Acrylates Copolymer as Film Former for ... - ACS Publications

Chapter 12

Downloaded by COLUMBIA UNIV on February 16, 2015 | http://pubs.acs.org Publication Date (Web): December 5, 2013 | doi: 10.1021/bk-2013-1148.ch012

Styrene/Acrylates Copolymer as Film Former for Improved Hair Surface Luster Fanwen Zeng,*,1 Miao Wang,1,2 Jennifer Collin,1 Alan Nakatani,1 Michaeleen Pacholski,1 John Reffner,1 and Curtis Schwartz1 1The

Dow Chemical Company, 727 Norristown Road, Spring House, Pennsylvania 19477 2Currently, L’Oreal U.S.A., 200 Terminal Avenue, Clark, New Jersey 07066 *E-mail: [email protected].

Shine (luster) is one of the most sought-after and desirable criteria for a hair care product, including hair styling. The purpose of a hair fixative polymer is to hold the hair style in place. In order to deliver hair shine, silicone is typically added as a separate ingredient in the formulation. However for the amount of silicone required to deliver shine to the hair in a hair styling or fixative product, the hold performance of the fixative polymer becomes compromised. This study describes the development and results of the Styrene/Acrylates Copolymer hair fixative that delivers both hold and shine to the hair, and the polymer properties behind it.

Introduction Shine is one of the most sought-after and desirable criteria for a hair care product. Shine is a sign of beauty, health and cleanliness. Loss of hair shine or dullness can occur due to hair damage from environmental factors such as sun, harsh cold weather or use of excessive hair treatments such as bleaching, coloring, and product build-up. Common approaches to restore hair shine include: 1) repairing the damage and brittleness; 2) removing build up; 3) moisturizing and increasing elasticity; and 4) smoothing to help the cuticles © 2013 American Chemical Society In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


to lie flat. Cosmetic ingredients used in personal care formulations to aid hair shine are for example, naturally derived triglyceride oils; silicone oils such as cyclomethicone, dimethicone, phenyl trimethicone, amodimethicone trimethylsiloxy amodimethicone; and esters such as PPG-3 benzyl ether myristate. While they impart shine benefit to hair, there are some drawbacks to these materials, mostly in leaving an undesirable feel on the hair, or reduction in hair volume, or both. Hair styling (fixative) polymers are the active cosmetic ingredients used in hair styling products (1, 2). Hair styling polymers are typically excellent film-formers that can change the texture or shape of hair, or hold it in place in a certain hair style. Hair styling products exist in various product forms such as hair spray, hair gel, hair mousse, and pomade. Depending on product forms, hair styling polymers are designed so that they are compatible with the formulation. Various copolymers ranging from poly(acrylates), poly(vinyl pyrrolidone), poly(vinyl acetate) poly(urethanes), and polyesters have been utilized in hair styling products. While the conventional hair styling polymers such as poly(acrylates), poly(vinyl pyrrolidone) and their copolymers provide excellent hold performance, formulators have been relying on adding silicone to provide shine. This results in the compromise of hold performance for shine benefit. In this paper, we describe the synthesis of a novel styrene/acrylate copolymer with high refractive index. The physical properties, shine, and hold performance of this new polymer in hair styling products were investigated in comparison with conventional hair styling polymers.

Experimental Polymer Synthesis The styrene/Acrylate copolymer was prepared by thermally initiated emulsion polymerization of monomers consisting mostly of styrene, butyl acrylate, methacrylic acid, as well as other co-monomers. This material has an average polymer solids of 40%, a mean particle size of 200 nm, and a pH of 3.5-4.0. The viscosity of this material is less than 10-20 cps as measured by Brookfield viscometer (LV2, 60 rpm, 25 °C).

Formulation Hair spray aerosol formulations were prepared by dispersing 8-10% solids of the polymer sample in 200 proof ethanol, fully neutralized by aminomethyl propanol to pH 8.0-8.5. The aerosol can was charged with 50% of the above solution, and then charged with 50% of dimethyl ether under pressure. Hair gel formulations were prepared by dispersing 1-2% solids of the polymer sample in DI water, fully neutralized by aminomethyl propanol to pH 7.5-8.0 followed by addition of an anionic rheology modifier to thicken the formulation. 192 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.

Hair Treatment Untreated hair swatches 8 inches long, weighing 2 g (European Dark Brown Hair, International Hair Importers, NYC, NY) were first positioned on cylinder for initial baseline measurement. Hair swatches were then sprayed at 30 cm distance for 1 second, and air dried for 15 minutes before measurement. Each sample test was repeated on 5 separate hair swatches.


Shine Measurement by Expert Panel Evaluation The tresses were evaluated in a shine box by six panelists. The shine results are a ranking of best (value of 1) to worst (value of 5). Results of the six panelists were averaged to give the rating.

Shine Measurement by Bossa Nova Technologies (Culver City, CA, U.S.A.) Polarized illumination coupled to a polarization analysis was used to differentiate between the specular (Gloss) and diffuse light. The light source was a neon light (6 Watts, 5500K color temperature). The data collected was then analyzed using equations and theories that consider the various band geometries of the specular and diffuse profiles.

Film Gloss A Micro-TRI-Glossmeter was used for measuring the film gloss. A 5 mil wet film was cast on a porous tile substrate, and air dried. Readings were taken at 20 and 60 degree angles. A 3 unit difference in measurement can be recognized by the naked eye, with higher readings corresponding to glossier surfaces.

Stiffness Analysis by Dia-Stron The hair tresses prior to curling were on the average 8 inches long and weighed 2.0±0.1 grams. They were washed using Tressemme® Deep Cleansing Shampoo (Unilever, UK) , then curled wet onto a 22 millimeter (mm) x 70 mm curler and held in place with a bobby pin. The curled tresses were allowed to dry on the lab bench overnight, or in a 45°C oven for 1 h. The curled tresses were then sprayed with test formulations from a distance of 30 cm in the hood, one second for both front and back of the curls. The curled, treated tresses were dried in a 45 °C oven for 1 h. Before the curl compression testing, the curler was removed carefully without disturbing the tress. The curled tress was placed on the miniature tensile tester, model MTT160 instrument (Dia-Stron Limited, UK). The curl was compressed to 25% of its initial diameter; the force-displacement curve was recorded. The peak force F (mgf) is reported to characterize curl stiffness. 193 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.

High Humidity Curl Retention (HHCR) Curled tresses were prepared and treated as in the Diastron curl compression test above. After drying, the curlers were gently removed from the tresses and the curls were suspended by clips in a humidity chamber at 90% relative humidity (RH), 25°C. The initial curl length was recorded. The length of the curled tresses was recorded at intervals over 8 hours. Curl retention was determined as [(L(0)L(t))/L(0)-L(i))x100] where L(0) is fully extended curl length, L(i) is initial curl length and L(t) is curl length at a specific time. Higher values indicate better humidity resistance performance.


Dynamic Mechanical Analysis (DMA) Solutions of the samples were cast in perfluorinated polymer Petri dishes and allowed to air dry in a convection hood. The samples dried very slowly and the time required to air dry sufficiently so the resultant films could be handled was approximately 2 weeks. After 2 weeks the films were still pliable and somewhat tacky to touch. The films could be removed from the Petri dishes without breakage and strips, approximately 5 mm wide, could be cut from the films with scissors. The strips were placed back into the Petri dishes and allowed to dry further in the convection hood, approximately one week. The dishes were then placed in a mild oven (50 °C) to assist with the final stages of drying for 3 days. Experience has shown that trying to speed the drying protocol results in films containing a considerable number of voids. Finally, the samples were removed from the oven and placed under vacuum for approximately 2 weeks to remove last traces of moisture and solvent. The film samples were tested on the TA Instruments Q800 Dynamic Mechanical Analyzer (DMA) using tensile film clamp fixtures. Each sample was tested from -50 °C to approximately 120 °C at a heating rate of 2 deg/min using the Temp Ramp/Freq Sweep Test in the DMA Multi-Frequency-Strain Mode. The applied frequency was 1 Hz. The Procedure Parameters were as follows: Applied Strain = 0.0075%; Preload Force = 0.01 N; and Force Track = 125%. A Soak Time of 5 minutes was employed before the start of data acquisition. The dynamic storage and loss moduli (E’ and E” respectively) as well as tan δ were recorded as a function of temperature.

Results and Discussion The principle function of hair styling polymers is that the polymeric materials deposit, adhere and form mostly seam and spot welds between hair fibers to hold the hair style in place. even in high humidity conditions or conditions where there is hair movement. The performance of hair styling polymers is strongly dependent on the polymer design and the resulting polymer properties. For example, the glass transition temperature (Tg) of the polymer can affect the film properties, stiffness, tackiness, and film dry-time. The polymer molecular weight can affect the formulation viscosity, which in turn affects spray particle size on hair fibers, which in turn affects hold. The spray particle size will have an impact on the 194 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


number and ratio of seam and spot welds. Typically, the polymer should be soluble in the formulation, can be removed from the hair through washing with water/ shampoo, yet is resistant to high humidity. These performance properties are controlled through an optimum incorporation of both hydrophobic and hydrophilic sections in the polymer. The cohesive and adhesive strength of the polymer to hair fibers can influence the aesthetics of hair styling, in which non-flaking is desirable. If the polymer does not adhere to the hair fibers and/or has low cohesive strength, flaking can occur. Acrylates copolymers are one of the most versatile classes of polymers that are currently used in hair styling polymers. Due to the availability of various side chain groups of (meth)acrylate monomers and excellent polymerization kinetic profiles with other monomers, Acrylates copolymers can be designed to be soluble in various hair spray formulations. Among them, alkaline soluble emulsion polymers became popular in the industry due to their versatility and economic efficiency. As supplied, the polymeric products are typically a milky white dispersion of polymer particles in water with high polymer solid content of at least 40%. They have a water-like viscosity and can be easily pumped to the production kettle at room temperature. Latex polymers with various glass transition temperatures, molecular weights, hydrophobicity, and morphology can be readily accessible. Typically, these latex polymers contain monomers with carboxylic acid groups. At polymerization pH, these carboxylic acid groups are protonated and the corresponding latex polymers have limited solubility in water. Upon neutralization with base, such as commonly used AMP-95® (2-Amino-2-methyl-1-propanol) (The Dow Chemical Company, Spring House, PA, U.S.A.), a clear solution is formed, resulting in excellent film forming properties upon drying. Latex polymers containing high refractive index monomers have been marketed in the floor care industry to produce excellent gloss and gloss retention. It is our intention in this paper to incorporate this concept to provide shine benefit to hair styling polymers with all characteristics as described above. Styrene/Acrylates copolymer described in this paper has a general chemical structure as illustrated in Figure 1. It has a high refractive index compared to Octylacrylamide/Acrylates/ Butylaminoethyl Methacrylate copolymer (OABMC), a conventional hair styling polymer and silicones as shown in Figure 2.

Figure 1. Chemical structure of Styrene/Acrylates copolymer (R1= H, Me). 195 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


Figure 2. Comparison of polymer refractive index.

Styrene/acrylates copolymer was formulated into a variety of hair spray formuations , for example 55% VOC with 1,1-difluoroethane (Dupont’s Dymel® 152a propellant), 55% VOC with dimethyl ether (DME) propellant, and 80% VOC. Table 1 shows a typical 55% VOC DME aerosol spray with styrene/acrylates copolymer. Shine and hold, the most important performance targets, were evaluated with several test protocols. In all studies, styrene/acrylates copolymer was directly compared with one commercial spray sample containing a polymer blend of Vinyl Acetate / Crotonates /Vinyl Neodecanoate Copolymer (VACVEC) and OABMC, and another commercial spray sample containing only OABMC.

Table 1. 55% VOC DME Aerosol Spray with Styrene/Acrylates Copolymer Phase

Ingredient

%Weight

A

Ethanol

27.0

A

Styrene/Acrylates Copolymer

12.50

A

2-Amino-2-methyl-1-propanol

1.5

A

Water

31.0

B

Dimethyl Ether

28.0

Comparison of hair shine benefit from Styrene/Acrylates Copolymer with VACVEC/ OABMC blend and OABMC was obtained from both expert panel evaluation study and shine measurement with Bossa Nova Technologies (3–5). Figure 3 shows a comparison study of shine rating from expert panel evaluation. Higher shine rating was obtained for two Styrene/Acrylates Copolymer prototypes than OABMC. A more objective shine measurement is based on goniophotometer developed by Bossa Nova Technologies. Figure 4 shows the principle of shine measurement and data analysis from Bossa Nova Technologies. 196 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


Figure 3. Comparison of shine rating from an expert panel evaluation study.

Figure 4. Shine (luster) measurement and data analysis from Bossa Nova Technologies. Images courtesy of Bossa Nova Technologies (4). Available at: http://www.bossanovatech.com/samba_hair_system.htm. 197 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


Hair tresses treated with Styrene/Acrylates Copolymer, VACVEC/ OABMC blend and OABMC respectively were subjected to shine evaluation with the Bossa Nova method. The corresponding shine (or luster) was calculated by employing either Reich-Robbins equation or Bossa Nova equation. As shown in Figures 5 and 6, Styrene/Acrylates Copolymer provides a much better shine benefit to hair than VACVEC/ OABMC blend and OABMC for both calculation methods. Therefore, both subjective expert panel evaluation and objective Bossa Nova measurement demonstrate that Styrene/Acrylates Copolymer delivers a superior shine performance in comparison with the conventional polymers.

Figure 5. Comparison of shine performance in 55 VOC 152(a) aerosols with Reich-Robbins equation.

Figure 6. Comparison of shine performance in 55 VOC 152(a) aerosols with Bossa Nova equation. The Styrene/Acrylates Copolymer provided higher shine performance to hair in comparison with conventional hair styling polymers. It is equally important that Styrene/Acrylates Copolymer can at least match the hold performance of the conventional hair styling polymers. A battery of hold measurement studies were performed to compare the performance of Styrene/Acrylates Copolymer with the conventional hair styling polymers: VACVEC/ OABMC blend and OABMC. Comparison of hold performance as measured by high humidity curl retention 198 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


(6), curl droop test, oscillation bouncing test, and Dia-stron curl compression (7) were shown in Figures 7, 8, 9 and 10, respectively. In high humidity curl retention and curl droop test, Styrene/Acrylates Copolymer has a very similar curl retention as VACVEC/ OABMC blend and OABMC. For oscillation bouncing test, Styrene/Acrylates Copolymer has a slighly better curl retention than OABMC, which is better than VACVEC/ OABMC blend. In Dia-stron curl compression study, Styrene/Acrylates Copolymer has higher peak stiffness and stiffness modulus than OABMC, which is better than VACVEC/ OABMC blend. The last two hold performance studies are in good agreement with each other. Based on all of these data, Styrene/Acrylates Copolymer has a silimar or slightly better hold performance than the conventional hair styling polymers.

Figure 7. Comparison of High Humidity Curl Resistance at 90% RH, 25°C.

Figure 8. Comparison of Hold Performance byCurl Droop Test. 199 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


Figure 9. Comparison of Hold Performance byOscillation Bouncing Test.

Figure 10. Comparison of Hold Performance by Dia-stron Curl Compression.

To explain the superior shine and hold performance, we investigated several polymer properties of Styrene/Acrylates Copolymer in comparison with the conventional hair styling polymers. The polymer film formation properties such as film smoothness and homogeneity (8) should play a beneficial role for hair shine as described above. As shown in Figure 11, Styrene/Acrylates polymer showed lower surface tension at early times compared to OABMC in ethanol solution. This lower Dynamic Surface Tension (DST) would provide better flow out and wetting of the formulation on hair prior to the formulation drying. 200 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


Figure 11. Dynamic surface tension of 5% polymer in ethanol solution.

Polymer molecular weight exerts direct impact on formulation viscosity as well as spray particle size. Scanning electron micrograph (SEM) surface analysis shows that fine spray particle size results in a smooth surface coverage, while large spray particle size results in cohesion between hair fibers and a coarse surface coverage. As shown in Figure 12, the molecular weight of Styrene/Acrylates Copolymer was fully optimized (left graph) so that a smooth surface was achieved. Both low DST and optimized MW for smooth surface spray should lead to a higher film gross. Figure 13 shows the comparison of film gloss as measured by micro-tri-glossmeter for 20 and 60 degree gloss. Styrene/Acrylates Copolymer has a higher gloss at both angles than VACVEC/ OABMC blend and OABMC. One needs to keep in mind that the film gross measurement employs different physics mechanism vs. the hair shine measurem.ent.

Figure 12. SEM surface analysis of hair treated with polymer with various molecular weight (left: optimized, right: un-optimized). 201 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


Figure 13. Comparison of film gloss as measured by micro-tri-glossmeter.

Finally, the mechanical properties of film formed from Styrene/acrylates copolymer was analyzed with Dynamic Mechanical Analysis (DMA). As shown in Figure 14, Styrene/acrylates copolymer has a high storage modulus at temperature up to 50 °C. This result is consistent with the strong hold performance of Styrene/acrylates copolymer as a hair styling polymer in the temperature range practiced by consumers.

Figure 14. DMA of Styrene/acrylates copolymer film. 202 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.

Conclusion


The Styrene/acrylates copolymer was demonstrated to provide proven better hair shine and equivalent hold in various hairspray formulations when compared to the conventional hair styling polymers. The better hair shine performance is achieved through a combination of the polymer’s high refractive index and superior product delivery, which impacts the polymer flow across the hair surface. This results in the formation of a smooth reflective film which gives outstanding shine while maintaining the hair hold performance. The Styrene/acrylates copolymer provides formulators a useful tool to achieve both shine and hold from a hair fixative polymer without compromise.

Acknowledgments The authors gratefully acknowledge advice and support from Mark Westmeyer, Martina Osti, Kathy Keller, Diane Routzahn, and Wei Gao.

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203 In Polymers for Personal Care and Cosmetics; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.

Acrylates Copolymer as Film Former for ... - ACS Publications

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