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In a comment to our article Home-made bioplastic sword!, Larry asks this:

I have been experimenting with bioplastic. In this article are you saying the only way to achieve a hard bioplastic is to use Gelatin. I don't want to use an starch from animal hooves. Is there a recipe to get a hard plastic by using Agar, Tapioca, corn, and/or potato starch? I noticed in "Brandons Remix" video he had made a hard disk like piece but does not say the recipe. Thanks.

This is a great question! Starch is very good for certain types of bioplastic, like thin flexible films or the type of bioplastic that is now commercially used for cups and utensils.  But starch does not produce a very good plastic for hard solid objects like buttons, decorations, cup coasters, and so on.  In the Green Plastics book, there are a number of recipes for hard solid plastic objects, but most of them use gelatin as the main or secondary polymer. 

But some people don't want to use animal products or bi-products in their projects.  They want to go a step beyond bioplastic and have vegan bioplastic: biopolastic that does not involve the harm or use of animals!

How can we do it?  There is a simple answer: algae!

Yes, agar (the main compound in algae that is used as a polymer to make bioplastic) produces a pretty good hard, inflexible plastic.... as long as you use a very small amount of plasticizer.  In our earlier article on algae plastic, HOW TO: make algae bioplastic, we give several recipes along with detailed instructions on how to do it.  (Make sure you check out that article.)   However, those recipes will generally produce a thin flexible film.

The recipe for pure agar bioplastic in that article is this:

3.0 g (1 tsp) agar
240 ml (1 cup) of 1% glycerol solution
180 ml (3/4 cup) water

Mix all of the ingredients together in the amounts above, and stir.  Keep mixing until there are no clumps and it is as dispersed as it's gong to get.  Then 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.  Carefully pour the mixture into a drying pan, and make sure to spread it out to let it dry.

NOTE: The above recipe will not produce a hard, inflexible piece of plastic!  It has way too much glycerol, which is the ingredient that is the plasticizer.  Remember the general formulation for all bioplastics is Polymer + Plasticizer + Additives.  In this case, the polymer is the agar and the plasticizer is the glycerol.

So how much glycerol should you use?  It depends on exactly how hard and inflexible you want the plastic to be.  I would recommend trying a few different ratios: this is like cooking, you'll probably have to do it a few times before it comes out "right".  But start with a ratio of 1/2 cup of 1% glycerol solution to 1 tsp of agar, to begin with, and see how that turns out.  You can then decrease or increase the amount of plasticizer depending on whether you want the end result to be harder or less brittle.

So have fun experimenting!  As always, if you end up with a successful project please send in photos or video of it and we will feature it here.

SOME FINAL TIPS AND TRICKS:

• Where can I buy agar?  If you're in school, your school's chemistry lab may have it or may be able to order it for you.  If not, you can actually order it yourself: just google "buy agar" and you will get some links.  I think they actually sell it on Amazon.com now, amazingly enough.
• How long will it take to dry?  You may have to be very patient, especially with a thicker mold for a thicker final product.  It may take a day or two to dry, and it helps if you keep it in a warm, dry environment while it is drying.  If it takes longer than a week, you probably want to scrap it and try again with less water or even less plasticizer.
• Are you using the right amount of glycerol?  Please remember that the recipe calls for a 1% glycerol solution.  If you measure out 1/2 cup of pure glycerol then you will be using 100 times the recommended amount!   You can buy glycerol in a solution form, but if it is more than 1% then you need to dilute it. For example, this product advertises itself as a 50% Glycerol Solution.  You need to cut that with a lot of water (do the math!) to bring it down to 1%.

Good luck!