[Bill_Toge]

the most likely explanation is that water is evaporating from the 40 °C sample over time, causing the percentage of lactic acid relative to the whole formula to increase

[Bill_Toge]

I should think it depends which fatty acid you use - if you can get hold of lauric and myristic acids, see if they create a different effect to stearic acid

[Bill_Toge]

which country/countries is this product to be sold in? many countries have different legal requirements for denatured alcohol

[Bill_Toge]

@Chemist77 at that pH it could double as a toilet cleaner

[Bill_Toge]

in addition to the above, glyceryl caprylate works well in combination with others - it’s strong against bacteria but weaker against yeasts and moulds

Cosphatec GmbH have a wide range of preservatives, with plenty of technical data behind them

[Bill_Toge]

try adding a few % of castor wax/hydrogenated castor oil - that’s good for increasing the set point of oils

[Bill_Toge]

Perry said:

The main ones that will be most useful are…

1. General Chemistry
2. Organic Chemistry

I don’t know what tertiary education is like abroad, but in the UK a general chemistry degree is only useful if you want to know how to a) pass a chemistry degree and b) become qualified to study for a Ph.D in chemistry

both of these skills are of extremely limited use in the workplace, unless you go into teaching/academia, or take a job which mostly involves sitting exams

[Bill_Toge]

ngarayeva001 said:

Edible skincare..  I saw a drinkable perfume yesterday. Made of 60% of gin…

blimey, if that were sold in the UK retail market it would have both Trading Standards and Customs and Excise baying for blood

[Bill_Toge]

have a think about this:

what single molecular property do PQ-10, quaternium-91, behentrimonium chloride and stearamidopropyl dimethylamine all have in common at pH 1.5-2.0?

[Bill_Toge]

depending on what else you have in the gel, it’s very likely to precipitate out of the gel as benzoic acid below pH 4

[Bill_Toge]

DAS said:

@Bill_Toge that’s interesting. And regarding temperature?. In my experience fatty alcohols will decrease viscosity above 35°, even using 1% or less. 

that depends more on what rheology modifier(s) you have in the water phase - if you use xanthan gum and/or a carbomer, there is little variation of viscosity with temperature, whereas if you use cellulose derivatives the variation is much larger

[Bill_Toge]

it also helps the phases separate quickly and cleanly, though any salt can do this job, not just magnesium ones

in my last job I managed to duplicate a Garnier product like this; it was one of the most lengthy and challenging formulating tasks I’ve ever undertaken, and the office staff, who were given the task of evaluating the prototypes, were the biggest collection of nit-picking fussy sods you could ever hope to meet (if only they’d held their own work to the same standard…)

[Bill_Toge]

yes, you need to use a different kind of surfactant to create lower-pH soap

Dove is a textbook example; it’s formulated at neutral pH, and its principal surfactant is sodium lauroyl isethionate

[Bill_Toge]

try adding it to cold water - it sounds like it’s hydrating too quickly

[Bill_Toge]

from an extensive series of experiments carried out a few years ago, I’ve found the two are both surface-active (though they are not emulsifiers) and have substantially different effects on the rheology of the product

fatty alcohols increase the zero-shear viscosity of the product, i.e. make it more solid when at rest, and cause the viscosity to decrease very sharply with applied shear force

stearic/palmitic acid has very little effect on the zero-shear viscosity, but increases the viscosity at higher shear rates, i.e. makes the product feel more ‘creamy’

[Bill_Toge]

from experience the BASF simulator is excellent for predicting UVA/UVB ratios, but the actual SPF achieved in practise tends to vary depending on the nature of the product

[Bill_Toge]

could make it easier to wash off?

it’d make the product ‘bloom’ (i.e. form a turbid dispersion) in water rather than just float to the top

[Bill_Toge]

amodimethicone is soluble in dimethicone and potentially soluble in wax as well: it could be acting as a co-solvent for these otherwise mutually insoluble substances

[Bill_Toge]

@EVchem I’ve only worked with them through their UK distributor, Aston Chemicals

there are some other firms who supply dispersions (e.g. Sensient, Worlée), but none with the same variety of products as Kobo

[Bill_Toge]

em88 said:

- Does it degrade or precipitate? Under what conditions?
It degrades. Water and temperature presence are enough.

that’s a new one on me - amides like urea are usually stable unless you have a lot of alkali present

just out of interest, what does it degrade to?

- Do ALL forms of Urea release formaldehyde?

Probably

only urea/formaldehyde condensates, e.g. imidazolyl urea, do this

[Bill_Toge]

from my experience with W/O emulsions in general, I’ve found hydrogenated castor oil is a very valuable addition to this type of product, as it gels the oil phase, renders it non-fluid and gives it more thermal stability

[Bill_Toge]

you can buy very fine hydrophobically-coated makeup-grade dispersions of pigments from various companies, e.g. Kobo Products Inc; this makes the job much easier

[Bill_Toge]

it does - it’s the only 100% reliable way of shifting smelly essential oils from metal surfaces, bar autoclaving them

[Bill_Toge]

if your GMS is the self-emulsifying grade, it’ll not be compatible with cetrimonium chloride; it contains sodium stearate, which is anionic

[Bill_Toge]

personally, I wouldn’t call that a significant change; depending on the product, it’s quite possible to have that sort of variation from batch to batch, even when it’s been made in an identical fashion from the same lots each time