Heat assisted twin screw dry granulation

A new “assisted” dry granulation method has been devised for the twin‐screw granulator. The method may be beneficial to drug preparation as it limits heat exposure to only one barrel zone, much shorter than melt granulation. Its mechanism was investigated using four placebo formulations, each containing a polymer binder with a glass transition temperature lower than 130°C. Variables of study included screw configuration, screw speed, barrel zone temperature, and moisture content. Granulated samples were characterized for size and porosity while feed powders were examined for their thermal transitions, interparticle friction, cohesion, and sintering rate. Results indicated that granule coalescence relied on melting of polymer binder in the kneading blocks by a combination of heat conducted from barrel and generated from screw speed friction. Successful granulation was possible with minimal addition of water, although varying the moisture content showed the relevance of the polymer's glass transition temperature and sintering progress. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Full range of continuous mixers

B&P Process Equipment Co. offers twin screw continuous compounding extruders in a 19–450mm screw diameter range. The CT Series of high torque/high speed twin screw extruders offer standard machine diameters from 25mm to 133mm and L/D ratios of up to 52:1. The screw and barrel components are segmented. In addition to the CT Series, the company offers the PC Series of high free volume ‘clam shell’ continuous compounding machines. Standard machine sizes are from 15mm to 160mm, with L/D ratios of up to 50:1. B&P adds that the modular barrel and segmented screw design with individual paddles and hexagonal shafts for simple screw design changes.This is a short news story only. Visit www.addcomp.com for the latest additives and compounding industry news     

Progression of wet granulation in a twin screw extruder comparing two binder delivery methods

The two available wetting methods for twin screw granulation, namely foam delivery and liquid injection, were studied in detail by examining granule development along the screws as powder formulation and screw design were varied. Granulation profiles were determined by particle size analysis of samples along the screws collected using the “screw pullout” technique. Analysis of the particle size and porosity of produced granules revealed only minor differences between the two methods of wetting despite the larger dropsize of liquid injection compared to foam delivery. Excipients like microcrystalline cellulose or hydroxypropyl methyl cellulose with poor spreading properties, quantified by their specific penetration time and nucleation ratio, made the differences more apparent. The general similarities in granulation independent of wetting method implied that binder dispersion in an extruder was dominated by mechanical dispersion. Screw design (i.e., location of kneading block) had the dominant effect on the granulation process in this study. © 2014 American Institute of Chemical Engineers AIChE J, 61: 780–791, 2015     

Energy dissipation rate and pressure fluctuations in a three phase fluidized bed with a large column diameter

The effects of liquid (0.02-0.10 m/s) and gas (0.0-0.10 m/s) velocities and particle size (1.0, 2.3, 3.0 mm) on the pressure fluctuations and energy dissipation rate in three phase fluidized beds were determined in a large column (0.376 m-I.D.× 2.1 m high). The standard deviation of pressure fluctuations and energy dissipation rate increase with gas and liquid velocities but, decrease in the radial direction of three phase fluidized beds. The energy dissipation rate was well correlated with dimensionless groups as: E_d=16.788Fr ₁ ^0.183 Fr _g ^0.139 (1-ψ)^0.442+1.265Fr _g ^0.143 Re^0.181.     

Investigation of the poly(vinyl chloride) extrusion process using a feed throat with a feed pocket

The effectiveness of the extrusion process depends on a number of factors, the most important being barrel design, e.g., longitudinal or helical grooves; screw, feed opening, and polymer hopper designs are significant in this respect, too. The effect of these factors on the extrusion process has been thoroughly discussed in the available literature. This notwithstanding, there is little information providing insight on the effect of a feed pocket made below the feed opening, on the side of the barrel toward which the screw rotates, on the main characteristics of the extrusion process. For the experiments, five special profile inserts with different feed pocket depths were made and then mounted in the extruder barrel equipped with a 25‐mm diameter screw. The extrusion of plasticized poly(vinyl chloride) (PVC) at the screw speed ranging from 30 to 150 rpm was investigated. Presented graphically as charts, the obtained results show the dependences of extrudate temperature, extruder screw torque, polymer output, power supplied to the extruder and conveyed by the polymer, unit energy consumption and energy efficiency on the feed pocket depth, and screw speed. It has been found that the feed pocket made in the extruder barrel has little effect on the course and effectiveness of plasticized PVC extrusion and does not worsen the studied properties of the received extrudate; yet, it should be taken into account to ensure the highest polymer output and lowest energy consumption. POLYM. ENG. SCI., 54:2037–2045, 2014. © 2013 Society of Plastics Engineers     

Effect of process variables on melt temperature profiles in extrusion process using single screw plastics extruder

Abstract

Melt temperature is an important parameter in the melt processing of polymers. However, it is not possible to control melt temperature directly, only to influence it using processing parameters such as processing temperature settings. It is therefore important to know the influence of controllable process parameters on melt temperature. In this work, the relationships between controllable process parameters and melt temperature have been investigated for a 50 mm S + B single screw extruder. The extruder was equipped with a thermocouple mesh at the die inlet to determine melt temperature. It was found that melt pressure, die size, feed section barrel temperature, and compression section barrel temperature had a negligible effect on the melt temperature profiles generated, while increasing the screw speed resulted in higher melt temperatures. The metering section barrel temperature had a significant effect on melt temperature, thermal conduction effects being more important than shear heating effects. Equipment wall temperatures, downstream of the screw, produced changes in the melt temperature in the melt located within 7 mm of the wall. It was found that melt temperatures can be significantly different from those set on the equipment.     

A simple method for identifying bubbling/jetting regimes transition from large submerged orifices using electrical capacitance tomography (ECT)

The bubbling–jetting transition regimes from large orifice submerged in water were investigated for various orifice diameters. A simple and fast way for identifying the regime transition was successfully developed using electrical capacitance tomography (ECT). In all the experiments deionised water was liquid phase and air was gas phase. Orifice gas velocity (V_N) and orifice diameter (d_o) were varied from 0.8 to 186 m/s and 4–21 mm, respectively. It was found that the V_N,trans. strongly depends on the orifice diameter. In the small orifice diameter (d_o < 10 mm), V_N,trans. greatly decreases with the increase of orifice diameter. However, in the large orifice diameter (d_o > 10 mm), the effect of orifice diameter on the transition velocity is insignificant. Finally, the data obtained by ECT compares with other works and the dimensionless orifice Reynolds number (Re_o ～11,000) is preferred to identify the bubbling–jetting transition regimes.     

Processing of polypropylene–clay nanocomposites: Single‐screw extrusion with in‐line supercritical carbon dioxide feed versus twin‐screw extrusion

This work investigates two different melt‐blending strategies for preparing compatibilized polypropylene‐clay nanocomposites, specifically: (1) conventional twin‐screw extrusion, and (2) single‐screw extrusion capable of direct supercritical carbon dioxide (scCO₂) feed to the extruder barrel. Proportional amounts (3 : 1) of maleic anhydride functionalized polypropylene compatibilizer and organically modified montmorillonite clay at clay loadings of 1, 3, and 5 wt % are melt‐blended with a polypropylene homopolymer using the two approaches. The basal spacing, degree of exfoliation, and dispersion of organoclay is assessed using X‐ray diffraction, transmission electron microscopy, and rheology. In terms of the latter, both steady shear and small‐amplitude oscillatory shear provide information about the apparent yield stress and solid‐like terminal behavior respectively. Finally, nanoindentation is performed to determine the room temperature modulus of each melt‐blended nanocomposite. The results reveal unequivocally that the high shear of the twin‐screw process is vastly superior to the single‐screw with in‐line scCO₂ addition in generating well‐exfoliated, percolated polypropylene‐clay nanocomposites. It is likely that increased contact time between clay and scCO₂ is necessary for scCO₂ to positively affect exfoliation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 884–892, 2007     

Gas holdup,bubble size distribution,and mass transfer in an airlift reactor with ceramic membrane and perforated plate distributor

The airlift reactor is one of the most commonly used gas–liquid two-phase reactors in chemical and biological processes. The objective of this study is to generate different-sized bubbles in an internal loop airlift reactor and characterize the behaviours of the bubbly flows. The bubble size, gas holdup, liquid circulation velocity, and the volumetric mass transfer coefficient of gas–liquid two-phase co-current flow in an internal loop airlift reactor equipped with a ceramic membrane module (CMM) and a perforated-plate distributor (PPD) are measured. Experimental results show that CMM can generate small bubbles with Sauter mean diameter d₃₂ less than 2.5 mm. As the liquid inlet velocity increases, the bubble size decreases and the gas holdup increases. In contrast, PPD can generate large bubbles with 4 mm < d₃₂ < 10 mm. The bubble size and liquid circulation velocity increase as the superficial gas velocity increases. Multiscale bubbles with 0.5 mm < d₃₂ < 10 mm can be generated by the CMM and PPD together. The volumetric mass transfer coefficient k_La of the multiscale bubbles is 0.033–0.062 s⁻¹, while that of small bubbles is 0.011–0.057 s⁻¹. Under the same flow rate of oxygen, the k_La of the multiscale bubbles increases by up to 160% in comparison to that of the small bubbles. Finally, empirical correlations for k_La are obtained.     

On the fluid dynamics of shaken bioreactors— flow characterization and transition

Phase‐resolved PIV measurements were carried out to provide a thorough characterization of the flow and mixing dynamics occurring in a cylindrical shaken bioreactor when operating conditions such as medium height h, shaking rotational speed N, orbital shaking diameter d_o, and cylinder inner diameter d_i, are varied. A scaling law based on the aspect ratio h/d_i, on the orbital to cylinder diameter ratio d_o/d_i, and on the Froude number Fr = 2(πN)²d_o/g, is derived to predict the incipience of flow transition occurring when the free surface orientation starts to exhibit a phase delay to the shaker table position along its orbit; depending on the combination of Fr, d_o/d_i and h/d_i the transport phenomena in the bioreactor are controlled by a horizontal toroidal vortex, or by a vertical one precessing around the cylinder axis. The free surface interfacial area was directly measured by image analysis to assess oxygen transfer potential and compared to an analytical solution valid for low Fr. © 2012 American Institute of Chemical Engineers AIChE J, 59: 334–344, 2013     

Agglomerate size evolution in modular twin‐screw extruder: Modeling and validation with CaCO3/LLDPE compounding experiments

The screw combination of twin‐screw extruder affects the filler size in inorganic filler‐reinforced polymeric compounds. This article tried to conveniently and precisely model the agglomerate size evolution in modular co‐rotating twin‐screw extruder. The break‐up process of agglomerate was analyzed to obtain the relationship between average deagglomerating energy (M) and agglomerate size, the result presented a mathematic relationship between M and agglomerate size. Numerical simulation study was conducted to consider the effect of kneading blocks (KB) or flight elements (FE) number on dispersion capacity of screw combination. The average deagglomerating energy, calculated based on POLYFLOW simulation, was introduced as major parameter to evaluate the dispersion capacity, which presented a proportional relationship to the KB or FE number. The model was developed by combining the agglomerate break‐up process and simulation results. In validation, CaCO₃/linear low‐density polyethylene (LLDPE) compounds were prepared by modular co‐rotating twin‐screw extruder with different screw combinations. The optical image analysis showed that CaCO₃ agglomerate size decreased with the KB or FE number rising, while it achieved minimum when the KB number was 4. The model was in accordance with the experimental results, and proved to be valid for KB and FE combinations in preparing CaCO₃/LLDPE compounds. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45535.     

Molecular weight control of poly(ethylene terephthalate) in extrusion process

A control strategy is developed to control molecular weight of recycled poly(ethylene terephthalate), PET, to overcome its degradation through an extrusion process. To obtain dynamic model of a twin screw extruder, steady‐state, and unsteady‐state experiments were performed. Discrete convolution models between inputs and outputs were obtained. Process inputs were considered as screw speed (SS), feed rate, and barrel temperatures and the output was viscosity average molecular weight (M_v) of the extrudate. SS and molecular weight of the product were chosen as the manipulated, controlled variable pair by considering singular value decomposition (SVD) technique. Model based PID controller and model predictive controller were used in the designed control scheme. By the simulation studies, both controllers were found to be successful for set‐point tracking, disturbance rejection cases; and were proven to be robust under modeling errors. POLYM. ENG. SCI., 54:459–465, 2014. © 2013 Society of Plastics Engineers     

Electrical Insulation and Radar-Wave Absorption Performances of Nanoferrite/Liquid-Silicone-Rubber Composites

Novel radar-wave absorption nanocomposites are developed by filling the nanoscaled ferrites of strontium ferroxide (SrFe₁₂O₁₉) and carbonyl iron (CIP) individually into the highly flexible liquid silicone rubber (LSR) considered as dielectric matrix. Nanofiller dispersivities in SrFe₁₂O₁₉/LSR and CIP/LSR nanocomposites are characterized by scanning electronic microscopy, and the mechanical properties, electric conductivity, and DC dielectric-breakdown strength are tested to evaluate electrical insulation performances. Radar-wave absorption performances of SrFe₁₂O₁₉/LSR and CIP/LSR nanocomposites are investigated by measuring electromagnetic response characteristics and radar-wave reflectivity, indicating the high radar-wave absorption is dominantly derived from magnetic losses. Compared with pure LSR, the SrFe₁₂O₁₉/LSR and CIP/LSR nanocomposites represent acceptable reductions in mechanical tensile and dielectric-breakdown strengths, while rendering a substantial nonlinearity of electric conductivity under high electric fields. SrFe₁₂O₁₉/LSR nanocomposites provide high radar-wave absorption in the frequency band of 11~18 GHz, achieving a minimum reflection loss of −33 dB at 11 GHz with an effective absorption bandwidth of 10 GHz. In comparison, CIP/LSR nanocomposites realize a minimum reflection loss of −22 dB at 7 GHz and a remarkably larger effective absorption bandwidth of 3.9 GHz in the lower frequency range of 2~8 GHz. Radar-wave transmissions through SrFe₁₂O₁₉/LSR and CIP/LSR nanocomposites in single- and double-layered structures are analyzed with CST electromagnetic-field simulation software to calculate radar reflectivity for various absorbing-layer thicknesses. Dual-layer absorbing structures are modeled by specifying SrFe₁₂O₁₉/LSR and CIP/LSR nanocomposites, respectively, as match and loss layers, which are predicted to acquire a significant improvement in radar-wave absorption when the thicknesses of match and loss layers approach 1.75 mm and 0.25 mm, respectively.     

超大长径比双螺杆挤出机制备聚丙烯腈初生纤维

采用自主研发的超大长径比(136)双螺杆挤出机实现了PAN初生纤维的纺丝制备,研究了PAN粉料质量分数(16％、20％、24％)、双螺杆挤出机机筒温度(50、60、70 ℃)、循环挤出次数(0、1、2)对PAN初生纤维力学性能及表面形貌的影响.结果表明,PAN初生纤维的拉伸强度随质量分数、机筒温度和循环挤出次数的增加而...     

Effects of the actual diameters and diameter ratios of barrels and dies on the elastic swell and entrance pressure drop of natural rubber in capillary die flow

The effects of the actual diameters and diameter ratios of barrels and dies on the elastic swell and entrance pressure drop of natural rubber compounds in an extrusion capillary rheometer were investigated. Either the barrel diameter or the die diameter was altered so that different barrel‐diameter/die‐diameter (D_B/D_D) ratios were obtained, both the barrel and die diameters also being varied simultaneously. The extrudate swell and entrance pressure drop were dependent not only on D_B/D_D but also on the actual diameters used. For fixed D_B/D_D ratios, the change in the extrudate swell was linearly influenced by the entrance pressure drop at low actual barrel and die diameters (D_B/D_D = 20/4–30/7 mm/mm) but was associated with a change in the material viscosity at high barrel and die diameters (D_B/D_D = 35/7–40/8 mm/mm). When the die diameter was fixed, the relationship between the entrance pressure drop and the extrudate swell was linear up to a certain value of the barrel diameter greater than 30 mm. Beyond this critical barrel value, the relationship became nonlinear and associated with the shearing stress generated by the formation of semipluglike flow patterns and the residence time of the material. For a constant barrel diameter, the smaller the die diameter was, the greater the extrudate swell was because of the increases in the extensional deformation and wall shear rate coupled with a reduction in the material residence time. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1762–1772, 2002     

Mass Transfer Characteristics during the Removal of Dissolved Heavy Metals from Waste Solutions in Gas Sparged Fluidized Beds of Ion Exchange Resins

The paper presents experimental results concerning the removal of cupric ions from a simulated wastewater effluent consisting of copper sulphate solution in a gas sparged fluidized bed of cation exchange resin. Variables investigated were: superficial gas velocity, particle diameter, bed height and the physical properties of the solution (adding glycerol). These variables were studied with respect to their effect on the solid-liquid mass transfer coefficient. The coefficient was found to increase with increasing superficial gas velocity. Increasing both particle diameter and bed height were found to reduce the mass transfer coefficient. The experimental data can be correlated by the equation J = 0.68 (Fr Re )^–0.143 (d_p/d)^–0.62 (d_p/L)^0.55valid for the following conditions: 1430 < Sc < 2488; 0.017 < Fr Re < 1.41; 6.33 × 10^–3 < d_p/d < 0.021 and 9.5 × 10^–3 < d_p / L < 0.125.     

A study of particle shape and size effects on hydrodynamic parameters of trickle beds

Uniform-spherical and cylindrical-extrudate particles are employed to study air-water downflow in a packed bed of 14 cm i.d. The effect of particle shape, neglected in the literature so far, is shown to be very significant. A packed bed of extrudates displays significantly greater global dynamic liquid holdup h_d and pressure drop, as well as a trickling-to-pulsing transition boundary at higher gas flow rates, compared to beds of spheres of comparable size. Moreover, packed extrudates exhibit a significant increase of holdup, h_d, in the axial flow direction, a trend reported for the first time as there are no similar data available in the literature; on the contrary beds of spherical particles are characterized by practically constant h_d in the axial direction. Although an explanation for this h_d axial variation is not obvious, one might attribute it to the anisotropy and non-uniformity of interstitial voids of packed cylindrical particles. For beds of uniform spheres, in the diameter range examined (3-6 mm), the effect of size on both dynamic holdup and pressure drop, although quite pronounced, is not as significant as the effect of particle shape. An extensive survey of literature data, obtained with similar spherical particles, suggests that small bed diameters have an appreciable influence on trickling-to-pulsing transition boundary. Comparisons are reported with literature methods for predicting the measured parameters; discrepancies between data and predictions may be partly due to the inadequacy of a single “equivalent” diameter to represent both shape and size of non-spherical particles; predictive methods performing best are also identified.     

Interfacial area and liquid side mass transfer coefficient in trickle bed reactors operating with organic liquids

Interfacial area and liquid-side mass transfer coefficients measured in a 5cm diameter trickle-bed reactor operating with organic liquids are presented d_p≤ 2.4 mm and cylindrical catalyst of size 0.9 mm × 5 mm. A few data concern also 5.9 and 6.4 mm Raschig rings. Gas and liquid flowrates a Mass transfer parameters have been determined by the chemical technique using the carbamation of the reactants cyclohexylamine, monoethanolamine or die results obtained at low gas-liquid interaction with low liquid flowrate are reported for the ionic aqueous systems CO₂-NaOH and O₂-Na₂SO₃. The variation of the mass transfer data, the gas pressure drop and the liquid holdup with the gas and liquid flowrates show that there exists a strong connection between these parameters. This has led to correlate the with the liquid-solid friction factor within a $\text{+}$30% accuracy.     

Axial dispersion in packed beds: The effect of particle size non-uniformities

The effect of particle size non-uniformities on axial dispersion coefficients during laminar liquid flow through packed beds has been studied. The investigations were carried out for binary mixtures of particles with diameters d₁ = 0.169 mm and d₁ = 0.360 mm.A generalized function to determine the increase of the axial dispersion coefficients in non-uniform beds relative to those obtained in uniform beds has been proposed.