Dear Valerie: I am working on a formula that calls for 2.5% of sodium PCA. The one I have on hand is sodium PCA 50%. Do I need to add more sodium PCA and less water since it’—Ratio Alger

Dear Ratio:
Thinking about the percent active of the material is always a good consideration, especially when you’re evaluating studies from raw material suppliers. Using 0.5% active matter in a study surely can cost a bit more than just using 0.5% of a material at times. Good job on catching the discrepancy between the formula and what you have on hand! When I was a lab technician, I worked on a cream that contained an emulsifier which turned out to be a partial tradename identified by the formulator that gave it to me to batch. When it went to production, they wrote the complete trade name down. Turns out the addition of a few letters meant it was a completely different raw material from what I used. Not a good situation to find yourself in when you have produced 40,000 pounds of Oops!

In your scenario, I would ask whoever gave you the formula for a certificate of analysis or specification sheet for the material used. This will point you in the exact direction as to whether they were using a solution of sodium PCA or not. My hunch is, they were. I have never encountered sodium PCA in powdered form, although you can find PCA on its own as a 100% active powder, without the sodium salt. Most suppliers offer around a 50% solution of Sodium PCA. It’s also unusual for a formulator to write down an ingredient in its percent active form on a batch card. Never say never, though!

If it turns out the formulator somehow used or denoted a 100% active Sodium PCA, you will need to head back to general chemistry and apply the dilution equation to this situation, C1V1 = C2V2 to get the right active content. This means you would need to adjust the formula to contain 5% of a 50% Sodium PCA solution, and QS the water by 2.5%.

If the formulator can’t produce any documentation, I would go ahead and use your 50% active Sodium PCA solution on hand at the 2.5% listed. After all, using 1.25% active Sodium PCA (2.5% of a 50% solution) is a nice quantity for skin or hair. Therefore, you would not need to adjust your percentages. Just plug and play.

One practice I always recommended to my young chemists is to calculate the theoretical percent solids of a formula and compare it to the actual solids realized during analysis of moisture loss. This not only prepares the chemist for production but teaches them to be cognizant of what activity of materials they are using. This way, if they need to find a substitute or are handling another person’s project, they’—Like for Like

Dear Like:
Carbopol¹ is a trademark of Lubrizol for its acrylic acid-based polymers, however, nearly everyone I have met in the lab uses the term Carbopol when they want to reference the INCI Carbomer. There are many other suppliers of carbomer and acrylic acid-based thickeners. I supposed it’s like Band-Aid. Does anyone use the term, “adhesive bandage?”

While the terminology gets tossed around, carbomer is certainly not a commodity and shouldn’t be treated as one. Carbopol 9XX series and Ultrez can be similar in certain aspects but there are also many obvious differences. It’s important to understand their nuances and consider the selection carefully. I always say, “an afternoon in the library can save weeks on the bench.”

While all “carbomers” have high yield and relatively high clarity (with exceptions), the main differences between them are in their INCI, routes of synthesis, flow/skin feel and electrolyte tolerance. Carbomer has been around for decades as a homopolymer of acrylic acid. Both 940 and 980 have the INCI Carbomer, but 940 is one of the originals, synthesized in benzene, while 980 is synthesized in an acetone-like cosolvent.² Although they are similar in viscosity and yield, I would choose to use 980 over 940 because it is not polymerized in benzene and is considered more toxicologically favored. The downside of using 980 is that it yellows over time due to impurities from the cosolvent. Both have similar electrolyte tolerance and clarity.

The Ultrez line was created as an extension of the original 9XX series and has a little more nuance between the grades. Ultrez grades 10 and 30 have Carbomer as the INCI and 20 and 21 have Acrylates/C10-30 Alkyl Acrylate Crosspolymer—at the end of the day they’re carbomers as we know them.

All Ultrez materials have varying electrolyte tolerance. Ultrez 10 is the least tolerant, 20 and 21 have medium tolerance and 30 has the highest tolerance. This is easy to remember—the higher the number, the higher the electrolyte tolerance! Electrolyte tolerance also lends to how fast the gel breaks on skin. The lower the tolerance, the easier it breaks from the skin’s natural salts. Ultrez 10 is the lightest in terms of skin feel, followed by 30, while 20 and 21 are the heaviest.

One advantage of the Ultrez series over 9XX is their ability to disperse. I like to reach for these because they’re a little easier to wet into your system than the 9XX series. With 940 or 980, you need a good vortex and a bit of time. One advantage the 9XX and Ultrez 10 and 30 have are the INCI name carbomer. This is much easier for a chemophobic consumer to swallow than anything with the word acrylates.

Most people think of using carbomer or acrylate crosspolymers at a neutral to high pH, but they can work at lower pH ranges, too. However, you may have varying clarity and viscosity performance below a pH of 5.5. This can be to your advantage (or disadvantage) if you’re working with fun actives like glycolic acid. Having an arsenal of different polymers at your fingertips allows you to select a different one if your system requires good viscosity and ultra-high clarity at a low pH (choose Ultrez 30) or low viscosity but high yield at a low pH (choose Ultrez 10). You won’t get this flexibility with the 9XX series.

I hope you see that there are substantial differences between “carbomers” and not all are created equal. While the 940 and 980 are similar in performance to Ultrez 10, they’re not generic equivalents. I’d like to think Ultrez is a little more sophisticated.

I encourage you to head on over to the bench and try making simple 0.5% solutions of each (don’t forget to neutralize them!) and see for yourself the tactile differences. I personally like the richness of Ultrez 30, but they have all their place in formulas. 

References

1. Carbopol and Ultrez are registered trademarks of the Lubrizol Corporation.
2. Carbopol Polymer Excipients – Homopolymers, Copolymers & Interpolymers, www.lubrizol.com/Health/Pharmaceuticals/Excipients/Carbopol-Polymer-Products