Flow visualization and extrudate swell of natural rubber in a capillary rheometer: Effect of die/barrel system

An investigation was carried out to examine the effect of die/barrel system on the flow patterns and extrudate swell of natural rubber in the barrel of a capillary rheometer, using a colored tracer as the visualization technique. The capillary rheometer used in this work had two dies located along the barrel, which is novel in rheometer design. The flow of the rubber in the upper barrel was dependent on the piston/barrel action and changed with piston displacement, whereas the complexity of the flow in the lower barrel was dependent not only on the piston displacement, but also on the geometry of the upper die design. The flow patterns that developed in the whole barrel were independent of the die located at the bottom of the barrel. In addition, the change in extrudate swell was associated with the flow occurring in the barrel, residence time, elastic characteristic, and the temperature rise during the flow. It was concluded that the general style of the flow patterns of natural rubber was greatly dependent on the die geometry that the material had previously moved past. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2525–2533, 2001     

Rheological properties,flow visualization and extrudate swell of NR compound by rotating‐die rheometer

An experimental apparatus coupled with a rotating die system was especially designed and manufactured to study the rheological properties, flow patterns and swelling behavior of natural rubber (NR) compound for different shear rates and die rotating speeds at a test temperature of 110°C, the results being compared with those by the static capillary die. It was found that NR compound used exhibited psuedoplastic non‐Newtonian behavior. The rotation of the capillary die could reduce the extrusion load. The wall shear stress for any given shear rates increased with increasing die rotating speed. The fluctuation of the entrance pressure drop increased with increasing die rotating speed. The flow pattern development in the rotating‐die rheometer was different from that observed in the static die. The flow patterns in the rotating die were clearly unstable and contained two flow components which included axial flow along the barrel and circumferential flow at the die entrance. The size and shape of the axial and circumferential flows were more dependent on the piston displacement. It was found that the swelling ratio of the NR compound decreased with increasing die rotating speed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Numerical investigation and visualization of polymer behavior within a capillary die

Numerical analysis of the flow regime within a capillary rheometer has been studied. The vector-based Remmelgas-Harrison-Leal (RHL), analogous to reptation-based polymer models, has been used to model the polymer dynamics. A series of computational methods for visualizing the flow characteristics of the whole region of the capillary rheometer are made including the area directly in front of the piston. Model predictions provide qualitative analysis of pressure drops observed at the entrance of the die, necessitating the use of the Bagley ends correction in practical rheology measurements. The results of the numerical code help reveal the complex flow kinematics that are involved in the entrance region to the capillary die as well as the barrel region in front of the rheometer piston. POLYM. ENG. SCI., 47:1688–1694, 2007. © 2007 Society of Plastics Engineers     

EPDM橡胶的流变特性实验研究

为了研究橡胶熔体流变性能对其加工成型的影响，利用毛细管流变仪对三元乙丙橡胶（EPDM）的流变特性进行了实验研究。实验结果表明：EPDM橡胶在毛细管挤出时，剪切速率对剪切应力、剪切粘度和挤出胀大的影响最大；挤出温度对三者有一定的影响；在长径比相同时，毛细管半径对剪切应力和剪切粘度几乎没有影响，但对挤出胀大影响较大。     

Melt flow behavior of blends from poly(vinyl chloride) and epoxidized natural rubber

Blends from poly(vinyl chloride) (PVC) and epoxidized natural rubber (ENR) were prepared in a Brabender plasticorder by the melt blending technique. The melt flow behavior of these blends with respect to blend ratio and temperature has been examined using a melt flow indexer and capillary rheometer. ENR decreases the Brabender torque, increases the melt flow index (MFI), and decreases the melt viscosity of PVC in the blends. Arrhenius plots were used to study the effect of temperature on melt flow index (MFI) and viscosity. Moreover, the flow behavior index (n′) obtained from capillary rheometer data was found to be dependent on temperature and blend ratio.     

转矩流变仪表征熔融聚合物的流变性能

采用温度校正后的转矩流变模型,研究了结晶与非晶聚合物的流变性能,并将流变结果与毛细管流变仪进行对比。结果表明,在非牛顿指数及流动活化能测量方面,转矩流变仪与毛细管流变仪测量结果差异较小;由于黏滞耗散作用,转矩流变仪在进行流变表征时需要进行转矩的温度校正;转子等效半径与几何结构有关,而与物料种类及加工条件无关;转矩流变仪测量的剪切速率范围较窄。     

The flow behavior and impact strength of poly(butylene-terephthalate) as a function of several processing variables

The flow behavior of poly (butylene-terephthalate) (PBT) has been investigated using a capillary extrusion rheometer. The behavior was measured as a function of temperature, moisture content, and residence time of the molten polymer in the rheometer barrel. The temperature and moisture dependence of PBT are compared with polycarbonate. The notched Izod impact strength of injection-molded PBT is also reported as a function of moisture content and residence time at processing temperatures.     

Study of polymer powder and melt rheology using a constant pressure,non-isothermal rheometer

A rheological analysis is proposed on a non-conventional, constant pressure, non-isothermal rheometer. The test usually starts with a polymer powder and ends with melt extrudate. The volume- (or displacement of plunger) temperature curve of the test is analyzed according to the following model: (1) at a temperature below the glass transition temperature, the test is related to the packing and/or compaction of powders, and also the compressive deformation of powders; (2) as the temperature is raised to where polymer flow begins, the test is analyzed according to melt viscous flow. The activation energy of flow of a polymer may also be estimated using this rheometer. Comparison and correlation of data using other techniques (e.g. torsional pendulum dynamic measurement, capillary rheometer, Rheometric dynamic spectrometer) will also be discussed.     

Rheology of Short Nylon-6 Fiber Reinforced Styrene-Butadiene Rubber

ABSTRACT

The rheological characteristics of short Nylon-6 fiber reinforced styrene butadiene rubber (SBR) were studied using a capillary rheometer. The study was done with respect to the effect of shear rate, fiber concentration, and temperature on shear viscosity and die swell. All the melts showed pseudoplastic nature, which decreased with increasing temperature. Shear viscosity increased in the presence of fibers. Introduction of fiber reduces the temperature sensitivity of the rubber matrix. A reduction in die swell was found in presence of fibers.     

Rheological properties of poly(vinyl chloride)/epoxidized natural rubber blends. Part I: Composition dependence and the effect of compounding conditions

Epoxidized natural rubber is a recently commercialized modified form of natural rubber. This paper is part of our continuing effort to study the responses of this new material to melt mixing and other shaping processes. The Shimadzu capillary rheometer was used to evaluate the composition dependence of miscibility of polyvinyl chloride/epoxidized natural rubber blends (PVC/ENR blends). The rheometer was also used to evaluate the effect of compounding parameters on the rheological properties of the blends. The results confirmed PVC/ENR blends as miscible systems that show a synergism in apparent shear viscosity highlighted by the positive deviation from the logarithmic additivity rule. These results based on capillary rheometry are also in very good agreement with our earlier attempt to predict optimum mixing from torque rheometry by using the Brabender Plastogram as an indicator.     

Rheological Characteristics of Short Nylon-6 Fiber-Reinforced Acrylonitrile Butadiene Rubber Containing Epoxy Resin as Bonding Agent

The rheological characteristics of short nylon-6 fiber-reinforced acrylonitrile butadiene rubber (NBR) were studied with respect to the effect of shear rate, fiber concentration, and temperature on shear viscosity and die swell using a capillary rheometer. All the melts showed pseudoplastic nature, which decreased with increasing temperature and in the presence of short fibers. Shear viscosity was increased in the presence of fibers. Die swell was reduced in the presence of fibers. Relative viscosity of the gum compound was less than one at all shear rates and temperatures. Activation energy of flow of the composite-containing bonding agent was higher at higher fiber loading and higher shear rates. Die swell increased marginally in the presence of the bonding agent.     

Dynamic behavior of a single screw plasticating extruder part I: Experimental study

The dynamic responses of a 2–1/2 inch single screw plasticating extruder and extrusion line were investigated. Step changes in screw speed, take-up speed, back pressure, and processing materials were used to determine the transient responses of barrel pressures, die pressure, melt temperature, and extrudate thickness. Dynamic responses of the entire extrusion line can be explained by the flow mechanism of the extruder and the logical properties of the polymer used. A capillary rheometer was also used to determine if it could simulate pressure responses in the extruder for screw speed changes. Results showed that capillary rheometer was helpful in estimating the short term pressure responses in the die.     

The influence of additives on the flow behavior of ABS

The flow and processing behavior of commercial plastics is determined not only by the characteristics of the base resin but also by the presence of additives of various kinds. In this study the influence of a number of additives on the rheological behavior of molten ABS was investigated using a capillary extrusion rheometer and a Weissenberg rheogoniometer. The additives studied included molding lubricants, rubber impact modifiers, flame-retardant additives, and residual unreacted components remaining from the polymerization process. The mechanisms by which these species affect flow characteristics are described.     

Developing critical extrusion parameters for nylon 6, nylon 66, and nylon 46 polyamide from the rheology data

This paper describes a new approach to the rheological characterization of engineering plastics such as nylon 6, 66, and 46 polyamides using a capillary rheometer. The melt viscosity data as a function of temperature, shear rate, and residence time were measured and evaluated to demonstrate how to accurately predict critical extrusion parameters, such as barrel temperature profile, stock temperature window, and the screw design requirements, for extruding strip, tubing, and profiles. The results of this work provide a practical and simple quality control tool to select a polyamide resin for optimum processing, and to develop critical processing parameters for extrusion.     

固体推进剂螺旋压伸挤出过程流变模型建立

在对固体推进剂的螺旋压伸过程进行研究的基础上,探究了一种新型的固体推进剂流变模型的建立方法,即采用最小二乘法拟合基于毛细管流变仪测试所得数据,得到初步固体推进剂流变本构模型,利用Polyflow有限元仿真软件模拟毛细管流变仪测试过程,对流变本构模型参数进行修正,确定最终的推进剂流变本构模型.通过实验数据拟合与有限元模拟...     

聚苯硫醚流变行为研究

采用高压毛细管流变仪研究了进口聚苯硫醚(PPS)树脂的流变性能,分析了剪切速率、温度对PPS树脂流变行为的影响。结果表明,PPS树脂的非牛顿指数均小于1;在低剪切速率下,PPS树脂的表观黏度对温度的依赖程度高于高剪切速率下的依赖程度;PPS树脂的黏流活化能随剪切速率的增加呈减小趋势,其结构黏度指数随温度升高而减小。     

Development of an in-line rheometer suitable for reactive extrusion processes

This paper presents the development of a novel in-line extrusion rheometer based on the flow of polymer through a wedge (vertically tapered slit). This rheometer is suitable for measuring changes in rheological properties on-line during reactive extrusion, because it can be used to estimate the viscosity for a range of shear rates without the need to change the polymer flow rate (i.e., extruder throughput). Equations have been developed to estimate the parameters of the power-law equation, used to describe the viscosity-shear rate relationship, from measurements of pressure drops along the wedge. An experimental in-line wedge rheometer has been built and used to measure the viscosity for a series of polypropylenes prepared via reactive extrusion. Viscosity measurements from the experimental in-line wedge rheometer are compared with measurements from a capillary rheometer. Good agreement is found between the capillary and wedge rheometer measurements.     

Die‐swell behavior during the short‐tube flow of rubber compounds

In this study, the flow properties and die‐swell ratios (B's) of two kinds of rubber compounds (SI was a calcium carbonate filled natural rubber compound, and SII was a carbon‐black‐filled natural rubber/butadiene–styrene rubber/cis‐1,4‐butadiene rubber compound) in a short‐tube extrusion flow were measured by means of a capillary rheometer under test conditions with a temperature of 90°C and an apparent shear rate varying from 10 to 4000 s^?1 to identify the effects of extrusion conditions on the rheological behavior of the materials and to estimate B. The shear flow roughly obeyed the power law, whereas B increased nonlinearly with increasing extrusion rate. Under the same shear rates, the viscosity of SII was higher than that of SI, whereas the values of B of SI were higher than those of SII. Furthermore, B of the rubber compounds was estimated by means of an extrudate swell equation published in a previous work. The results show that the predictions of B were close to the measured data from the experiments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Elongational viscosity of polymer melts: A lubricated skin-core flow approach

Previous work by this research group has shown that the use of a lubricated skin/core flow of polymer melts and a hyperbolic converging die results in an essentially pure elongational flow at a constant elongational strain rate in the core. The previous work was carried out on a laboratory-scale coextrusion system in a planar slit die; tracer particles and an image analysis system were used to confirm the predicted behavior. In this work, the technique was implemented first on the coextruder assembly, as a planar elongational rheometer, and then on a commercial capillary rheometer, as a uniaxial elongational rheometer for polymer melts. The later is achieved by replacing the standard capillary die with a hyperbolic axisymmetric die. A two-laycred billet is prepared for placement in the rheometer barrel by completely encapsulating the core polymer (the polymer to be analyzed) with a low-viscosity polyethylene skin. Commercial grades of polypropylenes, syndiotactic polystyrene, and nylon-66 were analyzed using this technique. Elongational viscosity at high extensional rates can be determined with this method; values in excess of 500 s⁻¹ have already been achieved. © 1996 John Wiley & Sons, Inc.     

PET熔体流变特性的研究与应用

作者用毛细管流变仪和Ｂｒａｂｅｎｄｅｒ流变仪测试了ＰＥＴ熔体的流变特性，发现熔体的粘度对温度非常敏感，熔体剪切变稀的现象很明显，并就粘度特性对物料加工温崐度等参数的影响及热流道的温度控制进行了讨论。