Homemade plastic recycling?

[Sporqster]

Hello, all,
Didn't know exactly where this post would belong, but I was curious as to if anyone had any experiences attempting to re-melt similar type plastics for the purpose of machining it, and what works best? Assume I know nothing and I'm about to ask dumb questions, and make rediculous suggestions.

obviously, compatible plastics would need to be collected... if, say, I collected a pile of ABS junk, ground it all up into little bits, put it in a metal shoebox - sized container sprayed with mold release and put it int the powdercoat oven at like 300deg, would I get a nice slab of ABS to machine goodies out of?

Polycarb?

anything that DOESN'T work? I would think I would avoid PVC as it gets a bit stinky when it melts...

[joecnc2006]

Originally Posted by Sporqster Hello, all, Didn't know exactly where this post would belong, but I was curious as to if anyone had any experiences attempting to re-melt similar type plastics for the purpose of machining it, and what works best? Assume I know nothing and I'm about to ask dumb questions, and make rediculous suggestions. obviously, compatible plastics would need to be collected... if, say, I collected a pile of ABS junk, ground it all up into little bits, put it in a metal shoebox - sized container sprayed with mold release and put it int the powdercoat oven at like 300deg, would I get a nice slab of ABS to machine goodies out of? Polycarb? anything that DOESN'T work? I would think I would avoid PVC as it gets a bit stinky when it melts...

THERE IS SUBSTANTIAL RISK IN MELTING/HEATING PLASTICS [ =POLYMERS ]
WITHOUT A FUME HOOD AND WITHOUT KNOWING EXACTLY WHAT IS IN THE PLASTICS.
IT IS NOT RECOMMENDED FOR THE REASONS LISTED BELOW AND SOME THAT DON'T
COME TO MIND:

1. There are two classes of polymers: thermoplastic and thermosetting.
The former will soften when heated; the latter will never soften, just
decompose, when heated. Bakelite is an example of the latter.

2. Some polymers produce toxic gases when heated. For example, vinyl
chloride produces HCl gas when heated.

3. Plastics are not pure materials; they are formulated products. Some
of the chemicals used to give the plastics their desired mechanical and
physical properties also form toxic vapors when heated. An example are the
common phthalate plasticizers.

4. Some polymers "unzip" when heated evolving monomer vapors. Acrylates
polymers are notorious for this. Acrylate monomers are toxic.

A safer route would be to use water dispensable gums [ e.g. algenates ]
like dentists use to form a denture. These harden and can be used to form
models from plaster of Paris, or self-reacting styrene formulations
available at hobby stores. Even in this case adequate ventilation is
necessary because styrene vapor is also toxic.

[Sporqster]

My purpose was to use things that would otherwise be trash and make it into something I can practice on the CNC with... and test up fit of parts made with a program before wasting a $100 block of aluminum on it... even if I lose some of the ideal mechanical properties of the material by remelting it. I also expect a techni-color spotty browinish mix of colors. no biggie to me for this purpose.

Sounds like my primary safety concern is the production of noxous gasses. Thus PVC's are out. The oven is vented and out in the garage - not in the living space. It's the oven I use for powercoating, so no food would be cooked in it, no concern there. Lets assume I put a big ol' box fan next to the oven and blow any escaping gasses out the open garage door. And I keep my distance for the most part. And wear a gas mask. Noxous funes should be minimized to levels generally encountered while cleaning the bathrooms.

Is there anything I can tell from the recycling codes on plastic parts that would tell me if it will be thermosetting or thermoplastic? Is this something I can google?

is there anytype of material that I could grind up and use without much worry of decomposition? From a mechanical properties point of view I would like to use polycarbonate. If I get a bunch of broken plexiglass for free, would it be ok to just melt down and machine on?

[joecnc2006]

What I do Is go to the local Plastic distributor and they have a lot of scraps that they sell by the pound (1.00)

[JavaDog]

Originally Posted by Sporqster Sounds like my primary safety concern is the production of noxous gasses. Thus PVC's are out. The oven is vented and out in the garage - not in the living space.

The EPA would really get angry with you! They usually don't take well to venting toxic gasses to the outside with no concern for where they go...

A lot of the guys on here use scrap wood to proto parts before doing the final design in Alum. Seems like a better option to me.

[home-tek]

Look at the Machinable Wax.

You can easily machine Machinable Wax without the need for costly and messy coolants or lubricants, because MACHINABLE WAX is "self-lubricating", "non-abrasive" and it will not fuse when machined at high-end spindle rpm's and feed rates.
Unlike wood or plastic, MACHINABLE WAX will not "gum up" on tool bits. Sharp edges can be maintained, accurate threads can be cut and thin wall sections maintained with the quality of surface finish capable of being produced by your cutting tools and machine. MACHINABLE WAX is not cellular, grainy, or abrasive so "voids" in machined surfaces (common with plastics and wood) and "tool wear" are negligible. Machinable Wax will also machine "within designated tolerances" to provide you with a dimensionally accurate prototype that can be assembled for checking.

You can also "saved" the chips, re-melt and reuse the wax!

[Sporqster]

Originally Posted by home-tek Look at the Machinable Wax. You can easily machine Machinable Wax without the need for costly and messy coolants or lubricants, because MACHINABLE WAX is "self-lubricating", "non-abrasive" and it will not fuse when machined at high-end spindle rpm's and feed rates. Unlike wood or plastic, MACHINABLE WAX will not "gum up" on tool bits. Sharp edges can be maintained, accurate threads can be cut and thin wall sections maintained with the quality of surface finish capable of being produced by your cutting tools and machine. MACHINABLE WAX is not cellular, grainy, or abrasive so "voids" in machined surfaces (common with plastics and wood) and "tool wear" are negligible. Machinable Wax will also machine "within designated tolerances" to provide you with a dimensionally accurate prototype that can be assembled for checking. You can also "saved" the chips, re-melt and reuse the wax!

Sounds like that's what I need to get ahold of. And it can be reused until it's too full of dirt to hold together, I suppose?

Where's the best place to get some of this stuff?

[home-tek]

Here is a couple of links:
http://www.freemansupply.com/index.htm
http://www.flexbar.com/PDF/20_21.pdf

[JavaDog]

That Machineable Wax is some cool ****!

Check out their video: HERE

[scwTech]

Hi,

I was wondering if the plastics are best melted in a vacuumn?

Is it heat or oxygen which causes the plastic to degrade, excepting the thermosetting plastics that is.

Thanks
scwTech

[scwTech]

Hi,
Wouldn't melting the plastic in a vacuumn eliminate the problems with vapors and chemical reaction with the air?
Thanks,
scwTech

[Geof]

Actually no because to maintain a vacuum you would have to pump on it, i.e. pump out all the nasties through your vacuum pump.

The way in which many thermo plastic materials are recycled into the solid brownish/greyish/mottled lengths that are used to build deck material or park benchs is by heat and pressure. The plastics are shredded or ground and then mixed in a screw extruder which heats and mixes them together. The pressure has two functions; it causes the plastics to fuse together at a temperature well below their melting point or depolymerization temperature and it raises the temperature at which they start to depolymerize and outgas.