34 SUN CARE
small and large micelles raises concerns. This observation may signal the onset of coalescence, a process that, if left unchecked, could progress to phase separation over time. One such example of the variation of micelle sizes is shown in Figure 5. Figure 6 demonstrates the variability in
behaviour of a single emulsifier, resulting in diverse micelle shapes when combined with various UV filters at an identical concentration (10%). All images in Figure 6 were captured at the same magnification. These differing micelle shapes can significantly influence the microstructure of the formulation, potentially resulting in varied efficacy performance. The presence of such varied micelle
sizes implies potential instability in the formulation, urging formulators to delve into proactive measures to rectify and optimize the microstructural composition. This nuanced understanding of micelle size dynamics underscores the importance of meticulous analysis in achieving not just emulsion stability but also the sustained performance and quality of cosmetic formulations. As researchers explore the intricacies of micelle behaviour, their findings contribute to the refinement of formulation techniques, ensuring that sunscreens meet the highest standards of stability and efficacy demanded by the industry.
Appearance of mineral UV filters In the context of mineral formulations, the appearance of agglomeration of TiO2
and ZnO
under light microscopy is characterized by the manifestation of dark black or brown semi- translucent particles (Figure 7). The specific hue of these particles is contingent upon the substances with which TiO2
The incorporation of TiO2
or ZnO particles may be coated. or ZnO into an
emulsion has the potential to transform the micelle structure, encompassing alterations in both shape and size. The dynamics of this transformation are influenced by various factors, including the size of the particle and the phase at which the addition occurs. Understanding these nuances is ever more important, especially in the present climate where consumer preferences are steering towards mineral-based sunscreens. The microscopic images in Figure 8 show a
simple O/W emulsion without any UV active, and the same emulsion where TiO2
has been added to the oil phase prior to emulsification.
Agglomeration of mineral UV filters In an ideal world, formulators expect the particles of titanium dioxide (TiO2
) and zinc O/W emulsifier, non-nano alumina-coated TiO2 Unstable W/O mineral sunscreen emulsion showing coalescence Stable W/O mineral sunscreen emulsion showing coalescence
20x magnification
20x magnification
Figure 5: Microscope images of a coalescing W/O emulsion, the left is an unstable emulsion and the right is a stable emulsion
oxide (ZnO) to be so small that they are scarcely discernible under microscopic evaluation. The overarching goal is to achieve an environment in which these inorganic UV filters are not only small but also uniformly dispersed throughout the formulation. This optimal dispersion enhances
the likelihood of attaining both stability and optimal SPF efficacy. Detection of agglomeration in the inorganic UV filters signals inadequate dispersion, a challenge that can sometimes be effectively addressed by incorporating additional energy input during the homogenization process. Alternatively, agglomeration may signify an incompatibility issue necessitating reformulation. In the case of Solaveil Clarus and Solaveil
SpeXtra, their particles, characterized by a spherical nature, facilitate easy dispersion. Any instance of agglomeration in these formulations would be deemed unacceptable, signifying underlying issues that could ultimately compromise SPF efficacy. Conversely, Solaveil MicNo, with its distinctive platelet structure and stacking morphology, allows for a certain level of aggregation without negatively impacting efficacy. In the assessment of Solaveil MicNo, a few,
evenly distributed, small agglomerates of less than 50 micrometres are deemed acceptable. However, the presence of a significant number of mid-sized or larger agglomerates would flag potential concerns in the formulation or processing procedures. This nuanced evaluation of agglomeration standards demonstrates the meticulous scrutiny applied to different formulations with different types of UV filters. It is always recommended to speak to your supplier to guide you on formulating your UV actives when formulating with a UV active for the first time.
O/W emulsifier, nano alumina-coated TiO2 When observing agglomeration, one may
explore various strategies to mitigate its occurrence. Adjustments to the process are one avenue for intervention, involving modifications such as elevating homogenization speed or extending the homogenization time to increase energy input. Alternatively, specialized equipment like
triple roll mills can be employed to address agglomeration challenges effectively. Another effective approach involves homogenizing the phase to which the inorganic UV filters have been added before emulsification, coupled with the homogenization of the final emulsion to yield a finer emulsion. This double homogenisation methodology in the production process can be highly effective at preventing agglomeration. When working with TiO2
or ZnO powders,
the addition of a dispersant becomes crucial in preventing agglomeration, as advised by experts. Options like Span 120 or polyhydroxystearic acid are viable dispersants, with a suggested initial usage rate of 0.1% dispersant per 1% powder. To guarantee the effective coating of the dispersant onto the powder, rather than its accumulation at the emulsion interface, a pre-dispersion method is recommended. This involves combining the powder
and dispersant with a portion of oil and homogenizing it before adding it to the remaining oil phase (inclusive of the emulsifier). This sequential process ensures that the intended dispersant covers the powder while the desired emulsifier remains at the interface, enhancing effectiveness and avoiding any displacement from the emulsifier to the dispersant. Optimizing the dispersant levels within the system is essential to maintain adequate
O/W emulsifier, non-nano uncoated ZnO
Figure 6: Microscope images of the same O/W emulsifier combined with various UV filters at 10% inclusion level, the first is a non-nano alumina-coated TiO2
, the second is a nano alumina-coated TiO2 PERSONAL CARE February 2024 and the third is a non-nano uncoated ZnO
www.personalcaremagazine.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80
