Since we chose FDM printing as our manufacturing method for the Off-Grid computer we had an almost overwhelming amount of different plastics to choose from so how did we narrow it down?
We had some specific goals with this product to help us, it needed to be fairly impact resistant since we envisioned this as something you'd keep in a bug out bag and maybe in some rough conditions with, and we also wanted to make sure the plastic wasn't going to ever deform from heat. This immediately eliminated PLA as it is not good in either of these departments. So next we looked at PETG which has good impact resistance and can withstand temperatures of about 160° Fahrenheit this works well as thats higher than inside of a car will get even in the middle of the summer. So PETG was a good choice for the outside case but we wanted the inner shell and the actual Raspberry Pi case to be a bit more rigid so we opted to use carbon fiber reinforced PETG. For the clips we chose carbon fiber reinforced polycarbonate since it will be constantly under strain while closed and this filament does not stretch when under pressure and for the gasket we chose TPU since its very similar to rubber and gives us a good seal to keep water and debris out of the Raspberry Pi.
Now that we had all that figured out we thought it would be fun and a good idea to try some other materials the first variant we made used the carbon fiber reinforced polycarbonate from the clips for the outer and inner shell meaning the entire case had a much higher temperature resistance of about 230° Fahrenheit (which means you will be past the safe temperature of the electronics in the Pi before the case has any issues) as well as much better impact resistance and a tensile strength equal to pure aluminum it's hard to imagine a situation where this cases limits would be tested, one draw back of this material is that the amount of carbon fiber in it means that it is only available in dark grey. After that we looked at glass fiber reinforced polypropylene which has some interesting properties that we thought might be useful such as having fantastic chemical resistance. Lots of plastics are susceptible to chemical damage even to solvents you may use all the time such as rubbing alcohol! This damage may not be apparent at first but over time it can weaken the plastics and make them very brittle. Glass fiber polypropylene however just brushes those off it can take acetone, hydrogen peroxide, hydrochloric acid, formaldehyde, sulfuric acid, nitric acid, motor oil, and more no problem. Glass fiber polypropylene even has a higher temperature resistance than carbon fiber polycarbonate at 280° Fahrenheit, it is however less impact resistant I suppose you can't have everything.
Those are all we have for now though in the future we would love to add more and we already have ideas such as a UL rates self extinguishing plastic, Nylon, and possibly glow in the dark filaments.
And of course during the process of figuring put which plastics to use we went out of our way to find and use American ones however there isn't many companies producing filaments in America almost all of them are Chinese so while we couldn't use all American filaments we made sure to at least do busines with companies that are investing in America, the glass fiber polypropylene, carbon fiber polycarbonate and TPU are all from Prusa who actually does make filament in America however those specific ones are made in the Czech Republic. The PETG is from Polymaker who make some filament in America however they do not specify which ones are made in America or not. In the future we are looking to purchase exclusively filaments made in America!