Today we’re doing something a bit different; I wanted to walk you all through the experiments I did while I was working on last year’s Christmas Tree Body Wash as The Tale of the Curdling Body Wash. It was a really interesting puzzle that I worked at for quite a while—I managed to isolate the trigger, but I still don’t know exactly what is going on, so my only solution for avoiding the curdling is avoiding the trigger. I thought I’d share my process and my results, and maybe we can crowd source a better answer!

The Tale of the Curdling Body Wash

 

This story starts last autumn as I was wrapping up my Formula Botanica course work. I developed a simple body wash using Caprylyl/Capryl Glucoside and Cocamidopropyl Betaine. I wanted to increase the lather, and I remembered reading somewhere that Hydroxyethylcellulose could help with that, so I swapped the xanthan gum I had been using for some Hydroxyethylcellulose (HEC). Magic! Not only was the consistency of the body wash dramatically improved, but the lather became absa-freaking-loutely amazing. Swoon. I made a few versions (different scents and different colours), bottled ’em up, and headed off to Europe.

 

 

Here was the formula at that point:

8.00% Glycerine
2.00% Hydroxyethylcellulose

70.50% Distilled water
12.00% Caprylyl/Capryl Glucoside
6.00% Cocamidopropyl Betaine

0.50% Liquid germall plus
1.00% fragrance or essential oil

Process: Whisk together HEC and glycerin. Add water, surfactants, and colourants, stir gently. Heat in a water bath, gently stirring relatively frequently (~once every 2–3 minutes) until thickened. Remove from heat, stir occasionally until cool, stir in cool down ingredients.

The Tale of the Curdling Body Wash

Once I got home I needed to wrap up my Christmas series, and I’d planned a Christmas Tree Body Wash. My experiments from earlier in the fall were looking great and seemed like the obvious choice for the base for the Christmas Tree Body Wash. So, I whipped up two versions: one with an essential oil blend, and one with a fragrance oil, as I’d been doing for many of the Christmas Tree series. Everything seemed to go swimmingly until I went back to the bottled body wash after twenty minutes or so… and they had both separated. There was a thin, watery liquid floating on top and a blob of gelatinous goo at the bottom. What on earth? The original samples from my coursework were still stable—crystal clear, silky smooth, and definitely not separating curdled disasters.

This was roughly the formula at this point:

8.00% Glycerine
2.00% Hydroxyethylcellulose

70.40% Distilled water
12.00% Caprylyl/Capryl Glucoside
6.00% Cocamidopropyl Betaine
0.10% lake dyes (blue + yellow = green)

0.50% Liquid germall plus
1.00% fragrance or essential oil (essential oil version was fir balsam + peru balsam, fragrance oil was balsam cedar fragrance oil)

The Tale of the Curdling Body Wash

In this photo you can see the separation—the liquid floating on top and the blob at the bottom.

Thinking it might be my process I tried many different ways of mixing up the solution—cold hydrating the HEC, warm hydrating, hydrating without stirring, hydrating with constant stirring, cold mixing everything with five constant hours of stirring (thanks, KitchenAid stand mixer). No dice.

Up next was isolating ingredients, making the gel adding one ingredient at a time, stirring, and waiting between additions. The fragrance/essential oil quickly outed itself as the problem. I tried many different fragrances and essential oils, noted what happened, and cross-referenced the chemical components (click here to learn how to do that) to find the common element between all the fragrances and essential oils in the experiments that split. It was benzyl benzoate. Once I had a hypothesis I tested it, intentionally choosing fragrances and essential oils that did or didn’t contain benzyl benzoate and adding them to small samples of the unscented body wash. The scents I used that didn’t contain it were “black salt & cypress” fragrance oil, fir needle essential oil, and “citrus mist” fragrance oil. Boom. The hypothesis held.

The Tale of the Curdling Body Wash

So many different experiments.

Failure! You can see the thin liquid seeping out of the jelloid blob.

Success! No seeping.

So, at this point I know what is causing the curdling, but I still have no idea why. I decided to broaden the experiment. I tried a slightly different version using an anionic liquid surfactant (Sodium Laureth Sulfate, pH 7.5) instead of a non-ionic liquid surfactant (the Caprylyl/Capryl Glucoside), adjusting the amount of surfactant and water to keep the active surfactant matter the same. Hydroxyethylcellulose is non-ionic, so its charge shouldn’t be a factor, but who knows!

8.00% Glycerine
2.00% Hydroxyethylcellulose

54.70% Distilled water
27.70% Sodium Laureth Sulfate
6.00% Cocamidopropyl Betaine
0.10% lake dyes (blue + yellow)

0.50% Liquid germall plus
1.00% fragrance or essential oil

This experiment split/curled before adding any fragrance or essential oil, so in this one it’s the Sodium Laureth Sulfate that’s the problem. That’s… weird. Maybe the charge of the surfactant is part of it? I did more experiments.

I made a batch of the first body wash, but without the primary surfactant (the Caprylyl/Capryl Glucoside).

The Tale of the Curdling Body Wash

Experimenting with different surfactants.

I used a lake dye that shirts in different pHs so you can really see which ones are basic and which ones are acidic.

I then divided it up and added 15% of a variety of surfactants:

  • Coco glucoside (non-ionic, pH 11.5–12.5)
  • Decyl glucoside (non-ionic, pH 11–12)
  • Disodium Laureth Sulfosuccinate (anionic, pH 5.5–6.2)
  • Sodium Lauryl Sulfoacetate (and) Disodium Laureth Sulfosuccinate (anionic, pH 5.2–6.2)
  • Sodium C14-16 Olefin Sulfonate (anionic, pH 8–9)

I chose these surfactants for the variety of charges and pH values, and because they’re all the liquid surfactants I own. They all have ASM values that are quite a lot lower than Caprylyl/Capryl Glucoside so it definitely wasn’t an even ASM challenge, but from previous experience I was pretty sure anything that was going to split would, regardless of ASM, as fragrances with 10% benzyl benzoate split as effectively as fragrances with 80% benzyl benzoate.

Without adding any fragrance of any kind, these were the results:

  • Coco Glucoside: split, pH ~8
  • Decyl glucoside: split, ph ~9
  • Disodium Laureth Sulfosuccinate: stable, pH ~4
  • Sodium Lauryl Sulfoacetate (and) Disodium Laureth Sulfosuccinate: tentatively stable, ph ~4
  • Sodium C14-16 Olefin Sulfonate: stable, ph ~5

So… now the non-ionic surfactants are breaking things, and the anionic ones are fine. This is counter to my first two experiments, where the non-ionic Caprylyl/Capryl Glucoside was stable without fragrance, while the anionic Sodium Laureth Sulfate split. Thinking it might be pH (since the basic ones were splitting while the acidic ones seemed stable) I weighed out some of a successful unscented batch using Caprylyl/Capryl Glucoside and added 1% triethanolamine to raise the pH to ~8.5 to see if it would split. It didn’t.

I then took the three alternative surfactant experiments that were stable (Disodium Laureth Sulfosuccinate, Sodium Lauryl Sulfoacetate (and) Disodium Laureth Sulfosuccinate, Sodium C14-16 Olefin Sulfonate), portioned some off, and added ~1% of a fragrance oil rich in benzyl benzoate. All three were initially stable; it’s now been over two months and the experiment with Sodium Lauryl Sulfoacetate (and) Disodium Laureth Sulfosuccinate has split while the other two remain stable.

I adjusted the original formula to use Sodium C14-16 Olefin Sulfonate with the same active surfactant matter:

8.00% Glycerine
2.00% Hydroxyethylcellulose

63.90% Distilled water
18.50% Sodium C14-16 Olefin Sulfonate
6.00% Cocamidopropyl Betaine
0.10% lake dyes (yellow + blue)

0.50% Liquid germall plus
1.00% fragrance or essential oil

After making the base I divided the it in two and included 1% fragrance oil to one half and 1% essential oil blend to the other. Both fragrance blends contained benzyl benzoate and caused the Caprylyl/Capryl Glucoside version to split very quickly. Both versions very initially stable, but then split after about four days (vs ~20 minutes for theCaprylyl/Capryl Glucoside version).

The Tale of the Curdling Body Wash

The Tale of the Curdling Body Wash

So, what’s going on?

I still have no idea. There seems to be some sort of reaction happening between HEC, benzyl benzoate, and a couple surfactants… but then there also seem to be some reactions happening between just HEC and the surfactants. Here’s what I’ve learned:

  • Basic non-ionic surfactants cause the body wash to split without any added fragrance
  • An acidic non-ionic surfactant (Caprylyl/Capryl Glucoside) + benzyl benzoate causes splitting. No benzyl benzoate, no splitting.
  • One basic anionic surfactant (Sodium Laureth Sulfate) caused splitting without any added fragrance
  • Another basic anionic surfactant (Sodium C14-16 Olefin Sulfonate) is stable until benzyl benzoate is added
  • Disodium Laureth Sulfosuccinate seems fine, while Sodium Lauryl Sulfoacetate (and) Disodium Laureth Sulfosuccinate splits (so the addition of the Sodium Lauryl Sulfoacetate is likely impacting the end product)
  • pH seems like it might be a factor, but I haven’t been able to find any reliable link

That’s where I’m at. If you have any insights I would love to hear them!

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