Propylene Glycol alternatives for made-from-scratch transparent soap

[Minerva's Curious Physick]

Both denatured alcohol and propylene glycol are in a class of chemicals called alcohols.

As others have said, denatured alcohol is ethyl alcohol plus something that we can not drink (often acetone or methanol) This is so that it is not taxed as drinking alcohol.

Clear soaps can be made with ethyl alcohol because the sodium salts of the fatty acids in the bar soaps are soluble in the alcohol and stay in solution even after hardening (a bar contains crystalized salts which make it opaque)

Technically, you can melt soaps made with ethyl alcohol; however, due to the low boiling point of the alcohol they will not be repeat-ably meltable and after the first time you melt it, some of the alcohol will evaporate and the soap will not be as clear.

This is where propylene glycol comes in. Propylene glycol (PG) will also produce a clear soap (although sometimes not as clear) and will allow the soap to be repeatedly melted. PG has a boiling point of 370 degrees Fahrenheit. This allows you to melt the soap many times and still retain its meltable characteristics along with its clear properties.

There are pros and cons to each.

Hope this is the right place for this thread! Looking for a good alcohol to use instead of Propylene Glycol in re-meltable transparent soapmaking, mostly because I probably can't say my soaps are all-natural if I use PG. Reading this thread, it sounds like ethanol is fine as long as I don't need to remelt, but since its boiling point is 172.8F/78.2C, it'll evaporate off in a microwave or a crock pot if I'm not careful (while remelting or while cooking it the first time). If PG is better because it has a 370F boiling point, I wonder if Propanediol 1,3 (made from corn) would work because of its' 415.4F/213C boiling point. I spotted this transparent soap at a local natural foods store this week, with "non-petroleum glycol" in the ingredients...

“Propanediol” is an ambiguous name for a compound (no positions given). Wikipedia links to a disambiguation site that links to both 1,2-propanediol (“propylene glycol”) and 1,3-propanediol (“trimethylene glycol”). Either one is rightfully called “propanediol”. From the inscripton on that label, it is not evident which of the two the manufacturer of this soap added.

 

[Minerva's Curious Physick]

It says "petroleum-free glycol", and after a quick search, I guess PG can be made from soybeans and canola!?

Does that make PG potentially natural, or is this where the difference between natural and synthetic gets weirdly squishy and debatable?

 

[ResolvableOwl]

is this where the difference between natural and synthetic gets weirdly squishy and debatable?

It has got “weirdly squishy and debatable” long before that, actually. Is NaOH “natural”? Our beloved NaOH, made from sea salt and electrical energy, liberating chlorine gas? Is it “natural” to cleave oil molecules to create soaps? Aren't these soaps compounds that have been created by the intervention of man, i. e. synthetic? Is it better to stress one's skin with “natural” 100% CO soap, rather than use “synthetic” mild cleaning agents? Is it better to sacrifice tons of soap to hard water (soap scum), than using water-hardness-insensitive syndets?

This is all highly debatable.

I've seen PG sold as explicitly derived from palm oil. Others explicitly from natural gas. Most has no provenance, which is a shame. I like the idea of some biodiesel makers to process the waste glycerol to PG as a value-added side product of car fuel production. Why not?
“Natural” is a pure PR/label appeal term, and prone to tunnel vision. Who aims at “nature-friendly” products, IMHO should put more value at all efforts throughout the supply chain (as far as possible) to minimise ecological footprint. For soap/detergents, this means the sewage/wastewater in the very first place (looking at you, EDTA!), but of course also origin (though it is not unambiguous if, say, PG is better from highly efficient fossil sources, or land-intensive agriculture, competing with food production).

All highly debatable…

 

[Minerva's Curious Physick]

Yeah, a massive part of it is label appeal. Using something that's a waste product of biodiesel does sound really responsible. Any idea if that's happening currently, or just a good idea?

 

[Minerva's Curious Physick]

Is this where the line between soapmaking and philosophy starts to blur?

It has got “weirdly squishy and debatable” long before that, actually. Is NaOH “natural”? Our beloved NaOH, made from sea salt and electrical energy, liberating chlorine gas? Is it “natural” to cleave oil molecules to create soaps? Aren't these soaps compounds that have been created by the intervention of man, i. e. synthetic? Is it better to stress one's skin with “natural” 100% CO soap, rather than use “synthetic” mild cleaning agents? Is it better to sacrifice tons of soap to hard water (soap scum), than using water-hardness-insensitive syndets?

This is all highly debatable.

 

[ResolvableOwl]

Is this where the line between soapmaking and philosophy starts to blur?

This too is highly debatable!

 

[lsg]

Propanediol is a corn sugar derived alternative to propylene glycol. It can be used as a 1:1 replacement

Source: Propanediol: An alternative to Propylene Glycol

 

[Minerva's Curious Physick]

It has got “weirdly squishy and debatable” long before that, actually. Is NaOH “natural”? Our beloved NaOH, made from sea salt and electrical energy, liberating chlorine gas? Is it “natural” to cleave oil molecules to create soaps? Aren't these soaps compounds that have been created by the intervention of man, i. e. synthetic? Is it better to stress one's skin with “natural” 100% CO soap, rather than use “synthetic” mild cleaning agents? Is it better to sacrifice tons of soap to hard water (soap scum), than using water-hardness-insensitive syndets?

This is all highly debatable.

I've seen PG sold as explicitly derived from palm oil. Others explicitly from natural gas. Most has no provenance, which is a shame. I like the idea of some biodiesel makers to process the waste glycerol to PG as a value-added side product of car fuel production. Why not?
“Natural” is a pure PR/label appeal term, and prone to tunnel vision. Who aims at “nature-friendly” products, IMHO should put more value at all efforts throughout the supply chain (as far as possible) to minimise ecological footprint. For soap/detergents, this means the sewage/wastewater in the very first place (looking at you, EDTA!), but of course also origin (though it is not unambiguous if, say, PG is better from highly efficient fossil sources, or land-intensive agriculture, competing with food production).

All highly debatable…

Oh my goodness; I keep rereading your points--you've definitely thought about this before. I'm just barely starting my business, and while I was hoping "all-natural" could be a rule (and customer appeal), a more nuanced approach does make a lot more sense, especially if Sodium Hydroxide lye isn't natural (is it?). The thing that cracks me up: just before your reply, I had spent a few days in SoapCalc hell trying to formulate soap for a couple of extremely dry-skinned friends who wanted great lather. I had finally started to accept that syndets really are their best bet (also learned what syndet stands for that week... I have so many acrynoms and portmanteaus to learn!). I've read SwiftCraftyMonkey's asides on what really is natural anyway, and who gets to decide, and she's saying the same thing. It sounds like chemists find this a little frustrating.

Nature-friendly sounds so vague, too, but the approach you describe sounds better than all-natural, whatever that is!

Whatever it's called, maybe I should just come up with a PR-friendly name for it, then actually explain the approach on a (not-yet-finished) website/email list/point of sale displays at the farmer's market... All Natural & Ecologically Responsible?

So thank you a ton for making me think long and hard about this.

 

[DirtyDeeSoaps]

This has been something I've puzzled over myself. I finally went with marketing my soaps as sustainable and old fashioned to avoid any debate over what constitutes "natural" soap.