PBT工程塑料生产中MFR的控制

针对使用BUSS捏合机生产聚对苯二甲酸丁二酯(PBT)过程中出现的熔体流动速率(MFR)与产品配方体系中低分子量PBT树脂用量间的异常关系进行了研究和分析。结果表明，混炼加工PBT时，产品的MFR取决于两个因素的综合作用，一为产品配方中高、低粘度树脂的比例；二为低分子量树脂对主机功率的影响。综合二者影响，PBT的MFR与低分子量PBT用量关系近似为y=0．0471x^2-3．6347x 107．83。     

Evaluation of the mixing performance for one novel twin screw kneader with particle tracking

In this article, a novel continuous twin‐screw kneader was proposed. The end‐cross section of the screw rotor consists of convex arcs and cycloidal curves and the rotors profiles were presented. The mixing performance of the novel twin screw kneader was simulated using finite element method (FEM) combined with mesh superimposition technique (MST). Statistical analysis was carried out for flow field using particle tracking technique to research the effect of geometry parameters and working parameters on the mixing performance. To study the dispersive mixing performance, specifically the maximum shear rate, maximum shear stress, maximum mixing index, residence time distribution (RTD) and RTD density function of tracer particles, and dispersive mixing is evaluated using the mixing index in combination with the shear stress. The results show that the changes of centre distance between female and male rotor have little influence on dispersive mixing performance, the lead of rotor has little effect on maximum shear stress and maximum shear rate, while it has an obvious effect on mixing index, cumulative RTD, and RTD density function. The rotor speed has obvious influence on mixing performance, and average residence time of material decreases greatly and the mixing ability is weakened, while the self‐cleaning performance of rotor improved obviously with the increasing of rotor speed. POLYM. ENG. SCI., 54:2407–2419, 2014. © 2013 Society of Plastics Engineers     

Techniques for compounding glass fiber-reinforced thermoplastics

The processing characteristics of various glass fiberreinforced thermoplastics (FRTP) and the basic approaches for their production are discussed. Experimental work on twostage production-scale continuous kneaders was conducted to define the most important process variables in compounding FRTP materials. Results demonstrate how processing conditions and screw design influence the temperature profile in the kneader and the glass-fiber length in finished products. Feed steek appearance (i.e., pellet shape and size), melt viscosity, and volume percentage of fibers are basic material variables. High quality products can be achieved through a careful, layout of the continuous kneader in order to minimize thermal degradation of the base polymer and to effect adequate dispersion of the glass fibers in the matrix.     

Influence of the melt viscosity and operating conditions on the degree of filling,pressure, temperature,and residence time in a co‐kneader

The effect of the melt viscosity and operating conditions on processing parameters in a co‐kneader with a discharge die was experimentally investigated. Filling ratio, pressure, temperature, and residence time distribution were measured. Experiments were performed with polypropylene resins. The viscosity of the melt was varied either by changing the regulation temperature of the kneader or the molecular weight of the polymer. The filling pattern in the co‐kneader shows the conveying capability of the various elements without any effect of the melt viscosity. Experimental residence time distributions remain the same at a given feed rate and screw speed, regardless of the viscosity of the material. The global degree of filling in a zone combining conveying elements, kneading elements, and restriction ring was found to be nearly constant in the conditions of this study and therefore a simple relation exists between the mean residence time and the feed rate. Beside expected variations of the die pressure and melt temperature when the viscosity, screw speed or feed rates change, a model based on heat equation and experimental data demonstrate the high capability of the co‐kneader for heat exchange and for the control of self‐heating during mixing. POLYM. ENG. SCI., 58:133–141, 2018. © 2017 Society of Plastics Engineers     

Co-rotating twin screw compounding studies of PVC formulations

A 50 mm twin screw extruder was used to study the melting profiles of various PVC formulations. Melt temperature and degree of flux are measured axially along various mixing paddle arrangements. The viscous work is correlated with the rheology of the PVC mass and effective shear rate of the intermeshing co-rotating screws. The results of this investigation are used to develop a conceptual model of compounding PVC formulations. The radial mixing patterns in paddle segments down the barrel length are analyzed by introduction of trace quantities of pigment added to the dry blend. The resulting residence time distributions coupled with localized shear rate distributions give a numerical evaluation of shear strain required to flux PVC particles into a continuous fluid mass. By proper agitator design, compounding of PVC formulations can be accomplished with minimal thermal history.     

Processing of reinforced plastics using multi-screw compounders

Polymer modification by addition of reinforcing agents represents a popular means of increasing physical property values. The polymer matrix has been forced to accept up to 55 percent by weight of fibrous reinforcement and 80 percent by weight of powdered types in order to meet application requirements. These materials demand sophisticated mixing equipment which must provide extensive intake and conveying capabilities, polymer wetting of reinforcement, and dispersion of reinforcement. This process must also be conducted with controlled shear intensity and excellent temperature and residence time control in order to respect polymer thermal sensitivity and product requirements. The extrusion process is a proven economical method for incorporating reinforcements into polymer resins. Co-rotating intermeshing twin-screw extruders are particularly suited for these tasks. Positive conveying, self-wiping, and shear intensive mixing characteristics provided by the screw mechanism satisfy requirements of reinforcement compounding. This mechanism allows interruption of streamline flow which is needed to disperse both high and low aspect ratio reinforcing agents into a polymer matrix. Mathematical representation of the benefits of twin-screw extrusion (relative to single-screw) related to pumping and mixing capability have been developed based on the classical pressure flow continuity equation with proper selection of boundary conditions.     

Residence time distributions in a co‐kneader: A chemical engineering approach

In this article, we have studied the residence time distributions (RTD) in a modular co‐kneader. Several papers have already addressed the co‐kneader modeling and operating mode but there is still a lack of experimental data on RTD. To investigate the RTD, we have used a colored tracer dispersed in polypropylene (PP) that was injected in the flow during the compounding of neat PP. The effect of operating parameters such as temperature, feed rate, and screw configuration was investigated, focusing on the influence of mixing and conveying elements in a zone where the polymer is molten. As can be expected, results on various screw configurations show that increasing the number of kneading elements makes the RTD longer. More interestingly, for a defined set of elements, their position does not change the experimental RTD. A chemical engineering approach was used to model the RTD, with an equation derived from a cascade of continuous stirred tank reactors. The model allows to retrieve an elementary RTD for each section of a defined type of elements and to propose a law for their combination in good agreement with experiments. POLYM. ENG. SCI., 55:1237–1245, 2015. © 2015 Society of Plastics Engineers     

Stratified two-phase flog of molten polymers in circular dies

A theoretical study has been carried out on the steady, axisymmetric two-phase flow of molten polymers in circular dies. For both fluids, the shear rate dependence of the viscosity is described by a power law and the temperature dependence by an exponential function. Taking into account viscous dissipation, a numerical program has been developed to predict the radial position of the interface between the two fluids, the developing temperature and velocity fields, the shear rates, the shear stresses, the pressure drop as well as the field of shear deformation and the residence time distribution for different thermal boundary conditions. The numerical program is applied to the flow of a high-viscous polymer melt, (high density polyethylene), surrounded by a small annulus of less viscous polymer ni lt, (low density polyethylene). Computed results are shown graphically.     

Reactive compatibilization of poly(butylene terephthalate)/low‐density polyethylene and poly(butylene terephthalate)/ethylene propylene diene rubber blends with a bismaleimide

The reactive compatibilization effect of a small molecule, bismaleimide (BMI), on poly(butylene terephthalate) (PBT)/low‐density polyethylene (LDPE) and PBT/ethylene propylene diene (EPDM) rubber blends were investigated. All the blends were prepared by melt blending in the mixing chamber of a Haake Rheocord. The particle size of dispersed phase was reduced by >ten times by adding 1.2 wt % of BMI as observed with scanning electron microscopy. The torque‐time curve recorded during mixing showed that the addition of BMI leads to a significant increase in the viscosity of PBT, LDPE, EPDM, and the blends. This indicates that a chemical reaction has taken place. It was confirmed that free radicals are involved in the reactions because the addition of a stabilizer to the blends has removed all the compatibilizing effect, and the torque‐time curve does not show any increase in viscosity. A possible mechanism of compatibilization is proposed. The shear forces during melt mixing cause the rupture of chemical bond in the polymers, which form macroradicals of PBT, LDPE, or EPDM. These macroradicals react with BMI to form PBT‐BMI‐LDPE or PBT‐BMI‐EPDM copolymers. These in situ‐formed copolymers act as compatibilizers to give a significant refinement of the blend morphology. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2049–2057, 1999     

卧式单轴捏合反应器流动与混合特性的数值模拟

选取卧式单轴捏合反应器为研究对象,搭建了一个可视化实验装置来研究其分布混合过程,并且通过三维有限元数值模拟方法和网格重叠技术获取了高黏牛顿流体在反应器中的流速分布、剪切速率分布与混合指数分布,进一步采用粒子示踪技术分析了全局与局部分布混合过程,对示踪粒子的运动轨迹进行统计分析得到了拉伸率与混合效率,并且考察了搅拌结构对流动与混合过程的影响。结果表明,实验与数值模拟结果吻合较好。捏合反应器中几乎不存在流动死区,搅拌轴上的动态捏合杆与搅拌槽壁面上的静态捏合杆之间存在周期性的捏合作用,可以强化自清洁性能、剪切作用、整体与局部分布混合过程、分散混合性能以及混合效率。拉伸率随着混合时间以指数形式增加,时均混合效率大于零。     

CSTR中苯乙烯本体热聚合过程模型化和仿真分析

建立了苯乙烯本体热聚合过程模型,分析讨论了苯乙烯在连续搅拌槽式反应器中进行热引发本体聚合行为．分别讨论了聚合温度和停留时间对苯乙烯的转化率、聚合速率、产物的相对分子质量及其分布、粘度和密度的影响,结果表明,聚合温度决定产物的相对分于质量及其分布,且对转化率、聚合速率及粘度均有较大影响;停留时间对产物的相对分子质量及其分布无明显的影响,对转化率、密度及粘度有较大影响．聚合温度和停留时间是苯乙烯本体聚合过程中的两个至关重要的操作条件,同时为方便工程应用提供了经验关联式．     

高相对分子质量PET降解速率研究

从涤纶工业丝纺丝装置上在线取样 ,研究不同温度下PET特性粘数与停留时间的关系。通过对实验值的拟合 ,给出了描述PET特性粘数与停留时间的关系的数学模型和以特性粘数表征的降解速率方程。结果表明 ,相对分子质量越大 ,温度越高 ,降解越快。根据数学模型得出的熔体允许停留时间 ,可以确定相匹配的产品规格与设备参数 ,在纺丝过程中应分段控制温度。     

Phase inversion during compounding with a low melting major component: Polycaprolactone/polyethylene blends

Most of the morphology development in compounding of immiscible blends is known to occur at short mixing times. In this investigation, the effect of rheology of the minor component on its tendency to form a continuous phase at short mixing times is studied. it was shown that phase inversion during compounding can occur even with a low-melting major component. Four different blends with polyethylene as the high-melting-point minor component and polycaprolactone as the low-melting-point major component were chosen. Rheological measurements on the individual components were made both in the solid and melt states. Softening temperatures from these measurements were more representative of the observed processing behavior than the peak values as calculated from differential scanning calorimetry data. Compounding runs in a batch intensive mixer indicated that the minor component formed the continuous phase at short mixing times, in the blends with the low viscosity polyethylene. This was shown to correlate with its low modulus in the solid state and its low viscosity in the melt. A ramped temperature protocol during compounding delayed the melting of polyethylene thus preventing phase inversion from occurring. The blends with the higher viscosity polyethylene did not show phase inversion during compounding.     

Numerical nonisothermal flow analysis of non-Newtonian fluid in a nonintermeshing counter-rotating twin screw extruder

A simulation technique for nonisothermal flow analysis of non-Newtonian fluid in a nonintermeshing counter-rotating twin screw extruder was developed by modifying the flow analysis network (FAN) method. The local shear viscosity in the flow field was calculated by an iteration method combing the three types of mean shear rate functions. The modified Cross model and an Arrhenius-type function for temperature dependence were also introduced. Streamlines in the flow field are represented by computing the movements of fluid particles based on the flux fields. The computed residence time from the streamlines led us to solve the energy equation by replacing the coordinate system. The profiles of pressure, shear rate, shear viscosity, temperature, and residence time were simulated. The influence of operating and geometrical parameters on the screw characteristics are discussed. Further, residence time distribution (RTD), strain distribution function (SDF), and interfacial area growth are predicted from the computation of streamlines to analyze the mixing capabilities of the extruder.     

PBT黏度的控制及其影响因素

讨论了PBT黏度的控制以及温度、压力、搅拌转速、停留时间等因素对黏度控制过程的影响。     

Kinetics of the thermal degradation of poly(1,4-cyclohexylenedimethylene terephthalate)

The kinetics for the thermal degradation of poly (1,4-cyclohexylenedimethylene terephthalate) (PCHDT) were evaluated by means of a melt extruder. The effects of temperature, residence time, and oxygen content of the gas blanketing the polymer during storage on degradation of PCHDT were determined. The rate of thermal degradation was measured in terms of the rate of decrease of inherent viscosity and the rate of increase of carboxyl end group concentration. Residence time, temperature, and their interaction all contributed significantly to the degradation. For the conditions investigated, the oxygen content of the blanketing gas had no measurable effect on degradation. Analysis of the kinetic data yielded equations based on a random chain scission mechanism. These equations enabled the prediction of inherent viscosity and carboxyl end group concentration as functions of temperature and residence time and the inherent viscosity and carboxyl end group concentration of the original polymer. The activation energies for decrease in inherent viscosity and increase in carboxyl end group concentration of poly (1,4-cyclohexylenedimethylene terephthalate) were determined as 38.7 kcal/mole, respectively.     

The effect of mixing time on the morphology of immiscible polymer blends

The effect of mixing time on the morphology, with the viscosity ratio and composition as parameters in the mixing process, was studied for two immiscible binary polyblend systems, polyamide/polyethersulfone (PA/PES) and poly(butylene terephthalate)/polystyrene (PBT/PS), by selective dissolution followed by macroscopic and microscopic observations. At a short mixing time, the morphology of each phase depends not only on the composition, but also on the viscosity difference of two phases, shown by the results of PA/PES blends with a viscosity ratio of 0.03. The lower viscous phase (PA) forms particles, fibrils, and layers successively with its increasing content and becomes a continuous one at low concentrations as the minor phase, while the high viscous phase (PES) appears mainly in the form of particles and directly becomes a continuous one at high concentrations. With increasing mixing time, the effect of the viscosity ratio becomes less and the morphology is determined mainly by the volume fraction of each phase. Particles are the final morphology of the minor phase. Only at a viscosity ratio of unity is the morphological development of two phases (PBT and PS) with mixing time the same, and any one of these two components is in the form of particles when it is the minor phase. At the composition near 50/50, fibrillar or continuous structure may coexist for both phases. The composition range of co-phase continuity is decided not only by the viscosity ratio but also by the mixing time. With increasing mixing time, this range becomes narrower and finally occurs at volume fraction of 50/50, no longer affected by the viscosity ratio. © 1996 John Wiley & Sons, Inc.     

Gelation of Plasticized Polyvinyl Chloride Compounds in a Co‐Kneader

The co‐kneader is a proper tool for processing polyvinyl chloride (PVC) compounds. Gelation of PVC is complex because of a narrow processing window. At low temperature, gelation is incomplete and leads to poor mechanical properties, while at high temperature, degradation may occur. The aim of this study is to gain a fundamental understanding of the gelation process of PVC in co‐kneaders. Careful examination of the gelation state of extruded PVC samples was carried out qualitatively by swelling the extruded samples in acetone and quantitatively by differential scanning calorimetry measurements. Gelation in various conditions of temperature and shear was firstly studied in a capillary device that ensures both pre‐shearing and extrusion through a circular die. This provided a reference basis for comparison with gelation state obtained in the co‐kneader. Samples were collected in the co‐kneader by means of opening the barrel. The gelation state was particularly examined in connection with the measured temperature at a fixed position along the screw at which a temperature sensor was positioned. The obtained results showed that the co‐kneader allows fast gelation with a mixing energy value lower than 200 kJ/kg when the temperature is higher than a critical value of 165°C for the studied formulation. J. VINYL ADDIT. TECHNOL., 2019. © 2019 Society of Plastics Engineers J. VINYL ADDIT. TECHNOL., 26:316–324, 2020. © 2019 Society of Plastics Engineers     

反向旋转卧式双轴捏合反应器混合特性的数值模拟

以差速反向旋转卧式双轴捏合反应器为研究对象,选用高黏牛顿流体糖浆为模拟物料,通过三维有限元数值模拟方法研究了高黏糖浆在捏合反应器中的流动过程,获取了流速和剪切速率的空间分布,进一步结合粒子示踪技术探究了分布混合过程与混合效率,并且考察了搅拌结构对流动与混合过程的影响规律。研究表明,捏合反应器中几乎不存在流动死区,桨叶末端和重叠区域的流速和剪切速率较高,且高流速和高剪切区域均随着捏合杆数目和捏合杆长度的增加而增大。捏合杆可以推动物料在圆周方向上的运动,在重叠区域存在周期性交互作用,进而可以强化分布混合过程。拉伸率随着混合时间以指数形式增加,且随着捏合杆数目和捏合杆长度的增加而增加。时均混合效率大于零,随着捏合杆数目的增大而增大,随着捏合杆长度的增加呈现先增大后减小的趋势。     

The effect of processing conditions on the rheological properties of blends of ultra high molecular weight polyethylene with high‐density polyethylene

Blends of high‐density polyethylene (HDPE) with small amounts of ultra‐high molecular weight polyethylene (UHMWPE) were prepared by melt mixing in a twin‐screw microcompounder. Two types of UHMWPE differing in their states of chain entanglement were used. The blend composition, time of mixing, and rotation speed of the screws were varied. Rheological properties of the blends were studied in oscillatory shear and uniaxial elongational tests. Reduction in phase angle measured in dynamic shear rheology and increase in extensional strain hardening were found to be useful indicators for quantifying the extent of mixing of the two components. Although the disentangled UHMWPE showed reasonable mixing with HDPE during typical residence times of melt compounding operations, the entangled UHMWPE remained essentially undissolved. The extent of mixing increased with mixing time and screw speed. POLYM. ENG. SCI., 59:821–829, 2019. © 2018 Society of Plastics Engineers