[ChemicalPyros]

Stearic acid and Cetostearyl alcohol ratios are through the roof, you should consider decreasing their percentage, or replacing them with something that has a lower melting point (I would recommend some Isopropyl Myristate and/or Caprylic/Capric Triglycerides). This should take care of the high viscosity of your product.

As for the burning sensation I think it may be due either to the Borax or the Kojic Acid, or to both. So I would recommend removing the Borax, and reducing the Kojic Acid ratio (maybe halve it).

[ChemicalPyros]

Hello  Zoe,

Triethanolamine and Stearic acid are not emulsifiers, unless you are reacting them together, in which case you have triethanolamine stearate (which is a surfactant, but used in soap and not in creams). In any case, without the formula there is little that can be done.

[ChemicalPyros]

Many waxes exist on the market, it is better to start with what is available readily. For your case I would recommend a wax such as beeswax, with some butter (shea, mango, cocoa, …), and the oils you wish to incorporate.

You should keep in mind several points:

• The melting point, you would not want it to melt easily in warm weather or become rock solid in cold weather.
• The “Sweating”, this has to do with the compatibility between the oils, butters and waxes. the “Sweating” appears usually in a Freeze/Thaw cycle.

[ChemicalPyros]

I agree with you that it is a myth that molecules migrate deep in the skin. Anyway that did not stop the pharmaceutical industries from developing methods and techniques to make it possible to send molecules via the skin. The easiest approach is to use penetration enhancers AKA adjuvants, they are molecules that help the transport of other molecules through the skin and/or help stabilize them enough. Another way is to encapsulate them (liposomes, silica spheres, …). Just keep in mind that the adjuvants are specific to the molecule you want, so you may need at least one adjuvant per active ingredient.

One example comes to mind: Lidocaine (in anesthetic creams) have a better effect and migrates easily through the skin in the presence of menthol. Another is honey and ascorbic acid, together they help regenerate collagen in the skin.

[ChemicalPyros]

I would not recommend using alcohol in formulations for the face. its vapor can irritate the eyes immediately. You can use a wax (natural obviously) to bind your oils and obtain an anhydrous formula where you won’t be needing any preservatives.

[ChemicalPyros]

You might need to add a filler to control the thickness and reduce the cost. I would suggest using starch. Some oils, or petrolatum can add a nice feel. Avoid low MW silicones if possible.

[ChemicalPyros]

Hello,
I would suggest that you try a “Knock-Off Test”. Where you eliminate one ingredient at a time, this way you can be sure what ingredient is causing the grey/green color.

Personally, I suspect the vitamin E, the quantity is a bit high. So I would recommend that you start by eliminating the vitamin E and see if the batch changes its color.

[ChemicalPyros]

Without more details about the formulation, such as is it an emulsion, or an oleaginous ointment.

As for the ZnO, it absorbs UV light, hence its use in sunscreen formulation, and on top of that it soothes the skin and reduces the redness or irritation, and it is hypoallergenic. So it is a very nice ingredient in your arsenal.
You can read more about ZnO here: https://www.ncbi.nlm.nih.gov/pubmed/28509652

The concentration of ZnO in relation with the spreadability can be a function of the viscosity of the medium in which it is dispersed, the size of the ZnO particles among other parameters.

[ChemicalPyros]

Hello 4mulate,

Could you please specify why you want to replace mineral oil and dimethicone. do you want more natural alternatives, or are they unavailable? 

[ChemicalPyros]

@jeremien

the technique you are mentioning necessitates the presence of a lammellar phase or at least a sponge phase in the middle of the ternary phase diagram. this limits the use of this technique to a few systems. also this technique requires mechanical stirring. you can refer to Solans et al., she has a lot of articles discussing this technique.

[ChemicalPyros]

Hello everybody,

@Doreen, studies showed that the best tocopherol is the γ-tocopherol, for several reasons (they are discussed in detail in this article: γ-Tocopherol, the major form of vitamin E in the US diet, deserves more attention.

as for the synergy between BHT and vitamin E, in some conditions it ca be found, but in most conditions they have a degrading effect on each other. (Dramatic solvent effect on the synergy between a-tocopherol and BHT

antioxidants).

@DiamondD, you should be careful about in-can protection, because some suppliers already add some antioxidants, and if you add your own they might actually accelerate the oxidization process. so it is better to check with the supplier beforehand, and double check the antioxidant you want to add, because they all have an optimal percentage to do the job.

[ChemicalPyros]

Emulsions are kinetically stable systems (it means that they are going to separate given enough time, your aim is to keep it together for long enough time to be totally consumed or to meet the expiry date, whichever comes first). The main parameters to control while making an emulsion are:

• The time and speed of the mixing (the higher the speed the smaller the droplets will be, and the longer the time of mixing the more homogeneous the size of the final droplets, your aim is to have small and homogeneous droplets).
• The choice of surfactants, because some surfactants are incompatible with the oils you are trying to disperse.
• The order of addition of the ingredients, usually the name of the emulsion is indicative of the order of addition, (a water-in-oil indicates that you prepare initially the oil phase and you add the surfactants to it, then you add the water or aqueous phase in small quantities while mixing), for an oil-in-water emulsion it is reverse). The speed of addition also plays a role in the stability of the emulsion, the slower you add the better the final emulsion.
• The use of a thickener can improve the stability of the emulsion, as well as make it more aesthetically pleasing.

All in all, it is a trial-and-error based process in order to obtain the best or sometimes acceptable outcome. just keep in mind that you are finding a compromise between all the parameters and what can be economically viable for you (you cannot mix it for 2 days for example, even if the outcome will be better, and you will never be able to try all the surfactants in the world, and so-on).

As for the thermally fragile ingredients, you can cool down the mixture then add it and mix, just take into account that if the ingredients are oil soluble just increase the mixing speed by at least 10% and reduce the mixing time, in order to force the ingredients into the droplets (the time reduction is to avoid temperature increase, so if you see that the ingredients are not totally dissolved, stop the mixing for a while then repeat the process till it is fully dissolved).

[ChemicalPyros]

Hello @aperson,
Thank you for your input, in my readings about the subject, I was able to differentiate between the two main category of tasks required from a cosmetic formulator. The first category is the function of the formulation (moisturizing, anti-ageing, cleansing, …), this category can be quantified up to a certain point, and experimental designs can be useful in this category. The second category is the aesthetics of the formulation, the knockout experiments are better suited for this category. To the best of my knowledge, there is no paper about the use of DOE in improving the feel or eliminating the stickiness from a formula, but there is plenty about improving the stability of an emulsion for example.

[ChemicalPyros]

Thank you @David for your insight. After more in-depth reading about the DOE, I find that applying it seems highly inefficient, and when it is useful it is the exception and not the norm, so I will be sticking to the Knockout experiments.

[ChemicalPyros]

For a microemulstion, the amount of surfactants is logical, but not commercially viable. So I would recommend you try other surfactant blends ( such as Tween/Span for different ratios). Another approach will be to soak the fragrance on fumed silica then dispersing it in water, it should give a relatively clear solution, though maybe a bit hazy.

[ChemicalPyros]

Thank you for your fast replies, and I agree with you that from a sensorial perspective it is better to use the knockout experiment. But I was looking from another perspective when I was researching the DOE, I was hoping that with this method I can increase the stability of emulsions, or obtain the maximum viscosity for minimum viscosity agents when multiple viscosity agents are present in a formulation, which are very quantifiable parameters. 

[ChemicalPyros]

Hello @Chemist_Ahmed, I would recommend the Optiphen ND (AKA Rokonsal ND) it is a great broadspectrum preservative system and can be used at low concentrations (0.2%) for surfactant systems.

[ChemicalPyros]

I have had experience in thickening oils using Resin Wax ( C30-45 Alkyldimethylsilyl Polypropylsilsesquioxane). This wax reduce the oily feel and is an excellent ingredient. The only problem is that it is relatively expensive and sometimes it forms crystals on the surface if cooled inappropriately.