How to Measure the Physical Properties of Hair and Hair Products

Today’s consumers are demanding healthier, shinier hair with a more natural look and feel. Hair fixatives can modify hair by imparting a permanent set and by increasing the stiffness of a fibre assembly. Instead of stiff fixed styles, consumers want hair fixatives that hold without being sticky, stiff or unnatural to the touch. However, the consumer perception of “touchable” hair fixative products actually comprises a number of physical and aesthetic characteristics. “Touchable” includes the flexibility of the style set, the softness of the hair, the “memory” properties of the style and the lack of stickiness. The next generation of hair fixative polymers will reflect these new sensory performance measures.

The majority of hair styling products that are found in the mass and salon markets contain synthetic polymers that hold the hair in place. However, naturally derived polymers, such as modified starches, can provide similar hair-holding properties with the added benefits of touchable hold, low tack, and a natural feel. Such formulation modifications require objective methods to quantify these claims. Various tests need to be employed to assess a range of physical qualities of the hair which are potentially affected by change of formulation. Texture Analysis provides the ability to measure all of the physical properties of hair and haircare products. The TA.XTPlus Texture Analyser enables tests to be performed in either compressive or tensile mode via a huge selection of attachments to hold the samples in order to provide the desired test action to measure the required property.

Typical Texture Analysis Tests for Hair and Hair Products

How to Measure Hair Combing Force

One of the methods that are used to determine conditioning efficiency is combability. Wet combability is measured under controlled conditions with an objective method using a Hair Combing Rig, in which a texture analyser measures the combing force required to pull a wet hair swatch (or tress) through a comb. It is usually necessary to first detangle and then to tangle hair in a controlled and reproducible way before the measurements. Blank hair swatches containing only water are run through the test to establish an initial benchmark. Then, the test solution is applied to the same swatch and measured for combability again to determine if, for example, the conditioner provides any improvements in combing. The maximum force to comb and the total work done are taken as comparative measures. A reduced combing force and work (usually calculated in percentage terms of a treated hair tress compared to the same tress treated with a blank formulation, i.e. no polymer) implies easier wet combability associated with the removal of entanglements of the hair fibres and can therefore be used to substantiate claims of improved manageability.

The combing force evaluation is equally effective for assessing combability of dry hair. All modified hair types (e.g. chemically treated (bleached), delipidised (by solvent extraction), and polymer treated hair) show an increase in dry combing forces as quantified by combing measurements. The combing work (g cm) and force as a function of tress distance would be substantially higher for all modified hair types compared to that of virgin hair and therefore this method can be used to assess, for example, the effect of addition of smoothing serums to dry hair.

Hair Combing Rig and typical comparative graphs

Hair Combing Rig and typical comparative graphs

How to Measure Hair Bending Strength

A simple objective stiffness or bending strength method can be performed where hair swatches are treated with polymeric solution, dried, and allowed to equilibrate at constant temperature and humidity conditions. The hair swatch is bent (typically employing Tensile Grips) to a certain degree and the force that has to be exerted is measured by the texture analyser. The test can yield information about the strength or stability of the examined hairs (the more resistance, the greater the stiffness) and the resulting hair volume, because flexural strength is one of the factors that have a considerable influence on hair volume.

Tensile Grips can be used to support hair fibres to determine stiffness/bending strength

Tensile Grips can be used to support hair fibres to determine stiffness/bending strength

How to Measure Shampoo/Conditioner Consistency

When formulating products such as shampoos and conditioners the materials to be used will depend largely upon the required end product consistency. A thin shampoo for easy pouring will require the addition of different ingredients or quantities than that required for a thick conditioner product. A product developer may wish to create a product that squeezes out of a tube and breaks sharply after squeezing. These consistencies can be assessed by either a forward extrusion test (simulating the force required to extrude the sample by the consumer) or a backward extrusion test which will give an indication of product physical failure and viscosity.

Forward and backward extrusion tests and typical back extrusion test curves

Forward and backward extrusion tests and typical back extrusion test curves

How to Measure Wax Stickiness

Hair waxes and pomades are the ultimate flexible styling product but are potentially heavy and greasy if not used in the correct quantity. They primarily hold hair through seam welds. This holding power is created by the waxy materials’ internal stickiness or cohesiveness. The waxy materials do not “dry” because they are not water soluble. The positive benefits of not drying means that the bonds can be easily remoulded by running your hands through your hair – the negative aspect is one of potential stickiness of formulations.

Exponent software provides the means of controlling the TA.XTplus Texture Analyser in a specialised Adhesive Test. A cylinder probe or spherical probe, if the product surface is not flat, applies a specified force to the surface of the sample for a specified time (to achieve a good bond between the two surfaces) and then moved away from the product at which point the force to separate the two surfaces is measured and used as a measure of product stickiness/adhesiveness/tackiness. The magnitude of the absolute positive value corresponds to the ‘stickiness’. The area under the profile represents the energy required to separate the wax from the probe, known as ‘work of adhesion’. The larger the maximum peak force, the stickier is the sample.

Cylinder probe and typical graphs

Cylinder probe and typical graphs

For a full summary of typical texture analysis tests that can be performed on hair and haircare products:

This information has been sourced, reviewed and adapted from materials provided by Stable Micro Systems Ltd.

For more information on this source, please visit Stable Micro Systems Ltd.

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