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Q&A: Why water and vinegar?

by Green Plastics

 

A couple of students have recently been trying to understand why certain ingredients are used in the creation of bioplastic.

Eliza Sham asks:

I am interested with your recipe to make bioplastic. What is the use of the water in adding to the starch to make bioplastic?
Please answer me.
Thanks a lot!:-)
ka yee kee asks:
Hi,
I want to ask what is the principle of the bioplastic and the use of water and vinegar
Thank you !

I think we can answer both of these questions at the same time!

Water: Water is used as a solvent to get the biopolymer (starch) into solution. When the solution is heated, the water helps the starch molecules to become disrupted and disordered (denatured). When dried, the disordered polymer chains become entangled and a neat film is formed. The process is called film-casting.

Vinegar: Starch dissolves better if a small amount of ions (electrically charged particles) are present in the mixture; the polymer molecules become disordered more easily, and the resulting cast films are somewhat improved. These added ions interact with both the starch and the small amounts of other polymers (lipoproteins) that are present in commercial starch. One way to add ions into the mixture is to use ammonium acetate. Ammonium acetate works very well in this respect because it forms ammonium ions and acetate ions in solution. However, ammonium acetate is not readily available. Vinegar is a practical alternative that you can use when making your own bioplastic. Vinegar contains acetic acid which forms hydrogen ions and acetate ions, and (importantly) it is readily available. This is why adding a little bit of vinegar is recommended specifically when making home-made bioplastic films from starch.

If you can’t (or don’t want to) use vinegar, ordinary table salt (sodium chloride) is a reasonable substitute; it forms sodium ions and cloride ions. Whatever is added, the ions that are formed in solution help to dissolve the starch and to denature the starch when the mixture is heated, so that when the mixture is dried, somewhat better films are formed.

Hope this helps! Happy experimenting.


Comments (12)

  1. Alisha says:

    I would like make bioplastic from organic waste what will u suggest to use

    • Green Plastics says:

      You need to find a basic polymer in that waste that can be used as the “backbone” of the plastic.

      In the bioplastic industry, they are very good at both finding polymers in waste and creating polymer molecules from waste.

      For example: chitin, found in shimp and crab shells, is a polymer and can be used to make bioplastic.

      Cardinol, a molecule found in cashew shells, is not a polymer but can be made into a polymer by an industrial process. We’ve written more about that here:

      http://green-plastics.net/posts/35/the-science-of-cashew-shells/

      But having a polymer is a necessary part of making a plastic. Most of the recipes we talk about on this website use starch, a naturally occurring polymer, in their formulation.

  2. ambut says:

    Why is glycerin used in plastic making?

    • Green Plastics says:

      Glycerin is a PLASTICIZER, which is one of the two key ingredients needed to make a plastic: plastics are polymer + plasticizer.

      The plasticizer is there to interact with the polymer to make it flexible and strong. Plastics with more plasticizer are tough and bendable, like saran wrap. Plastics with less plasticizer are hard and brittle, like a plastic toy. Glycerin is used in bioplastics because it is natural and biodegradable, and so it can be used to make an environmentally-friendly plastic.

  3. Mia says:

    why is cornstarch used in plastic making?

  4. Thanks very much. I found knowing what the additives do to be very helpful. Saves me looking up a research paper! 🙂

  5. shreya says:

    What is the chemical reaction taking place while converting it to bioplastic?

  6. Umar Azmi says:

    How to improve the bioplastics by altering the chemical composition?

  7. Vivian says:

    Why do you need hydrogen ions and acetate ions from the vinegar? Why is it essential to making a bioplastic?

  8. Daniel Ewusi-Essel says:

    can a bioplastic be melted and solidified to regain its properties?

  9. Pauline says:

    what is the role of vegetable oil in the plastic? can i use alpha amylase to test the biodegradability of my bioplastic?

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