DIY Menthol Crystallising?

[stevenmu]

I made up a 100ml batch of menthol liquid using flavouring, PG base and VG from Inawera. I made it to roughly 6mg strength, with 5% flavouring and about 80/20 VG/PG.

It was fine, but way too mild for my taste (inawera's menthol seems to have change, much milder and less eucalyptus-ish). So after vaping about 30ml I decided to throw another 5ml of the menthol flavouring it. When I DIY, I tend to make up a 100ml batch in a 100ml bottle, and then pour some out into a 30ml or smaller bottle to carry with me. So I put the extra 5ml flavouring into the remaining 70ml I had in the big bottle and gave it a good shake to get it all mixed up. Normally at this point I'd sit it in a warm water bath for a little while, but was in a rush out to work so didn't bother this time.

When I started pouring it out into a smaller bottle to take with me, I noticed there was a lot of crystals in it bunching up in the mouth of the bottle. If you've ever put juice or a soft drink in the freezer to quickly cool it, but left it there slightly too long, it was exactly like that.

I know when you use menthol crystals, if you use too much they can re-crystallise, but would that make any sense if you took a pure liquid flavouring, and then effectively diluted it down more?

Or is there some other thing that can go wrong with PG/VG, potentially making it unsafe to vape?

 

[Hoosier]

Menthol is menthol, so the liquid you are using was made from the natural form, crystals.

When the suspended menthol has the carrier agent drain away, it is normal for the crystals to reform. I usually notice it more on the threads of the bottle, but it isn't unusual for it to appear at the mouth. Warm it up and shake it, it will be fine.

(Any chemists know if this effect is precipitation?)

 

[stevenmu]

That makes a lot of sense, thanks.

I guess so that they use some carrier that works more effectively than the PG/VG, so when the PG/VG dilutes the carrier it's causing the crystals to precipitate out.

I don't remember much of the little chemistry I did, but I think it does count as precipitation. A quick look on wiki turned up "Precipitation may also occur when an antisolvent (a solvent in which the product is insoluble) is added" which is think is roughly what happened here.

 

[ajventi]

I think precipitate is the proper term. Is menthol completely insoluble in VG? Because this is what happens with a supersaturated solution. I've never worked with menthol in crystal form, so I don't know the solubility in PG or Ethanol. Did this bottle go through any extreme temperature fluctuations in it's life? And can you say the crystals definitely weren't there before hand.

 

[stevenmu]

They definitely weren't there when I mixed the batch initially about a week ago, and I have been carrying some of that around since in a clear bottle and there was none in that either. The large bottle isn't clear, and there could easily have been crystals formed in it without me noticing until after I'd added the extra menthol and tried to pour some out. The bottle hasn't gone through any extreme temps, just normal ambient household temps, though it does get quite cold without the heat on at the moment.

I have heated a 15ml sample and it's gone back to looking pretty normal, if slightly misty. I'm pretty sure now it was just the menthol crystallising. I was a little worried it might have been some other weird reaction, but that doesn't seem to be the case.

Is menthol completely insoluble in VG? Because this is what happens with a supersaturated solution. I've never worked with menthol in crystal form, so I don't know the solubility in PG or Ethanol.

From what I have read in other posts by people who use crystals directly, they are slightly soluble in PG/VG, but much more so in ethanol. Most people seem to use PGA/Everclear to dissolve a lot of menthol, then add that to their liquids. I'm guessing the menthol flavouring I got from Inawera uses something in which menthol crystals are much more soluble, and adding too much of it to the PG/VG had the effect of diluting the solvent leaving me with an effectively super-saturated solution.

 

[ajventi]

I did a quick search and found an aromatherapy site that said Menthol was barely soluble in Glycerine. Then did a quick calculation and figured your final blend, adding 5-mL to your 70-mL bottle gave you 12% of the original Menthol flavoring. With the high amount of VG in there I think you just don't have enough solvent to hold the menthol in solution. IDK about solubility in PG, but even if PG was a good solvent there's not even 12-ml of PG in that bottle. Heating it up may dissolve them, but heating is just a temporary change in solubility. Eventually if it's super-saturated those crystals should fall out again.

 

[stevenmu]

Thanks for the reply. Seems you're right. I found that heating does dissolve it all again, and it happily stays in solution for a few days even after it has cooled back down, but as soon as one bit of crystal seems to form, that prompts a load of others to form too (which sounds about right from what I remember from chemistry).

It vapes perfectly when it is all dissolved properly, it's very very strong obviously, but I have been using up some bogegate era cartos that are terrible for flavour so it balances out nicely

(next batch will be a lot weaker though)

 

[ajventi]

The first crystal takes a long time to form, but once a crystal does drop out it acts as a substrate for the rest of the menthol to crystallize. There's a process called seeding where basically you could drop a small amount of crystals into the saturated solution and it will speed up the precipitation.

 

[purelyscientific]

Its just simple recrystalization.

As a solution is heated its ability to hold more of whatever you dissolve in it is increased.
When you max out how much can be dissolved in it at a certain temperature then cool it they will naturally precipitate out.

This happens with my ethyl maltol solution when I put it in the freezer for storage. It forms really cool spike-like crystals.

but as soon as one bit of crystal seems to form, that prompts a load of others to form too (which sounds about right from what I remember from chemistry).

I believe those are called nucleation points. More points=More places for them to form.