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Hello greenplastisnet,

I am looking for a ratio of ingredients for a durable plastic that Is not as flexible, but still, wont break when I hit something with it. Would I use no Glycerin at all? or do you need at least some Glycerin for it to work? I am experimenting different materials for a cheap plastic katana.

RESPONSE FROM GREEN-PLASTICS.NET:

This sounds like a fun project, but I will tell you from the outset... getting the right formulation for a katana will probably take some time, trial and error!

Your best bet will be to use a gelatin-glycerol bioplastic with a very low level of glycerol.  This produces a hard, inflexible plastic that is good for creating solid objects.  I've made buttons and coasters and ornaments before, but never anything as large as a plastic sword.  It shouldn't be too brittle, but you may want to try adjusting the amounts a little bit over several trials: remember that less glycerol means it is more brittle.

We have posted the formulation for this kind of plastic before, but in case you missed it:

Combine 3.0 grams (1/2 tsp) glycerol and 12.0 g gelatin (4 tsp) with 60 ml (1/4 cup) hot water.

Depending on how large the sword is, you may need to increase these amounts.  Just remember to keep them in the same proportions (i.e. either double everything, or quadruple everything, etc).

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 going 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.

You will want to carefully pour the mixture directly into the mold that you are using to create the shape of the sword.  I assume you have already created a mold.  If not, then of course that step has to come first!

How long it takes to dry will depend on the temperature and humidity in the room, and how thick the final product is. It may take several days, and 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.

One final comment: We assume that the plastic sword is meant for all fun and games and that you don't intend to do any harm with it.  But please remember: just because it's bioplastic doesn't mean it won't hurt!  You can absolutely hurt yourself or others, even if you are just playing around, by whacking eachother with plastic swords.  So please be very careful.  The plastic formulation describe here is solid and hard: you may want to wrap your final product with padding, if you intend to use it in "mock combat."

Good luck!  Let us know how it turns out.