Phase equilibria effect on catalytic olefin polymerization

There are many reasons why phase equilibria during the catalytic polymerization are important and why many researches are interested in exploring them. In any type of catalytic polymerization (solution, slurry, gas-dispersion) the proportional relation of the monomer concentration at the active catalyst site to the polymerization rate is essential. Phase equilibria between a solvent, polymer, monomer(s) and co-monomer(s) and related transport processes are important not only for the polymerization kinetics itself, but also the polymer structure formation or subsequent product degassing are closely related to them. Nowadays many experimental techniques are available (e.g. DSC with pressure cell, low-field NMR, (co-)sorption balances), thus the thermodynamics of polyolefins is persistently studied and a lot of new quantitative knowledge about polyolefin thermodynamics was accumulated. But still there is a need for new data required by new or existing production processes and new grades of polyolefins. In this contribution we present data relevant for gas-phase and slurry polymerization, i.e. sorption equilibria of polymer/solvent(g) and polymer/diluent(l) systems respectively. Sorption of gaseous penetrants in polymer particles was measured by gravimetric method and the results go hand in hand with swelling data measured in video-microscopic apparatus. Thus we gradually developed a huge database of experimental results including sorption of commonly used hydrocarbon penetrants (C2-C7) in various polyethylene and polypropylene samples (covering the full spectrum of commercially produced grades) at different temperatures (relevant to polymerization conditions). Moreover, by using a pressure-decay apparatus we are able to determine also kinetic parameter – diffusion coefficient of gases in polyolefin particles. Sorption of liquid penetrants in polyolefins was measured using new methodology developed in our laboratory and we present results for the system polymer (PE or PP) and liquid hydrocarbon (C6-C8). Solubilities are measured at different temperatures. Next we present swelling equilibria of polyolefin particles in various liquid diluents and preliminary results of co-swelling experiments for the system PE-hexane-ethylene are discussed. Podivinská M., Jindrová K., Chmelař J., Kosek J.: Swelling of polyethylene particles and its relation to sorption equilibria under gas-phase polymerization conditions, Journal of Applied Polymer Science, 2017, 45035: 1-7. Chmelař, J., R. Pokorný, P. Schneider, K. Smolná, P. Bělský and J. Kosek (2015). Free and constrained amorphous phases in polyethylene: Interpretation of 1H NMR and SAXS data over a broad range of crystallinity. Polymer 58: 189-198. Chmelař J., Smolná K., Haškovcová K., Podivinská M., Maršálek J., Kosek J.: Equilibrium sorption of ethylene in polyethylene: Experimental study and PC-SAFT simulations, Polymer, 2015, 59: 270-277. Chmelař J., Haškovcová K., Podivinská M., Kosek J.: Equilibrium Sorption of Propane and 1‑Hexene in Polyethylene: Experiments and Perturbed-Chain Statistical Associating Fluid Theory Simulations, Industrial and Engineering Chemistry Research, 2017, 56, 6820−6826

A model of surface roughness effect on triboelectric charging of particles

Tribocharging increases due to deformation and penetration of surface asperities, enlarging the real contact area. These experimental results translate into a theoretical description of particle charging that resolves the surface topology. Based on these findings, we propose a model that predicts the dependence of the particles' saturation charge on the impact velocity and surface roughness.Comment: 5 pages, 4 figure

Evolution of high impact polypropylene morphology upon thermal treatment

Morphology and especially the rubber content and distribution in high impact polypropylene (hiPP) are the crucial factors determining the material mechanical properties such as toughness and impact resistance. The final properties are influenced by the size of rubbery domains and their compatibility with the iPP matrix. The hiPP morphology is affected during each stage of its evolution. During the polymerization, the polymer powder with the semi‑continuous rubbery network is predetermined by the replication phenomenon, where the forming polymer particle copies the catalyst architecture and the rubber phase grows on the catalyst fragments distributed in the homopolymer particle. Thus the principally controlling parameters affecting the particle morphology are the catalyst itself, reaction conditions and the rubber content [1]. On the other hand, during the particle melting in the extruder, the phase separation takes place and the final morphology is governed by the rubber composition and molar weight (i.e., by the viscosity ratio between the polymer matrix and the rubber). The suitable set of accurate characterization methods has to be employed to comprehensively map the heterophase polymer morphology and the appropriate statistical descriptors then allow to objectively describe the polymer overall morphology [2]. For the hiPP morphology mapping, the combination of X‑Ray microCT, AFM and confocal Raman microscopy was employed in our work. This contribution explains the influence of various rubber content and composition (i.e., ethylene/propylene ratio) and various viscosity ratios between rubber and polypropylene matrix on the hiPP morphology. The morphology evolution upon thermal treatment including the phase separation was studied in the wide range of melting times and melting temperatures. Finally, the influence of hiPP morphology on its mechanical properties is demonstrated with respect to various rubber characteristics. ____ [1] Smolná, K., Gregor T., Buráň Z., Kosek J.: Formation and Distribution of Rubbery Phase in High Impact Polypropylene Particles. Macromolecular Materials and Engineering, 2016. 301(4): p. 390-400. [2] Smolná, K., Gregor T., Kosek J.: Morphological analysis of high-impact polypropylene using X-ray microCT and AFM. European Polymer Journal, 2013. 49(12): p. 3966-3976

Vanadium redox flow battery - membrane selection and characterization

The increasing share of renewable energy sources in the total energy production emphasizes the need for a reliable and cheap stationary energy storage. Such a tool allows to baffle hardly predictable non-stabilities in output power of photovoltaics or wind turbines on the power transmission level. Vanadium redox flow battery (VRFB) appears as a promising solution for the stationary energy storage as it offers high efficiency (80% DC-DC), foolproof arrangement of decoupled power (kW) to capacity (kWh), extended durability and fast demand response. However, the broader commercialization of the technology is still obstructed by relatively high investment costs. In redox flow batteries, electrolytes are not stored in the battery construction but in an external tank and are continuously pumped through the battery stack where electrical energy is transformed on inert electrodes into chemical during charging and conversely during discharging. Battery stack is composed of several serially connected cells. Each cell consists of positive and negative half-cells which are mutually separated typically by ion-exchange membrane. In VRFB, both electrolytes comprises vanadium salts dissolved in diluted sulfuric acid (i.e., (VO2)2SO4 and VOSO4 in positive electrolyte and VSO4 and V2(SO4)3 in negative electrolyte). Price of the ion-exchange membrane, one of the key components of the battery stack, represents 5 - 15 % of the overall costs typically. Long term durability of membrane in acidic electrolytes is vitally necessary for VRFB function. Please click Additional Files below to see the full abstract

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements