Mixing Of Blends Research Articles

Discrete element method simulation of binary blend mixing of cohesive particles in a high‐intensity vibration system

AbstractThe effects of processing intensity, time, and particle surface energy on mixing of binary cohesive powder blends in high‐intensity vibration system were investigated via discrete element method simulations. The mixedness was quantified by the coefficient of variation, Cv; lower being better. The mixing rate, which is the speed at which homogeneity was achieved, was inversely proportional to the mixing Bond number, defined as the ratio of particle cohesion to the shear force resulting from the mixing intensity. Results show that both increasing processing intensity and reducing surface energy led to a faster mixing rate. However, the mixedness improved initially as mixing action (the product of mixing rate and mixing time) increased, but later deteriorated upon its further increase. Thus, both mixing rate and mixing intensity need to be tuned for optimum mixing performance depending on the cohesion level of particles; too high or too low mixing action should be avoided.

Description of the Droplet Size Evolution in Flowing Immiscible Polymer Blends.

Control of the phase structure evolution in flowing immiscible polymer blends during their mixing and processing is fundamental for tailoring of their performance. This review summarizes present state of understanding and predictability of the phase structure evolution in flowing immiscible polymer blends with dispersed structure. Results of the studies of the droplet breakup in flow, important for determination of the droplet breakup frequency and of the size distribution of the daughter droplets, are reviewed. Theories of the flow-induced coalescence providing equations for collision efficiency are discussed. Approximate analytic expressions reliably describing dependence of the collision efficiency on system parameters are presented. Available theories describing the competition between the droplet breakup and coalescence in flow are summarized and approximations used in their derivation are discussed. Problems with applicability of available theories on prediction of the droplet size evolution during mixing and processing of immiscible polymer blends, which have not been broadly discussed so far, are addressed.

Polyolefin-Polar Block Copolymers from Versatile New Macromonomers.

A new metallocene-based polymerization mechanism is elucidated in which a zirconium hydride center inserts α-methylstyrene at the start of a polymer chain. The hydride is then regenerated by hydrogenation to release a polyolefin containing a single terminal α-methylstyrenyl group. Through the use of the difunctional monomer 1,3-diisopropenylbenzene, this catalytic hydride insertion polymerization is applied to the production of linear polyethylene and ethylene-hexene copolymers containing an isopropenylbenzene end group. Conducting simple radical polymerizations in the presence of this new type of macromonomer leads to diblock copolymers containing a polyolefin attached to an acrylate, methacrylate, vinyl ester, or styrenic segments. The new materials are readily available and exhibit interfacial phenomena, including the mediation of the mixing of immiscible polymer blends.

Prediction of the yellowing of styrene-stat-acrylonitrile and acrylonitrile-butadiene-styrene during processing in an internal mixer

Abstract The objective of this study was to build a model that can predict the yellowing of styrene-stat-acrylonitrile (SAN) and acrylonitrile-butadiene-styrene (ABS) during processing in an internal mixer. Considering the change of color of SAN and ABS as they degrade, we correlate the yellowing of SAN and ABS to process parameters. We propose a method to represent the energy of mixing of polymer blends in an internal mixer to understand the complex mixing process of materials under different mixing conditions. Indeed, during processing, the properties of polymers could be affected by both thermal and mechanical degradation leading to several mechanisms of degradation. We presented a simplified model “h” taking into account the contribution of each process parameters applied in the internal mixer. Three process parameters were studied: the temperature T, the rotation speed of the blades V, and the residence time t. Thanks to this method of approach, a good correlation between the yellowing of styrenics and the mixing energy in the internal mixer was described. We validated this equation with two polymers: SAN and ABS, and this model can now predict the yellowing of SAN and ABS as a function of the process parameters in an internal mixer.

Flow‐induced crystallization of polylactide stereocomplex under pressure

ABSTRACTAlthough shear and pressure fields always coexist in practical polymer processing, their combined influence on the crystallization behavior of polylactide stereocomplex (SC) is ambiguous due to the limit of experiment device. In that case, a homemade device was employed to prepare samples under the coexistence of shear and pressure and explore the crystallization behavior of SC. Differential scanning calorimetry and synchrotron radiation were used to investigate the combined effect of shear flow and pressure on SC crystallization. The results show that shear flow was helpful for SC formation. Shear flow promoted the phase mixing of the polymer blends and improved the nucleation efficiency of SC. Pressure had a negative effect on SC formation because of the decrease in free volume. Regard to polylactide homogeneous (HC), pressure played a positive role on HC formation. Pressure suppressed the formation of SC network which could impede HC generation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46378.

Air-fuel mixing and combustion behavior of gasoline-ethanol blends in a GDI wall-guided turbocharged multi-cylinder optical engine

The investigation of phenomena involved in gasoline direct injection 4-stroke, 4-cylinder, optically-accessible engine were carried out at part load and speed condition with different ethanol-gasoline blends. The influence of injection pressure on ethanol addition, at percentages of 10%, 50% and 85%, was investigated by conventional and optical diagnostics. Combustion characteristics, such as mass fraction burned, heat release rate and combustion duration were calculated based on in-cylinder pressure curve data, Emissions of UHC, NOX, CO, CO2, and PM were measured. The injection and combustion phase by high spatial and temporal optical measurements were characterized. The spray penetration, and the flame structure and propagation speed were obtained by optical data.The addition of ethanol in gasoline allowed an improvement of engine performance in terms of IMEP and COVIMEP and emissions. In particular, for E50 the better performance was obtained thanks to an earlier vaporization during the injection and a spray almost compact with a higher penetration especially at 100 bar, that avoided the formation of liquid fuel deposits on the piston and subsequently pollutants in the exhaust. Meanwhile, for E85 the spray was characterized by a slower vaporization that created a less homogeneous charge and reduction of the flame front propagation in the late propagation phase. This allows a faster and more efficient combustion with respect to fuels characterized by high gasoline fraction.Finally, E85 and E50 showed higher values of the integral flame luminosity in the first phase of combustion due to the higher flame speed with respect to gasoline one. Moreover, the chemiluminescence imaging confirmed a lower number of diffusive flames with respect gasoline and E10 in the late combustion phase, when the flame burns the fuel film on the piston crown. These results validated the lower emission of UHC and smoke of E50 and E85 with respect to gasoline and E10.

Effect of Diethyl Ether Addition to Palm Stearin Biodiesel Blends on Nox Emissions from a Diesel Engine

Biodiesel is a renewable substitute for mineral diesel and has several advantages those include reduced toxic emissions, biodegradability and good lubricating property. Despite these advantages, many researchers have shown that biodiesel emits higher NOx (Nitrogen oxides) emissions than the conventional diesel. Choice of biodiesel, blends in optimum percentage and reduction of the duration of premixed combustion by shortening the ignition delay period are some of the effective methods to reduce the NOx emissions. An attempt has been made to reduce the toxic emissions using the biodiesel palm stearin and Cetane improver additive DEE (Diethyl Ether). The DEE is added to the palm stearin biodiesel blends B10, B20 and B30 at 0.001%, 0.003%, 0.005% by volume in each case and tested for emissions in a 4 stroke single cylinder diesel engine at different loads and compared with the emissions of sole blends and sole mineral diesel. Results showed that significant reduction in NOx emissions can be achieved with the blends of Palm stearin together with DEE additive and also CO and HC emissions could be achieved with appropriate mixing of blends and additives.

High shear mixing of lactose and salmeterol xinafoate dry powder blends: Biopharmaceutic and aerodynamic performances

This work aimed to investigate the effect of a high shear mixer on the biopharmaceutics and aerodynamic performances of salmeterol xinafoate/lactose blends for inhalation. The influence of mixing energy during blending on powder bulk properties, aerosolisation and in vitro dissolution rate of drug was studied. There was a clear dependence of the blends bulk characteristics on the mixing rate and time that affected the emitted dose. The fine particle dose or respirable fraction of salmeterol xinafoate was favored by the mixing intensity leading to the disaggregation of the drug particles. An important dependence of the extra-fine drug particles on the mixing conditions was determined. The effective dispersion on the carrier particles of the salmeterol xinafoate improved the dissolution rate of the drug from the blend. This was due to the drug particle size distribution in the blend. When the fine particle dose of different blends was dissolved, no differences among the dissolution rates were observed.

Assessing distribution of nanosmears due to mutual interaction of additives in high shear mixing of pharmaceutical blends

The objective of this study was to investigate the mutual interaction behavior of magnesium stearate (MgSt) and colloidal silica (CS) affecting their smear coating phenomena on excipient and active ingredient particles during shear mixing of pharmaceutical blends. Multiple pharmaceutical blends were processed in a v-blender under high shear condition by simultaneously varying the mixing orders of blends and concentration of additives. Uniformity of smeared patterns of additives was found to be affected by the physical and chemical nature of excipient surfaces. Although, an increase in concentration of lubricant in the formulation increased the amount of smeared lubricant coating on surrounding particles, the hydrophobic behavior was found to be predominantly dependent upon the order of mixing of constituent components of additives. More interestingly, prior mixing of the blend with MgSt followed by other components although increased the smearing area, surprisingly decreased the hydrophobic behavior, indicating a strong interaction parametric effect of MgSt with CS. For the first time, this work successfully demonstrated the limits of additive concentration in the blends governing the smearing at nanoscale. A phenomenal increase in nanosmearing area of CS compared to MgSt also prolonged the dissolution of tablets, indicating a strong interaction effect of both additives at nanoscale.

Compatibilization of starch–zein melt processed blends by an ionic liquid used as plasticizer

An ionic liquid (1-butyl-3-methyl imidazolium chloride [BMIM]Cl) was used as a plasticizer in starch, zein and their blends; and compared to glycerol, a classical plasticizer of starch. Thermoplastic plasticized biopolymer materials were obtained by melt processing using a twin screw microcompounder. Such a device allows simulating a twin screw extrusion process on small batches of a few grams, and to evaluate the necessary specific mechanical energy input for native starch destructurization; and the final apparent melt viscosity. Both were shown to be significantly reduced for starch in presence of [BMIM]Cl (compared to glycerol), while zein processing behavior was less sensitive to the plasticizer used. This induces significant starch/zein viscosity ratio differences, which affect melt mixing of the starch zein blends. In starch rich blends, this results in smaller zein aggregates in the case of [BMIM]Cl.The characterization of the materials indicates that, compared to glycerol, the use of [BMIM]Cl leads to less hygroscopicity, a more efficient plasticization of both starch and zein phases and a compatibilization of starch/zein blends.

Effect of mixing time on the bed density, and microstructure of selective laser sintered (sls) aluminium powders

The effect of mixing time on the homogeneity of aluminium powder blends and its SLS processed density and microstructure has been explored with a view to providing a basis for quality control. The degree of mixing of the powder particles was quantified in terms of the standard deviation of the bed density of the blended powder. The accuracy of the degree of mixing of aluminium powder's blends obtained at the optimum blending time of 10 minutes is determined by the powder properties and this significantly influenced the powder's bed density. By increasing the mixing time above 10 minutes, particulate agglomeration which inhibit good packing of powdered particles occurs, thus, sintered density decreases and porosity increases. Therefore, high porosity in the powder bed hinders effective thermal conductivity between aluminium particles, thereby, leading to deterioration of the sintered density and microstructure of the SLS processed samples.

In-line quantification of drug and excipients in cohesive powder blends by near infrared spectroscopy

This work was aimed at investigating the utility of near infrared (NIR) spectroscopy for simultaneous in-line quantification of drug and excipients in cohesive powder blends in a bin blender. A model formulation containing micronized chlorpheniramine maleate (μCPM), lactose, microcrystalline cellulose (MCC) and magnesium stearate (MgSt) was selected for the blending study. An optical head comprising a sapphire window mounted on the lid of the bin was used to collect in-line NIR spectral data of the powder blends. Validated partial least square (PLS) calibration models were used to quantify each component from the NIR spectra of the blends. Additionally, effects of premixing by sieving and high shear mixing and use of an internal prism fixed within the bin on the mixing performance of each component were studied. The statistical results obtained for PLS calibration models and their validation showed the sensitivity of NIR for accurate quantification of blend components. The blend prepared with high shear premixing and with prism achieved uniformity more rapidly than that with high shear premixing but without prism during blending in a bin blender. Premixing using sieving proved to be inadequate for uniform mixing of the blend components as none of the components except MgSt achieved uniform distribution after the preset blending time when blended in the bin blender. This study demonstrated that by high speed sampling and rapid spectral acquisition, distribution of individual blend components can be assessed with high accuracy during blending. Furthermore, high shear premixing facilitated rapid distribution and uniformity achievement of blend components. This technique may be used to monitor the relative distribution of individual blend components in real time and thus, to assess the performance of a bin blender for mixing of cohesive multi-component powder blends during development and production.

THE EFFECT OF TYPE ZEOLITE ON THE GAS TRANSPORT PROPERTIES OF POLYIMIDE-BASED MIXED MATRIX MEMBRANES

The permeation rates of O2, N2, CO2 and CH4 has been studied for polyimide-polyethersulfone (PI/PES) blends-zeolite mixed matrix membranes synthesized in our laboratory. The study investigated the effect of zeolite loading and different zeolite type on the gas separation performance of these mixed matrix membranes. Frequency shifts and absorption intensity changes in the FTIR spectra of the PI/PES blends as compared with those of the pure polymers indicate that there is a mixing of polymer blends at the molecular level. Differential scanning calorimetry measurements of pure and PI/PES blends membranes have showed one unique glass transition temperature that supports the miscible character of the PI/PES mixture. The PI/PES-zeolite 4A mixed matrix membrane with 25 wt % zeolite loading produced the highest O2/N2 and CO2/CH4 selectivity of around 7.45 and 46.05, respectively.

Challenging multiphase complex fluids for applications

Modern processing technology is calling the scientific understanding of dynamic processes, where the science of complex fluids plays a central role. We summarize our recent efforts using the generic approaches of multi-scale physics of complex fluids on apparently irrelevant processes, i.e. the mixing of polymer blends, the processing of thermoplastic(TP) toughened thermosetting(TS) composites using phase separation of TP in TS, as well as the enhanced oil recovery using polymer soft gel. It is emphasized that the thorough physical understanding in multi-scales of time and space through the joint efforts of experiment and theory in each scale is the key issue for the modeling of various processes.

Effect of processing conditions on compatibility of nylon 6/polystyrene blend

AbstractThe morphology of nylon 6 and polystyrene (PS) blend with styrene‐maleic anhydride copolymer (SMA) as a compatibilizing agent was studied. The long‐time mixing of blends exhibited slight decrease in storage modulus and larger domain size. This may be caused by imidization between amine end‐group of nylon 6, and SMA produce the water, which hydrolyzes an amide group of nylon 6 and results in the decrease of viscosity. As the morphology change in blend influence on physical properties, it is found that modification of nylon 6 by SMA has a better morphology and good physical properties with shorter mixing time. However, the morphology investigation in nylon 6/PS blends reveals that the effect of mixing time was negligibly small. Addition of small amount of SMA into nylon 6/PS blend has proved to give improvement in physical properties. This behavior is based on the concentration of water derived from imidization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1–7, 2006

Free Energy of Mixing of Cross-Linked Polymer Blends

Free energy of mixing of cross-linked polymer blends is derived, as a modification to the Flory-Huggins-de Gennes free energy functional for linear polymer blends. The latter arrives from the assumption of mean-field, short-range thermal interactions among ideal Gaussian chains. However, upon cross-linking a linear chain, the chain no longer remains Gaussian; new chain architectures belying the threadlike image of linear chains emerge. Fractal dimensions of these nonlinear chain clusters convene and command new entropic interactions. Topological constraints by cross-links introduce long-range nonequilibrium elastic forces. Relatively shorter range steric repulsions between fractal network surfaces may arrive if cross-linking is carried out inside the blend's thermodynamically unstable region. Modified free energy has been used to highlight experiments on phase instability of cross-linked polymer blends.

UV fluorescence monitoring of the mixing of molten polymers in a batch mixer

AbstractA fluorescence monitoring device was developed to study the distributive mixing process inside the chamber of a batch mixer. A bifurcated UV‐fluorescence probe was implemented instead of the thermocouple measuring the temperature of the melt. Hydroxymethyl anthracene was used as fluorescence tracer and was preliminarily dispersed in the minor component. Furthermore, the main polymer of this study was a copolymer of ethylene and vinyl acetate (EVA). Structure development during mixing of miscible polymer blends, low viscosity ratio blends (plasticizer/polymer), and immiscible polymer blends was investigated by this method. It was shown that the mixing process of a miscible system depends on the shear rate, which governs the temperature of the melt and consequently the melting process of the solid masterbatch‐tracer at the early stages of mixing. On the other hand, the presence of a miscible component of very low viscosity, as, for example, mixing of DOP in EVA, delays the onset of mixing. This lubricant effect was shown to be due to the fact that DOP migrates to the wall of the chamber rather than inside the polymer, though it is well miscible with the EVA phase. The study of immiscible polymers, as, for example, polypropylene in EVA, did not show any fundamental difference with miscible polymer blends. This observation is actually inherent to the UV‐fluorescence tracer disperesed in a masterbatch system, which allows quantification of the distributive mixing process only.

Flow through a convergence. Part 2: Mixing of high viscosity ratio polymer blends

AbstractDispersive mixing of high viscosity ratio blends was studied in a converging flow using a capillary rheometer equipped with dies having different entry profiles. Three inhomogeneous bimodal polyolefin blends, with stress‐dependent viscosity ratios ranging from 8 to 450, were used in this work. Such magnitudes of viscosity ratio indicate that the dispersed droplets can be mixed only in an elongational flow field. The mixing efficiency was found to be dependent on both the profile of the convergence and flow rate. At the lowest flow rates, the dispersive mixing efficiency was very low, but it increased with an increasing flow rate until a profile‐dependent maximum. This maximum mixing efficiency was observed prior to fracture of the matrix material, after which the efficiency decreased. Stress and deformation fields within different profiles were estimated by numerical simulation using the K‐BKZ equation, and the results were used to interpret experimental results. The dispersive mixing efficiency was found to be proportional to the maximum elongational stress within the converging section, and to the length of the region where the critical conditions for elastic fracture of droplet material were met. It is shown that the dispersive mixing mechanism in high viscosity ratio blends is mainly dictated by elastic fracture of the droplet, and hence is applicable over a wide range of polymer blending processes.

Mixing and Spinnability of Polymer Blends on the Example of the Polyamide 6.6—Poly(Ethylene Terephthalate) Model System

The method of combined evaluation of the quality of mixing and the quality of a polymer blend allows predicting the character of the change in the disperse structure of the blend when the extrusion process parameters change. The spinnability criterion, which is the ratio of the parameters of the extruder deformation field — ratio of shear strains (average and minimum, determined in the section @zeta;3), prespinneret, and spinneret drawing, allows explaining the change in the spinnability of PA6.6—PET polymer blend melts when the process parameters change from unified positions.

A simple model for baroplastic behavior in block copolymer melts

A simple model for the free energy of mixing of compressible polymer blends is derived, based on the regular solution model. Its ability to predict phase behavior for weakly interacting polymer pairs using only the pure component properties of mass density, solubility parameter, and thermal expansion coefficient is illustrated for mixtures of polystyrene and poly(n-alkyl methacrylates) with n⩽12. The model yields a clear explanation for the strong pressure effects observed in some of these systems, including the first reported baroplastic elastomer.