top of page
  • Writer's pictureIan Yew

Are Bioplastics Really Environmentally Friendly?

Edited by Season Wang.



Bioplastics are commonly known as the more environmentally friendly version of plastics. It is created from bio-based materials, which are partially or wholly made of renewable resources. Despite this, bioplastics are not fully embraced as an alternative to original plastics. The truth behind the perceived biodegradability of bioplastics is far more complex than expected. There are many types of bioplastics, and various factors contribute to their degrees of biodegradability, ranging from chemical components contained to the environmental conditions in which they lie.


Today, fossil-fuel plastics still dominate among users of plastics. These include PET, HDPE, PVC, LDPE, polypropylene, polystyrene, and many more. All of them are used for different applications⁵. However, they all have one thing in common: the carbon-carbon bonds found in the long polymer chains that they are fabricated from. These bonds are constructed by linking individual monomers of propylene under intensely heated conditions. The extreme requirements needed for the polymerisation of propylene to happen makes the chemical process impossible in nature. With nature being unable to synthesise carbon-carbon bonds, it is simply not attainable to reverse it for the plastic to biodegrade. These bonds are too difficult to break, and lots of energy is required for them to be broken¹¹.


Polylactic acid (PLA), achieves its highest percentage of biodegradability in compost. However, it has a higher range of biodegradability than PBAT, lying between 60% and 70% after 30 days. This is achieved with a temperature of 58°C and a relative humidity of 60%. Yet, PLA’s biodegradability percentage in a simulated marine environment is around 3% to 4%. This can only be accomplished after 180 days which is comparatively lower than other types of bioplastics such as PHA. It has a percentage from 52% to 82% after 12 months¹².


According to an article published by Luo et al. (2019), the mechanism of the biodegradation of PLA involves two steps⁶. First, the polymer is hydrolysed with the help of heat and moisture. The long chain is broken down to polymers with low molecular weight and then to lactic acid. Next, microorganisms mineralise the oligomer fragments and lactic acid. The main products generated during aerobic and anaerobic biodegradation are carbon dioxide and methane, respectively⁶.


There are multiple factors affecting the rate of biodegradation of PLA bioplastics. The biodegradability of PLA increases as the temperature rises. This is due to the increase in flexibility in the polymer chain, thus allowing hydrolysis to occur more easily and the microbes and enzymes involved to be attached. Therefore, this explains the relatively high temperature needed for PLA to be biodegraded effectively in compost. However, temperatures beyond thermophilic conditions (45°C to 65°C), slow down the rate of biodegradation as microorganisms are killed at such high temperatures. The pH level of a medium also affects biodegradation. PLA bioplastics have the unique property of decreasing the pH of the medium surrounding them. Usually, the optimum pH for biodegradation of other types of bioplastics would be a neutral pH. In the case of PLA bioplastics, a moderately alkaline medium during composition has been found to speed up the hydrolysis of the PLA polymer and hence, its biodegradation⁴. The state of the PLA solid also plays a role in its biodegradability.

Polybutylene adipate terephthalate (PBAT), like PLA, biodegrades in three main mediums: compost, soil and simulated marine environment. The degree of biodegradability of PBAT in a compost environment ranges from 34% to 67%, which is the highest percentage that can be achieved for PBAT in 45 days. This data was taken from an article published by Zhao et al. (2020), who conducted experiments on the biodegradability of bioplastics under different environmental conditions¹². However, the catch is that the optimum temperature for this percentage of biodegradability to be attained is as high as 58°C. Therefore, PBAT cannot be disposed of in a natural environment and still be expected to biodegrade effectively.


Although PBAT can biodegrade in soil from 10°C to 25°C without intense heating, it has a significantly lower degree of biodegradability of 6.6% in this medium compared to in compost. Furthermore, this percentage can only be acquired after 120 days. Despite the low biodegradability percentage, it is actually still comparatively higher than some other types of bioplastics such as PLA and PBS in the same medium¹². That is due to the distinct chemical structure of PBAT that distinguishes it from some of the other types of bioplastics. PBAT is an aliphatic-aromatic compound; its aliphatic chain speeds up its biodegradability under some environmental conditions. Their aromatic structure clearly explains their resistance to hydrolysis and microbial reactions, preventing biodegradation⁶.


PBAT has a degree of biodegradability of around 1% to 1.4% in a simulated marine environment, according to the experiment conducted by Zhao et al. (2020)¹². This occurs when the temperature of the water is 29°C. The biodegradability of bioplastics in marine environments is a key indicator of their environmental friendliness since marine environments are most seriously damaged by the littering of plastics. Microplastic from fossil fuel-based plastic can cause several health problems in marine animals. These include endocrine disruption, development disorders and reproductive issues that have a devastating effect on the food chain⁴. The degree of biodegradability is accomplished within 28 days. However, the speed of biodegradation in marine environments varies throughout the globe due to the difference in temperature, pH and other environmental factors.


One of the biggest obstacles to the widespread use of bioplastics is their permeability to low molecular weight gases, water vapour and organic molecules⁹. Pietrosanto et al. investigated the permeability of different combinations of biopolymers and PBAT¹⁰. It found that the higher the content of PBAT in the different blends, the higher their permeabilities to oxygen. PLA and cellulose-based oil palm bioplastics have also been discovered to possess the same weakness. This undermines their ability to be used as a viable food packaging that can preserve or at least prolong the edible state of food. Therefore, bioplastics are often limited to being used as bags for carrying fresh vegetables in the food and beverage industry as it prevents fogging on the inner surface of the bag due to its permeability to water vapour¹⁰.


While bioplastics do present some positive environmental effects, there are some side effects that come with their use. The first indicator that it has potentially negative side effects is shown in the degree of biodegradability. As mentioned earlier, bioplastics are not necessarily completely biodegradable, given their dependence on their chemical makeup and environmental conditions. “Whether bio-based plastics are ultimately better for the environment than oil-derived ones is a big question based on many 'ifs’. Depending on the type of polymer used to make it, discarded bioplastic must either be sent to a landfill, recycled like many (but not all) petroleum-based plastics, or sent to an industrial compost site. If PLA [bioplastic] does leak out, it also will not biodegrade in the ocean,” claimed Jenna Jambeck, an environmental engineer and National Geographic Engineer at the University of Georgia³.


According to an article published by Cho R. (2017), most bioplastics need high-temperature industrial composting facilities to be broken down, and very few cities have the infrastructure required to facilitate their biodegradation². Gibbens S. wrote in an article published by National Geographic (2018), that without that intense heat, bioplastics won't degrade on their own in a meaningful timeframe, either in landfills or even your home compost heap³. If they end up in marine environments, they'll function similarly to petroleum-based plastic, breaking down into micro-sized pieces, lasting for decades, and presenting a danger to marine life¹. As a result, bioplastics often end up in oxygen-deprived landfills, where anaerobic biodegradation takes place. Therefore, they may release methane, a greenhouse gas 23 times more potent than carbon dioxide⁸.


The environmental friendliness of bioplastics is entirely subjective due to its utter dependence on its chemical components and environmental conditions. A broad range of plastics is classified as ‘bioplastics’, blinding the public from the various types of bioplastics and their differences. Bioplastics can be environmentally friendly if the conditions are right and the process of biodegradation is conducted properly.


 

References:

  1. Carney Almroth, B. and Eggert, H. (2019). Marine Plastic Pollution: Sources, Impacts, and Policy Issues. Review of Environmental Economics and Policy, 13(2), pp.317–326.

  2. Cho, R. (2017). The Truth About Bioplastics. [online] State of the Planet. Available at: https://news.climate.columbia.edu/2017/12/13/the-truth-about-bioplastics/.

  3. GIBBENS, S. (2018). Bioplastics—are they truly better for the environment? [online] Environment. Available at: https://www.nationalgeographic.com/environment/article/are-bioplastics-made-from-plants-better-for-environment-ocean-plastic.

  4. J, V.-B. (2019). Polylactic acid (PLA) as a bioplastic and its possible applications in the food industry. Food Science and Nutrition, 5(2), 1–6. https://doi.org/10.24966/fsn-1076/100048

  5. Jiao, J., Zeng, X. and Huang, X. (2020). An overview on synthesis, properties and applications of poly(butylene-adipate-co-terephthalate)ePBAT. Advanced Industrial and Engineering Polymer Research, 3, pp.19–26.

  6. Luo, Y., Lin, Z. and Guo, G. (2019). Biodegradation Assessment of Poly (Lactic Acid) Filled with Functionalized Titania Nanoparticles (PLA/TiO2) under Compost Conditions. Nanoscale Research Cho, R. (2017). The Truth About Bioplastics. [online] State of the Planet. Available at: https://news.climate.columbia.edu/2017/12/13/the-truth-about-bioplastics/.

  7. Metro, M. (2021). 5 Types of Bioplastics: Starch, Cellulose, Protein, Organic, Aliphatic Polyesters. [online] Green Business Bureau. Available at: https://greenbusinessbureau.com/green-practices/products/5-types-of-bioplastics-starch-cellulose-protein-organic-aliphatic-polyesters/.

  8. Oakes, K. (2019). Why Biodegradables Won’t Solve the Plastic Crisis. [online] BBC. Available at: https://www.bbc.com/future/article/20191030-why-biodegradables-wont-solve-the-plastic-crisis.

  9. ‌P.R.D. Weerasooriya, R. Nadhilah, F.A.T. Owolabi, R. Hashim, H.P.S. Abdul Khalil, Z.A. Syahariza, M.H. Hussin, Salim Hiziroglu, M.K.M. Haafiz, Exploring the properties of hemicellulose based carboxymethyl cellulose film as a potential green packaging, Current Research in Green and Sustainable Chemistry, Volumes 1–2, 2020, Pages 20-28, ISSN 2666-0865

  10. ‌Pietrosanto, A., Scarfato, P., Di Maio, L., Nobile, M.R. and Incarnato, L. (2020). Evaluation of the Suitability of Poly(Lactide)/Poly(Butylene-Adipate-co-Terephthalate) Blown Films for Chilled and Frozen Food Packaging Applications. Polymers, 12(4), p.804.

  11. Wolchover, N. (2011). Why Doesn’t Plastic Biodegrade? [online] Live Science. Available at: https://www.livescience.com/33085-petroleum-derived-plastic-non-biodegradable.html.

  12. Zhao, X., Cornish, K., Vodovotz, Y. (2022). Narrowing the gap for bioplastic use in food packaging: An update. Environ. Sci. Technol. 54, 4712–4732.


74 views0 comments

Recent Posts

See All

Comments


bottom of page