What is the best procedure of making a kojic soap?

Kimjiwon

Hello fellow chemist! I am developing a kojic soap combine with coconut oil, sodium hydroxide, sodium lactate, kojic acid dipalmitate, 6 copolymer, hydroxyethylcellulose, hydroxypropyl guar, Madecassoside, EDTA, and BHT. I am using a cold process cause it is the require procedure. The problem is I don't get the right procedure for this. I have a lot of trials mixing and changing phases to make it right. But all the result will end failed, It becomes brittle and like chalk. I don't what to do. Can someone help me? 

Belassi

To begin with, change the coconut oil to a blend with more oleic and less stearic etc., begin with a 50-50 olive oil/coconut oil blend and see how that turns out. You've probably got too many solids in there too.

lmosca

I would start by asking the percentages/amounts of your ingredients; however, I feel that a more pressing question would be: why are you trying to put kojic acid dipalmitate and madecassoside in soap?

What goal are you trying to achieve here?

In addition to that, why are you adding hydroxyethylcellulose and hydroxypropylguar?

Pharma

Kimjiwon said:

...sodium hydroxide...kojic acid dipalmitate, 6 copolymer...hydroxyethylcellulose, hydroxypropyl guar, Madecassoside...

Kojic dipalmitate will be degraded by sodium hydroxide to kojic acid sodium salt and sodium palmitate and madecassoside will be split in half resulting in free triterpene and a sugar chain.

What is 6 copolymer?

HEC and hydroxypropyl guar will probably degrade depending on the conditions. They are in theory fairly alkali resistant but still hydrolyse at high pH (pH above 10-12) and high alkali concentration (time and temperature contribute as well, obviously). They also have a lower viscosity at high pH and HEC as an example starts oxidising to some sort of carboxycellulose if pH remains high enough for several days. Furthermore, these gellants take more time to settle at high pH and hence might give an uneven, grainy appearance in a soap.

Maybe just try soap without all this fancy stuff i.e. only oil and sodium hydroxide, probably sodium lactate since this shouldn't disturb anything, and go from there, adding one by one to tweak your product towards the desired consistency. And, as @Belassi said, don't use pure coconut oil because that one will not be supple, let alone together with gelling agents. Why the heck are you adding gelling agents anyway?

lmosca

All "Kojic soap" commercialized is loaded with yellow and red pigments, I am guessing to mask the color morphing due to the oxidation of kojic acid to the quinone form. Its oxidation should be even more favored at alkaline pH.
O-glicosides, like madecassoside, HEC etc... will decompose fairly quickly in alkaline pH. While stability is usually recorded between a restricted range of 2-12, at the initial stages of saponification temperatures will rise and pH will be undefinable, but high, and hydroxide activity will be very high for the first 24 hours. 

Pure coconut oil-based soap will be so stripping I would consider it for use as a degreaser for motor oil, unless formulated with a large excess of oil (10-15% superfat). 

The thickening/gelling agents do not have any reason to exist in such soap. Why are they there in the first place?

High levels of sodium lactate can make soap brittle. It is recommended to use below 1% of sodium lactate in proportion to oils weight. More than 2-3% will cause sweating, unnecessary brittleness, and conspicuous acceleration of saponification. 

Out of curiosity, I've had a quick search for kojic soap and all vendors recommend, in case of dry skin and tightness (that for sure you'll have after using alkaline soap), to follow with a lotion containing kojic acid. I've never considered it as a marketing strategy, but that seems absolutely genius (evil, but genius).

Edit: As with anything soap, why bothering adding fancy actives? 
The purpose of soap is to clean and make things smell good (and that last one is even optional). Keep kojic acid for things that actually work, too many yeasts and fungi have been inconvenienced to have it go down the drain.

Wickers

Where do you find madecassoside/madecassic acid/asiatic acid (if you know)?

Dr_Sara

Kimjiwon said:

 I am using a cold process cause it is the require procedure. The problem is I don't get the right procedure for this. I have a lot of trials mixing and changing phases to make it right. But all the result will end failed, It becomes brittle and like chalk. I don't what to do. Can someone help me? 

I thought I wuld comment on soap making an your base recipe before adding the additional ingredients. 

Coconut oil will make a VERY hard soap. You should add a liquid oil. Another reason your soap may be brittle is that you are using too much NaOH. 

Why do you need to use the cold process? I am not sure what you mean by "changing phases"? upon addition of the lye solution, the oil phase begins to thicken and contimues to do so until the soap is finished.

If you send your formulation, I would be happy to tweak it for you.
Kind regards,
@dr_sara ;

Dr_Sara

I just had a look online and found the following ingredient list: This is not in the appropriate format for EU labelling. It looks like a glycerin soap to me.

Ingredients overview

Cocos Nucifera (Coconut) Oil, De-Ionized Water, Sodium Hydroxide, Fragrance, Kojic Acid, Glycerin, Aqua, Xanthan Gum, Caprylyl Glycol, Glucose, Chondrus Crispus (Carrageenan), Phenoxyethanol, Ethylhexylglycerin, Cocodiethanolamide, Mineral Oil, Melaleuca Alternifolia (Tea Tree) Oil, Ci 15985, Ci 19140, BHT

They probably make the coconut soap first (the appearance of this does not matter much because it will be dissolved in glycerin). 
Cocos Nucifera (Coconut) Oil, De-Ionized Water, Sodium Hydroxide,

Then the Sodium Cocoate is dissolved, the glycerin soap made and the additional ingredients added. 
Fragrance, Kojic Acid, Glycerin, Aqua, Xanthan Gum, Caprylyl Glycol, Glucose, Chondrus Crispus (Carrageenan), Phenoxyethanol, Ethylhexylglycerin, Cocodiethanolamide, Mineral Oil, Melaleuca Alternifolia (Tea Tree) Oil, Ci 15985, Ci 19140, BHT