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

by stasterisk

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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!

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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!

i have been doing many experiments with hdpe and i melted down some milk jugs and 5 gallon buckets and bottle caps what you will notice is that milk jugs dont flow as well as buckets and bottle caps do when they are melted the reason is because milk jugs are blow molded and buckets and bottle caps are injection molded hence the higher flow rate of the bottle caps and buckets. however the melted down milk jugs are stronger than the bottle caps and buckets and i did have a lot of luck melting down translucent hdpe containers such as milk jugs you just need to clamp the mold under pressure and you should get very good results i used a cylindrical mold from a pipe and sort of made a piston with scrap metal and i simply melt the milk jugs in the tube and then press down on the piston and when it hardens you have a smooth hdpe round rod i made pulleys this way by turning it on the lathe and gears and the hdpe melted so perfect that it was indistinguishable from hdpe round rod you buy at the store. by the way dont clamp hdpe 5 gallon bottles or bottle caps they will simply flow into the mold without any pressure only clamp milk jugs and other translucent containers under pressure. hope this helps

Thanks for those details. I was wondering why the bottle caps and such seemed to melt 'easier' than some hdpe containers. It's not melting easier, it just flows a whole lot better.

yeah the bottle caps will flow more like honey and the containers have more of a consistency like dough its all due to the molecular chain length of the hdpe. if you make something that requires structural strength with the hdpe such as plastic lumber the best type would be milk jugs or detergent bottles if you want a better flowing plastic for injection molding use bottle caps. one other thing i recently found out was that the melted plastic should be kneaded with oven proof gloves because the flakes of hdpe cut from the bottles may have invisible areas of stress even it looks like it melted together uniformly kneading it will blend the plastic evenly and remove the areas of stress between the melted flakes. eventually i will be able to eliminate this step by building a filament extruder which extrudes flakes into a long filament and then ill be able to chop the filament into pellets because the pellets wont create areas of stress unlike the flakes. anyways its probably not required to do all of this for what your doing but its just some useful information i decided to share

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

you are right about the milk jugs being stronger they are normally blow molded which uses hdpe with a high molecular weight or in other words much stronger than bags. another awesome thing about milk containers is that they are pure hdpe without any colorant added which is great. unfortunately since its so strong it will not flow well into your mold without pressure. what i do i put it in a mold wait till it turns clear and then clamp it under pressure in the same mold this will avoid rapidly cooling the plastic in a seperate mold and will make it very consistent. i have had great luck doing it this way and i can make plastic 2 x 4 s which are perfect for machining make sure you clean the container if you clean it it will be perfectly white without any discoloration and also dont leave it in the oven after it turns clear this will cause the plastic to discolor and take a yellow tint to it

and no oil or wax is needed i the plastic will still heat evenly without it and as long as you take it out when it turns clear it will still be perfectly white

Hey Dean48, I think you missed the point of this instructable. Her focus here was not on how to simply melt the plastic. We all know that heat will do that.Nor is the focus on molding a perfect finished piece. (I think that parts obvious.)Her focus here is on how to do it with NO FUMES. NO FUMES! (I thought it was worth repeating...)That's why all the discussion of oils and wax. The theory and function is that you are submerging the plastic in something else which prevents the toxins from escaping into the air you breathe. Therefore, your comment "no oil or wax is needed" is completely inappropriate.You may have valuable tips to share in general, but you should keep in mind the focus of the instructable. Otherwise, just go make your own.

sorry didnt mean to upset anyone but hdpe is a very safe plastic and is chemically similar to paraffin and shouldnt produce any smelly fumes now with that being said i still reccommend anyone that does it to do it outside or a ventilated area because some kinds of hdpe may have tiny amounts of additives in it while not being neccessarily harmful it would still be better to do it in a ventilated area. anyways oil will still allow toxic substances to release fumes such as lets say your melting pvc which is a completely different kind of plastic that does release toxic fumes when melted the oil would not stop the fumes from being released the fumes would still bubble to the top of the oil and then escape into the air, by the way you should never melt pvc as it releases very nasty fumes when melted unlike hdpe.

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.

After I take the plastic and oil mixture off the burner, do you think it would be okay to add acetone to break down the plastic further into a liquid? I think I read that LPDE (plastic bags) is soluble after 115 F. So I was thinking that while it is still hot, I could add acetone to break it down into a liquid. But this also seems dangerous as acetone is extremely flammable. Any thoughts?! I'd try it, but my wife would kill me if I burned down our kitchen.

Acetone plus heat would make an explosive cloud. I believe this is why meth labs explode on a regular basis. .

dont do that the acetone will not make the hdpe flow better only styrofoam is soluble in acetone not hdpe. this would also cause the acetone to boil releasing fumes which can than flash fire which would be very bad. to shape hdpe you must put it under pressure and clamp it in a mold in your oven. some types of hdpe melt better than others.

Definitely sounds hazardous, and I have no idea what would happen -- but I'd love to hear how it goes if you try it! stay safe!

I find it easier to use wood for the mold. Wax paper as a release barrier or if you can find it some teflon sheets and clamps to hold it all together. You could use screws but the clamps will let you add more pressure. Bake it with a old toaster oven so you won't contaminate food with the home oven.

You can find re-usable Teflon sheets in the baking aisle of the dollar store.

If you dissolve styrofoam peanuts in accetone you can get very similar results to this.

yes but styrofoam which is polystyrene is much weaker than hdpe and will fracture much easier than hdpe will

Wouldn't that be napalm? lol

You could use it like that but if you try to squeeze as much acetone out as posible and then let it dry in a mould.

I am in to vacuum forming plastic. However the sheets are not cheap. Has anyone experimented with making sheets out of thermoforming plastic such as milk jugs? I work at a company that uses pelleted plastic, and I really want to try this technique on some of those pellets. I have read around 80 comments so far, but have not seen anyone mention using a deep fryer with a temperature control. Does anyone see a drawback to using one?

Hi babycody, I just saw your question about thermoforming plastic such as milk jugs. I used to love to play with this stuff. It melts between 350 and 400 F dry oven temp. It stays pliable for about 10 minutes if you want to stretch or trim it. I've also melted layers into bread pans for door stops. Once it has melted at high temps and cooled, it will not melt again so be sure of the form or melt at lower temps. Once it gets to the liquid state, work with it quickly to press into forms. It reacts to cool air to harded in as little as 5 minutes. Other ways I've worked with it is cutting it into the shapes and soften the edges with a bic lighter.

The HDPE plastic used in <a href="https://www.youtube.com/watch?v=rpXq6mnbCus&feature=youtu.be&t=5m35s" rel="nofollow">https://www.youtube.com/watch?v=rpXq6mnbCus</a> apparently is remeltable as shown in that video. I conjecture that "remeltability" may depend upon the type of plastic, though.

those are bottle caps which are normally injection molded at a factory this means those bottle caps have to be made of an hdpe grade that flows well into a mold therfore bottle caps will flow without any pressure unlike milk jugs and detergent containers

fantasticcc

i haven't tried it out yet but maybe too much oil. if it's a deep fryer with a basket you will need quite some oil in it to establish contact with the bags. and another possibility would be the risk of molten plastic bits falling or seeping through the basket. thus either creating a bit of a mess or disintegrating the whole block.

From what others have said in the comments, you can use a deep fryer but you'd probably want to put it in another container of some sort to contain the plastic bags. Something like an empty coffee or soda can. My theoretical process: 1. Put some oil in the can to act as a mold release agent. Swirl around edges to get good coverage. 2. Put shredded plastic bags into can. 3. Put can into (cold) deep fryer. (If oil gets in the can this is apparently OK.) 4. Turn on deep fryer and set to target temperature. 5. Profit! No idea if it'll work, but at least it's a start.

If you use an electric skillet to heat the oil with your plastic in a pan sit in the oil you can get very good tempurture regulation.

I am very interested in your process. What I would like to know is if you can make bigger items? I was thinking about making a small house or shed basically a work area out of the plastic. I know it will take a long time and I have that but what I need is how can I make a mold for the shapes I would like to use. Any idea???

Karen, just use a brick/clay mold. You can just take some scrap wood or plywood and tack it together, pour in your plastic. Just break the plastic out of the wood when you're done, or make large batches at once and take the cool solidifying plastic out of the mold before it dries completely. The key to building large structures is conformity in the Western world. Clay you can flex, plastic bricks, not so much!

Along those same lines: See <a href="https://www.youtube.com/watch?v=rpXq6mnbCus&feature=youtu.be&t=5m35s" rel="nofollow">https://www.youtube.com/watch?v=rpXq6mnbCus</a> which specifically uses HDPE plastic with a wood and clamps to force the softened plastic into thick sheets.

I haven't made this yet, but may I suggest that a way to eliminate the greasiness would be to make a double pot assembly like double boiler except that the inside pot is smaller and set INSIDE the outside pot. Fill the gap between the two pots with oil so the inside pot is in dirrct contact with the inside pot. To be clear the oil needs CONTACT the outside surface of the inner pot to transfer heat, you DO NOT want to heat he oil until it smokes. As for the parafin idea, DANGEROUS, heating parafin too much ( usually by a double boiler to avoid overheatin and sudden ignition ) may suddenly burst into flame and you'd have an oil fire whose fuel could splash, stick and solidify into molten flaming globs on anything it touches including you. Finally a second hand deep frier with temperature control may be ideal, you may be able to eliminate the oil all together. Some diy jewelers have made injection wax pots by clamping the lid and using a manual air pump to a GENTLE positive pressure for injecting hot wax into mold for lost wax positives. Too hot wax or smoking oil BAD, hope this helps someone. Hope this helps. Tim

Just in case anyone is wondering about different plastic safety: <a href="http://www.cutoutandkeep.net/projects/the-very-important-guide-of-plastic-safety" rel="nofollow">http://www.cutoutandkeep.net/projects/the-very-imp...</a> Happy crafting :)

Im looking for a way to make a tridimensional chess board star trek style, would using plastic in this manner work for that. As far as sturdiness goes? Im thinking if it turns out to rubbery it will just bend over and wouldnt hold the weight of the boards.

I'm no academic, just a simple soul who's interests are in environmental issues. I am responsible for loads of recycling and this idea of yours is very exciting. May I ask you to check what I intend to do.Large pan with a little oil inside.Place plastic bags in a metal loaf tin (greased.)Place loaf tin in pan of oil.Heat at 350 degrees until mushy.Press plastic mush with weights.Allow to cool in the loaf tin.Is this right?

It seems fine to me. I would be careful about the plastic sticking, but if it's a low temperature then you'll be fine.

Use the canola oil in a deep fat fryer as a double boiler to get the higher temperature, but no contact to the oil. Instead of a basket, use a thin walled aluminium sauce pan( better conductivity) shred the bags in a cheap shredder and dont worry abouy it overcooking if you have a thermostatically controlled fryer... Just let it sit for a while till it all melts together... ;)

Hi. Id like to use this to make a foregrip and buttstock for a paintball fun wpuld this be durable enough to withstamd the force of being shot amd being held tightly while running and combat and thungs of the sort? And how do i shape it? Can i carve it down to size?

<a href="http://www.instructables.com/member/maewert/" rel="nofollow"></a><a href="http://www.instructables.com/member/maewert/" rel="nofollow">maewert</a><div>when:</div><div>Nov 17, 2014. 6:54 AM</div><div>subject:</div><div>Recycled HDPE bricks</div><div>Building bricks for housing using recycled HDPE sounds very interesting. To make it viable you'd need to do it on an industrial scale and have lots of plastic on hand. I don't know Bay island but if they are swimming in waste plastic then maybe. You'd also need to estimate the cost of the energy to heat the plastic. It is conceivable to build a large 3d printer that can directly print the walls of the house. I've seen some on the 'net only but they can print maybe single rooms I think around 14 feet in diameter (kinda like a plastic yurt). I wonder how you would have to coat the plastic to provide UV protection. An interesting set of problems. I wish you the best in this effort.</div>

Great Idea, I love It. To make the wheel more uniform you could also clamp something circular on top of it while it is cooling.

Hello, I am in Kara, Togo West Africa, trying to stop malaria in this city of 100,000. The root cause is plastic bags that block the drainage canals, and rivers, making dams that allow mosquitoes to lay larvae. Presently, the locals burn some of the plastic bags, but never enough. This pollutes, and burning plastic cannot be healthy. I would love to have the same process done using mirrors, or to make some form of solar concentrator that melts the plastic down into manageable size. Then maybe we can make hoe handles, or shovel handles from the plastic, if really good we could make roof rafters. How to use mirrors to concentrate on plastic oven cheap? I think an oven melts plastic different than putting onto a burner. Andy Lee Graham / hoboontheroad AT Yahoo.com / MalariaNIMBY.org

hobotraveler > make homemade rocket stoves. Well tended fire is as efficient as a good stove. Melt your plastic and re-use.

great

You could have a look at something like this<iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/XFw7U7V1Hok" width="500"></iframe><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/Kj7aS7ToNWs" width="500"></iframe>no need for electricity then :)

HoboTraveller, you most certainly CAN concentrate enough solar to do this. One way would be to use a dish shaped frame (such as an old style dish antenna) and attach the mirrors to it - they would generally focus on the dish's central point, put a pot full of plastic there and, I dunno, a metal funnel at the bottom? It'll probably burn from time to time but should work. Another way might be to use the focusing screens off of large TVs that have been thrown out. You can find instructions for these kinds of large solar devices, just look for fun terms like "solar death ray" and the like.

I think the best way to make this work would be to build a small rocket stove get a pan with a side tap use the tap open as to fill moulds and feed into HDPE threw the top of pan cannot see a need for any oil myself needs doing outdoors

just had a ten minute think about this one, can you not build a small rocket stove with a pan with a side tap on top so you just fill the pan with HDPE 2 inside it thus it will fall like a hopper as it melts threw the side tape into your mould? seems real simple to me without using oils

can we use nay kind of plastic for this?

anything made of plastic

Ok

great stuff