In the light of clean
beauty and sustainability requirements emerging
in the personal care market, the urgent need for the replacement of
silicones in hair conditioners—with comparable performance
and customer experience—has been highlighted in the industry.
In this context, the goal of the present study was to investigate
the physical effects of different silicone-free conditioner formulations
on Mongolian hair after damage due to bleaching and compare the results
to property changes induced by a classical silicone-containing formulation.
To that end, the morphology, structure, and composition of strands
and individual fibers of this hair type were characterized before
and after bleaching by means of optical microscopy, atomic force microscopy
(AFM), and X-ray photoelectron spectroscopy (XPS). It is shown that
oxidative bleaching causes significant damage to the native hair surface,
leading to local depletion or even large-area removal of the outer
hydrophobic lipid layer. This results in enhanced wettability of the
bleached hair by water (as confirmed by contact angle measurements)
and is accompanied by an undesired loss of hair gloss and softness.
Upon treatment with suitable cosmetic emulsions, the natural hydrophobicity
of intact Mongolian hair can be partially or fully restored, with
silicone-free formulations having effects similar to those of established
silicone-containing products. The successive influence of bleaching
and conditioning was further monitored using inverse gas chromatography
(iGC), a technique that probes changes in surface energetics and polarity
over an ensemble of an entire hair strand through interactions with
specific molecules at the solid/gas interface. The resulting data
mirror the macroscopic behavior of the bleached/conditioned hair and
provide a quantitative scale for measuring damage and repair effects.
Most notably, the effect of bleaching and subsequent conditioning
on the haptic perception of hair strands could also be quantified
with the aid of a biomimetic measurement system, which identifies
increased friction (both tactile and sliding) as the major cause for
the strawy feel of bleached hair and indicates successful relubrication
after treatment with suitable conditioner formulations. Finally, the
different physical properties determined for native, bleached, and
reconditioned Mongolian hair are found to be reflected in application-oriented
tests, namely
in vitro
measurements of wet and dry
combing work. Overall, the data collected in this work shed novel
light on the surface properties of Mongolian hair and highlight that
effective hair conditioning after damage can be achieved without silicones
in advanced cosmetic emulsions based on octyldodecyl myristate and
glyceryl oleate.