同向啮合双螺杆挤出机挤出过程的计算机模拟

计算机模拟研究了聚苯乙烯在TSE-35A型同向啮合双螺杆挤出机的挤出过程.计算得到不同喂料速率与不同转速下的停留时间分布,并与在线荧光法测量值对比,二者基本相符.确定了停留时间与螺杆转速及喂料速率之间的函数关系式.模拟结果还预测了喂料速率、螺杆转速等工艺参数对双螺杆内流场变量,如温度、填充率、压力及粘度等的影响.模拟计算有助于了解双螺杆挤出机内部聚合物材料流动状态及停留时间长短,从而指导实际聚合物生产.     

Rubber Powder – A Perspective Filler of Thermoplastics

Rubber powder, ground at ambient temperature, was compounded with polypropylene using only 16 L/D of a co-rotating twin screw extruder. An optimum of extruder configuration and selected process parameters were found for compounds with a rubber filling rate of 50 wt.-%. Restrictions of a reactive compounding were taken into account. The dispersion of the rubber powder is not a limiting process. A compound containing 70 wt.-% rubber powder showed to be overfilled.     

Thermal degradation of high density polyethylene in a reactive extruder

The thermal degradation of high density polyethylene was conducted in a reactive extruder at various screw speeds with reaction temperatures of 400 °C and 425 °C. The residence time of the extruder was estimated and the molecular weight distribution of the fed plastic and reaction products was analysed using gel permeation chromatography. A continuous kinetic model was used to describe the degradation of the high density polyethylene in the reactive extruder. The breakage kernel and the scission rate model parameters were estimated from the experimental data for a variety of cases. It was found that purely random breakage and a scission rate which had a power law dependence on molecular size of 0.474 best described the experimental data.     

On-line monitoring of the residence time distribution along a kneading block of a twin-screw extruder

An on-line Residence Time Distribution (RTD) measuring set-up that enables the characterisation of twin screw extruders at short axial increments is presented. It uses the light emission of a fluorescent tracer (perylene) to generate concentration versus time curves, which are then used to determine the usual RTD parameters, delay time, mean residence time and variance. The system is initially mounted on a rectangular die coupled to a single screw extruder, on-line and off-line measurements being directly contrasted. Then, the optical probe is positioned at several points along the axis of a modular co-rotating twin screw extruder, on-line and off-line data being again compared. Having gained confidence in the measuring technique, an experimental unit utilizing a transparent barrel is used to characterize the evolution of RTD along a kneading block of a twin screw extruder.     

A novel apparatus combining polymer extrusion processing and x-ray scattering

A novel apparatus was designed and constructed combining polymer extrusion processing and x-ray scattering. It allows direct, real time monitoring of structure and temperature development in polymer material during extrusion. The apparatus involves a vertical industrial extruder equipped with a four-roll stretching device to mimic the processing environments of uni-axially oriented films or sheets, a simultaneous small and wide angle x-ray scattering system and an infrared thermometer as detection unit. The charging barrel of the extruder and the stretching device can be moved upward and downward precisely. By moving the sample along the center line, structure and temperature development as a function of position can be obtained. The performance of the apparatus was verified by a test experiment, which allows us to establish the relationship between processing parameters and evolution of structure with different length scales, and may lead to a better understanding of the physics in polymer processing.     

Simulation of liquid cooling of an extruded sleeve plastic film

A mathematical model of a liquid cooling was considered for a tubular plastic film produced by extrusion down. The developed model allows for a preset film speed (extruder) and film parameters to determine a length of a cooling zone or for a preset length of the cooling zone calculation of maximum speed of the film with the preset parameters.     

Détermination de l'aptitude à l'extrusion de polyéthylène basse densité pour le gainage des cables—II. Influence des propriétés rhéologiques sur le comportement à l'extrusion de polyétyhylène basse densité

In the first part, the influence of physical-chemical characteristics of various low density polyethylenes on their rheological properties has been shown. The studies of these polymers were carried out with a laboratory extruder, and the fundamental rehological parameters were evaluated. These parameters affect the behaviour of polyethylene during processing and their values can be used for control.     

酞侧基聚芳醚砜和聚芳醚酮的相容性

本文报道注射级酞侧基聚芳醚砜(PES-C)和聚芳醚酮(PEK-C)共混试样的玻璃化转变行为和部分力学性能的研究结果。并讨论共混工艺对相容性的影响。 PES-C和PEK-C树脂均由中国科学院长春应用化学研究所徐州工程塑料厂合成,在三氯甲烷中的比浓粘度ηsp/c(20℃)分别为0.45和0.47。将粉状树脂在GH-100Q高速搅拌器内按配方混合,并在烘箱内干燥后,用SHJ-30双螺杆挤出机在320～350℃(物料温度)挤出造粒。     

淀粉与木糖醇共混物的性能

淀粉与木糖醇共混物的性能于九皋，郑华武（天津大学化学系天津３０００７２）关键词淀粉，木糖醇，共混，热塑性研究具有环境条件下可降解的塑料已成为国内外专家学者广泛关注的研究课题。淀粉具有类似高聚物的分子结构，但由于分子量大，分子之间的亲合力强，很难加工成...     

Processing window for extrusion foaming of hydroxypropyl methylcellulose

Foamed materials are gaining an increased interest due to their good mechanical properties in relation to their low densities and an increased industrial demand can be expected. A few less attractive issues can however be associated with commodity foamed products. For instance the raw-material often originates from non-renewable, fossil-based, sources. Furthermore, degradation in nature is slow, therefor the disposed product is burned or end up in landfills. One possibility to reduce the impact on nature could be to produce foams from natural polymers such as starch or cellulose. In this study the possibility to produce foams from hydroxypropyl methylcellulose (HPMC) with water as blowing agent, by continuous extrusion, was investigated. A pre-study using a capillary viscometer, batch-extruder, was conducted to evaluate the foamability of HPMC. Due to promising results further experiments were conducted with a single-screw extruder. The goal was to find an adequate processing window for foaming. It was concluded that HPMC could successfully be foamed by continuous extrusion, although a careful tailoring of the processing parameters was required. Crucial parameters were here the temperature, pressure and residence time distribution in the extruder. Regions of the extruded foams were examined using optical and scanning electron microscopy and HPMC foams with a density in the range of that of fossil-based polymeric foams could be produced.     

Simulations of cyclic voltammetric and chronoamperometric electrode responses at a disk electrode using combinations of spherical and cylindrical electrode geometries

Using geometric models based on one-dimensional transport at spheres and cylinders, three methods for improving the simulation of voltammetric behavior of a disk electrode have been explored. One method is based on the common assumption of equivalency between the limiting currents for a disk and a hemisphere under steady-state diffusion conditions. The second method involves the use of a partial-sphere geometry which is a better approximation that is suitable at the extreme diffusional limits achievable at a disk electrode of fully planar and steady-state transport. The third method, which is generally applicable, is a further refinement that uses a combination of appropriate one-dimensional spherical and cylindrical geometries. The results demonstrate that reasonably accurate approximations of disk behavior for several reaction mechanisms can be achieved in a fraction of the time required to compute the more rigorous two-dimensional model. We propose that the approximation serve primarily as a fast way to explore system behavior and establish approximate values of the relevant parameters. More accurate computations can then be performed using the two-dimensional model.     

Polystyrene prepared by reactive extrusion: kinetics and effect of processing parameters

The conversion and residence time were investigated during the bulk polymerization of styrene in a twin screw extruder. It was found that polymerization mainly occurred in the zone between 400 and 1000 mm along the screw axis in the extruder, corresponding to the residence time of the reactants ranging from 1 to 4 min in the extruder. Furthermore, the processing conditions (feed rate, screw rotation rate) and average molecular weight of the polymer have a great effect on the residence time. Based on dimensionless analysis, a model of the residence time has been built‐up, which has been confirmed by the results of realistic measurements. A kinetic model of the polymerization has also been established under the assumption that the screw extruder can be regarded as an ideal plug flow reactor. Copyright © 2004 John Wiley & Sons, Ltd.     

Volatile Depletion in Planet-Forming Disks

Newly born stars are surrounded by gas and dust with a flattened axisymmetric distribution termed protoplanetary disk, in which planets are formed. Observations of these objects are necessary for understanding the formation and early evolution of stars and planets, and for revealing the composition of the raw material from which planets are made. Numerical models can extract important parameters from the observational data, including the gas and dust mass of the disk. These parameters are used as input for further modeling, e.g., to calculate the chemical composition of the disk. A consistent thermochemical model should be able to reproduce the abundances of different species in the disk. However, this good wish has been challenged for many disks: models over-predict the emission line intensity of some species; namely, they are depleted (with respect to expectations from canonical models). In this review we show how this disparity indicates that dust evolution has significant effects on gas chemistry, and may indicate the earliest stages of planet formation.     

Mechano-radical formation in polypropylene by an extruder action and its after-effects

Free radical (mechano-radical) formation caused by the mechanochemical effect of an extruder was experimentally proved on polypropylene by (ESR) combined with the spin trapping method. In this experiment the commonly used spin-trapping agents were found to be useless because of the higher temperature in the extruder, but the hindered amine light stabilizer (HALS), bis-(2,2,6,6-tetra-methyl-4-piperidinyl) sebacate, was found to be a good spintrapping agent in the extruder action. The enhancement of the photodegradation was found for the fractured polypropylene, which had experienced the extruder action. The series of reactions initiated by the mechano-radicals formed in the extruder are discussed. It is most reasonable to assume that the polypropylene is contaminated with ketons after passing through an extruder, even if the sample has been pure before the passing through the extruder. Since the ketons play the role of chromophore, the presence of ketons in the fractured samples is an origin for the enhanced photodegradation of the fractured polypropylene.Dedicated to Professor Hans-Henning Kausch on the occasion of his 60th birthday     

Water‐assisted melt compounding of nylon‐6/pristine montmorillonite nanocomposites

An exploratory pioneering study on the fabrication of nylon‐6/montmorillonite (MMT) nanocomposites with the aid of water as an intercalating/exfoliating agent via melt compounding in a twin‐screw extruder was conducted. Commercial nylon‐6 pellets and pristine MMT powder were directly fed into the hopper of the extruder. Water was then injected into the extruder downstream. After interactions with the nylon‐6 melt/pristine MMT system, water was removed from the extruder further downstream via a venting gate. As such, no third‐component residual was left within the extrudates. Transmission electron microscopy micrographs showed that pristine MMT was uniformly dispersed in the nylon‐6 matrix. The contact time between water and the nylon‐6/pristine MMT system inside the extruder was so short that nylon‐6 was subjected to very little hydrolysis, if any. The resultant nanocomposites showed higher stiffness, superior tensile strength, and improved thermal stability in comparison with their counterparts obtained without water assistance and the nylon‐6/organic MMT nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1100–1112, 2005     

Development of new polyolefin films with nanoclays for application in food packaging

Nanomaterials have been demonstrated to possess novel characteristics that can be applied in developing new packaging with better properties than packaging produced with micromaterials. Such developments include the production of packaging with improved barrier properties, which applied to the food industry will extend the shelf life of a food, thereby expanding its marketing potential. The present study entailed the optimization of experimental variables (pressure, temperature, processing time, feed position, etc.) involved in the elaboration of polypropylene and polyethylene films with nanoparticles, to obtain a film with good exfoliation, barrier and mechanical properties. SEM, TEM and XRD were also evaluated as tools for determining the degree of exfoliation of nanoparticles. Optimization of the technology involved in production of an exfoliated nanocompound is a complex process in which multiple variables and parameters are involved. The results of the study showed that the feed position of the nanoparticle in the double screw extruder is of vital importance in obtaining an exfoliated film. The maximum temperatures used in the extruder were 170 °C and 130 °C, for polypropylene and polyethylene respectively.     

Turbulent drag reduction characteristics of poly(acrylamide-co-acrylic acid) in a rotating disk apparatus

The effects of experimental parameters such as temperature, polymer concentration, and rotational speed of the disk on drag reduction properties of water-soluble copolymer of poly(acrylamide-co-acrylic acid) in a turbulent flow were examined. Drag reduction (DR) efficacy up to 45% was found to be dependent on its medium temperature in a rotating disk apparatus. When the temperature was increased, the copolymer was found to be much susceptible to mechanical degradation, indicating that polymer chain scission becomes more severe at elevated temperatures. In addition, the optimum copolymer concentration for high DR efficacy was also observed.     

Fracture studies of polypropylene/nanoclay composite. Part I: Effect of loading rates on essential work of fracture

Polypropylene (PP)/Montmorillonite (MMT) nanoclay based composite was prepared by melt compounding with maleic anhydride grafted polypropylene (MA-g-PP) as a compatibilizer in a twin-screw extruder, and the test specimens were injection molded. Mechanical properties such as tensile modulus, flexural modulus, yield strength and maximum percent strains were measured for pure PP and PP based nanocomposite to establish the effect of clay platelet reinforcement. The fracture properties were measured by using the essential work of fracture (EWF) method. PP/clay nanocomposite shows 25% improvement in specific EWF compared to pure PP. The variation of EWF parameters with loading rate is discussed, whilst the mechanisms of fracture are considered in a subsequent paper.     

Preparation and characterization of vinyltriethoxysilane grafted ethylene propylene diene terpolymer/linear low density polyethylene (EPDM‐g‐VTES/LLDPE) blends

Graft polymerization of vinyltriethoxysilane (VTES) onto ethylene‐propylene‐diene terpolymer (EPDM) was carried out in toluene using dicumylperoxide (DCP) as initiator. Effects of various parameters (EPDM content, VTES content, reaction time, reaction temperature and initiator concentration) on the grafting efficiency of VTES onto EPDM were investigated. At the optimum grafting efficiency conditions, EPDM‐g‐VTES was developed by melt mixing in a twin screw extruder and then linear (l), statically vulcanized (s) and dynamically vulcanized (d) blends of EPDM‐g‐VTES with linear low‐density polyethylene (LLDPE) with varying percentage compositions were prepared by melt mixing in the twin screw extruder. The grafting of VTES onto EPDM and its crosslinking was confirmed by FT‐IR. The characterization of mechanical properties such as tensile strength, elongation at break, Young's modulus and hardness, differential scanning calorimetry (DSC) analysis and morphology were studied and compared for the EPDM‐g‐VTES/LLDPE blends. The study reveals that the dynamically vulcanized blend improves the mechanical and thermal properties due to the presence of efficient interaction between component polymers when compared with other blends. Copyright © 2005 John Wiley & Sons, Ltd.     

In-line monitoring of droplets deformation and recovering and polymer degradation during extrusion

An extruder can be operated as a torque rheometer by setting an external control of the processing variables and adding an in-line optical detector and an on-off mechanical valve at the extruder die exit. Various operational modes can be used including constant, ramp and sinusoidal changes of the die-head pressure. With the valve closed, a fixed amount of polymer is added and the extruder put into operation, controlling the screw rotation speed via software, having a proportional/integral/derivative controller. Polymer degradation can be followed recording changes in barrel pressure and torque. After processing, the valve is opened and the molten polymer discharged under a controlled die-head pressure, manipulating again the screw rotation speed. The polymer mixture morphology can be scanned during the discharge of the melt flow by the in-line turbidimeter, showing the deformation/recovery of the second phase droplets.