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I left scented candles in a polypropylene container, for many weeks.

How do I remove the smell?

I've tried:

  • Hand wash with Dish Soap (a few times)
  • Hand wipe with Isopropyl Alcohol (a few times)
  • Dishwasher 'hardcore mode' Cascade Pods (a few times)
  • Airing it out (many days)
  • Weak but direct sunlight (hours)
  • Left for any days while filled with either: (new to old)
    • 85% Isopropyl Alcohol (~15% full)
    • 10% Hydrogen peroxide (full)
    • I think I tried 5% Acetic Acid, & have unused 30%
    • Sodium Bicarbonate (30% full)

Container Specs:
5L rectangular: 15W x 21L x 14H(cm).
Decent(ish) lid seal, but two small holes in top.
If filling with a solution, I'll want to try to displace some volume first. Depending on solution, I may need to know what can/can't be used for displacement. Refilled disposable water bottles can lower it from 5 to 2.5L

Potential Methods:
I have a professional background in laboratory research: biochem & bio. I can perform reactions if useful. I don't have any lab-grade chemicals right now, but I do have equipment/tools and a variety of commercial strength products.
I'm open to buying ~laboratory-grade supplies to solve this problem, considering expense and ventilation limitations. Sadly, I don't own a fume hood. Retailer recommendations are welcome.

In Short:
I'll fight to save this polypropylene potpourri.
If there is no good solution, then please suggest a Hail Mary, even if it risks destroying the container.

4/14/24 Update - Help Received & Regroup Required:
I'm new and impressed by all of this valuable/prompt help.
It seems there is so much shared insight because my Q doesn't have a singular A.
Many options are promising, but I have become confused overall.
Based on all the help so far, what order should these options be tried in? Unpredictability will require an ordered plan for testing options.
The order confuses/concerns me because each test may alter the efficacy/danger of the next. Danger to me, but more likely just the polypropylene.
Until a plan is defined, how should I store/prepare the polypropylene?

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  • $\begingroup$ Given that the smelly component was once a component in a candle, it'll likely dissolve in wax. What about putting some unscented paraffin in there with the hopes that it'll grab up the stink? Alternatively, hot water might assist in getting any waxy residue to melt. $\endgroup$
    – Melanie Shebel
    Commented Apr 12 at 6:21
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    $\begingroup$ @Melanie Shebel - Fascinating idea. Thank you for the quality edits. However, you left "solve" in italics haha. $\endgroup$
    – JJ123
    Commented Apr 12 at 7:28
  • $\begingroup$ PE/PE bottles and scents are slowly in, slowly out and then some scenario. There is not much to do about it. One could very short time try to extract surface layers by a solvent, but the smell with return quickly. $\endgroup$
    – Poutnik
    Commented Apr 12 at 8:00
  • $\begingroup$ I have removed chicken tikka masala smell from polypropylene containers (it was sold in the container, which I wanted to re-use) by soaking with a dilute solution of bleach for a few hours. Strangely, sometimes it works and sometimes it doesn't. $\endgroup$
    – Andrew Morton
    Commented Apr 12 at 12:03
  • $\begingroup$ @poutnik - That rate of diffusion being the limiting factor makes sense, but do I understand properly that it would be equal rates in or out of PP? If so, this puts me in quite a pickle due to how long the initial exposure was. --- Would it then be the case that the PP would smell at a constant intensity for a very long period of time, and then suddenly enter a rapid decline in off-gassing(proper term?) concentration as the absorbed aromatics are nearly depleted? --- If all this is true, then heat may be the only true diffusion facilitator. Though mentioned below, what is your stance on heat? $\endgroup$
    – JJ123
    Commented Apr 15 at 20:35

2 Answers 2

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The answer depends on (1) how patient you are (how much time you have), (2) how low a concentration of the offending substances you need to obtain, (3) whether you have someplace you can leave the box open indefinitely.

If the substances diffused into the PP they will presumably eventually be able to diffuse out. The release profile will depend on the absorption and distribution of the substance in the PP (the AD part of ADME). Knowing these properties would help predict whether the release will be fast or slow. If the affinity for PP is not unusually high and they diffuse quickly through the plastic then the release should be on the order of the amount of time it took them to diffuse in. However, (1) as the concentration of the perfumes in the wax may have been rather high, a high concentration may have volatilized and absorbed into the PP, and (2) if the substances have a high affinity for the PP they may form a relatively thin profile near the surface and diffuse slowly into the plastic (accumulating inside) and drift back out slowly.

You may also be sensitive to the odor of these compounds, so that the required final concentration will have to be very low to not be noticed any more.

Your best option is to leave the container open somewhere allowing it to aerate. I would avoid using any harsh chemicals or direct sunlight that will potentially damage the plastic. They won't accelerate release (the substances are assumed to be fairly volatile anyway). A higher temperature (within reason) should accelerate release. Heating means slightly above room temperature, not in an oven. Physical (besides slightly higher temperature) or chemical treatment won't accelerate release from within the PP. The perfume in the material has to diffuse out. Abrasion might help if it did not penetrate much but don't recommend. In that case washing once in a while might be good enough but again since it's volatile not even that should be necessary. It's just a question of time really.

If you want to keep the box closed rather than aerate you can place a box of cat litter, bicarbonate, or activated carbon inside.

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  • $\begingroup$ Thank you, this is very helpful. Then this information may be helpful... This was 4 different: candles, scents, and types of wax. If valuable, I can search for that info. Remained ~~80% air-tight closed for 1-4mo, idk. After left opened, the smell is very faint, nostrils to PP faint (ha). Closed for ~~30-60min builds noticeable smell again. I'd assume a linear release rate, but idk for a closed system. If a thin profile, would abrasion help? If heat would help, my oven goes down to 170F, or slow cool. A paraffin block? Parafilm lined? Short exposure to UV light? $\endgroup$
    – JJ123
    Commented Apr 12 at 7:53
  • $\begingroup$ I edited slightly. I removed the bit about paraffin, that's likely to cause more trouble. $\endgroup$
    – Buck Thorn ♦
    Commented Apr 12 at 8:32
  • $\begingroup$ Thank you for the further insight. --- Do you mean to say that using any wax as an aromatic sink will be unhelpful or even problematic? I can see why it might be unhelpful, but why an issue? You would use paraffin for a sink if it was a paraffin candle, but what about a soy candle? --- Do you mean that the air diffused aromatic will resist release if in contact with any liquid? --- If filled with cat litter and sealed, could a slight negative pressure help at all? I doubt it. $\endgroup$
    – JJ123
    Commented Apr 12 at 20:43
  • $\begingroup$ Original thought was that liquid paraffin or similar liquid with low aromatic content would provide a sink. Diffusion into solid wax is likely slow (as into plastic), but it might work. But then so might baking soda or other safer absorbents. I didn't look into the solubility of perfumes in waxes generally but eg ethers would be quite soluble. $\endgroup$
    – Buck Thorn ♦
    Commented Apr 13 at 17:59
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The search terms I'd suggest are "accelerated off-gassing" and "plastic deodorization". Here is a search result that looks relevant: https://www.sciencedirect.com/science/article/pii/S0048969721075458

The highlights of the paper are (and I emphasize that for your safety these are done one at a time): a strong base plus certain detergents (dish soap plus laundry detergent (cheap classic formulas, not fancy new stuff)), organic solvents (alcohol doesn't count), or heat plus time.

Are you confident your oven keeps a steady temperature and won't melt it? If so, bake it at a safe temperature for 24 hours. If not, leave it in the hot sun for a few days, or put it in the dryer with your clothes a few times.

A (toxic) approach I would try is to fill it with gasoline for a few days or until you notice it evaporating too much. This is a cheap organic solvent with similar solubility characteristics as the candles you left in it, so the odor compounds should have good affinity and will leach into solution. The plastic will smell like gasoline afterwards. Is that preferable? You can probably bake the smell out, but I'd do it when you aren't home. "Deodorized mineral spirits" is a less smelly and less toxic (still fairly cheap) alternative.

Lastly, I notice you didn't try bleach or ozone. I wouldn't expect deep penetration into plastic, but bleach and ozone stand apart from almost everything else in their ability to chemically neutralize smells. I have used a small 5V USB ozone generator in refrigerators that have had food go bad to good effect.

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  • $\begingroup$ This is all very useful, thank you. A few followup clarifications. --- What would you define as a sufficiently strong base? Or do you just mean a solution of significantly high pH, regardless of base? If so, how high do you guess? --- Do you recommend a source for NaOH? Easiest option for strong bases are drain cleaners, but likely not a good idea here, right? --- What is the result of mixing dish soap with laundry detergent? --- I'll measure oven. Temp limit? --- I considered ozone, but it seemed infeasible due to 5L volume, no? You suggest 5V USB, any certain one? $\endgroup$
    – JJ123
    Commented Apr 12 at 21:08
  • $\begingroup$ "Deodorized" mineral spirits seem suspiciously too good to be true. I'll try it, but I assume the deodorization makes it far too ~sneaky~ to ever use safely indoors anywhere. Unless "deodorized" is a bit of hyperbole. $\endgroup$
    – JJ123
    Commented Apr 12 at 21:11
  • $\begingroup$ Mineral spirits stinks. Deodorized mineral spirits stinks much less. $\endgroup$
    – James Gaidis
    Commented Apr 13 at 2:41
  • $\begingroup$ @JamesGaidis - Well that's concerning. I'm very urban, so I have limited ventilation options: apartment, roof, back alley... Can you provide a more commonly encountered reference stink? Something of similar stink intensity & profile so I can imagine deodorized mineral spirit stink? $\endgroup$
    – JJ123
    Commented Apr 13 at 4:03
  • $\begingroup$ The stink of regular mineral spirits isn't really that obnoxious, but it lingers. Deodorized MS has some of the heavier molecules (not all!) distilled off, but still has an "organic" odor. Different people react differently, but consider rubbing alcohol (70%): stinks (? - yes and no - maybe slight for most people). IMHO, deodorized MS is comparable, but "heavier" than rubbing alcohol. Roughly. $\endgroup$
    – James Gaidis
    Commented Apr 13 at 14:54

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