Measuring the Stiffness of Hair

New Hair Stiffness Rig

Analytical technology can help the hair industry substantiate ambitious marketing claims about shampoos and conditioners that claim to leave hair soft and manageable, make hair look more youthful or increase volume. When a hair product is marketed, certain claims are written on the packaging or in adverts with statements regarding its performance and efficacy. These claims must be substantiated with laboratory testing to prevent misleading consumers and going against legislation – manufacturers cannot assert that products have properties they do not have. The test used is determined by the claim being made. E.g. a claim for ‘improved softness’ might be substantiated with a bending test using a newly available Hair Stiffness Rig.

Some changes to the physical properties of hair are intentional (the addition of conditioners or serum for added smoothness), whereas some are unintentional (bleaching, which induces brittleness and stiffness). No matter the property in question, the quantification of hair properties is important to the development of new hair products and treatments. Sensory panels are useful, as hair is a material with a complex pattern of properties and variables, so it is a challenge to measure its properties exactly as a consumer might feel them when they are styling their hair, or what they take to mean ‘softness to the touch’. However, instrumental testing is much faster to perform, and the results of an instrumental test do not rely on the operator, unlike those of a sensory test, no matter how thorough sensory training has been. Consequently, instrumental quantification of hair properties should be a standard part of any hair testing regimen. 

The bending force of a hair bundle can be used as an indicator of softness/stiffness using a Hair Stiffness Rig attached to a Texture Analyser. The effect of various hair treatments on softness can be determined by measuring the tress’s bending properties before and after treatment. For a treatment such as bleaching, a single bend cycle test may be used, or an average bending force from a cycle of ten three-point bend tests is calculated for each sample.

This is also applicable to measuring the efficacy of conditioner formulations containing new softening ingredients. However, to prove the holding power of fixatives such as hair spray, the drop in bending force is calculated from the first to last cycle, as the polymer holding cast is broken after the first deformation. The hair bundle is clamped at one end and the remaining length placed on two supports. The Texture Analyser probe descends vertically on the sample a set number of times, applying pressure to the central section of the hair bundle. The stiffness of a hair fibre is increased when a polymer-based substance such as hairspray is applied. Hairspray formulations can be modified for a lower or higher stiffness by polymer cross-linking or introducing bulky side groups.

The graph below was taken from a 5 cycle test of a sample with a hairspray cast. The cast was broken during the first cycle, with a large force drop to the second, and subsequent force drops through the final cycles. These forces can be measured using a macro within Exponent software.

Assessments of hair such as tensile testing and three-point bend testing are useful for keeping a record of more fundamental properties, but imitative tests such as the measurement of combing force, volume and body measurement via laser profiling, and the suppleness test are useful for representing hair in the way in which it is felt and handled in reality.

There is a Texture Analysis test for virtually any physical property. Contact Stable Micro Systems today to learn more about our full range of solutions.

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For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

No-one understands texture analysis like we do!

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