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Let’s talk seriously about the rheology modificators
Hello. I know there are so many topics at the forum regarding the rheology modificatiors, but when I am trying to find more detailed information I get lost. Some of the topics have incomplete information, some are based on assumptions. So I would like to ask the members here which are more experienced, what is the right approach to work with polymers, and why?
I would like to focus my question over the two of the most used polymers - the xanthan gum and the Carbomers.Usually I am using the Evonik’s leaflets as a guide of how to properly use their emulsifiers. Most of the others companies have a restricted access to their formulations, but Evonik and Hallstar doesn’t. In the TEGO Care PSC 3 leaflett is mentioned a very interesting detail: “It is recommended to combine TEGO ® Care PSC 3 with Xanthan Gum (0.2% for creams and 0.3 to 0.5% for lotions) in order to optimize the texture and stability of the emulsions. In order to avoid a negative impact on the lamellar structures formed by the emulsifier and consistency enhancers, it is recommended to add Xanthan Gum below 40 °C to the emulsions.”I’ve seen a lot of formulations, and there the place where we can put the Xanthan gum in the process vary a lot. In some cases it’s in the water phase from the beginning, in others it’s in the cool down phase. From what I understand from this leaflet, the emulsifier and the consistency enhancers need time to form the lamellar structures during the cool down, so if we add the Xanthan gum at the beginnng, we will mess this process?Also I’d like to mention that i’ve read somewhere that the high shear mixing / homogenisation have a negative impact to the Xanthan gum gels.Now I’d like to ask a question about the Carbomers and their high-shear stress resistance. According to this publication: https://realizebeauty.wordpress.com/2022/04/04/carbomer-chemistry-high-speed-mixing-homogenising/There is a serious risk of damaging of the polymer chains. This damage manifests as a non-recoverable loss of viscosity – so the end gel or product is thinner than it otherwise could be.As far as i understand this is applicable only for the pre neutralized carbomers and/or those who doesn’t need a neutralisation. Because once the polymer has create it’s own chains, every high shear force will have a negative impact on it.And still, when I incorporate the sodium carbomer in my lotions at 40 degrees, can I use my homogeniser for a couple of seconds to spread the carbomer more evenly, off course at the lowest speed? -
6 Replies
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@ggpetrov I’m not sure adding carbomer to an emulsion at 40°C would be enough. Keep in mind that at that temperature, a good deal of the micellar structure has already formed. I’d make a test, trying both ways to add it, and evaluate the final result and the stability.
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I like ketchitos suggestion, you could do the same to evaluate your concern of homogenisation damaging your final viscosity- Split the batch and homogenize half as you normally would. If it’s really for a few seconds I doubt there would be a noticeable impact, but that’s what experimentation is for.
I always add xanthan gum and other hydrocolloids to the water phase relatively early on- these gums need time to hydrate and they tend to swell better in pure water (or as close to it as you can get).
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I’ve seen Belinda Carli from The Institute of Personal Care talk about it on their channel a few times, like in this video here.
Briefly, she points out that high shear is not the same as high RPM. Shear is related to the type of blade that is used in the homogenizer, so even if you stir at low RPM, the shear will remain the same if you don’t change the blade type.
In this case, the recommendation is that you opt for a low shear blade. -
Carbomers are much, much more robust than everyone thinks they are, especially the less crosslinked ones. Do not worry, use your homogenizer. Regarding order of addition for ALL polymer resins and gums natural or synthetic: allways disperse in water alone first! The exception are the HASE thickeners, those can usually drop in later. I never understood the whole “disperse (resin or gum) in glycerin or oil or whatever then add to batch.” Madness.
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ggpetrov said:Also I’d like to mention that i’ve read somewhere that the high shear mixing / homogenisation have a negative impact to the Xanthan gum gels.Now I’d like to ask a question about the Carbomers and their high-shear stress resistance. According to this publication: https://realizebeauty.wordpress.com/2022/04/04/carbomer-chemistry-high-speed-mixing-homogenising/There is a serious risk of damaging of the polymer chains. This damage manifests as a non-recoverable loss of viscosity – so the end gel or product is thinner than it otherwise could be.As far as i understand this is applicable only for the pre neutralized carbomers and/or those who doesn’t need a neutralisation. Because once the polymer has create it’s own chains, every high shear force will have a negative impact on it.And still, when I incorporate the sodium carbomer in my lotions at 40 degrees, can I use my homogeniser for a couple of seconds to spread the carbomer more evenly, off course at the lowest speed?Just do as someone mentioned above….test it.
Here is what I do…. strip away the formula…it will only confuse you.
Take the correct amount of water the formula would have….and the correct amount of gum/carbomer/polymeric…whatever you want to test. And mix these two sole ingredients. Hit with as much shear as you think you will use, were you to make the entire formula.
You have your answer. And I think you will find the result will be as @chemicalmatt has suggested…. no problem. It always has been for me.
Sometimes you’ll find the brilliance in simplicity.
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@ggpetrov Just a few general points:- Rheology modifiers aren’t always polymers (true, most are).- Rheology as a colloquial term may refer to feel, viscosity, spreading behaviour, stability, hydration and speed of evaporation, and other effects.- Polymers may be added for any of these reasons. Depending on the aim, the time of addition can differ.- Proposed reading: Rheology Modifiers Handbook by D. B. Braun & M. R. Rosen.- The believe system (mentioned by @ketchito ) that emulsions are micellar structures is only true for some semisolid preparations. The modern view is (but may still be inaccurate or incomplete) that onion skin like lamellar liquid crystals encircle oil droplets. This by itself modifies rheology and stability. It’s these crystalline structures which tend to be distrubed by too early gelling of the water phase. If an emulsion relies on lamellar liquid crystals (which is the case with several emulsifiers like diverse glucoside and polyglyceryl esters and possibly all mixtures with fatty alcohols), gelling should be done after formation of those liquid crystal structures. It may work with early gelling as well but the outcome will not be the same. Sure, it depends on the % and type of polymer you’re adding and why you’re using it.- Ever wondered why formulations with ‘newer’ and ‘eco-friendly’ emulsifiers sometimes take a few days to ‘ripen’? I wondered too… turns out that the they need as long because of the formation of lamellar liquid crystals. Because the first step depends on diffusion, a higher viscosity is bad. The second step is rearrangements and changes in crystal modification where polymers don’t interfere.
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