Plastic Smithing: How To Make your own HDPE Plastic Anything (DIY plastic lumber)

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!

Comments

[truenorthd65]

The answer to the oil residue issue is simple. You used a double boiler with water in the outer vessel and it didn't get hot enough. Just use a double boiler with oil in the outer vessel. The will be no contact between the oil and your plastic and you will get a nice melt.

[stasterisk]

ah, unfortunately the double boiler works because water boils.. and oil burns rather than evaporates, so I feel like you wouldn't get the same effect, and probably that you'd end up with a smelly awful burning (spattering) oil effect instead.

[Broom]

Um, not really true. A double-boiler works because (1) water is an excellent heat conductor, and (2) boiling water holds a constant temperature that is really useful for cooking.

Oil is also an excellent heat conductor, and you can regulate the temperature with your stove settings. It should work well.

[caruncles]

Has anyone tried a blow-dryer?

[cdubnbird]

i successfully double boiled the grocery bags using oil as the medium. i had a lid on the container filled with grocery bags but it was not needed. I operated at a temperature of 350 degrees F for approximately 30 minutes. I first shredded and melted 2 plastic bags and then decided to try a whole bag- it works just as quickly. I melted 18 whole bags and 2 shredded bags in 30 minutes at 350 degrees F in a vegetable oil bath. There were no fumes and the plastic never caught on fire. The only downside to this was that the plastic was extremely hard to form after it was melted it seems to retain the basic shape of a blob or something like that even when i compressed it into a circular mold. Great instructable, thanks!

[themachand]

I'm wondering if you where to shred the plastic and pack a plaster mold and then use an oven/kiln to melt the plastic slowly. adding more plastic as the melted plastic fills the mold.

You would be able to control the temperature to a fair degree and not burn the plastic.

Maybe do in two batches. the first to melt small bits together and form pellets that don't have trapped air bubbles and then melt the pellets together for larger finished items.

[cdubnbird]

 perhaps, i expected the plastic to melt and become a fluid and take the path of least resistance and thus evenly distribute along the bottom of the pan but it doesn't work like this.  the plastic does melt to the point of being maliable but it never turns into a fluid.  and to make a correction i guess i used an oil bath not a double boiler- i didn't know there was a difference. (i used oil in one pot directly in contact with another pot with plastic inside the second.)  a kiln may work better but i believe you'll find that the plastic likes to take the shape it was as soon as it was melted. it's very hard to form.

[atman]

I believe truenorthd65 is trying to describe an 'oil bath' which is not the same as a double-boiler. In an oil bath the inner pot is in contact with the oil, which is heated. This will give excellent temperature control, and one can easily maintain a temperature of 250-300 using a high-temp oil like peanut oil. It does get oil all over the bottom of one's pan, and tends to be a little bit messy in the cleanup generally. But you'll get your plastic truly melted this way.

[imagigadgets]

If you used plastic bottles that were clear, could you forge something clear?
I ask because I'm looking for a cheap substitute for Plexiglass, mostly for its... clarity.

[twotowner]

I decided to try the plastic melting yesterday. I had the opportunity to try it using wax instead of oil because that is what I had on hand. (Wife had a paraffin wax therapy unit she hasn't used in years) I started out trying a double boiler method. But even after getting the wax up over 300F on my candy thermometer, the plastic bag I was testing really wasn't melting much and the milk jug plastic not at all. (I wanted to try the jug plastic because it seemed tougher) I eventually gave up and put the jugs directly into the wax. This worked quite well. I was a bit concerned that the heat had to be up close to 320F on my thermometer to get close to workable plastic. It made me wonder if the thermometer could be in error. With a lot of stirring, I managed a reasonably consistent plastic mass. Scooping it out into the pot I was using for a mold was a little hard. I've got to find a decent utensil for that part that wont hurt the non stick pan and stand up to the high heat. I think the end result of the pour was pretty good.  One thing I would correct the next time I do this would be to thoroughly wash the milk jugs. While I didn't encounter any fumes from the plastic getting too hot, the smell of bits of dried, rancid and then burned chocolate milk is another matter altogether! :p

[nax]

I wonder if the oil/wax serving as a heat transfer medium is the critical factor?

That would also account for the melting without burning: the plastic is heated more evenly. Without the oil/wax, most of the plastic is not getting hot, but the tiny part in contact with the pan is real hot and burns.

I was also wondering about using an electric frying pan or something along those lines.

[zimitt]

Why not just use the oven???

[Qcks]

There's some other ways you could cut the grease besides moving to a wax based processing technique, though it does involve volatile chemicals. Finger Nail Polish Remover (Acetone) and Brake Cleaner or Starting Fluid (types of Ether) would work as degreasing agents too, though for different reasons.

[nutsandbolts_64]

What's the melting point again? I need it in Celsius so that I can adjust our induction cooker to the right temperature to melt it. I'll try to get a smaller one to experiment with outside, there was one mix of plastics that makes really strong plastic. I only remember type 2 plastic, and then type 6? Anyways my point is that experiment w/ different mixes of plastics to get varying qualities. Hope I helped :)

[merkalation]

can you use vegatable oil?

[nodnol]

so many cat toy possibilities. Nodnol tired of buying kitty toys that will break/get lost/get dragged into litter box and thrown away =)

[Unit042]

I tried this bag-melting thing recently, attemting to acquire a cheap, dispensable material from which to make robots. My setup was a pie tin held over a candle. What small heat area there was, was too hot! I also discovered that, once melted, the liquid plastic is actually flammable, sort of.... Anyway, you have some good ideas here. Next time it's a good temperature outside, you can bet I'll have my plastic! (Oh, and feeding this stuff into an injection mold gives me yet another idea: ammunition for a robotic 3D rapid prototyper!)

[ac-dc]

1) Either use thicker metal to spread heat better, or a heat source that is spread out more. A grill outside is a nice option. 2) Cover the top of the pan or pot. Fire requires oxygen, without which it won't burn. By cover I mean just a lid, do not make a bomb by making it a tightly sealed container that won't allow the expanded air and plastic pressure to escape.

[spartandude]

A water filled pressure cooker would work to melt this. You must have a pressure of 29.82 psi (will give you a constant 250 °F). This is actual pressure not gauge. To adjust for actual pressure from a gauge reading add your ambient air pressure to the gauge reading. There are a few ways to get your ambient air pressure (since it changes with elevation): 1) A. look up your elevation (google maps, etc.) B. look up atmospheric pressure on an elevation table. C. calculate. 2) A. Measure temperature of boiling water. B. Look up corresponding pressure in water tables. 3) experiment. To change pressure in a typical pressure cooker add or remove weight from the vent. You can also get an approximation of the gauge pressure by measuring the weight of the blow off valve, measuring the area of the tube it sits on then calculate the PSI. Sorry if this is too complex, but I hope it helps. Peace.

[UnsungMaster]

You could try soaking the final product in alcohol (isopropyl, ethanol, etc). This would allow you to use oil AND avoid a greasy residue.

[Rippedstar]

ZOMG IT ACTUALLY IS BOUNCE :D IMA MAKE IT!!!!!!!!!!!!!!

[ktenney]

What about using a pressure cooker and water? Would that reach the required temperatures?

[HillBilly Homer]

Is there any oil residue?

[stasterisk]

some - you can wipe off the outside with a paper towel and that mostly takes care of it.

[Bondo]

Thanks for posting this! I've been saving up some HDPE (Those red Folgers coffee containers) with the goal of melting it and mashing it into a crude mold to produce a block of plastic that I can drill, mill, saw, file etc. and make something useful or at least purty.

[stasterisk]

Awesome! And you can save the shavings and do the same thing again! Let me know if you improve the technique! I shredded a bunch of bags to try out Auger Duval's suggestion, below, but I haven't tried it yet.