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The basics of making corn starch bioplastic

by Green Plastics

 

zia ur rehman wrote in with this question:

I am a student of biotechnology in University of Peshawar,
Pakistan. Now a days i am working on a project to make bioplastic
(PLA polylactic acid specially) from starch (CORN/ Sugarcane). I
wants to ask you the exact procedure and materials I require. I will
also add some of the ingredients to increase its stiffness, and also
will work to make it better.

Zia, thank you so much for your email! I think it’s great that you are going to work with bioplastics for your school project. Projects that involve making your own bioplastic are a great way to learn, first hand, about how different materials and of ingredients affect the properties of a plastic. As you will learn, including different ratios of polymer and plasticizer, as well as other additives, can vastly alter when strength, flexibility, stiffness, and other properties of the end result.

However, I would like to caution you on a bit of terminology to start out with: PLA stands for “polylactic acid” which is a particular material that some bioplastic is made out of. Although originally PLA does come from a starch source, like corn, it has to be created through a very complicated process that can only be done at an industrial manufacturing plant.  So if you have a project where you are making starch plastic at home, it is NOT technically “PLA plastic.”   But you are correct in calling it “start plastic.”  We talk a little bit more about the difference between PLA and starch plastic in another article here.

However, let’s talk about a home project of how to make starch plastic!

Corn Starch Green Plastics: An Introduction to the New Science of Biodegradable Plastics by E.S. Stevens. This book will get you started with a wide variety of recipes and step-by-step instructions on making bioplastics with different properties, ranging from hard inflexible plastics to thin flexible sheets and laminates. In addition, the book carefully explains the theory behind bioplastics, with in-depth discussions of chemistry concepts as well as environmental concepts related to biodegradability and renewability.  This book can be ordered online from Amazon.com however I do not know if it can be purchased from and shipped to Pakistan.

In case you cannot buy the book online from where you are located, we have a number of articles and references for you on this website.

The first reference that I would recommend is Brandon’s Video.  He talks through the actual process that he uses.  If you have difficulty understanding exactly what he is saying, there is a transcript available on that page if you scroll down below the video itself.

Some people have had difficulty with his recipe, however, so I will provide you with two other pure starch-based bioplastic recipes.  I would still encourage you to look at his video so that you can see the procedure to use, in action.

Recipe 1: starch + salt + glycerol

  • 3.0 grams (1 tsp) starch
  • 45 mg salt
  • 160 ml (2/3 cup) of 1% glycerol solution

Recipe 2: starch + salt + glycerol + sorbitol

  • 3.0 grams (1 tsp) starch
  • 45 mg salt
  • 120 ml (1/2 cup) of 1% glycerol solution
  • 0.75 grams (1/4 tsp) sorbitol
  • 40 ml (1/6 cup) water

How do I make a 1% glycerol solution?

Sometimes when you buy glycerol, you can buy it already in a 1% solution. When you do purchase your glycerol, make sure you read exactly what you have so that you know whether you have a diluted solution or pure glycerol. If you have purchased pure, undiluted glycerol, you can create a 1% solution by mixing up a solution that has 10 ml of glycerol for every liter of water. This will give you a solution that is “1% by volume.”

How do I get exactly 45 mg of salt in the mixture?

You can use simple table salt (sodium chloride) for this. If you put 9 grams of salt in a liter of water, then 5 ml of the solution will contain 45 milligrams of salt.  You can then use this 5 ml of salt solution added to regular water in order to mix up your glycerol solution, according to the instructions above.

(If you are curious what the salt is for, chemically-speaking, we talk about it in this article: Why water and vinegar?)

What do I do when I have all of the ingredients?

Mix all of the ingredients together in the amounts above, and stir.  Keep mixing until there are no clumps, and heat the mixture to 95 C or to when it starts to froth (whichever comes first). Stir the mixture while you are heating it, and once it is at the right temperature (or starts to froth), remove the heat and keep stirring.  Scoop out excess froth with a spoon, and make sure there are no clumps.  The mixture will start to froth a great deal if it is overheated, so be sure to remove it from the heat and stir, scooping out excess froth if necessary.

You will want to carefully pour the mixture directly into the mold that you are using. How long it will take to dry will depend on the temperature and humidity in the room, and how thick the final product is. It may take several days, so be patient! Sometimes people find that it helps to blow it with a blow-dryer for a period of time.  If your first batch turns out too sticky or slimy, you can try it again with slightly less plasticizer (glycerol).

 

 


 

 

These two recipes are for pure starch-based plastics.  If you are interested in looking at alternatives that use other polymers, such as agar or gelatin, there are a number of articles on this website with recipes for non-starch bioplastics, including:

Starch does not produce a very strong bioplastic, and it is not very good for making hard plastic objects.  If you want to try to make the starch plastic stronger or harder, I would recommend that you try blending the starch polymer with one of these other polymers.  Remember, the recipes that we give you here are the starting point, not the finishing point! From here, try changing the ingredients and proportions and see what happens!

Good luck with your project, and happy experimenting!

 

Remember, if you have successfully made bioplastics using our recipes or suggestions please send photos or video to project@green-plastics.netThis e-mail address is being protected from spambots. You need JavaScript enabled to view it and we will post it on the website and help give you some publicity!


Comments (17)

  1. Ash Grim says:

    These recipes are great, but how much pre-set, liquid starch plastic do they make?

  2. nader sobhy says:

    can this be done with plastic and another question is what is the hypothesis and what is the dependent and independent variable

  3. nader sobhy says:

    sorry i mean can it be done with potato

  4. Palak says:

    I am a student. I liked the Corn Starch Experiment. I want to try it at my school. I need exact Materials Required, Procedure, Observation, Conclusion and Advantages. Please

  5. Ian says:

    I am doing my science fair project on bio-plastics and I was wondering if there is any substitute for glycerin that works well?

  6. Hello,

    I am wondering what the sorbitol is for?

    Thanks,
    Les

  7. Any recommendation/recipes for a flexible binding biopolymers? Looking at making Started plugs for hydroponics using peat moss.

  8. Anuradha Biswas says:

    Can the plastic be dried in a day or two? If so, how ?

  9. L Jensen says:

    Is the plastic made with potato or corn starch water proof?

  10. asdfghjkl says:

    hmmm interesting

  11. kent says:

    Any suggestion how to make a mold for plastic cup?thanks

  12. What is the function of salt in the recipe? Why do other recipes use vinegar?

  13. Akashi says:

    Can corn flour be used in place of corn starch?

  14. Vicky says:

    Hey, I did this experiment for my science class, and I need to know what are the reactions occurring here because I can’t tell by myself. Could you please tell me? My research is for Tuesday! Thank youuu