I made a new batch of my syndet shampoo bars today since the last bar from my previous batch is down to a tiny sliver. I thought of this thread and decided to pay extra attention to how long it took to dissolve the SCI for this new batch. I used a "sous vide" method to do this, meaning I put the ingredients in a bag and heated the bag in a hot water bath. Here's my report --
I currently have SCI in noodle form. The noodles are small rods about 1/16" / 2 mm wide and about 1/4" / 6 mm long. I mixed these SCI noodles with the two liquid surfactants in my formulation -- C14-C16 olefin sulfonate and cocoamidopropyl betaine (CAPB). The proportion of wet to dry surfactants was 1 part liquid surfs to 1.4 part SCI noodles by weight. I weighed these surfs into a heat-resistant clear plastic bag. No other ingredients were added to the bag at this point.
(True confession -- I have dumped all my shampoo bar ingredients together and tried to dissolve the SCI noodles that way. It seems like this should work, right? Nope.
I learned the hard way that SCI dissolves completely in less time if it's mixed
only with liquid surfs, as described here.)
I rolled the top of the bag over several times, clipped it with a metal binder clip, mixed the surfs by massaging the bag, and immersed the bottom part of the bag into a 180-190 F / 80-85 C water bath. I did my best to ensure the surfs stayed submerged in the hot water while keeping the rolled top above the water.
Every 5 to 10 minutes, I pulled the bag out of the hot water, set it in a towel to protect my hands, and massaged the bag to mix the ingredients inside. After 20 minutes of heating and mixing, the noodles were roughly 1/2 their original diameter.
After 30 minutes, I had to look hard to see the noodles, but a careful check showed small fragments were still present. As
@KiwiMoose mentioned, the mixture at this point was a lot more runny than it was when I started. I would have been happy to stop dissolving the SCI at this point and move on with the rest of the process, but in the interests of science, I kept going.
At 45 minutes of heating and mixing, I could no longer see any trace of the noodles, even when I spread the mixture into a thin layer inside the bag and held the mixture up to a bright window.
At the 45 minute mark, I opened the bag, added the remaining surfactant (SLSa) and other ingredients, closed the bag and massaged to mix. I always add a small drop or two of colorant (ultramarine blue powder today) to the final ingredients to help me decide when the paste is fully mixed (more in the next paragraph). The mixture was rather stiff and lumpy at this point.
The bag went back into the hot water bath for 10 minutes. After heating, the ingredients were much more pliable, and I spent a solid 5 minutes massaging and mixing until the colorant was fully mixed in and the paste was a uniform color, which is my sign the ingredients are well mixed. Back into the hot water bath to warm up for 5 minutes. I then briefly mixed the paste, squeegeed the paste into the bottom of the bag, clipped a corner off the bag, and piped the paste into my molds.
Conclusion -- SCI noodles dissolve well if combined with liquid surfactants only. Gently heat in a hot water bath while mixing every 5-10 minutes. Using an efficient "sous vide" method to heat the mixture, the SCI dissolved in 30-45 minutes. If another heating method is used, the process may take more time.
