Planet 5 min
Biosourced plastics: plant carbon makes a comeback
Biomass-based plastics are an fascinating alternative to traditional plastics. They are part of the large family of bioplastics, a generic term that encompasses many things. Let's try to get a clearer picture at a time when combating global warming also involves the decarbonisation of the plastics industry.
Biosourced plastics: plant carbon makes a comeback
Biosourced plastics: plant carbon makes a comeback

Bioplastics take root

A bright future ahead

In less than a century, fossil fuels - oil, gas and even coal - become the primary raw materials used to manufacture almost all plastics. In 2020, almost 370 million tonnes of plastics were produced worldwide, but manufacturing them requires only about 4% of the fossil resources extracted each year. However, the rising cost of these raw materials and the environmental needs of combating global warming mean that manufacturing plastics from renewable raw materials is not really a new development, but one that is experiencing more than a simple revival of interest. In this context, "bioplastics" have a lot to offer. Examples of applications already exist and should significantly increase the presence of these "green plastics" in the next few years.

 

As an essential link in the decarbonisation of plastics, there is every indication that biosourced polymers will become increasingly important over the next few decades.

According to European Bioplastics, global bioplastics production capacity is expected to increase from about 2.4 million tonnes in 2021 to about 7.6 million tonnes in 2026. This will take the share of bioplastics in global plastics production above the 2% mark, compared to less than 1% at present.

However, this is still too little to allow the plastics eco-system in Europe to aim for zero net greenhouse gas emissions by 2050. At least that is what a recently published study by environmental consultancy Systemiq says. While the study confirms the need for continued investment to optimise both mechanical and chemical polymer recycling processes, it notes that this will not be enough. According to the authors of the study, a potential solution to the issue lies in the development of biosourced plastics, whose share in European plastics consumption will have to amount to nearly 20% of the plastics used if the Zero Emissions target is to be met.

What are “bioplastics”?

Biosourced plastics, biodegradable plastics, bioplastics, biopolymers... for the past fifteen years, the family of bioplastics has been growing steadily. However, the common prefix can be misleading as it is used for many polymers with very different characteristics.

 

Whether they are biosourced or derived from hydrocarbons, polymers are above all a product of organic chemistry, namely carbon chemistry. Carbon is the fourth most abundant element in the universe.

On the one hand, there are “biosourced” plastics whose name means that they are derived in part or in full from biomass resources *, whether plant (plants, wood, algae, etc.) or animal (micro-organisms). Whether traditional or biosourced, a polymer is a product of carbon chemistry, known as organic chemistry. It is this carbon that is traditionally extracted from petroleum products after steam cracking in the form of ethylene, propylene, acetylene, benzene and other basic molecules intended for use in the manufacture of plastics.

The whole point of biosourced plastics is to get this same carbon from the biomass, from which it is extracted by various chemical or biochemical processes. However, what has led to and still explains the predominance of fossil raw materials in the manufacture of plastic materials is the extreme concentration of carbon within them, which no biomass source can compete with.

* Biomass is the material produced by living organisms such as plants, animals, fungi, bacteria, etc. It should be noted that today, the vast majority of biosourced plastics are produced from plant biomass.

Another branch of the family is that of “biodegradable” plastics, which can be derived either from renewable resources or from fossil resources such as gas and oil. PBAT (polybutylene adipate-co-terephthalate), for example, which accounts for nearly 20% of the world's bioplastics production, is a polymer of fossil origin, which is biodegradable.
In the first case, the most important consideration is the origin of the raw materials from which plastics are made. In the second case, the most important feature is their degradation and therefore their end-of-life (which is not the subject of this article). One important fact should be kept in mind, however: a biosourced plastic is not necessarily biodegradable... and vice versa.

Biosourced polymers can be broken down into two further sub-categories.

The first, the most common, is that of renewable versions of petro-sourced polymers. Thus, a biosourced polyethylene (biosourced PE), for example, will be composed of ethylene produced from sugar cane or another plant. Its characteristics and performance are exactly the same as those of its fossil-based counterpart. Like it, it is 100% recyclable and no more biodegradable.
The second sub-category is that of polymers produced exclusively from biomass and which have no fossil equivalent. They have their own chemical structure and technical properties.

Produced relatively recently on an industrial scale, these polymers are mostly derived from starch or plant sugar. Among the best known are polylactic acid (PLA), polybutylene succinate (PBS), polyamide 11 (Rislan®) and the latest, polyhydroxyalkanoates (PHA) which are natural polyesters produced by certain bacteria.
All these biomass-based bioplastics are still in their infancy.

 

Some bio-based plastics are produced from bacteria. These manufacturing processes are relatively new and show great promise.

They have much room for improvement, just as traditional petroleum-based plastics whose properties have been refined and optimised over decades of research.

Bioplastics are keen to be even greener

Although some consider them to be a miracle solution, there are still a few obstacles to their development, the first of which is their higher cost compared to traditional polymers. The solution to this would be mass production, which would render them less expensive to produce through a mechanical process.

Above all, although aiming to reduce the CO2 impact of plastics production and making them renewable is a noble cause, we must ensure that the cure is not worse than the disease.

Biosourced plastics are mainly produced from food crops, such as maize or sugar cane, because they are rich in carbohydrates and therefore in carbon. In 2021, about 0.7 million hectares of land were used to produce all biosourced plastics. This accounts for just over 0.01% of the world's agricultural surface area. With an expected production of around 7.5 million tonnes in 2026, the surface area dedicated to bioplastics could reach just under 0.06% of this surface area*. According to Systemiq, Europe alone will need more than 9 million tonnes of biosourced plastics by 2050. In order not to compete with food and feed resources, the green chemistry industry is making the sustainable supply of raw materials a prerequisite for the production of sustainable polymers.

* Source: European Bioplastic

 

Sourcing sustainable plant-based raw materials is now a priority for many bioplastics manufacturers.

Brazil's Braskem, a pioneer in the production of biobased polymers, is already producing its biosourced PET exclusively from the residues of sustainable sugar cane production, as the plant is grown in regions with abundant rainfall and does not require irrigation systems other than those fed by rain.

As technology evolves, it is now possible to focus on using non-food crops such as cellulose (wood) and algae and the inedible by-products of food crop production. For example, the American company Trinseo has just launched a bioABS called Magnum Biomax for the automotive market, which contains 80% biosourced materials. Produced from used cooking oil and paper industry residues, this green ABS is 100% identical to its petro-sourced version, but with a carbon footprint six times smaller and without encroaching on food crops.

Food crops generate large quantities of cellulosic by-products, such as straw, maize stalks and bagasse. Often left in the fields after harvesting, these by-products biodegrade in quantities that are often greater than necessary to restore the soil. In certain regions of the world, this green waste is incinerated to produce energy.

Another, more interesting option would be to use these plant resources in biotechnological processes for industrial purposes, including the production of bioplastics.

 

Second-generation raw materials (not suitable for human or animal consumption) are in the spotlight. Research is intensifying to convert them into biopolymers.

 

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