EMULSIONS
three months. At 25°C, the polydisperse pattern appeared after three months. Formulation D began with a droplet size of 2.1 µm and ended with 18.6 µm (20°C) and 47.4 µm (25°C). The polydisperse patterns correlate with crystallization (Figure 5). After three months, sonication was used to
evaluate droplet size changes. Formulation C returned to initial droplet size, while Formulation D showed complex behaviour: at 20°C, initial droplet size was mostly restored with some larger droplets/aggregates; at 25°C, larger droplets/aggregates remained, along with slightly smaller droplets. (Figure 6)
Viscosity Throughout the study, all samples showed a consistent shear-thinning behaviour, Figure 7, hence a shear rate of 10 s-1
storage-induced changes. Formulations A and B showed no viscosity change at 20°C and 25°C. Formulation
A maintained ˜460 mPas at 20°C, while Formulation B started at 500 mPas. At 25°C,
viscosities were ˜440 mPas and 470 mPas, respectively. Formulations C and D showed increased
viscosity after one week at 20°C, with rapid increases over the next month, then slower increases between months 1 and 3 (Figure 8). At 25°C, Formulation C’s viscosity increased after three months, while Formulation D’s increase began after one month (Figure 9).
Overall discussion The emulsion with 100% Lipex SheaLiquid TR showed no crystallization, droplet size, or viscosity changes at any temperature. Adding a crystallizing material induced changes in viscosity and droplet size. Crystallization correlated with increased droplet size or aggregates, which were partially coalesced with weak bridges, and increased viscosity. Despite variations in crystallization rates, crystallization consistently induced changes in droplet size and viscosity. The final fate of these emulsions is
Formulation C stored at 20°C with and without sonication
20 15 10 5 0
0.1 -5 Formulation C stored at 25°C with and without sonication was used to assess
25 20 15 10 5 0
0.1 -5 1 10
■ Formulation C, 3 Months
■ Formulation C, 3 Months with sonication
■ Formulation C Day 0
100 1000µm
20 18 16 14 12 10 8 6 4 2 0
-2 0.1 1 10 100 1000µm
Figure 6: Droplet size distribution. Droplet size (µm). With and without sonication at Day 0 and after three months of storage. Day 0 at the bottom and three months at the top
unresolved, as formulations C and D with high levels of refined shea butter continue to develop. The rate of crystalline phase development and polymorphic change is slower in emulsions19
compared to bulk oil systems.20 A 5°C storage temperature difference results
in significant behavioural differences and potentially alters the crystallization pathway. The 2-L structure developed by formulations C and D at 25°C cannot be fully explained by their shared composition. In Formulation D at 20°C, the 2-L peak is detectable from day one, becoming more distinct after one week and remaining stable. The 3-L peak develops clearly after a week
and continues to evolve. At 25°C, the 2-L peak is strong from the outset and develops over time, while the 3-L peak appears only after three months. Throughout all measurements, only β’-formations are observed. While pure SOS crystals typically
crystallize in 3-L, β’-formations, more complex triglyceride compositions initially
Formulation A■ Formulation B ■ Formulation C ■ Formulation D ■
100000 10000 1000 100 10 1
0.1 1 10 100 1000 10000
Figure 7: Viscosity of emulsions. Viscosity measured on emulsions after three months shows shear thinning properties
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form 2-L, β’-formations, then transform into 3-L, β’-formations.21
This suggests that the
crystallization pathway varies between 20°C and 25°C.
Conclusions Materials that crystallize can cause unexpected changes in droplet size and viscosity. Understanding both the crystallizing material and the emulsifier system is essential for emulsion stability. Refined shea butter, a crystallizing material,
has a crystallization rate highly sensitive to temperature. The study shows that its crystallization rate within o/w emulsions is very slow, making them susceptible to storage temperature. Significant variations were observed depending on whether the emulsion was stored at 20°C or 25°C. In addition the study shows that there is a correlation between crystallization and change in viscosity and droplet size, indicating that post-production conditions strongly influence the final outcome. In contrast, using liquid shea oil, which does
not crystallize, had no impact on viscosity or droplet size, nor any dependence on post- production conditions affecting final product quality.
Authors’ acknowledgement A special thanks to CR Competence, Lund, Sweden who performed the study on behalf of AAK
References 1. Rousseau D. Fat crystals and emulsion stability. Food Research International. 2000; 3-14
2. Spicer PT, Hartel RW. Crystal Comets: Dewetting during emulsion droplet crystallization. Australian Journal of Chemistry. 2005; 58, 655-659
3. Ngukeng PBC et al. The Current state of knowledge of shea butter Tree (Vitellaria paradoxa) for nutritional value and tree improvement in West and Central Africa. Forests. 2021; 12, 2-3
November 2025 PERSONAL CARE 1 10 100
■ Formulation C, 3 Months
■ Formulation C, 3 Months with sonication
■ Formulation C Day 0
1000µm
20 18 16 14 12 10 8 6 4 2 0
-2 0.1 1 10 100 1000µm Formulation D stored at 25°C with and without sonication
■ Formulation D, 3 Months
■ Formulation D, 3 Months with sonication
■ Formulation D Day 0
Formulation D stored at 20°C with and without sonication
■ Formulation D, 3 Months
■ Formulation D, 3 Months with sonication
■ Formulation D Day 0
67
PC
mPa.s
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