When Bioplastic Goes Bad

Time to try another recipe for bioplastic. I’m still hoping to find a simple, affordable material that can be made from waste ingredients (so we don’t use oil for trivial products) that rots away when no longer required… and that could be manufactured in a cottage industry.

The third recipe for bioplastic that I tried was “microwave bioplastic”, which is typically made from cornstarch (1 tbsp), water (1 tbsp) and vegetable oil (two drops). Bioplastic doesn’t come much simpler than this, nor much quicker. A microwave oven is used to heat the mixture for twenty seconds or so, and then you knead the result, and mould it into shape… and you’re done.

I made a small ball of the material, and set it aside to dry. Once again, it appears we’re looking at a thermosetting process here: the bioplastic doesn’t simply harden as it cools. It took about a day to set, and the ball split apart as it dried. The fragments were hard, like a ceramic, making the first time I’ve been able to report a material with the kind of strength that would be sought in many plastic products… but my sample had distorted beyond any kind of usefulness.

Microwave bioplastic ball

Microwave bioplastic: surprisingly hard… but hopelessly distorted during drying.

“Don’t let it dry too quickly,” is the advice from the Internet bioplastic community. The problem of splitting in microwave bioplastic is well known. I kept the next sample under wraps, with just a few air holes. After a week…

Microwave bioplastic cup, decomposing

Something is rotten in the state of bioplastic

My bioplastic, deliberately kept moist to prevent splitting apart, had begun to rot even before it had dried. I removed the plastic covering and left the festering thing to compost itself… and it promptly split apart.

Microwave bioplastic, broken apart

Not all things that are furry are cute.

Verdict: this isn’t the bioplastic we’re looking for.

It’s said that bad doctors get to bury their mistakes, while bad architects can only recommend that you plant a row of trees. Bad bioplastic engineers have the best of all possible worlds: the evidence of their mistakes removes itself – and surprisingly quickly.

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…

Bioplastic Revisited

Undaunted by the difficulties encountered during my first experiment with a home-made bioplastic, I determined to keep on trying. The story so far: I’m hoping to be able to recommend to my readers a bioplastic that might be made easily from abundant or waste material, that can be substituted directly for an oil-based material, and that is biodegradable.

Now, obviously the simplest way to meet these requirements would be by desk research, but I decided that for once “seeing is believing”. I’m intrigued by the amateur bioplastic scene because this seems more likely to make a new contribution towards sustainability. I’m thinking that a resource-poor country could really benefit from a grassroots bioplastic revolution, so I’m less interested in high-tech solutions, and more in what can be demonstrated by stovetop hackers. This led me to attempt to make some ‘milk plastic’, but the results were less than satisfactory: I produced a material that exhibited significant shrinkage and distortion during drying, and that I found very difficult to mould, while producing parts of very limited strength. I did some additional research in an effort to find out what might have gone wrong, and discovered new advice that I should use a cheesecloth to squeeze excess moisture out from the curdled bioplastic, and then ‘knead’ the material for a while. This is at odds with the instructions I had got from the Smithsonian, which said to leave some moisture in, to prevent cracking. I’m finding most bioplastic recipes very vague, and in some cases contradictory. Experimentation is required!

Further reading revealed that the scientific name for ‘milk plastic’ is casein plastic. The Plastics Historical Society provide a good deal of information about its commercial use, and I was surprised to learn just how long ago it started, being patented in 1899. Galalith (sometimes marketed as Erinoid in the UK) was used to make buttons, pen barrels, knitting needles, knife handles, buckles…

Casein buttons

All kinds of useful gadgets. But mostly buttons.

What? That stuff I found to be about as durable as chocolate, and far more difficult to mould, due to shrinkage? How could that be strong enough to make knitting needles? The secret (as discovered by French chemist Auguste Trillat) comes from hardening it by soaking in a 5% formaldehyde solution for a long period. This isn’t something that you’ll find the stovetop bioplastic enthusiasts doing, and rightly so since formaldehyde is carcinogenic. Still, when so treated, the material becomes surprisingly durable; it polishes up well, and dyes very well, to produce some distinctive pastel colours that were characteristic of the interwar period.

If you do happen to soak your milk plastic in a 5% formaldehyde solution (for up to a year, for a piece 25mm thick) it turns rigid – but while doing so, the material shrinks and distorts. Fine moulding while it’s in the plastic state is therefore impractical and most Galalith products had to be machined from solid sheet or bar, rather as we do with certain low-volume production runs today. By 1928 a process was developed whereby the material could be moulded directly into buttons, which reduced cost and opened up possibilities for new shapes. Casein plastic buttons had found their niche, being better than other early plastics in terms of surviving the rigors of washing, dry cleaning and ironing.

I’m reminded of a (frankly awful) verse from 18th century poet and physician John Armstrong, whose tribute to Cheshire cheese (!) saw it described as “tenacious paste of solid milk”. If you’re a vegan, you probably don’t fancy the idea of your buttons or the handles of your cutlery being made from this particularly tenacious form of milk, but keep in mind that in 1899 materials commonly used in the manufacture of household goods still included ivory, bone and horn, so perhaps Galalith was the lesser of two evils.

The manufacture of goods from Galalith halted during the Second World War, when milk was needed for feeding hungry populations, and the development of new materials had rendered it largely obsolete by the time supplies were restored. Nowadays, only very low volumes of specialist buttons are made this way.

With all these limitations, we can forget about casein plastic being a sustainable solution. The need to harden it with a carcinogenic chemical is a major obstacle, while batch manufacture that takes up to a year (and still requires subsequent machining) just about disqualifies it. I turned my attention to starch-based biopolymers instead.

Meanwhile, the bioplastic ‘Volkswagen Polos’ that I had made using an ice cube took a week to dry right through, shrinking and distorting as they did so. The early 20th century solution to this would have been to start out with a much bigger lump of material, and to have machined it down to the desired shape after a long soak in formaldehyde solution. I chose instead to leave my failed experiments out in the garden to see how long it takes for the action of sun, rain and microbes to turn them into compost.

The ice cube tray VW Polo...

The ice cube tray VW Polo. The pale upper parts failed to fully set while within the mould cavity. Poor workability means this is no substitute for modern plastics.

...a disappointing bioplastic experiment.

When fully dried, much of the shape had been lost: a disappointing first attempt with bioplastic.


A Stovetop Bioplastic Experiment

A little while ago I wrote that you could make bioplastic, and that it was simple to do so. There are plenty of websites that tell you this, and countless chirpy teenagers demonstrating various techniques on YouTube… but I decided I’d better put the whole thing to the test.

For my first experimental bioplastic , I tried polylactic acid (PLA) – simply because I had some milk left over and it wasn’t going to last much longer. I used a recipe provided by the folks at the Smithsonian, which appealed to me because of its simplicity. Later, I’d try some things that required me to buy ingredients, but for this one all I needed was milk and a little vinegar.

Selecting an old saucepan (just in case something horrible was produced – it wasn’t) I warmed up the milk to the point where velvety bubbles were just beginning to appear. Meanwhile, I mixed in some food colouring, to make things more interesting. Then I added vinegar, in a ratio of one tablespoon of vinegar to one cup of milk. (Why do American recipes always use the ‘cup’ as a unit of measure? Which cup? They’re all different sizes…)

Pan of milk, vinegar and food colouring.

Bioplatic. It’s what’s for dinner.

I kept on stirring, and pretty soon the mixture polymerised… which is a nice way to say that it curdled, just as if I had added lemon juice to cream when cooking. The result was a vile-looking mixture of thin, clear liquid and small rubbery chunks with the consistency of cottage cheese. The chunks were what I was after.

I poured the whole lot through a sieve, to retain the chunks. Some of the smaller chunks slipped through and I had a momentary panic that I was pouring plastic down the drain, where it might clog… then I remembered that this is bioplastic, so it can be depended upon to rot away quite quickly. Score one point for home-made bioplastic!


I would estimate that I got about 10% chunks, 90% waste liquid.

I scooped the chunks out of the sieve and dabbed at the mixture with kitchen roll to remove excess liquid. Then I thought, what on Earth am I going to do with this bioplastic anyway? A quick search of the kitchen revealed an ice cube tray (a promotional freebie that makes ice cubes in the shape of VW Polos) so I decided to make some bioplastic Polos. I spooned the chunks into the cavities and pressed it down as best I could: the process was nothing like any plastic moulding I’ve done before, and that was a disappointment: I’d read that bioplastics could be substituted for oil-based plastics in existing processes. Not this one… or at least, not with this recipe.

Ice cube tray

Who knew you could make VW Polos from bioplastic?

One of my concerns was that this experiment would smell really bad. I don’t like milk very much at the best of times, and heating it and then leaving it around the house for several days really didn’t seem like a good idea. I’m pleased to report, however, that the only smell coming from the experiment after two days was a faint smell of vinegar.

Now, something that has surprised me in many of the bioplastic recipes I’ve read is a requirement to let them dry. They set over time, it seems. That’s another disappointment, because it reduces their utility a little… but perhaps I could make some bioplastic, let it ‘dry’ and then soften it with heat and mould it like a regular thermoplastic? Well… we shall see. I suppose that’s my end goal in these experiments: to identify an easily-made, biodegradable plastic that can be substituted directly for something like polystyrene, or PET. Imagine the benefit if an existing waste material such as food industry byproducts could be used to make packaging, reducing dependency upon oil imports and simply turning back into soil at the end of life!

The ‘milk plastic’ exhibited a tremendous amount of shrinkage as it dried. The ‘ice cube’ VW Polos became a lot narrower (around 25%) as they dried. Clearly, there was a lot of liquid left in the mixture, and it all had to evaporate away. This is a problem because working with PLA in this way seems to be a race against time: will the plastic set before it biodegrades? Again, I don’t really want rotting milk products around the house.

Mould shrinkage

Nasty shrinkage – at least 25% – during drying.

The ice cube tray proved to be a poor choice of mould, as it inhibited drying. After two days, I tried to dig the first Polo out of the tray, and found that it was still gooey inside. A better result came from some surplus bioplastic that I had left on a porous surface; it dried much more thoroughly, and shows no sign of decomposing. Best of all, once dry, it had no smell.

Dried bioplastic

To quote Lord Percy Percy: “A nugget of purest green!”

The strength of the material was nothing spectacular: I would estimate it was about as strong as a wax crayon: not much use for an industrial application, then. You might manage to make plant pots out of the stuff (so that seedlings can be put in the ground without removing them from the pot) but you can do that with fibrous pots made from pressed peat anyway. Another issue with this bioplastic recipe is that it isn’t really ‘green’ enough – milk is produced by farming, which may not use sustainable methods. Also, it involves using a food in a non-food application, which isn’t really ethical while not everybody has enough.

All in all, ‘milk plastic’ was a disappointment, although a useful learning experience. It took time, effort and energy to produce something that had only limited practical application. Meanwhile, the milk bottle that I washed out and put in the recycling consisted of 37 grams of virgin HDPE (an oil-based plastic) that I expect will be burnt for energy recovery. I would have come closer to my goal by grinding up the milk bottle into granules, and using that in a moulding process (exactly as some 3D printing enthusiasts are now doing). The HDPE is easier to work with, stronger, chemically more stable, and simply better at virtually everything except rotting. What a waste!