by Green Plastics
Recently Ankur Sharma wrote to us:
Hello, I really appreciate your effort to make these videos and information
But i was thinking of making corn plastic utensils (glass, plate, knife etc.).
I would really want some tips from u. do i need molds. If i put the materials in a mold after cooking to let it dry, is it going to work. will i have plastic in shape of the mold. what should be the proportion of glycerin:vinegar if i want my plastic to be hard and not very flexible.
Also can i use the process which is used in the youtube video – How to make bioplastic(extended version)
or do i need more materials
i am awaiting a reply eagerly.
Thanks and again really appreciative work. Well done!
Thank you for your letter, Ankur!
First, I want to start out talking about some basic definitions.
When you hear about commercially-produced “corn plastic” utensils and cups, generally you are hearing about bioplastic that is based on the polylactic acid (PLA) polymer. Polylactic acid is polymer that is created by polymerizing lactic acid molecules. In simple English, PLA is a long chain molecule that is created by linking (polymerizing) a large number of lactic acid molecules together. The lactic acid is created by fermenting starches and sugars, and most commonly corn starch is the source for these commercial products. Thus, these products are called “corn plastic” or “corn starch plastic”.
The sequence of events in the commercial creation of this kind of plastic is therefore as follows:
(Image to the right is from Toyota Corporation.)
All of this chemical processing is far beyond what you can achieve in your own home, although you can read and learn a great deal about this process on the web. For some of the basic chemistry of PLA polymerization, I would even recommend Wikipedia: Polylactic Acid.
So what can you make in your own home? You can make plastic from starch in your own home. However, the polymer basis for the plastic will not be PLA, it will be the starch itself.
Yes! Starch is a polymer molecule. Specifically, it is a type of polysaccharide. Whereas PLA is composed of a long chain of Lactic Acid molecules, starch is composed of a long chain of glucose molecules. When you are making “starch plastic” using the instructions that we provide on this site, or in Brandon’s video, you are using the actual starch molecule as the polymer chain in the material.
Q: If starch is already a polymer, why do commercial companies go through all of that trouble (the steps above) to convert starch to PLA? Why not just make starch utensils?
The problem is the starch, by itself, does not make a very sturdy plastic. You can make thin flexible films that can be very useful, but it is generally too flexible and too weak to make solid objects like cups or utensils. For the most part, starch plastic is good for making wrapping material, packaging, and coating films. This is why “corn plastic utensils” means “PLA utensils” and not “starch utensils”… even though the PLA originally is made from starch to begin with!
Uh oh. So where does that leave you?
Unfortunately, it means that you may have to alter your plans slightly if you want to make your own bioplastic utensils. That is, you probably don’t want to start using starch as your biopolymer.
Fortunately, however,there are other biopolymers that you can use in order to make stronger, harder bioplastics in your own home. My recommendation would be to start with gelatin as your polymer, and to follow our ingredients and instructions in these articles:
Both of these articles provide specific formulations for hard, inflexible plastic objects, which should be good for your goal of making utensils. In either case, you will want to make sure that you make the mold first, and that you leave enough time for the plastic material to try once you have poured it into the mold.
If you are not satisfied with your results using gelatin as a polymer, you can also use agar. The recipe and instructions are here:
How to: make algae bioplastic (agar biopolymer)
This is a very popular formulation that produces very good results, and by manipulating the amount of sorbitol that you include you can make it harder or more flexible, depending on your needs.
Good luck with your project, and happy experimenting!