Emulsion Stability

JonahRay

I'm looking for some input regarding stability issues I'm having..

I have samples at RT, samples at 50C and samples cycling between freezer/RT/50C. The samples at 50C are showing signs of instability but the samples in freeze/thaw cycle have gone through two rounds and show no issues at all... I thought freeze/thaw was more intense than just one temperature consistently... The issues that I'm experiencing at 50C consistently are not acceptable but the results of the current freeze/thaw are... I'm not sure what to really do with that information

EVchem

Why do you use 50C? 50C is a bit high for most products, we use it in our lab for two reasons- being short on time and  replicating certain warehouse conditions.  If a product fails 50 I don't consider it an automatic need for reformulation.

JonahRay

We used 50C throughout our development process and so for consistency sake we kept it at 50C. Would you say F/T is a better indicator of the stability of the emulsion?

Perry

50C is not an unreasonable temperature for which to do stability.  We went as high as 54C.

The problem with making decisions about samples stored at 50C is that you're getting close to the melting point of some of the ingredients which can have effects on product stability that you would never see in real life. In this way, the 50C samples may not be usefully predictive of the future.

JonahRay

The emulsifier is cetearyl glucoside/cetearyl alcohol (melting point between 60C-70C) and there are some other thickening agents for the water phase.

I'm doing a more accelerated F/T, from freezer to RT to 50C 3 times over and its going well after 2 cycles. @Perry would you say those results are more reliable?

Maybe I should have done 45C if that is more the standard, they may hold up at that temperature..

JonahRay

^ Sorry and Glyceryl Stearate SE as well.

Pharma

Melting point 60-70°C for the whole oil phase?

How does consistency change of the pure oil phase @ 50°C compared to RT?

What type of emulsion do you have? Probably lamellar... 50°C seems high to me but that's from a different point of view (pharmacy v.s. cosmetics).

JonahRay

The other components of the oil phase are liquid at RT, we heat to 70C before emulsifying oil and water phase and the emulsion is O/W. 

Pharma

What if 50°C is close to phase inversion temperature?

JonahRay

Hmm, well if that is the case, lets say I'm shipping across North America, how important do you think stability at 50C is - with the knowledge that it can withstand F/T from freeze - RT- 50C?

DAS

Very. You need to consider the worst case scenario. A truck on the road under the sun can easily heat up to 50°, even more. I'd consider tweaking the formula a bit. Far better now than after losing an account and your reputation.

MarkBroussard

@JonahRay

I think the problem is your Cetearyl Glucoside (and) Cetearyl Alcohol emulsifier.  It tends to yield thin, runny emulsions that are not particularly heat stable, so it is not surprising that you are having difficulty at 50C in an accelerated testing scenario. 

What happens to the emulsion if you remove it from the oven after several days at 50C and let it sit overnight? ... Does it revert back to the same or similar viscosity as your RT samples or does it seem to permanently lose viscosity? ... I suspect the latter.

I tried a few formulations with this emulsifier and ended up reformulating all of them with a different emulsifier.  FWIW:  I no longer use this emulsifier in any formulations.

JonahRay

@MarkBroussard What would suggest as a replacement. The viscosity of the formulations are actually quite high though I'm actually having issues with separation so they won't go back once at RT.

MarkBroussard

You could try Olivem 1000 or RitaMulse or Myristyl Myristate with a touch of Stearic Acid yields a nice emulsion

JonahRay

It might be too late for reformulation in this case. Maybe 50C is pushing it... I could try stability at 45C instead of jumping to reformulating maybe. I've had pretty great success with that emulsifier and I like the feel it imparts.

DAS

Transportation is a lottery, but perhaps you could improve the packaging. Adding polystyrene beads or something like that it's the cheapest I can think of.

MarkBroussard

@JonahRay:

This really comes down to a business risk decision.  If you really think that the product may be subject to 50C for extended periods of time then you need to make sure it's stable at 50C, particularly since you now know that it will separate and not reconstitute when subjected to constant 50C for extended periods of time.

LOL, simply lowering your test criteria to 45C may give you a Pass where 50C gives you a Fail, but what does that really get you?  A product that still fails at 50C.  If you took that approach, then every product could be deemed stable if you simply continue lowering the test criteria at which you deem something to be stable until your product passes.

Pharma

MarkBroussard said:

...If you took that approach, then every product could be deemed stable if you simply continue lowering the test criteria at which you deem something to be stable until your product passes.

Isn't that common practice? *cough-cough*

MarkBroussard

@Pharma:

Well ... product stability is a subjective determination after all.  Stability at 50C is a much more relevant requirement if you are shipping product in India, for instance, than if you are shipping in the US where air conditioned vehicles and warehouses are much more common.

JonahRay

@MarkBroussard Not lowering for the sake of fudging stability but for getting results for more reasonable conditions. If it's going to be stable at 45C then I'd like to keep the current formula and be mindful of temperature when shipping. Others seem to be reasonably confident off their 45C stability data.

If it fails 45C after 8+ weeks then that's another story.

MarkBroussard

@JonahRay

I was just teasing with you Jonah.  If you are comfortable at 45C and have had other formulations with this emulsifier pass on stability at 45C, then you should be in good shape.