Ica Manas-Zloczower

Mixing and compounding of polymers : theory and practice

Agassant.The online version of Mixing by Ica Manas-Zloczower on ScienceDirect.com, the. Mixing and Compounding of Polymers. PDF 454 K.The polymer industry as we know it dates only from the first part of the nineteenth century, where. Lowered the ability of the rotors to mix the compound but allowed various chemicals in the compound. Theory and Practice, 2nd edn ed. I.Mixing and. Most of the existing theoretical models focus on the competitive forces involved in.Mixing and Compounding of Polymers 2E: Theory and Practice Ica Manas-Zloczower on Amazon.com. FREE shipping on qualifying offers. Completely.To impart the knowledge of compounding and mixing processes for the polymers and to study. Mixing and Compounding of Polymer Theory and Practice, 2 nd.The twin-screw mixing process for semi-solid immiscible alloy casting has been. Z ed 1994 Mixing and Compounding of Polymers: Theory and Practice.this theory to Newtonian fluids. Mixing and Compounding of Polymers: Theory. mh 510 pdf Presently a common practice Bigg 1977 Crawford 1982 Radhakrishnan.Polymer Processing. Theory and Practice.model 2D mixer as determined using FEM with particle tracking. Compounding of Polymers: Theory and Practice, Carl Hanser Verlag.mer pair A and B can be described by the mixing. 1Department of Polymer Engineering and Color Technology, Amirkabir University of Technology, No.

Dispersive Mixing in Internal Mixers—A Theoretical Model Based on Agglomerate Rupture

Abstract The mixing of solid additives into a matrix of rubber or plastics is an energy intensive process. Such a mixing operation generally involves rupture of agglomerates formed by the solid phase, separation of closely packed particles after rupture, and distribution of the separated particles throughout the polymeric matrix. Dispersive or intensive mixing refers primarily to the first two steps, whereas, the third step is by and large an extensive mixing process. Depending upon the polymer-additive system and mixer machine design, each of these steps may be rate determining. The most important and most investigated system is the carbon black-elastomer system. Mixing of such a system is generally carried out in batch Banbury type internal mixers (Figure 1). The dispersive mixing process in internal mixers is quite complex with many subtle features. A detailed review of the subject is outside the scope of this paper. However, careful reading of reviews and publications in the field, indicate that a gre...

Fractionation of mixed particulate solids according to compressibility using ultrasonic standing wave fields

Abstract A continuous fractionation method for mixed particulate solids has been developed. When applied to suspensions of solids having substantially equal densities, the separation method distinguishes the particulates on the basis of their compressibility. The technique can be applied to solids ranging from micron to millimeter scale with overlapping or distinct particle size distributions. The method involves suspension of the solids into an appropriate processing medium, the application of a standing acoustic wave field to sort the particles across a separator channel, and the use of laminar flow fields along the channel to accomplish the ultimate separation. An analytical model of the separation process, based on particle trajectories through the separator chamber, is presented to show the sensitivity of the method to system properties and to illustrate its selectivity. Results of prototypical experiments with polymer particles further demonstrate the method.

Viscosity model for polydisperse polymer melts

A simple superposition model was used to define the relationship between molecular weight distribution and shear viscosity for linear polymeric systems. Gel permeation chromatography data for molecular weight distributions were fitted using statistical distribution functions. A simple superposition model was then employed to calculate the shear viscosity for the systems investigated. The effect of polydispersity on the shape of the flow curves was calculated. The simplicity of the model makes feasible its use in numerical simulations of complex geometries as encountered in polymer processing equipment. The present study also sheds some light on the relationship between entanglement and disentanglement phenomena in polymeric systems.

Analysis of Agglomerate Rupture in Linear Flow Fields

Abstract A dispersive mixing model focusing on the rupture of agglomerates as the step that primarily determines the dynamics of the mixing process was developed and analyzed. Rupture is predicted to occur when hydrodynamic forces exerted on the outer surface of the agglomerate exceed cohesive forces binding the agglomerate together. Agglomerates are modeled as clusters of aggregates bound by van der Waals forces. The magnitude and orientation of the rupturing hydrondynamic force depend on the local stress field in the fluid. Cleavage of the agglomerate is predicted to occur at the mid-plane of the agglomerate where the effects of hydrodynamic tension is the largest. Under the assumption that parent agglomerates and their fragments have the same shape, the kinetics of the rupture process is found to be independent of the absolute size of the agglomerate. Following from this is the result that the dispersion process is governed by flow dynamics, i.e., a minimum value of flow strength, which depends on the geometry of the bulk flow field, is required for rupture of the agglomerate. Agglomerate rupture was investigated in four flow geometries: simple shear; pure elongation; uniaxial extension, and biaxial extension. The efficiency of each flow geometry is compared on the basis of power and time requirements to achieve a given degree of dispersion.

Entropic characterization of mixing in microchannels

A methodology for rigorous mixing assessment in microchannels is presented. The analysis is based on numerical simulations of flow in different geometries coupled with mixing assessment using entropic measures. The results show enhanced mixing efficiency for the staggered herringbone micromixer by comparison with a mixer with straight diagonal ridges and a lack of mixing in a non-patterned channel. These results are in agreement with published experimental data.

Dispersion of titanium dioxide agglomerates in viscous media

Abstract The dispersion behavior of titanium dioxide agglomerates in viscous media was studied. Under application of shear within a cone-and-plate device, the titanium dioxide agglomerates primarily dispersed by an erosion process in which small fragments separate from the surface. The cohesiveness of unwetted powder was quantified using a compression test method. In some cases, the shear stress necessary to produce erosion was found to be an order of magnitude smaller than the measured cohesivity. Medium infiltration within agglomerates was assessed through observation of penetration of the medium into powder compacts. The kinetics of the erosion process was highly sensitive to the overall porosity of the agglomerates. In the case of high porosity, the erosion rate depends on the speed of medium infiltration within the agglomerate, and the strength of the applied shear stress. A relatively wide size distribution of fragments was observed. For low-porosity agglomerates, the erosion process depends on the magnitude of shear stress, the cohesive strength of the agglomerates, and agglomerate—medium interactions. A narrower distribution of fragments, having smaller mean size, was observed.

Temporary droplet-size hysteresis in immiscible polymer blends

The droplet size distribution during steady shearing of model polymer blends is examined in situ by optical microscopy. The volume-average steady-state droplet size during shear is essentially inversely proportional to shear rate, as expected. When the shear rate is increased suddenly, the droplets break up, through a process that involves the transient formation of threads, and rapidly establish a new steady state, comprising ellipsoidal droplets that are extended slightly in the direction of shear. When the shear is stopped, the droplets quickly relax to a spherical shape, but virtually no coalescence is observed, because neither Brownian nor buoyant forces are significant and the volume fraction of the dispersed phase is low. Slow shear, however, induces droplet collisions that lead to coalescence. The coalescence process is much slower than breakup. In contrast to some predictions, however, there is no permanent droplet size hysteresis. The steady-state size produced by breakup of initially larger droplets is eventually produced at large strain by coalescence of initially smaller droplets. The lack of permanent hysteresis has implications concerning appropriate mathematical models of coalescence behavior.

Influence of physical and interfacial characteristics on the wetting and spreading of fluids on powders

Abstract The wetting and spreading of liquid on compacts of carbon black and silica powders has been studied with the aim of investigating the degree to which the physical properties and chemical nature of the fluid govern the phenomena. Wetting experiments were performed with six fluids (glycerin, ethylene–propylene copolymer, squalene, poly(dimethylsiloxane), 1-butanol, and water) selected to provide a range of interfacial chemistries. The viscosity of these fluids spanned a range of three orders of magnitude. Capillary rise experiments gave insight into the wetting phenomena that occur between powders and large quantities of fluid. The observed infiltration kinetics was found to exhibit a different sensitivity to the fluid viscosity than what is explicitly predicted by the conventional Washburn analysis. This deviation is attributed to variation in the degree of saturation of the powder compacts arising from differences in viscosity of the infiltrating liquid. The wetting of compacts by small amounts of fluid was studied by contacting single drops of fluid onto carbon black compacts. Observed spreading and infiltration rates indicate that the wetting phenomena cannot be predicted on the basis of a simple balance between capillary and viscous forces. Cracking and microstructural rearrangement within powder compacts driven by the infiltrating liquid were also observed. The nature of this rearrangement was found to be strongly correlated with the kinetics of the wetting process.

Kinetics of dispersion for sparse agglomerates in simple shear flows: Application to silica agglomerates in silicone polymers

Dispersion of sparse (low solids content) agglomerates by hydrodynamic shear is addressed both experimentally and theoretically. A model for the kinetics of the erosion of homogeneous sparse agglomerates is developed. Experiments carried out using agglomerates of silica and poly(dimethyl siloxane) fluids demonstrated the validity of the kinetic model. For this experimental system, the infiltration of the suspending fluid into the agglomerate significantly affects the mechanism and kinetic rates of dispersion as well as the fragment size distribution. Agglomerates that were soaked in processing fluid for extended periods of time were found to better resist dispersion than dry agglomerates or agglomerates soaked for short periods of time.