Following the remarkable boom experienced by bioplastics in recent years, many companies are considering the possibility of replacing their conventional plastic products with biodegradable or bio-based alternatives. To provide an informed answer to this question, OiKo has carried out a comparative study between polypropylene and bioPE, a type of polyethylene made from biomass. Our goal is to provide rigorous information about the environmental performance of both options. However, before we delve into this analysis, it is imperative to understand what exactly bioplastics are and the implications of their manufacturing process.
A bioplastic is one of a large family of materials with different properties and applications. According to European Plastics, a bioplastic is a bio-based and/or biodegradable plastic. Bio-based refers to the fact that it is made from biomass (plants) derived from corn, sugar cane, or cellulose. Biodegradable means that microorganisms (bacteria, fungi, algae) present in a medium convert it into natural substances. But the reality is that some bio-based bioplastics are not biodegradable, and some plastics made from fossil resources are at the same time biodegradable through additives that promote their degradation. One of the best-known bioplastics with both characteristics is Lactic Acid (PLA).
It seems incredible to obtain a material as synthetic as plastic from a tree branch or corn, but in the end, it is not so strange, nor so new.
If we look at the composition of oil and plastics, we see that it is based on carbon and hydrogen, the elements that make up all living matter.
Plants are a source of carbon and hydrogen chains that can easily be transformed into plastics. So easy that there is no such innovation to obtain plant-based plastics either, as we can recall, noting that the first plastic, invented in 1860, was synthesized from cellulose. To be orthodox, we could say that the origin of plastics is biological.
The important thing is not to confuse the natural origin of the material with the fact that it can be biodegradable, which are different issues, and that is where the real innovation lies.
Now, let's focus on bioPE, a polyethylene produced from biomass, namely sugar cane. So far, it sounds great, but let's look at the transformation process to turn this sugar cane into a plastic. The first step is to cultivate it, a process that involves farm machinery, fertilizers, pesticides, and water. Once harvested, the crop is washed, cut, and crushed to obtain the glucose contained in the sugar cane. The glucose is fermented to obtain ethanol, which becomes bioPE after a process of distillation and polymerization. This whole process requires the use of chemicals such as fertilizers and pesticides in the cultivation of sugar cane, and energy to operate the agricultural machinery and carry out the different transformations that the sugar cane undergoes until it becomes bioPE.
Once the manufacturing process is understood, the next step is to study the environmental impact of bioPE production in different impact categories, which can be grouped into impact on the ecosystem, resource conservation, and human health, using a life cycle analysis. At the same time, the alternative fossil-based plastic, in this case polypropylene, is studied to compare results.
If only the Global Warming category, which quantifies the carbon footprint in kg CO₂, is taken into account, the bio option has a lower impact than the fossil option.
The study shows there is a reduction of up to 40% in CO₂ emissions when replacing PP with bioPE. However, a transfer of impacts is detected, and as the Global Warming category decreases, the rest of the categories increase their impact.
That demonstrates that while bioplastics present new opportunities, it also poses several risks. Their use reduces CO₂ emissions in production as long as the crop is managed responsibly, but this massive cultivation would have a high environmental impact on land use. The data speak for themselves:
If all plastics were to come from crops, it would take the equivalent of the entire corn production of the US, the world's largest corn producer at 350 million tonnes per year, to produce them.
The use of agricultural land for industrial use is a controversial issue because of the social implications it entails. Such high pressure on agriculture implies an unacceptable social impact and a change in land use that is difficult to justify. At the same time, an increase in the impacts related to the opening up of new farmland is equally unsustainable. In this sense, crops destined for biofuels and bioplastics are grown in tropical latitudes, which would imply the deforestation of rainforests and primary forests with an even higher impact than the supposed reduction of CO₂ emissions.
Pesticides and fertilizers used in intensive agriculture affect ecosystems and human health, which must also be considered. Eutrophication generated by phosphates and nitrates from industrial fertilizers is rising as one of the main impacts today. On the other hand, pesticides are toxic and bioaccumulative substances used to increase crop productivity. They are responsible for diseases such as Parkinson's disease and many types of cancer.
However, one point in favor of bioPE is that, unlike other bioplastics such as PLA, it does not interfere with the conventional recycling system and, therefore, can be recycled in the same waste stream and with the same technology as conventional plastics. But, as discussed above, bioethanol production is energy-intensive, and an energy mix based on fossil fuels can lead to a higher demand for oil equivalent than a fossil-based polymer.
In summary, the choice between bioplastics, such as bioPE, and conventional plastics, such as polypropylene, is not simple. Therefore, it is crucial to take each specific case into account and analyze it carefully to determine the best option. There is no one-size-fits-all solution, and the choice between conventional plastics and bioplastics must be based on a detailed assessment of local conditions, resource availability, waste management, and specific environmental goals. Continued research will refine and improve existing technologies, as well as discover innovations that can pave the way to sustainability.
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