Biobased polymers are generally accepted to be any polymer that is built from renewable material, is biodegradable, or both. Not all biobased polymers are biodegradable, and not all biodegradable polymers are compostable (FPF reported). This overlapping and sometimes ill-defined terminology creates confusion among consumers and inefficiencies in the plastics value chain when certain plastics are mismanaged (FPF reported). For this reason, the International Union of Pure and Applied Chemistry (IUPAC) suggest using the term “biobased polymer” instead of “bioplastic”. Three recent papers review the biobased polymer field, attempting to outline currently accepted terminology, the biobased polymer supply chain, and particular traits of biodegradable and non-biodegradable biobased polymers.
A systematic review published online May 25, 2021 by Ardra Nandakumar et al. in Renewable and Sustainable Energy Reviews investigated the different types of biobased polymers, their properties, and the greenwashing and economic challenges around proper disposal. The authors give six broad categories of sources for biobased polymers: starch, cellulose, aliphatic polyesters, protein, lignin, and chitin. However, they report that some polymer stakeholders argue “plastics that are completely petrochemical in nature, like polycaprolactone (PCL) and poly(butylene adipate-co-terephthalate) (PBAT), may also be considered as a [biobased plastic] as they are completely biodegradable.” According to Nandakumar et al., the term “biodegradable” is not well-defined but is generally applied to a polymer that “decomposes within a few months.”
Octavio García-Depraect, from the Institute of Sustainable Processes at the University of Vadolid, and their co-authors specifically reviewed biodegradable biobased polymers including “a critical evaluation of terminology and international standards to quantify polymer biodegradability.” In their paper in Biotechnology Advances, García-Depraect et al. affirm that the variety of polymers and disposal processes “frequently results in misinterpretation of the terms degradable, biodegradable, biobased, or compostable.” They continue, “biopolymers are biodegradable polymers produced by living organisms,” including, for example, some of the sources mentioned above: starch, cellulose, proteins, and nucleic acids. “On the other hand, biobased polymers are synthesized (man-made) from biomass as a renewable resource derived from plants, animals, or microorganisms” and may not biodegrade.
A polymer is biodegradable, according to ASTM International (ASTM), if it can eventually break down to “carbon dioxide, methane, water, inorganic compounds, or biomass” through the action of microorganisms. The term “compostable” is slightly more specific. For a polymer to be considered compostable according to ASTM, it must biodegrade as above but “at a rate consistent with other known compostable materials and leave no visible, distinguishable or toxic residue.” García-Depraect et al. propose the term “biotechnological recycling (bio-recycling)” to describe the use of enzymes and microorganisms in a technological setting for the purpose of downcycling, upcycling, or recycling biobased polymers. A material that can go through biotechnological recycling using enzymes, for example, may be a biodegradable polymer but still may not be compostable in a standard garden or industrial compost system.
As such, not all biodegradable plastics breakdown in the natural environment. Lott et al. described in Frontiers in Marine Science their findings from placing three types of biodegradable plastic materials in marine environments in the Mediterranean Sea and Southeast Asia. They found all three plastics, polyhydroxybutyrate (PHB), polybutylene sebacate (PBSe), and polybutylene sebacate co-terephthalate (PBSeT) biodegraded over time but “biodegradation performance of the materials differed by orders of magnitude depending on climate, habitat and material.” PHB, for example, had a decomposition half-life less than eight weeks on the Southeast Asian seafloor but nearly three and a half years in the open water of the Mediterranean. PBSe and PBSeT had similarly wide degradation half-lives: 14 weeks to over 7 years, and 21 weeks to over 2 years, respectively. Lott et al. conclude that “biodegradable plastics are less likely to accumulate or persist than conventional plastics” but “plastic lost to the environment is pollution, even if biodegradable.”
In a review on non-biodegradable biobased polymers in the Journal of Cleaner Production, Md Hafizur Rahman and Prakashbhai R. Bhoi say that “approximately half of the current biobased plastic market is not biodegradable.” The authors further clarify, “that the majority of the current world biobased plastics have similar chemical compounds [as] traditional plastics. Therefore, most of the biobased plastics are prone to exhibit similar problems as traditional plastics” including as marine litter and sources of microplastics. According to the authors, “non-biodegradable biobased plastics are advantageous from an environmental point of view, as they are produced from biomass. They will reduce the carbon footprint and will develop a positive impact on our environment, provided that their waste is not mishandled like traditional plastics.” However, IUPAC has clarified that biobased polymers are not automatically more environmentally friendly than traditional polymers, and life cycle assessments must still be undertaken. Rahman and Boi outline how biobased polymers can be incorporated into the current plastics recycling infrastructure as a move towards a more circular economy.
Nandakumar et al. in their review of bio-based polymers don’t go into the same depth as Rahman and Bhoi, and Garcie-Depract et al. but they still incorporate some of the ideas mentioned in both papers incorporated together in end-of-life pathways for bio-based polymers as a whole. They end their review stating biobased plastics are not the solution to littering and waste reduction – that will rather take behavioral change – but they think biobased plastics can help “to reduce our dependence on as many non-renewable resources as possible so as to promote sustainable living and a greener future.”
Nandakumar, A., et al. (May 25, 2021). “Bioplastics : A boon or bane?” Renewable and Sustainable Energy Reviews
García-Depraect, O., et al. (May 17, 2021). “Inspired by nature: Microbial production, degradation and valorization of biodegradable bioplastics for life-cycle-engineered products.” Biotechnology Advances
Lott, C., et al. (May 6, 2021). “Half-Life of Biodegradable Plastics in the Marine Environment Depends on Material, Habitat, and Climate Zone.” Frontiers in Marine Science
Rahman, M.H., and Bhoi, P.R. (April 20, 2021). “An overview on non-biodegradable bioplastics.” Journal of Cleaner Production
Zack Fishman (May 29, 2021). “Many biodegradable plastics fully break down in water environments — though it can take decades.” The Academic Times
Science Advice for Policy by European Academies (May 21, 2021). “Biodegradable plastics: How do we engage with consumers and society?”
Science Advice for Policy by European Academies (December 14, 2020). “Biodegradability of plastics in the open environment.”
European Commission (March 2020). “Relevance of biodegradable and compostable consumer plastic products and packaging in a circular economy.”
Biodegradable Products Institute (2020). “Guidelines For The Labeling And Identification Of Compostable Products And Packaging.” (pdf)
European Bioplastics (2016). “Bioplastics – Industry standards and labels.” (pdf)
Vert, M., et al. (January 11, 2012). “Terminology for biorelated polymers and applications (IUPAC Recommendations 2012).” Pure and Applied Chemistry