Use of 3D printed rheometer geometries for improved scale-up of lamellar structured liquids
Podium 58
Presented by: Grace Cunningham
Many formulated products found in the cosmetic and personal care industries are structured liquids. For example, the structure of many cream-based products is a lamellar gel network (LGN) comprised of surfactant bilayers. As with all formulated products, a combination of formulation and processing steps are integral to generating the desired microstructure, which in turn are responsible for the rheological properties of the system. In the case of lamellar gel networks, the interconnected system of bilayers generates a highly-shear thinning product with a high yield stress that make it desirable for the formulation of cream-based products. Despite the prevalence of the LGN structure for formulating cream products, there is relatively little insight into the impact of processing conditions on the final product rheology. Previous work by Cunningham, et al. (2021) utilised a vane in cup geometry with a rheometer to prepare LGNs at different time, temperature and agitator speeds. Key results showed that at constant temperature, there was a consistent power per unit volume required to achieve the maximum viscosity value, regardless of the agitator speed and total processing time. Therefore, it would be highly beneficial to explore the applicability of power per unit volume as a scale-up factor for optimising the manufacture of lamellar structured liquids.
A limitation of the previous work is that a vane geometry is not representative of the typical geometries used to manufacture structured, high viscosity liquids, which comprise of close clearance designs such as anchor or helical ribbon. Thus, to improve the geometric similarity between rheometer scale (40 g), lab (2 kg) and pilot scale (50 kg), typical agitator designs were designed and fabricated via 3-D printing. The four designs chosen were a 4-bladed vane, a commercially available TA helical ribbon, and two 3D printed geometries (helical ribbon and anchor). This enabled exploration of the differences in mixing and viscosity measurement in the formulation of lamellar structured liquids using these different geometrically similar geometries, at different scales.
A TA instruments DHR-II rheometer was used prepare and characterise a model lamellar structured liquid according to the formulation and methods outlined in Cunningham et al. (2021). The samples were prepared with the four geometries and characterised by measuring flow curves and the yield stress after samples had aged for at least 24 hours.
Differences were observed in the viscosity profiles of the lamellar structured liquids prepared with the different geometries under the same processing conditions, which may be ascribed to different mixing profiles within the vessel. This was also reflected in differences in the final rheological properties of the samples. This work highlights the importance of mixing profile and efficiency in the generation of the LGN structure at a rheometer scale. Furthermore, the use of 3D printed geometries has improved geometric similarity across three different scales to improve scale-up procedures for structured liquids.
Acknowledgments
Thanks to Darren Lamb, Emily Robinson, Adam Rowatt and Serena Todd at University of Strathclyde for their work on the development of the 3D printed rheometer geometries as part of a Master’s project collaboration with Unilever.
A limitation of the previous work is that a vane geometry is not representative of the typical geometries used to manufacture structured, high viscosity liquids, which comprise of close clearance designs such as anchor or helical ribbon. Thus, to improve the geometric similarity between rheometer scale (40 g), lab (2 kg) and pilot scale (50 kg), typical agitator designs were designed and fabricated via 3-D printing. The four designs chosen were a 4-bladed vane, a commercially available TA helical ribbon, and two 3D printed geometries (helical ribbon and anchor). This enabled exploration of the differences in mixing and viscosity measurement in the formulation of lamellar structured liquids using these different geometrically similar geometries, at different scales.
A TA instruments DHR-II rheometer was used prepare and characterise a model lamellar structured liquid according to the formulation and methods outlined in Cunningham et al. (2021). The samples were prepared with the four geometries and characterised by measuring flow curves and the yield stress after samples had aged for at least 24 hours.
Differences were observed in the viscosity profiles of the lamellar structured liquids prepared with the different geometries under the same processing conditions, which may be ascribed to different mixing profiles within the vessel. This was also reflected in differences in the final rheological properties of the samples. This work highlights the importance of mixing profile and efficiency in the generation of the LGN structure at a rheometer scale. Furthermore, the use of 3D printed geometries has improved geometric similarity across three different scales to improve scale-up procedures for structured liquids.
Acknowledgments
Thanks to Darren Lamb, Emily Robinson, Adam Rowatt and Serena Todd at University of Strathclyde for their work on the development of the 3D printed rheometer geometries as part of a Master’s project collaboration with Unilever.