MYOGing custom-sized HDPE containers.

[David Thomas]

In another thread, Daren and Joshua expressed interest in a container for alcohol fuel that was shorter and wider than commonly available (so it would fit nicely in a pot).  I pointed out that you can weld HDPE with the drips from burning HDPE and I just found some time to putter in the garage.

I used a very thin-walled drinkable yogurt “Kefir” container – tall and 1-liter capacity to start.  I cut it down a LOT in height.  It was close to gallon-milk-jug thickness and far thinner than gallon-windshield-washer-fluid containers.  Mark your cut lines (wrapping a sheet of paper around the container gives a nice guide line).  I use scissors, NOT a razor knife, for safety reasons.  Then cut the discards into 1/4″ strips.  You don’t need a lot of strips.  I cut out almost all of the middle section, so the remaining pieces weren’t very flexible and I couldn’t jam one end totally inside the other (that would have been easier if I hadn’t cut it down so much).  So I cut two slits, 180 degrees apart in the top section and one side of top went on the inside and the other side went on the outside of the bottom:

I secured two opposite sides with tape as I first welded the untaped sides.  The strips are easy to light with a match or lighter and super easy to light if you taper the end.  I mean, so super easy and it burns so well, keep this in mind if you’re ever desperate to start a fire and have any HDPE containers with you:

I did it barehanded no problem, but I’d recommended a leather glove to hold the container since there is the possibility of dripping molten, burning HDPE onto your skin.  Don’t dribble a lot in one place or you can melt through the container (I never did, but I’ve been fixing ski bases and kayaks and Nalgene bottles like this for decades).  I did a sequence of single drops as a rotated the container under the flaming strip and went around three times.  Then I took it in the house, fill it with water and squeezed it a bit.  There was one obvious leak that I could have found visually and another pinhole leak that both sealed up when I added some more drops of molten HDPE to those areas.  Here’s the finished container:

For OP’s application, I first thought, “hydrogen peroxide container” and I’m still thinking that.  HDPE.  A little thicker wall.  Cheap (a loss-leader during hunting season at a buck each for the liter container).  Tall, cylindrical, with a flatter top than most drink containers, so there is less wasted height.  Or, of course, my favorite – dumpster-diving at the recycling center and seeing what catches your eye.

Note that everything needed for this project, other the donor container weighs 32 grams and is already in your pack:

Being all HDPE (original container and the new welded seam), you can still put the whole thing in the dishwasher and get it really clean after a trip).

Flame On!

[R]

Interesting – thanks for the demo.

Have you ever tried this with a soldering iron instead of open flame?  *If* it works, I imagine you’d have better control, no soot and a cleaner final product.

I’d take a stab at this right now, but I don’t have anything suitable in the recycling bin at the moment.

[jimmy b]

David, thanks for taking the time. Nice tutorial.

[David Thomas]

Rene,

There are plastic welders that use hot air or an electrically-heated “gun” like an oversized hot glue gun to melt various plastic filler materials.  I’ve wondered how well different types of hot glue would work for this.  Maybe I’ll try it sometime.  I know that molten HDPE sticks to solid HDPE quite well.  It actually does seem to “weld” to the main piece by melting part of the main piece and then re-solidifying.

I think a soldering iron could work on thicker material like a ski base or a kayak.  On this very thin-walled material, it be easy to apply too much molten filler.  One drop at a time seems to work.

We’d use an official plastic-melting gun to repair ski bases in the shop (we were charging people).  But on the slopes, or in the hotel room, or on the trail, I’d just use a stick of “P-Tex” or any other source of HDPE, light it on fire, and dribble it into the gouge, let it harden, and sand it flat.  The burning method does leave those little flecks of dark material.

[Valerie E]

I wonder whether plastic glues meant for making models would work on HDPE.

Plastic glue of this kind is essentially dichloromethane CH<span class=”bbc_size”>2</span>Cl<span class=”bbc_size”>2</span>, which is a powerful organic solvent.
It literally dissolves the plastic and then allows it to re-harden as the DCM evaporates.
It has a distinctive odour and is highly volatile.

Do not sniff!  Use in a well ventilated area! It’s considered to be a carcinogenic substance, but if adequate care is used, it should be fine to use.

[Ken M]

Adhesives…About the only way to bond High Density Polyethylene (HDPE) or Low Density PE is to weld them to each other.  There’s something with it’s molecular structure that will not give an adhesive a “bite” to hold on to.  And these poylethylenes are almost completely resistant to any solvents so they can not be chemically melted together.  Repairs to polyethylene items like skis mentioned above or my polyethylene kayak entails melting the plastic together.  I’m sure you can find a better explaination on the web.

There are some high tech adhesives out there (expensive) that claim to be able to bond polyethylene.  My meager experience with them in our machine shop was that they worked…for a while.  Never had any great luck with them but things may have changed in the last few years?  And were they food grade?  I doubt it.

Just a side note:   Some adhesive coated tapes will hold pretty well onto polyethylene.  I find that industial grade velcro is very tenacious.  Also, I have found that a double-sided outdoor mounting tape is very grippy on polyethylene items. Tape is not really an option for what David was trying to do in his original post.

-KenM

[David Thomas]

Valerie:  Thanks for the thoughts about Dichloromethane – it’s one I don’t think of routinely, and certainly could be handy for solvent-welding other types of plastics.  A chemical compatibility chart for methylene chloride (same stuff) reports “HDPE at 20C° shows some effect after 7 days.”  So while HDPE wouldn’t make a great long-term container for “di-clo”, it wouldn’t be dissolved sufficiently to effect a joint.  My day job is cleaning up chlorinated solvents (and fuels and rocket fuels, etc) so I read a lot of toxicology reports.  So in addition to good ventilation, I’d be wearing a half-face respirator with activated-carbon cartridges, as I do when solvent welding PVC pipe.

Ken: my experience matches yours – HDPE is easy enough to join with molten HDPE but any other joint is both elusive and sketchy.

What I haven’t researched yet is if there are a glue-gun-sticks of HDPE.  That would be sweet – just pull the trigger, no drips, no flames, no bits of soot in the melt.

Worse still is cross-linked polyethylene (“PEX” or “XLPE”) because the polymer molecules are chemically joined to each other.  That makes it even more stable and chemical resistant, but eliminates the type of welding that LDPE and HDPE allow.  Early in my engineering career, I dropped a 3,000-pound XLPE vessel, putting a gash in it.  A long, extensive search for a patch of any kind was fruitless.  It doesn’t melt, it only decomposes at higher temps.

Speaking of watercraft, something I just learned: PEX is also used in many canoes and kayaks. The PEX is listed by the name Ram-X (some Coleman canoes), and other brand specific names. Because of the properties of Cross-Linked Polyethylene, repair of any damage to the hull is rather difficult. Some adhesives, such as 3M’s DP-8005, are able to bond to PEX, while larger repairs require melting and mixing more Polyethylene into the canoe/kayak to form a solid bond and fill the damaged area.

[Author]

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