Thursday, February 3, 2011
Thickeners: Hydroxypropyl methyl cellulose (HPMC)
The cellulose derivatives, like HPMC and hydroxyethyl cellulose (HEC) are created through a reaction of cellulose with ethylene or propylene oxides or both to create these products.
HPMC is kinda weird because it's very soluble in cold water and almost insoluble in hot water (and remember, things tend to be more soluble when you add heat, which is yet another reason to heat and hold our products!). With most of our thickeners, we add them to the water first and allow them to hydrate before heating; with HPMC, it's best to add it to cold water and allow it to hydrate but don't add it to the heated water phase of our products. We'd then add that to the cool down phase of our products. I know, it's weird! This is because it doesn't gel in heat, it gels in cold, so it basically congeals to create a semi-flexible mass. The more HPMC you add, the lower critical temperature needed to achieve gelling.
Yes, I know that last paragraph is very strange and I'm trying to wrap my head around it. I've searched through tons of manufacturers' recipes and although I've found a few where the HPMC is used in the water phase and heated, almost all of them suggest adding it at the end or making the entire surfactant based product cold.
If you want it to just be part of your lotion to offer a silky feeling, then add it to the heated stage at 0.1% to 0.3% and use it as part of your heated water phase. If you want to use it as a gelling agent for something like a shampoo or even a shower jelly (this is why this series started - I hate carageenan and need something else, and HPMC sounds like the right ingredient), then you can sprinkle it into cold distilled water and add it at the end of the process with the cool down ingredients. (Make sure it is distilled water because we don't want beasties or other contaminants in our products!) Use it at 0.2% to 0.5% in surfactant based products. Or add it to your conditioners at the same amount in the same way (only don't reserve all the water for the conditioner - take out about 10% or so and use that at the end of the process). The general suggested usage rates for HPMC is 0.3% to 1%, with the up to 1% being for proper gels like shaving gels.
HPMC is a great thickener for surfactant based products like shampoo or body wash because it doesn't need salt to thicken, so it will thicken things like decyl glucoside, sulfosuccinates, and SLeS, all of which are difficult to thicken with salt. It won't interfere with our surfactants' cloud point or titer point, which means you can achieve a clearer product. Like the other gelling ingredients we've seen so far this week, it offers freeze-thaw stability, meaning it will work like anti-freeze for our products.
Finally, because HPMC is pseudoplastic (which means it exhibits shear thinning) we can make our products quite thick and still have them squeeze out of the bottle.
Join me tomorrow for fun with xanthan gum (reprised).