Multilayer coextrusion of rubber compounds

This research work presents the first continuous multilayer coextrusion system for high viscosity elastomeric materials. Three unvulcanized rubber materials were chosen to validate the system: two butyl rubbers and a polyisoprene. The elastomers were characterized under oscillatory shear and the results used to perform computational flow simulations to investigate the effect of geometry on the flow path and flow rate. Successful extrudates of 8 and 32 layers were extruded at two different throughput rates for rheologically matched and rheologically mismatched material pairs. The results show good layering performance for both systems with little existence of viscous encapsulation and acceptable pressure drops. Computational and experimental results both show a nonuniform layer thickness distribution due to the geometric design of the layer multiplier extrusion dies, which were designed to minimize pressure drop in the system. This nonuniformity decreases with increasing number of layers. POLYM. ENG. SCI., 55:1520–1527, 2015. © 2015 Society of Plastics Engineers     

Modeling of three‐dimensional flow and heat transfer in polystyrene foam extrusion dies

A three‐dimensional mathematical model was developed to investigate the nonisothermal, non‐Newtonian polymer flow through the dies used in the polystyrene foam extrusion process. The model, based on the computational fluid dynamics (CFD) code, Polyflow, allowed for the shear rate and temperature dependence of the shear viscosity of the blowing agent laden polystyrene melt. The model also accounted for viscous heating. The shear viscosity of the polystyrene‐blowing agent mixture was measured experimentally at several temperatures. The model was used to calculate pressure, flow, and temperature distributions in two different dies used for industrial‐scale extrusion of polystyrene foams. The article presents a selection of computed results to illustrate the effect of die design on uniformity of flow at the die exit, the overall pressure drop in the die, relative magnitudes of pressure drop in the land section versus the rest of the die, and temperature distribution in the die. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Ultrasonic oscillations effect on rheological and processing properties of metallocene‐catalyzed linear low density polyethylene

The effects of ultrasonic oscillations and die materials on die pressure, productivity of extrusion, melt viscosity of metallocene‐catalyzed linear low density polyethylene (mLLDPE), as well as their mechanism were studied in a special ultrasonic oscillations extrusion system developed in our lab. Die materials used in our experiment included steel, brass, and polytetrafluoroethylene (PTFE)_. The experimental results showed that ultrasonic oscillations as well as die materials have great influence on the rheological and processing behavior of mLLDPE. Ultrasonic oscillations can greatly increase the productivity of mLLDPE melt extruded through different dies, and can decrease the die pressure and the melt viscosity of mLLDPE. Compared with steel or brass die, mLLDPE melt extruded through PTFE die is more sensitive to ultrasonic oscillations. A possible mechanism for the improved processability of mLLDPE is proposed in this article. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1873–1878, 2003     

Measurement of the pressure dependence of viscosity of polymer melts using a back pressure‐regulated capillary rheometer

The effect of pressure on the melt viscosity was experimentally investigated for five polymers: polycarbonate (PC), acrylonitrile‐butadiene‐styrene (ABS), polystyrene (PS), polypropylene (PP), and low‐density polyethylene (LDPE). Measurements were carried out using capillary rheometer modified to allow regulation of back pressure. To enable correction for the entrance pressure drop, two round‐hole dies were used: a 1‐mm diameter die of length 10 mm and an orifice die of the same diameter. For determining the pressure coefficient from the experimental viscosity data, time‐pressure superposition was applied to generate a master curve to which the Carreau‐Yasuda model was fitted. The resulting pressure coefficients revealed that for the polymers studied the order of the degree of the pressure dependence is as follows: PS > ABS > PC > PP > LDPE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Novel Liquid‐Flow Splitting Unit Specifically Made for Numbering‐Up of Liquid/Liquid Chemical Microprocessing

A liquid‐flow splitting unit for dividing one main liquid stream into six substreams was developed without the need for active flow regulation. The tool has six fluid connectors that allow the numbering‐up of a respective number of microprocess devices for liquid or liquid/liquid processes. One such liquid/liquid process for which the current tool design and tests in particular have been conceived, is the forced precipitation of precious inorganic powders by the segmented flow tubular reactor (SFTR) technique. Such investigations were performed with six micromixers of impinging‐jet or interdigital separation layer type attached to the liquid‐flow splitting unit. Fluid equipartition is achieved via the action of the microdevices as flow resistors, thereby increasing the pressure drop of the system. Liquid splitting was carried out in a cylindrical liquid tank with one inlet and six outlet holes that also served for pulsation dampening. By CFD simulations the impact of two important geometric parameters of this tank, namely, the height at a given diameter and the position of the inlet hole, on the fluid splitting was studied. In addition, the influence of the injection direction with respect to the normal of the tank was analyzed. It turned out that in the presence of flow resistors (typically generating a pressure drop at about 60 mbar) this impact is negligible, i.e., principally, a large flexibility on design and operation is provided. Without these resistors, the before‐mentioned parameters in turn have a large impact that is discussed in detail. Experiments with a liquid‐flow splitting unit and six coupled impinging‐jet micromixers using water as liquid proved a reasonable fluid distribution with a standard and maximum deviation of the substream flow rates of 4 and 11 %, respectively. These deviations are mainly caused by different pressure drops (Δp) of the individual impinging‐jet mixers as a result of tolerances in the microfabrication method, die sinking μEDM manufacture. Already small differences in the microstructured outlet hole diameters (d = 300 μm) of the impinging‐jet mixer have a large influence due to the d^–4 ～ Δp dependence. Additionally, attaching specially adapted interdigital separation layer micromixers to the liquid‐flow splitting unit, a minimum/maximum (standard) deviation of the water distribution below 5 (2) % could be achieved. To obtain this improved result, it was necessary to optimize the choice of material, the design of the microstructure inside the mixer, and the fabrication process.     

Effect of die temperature on the flow of polymer melts. Part I: Flow inside the die

The effect of die wall temperature on the flow of polymer melts in circular capillary dies was studied. At constant flow rates, it was found that die wall temperature had a greater effect on the pressure drop than melt temperature. A capillary die with two circular channels with different diameters was designed to simulate the profile extrusion. Changes of wall temperature varied the flow rate ratio between the two channels. An implicit finite difference method was used to simulate the velocity and temperature profiles inside the die. Values predicted by this model matched well with experimental data for both dies.     

Pressure drop through tapered dies

A simple method is presented for calculating the pressure drop for the flow of power law liquids in dies with a wide slit profile and with vertical and/or lateral tapers, as well as in dies with the shape of a circular truncated right cone. Tapered dies are known to give improved extrudate quality and/or higher output rates without encountering extrudate defects which occur in dies with parallel channels at similar extrusion pressures. A possible ultimate optimization of the extrusion process—as far as die design is concerned—is discussed. It is suggested that this be based upon an extension of the method from dies with a rectilinear convergent taper to dies with a curvilinearly converging channel aspect the generation of which latter is indicated.     

塑料异型材挤出口模设计的数值模拟概述

从挤出口模设计原则出发,综述了数值模拟技术在塑料异型材口模流道的曲面构型,入口角和压缩比、降低或消除挤出胀大和挤出口模成型段的设计、熔体流动平衡和压力降的研究进展,以及口模设计的发展趋势.     

Functionalizing polymer surfaces by field‐induced migration of copolymer additives—role of shear fields

Flow‐induced migration polyethylene‐co‐methacrylic acid (PE‐co‐MA) and polystyrene‐b‐polydimethylsiloxane (PS‐b‐PD MS) copolymer additives in commercial long‐chain branch polyethylene (PE) and narrow‐molecular distribution polystyrene (PS) hosts was investigated in a capillary flow device. Attenuated Total Reflection Fourier Transform Infrared (ATR‐FTIR) spectroscopy and Dynamic Contact Angle (DCA) measurements were used to characterize surface composition of polymer specimen following extrusion through metallic dies with various length‐to‐diameter (L/D) ratios, (1100 ? L/D ? 3000). Results from experiments covering a broad range of shear rates and polymer residence times in the dies are reported. Provided that the polymer residence time in the die is sufficiently long, shear is found to increase the concentrations of low molecular weight copolymer additives on the host polymer's surface. The surface composition of copolymer additive is found to vary strongly with the wall shear rate and die L/D ratio. Decreasing the die diameter at fixed flow rate is found, for example, to be a more effective method for enhancing transport of additive to a polymer's surface than increasing shear rate at fixed diameter. A mechanism based on shear‐induced diffusion is proposed to explain the observed migration.     

Poly(butylene succinate‐co‐butylene adipate)/polyethylene oxide blends for controlled release materials: A morphological study

Varying the formulation and processing conditions of polymer blends allows the design of materials with a large range of morphologies. Active materials embedding active compounds in a devoted phase are promising applications of such blends, offering possible various transport properties. In this study, 13 poly(butylene succinate‐co‐butylene adipate) (PBSA)/polyethylene oxide (PEO) blends were extruded in a slit die. Their morphologies were characterized by water extraction (selective PEO dissolution), FTIR spectroscopy, and differential scanning calorimetry. Transport properties were assessed by water vapor permeation and fluorescein release as model migrant. Indeed, the desorption in water of fluorescein (previously entrapped in PEO) was monitored to preliminary investigate the release properties of these materials: two morphologies were obtained (i) pseudo multilayer films made of PEO‐rich layer/PBSA‐rich layer/PEO‐rich layer and (ii) PEO nodules dispersed in the PBSA‐rich matrix for the highest PBSA contents. The first systems were erodible ones with an uncontrolled fast delivery by PEO dissolution whereas the second ones showed a controlled release by permeation through the PBSA matrix from PEO nodules. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42874.     

Slip effects in tapered dies

Approximate analytical equations are derived for the calculation of pressure drop of power‐law fluids for viscous flow through tapered dies for a wide range of wall‐slip conditions. The predicted pressure drop values are compared with two‐dimensional (2D) finite element calculations to identify contraction angles for which the analytical equations can be used. It is found that the disagreement increases with increase of the contraction angle and with increase of wall slip. At a given flow rate, the pressure drop from the analytical equations is found to decrease continuously with contraction angle, which agrees with the 2D calculations only at small contraction angles. At larger contraction angles, the 2D calculations show that pressure drop increases with contraction angle as opposed to the no‐slip case where pressure drop saturates. The existence of a minimum pressure at a specific taper angle depends on the rheological parameters of the fluid and the degree of slip (slip‐law exponent), and has scientific importance for the die designer. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effects of Temperature on the Filtration Characteristics of a Dual‐Layer Granular Bed Filter

The effects of temperature on the filtration efficiency and pressure drop of a dual‐layer granular bed filter were investigated in a hot dual‐layer granular bed filter with experimental dust. Enhanced higher filtration efficiency was obtained with higher filtration temperature, and the removal efficiency of ultrafine dust was also at a high level. Simultaneously, the total pressure drop maintained at an acceptable range. The results demonstrate that the dual‐layer granular bed has excellent prospects for application to low‐temperature coal pyrolysis.     

Catalytic upgrading of bio‐oils by esterification

Biomass is the term given to naturally‐produced organic matter resulting from photosynthesis, and represents the most abundant organic polymers on Earth. Consequently, there has been great interest in the potential exploitation of lignocellulosic biomass as a renewable feedstock for energy, materials and chemicals production. The energy sector has largely focused on the direct thermochemical processing of lignocellulose via pyrolysis/gasification for heat generation, and the co‐production of bio‐oils and bio‐gas which may be upgraded to produce drop‐in transportation fuels. This mini‐review describes recent advances in the design and application of solid acid catalysts for the energy efficient upgrading of pyrolysis biofuels. © 2015 Society of Chemical Industry     

Effects of die geometry on cell nucleation of PS foams blown with CO2

This paper investigates the effect of varying the geometry of the die on the cell nucleation behavior of extruded PS foams blown with CO₂. Three interchangeable groups of carefully calibrated filamentary dies have been used in the experimental study. The dies were deliberately designed to have either different pressure drop rates while having identical die pressures and flow rates, or different die pressures while having identical pressure drop rates and flow rates. The experimental results revealed that the geometry of the die governs the cell density of extruded PS foams, especially because of its significant effect on the pressure drop rate across the die. However, the effect of the die back pressure on the cell density was found to be marginal, whereas its effect on the cell morphology was found to be predominant. In addition, regardless of die geometry, the CO₂ content proved to be a very sensitive parameter with respect to the cell nucleation behavior of extruded PS foams. On the other hand, the cell density was slightly improved by an increase of the tale content, especially at reduced concentrations of CO₂.     

Injection molding of delamination‐free ultra‐high‐molecular‐weight polyethylene

When ultra‐high‐molecular‐weight polyethylene (UHMWPE) in powder form is injection molded, the so‐called delamination layering occurs near the skin of the parts. This layering defect hampers UHMWPE's superior wear resistance property and part surface quality. The delamination layer was caused by a combination of excessive shear stress near the part surface and high degree of molecular entanglement of UHMWPE. A mold insulation method that delays the rapid cooling of UHMWPE to reduce the shear stress and improve the polymer chain “interdiffusion” across the entangled chain bundles was used to eliminate the delamination layer. When the insulation layer thickness and mold temperature were optimized, the delamination layer was eliminated completely while still maintaining a reasonable cooling/cycle time. The delamination‐free parts were found to regain UHMWPE's superior impact resistance and tensile properties. POLYM. ENG. SCI., 59:2313–2322, 2019. © 2019 Society of Plastics Engineers     

Determination of steady-state elongational viscosity for rubber compounds using bell-mouthed dies

A bell-mouthed die geometry was designed to cause convergent flow at a constant, uniform, elongational strain rate. An equation was derived, which showed that steady-state elongational viscosity could be calculated from a plot of pressure drop due to elongation against a simple function of die length. To obtain values of pressure drop due to elongation, it was necessary to correct the total pressure drop measured across the bell-mouthed dies for the contribution from shear occurring near the die wall. For this purpose, a simplified shape for the bell-mouthed dies was assumed, comprising several parallel sided segments. Applying a formula to pressure drop data measured across straight dies corresponding to these segments gave an estimate of the pressure drop due to shear across the bell-mouthed dies. Pressure drops due to elongation were determined by subtracting the pressure drop due to shear from the total pressure drop measured across the bell-mouthed dies. Measurements were also carried out with lubrication to validate the shear correction method. The results indicate that for the compound used in this study, a combination of bell-mouthed and straightsided dies can be used in a conventional capillary rheometer to determine steady-state elongational viscosity. An elongational viscosity of 190 kPa s at 90°C and at a strain rate of 10 s⁻¹ was determined for a simple styrene-butadiene rubber compound. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1139–1150, 1997     

Fabrication of Three‐Dimensional Wavy Single‐Chamber Solid Oxide Fuel Cell by In Situ Observation of Curvature Evolution

This study presents a fabrication process via experimental observations for curved porous multilayer structures with a single‐step, co‐sintering operation. Active monitoring of the shrinkage behavior of each porous layer during the co‐sintering process leads to minimize mismatched stresses along with avoidance of severe warping and cracking. During co‐sintering, in‐plane stresses are developed in each layer due to differing shrinkage behaviors between layers. Analysis of curvature evolution using in situ monitoring of the structure was performed in the design of a curved multilayer structure via the co‐sintering process. Materials used are NiO/CGO for anode; CGO for electrolyte; and LSCF for cathode. These materials are tape casted with 20 μm thickness and stacked to form bi‐ and triple‐layer structures by hot‐pressing. Bilayers, consisting of NiO/CGO‐CGO and CGO‐LSCF, were co‐sintered up to 1200°C. The maximum sintering mismatched stress was calculated at the interface of bilayer structure. In situ observation, to monitor the shrinkage of each material and the curvature evolution of the bi‐ and triple‐layer structures, was performed using a long focus microscope (Infinity K‐2). Thereby, viscosity, shrinkage rate of each material, and curvature rate were calculated to determine the mismatched stresses. The monitored results contributed to development of novel design of curved 3D multilayer structures during co‐sintering.     

聚结层排布对高压天然气净化用滤芯过滤性能影响的实验研究

本工作利用聚结滤芯过滤性能实验装置,通过改变滤芯内部的滤材排布,研究了聚结层为单一滤材以及由不同滤材排布组合的滤芯过滤性能,分析了聚结层排布方式对过滤效率、压降、饱和度及液体分布的影响。结果表明,由单一滤材组成的滤芯过滤效率随滤材孔径减小而增大,但孔径最小时由于压降较高,导致滤芯综合过滤性能反而最差。疏油在前、亲油在后的聚结层排布方式可提高滤芯过滤效率、减少液滴二次夹带,且以两层相同滤材交错排列的滤芯过滤效率比单层滤材交错排列明显更高,压降也相对较低,使得综合过滤性能显著提升。继续增加进气侧的疏油滤材层数可延缓压降增长、提高运行寿命,滤芯稳态品质因子达到最大值(0.30 kPa-1)。聚结层排布方式对滤芯过滤性能的影响主要通过改变液体分布形式而实现,且末层滤材的通道结构变化是导致不同聚结层排布方式的滤芯过滤性能出现差异的主要原因。     

Optimization‐based design of polymer sheeting dies using generalized Newtonian fluid models

A polymer sheeting die design methodology is presented, which integrates finite element flow simulations, numerical optimization, and design sensitivity analyses to compute die cavity geometries capable of giving a near‐uniform exit velocity. This work extends earlier die design methods to include generalized Newtonian fluid (GNF) models that represent the shear‐thinning behavior of polymer melt. Melt flow computations and design sensitivity analyses are provided using the generalized Hele‐Shaw flow approximation with isothermal power‐law, Carreau‐Yasuda, Cross, Ellis, and Bingham fluid models. The nonlinear equations for die cavity pressure are solved using the Newton‐Raphson iteration method and design sensitivities are derived with the adjoint variable method. The die design method is applied to an industrial coat hanger die, in which a design parameterization is defined that allows for an arbitrary gap height distribution in the manifold of the die. In addition, die performance is assessed and compared for power‐law and Carreau‐Yasuda fluid flow over a range of die operating conditions. Pareto optimal die designs are also considered in this study. POLYM. ENG. SCI., 45:953–965, 2005. © 2005 Society of Plastics Engineers     

Correlating gas–liquid co‐current flow hydrodynamics in packed beds using the F‐function concept

A phenomenological model based on the generalization of the single‐phase Forchheimer equation was recently proposed for predicting pressure drop and phase saturations in gas–liquid co‐current horizontal and downward high‐pressure packed beds. Here, we extend the model to packed‐bubble (co‐current upflow) and trickle‐bed operation using phase saturation power laws similar to Corey relative permeabilities. The power‐law exponents were fitted using a wide pressure gradient and liquid saturation databank in co‐current up/downward packed‐bed flows. It was found that this approach, as well as other in the literature developed for down‐flow reactors apply also to upward flows; the prediction accuracy was comparable for both flow directions to existing literature approaches. Copyright © 2004 Society of Chemical Industry