32 SILICONES Ethanol 1% PEG-12 Dimethicone in Ethanol A’
Formulation Space
B’ D’ C #3 #2 10% PEG-12 Dimethicone in Ethanol #1
Gel B (10%Carbo /TIPA Gel in Water)
PEG- 12Dimethicone
0.0000 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000 1.0000
Gel B (10%Carbo /TIPA)
0.0000 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000
PEG/PPG 18/18 Dimethicone
1.0000
Figure 2: Pseudo-tertiary phase diagram of Ethanol/PEG-12 Dimethicone (BRB 526)/Gel B(10% Carbomer 940/Triisopropanolamine 1: 0.775 w/w). A’, B’, C’, and D’ are all isotropic system points.
crystal-clear mixture in any ratio. Thus, it is speculated that the denaturing agent or trace impurity in SDA 40B may have caused such cloudiness. During COVID-19, the alcohol world market is somewhat chaotic to say the least. Different players offer different qualities. It is strongly recommended that formulators in this area conduct similar screening experiment to check the quality of reagents before further experiment and production. Checking at this stage would be wise and could save a lot before going deeper into R&D and production cycles. From the above pseudo-binary mixing,
the first non-silicone simple clear hand sanitiser base #1 is obtained. It has a composition of (70% ethanol, 29.7% water, 0.17% carbomer 940, and 0.13% TIPA) with 3000 mPa·S in viscosity. This satisfies WHO’s hand rub ethanol regulation of
Figure 3: Pseudo-tertiary phase diagram of Ethanol/PEG/PPG-18/18 Dimethicone (BRB 523)/Gel B(10% Carbomer 940/Triisopropanolamine 1: 0.775 w/w).
minimum 60% ethanol. It also preserves room for benefit agents. Base #1 is a relatively weak gel which liquifies quickly on hands. So, a higher gel strength is being studied. With 10 times more gelling agents in gel
B a stronger gel can be built. Using a similar method, Base #2 is a clear gel with much higher ethanol level. In the personal care industry, the upper non-irritation limit for TIPA was 1.1%.2
10% gel B has 0.44% TIPA content and therefore is safe. Base #2 exhibits enhanced viscosity and total clarity with the composition of (90% ethanol, 9% water, 0.56% Carbomer 940, and 0.44% TIPA). Further other benefit agents and water can be added in base #2 later. Also, combination of base #1 and #2 allows continuous gel strength adjustment when other ingredients are added. Such a wide
formulation space of aquo-ethanol hand sanitiser gives total optical clarity and allows further exploration on silicone effects below.
The formulation made from
PEG-12 Dimethicone in hand sanitiser gel In this section the impact of PEG-12 Dimethicone (BRB 526, HLB 13) is investigated on moving the phase boundary of isotropic gel region in the diagram. Two techniques, i.e., pseudo- binary and pseudo-tertiary mixing, are efficient tools to explore phase diagrams of (gel A or B)/ethanol/PEG-12 Dimethicone. For the pseudo-binary mixing, 1% and
10% PEG-12 Dimethicone in ethanol as two stock solutions are prepared on one end. On the other end either gel A or gel B is available. With a high-quality ethanol, phase points in the diagram of (gel
Figure 4: Examples of different phase behaviours. Left to right – clear gel, translucent gel, gel with minor phase separation, complete phase separation into liquid and precipitation.
PERSONAL CARE EUROPE November 2020
Clear Gel
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