Biobased plastics, the good and the bad
3/17/16

Companies haven’t started doing it yet but, technically, there is nothing to stop them from making plastic out of sugar beet or wheat. Good for the environment? Let’s not be too hasty. A study by Sandra Belboom, a research engineer at the University of Liège, shows that there is a considerable gain in terms of CO2 emissions compared with the use of fossil fuels. But this process also has significant side effects, such as an increase in acidification and eutrophication.

Between 2008 and 2012, oil was on everyone’s lips. Its price soared, sending the finance sector into a spin, and leaving car drivers in despair at the petrol pump. A rapid alternative to the black gold and all its derivatives was needed! Biofuel would save the day. Public authorities released funds, studies were launched… then, as oil prices gradually returned to a more acceptable rate, biofuel was pushed to the wayside. The initial enthusiasm had gone. However, it wasn’t just a new fad, and scientists are continuing their research. Such as Sandra Belboom, a research engineer at the University of Liège’s Chemical Engineering research unit.

When this chemical engineer began her thesis in 2009, her theme couldn’t have been more topical (read Bioethanol: time to stop comparing apples to oranges). What is the best use for bioethanol, a biofuel that can be produced from sugar cane, sugar beet or wheat, and can replace the fuel (partly or completely) in our petrol tanks? “Considering current oil prices, it’s quite clear today that reducing fossil fuels is no longer a priority”, she admits. “But the challenges regarding CO2 are still considerable. Opting for biobased products is one possibility when it comes to reducing carbon dioxide emissions”.

plastiques polymeres

For this new research, whose results were published last January (1), Sandra Belboom continued to investigate the properties of bioethanol. Not just as a possible fuel source, but also for use in the production of plastic. That’s the magic of chemistry: if you remove a molecule of water from ethanol, the result is ethylene, which lies at the source of many manufactured products, such as polyethylene, the plastic that is part of our daily lives. This time, the researcher put sugar cane aside to focus on sugar beet and wheat, for geographical reasons: the last two grow here! Hence, Belgian specialists are familiar with all the specificities. An important aspect within the framework of the approach favoured by the engineer, i.e. life cycle assessment. “It’s a method that will be able to assess the potential environmental impacts of a product by taking into account its whole life cycle. From the extraction of the raw materials up to incineration”, she explains. “This overview allows you to highlight any possible pollution transfers”.

Take, for instance, the use of bioethanol as a biofuel. At first sight, it appears like a good idea from every angle. Since the carbon it contains comes from plants, the CO2 released during its combustion is neutral since this CO2 was originally absorbed by plants. On the other hand, to produce it, it is necessary to put fertiliser on the fields, use tractors, develop transformation techniques, etc. “If we don’t look at all the aspects, biofuel seems wonderful and a great replacement for petrol! But a life cycle assessment shows that the production processes could counterbalance the advantages of using it. The benefit of this method is that it doesn’t only take into account CO2, therefore the consequences for the climate, but also other types of environmental impacts”.  

So what about bio-ethylene? Does making plastic out of sugar beet and wheat really reduce carbon dioxide emissions? Should other types of pollution be taken into consideration? If the environmental benefit is negligible, would it make any sense to import products from the other side of the world? To answer these questions, Sandra Belboom worked in four stages. First of all, she defined the purpose of the study and the boundaries of the system (in this case, from cultivation to incineration), so she could then gather the necessary data in order to calculate the balances of materials and energy at each stage, ascertain the environmental impacts and interpret the results. The information-gathering phase was the longest. Hence the interest of having detailed knowledge about all the aspects associated with cultivating sugar beet and wheat. Rather than using generic data, Sandra Belboom wanted to stick as closely as possible to Belgian reality. She collaborated with Professor Bernard Bodson (Gembloux Agro-bio Tech). She also approached the BioWanze plant (near Huy), the biggest Belgian producer of bioethanol, at the leading edge of wheat processing, and used the available literature to study sugar beet. Finally, plastic producers were contacted in order to identify the quantities of energy required for polymerisation, yield, etc. “In short, we used different bricks for the construction”, she sums up. Something which, to her knowledge, had never been done before. At least for sugar beet and wheat; sugar cane has already been studied extensively in Brazil. 

(1) Does biobased polymer achieve better environmental impacts than fossil polymer? Comparison of fossil HDPE and biobased HDPE produced from sugar beet and wheat, in Biomass & Bioenergy (2016).

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