types of bio-based plastics are indistinguishable from conventional fossil-based plastics in terms of their chemical composition, properties and decomposition characteristics. As the name suggests, they are manufactured from at least some biologically produced compounds, typically of plant or microbial origin. However, the terms ‘bio-based’ or ‘plant-based’ can be ambiguous as they do not convey what proportion of the plastic is bio-based. Polyethylene terephthalate (PET) illustrates this problem.
PET – partially bio-based but not biodegradable
PET is a polyester that is manufactured from ethylene glycol and either dimethyl terephthalate or terephthalic acid. Ethlylene glycol comprises approximately 30% of the final PET material and can be made from plants, such as sugar cane or sugar beet. However, plant-based terephthalic acid is not yet available, which would be required to make PET 100% bio-based. Large companies, including Coca-Cola, are currently investing in research on ways to produce the entire PET plastic from bio sources.12
7. These types of plastics are also sometimes referred to as oxo-biodegradable plastics.
8. European Commission, 2018; United Nations Environment Programme, 2015. Biodegradable plastics and marine litter: misconceptions, concerns and impacts on marine environments, p. 22.
9. Hann et al. 2016. The impact of the use of “oxo-degradable” plastic on the Environment. Final report for the European Commission DG Environment, p. ii.
10. European Commission 2018, p.3
11. European Commission 2018, pp.7-8.
12. Anderson, 2015. Great Things Come in Innovative Packaging: An Introduction to PlantBottle™ Packaging. https://www.coca-colacompany.com/plantbottle-technology