How to measure the physical and dimensional properties of hair – Combability

Measurements using Texture Analysis

Hair Combability

Consumers often desire fullness of hair which is associated with hair volume. One of the mechanisms by which hair volume is achieved is by increasing hair fibre-to-fibre friction. However, if this friction is too high, combability may be negatively affected.

It is well known that conditioning shampoos and hair conditioners are used to provide a variety of benefits to hair: they reduce the combing force, enhance the gloss, give smoothness and antistatic properties and they improve the manageability of the hair. 

Various types of benefit agents including cationic surfactants, polymers, emollients, and special compounds such as vitamins, UV filters, etc. contribute to cosmetic properties. For example, silicones are insoluble oils that are commonly use as conditioning agents for hair as they can effectively reduce combing friction of hair and provide a soft, smooth feel and a shiny appearance. UV inhibitors are becoming more commonly used in shampoo formulations for preventing damage and hair colour fading.

An imitative test is used industry-wide for measuring the force required to run a comb through a treated hair sample, in the form of a ‘hair combing test’ on a Texture Analyser, assisting manufacturers in the development of more effective conditioning agents. The Hair Combing Rig allows manufacturers of shampoos, conditioners and smoothing agents to evaluate the ‘combability’ of treated hair samples to substantiate claims of ‘improved manageability’.

This rig involves a tress sample clamped at the top and allowed to hang freely from a stand. A comb attachment is fixed to the load cell and is pulled down through the hair sample, allowing frictional forces to be measured. The assembly is positioned on the Texture Analyser and the supported length of hair is held vertically, near to the comb. When instructed, the arm of the Texture Analyser brings the comb down through the hair, recording the necessary force as it moves. At the end of a stroke, the comb is mechanically disengaged and moves back to its starting position to begin the next combing cycle. This allows multiple combing strokes without disturbing the hair on the upward movement in order to replicate consumer action.

Comparison of serum- and fixative-treated hair tresses using Hair Combability Rig

Wet Combability

In a wet combability test, 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. In practice, the hair is brought to a “wet state” by applying a defined water content.

Dry Combability

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 (in 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.

A dry combing test is also useful in substantiating claims for fixatives that are easy to comb out of dry hair.

Momentive Performance Materials Inc., a major manufacturer of silicones for the personal care sector, installed world-leading texture analysis technology to explore and substantiate the effectiveness of Silsoft Silk* conditioning agent. 

Thanks to the TA.XTplus Texture Analyser, Momentive now has detailed convincing data showing the effectiveness of their conditioning agent in various shampoo and conditioner applications. Wet friction assessments were complemented by wet and dry combing tests and human sensory panels which gave a fully rounded view of the silicones’ efficacy.

Read the next instalment How to measure the physical and dimensional properties of hair – Tensile and Bend Tests on the blog next week. 

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.XTplusC 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.

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