[Bill_Toge]

depends on your target demographic

at my last place we sold late-90s formula shampoos in 5-litre jerrycans to a company that supplied hotels, sports clubs, leisure centres etc.; these were thickened with CDEA and there were never any queries about it, never mind complaints

as an aside, one interesting CDEA-containing formula I’ve come across was Dettol’s cationic handwash supplied with their hands-free dispensers around 2011/2012, which relied on CDEA to thicken the product and enhance the foaming; alternative surfactants just didn’t cut it, and the patent covering the formulation was definitely written with that knowledge in mind

[Bill_Toge]

as far as I can tell (speaking as a complete outsider both to the USA and its cosmetics industry), the regulations are sufficient, but the FDA is incredibly overstretched in carrying out the enforcement of said regulations, meaning that a lot can slip under the radar

a good first step would be for the enforcement to be devolved to state-level agencies, as is done in Europe, and having the FDA coordinate all the data from those agencies

[Bill_Toge]

the fact that the Guardian used to be an upstanding reliable newpaper 20-25 years ago makes it particularly tragic; since becoming a corporation in 2008, their quality standards have dropped through the floor

anyone who identifies as an upper-middle class white woman can write in the Guardian these days, especially if they have a trust fund

[Bill_Toge]

Perry said:

They list industrial VCP (or VOC) at 15% compared to 38% personal care. Is that something different?

I’ve no idea how they managed to come up with that figure, given that their measurements came entirely from residential and commercial properties, and the roads adjacent to them

the whole thing seems like a bodge job, and the fact it was published in a peer-reviewed journal is a damning indictment of the ongoing decline in academic standards

[Bill_Toge]

they seem to have completely neglected the industrial use of volatile solvents, which severely dwarfs consumer use

[Bill_Toge]

vanillyl butyl ether is an effective warming agent, as is camphor

[Bill_Toge]

in my experience, sodium thiosulphate is used as a chlorine-neutralising agent, and as @Abdullah says, EDTA will remove copper

[Bill_Toge]

sunscreen-grade titanium and zinc oxides are coated with a variety of materials, depending on the manufacturer: silicones, jojoba esters, myristoyl myristate, lauroyl lysine, stearic acid… basically, anything hydrophobic that’s solid near room temperature

[Bill_Toge]

another question to ask is whether it’s the substance itself that’s causing the irritation, or an impurity in it - particularly given that it’s made from propylene oxide, and the level of unreacted started material is likely to be much higher in technical grades than in pharmaceutical grades

as an example: lanolin was considered an irritant for many years, before it was more thoroughly refined to remove the residual pesticides

[Bill_Toge]

emma1985 said:

Thank you so much Bill. Question, would you say Castor Wax is particularly good for stick products, and particularly different from other hydrogenated oils like Olive Wax (Oliwax,) Almond Wax, etc?

there’s a major fundamental difference between it and other waxes on the chemical level - castor oil contains a lot of ricinoleic acid, which is oleic acid with a hydroxyl group on the 12 position, and hydrogenation basically straightens out the molecule from its normal wedge-like shape and allows it to form polymeric structures much more easily

for this reason, castor wax / hydrogenated castor oil is well known for its ability to form gels in oil-based formulas

[Bill_Toge]

does it smell like rotten eggs?

if so, it sounds like your kaolin contains a lot of sulphur

[Bill_Toge]

castor wax / hydrogenated castor oil is a very, very useful material in sticks and other anhydrous products - it gels oils and gives them more thermal stability

[Bill_Toge]

try sodium cocoyl glutamate, that’s got a very pleasant after-feel

[Bill_Toge]

ozgirl said:

The Ecolab product does not contain an alkyl polyglucoside surfactant. The glucoside surfactants often have a high pH (11-12) which could also be raising your overall pH and causing the precipitate.

Try removing the glucoside and see if that fixes the issue.

also, the Ecolab product contains an amphoteric surfactant (the amine oxide) which could very well help the chlorhexidine remain in solution by partially shielding the high positive charge

[Bill_Toge]

it’s not reacting with alcohol, alcohol reduces its solubility in water

[Bill_Toge]

chlorhexidine is a notoriously cranky material to work with, having a +4 charge on the cation - it’s most likely the alcohol that’s causing you grief

[Bill_Toge]

betaine forms a hydrogen-bonded complex with salicylic acid rather than a salt, which increases its solubility; I’ve formulated with it at pH 3.0-3.5, with a 2:1 molar ratio of betaine to acid and it remains relatively soluble (you still need some alcohol or DMI for maximum solubility)

[Bill_Toge]

if you want it to prevent bacterial growth, you need a concentration of around 30-35% w/w, which will make any kind of liquid soap horribly sticky and seriously inhibit the foaming; if you want it to prevent the growth of yeasts and moulds, the required concentration is higher still

[Bill_Toge]

how can an emulsion with a cationic non-ethoxylated emulsifier
invert, in a manner consistent with the conventional laws of
thermodynamics? (answers on a postcard, please)

water in
oil emulsions are very difficult to form, because they’re the only
possible route to uniformity in a situation where all other routes are
physically impossible 

to me, this looks like
it’s down to a difference in cooling rates, which has led to differently
sized droplets - have the batches all been made in containers of the
same size, shape and material, and also, have you tried homogenising the
coarse emulsions?

[Bill_Toge]

in my experience, I’ve found that all three can be used interchangeably, but cetearyl alcohol is the cheapest

[Bill_Toge]

another point to mention is that the emulsion is formed at a relatively high temperature - W/O emulsions should be formed at as low a temperature as practically possible (oil phase set point plus 5-10 °C), so there’s little variation in emulsifier solubility with temperature, and less risk of destabilisation on cooling

2-3% hydrogenated castor oil (castor wax) will give some thermal stability, and further to @Pharma and @ngarayeva001 ‘s points about emulsifiers, I’d recommend adding a polymeric emulsifier, e.g. PEG-30 dipolyhydroxystearate

[Bill_Toge]

also, if memory serves, DMDM hydantoin decomposes in alkaline conditions

[Bill_Toge]

the other point to bear in mind is that sodium and chlorine ions carry an electrical charge, even when solvated in water, and will interact with the skin in a different manner to an uncharged molecule such as glycerine

[Bill_Toge]

from the ingredients list, it looks like they’ve included caramel and molasses to support the claim of ‘brown sugar’ but the particulate matter itself is some kind of non-sugar abrasive; if it were actual sugar, it would be listed as ‘sucrose’, and as you say, it would have dissolved long before it got to the point of sale

[Bill_Toge]

carbomer only works in water-based systems - it won’t hydrate in oil