Ask any 10 people what bioplastics are, and the odds are that nine will get it wrong.
In the past, misunderstandings and misconceptions about bioplastics have tended to color the perception of these materials in the market, and these prejudices are still evident even today. Feedstock, supply and processability concerns, coupled with a lack of insight into the various different types of bioplastics, have long hampered the broader acceptance of these materials by the industry.
One common, very persistent error is the belief that bioplastics are the same thing as biodegradable plastics. This, to be clear, is categorically false.
While many early, primarily starch-based bioplastics may have been created to be biodegradable, this was certainly not the case for all. One of the earliest proponents of bioplastics was Henry Ford, who thought that industry and agriculture should be complementary to one another. He believed that plastic made from soybeans could be developed into a strong, lightweight and safe substitute for traditional metals. In the 1930s, he built a soybean laboratory in Greenfield Village, where experiments led to the development of soy-based oils and plastics for use in Ford Motor Co. vehicles. However, the outbreak of World War II halted all research efforts in this area, and the post-war availability of cheap and plentiful petroleum brought down the cost of manufacturing plastics based on oil.
As a result, Ford's dream of farmers being part of the industrial process receded into the background — but never wholly died. In France, the merits of plant-based plastic continued to be recognized. In fact, specialty chemical company Arkema celebrated in 2017 the 70th anniversary of Rilsan, its nonbiodegradable castor oil-based family of bio-based nylons. One of its first applications was to make the fuel lines of the legendary Citroën DS, back in the 1950s.
Bio vs. bio-basedDispelling the notion that bioplastics do not equal biodegradable plastics has proven more arduous that expected, leading the bioplastics industry to reconsider the terms used to designate these materials.
Properly speaking, bioplastics refer to materials based on biomass, materials that are biodegradable, or a combination of both. However, there are fossil-based plastics that are biodegradable, and there are renewably based plastics that are not. Biodegradability is therefore simply one of the properties a particular plastic may have — among many others — and not a defining factor for classifying a material as a bioplastic, or not.
For this reason, the preference today is to use the term bio-based to distinguish these materials from conventional, petroleum-based plastic materials. Biobased plastics are plastics — biodegradable and nonbiodegradable — that are derived either in part or wholly from hydrocarbons derived from renewable resources, such as biomass.
Natural vs. manmadeMany bio-based polymers occur naturally, requiring only to be extracted and slightly modified to become a bio-based plastic material. The backbone chain of the natural polymer is retained. Examples include polysaccharides, cellulose, starch, proteins and even the PHAs produced by bacteria.
There are also various bio-based polymers that, while derived from renewable biomass, nonetheless qualify as synthetic. Such polymers are derived from bio-based monomers that subsequently undergo chemical reactions to become bio-based polymers. Examples include the biopolyesters PLA and PEF, sugarcane-based biopolyethylene, nylon 4/10 and 11, which are derived from castor oil.
Feedstock debateA much-heard argument against bio-based plastics is that using arable land to grow food crops to produce plastics is wrong. Currently, the two main crops grown for this purpose are corn and sugarcane and, to a lesser extent, sugar beet and cassava. The amount of land this required at the end of 2017, according to calculations by European Bioplastics, equaled 0.016 percent of the global agricultural area.
"Even with the predicted high growth rates of the bioplastics industry over the next years, the land-use share would only slightly increase to up to 0.021 percent of the agricultural area by 2022," says the association.
Manufacturers of bio-based plastics are exploring the use of other biomass sources — lignocellulosics, sewerage, methane, nonfood crops and agricultural byproducts and food crop waste, to name but a few. And a group of leading global brands, including Coca-Cola Co., Danone, Ford Motor Co., H.J. Heinz Co., Nestle, Nike Inc., Procter & Gamble Co. and Unilever, have set up the Bioplastic Feedstock Alliance to support the responsible development of plastics made from plant material and help to build a more sustainable future for the bioplastics industry.
"Consumers across the world increasingly are looking for more sustainable products, including those made from plant-based plastics. With increasing market demand for food and fiber in the coming decades, responsible sourcing of these materials is the key to enabling sustainable growth," the Alliance states on its website.
Not everyone is convinced of the need for nonfood crop feedstocks, however. As Michael Carus, the founder and director of nova-Institute an independent institute, offering research and consultancy with a focus on bio- and CO2-based economy, has repeatedly argued: "Second- and third-generation feedstocks are expensive to process, requiring more energy and more resources. But most important, planting fields with food crops means that these can always be diverted back for use as food, if necessary, in the case of famine. We are not in competition with food, then, but offer a backup plan."
Why bother?If they're not biodegradable, then why the push to develop bio-based plastics at all? It is a question often asked by consumers and processors alike, and one that is perhaps best answered by Michigan State University professor Ramani Narayan.
As he explains it, bio-based plastics make sense because of the inherent value of reducing the carbon footprint of plastic materials. What is more, plant biomass is renewable and grows everywhere, creating opportunities for rural, agrarian economies.
Derived from biomass, a bioplastic will have a smaller carbon footprint by virtue of the fact that at the end of life, the amount of CO2 released into the atmosphere will never exceed the amount originally absorbed by the plant from which it was made. This is far less disruptive to the carbon cycle than when using conventional petroleum-based plastics, which, in addition to the fact that they are based on a depletable resource, by their very use add new carbon to the atmosphere from fossil sources.
End of lifeWith bioplastics, just like conventional plastics, the end of life is an aspect that needs to be managed.
Biodegradable bio-based plastics are a case in point. A common misconception is that biodegradable means that a product made from these materials will somehow disintegrate spontaneously in the environment. The fact is most bio-based biodegradable plastics will degrade only under specific conditions such as those found in industrial composting facilities.
Some types have been engineered for home composting. A small number of companies have developed a few PHA grades said to be marine-degradable. Danimer Scientific announced the development of the first fully marine biodegradable plastic straw in September 2018, while Bio-on SpA produces a PHA product designed to replace microplastic beads in cosmetics.
Nonetheless, biodegradable bio-based plastics are emphatically not the solution to plastic waste, litter or the plastic soup. Where they are useful are in applications where biodegradability is functional — think mulch films — or in single-use food packaging, which is often too contaminated to be adequately recycled.
The circular futureAs the world moves away from a linear system toward a circular economy, the realization is growing that plastics — bio-based and otherwise — are a resource far too valuable to simply consign to landfill.
In a circular system, just as for fossil-based plastics, the preferred end-of-life option is recycling. Bio-based PET and polyethylene resins — the so-called drop-ins that have a chemical structure that is identical to their fossil-based counterparts — are recyclable within the current recycling system. For the newer materials, such as PLA, the volumes have been too low to establish a separate, efficient recycling stream. For the establishment of a truly circular and environmentally optimal system, the recycling rates of these plastics must increase.
And where recycling is not possible, incineration or anaerobic digestion is the next best solution, at least according to the report "Bio-based Plastics in a Circular Economy" by CE Delft, a Dutch consultantcy firm.
According to the report, incineration with energy recovery and anaerobic digestion with biogas production both lead to the production of renewable energy at the end of life. The main difference with incineration of fossil plastics is the emission of biogenic CO2 instead of fossil CO2.
More importantly, as they emphasize, the current plastics system is a linear one: There is as yet no circular fossil economy, so replacing petroleum-based plastics with renewably sourced materials will not automatically result in the emergence of a circular economy.
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