Home Cosmetic Science Talk Formulating Free vs Bound Water

  • Free vs Bound Water

    Posted by Cafe33 on February 12, 2020 at 9:33 pm

    I am making Syndet bars using ground SCI as a main ingredient. My formula also contains 2% Sodium Lactate 60% solution. That means 1.2 % actual Sodium Lactate and 0.8% of Water. 

    1st Question - Am I right to assume that this 0.8% water is bound by the Sodium Lactate even if it is added to an anhydrous mixture of dry powder surfactants? Does it essentially stay bound? 

    Aside from this 0.8% water, my formula also contains 5.60 % free water from CAPB. 

    2nd Question - When water is used as a binder, is it considered bound or is that simply a term for free ions dissolved in water?

    I have on hand Sodium Chloride, Sodium Citrate and Silicon Dioxide (Colloidal and regular)

    3rd Question - How do I measure binding power of the different salts? 

    I know that 1g of water dissolves 0.35g of NaCl from a simple google search. 

    4th Question - Does this mean that 0.35 g of NaCl binds 1.00 g of water or is there more to it?

    5th Question - Are there any potential complications to adding any of these salts directly to CAPB? Would using high amounts of Sodium Citrate lower the pH too much?  

    I know these are a lot of questions but I would really appreciate some answers. I have been reading many books and running many tests, but sometimes answers to simple questions are difficult to find on my own.  

    Cafe33 replied 4 years ago 5 Members · 8 Replies
  • 8 Replies
  • Cst4Ms4Tmps4

    Member
    February 13, 2020 at 8:22 am
    I have been reading many books and running many tests, but sometimes answers to simple questions are difficult to find on my own.  

    I agree with you on that! Sometimes one head is not better than two or more than two. Also, whatever we read can be very biased.

    I think, what you are trying to achieve is to harden SCI bar.

    I do not know whether or not the word ‘binding’ applies here because it looks like it is about ions, to me. Maybe is ionic bond.

    Binding usually is used on thickeners. Such as all kinds of ‘cellulose’, ‘gums’, gelatin, natural or synthetic. You can find these in tablets and capsules.

    The said 0.8% water in Sodium Lactate tends to evaporate from (some surfactants). This is the reason why most surfactant systems have humectants such as Glycerol to prevent pump nozzle from bring obstructed as the solution dries. You can see some shampoo/wash can end up like snot and ‘dries’ there.

    Sodium Citrate is basically pH neutral. No matter how you add it in anything, that anything stays at the same pH.

    I never make syndet bar but I used SCI, however I did not notice the effect of adding NaCl directly to CAPB. (Because I did not bother :D )

    Only yesterday did I notice that SLES and CAPB combination is enough to thicken the mixture without NaCl. Very awesome! This phenomenon is vanished as soon as more water is added (to make the final product up to 100% or 100g).

    I do not understand what you meant by my formula also contains 5.60 % free water from CAPB”. Does that mean the CAPB you have is actually 94.4% purity? Is this high purity even possible?  ::open_mouth:

    It could be similar to products that claim to have 20%, 60%, 80%, or more Sodium Hyaluronate/Hyaluronic Acid. Absolute nonsense. Fair enough they say the “nano” one has the lowest molecular weight, can penetrate the skin deeeeeeeep into the dermis. None of them dares to come up and prove how much SA they actually can mix with water, not even with the nano one. Oh sure, now they say SA is too expensive to merely prove. Excuses upon excuses.  :|

  • Cafe33

    Member
    February 13, 2020 at 4:31 pm

    Thanks for your response. I am using 30% Active CAPB. I have access to 37% and around 47% if Im not mistaken. I have to buy 200kg and 800kg of each respectively. I also have access through Evoniks to dry CAPB which is around 80-82% Active. 

    I am using 8% CAPB which corresponds to 5.60% water. The book I am reading named Soap Manufacturing Technology, water is referred to as a binder. It is in fact a binder. 

    My goal is to increase dish stability, I dont want the bar to get runny when exposed to water. The hardness has been good, just looking for the best formulation.

      

  • chemicalmatt

    Member
    February 14, 2020 at 5:09 pm

    The term free water may be misleading, since Aw (water activity) is a factor of all constituents involved with or interacting with the water present. I always use the term “bound water” to mean the hydrate - or water molecules - actually inherent in the material itself.  E.G. Borax decahydrate has 10 moles bound water.

  • bill_toge

    Member
    February 16, 2020 at 8:59 pm
    what you call the ‘binding power’ of a salt is its solubility in a given solvent - there are many methods to determine this, simple and sophisticated, and solubilities of relatively common substances are widely published
    when the term ‘binder’ is applied to cosmetics and other formulated mixtures, it is typically used to mean a substance which acts to keep the mixture physically homogeneous; it is an entirely separate meaning which has nothing to do with the substance’s power to solvate
  • Cafe33

    Member
    February 16, 2020 at 9:40 pm

    Thank you chemicalmatt. 

    Aw (water activity) is a ratio of water vapor pressure of the sample over the vapor pressure of pure water itself.  So it is slightly more complex than what I had previously thought. Can a lab used for challenge testing measure Aw of a sample? I am about to send multiple samples for challenge testing.

    So NaCl lowers vapor pressure of water and so do other salts such as Sodium Sulfate, Sodium Lactate and Sodium Citrate.

    What about something like a powdered surfactant such as sodium coco sulfate? Would that also lower the vapor pressure of free water and in what way?   

  • Agate

    Member
    February 18, 2020 at 8:31 pm

    Can a lab used for challenge testing measure Aw of a sample?

    As far as I’m aware, testing Aw requires specialised equipment, you’ll have to ask your lab if they have it or not.

  • Cst4Ms4Tmps4

    Member
    March 3, 2020 at 11:55 pm

    @Cafe33

    You are welcome. I am not a chemist but I love sharing and probably love imposing what I know on other people as well. Hahahah! I am just a damn excited and curious individual working on many many things related to science and technology.

    I learn new things every day! 80-82% CAPB exists!

    Oh, you want syndet bar to stay solid and not runny when exposed to water.

    I cannot say much about syndet because I do not have much experience with it. But I do know a little about soap. Yes, good old soap or ‘soap salt’ some people call it.

    - I noticed that soap made with a lot of coconut oil is not only very hard but also pretty solid in the presence of water.

    - Soap made with olive oil is mushy but not easily consumed in water.

    - “Goat milk soap” tends to melt in water quickly.

    Something to do with the fatty acids used. The length of carbon chain.

    I think you want to replicate Dove syndet. Maybe THIS would assist you. 

    As a general ‘rule’, if you want to make solid stuff it is best to use all stuff (ingredients) which stay solid at room temperature (Room temperature is a bit subjective depending on where you live. I live in a tropical climate where temperature is high, many waxes and oils are either soft or liquid). What I mean is remove CAPB and see the result. Salt is extremely hygroscopic. I do not know what else is in your formulation. Glycerin must also go away.

    As for the salt, I do not know why many soap makers swear by Sodium Lactate “hardens” soap. From what I see, soap becomes more pliable with Sodium Lactate than soap without the salt. The same is true for high Glycerol soap. Perhaps the sure sign is soap is smooth-looking.

    I do not think syndet needs extra any kinds of salts.

  • Cafe33

    Member
    March 9, 2020 at 1:07 am

    Thank you for your responses. 

    Cst4Ms4Tmps4, the syndet bars I am making are staying solid even when incorrectly stored in the shower. I am simply looking for the best possible system. 

    The Dove bar is a great starting point and you can find detailed description of its formulation and evolution in Chapter 4 of Soap Manufacturing Technology. 

    I have tried Combo bars using Sodium Palmitate (10%). It was an interesting creation but I found that the bar gets mushy and runny much faster. It was certainly easier to press. 

    The inherent problem is Glycerine. My purchased Sodium Palmitate contains 12% Glycerine, and even 1.2% in the syndet bar created a problem. 

    I found that an emulsifier such as Polawax was a good replacement for Soap for creating a proper structure in a Syndet bar. Now I will need to find a powdered humectant other than d,l panthenol. The price is not such an issue as some of the Syndet bars will be facial cleansers. For Body bars, the sale price would be too high as the bars runs out too quickly. 

    Sodium Lactate - 2% is what I use. I found 3% created some tackiness. 
       

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