How to formulate a detergent – THEORY pt. 1

How to formulate a detergent

In this post I am going to talk about the formulation of detergents like face-wash, shampoo, shower gels, bubble bath and so on…

All these detergents are made starting from a family of ingredients: SURFACTANTS.
Surfactants are compounds that lower the surface tension of a liquid and therefore they emulsify the grease and the dirt on our skin and help us to wash it off with the aid of water.

Surfactants can be divided in four groups according to their ionic nature:
– cationic – positive charge when ionized. They are mostly used in conditioners.
– anionic – negative charge when ionized. They are largely used in detergents and shampoos and provide good detergency and lather. In this family we ding: SLS (sodium lauryl sulphate), SLES (sodium laureth sulphate), ammonium lauryl/laureth sulphate, sodium lauroyl sarcosinate, disodium laureth sulfoccinate.
– non-ionic – no charge (unionizable). They are lauryl glucoside, decyl glucoside, coco glucoside, caprylyl/capryl glucoside. These are usually not used in shampoos because they don’t leave a comfortable feeling on the hair (it makes them feel dry) unless they are included in the formulation in small amount (and therefore they work more as foam stabilizers). 
– amphoteric –
 both positive and negative (depending on the pH). These are used a lot in shampoo formulation: specially if combined with SLES they help the shampoo to be thick and they also decrease the irritancy (read this in a relative way 🙂 ). They are for example: cocamidopropyl betaine, lauramidopropyl betaine, coco-betaine, cocamidopropyl oxide.

THE ACTIVE MATTER of a surfactant:
How “strong” do we need our detergent to be? This of course depends to what we aim to make: if we are going to make a bubble bath it will need to have a higher washing ability than a face-wash, which should, on the contrary, be very gentle and delicate. The washing ability of a detergent is determined by its “Active Matter” coefficient: every surfactant has an “active matter coefficient” which is a number in percentage (for example the SLES coefficient is 27%) and this tells us “how much active washing substance there is in our SLES… and in this case it is 27%”. This is because the liquid surfactants which we can easily find sold online are usually made of the real surfactant and water (so the active matter is not 100%). You should find out this number from where you purchase your surfactants (if they are not mentioned on the page, send an e-mail to the supplier).

Generally the active matter of surfactant we want in our detergent depending on its aim is this:
Face wash – lower than 10%
detergent for intimate use – around 5%
shampoo – between 10% and 15%
shower gel – between 18% and 20% 
bubble bath – between 20% and 25% (this is because the bubble bath should go directly in the water while the shower gel is supposed to be rubbed directly on the skin)

So now you might be thinking that to make a good shampoo you just need 45% SLES and rest of water and tadaaa… well… NO 😀
It is true that the 45% of SLES plus 55% water would give you a solution with 12.15% Active Matter (45*27(which is the active matter coefficient of SLES):100= 12.15) however there is something very important you still need to know:

In a formulation a single surfactant results more harsh than an equal “active matter %” formulation made with different surfactants.
To make it simple: if you mix surfactants together, you will have a milder results than using the surfactants alone.
A particularly happy mix is SLES with a betaine (usually I have cocamidopropyl betaine) because not only the betaine lowers the harshness of the SLES, but it also thickens the solution.

Generally when formulating you should use:
– anionic or non-ionic surfactant; it is the surfactant which we will add in our detergent at higher %.
– anphoteric surfactant; it will make the first surfactant more mild.
– extra surfactants: these are used in very low percentage and are added to improve the lather or the consistency of the detergent.

To be continued… 😉
[Theory of Formulating a Detergent Part 2]

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