I am formulating a toner that contains 2% salicylic. Target pH of the toner is 4.5 to 5.5 (pKa of SA is 2.97 so I adjusted target pH to be higher than this). I mixed it under gentle heating with 2% glycerin, 8% 1,3-propanediol and 0.8% PEG-40 hydrogenated castor oil to fully solubilize the acid.
I added this premix into water with EDTA and 0.8% NaOH. I added other actives and extracts.
Im worried if this doesn't work.
My colleague made the formula. She was able to dissolve the SA by heating it in water, thorough mixing and added with NaOH. Her output was a clear solution. Our client approved her formula. Then 3 months passed, I checked her retention sample. Then I noticed suspending precipitates in it. So I modified her method as I've detailed above.
I wanna know if my method was right just so no precipitation would happen. If it's not, is there other way to do this right?
Comments
By adding sodium hydroxide you’re creating sodium salicylate which won’t be able to penetrate, but is definitely more water soluble.
if you care about performance you may want to avoid NaOH altogether and just use a higher percentage of polyols in the formula. You want the free acid available as much as possible for maximum effect.
But let’s see what others say here.
I did try cooling down the SA premix but it just crystallizes. This is when I thought I need to adjust the pH of water first, make it alkaline, before adding the SA premix so that it won't crystallize.
I’ve been trying to formulate a shampoo for myself with salicylic acid, and if proven effective in salicylate form it would make this so much easier.
You will need on the order of 25% to 30% Propanediol. Add 1% Sodium Citrate and that will help solubilize the SA. As mentioned above, ditch the NaOH. Keep your pH between 3.0 and 4.0. Add 2% Polysorbate 80.
See website for details www.desertinbloomcosmeticslab.com
I can see this is not going to be an inexpensive product.
I was in fact formulating a salicylic acid toner as well, and 20% PG did not work on its own, but didn’t try > 25% as suggested. Didn’t spend any more time on it and used alcohol.
See website for details www.desertinbloomcosmeticslab.com