Breaking Down Plastics: Bioplastics
What are bioplastics? At a first glance, bioplastics sound like plastics made from biological sources instead of petroleum as its raw material. But “bioplastics” are more complex than that.
Plastics come in a wide variety of formats and shapes, from flexible, rigid, soft, transparent, etc. The word plastic itself, when thought carefully can be confusing. In the general meaning of the word, plastic is a descriptor of a material (or matter) meaning that it can change its shape. For example, in neurobiology, the term plasticity refers to the capacity of the brain to reshape itself in learning processes.
On the other hand, plastic is mostly used referring to the rigid materials that come from chemical work done on petroleum, as opposed to gasoline (fossil fuels). This second definition comprises most of our experience with materials, from day-to-day items such as cups, cutlery and even the case of the computer where this post was written.
Can we make “plastics” from sources other than petroleum, like plants? Will this material be called plastic or bioplastic? What if they have the exact same properties as oil-based plastics? Does the source and destiny of these materials matter?
Take a look at the next figure with four different categories of plastic materials.
But what is the difference between these categories?
They consider the source of the material and the end-of-life in a short time frame. There are plastics made from petroleum that can degrade well enough to be called biodegradable, and there are biologically-sourced plastics that can’t biodegrade at all.
The most environmentally friendly option seems to be a material from a sustainable source (to minimize oil extraction) and that can fully biodegrade (avoid long-term pollution).. This makes us ask more questions. What is the best source to make these materials to compete against traditional plastics? What are the most desirable characteristics for these plastics? Under what conditions should they degrade?
https://sj.jst.go.jp/stories/2021/s0927-01j.html
Plastic pollution crisis has been a major concern for the last decades due to the double edge consequences of plastics. Their mechanical properties are designed to perform under harsh weather conditions, being lightweight and resistant, having versatile uses, and the most appealing one, they are very cheap. All of these properties have made plastic production a very profitable business worldwide, with a forecasted production of these materials of 445 million tons annually for 2025.
But these same properties make plastics so durable and easily disposable that most of these tons remain in landfills, are burnt or are lost on every ecosystem, reaching as far as the bottom of the ocean. One of the main challenges in manufacturing bioplastics is the availability and consistency of raw materials. Some raw materials, such as avocado seeds and other industrial waste products, can be difficult to source in large quantities and may not be consistent in their composition, which can make manufacturing bioplastics challenging.
The most popular “biologically-sourced and biodegradable” bioplastic is PLA (poly-lactic acid). This material has great physical properties, has consistency when melted and molded, can be shaped into almost every shape and it's very durable. The main source of this material is starch, which comes from potato or corn, and after its usage it can be degraded using composting to be used again as natural fertilizer.
https://newatlas.com/bioplastic-pla-cheaper-production-process/38498/
However, PLA fails on two main sustainability issues, the raw materials and the easy return to the ecosystems, why?
Starch comes from potatoes and corn, two very important food sources around the globe, thus using them to produce single-use cutlery puts food systems on the edge. Is shifting the problem towards food systems solving our plastic needs? Moreover, corn used for PLA is made without care for the environment, they are being grown using toxic chemicals because they are not for human consumption. Is that truly sustainable?
A scientific study in 2017 on greenhouse gas mitigation and plastics in the US concluded that “due to heavy reliance on agriculture, bio-based products tend to score poorly on environmental metrics, such as ozone depletion, acidification, eutrophication, water use, and food security” [2].
The second problem is that PLA products need to be collected after being dumped to achieve a process called industrial composting, which is different to home composting. PLA products have to be collected, and taken into special landfills for organic waste composting. That does not happen, very few cities have the required infrastructure for composting [3], and many organizations using compostable biopolymers continue to send their waste to landfills [4] keeping the waste stream similar to a fully oil-based plastics economy.
Is that a human management problem? Yes it is. So, even though PLA has great potential, it is not a one-fits-all solution. We hope this small post will get you thinking on how day-to-day life things are made of, and why nothing is as simple as may seem.
References:
- Shah, Manali & Rajhans, Sanjukta & Pandya, Himanshu & Mankad, Archana. (2021). Bioplastic for future: A review then and now. World Journal of Advanced Research and Reviews. 9. 056-067. 10.30574/wjarr.2021.9.2.0054.
- Posen, Daniel et al. (2017) Greenhouse gas mitigation for U.S. plastics production: energy first, feedstocks later. Environ. Res. Lett. 12 034024
- Hottle, T. A., Bilec, M. M., & Landis, A. E. (2013). Sustainability assessments of bio-based polymers. Polymer degradation and stability, 98(9), 1898-1907
- Meeks, D., Hottle, T., Bilec, M. M., & Landis, A. E. (2015). Compostable biopolymer use in the real world: Stakeholder interviews to better understand the motivations and realities of use and disposal in the US. Resources, Conservation and Recycling, 105, 134-142.
