近熔点状态下聚乙烯在收敛流道模具连续挤出自增强

采用楔形收敛流道挤出口模，通过控制挤出成型工艺获得了聚乙烯自增强片材，研究了制品结构性能之间的关系，结果表明：聚乙烯自增强片材连续挤出成型存在成型温度窗口，在此成型温度窗口内，聚乙烯自增强连续挤出片材在平行于拉伸方向可以形成大量排列有序，取向程度很高的微纤结构，这些微纤结构成为片材的增强相，赋予片材以极高的纵向强度。     

Stress optical studies of oriented poly(methyl methacrylate)

A series of samples of oriented poly(methyl methacrylate) was produced by hydrostatic extrusion at temperatures below the glass transition temperature. The development of orientation in the process was monitored by the measurement of birefringence which was shown to depend on the extrusion temperature as well as on the applied deformation. Additional information to characterize the oriented state was obtained by measuring the shrinkage force which developed when the oriented sample, constrained to constant length, was heated to a temperature just above the glass transition temperature; specimens free to contract all recovered to the isotropic state and original dimensions on annealing at this temperature. Most measurements were made on specimens ‘as extruded’ with additional studies made on specimens annealed at temperatures above the extrusion temperature but below the glass transition. The data, which have strong implications with regard to deformation mechanisms, are interpreted both at a molecular level in terms of deviations from an ideal rubber network, and at a more phenomenological level in terms of the Mooney-Rivlin equation.     

High-Temperature Extrusion Behavior of a Superplastic Zirconia-Based Ceramic

Workability of 3-mol%-yttria-stabilized tetragonal ZrO₂ has been gauged through a series of extrusion experiments performed under vacuum with graphite dies at 1500°C and 35 MPa piston stress. It is shown that dense and smooth extrusions can be obtained from solid billets when graphite paper is used as a lubricant. Sigmoidal dies and conical dies with cone angles of 18.4°, 26.6°, and 45° and diameter ratios of 1.5, 2, and 3 were used to explore extrusion behavior. Observed piston velocities correspond to what may be predicted from the experimental uniaxial constitutive creep equation and a simple slab analysis. A precise analysis, however, is not attempted because of lack of steady-state behavior of the material itself.     

Thermoforming of liquid crystalline polymer sheets

Liquid crystalline polymer (LCP) extruded sheets were further processed by the conventional thermoforming method. The available processing temperature range was defined through the structural, thermal, and elevated temperature mechanical characterization of the extruded sheet. This temperature range was found for LCP to be quite narrow, in the proximity of the crystal-mesophase transition. The structural changes imposed on the LCP sheet during forming and its thermal stability were investigated using wide angle X-ray diffraction, mainly for the determination of the chain orientation distribution, DSC, and dynamic mechanical analysis. Thermoforming onto a symmetrical male mold was found to enhance the orientation in the extrusion machine direction and even change the preferred orientation in the extrusion transverse direction to orientation along the thermoforming direction. Annealing at the thermoforming temperature range results in a more ordered and thermally stable structure accompanied by just a slight orientation loss.     

Analysis of the performance of cooling extruders in thermoplastic foam extrusion

The performance of cooling extruders widely used in thermoplastic foam extrusion was analyzed, by numerically solving the equations of motion and heat transfer. Analysis of cooling extruders does not require a consideration of the melting behavior of polymers, thus simplifying the system equations considerably. The flow geometry analyzed was an unwound screw channel of a single-screw extruder, i.e., a rectangular channel of uniform height followed by diverging and converging sections. Due to the cooling of both the extruder barrel and the screw, the heat transfer equation considered includes the terms describing the convective heat transfer in the down-channel direction and the conductive heat transfer in the cross-channel direction, in addition to the terms describing the viscous shear heating. For the analysis, a power-law model was used as the constitutive rheologlcal equation, describing the viscosities of a mixture of a fluorocarbon blowing agent and a low-density polyethylene melt (or polystyrene melt). The parameters in the Theological model were determined using the data of Han and Ma (13). In obtaining numerical solutions of the equations of motion, an integration method was employed to overcome the problem of numerical instabilities. The present analysis predicts the profiles of developing temperature and velocity in the down-channel direction, and the profiles of temperature, velocity, shear rate, and viscosity in the cross-channel direction. In presenting the results of computer simulation, emphasis is placed on the effects of cooling the extruder barrel and screw on the performance of cooling extruders, in terms of the pressure drops along the extruder axis and the mechanical power consumption. This study provides a rational basis for the design of cooling extruders widely used in thermoplastic foam extrusion and for the selection of optimum extrusion conditions in producing thermoplastic foams.     

Structural,mechanical, and thermal properties of extruded sheets of a liquid crystalline copolyester

Structural, Mechanical, and thermal properties of extruded sheets of a liquid crystalline copolyester containing p-hydroxybenzoic acid and 2-hydroxynaphthoic acid were investigated using X-ray diffraction measurements, differential scanning calorimetry, rheovibron measurements, and scanning electron microscopic observation. The extruded sheets of the thermotropic copolyester are composed of layered structures containing skin and core layers. A skin layer comprises fine fibrils oriented almost parallel to the extrusion direction. A core layer contains poorly oriented thicker fibrils or platelike structures. The orientation function of sheets and their tensile dynamic modulus parallel to the extrusion direction increase with increasing draw-down ratio of the sheet. Annealing of the sheet caused the increases in the temperature and the heat of crystal—mesophase transition, the heat-resistance to the mechanical tensiles properties, and the inherent viscosity of the polymer. The effect of annealing on the structural properties of the extruded sheet was discussed. © 1993 John Wiley & Sons, Inc.     

Solid-State Extrusion of Isotactic Polypropylene Through a Tapered Die. I. Phenomenological Analysis

Abstract

The solid state extrusion of isotactic polypropylene through a tapered die was conducted under various extrusion conditions using a piston-cylinder type extruder. The equation for evaluating the extrusion pressure was derived based on the plasticity theory as a function of die geometry and frictional coefficient between die wall and material. The integrand of the equation includes the yield stress as a function of true strain, which was given by the tensile properties of the same polymer. The data of lower degree of processing were fairly well described by the equation, but the estimation was not so accurate at high extrusion ratio. The molecular weight dependence of extrusion pressure was very small in solid state extrusion compared with the case of melt viscosity. This fact showed that the local inter-molecular interaction is a predominant factor in solid state extrusion. The effect of frictional resistance on a cylinder part was found to be negligible in our experimental conditions.     

Processing and physical properties of native grass-reinforced biocomposites

Big blue stem grass fiber-reinforced high density polyethylene powder biocomposites were fabricated using two separate processing schemes: (1) by compounding biofiber with the thermoplastic powder in an extruder and subsequently injection molding the extrusion pellets and (2) by combining biofiber and the powder thermoplastic powder using a modified sheet molding compounding (SMC) line and subsequently compression molding the sheet material. The physical properties including storage modulus, heat deflection temperature (HDT), notched Izod impact strength, and morphology were evaluated with dynamic mechanical analysis, Izod impact strength measurement, and microscopy observation. It was found that compression-molded specimens achieved similar modulus values to injection molded specimens for grass-reinforced high density polyethylene (HDPE) composites. The stiffness of the compression-molded specimens is related to the consolidation state of the samples, which depends on compression molding conditions such as temperature, pressure, and mold type. Compression-molded specimens exhibited a higher HDT and notched Izod impact strength compared to injection-molded samples. Grass fiber-reinforced cellulose acetate butyrate (CAB) biocomposites made with SMC processing had similar physical properties with grass fiber-reinforced HDPE composites, which indicates that natural fiber-reinforced CAB biocomposites have the potential to replace polyolefin-based composites for automotive applications. POLYM. ENG. SCI. 47:969–976, 2007. © 2007 Society of Plastics Engineers.     

The influence of extrusion parameters on the mechanical properties of polypropylene sheet

Extruded thermoplastic sheet is widely used in the production of thin-gauge tubs and containers for the food and beverage industry using the thermoforming process. The production of high quality thermoformed parts is critically dependent on the standard of extruded sheet feedstock used. The extrusion process itself imparts a thermal history to the sheet, and this in turn partly dictates its subsequent thermoformability. This paper assesses the influence of various extrusion parameters on the mechanical and morphological properties of polypropylene sheet, with a view to defining the optimum extrusion conditions for polypropylene. The extrusion parameters under consideration are chill-roll temperature, line speed, sheet thickness and melt temperature.     

中国涤纶长丝设备市场分析及预测

介绍了2010-2011年中国涤纶长丝产量、品种结构,以及涤纶预取向丝(POY)设备、全拉伸丝(FDY)设备、拉伸变形丝(DTY)设备市场增长情况,预测了2012-2013年涤纶长丝设备的市场情况及未来涤纶长丝设备技术发展方向.     

Aliphatic polyesters as models for relaxation processes in crystalline polymers: 4. Dielectric relaxation in oriented specimens

To investigate further the effect of the crystal phase on amorphous-phase relaxation, samples of 6-6, 5–7, and 6–10 polyesters have been oriented by extrusion in the solid-state through a tapered die and the dielectric constant and loss measured both parallel and perpendicular to the extrusion direction. The data have been analysed quantitatively in terms of the Cole—Cole phenomenological equation and relaxation times, width parameters and relaxation strengths determined. For the β (glass—rubber relaxation) the relaxation times are shifted 2–3 orders of magnitude to longer times and the relaxation is broadened slightly compared to the unoriented polymers. There also tends to be reduction of overall parallel and perpendicular relaxation strength for the β process on orientation. The γ processes show little effect of orientation on relaxation time and width and do not show reduction of overall relaxation strength. These observations are consistent with crystal displacement further restricting amorphous-phase longer-range segmental motion (β process) but having little effect on the locallized motions associated with the γ process. Both the γ and β processes show anisotropy in relaxation strength. The anisotropy is analysed with a newly developed theory to separate inherent phase anisotropy from apparent anisotropy due to composite or form effects. The average angle made by the lamellar surface normal to the extrusion direction enters as a parameter in the theory. Measurements of relaxed specimen $\text{ε}{}_{\mathrm{}}$ and ε_⊥ values for both the γ and β processes serve to determine both f_a the amorphous-phase orientation function and the average tilt angle for the specimens here. This is possible because for the γ process relaxation strength is small and specimen anisotropy is dominated by inherent phase anisotropy but for the γ + β processes larger relaxation strength leads to specimen anisotropy being strongly influenced by crystal—amorphous phase composite effects. Values of f_a are in the range of 0.05–0.20 for specimens with f_c in the range 0.5–0.9. Indicated lamellar tilt angles are in the range of 24°–80°.     

Fiber orientation control of short‐fiber reinforced thermoplastics by ram extrusion

In this study we examine the fiber orientation distribution, fiber length and Young's modulus of extruded short‐fiber reinforced thermoplastics such as polypropylene. Axial orientation distributions are presented to illustrate the influence of extrusion ratio on the orientation state of the fibrous phase. Fibers are markedly aligned parallel to the extrusion direction with increasing extrusion ratio. The orientation state of extruded fiber‐reinforced thermoplastics (FRTP) is almost uniform throughout the section. The control of fiber orientation can be easily achieved by means of ram extrusion. Experimental results are also presented for Young's modulus of extruded FRTP in the extrusion direction. Young's modulus follows a linear trend with increasing extrusion ratio because the degree of the molecular orientation and the fiber orientation increases. The model proposed by Cox, and Fukuda and Kawada describes the effect of fiber length and orientation on Young's modulus. The value of the orientation coefficient is calculated by assuming a rectangular orientation distribution and calculating the fiber distribution limit angle given by orientation parameters. By comparing the predicted Young's modulus with experimental results, the validity of the model is elucidated. The mean fiber length linearly decreases with increasing extrusion ratio because of fiber breakage due to plastic deformation. There is a small effect on Young's modulus due to fiber breakage by ram extrusion.     

Toward a viscoelastic modeling of anisotropic shrinkage in injection molding of amorphous polymers

A novel approach to predict anisotropic shrinkage of amorphous polymers in injection moldings was proposed using the PVT equation of state, frozen‐in molecular orientation, and elastic recovery that was not frozen during the process. The anisotropic thermal expansion and compressibility affected by frozen‐in molecular orientation were introduced to determine the anisotropy of the length and width shrinkages. Molecular orientation calculations were based on the frozen‐in birefringence determined from frozen‐in stresses by using the stress‐optical rule. To model frozen‐in stresses during the molding process, a nonlinear viscoelastic constitutive equation was used with the temperature‐ and pressure‐dependent relaxation time and viscosity. Contribution of elastic recovery that was not frozen during the molding process and calculated from the constitutive equation was used to determine anisotropic shrinkage. Anisotropic shrinkages in moldings were measured at various packing pressures, packing times, melt temperatures, and injection speeds. The experimental results of frozen‐in birefringence and anisotropic shrinkage were compared with the simulated data. Experimental and calculated results indicate that shrinkage is highest in the thickness direction, lowest in the width direction, and intermediate in the flow direction. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2300–2313, 2005     

振动力场下单螺杆挤出机聚合物熔融过程模拟

采用数值模拟方法对振动诱导挤出熔融过程中振动参数的影响规律做了深入系统的研究。利用大型通用有限元软件ANSYS作为汁算机仿真平台，利用振动力场作用下聚合物依时性非线性粘弹特性和自行修正的具有松弛谱特性的Maxwell本构模型，对振动诱导挤出熔融过程在不同振动参数作用下的响应情况进行模拟分析。结果表明在一定振动参数范围内振动力场的引入有利于加速熔融进程。     

不同进气角度对片材气辅挤出成型的影响

采用气辅助挤出成型技术,分别以垂直进气和平行进气2种方式进行了片材挤出实验,根据流变学原理建立了片材三维气辅挤出模型,利用有限元方法对0°、15°、30°、45°、60°、90° 6个不同进气角度下熔体在口模内的挤出过程进行了数值模拟。结果发现,改变进气角度对片材挤出制品造成了不同的影响,进气角度为90°时熔体在口模内的变形程度最大,随着进气角度的减小,熔体的变形程度减小;15°~30°的进气角度对聚合物片材气辅挤出成型最有利。     

异型材挤出成型过程三维等温黏弹性的数值模拟

针对异型材挤出成型流动过程的特点，基于PTT黏弹性本构模型，经合理假设，建立了描述其成型过程的三维等温黏弹性理论模型，并通过DEVSS／SUPG、最小元法Mini—Element和罚函数法等稳态有限元技术，建立了与该模型相适应的快速收敛的稳态有限元数值算法，并以此通过有限元数值模拟，系统研究了松弛时间和进口流量对异型材挤出成型过程的影响，得出了离模膨胀随松弛时间、进口流量增大而增大的规律。并通过理论分析，揭示了第一法向应力差决定离模膨胀的机理。数值模拟结果与传统的挤出实验研究结论相吻合。     

Modeling of visco‐hyperelastic behavior of transversely isotropic functionally graded rubbers

In this article, visco‐hyperelastic constitutive model is developed to describe the rate‐dependent behavior of transversely isotropic functionally graded rubber‐like materials at finite deformations. Zener model that consists of Maxwell element parallel to a hyperelastic equilibrium spring is used in this article. Steady state response is described by equilibrium hyperelastic spring and rate‐dependence behavior is modeled by Maxwell element that consists of a hyperelastic intermediate spring and a nonlinear viscous damper. Modified and reinforced neo‐Hookean strain energy function is proposed for the two hyperelastic springs. The mechanical properties and material constants of strain energy function are graded along the axial direction based on exponential function. A history‐integral method has been used to develop a constitutive equation for modeling the behavior of the model. The applied history integral method is based on the Kaye‐BKZ theory. The material constant parameters appeared in the formulation have been determined with the aid of available uniaxial tensile experimental tests for a specific material and the results are compared to experimental results. It is then concluded that, the proposed constitutive equation is quite proficient in forecasting the behavior of rubber‐like materials in different deformation and wide ranges of strain rate. POLYM. ENG. SCI., 56:342–347, 2016. © 2016 Society of Plastics Engineers     

Transverse orientation dies for solid-state extrusion of polymers. Part II: Orientation and properties of extrudates

Biaxial orientation in polymer products is normally brought about by the application of planar tensile stresses to sheets or films in either the “plastic” or “rubbery” state. More recently, other techniques have been explored as, for instance, the superimposition of rotational components in planes perpendicular to compressive forces. The present work is concerned with the solid-state extrusion of very high molecular mass crystalline polymers, such as poly(tetra)fluoroethylene (PTFE) and ultrahigh-molecular-weight polyethylene (UHMWPE), using dies featuring converging and diverging walls perpendicular, to each other and with a cross-section area at the entry being the same as at the exit. Measurements of birefringence and tensile strength on solid section extrudates have shown that dies with small converging angles, known as fish tail dies, produce a uniaxial type of orientation along the transverse direction, while dies with large converging angles at the entry region give rise to an unbalanced biaxial orientation.     

Three-block copolymers: morphologies and stress - strain properties of samples prepared under various experimental conditions

The structural and morphological characterization of a styrene-butadiene-styrene thermoelastic three-block copolymer (Kraton 1101) is reported together with the stress-strain properties of specimens prepared with different techniques (compression moulding, extrusion, solution casting). The influences of the extrusion and of the annealing treatment at high temperature on the morphology (and therefore on the stress-strain properties) are considered in detail because the structure of the specimen becomes particularly simple; it consists of polystyrene cylinders arranged along the extrusion direction and embedded into the rubbery matrix. The rods along the axis lead to a continuous polystyrene phase, so that the plugs exhibit the Mullins and hardening effects already observed for other copolymers. Films cast from toluene are also investigated; the rate of evaporation of the solvent shows a remarkable influence on the morphology of the material and, of course, on its physical properties. An explanation for the hardening effects at high values of deformation is also suggested, supported by optical birefringence measurements on compression moulded specimens after strain.     

塑料电磁动态挤出机中挤出压力对振动强度的响应

采用自行修正的Tanner本构方程,对塑料电磁动态塑化挤出机中挤出压力对振动力场的响应进行了研究,建立了振动力场下挤出压力响应的理论模型,分析了振动力场作用下挤出压力降低的原因,并从实验方面进行了验证,结果表明,理论分析的结论是基本合理的。