Bio-based: when plastic goes green

Since the rediscovery of the “seventh continent” of plastic in the Pacific Ocean, known since 1997 [1], plastic has become an undesirable. So much so that in France, the Energy Transition Act incorporates in the Environmental Code the reduction of the environmental impact of certain single-use plastic products such as cotton rods and disposable dishes [2]. They will be banned for sale from January 2020.

In 2018, the European Union adopted a directive to reduce the environmental impact of certain plastic products [3], focusing on the most widespread plastic waste found on beaches, such as plastic plugs which will have to be in solidarity with the bottle from 2021.

As consumption patterns are difficult to change, the regulations focus on plastic products rather than on the origin of pollution, namely the creation and management of plastic waste.

It is in this context that so-called “bio-based” plastics have found their place as alternative materials to petroleum-derived plastics. But what are these plastics? Are they serious alternatives?

These materials, also called “biopolymers” or “bioplastics,” are polymers of plant or animal origin, i.e. derived from biomass. Polymers or plastics commonly used in food packaging are derived from oil.

The term “bio-based” indicates the origin of the material. He doesn’t prejudge his end of life. Thus, a bio-based polymer, like a polymer derived from oil, can be biodegradable, recyclable, compostable or valuable by incineration.

Today, the term bio-based incorporates any material made up of a minimum of 40% of plastic from biomass [4]. This definition is incorporated into the Environment Code where bio-based plastics are not considered “plastics” in the same way as petroleum plastics and can be used in the manufacture of cotton rods or disposable dishes 2020.

However, bio-based plastics have existed since the beginning of the 20th century. They have not been able to find a market to develop for reasons of direct competition, particularly with petroleum-derived plastics, which are much less expensive and have a wider range of properties, thanks in particular to the possibility of more important chemical combinations. In the 2000s, the development of new bio-based plastics accelerated, in response to the question of the depletion of non-renewable natural resources such as oil.

Today, bio-based plastics come under two distinct categories:

Synthetic bio-based plastics

The principle of making these plastics is the same as for petroleum-derived plastics. Molecules are extracted from biomass and then used for the chemical synthesis of a polymer. Thus, it is possible to find bio-based PET 1 or HDEP 2, these plastics being used in the manufacture of food bottles. They have properties identical to those of their oil equivalents: they are not biodegradable or compostable. PLA 3, often used as a replacement for PET for the manufacture of water bottles or compostable cutlery, is in this category.

Natural polymers

Unlike synthetic plastics, the materials used are not chemically modified: the main material is a natural polymer (starch for example) that is processed by thermomechanical processes. The addition of additives makes the material more malleable and resistant to certain conditions of use. Applications are limited for this type of bio-based plastic because the modification is made by mixture and not by chemical means. This greatly reduces the potential for changes in the properties of the material extracted from biomass.

Let’s take an example: the starch used in the manufacture of compostable bags is hydrophilic, which makes it very sensitive to the conditions of use. Without modification, it has neither the fluidity nor the mechanical resistance necessary for its shaping. In order for it to present these new performances, it is mixed with other polymers derived from oil. Glycerin is also added to make it more fluid during its shaping. But manufacturers ensure that these changes do not call into question the composting of the film obtained.

Bio-based plastics pose a socio-economic problem related to the use of resources that can be used for food. The use of food industry waste, such as bagasse (sugarcane residue), is an alternative that is beginning to develop, with conclusive industrial applications.

Bio-based plastics are therefore an alternative to petroleum-derived plastics, but cannot completely replace them. As Ademe [5] points out, bio-based plastics are economically and environmentally interesting because they allow the use of renewable resources for the manufacture of plastics. But their environmental and societal impact needs to be studied by considering the issues related to sustainable soil management.

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