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Formulating effective and stable W/O emulsions

by james.runkle@drummondst.com james.runkle@drummondst.com No Comments

Cosmetic chemists are an innovative, curious, and creative group of scientists, continually looking to formulate the most effective and pleasing products for the world’s consumers. Yet when asked to create the galenic forms most often requested by marketing – creams and lotions – the “default emulsion” is almost always oil-in-water (O/W). While O/W systems offer good sensory properties and ease of manufacturing, the primary alternative system – water-in-oil (W/O) – offers distinct advantages, among them long-lasting adherence to the skin and improved water resistance. So why isn’t W/O used more often? Because (a) it is difficult to create a stable W/O system, and (b) the esthetics of a W/O emulsion are often undesirable (sticky, tacky, thick…).

Let’s cover some key concepts to enhance stability when formulating W/O emulsions:

  1. When making W/O emulsions, high energy is required

Why do we need high energy when making a W/O emulsion? High energy brings several benefits to your W/O system, altogether contributing to a stable emulsion:

  1. Creates high energy dissipation rates 1,2
  2. Controls particle size of the dispersed phase of the emulsion 1,2
  3. Reduces interfacial tension 1,2

To achieve the desired results, one may use high-energy equipment such as a rotor stator/homogenizer or a deflocculator at moderate to high shear.

Let’s take a closer look at each…

A) Dissipation rate refers to the rate of conversion of turbulence into heat by molecular velocity.

Here is a simplified energy flow chart when you are creating a W/O emulsion:

Turbulence, initiated by the high-shearing rotor stator, transfers its energy into kinetic energy within the W/O system. That energy of motion is converted into the large velocity gradients of the dispersed droplets of various sizes. And finally, the energy of the rapidly moving particles is converted into heat through dissipation.2

This is a very simplified flowchart, as there are many other variables involved, but the take-home message here is that the higher the conversion of energy into heat, the higher the dissipation energy, the more kinetically stable emulsion. Essentially, we do not want any energy left in the emulsion, especially in those water droplets because that can lead to instability.

B) The energy applied when creating a W/O emulsion affects the particle size of the internal phase of an emulsion.

As mentioned before, high energy processes will use rotor stators/homogenizers, while a low energy process may use simpler blades (turbine stirrer, propeller, or blade stirrer). If you use high energy, you will achieve a finer, more evenly dispersed emulsion, which is exactly what you want, as this is more stable.

But if homogenization is too mild, due to your equipment and/or shearing speed, your W/O emulsion will be highly poly-dispersed, meaning, there will be a wide size distribution in the dispersed droplets, which can lead to instability. 

C) And finally, we need to use high energy with W/O systems because it reduces the interfacial tension (energy present at the water-oil interface).

This benefit is a result of the other two: The more heat that is given off, the less energy and mobility in the dispersed water phase. And the smaller the average droplet size of the dispersed phase, the more the stability increases. Altogether, there is less energy remaining at the water-oil interface, so water droplets are less likely to coalesce and will remain stable within the continuous oil phase. 

  1. Electrolytes must be used

Electrolytes – inorganic salts such as magnesium sulfate or sodium chloride – must be present in the emulsion because they will stabilize your system through various mechanisms of action. For example, NaCl has been shown to decrease the particle size through electrostatic and steric repulsion in the droplets.3 CaCl2 has proven to decrease attractive forces between water droplets.3 And MgCl2 can reduce interfacial tension and enhance interfacial film strength.3

Each of these mechanisms may prevent one or more of the following from happening.

1) Ostwald ripening, also referred to as disproportionation, is caused by the difference in solubility in emulsion droplets. Smaller droplets are more soluble than larger ones, and with prolonged time, the smaller droplets tend to diffuse in the bulk and are deposited on larger droplets. Therefore, larger droplets eventually grow at the expense of smaller ones. Adding salts will counterbalance the driving force for Ostwald ripening, which is related to the total pressure and pressure in the droplets.3

2) Sedimentation is another unstable condition where there is no change to the droplet size, but droplets move to the bottom. The addition of various salts could improve stability by decreasing particle size and reducing the interfacial tension. Salts can allow for tighter packing of surfactant molecules at the O/W interface.3

3) Coalescence is when droplets join, creating larger sized droplets with water separation at the bottom. Adding salts will reduce the attractive forces between water droplets, which will reduce their collision frequency, and thereby prevent droplet coalescence and increase emulsion stability.3

  1. Depending on the emulsifier, the polarity of the oils used must be specific

Unlike O/W systems, the polarity of the oils used in the oil phase has an outsized influence on the stability of the emulsion, and the performance of high-polarity vs. low-polarity oils will be significant. This is because of the “like dissolves like” rule. In general, chemicals of similar polarities demonstrate better interaction. If the lipophilic tails of your emulsifier are polar, perhaps having esters or hydroxyl groups in its carbon backbone, for example, then the emulsifier is better suited in an oil phase of medium to high polarity. The opposite holds true as well. If the polarity of the oil phase does not match that of the emulsifier, the emulsion will not be stable.

Now, let’s talk briefly about the esthetics of W/O emulsions

W/O emulsions are often tacky or draggy, leaving an unpleasant skin feel and an uncomfortably thick layer of product. Also, as W/O systems are often used with pigments, many common emulsifiers do not have the correct compatibility with the wide variety of pigments used today, resulting in non-homogenous dispersions of the pigments within the emulsion. Many traditional W/O emulsifiers were not designed to address issues of skin feel or pigment dispersion, but modern advances in esterification chemistry allow for the creation of a new generation of emulsifiers that provide perceptibly improved sensory characteristics.

It can be suggested that the use of an emulsifier based on polyglycerol chemistry is especially suited to W/O systems due to enhanced stability resulting from large polar headgroups. (Incidentally, polyglycerol chemistry is considered “green” and advantageous when formulating natural or clean products…) Esterifying a polyglycerol backbone with other esters will significantly effect both skin feel and pigment dispersion properties; for example, the use of a ricinoleic acid ester could provide fluidity and improved skin feel, while the use of a hydroxystearic acid ester could improve the dispersibility of both coated and uncoated pigments.

With these concepts in mind, formulating a W/O emulsion can result in an elegant product satisfying the end consumer while meeting the requirements of marketing, allowing the creativity of the chemist to move “beyond the box” of traditional cosmetic emulsions.

References

  1. Turbulence and multiphase flow. http://www.lowshearschool.com/?page_id=16919
  2. The effect of shear on oil-water mixture. http://www.lowshearschool.com/?page_id=16933
  3. Zhu Q , Pan Y, Jia X, Li J, Zhang M, Yin L. Review on the stability mechanism and application of water-in-oil emulsions encapsulating various additives. Comprehensive Reviews in Food Science and Food Safety, 18 (6): 1660-1675, 2019

Leor Fay Tal is the Technical Marketing Leader for the Personal Care division of Gattefossé USA. She delivers information on trends and consumers, provides technical marketing support to the company’s sales teams and agents across North America, Canada, and Mexico, and works to promote knowledge and understanding of the company’s ingredients. Prior to Gattefossé, Leor Fay had worked in the R&D Powder Laboratory and then as the Raw Material Regulatory Affairs Specialist at MANA Products. Leor Fay is also an active member of the NYSCC. She organized the April 2018 event Cosmetics in the Middle East, A Regulatory Perspective and now serves as the Secretary for the executive board.

 

 

 

 

Ben Blinder is the Senior Director for Gattefossé USA – Personal Care Division, where he is responsible for the strategic direction and performance of the cosmetic business for Gattefossé in the US and Mexico. Ben holds a chemical engineering degree from Lehigh University and has been working in the personal care industry for 32 years, with extensive experience in strategic and long-range planning, sales and technical management, and new technology search/discovery.  Ben also serves on the NYSCC Scientific Committee.

 

 

 

 

Sunscreen Monograph Proposed New Rules and its Impact on Formulations-Part II

by NYSCC NYSCC No Comments

In my recent blog published in August, changes to the current sunscreen tentative monograph were proposed.  These changes are probably the most drastic changes to the sunscreen monograph since its inception.  In this section, I would like to tackle two key areas related to the changes requested by the FDA.  The first one is the human pharmacokinetics Maximal Usage Trial (MUsT) for sunscreens conducted by the FDA and published in the Journal of the American Medical Association in May 2019.  The second is the response from the Personal Care Product Council (PCPC) to the requests from the FDA for additional safety data.

The FDA conducted a MUsT trial on 4 sunscreen formulations.  The products consisted of 2 sprays, one lotion and one cream. A detailed description of the products used in the study and the sunscreens concentrations used is displayed in Table I below.

Table I

Concentrations of sunscreens in all treatments

Treatment Percent sunscreen contents per label
Avobenzone Oxybenzone Octocrylene Ecamsule
Spray 1 3.00 6.00 2.35 0.00
Spray 2 3.00 5.00 10.00 0.00
Lotion 3.00 4.00 6.00 0.00
Cream 2.00 0.00 10.00 2.00

Twenty-four subjects were enrolled in the study and were randomized into 4 groups.  Each treatment was studied on 6 individuals. All subjects finished the study except one.  Products were applied at a rate of 2 mg/cm2 on 75% of the body area.  Products were applied by a trained expert and were re-applied every 2 hours four times a day.  The study ran for 4 days and panelists were kept indoors.  Thirty blood samples were collected from each panelist over a period of 7 days and were analyzed for their concentration of sunscreens using a validated HPLC method.

Mean maximum plasma concentrations for all sunscreens were calculated for the four treatments and are displayed in Table II.

Table II

Geometric mean maximum plasma concentration for all treatments

Treatment Geometric Mean Maximum plasma concentration, ng/mL (%CV)
Avobenzone Oxybenzone Octocrylene Ecamsule
Spray 1 4.0 (60.9) 209.6 (66.8) 2.9 (102) Not applicable
Spray 2 3.4 (77.3) 194.9 (52.4) 7.8 (113.3) Not applicable
Lotion 4.3 (46.1) 169.3 (44.5) 5.7 (66.3) Not applicable
Cream 1.8 (32.1) Not applicable 5.7 (47.1) 1.5 (166.1)

As seen from the table, all sunscreens tested had higher blood levels than the FDA proposed threshold of 0.5 ng/mL.  These levels were also achieved on the first day of treatment.  The levels obtained triggered the FDA to request safety data not only on the sunscreens studied but also on the 12 sunscreens listed in the monograph.  In addition, the FDA requested MUsT studies to be conducted by the manufacturers on several dosage forms to establish proper guidelines for usage based on safety and efficacy.  Regardless of the results obtained, the FDA insisted on the fact that individuals should not refrain from using sunscreens.

In response to the request from the FDA, the PCPC sent a letter to describe the protocols and studies suggested by the council as well as a timeline.  The PCPC suggested to conduct, in addition to MUsT studies, several surveys on usage of sunscreen products to guide the council in designing the MUsT studies.  The timeline extends till 2023 which should give the industry some breathing room in terms of formulations.  Once the studies are received and completed, an additional timeline delineating the safety of the selected molecules will be proposed.  In the council’s response, two sunscreens were not considered for MUsT studies.  These are Cinoxate and Dioxybenzone.  The fate of these two sunscreens is not determined at this stage yet.

The sunscreen monograph has been evolving for the past 35 years to keep up with the advancement in science.  Formulators, and companies in the field of sun care will have to adjust one more time to the changes.  These changes bring a lot of new challenges and opportunities to innovate and lead.


 

Biography

Dr. Fares started his career in personal care studying the effect of solvents on sunscreen chemicals.  His interest in skin drug delivery especially from polymeric matrices grew during his graduate work at Rutgers, where he completed his Ph. D. in Pharmaceutics.

Dr. Fares worked at Block Drug and GlaxoSmithKline where he held positions in research and development in the areas of skincare and oral care.  After that, he joined L’Oreal where he held several positions of increasing responsibility leading to AVP of skincare.  He is currently the Senior Director of skincare and oral care at Ashland Specialty Ingredients.  Dr. Fares is the author of many publications, and patents and made many presentations in national and international meetings in the areas of suncare, skincare, and oral care.

 

NYSCC Suppliers’ Day Partners with Cosmetic Executive Women (CEW) on New Beauty Award for Supplier’s Innovative Ingredients and Formulation

by james.runkle@drummondst.com james.runkle@drummondst.com No Comments

All Things Beauty to Be Celebrated May 2019 in NYC

 

(New York, NY, December 2018)—The New York Society of Cosmetic Chemists  (NYSCC) has renewed its partnership with CEW by sponsoring a new category in its prestigious Beauty Awards program the “Supplier’s Award: Ingredients and Formulation.”  Mirroring the Academy Awards Science and Technical Achievement awards, the winner of the Supplier’s Award will be announced in advance at the 40th Annual Suppliers’ Day taking place May 7-8, 2019 at the Javits Convention Center in New York City. The winner of the Supplier’s Award will also be recognized at the CEW Beauty Awards luncheon on May 17th at the New York Hilton that attracts more then 3,000 attendees.

Any ingredient and formulation provider that has demonstrated innovation and new technology can submit to the CEW Supplier’s Award.  The deadline for submissions is January 15, 2019.   The submissions can only be entered from a supplier, there is no year limitation, and natural and synthetic ingredients can be entered.  For the submission form and more information click here or email: beautyawards@cew.org

A curated panel of judges from leading beauty and personal care brands including members of the NYSCC Scientific Advisory Committee will select the finalists of the “CEW Supplier’s Award: Ingredients and Formulation.”  Finalists will be announced on April 2, 2019.

“Increasingly, the line between marketing and formulation is being challenged and blurred in product development and this award highlights how all the elements and departments—ingredients, formulation and new technology—need to work together for successful product launches,” said Cathy Piterski, Chair, NYSCC.

The NYSCC Suppliers’ Day is the main trade show and conference for beauty

ingredients, formulations, and delivery innovations.  New educational programming, expanded features and enhanced industry alliances taking place at the event in 2019 include:

-“Fragrance: The Invisible Art,” an all-day, in-depth Fragrance Program, co-produced with the American Society of Perfumers featuring experts in perfume, scent, essential oils, consumer trends, and more.

 

-Spotlight on the important topic of “Safety & Testing.”  Suppliers’ Day will be collaborating with IKW, a leading European Association for German Cosmetic, Toiletry, Perfumery and Detergent, to create a program that addresses important safety and lab testing topics in the industry today.

 

-Suppliers’ Day 2019 has also added a new exhibit hall at the Javits Center, making it the largest event in the show’s history.  This hall will also feature presentation theaters and an innovation hub that will experientially complement specific theater presentations.

 

-Enhanced student engagement with an expanded Future Chemists Workshop that will include college students from Florida, Illinois and other states across the country, as well as a segment for bench chemists who are new to the industry.

 

“I am looking forward to Suppliers’ Day 2019 being the most immersive and experiential event in cosmetics chemistry and product development for our attendees.

Being our 40th Anniversary, we will also look back at the evolution of our industry over the decades and explore current trends that are elevating the importance of formulation and ingredients in beauty innovation,” said Sonia Dawson, Chair-elect, NYSCC.

For more information on NYSCC and Suppliers’ Day visit: https://nyscc.org/suppliers-day or email: suppliersday@nyscc.org.   Companies interested in exhibiting or sponsoring the NYSCC Suppliers’ Day in 2019 should contact Jane McDermott, jmcdermott@nyscc.org or call 212.786.7468.

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About New York Society of Cosmetic Chemists (NYSCC)

Dedicated to the advancement of cosmetic science, the New York Society of Cosmetic Chemists, www.nyscc.org, strives to increase and disseminate scientific information through meetings and publications. By promoting research in cosmetic science and industry, and by setting high ethical, professional and educational standards, we reach our goal of improving the qualifications of cosmetic scientists. Our mission is to further the interests and recognition of cosmetic scientists while maintaining the confidence of the public in the cosmetic and toiletries industry.  Connect with NYSCC on Twitter and Facebook at @NYSCC and Instagram: @NYSCCMAIN

 

About CEW:

CEW is an international organization of 9,000 individual members representing a cross section of beauty and related businesses. The composition of membership includes leading brands, indies, retailers, media and suppliers. CEW’s primary purpose is to provide programs online and in person to develop careers and knowledge of the beauty industry. CEW provides opportunities to connect and gain industry knowledge through networking events, trend reports, industry newsletters, interactive workshops and industry leader talks. For more information, please visit https://www.cew.org/.

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