16 Sep 2019

Preparing bioplastics for analysis using Specac Film Makers |Spectroscopy Solutions

Bioplastics are a viable solution to the mounting problem of synthetic plastic waste. Even with increasing recycling rates, around 53% of waste in the US is sent to landfill, with plastic waste making up around 19% of that1. Although there are signs that people are becoming more attuned to the environmental damage plastic waste can cause, the fact remains that is a crucial part of our everyday lives, from packaging to clothing. Biopolymers produced from natural and renewable resources are seen as key in the effort to produce a viable alternative to synthetic plastics. They are also attractive from an economic standpoint as they are abundant, inexpensive, environmentally friendly and biodegradable.

a plastic bottle

Plastic films are particularly important in food packaging, where they are used to contain and protect the food from damage and spoiling. Plastic is often an unavoidable part of the produce that is delivered to us, with many of our regular foodstuffs not possible to be carried in supermarkets without the use of plastic films. 

Fortunately, there is a large source of potential bioplastic that is recovered from agricultural by-products. These proteins typically do not constitute the edible part of the plant and are instead recovered from the co-products that arise when the initial crop is processed into another form. They can be from a variety of sources including soy protein concentrates and isolates from purified soy flour2, potato protein concentrate extracted from potato fruit water3, and legume waste formed from the residues from processing peas, beans and lentils4.

There are three key steps for producing films from protein-based materials5. The first is to break the bonds between the protein molecules that allow them to hold their shape using chemical or physical means. If any covalent cross-links remain in the next step, they will increase the viscosity of the melted polymer and make homogenization much more difficult. The next step is to re-arrange the newly mobile polymer chains into the desired form. This can be done by molding, extruding or any other of the methods used to create conventional plastics. Finally, new bonds are allowed to form that will stabilize the biopolymer. With a thermoplastic polymer (workable at higher temperatures) this is typically achieved by simply letting it dry at a lower temperature than that it was formed. 

These steps can be undertaken during the same process or split up into parts. There are two main routes, either wet processing technologies, and low-moisture processing technologies. The wet processing side uses techniques such as casting and calendaring, whereas low-moisture processing uses extrusion and injection molding. 

The method used depends on the protein, but they do not have enough plasticity by themselves to handle such stresses6. This requires the use of a plasticizer to reduce intermolecular forces and increase polymeric chain mobility so that the final form is a consistent and stable shape. The plasticizer also reduces the glass transition temperature of thermoplastic proteins, making them workable at lower temperatures, allowing for a more economical process.

Before these bioplastics can be brought into mass production, they must be tested in other areas to ensure they are able to compete with existing synthetic polymers. The three key areas that are assessed are mechanical strength, water sensitivity, and cost. It isn’t prudent to produce large amounts of bioplastic for testing, so a common methodis to produce small scale samples for the laboratory by pressing the protein between two heated plates at a constant pressure. This method is capable of producing samples of a constant thickness relatively quickly and does not require expensive equipment. 

To aid in this ongoing search for high-quality, biodegradable polymers, Specac offers a range of filmmakers designed for use in any research environment, be it academic or industry. The product range covers all bases and allows quick and simple fabrication of high-quality thin films made from plant proteins.

For laboratories where space is limited, the Specac handheld film-maker is perfect7. It has a small footprint that allows it to be placed alongside other equipment on a workbench and is ideal for processing proteins into a form fit for analysis by infrared transmission spectroscopy, or another analysis method. With a heating element that allows precise temperatures from ambient to 250 °C, it is well suited for hot pressing of often delicate protein-based polymers, with constant and reproducible thicknesses from 50 to 500 µm and 15mm diameter.

a constant thickness film maker

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If you already own one of their presses and are looking to produce polymer films, Specac also offers conversion kits8. Consisting of the Atlas Constant Thickness Film Maker and Atlas Heated Platens, these kits can be used with existing Specac presses to form polymer films of highly reproducible thickness, from ambient to 300 °C. 

If you are working with protein-based biopolymers and would like to know more about these products or any of Specac’s range of presses, please visit their website at www.specac.com, to discover how they can help with your research.|

References

  1. National Overview: Facts and Figures on Materials, Wastes and Recycling. United States Environmental Protection Agency(2015).
  2. Mercedes Jiménez-Rosado, Victor Perez-Puyana, Felipe Cordobés, Development of superabsorbent soy protein-based bioplastic matrices with incorporated zinc for horticulture. J Sci FoodAgric99, 4825–4832 (2019).
  3. Online, V. A. RSC Advances Commercial potato protein concentrate as a novel source for thermoformed bio-based plastic fi lms with unusual polymerisation and tensile properties. 32217–32226 (2015). doi:10.1039/C5RA00662G
  4. Change, C. & Estanga, E. G. LEGUVAL — Result In Brief. 7–8
  5. Verbeek, C. J. R. & Van Den Berg, L. E. Extrusion processing and properties of protein-based thermoplastics. Macromol. Mater. Eng.295, 10–21 (2010).
  6. Jerez, A., Partal, P., Martínez, I., Gallegos, C. & Guerrero, A. Protein-based bioplastics: Effect of thermo-mechanical processing. Rheol. Acta46, 711–720 (2007).
  7. Specac. Mini-Film Maker | Polymer Film Maker. Available at: https://www.specac.com/en/products/sample-prep/films/film-makers/mini. 
  8. Specac. Constant Thickness Film Maker. Available at: https://www.specac.com/en/products/sample-prep/films/film-makers/constant. 

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