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Q&A: bioplastic from fruit peels?

by Green Plastics

 

Paula wrote in with this question:

we’re making bioplastic using pectin extracted from fruit peels. but our product just looks like jelly. i learned from watching the video that amylopectin is not enough. can you please suggest any additive?

 

Paula, I think that bioplastic made from fruit peels is a fantastic idea for a home project! On this website, we have had discussions and recipes for home-made plastic made from everything from algae to gelatin, but we haven’t actually talked about fruit peels yet.  I’ve never actually tried using pectin (the polymer from fruit peels), but it should produce a good product. Plus, it follows a general topic of interest that is popular these days, and that is: how can we actually produce plastic from materials that otherwise would be considered waste?  (I’m excited to see what you can come up with.

However, as you experiment, there are a few things that you need to keep in mind.  One is the most basic equation that describes all plastic:

 

plastic = polymer + plasticizer + additives

 

Sometimes you can do without additives, but if a material doesn’t contain at least a polymer and a plasticizer, then it’s simply not plastic.

Amylopectin is a polymer that should be able to produce a good bioplastic. Unfortunately, I cannot tell from your question what you are using as a plasticizer, or if you are using one at all. You refer to “the video”, and if you are referring to our home-made bioplastic video online, then you may have tried using glycerin as a plasticizer, since that is the plasticizer that Brandon uses in his demonstration.  If you have not tried this, and your recipe did not have any plasticizer, then it will not produce plastic.  The substance that you get will gradually dry over time, passing through a gel stage (much like jello) and eventually hardening into a brittle sheet that will break up into small pieces.

On the other hand, if you tried adding glycerin (or some other plasticizer) and added too much, then the final product will remain sticky and weak and may have a consistency much like jelly, like you described.  If it remains like this after a number of days, the most likely cause is too much plasticizer.  This is actually a very common mistake that people make, and unfortunately it is because of people mis-reading the way recipes for bioplastic are often written.  For example, in another post we have provided a recipe for a agar-and-glycerin plastic that looks like this:

 

3.0 g (1 tsp) agar
240 ml (1 cup) of 1% glycerol solution
180 ml (3/4 cup) water

 

This means that you have to use 240 ml of a solution that contains one part glycerin for every 99 parts water.  That is actually a very, very diluted form of glycerin. If you do not measure this accurately, so that you have a glycerin solution that is too strong, then you will end up with jelly instead of plastic.

Generally speaking, when you are casting biopolymer films, this is what should happen.  You will first see a thickening of the mixture. When you pour the mixture it will pass through a gel stage (much like Jello). After that you have to let the gel dry, a process that may take several days (depending on the humidity). After the gel dries completely it will be a flexible film. Too much plasticizer and the film will be sticky and weak; too little plasticizer and the film will be very brittle, but tough. You have to find the right amount of plasticizer.  And often this is something that you can only figure out by trying different things and experimenting… especially when you are experimenting with a new polymer!

Best luck with your bioplastic project!

 

Remember, if you have successfully made bioplastics using our recipes or suggestions please send photos or video to project@green-plastics.net and we will post it on the website and help give you some publicity!

 


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