[Bill_Toge]

are you saying you want to use carbon dioxide as a propellant for an aerosol spray?

[Bill_Toge]

if you want to look up particular ingredients, this is a good place to start:

http://ec.europa.eu/consumers/cosmetics/cosing/

and the full lists of forbidden substances, restricted substances, permitted colours, permitted preservatives and permitted UV filters can be found here:

http://ec.europa.eu/consumers/cosmetics/cosing/index.cfm?fuseaction=ref_data.annexes_v2

good luck!

[Bill_Toge]

you need to use another (non-abrasive) grade of silica alongside your Zeodent 116 to thicken your formula and give it the right rheology

if you want to stick with the same supplier, it looks like Zeodent 153, 163 or 165 would be suitable:

http://www.hubermaterials.com/products/silica-and-silicates/dental-silicas/huber-thickener-silicas.aspx

in my experience, thickening silicas have very low density and generate a lot of airborne dust, so take care when handling them!

[Bill_Toge]

what powder are you using

[Bill_Toge]

lots of things could

[Bill_Toge]

is your oil phase fully melted, and at the same temperature as your water phase (or to within a few degrees) when you add the two together?

when I’ve seen that happen it’s usually caused by the oil phase rapidly cooling when it’s mixed in to the water phase

personally I don’t think it’s down to any of your materials, especially given how robust and versatile Arlacel 165 is an emulsifier

[Bill_Toge]

1) yes - the emulsion will look less smooth, can appear more translucent and can lose some of its uniformity

2) in general, you can’t easily match the densities of the oil and water phase; also, glycerine will have the opposite effect, as it’s denser than water - about 1.3 g/cm³ at room temperature if I remember rightly (water is about 1.0 g/cm³)

besides, in practise the density difference is pretty insignificant compared to the other factors governing emulsion stability (dispersed droplet size, nature and amount of emulsifiers, rheology of continuous phase)

3) you can add thickeners to the dispersed phase if you want, but they’d mainly affect the emulsion’s rub-out properties and have a very marginal effect on the stability

4) positive and negative charges are attracted to each other; if your charged emulsifier is drawn away from the interface of the continuous and dispersed phases by attraction to an oppositely-charged substance in the continuous phase, your emulsion will eventually break down

5) no general answer to this one, it depends very much on the formula!

[Bill_Toge]

hexylene glycol (IUPAC: 2-methyl-2,4-pentanediol, CAS # 107-41-5) is a very effective thinner too

[Bill_Toge]

as long as you’re consistent, and keep records of receipt and purchase, it doesn’t really matter how you classify them - but the best systems are the simplest ones, with the least potential for convolution and inconsistency

my current employer has one set of codes for chemicals, another set for dyes and another set for fragrances, and yet we still manage to keep track of it all, even though those groups comprise nearly 800 distinct materials in total

the place I worked at before used a generic eight-digit number format to refer to raw materials, bulk liquids, packaging components, finished products, bottles, blow-moulding raw materials, spare parts for machines, and any other item of movable stock - but each component type had a unique sub-set, and the type of component could be recognised by the first three digits of its code

whatever you do, don’t re-use old codes for new components, as that will knack things right up and create no end of confusion further down the line

[Bill_Toge]

in a word, no

the only potential source of nitrosamines in betaine is cocamidopropyl dimethylamine (an impurity, present in trace amounts), and it only forms nitrosamines in presence of a nitrite source (e.g. bronopol)

betaines themselves can’t form nitrosamines at all, as they don’t have the right chemical functionality

[Bill_Toge]

the fact it’s got cetrimonium chloride in it means that xanthan gum and carbomers wouldn’t work either, as they’re anionics

Methocel (hydroxymethylpropyl cellulose) is a good thickener for shampoos, as it gives long-flow rheology and helps boost the foam; it’s non-ionic too, so you shouldn’t have compatibility issues with it

[Bill_Toge]

how much SLES and salt have you got in this formula?

[Bill_Toge]

when mixing the two phases together, do you use a high-shear mixer (e.g. a Silverson, or a Greaves)?

in my experience W/O emulsions separate or Ostwald ripen if they’re not sheared enough, regardless of how well formulated they are

[Bill_Toge]

test strips are not a good way to measure pH quantitatively in any type of product - you’d be better off using a pH meter with an electrode

[Bill_Toge]

@milliachemist sorry, I meant that Dow/Rohm & Haas only sell them in IBCs - if we’ve wanted less than 500kg we’ve always bought it from Univar

[Bill_Toge]

my two pence worth:

1. if possible, switch from sodium metabisulphite (Na₂S₂O₇) to sodium sulphite (Na₂SO₃) - it’s chemically more robust, and the lower molecular weight means you’ll need less of it to achieve the same effect; having made up an 0.5% solution of sodium sulphite in the lab and acidified it, I found that no odours were evident until I’d added several percent of citric acid and the pH was well below 4

for what it’s worth, the company I work for has a history of successfully manufacturing oxidative hair dyes containing bases chemically similar to hydroquinone, in alkaline formulas (much more likely to promote auto-oxidation than acidic formulas) and we’ve found 0.2% sodium sulphite works well, provided the product is given the absolute minimum exposure to air (this usually involves covering the surface of the bulk liquid with a plastic sheet)

2. set the pH of your formula as high as you can get away with, so you don’t have to use as much acid in the formula, and reduce the risk of degrading your antioxidant

3. put a chelator in the formula - metal ions, particularly iron and copper, are terrible for inducing auto-oxidation in oxidative dyes, and from what I understand the same is true of hydroquinone

hope this helps!

[Bill_Toge]

was there any difference in the amount of acid you needed to adjust the pH in the 2% and 5% hydroquinone formulas?  (I ask as the actual quantity of acid is sometimes a more significant factor than the pH itself)

in my view, the only other thing in that formula which has any potential to generate a volatile substance almost instantly is hydroquinone itself - if it were oxidised

[Bill_Toge]

I suspect your sodium metabisulphite is the culprit

in acidic media it degrades into sulphur dioxide, which has a harsh, acrid smell and is very nasty stuff altogether

[Bill_Toge]

@milliachemist, Acusol OP 301/305 are from Dow (formerly Rohm & Haas) - they only sell it in IBCs, so unless you’re using huge amounts of it you’re better off sticking with Univar

[Bill_Toge]

if you don’t want to use alcohol, surfactants and co-solvents are the way to go

I’ve found ethoxydiglycol/diethylene glycol monoethyl ether works well at low levels (1-2%)

also, at my last workplace we produced a medicated shampoo with 2% salicylic acid, about 11% active SLES and no organic solvents; provided the batch was heated to 40-50°C prior to addition, and the salicylic acid was given enough time to mix in (1-2 hours for a 5000kg batch), we had no solubility issues even at low temperatures

[Bill_Toge]

there might well be a microbial risk too - materials obtained by mining are usually crawling with bacteria and need to be irradiated to meet cosmetic manufacturing standards (see also talc, clays)

[Bill_Toge]

from a production perspective, sticks are no different to other hot-fill products; the only real difference is the packaging is more complex than the simple jars or tubs used in typical hot-fills

as the dispenser has a mechanism inside, you’ll need to do pack functionality tests alongside your usual stability tests to ensure your product remains dispensable and easy to use throughout its shelf life

as far as formulation goes, hydrogenated castor oil and carnauba wax are good if you want to give the product a hard consistency - the only potential drawback, depending on your process capabilities, is you need to heat them to 80-90°C to melt them

[Bill_Toge]

another reason the oil phase is prepared separately is to allow all the solids to melt before they’re added to the water phase, ensuring that a uniform emulsion is formed

if you need to, you can sequentially add the oil phase ingredients to the water phase (for instance, if you’re producing it on an industrial scale and there’s no premix vessel available on the plant), but you’ll need a sharp eye to ensure the ingredients are all fully melted and a good shear mixer to ensure it gets thoroughly mixed

for an O/W emulsion, it doesn’t matter whether you add the oil to the water or vice versa (e.g. we had an O/W sunscreen formula where the oil phase had such a large volume that the only practical way to make it on the plant was to add the water to the oil phase), but for a W/O emulsion you must add the water to the oil - if you do it the other way round you’ll end up with the water phase becoming continuous, and the oil phase will fail to mix with it

the reason is that the attractive intermolecular forces are stronger within water than they are within oils; water droplets have a much greater tendency to coalesce than oil droplets, which is why water will form the continuous phase unless it’s physically prevented from doing so, and also why W/O emulsions generally need more rigorous stabilisation than O/W

also, the nature of the continuous phase depends on the nature of the emulsifier(s); the relative volumes of the continuous and dispersed phases are irrelevant

[Bill_Toge]

• Customer changes the brief

in fact it happens so often that you could fill two or three slots with that answer

[Bill_Toge]

I’ve found gellan gum (available from CP Kelco, tradename Kelcogel) works remarkably well as a suspending agent and gives almost no viscosity - it’s been used to suspend the glitter in Aquafresh Ultimate Sparkling mouthwash, and the bits of jelly in Orbitz soda

if you do use it, make sure you’ve got a good preservative - it’s a polysaccharide and it can sustain microbial growth