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Inconsistent cream properties. Smooth one time, coarse the next
Hi all, I am having issues with a small batch skin protectant cream I am making. The issue is that it sometimes comes out very smooth and creamy and other times is more viscous and coarse with one batch actually failing in a chunky mashed potato state. The product is an oil in water emulsion. It contains multiple emulsifiers including BTMS50, cetyl and cetaryl alcohol and sorbitan stearate. It also has skin protectant ingredients including dimethicone and lanolin. The cream is made by mixing oil and water phases at about 75 deg C with a hand held immersion blender to homogenize. Blending is continued while still heated and then during cooled down until about 61 deg C where it is no longer effective. Batch size is about 10 kg. Immersion blender is 1HP. The problem is that some batches finish into a beautiful smooth cream and others are coarse. I have not been able to determine what causes the two different results. All ingredients are exactly the same. The amounts of each are the same. The heating times are the same. The blending time is the same and yet I get two different results. I realize this is most likely straying into the art part of cosmetic manufacturing but I would love to hear any suggestions. Thanks!
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33 Replies
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hi There
are both stable creams or is one Brocken?
Do you Still have samples of both outcomes of your Productions?
If so and they both are stable, have you Tried if one of them is maybe oil and water and the other one is water in oil?
Sometimes if you are right on the edge of a Turning point with the formulation the amount of water that evaporates during heating is enough to switch the system and give you another Formulation.
You can test it with a Water-soluble colorant just solve it in Water at around 0,5 % and at it to both formulations just on the top without stirring. If the Colorant stays at the top you have water in oil formulation if it dissolves over time ( maybe one night or two) you have an O/W emulsion there.
Or fast but not as scientific put some of the Cream on the hand if you can scrub it off with water you have an O/w if you can not and the water is peeling off your skin like a lotus effect you have a W/O emulsion. -
Very interesting point. I was wondering if I was loosing significant water in the heating phase even though the vessel is covered. Both creams seem quite stable. it is the appearance that is the issue. I might be right on the ragged edge of O/W vs. W/O. I’m not sure the viscosity is that different (no viscometer available) but you can see a difference when putting it into jars. Should I just start with more water to account for loss?
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Sorry just something basic to ask - Do you weigh your water ingredients vessel before and after heating so you actually know how much water you may lose each time as this will likely vary? If so Add back the lost water (using water heated at same temp). Just a very basic suggestion and not likely to add anything of value compared to all the other excellent answers given (which I learn so much from so thanks all :))
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Calculating lost water after heating will drop the temperature considerably. Normally I add 7% extra water in the beginning itself to compensate that loss.( This is for 100 gm batch. For 200/300 gm. batch size it may be reduced to 5%) For conditioner batch especially with BTAC you may need around 8% as BTAC is solubilized @ 85 degree Celsius.
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@Stivtoo Is vessel/beaker the same in both cases (this can impact on required energy and cooling time)? and your cooling time (if this changes, emulsion structure could be different)? Also, for how long you homogenize your product to make the emulsion (temperature should be mantained through the emulsion process).
Also, some products benefit from an extra mixing before reaching 50°C.
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I heat and hold the oil phase at about 75 C for 1 hour the water phase is brought up to 75C just before mixing. Vessels are water jacketed stainless steel. I’ve used the same vessels every time for good and bad batches. I homogenize from mixing at 75 C for about 30 min. then continue while cooling until about 61C
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Stivtoo said:I heat and hold the oil phase at about 75 C for 1 hour the water phase is brought up to 75C just before mixing. Vessels are water jacketed stainless steel. I’ve used the same vessels every time for good and bad batches. I homogenize from mixing at 75 C for about 30 min. then continue while cooling until about 61C
Why you hold oil for 1 hour?
I melt it, mix it and that is it. -
@Stivtoo After the 30 min of mixing, do you reduce (or remove) the mixer speed during the cool down phase? This helps release air and enables formation of micellar structure.
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I have tried to remove the mixer after the initial 30min blend. Sometimes its fine but other times you can see phases separating. On these occasions I keep blending till it has cooled to 61C. Not sure what causes the different outcomes.
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for me still, looks like a phase switch have you tried testing O/W and W/O properties if both are the same or different?
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@ketchito is onto the solution here, in two parts, but let me add some clarification. Cationic emulsions such as yours @Stivtoo require low shear and a long cooling gradient to form lamellar liquid crystal matrices. If the only tool you have is a homogenizer, you will see inconsistent results like you have, and not much to do about it. I would apply the homogenizer for only 5 minutes (@Abdullah is right, 30 minutes unnecessary) at 75C, then begin cooling SLOWLY while mixing with a low shear Lightnin’ mixer at low-moderate speed. Once you get to 40 -45C and thickened you can zap it again with the homogenizer to smooth out even more. @Gordof is correct here: what you see is inversion, your emulsion doesn’t know what it wants to be. Slow cool at low shear and it will be consistent each time.
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how can an emulsion with a cationic non-ethoxylated emulsifier
invert, in a manner consistent with the conventional laws of
thermodynamics? (answers on a postcard, please)water in
oil emulsions are very difficult to form, because they’re the only
possible route to uniformity in a situation where all other routes are
physically impossibleto me, this looks like
it’s down to a difference in cooling rates, which has led to differently
sized droplets - have the batches all been made in containers of the
same size, shape and material, and also, have you tried homogenising the
coarse emulsions? -
@chemicalmatt, I remember @Perry mentioned they had/have a common practice to add water at the end to speed up the cooling (reduced cooling time from 6 hours to 2 hours if my mind works). You are saying it needs slow cooling down.
When I do my conditioner, I use homogeniser for a few minutes (until smooth glossy emulsion forms) and after I let it cool down under low shear.
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Pardon the naive question, but what is the difference between a homogenizer and a low shear mixer?
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lwere said:Pardon the naive question, but what is the difference between a homogenizer and a low shear mixer?
Homogeniser does mix things under high shear. Creating a really small droplets. That helps with stability, feel, etc …
Perfect for most emulsions. Not suitable for most polymers, as it cuts the long chains.
Low shear mixing is mostly done by hand or overhead mixer. Like on the picture below - propeller for example.
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I think the images are inverted in that diagram @Paprik (homogeniser and rotor stator are swapped) but i like that description otherwise
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All my mixing batching containers are stainless jacketed non pressurized vessels. Always the same ones. I use city water cooling to reduce the temp. after homogenizing. I can surely try a short homogenization followed by a low shear cooldown which takes 2-3 hours. My cooldown adds are Germall Plus, Panthenol and Vitamin E. I used to add the dimethicone ingredient after cooldown (~45C) because I had heard anecdotally that it can decompose at higher temps but others said that was not the case and I haven’t seen any problems adding at 75C. I do wonder though because the dimethicone surely imparts gloss and flow to the product. Maybe I should move it back to cooldown adds?
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I add dimethicone under 50°C too.
Don’t have any other explanation other than following suppliers recommendation.
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@Paprik i mix dimethicone with oil phase, heat to 60-70°c and make the emulsion.
Is it necessary to add dimethicone below 50°c?
How do you add it? I mean when emulsion is made you reduce the temperature and add dimethicone, then do you homogenize again?
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Abdullah said:@Paprik i mix dimethicone with oil phase, heat to 60-70°c and make the emulsion.
Is it necessary to add dimethicone below 50°c?
How do you add it? I mean when emulsion is made you reduce the temperature and add dimethicone, then do you homogenize again?
I actually thought it should be in the oil phase too, but when I checked some suppliers data, they recommend add that below 50°C. So I do it.
I usually add 1 - 2% only, so I add that with my heat sensitive ingredients in the cool down phase under low shear.
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Paprik said:Abdullah said:@Paprik i mix dimethicone with oil phase, heat to 60-70°c and make the emulsion.
Is it necessary to add dimethicone below 50°c?
How do you add it? I mean when emulsion is made you reduce the temperature and add dimethicone, then do you homogenize again?
I actually thought it should be in the oil phase too, but when I checked some suppliers data, they recommend add that below 50°C. So I do it.
I usually add 1 - 2% only, so I add that with my heat sensitive ingredients in the cool down phase under low shear.
I should try that too.
What viscosity do you use?
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@Abdullah, I have 350 and Dimethicone fluid, which is 10 cps.
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@Abdullah, sorry mate, I do not answer for this.
I mostly use 350 at 1 - 2%.
I bought the 10 fluid just for the feel, but haven’t really work with it yet. -
Hello Everybody. Recently I had the same problem with formulating hair conditioner. @ketchito & @Abdullah guided me. I have made small batches (100gm) & may take commercial batch incoming month.
What you said is correct: inconsistent results. You have to be precisely accurate as far as processing of LGN is concerned.
What I learned from theory is:-
1) Add incompatible ingredients such as silicone after the LGN is formed
2) Add oils, esters in oil phase for equal distribution.
3) To avoid instability mix vigorously close to phase transition temperature.
However as adviced by @ketchito I added silicones in oil phase itself & it not only worked out well but resolved the issue even for large batches. I am unable to upload 3 most important documents related to this topic. But still @chemicalmatt comments are self explanatory.
I really appreciate people who apply this theory even for Skin care products. In my experience the results are truly unpredictable.
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Here are those links for 2 documents I referred above. 1)https://www.researchgate.net/publication/314604663_Lamellar_Gel_Network
2)https://www.sciencedirect.com/science/article/pii/S0009250921003171#:~:text=Increasing%20the%20temperature%20reduced%20the,the%20majority%20of%20the%20process.
Hope this will be useful for better understanding of LGN🙂
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Do you have these documents?
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