Sodium Stearate-Based Stick

Hello!

I've been working on a propylene glycol-free deodorant stick for quite a while now and have landed on something that's stable, little to no sweating, and doesn't shrink. It's ~6% sodium stearate, ~25% water, 2% glycerin, 10% starch with the q.s. going to zemea propanediol. I find the 2% glycerin is enough to help the stick solidify properly but not too much to minimize sweating. 

I'm working on a similar stick structure for a customer who wants to reverse engineer their current product. I'm at ~7% sodium stearate, ~40% zemea propanediol and ~45% water. No starch or glycerin since their current product doesn't contain either. I've found this base is pretty stable, little sweating, however it's shrinking in the 40C and 50C ovens. 

I understand shrinkage is pretty much to be expected (as is some sweating), however it's pretty significant and something I'd like to minimize. Based on the differences between these two formulas, it seems like the glycerin or starch is preventing the shrinkage of the stick. I was hoping someone may have some insight on this type of formula since I haven't been able to find much online, or some suggestions on paths I can take forward.

Thanks!

Comments

  • chemicalmattchemicalmatt Member, Professional Chemist
    @gdabain You have too much unbound water in Formula #2. Lower the water concentration and q.s. with a more PG and some higher homolog such as butylene glycol or dipropylene glycol. Also, I do not  think starch is doing much "preventing" since it is not solvated but suspended. It absorbs some water but not that much. Cheers! 

  • gdabaingdabain Member
    Thank you for the advice! In the second formula, I did a version with ~25% water and noticed the batch didn't go clear when heated (most of my other batches are clear at 82 C, indicating to me that the sodium stearate is properly dissolved). This mixture also began solidifying at ~78 C whereas the pour temp for my other batches hovers around 70 C. Did I reduce the water TOO much you think?
Sign In or Register to comment.