Heat transfer - will my lipstick formula melt in the storage package?

[Makeup Chemist]

Hi, I am a makeup formulator and need to make a lipstick that would be stable at 50ºC.
The stability is tested in a chamber with an inner temperature of 50ºC.
The lipstick is in a plastic packaging - a regular one that can be seen in any store.

The question is: Will the temperature of the lipstick itself reach 50ºC?
Would part of the heat get "stopped" by the packaging and the actual lipstick would actually get heated to less than 50ºC? I vaguely remember from uni that coefficient of heat transfer and that there was some loss of temperature down the line when it reaches the final object?

The whole objective of the experiment: even if the melting point of the formula is 48-49ºC, that does not necessarily mean that the lipstick bullet will melt over at 50ºC into its packaging.

Any thoughts please, and thank you!

 

[davenn]

Hi
welcome to PF

The question is: Will the temperature of the lipstick itself reach 50ºC?

I would say most likely

Would part of the heat get "stopped" by the packaging and the actual lipstick would actually get heated to less than 50ºC?

If it is less, probably only a few deg's less ... consider a "TV dinner" in its packaging and put into an oven ... there's no problem heating it upDave

 

[Merlin3189]

Yes, it will reach 50ºC if you leave it long enough. The package will insulate it to some degree, which means it slows down the rate of warming. How much and how long you need to leave it is difficult to say and probably best determined by experiment.

Even if you put an object in the oven with no insulation, it will take time for heat to be transferred and the temperature to rise. The rate of heat transfer will be propotional to the temperature difference between the object and its surroundings. If the oven is at 50ºC then the temperature of the object (lipstick) will approach 50ºC asymptotically - ie. theoretically it takes for ever! But the oven won't be at exactly 50ºC all the time, so you will get to the lower bound eventually.

The other factor is that, if the MP were 50ºC, then it will not melt immediately it gets to 50ºC. You need to continue supplying heat to change the state from solid to liquid. But probably it doesn't have a clear melting point, but melts over a range of temp.

All in all, I'd think your oven should be a few degrees warmer than your expected MP. If it warms slowly and you take the lipstick out when it has half melted, then it will be at its mid MP even though the oven is warmer.

If you can measure and graph the temperature of a sample as it warms or cools, the flattening of the slope will indicate the melting range. (This could be a sample in a test tube or something. The package is irrelevant here.)

If you just want to know if the lipstick is ok up to 50ºC, pop it in the oven and leave it for a week. If it's not deformed by then, I'd guess you're safe.

But this is just based on my limited experience of finding MPs in an ordinary chem lab. There must be a history of this sort of testing amongst your industry. Try to find someone versed in the art.

 

[Makeup Chemist]

Thank you so much!
Actually few degrees means A LOT in our world. So if the bullet stays at 48-49ºC, that would be all we need.

Wow Merlin 3189, you are so knowledgeable, I admire that! I can definitely put the lipstick in the oven and I do it regularly with every new formulation.
Now I have to act the other way around. My current formula melted since its melting point is 40-45ºC and that is because our client requested this soft texture.
It's a new trend with lipsticks.
So I have to strengthen the bullet to not melt at 50ºC, but keep the nice texture. It's quite challenging.
The problem is what melting point to target? I was hoping that m.p. of 48-50ºC would be fine.. I was hoping that the bullet doesn't reach exactly 50ºC.
Yes, the duration is at least 1 week.

Thank you!