Analyzing Deposition from Rinse-off Hair Products

Jan 13, 2014 | Contact Author | By: Qing Huang, Zhen-Wu Mei, Koji Takata and Jianzhong Yang, Beauty & Health Innovation Co., Ltd.
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Title: Analyzing Deposition from Rinse-off Hair Products
quantitative analysisx silicone depositionx shampoox rinse waterx dry combing forcex
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Keywords: quantitative analysis | silicone deposition | shampoo | rinse water | dry combing force

Abstract: The most common approach to determine ingredient deposition on hair is to analyze the treated tresses, but this poses several challenges. Instead, the authors describe a novel approach based on determining the amount of ingredient collected in the rinse water, and back-calculating the amount deposited on hair. Development and validation efforts discussed here use polydimethylsiloxane as a model compound.

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Q Huang, Z-W Mei, K Takata and J Yang, Analyzing Deposition from Rinse-off Hair Products, Cosm & Toil 128(11) 810 (2013)

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The fundamental benefits sought by hair care consumers relate to cleansing and care, and with the exception of cleansing, most of these benefits are delivered by conditioning ingredients deposited onto hair to change surface properties such as friction and surface energy. However, simply adding more ingredients to a formula will result in higher costs and may not even improve product performance, especially for a rinse-off product. To develop a hair care product with a high performance-cost profile, knowledge of the deposition efficiency of ingredients is key. In addition, correlating this deposition profile with consumer feedback will provide important guidance for formulators as they develop and optimize hair care products. In relation, traditional techniques to measure deposition are reviewed here, and a novel approach is introduced.

Measuring Deposition

During washing, deposition and rinse-off are opposing behaviors. The driving force behind an ingredient’s deposition is related to its affinity to the hair surface. This is affected by chemical and physical properties such as hydrophobicity, charge type and density, molecular weight, particle size, conjugation/inert action with other ingredients, etc. Logically, if the affinity of an ingredient to the hair’s surface is stronger than the forces rinsing it away, the ingredient will remain on the hair surface. Many studies have been conducted to increase this deposition onto hair. To study deposition efficiency, a reliable, easy-to-use quantitative method is critical and thus far, two approaches generally are used: direct measurement and indirect measurement with extraction.

Direct measurement: Direct measurement analyzes treated hairs for the presence of ingredients. For example, x-ray fluorescence (XRF) can measure silicone deposits on hair by image analysis; however, XRF is limited to only silicone ingredients, and it cannot differentiate between pre-existing silicones on hair and those applied by test products. Thus, image analysis methods are usually not quantitative or suitable for routine deposition studies.

Indirect measurement with extraction: The indirect approach, which is more commonly used, analyzes extracts taken from a treated hair sample. The test product containing the target ingredient is applied to hair via a predetermined protocol, the treated hair is extracted using organic solvent, then the extract is collected and measured to determine the ingredient(s) and amount(s) present. Depending on the polarity of the target ingredient, different solvents can be used to prepare the test samples. For example, to analyze silicone, toluene and methyl isobutyl ketone (MIBK) often are used; for cationic surfactants, trichloromethane or methanol. Thus, to analyze silicone and quats, the preparation of samples must be done separately, which is time-consuming.

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Table 1. Recovery of silicone from rinse water

Table 1. Recovery of silicone from rinse water

As shown in Table 1, recovery of the silicone polymer was 108% and the RSD% was 1.26%.

Table 2. Silicone deposition measurement

Table 2. Silicone deposition measurement

The rinse water was analyzed with proton NMR following the sample preparation procedure described; the silicone deposition results are summarized in Table 2.

Figure 1. Combing tester

Figure 1. Combing tester

The combing tester utilized was equipped with: two shower heads; two combing arms to which brushes were connected vertically to a potential displacement meter—hereinafter referred to as the arms; and a hair tress holder connected to a load cell (see Figure 1).

Figure 2. Representative 1H NMR spectrum of rinse water sample

Figure 2. Representative <sup>1</sup>H NMR spectrum of rinse water sample

A typical 1H NMR spectrum is shown in Figure 2.

Figure 3. Silicone deposition results of samples with different levels of silicone

Figure 3. Silicone deposition results of samples with different levels of silicone

Comparing the silicone deposition amounts of samples with different PDMS levels, i.e., 0.0–5.0%, it is obvious that initially, the amount of silicone deposited increased with increasing silicone content (see Figure 3).

Figure 4. Correlation between silicone deposition amount and dry hair combing force

Figure 4. Correlation between silicone deposition amount and dry hair combing force

Figure 4 compares the dry hair combing forces of samples treated with GS-S0 and GS-S1, revealing that silicone deposited onto hair reduced the dry hair combing force significantly.

Footnotes (CT1311 Huang)

a The hair samples used for this study were obtained from Beaulax.
b Combing Tester SK-3A is a device from Techno Hashimoto.
c All materials were purchased from Wako Pure Chemical Industries, Ltd.
d The 500 MHz NMR instrument is manufactured by Bruker.

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