Week | 17
Wildcard Week
23 May 2018 09:48:
This week’s assignment was to design and produce something with a digital fabrication process (incorporating computer-aided design and manufacturing) not covered in another assignment. The task is quite open and we are all already busy working on our final projects, so it’s been a difficult task to put much time on.
In any case, I wanted to explore the concept of a package with a “lifetime”: a wrapping material that would open itself on its own depending on the time it takes for the material to decompose. Agrosourced bioplastic seemed to be the best option to start with, so I decided to make bioplastic and study how to create a casing by folding two plastic surfaces together and sealing them with the help of the laser cutter to melt its borders and permanently join both sides.
My goal this week is to experiment making biodegradable plastic and explore the possibilities of an alternative packaging. What I find the most interesting in using bioplastic is that the packaging could have a lifetime, just like its content has. In food packaging, as an instance, it does not make sense to have a wrapping that lasts way longer that the food wrapped itself, does it ?
What is bioplastic ?
To be considered a bioplastic, materials used need to be biodegradable and come from renewable biomass sources. Its use, as opposed to regular plastic, aims to reduce traditional plastic waste that threatens the environment. From clogging sewage to polluting the oceans and threatening several marine species that eat it as a mistake, regular plastic usage needs to be urgently decreased.
Usually made from vegetable starch and glycerin, the starch-based bioplastic is built upon long polymer chains that result from biomass starch (like corn-starch) combined with glycerol (like glycerin) under heat. There are other forms of bioplastic, apart from the starch based, like PHB, a product of bacteria processing glucose and PLA, which is a semi-biodegradable easier to produce in large scale, as its manufacturing process and its qualities are similar to that of PET, a fossil-fuel-based plastic. Here’s a very visual example on how corn is used industrially to generate plastic.
I decided to make gelatin-based bioplastic, as it is actually easier to work with than starch and should produce stronger pieces of solid plastic, so that I could later lasercut.
Gelatin-based bioplastic is not vegan, of course, as it is made of collagen obtained from various animal body parts. It is commonly used as a gelling agent in food, drugs, cosmetics , etc.
I did my own Bioplastic, following the recommendations from Clara Davis in this FabTextiles documentation. But the recipe is quite easy and with only 3 ingredients: cold water (120g), gelatin powder (24g) and glycerol (6g).
Since this week we had a holiday and I couldn’t wait for the plastic to dry to start experimenting with the laser cutter, I have used some previously made bioplastic to test the sealing process.
I started by putting the plastic directly in the laser honeycomb and used the following parameters for cutting: Power: 3, Speed: 0.3 and Frequency: 1000hz.
It didn’t go very well, the laser cut through the first layer of the bioplastic, but, surprisingly, it didn’t cut though the second layer. I realised that it happened due to the fact that the layers were not exactly joined when the laser cutter went over them and I also clearly had to find a way to make an accurate positioning relation between the laser and the part to be cut.
So I decided to cut a board that would be used to hold the bioplastic together, making sure the borders are joined at the moment the laser passes and also, make all passes in the same register.
I started by doing a sketch in fusion and tried to export as a drawing (as I usually do with all models) and, for some reason I still wasn’t able to find out, the PDF wasn’t being saved correctly:
So, since I don’t have an illustrator license, I decided to jump to Photoshop and redo the shapes, and export is a PDF:
Here’s the file done in Photoshop
The problem is that Rhino (we use Rhino to print from when using the laser cutter) did not understand the PDF file, so I had to redo the shapes at Rhino in the end. Unfortunately, I didn’t save the Rhino file, since I didn’t expect to redo it from scratch and doing it in a hurry, I forgot to save it from our shared computer. But it has been done following exactly the design of the photoshop layout I have posted above.
The first pass didn’t cut through (which was good), but, it just burned the first layer of the plastic, not reaching the second layer. I was using different parameters: Power: 20, Speed: 1.7 and Frequency: 1000hz. :
I decided to go for a second pass with different parameters: Power: 60, Speed: 1.7 and Frequency: 5000hz.. I increased the frequency after reading on Trotec’s website that “if you want to achieve a smooth edge when cutting acrylic, you need higher temperatures and thus this value is set to at least 5,000 to 20,000 Hz. On the other hand, when cutting wood a low frequency of 1000 Hz is necessary in order to achieve, for example, the brightest possible cutting edge.” Since my idea was more to “melt” than to cut, it made sense to change the frequency dramatically.Since I increased the power, I have also lowered the honeycomb 5 cm, in order to defocus the laser beam a bit.
Result:
The result was OK. It did seal the plastic, combining both sides as expected, but the sealing was rather fragile. When applying to much pressure, it could be open, probably due to the lack of adhesion from the other side of the plastic.
So, If I had to make this again, I would:
1 - Turn the bioplastic over so that I could have a second pass of laser from the other surface as well, helping the bottom side to melt more and, theoretically, adhere more to the top layer.
2 - Establish better parameters for having more control over the positioning of the register boards / bioplastic / laser. In my case, I had problems with maintaining all variables (laser 0, honeycomb position -it moved-, wood boards, print file and plastic) in the same register, but it can be done with more detailed planning and repeating the same print job recurrently.
3 - Unless the Bioplastic is made in a somewhat “industrial” scale, it is hard to reproduce the same production parameters perfectly, what would implicate in sealing parameters different every time, depending on the thickness and density of the plastic produced. Therefore, though the technique was interesting to explore, it had to be done under much more controlled circumstances, so that the process could be repeated in scale.