Problems producing a stable oil-in-glycerin emulsion?

Unknown

Hi there

I'm trying to produce a stable, high-viscosity oil-in-glycerin emulsion using lecithin and MCT oil. 

The problems: Even when it seems to start working, my mixture often liquifies the moment I remove the source of agitation (a hand mixer). Mostly, I get a slightly viscous fluid that seems semi-stable, though it never progresses past this point, and I can see superfine 'flecks' of oil on the surface of the emulsion.

I've tried increasing the initial viscosity with the addition of tapioca starch, but this isn't yielding adequate results.

What am I doing wrong? My suspicions:

• I'm using the wrong surfactant. (I want a 'natural' emulsifier that's also easy to understand on product labels, so lecithin seemed a good fit.)
  
• I'm overdoing the lecithin (is using too much of a surfactant something to worry about?).
  
• The hand blender is applying the wrong kind of shear (sometimes I get better results making, say, mayo using a whisk).
  
• The MCT is not viscous enough to start the process off.
  
• The polarity/surface tension of the glycerin requires a different strategy to making an analogous emulsion such as mayonnaise. I can see hints of this in the way the oil 'takes'; it seems less enthusiastic, shall I say, to incorporate itself. 
  
• I'm barking up the wrong tree entirely.

Either way, I know this should work, and I've seen it almost work. I just don't know what I'm doing wrong, because isolating the variables is hard when it's not possible to isolate a certain variable beyond certainty (a hand blender; I mean, c'mon).

Optional reading: First off, I'm super new at this. I'm not a chemist. I have a rudimentary knowledge of emulsification: partitioning of immiscible liquids in shells of surfactants surrounded by a continuous medium; the higher the intermolecular impact velocity the better (right?), so high sheer and high initial viscosity are desirable.

Anyway, help would be immensely appreciated!

Belassi

Probably the first item is your hand blender. Almost all of them are low-shear because the cup wall is too far away from the blade tips. Secondly we need to see the ingredient list and percentages before we can help. I've no idea what "MCT" means, can you provide the proper INCI term please?

johnb

What is the function of this product? Is it required to be water free? If not, how much water is tolerable?

Unknown

Hi everybody. First, thanks for the quick response.

@johnb: The formulation is to function as a moisturiser. I am trying to exclude preservatives; I'm given to understand that no water is tolerable in such a case? 

@Belassi: The list of ingredients and percentages (with INCI terms):
Caprylic/Capric Triglyceride (80%)
Glycerin (19%)
Lecithin (1%)

I'm working with an extraordinarily tight budget (startup woes!), so I cannot afford much in the way of equipment upgrades, alas. I'm up to DIY solutions though, if any exist.

Merry Christmas to those of you who celebrate it, by the way!

johnb

Christmas greetings to you, MsAntipodes.

Have you considered the user acceptance of this mixture? It does seem a rather odd combination, even if it were possible to obtain a stable emulsion.

I could imagine that glycerin at that concentration, in the absence of water, could act as an agent to draw moisture from the skin rather than act a moisturiser.

MarkBroussard

@MsAntipodes:

You'll get much better results making a stable Oil/Glycerin emulsion using either Sucragel or Sucrose Ester emulsifiers www.sisterna.com/personal-care/sucrose-esters

The problem with your approach is twofold:  It is somewhat difficult to make stable Oil/Glycerin emulsions and they tend to be quite sticky because of the high percentage of Glycerin.

It is much easier to just use a preservative.

Also, 1% Lecithin ... if you're going to stick with Lecithin, best to use 4% to 6% and in combination with a sucrose ester.  You're never going to get an emulsion using just 1% Lecithin.

johnb

I have managed to make a "sort of" stable emulsion using a homogeniser.
The esthetics of this on the skin is quite unpleasant. It is strangely sticky and does not absorb well into the skin.

I'm not suggesting using  homogeniser, it's just that I saw that as an easy way of getting at least a semistable product for an initial in-use test. The homogenised emulsion is slowly separating now (eight or so hours after making) but I suggest you give some attention user acceptance of this type of mixture before you proceed much further.

Bobzchemist

I think you really need to make sure that your target market wants this kind of aesthetic feel before you go any further. You might want to use a syringe homogenizer/emulsifier setup to make small samples for this.

http://cadenceinc.com/catalog/product-group/micro-emulsifying-needles/

I'd also look into powder/gel/fiber types of emulsifier if I was trying to do this.