The Great Plastic Remake – Bioplastics

This is post 3 of our series of 3 posts supporting outreach activities to understand the role of bioplastics and molecular biosciences in addressing plastic waste. On this post we learn about bioplastics and explore their properties and potential.

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Overview

This is the third post of the series on plastics linked to Special Session of the 45th FEBS Congress, organized by the FEBS Science and Society Committee (read also post 1 and post 2). Here we explore how bioplastics could be part of the solution of dealing with plastic waste. Read.

Background information

What are bioplastics?

Bioplastics are derived from organic matter other than fossil fuels. Natural polymers such as polysaccharides (e.g., from starch, cellulose, pectin, or chitin) and proteins (e.g., from collagen and gelatin, casein or gluten) can be made into bioplastics.

Bioplastics can also be made from monomers derived from, for example, bioethanol or lactic acid. Bioethanol can be obtained from fermented sugarcane and other crops and is used to produce bio-polyethylene (Bio-PE) and bio-polyethylene terephthalate (Bio-PET). Lactic acid can be produced by bacterial fermentation of sugars derived from crops and is used to produce polylactic acid (PLA). And while this is mainly still at pilot stage, bioplastics can also be generated from gases such as CO, CO2 and methane.

Bioplastics can also be made directly by some bacteria. Biopolymers such as polyhydroxyalkanoates (PHAs) accumulate in inclusions in the bacteria’s cytoplasm, and different bacteria are able to produce biopolymers with varying properties. The bacteria can feed on several substrates, such as sugar beets or sugar cane bagasse but - to improve sustainability - different agricultural, industrial and urban types of waste are also being explored, such as vegetable oils and animal fats (e.g., waste from the dairy industry and residue from slaughterhouses).

Other microorganisms can also make biopolymers. Fungi can generate chitosan, a biopolymer usually derived from the shells of crustaceans. Fungal chitosan, unappealing as it sounds, is an extremely promising material for biomedical applications and other high-end use. Sources of fungi can be obtained from, for example, waste from the baking and brewing industries and from the making of penicillin.

Are bioplastics biodegradable?

Bioplastics are not necessarily biodegradable. Bioplastics derived from cellulose and starch, as well as PHA and PLA, can in principle be biodegradable. However, the process might take a long time and biodegradable bioplastics released into the environment might still pollute and be a hazard to marine life. They also do not address the problem of overproduction of plastic waste.

Bioplastics can also be made to be practically indistinguishable from conventional plastics and will thus not be biodegradable. For example, bio‐polyethylene (bio‐PE) obtained from bioethanol is still made of polymers of ethylene monomers and it has the same properties as polyethylene derived from fossil fuel. This type of plastic is useful to industry as it can replace traditional polyethylene without needing to adjust industrial processes and, in principle, is more sustainable than those derived from fossil fuels, though it is not clear that they generate much less CO2 when all factors are considered, such as the upstream use of fertiliser to grow the biomass, the pre-processing of the biomass, etc. It is important to note that plastics derived from fossil fuels can, technically, be made to be biodegradable.

Compostable bioplastics have been designed to completely biodegrade in commercial or industrial composters, where the high temperatures and humidity allow microorganisms to break these bioplastics down. However, if compostable plastics end up in landfills, they break down really slowly and, as they biodegrade, can release methane, a potent greenhouse gas. Compostable bioplastics should also not end up in the recycling stream, as it can contaminate other plastic materials and prevent them from being recycled.

So, are bioplastics the solution to sustainable plastics?

Thus, to assess the sustainability of a bioplastic we need to consider the source and pre-processing of the biomass, its final chemical composition, how long it takes to break down, whether it can still pollute (e.g., through its additives), what is its impact on global warming (i.e., CO2 produced), and if it can be recycled or reused, as well as whether suitable sorting, recycling and composting facilities are available. Additionally, products made with bioplastics need to be labelled appropriately and consumers need to become better informed about them.

Ultimately the cost and physicochemical properties of the bioplastic will be key to obtain industry and consumer support. Plastics derived from fossil fuels are cheap and innovative, so bioplastics need to compete against that.

In principle, through research and innovation in biotechnology, all polymers and additives used in the plastic industry and currently derived from fossil fuels could be made from biomass in biorefineries. The issue to consider is which processes are scalable and economical, as well as which ones ultimately produce less CO2 than plastic from fossil fuels. The use of renewal energy in the production of bioplastics will be key to make them truly sustainable.

Research and innovation to address plastic waste is taking place beyond bioplastics, as exemplified by the discovery a few years ago of poly(diketoenamine), a new polymer that can be recycled repeatedly, or by the discovery of PETase, an enzyme that can break down PET plastic.

What are molecular bioscience researchers working on?

The most promising area for bioplastics might be packaging, for consumer products and for business-to-business applications, such as packaging used when goods are transported. A lot of scientific and technological research is being carried out in this area.

Some bioplastics have novel properties that could be useful to the packaging industry. For example, bioplastics can be permeable to water vapour, which can be a problem in many settings but can be useful when packaging fruit and vegetables, which have a high water content. Other intrinsic characteristics of bioplastics, such as how they respond to food odours, to stretching and folding, to sealing, and to printing, can also be explored to develop new products. The useful properties of bioplastics can expand significantly by adding fibers and nanoparticles, as well as compounds such as antimicrobial or antioxidant agents, natural pigments, and flavours. However, the EMF has highlighted that having fewer types of bioplastics, each type presenting in larger volumes, would make recycling more commercially viable.

Innovation is also needed when bioplastics accidentally leak into the environment, to make them ‘bio-benign’ by, for example, making them break down more quickly in water or not carry additives that are toxic. Designing bioplastics that have those properties, work as packaging, and can be scalable and cost effective, requires ongoing research and technical innovation.

Activities

For this post we specifically propose an activity that shows how to make bioplastics in the lab, as well as other activities to consider.

How to prepare bioplastics in the lab

Refer to the protocol in this post's appendix to develop an activity that shows how polysaccharide- and protein-based bioplastics can be made in the lab.

A simpler version of this experiment can be developed for younger children, where they can make plastic from starch. This video from the Royal Society of Chemistry, this one from the University of Southampton, this one from MIT or this one from Canterbury Christ Church University,  are useful examples. There are also examples on how to create bioplastic from milk casein: search the GEO sustainable channel for their bioplastic videos.

Additional activities to consider:

Additional information

These videos and websites provide additional sources of information:

Appendix

Protocol for the manufacturing of biodegradable and/or edible film in the laboratory.

  1. A) Preparation and characterization of the polymeric film forming solution (FFS):

Different amounts of the selected biodegradable and/or edible polymer were dissolved in a specific solvent (water or organic solvent) at the chosen pH and kept on stirring until a clear solution was obtained.

The prepared polymeric solutions were initially evaluated according to the following characteristics: solution appearance, solution viscosity, stability (zeta potential measurements), particle average size, and drying time to obtain films under different experimental conditions (temperature, relative humidity (RH), etc).

The appearance of the solutions was evaluated visually or mechanically and described as transparent or opaque, coloured or not, with or without precipitation of the polymer.

The FFS may contain some other components other than the polymer, such as a plasticizer (like glycerol or sorbitol) able to create space between the polymer chains and, consequently, to enhance the extensibility of the derived film. Other additives might be further macromolecular (such as a different polymer) or small molecular weight components (bioactive compounds) able to improve some features of the derived films.

  1. B) FFS casting and drying:

FFS was cast into a Petri dish and placed to dry in a climatic chamber (oven) at a specific temperature (generally 25°C) and RH (generally 50%). For a preliminary evaluation of drying time, the films were formed in small containers. When the film seems to be dried, a glass slide was placed gently on the surface of the film. If no liquid droplets are visible on the glass after removing it, the film was considered to be dry. If liquid droplets were still visible on the slide, the test was repeated at longer times.

Additionally, the outward stickiness of the films can be estimated by pressing cotton wool on the dry film with minimum pressure. Stickiness was rated high if heavy amount of fibers were retained on the surface of the film, medium if a thin layer of fibers was formed on the film and low if no adherence of fibers was noted.

When completely dried (FFS 50 mL generally dried in 24 h), the visual appearance of the films was assessed. Uniform films were rated high in attractiveness, while non-homogeneous films were considered to be less attractive.

  1. C) Film characterization:

The main features of the prepared materials to be determined are a) the thickness and the macroscopic (color, transparency, manipulability) as well as microscopic morphological (by SEM and AFM) properties of their surface and cross-section, b) the mechanical properties of resistance (tensile strength) and extensibility (elongation at break), c) the barrier properties mostly against water vapor and gases (oxygen, carbon dioxide, etc.), d) their hydrophylicity (moisture content, solubility in water, swelling capacity), e) hydrophobicity of their surface (contact angle measurements), f) thermal properties, g) structural characteristics of film matrix (by FTIR, NMR, etc.), h) possible biological properties (antioxidant and/or antimicrobial activities by in vitro and in vivo experiments), i) ability to release specific agents, l) biodegradability and compostability, m) packaging of different products by coating and/or wrapping, n) improvement of food shelf life after packaging.


Photo by Thomas Kinto on Unsplash

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