Melting plastics...

[Externet]

Greetings.

Seen a couple of machines that melt shredded plastics in used hot oil for the process of recycling.  Seems there is not much mixing as plastics being heavier, stay submerged by the bottom of the vessel in  a nearly liquified state layer.  Seems the oil is just the media to convey the heat source thoroughly.

What would differ choosing used motor oil, used vegetable oil, used transmission fluid, used hydraulic oil ?  Would any be more convenient than other ?

[Enthalpy]

Hi Externet!

Some polymers are excluded here: the polyolefins (PE and variants, PP, the rare PB, PMP...) as they dissolve in mineral oil, even at room temperature. The chips you saw sank neatly in oil, this indicated polymers heavier than polyolefins.

Transmission oil, brake oil, hydraulic oil is about the same, except that brake oil have additional standards and names. This description is too vague: several families exist with completely different chemical compositions, at least 6 for brake fluid. For instance polyglycol+water would supposedly lose water before the polymer melts and would probably dissolve POM, maybe polyesters. They also include many additives, often undisclosed, that may pollute the polymer chips. Some are denser than many polymers. Not my first choice.

While mineral lubricant oil is more stable at heat than vegetable oil, I see drawbacks to it. Almost always, it contains polyglycols to stabilize the viscosity at heat, and these are better solvents for POM and maybe polyesters. They always contain many additives, often undisclosed, that may pollute the polymer chips. When used, they also contain metal nanochips that will botch, or at least taint, the recycled polymer.

Vegetable oils are at least better known. They include no additive usually, just the mix of triglycerides. Their stability at heat varies, where saturated oils like coconut or palm survive better than highly unsaturated ones like linseed, and traditional peanut, sunflower, maize are good. This is known from cooking. Used cooking oil contains impurities that are often removed, first by good filtration: check what is done before burning these recycled oils in Diesel engines.

In every case, I'd try to have a flash point well over the operating temperature, but this looks difficult.

Hot liquid is interesting to melt chips quickly but has drawbacks. Did you consider microwaves? Hot nitrogen with active movement?

[Externet]

Thanks again for your always extensive and complete expertise.

Preference to filtered used cooking oil of the proper flash point will then be.  Microwaves not considered as aiming to third world processing.  Something in the style of :

----> https://www.youtube.com/watch?v=wPe5a8lGAhg 

Finding a product that highly motivates production is  key. At some places they report motor oil, others cooking oil.

---->  https://www.youtube.com/watch?v=594HFX_Oh40

 

Edited December 28, 2019 by Externet
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