Rheological characterization of linear low-density polyethylene–Fischer–Tropsch wax blends

The thermal and rheological behavior of blends of a Fischer–Tropsch (F-T) wax with linear low-density polyethylene (LLDPE) were investigated by differential scanning calorimetry and cone-and-plate rheometry. F-T wax is used as a possible low-cost processing aid alternative for LLDPE masterbatch applications. The melting- and crystallization thermograms indicated a two-phase solid-state morphology and full compatibility in the fully molten material. Both the high-melting and low-melting phase contained co-crystalized wax and polymer. Rheological data of F-T wax-LLDPE blends over the full composition range was also obtained. The zero-shear viscosity data was adequately predicted by the Friedman and Porter mixing rule: $\mathrm{\eta }={\left(w_p{\mathrm{\eta }}_p^{1/\mathrm{\alpha }}+{w_w\mathrm{\eta }}_w^{1/\mathrm{\alpha }}\right)}^{\mathrm{\alpha }}$ with α = 3.4. This implies that the melt viscosity is dominated by the effects of polymer chain entanglement and that the main consequence of adding the wax is to reduce the concentration of the polymer present. The complex viscosity also fitted this model albeit with α = 4.81. All Han plots, that is, plots of the logarithm of the storage modulus (G') against the logarithm of the loss modulus (G"), were linear. Within the experimental uncertainty, they were essentially unaffected by variations in blend composition, temperature and the applied angular frequency. Additionally, Cole–Cole plots were also in agreement that wax-LLDPE blends are miscible at melt state. This supports full miscibility of the F-T wax-LLDPE blend system down to temperatures as low as 120°C.     

Tailor‐made controlled rheology polypropylenes from metallocene and Ziegler–Natta resins

Production of controlled rheology polypropylenes (CRPPs) is practiced industrially by modifying existing commodity Ziegler–Natta resins through peroxide‐induced β‐scission reactions, resulting in materials with controlled rheological properties and accompanying narrower molecular weight distributions (MWDs). In this work, this methodology was studied using both metallocene‐based polypropylenes (mPPs) and Ziegler–Natta‐based polypropylenes (ZN‐PPs). Numerical simulations based on a previously proposed kinetic model indicated that the nature of the starting resin has a significant effect on the control of MWD polydispersity index (PDI) and weight‐average molecular weight ( ${\overline{M}}_W$) of the resulting CRPP. Based on these observations, experiments were carried out to demonstrate the feasibility of producing CRPP with targeted molecular and rheological characteristics. Commercial mPP and ZN‐PP resins were selected to produce CRPP with similar ${\overline{M}}_W$ or melt flow rates (MFRs) but varying PDIs. The rheological properties and MWDs of these materials were evaluated through oscillatory shear and gel permeation chromatography (GPC) measurements and their extrusion behavior was briefly studied and assessed with respect to these properties. POLYM. ENG. SCI., 59:1114–1121 2019. © 2019 Society of Plastics Engineers     

Insight of molecular interactions between short-chain tetraalkylammonium bromides and cetyltrimethylammonium bromide: A spectroscopic and thermodynamic approach

The influence of tetraalkylammonium salts, viz., tetraethylammonium, tetrapropylammonium, and tetrabutylammonium bromides (0.005, 0.010, 0.015 mol kg⁻¹) on the micellar behavior of aqueous solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB, 0.2–2 mmol kg⁻¹) over the 298.15–313.15 K temperature range has been studied by conductometric method. From conductivity versus surfactant concentration plots, the critical micelle concentration (CMC) of CTAB has been determined, which shows that the tetraalkylammonium bromides promote the formation of CTAB aggregates. Further, from the temperature dependence of CMC values, the degree of ionization, the counterion binding constant along with some thermodynamic parameters of micellization, such as standard free energy change ($\mathrm{\Delta }{G}_m^o$), standard enthalpy change ($\mathrm{\Delta }{H}_m^o$), standard entropy change ($\mathrm{\Delta }{S}_m^o$) have been calculated. From the values of $\mathrm{\Delta }{G}_m^o$, $\mathrm{\Delta }{H}_m^o$ and $\mathrm{\Delta }{S}_m^o$, it has been concluded that our ternary system is both enthalpy as well as entropy controlled. Similar CMC values were obtained from UV–Visible spectrometry measurements, using pyrene as a probe at ambient temperature. Also ¹H-NMR and FTIR methods give a greater understanding of the molecular scale interactions between the tetraalkylammonium bromides and the cationic surfactant.     

General correlation for pressure drop through randomly-packed beds of spheres with negligible wall effects

Pressure drop in fixed beds has been studied for over a century and a large number of conflicting correlations exist in the literature. Contributing factors to these differences include the use of particles of different shapes, the presence of wall effects in beds of low tube-to-particle diameter ratio (N) and parameter fitting over limited ranges of modified Reynolds number ${\mathit{Re}}_m=\frac{\mathit{\rho v}{d}_p}{\mu \left(1-\epsilon \right)}$. The present work, in contrast, considers the entire Reynolds number range for perfect spheres in unbounded (high-N) random-packed beds. An asymptote-based correlation has been developed based on published data for extremely high ${\mathit{Re}}_m$ and on new particle-resolved computational fluid dynamics (PRCFD) results for extremely low ${\mathit{Re}}_m$. The resulting equation is given by: $\frac{∆P}{L}\frac{d_p}{\rho v^2}\frac{{\epsilon }^3}{\left(1-\epsilon \right)}=\frac{160.0}{{\mathit{Re}}_m}+\left(0.922+16{\mathit{Re}}_m^{-0.46}\right)\frac{{\mathit{Re}}_m}{\left({\mathit{Re}}_m+52\right)}$. This equation fits a literature data set of 541 points with average error 5.66%, and shows correct limits for both high and low ${\mathit{Re}}_m$.     

Indirect urea electrooxidation by nickel(III) in alkaline medium: From kinetic and mechanism to reactor modeling

This study consists in the determination of two kinetic laws of urea oxidation (UO) and electrooxidation (UEO) in alkaline media on nickel(III). Two kinds of active sites were examined, the first one derived from a Ni(OH)₂ powder and the second from a massive nickel electrode. Partial orders of nickel(III) (two for UO and five UEO) enable to conclude about (i) the urea adsorption on two nickel(III) sites and (ii) that a multistep oxidation of urea occurs involving five nickel(III) site electroregenerations. A multipathway mechanism is also proposed to explain UEO facilitated by the nickel(III)/nickel(II) mediation system, and to predict the by-products' formation previously identified ($\mathrm{N}{\mathrm{O}}_2^{-},\mathrm{N}{\mathrm{H}}_3,\mathrm{OC}{\mathrm{N}}^{-},\mathrm{C}{\mathrm{O}}_3^{2-}$). At last, a model combining the UEO kinetic law previously established, with diffusive and convective transport phenomena was developed. A consistent correlation (maximum deviation of 6%) between laboratory electrolysis results with the model' predictions was obtained under different operating conditions, enabling the validation of this model.     

Tunable size and shape of conductive poly(N‐methylaniline) based on surfactant template and doping

Poly(N‐methylaniline) (PNMA) is one of the polyaniline derivatives with N‐substituted position. Polyaniline derivatives have attracted attention due to their higher solubility in common solvents than pristine polyaniline, but they still possess lower electrical conductivity. In this work, PNMA was synthesized via chemical oxidative polymerization in an ethanol–water system. The effect of surfactant type, namely anionic sodium dodecylbenzenesulfonate (SDBS), cationic cetyltrimethylammonium bromide and non‐ionic Tween20, on the electrical conductivity, doping level and morphology was investigated. PNMA prepared with the SDBS system possessed the highest electrical conductivity among the obtained PNMAs with and without surfactants. The effect of $N_{{\mathrm{\text{HClO}}}_4}$/N_NMA dopant mole ratios on the re‐doping, crystallinity, morphology and particle size was also examined. Using an $N_{{\mathrm{\text{HClO}}}_4}$/N_NMA mole ratio of 10:1 in the re‐doping process provided the highest electrical conductivity of 15.53 ± 2.5 S cm^?1, a doping level of 55.59%, along with hollow spherical particles with the thinnest membrane. Electron microscopy images revealed that the morphology of PNMA particles depended mainly on the surfactant type but not the $N_{{\mathrm{\text{HClO}}}_4}$/N_NMA mole ratio. © 2019 Society of Chemical Industry     

The critical mass for the unconfined vapour cloud explosion of compressed and liquid hydrogen

The (unconfined) vapour cloud explosion (VCE) is a dramatic phenomenon that generates a severe pressure wave with a high potential to damage assets and produce injuries in the far field. This definition applies also to hydrogen. Nevertheless, no clear tools and methodology have been so far developed and tested for this highly reactive gas, and even advanced numerical simulations lack validation and suffer from large uncertainties. In this view, the comprehension of the physic which subtends this dramatic phenomenon for the specific case of hydrogen is still a central issue. This paper revises some of the most adopted theories on VCE based on classical acoustic theory and models for pressure wave propagation and provides a consequence-based, threshold (minimum) value for the critical mass of hydrogen $m_f^{\text{crit}}\left(4.0\mathrm{kg}\right)$ which is needed—at a stoichiometric concentration in air—for a vapour cloud to behave as a VCE. To this regard, any non-stoichiometric hydrogen concentration in air or lower amount of hydrogen would decrease either the flame Mach number $M_{\mathrm{f}}$ or the total energy, thus resulting in negligible overpressure. In this sense, the effects of buoyancy, diffusivity, and weather conditions on the dispersion of hydrogen should be taken into account. The results are valid either for compressed or cryogenic liquid tanks and can be adopted for the sake of distinction between hydrogen flash fire and VCE; for the hazard analysis of hydrogen production and storage; and more in general for the risk assessment of hydrogen systems.     

Phase transition of hafnon,HfSiO4, at high pressure

The high-pressure behavior of hafnon has been systematically investigated by combining in situ synchrotron X-ray diffraction, Raman, high-resolution transmission electron microscopy (HRTEM) techniques, and theoretical simulations. Hafnon starts phase transition at 26.6 GPa and completes the transition to an irreversible scheelite phase ($I{4}_1/a$, Z = 4, a₀ = 4.712 Å, and c₀ = 10.378 Å) at ∼45 GPa. The HRTEM observation of an interface between hafnon and scheelite phases allows atomic scale understanding of the transition process with a relationship of (200)_h‖(112)_s, ${(00\overline{2})}_{\mathrm{h}}\parallel {(\overline{1}10)}_{\mathrm{s}}$//, and ${[010]}_{\mathrm{h}}\parallel {[\overline{1}\overline{1}1]}_{\mathrm{s}}$. Hafnon shows a significantly lower transition pressure (∼12.6 GPa), as calculated from the relative enthalpies, than the measured pressure (∼26 GPa), indicating a kinetically hindered process involved in the transition. A high pressure low symmetry phase in hafnon ($I{\overline{4}}_{2}d$) is identified by the simultaneous appearance of two Raman modes (∼75 and 450 cm⁻¹) at 26.6 GPa and their subsequent simultaneous disappearance at 36.7 GPa. These results are important to understanding the mechanism of the zircon-scheelite transition for both zircon and hafnon.     

Modelling and parameter estimation of trans-β-farnesene coordination polymerization

trans-β-Farnesene is a bio-derived terpene monomer that can polymerize, generating polymers with properties that can be similar to the properties of conventional petroleum-derived polymers. For this reason, in the present study, several coordination polymerizations of trans-β-farnesene are carried out using the Ziegler–Natta catalyst system composed by neodymium versatate (${\mathrm{NdV}}_3$), diisobutylaluminum hidride (DIBAH), and dimethyldichlorosilane (DMDCS) in order to evaluate the influence of key operation variables on the control of average molar masses and monomer conversion. A phenomenological model is proposed to describe the coordination polymerization of trans-β-farnesene, and the kinetic parameters required to simulate the reactions are estimated. The initial concentration of DIBAH used as a chain transfer agent (CTA) is calculated by a data reconciliation procedure since this very active compound can participate in undesired side reactions. It is shown that the initial monomer, DIBAH, and ${\mathrm{NdV}}_3$ concentrations exert strong influences on the monomer conversion and average molar masses of (poly)farnese while the temperature effect is not so pronounced. The proposed kinetic mechanism was able to predict well the experimental data collected during the reactions, with the successful reconciliation of CTA concentrations and estimation of model parameters.     

X-ray characterization of three possible edible oleogelators: Experiment and theory

Three oleogelator molecules (Triacontane (TC), Stearic acid (SA), and Behenyl Lignocerate (BL)) were studied individually, in pairs, or all together to make an oleogel using triolein as the oil. WAXS, SAXS and USAXS were used to elucidate the solid structures from angstroms to a few micrometers. A two-dimensional mapping of atomic positions for each molecule was carried out to understand the crystalline multilayer structures formed. We assumed that the molecules were rigidly extended and that they underwent no significant (hindered) rotations so that the free energy is determined by the Lennard-Jones interactions of closely packed multilayers. TC molecules were predicted to form a tilt angle of ${\theta }_t\approx 33°$, yielding a SAXS line at $q\approx 0.194$ Å^─1, in acceptable agreement with the measured $q=0.181{\AA }^{-1}$. For SA crystals ${\theta }_t\approx 33°$ (predicted) yielding a SAXS line at $q=0.150{\AA }^{-1}$ compared to $q=0.159{\AA }^{-1}$ (observed). No mixed crystals were observed for any pair of molecules or when all three were used. USAXS data showed that SA forms large nanocrystals compared to TC and BL. All three combinations of molecular pairs showed basic scatterers smaller or similar to those of individual molecules. The theory presented here, together with the experimental results, showed why no mixed crystals are formed from two or all three molecules. Data from the USAXS region suggested that, when using all three molecules, a more compact fractal structure was obtained, compared with those if one or two of the molecules were used.     

Influence of weak electrostatic charges and secondary flows on pneumatic powder transport

The dynamics of the transported powder determines the functionality and safety of pneumatic conveying systems. The relation between the carrier gas flow, induced by the flown-through geometry, and the powder flow pattern is not clear yet for electrostatically charged particles. This paper highlights the influence of relatively minor cross-sectional secondary flows and electrostatic forces on the concentration and dynamics of the particles. To this end, direct numerical simulations (DNS) capture the interaction of the continuous and dispersed phases using a four-way coupled Eulerian–Lagrangian strategy. The transport of weakly charged particles in channel flows, where turbopheresis defines the particle concentration, is compared to duct flows, where additional cross-sectional vortices form. For both geometries, the Stokes number ($St=8,32$) and the electrical Stokes number (${\mathit{St}}_{\mathrm{el}}=\left[0,1,2,4\right]\times {10}^{-3}$) are varied, and the turbulent carrier flow was fixed to ${\mathit{Re}}_{\tau }=360$. The presented simulations demonstrate that secondary flows, for the same ${\mathit{Re}}_{\tau }$, $St$, and $S{t}_{\mathrm{el}}$, dampen the effect of particle charge. In a duct flow, vortical secondary flows enhance the cross-sectional particle mobility against the direction of electrostatic forces. Compared to a duct flow, in a channel, the wall-normal aerodynamic forces are weaker. Thus, electrical forces dominate their transport; the local particle concentration at the walls increases. Further, electrostatic charges cause a stronger correlation between the gas and particle velocities. In conclusion, despite being weak compared to the primary flow forces, secondary flow and electrostatic forces drive particle dynamics during pneumatic transport.     

Computational fluid dynamic study of polycaprolactone nanoparticles precipitation in a co-flow capillary micro-tube

Polycaprolactone nanoparticles (NPs) were produced in the co-flow glass capillary device with $250\mathrm{\mu m}$ tip dimension. NPs size was 990 nm for continuous phase velocity, and $u_c=0.05\mathrm{m}/\mathrm{s}$ and 426 nm for $u_c=0.2\mathrm{m}/\mathrm{s}$. The droplet formation process in the co-flow microchannel was also simulated using computational fluid dynamic (CFD). Employing a digital image analysis technique, a cut-off value of 0.81 for the dispersed phase volume fraction was proposed for the determination of droplet size. A scenario was expressed for NP formation from micro-droplets. Moreover, after conducting 27 CFD simulations, a dimensionless exponential form correlation was proposed for droplet size estimation. In this generalized map, there were three distinct regions based on the relative capillary numbers of continuous to dispersed phases. It was revealed that at a constant dispersed phase velocity, by increasing the continuous phase velocity, more small NPs are formed. The results show that the ratio of micro-droplets to NPs size was between 735 and 755.     

Double Smoothed Volatility Estimation of Potentially Non-stationary Jump-diffusion Model of Shibor

The occurrence-50 of economic policies and other sudden and large shocks often bring out jumps in financial data, which can be characterized through continuous-time jump-diffusion model. In this article, we present the double smoothed non-parametric approach for infinitesimal conditional volatility of jump-diffusion model based on high frequency data. Under certain minimal conditions, we obtain the strong consistency and asymptotic normality for the estimator as the time span T → ∞ and the sample interval ${\mathrm{\Delta }}_n\to 0$. The procedure and asymptotic behavior can be applied for both Harris recurrent and positive Harris recurrent processes. The finite sample properties of the underlying double smoothed volatility estimator are verified through Monte Carlo simulation and Shanghai Interbank Offered Rate in China for application.     

Prediction of the photofading of 1-H or 1-ethyl derivatives of 3-cyano-6-hydroxy-4-methyl-5-(p-X-phenylazo)-2-pyridone dyes and their azo-hydrazone tautomerism: A theoretical study

The lightfastness calculations for photofading of monoazo pyridone dyes were performed. For this purpose, all-valence molecular orbital method PM3 was applied. Frontier electron density distribution on the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was examined. The obtained parameters seem to reflect the tendency for an electrophilic attack with a singlet oxygen (¹O₂) atom or a nucleophilic attack with superoxide anion (O₂^●─) on a particular atom in a molecule. Reactivity indicators for superdelocalisability ($S_r^{\mathrm{E}\left(\mathrm{N}\right)}$) and electron density distribution in ground and excited state were calculated. Superdelocalisabilities enable the fastness values to be explained in different chemical molecules depending on tautomeric forms in which they may occur.     

Mixing rules for high density polyethylene-polypropylene blends

High-density polyethylene (HDPE) and polypropylene (PP) blends of varying composition have been evaluated in an effort to establish a mixing rule for melt flow index (MFI). In addition, a previously established relationship between MFI and $\overline{M_w}$ for linear polymers was also evaluated for these blends. It was found that a parabolic relationship existed between the composition (by weight fraction) and MFI and that the MFI and $\overline{M_w}$ relationship held for this set of polymeric materials. Additionally, all properties and relationships were evaluated over five extrusion cycles, which showed minimal to no deviations over the five cycles.     

Defect mechanisms,oxygen vacancy trapping ability in rare-earth doped BaTiO3 from first-principles and thermodynamics

The defect mechanisms of rare earth (RE) doped BaTiO₃ have a strong impact on the electrical performance of the multilayer ceramics capacitors (MLCCs). Oxygen vacancy is the main reason for the device degradation over longtime use, while the effect of the doping strategy on controlling the oxygen vacancies is not yet quantitatively understood. In this work, the grand canonical thermodynamic defect model based on first-principle calculations is applied to evaluate the defect mechanism of RE-doped BaTiO₃ under practical experimental condition. The charge compensation and prior site occupancy of RE are found not only associated with ionic size but also exhibit transitions with oxygen partial pressure and doping concentration. Furthermore, the oxygen vacancy trapping ability of RE ions is evaluated from the perspectives of thermodynamics and kinetics. The migration barrier among first nearest oxygen sites dramatically changed depending on the RE site occupancy. The large trapping ability is contributed by the relatively large negative binding energy of the defect complex and comparable RE concentrations substituted on Ba and Ti sites. The two conditions can be achieved in amphoteric ions doped systems, while in pure donor doped BT only one of these conditions can be satisfied. Although the self-compensated defect complexes exhibit the highest binding energy, the trapping ability contributed by different defect complexes (${\mathrm{RE}}_{\mathrm{Ti}}^{{}^{\prime }}$, ${\mathrm{RE}}_{\mathrm{Ba}}^{·}$, RE_Ba − RE_Ti) is generally comparable in these systems. This feature of amphoteric RE ions accounts for the improvement of the lifetime and reliability of MLCCs.     

Convective heat transfer coefficient for the side-wall in a fixed bed

Fixed beds are widely used in the chemical and process industry due to their relatively simple yet effective performance. Determining the radial heat transfer at the wall in a fixed bed is crucial to predict the performance of columns. Heat transfer parameters often need to be obtained experimentally. Various Nusselt ${\mathrm{Nu}}_w$ versus Reynolds ${Re}_p$ correlations in literature show considerable scatter and discrepancies. The tube-to-particle diameter ratio $\frac{D_{\mathrm{t}}}{D_{\mathrm{p}}}$ and boundary conditions on the particle surface have been understood to affect heat transfer near the wall by virtue of influence on the near-wall porosity and mixing. In this work, a fixed bed consisting of mono-disperse particles is generated via gravity-forced sedimentation modelling utilizing the discrete element method for a $\frac{D_{\mathrm{t}}}{D_{\mathrm{p}}}$ ratio of 3.3. The system is meshed and imported in a computational fluid dynamics (CFD) solver. Fluid inlet velocity is varied to get ${Re}_p\in \left[1,1500\right]$ corresponding to the laminar and turbulent flow regimes. The particles are treated as boundaries with Dirichlet, Neumann, and Robin boundary conditions applied for the closure of energy balance. Another set of simulations is run with particles modelled as solids with varying thermal conductivities ($k_s/k_f$). The heat flux and volume-averaged fluid temperature calculated during post-processing are used to determine the wall heat transfer coefficient and, subsequently, the wall Nu number. Fifteen ${\mathrm{Nu}}_w$ versus ${Re}_p$ correlations are compiled and analyzed. A new semi-empirical correlation for the wall Nusselt number has been developed for a fixed bed packed with monodisperse spheres for $\frac{D_t}{D_p}=3.3$ and results compared with data published in literature. Additionally, the impact of buoyancy effect on the wall Nusselt number has been studied.     

The evaluation of extensional viscosity of highly filled polyolefins composites films with calcium carbonate

This article reports the results of the extensional viscosity ( ) of polyolefins composites films. The test material was composed of ternary MDPE/iPP/CaCO₃ composites with a calcium carbonate content of 48–72% by mass. The concentrations of the composites and reference materials that were PE‐MD/iPP mixtures are summarized in Table 1. For all materials the viscosity curves (rotational rheometer) and the change in mass flow rate were determined. Two types of investigated films were produced: cast films and blow films. The extensional viscosity of films (thickness ≈ 80 μm) was performed on a SER‐2 Universal Testing Platform. The influence of the addition of calcium carbonate, extrusion techniques and the direction of sample cut (MD and TD) to change the extensional viscosity were discussed. The extensional viscosity measurements ( ) were taken at a temperature of 140°C and for a strain rate (Hencky strain rate) of = 0.1, 0.2 and 0.5 s^?1. POLYM. ENG. SCI., 59:E155–E163, 2019. © 2018 Society of Plastics Engineers     

Investigation of the equilibrium constant of NO absorption into diethylenetriaminecobalt(II) solution

Diethylenetriaminecobalt(II), [Co(DETA)₂]²⁺, formed by diethylenetriamine (DETA) coordinating with Co(II) ion, can be used to remove NO from flue gas. Diethylenetriaminecobalt(II) is capable of binding NO to form metal nitroso complexes. The determination of the equilibrium constant of the reaction between [Co(DETA)₂]²⁺ and NO is important to the development of the technology for the elimination of NO from exhausted gas streams with diethylenetriaminecobalt solution. In this paper, the equilibrium constants of this reaction have been determined by a series of experiments in a bubble reactor at the range of 30–70°C under atmospheric pressure in the [Co(DETA)₂]²⁺ solution of pH 7.5. All experimental data are in good agreement with the following equation: $K\left(\mathrm{T}\right)=1.8619\times {10}^{-6}\exp \left(\frac{4677.52}{T}\right)\left(\mathrm{L}\cdot {\mathrm{mol}}^{-1}\right)$, where the changes in enthalpy and entropy are ΔH⁰ = −38.89 kJ ⋅ mol⁻¹ and ΔS⁰ = −109.7 J ⋅ K⁻¹ ⋅ mol⁻¹, respectively.