Silicone for conditioning and UV protection

The tensile strength value was taken as “load 15%” [mN], i.e. the force value at 15% elongation. [MTT670, Diastron, ndover, UK]. The value of Delta-Load is the difference before and after the treatment procedure. After measurement of the start value the hair fibres had to be relaxed by soaking in water for 2 hours.

Keratin integrity

The fibre keratin integrity has been investigated by differential scanning calorimetry [F.J.Wortmann, C.Springob, G.Sendelbach, J.Cosmet.Sci. 53, 219-228 (2002)]. This method delivers information about the degree of damage to the keratin structure of the hair fibre. In the test setup, flat tresses (European human hair, single bleached) of 0.5 cm width have been used. The tresses underwent 4 treatment cycles, including a shampoo (0.5 g/tress for 30 sec., 1 min residence, 1 min rinsing) followed by a conditioner (0.5 g/tress, 2 min residence, 2 min rinsing). In the shampoo tests, the application was repeated once in each cycle without applying any conditioner.

In the conditioner tests, the control shampoo as well as the test conditioner formulations were applied only once per cycle. After drying at room temperature the tresses were irradiated for 4.25 h (does rate of approx. one day sunlight). To maintain homogeneous irradiation the hair tresses were spread to single fibres. Finally the hair tips were cut to the required amount for the DSC determination. Each application was conducted threefold.

Colour measurement

Colour has been measured using a CIE-L*a*b Colorimeter [spectrophotometer micro colour, Dr.Lange, Düsseldorf, Germany]. The colour variations are expressed as integral difference ‘delta-E’, where changes of brightness (L*), red-green (a*) and blue-yellow (b*) shift are considered. Best differentiation was obtained when conducting the measurement directly before and after irradiation, without any intermediate treatment. Shampoo as well as rinse conditioner application lead to fading of a hair dye. The interpretation of colour measurements obtained from superposition of both, UV irradiation and treatment with formulations would not be accurate. In the operation procedure flat glued tresses of single bleached European human hair, 4 g weight, 16 cm length and 2 cm width, were used. The dye was applied according to all steps given in the operating guidelines delivered by the package. Eleven tresses were treated with each single colouration kit. After a drying time of minimum 24 hours, the tresses were treated by the test formulations, shampoo and (in case) conditioner. The tresses were dried again. The colour value has been determined by 12 single measurement of the CIE-L*a*b*- colour values. Seven hours irradiation time was chosen to apply a dose rate of approx. two days sunlight. Following, the colour values were taken again and the integral colour change “delta-E” was calculate using the following formula:

ΔE*= √(ΔL*)²+(Δa*)²+(ΔB*)²

Results

Tensile strength

The UV-fraction of sunlight irradiation can cause a reduction of the tensile strength of hair fibres. The test conditions in this study for unprotected hair fibres resulted in a reduction of the force measured at 15% extension by about 5 mN per fibre.

This is a change of about 3% relative to the starting value. Some of the UV filters provided protection when used in a conditioner formulation. The best effect observed was up to 40% less reduction of the tensile strength change when using ABIL UV Quat 50. PA-2 provided the same efficacy. The other two products evaluated in this test did not score protection values which were significantly different from the control formulation, which was CTAC. Figure 3 shows the data in comparison.

Keratin integrity

The DSC data exhibited high reproducibility and small standard deviation. Non-irradiated hair shows a DSC signal at about 154°C, while the treatment without protection lead to a reduction of the decomposition temperature to about 142°C. The standard deviation in the data of this evaluation is below ±0.5°C. The best protection of the keratinous structure according to DSC measurement was provided by ABILUV Quat 50. The best protection effect was observed with conditioner application and yielded 28%. In shampoo application, ABIL UV Quat 50 provided about 10% protection.

Colour protection

The colour change generated by the equivalent of approximately two days sunlight was about 2 to 3 units of delta-E for the permanent dye and about 3 to 4 units for the demipermanent dye. It was possible to show that the use of a UVabsorbing material in a rinse-off formulation leads to an improved preservation of the colour. This was observed in both application types, shampoo and conditioner.

The use of ABIL UV Quat 50 in both shampoo as well as rinse provided the best protection effect for the permanent colouration. Non of the other materials provided better performance The colour fading was reduced by of 50% in the shampoo and about 40% in the conditioner application (see Fig. 4 and 5). Besides ABIL UV Quat 50 also Polyamide-2 performed well in the shampoo application while Polyquaternium-59 provided a good performance in the conditioner formulation.

The protection effect for the demipermanent colouration was less clearly differentiated among the test material. In conditioner applications, ABIL UV Quat 50 reduced the fading by about 50%. In this comparison a maximum effect of 65% protection was obtained with PS-15. In shampoo applications, the protection of the demi-permanent dye was generally smaller with about 20%. Here a maximum effect of 25% was observed by both ABIL UV Quat 50 and PA-2 (See Fig. 6 and 7).

Conclusion

The fastness of hair dyes against sunlight fading is improved by using UV-absorbers. The damage of hair by sunlight including UV is also expressed by a loss in tensile strength. This degradation effect as well as the UV-impact on the integrity of the hair fibre keratine can be reduced too. The investigated UV filters can be incorporated in shampoo or rinse formulations for frequent application which sufficient success, when the ingredients are substantive. This necessary substantivity to the hair fibre surface is provided by cationic groups. Siloxane derivatives, with their specific surface activity, also have sufficient substantivity.

The new siloxane copolymer ABIL UV Quat 50 with a high content of UV absorbing methoxycinnamic acid groups and a small ratio of cationic functions combines both characteristics, silicone and cationic. This ingredient provides overall best protection in both types of rinse-off formulations, shampoo and conditioner.