Association Behaviour and Physicochemical Properties of Dihydroxystearic Acid and Octyl Dihydroxystearate, and Their Applications in Cosmetics

The phase behaviour in ternary system had been studied at 85°C under visual observation by polarizing light and they were confirmed by polarization microscope. It was found spherulite and needles type of crystal for DHSA and Octyl dihydroxystearate respectively. The polymorphs were typically distinguished by differences in their X-ray spectra using X-ray diffraction spectroscopy. Polymorph DHSA and Octyl dihydroxystearate in MCT exist as beta prime (β’) and beta (β). The results also showed that mixture of DHSA/ Octyl dihydroxystearate in different type of third component (MCT and ethanol) may posses only stable β’ form, only stable β form or both β and β’ form. A rheological analysis showed the deformation and flow behaviour of DHSA / Octyl dihydroxystearate and MCT respectively. From hysteresis value, the correlation between the crystal polymorph and decreasing of ratio DHSA plays an important role with the structure breakdown. Instability of polymorph gave vary and unpredictable viscosity value to the mixture of DHSA and Octyl dihydroxystearate. Study of frequency sweep gave idea viscoelastic properties of DHSA and Octyl dihydroxystearate in MCT. Most samples gave result of storage modulus was always higher than the loss modulus (G’>G”). Loss modulus higher than storage modulus (G”>G’) for 30:70 of DHSA/ Octyl dihydoxystearate at 85% MCT. Their needle and spherulite microstructures, which confer a brittle or smooth feel, were useful in the formulation of concealer stick. The concealer sticks were prepared by adding DHSA, Octyl dihydroxystearate, and MCT as main components combined with fillers, pigment, binders and fragrance. The concealer stick with different ratios of DHSA and Octyl dihydroxystearate gave different results in its stability. The stability test included breaking point, heat test, hardness test, slip melting point, softening point and humidity. Formulation at 20:80 DHSA/ Octyl dihydroxystearate was chosen as the best formulation due to the physical properties previously which consist of β polymorph densely packed spherulite crystal. When compared to commercial, this formulation showed a better result in terms of softness and strength effect of the sticks.

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