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The science of cashew shells

by Green Plastics


If you watch the media for news of bioplastics (the way that we do, here at Green Plastics), you will have noticed that for the last few days the Big News has been cashew-based plastics.

The Independent announces:

A unique plastic made from cashew nut shells could be used in consumer electronics by 2013.

Japanese company NEC Corporation has announced the development of a first-of-its kind biomass-based plastic — bio-plastic – produced using non-edible plant resources such as cashew nut shells. The plastic is durable enough to be used in electronic equipment and NEC expects that with continued research bio-plastic could be used in a range of electronic devices by 2014.

Raw_Cashew_Nut_In_ShellEveryone is applauding from every side. The plastic is durable, heat-resistant, and water-resistant, so it would be safe to use in all kinds of electronic equipment from cell phones to laptops. It would make the creation of electronic devices more environmentally friendly. And because it is based on cashew shells, we can make as much of it as we want to without endangering our own food supply.

But with all of the publicity surrounding this breakthrough, you might want to know a little more about the science behind it.

The first thing to know is that this type of plastic follows the same basic formulation as any other bioplastic, and is a combination of three things: a polymer, a plasticizer, and additives. Just like the kind of bioplastic that you can make in your kitchen. As we have mentioned again and again, you get different properties from bioplastic by varying the types and ratios of each of these three basic components.

What NEC did is come up with a particular formulation of polymer + plasticizer + additive to create a new type of plastic with useful properties. In this case, they have combined two types of polymer together. The main polymer that they use is cellulose, which is produced in large amounts by plants, including grass stems, etc. They then added a small amount of polymer created from cardanol, which is an oil that is found in abundance in cashew nut shells.

I say “polymer created from cardanol,” because cardanol itself is not a polymer. But, it can be made into a polymer through the process of polymerization—in much the same way that you can convert lactic acid (not a polymer) into poly-lactic acid, (the polymer used to make PLA plastic).

Add to this some plasticizer and additives and their own special processing techniques (patented, I’m sure), and viola!… one of the strongest, most heat-resistent forms of bio-plastic yet! With the added bonus that both cellulose and cardanol come from non-food sources (e.g. grass and cashew shells).

Of course, it isn’t as if NEC discovered cardanol. People have been experimenting with polymerizing cardanol for a long time. (You can, for example, this experiment that describes polymerizing cardanol and mixing it with another polymer. The science is pretty dense, if you are a beginner student, but scan through to the “Experimental” section and you can read what they did.) The break-through comes when finding just the right ingredients to combine with just the right process.

If you are a student interested in working in the area of bioplastics and polymer chemistry, this is one of the biggest take-home messages you can have: experiment, experiment, experiment. All around the world there are scientists frantically trying all sorts of combinations of the Basic Three Ingredients (polymer, plasticizer, additive) to find (and patent) that perfect combination that makes plastic with interesting new properties. With a little bit of creativity, who knows what they will come up with next?

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