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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!:-)

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.