Making a plastic container air-tight
November 17, 2016 12:54 AM   Subscribe

Can you help me with a quest to reuse plastic peanut butter jars?

I've always saved plastic peanut butter jars since they seem useful for holding a variety of items. However, recently I've discovered that the jars I've been saving are not actually air-tight. If you fill up a jar half way with water and then squeeze the sides, you can hear air escaping, and if you turn it upside down and squeeze, water dribbles out. This happens despite the lid being very snug.

At first I thought it was because the lip of the jar was irregular from remains of the foil seal. As an experiment I used some fine sandpaper taped to a hard flat surface and sanded the lip until it was flat, even, and parallel. Water still leaks out when you squeeze the body of the jar. (And not from any one spot in particular, from everywhere, which tells me it's not due to a low spot.)

So I'd like to put some compliant material in there to make a gasket. I thought about cutting out a circle of just the right size out of card stock, which would probably be fine for storing dry things. But I'd like to be able to wash the lid, and I'd also like to be able to store liquids. Card stock doesn't seem like it would hold up very well.

1. I know it's a long shot, but is there any kind of preexisting/premade solution for this, like a rubber gasket designed for standard lid sizes?
2. Assuming there isn't, is there some kind of plastic that I can buy sheets of and cut out a circle from, but which will have just a little bit of give/spring? (And how do I keep it attached to the lid? Perhaps spray adhesive?)
3. I've thought also about maybe putting some tape on the underside of the lid, but what kind, and how do I deal with bending tape to the radius?
4. Is there a better solution that I haven't thought of?

To be clear these are regular store brand plastic peanut butter jars with standard red plastic polypropylene lids. The lids say 89mm which I'm assuming is the inside diameter and likely an industry standard.

Also, I know that it's probably not absolutely essential for a container to be air-tight to be useful, however I'm really turned off by the fact that if you put liquid in there you can make it leak out by just squishing the sides of the jar. And I know I could just buy mason jars or whatever, but I've got all these jars sitting around already.
posted by Otto Franz Joseph Leopold von Soxen-Puppetten to Home & Garden (26 answers total) 1 user marked this as a favorite
Maybe circles cut from craft foam sheets? Attached with a tiny bit of hot glue? Not sure I would trust this for liquids not stored upright or leave them to soak in water overnight or anything, but it seems worth a shot.
posted by charmedimsure at 1:16 AM on November 17, 2016

I was going to say U-channel, but you'd want it pretty thin. Try plumbers tape around the thread. A circle cut to fit from an ice-cream container lid?
posted by quinndexter at 1:35 AM on November 17, 2016

Maybe silicone baking sheets. Or if the size happens to work, round pieces cut from the muffin molds in a silicone muffin sheet.
posted by Too-Ticky at 1:39 AM on November 17, 2016

When cooking the Indian dish biryani in a pot, I've come across recipes that tell you to make dough, use a rope of it to seal the lid of the pot to ensure thorough cooking, and then discard the dough afterwards. That's probably not long-lived enough for most purposes, but...

Maybe you could put a bead of molten wax around the edge of the lid before sealing the jar? If you had wax or something similar that melts readily enough, maybe it would come off in a dishwasher, for re-usability.
posted by XMLicious at 1:56 AM on November 17, 2016

Depending on how big the gaps between the threads are, would a few layers of some PTFE tape do the trick? You should be able to find it in the plumbing section of most DIY stores.
posted by A Robot Ninja at 2:36 AM on November 17, 2016

craft foam sheets that have an adhesive backing would be perfect for this. easy and cheap.
posted by 5_13_23_42_69_666 at 3:04 AM on November 17, 2016

Food-grade silicone sealant might do the job. You'd just need to put a thin bead of it around the inside of the lid (in the corner between the flat and the edge). That's effectively what a lot of jars have for a seal, so it ought to work.
posted by pipeski at 3:21 AM on November 17, 2016 [1 favorite]

I also came to say teflon tape, the thing mentioned twice above already as plumber's tape and PTFE tape. All the same thing. It's good stuff.
posted by phunniemee at 4:22 AM on November 17, 2016

Canning wax. Melt in a small pot, pour a little into the lid, let cool without disturbing.

You can also buy small rubber sheets for making gaskets -- in the plumbing section of hardware stores -- but cutting them to exactly the right size and shape would be difficult. The one I had was 1/8" or 1/4" thick. Plus, if you're going to that expense, you could just get some glass jars with better lids.

I recently discovered you can order one-piece lids that fit mason jars.
posted by amtho at 4:49 AM on November 17, 2016

The folks at Fillmore Container in Lancaster, Pa. might be able to help. They offer this coated liner for G70 lids (here's the complete list of closures). Or maybe give them a call and see whether they have a better solution?

I canned hot sauce in bottles this summer and learned from the Fillmore site that what gets compressed in bottle lids is the plastisol underneath. Once that's been deformed by heat and/or pressure, it will never again be airtight.

Good luck!
posted by MonkeyToes at 4:50 AM on November 17, 2016 [1 favorite]

I Googled for 'food-grade rubber seal' and quickly found suppliers of appropriate materials. Unfortunately the ones I looked at were not economical enough, when purchased in small amounts, to be worth it. Canning jars are cheap.
posted by jon1270 at 4:56 AM on November 17, 2016


posted by jon1270 at 5:09 AM on November 17, 2016

BTW, I would avoid trying to adhere a gasket to the lid. When the adhesive starts to fail, stuff will get underneath it and be impossible to fully clean out. Just go for a snug fit and leave it removable.
posted by jon1270 at 5:29 AM on November 17, 2016

Before you try any fixed solution, do this first: take a piece of cling film, cover the open jar, then put the lid on.

In most cases this will seal the jar.
posted by bonehead at 6:01 AM on November 17, 2016 [7 favorites]

These jars are only airtight because of the thermal foil seal, so they're a use-once item. Recycle 'em and use mason jars.
posted by scruss at 6:02 AM on November 17, 2016 [3 favorites]

I was coming in here to say what bonehead just suggested.

Some of the suggestions in this thread are not food-safe.
posted by gregr at 7:09 AM on November 17, 2016 [2 favorites]

Do the jars leak if you don't squeeze them? Is it possible they're airtight until you squeeze them and deform the jar enough to make a gap in the seal?
posted by yeahlikethat at 7:09 AM on November 17, 2016 [1 favorite]

Some of the suggestions in this thread are not food-safe.

I personally would be quite wary of solutions from the hardware section (unless certified foodsafe).
posted by bonehead at 7:26 AM on November 17, 2016

These jars are only airtight because of the thermal foil seal, so they're a use-once item.

yes, exactly this. the problem is that these are rubbishy jars that are not intended for long-term or repeated use.
posted by poffin boffin at 10:31 AM on November 17, 2016 [1 favorite]

Parafilm isn't 100% air-tight, but it is waterproof and may work for your needs. You can get some free by asking any lab biologist. (You could MeMail me an address and I could send you some.)
posted by maryr at 10:38 AM on November 17, 2016 [1 favorite]

You can get Parafilm from Amazon. I considered recommending it, but it's not certified foodsafe, at least that I can tell.

I know, it gets used on biosamples all the time, but it does leave residues---we can't use it for environmental chemistry samples at all. It can cause reactions in people with latex allergies, apparently.
posted by bonehead at 11:03 AM on November 17, 2016 [1 favorite]

Silicone O-Rings are available in FDA forulations. They are pretty cheap, washable, re-usable and easy to insert into the lid.

For example the peanut butter jars we have measure 3 3/8th inches in diameter across the opening. This o-ring would probably work or you might find one a size larger would stay in the lid better.

You can also buy o-ring cord which allows you to make custom sizes but it's quite a bit of work and more expensive.
posted by Mitheral at 1:25 PM on November 17, 2016

For any kind of re-use, you need materials that are food safe, do not degrade over time, and are washable / sterilizable. Flexible plastic jars are not the best for storing liquids -- it can lead to contamination because they either leach chemicals into the liquid or can't be fully sterilized (they would melt) and bacteria would get in.

Maybe start buying peanut butter in glass jars for liquid storage later? You can use the plastic ones for storing and organizing dry goods and small misc objects (screws, paper clips, etc).
posted by ananci at 2:58 PM on November 17, 2016

I have a suggestion for going forward: buy a different brand. They are definitely not all leaky. I know this because an acquaintance once showed up with holes crudely made in the lid of a PB jar and the jar had the dregs of quite a lot of coffee. It totally looked like, and was, a drug delivery device. It wasn't a posh brand of PB (brand forgotten though, apologies) but it made it as an in-car travel mug for a hot beverage, which was pretty impressive for a disposable thin plastic.

That said, I don't think I'd use it for regular, extended food storage. Dry goods, maybe.

I just posted about melted plastic bead crafts -- if you just don't want to waste them, cut them down a bit, get some other more colourful plastic, and start melting them down to make new things?
posted by kmennie at 8:22 PM on November 17, 2016

Hot glue around the inside of the lid, maybe? I'm with some of the others here though--if you're going to use these for food storage, I'd stick with dry goods or small amounts of liquids that aren't likely to escape if the jar is squeezed too hard.
posted by helloimjennsco at 5:47 AM on November 18, 2016

Following kmennie's comment: I use Trader Joe's peanut butter jars as disposable water bottles and I've never had one leak.
posted by metasarah at 7:40 AM on November 21, 2016

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