Now that my patent has long since expired, and the big batch I had made a decade ago has separated considerably, I might as well publicize here my foam formula.
standard commercial solutions of:
diammonium lauryl sulfosuccinate, 4 parts
lauramidopropyl betaine, 3 parts
disodium laureth-3 sulfosuccinate, 2 parts
By "standard", I mean the usual concentrations sold in commerce, which for the sulfosuccinate esters is about 40% total solids, and for the betaine about 35% total solids (of which up to 5% is NaCl). Densities are close enough to each other that it hardly matters whether you use parts by weight or volume. If you insist on working in percentages, just multiply parts by 11 and do what you will with the other 1%.
The order of mixing is important if you want to do this easily. Do not mix the last 2 ingredients first, because alkamidopropyl betaines and ethoxylated surfactants jell when mixed in most ratios, and will then take a lot of work to mix with the diammonium lauryl sulfosuccinate solution. Instead mix the diammonium lauryl sulfosuccinate with either the lauramidopropyl betaine or the disodium laureth sulfosuccinate thoroughly before slowly mixing in the other one. No heating should be necessary.
The solutions usually come already preserved (with formaldehyde donors in the case of the sulfosuccinates, sometimes another kind in the case of the betaine), so no further preservative is necessary if you don't dilute the mixture significantly. However, many people would want it diluted in various applications, so you're on your own preserving them, and I don't know about stability time when diluted either.
Sulfosuccinate esters are relatively unstable as surfactants go, but after mixing with the betaine surfactant the mixture should be adequately stable for at least a couple of years stored at moderate temperatures, slowly separating as years go on beyond. The mixture will also separate at low temperatures (and will do so more readily the older it gets); if that happens, gentle warming & remixing is called for. If you mix with fragrance oils or essential oils, beware of the ones said to accelerate saponification; they will attack the sulfosuccinate esters as well, resulting in funky, curdled-looking (though still usable) mixtures. High temperatures over long periods (or done repeatedly) also accelerate breakdown.
With no further buffering, the mixture comes out to a pH of between 5.5 and 6.5, depending on variations in the starting materials (which also lead to some variation in viscosity without salt adjustment). The betaine solution is a fairly good pH buffer and also makes the mixture resist microbial growth better than many surfactants do. Although I specified "laureth-3" above, sulfosuccinate esters in the range of 2-3 moles ethoxylation may be used.
Whether you can obtain these surfactant solutions in quantities convenient for you, I don't know. It may be possible at least time from time to get them in 5 gal. pails (as we did for a co-op buy of the mixture in the 1990s).
The application I developed this for was bubble bath. In particular I was looking for one that could be tolerated by people who were susceptible to urinary or genital irritation from surfactant-based products: bath foams, emulsified bath oils, shaving cream, soaps, etc. In that I believe I succeeded spectacularly. Individuals who had such problems could use this stuff far beyond where others would've given them an irritant vulvitis, vulvovaginitis, or urethritis, expressed as pain, burning, or itching, especially on urinating, for a period after use. Therefore I also had it tried out as a peri-vaginal cleaner. I finally hit the limit of tolerability as a perivaginal wash in someone who was pregnant, and who even when not pregnant would suffer a burning sensation when soap merely ran into her crotch from above in the shower; the fact that she was able while pregnant to wash directly with this stuff on a wet washcloth and experience only some mild tingling says something as to its low irritancy. As to use as bubble bath, I finally found, interestingly enough, a man who would start to get some urinary burning after he used it daily for several days in a row, while other bubble baths he was simply unable to use 2 days in a row without that problem. I usually had bubble bath testers (frequently children) deliberately sit in the bath with it before all the water had run into the tub. I also tested even more stringently in a few users (warning: yuck factor).
As to skin irritancy, it is milder than most, although it still is defatting and certainly not a substitute for bath oil. Colgate tried an earlier version (like the above if you subbed equal parts of sodium laureth-3 sulfate and (extra) diammonium lauryl sulfosuccinate for the disodium laureth-3 sulfosuccinate) in human repeat insult testing, and it came out 2nd lowest of 14 (including some baby shampoos) in irritancy; on general principles, the version here with the laureth sulfosuccinate should be even milder).
However, I was also pleased with the density of the foam this stuff makes. It is not what you'd consider a high foamer in the sense of having a great volume of "flash foam"--the sort of fluffy bubbles you get from running water fast from the faucet into the tub with most bubble baths. Rather, it makes a heavy, wet, lathery kind of foam, and benefits a lot from being well aerated (as by vigorous splashing or use of jets). When swished up, it gets to and stays in that dense, lathery state of foam faster than others. Children in particular find this more fun to play with than light fluffy foams that break easily. Also, the foam it produces on bath water does not sting eyes, while many drier, fluffier foams do. Bathing with this stuff in the water seems to leave skin softer than plain water, soap and water, or other bubble baths.
The formula is also useful for shampoo. It is not a zero eye sting formula, although when it runs into eyes from a lather on the head, it does sting less than soap or most shampoos. It also seems to impart more conditioning to hair than others, probably because of the high betaine content.
Many variations on the formula are possible. Those who are unable to find lauramidopropyl betaine in convenient amounts may try cocamidopropyl betaine, although the foam will suffer noticeably. However, if you have easier access than most to alkamidopropyl betaines in convenient amounts, the best is a 60:40 mixture of lauramidopropyl and palmitamidopropyl betaine, which gives a cottony foam and extra skin softening.
To make a tablet version somewhat similar to the above formula (albeit not quite as foamy), mixing disodium lauryl sulfosuccinate powder and spray dried cocamidopropyl betaine (which might not be commercially available) 1:1 works. It may be feasible to make a foaming bomb using disodium lauryl sulfosuccinate powder and an alkamidopropyl betaine solution with an excess of dry materials.
Enjoy.
standard commercial solutions of:
diammonium lauryl sulfosuccinate, 4 parts
lauramidopropyl betaine, 3 parts
disodium laureth-3 sulfosuccinate, 2 parts
By "standard", I mean the usual concentrations sold in commerce, which for the sulfosuccinate esters is about 40% total solids, and for the betaine about 35% total solids (of which up to 5% is NaCl). Densities are close enough to each other that it hardly matters whether you use parts by weight or volume. If you insist on working in percentages, just multiply parts by 11 and do what you will with the other 1%.
The order of mixing is important if you want to do this easily. Do not mix the last 2 ingredients first, because alkamidopropyl betaines and ethoxylated surfactants jell when mixed in most ratios, and will then take a lot of work to mix with the diammonium lauryl sulfosuccinate solution. Instead mix the diammonium lauryl sulfosuccinate with either the lauramidopropyl betaine or the disodium laureth sulfosuccinate thoroughly before slowly mixing in the other one. No heating should be necessary.
The solutions usually come already preserved (with formaldehyde donors in the case of the sulfosuccinates, sometimes another kind in the case of the betaine), so no further preservative is necessary if you don't dilute the mixture significantly. However, many people would want it diluted in various applications, so you're on your own preserving them, and I don't know about stability time when diluted either.
Sulfosuccinate esters are relatively unstable as surfactants go, but after mixing with the betaine surfactant the mixture should be adequately stable for at least a couple of years stored at moderate temperatures, slowly separating as years go on beyond. The mixture will also separate at low temperatures (and will do so more readily the older it gets); if that happens, gentle warming & remixing is called for. If you mix with fragrance oils or essential oils, beware of the ones said to accelerate saponification; they will attack the sulfosuccinate esters as well, resulting in funky, curdled-looking (though still usable) mixtures. High temperatures over long periods (or done repeatedly) also accelerate breakdown.
With no further buffering, the mixture comes out to a pH of between 5.5 and 6.5, depending on variations in the starting materials (which also lead to some variation in viscosity without salt adjustment). The betaine solution is a fairly good pH buffer and also makes the mixture resist microbial growth better than many surfactants do. Although I specified "laureth-3" above, sulfosuccinate esters in the range of 2-3 moles ethoxylation may be used.
Whether you can obtain these surfactant solutions in quantities convenient for you, I don't know. It may be possible at least time from time to get them in 5 gal. pails (as we did for a co-op buy of the mixture in the 1990s).
The application I developed this for was bubble bath. In particular I was looking for one that could be tolerated by people who were susceptible to urinary or genital irritation from surfactant-based products: bath foams, emulsified bath oils, shaving cream, soaps, etc. In that I believe I succeeded spectacularly. Individuals who had such problems could use this stuff far beyond where others would've given them an irritant vulvitis, vulvovaginitis, or urethritis, expressed as pain, burning, or itching, especially on urinating, for a period after use. Therefore I also had it tried out as a peri-vaginal cleaner. I finally hit the limit of tolerability as a perivaginal wash in someone who was pregnant, and who even when not pregnant would suffer a burning sensation when soap merely ran into her crotch from above in the shower; the fact that she was able while pregnant to wash directly with this stuff on a wet washcloth and experience only some mild tingling says something as to its low irritancy. As to use as bubble bath, I finally found, interestingly enough, a man who would start to get some urinary burning after he used it daily for several days in a row, while other bubble baths he was simply unable to use 2 days in a row without that problem. I usually had bubble bath testers (frequently children) deliberately sit in the bath with it before all the water had run into the tub. I also tested even more stringently in a few users (warning: yuck factor).
As to skin irritancy, it is milder than most, although it still is defatting and certainly not a substitute for bath oil. Colgate tried an earlier version (like the above if you subbed equal parts of sodium laureth-3 sulfate and (extra) diammonium lauryl sulfosuccinate for the disodium laureth-3 sulfosuccinate) in human repeat insult testing, and it came out 2nd lowest of 14 (including some baby shampoos) in irritancy; on general principles, the version here with the laureth sulfosuccinate should be even milder).
However, I was also pleased with the density of the foam this stuff makes. It is not what you'd consider a high foamer in the sense of having a great volume of "flash foam"--the sort of fluffy bubbles you get from running water fast from the faucet into the tub with most bubble baths. Rather, it makes a heavy, wet, lathery kind of foam, and benefits a lot from being well aerated (as by vigorous splashing or use of jets). When swished up, it gets to and stays in that dense, lathery state of foam faster than others. Children in particular find this more fun to play with than light fluffy foams that break easily. Also, the foam it produces on bath water does not sting eyes, while many drier, fluffier foams do. Bathing with this stuff in the water seems to leave skin softer than plain water, soap and water, or other bubble baths.
The formula is also useful for shampoo. It is not a zero eye sting formula, although when it runs into eyes from a lather on the head, it does sting less than soap or most shampoos. It also seems to impart more conditioning to hair than others, probably because of the high betaine content.
Many variations on the formula are possible. Those who are unable to find lauramidopropyl betaine in convenient amounts may try cocamidopropyl betaine, although the foam will suffer noticeably. However, if you have easier access than most to alkamidopropyl betaines in convenient amounts, the best is a 60:40 mixture of lauramidopropyl and palmitamidopropyl betaine, which gives a cottony foam and extra skin softening.
To make a tablet version somewhat similar to the above formula (albeit not quite as foamy), mixing disodium lauryl sulfosuccinate powder and spray dried cocamidopropyl betaine (which might not be commercially available) 1:1 works. It may be feasible to make a foaming bomb using disodium lauryl sulfosuccinate powder and an alkamidopropyl betaine solution with an excess of dry materials.
Enjoy.
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I was one of those children, so was my DD, and now the grandchildren. Very, very much appreciated in the world of skin irritants and enjoying a pleasant bath.
