Introduction: How to Recycle HDPE Plastic the Easy Way

Picture of How to Recycle HDPE Plastic the Easy Way

After spending 2 hours cutting up a single milk bottle with kitchen shears, I knew I couldn't do it again.

I felt like a late night infomercial and may have actually uttered the phrase, "There has to be a better way!"

Turning old milk jugs and bottle caps into useable stock for making. In this short video I process a 2 milk bottles and about half a dozen bottle tops into a 1 1/2" x 3" x 5" turning block.

You could just as easily press this into sheet material for use in box inlays or scroll saw art. The possibilities are endless. The total processing time was under an hour from bottle to blank! Less than waiting for a glue up!

The result is a stunningly colorful blank ready for some new project!


pbarsamian (author)2014-11-16

Of course I am wondering about 2 things: 1.) the state of the expensive Vitamix blades after grinding plastic, 2.) the fumes from melting the plastic

kludge77 (author)pbarsamian2014-11-16

2. No fumes that I could detect.

1. The Vitamix made drinks Wednesday and performed as per usual. That being said, my wife has made it very clear it doesn't get to go on another shop field trip... :)

Rimwulf (author)kludge772015-12-07

of course its a "VitaMix" it can grind cement into dust yet it can't do a thing to strawberry seeds they're impervious to the vitamix powers

Rimwulf (author)kludge772015-12-07

of course its a "VitaMix" it can grind cement into dust yet it can't do a thing to strawberry seeds they're impervious to the vitamix powers

ChrisK12 (author)kludge772015-03-27

Yeah, those fumes your olfactory bulb can't respond to are always really safe to inhale...

mjohnson35 (author)ChrisK122015-11-08

HDPE does not fume below 350.

inkerbel (author)kludge772014-11-21

I'm curious if the plastic pieces scratched up the container at all. I honestly don't know if my husband would have survived doing that to my Vitamix!
That said, I've been tempted to put non-food items into my Vitamix container as well, so I'm considering buying a second container if I can find a used one somewhere at a price I'd be willing to pay.

GenerallyOdd (author)kludge772014-11-17

Every workshop needs its own my opinion...wish they weren't so expensive. But the good news is that you can often pick up a blender at a rummage sale for a couple of bucks. And if you take out the guts, they're mostly recyclable.

pbarsamian (author)kludge772014-11-16

that is so strange. my father, in his reduced state, accidentally melted a bunch of that stuff and the stink was terrible.
Your wife is smart!

radamquigley (author)2014-11-13

I have done this but use the Christmas cookie tins as the mold. It allows the plastic to melt into bricks, and you can cut down to size from there.

Light_Lab (author)radamquigley2014-11-16

Polymers seldom melt sufficiently to consolidate without some compression. Kludge77 did the right thing by softening then pressing into a mould. If you just heat polymers for a long time and/or very high temperature you will get massive decomposition (yellowing) before they melt into a solid block.

blorgggg (author)Light_Lab2014-11-20

Nice point

RedBinary (author)Light_Lab2014-11-16

Time is an issue, however most types of HDPE in small enough granules will join without compression. As I said elsewhere in the comments here I would actually recommend experimenting with a temperature range of 400-450F as that is the temperatures we use at my work to get the plastic to a nice light consistency without burning for cleaning it from metal tooling. The process uses high pressure compression and a temperature profile starting at around 330F and ending in the range of 350-365F. This lower temperature for the process allows for better surface appearance of the pressurized plastic and quicker cooling for the industrial process, but for creating "ingots" that cool at room temperature over a non-specified "cycle time" it would not be an issue. You wouldn't expect to see any decomposition of HDPE at 450F until molten at an extended time frame of maybe 20 or 30 minutes. Maybe even longer than that.

Light_Lab (author)RedBinary2014-11-19

Yes HDPE powder can be sintered as low as 130C depending on grade. One of the research projects I worked on involved developing sintered polyolefin prosthetics. Sintering provides an open pored structure and this porosity weakens the material mechanically. I am sure that most uncompressed sinters would not survive lathe work. Moreover the porosity is very dependent on the polymer particle size. Roughly stacked polymer chips would produce a poorly sintered structure.

Sintering density is improved with elevated temperature and time. Polymers are good thermal insulators and getting the heat to penetrate to the centreof the powder of a large enclosed mould can take a very long time. Often hours not minutes. The outer layer is subjected to the full time and temperature. In our work we found the manufacturers decomposition temperatures to be very optimistic.

I once made an experimental series of consolidated sintered blocks (~150mm cube) using a range of conditions up to 250C and up to 4 hours, easily eclipsing the conditions you suggest. Every reasonably undecomposed sample turned out with only a consolidated skin ~2-3cm thick, the centre particles were still free flowing. I eventually achieved marginal success by repeatedly pulling the hot mould out of the oven and standing on it and then returning it to the oven. i{^_^}

BUT it does depend on what you call acceptable mechanical strength, density and decomposition; the medical standards for prosthetics are very strict. If what you made didn't fall apart; smell really bad; or end up in a child’s mouth it could be acceptable for some applications.

kludge77 (author)radamquigley2014-11-13

That is brilliant! I'm totally going to do that!

I think those blocks would be great for turning pens You can find kits for that at Rockler Hardware

radamquigley (author)kludge772014-11-13

you will have to flip it once or twice so all the air trapped inside gets pushed towards the surface. The smaller tins (the rectangular ones) work best and punch a hole or two on top to vent the gas it lets off. For some reason placing large strips on the bottom and then adding smaller cut pieces keeps it from burning or getting that brown edging. Hope it helps...

StevenL107 (author)2017-10-01

Maybe I need to find a Vitamix blender because I chunked a bunch of milk bottle strips into my Cuisinart blender for five minutes and it had zero effect.

Eddie_T (author)2015-11-19

I would like to make a sheet that could be rolled into a cone shape to make a cyclone dust separator similar to the Dust Deputy. Maybe starting by cutting and flattening 5 pound whey protein containers, then somehow joining them into a larger sheet.

trmoses (author)Eddie_T2017-02-14

a lot of work for a $50 dust collector... but maybe. I have had some success with melting plastic into sheets in a cookie tray.

trmoses made it! (author)2017-02-14

I cut my milk jugs into 1 inch by 4 inch strips with trauma shears in just a minute or two per jug. These melted easily at 400F in under 20 minutes, and went under the clamp. No joy at pulverizing in my food processor. No cool speckled look, but appears solid, no voids or inclusions. Also, my chop saw produces great shavings, but I'll need to set up a collector without all the wood dust if I want to re-use them.

trmoses (author)2017-02-13

Pbarsamian: The fumes are there and bad for the lungs. Nothing that cant be ventilated away. Maybe not a good winter project without a fume hood or ventilation system...

Mark 42 (author)2016-03-23

My wife has a BlendTec blender... expensive, but very robust:

carol.franks.927 (author)2014-12-31

What if you left the bottle/jug complete and used a torch or something hot to melt it down?

This type of plastic needs to be heated carefully or it will decompose instead of melt. If you tried it with a torch you'd most likely end up with a flaming lump of goo and a bunch of toxic fumes. Anything over ~500 degrees F will start it decomposing.

canemaker49 (author)2016-03-18

i make walking canes. i can see some very unique handles in the future. i want to molds for some crystal door knobs i have. another branch of creativity, thanks!

DragonDon (author)2016-03-02

I finally got around to getting an extra blender/toaster over so the wife won't complain :)

I took a plastic jug, cut it up into relatively small sizes, with the notion to make the 'blending' a bit easier but what I found was that the plastic pieces just for 'battered around' and not much chopping action.

I tried on various settings, high-low, tried pulsing.....nothing seemed to help. Just not the right blender? Should I have left the pieces bigger to start with?

DragonDon (author)DragonDon2016-03-08

I just figured out why....the blades got bent and broke. There was nothing to chop that's a cheap blender! I need one of these!

Mallymal (author)2016-02-05

wow, that is epic!! I was just looking on eBay for plastic for turning and it's so expensive. That is pure genius. Did you try melting it in an old pan on a camping stove? I might try that (probably outside!.,)

The Fishing Hobby made it! (author)2016-02-03

I really like this idea. I needed to make some plastic parts and this allows a little creativity in colors. This is a purple and black cylinder that I did. I used a 2 & 1/4" aluminum cylinder and turned some maple blocks to fit inside and used a manually operated log splitter (the type that uses a bottle jack) to compress it. This is after a quick rough machining on a hobby metal lathe. This stuff is going to work out great for the parts I need to make! Thanks for the video, it gave me a great head start on how to go about it.

Longwell (author)2016-01-21

I heard the oven timer ticking. Please tell how long and what temp. A regular blender doesn't do this. Can't afford a Vitamix. Are the cutters different or just hyperspeed? If you're going to turn it, why not use a cylindrical mold? Thanks

Rimwulf (author)2015-12-07

So. Many. Baking jokes. Must resist.

holymoses (author)2015-08-10

I would try to refresh the sandpaper on my grinding machine with it, jist like a big rubber....this would also work with a hand full of plastic bags.

Ever tried yourself?

Tomahawk92 (author)holymoses2015-08-11

Seems like it might be too stiff for that. The rubber blocks they use for cleaning sanding disks is softer, like a bump stop for semi trucks or a very stiff eraser. This is going to be the consistency of a plastic cutting board.

patatarium (author)2015-03-09

you can makr games dices

Rifco (author)2014-12-08

Love the instructable. I was thinking of a great way to make a uniform thickness for smaller thinness requirements that might be hard to male with a mold and came up with the idea of using an old pasta machine to make thinner pieces for making workshop jigs. One of the hand crank, adjustable thickness models where you just add a still warm blank and roll to size.

Anrym (author)2014-11-21

Do you think this can be used to make a plaster mold?

pbarsamian (author)2014-11-21

I just looked up plastid #2. It can emit estrogen like fumes, and is very often corrupted with BPA. Even with a hood and vent system, melting this appears to be a pollutant and health hazard. I love the idea of recycling yourself, but this doesn't look like a good idea.

paintphone (author)2014-11-21

Im stoked to make a brick !

greendragonflyz (author)2014-11-20

Deadly fumes?

antagonizer (author)2014-11-20

I've actually built and designed the automation for plastics recycling and granulation and set up a few plants, and what you're doing is identical, only on a smaller scale. Well done. One thing to warn you about, though, is many manufacturers line their type 2&4 containers with type 8. Regulations in Canada and the US basically exempt them from listing it on the packaging, I.E. PETE uses HD caps and rings but they only list the PETE. Just be careful when you heat it as a few people in my industry (including myself) have had health issues related to type 8. You can do the flex test. Bend it in half and if a layer, on the inside, peels away like paint, you know it's lined.

sbradley2 (author)2014-11-20

Excellent instruction, going to give this a serious try. No worries about using the blender or the oven either. I live on my own :)

anujpatel89 (author)2014-11-20

This looks awesome! I do have a question though. I'm not a chemist at all, so if it's a simple question, excuse me. In this process of melting, would you not accidentally be inhaling any toxins?

Igor22 (author)2014-11-20

Isnt this toxic?

amansinghaljpr (author)2014-11-20

Your instructable was very nice and you should apply for make energy contact

kludge77 (author)amansinghaljpr2014-11-20

Thanks! I'm glad you liked it!

swkippy (author)2014-11-20

why not use it for 3d printing filament?

r-philp (author)2014-11-13

Did you have much of a problem with fumes when heating your plastic?

kludge77 (author)r-philp2014-11-13

Honestly? None. I'm told if you keep the heat under 350F there aren't fumes. lacquer smells worse that was I was doing...

RedBinary (author)kludge772014-11-16

Wasn't sure where to make this comment so I'm putting it here and hopefully it's the best place for it. I've worked in commercial molding of HDPE for the last >20 years. I have to admit that I was NOT expecting the blender to shred the plastic so nicely! The result looks very similar to what comes out of our industrial granulators and shredders that we use to recycle processed scrap back into the system!

There are a lot of varieties of HDPE - different specific densities, chain length, etc. None of them, however, should put off any kind of toxic fumes - even when actively burning. Colorant may or may not, though. Regardless, 335-375F is the range we typically use in our temperature profiles. When we are disassembling tooling that we want the plastic to be most malleable we will bump that area up to anywhere between 400-450F. This would still be a safe range for you to melt your plastic and would allow it to form to your mold in a mass with minimal handling for air pockets. The higher end of that range could result in burning of the plastic that is exposed to oxygen if left for too long, however.

About This Instructable




Bio: Come spend some time in the shop. I'm a hobbyist woodworker and professional computer geek in Northern California. I guess my projects will vary ... More »
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