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S. Schlay, K. Schacht, A. Lohmann, U. Storzer

Breathable Nail Polish on the Basis of a New Blend: A Complex of Water-based Polymer and Functional Vegan Silk

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Introduction

Well-groomed hands and nails have been of central im-portance for the people of every period. Especially perfect nails are a must-have feature in business as well as private life. Nail polish has become an essential, indispensable tool to achieve beautiful nails. Some women use it for deco-ration, others want to protect their nails, or both. Today the nail care industry offers a great variety of different technologies next to traditional lacquer-based nail polish-es, for example acrylic nail solutions, nail strips (nitrocellu-lose-based), water-based formulas or lately “breathable” polishes. However, not every consumer product is harm-less to the fingernail. According to Mintel, 25 % of women from the United States who use nail services have con-cerns regarding harmful substances [1]. Apart from this, a quarter of British women are interested in nail polish with nourishing effect [2]. In general, the manufacturer will be facing the challenge to develop innovative solutions, while minimizing the use of harmful chemical ingredients. As mentioned before, one of the new generations in the nail polish market are water-based nail polish systems. The technology can operate without solvents and releases no volatile chemicals. Therefore, a pleasant side effect for the customer is a very low odor during application as well as removal. Overall, water-based polishes are non-flamma-ble, non-toxic, biodegradable and safer to individuals with concerns of sensitivity, for instance, pregnant women. Moreover, by combining a water-based polymer and the functional, vegan silk, a water and oxygen vapor permea-bility can be ensured.With their proprietary technologies Silkgel and Syntran®5620CG both companies, AMSilk and Interpolymer, approach the per-

meability issue from different angles. While the Silkgel is sus-tainable and non-animal derived, the Syntran® polymer rep-resents the current state of the art of water-based polymer technology.

Water-based Polymer (Syntran®5620CG)

Interpolymer’s water-based polymer emulsion Syntran®5620CG is a recent entry into the nail polish market. This innovative polymer is specifically designed to formulate water-based nail polishes. Its technology platform named SAFE, an acro-nym that means “State-of-the-art” Acrylate Film-Forming Emulsion, stands for the unique toxicological and Eco toxi-cological properties of this polymer. In order to achieve ap-plication properties comparable to these of solvent-based systems, especially such as hardness, initial gloss, gloss re-tention and the dry to touch time, Interpolymer introduced a unique combination of different crosslinking mechanisms in an optimized balance. Each crosslinking system is playing a specific role in terms of the different steps in film forma-tion during the application of the nail polish formulation. As a result, this acrylic polymer emulsion exhibits in nail polish formulations an excellent initial gloss (80 @ 200 µm – evaluated with a 20° gloss meter after the application of one coat) and high gloss retention. It equally exhibits ex-cellent water and wear resistance, hardness and adhesion to the nail surface. The SAFE technology eliminates many of the concerns with regard to safety hazards, toxicity and VOC issues currently facing all the solvent-based nail pol-ishes. Due to the absence of any organic solvent, the use

Breathable Nail Polish on the Basis of a New Blend: A Complex of Water-based Polymer and Functional Vegan SilkS. Schlay, K. Schacht, A. Lohmann, U. Storzer

abstract

Beautiful and healthy nails take on more and more significance for many customers. Thus, when developing new and inno-vative nail polishes, breathability is a significant factor. In this paper, breathability of nail polishes, which is often referred to

as a combination of air/O2 and water vapor permeability, was investigated. For this purpose, two solvent-based nail polish for-mulations were benchmarked against two water-based nail polish formulations according to DIN-Norm 53122-1 and 53380-3. The data clearly indicate, that water-based nail polish formulations based on Syntran® polymer perform considerably better. In combination with Silkgel, the hybrid polymer Silktran® is formed, which increases both oxygen and water vapor permeability, making this novel hybrid polymer a unique best-in-class performance product.

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of this technology enables a simplified production process of nail polish formulations without the need of ATEX ap-proved facilities consequently leading to environmentally friendlier products. Nail polish formulations based on SAFE technology are, especially when compared to traditional organic solvent-based nail polishes, free of irritating smells and therefore gives formulators the big advantage of cre-ating fragrance containing nail polishes.

Functional Vegan Silk (Silkgel)

Silkgel is a high-performance ingredient for the personal care industry. Developed and manufactured via an estab-lished biotechnological process, this silk technology is sus-tainable, biocompatible and entirely bio-based. The inno-vative production possibility enables a non-animal derived silk with its full functionality. The product is registered by The Vegan Society. The performance of functional, vegan silk is not comparable to traditional silkworm silk. AMSilk’s vegan protein has unique properties to offer (e.g. breathable skin protection); it is not hydrolyzed, and is very well tolerated by the skin. In addition, the functional silk features a high and consistent quality. The semi-fin-ished Silkgel consists of pure silk, water and preservative, and is suitable for a wide variety of personal care prod-ucts in the fields of skin care, hair care, color cosmetics and fragrances, among others. The formulation of Silk-gel into applications enables innovative, unique proper-ties such as breathable skin and in this case, nail protec-tion. A thin silk film shields from negative environmental impacts. These environmental impacts are manifold, for example pollutants (thus providing an anti-pollution effect), irritants, microbes and harmful chemicals. Due to the combination of AMSilk’s func-tional silk and Interpolymer’s wa-ter-based polymer, innovative nail polish formulas can be achieved which permit water and oxygen vapor permeability as well as oth-er defined benefits.

Innovative Breathable and Water-based Nail Polish Technology

Although the Syntran®5620CG polymer already exhibits a very high oxygen and water vapor per-meability which outperforms the permeability of solvent-based nail polish polymers, this aspect was still a goal of further joint research

and development efforts within AMSilk and Interpolymer. This cooperation resulted in the new hybrid polymer emul-sion Silktran®5621 based on Silkgel and Syntran®5620CG. In contrast to published formulations of polymers com-bined with protein-derived hydrolysates, the proprietary and innovative formulation process developed for the manufacturing of Silktran®5621 enables the extraction of the entire functional silk polypeptide from its gel matrix into the polymer emulsion. The data shown in Figs. 1A–D demonstrate the time dependent evolution of the particle size distribution taken during the manufacturing process of the hybrid polymer. The particle size distribution indicates that the bulky protein is fully absorbed into the polymer droplets to form a mono modal distribution of hybrid polymer droplets.

Formulations

Clear nail polish formulations as well as colored nail pol-ish were developed with this new acrylic hybrid polymer. Thanks to its aqueous composition, the hybrid polymer is compatible with other water-based actives and can equally be promoted in the nail care treatment segment. Marketing claims like hardening, hydration, health, protection can be easily obtained with the addition of water-based actives. As 75 % of the global nail polish market is represented by pigmented formulations [3], it is also important to offer sample formulations for colored nail polishes. The typical composition of a pigmented nail polish formulation is given

Fig. 1 Time resolved PSD during formulation process. A: Syntran®5620CG, B: Syntran®5620CG + Silkgel 1 minute after application, C: Syntran®5620CG + Silkgel 30 minutes after application and D: Syntran®5620CG + Silkgel 90 minutes after application.

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in Tab.1. The basic components of this formulation are in principal the same as in a solvent-based formulation. It contains a solvent (water), a film forming agent and plasticizers. The film forming agent is the new acrylic hy-brid polymer Silktran®. The polymer dispersion on its own does not form a film but a crystalline powder on drying. Therefore, plasticizers are present in the formulation to reduce the Minimum Film Formation Temperature (MFFT) of the final formulation, permitting it to be transformed into a clear, durable film when allowed to dry at room temperature. Two types of plasticizers are used – perma-nent and volatile (also referred to as coalescent). Perma-nent plasticizers are absorbed completely by the polymer upon drying and remain in the film to provide continuous plasticization. Coalescents, which volatilize during the dry-ing process, are used to temporarily lower the MFFT of a nail polish during the drying phase. Therefore, the amount and types of the various plasticizers required to produce an optimized nail polish film are of critical importance [4]. At this point, Silktran® is very well compatible and can be combined with many plasticizers according to customer requirements.For the development of a pigmented formulation it is fur-ther crucial to stabilize the pigments in the formulation while still keeping good leveling properties on the nails. In order to balance these properties in an optimum way, a thixo-tropic thickener is used, which builds up enough viscosity to maintain the pigments in suspension while the system in the bottle is at rest and drops viscosity to obtain a good leveling on the nail when a force is applied, i.e. with the application brush. The choice of the pigment dispersions is also very important to obtain vivid and intense colors in the final nail polish formulations. In order to keep the high quality of the fi-

nal formulations in term of wear resistance, water resis-tance, proprietary pigment dispersions based on organic pigments and a specific styrene-acrylates copolymer resin were developed.

Results and Discussion

The water-based pigmented nail polish formulation (entry 2 in Tab. 2), based on the hybrid polymer was referenced against the corresponding formulation based on the pure water-based polymer without protein (entry 1 in Tab. 2). In order to benchmark the product, the hybrid polymer was fur-thermore referenced against two commercially available sol-vent-based nail polish formulations. One (entry 3 in Tab. 2) was chosen because the manufacturer outlines its water and air permeability properties and the second (entry 4 in Tab. 2) as a typical standard nail polish formulation.

Preparation of Dried Nail Polish Films

Each nail polish formulation was applied with a thickness of 500 µm on test cards A5 22/5B from the company MTV

Tab. 1 Typical composition of a pigmented nail polish formulation with Silktran®.

Phase Name Supplier INCI Name % Weight

A Silktran® 5621 InterpolymerStyrene/Acrylates/Ammonium Methacrylate Copolymer (and) sr-spider Polypeptide-1

80.25

B

Finsolv PG-22 Innospec Dipropylene glycol dibenzoate 2.70

Dowanol PnB Dow Propylene glycol n-butyl ether 4.95

Syntran® KL 219CG Interpolymer Ammonium Acrylates Copolymer 1.35

C12.5 % aqueous solution of Laponite XLS

Altana Sodium Magnesium Silicate and Tetrasodium Pyrophosphate 2.50

D Syntran® Red A Interpolymer CI 73360 8.25

100.00

Tab. 2 Water-based (No. 1 + 2) and solvent-based (No. 3 + 4) nail polishes.

Entry No.

SampleRelative

Humidity [ %]T [ °C]

1 F-76-67 with Syntran® 5620CG 47.8 23.6

2 F-76-28 with Silktran® 5621 49.2 24.7

3 Benchmark 1 57.4 23.8

4 Benchmark 2 62.8 22.3

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Messtechnik oHG (Fig. 2 A + B) to reach the fully cured final thickness of app. 100 µm in case of the water-based nail pol-ish formulations and of app. 50 µm final thickness in the case of solvent-based formulations. The water-based nail polish formulations were dried for approximatively 4 hours before removing them from the support and the solvent-based nail polish formulations were left to dry for approximatively 1 hour (Fig. 2 C + D).

Determination of the Oxygen Permeability

Data of the OTR (oxygen transmission rate) measurement according to DIN 53380-3 at 23 °C and 50 % r.h. were ac-quired on an OX-TRAN Model 2/20 from MOCON Inc. (tests were conducted at Fraunhofer IVV [5]). The dried films are stabilized using aluminum foil (Fig. 3). In case of a deviation of >10 % between two OTR values a third determination is

used. The OTR values are given in the unit cm3/(m2 d bar) and were normalized to a thickness of 100 µm in order to allow direct comparison of different materials independently of the film thickness [6].The data (Fig. 4) acquired clearly indicates a sharp increase in the O2 permeability when switching from solvent- to wa-ter-based nail polish formulations. The nail polish formulation based on the pure water-based polymer exhibits with a val-ue of 758 cm3/(m2 d bar) a 3.6 % slightly higher OTR when compared to the formulation based on the hybrid polymer (731 cm3/(m2 d bar)). However, its OTR still outperforms the ‘breathable’ solvent-based nail polish formulation with a val-ue of 638 cm3/(m2 d bar) by 12.3 % and the standard sol-vent-based formulation (579 cm3/(m2 d bar)) by 20.1 %.

Determination of the Water Vapor Permeability

The gravimetric screw cup method according to DIN 53 122-1 was used to measure the WVTR (water vapor transmission rate) of the dried films at 23 °C and 85 % 0 % r.h (Fig. 5) (tests were conducted at Fraunhofer IVV). The WVTR is cal-culated by the following equation: WVTR=24/t ∙ ∆m/A ∙ 10x4. Where t is the period of time between two weight measure-ments in hours, ∆m represents the weight difference between

Fig. 2 Preparation of nail polish films. A + B: Applying of nail polish, C: drying phase and D: removing of film from test card after drying time.

A

B

C

D

Fig. 3 Specimen mounted in OTR device; one side of the perme-ation cell is flushed with pure oxygen, the other side is carrier gas leading to the oxygen specific sensor, both cells are permanently flushed with the respective gas. Due to the difference in partial pressure different oxygen will permeate through the sample and is detected by the sensor; all gas streams are humidified to 50 % r.h.

Fig. 4 Normalized oxygen permeability of the tested nail polishes at 23 °C and 50 % r.h. in cm3 100 µm/(m2 d bar). The samples were normalized to a film thickness of 100 µm.

Fig. 5 Set of samples in the climate chamber during WVTR determi-nation; inside of the cups is filled with drying agent, climate was set to 23 °C/85 % r.h.; increase in mass due to water vapor permeation was monitored during storage and was the base for the evaluation.

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Conclusion

Water-based nail polishes claim breathability as well as water permeability. To this end, oxygen and water vapor permeabil-ity benchmarking tests according to DIN-Norm 53122-1 and 53380-3 were carried out. Water-based nail polish formula-tions, containing either the hybrid polymer Silktran® or the pure polymer Syntran® as well as commercially available sol-vent-based nail polishes were tested. Both water-based nail polish formulations showed a substantial improvement with respect to their oxygen permeability and an even higher dif-ference in their performance with respect to their water vapor permeability when compared to the solvent-based nail polish formulations. Regarding water vapor permeability, the hybrid polymer exhibited best properties.Regarding a combination of gas (O2) and water vapor perme-ability, which is often referred to as “breathability” , the wa-ter-based nail polish formulation containing the hybrid poly-mer Silktran® can be claimed as providing best performance.

References

[1+2] Emmanuelle Moeglin (2016): Mintel, „Beauty spot: nail colour-care“, http://

www.mintel.com/blog/beauty-market-news/beauty-spot-nail-colour-care,

06.07.2017

[3] Expression Cosmétique, March-April 2011, N°08, p.14, “Nail polish experienc-

es no crisis!”

[4] The birth of a floor polish film, INTER-

POLYMER Advances, 1999

[5] Fraunhofer-Institut für Verfahren-

stechnik und Verpackung, Giggen-

hauser Str. 35, 85354 Freising, Ger-

many

[6] DIN 53380-3, Testing of plastics – De-

termination of gas transmission rate

– Part 3: Oxygen-specific carrier gas

method for testing of plastic films and

plastics mouldings

[7] DIN 53122-1, Testing of plastics and

elastomer films, paper, board and

other sheet materials – Determination

of water vapour transmission – Part 1:

Gravimetric method

two weight measurements in g and A is the test area in cm2. The WVTR values are stated in the unit g/(m2 d) and normal-ized to a thickness of 100 µm in order to allow a direct com-parison of different materials independently of the coating thickness. A fourfold determination was performed in all cas-es [7].As in the case of oxygen permeability, excellent water vapor transmission rates can be achieved with the water-based nail polish formulations, whereas the hybrid polymer-based for-mulation shows the highest value with 32 g/(m2d). Its WVTR is 15.2 % higher than the WVTR of the pure water-based poly-mer nail polish formulation (27 g/(m2d)) and by 43.9 % higher than the “breathable” (18 g/(m2d)) and respectively 34.3 % higher than the standard (21 g/(m2d)) solvent-based nail pol-ish formulation. However, in case of WVTR the solvent-based nail polish formulations show even a higher reduction com-pared to both water-based nail polish formulations. (Fig. 6)

Fig. 6 Normalized water vapor permeability of the tested nail pol-ishes at 23 °C and 85 % r.h. in g 100 µm/(m2 d). The samples were normalized to a film thickness of 100 µm.

contact

Sabine SchlayAMSilk GmbH

Am Klopferspitz 19 im IZB82152 Planegg/Munich | GermanyE-Mail: sabine.schlay@amsilk.com

Dr. Kristin SchachtAMSilk GmbH

Am Klopferspitz 19 im IZB82152 Planegg/Munich | Germany

E-Mail: kristin.schacht@amsilk.com

Audrey LohmannINTERPOLYMER Sàrl6 rue Marie Curie

67160 Wissembourg | FranceE-Mail: alohmann@interpolymer.fr

Dr. Uwe StorzerINTERPOLYMER Sàrl6 rue Marie Curie

67160 Wissembourg | FranceE-Mail: ustorzer@interpolymer.fr