So you have these two extremes in the soap market, Dr. Bronner's and everyone else, one being potassium alkanoates and the others mostly a mixture of
alkanoyltaurates and various gelling and foaming agents. Dr. Bronner's has a couple of advantages: notably, it doesn't require preservatives like
diazolidinylurea and methylisothiazolinone, because it doesn't contain any nitrogen or any elements other than carbon, oxygen, hydrogen and potassium,
which makes it hard for things to grow in it. That's useful because preservatives are often contact allergens -- methylisothiazolinone was Contact
Allergen of the Year -- because after all they're meant to kill things. Also, the high solubility of the potassium ion gives it good foaming qualities
without using as many foaming agents, although this is partially because it's just more concentrated.
The disadvantages of Dr. Bronner's are a pretty high pH and the cost of potassium, and (arguably) the soap is easy to spill. Overall it's a good deal,
so it's pretty popular.
But you can actually lower the pH quite a bit without using any nitrogen or sulfur, using a fatty acid ester of lactic acid, since alpha-hydroxy
acids generally have a pKa about 1 point lower than the deoxygenated acid and the O-acyl might lower that another 0.3 or so. What's cool is that with
lactic acid these esters are still kinda food-grade and they're used in bread (?!):
Bread is usually made with calcium stearoyl 2-lactate which has two lactate units; it's my rudimentary understanding that the increased number of
lactyl units decreases the lipophilicity of the salt and therefore the "soapiness" which is good for breadmaking but obviously bad for soapmaking, and
also the calcium salt is less water-soluble and hygoroscopic which is again good for bread and bad for soap. I don't think alginate will affect
foaming or cleaning too negatively as it's got a bunch of charges on it so it's highly soluble
The other idea I had was to use potassium alginate as a thickener. This is again food grade and it's also a C/O/H/K compound which is good. I'm not
sure if the resulting soap would still be shelf-stable or if the high pH of Dr. Bronner's is essential to it's stability. However it still seems like
a solution of the two potassium salts would be insufficient to support life. Of course alginate is usually supplied as the sodium salt and you end up
using more potassium but it usually makes it easier to work with the dilute soap...
Anyone know anything about this stuff?Metacelsus - 15-5-2017 at 10:20
How stable are those lactylate esters with respect to hydrolysis? Storage stability is a required characteristic of soap formulations.
From Wikipedia (I couldn't access the original source):
Quote:
In the presence of water, lactylates will break down (hydrolyze) into fatty acid and lactic acid.
clearly_not_atara - 15-5-2017 at 10:28
Looks like I'm not the first to thunk of this; Metacelsus's concern is in here but I'm in a hurry...
