Quantifying Polymer Deposition on Hair Fibers by Microfluorometry


Anthony J. Ribaudo Sr. Retired from TRI Princeton, 601 Prospect Ave., Princeton, NJ 08540


antuni@aol.com


Abstract: Positively charged (cationic) polymers are one of the most important types of polymers used in haircare products. Because of their high degree of substantivity to hair, they are useful in shampoos and conditioners. Numerous studies have shown that cationic condi- tioning compounds protect against hair damage caused by cosmetic chemical treatments and grooming practices. When hair care prod- ucts are being developed, it is crucial that formulators determine the depositional characteristics of the polymer from a functional as well as a cost perspective. Microfluorometry can be used to quantitatively determine the amount of a polymer deposited on the surface of hair fibers and to determine the extent the polymer penetrates into the hair fibers. The data output is the fluorescent intensity obtained from scanning along a predefined length of hair fiber.


Keywords: fluorophore, cationic polymer, sulforodamine-b, epi-fluo- rescent image, hair cuticle


Introduction Te global hair care market was estimated to be worth


US$85.52 billion in 2017 and is expected to reach US$106.57 billion by the end of 2023, recording a compound annual growth rate (CAGR) of 3.7% during the forecast period of 2018–2023. Te majority of the global population has become beauty conscious, and people are being more inclined toward beauty-enhancing products [1]. Human hair is a keratin (fibrous protein) that grows from


large cavities called follicles. Hair serves protective, sensory, and sexual attractiveness functions. Morphologically a fully formed hair fiber contains three and sometimes four differ- ent types of structures. Te surface of the hair fiber contains a thick protective coating, which consists of layers of flat over- lapping scale-like structures, called the cuticle that is generally 6–8 layers thick. Te cuticle layers surround the cortex, which contains the major part of the fiber mass. Te cortex consists of spindle-shaped cells that are aligned


along the fiber axis. Cortical cells contain the fibrous proteins of hair. Ticker hair oſten contains a porous region called the medulla, located near the center of the hair fiber. Te fourth unit is the intercellular cement that glues or binds the cells together, forming the major pathway for diffusion into hair fibers [1]. Te fracture surface of a typical hair fiber, shown in Figure 1, reveals the fibrous character of the cortex as well as the outer cuticle layer. It has been well established that when hair is exposed to chemical and mechanical modifications, irreversible changes may take place that could lead to hair damage [2–8]. By combining force measurements, sensorial tests, and


analytical methods, namely zeta potential measurements and atomic force microscopy, it has been shown that poly- mers improve the overall performance of shampoo formula- tions. Positively charged (cationic) polymers comprise one of the most important types of polymers used in hair products. Because of their high degree of substantivity (ability to adhere)


24 doi:10.1017/S155192951900066X


to hair, these polymers are useful in shampoos and condition- ers. Studies have shown that cationic conditioning compounds protect against hair damage caused by cosmetic chemical treatments and grooming practices [1,8]. Te objectives of this study were to quantify the amount of


polymer that deposits on the cuticle and to determine the extent of penetration into the hair fibers at three different concentra- tion levels (0.1%, 0.01%, and 0.001%) using microfluorometry. Te polymer for this work was the cationic polymer polyqua- ternium 44 since studies have shown that it has excellent con- ditioning characteristics on wet hair, without sacrificing the properites of removability and absence of build-up [8].


Materials and Methods Microfluorometer. A microfluorometer integrates a fluores-


cent microscope with a spectrometer designed to measure fluores- cence intensity (FI). Te combined instrument can be configured to measure the transmission, absorption, reflectance, polariza- tion, and fluorescence of a sample down to the micron level. A dia- grammatic view of a microfluorometer is shown in Figure 2. Te operating principle of the microfluorometer involves passing light of a specific wavelength from an arc-discharge lamp or other light


Figure 1: Fracture surface of hair fiber. Scanning electron microscope (SEM) image acquired in secondary electron mode.


www.microscopy-today.com • 2019 July


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