Plastic Smithing: How to Make Your Own HDPE Plastic Anything (DIY Plastic Lumber)

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Introduction: Plastic Smithing: How to Make Your Own HDPE Plastic Anything (DIY Plastic Lumber)

About: Hi! I'm Star Simpson! I'm a real me! See more at [http://stars.mit.edu stars.mit.edu]. photo by [http://bea.st/ Jeff Lieberman] (http://bea.st) stasterisk - my name is Star, and when I was 13 I si…

How to make really good hard plastic while reusing and recycling plastic bags at home! Via this method, you can make ANYTHING you want to, out of hard, lightweight, real plastic that's astoundingly durable. It comes out very similar in texture to recycled plastic lumber.

best of all, this method involves no fumes!

I'm gonna show you how to make plastic wheels for your robot!

I first heard about stewing plastic bags to make new things from Dave Huebsch's book " Village Assignment " about interesting adventures had while running a charity/NGO (" Common Hope ") in Guatemala. He, amazingly, repaired the bottom weight-carrying main bearing of a washing machine with a big plastic disc made of stewed plastic bags, which actually was such a good stand-in replacement that it held up for several years. (and here are some more Guatemalan Handy Tricks)

I had to try it right away, and the first couple times I just burnt plastic, until I came up with this method.

By the end of this, you'll be able to make yourself a knife sheath, mold around your shoes and make DIY hard-toe sneakers, wheels, bearings, bushings, or any kind of plastic part! Take pictures and post them in the comments!

Step 1: Materials

Collect all the plastic bags you can get, they shrink down a lot.
Shredding them will make your final texture finer.

Use an old pot that you aren't going to use for food any more, or get one secondhand for really cheap at a thrift store.

Find a stick or something else you can use for a spatula.

I liked the clothespin a lot because I could pick things up as well as stir.

Oh, and oil! (I used canola because it was right there next to my stove. If you're, for example, making a bearing you can impregnate it with your personal favorite grease.)

So grab your favorite oil, here's why:

Plastic bags are made of LDPE (low density polyethylene) which melts at 248 F.

I got the temperature wrong and tried doing this in a homemade double boiler filled with water (to regulate the temperature to water's boiling point), which, of course, just made hot plastic bags.

After the double-boiler mistake I re-read the LDPE melt-point and discovered my folly! So I came up with melting them in oil.

Cooking oil boils around 350, which is far too hot for plastic, and which you don't want anyway (splashing boiling oil = no fun unless you're a hun), so I keep it to a nice low-viscosity canola oil heat and things work just fine.

If you wanted a smooth, non-oily finished surface, consider using wax instead.

ALSO: oil is not required per se --
if you had a constant temperature hot surface that you could guarantee to keep down around the melting point, you could do this just fine with no oil or wax!

Step 2: Add Oil, and Stew.

It doesn't really matter what polyethylene you use, you can melt HDPE plastic bottles in too, if you want.

That is, Resin Identification Code #2 and #4 are both good.

Polyethylene Terephthalate, that is PETE/PET or #1, may also work.

EDIT: Thanks to reader concern, I will state what may not be obvious from the pictures: there are no fumes. There's no smoke, no fans, no inhalation hazard. If there's smoke or fumes, you're doing something wrong and you're burning the plastic. That's why you use oil for temperature regulation.

The plastic bags do this alive-shrinky thing that looks really neat, so I took a video!


Step 3: Mash It

When it's tacky like chewing gum, start mashing it around to get the different bag-lumps to stick to each other. A hand blender would be exceptionally helpful in this situation, but I chose to merely wreck one of my mom's forks instead.

Step 4: Get Moldy

Now, while it's still pliable, put it into the form you want!

Since I'm just experimenting, I grabbed a salsa container that looked about the right shape for a wheel mold, and a wine bottle to make the hole in the middle.

I don't know any special techniques for molding and casting, but matt, rachel, bilal, paul, freemanmfg and smooth-on do!

If you were a molding ninja, you could make a plastic positive of your own face!

Step 5: Freeze

Let it cool like cookies, or if you're impatient, make it cool faster in the freezer.

Step 6: Enjoy!

There's the finished thing. It's got a lot of visual texture/color swirls, but it's actually a pretty regular surface. The circle turned out very well, and you can carve on this, machine it, turn it, and drill it, if you want something more precise.

This shows the finished product, the wheel, as well as another disc I made, and a video of just how surprisingly bouncy homemade plastic is.



Improvements to make:

I'd love to try using wax, instead of oil, so that the final surface is less greasy.
Shredding the bags beforehand would probably give a more homogeneous texture.

Also exciting! If you machined down a brick like this into large-ish chunks, you could feed them to your homemade injection molder! DIY action figures, hooray!

2 People Made This Project!

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386 Discussions

0
KarenP139
KarenP139

4 years ago

I tried melting a block of polyethylene in an oven today. There was a lot of smoke and the outside was starting to brown The polyethylene had softened (and gone transparent) but was not at all melted. There's a chance that the smoke was at least in part from paraffin left over on the tray from the last thing I melted, but that wouldn't explain the browning. Is it normal for the polyethylene to do this? I'm surprised I didn't get any melt at all.... maybe it needed more time, but with the smoke and browning, I didn't want to risk a fire.

Is the oil how you prevented smoking/browning, aka keeping it away from oxygen? Does it just melt at the bottom of the oil? How do you separate the polyethylene from the oil? Can you just pour it off? My purpose of melting it is to coat some aluminum tube segments.

I could always try melting it in a microwave (in a glass jar), but I only have one microwave and don't want to ruin it... I tried setting things up to melt it with an acetylene torch outside but couldn't find a lighter that worked, and didn't have the nenn to go to a store and pick up a new one :Þ

0
KarenP139
KarenP139

Reply 4 years ago

Just an update... I tried it in a pan on the stove, with a layer of oil over it. First I tried motor oil, thinking that it'd be a lower risk of burning, but it very quickly started giving off a bad smell, so I wiped up what I could and replaced it with cooking oil. I've hit a point where it's not melted, but I'm not comfortable turning up the temperature any more because of the amount of plastic (or residual motor oil?) smelling smoke coming off of it. So again no luck :(

0
KarenP139
KarenP139

Reply 4 years ago

Okay, it gets weirder. Now that it's cooled I could check each individual component. The smell seems to be coming from the plastic, not the oil. The oil just smells like used cooking oil. However, the oil does not *look* like normal used cooking oil, it looks... don't know how to describe it, "partly polymerized"? Like, still fluid, but slightly gelled, or containing some slightly gelled material? Yet it's far too cold for polyethylene.

Not sure what's going on here....

0
Chimonger
Chimonger

Reply 2 months ago

The fumes you smell, are toxic, & can do lasting damage to your airways. Do not heat plastics indoors, much less motor oil!!!!!!😱

0
capturedfire
capturedfire

Reply 2 years ago

melting plastics in hydrocarbons is how jellied petroleum (napalm) is made

0
KarenP139
KarenP139

Reply 4 years ago

(might just be that the oil was thick to begin with, I don't know)

0
Sherbert-
Sherbert-

Reply 2 years ago

don't try the microwave. It wont work. ! Microwave needs water ! it cant heat dry stuff

0
Chimonger
Chimonger

3 years ago

Pretty cool! Someone some years ago, learned that by mixing different plastics together and form bricks, the resulting bricks were stronger than regular bricks...something about cross-linking polymers.

Your donut blocks could be interesting as stacked on rods, maybe chicken wire on both sides then plastering inside and outside of the "wall". Or make a mold that could do a double-donut [an "8"], do the blocks could be interlocked on rebars.

0
JacobE62
JacobE62

Reply 1 year ago

I've been searching around on the internet trying to find something about cross-linking polymers with recycled plastics but you're the only source that says it's possible... where did you hear that? What plastics do you think could be combined? HDPE and PETE?

0
Chimonger
Chimonger

Reply 1 year ago

https://www.forbes.com/sites/lauriewinkless/2016/07/21/these-houses-are-built-with-blocks-made-from-waste-plastic/#3b0c7fa17894
Is one method; requires shredding/cutting, mixing.

https://www.ecobricks.org
Another method...uses plastics as found, mostly.

But this is closest toehold youtube I saw years ago:
https://www.instructables.com/id/HomemadePlastic/
Best yet: less fumes, because the plastics are stewed, not higher-heat melted.

The old Youtube I saw, the guy specifically mentioned 1st melting one kind of plastic, then melting another kind, then while both were still liquified, “folding those 2 together”, which caused the 2 kinds to react together, to form a very strong [structurally strong!] brick, after pouring it into a brick mold.

https://www.youtube.com/watch?v=W_XUJwINdLw
This one uses a sandwich griller timely his plastics together.
There are more out there.

Melting plastics emit dangerous VOC’s [volatile organic compounds..chemicals that go into the air and water, which can make living creatures sick, worse over time].
Perhaps the sandwich cooker and the stewing methods, emit less VOCs?
0
JacobE63
JacobE63

Reply 1 year ago

All of your links don't actually reference your claim that there are two types of plastic that you can melt together to create a stronger plastic... if you can try finding that old youtube video that would be helpful

0
Chimonger
Chimonger

Reply 2 months ago

It’s been several or more years ago. Those are the best I could come up with; unable to find original site, as that was stored on a computer that croaked about 3 computers ago.
The guy was using something like milk jugs as one kind, & plastic bags as another. It made a marbled effect, as he didn’t stir it to mix it 100% mixed. He did some shade-tree pressure & strength tests, which showed the could be weight-bearing p, say, in a wall of a small building. That was compared with blocks made of only one kind of plastic, which were not as strong.
This project reminded me of that.

0
NoviceRick
NoviceRick

Reply 2 months ago

Its very strange to me its so hard to find information on this. But I have been reading how plastic is made and it is just chains of hydrocarbons, different plastics have different length chains. The longer the stronger. So it shouldn't matter what plastics you combine, other than that different plastics have different melting/boiling temp. I suspect the truth is so simple its just not talked about. From what it looks like to make homogenous plastic you just have to break it down mechanically to 1-3mm size pieces, heat and kneed it, and at that point it can already be injection molded or turned into pellets (PE pellets)

1
EyanM
EyanM

Reply 1 year ago

I'm looking for something very similar like in a bread pan

1
10bird.girl
10bird.girl

2 months ago

I save all my plastic bags and slice them into strips, store them until the grocery bag is full. Then, I line a foil turkey pan with parchment paper (so the plastic doesn't stick to the pan, which is harder than anything to peel off). Parchment paper prevents the sticking and in the over it goes at 250 F for as long as it takes. Once the bags begin to soften/melt, I place a parchment over the top then a heavy plate that fits the turkey pan, and a couple bricks on top of that to squash it down. When it's melted into a solid block of plastic, I dump it into the recycle bin because I don't know what else to do with it and I refuse to throw the bags into my regular waste can and see them flying all over the waste mgmt. site.

1
10bird.girl
10bird.girl

Reply 2 months ago

Maybe I start using them for bricks in. my garden.

0
Teressa2019
Teressa2019

1 year ago

Hi i am making a diamond! Plastic mold comes in handy along with glitter and coloring

0
wabana
wabana

Question 2 years ago

Does anyone have knowledge of melting plastic and retaining its pliability? I want to make molds for pouring concrete into. The plastic I have melted so far has set a bit too rigid for casting anything with undercuts. Recycling plastic for making the molds for the concrete would make good use of what would otherwise be pollution.