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Ever since I got a dog who loves to sniff and chew most things that come across her path, I have been hyper-aware of plastic bottle caps thrown onto the street/sidewalks/grass/etc. Most caps are HDPE 2 and HDPE 5. I have been collecting for a year now and wonder if I could safely melt the caps and remold them into something useful. My questions:

  1. Is it safe to melt HDPE2 and HDPE5 to a pourable form? I know that burning plastic emits harmful fumes, but what about melting it?
  2. Would melting and re-shaping HDPE 2 and HDPE 5 compromise the integrity of the plastic or does it cool and set to its original integrity?
  3. Do I need to melt HDPE2 and HDPE5 separately? Can they be mixed?

I do not want to do this in my home. There is a local glass blowing studio I would consider talking to about using equipment. Any other suggestions?

Please consider saving your plastic bottle caps and donating them to a responsible recycler. Dog and animal owners thank you!

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    $\begingroup$ Why would it mater to the dog? Are you afraid it will eat them? I mean, of all the things dogs come across every day, bottle caps seem like the last thing to worry about. I've had dogs all my life and while they'll happily gnaw at plastic, I've never had one actually eat it. What you are suggesting is still a wonderful idea and I absolutely hope you'll do it (if it turns out to be feasible), I just don't understand why it would make any difference to your dog one way or another. $\endgroup$
    – terdon
    Commented Mar 27 at 13:48
  • $\begingroup$ Consider preciousplastic.com has details and plans for small batch plastic recycling. $\endgroup$
    – user144830
    Commented Mar 29 at 18:45
  • $\begingroup$ Terdon: Dogs will eat anything We should be more concerned about not littering the environment. $\endgroup$
    – jimchmst
    Commented Mar 30 at 0:44

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Home extrusion of LDPE or HDPE is impractical. Products made from these plastics are extruded under pressure (as much as 500 to 1,000 atmospheres!) at lower temperature, since raising the plastic to a temperature at which it could be poured leads to decomposition.

As for safety, even commercial equipment operated by professionals can fail catastrophically.

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With care and proper equipment plastics especially the thermoplastics such as polyethylene, polypropylene and the terephthalates melt and do not decompose at the melting points. They will ignite if finely divided and the foamed plastics might be dangerous. Plastics will decompose at a specific, rather narrow, temperature range usually above the autoignition T of the vapors, so high temperatures in air can result in a BLEVE [look it up] and must be avoided. I recommend that you do not do it. Recycle the caps and work towards laws that demand more and more complete plastic recycling.

I, possibly We, applaud your efforts. Give your Dog an extra pet from all of us.

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  • $\begingroup$ Thank you for mentioning BLEVE. $\endgroup$
    – jvb
    Commented Mar 27 at 21:39
  • $\begingroup$ Note that polystyrene plastics are known for releasing styrene fumes even in the proper temperature range. This is an issue for 3D printing with ABS or ASA filament. Some plastics can also absorb water and foam, spatter, or potentially cause steam explosions if confined and heated. $\endgroup$
    – Christopher James Huff
    Commented Mar 29 at 16:17

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