Over the past 20 years, consumer demand has grown for products designed to treat hair damaged by thermal, mechanical and chemical insults. According to Kline and Company, conditioners, especially intensive treatments, remain the fastest growing category in hair care. Most conditioning technologies currently employed in rinse-off systems lend benefits to hair that last for only a day or two. Thus, conditioning technologies designed for long-lasting performance to restore hair closer to its virgin state are desired. Technology that offers good conditioning upon initial use, yet continues to activate conditioning through multiple shampoo-based wash cycles, may better serve consumers in their efforts to retain conditioning effects for an extended period of time.
Normally, polymers deposited on the hair surface from a cationic polymer shampoo perform the dual role of conditioning and delivering ingredients such as silicones.1, 2 One of the main requirements to deliver lasting conditioning from a rinse-off system is the capability to withstand multiple surfactant wash cycles. The present article describes the development of such a technology—a highly cationically charged homopolymer based on acrylates chemistry (INCI: Polyacrylamidopropyltrimonium Chloride)a, referred to as polyAPTAC. This polymer acts via a novel mechanism termed in situ controlled flocculation (ISCF)b to control cationic polymer charge sites and allow for their flocculation in situ during next-day cleansing with anionic shampoo components (see Figure 1).
Specifically, hair is washed with a shampoo containing positively charged polyAPTAC polymer, which is attracted to the damaged, negatively charged hair surface. The polymer carries an excess positive charge to enable the formation of flocculates on the hair surface in situ when hair is treated with anionic surfactants. During flocculate formation, hydrophobic lauryl groups from sodium laureth sulfate (SLES) coat the hair surface, creating a hydrophobic layer on the hair. If silicones or other oils are present in the shampoo, they also are attracted to the hair surface during flocculate formation, further boosting their deposition.
A variety of performance-related measurements were made with control and test products, and compared with a commercial conditioner to confirm this in situ controlled flocculationb mechanism and compare efficacies. To study deposition, two-dimensional imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM) were employed. Conditioning performance was monitored by wet combing correlated with silicone deposition tracking. Hair hydrophobicity was measured by pseudo-static water contact angle measurements. Finally, to determine buildup on hair, a specially designed streaming potential instrument measured flow rate data and zeta potential of the hair surface in situ during treatment cycles.
Materials and Methods
Double-bleached, European hair in 26-cm tresses and bleached Chinese hair served as the test substratesc. The level of damage was determined by measuring both water contact angles and Fourier transform infrared spectroscopy (FTIR) sulfonic acid peak intensity at 1,040 cm-1; longer bleaching times increase surface hydrophilicity, resulting in a higher sulfonic acid peak intensity. Tresses were washed with a 4.5% sodium lauryl sulfate solution prior to treatment, with a minimum of three hair tresses per product used.
A simple formula based on a cationic surfactant, stearamidopropyl dimethylamine at 0.7% w/w, fatty alcohol, cetearyl alcohol at 2.5% w/w, and hydroxyethylcellulose at 1% served as the base chassis without polyAPTAC. When testing with polyAPTAC, 1% active material was added (5% as is; material is 20% active in water). The non-conditioning shampoo tested contained 12% w/w SLES (2EO), 2% w/w cocamidopropyl betaine and 1.5% w/w sodium chloride.
Wet-combing: Wet-combing work is a direct measurement of conditioning efficacy. Conditioned hair requires less force to comb. The equipment used for this study was a texture analyzerd. Five combing cycles were performed on each tress at 23ºC and 50% relative humidity (RH), and the average was calculated. The tresses were not detangled before measurements.
Silicone measurement: Silicones are widely used to improve hair conditioning, and the performance of a conditioner reflects the distribution of silicone oils along the hair fiber. Also, the more damaged the hair surface, the more difficult it is to deposit silicone on hair. Therefore, relative silicone surface level (RSSL) measurements were taken using Attenuated Total Reflection (ATR) in conjunction with infrared (IR) spectroscopy. This technique uses the ratio of the silicone band peak height [near 796.5 cm-1 (tangent baseline)], to a reference band from an area slice of hair [from 940.1 cm-1 to 919.9 cm-1 (tangent baseline)] to determine the relative surface silicone level, as shown in Equation 1.
Peak Height (at 796.5 cm-1) = RSSL (with 0.05 detection limit)
Peak Area (940.1 cm-1 – 919.9 cm-1)
In previous studies, this surface silicone measurement method correlated well with total extracted silicone levels across a range of concentrations (300–4,000 ppm).1
Contact angle measurements: Virgin hair has a hydrophobic surface and is most often described as smooth and shiny. Restoring the hydrophobicity of damaged hair helps to renew its look and feel. In relation, pseudo-static contact angle measurements of water on the hair surface are an indicator of surface hydrophobicity; the more homogenous the polymer is deposited, the higher the contact angle. For pseudo-static contact angle measurements, a portion of the hair tress was stretched on a specially designed plate to suspend the fibers together in space, forming a “single” surface. To apply a deionized water droplet (~0.008 g), a 1-mL disposable syringe with a stainless steel, regular-beveled Luer-lok needle (27 G x ½”)e was used. The syringe was mounted such that its tip was ~0.5 cm above the hair fiber surface. Photographs of the water droplets on hair were taken at 1 sec or 10 sec using image analysis softwaref. Three trials were carried out for each sample.
Streaming potential measurements: By monitoring the flow rate of a diluted, 1 mM KCl salt buffer solution through hair fibers, the thickness of an absorbed polymer on hair can be measured. If a polymer treatment builds up on hair after continued use, decreases in the flow rate—i.e., electrokinetic permeability—will be detected. A streaming potential instrument was therefore designedg to measure both the zeta potential (i.e., surface charge of hair, with and without hair care ingredients) as well as its electrokinetic permeability, which is accomplished by gravimetric means within the instrument. For this method, the hair is treated in situ so that the history of a given hair plug or bundle is known, which can help to determine whether or not buildup is occurring.1
SEM: The deposition behavior of polyAPTAC was monitored by post-treating previously polymer-treated hair with polybead carboxylate microspheres (1.0 μ)h and imaging the spheres on the hair surface using SEMj. The beads are anionic and will stick to hair only if cationic charges are present from the polyAPTAC film. For post-treatment, hair was immersed in a 0.01% w/v solution latex in 10-3 KCl for 5 min, after which it was immersed in a deionized water rinse system for 5 min. Subsequently, hair fiber samples were coated with 10-nm gold and analyzed by SEM.
ToF-SIMS: Deposition studies also were carried out using a ToF-SIMS instrumentk. In this technique, the composition of a solid surface—in this case, hair—is probed with an ion beam and the ejected secondary ions are analyzed. This is an extremely sensitive technique and special care must be taken so as not to contaminate the samples. Analysis parameters were: ion/energy Bi3+; 30 keV (polarity: positive and negative); lateral resolution of 3–5 μm for routine analysis at full mass resolution; and 300–500 nm at nominal mass resolution. An untreated bleached Caucasian hair tress was used as the reference. Hair tresses were treated with a 1% w/w solution of the polyAPTAC conditioning polymer, followed by cleaning with a 3% w/w sodium dodecyl sulfate solution, then rinsed with deionized water and blow-dried while combing.
Results and Discussion
Wet-combing: As stated, conditioning efficacy was studied by wet-combing. Pre-washed tresses were initially treated with 0.2 g per gram of hair with test conditioner, with and without silicones, and rinsed. The wet-combing work was then measured. To study lasting efficacy, the same tresses were washed again with 0.1 g per gram of hair with a non-conditioning shampoo one, three and five times. After every step, the wet-combing work was measured. The results were compared with a commercial conditioner designed for damaged hair, as shown in Figure 2.
All the test conditioners performed well after the initial rinse-off step; however, the commercial conditioner and base conditioner lost their efficacy when tresses were washed once with non-conditioning shampoo. The conditioners containing polyAPTAC maintained their conditioning efficacy, even after five washes with a non-conditioning shampoo.
A similar study was carried out on a mannequin head of bleached Caucasian hair. The left side was treated with a silicone-containing commercial conditioner designed for damaged hair, and the right side was treated with the base conditioner containing 1% polyAPTAC. After the initial treatment (see Figure 3A), the difference between these treatments already was visible. After three washes with non-conditioning shampoo, then 5 min (see Figure 3B) and 15 min of combing (see Figure 3C), the left side remained tangled; the right side, treated with polyAPTAC technology, maintained efficacy similar to its initial state.
Silicone measurement: As noted, the RSSL of hair prepared similarly to the wet-combing experiments was measured. Pre-washed bleached Caucasian and Chinese tresses initially were treated with 0.2 g per gram of hair of a commercial silicone-containing conditioner, with and without polyAPTAC, and rinsed. Silicone deposition was then measured. To study lasting efficacy, the same tresses were washed again with 0.1 g per gram of hair of a silicone-containing commercial shampoo, one, three and five times; after every step, silicone deposition was measured. Results are shown in Figure 4. Note that the level of hair damage (bleaching vs. virgin hair) was considered as the basis for measuring performance, not hair type.
As shown, silicone deposition was significantly improved due to the in situ controlled flocculation mechanism of polyAPTAC. After the initial conditioning, the polymer formed flocculates with surfactants, thereby increasing silicone deposition after hair was washed with silicone-containing shampoo. With polyAPTAC present on the hair, all washes during the five-wash test period allowed additional silicone deposition on hair.
Contact angle: As noted, pseudo-static contact angle measurements of the hair surface indicate surface hydrophobicity, which also relates to any surface treatment. A more homogenously deposited polymer creates a higher contact angle. As Figure 5 shows, virgin Caucasian hair is very hydrophobic, measuring a contact angle of 115 degrees. In addition, a water droplet applied to the hair surface remained for 10 min. In contrast, when the hair was double-bleached, the contact angle was reduced to 85 degrees, and the water droplet was absorbed in 1 min.
The test base conditioner on bleached hair showed little influence on surface hydrophobicity. The commercial repair conditioner containing silicones increased the initial contact angle, although it did not prevent water absorption. When the bleached hair was treated with the base conditioner containing 1% polyAPTAC; however, the initial contact angle was increased and the water absorption clearly was reduced. To confirm the in situ controlled flocculation hypothesis, hair tresses were then washed twice with a non-conditioning shampoo; results indicated the surface hydrophobicity improved further, reaching levels close to virgin hair.
Streaming potential: Flow rates of diluted, 1 mM KCl salt buffer solution through hair after different treatments are shown in Figure 6. The flow rate of untreated hair was first measured, then hair was treated with 0.1% active polyAPTAC solution in demineralized water, rinsed with water, and washed with a surfactant mixture. This cycle was repeated twice. Results showed the electrokinetic permeability remained unchanged after repeated treatments with polyAPTAC, indicating no buildup from the polymer.
SEM: As noted, to understand overall polymer deposition on bleached hair, studies were carried out using SEM (see Figure 7).5 Hair previously treated with polyAPTAC was also treated with polybead carboxylate microspheres (1.0 μ), which bear a negative charge. The positively charged conditioning polymer, already attracted and bound to the negatively charged hair surface, was found to attract the negatively charged microspheres. This provided an indication of the overall bulk distribution of the polymer on the hair’s surface, which as shown in the SEM micrograph, was fairly even.
ToF-SIMS: As stated, both untreated bleached and polymer-treated bleached hair were examined by ToF-SIMS, which corresponds to all the positive ions emanating from the hair surface. As Figure 8 shows, in general, untreated bleached hair resulted in stronger peaks, corresponding to typical species found in hair; these include nitrogen-containing hydrocarbons, e.g., CN-, CNO-, C3N and CSN. On the other hand, hair treated with the conditioning polymer exhibited other nitrogen-containing hydrocarbons, such as CH4N+, C3H8N+, C4H10+, C4H8N+, C5H10N+ and C6H10NO+. These species point to the presence of the polymer on the hair surface. Further, the distribution of the polymer was again found to be uniform throughout the entire hair surface, not only at cuticle edges, which is crucial to restoring the hydrophobicity of hair.
The results of this study show the new polyAPTAC technology provides long-lasting conditioning to damaged hair without measurable buildup. Its mechanism is based on in situ controlled flocculation, which enables the technology to restore the hydrophobicity of hair to levels similar to a virgin state. The series of performance-related measurements described here thus appear to confirm the in situ controlled flocculationb principle.
- P Erazo-Majewicz, JA Graham, and CR Usher, Assessing the targeted conditioning performance of cationic polymers, Cosm & Toil 125(9) 24-30 (2010)
- R McMullen, D Laura, T. Nuutinen and B Kroon, Investigation of the interactions of cosmetic ingredients with hair by dynamic electrokinetic and permeability analysis, Proc HairS’ 13, Lübeck, Germany (Sep 4-6, 2013)
- RY Lochhead and LR Huisinga, Advances in polymers for hair conditioning shampoos, in Hair Care: From Physiology to Formulation, AC Kozlowski, ed, Alluredbooks, Carol Stream, IL (2008) pp 123-136
- P Erazo-Majewicz and SC Su, Cationic conditioning—Polymer deposits on hair, J Cosmet Sci 55 125-127 (2004)
- MJ Hafey and IC Watt, The interaction of polymer latex particles with wool fibers, J Coll Inter Sci 109 181-189 (1986)