HDPE Recycling

[Lil Foot]

A few years ago, one the plastics suppliers that I dealt with for years stopped selling to the public, and the other went out of business.
I needed some colored plastics for a few upcoming jobs, so i thought I would try recycling HDPE. (High Density Poly Ethylene)
I take no credit for the process- there are lots of youtoob vids showing how to do it. Start by watching some of those. But I thought I'd show what has worked (and not worked) for me. This process is labor intensive, so it may not be right for everyone.

First, you need an oven. I use a couple of garage sale toaster ovens; larger means larger molds, larger batches.
You can use one, but two works better, one to heat the plastic, one to heat the mold.
I don't recommend the kitchen oven, (PO'ed wife) heating will produce whatever smell the contents of the bottle held.
You will need a good supply of parchment paper, (the kind for cooking) this plastic sticks to just about everything but parchment paper.
Some high heat gloves are essential, and a hydraulic press. Mine is 12 ton.
An infrared heat gun is handy, but not essential.

Use only CLEAN #2 plastics, from laundry detergent, antifreeze, cleaning agents, shampoo, body wash, milk & orange juice jugs, etc.

Avoid like the plague anything that contained oil- motor oil, hydraulic oil, gear oil, and the like. No matter how hard you clean, you cannot get the oil residue out, and it will leach out during heating, ruining the whole batch of the plastic. Don't ask me how I know this.

I also avoid any harsh chemicals. (weed killer, bug killer, etc)

Cut the CLEAN, DRY bottles into pieces; about one inch seems to be a good compromise, larger is harder to heat & get rid of air voids, smaller works better, is more homogenous & less trapped air, but is way more labor intensive.
I use a utility knife & LARGE sheet metal snips. Now that I have a sheet metal shear, I will use that.

I initially used wood molds like most youtoob vids, but found they produced too much waste- voids, poor fill in in the corners, lots of warping. (but a good starting point)

I then tried aluminum cans with wood top plates, better because you can heat the can, but still not great.

Molds I machined work the best, they can be heated, and then the plastic can be squished in the hydraulic press.

Caution- PLASTIC & MOLDS & OVEN ARE HOT!

 

[Lil Foot]

Place the CLEAN/DRY cut plastic in/on a parchment paper lined pan and heat to 350F.
If you can heat the mold too, but I never heated wood molds, (obvious reasons) but I heated aluminum cans and not the wood top plates.
As the plastic softens, use the gloves and more parchment paper to "knead & fold" the plastic- for mixing and removing air. The more you stretch & fold, the more "wood grain" effect you get. (1st two pics below)

When you are satisfied (or just tired of the process) place in mold, (lined with parchment paper if not metal) and press with clamps ot hydraulic press. Plastic cools (stiffens) quickly, so don't dally.

All of the rectangles below were done in wood or aluminum can molds, the cleaned up on the mill.
(lots of waste)
All of the rounds were done in the metal molds, and are as molded, no machining done.

Caution- PLASTIC & MOLDS & OVEN ARE HOT!

 

[bird dogger]

That's some very cool stuff, Bill! I can already think of a few fun projects for that process. Very interesting, for sure. Thanks for showing this. Another winter project on my "to do" list!
regards,
david

 

[Lil Foot]

One thing I have been disappointed in is the fact that I still have not been able to produce a single, not mottled or varied, consistent solid color. All the bottle contents, no matter what their content, seem to slightly (or greatly) alter the color of the plastic inside the bottle. So, red is almost always mix of red & pink, dark blue is almost always a mix of dark & light blue, etc. This seems to be amplified by the heating.
The closest I have come is the black bar pictured below. Smaller pieces & more folding may minimize that effect.
On the other hand, the mixed effect is kind of attractive in it'e own right.
I have made several desktop nameplate holders, and seven gavel sets for folks.

Caution- PLASTIC & MOLDS & OVEN ARE HOT!

 

[Lil Foot]

When I put these molds in the press, I put a lot of pressure on them initially, then every 5 minutes or so, I give them another couple pumps. Pretty soon, I can't get any more ram travel, and I know the voids (air) are all gone. After cooling for several hours, I take the bottom of the mold off & use the press to push out the plastic. The result is an extremely strong, dense, stable, easily machined plastic that holds dimensions incredibly well. It produces great finishes with little effort. It is easy on machines & cutters, and it is easy to clean up the chips.

The current molds are 1 5/8" x 13", and 3 1/4" x 8", made from stuff I had laying around.

I have been meaning to take that large yellow, blue, & white round pictured above above machine it into a mallet head, and then put it on a long handle to use as a big plastic mallet, just to see how it will hold up.
Because of the caregiver thing, I haven't had the time to do more of this, but if I do, I'll post again.

Please feel free to ask for clarifications if I haven't been clear on some thing.
Have to cut this short right now to go to the inlaw's again.

Caution- PLASTIC & MOLDS & OVEN ARE HOT!

 

[Lil Foot]

I forgot to mention, plastic with any metal flake effect produces a shimmering effect that is very attractive. Check the 1st pic of the send post.

Caution- PLASTIC & MOLDS & OVEN ARE HOT!

 

[hagrid]

Avoid like the plague anything that contained oil- motor oil, hydraulic oil, gear oil, and the like. No matter how hard you clean, you cannot get the oil residue out, and it will leach out during heating, ruining the whole batch of the plastic.

How could you have possibly discovered this information?!

 

[Lil Foot]

How could you have possibly discovered this information?!

I told you not ask me that!

My 1st attempt at this was completely successful, producing the block in the 1st pic, second post.
The next couple attempts were failures; no strength & de-laminations. I could smell & feel motor oil, so I thought I had failed getting the material clean. I spent an inordinate amount of time cleaning the next batch of bottles, only to fail again. That's when I realized the problem was material from oil bottles.
It just does not work., and it is too labor intensive to waste time on.

Once word got out what I was doing, well meaning friends, relatives, and neighbors began sending #2 bottles until I had no place to store them. I now only accept cleaned bottles, preferably in bright or unusual colors.
1st box (16"x14"x12") is cut material waiting to be used
2nd box (27"x24"x13") are bottles waiting to be cut

 

[johnjk]

Very cool. Have you thrown any on a lathe and turned bowls ?

 

[Lil Foot]

I did a change cup/pencil cup, but no pic.
Right now, I'm limited by the size of the molds I have, but I could make bigger molds, just takes money
(I have) and time. (I don't have)

 

[Russell King]

McMaster Carr sells plastic in various materials and shapes so may be a source for solid colors if you ever must have a solid color.

 

[Lil Foot]

Yup, they are not cheap, but they have a decent selection.
I've actually found some great deals on plastic remnants on eboy.

 

[Russell King]

The color mixture is very pleasing the way you are doing it though.

 

[thirdroc17]

I formed HDPE for 21 years, while you say "Caution- PLASTIC & MOLDS & OVEN ARE HOT!", don't forget to add the fumes you're breathing are toxic.

My doctor told me to get a different job before any more damage was done.

 

[Lil Foot]

You are correct, I neglected to say do it in a well ventilated area. Thanks for the correction.

 

[thirdroc17]

You are correct, I neglected to say do it in a well ventilated area. Thanks for the correction.

I'm far from being good at safety police, but when it comes to heating plastic, it just scares me and I had to say something. HDPE isn't as bad as ABS and styrene is, I'll grant you that. My employer insisted it was "safe", then I went to the library and checked out some organic chemistry books.....

PS: Wish my BX had gear drive!!!!!!!!!!!

 

[Lil Foot]

I neglected to mention that you need to remove all labels from the bottles- paper with glue, painted, silkscreened, whatever. Again, it will affect adhesion. Easiest to just cut them off & discard.
Also, I have never seen any caps that are HDPE, they are always some other kind of plastic, so don't use them either.

 

[skeets]

Ths is interesting. some place I had seen or read about using milk jugs to make a holster kind of like kydex . SO I tried it use an old oven that was being scraped out inthe garage I took I think 3 or 4 jugs and heated them till they were plyable then laid them on top of one another and then heated again,, And laid them ober the gun and pressed them in place with some old heavy foam and clamps. Yes it did work but really left something to be desired to work with

 

[Lil Foot]

Never tried anything like that process, but it would probably work well a vacuum chuck, but that is beyond most home shop capabilities.