iGC Symposium Online 2021

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.

Speakers: Sk Faisal Kabir & Ellie Fini Abstract: This study examines the merits of surface activation of rubber using various bio-oils to improve rubber-asphalt interaction. To do so a hybrid method combining microwave irradiation and bio-chemical treatment was used to graft biomolecules onto the exterior surface of the rubber. Five surface activated rubbers were prepared using waste vegetable oil, wood pellet, miscanthus, corn stover, and castor oil. The effectiveness of each oil was examined by measuring the chemisorption of the bio-oil and elastic recovery of bitumen containing rubber particles treated with each bio-oil. Our quantum-based density functional theory calculations showed presence of both physical and chemical interactions between polar aromatic components of bio-oils and rubber. Among studied bio-oils, wood-based bio-oil found to have the highest content of polar aromatics such as phenolic resins leading to its enhanced interaction with rubber. This was evidenced in percent recovery, which was nearly doubled (from 13% to 24%) when wood-based bio-oil molecules were grafted onto the surface of rubber. Overall, wood-based bio-oil was shown to adsorb well to the rubber surface and reduce its tendency to separate from bitumen by 82%. The study results showed how composition of bio-oil affects its efficacy to activate rubber surface. It also proved the technical merits of using surface activated rubber to reduce segregation between rubber and bitumen which commonly occurs in rubberized asphalt. Therefore, the outcome of this study promotes recycling of waste tire to promote sustainability in pavement construction.

... 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

... Heat of Sorption Derived Solubility Parameter Speaker: Dr. Anett Kondor, Surface Measurement Systems Inverse gas chromatography (IGC) is a rapid technique to determine thermodynamic parameters of gas–solid interactions and to characterize physicochemical properties of solid substrates. IGC offers its applicability where it is difficult and even impossible to characterize the surface of some forms of solids (powders and grains) by means of other popular techniques as wetting method or FTIR. Actually, the solids and liquids in every form can be easily studied by means of IGC [1]. High Temperture Measurements Adsorption isotherm data of some alkyl aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) measured in the temperature range of 423–523 K on a partially dealuminated faujasite type DAY F20 zeolite by inverse gas chromatography. The temperature dependent form of Tóth’s equation has been fitted to the multiple temperature adsorption isotherms. The gas–solid equilibria and modelling were interpreted on the basis of the interfacial properties of the zeolite, by dispersive, specific and total surface energy heterogeneity profiles and distributions of the adsorbent measured by surface energy analysis. Solibility Parameter Analysis Determination of solubility parameter for solid materials by means of inverse gas chromatography is based on the model of adsorption described by Snyder and Karger and requires the knowledge of value of adsorption energy (EA) or Heat of Sorption determined from temperature dependence of specific retention volume [1]. References [1] A. Voelkel et al., Inverse gas chromatography as a source of physiochemical data, Journal of Chromatography A., 1216 (2009)