Case Study: Assessing Emulsion Stability and Formulation Techniques

This case study delves into the critical aspects of emulsion stability within the cosmetic industry, emphasizing the balance between stability and rheological features. It explores the evaluation process, encompassing environmental and product-related factors, and highlights the significance of the United Kingdom cosmetics stability guide (UKCSG). The study addresses fault-finding, focusing on the role of emulsifiers and the hydrophilic-lipophilic balance (HLB) in achieving stable oil-in-water emulsions. It provides a guide formulation, detailing the selection of emulsifiers like Soliol™ E and their impact on product stability. The case study underscores the importance of consumer needs, regulatory requirements, and the application of scientific principles in developing successful cosmetic products. The conclusion highlights the effective use of HLB as a tool in evaluating product behavior and its positive impact on industrial processes, aligning with contemporary consumer preferences and market dynamics. The case study also provides a guide formulation and selection of suitable emulsifiers.

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Stability of Emulsions
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Introduction
The development of a successfully stable cosmetic product should always take into account,
besides regulatory requirements, the consumer needs which are consistently evolving in
contemporary society. Highly standardized raw materials can be used to overcome most of the
technical problems such as poor absorption of actives on the skin, instability of the ingredients,
quality, dispersion problems, and efficacy concerns. The most challenging task for formulators is
achieving the balance between the stability of emulsions and the rheological features. (Di
Giorgio, Salgado, and Mauri, 2019) This case study focuses majorly on how stability is achieved
in these industries.
Stability evaluation
The stability of the emulsified finished products depends on two broad factors. That is;
environmental factors and product-related factors. Environmental factors include; temperature,
light, and humidity and are not only limited to these. Product-related factors include;
manufacturing process, physical and chemical properties of the substance, nature of the materials
of packaging and nature of the container-closure system. Thus several stability considerations the
choice of excipients, their levels and the process development are given topmost priority in the
evaluation and the development stage of the product.
In this case, the stability is evaluated according to the United Kingdom cosmetics stability
guide , (UKCSG). First, the formulation is to be subjected to centrifugation test for thirty minutes
at three thousand rounds per minute and if the sample remains stable; it is approved for the next
stage. It is then subjected to oven for heating at temperatures of 50°C, cooling which is done in

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the refrigerator at 5°C, and also done at room temperature 25 °C. This should take ninety days
and is done to check on temperature stability.
The following evaluations will also be done simultaneously. The PH will be evaluated by taking
an aliquot of the sample of the emulsion and put distilled water by using a potentiometer. (In
triplicate). The ability to flow, (viscosity), will also be determined by a rotational viscometer in
triplicate. The organoleptic characteristics will also be determined by the following factors:
1. No change in appearance or color
2. Small loss of color
3. Complete loss of color
4. Traces of inconsistency and any change in color
The readings will be done at intervals 0f 0, 7, 15, 30, 60, and 90.
Fault finding
Oil droplets are observed to appear on the surface samples which were persistent even after shear
mixing at high rates. This was because our methodology was not exhaustive enough to weaken
the interfacial tension produced by the two phases, in our case which is oil in water (o/w).
(Bremmell et al. 2019.) This is always achieved by mixing at higher rates which is viewed as not
even sufficient to give longer stability. Emulsifiers or even their combinations are required offer
stability to the dispersed phase. Surfactants which are both hydrophobic and hydrophilic are
suitable to be used as emulsifiers since they significantly lower the interfacial forces and also
decrease the coalescence of the droplets.

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With the information provided, we can utilize the hydrophobic to the hydrophilic ratio of our
molecules, hydrophilic-lipophilic balance (HLB). When emulsifiers are added to the oil in water
mixture, they surround the oil layer with their nonpolar ends while the polar ends will be
attracted to the water. In this case, they will manage to lower the interfacial tension thereby
stabilizing the oil droplets and deterring from coalescing. (Yamasaki et al. 2019).
Figure 1 is a demonstration of the polar and nonpolar ends of emulsifiers.
https://www.aocs.org/stay-informed/inform-magazine/featured-articles/emulsions-making-
oil-and-water-mix-april-2014
Every emulsifier has different HLB value which is used to predict its ability to stabilize
emulsions. Soliol™ emulsifier with HLB of 14.5 is suitable in our case since it lies in the range
above 10 in the HLB scale, and is better in stabilizing oil in water emulsions. However Glycerol
oleate which has HLB of 2.5 lowers, the average of the two to 8.5 which lowers its stability
again. (Ding et al. 2019).
It is also important to note that different oils have different HLB requirements as depicted in our
information table. By matching their HLB values, i.e. that of the emulsifiers and oil, it
significantly increases the chances of producing a more stable emulsion. (Dhivya et al. 2019).
Thus this knowledge has a positive impact on the industrial processes from stability evaluation to

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efficacy evaluations. The most challenging task for formulators is achieving the balance between
the stability of emulsions and the rheological features.
Figure 2 emulsions offer different stability.
https://www.aocs.org/stay-informed/inform-magazine/featured-articles/emulsions-making-
oil-and-water-mix-april-2014
Guide formulation
Given that information in the table, I would first determine the required HLB of the oil phase
choose the best combination with my surfactants.
The total oil phase combination is 13% and it is made up of:
10% olive oil, 76.9% of the combination required HLB of 7.
1% avocado oil, 7.7% of the combination required HLB of 7.
1% jojoba oil, 7.7% of the combination required HLB of 6.
Sweet almond oil 1%, 7.7% of the combination required HLB of 7.
Total HLB would, therefore, be determined by:
Olive oil contribution 0.769 ×7= 5.383

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Avocado oil contribution 0.077×7= 0.539
Jojoba oil contribution 0.077×6 = 0.462
Sweet Almond oil contribution 0.077×7= 0.539
Total HLB required =6.923
We can now determine the HLB blend of our surfactants to match the oil phase in the same way,
Contribution by the soliol™ is 0.65×14.5= 9.425
Contribution by glycerol oleate =0.35× 2.5= 0.875
Total HLB required is 10.3
The oil phase is then prepared by dispersing the soliol™ emulsifier and glyceryl oleate in a
mixture of capric caprylic triglyceride emollient, a synthetic emollient, at a temperature of 75̊C.
The oil phase is then added to the mixture using a mixer and homogenized for 10 minutes at
4500 rounds per minute. (Lodaya et al. 2019).
Selection of suitable emulsifier.
Given the grades in the table, I would recommend being soliol™ E which is Ecocert approved,
not vegan, organic approved raw material and goes for a price of £35.00/kg. This is because the
world has gone organic and everyone tries to avoid anything that is associated with cancer. Since
our finished products are going to be certified our materials must also be certified even though it
is going to affect the consumer price. (Ferreira et al. 2019). Having in mind that cheap is
expensive; we are also going to be selective in our target market. It is still going to attract a
larger market since it is not vegan; therefore it incorporates both people who use and does not
use animal products. It would, therefore, be globally accepted.

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The emulsifier of choice should also be screened for factors like; free from palm oil since this is
also a consumer concern. If in case it is present then it should be at sustainable quantities and the
supply should have a sustainable stamp. It should also be checked if it requires a co-emulsifier.
This is because the emulsifier can time not be efficient enough when it is used alone. The
optimum working PH should also be considered. ( Vinner et al. 2019).
Conclusion
This case study depicts a successful case of the development of a new formulation aimed at
achieving quality requirements in terms of stability. The study clearly shows that the knowledge
of HLB is an effective tool in the evaluation of product behavior in terms of its stability. ( Sy,
Dieng, and Diarra, 2019). Thus this knowledge has a positive impact on the industrial processes
from stability evaluation to efficacy evaluations. In modern society today, the cosmetic
environment is dictated by the consumers, influenced by the volatility of the market and
regulated by the government. The case study clearly shows how chemists are geared towards
developing stable and safe products with desirable properties.

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REFFERENCES
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