V4 BeyondPlastic – [PROCESS] Container from Peels
In general, our approach to work with potato peels is pretty low-tech with only two ingredients in the material mix, hence the outcome material can’t be called really durable. So we thought that a great application for it would be a product with a short life span. Since we don’t like single-use plastic, we decided to make a biodegradable alternative to a styrofoam take-away container.
The mould for the container is also a learning tool itself. It is so far the most complex mould we have for biomaterials. By increasing the complexity we aimed to push further the material boundaries and learn more about its properties.
If you are curious about the process of making a heatable mould, you can check out this topic
Our actual heat pressing process is still experimental, and so far the most successful approach is this:
Ingredients: 70% of peels mixed with 30% of water
We take 125g of peel powder and 53g of water to make a container 230 x 150 x 31 mm, with 1.5 mm wall thickness
Temperature: The mold is heated up to 90°C.
The settings may vary here. Normally, when we work at a lower temperature we cook it for a longer time and vice versa. Check the google doc below for more examples.
Mould release: The material is pretty sticky when it comes to the heat, so we need to apply some mould release like oil or other lubricants first.
More info on what we tried so far here.
Pressure: 10 min with 7 metric tons.
If the pressure is too low, the surface appears weaker with lots of tiny cracks.
Taking out: It’s better to release the pressure slowly, otherwise the steam will come out too fast and might damage the surface.
We also tried different ways to get the container out of the mould in case it gets a little stuck. For example wooden or plastic scrapers or blowing air from a compressor.
When working on the take-away container we learned about other properties that make this biomaterial great (except for being nicely hard of course):
The material has very good distribution properties and after starch started gelatinizing the mass easily spreads in a mould. The more water you add, the easier the materials spreads through out the mold. However, we found that potato peels spread pretty good with 30% water added.
Our take-away container has pretty steep walls and little pins that stick out, but the material easily reaches the top and spreads into all parts of the mould most of the times.
Good distribution allows covering even small details and it works well with both fine powder or bigger flakes. The pressure around 5 – 7 metric tons is good enough for filling up all details and sealing the surface.
On the bottom of the container we added an imprinted logo and a stripe pattern. Both appear very sharp and clear. As for the little pins on the top side, those work well from the distribution perspective but should be designed differently. They are too small and hence too weak, which makes them fall off easily.
Aaand in case you wonder what P5 means, it stands for Precious Potato Peel Powder Plastic:)
As it was our first experience of using a complex mould for pressing potato peels, we surely faced some challenges. The experiment is still ongoing, but here is what we know so far:
A freshly pressed container is still a bit moist and flexy. While water leftovers evaporate and the material hardens, surfaces without edge support may deform and bend.
To fix this we added an L-profile to the side walls of the container by just extending the edges on the mould. Worked out pretty well.
It goes together with deformation when the moisture dries out.
Just keep in mind this 10% size difference when designing a mould.
This is so far the biggest and the most unpredictable challenge when it comes to pressing potato peels in a heatable mould. In other processes, like extrusion or “cold” pressing precooked peels, the material normally doesn’t get stuck to the mould.
So far, we haven’t found a solid way to fix sticking yet but we know three main things that help. 1. The temperature should be kept in a mild range of 75°C – 95°C. Even though we had some unsuccessful try-outs within this range too, overheating is almost a guarantee that the next thing you do is cleaning your mould from a deadly stuck potato. 2. Mould release is handy here too. We tried several vegetable oils with different viscosity and a different smoke point (rice bran, sunflower, and olive oils) as well as baking spray and baby powder, but we still keep looking. More on those*here. 3. Mould polishing. Sanding off tiny roughness from the aluminum mould and polishing it, seem to make the mould surface a bit less sticky.
We learned that sharp corners are actually possible, distribution is good enough for it, and the corners hold well. However, they make taking the container out from the mould a bit more tricky, because of the material stickiness. Also, a radius would give more stability to the walls.
We wrote down the recipes of a few interesting experiments we made to find the optimal process of pressing potato peels. All these were pressed in the heatable mould for the take-away container, with varying temperatures, time, ingredient ratios, and recycled material. If you are working on experiments with potato peels this might be interesting for you:
Some other learnings:
Different starter material.
At some point, we realized that even though we (and the whole V4 team) love potatoes we simply can’t eat that many to have enough peels for our experiments. So we contacted a Dutch potato producing company Peka Kroef who kindly provided us with some of their waste stream peels. They use a different peeling process (steaming) and grind the peels straight away, so we got those as a pulp which we then dried in the oven. Compared to our kitchen peels, this starter material has a different color and smell and might have a different starch content because of the steaming peeling process.
We also tried to reuse some failed try-outs – grind them back to powder and press again. In general, recycled material is way weaker than raw mostly because of some oil content in the mix (a leftover mould release oil from the previous pressing), and cooked starch. It is possible to make it work when some additional starch is added, but keep in mind different texture and still a bit weaker outcome.
Thanks! We normally dry them in an oven, spreading peels on several trays. I wrote some info here. It is better to grind completely dry peels because coffee grinders and blenders for powder work better with the dry matter. At some point earlier we broke a coffee grinder with a bit wet peels:)
We also tried to do vice versa, to grind peels first and then dry. This works but adds an extra step, as you need to grind one more time after the mass dries out because it dries as a whole “piece”, not as a powder.
Ok, thanks. I’d read the earlier post but forgotten some of the details. I’m going to try this in a low-tech way. I’ve already saved some peels but put them in the fridge, I realise this was the wrong thing to do now! I’ll spread them out to dry in my greenhouse, even in cold weather I think they’ll dry out in a few days and I’m not in a hurry. I’ll let you know how I get on.
Would make great plant pots with seeds incorporated.
Great project! This would be a perfect fit with our festival. With DGTL festival we try to make the foodcourt circular and this could be a solution in the near future! Keep up the good work
btw, it has a savoury looks 😀
Hi,is this peel container waterproof.do u have idea how to make starch waterproof.i did similar experiment using starch powder and wood pulp fiber and water.got good wall finished foamed cup.but its not waterproof
“Pressure: 10 min with 7 metric tons. If the pressure is too low, the surface appears weaker with lots of tiny cracks.”
You have amazing work in getting the product right. What i want to know is does it really need a force of 7000kg on the die to get the finished product. Because it sounds way lot. Or is 7MT the press capacity and have you used much lower pressure at the guage which will eventually reduce force on the die?
I am also in process of building such machine but really not sure of what should be the force on the die.
Thanks a lot
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