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Q&A: Help me with my cassava starch plastic

by Green Plastics


Ploy Chidapa wrote in with a question and a video:

Dear Green Plastics,
Hello. I try to make bioplastic for my science project in my school by 16g. of cassava starch, 15 ml. of glycerin, 15 ml. of vinegar and 100 ml. of water.
but it’s not flexible, easy to tear and a lot of bubble like this video http://youtu.be/HO1yjGghhoI.
Please give me some suggestion. I am waiting for your answer. Thank you


Thank you for your great question, and the video.  I can clearly see the problem that you are talking about: your end result is pretty stiff and inflexible, tears easily, and has a lot of bubbles and waves in it.

The easiest problem to solve will be the texture and bubbles.  The mixture can’t be too thick when it’s being made and heated. If it’s too thick, air bubbles will get trapped in the mixture when it’s heated and won’t be able to get out. Try adding more water. It will take longer to dry, of course, but that will help to get rid of the bubbles. You should also make sure that it’s heated long enough for the starch to get “dissolved” completely, and you should be able to skim any “foam” that might form during heating from the top.  The overall idea is to make sure that you take your time during the “cooking” phase, and make sure there are no lumps in the mixture before you pour it into whatever form it will be drying into.

The problem of the plastic being weak and inflexible may be more difficult to solve.  The most obvious way to increase the flexibility of a bioplastic is to increase the amount of glycerol (the plasticizer).  This will make the end result more bendable, but it will also make the plastic weaker. So this might aggravate the problem of the plastic tearing easily.

One of the reasons for this is just inherent in starch-only plastic. Starch, by itself, generally does not make a very strong film. I don’t know the parameters of the project, but if you could add some gelatin to the mixture to provide a stronger polymer, that would help.

Either way, good luck with your next batch, and happy experimenting!


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