Johnish

Thanks for the response and link Sensei. It's very interesting. Thanks for your response as well jjoensuu. Having spent some time recently reading about plastic I've come to appreciate how amazing a material it is. Some types of plastic like HDPE and PP have incredibly chemical resistances which is great for storing and transporting caustic chemical. It's cheap, and durable making it great for food packaging. It's hard to imagine modern life without it. It seems such a shame that so much of it ends up as trash. Some day when fossil fuels are more expense I think people will come to appreciate it more.

From my reading various places online it seems that plastic recycling would benefit from a cheap and easy method for identifying different plastics. Resin codes can be used but they are definitely not easy. They require someone to search around on the product to find them. That takes a lot of labor especially sense the codes are in many different places and some times very small. Some products don't have any codes on them at all. An easier way to identify plastic is to use specially made IR-FT spectrometers, but they are definitely not cheap. This limits there use and decrease the economic viability of recycling. Basically it seems to me like right now only municipalities that can afford expense equipment and places with low labor costs can recycle post consumer plastic economically (or at least close to it). Is there a cheap and easy way to identify plastic? Do you think that maybe some cheaper none FT kind of near infra red spectrometer would be good enough to sort different types of plastic? Maybe something that uses an inexpensive photo diode. It seems like a combination of a Lead(II) sulfide photo diode and a silicon one would cover the required wave lengths and be really inexpensive. If not that then maybe try to find an inexpensive Germanium one. As for the rest of the machine I was thinking maybe something with a rotating grating like what was talked about in this video. I've been thinking about how you could keep track of the angle of the grating and so far all I've come up with is put some bright dots on it and use an inexpensive Image Sensor and some software to calculate it. The other idea I've had is to maybe use an Rowland Circle grating like what was talked about on this tread here. Maybe find a way to make some cheap holographic gratings on a piece of aluminum foil and put it into some circular apparatus. For the sensor part I was thinking about maybe salvaging old DVD Drives. They already have a silicon photo diode so I was thinking that maybe if you replaced the laser with a Lead(II) sulfide photo diode it might work. I don't know if the optics in a DVD drive would still work for the weave length involved. I also don't know if the control board in a DVD can be made to work for this. Another issue is that the reader arm moves in a strait line not a circle. I also don't know how big a circle would be needed for the wave lengths involved. Also I don't know how to tell where the sensors are at any given time. Really all this stuff is way over my head. Does any of this have the potential for cheap easy plastic identification, and if not do you have any ideas that do. Thanks.