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)

Speaker: Dr. Michael Papantonakis, US Naval Laboratory The diverse spectrum of sorbent materials in use today reflect the contributions of various physical and chemical properties, whether those physical or chemical properties are intrinsic to the materials or the result of directed modifications. This talk will describe the characterization of a number of sorbent materials developed for a program targeting a broad class of hazardous chemicals including chemical warfare agents and toxic industrial chemicals. Inverse gas chromatography was one tool used to characterize the materials developed for this program, evaluating how well they achieved the program goals of preferential sorption of certain target chemicals or chemical classes and insensitivity to potential clutter material such as humidity or hydrocarbons. Testing the sorbent materials at different stages of sorbent development allowed the effectiveness of the functionalization strategies to be assessed. The IGC results will be compared to other conventional analytical techniques employed in the program.

Speaker: Dr. Richard Durand, Sun Chemical Formulated products such as inks and coatings require the management of a variety of material choices to attain the desired performance outcome. It is important to define material property relationships to key performance attributes for the formulated product. An in-depth knowledge is needed of the surface and various physicochemical properties of many different solids, polymer materials within a formulation as well as an additional set of relevant material properties of substrate surfaces. These details are critical to understanding processing and post application relationships like wettability, dispersion, adhesion, etc. Several examples of how IGC can provide insight into properties that may be underlying drivers for performance are discussed. Examples of studies involving pigments and substrates are described.

Speakers: Dr. Stephanus Axnanda, Merck In the pharmaceutical industry, the physical properties of a crystalline drug substance are very important to understand. In particular, the amorphous and crystalline content of an API may impact processing, storage, formulation and absorption . Furthermore, pharmaceutical materials can exhibit polymorphism, and bulk crystalline characterization techniques such as XRPD, thermal analysis, and solid-state NMR have been successfully applied in understanding crystallinity of pharmaceutical components. However, surface effects easily escape detection with these commonly used laboratory techniques. In some cases, disorder or amorphous content may have a disproportionately greater effect on drug substance and drug product performance attributes (stability, dissolution kinetics, etc.). The ability to differentiate surface and bulk crystallinity will be an important characterization aspect in developing a robust pharmaceutical product. With the use of a surface characterization technique to study surface crystallinity, better understanding of solid-state properties of pharmaceutical components will be achieved. iGC will be used to correlate the surface and bulk crystallinity of pharmaceutical materials (lactose) by comparing the surface energy of lactose in different crystallization forms.

Speakers: Dr. Jeremiah Woodcock, NIST Cellulose nanomaterials (CN) shows great promise for commercial applications in a broad range of products including paper, polymer composites, electronics, paints, concreate, and insulation. A wide variety of chemistries have been developed to label and track these CN. This includes the use of such reactions as dichlorotriazine/alcohol, Schiff base, and esterification reactions with good success. However, many of the labeling strategies result in a significant change in surface energy of the cellulose. In such as food packaging, drug delivery systems, and biocompatibility, these changes are not desirable. A significant enough change in surface energy results in different adhesion characteristics which can have adverse effects not readily forecasted. To this end, characterizations tools that can track extent of surface modification at nanomolar concentrations of the bulk material are needed. In this work, the surface of cellulose nanofibers was modified using 13C enriched ethyl iodide using a heterogenous process of gas phase reagent and concentrated solution of substrate. The gas phase ensures uniform coverage of the substrate and the ability to control small concentrations in a give volume. The modification of surface energy was monitored using iGC-SEA and quantified with 13C solid state NMR. The iGC was found to be quite sensitive to these small changes in surface chemistry.

Speaker: Dr. Elizabeth Denis, Pacific Northwest Laboratory The overall goal of this work is to better understand the chemistry of gas-media interactions and how volatile compounds are transported through geological materials. Inverse gas chromatography (iGC) allows us to characterize and quantify the physicochemical properties of powdered solid samples (e.g., soil and sand) of various mineralogical makeup and grain sizes. The results help to decipher sorption effects for geologic materials under different temperature and humidity conditions. Complementary to our commercial iGC (SMS iGC-SEA) with a flame ionization detector, we developed an in-house iGC coupled to a mass spectrometer that will help us to evaluate compounds that are in the gas-phase at room temperature and non-carbon probe gases. Geologic materials can be very heterogeneous both physically and chemically. Characterizing the properties of individual organic and inorganic components can help elucidate the primary factors influencing volatile interactions in more complex mixtures. Based on our collected heat of sorption values, soil and bentonite clay have greater sorption to non-polar alkanes than simpler single mineral media (quartz sand, salt, calcium carbonate). The interactivity of soils and clays are likely heightened by the variety of bonding sites in the complex structures compared to the single mineral media. For diffusion coefficient, we have observed a positive correlation with temperature and that there is less variability in results between samples of homogeneous sorbent material than heterogeneous soil. This talk will discuss the capabilities and potential challenges of characterizing physicochemical properties of geological materials using iGC.

...IGC and Continuous Processing of Powders Through the Relation with Other Powder Properties Speaker: Dr. Gerardo Callegari, Rutgers University Understanding the relationship between material properties, process parameters, and product performance is the key technical element needed to model, design, optimize, and control a manufacturing process. This is especially useful in continuous manufacturing where the process is usually at a state of control. To accomplish this, system responses are usually semi-empirically related to powder “bulk” material properties as density, flowability and electrostatic behavior. Here, we are seeking to relate bulk properties to more fundamental properties at the particle scale, as surface energy and particle size. This allows for a more mechanistic understanding of those relations.  In doing so, we also discuss some of the possible problems associated to using IGC to measure the polar components of the surface energy and, in some cases, how to overcome them.

...High-Performance in Microplastics by Surface-Coating with Amphiphilic Janus Nanocellulose Speaker: Dr. Tetsuo Kondo, Kyushu University A facile and unique process for nanocellulose/polypropylene (= PP) composites with a higher impact strength has been attempted. It was allowed via “cell wall cell plastics” by surface-coating of microplastic particles with amphiphilic Janus nanocellulose prepared by the aqueous counter collision (= ACC) method. Amphiphilic ACC-nanocelluloses were spontaneously adsorbed onto PP micro-particles by 0.03 wt.% only by mixing in water under an ambient condition. Their surface PP region exhibited the melting point depression to 155°C from that for neat PP. Following the nanocellulose-coated PP particles were pre-compressed at 155°C, the PP particles were connected with ACC-nanocellulose by the formation of 3D networked closed honeycomb structures. Then, the closed honeycomb network of ACC-nanocellulose played a role as a scaffold for further melting and subsequent crystallization of the core PP domains. The molded nanocellulose/PP composites exhibited an increase in impact strength by 30-40%, as well as an increase in Young’s modulus and tensile strength, despite 0.03 wt.% of nanocellulose content. This suggested that PP was efficiently reinforced by nanocellulose-honeycomb framework structure embedded in the composite.

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.