How can I repair cracked LDPE without a plastic welder?

Question

The cold weather has brittled my recycling bin and cracks have developed around the lid handles due to being peeled off in freezing weather. It's gotten so bad, that the lid no longer performs its function of keeping water out of my paper recycling.

I could buy a new bin, but it seems a shame to toss it when only the lid is affected. Also, tossing a bin is difficult without a larger bin to put it inside of.

I'd like to repair it!

The bin is made out of low-density polyethylene (LDPE), which has a melting point of 110C and bonds poorly with most adhesives.

Ideas I've had:

• Duct tape. Probably won't last that long, and hard to form a watertight seal.
• Welding with a blow dryer. Probably not hot enough.
• Welding with a hot frying pan. Probably hot enough, but might be hard to achieve the accuracy needed.
• Welding with my soldering iron. Probably hot and accurate enough, but would ruin my soldering tip :(

So, the question is, how can I repair these cracks without buying a plastic welding kit?

Answer 1

I'm not exactly sure what a "plastic welding kit" is, but I've made almost identical repairs with a Benzomatic propane torch (the blue can). The trick (in my case) was getting the pieces lined up enough so that they would stick to each other when heated, and for that I would use duct tape on the opposite side of the side I was heating, then remove that tape and reverse it for the other side, just for extra strength. It will never be as strong as the original, but if all you're interested in for now is a water tight seal, then it's a start.

For reference, the can I'm talking about is here:

http://www.amazon.com/C-R-Laurence-LP1759-Standard-Cylinder/dp/B002DVN7OU/

They are relatively inexpensive (US$10) in hardware stores, and may or may not come with a torch top, depending on which option you buy.

If you want to get really fancy, find other sources of LDPE (Plastic #4 if things are labelled) and make strips of "plastic solder" to add plastic to your weld. This is much more work, but will make the weld much stronger in the long run.

If that's your idea of a "plastic welding kit" then of course feel free to ignore this answer, but again, I've had success with this, and having a propane torch around the house can be pretty useful for other projects too.

Side note, the yellow Benzomatic cans are Map-Pro gas, and burn much much hotter than required for plastic, (can heat steel enough to bend small pieces) so definitely don't get that or the red can. (Not sure what it is, but I know it's used in welding along with the Map-pro.)

Answer 2

Styrene/butadiene copolymers such as Goop bond somewhat to polyethylene, and are flexible and elastic, though they harden with years of exposure to light and air.

Polyethylene "candles", such as P-tex, are sold to repair gouges in ski bases, but might not bond in a deep crack, nor would it have the tensile strength of pressure-molded poilyethylene.

However, from your picture, there are evidently a number of cracks in the container. Once polyethylene becomes so embrittled that it cracks in one spot, I find that it soon cracks (or even crumbles) elsewhere. If you have recycling pick-up, with others handling the bin, it would not receive delicate handling. For that reason, I would not spend much time or money on repair, where the whole container is likely to disintegrate. If your recycling service takes high-density polyethylene (HDPE, "2" in a triangle), then cut or break the old container and put it in the new.

Answer 3

I have repaired similar plastic items (in my case, a compost-holder) by pre-drilling holes and driving woodscrews into a suitably shaped piece of wood somewhere behind it. Your picture is not too clear, but here's a sketch: Don't use a countersunk screw, that would probably split the plastic. This will give you a stable mechanical basis which you can then waterproof with whatever is convenient (silicone perhaps).
Success!

Answer 4

Clean it with alcohol, heat it up with your hair dryer, apply some second glue (whatever you have), press the pieces together, tape them that way and leave them for a couple of minutes. It works out well with every type of plastic that I tried to stick together. You can also try with a thick needle and a lighter to do the so called "stitching", like you are welding it together. However with that method usually it cracks open after a couple of days...If you don't care how it looks and you just want it to get super strong, get a thin wire, needle and lighter (or something to heat the needle with). Make holes near the edges with the heated needle, run the wire like an actual stitch and tighten it. This is rock solid!

Hope that I have helped :)

Answer 5

I’ve used a pencil-type soldering iron (with screw-on interchangeable tips) to easily repair cracks on HPDE (#2) and LDPE (#4) plastics. I’ve started collecting various colors of HDPE and LDPE so the repair work doesn’t look too off-color. The main points are:

• work slowly in sections
• tack melt the plastic with 1/4” separations on both sides
• use whatever-color plastic repair strips to melt the plastic crack about 1/2” wide
• hold the repair work to the light and check for pinholes

I’ve repaired the following:

• 50-gallon HDPE trash can cover
• 5-gallon HDPE utility bucket… holds water
• HDPE toolbox tray with 4”x4” cutout… holds my sockets in it without cracking
• cracks in a 9”x9”x14” LDPE sewing box
• HDPE housing for a stationary bike’s control and display module (this was done in four sections, and required complete disassembly and reassembly)
• Etc…

Answer 6

Don't use grocery shopping bags. They are HDPE, not LDPE. I'm not sure about ldpe but nothing sticks to hdpe. If you are sure it is ldpe then try the plastic welding or gorilla glue for plastic.

Answer 7

I'm not sure if it would work but in plumbing UPVC pipes can be "welded" using something called MEK.

It works by slightly melting the UPVC and then evaporating (it's an organic solvent) which causes the joint to set. It works well with pipe joins but might not stand up to repeated flexing.

Test it's effect on a small area before using on the repair. If it softens the UPVC then paint it on the affected joint and press the edges together and clamp with a wooden clothes peg (or two) until set.

Should work, but I've never used it on LPDE before.