Another day, another bioplastic

The story so far: I’m making occasional efforts to follow recipes for simple stovetop bioplastics, found on the Internet. I’m hoping to learn enough about the possibilities to be able to find a simple, affordable one that can be made from abundant materials, and substituted for conventional oil-based materials.

Just imagine the benefits if a material could be identified that is renewable, and biodegradable. If processing was simple enough that anybody could set up a business to make the stuff, and if it was inexpensive enough to be used in packaging? We could make litter a thing of the past… and stave off the problems of oil depletion.

In my first test, the casein plastic had been a disappointment… but who wants to make artefacts out of curdled milk, anyway? My next effort was with a starch-based bioplastic, consisting of cornflour, vinegar, gelatin and water. That’s two ingredients out of the kitchen cupboard, one from the tap, and one from my local pharmacy. Gelatin is the one you’re least likely to have on hand, although it’s inexpensive and renewable – a byproduct of soap manufacture, used in baking and the like. (You needn’t worry that going into the pharmacy and asking for gelatin is going to make them think you’re running a drug lab, or something…)

The ingredients were combined:

  • one tablespoon of cornstarch,
  • four tablespoons of water,
  • a teaspoon of glycerin, and
  • a teaspoon of vinegar.

(It’s said that varying the quantity of gelatin used affects the stiffness of the plastic… adding a variable to the already somewhat imprecise bioplastic recipes I’m finding…)

Everything was thoroughly mixed, while cold, and then stirred vigorously while heat was applied. (I added some food colouring at this point, just for fun.) You know it’s polymerising when it turns into a semi-translucent gel, and begins to form clumps. Presently, it starts to bubble, and it’s time to remove it from the heat. You’re left with a substance that only the special effects director in a science fiction movie could love.

And then? Then you pour it out of the pot, and spread it on a non-stick surface. Once again (as with the casein plastic) it’s time to play the waiting game: the plastic must dry.

Not cool, but dry. My disappointment with bioplastics looks set to continue, as the industrial applications for a plastic that has to dry like plaster seem somewhat limited… but that’s the way things are, at least with this particular material. In any case, I decided to try the material and report on what I got.

I’d made a double-sized batch, which may have been a mistake. I spread it out as best I could in a non-stick over tray, covering it to a depth of about 5mm. This thickness will have affected the drying time; after three days I still had clammy, weak bioplastic, with all the engineering properties of jelly.

Weak, flabby and cracking up... and my bioplastic’s not much use either.

Weak, flabby and cracking up… and my bioplastic’s not much use either.

At the same time, the material revealed its Achilles’ heel: it shrank as it dried, not just becoming a thinner deposit, but cracking like a lakebed in a drought. Some pieces curled up at the edges as they dried, too. Other people have had greater success with this material, producing large, thin sheets that resemble plastic bags. That’s not a bad idea, substituting for plastic bags with a biodegradable and renewable alternative… but it seems I will have to look elsewhere if I want to make three-dimensional products from bioplastic.

Thin deposit

Thin deposits of the material were soon dry, and proved surprisingly strong.

Eventually, the plastic became quite durable, although the random fractures from the drying phase will likely pose a problem if one is trying to make regular shapes, rather than just bioplastic ‘crisps’. (If you can think of a use for bioplastic crisps, let me know: I can supply them in quantity.)

Bioplastic crisps

Bioplastic crisps. Not manufacturing’s finest hour, to be honest.

A point is reached where this plastic loses its flexibility, and you’re left with rigid pieces that are about as durable as if you made them from Fimo… with the advantage of there being no oven baking stage, but on the downside having a long drying time, and the problem of cracking – both problems apparently absent when the plastic is made in very thin layers.

Now, having gone to all the trouble of making this bioplastic, naturally I set about making it rot away to nothing. In an indoor environment, the plastic seems to survive more or less indefinitely. Sustained contact with a small amount of moisture had the effect of washing some of my food colouring out of the plastic, but didn’t otherwise spoil it, while strong sunlight seems to have caused the plastic to fracture internally. Previously translucent sections developed fissures internally, looking like opaque flakes, and scabs of the material began to break away.

Degrading bioplastic

The material lasted indefinitely while indoors, but left outside for just a week, this piece is beginning to break up.

This rapid biodegredation is an intriguing possibility for a fast food container, or somesuch… although not with any manufacturing process I have yet been able to conceive of. (Maybe something like slip casting, as it’s used in pottery?)

Time will tell. If anybody has advice for amateur bioplastic hasckers such as me, the comments section is open…

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