塑料挤出成型发展概况

介绍塑料挤出成型原理的研究发展、挤出成型主要工艺参数和挤出成型的新工艺,通过对挤出成型主要工艺参数(机筒温度、口模温度、螺杆转速与挤出速率和牵引速率)和挤出成型的新工艺(反应挤出、固态挤出和共挤出技术)的研究,进一步展望了挤出成型设备的发展趋势。     

超高相对分子质量聚乙烯固相挤出过程研究

采用一种新型超高相对分子质量聚乙烯成型技术—固相挤出成型。采用扫描电子显微镜观察了制品成型前后内部微观结构变化;采用差示扫描量热分析,研究了不同挤出温度与口模拉伸比对挤出制品热性能的影响。结果表明,相对熔融挤出成型,固相挤出成型制品光滑、透明、密度较大;制品内部产生大量的微纤结构,结晶度提高,分子链取向增强,拉伸强度提高了2.7～4.5倍,拉伸弹性模量提高了42倍;另外,熔点上升了3～5 ℃、熔融焓及结晶度分别提高了8~10个百分点。     

Low temperature solid‐state extrusion of recycled poly(ethylene terephthalate) bottle scraps

The processing of poly(ethylene terephthalate) (PET) involves thermal and hydrolytic degradation of the polymer chain, which reduces not only the intrinsic viscosity and molecular weight, but also the mechanical properties of recycled materials. A novel PET/bisphenol A polycarbonate/styrene–ethylene–butylene–styrene alloy based on recycled PET scraps is prepared by low temperature solid‐state extrusion. Hydrolysis and thermal degradation of PET can be greatly reduced by low temperature solid‐state extrusion because the extrusion temperature is between the glass‐transition temperature and cold‐crystallization temperature of PET. Modification of recycled PET by low temperature solid‐state extrusion is an interesting method; it not only provides an easy method to recycle PET scraps by blend processing, but it can also form novel structures such as orientation, crystallization, and networks in the alloy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2692–2699, 2006     

Solid state extrusion of vinylidene fluoride (VF2)/vinylidene trifluoride (VF3) copolymers. I: Dynamics of solid state extrusion

Solid state extrusion dynamics of poly(vinylidene fluoride) and its copolymers have been studied using an Instron capillary rheometer with specially designed die set. At and above the Curie transition temperatures, the copolymers rapidly soften while preserving the semicrystalline structure. This allows them to be solid state extruded between this temperature and melting temperature. The processing windows within which high quality extrudates can be obtained were established for two copolymer compositions and they were found to be much wider than those typically observed in semicrystalline homopolymers such as polyethylene and polypropylene. Extrudate swell under all solid state extrusion condition remains constant and is always less than 1 and it was found to increase above this value as the extrusion temperature increased through the melting region which is typical of melt extrusion of these polymers.     

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.     

Microhardness of extruded high density polyethylene fibers

High-density polyethylene of high tensile modulus has been produced by solid state extrusion using an Instron capillary rheometer. Microhardness measurements on these ultraoriented fibers have been made to assess their perfection from values of the tensile elastic modulus and shear strength. The microhardness tests were measured using a Vickers square diamond. The microhardness increased with the common temperature for crystallization and extrusion, likely due to improvement in the lateral packing of microfibrils. The variation of microhardness with draw ratio is also illustrated.     

Ultradrawing of thermoplastics by solid state coextrusion illustrated with high density polyethylene

Ultra-thin films of high density polyethylene of high orientation have been produced by the recently developed technique of solid state coextrusion. The films were prepared under moderate conditions, without lubricant in continuous lengths by extruding through conical dies of extrusion draw ratio up to 36. This is a draw ratio higher than achievable by conventional solid state extrusion at comparable processing conditions through slit dies. The ultra-thin films of high orientation were transparent and exhibited dead bend. The physical and mechanical properties were evaluated and compared with the properties of the same high density polyethylene extruded through a slit die. The increase in the melt point, crystallinity, tensile modulus, and birefringence indicates that the method is very efficient for the production of ultra-thin and highly oriented films. An experimental technique is also presented for preparing billets of controlled and uniform initial morphology and free of voids.     

Crystallinity and Property Enhancements in Neat Polylactic Acid by Chilled Extrusion: Solid‐State Shear Pulverization and Solid‐State/Melt Extrusion

Polylactic acid (PLA) is a biopolymer of significant interest to both industry and the scientific community, but an incomplete understanding of the practical processing‐structure‐property relations is limiting its application range. The study applies alternative, chilled extrusion technologies called solid‐state shear pulverization (SSSP) and solid‐state/melt extrusion (SSME) to neat, commercial PLA, and investigates the effect of the resulting morphological features upon the thermomechanical behavior. Although conventional, heated twin‐screw extrusion leads to significant thermal degradation of PLA chains, which in turn facilitates crystal growth due to enhanced chain mobility, chilled SSSP imparts chain defects and branching, which serve as heterogeneous nucleation sites in the polymer and promotes the formation of a rigid amorphous phase. A hybrid SSME process brings unique interplay of both chain architecture effects, resulting in a synergistic thermomechanical behavior involving the α' crystal polymorph formation. POLYM. ENG. SCI., 59:E286–E295, 2019. © 2019 Society of Plastics Engineers     

800 mm × 340 mm辊式挤压成型机的开发

辊式挤压成型机是复合肥挤压造粒生产线的核心设备.介绍辊式挤压成型机的工作原理及主要性能,阐述设备的主要技术特点及其控制方法,为该类设备的大型化发展奠定了基础.     

Solid‐phase extrusion of polyamide‐6 by using combined deformation schemes

Potentialities of new combined deformation schemes, including the solid state extrusion through conical die (ED) and equal‐channel multiple angle extrusion (ECMAE) implemented in different sequence to modify structure and properties of semicrystalline polymers, have been studied for polyamide‐6 as an example. It is shown that deformation by the ED‐ECMAE scheme gives the best complex of physical and mechanical properties. A significant improvement in elastic and strength properties of polyamide‐6 with the conserved high level of plastic characteristics has been observed. There was only a slight anisotropy and dispersion of microhardness across the extrudates. A more uniform oriented structure with lamellae orientation along extrudate's axis has been formed in semicrystalline polymer because the ED‐ECMAE scheme implementation. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

自增强聚烯烃复合材料挤出成型技术的进展

重点介绍了凝胶纺丝超拉伸、口模牵伸、固相等静压挤出和熔体挤出等几种挤出自增强技术,讨论了制品的成型机理及对制品性能有较大影响的工艺参数,并对制品在成型过程中结构变化作出了描述     

橡胶冷喂料挤出过程轴向温度分布

对橡胶冷喂料挤出过程轴向温度分布进行了实验及理论分析。计算并测定了螺杆轴向湿度分布,确定了胶料沿螺杆轴向的温度变化规律,提出了橡胶冷喂料挤出不同于塑料挤出熔融过程的粘流转变概念。     

Axial‐feed thermoforming of oriented polypropylene tubes

The effect of newly developed axial feed thermoforming process (AFTF) on mechanical properties and morphology were investigated to gain a better understanding of structure–properties–process relationship. The starting material for AFTF is an oriented polypropylene tube (OPP) produced in uniaxial direction by using solid state extrusion process. Morphological changes from solid‐state extrusion are briefly reported. A die‐less bulge testing system was designed to bulge OPP tube at a high temperature in biaxial direction. Wide‐angle X‐ray diffraction, field emission scanning electron microscope, and optical microscopy were used to characterize the microstructure of the extruded and bulged samples of OPP. In addition, tensile tests were carried out at room temperature of samples machined from the extruded and bulged tubes along the axial and hoop directions. The results show that tensile strength increases with draw ratio in extruded samples as well as improvements in ductility were obtained in die‐less bulge tests with an increase in axial feed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

A Computer Model for Single-Screw Plasticating Extrusion

A fully predictive computer model has been developed for a single-screw plasticating extrusion (with conventional screws). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, melt conveying) and the die, and describes an operation of the extruder-die system, making it possible to predict a mass flow rate of the polymer, pressure and temperature profiles along the screw channel and in the die, solid bed profile, and power consumption. Moreover, mixing degree, temperature fluctuation and viscoelastic properties of the polymer are estimated. The simulation parameters are the material and rheological properties of the polymer, the screw, hopper and die geometry, and the operating conditions (screw speed and barrel temperature profile). Such a comprehensive approach to the modeling of extrusion creates the possibility of optimizing the process, for example, from the point of view of the quality of extrusion. The model has been verified experimentally for a low-density polyethylene on a 45 mm diameter single-screw extruder.     

Microcellular extrusion of PLA utilizing solid‐state nucleation in the gas‐saturated pellet extrusion process

In this study, we explore the use of solid‐state nucleation in polymer pellets as a means to create microcellular PLA foams in extrusion. This is achieved by using gas‐saturated PLA pellets as input to the extruder. Foam density, bubble size, and bubble density is reported and compared with microcellular foams created in the gas‐injection extrusion process. PLA pellet gas concentrations between 17 and 29 mg CO₂/g PLA was found to produce quality microcellular foams in this process. Gas concentrations within this range were achieved by varying methods that included partial saturation, desorption from full saturation, and blending saturated with unsaturated pellets. This gas concentration window that produced microcellular foams was found to be independent of the saturation and desorption process used to achieve the desired concentration. We further compare the pressure drop and pressure drop rate of the gas‐saturated pellet extrusion process showing that similar foams can be produced at pressures orders of magnitude lower than the alternative gas‐injection extrusion processes. Investigations into extrusion pressures support the hypothesis that the gas‐saturated pellet extrusion process utilizes solid‐state nucleation in the feed section of the extruder to achieve high bubble density foams. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

固态挤出HDPE性能与结构研究

采用4个不同拉伸比的口模，在较低速度下对高密度聚乙烯(HDPE)成功地实现了固态挤出。结果表明，试样的拉伸强度最大提高到250MPa。采用SEM测试分析其微观结构表明，试样中生成了大量高度取向的微纤结构；DSC分析表明，试样的结晶度增加，晶片增厚，晶体的尺寸更加均匀。     

Modelling of multi gas/solid reactions – effect of structural parameters

A unified gas/ solid reaction model has been formulated for multi reactions with multi gas and solid species. The transient formulation has been followed by finite-difference method and subsequent solution via an iterative procedure. The simulation produces intermediate results for concentration profiles of various components and pressure and temperature distribution, in addition to various structural parameters within a reacting pellet. The effect of structural parameters is analysed. The general formulation allows homogeneous and heterogeneous reactions. Solid state processes can also be accommodated.     

基于固态成型工艺聚合物基复合材料自增强技术研究进展

针对当前聚合物实际强度远低于理论强度的问题,介绍了固态挤出、固态拉伸等自增强技术的制备流程及其工艺特点。此外,通过分析固态形变过程中试样内部的微观形貌与分子构型,进一步研究聚合物基复合材料固态加工过程中的自增强机理。最后,通过归纳总结影响试样增强效果的因素,进一步探索聚合物基复合材料的性能上限,拓宽其在不同领域的高性能化应用。     

单螺杆挤出过程固相破碎碎块径向熔融机理研究

首次建立了单螺杆挤出过程固相多点破碎球形块径向熔融模型，并推导出球形块内部温度分布公式。根据固相加速实验结果，提出固相碎块轴向熔融长度计算公式。利用上述公式，对LDPE和PP进行了计算，此外，分析了三种规则几何体与熔融速度关系，指出了细化碎块实现稳定挤出的途径。     

聚合物及其加工技术研究的一些新动向

扼要介绍了用于聚合物加工的振荡挤出模具、固态成型加工技术、用于聚合物合金设计系统探索性研究的工具软件、可降解的聚合物、永久性抗静电聚苯乙烯共混材料和以弹性体为基材的纳米复合材料等方面研究的一些新动向.