Solution Settling

Dear Valerie: I’ve been working with hydroxypropyl methylcellulose in a shampoo but can’t seem to get it in solution. It just settles at the bottom. Any tips? 

—Bottom Feeder

Dear Bottom:

I love HPMC but it does take technique to work with it. I haven’t met too many chemists outside of the haircare field who are familiar with it. It’s cousin (second cousin?) hydroxyethylcellulose (HEC) is multitudes easier to work with; disperse it in pretty much any amount of cold water with strong mixing. Heat the batch up or adjust the pH upward, the glyoxal shell falls off and the HEC swells into a nice gel. Done!

HPMC is much pickier. The water in your formula is the most critical factor to successfully working with HPMC, and it comes down to quantity, temperature and timing.

HPMC prefers less water for dispersion, and the water must be hot, hot, hot! I’m not joking, it will not go in water that’s cold or warm or hot. Your batch must be blazing! The minimum temperature for HPMC dispersion is 80-85ºC. Don’t cheat this part—you’ll regret it the moment gelatinous blobs form from lack of heat, and you must start over. Pour your water into your main vessel, heat it up, generate a strong vortex, sprinkle the HPMC in (or pour in a slurry) and allow it to mix for 30 minutes. When you think it’s done, add 10 more minutes before proceeding with your batch.

Hold Your Water!

It’s not just how hot the water is that’s crucial, but also how much and when you add it. Usually, when dispersing a cellulosic or gum, the more water, the better. HPMC is the opposite. I essentially cut my water phase in half—the first portion is what I initially charge the vessel with and begin heating. If your water phase is large, try 1/3 up front. Once hot, I add my HPMC, let it mix (plus 10 minutes), and then pour in the rest of the water, cold. Yes, cold! This will allow the HPMC to swell and stretch out. It also partially cools your batch down. You can add the rest of your ingredients after. If anything is a solid and needs to be melted, you can add it before your final injection of water.

I’m sorry to rehash this again, but I absolutely must reiterate the importance of the initial heating step. Don’t make the mistake of trusting your thermometer. If you aren’t calibrating your thermometers at least once per month, like I do on the last day of each month, you need to start. A bad temperature reading is not only the dumbest reason a batch fails and wastes your time, but it creates inconsistency from batch to batch. This is especially true in hot pours. I can’t tell you how many times I’ve seen a bad temperature reading cause the demise of a batch. Put it on your calendar to do and think of me while you do it. I’ll be thinking of you! 

Valerie George

askvalerie@icloud.com

Valerie George is a cosmetic chemist, science communicator, educator, leader, and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care at her company, Simply Formulas, and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist or showcasing her favorite ingredients to small brands and home formulators at simply-ingredients.com