Would changing the concentration of lye affect the properties of soap

[soapexperiment]

I am considering making soaps with different lye concentrations ranging from 20% to 50%. The lye concentrations will be altered by controlling the water to lye ratio. Obviously, the fats/oil used would remain the same for all independent variables as it is a controlled variable. However, my question is: would this affect the properties of soap, e.g. hardness, foaming capacity, cleaning capacity and etc.?

This is for my chemistry experiment.

Thank you

 

[jcandleattic]

However, my question is: would this affect the properties of soap, e.g. hardness, foaming capacity, cleaning capacity and etc.?

Higher super fat (aka, more fats than lye) would change the ability to lather, but other than that, really nothing else would change much.
If you are only changing the lye solution concentration then, no, the actual properties of the bar would not change. Depending on the water content may change how/when you take it out of the mold, but really, in my experience that's the only thing that has changed, and once the bar is cured, how the bars looks, reacts, etc., remains the same.

 

[soapexperiment]

Ok, thank you for your reply.

I am also considering changing the type of fat (saturated or unsaturated) and I will test the different properties of it, including hardness, pH, foaming capacity and cleaning capacity. Would this change the properties drastically? For unsaturated fats, I chose Castor Oil, Sunflower Oil and Olive oil. For saturated fats, I chose Coconut oil, Coca Butter and lard. These have been chosen for the differences in the fatty acid composition which would allow a deeper analysis into how different fatty acids leads to different soap properties.

Furthermore, what things could I change in the composition of soap in order for the properties to be changed and can be analysed chemically? Could I change the superfatting % of the soap? Would this change the previously mentioned properties?

 

[ResolvableOwl]

Welcome to SMF, @soapexperiment !

I like this idea!
In essence, you are only changing the water content of the soap batter. In theory, the final soaps (after prolonged cure) should be identical, but in practice, you will without doubt notice differences. I bet that quite a few people would be thrilled about such a systematic experiment.
From the perspective of a soapmaking practitioner, a major thing that is influenced by lye concentration (but not necessarily noticeable in the final soap) is speed in the sense of time to trace, i. e. how much time and/or mechanical torture (stick-blending) it takes for the lye and the oils to combine into a smooth, thick batter.

There is a situation during the saponification that is called gel phase where the soap has a vaseline-like look and consistency. It is well-known that forcing and avoiding gel phase is controlled, besides temperature, by lye concentration. Although the final soap (final = after >6 weeks cure) isn't so much different, it looks different. Have a look at Auntie Clara's blog seriers about the Ghost Swirl Ghost Swirl Soap Archives - Auntie Clara's Handcrafted Cosmetics that exploits (and explains) these differences for a visual effect.

Note that ghost swirl, glycerin rivers, etc. are effects that do not depend on the chemical composition of the soap, but the way that the soap molecules are arranged within the microstructure (ordered or clumped, crystalline or random). This has not so much to do with traditional chemistry, hence the preferred analysis techniques are likely microscopy, X-ray diffraction, or NMR. If you haven't made gross mistakes, pH is one of the less interesting parameters to measure in soap.

 

[soapexperiment]

I will be working in a school lab so I am certain that there is no X ray.

Could you suggest other ways of analysing soap properties?
p.s. @ResolvableOwl could you please tell me which part of my experiment you are referring to?

 

[ResolvableOwl]

I was referring to the chemical analysis of the finished soap. The hydroxide reacts with the oils, and the water is an uninvolved spectator, so its concentration does not change the products, and chemical analysis (pH measurement, titration, precipitation, extraction, photometry…) is insensitive to it.

One interesting property is longevity/solubility. It is both of fundamental and practical relevance, as well as easy to measure without high-tech apparatuses. I remember such an experiment by in the great book “Scientific Soapmaking” (page 311f) from Kevin Dunn. He has suspended rods of soap into water, and watched how fast they would pull water, swell, and eventually dissolve/fall apart. He refers to an obscure journal article from 1943. Which happens to be available these days of globalisation of knowledge : https://doi.org/10.1021/ie50405a015 and there is also a PDF version without subscription (page 1011, PDF page 93).

 

[soapexperiment]

Oh Wow! Thank you!

But would the properties significantly change for different oils/fats?

 

[TheGecko]

I am considering making soaps with different lye concentrations ranging from 20% to 50%. The lye concentrations will be altered by controlling the water to lye ratio. Obviously, the fats/oil used would remain the same for all independent variables as it is a controlled variable. However, my question is: would this affect the properties of soap, e.g. hardness, foaming capacity, cleaning capacity and etc.?

The simple answer is 'no'. The only thing you are changing with the various Lye Concentrations is the amount of water being used.

The less simple answer is that the solubility (longevity) of the soap of the soap would be affected if all Lye Concentrations were 'cured' for the same time because of the amount of water still present in the soap. Think 'cake' brownies vs 'fudge' brownies. Cake Brownies are light and fluffy...put the brownie in a bowl and add milk and the brownie will soon fall apart and turn to mush (yum). Fudge Brownies are dense and heavy...put the brownie in a bowl and add milk and the brownie is just going to sit there...a big, fat gooey lump of chocolate goodness surrounded by milk (also yum).

I live in the Pacific Northwest of the United States...we typically get a lot of ran during the Fall/Winter months and between the cooler temps and the damp, I noticed that my soaps made with a 33% Lye Concentration were taking longer to cure. Someone suggested increasing my Lye Concentration to 35%...which lowered the amount of water and to run a fan. Now the amount of water between 33% and 35% isn't a whole lot, but it did reduce my cure time.

 

[soapexperiment]

Thank you for your help!

But still I would like to ask whether different types of fats would change properties?

Can I also make my samples of soap in 2 days?

 

[soapexperiment]

Can I also make my samples of soap in 2 days?

 

[AliOop]

Thank you for your help!

But still I would like to ask whether different types of fats would change properties?

Absolutely. That is the reason we all use varieties of different recipes.

 

[ResolvableOwl]

Can I also make my samples of soap in 2 days?

You can make them in 2 days, but they won't be cured by then. Even if you make your series right now, you will be just barely ready to unmould (safe to touch without gloves) in 2 days, especially when you have little to no previous experience in soapmaking.
Soaps with that different lye concentration will be VERY different from each other. But this is transient, and will literally “cure out” over a few weeks (like @TheGecko said). In particular, the early properties are NOT representative of the behaviour of the soaps after a proper cure of at least four weeks. Sorry.

 

[TheGecko]

But still I would like to ask whether different types of fats would change properties?

Yes. Part of the saponification process is that Sodium Hydroxide breaks down fats into Fatty Acids (a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated ) and Glycerin. The Fatty Acids are Lauric, Myristic, Palmitic, Stearic, Ricinoleic, Oleic, Linoleic, and Linolenic and the amounts will affect the "properties" of soap.

Can I also make my samples of soap in 2 days?

Cold Process Soap typically saponifies in 18 to 48 hours depending any number of factors and will be safe to use. But will it be good to use? No. Water evaporation is only part of the curing process. @DeeAnna calls is science, I call it magic...same difference. There is a crystallization process that occurs as soap cures...that makes for a long lasting, gentler, more luxurious bar of soap. I have a really good recipe, but if you try to use it right away, it sucks. I don't even like to test bars until at least four weeks have passed. At eight weeks (and longer), it is a fantastic bar of soap that is moisturizing with tons of silky lather.