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





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 []. photo by [ Jeff Lieberman] ( stasterisk - my name is Star, and when I was 13 I ...

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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375 Discussions

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

5 replies

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 :(

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....

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

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

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


Question 2 months 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.

Hi, I think the google videos are broken. I guess re-publishing the videos on youtube would be possible, then re-linking to them here. Please do, I want to see melting plastics! :)

Sorry - My dyslexic fingers again - Should read create strips 3/4" square, or 5/8"square!

Hello all. I am just getting started in Pen making. Will the finished plastic turn on a lathe OK? I could easily make a mould to create strips 3/4" square, or 58" square which are the requirements for a slimline pen. Has anyone any idea how many plastic bags it would require to make a 6"X3/"x3/4" bar? And what oil would be best for this project? I also have an induction hob! Grateful for any replies, John. PS cutting on the lathe will be by carbide cutters. Thanks, John

Can the plastic bags and bottles be melted down enough to pour into a mold like pouring molten metals?

Use a toaster oven ($10 at my local thrift store) heat HDPE, PP, PE or LDPE to 375-400F for an hour, take it out knead it like taffy, repeat 2-3 more times, then let it cool under pressure (I use a wood mold and c-clamps). You end with a hard, solid plastic with no voids that you can drill, cut, sand, polish into just about anything! I make tool handles, washers, repair parts, coasters, cutting boards, etc. The finished product is better and stronger than store bought!

Ok so how will I know exactly what type of plastic the bags are made of? Is there a symbol to look for or what?

Thanks :)

3 replies

Plastic goods are supposed to have the resin code on them. Its difficult for Bags ( shopping bags ) The bags are 99 % of the time LDPE

Could I get opinions on whether or not my idea will work?
-Use an induction cooker to heat a pan filled with HDPE material and a little oil to about 250 degrees. Heat and stir until evenly melted. (I think the induction cooker has the means to maintain a steady temperature.)
-Make a wooden mold that uses a 2x4 for a bottom and has wooden sides and ends. Line the mold with parchment paper.
-Pour (or drop) the melted HDPE into the mold. Lay a piece of parchment paper on top.
-Place another 2x4 on top that's the exact same size as opening on the top of the mold. Clamp the top down and allow to cool.

This should create a solid block of 2x4 HDPE. The length will be limited by how much HDPE I can melt at one time. I'm hoping I can create 2x4 lumber and build a small bench.

3 replies

Have you tried this ? It should work ! Will be good to hear your result

There are mold release waxes that you can apply to your forms.

Strictly speaking, wouldn't the oil be unnecessary (except as a thermometer)? I don't expect it'd ruin anything, though. Wood and parchment paper catch fire at 300F and 400F respectively, so should be no surprises there.

As for the mold, your plan has you creating essentially a square tube. It could be challenging to make the fit perfectly tight with zero bowing along a void for a full 8' 2x4, but I also don't think a perfect fit would be necessary. I think the bigger potential source of problems would be in lining this tube with parchment paper. Just getting it in would be one challenge; you could possibly wrap the parchment paper around a clean 2x4, insert the lumber and then remove it, leaving only the paper lining. But even then, you would need to arrange the parchment paper in such a way that it can't pop out and stick out into the void; you don't want the paper to get caught on the plastic, folding up
and crumpling and pressing marks into your final product.

I think a safer way to ensure a smooth final product would be to make a mold that opens up along the length of the 2x4, instead of just at the ends. This would make it easier to work with the parchment paper liner: you'd just clamp a flat lid over it all once the mold is full. I admit, though, that such a system wouldn't have as much flexibility to account for varying amounts of plastic. It might be possible to make the mold extendible by building it a bit like a pinewood derby car track: long and shallow, with one of its ends (the "car") movable so that the void can be lengthened or shortened as needed.