Recycling Vinyl

[Flumixt]

Looking at vinyl windows the question came up of how much the % of recycled vinyl used affects the structure quality.

The question in my mind is just how is the recycled stuff incorporated into the product? Is it just a ground up filler? Or does it get re-polymerized? If the latter there shouldn't be any difference between a virgin and recycled product. I don't see how melting the stuff down re-polymerizes it. If its just a filler it seems to me it would make a LOT of difference.

So! Is "regrind" added to new vinyl just a filler or is it re-polymerized?

 

[MikeHalloran]

For any thermoplastic, regrind is, well, ground, i.e. physically reduced to fine particles, and then added to the melt. It is not converted to a monomer or to the polymer's chemical precursors, and then re-polymerized.

Addition of regrind almost always makes the mechanical properties of a polymer worse. Where that would be a problem, the part designer will specify minimum mechanical properties, or more commonly, max percent regrind.

There is a strong economic incentive to use regrind, because the actual scrap rate of a production shop is substantial. I.e. injection mold sprues for a single shot of product may exceed the mass of actual product produced. For every startup of both injection molding and extrusion, a lot of 'not quite right' product comes out before the machines stabilize and start producing what you actually want. If you can't grind that stuff up and re-use it, you need to rent a really big dumpster.

;---
Re-polymerization, as you call it, is at least theoretically possible for some polymers, but so far as I know, it's not economically attractive and is not done commercially. I'd imagine it would produce some really ugly waste streams, and there would be challenges associated with separating the common fillers like talc, silica, glass fiber, teflon fiber, lead, and who knows what.




Mike Halloran
Pembroke Pines, FL, USA

 

[Flumixt]

Thankyou for the comeback. Very clear! Always wondered about this. Looks like my thinking was at least in the right direction. I never thot about the sprue, slag and startup etc.

 

[moltenmetal]

Mike: you're bringing back old memories- summers during high school I was a "pellet monkey", filling injection moulding machines, grinding sprues and bad parts and mixing the re-grind with the fresh resin pellets. But it sure beat operating a moulding machine! The same task every 25 seconds, all day long...a real waste of a human being!

 

[MikeHalloran]

Mind- numbing jobs like that are generally well- suited for robots ... except this one.

Even when bored out of his skull, a kid can do a better job of detecting when something is not right, and can decline to start another cycle.

... so far. Robots are getting better, and kids are ... not like they used to be. I keep hoping that's only a perception problem.


Mike Halloran
Pembroke Pines, FL, USA