As I mentioned yesterday, decyl glucoside has two main drawbacks - a high pH (as high as 11.5) and difficulty thickening. Let's take a look at those issues!
In this recipe, the pH was too high thanks to both decyl glucoside and disodium cocoamphodiacetate, but I used my trusty pH meter to measure it and citric acid to bring it down to a reasonable level. (You can reduce pH through the use of various acids, but citric acid is the cheapest and easiest to find.) In this recipe for a foaming facial cleanser, I had a good pH of 6.05, but I only used 5%.
If you want to use decyl glucoside in any serious amounts - I'd say 10% or more - I would invest in a pH measuring device. I have used the strips in the past and I didn't find they worked well for me, but you can give them a try if you wish.
pH is a major issue, and you really must keep this in mind when making any product. If you make something out of the right pH range, you can cause problems with your hair or skin. You can't just throw 20% decyl glucoside into a recipe and assume the pH will be right as the odds are good you've just thrown something that was in the right range - 5.0 to 6.0 - into the alkaline range - over 8.
Weekend Wonderings: Reducing pH
Chemistry Thursday: Let's take a look at pH
Chemistry Thursday: How to measure pH?
Weekend Wonderings: The importance of pH in shampoo (scroll down a bit)
The other issue is that we can't thicken decyl glucoside easily, which is one of the reasons I tend to use it in foaming bottle products. There are three main ways we thicken our products: by increasing the concentration of the surfactants, by increasing micelle size, and by creating gels.
Increasing the concentration of the surfactants isn't just about adding more surfactants; it's about fooling the system into thinking there are more surfactants. We don't want to add more decyl glucoside because of the high pH, so can we fool it? We can, and we can do this by adding salts or electrolytes. But here's the problem - decyl glucoside doesn't care about the salt curve or electrolytes, so it won't work. It might work for the other surfactants you're using, but it seems like people want to use it on its own, so salt isn't an option.
Can we increase the micelle size of decyl glucoside? Sure, we can add fatty ingredients like Crothix or glycol distearate, but these things aren't as effective as they could be and you could be using huge amounts to get some minor thickening.
I tried it with a shampoo I designed to be for oily hair, and I had to add so much Crothix to the product that it felt slimy! Your experience may vary!
Can we create a gel? Yep! That's the recommended way to thicken a product with loads of decyl glucoside. Try using xanthan gum at the suggested usage rate of 0.1% to 0.3%, Amaze XT at up to 2%, or other gel making things like carbomers or guar gum at the suggested usage rates. Make sure you aren't using things that will break the gel. This is a fine art, and I suggest reading all you can before you try it, then keep amazing notes!
Take a look at this post at the Chemist Corner forum for some ideas. Or check out this document on the topic. And remember to balance the pH before you start the thickening process! Or do what I do and use a foamer bottle for your product and avoid all that thickening stuff! :-)
Now that you have a few ideas of how to use decyl glucoside, let's take a look at how we can use it in our products! Join me Friday for a few ideas on how to substitute it for other surfactants before we use it in a few products we'll formulate from scratch.