by Green Plastics
In an Student’s Corner earlier article, Can I make waterproof bioplastic?, we talked about a commonly-asked question: how might it be possible to make environmentally-friendly plastic that is also waterproof. It turns out that it is not an easy thing to do. (Go ahead and read that article to find out more.)
However, in response to that article, Maya left a comment with a very interesting and ingenious question:
If I change the plasticizer (I was using glycerol), to something hydrophobic, would that make the bioplastic waterproof? If so, is there any such plasticizer that is easily accessible? I’m trying to make bioplastic waterproof, for my science fair experiment. I read that glycerol, sorbitol and camphor are all hygroscopic…the opposite of what I need.
This is a very astute question, and something that scientists have been thinking about for some time.
There is a dilemma though. For a molecule to plasticize a biopolymer like starch or gelatin, it has to interact with the biopolymer. Unfortunately, the precise nature of the polymer-plasticizer interaction is not yet that well understood. The well-known plasticizer molecules (like glycerol and sorbitol) interact with those biopolymers precisely because they are themselves hydrophilic. A hydrophobic molecule won’t interact well with hydrophilic biopolymers (like starch) and are likely not going to be an effective plasticizer.
So far no one has an answer to this dilemma. That doesn’t mean that it is not possible … There may be a way around it, by “thinking outside the box”. Finding a solution (or even a partial solution) will be a great breakthrough.
One of the great things about the field of bioplastics is that it is so new, with so much unknown territory, is that a good chemistry student can come up with exactly the right questions to ask… and could even be the one to come up with the answers.