Quantifying the Performance of Hair Styling Products—Part 2

Aug 21, 2014 | Contact Author | By: Trefor Evans, PhD, TA Evans LLC
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Title: Quantifying the Performance of Hair Styling Products—Part 2
stylingx humidityx polymerx filmx glass transition temperaturex plasticizationx
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Keywords: styling | humidity | polymer | film | glass transition temperature | plasticization

Abstract: A previous article discussed traditional measurements to assess the properties of hair spray products. However, the properties of polymer films deposited by these products are not constant and can be altered by both formulation means and environmental conditions. This article highlights additional useful measurement techniques for characterizing these film properties.

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T Evans, Quantifying the Performance of Hair Styling Products: Part 2, Cosmet & Toil 129(9) 42 (2014)

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This article is the second of two discussing instrumental testing methods with applicability to the hair styling area. The previous article1 discussed consumer language associated with these products—in particular, the term hold. Instinctively, there is a tendency to equate this word with style longevity, but also discussed was the strong link of hair stiffness to consumer perception of this attribute. In short, while consumers profess the desire for products that do not adversely affect the feel properties of hair, this stiffness appears to act as the cue that the products are working.

In keeping with this discussion, the earlier article described the two most commonly used methods for evaluating styling products in the laboratory: high humidity curl droop experiments for style longevity, and mechanical bending experiments to assess hair stiffness. However, it is worth pointing out that the properties of polymer films deposited by styling products are not constant, and performance criteria can change dramatically as a result of formulation and environmental factors. This article discusses additional evaluation gauges to help hair product development scientists with formulation optimization.

Film Casting

Perhaps the simplest and undoubtedly one of the most insightful exercises involves casting polymer films from prototype and finished formulations. This is achieved by spraying or pouring the product into a suitable receptacle, then setting it aside for a few days to allow for the evaporation of volatile ingredients and drying of the film (see Figure 1). At the end of this duration, the visual properties of the film, i.e., color and clarity, can be observed while simultaneously gaining an appreciation of its hardness.

The mechanical properties of the resulting film are dictated by a number of variables. Most obvious is the selection of the polymer itself, but these characteristics can be significantly modified by formulation ingredients. The most common means of manipulating stiffness are through the selection and use levels of a neutralizing agent. The solubility of polymers containing carboxylic acid functionality can be achieved and facilitated by raising the pH, which generates the carboxylate ion and produces charged groups on the molecule. This is generally accomplished through the use of small organic bases, e.g., amino methypropanol (AMP), which also become entrapped in the polymer coating and in doing so, act as plasticizers that soften the resulting film.

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Table 1. DVS experiment showing moisture adsorption by a styling polymer film with increasing RH

Table 1. DVS experiment showing moisture adsorption by a styling polymer film with increasing RH

Both formulation and environmental factors play major roles.

Figure 1. Casting polymer films from hair spray formulations

Figure 1. Casting polymer films from hair spray formulations

This is achieved by spraying or pouring the product into a suitable receptacle, then setting it aside for a few days to allow for the evaporation of volatile ingredients and drying of the film.

Figure 2. DVS experiment showing moisture adsorption by a styling polymer film with increasing RH

Figure 2. DVS experiment showing moisture adsorption by a styling polymer film with increasing RH

Shown here are the results of a film cast from a skeletal formulation based on a popular hair spray polymer that was allowed to equilibrate in 10% increments up to 90% RH.

Figure 3. Bond adhesion carousel

Figure 3. Bond adhesion carousel for use with a Diastron mini tensile tester

Bond adhesion is a potentially tricky measurement that can be performed using a carousel designed especially for use with the Diastron 600 series of mini tensile testers.

Figure 4. The bond adhesion strength of a polymer film as a function of its stiffness

Figure 4. The bond adhesion strength of a polymer film as a function of its stiffness

Shown here is a schematic that illustrates the relationship between the bond strength of the spot welds and the stiffness of the polymer film.

Biography: Trefor Evans, PhD

Trefor Evans, PhD

Contributing author Trefor Evans, PhD, has worked in the hair care industry for more 20 years, with the majority of his time spent as a manager in the product development labs of Helene Curtis and Unilever. He also served for fi ve years as director of measurement services at TRIPrinceton before establishing his own consultancy, TA Evans LLC.

Evans holds a doctorate in physical-analytical chemistry and specializes in measurement science. He holds seven patents related to hair care, and has published numerous articles in trade magazines and scientific literature. His work has been awarded twice by the Society of Cosmetic Chemists, and he is a co-author and co-editor of the book Practical Modern Hair Science, published by Allured Business Media.

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