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Q&A: Elastomeric bioplastic?

by Green Plastics


Tyler Favre wrote in to ask:

Sticking with green alternatives and following the recipes provided on the site; is there a way to make the bioplastic more elastomeric and stretchy? Something more akin to rubber or silicone?

Thanks for your question, Tyler!

Considering just the bioplastic formulations that can be cast easily at home as films, the general rule is that the more plasticizer (e.g., glycerol), the more easily the film can be stretched. For example a film cast from a heated solution of 50% agar and 50% glycerol can be stretched to about 150% of its original length before it breaks; i.e., its “elongation to break” would be around 50%. A gelatin-glycerol cast film might behave similarly. But as you increase the amount of plasticizer, you would also decrease its strength, so there’s a tradeoff between flexibility and strength. Additives might improve the strength but that’s a separate issue.

A commercial biodegradable plastic, such a starch-based garbage bag, processed by extrusion, can have significant strength (as it must to serve as a garbage bag) and still have an elongation of several hundred percent. Additives improve the properties as well.

But, in both cases, while you might speak of films that are more “stretchy” they wouldn’t be called elastomers which, as with rubber, can be significantly deformed and still return to the original shape when the stress is removed.

Happy experimenting!

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