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Home-made bioplastic sword!

by Green Plastics


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.




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.

Comments (9)

  1. I tried this out and it set into a jelly like substance very quickly. I took the pieces out of the mold and put them aside thinking this mix would be to soft and weak but it actually seems to be hardening. The center and bottom of the piece is still soft but the exposed surface on the top is very plastic like indeed and I can tap a finger nail against the surface. Is this what I’m aiming for? Is the soft jelly not the final product but the first stage of ‘hardening’?
    I see that this recipe was posted quite a few years ago so I doubt I’ll get a response but I’ll be sure to return and post my findings for anyone that stumbles onto this page in the future.

    • Green Plastics says:

      The drying can take a long time, and depends a lot on the environmental conditions. You want to make sure it’s drying in a cold dry place. Sometimes I’ve let things dry in a garage or even in the refrigerator (but not the freezer!!).

      I’ve seen a lot of people get frustrated with their bioplastic project “never drying”. In some cases they are not patient enough, but in other cases it is because they used too much glycerine or accidentally used a concentration that was too high. Remember glycerine (glycerol) is a “plasticizer”: the more you use, the more flexible and soft it is, the less you use the harder the plastic is. Use too much: it’s soft and gooey! LOL

      So if it NEVER gets totally hard, and you used the (1/2 tsp) glycerol solution, check the concentration of the solution and maybe try doing a variation of the recipe where you use a more diluted glycerol solution and see if that helps!!

  2. C MJ says:

    I used a variation of this recipe to make hair combs and my end result ended up warped and shrunken. I’ve read online somewhere that using wood flour as a filler may help with shrinkage (I haven’t tried it yet). Have anyone else experienced warping and shrinkage? If so do you have any suggestions on how to minimize it? Thanks!!!

  3. Hi, I’m from Brazil, I cannot find anything like gelatin-glycerol in here. Can you tell me please the chemical name? Thanks.

  4. Angel says:

    I have experience with the shrinking aswell. Anybody know how to controll this?

  5. Krishna Sanz says:

    Hi, I would like to know how long stays this bioplastic in good conditions outdoor? and if I use more glycerin to do it flexible, it would be less durable?

    • Krishna Sanz says:

      thanks so much for all of this information on your web, it is great!!

    • Green Plastics says:

      How long a bioplastic will last depends on a lot of factors, including heat, moisture, and other things. Remember that “biodegradation” is literally “degradation by the actions of microbes”, so anything that influences how many microbes there are and how active they are will impact how quickly the plastic degrades. Other factors that lead to physical degradation will also make a difference: things like exposure to sunlight or anything that will cause the plastic to splinter or break.