SILICONES 35


Table 3: Composition summary of the screening formulations for BRB silicones. Phase A1 A2 B1 B2 C1 C2


Product


Carbomer 940 Water


Triisopropanolamine Water


BRB Option A,B or C Ethanol


Carbomer Water


Triisopropanolamine Water


(See Below) Ethanol


INCI %


0.34 17.4 0.26


10.00 2.00 70


Procedure: Step 1: Add A1 and A2 and stir well to form homogeneous opaque slurry in one beaker. Step 2: Separately dissolve B1 in B2 in another beaker. Step 3: Gradually add the solution from Step 2 into the slurry in Step 1: Mix well until a thick transparent gel formed. Step 4: Now choose different option A, B and C for different emphases can be added here too. Homogenize the mixture well to form final hand sanitiser.


Three BRB proprietary Blends (option A,


B, C) have the following compositions: l 2020A: 5% of BRB 1860 and 95% of BRB 526 (PEG-12 Dimethicone)


l 2020B: 50% of BRB 1860 and 50% BRB 526 (PEG-12 Dimethicone)


l 2020C: 50% of BRB 1860 and 50% BRB 523 (PEG/PPG-18/18 Dimethicone)


Physical properties Clarity, pH, and viscosity data are summarised in Table 4. In the study shown in Table 4 there is


some learning against the HLB rule intuitively. It is maybe understandable with high HLB from 8 to 13, PEG/PPG-18/18 Dimethicone and PEG-12 Dimethicone can form clear gels, with the latter most easily. However, PEG-10 Dimethicone is a total surprise since its HLB is only 4.5, more on the hydrophobic side. Cetyl PEG/PPG-10/1 Dimethicone only forms cloudy emulsions in this chassis. This is not surprise at all since both low HLB and alkyl moiety prevent enough hydrophilicity. Without binding by the theory, it is


Silicone Copolyols


523 526 432


speculated that any sufficient PEG type silicone copolyols without long chain alkyl group, regardless of containing PPG moiety or not, will have a fair chance to yield clear gels in BRB optimised formulation system with some unique combination. All gels had pH around 6, there is no need to drive pH to 7 or higher due to a long buffer zone. Silicone copolyls can alter the gelling


network, sometimes enhanced, other times weaken even destroy the gelling mechanism but never be a bystander as shown in Figure 4. That is the reason the phase diagram work is highly valuable here. Overall higher HLB tends to drop the viscosity more than low HLB. All clear gels here are shear-thinning and have a “short” spreading behaviour. This is a desirable rheological property for consumers. The yield values of them are obvious as they trapped air bubbles during formulation. Such yield value combined with surface activity of silicone copolyols helps to stabilise additional benefit agents, even other insoluble silicones.


Table 4: Physical properties of selected silicone copolyols.


Cold processable emulsifiers/co- emulsifiers for long stability emulsions


PEG/PPG-18/18 Dimethicone PEG-12 Dimethicone


Cetyl PEG/PPG-10/1 Dimethicone 6340, 6341 PEG-10 Dimethicone


Viscosity (cSt)


2,000 300


1,250 600


Table 5: Summary of physical properties of selected gels in this study. Performance


Blank PEG-12 Dimethicone


pH 7.00


Viscosity (Spindle #4, 6RPM, mPa•S) 31400 Viscosity (Spindle #4, 12RPM, mPa•S) 17550 Viscosity (Spindle #4, 30RPM, mPa•S) 8419 Viscosity (Spindle #4, 60RPM, mPa•S) 5030


November 2020 7.10


20000 12000 5980 3650


PEG-10


Dimethicone 7.00


23500 13350 6459 3800


Calculated HLB


8


13 5


4.5


PEG/PPG- 18/18


Dimethicone 7.06


21500 12300 6080 3620


Water


solubility Yes


Yes No No


Cetyl


PEG/PPG-10/1 Dimethicone


7.01


32300 18200 8740 5140


TMS BRB1860 DM55 DM66 7.06


74300 46150


6.98 7.00 7.00


Overflow 7000 Overflow 4160


25000 30600 32000 14250 17100 18200 8300 8800 4890 5280


Sensory testing A six-membered performance panel were used for performance testing. This is a single blind panel. Only the panel director can see the product labels. True ingredient names were masked and only randomly assigned characters were used for products. The panel director took 2 mL of product by syringe and placed on subjects’ hands. The product containers were hidden from all subjects. Subjects then rub each product by hand and report sensory scores to the panel director for records. After each evaluation subjects washed


their hands with soap thoroughly and dry with a clean paper towel. After rest 2 min, subjects resumed the next evaluation. Several repeats were added intentionally to check for score consistency and found to be satisfied. The sensory scores of all products were


summarised in the Table 6 and Figure 6, 7, 8. Through the sensory panel testing, a


good understanding of the winning formulation is gained. Note double transparency from those crystal-clear gels probably carries the most significant weight in overall judgment. Among five crystal-clear gels, the blank


gel is used as baseline which has low scores in perceptions related to moisturisation, softness and skin conditioning. This coincides with the unmet consumer needs. The conventional glycerin/Propylene glycol was used as benchmark control here. It also exhibits with problems: prolonged dry time; tackiness, coated feel and non-silky after- feels. It gives an unnatural feel and does not spread as easily as others too. This strengthens a reasoning to make


the hand sanitiser gels with silicones. Basically, silicones fixed those shortcomings to provide superior sensory after-feel to consumers. BRB1860 gum blend yields a translucent gel, this prevents it being No. 1 in this performance series despite its overall highest scores. Among four silicone copolyols gels


studied, the PEG-12 Dimethicone and PEG- 10 Dimethicone are both clear winners in terms of overall performance scores with the PEG/PPG-18/18 Dimethicone gel behind. The Cetyl PEG/PPG-1/10 Dimethicone yields no clear gel, which squarely eliminated it from further consideration. Cost-wise PEG-12


Glycerin/


Propylene Glycol


7.20


26800 15000 7260 4360


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