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

Speaker: Dr. Maria Holuszko, University of British Columbia Flotation is the main concentration process for recovery of valuable minerals, and it has been successfully applied for more than hundred years in mining industry. In simple terms, in froth flotation mineral particles are made hydrophobic by adsorption of chemical reagents referred to as collectors then the hydrophobic minerals are attached to the air bubble and carried over to the top of the flotation cell to be collected as a concentrate. In flotation, many interfacial interactions occur between gas/liquid/solid (mineral) surface molecules. The interfacial behavior of minerals is controlled by the surface energy of the mineral (solid). The wetting process occurs when the adhesion force between a solid-mineral and liquid is greater than the cohesion force between the liquid’s molecules while non-wetting (hydrophobicity) condition is required for flotation (Leja, 1983). Many methods have been developed to study the wetting characteristics of minerals relevant to flotation. Some of these methods include contact angle, film flotation, displacement pressure, and penetration rate, heat of immersion, immersion/sink time, imbibition time, and induction time measurements of fine powders (Buckton, 1990; Good and Li, 1976; Arkhipov et.al.2011). However, there are many limitations to each of the methods, and in all of these methods physical properties of particles like size, shape affect the final results, while surface energy of solids can provide good means for evaluation of degree of hydrophobicity for particulate solids. In addition, IGC system was shown to be successfully used to map the surface energy of mineral particles and provide parameters to evaluate their wettability independently of minerals’ physical characteristics. It has been shown that the surface energy distribution i.e.  the distribution of dispersive and acid/base surface energy components can be used for correlation with the addition of reagents and response of minerals in flotation (Ali et al. 2013; Mohammedi-Jam et al., (2014). In addition, the hydrophilicity index can be derived to assess the surface properties of heterogeneous minerals systems such as coal (Niu et al., 2018). Froth flotation has also been used to recover various types of plastic from their mixtures (Wang et al., 2013; Wang et al., 2015. Plastic flotation is usually used for selective separation for the purpose of reuse or to obtain a pure quality product (Fraunholcz, 2004; Shent et al., 1999). In mineral flotation, the challenge is typically in making the minerals’ surfaces selectively hydrophobic. While in plastic flotation the opposite is true, since most of the plastic polymers are highly hydrophobic, plastic surfaces need to be made selectively wettable-hydrophilic if an efficient separation of different plastics is required. In plastic flotation, a variety of depressants are usually studied to facilitate selective bubble-particle attachment while exploiting differences between surface energy of various plastic polymers for achieving selectivity (Buchan, R., & Yarar, B. (1995). The attempts are also made to investigate the mechanisms of their adsorption on different plastics and the IGC can be used to facilitate development of such understanding. The presentation will review practical application of IGC in flotation as applicable to mineral processing as well as in flotation of plastic and non-metal fractions from e-waste recycling streams.