Make Your Own Plastic

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Posted in TechnologyReuse

Introduction: Make Your Own Plastic

About: I'm a mechanical engineer seeking to further my understanding of automotive design. My first love is cars, but I enjoy designing and building a plethora of random stuff.

Many of us use plastic in our projects, but did you know you can melt down and reuse much of the plastic found in your house? In this instructable you'll see how to recycle plastic to be reused for whatever you want.

Step 1: What Type of Plastic Can Be Reused?

For this method we will be reusing high density polyethylene (HDPE) plastic. You can identify this plastic by the recycling symbol on the bottom of most plastic containers. HDPE will be identified by a small "2" in the center of the recycling symbol, and will sometimes even be accompanied by "HDPE" written next to the symbol.

When compared to ABS plastic:

HDPE:

  • density - .958g/cc
  • tensile yield strength - 20.6MPa
  • melting point - 129 C

ABS:

  • density - 1.05g/cc
  • tensile yield strength - 41.5MPa
  • melting point - 220 C

While HDPE is not as strong as more widely used polymers such as ABS, it is good for low stress applications such as project enclosures, lightweight mounting solutions, and more. And the best part, it's free!

Step 2: Materials and Tools

To start this project you'll need:

Materials:

  • HDPE plastic in the form of containers and/or plastic bags
  • Baking pan
  • Wax Paper
  • Non stick cooking spray

Tools:

  • Scissors
  • Oven or toaster oven
  • Gloves (preferably welding gloves or similar heat resistant gloves)

Step 3: Preparations

If you decide to use plastic containers such as milk jugs you'll need to cut up the plastic into smaller pieces. Using your scissors cut the plastic into nickel sized pieces. If you use plastic bags it helps to tie them in a knot. Plastic bags tend to shrink in peculiar ways when they melt, knotting them makes them easier to work with. Once you've cut up your plastic into small pieces preheat your oven or toaster oven to 350 degrees Fahrenheit. Make sure you do this in a well ventilated area! While the plastic shouldn't release an excess of fumes if done at the correct temperature, any fumes it does release will be nasty and should be avoided.

Next you'll want to grab what ever you decide to use to melt your plastic in. An old cooking sheet or pan can be used. Line the pan with a sheet of wax paper and spray a light coat of non stick spray or similar lubricant across the sheet.

Another option, if you've built the furnace shown in my last instructable, you can cast aluminum molds for melting down your plastic.

Step 4: Time to Melt!

Place your plastic into your pan or mold and place in the oven. Cooking should take between 30 minutes and an hour depending on your oven. Keep an eye open for signs of burning and adjust the heat as necessary. The plastic will go soft and malleable as it melts. Once all of the plastic is melted you'll want to grab your pan or mold out of the oven (make sure you have your gloves on!) and check for gaps and voids in the plastic. If you want cleaner edges on your plastic, fold the edges of the plastic over on itself. Once you're happy with your plastic, throw it back in the oven for another 10-20 minutes to melt down and make the part solid.

Once your plastic is done you'll need a way to keep pressure on top of the plastic while it cools. Otherwise the plastic will try to buckle and warp as it cools. This can be done with a couple of pieces of wood and either a couple of clamps or a heavy weight.

Step 5: Make Something!

Once your plastic is cooled it can be used for whatever you can think of! You can trim it and make plastic stock for later use, or cut and machine it into anything you come up with. I've found that a small jig saw works well for cutting and 80-180 grit sand paper for shaping.

Go and use your plastic for your next project and thanks for checking out my instructable!

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    96 Comments

    I like the idea of melting plastic. I've been thinking about making blocks with melted plastic and building a shed with it. I crochet with plastic bags, I cut them into strips, across the bag, I link the strips together, roll it into a ball and crochet. I make rugs and bags.

    I wonder if I chip/shred/cut it up and put it in a metal tray in a solar oven and leave it for the day while I went to work if it would it melt down into the pan and leave a flat sheet of plastic. Might have to build a solar oven and cut up the milk jugs to find out. Anyone try something like this.

    It looks like a great loss of energy, when used just for the sake of recycling plastic.

    But could be done in winter, though:
    while melting the plastic, you will heat up the house too!

    8 replies

    How do you think plastic is normally recycled?

    Even if it is recycled this way (though i doubt they use kitchen ovens and melt 1-2 kg of plastic), the economics of scale would make industrial recycling more effective and less wasteful.

    All this topic stresses the issues of pervasiveness plastics and it's recycling... Too many problems off the plastics.

    Shouldnt do it inside.

    Yup, good point, as the fumes are not good for your health, most probably. In that case, I would think of other possible recycling methods - this one based on melting is a huge waste of energy, I think...

    Anyway, biodegradable PLA is the future for the plastic bags, I hope. At the moment it is better to avoid plastic bags in the first place (e.g., switch to cotton bags, which are more durable and sustainable).

    PS: this is not to criticize the author! Just "my 5 cents")

    It is less wasteful then tossing in the trash but I think this would make a good source of machinable plastic for prototyping parts and it will be cheaper then buying new plastic. If you have a use for the stuff this is a good idea and no more wasteful then baking a potato.

    "Two cents"...No criticism...Just getting mine in, as well. :-)

    there is a site on the net that has all the blue prints for making anything out of recycled plastic.including the machines from shredders to extruders. check out precious plastic.com

    Cool, I am busy getting the parts together to build the shredder. Also very tempted to buy the DIY kit from Filastruder

    Hi dan3008,
    Check out Preciousplastic.com. They have open source plans for a shredder, extruder, injection mold machine and compression machine.

    I've got a copy of tgeir plans saved on my desktop :)
    Its only time and finances stopping me already having one :)

    can i melt it in boiling water by adding salt to the water to raise its boiling point

    1 reply

    No. The so-called melt temperature of hdpe is about 350 degrees F. The boilding point of salt water is only a few degrees higher than unsalted which is 212 deg. F.

    I have a broken plastic gear I need to replace. It costs $45 just to have the company look at it to decide "yep it is a broken gear". Before they will send me one. Of course I have topay for shipping each way as well.

    Ok so this gives me an idea for replacing said gear.

    Thanks for this :) Two thumbs up :)

    hmmmm, I carve things out of wood, dolls, animals etc I have seen the "ivory like" plastic that is sold on eBay to carve I wonder if this would work? Also could be made into dollhouse furniture maybe sounds like great uses for me thanks!!!