Pressure build-up in 15% Ascorbic acid emulsion during stability testing
Laurannecarly
Member
in Formulating
Dears,
We've been experiencing significant pressure build up/bubble formation after 2 weeks of 40 degree stability testing with an emulsion. There is minimal discolouration of the Ascorbic acid at this stage, so we are doubting whether this is related to the oxidation of the ascorbic acid. We cannot seem to solve the problem and would appreciate any thoughts.
The formula includes the following and is cold process.
Oil Phase:
- 2.5% Sepinov EMT 10 (Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer)
- 1.2% Sucrose Stearate
- 0.5% Sepiplus 400 (Polyacrylate-13 & Polyisobutene & Polysorbate 20)
- 5% Ecosilk (Isoamyl Laurate and Isoamyl Cocoate) --> to reduce stickiness of ascorbic acid
- 12% Sweet almond oil
- 1% Tocopherol
Water Phase:
- 3.5% Dermosoft 1388 Eco
- 2% Sodium PCA
- 2% Glycerin
- 1% Panthenol
- 0.3% Sodium Phytate
- 0.1% Xanthan gum
- Water up to 100%
Post:
- 0.1% Ethylhexylglycerin
- 15% Ascorbic acid
- 5% Lactic acid
- 5% Sodium hydroxide solution (20% Sodium hydroxide solution)
Should point out that this is to have a 6 month expiry date from production as obviously the formula contains water and ascorbic acid.
Would highly appreciate any thoughts.
Best regards
We've been experiencing significant pressure build up/bubble formation after 2 weeks of 40 degree stability testing with an emulsion. There is minimal discolouration of the Ascorbic acid at this stage, so we are doubting whether this is related to the oxidation of the ascorbic acid. We cannot seem to solve the problem and would appreciate any thoughts.
The formula includes the following and is cold process.
Oil Phase:
- 2.5% Sepinov EMT 10 (Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer)
- 1.2% Sucrose Stearate
- 0.5% Sepiplus 400 (Polyacrylate-13 & Polyisobutene & Polysorbate 20)
- 5% Ecosilk (Isoamyl Laurate and Isoamyl Cocoate) --> to reduce stickiness of ascorbic acid
- 12% Sweet almond oil
- 1% Tocopherol
Water Phase:
- 3.5% Dermosoft 1388 Eco
- 2% Sodium PCA
- 2% Glycerin
- 1% Panthenol
- 0.3% Sodium Phytate
- 0.1% Xanthan gum
- Water up to 100%
Post:
- 0.1% Ethylhexylglycerin
- 15% Ascorbic acid
- 5% Lactic acid
- 5% Sodium hydroxide solution (20% Sodium hydroxide solution)
Should point out that this is to have a 6 month expiry date from production as obviously the formula contains water and ascorbic acid.
Would highly appreciate any thoughts.
Best regards
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- 5% Lactic acid
- 5% Sodium hydroxide solution
acid + base -> salt + water
I once worked on a VO5 Hairdressing problem where some lots of tubes (aluminum) were generating gas and bloating. The exact same formula put in a different tube didn't have the problem. I never did figure out what was causing it but it had something to do with the coating of the tube. We changed tubes lots and the problem went away.
To respond to Perry's question, initial pH is 3.8, final pH is 3.5 after 4-week stability testing. Though this might be due to the fact that the Ascorbic acid has not properly dissolved yet immediately after production.
Should point out that the pH of the water phase is very high (pH 9) due to the Sodium phytate.
The material is glass. We use 15ml transparent glass samples to perform testing at this stage (brown borosilicate glass will be the final packaging).
Please also find a picture of the sample with the white paper towel used as a colour reference. Note that most discolouration has occurred at the surface, there is less discolouration throughout the emulsion. There is approximately 15% expansion in volume after 4 weeks of stability which is very significant.
We are still struggling with this formulation issue and cannot seem to solve it. Would love to get your thoughts on this. Here are the findings up until now based on further testing:
- It does not seem to be related to the packaging in which the samples are stab tested
- When the Ascorbic Acid is taken out, the problem is resolved, so it is related to the Ascorbic acid
- The problem already arises without any discolouration of the AA happening, so we highly doubt it is just due to oxidisation.
- We've also made sure the AA has been completely dissolved, so it does not seem to be related to that
- We've tested with a Sodium hydroxide solution as well as Sodium citrate solution to adjust pH which also does not seem to impact it
- We've tested with Phenoxyethanol/Ethylhexylglycerin as an alternative preservative, but actually it seems to make it slightly worse
- We've tested with two forms of vitamin C, the crystallised form as well as the ultra fine powder form from DSM, both produce the same issue
- Initial results show - this is not yet confirmed - when we increase the level of sucrose stearate, there seems to be more bubble formation, but it's not the whole problem as without it, it's still occurring
Any thoughts would be much appreciated.
Have a good day!
Will also test with knocking out the water phase ingredients.
Have not tested with plastic packaging yet. Only two different kinds of glass: clear glass jars and borosilicate amber glass vials.
One more thing; I had a suggestion at some point that there might be traces of enzymes in the formula that could cause gas formation. Have you had any experience with that?
Very interesting. I should point out, we don't heat the formula whatsoever, it's cold-process. So perhaps that still opens up the enzyme option? Interestingly, there is only gas formation in the presence of Ascorbic Acid, so it must be that if there is enzymatic activity, it's mainly reacting with the AA.
The reason I raise the enzyme option is also because of the phenomenon that the gas formation increases as we increase the sucrose stearate. And perhaps the sucrose acts as a source for the enzymes?
Regarding your second point, are there any other emulsifiers you would recommend? Or in general, is there any additive that could enhance the stability of the AA (in an O/W emulsion) that we've not included?
Perhaps it's due to the fact our product is an emulsion with a higher viscosity than 15% AA serums in the market (e.g. C E Ferulic by Skinceuticals, Paula's Choice C15 and C Firma by Drunk Elephant). We perhaps see anaerobic oxidation quicker (vs aerobic) as throughout the emulsion, there is limited direct contact with oxygen due to the higher viscosity.
It does make us wonder though how these brands can achieve the 15% AA and have it be relatively stable for up to 3 years. Though I guess all of these serums have a yellow to orange colour which either indicates some oxidation and / or the use of ingredients to give an orange colour to cover up oxidation over time. Feedback on these products is very positive, although the metal-like smell indicating at least partial oxidation is not uncommon.
I do have to point out that at lower temperature stability testing (32-35 degrees) when compared to the 45 degree samples for accelerated testing the lower temperate sample have significantly less pressure buildup (when corrected / converted to the same shelf life).
We are now testing at lower concentrations to see if we can achieve an acceptable shelf life.
Also I believe C Firma is still being investigated for violating the skinceuticals patent for C E Ferulic . https://www.vox.com/the-goods/2018/11/16/18098503/loreal-drunk-elephant-skinceuticals-lawsuit
Interestingly, we've also ran experiments with Ferulic acid just to try it and have not found it to make any difference.
Apprecier is a stabilized provitamin C formed from L-ascorbyl 2-phosphate (aqueous Vitamin C) and L-ascorbyl 6-palmitate (oil soluble Vitamin C), an amphipathic compound.
It's terrifically expensive. Early results really impressed me. At 2% I was getting visible wrinkle reduction and skin tone lightening, after about 3 weeks use as a night cream. My first problem was selling price. The formulation was very expensive and the fancy airless pump, too. Then there was the box, the instruction pamphlet...
Then came the stability problem. At around 7-8 weeks, it began to turn brown. It ended up a latte sort of colour after about 10 weeks.
Given the production and packaging cost, high selling price, and poor shelf life, I decided to cut my losses.
We are also now looking into derivatives (probably MAP), but I personally just still can't seem to accept letting go of Ascorbic Acid completely.
One of the samples we had created included Resveratrol, which is a rather impossible combination but just an interesting experiment. Yet when comparing a sample with and without the Resveratrol there is barely any pressure buildup in the Resveratrol sample. There is aerobic oxidation occurring though. It seems to be the Ascorbic Acid is primarily / initially oxidising as the emulsion slowly turns yellow, before turning into a latte like colour on stability. (Whereas we found Resveratrol just turns into a latte like colour when oxidising.)
Though this is quite interesting as there is no gas formation which is what we're after. Yet the issue is that the Resveratrol sample separates after 5 days at 45 degrees... We can repeat this sample along with variations of your other instructions (including the use of a more stable oil, citric acid, removing PCA, removing vit E) just to see how Resveratrol impacts it. What do you think?
It seems you are most probably right about the CO2, as when I test a vial with pressure buildup / bubbles, it immediately extinguishes the flame (no pop).
It would indeed be good to get a better understanding of what oxidation is occurring as well as understanding residual unoxidised Ascorbic Acid at the end of stability, will look into this.