SUN CARE
■ Highlight issues in the manufacturing process e.g. undispersed UV filters (see Figure 2) or thickener ■ Analyse the effects of emulsifiers, thickeners and preservatives.
Screening for incompatibilities Screening of formulation issues before they manifest visually as separation is an approach that can eliminate the need to wait for full stability results, offering a real-time assessment of potential challenges. The illustrative example in Figure 3 provides
insight into the effectiveness of microscopy in discerning compatibility issues within a water-in-oil (W/O) emulsion. Using the same formulation chassis, but incorporating a change in wax, the left-hand microscope image shows formulation where Wax A demonstrates incompatibility with one of the emollients in the system. This incompatibility manifests as a clear separation of the emulsion microstructure, a phenomenon not yet perceptible as phase separation in the bulk formulation. The microscopy images highlight the
nuanced nature of formulation dynamics, showcasing the distinct advantages of this analytical technique. In response to the identified incompatibility, a straightforward adjustment is made by substituting Wax A with an alternative wax, while keeping all other parameters constant. This modification results in a formulation characterized by a notably smaller micelle size and enhanced homogeneity. Consequently, the revised formulation exhibits reduced susceptibility to separation over time. By integrating microscopy at this stage, formulators can address compatibility issues promptly, fostering a more efficient and informed approach to cosmetic formulation development.
Micelle size identification Micelle size is critical to understand emulsion stability. A small evenly distributed micelle size usually suggests a stable formulation; therefore, an optimum formulation should have a small and homogenous micelle size distribution. Microscopy is a vital tool for precisely measuring particle and micelle size, offering both automated and manual methodologies. Automated microscopy introduces efficiency and accuracy into the process. On the other hand, manual microscopy methods provide scientists with a hands-on, detailed examination, allowing for a nuanced understanding of the emulsion’s intricate structure.
O/W Sunscreen Emulsion with Emulsifier A / 20x magnification
W/O Emulsion with TiO2 20x magnification
33
Figure 2: Microscopy image of TiO2 formulation process
W/O Emulsion with Wax A 20x magnification
dispersion that has not been mixed correctly during the
W/O Emulsion with Wax B 20x magnification
Figure 3: Microscope images of W/O Emulsion with two different types of waxes, wax A shows signs on instability and wax B is a stable systemformulation process
In the quest to optimise the micelle size,
one can adjust the process (energy input), specifically the energy input, or opt to change the emulsifier. Different emulsifiers can show different micelle sizes, even when all other factors and ingredients remain constant. Consequently, there is no predetermined ‘optimum’ or expected micelle size that one should target to establish a stable system. Instead, the emphasis should be directed towards scrutinizing size distribution and homogeneity, prioritizing these aspects overachieving a specific absolute micelle size. Figure 4 shows how in the same chassis, with different emulsifiers, process changes
O/W Sunscreen Emulsion with Emulsifier B / 20x magnification
which lead to a smaller micelle size are likely to also improve SPF due to improved dispersion throughout the formulation of the UV filters. The distribution of micelle sizes within an emulsion is an important indicator of stability, and this characteristic is often crucial in formulating cosmetic products. In the assessment of micelle size, a small and uniformly distributed micelle size tends to correlate with a more stable formulation. The ideal formulation, therefore, is characterized not only by a small micelle size but also by a homogeneous distribution of micelle sizes. Under microscopic analysis, the identification of a formulation exhibiting a spectrum of both
O/W Sunscreen Emulsion with Emulsifier C / 20x magnification
Figure 4: O/W emulsions various different emulsifiers showing different micelle sizes
www.personalcaremagazine.com February 2024 PERSONAL CARE
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
