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What polymers can I use?

by Green Plastics

 

In a comment on one of our articles, student Maya asks question:

For my science experiment I’ve now decided to substitute the polymers in the bioplastic recipe.

I wanted to use chitin, and lignin and corn starch. But both lignin and chitin are really hard to find. Is there a place/website to buy a small amount of chitin for a low price (I didn’t see one)? I read that peanuts have a large amount of lignin. Could I extract the lignin? And if I do extract something, how do I know it’s lignin?

What other polymers could I use? Could I use natural rubber as a polymer? You suggested at one point the use of shellac as a coating, but it is also a polymer. Could it be the polymer in a bioplastic?

Thanks for your help!

Thanks for your questions, Maya! I’m glad to see that you are thinking creatively about trying different materials and different combinations of ingredients.

The bioplastics on this web site are all made with water-based formulations (recipes). The polymers, therefore, have to be soluble in water. The alternative polymers you mention (shellac, chitin, lignin, and rubber) are not normally soluble in water. They can be made soluble in aqueous solutions at very high pH values (i.e., in very caustic solutions), but that is something that has to be left to trained chemists because of the safety concerns working with highly caustic solutions.

Besides starch, some other biopolymers that can be used are gelatin and agar. We talk about both of these types of plastic on this website, and there are even more recipes included in the Green Plastics book.

Gelatin is readily available in supermarkets as “unflavored gelatin.” Gelatin makes very nice cast biodegradable plastics. Agar is not as readily available, but there are some places that you can order it online, and it might be available for chemistry teachers through chemical supply houses.

To answer your question about extracting lignin yourself: no you wouldn’t be able to extract lignin from wood. That is a very complex and difficult process.  Even when it is done by trained chemists it is not easy.

Remember: only water soluble polymers can be used in the bioplastic recipes that we have here for home-made bioplastic. The reason we recommend shellac as a water-proofing coating for some bioplastics is precisely because it is so “hydrophobic” (water-hating). In other words: it is good for water-proofing because it is not water-soluble, which unfortunately means it is not a candidate for the polymer in bioplastics cast from aqueous solution.

If you want to experiment with a polymer other than starch, the best candidate would be gelatin or perhaps agar.

Happy experimenting!


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