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.