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Some questions about SLS in hard water
We have 3 types of SLS available locally.
SLS liquid 30%
SLS powder 95%
SLS powder 70%.
SLS liquid has pH ~6 and SLS powders have pH 11-13 @1%
I did some experiments to see there compatibility with hard water.
In soft water 10% and 0.3% AS solution of all three SLS products are clear.
In hard water of well however
0.3% AS SLS liquid becomes pearly and that pearl moves around when you mix it. That pearl doesn’t precipitate after one day. (Photo attached)
0.3% AS SLS powders become cloudy and in less than one day, a white powder like thing precipitates. That precipitated powder was easy to remove by just rubbing it with dry fingers.
Questions:
1: Is SLS just supposed to become cloudy in hard water or it is supposed to precipitate too?
2. Why my SLS liquid doesn’t precipitate but SLS powder does?
3. Is this cloudiness or precipitation of SLS powders because of SLS incompatibility with hard water or because it is salting out or anything else? I did increase pH of 0.3% AS SLES which was clear in hard water to 11-13 with sodium hydroxide and it became cloudy and precipitated too.
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6 Replies
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Questions 1 and 2 have to do with pH. Your first solution that is only cloudy might also precipitate over time, or if you increase the pH to the level of your second solution. Keep in mind that the interaction of hard water ions and anionic surfactants is electrostatic, and thus has to do with pH.
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Yes, that liquid SLS precipitated too after 2nd day but unlike SLS powder solution, when i mixed it again, that precipitation dissolved in solution easily and it became cloudy again and when i added EDTA to it, it became clear.
With SLS powder solution the precipitation didn’t mix again and was attached to glass and spoon. Although it was removable by rubbing with hand.
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Check the pH of both solutions.
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Hello @abdullah. I’ll add to the always observant @ketchito that besides pH to 8.0-plus, this formula of yours really calls for a hydrotrope. CAPB or other amphoteric is not the best but can work. Sodium xylene sulfonate works better and at low use, is good with SLS, and is inexpensive. Eid Mubarak to you and yours.
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