Adjusting final volume & pH

I am experimenting with sepimax zen.  By the end of preparation if I am not ok with consistency I add more of gelling agent. But this makes the formula more than 100%. So can I leave some room for water and can that be added after I finalize the amount of gelling agent?

For instance The final make up volume with water was 80%.I used 79% of water and as per my formula 0.5% of zen and later added 0.2% more. Left it overnight to hydrate and when stirred I was fine with consistency. Then I added the balance 0.8% water. Am I doing right? Is this the way to do?

Similarly even for pH adjustment how can it be done after getting the end product. Should I first adjust pH of water phase and then go for emulsification? If at the end pH of cream alters how do I adjust without not exceeding 100%. And also will the added adjuster go into the cream without seperating?




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  • @Learntounlearn Do you always find you need to add water at the end? If so, you may want to drop your Sepimax Zen level from the beginning. You should try and keep the level the same once you find the right level as it will be much more challenging to adjust on a manufacturing scale. You may have some variation between batches, but you should still be able to set a specification (e.g. 20,000 - 30,000 cP) for viscosity and know that it will end up in this bracket. 

    However, sometimes in a hot process you will notice water loss - in this case, weigh the vessel before you start the procedure, and then you can make up the weight to the total batch size with water again at the end. Personally I prefer to avoid this where possible as you will always lose some of your formula to the stirrer, spatula, viscometer, pH meter etc as well so it's not exact, but that's what the industry tends to do. On a manufacturing scale, you would use a closed vessel so during cooling all the evaporated water will condense and drop back into the mixture, so in that case it's not such a problem.

    In the lab, always check and adjust the pH at the end (however some formulations may require adjusting in the middle as well, e.g. if using carbomers). In that batch, you will end up with more than 100%, but then for your next batch you can take the amount of pH adjuster you required out of the water level so that it adds up to 100% again. This is why many formulations list pH adjusters, colours, fragrance etc as "q.s" and the water as "To 100%", because it is up to you to decide on the appropriate amount of those and then take it out of the water portion.
    E.g. if water is at 72.65% in my first batch, and I end up adding 0.61% of citric acid at the end to adjust the pH, I will include this amount of citric acid on the batch sheet as a separate ingredient and start with 72.04% water to account for the amount needed. If it turns out you don't need it all, that's ok, but at least you have accounted for it.


    I hope that makes sense?
  • Hi
    Thank you so much for your reply
    My current batch came out perfectly but the problem is I don't need to add anymore zen now but to make it to 100% I need to add 1.5 gms of water. Will it be ok to add the remaining water after the preparation has gelled?

  • @Learntounlearn Occasionally you will need to leave the formulation be once it's made, but in most cases you will be fine diluting slightly at the end. If you're unsure, try adding it proportionally to a very small portion of the formula before adding that back into the main mixture. That way you will see the effect on that small amount first before you spoil the whole batch.
  • MarkBroussardMarkBroussard Member, Professional Chemist
    @Learntounlearn:

    You're getting hung up on the numbers adding up to 100%, which really is not relevant if you are making final adjustments to adjust pH, etc. 

    For pH, just make your batch, measure the pH, and then add whatever quantity of pH adjuster is required to get the end product to your target pH. 

    Same with the thickening polymer ... calculate your formula to 100%, then add the requisite amount of each ingredient.  There is no need to be adding additional water at the end just so the numbers add up to 100% if you are happy with the final viscosity.  The fact that you are adding water to "top up" at the end of the process, means you are not adding the proper amount of water at the beginning of the process.
    Chemist/Microbiologist formulating in the Organic & Naturals arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program guidelines focused skincare & haircare products. 

    See website for details www.desertinbloomcosmeticslab.com
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