Fragrance Oil vs. Temperature

[LuvOurNewf]

Does the temperature of the oils that you soap with have an effect on weather or not a fragrance oil "sticks"?

I tend to soap between 110* - 120* and I'm wondering if I'm too hot for certain FO's.

 

[Crocoturtle]

you can look up the flashpoint of your FO. Most I have are rated 150 and above. If you soap above the flashpoint your FO will just evaporate.

 

[VanessaP]

No. Flashpoint is the temperature at which the FO will light on fire when exposed to an open flame. If it just evaporated above a certain temp, then half my HP soaps wouldn't smell at all. And they do.

 

[Crocoturtle]

No. Flashpoint is the temperature at which the FO will light on fire when exposed to an open flame. If it just evaporated above a certain temp, then half my HP soaps wouldn't smell at all. And they do.

You probably have just been lucky. Most flashpoints are way above the regular tempurature for soaping. The only time it would really be an issue is if you were doing hot process without a thermometer. But yeah, if it "flashes" that means it's evaporating. That's what that means, it's the temperature it becomes a vapor and can catch fire.

 

[VanessaP]

I don't use a thermometer when I make HP and rarely use one when I make CP. I've used FOs with flashpoints of 108 and 120. When I make CP, I force gel in a 170 degree oven. Still have loads of scent. It is the point at which the oil will catch on fire when exposed to a spark or open flame.

http://www.cajuncandles.com/frequently-asked-questions.html

http://www.lonestarcandlesupply.com/frequently-asked-questions/product-specific/fragrance-oils/#24

http://www.candlesupply.com/flashpointinfo.html

http://www.candlescience.com/faq/26/fragrance-oil/what-is-flashpoint/

 

[Sunny]

It's a longstanding point of confusion... Vanessa is correct.

LuvOurNewf, I soap very warm and do not have problems with fragrance sticking most of the time - if I do, it may be that I didn't use enough of that particular fragrance, or sometimes it's just a fader (as coconut scents often are, just for an example).

 

[LuvOurNewf]

Sunny,
Thanks. I was hoping it was the amount of FO and not temperature as I haven't really had any problems with my recipes.

The FO I use all pretty much say to use a max of 5% but it sounds like I need to go a little out of the box, not drastically but enough to see if it makes a difference.

 

[new12soap]

The temps should not be a problem, but you should NOT exceed 5% (or the supplier's recommendation for the particular oil). You can try doing hot process and adding the FO after the cook, which sometimes helps with difficult fragrances. Some people have had good luck using corn starch as an anchor but I cannot swear that makes a difference. But, unfortunately, some scents simply do not stick in soap.

 

[Oingo]

Flash Points and Evaporation Rates

I want to clarify about flashpoint and evaporation. In the context of flash points, the word "flash" means "ignite"; it doesn't mean "evaporate." In other contexts, "flash" can mean "evaporate" -- for example, people talk about solvents "flashing off" and that means they are evaporating. But when you are talking about flashpoints, "flash" means "ignite." Always.

Things evaporate well below their flash points. Leave a little puddle of water out on your counter and come back in a month -- it will probably be gone. But the flash point of water is, well, infinite, because water can't burn. It will turn to steam and evaporate before it burns. You can light a spark around steam all day long but the spark will never ignite the steam, unless maybe there are other flammable things things mixed into it. That being said, increasing the temperature of a liquid usually increases the evaporation rate. Boiling water will evaporate a lot faster than room temperature water.

When things evaporate, they make vapors. The concentration of vapors is highest near the surface of the thing that is evaporating, and it falls off as you move away. You can see this when you look at dry ice fog, for example. The CO2 vapors are thickest near the ice. (Since dry ice is a solid turning into a vapor, it’s called “subliming” instead of “evaporating” but the vapors behave the same nevertheless.) But in nature and physics, nothing likes to be overcrowded. Increasing the concentration of vapors generally increases the rate of dissipation, all other things being equal.

Liquid evaporation and vapor dissipation don’t necessarily happen at the same speed. In fact, the speeds are usually different. So essentially you have a race. If the evaporation rate is only a tiny bit faster than the dissipation rate, the mixture of gasses near the surface of the liquid is mostly air. Even if the liquid is flammable, that mixture of {nearly all air + just a few molecules of vapor} might not ignite in the presence of a spark. But if the evaporation increases a lot relative to the dissipation rate – as it would if you increase the temperature of the liquid without, say, adding a fan to blow or pull the vapors away – the concentration of vapors would increase. You would accumulate more and more vapors in that space near the surface of the liquid. Then, if the vapor is flammable, you would eventually reach a concentration that **does** ignite in the presence of a spark.

In fact, that is how flash points are determined. That is one of the exact methods, the so-called “open cup” method.

This critical, ignitable, concentration is different for different substances so the flash point depends on both the evaporation rate at different temperatures, and the flammability of the substance.

Why does this matter to a soaper? After all you are not lighting flames around your solutions, right? Well, sometimes you can get a spark from electrical / mechanical equipment, for example from a hand mixer or even from striking a metal spoon against a metal bowl. A hot process or melt-and-pour soaper might not let their cooked soap cool enough before adding an FO with a particularly low flash point. A CP soaper might try to add an FO to a seizing batch that is gelling and generating uncontrolled amounts of heat in the bowl. So it is definitely safer to pre-mix your FO's into a bit of carrier oil and add them when you know by measuring that the soap batter is cooler than the FO flash point. (Explosive dust from pouring things like milk powder or cornstarch might be a bigger problem for a small business owner trying to make soaps in larger batches in their garages, but I digress.)

Mostly, the flash points will affect you if you order FOs through the mail. If the flash point is below a certain number, all sorts of regulations apply and you can no longer ship the material through regular mail. Companies like Fedex maintain special licenses to handle materials with lower flash points and they use special procedures. The company selling the material must use special packaging materials. So the cost can go up. If a company is dealing with price-sensitive customers, they might try to get around this by diluting the FO so it can be priced comparably to FOs that don't require all the special handling. You would never know it.


(I am a geeky chemist – I love this stuff, and I deal with it frequently in my profession. )