Question

Two plastics that are targeted for recycling from household waste are PETE (1) ( plastic soft drink bottles/ peanut butter and salad dressing containers) and HDPE (2) ( milk, water, juice containers/ plastic grocery bags). One of the problems of recycling such materials is separating them. Suppose you have been hired to set up a process for separating large quantities (many tons) of waste plastic that is a mixture of PETE and HDPE. Describe how you might perform this separation.

Any help would be much appreciated!

Answer 1

Hm whenever you have a problem like this it's helpful to know (in terms of physical and chemical properties) what you're trying to separate.

I would heat them up to about 280\(^{\circ}\)C (both of their melting points are below there) and shake them, PETE will sink to the bottom because it's denser. From there you'd need to have a way to separate the liquids, you could scoop up the liquid on the top or drain the bottom liquid from the bottom.



HDPE \(\rho\)=0.93 to 0.97 g/\(cm^3\)
PETE \(\rho\)=1.370 g/\(cm^3\)


NOTE: Although this works, it's probably not economically viable.

http://en.wikipedia.org/wiki/High-density_polyethylenehttp://en.wikipedia.org/wiki/Polyethylene_terephthalate

Answer 2

The links got all mixed up in the post

http://en.wikipedia.org/wiki/High-density_polyethylene

http://en.wikipedia.org/wiki/Polyethylene_terephthalate

Answer 3

thank you so much!

Answer 4

@aaronq i know this is pretty late, but why would you need to heat the substances to separate them?

Answer 5

so they are in the liquid phase @natadani4999

Answer 6

are able to diffuse across one another, and "stack" as i've drawn them above