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Dr Xuzi Kang - Staff Scientist at TRI
Holly Honoré - Summer Internship Student at TRI
Out of all the product types in haircare searched for on-line, conditioner products account for 37% of inquiries, a much larger share than shampoos (22%), electricals (17%), and accessories (9%). Consumers are most curious about moisturizing (i.e. conditioning) and color protection benefits. As cosmetic scientists we know that the conditioning performance of hair conditioners can be tested on both wet and dry hair. The most common techniques used at TRI are combing force measurements and hair friction measurements. However, both methods usually measure wet conditioning effects on hair that has already been well rinsed. In reality, consumers sense the lubrication effects of conditioners as they spread them on hair, as they massage them in and as they rinse them from the hair. All this information is lost in a standard wet combing or wet friction test.
In a recent study, Dr Xuzi Kang, with the help of her summer intern Holly Honoré, have investigated
whether for the three-point-bend test can be used as a dynamic measure of wet lubrication effects.
In theory, the great advantage of the three-point-bend test is that it can measure tress stiffness at different stages of the wash cycle non-invasively. This is unlike comb testing or friction testing that disturb the film of conditioner left on the hair, making repeat measurements on the same tress difficult.
Baseline data – Effect of Hair Damage on Wet Hair Properties
Baseline studies investigated the effects of bleach damage on wet tress properties, as measured by the three-point bending apparatus. Results showed (Figure 1) treatment with bleach often led to significant hardening (Peak Force) for both medium brown (straight) and multiethnic (wavy hair) tresses. The toughness (AUC) data mirrored this, with a similar distribution of data points. We believe these effects to be related to cuticle damage from the bleaching and an increase in surface friction. Surprisingly, hardening and toughness sometimes reduced with 9% bleach versus 6% bleach. Clearly, extensive bleaching can bring smoothness to the hair. This could be related to the removal of loose or lifted cuticle scales.
Figure 1: (a) Hardness data for medium brown and multiethnic hair tresses both in virgin state and after 6% and 9% bleach treatment; (b) Toughness data for medium brown and multiethnic hair tresses both in virgin state and after 6% and 9% bleach treatment.
Effects of Conditioner 1
Next, wet virgin hair and wet 6% bleached hair were treated with conditioner 1. Hardness data were collected for wet tresses containing conditioner, then after rinsing for specified time intervals. In both cases, treatment with conditioner led to a decrease in hardness and, as the conditioning product was rinsed away, the hardness increased, Figure 2. After washing for 210 seconds, wet virgin hair recovered a similar hardness to the original sample whereas the 6% bleached sample showed a plateau in hardness recovery after 240 seconds. These data suggest that, in the 6% bleached sample, some of the conditioning agent is remaining on the hair shaft and impacting upon the hardness behavior whereas this is not the case for medium brown virgin hair and any benefit of the conditioner is lost during rinsing.
Figure 2: (a) Hardness data for wet virgin medium brown tresses upon initial application of conditioner 1 and then with subsequent rinsing; (b) Hardness data for wet 6% bleached medium brown tresses upon initial application of conditioner 1 and then with subsequent rinsing.
Effects of Conditioner 2
The experiment was repeated for a second product, conditioner 2. Again, wet virgin hair and wet 6% bleached hair were treated with conditioner, and data points were taken when the conditioner was present and after rinsing for specified time intervals. In both cases it looked like significant quantities of conditioner remained and hair was less hard after treatment, Figure 3.
Figure 3: (a) Hardness data for wet virgin medium brown tresses upon initial application of conditioner 2 and then with subsequent rinsing; (b) Hardness data for wet 6% bleached medium brown tresses upon initial application of conditioner 2 and then with subsequent rinsing.
Conclusion
This small study investigated whether three-point-bend test can be used as a dynamic measure of
conditioning performance. Overall, our results showed key differences between two conditioner
products in terms of conditioning and rinsing behavior. Conditioner 1 was much more easily
removed from the hair than conditioner 2. Conditioner 2 had longer lasting wet detangling effects.
Information about the dynamic wet lubrication performance of conditioning products and their
ease-of-rinse will be very useful to formulators wishing to deliver high-performing formulations in
the future.
Future studies will investigate the use of the wet three-point-bend method for the investigation of the dynamic wet lubrication properties of 2-in-1 shampoo products designed to deliver high levels of wet detangling at the early stages of the washing cycle.
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