Working with Salicylic Acid - recrystalization issue and other questions

simonasimona Member
edited June 2014 in Formulating
Disclaimer: I am formulating for personal use only
===================================

What is the best method for solubilizing SA ? And how do I overcome instant recrystalization as I add the water? 

example: for a 2% SA gel, I used: 
- 2% SA
- 8% propylene glycol
- 2% ethoxydiglycol

I do not have my notebook here, but I separatelly made a gel with either 0.5% or 1% sclerotium gum, as I wanted to add 1% vitamin E to the mix (I pre-made a 50%-50% mix of dl-alpha tocopheryl acetate and d-mixed tocopherols). I also remember using 1% or 2% panthenol.

Process:
- weigh SA 
- add PG
- add EDG
- mix well until a clear solution is formed (I mixed with no heat and the mixture was clear after a few minutes mixing
- slightly heat the water and mix sclerotium gum until the gel forms
- pour the gel on top of the SA + Solvents blend.

What do I get? That is right - SA crystals. They go away as I heat the mixture and come back as it cools down.

=======================

1. I have asked around and I have received this advice: I should use Na citrate as a buffer (I was going to use NaOH to raise the pH to 3.5-3.8). I was under the impression that I should do that before adding the water , to raise the pH to a 3.8 and later, if needed, to bring it down with lactic acid. I just got my hands on some na citrate so I may try this, but it is very difficult to measure with great accuracy, when you make a 50g or 100g batch! So, if you were me, how would you use the Na citrate and when in the process? if I am to add it to the SA+solvents mix, I will not be able to measure the pH , so I wonder: how much should I use ?

2. after seeing the crystals forming, and as I has some PG leftovers in my bottle, I decided to add some more to the mix (I did not weigh it though). And I also added some PS20 (1-2% in the end, as while mixing and heating water eventually evaporated itself from my beaker). It looked like my gel was finally crystals free, so I decided to put it in my airless opaque container and use it. After a week or so I noticed tiny crystals of SA in the gel. SO it really needs further investigation of the formula :). But the question is: is it still safe to use, or the SA crystals will be ineffective when present on skin? 

==
edited as I can't spell today! 

Comments

  • simonasimona Member
    edited June 2014
    =====
    PART 2
    =====


    3. I used a product from Paula's Choice and I am puzzled by their recipe: 
    Water, Methylpropanediol, Butylene Glycol (slip agents/penetration enhancers), Salicylic Acid (beta hydroxy acid/exfoliant), Camellia Oleifera (Green Tea) Leaf Extract (anti-irritant/antioxidant), Polysorbate-20 (solubolizing agent), Sodium Hydroxide (pH balancer), Tetrasodium EDTA (chelating agent).

    a. how come their product is crystal clear? As I add PS-20, my solution turns milky of various degrees. Is the PS-20 in such a low percentage that the solution clarity is not affected? 

    b. how much solvents would you say they use? MPD and BG - could they be more than 10%? 20%? I only have propylene glycol, dipropylene glycol, ethoxydiglycol  and some MPD that I can use and, as these do not come cheap and from my country, I can't afford to test too much and waste ingredients. 

    c. the pH is low - 3.5-3.8. Why do they use tetrasodium EDTA ? I would have thought that perhaps disodium EDTA would have been a better choice, can anyone shed some light here? 

    d. green tea extract is amber brown. How much would they use to have a crystal clear solution, no colour? less than .5%? Just curious on the matter


    I also remember someone posting a chart on how much PG (and also various other solvents) are needed to solubilize 2g of SA. There was also another chart, can't find it now, but it was saying than a 40% propylene glycol solution in water can solubilize 2% SA . Would it make sense for the PC product above to have such a high % of solvents, or is there another production trick I am not aware of, like addint tetrasodium EDTA or NaOH solution to the sa + solvents mix prior to adding the rest of the water?

    Going to work now, as I already ask too many questions. They may be stupid, as I do not have the chem. background and all my knowledge comes form experimenting and reading whatever I can on my own, so please forgive me if I talk too much :)

    All inputs highly appreciated! 

    p.s. I know that ethanol is a great solvent for SA , but I avoid it on my skin, so I am stuck to other solvents
  • Chemist77Chemist77 Member, PCF student
    edited June 2014
    Simona I had a crystal clear formula (though there is no polymer involved here) with MPG 35-40%, DPG around 3%, little eucalyptus and mint oils. The formula stays clear and no crystallization has been observed till yet (1 year almost), try adding a little surfactant to keep the SA (mine was 1% in the formula) from recrystallizing. I had used Sodium Lauroamphoacetate around 2-3%. Now coming to your gel I guess you can try incorporating in your polymer gel (whichever you feel would be best for you) this concoction and give it a try. Though I am not very sure about the success chances nonetheless you can always try.
    The product was a callus remover, FYI. 
  • simonasimona Member
    edited June 2014
    Thanks, Milliachemist! 

    My product is intended for a daily use (twice) , morning and evening, as leave in treatment for my very oily skin, prone to blackheads. So my other concern is whether I should use that much solvents (40% ) or not. I am not sure how PC's product is made, if they have the same amount of MPD + BG or not, so... would it be safe ? :)

    and yes, I wear sunscreen 30 and above on a daily basis. 
  • Chemist77Chemist77 Member, PCF student
    edited June 2014
    Well let's hope someone more learned can give a better input here. MPG with that high dosage might produce allergies in certain skin types so it would be better if someone can guide you in a better direction.
  • simonasimona Member
    Thanks, @milliachemist! :)
  • Simona, I guess, the simplest way to fight your problem is making an alcohol SA solution and use it on a daily basis. I don't know the reason you avoid the ethanol on your skin - but I gues it's the best and safest choice.

    Otherwice, BG and PG would be safe too. I can even say ( don't beat me :) :) :) ) - You may want to use even Acetone -( the purest grade) for your skin - but it depends on how oily your skin is. This is widely known method among professional cosmetologists. Right after applying the Aceton based SA solution, the microcrystals may appear on the skin surface and it would look "frosted" - but they would still work.

    And the last suggestion: Are you sure your skin is "oily", or it's a kind of Hyperhydrosis? In this case you may want to use other actives than SA.
  • simonasimona Member
    @Vitalys,

    Alcohol irritates my skin, so I really want to avoid it. It becomes red and it swells - same with fragrances. I am better since I skipped alcohol , 2 years ago.

    Indeed, ethanol is the simplest way , but sadly not for me. I should order some butylene glycol and study more into how to use Na Citrate (I'll test when I have the time).

    And indeed, my skin is oily, it's not hyperhydrosis. And blackheads prone. 

    thanks a lot for your insights!
  • DavidWDavidW Member, PCF student
    What is this product you are making?  Is it a face wash, a serum that you leave on your skin....

    If you significant;y increase PG and decrease water it will help.
    Add 1% sodium citrate to water first and mix till dissolved.
    Sal acid will go into PEG-400 if you can use that.

    The other thing you can do is raise the pH up till the salicylic dissolves.  Not sure what pH it will end up being and not sure if this does anything to the salicylic but it will help dissolve it.
  • simonasimona Member
    Sorry , everyone, I had a couple of really difficult weeks in the office so I could not focus on anything else. 

    @DavidW - what I indend to do is a leave in 2% SA exfoliating gel. I am planning for the next week to use 1% Na Citrate, when I will have some spare time. Also, thinking to use 15% PG from start. the pH I am aiming to reach is 3.5 - 3.8. Preferably 3.5.

    THanks, everyone, for all advices! I will definitelly follow up here with my next experiment's results. 
  • Hello Simona, Have you solved the problem of recrystallization because i have the same issue 
  • simona said:
    Sorry , everyone, I had a couple of really difficult weeks in the office so I could not focus on anything else. 

    @DavidW - what I indend to do is a leave in 2% SA exfoliating gel. I am planning for the next week to use 1% Na Citrate, when I will have some spare time. Also, thinking to use 15% PG from start. the pH I am aiming to reach is 3.5 - 3.8. Preferably 3.5.

    THanks, everyone, for all advices! I will definitelly follow up here with my next experiment's results. 
    15% PG will not help you resolve the problem. I've made some sample and the Glycol must use at least 20% - 25% to make SA not recrystallization. And with 30% glycol you can add at least 10% AHAs to your formulation
Sign In or Register to comment.