iGC Symposium Online 2021

Speaker: Dr. Kristian Waters, McGill University

Speaker: Alina Dumitru, Imperial College London Abstract: Achieving optimal powder flow in pharmaceutical powder processing is often a challenge due to handling fine, cohesive excipients and APIs (Valverde, et al. 2000). Generally, poor flow behaviour is encountered with small particles due to the strong interparticle interactions associated with such systems (Zhou, et al. 2011). Although particle size contributes greatly to explaining powder flow patterns, it is thought that surface chemistry can play a significant role in underpinning powder flow behaviour for many formulations in the pharmaceutical sector. This study was designed to systematically focus on the effects of surface chemistry, and in turn surface energy, on the powder flow performance of four model systems prepared through controlled surface functionalisation of D-mannitol powders. IGC was used as a physical characterisation method to assess the surface energy and thus chemical alterations undertaken on D-mannitol, as well as the surface area. Powder flow performance was assessed using the FT4 Powder Rheometer, where dynamic, bulk and shear properties have been analysed. It was found that the surface chemistry can be responsible for altering the flow properties of these powders, whilst other key material attributes such as particle size distribution or particle morphology remain unchanged. Increasing the hydrophobic character of the samples, a positive correlation was observed in the total flowability energy, where less energy was required to instigate powder flow for lower surface energy functionalisations, such as phenylated-mannitol and methylated-mannitol. A key finding which can surely present broader implications for many pharmaceutical powders was seen with the fluorinated powders developed, where the electrostatic charge associated with this superhydrophobic sample, overwhelmed the low surface energy character of the fluorinated sample. This work emphasises the importance of investigating a broader range of powder surface chemistries as well as developing a deeper understanding of the electrostatic behaviour of powders which have fluorinated surface groups.

... and modified starch powders Speaker: Dr. Rodolfo Pinal, Purdue University Starch is widely used in the pharmaceutical and food industries. The utility of starch is due to its versatility; it is a type of material that can provide different specific functions directly linked to the performance of the pharmaceutical or food product. The digestibility and powder flow properties of starch are two areas of considerable interest in industrial applications. Material properties affecting the digestibility of starch are critical to drug and nutrient release in pharmaceutical and food products, respectively. Starches from different sources were compared for their physical and functional attributes in this study, covering digestibility and powder flow properties. In the digestibility investigation, the different starches were very similar to each other in terms of particle size and water sorption isotherms. Surface energy analysis using IGC indicated that the digestibility of the starches correlates with the relative magnitude of the dispersive surface energy. Further analysis using XPS was applied in order to discern and rank order the specific type of functional groups associated with the digestibility of the starch. It was found that the rank order of digestibility follows the rank order of the hydrophobicity of the carbon-bearing functional groups exposed on the surface of the powder. Regarding the flow properties of starch powder, the investigation utilized a set of commercially available grades of modified starch. All but one of the grades of chemically modified starch in the study exhibited X-ray amorphous diffraction patterns. The starches exhibited appreciable differences in their particle size distributions, as well as on their water sorption isotherms. The bulk powders were characterized utilizing standard static and dynamic methods of evaluation for flow properties and related parameters. Surface energy distribution maps using IGC were also obtained for the different lots. Multivariate analysis revealed that the widely used powder-flow related parameters were not the best descriptors of the ability of the starches to freely flow as powders. Instead, the Ka/Kb ratio obtained from the IGC analysis was found to be the descriptor most closely associated with ability of the powders to flow