Texture Analysis in the Nailcare Industry: 3: Mechanical properties of dry polish

A manicure is subject to a lot of abuse as the wearer goes about their daily life (opening jars, cooking, typing on a keyboard). 

For repeat purchase of a nail polish, it must be able to stand up to this type of use. As well as the adhesion properties mentioned above, the stiffness and toughness of a polish are all extremely important. 

An overly stiff, brittle polish would be undesirable as it would break when a nail is bent when opening a soda can, for example. The low stiffness is important for the polish to follow the nail as it bends. A high strain to failure is also crucial, or the polish film would break under the slightest deformation.

Figure 4: Film Support Rig

All of these properties can be examined using a biaxial tension method. A 3cm by 3cm film specimen is cut from a 21cm strip set in a purpose-built PVC vacuum formed mould. It is then tested in the Film Support Rig (Figure 4), with a circular clamp surrounding a 1cm diameter circular aperture. 

A 5mm stainless steel ball probe is driven down into the sample, applying force until rupture. Stress and strain are recorded, from which the mechanical properties of the dry nail polish can be easily determined using the ready-made analysis macro.

Using this method, manufacturers can identify weaknesses and adjust nail polish formulations accordingly. 

Figure 5: Two different polish samples tested
two days after their initial pour into the mould:
a gel polish and a quickdry polish 

Figure 5 shows puncture tests on two samples. The red curve shows a stronger, stiffer polish compared to the other  sample. Their toughness values are similar, with toughness given by the area under the curve. In addition, by cutting the samples and testing the same batch daily over the course of a week or fortnight, the change in character of the polish can be assessed over the timescale of a manicure. 

A polish with desirable properties is only a high quality product if those properties are retained day after day. The customer would be disappointed if their manicure degraded quickly and started chipping after three days.

Figure 6: Pink quickdry polish
two days, five days and ten days
after initial pour into mould

Figure 6 shows tests on three samples of the same polish carried out two, five and ten days after the polish was poured from the bottle.

Figure 7 shows best fit line graphs of toughness, stiffness and failure strain of three different samples over the course of 11 days. The blue sample is the most desirable as its toughness remains constant, it is the least stiff and its failure strain is always greatest.

Figure 7: Pink quickdry polish – two days, five days and ten days after initial pour into mould

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We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.
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.

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