The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
Analysis of flow and pressurization in single-screw extruders can be carried-out using one-, two-, and three-dimensional flow analyses. In one-dimensional analysis, the extrusion flow can be represented by the idealized model flow between infinitely long and wide parallel plates, i.e., the Generalized Couette flow, thus enabling the generation of analytical solutions. In two-dimensional analysis, the screw geometry is unwrapped in the helical direction of the screw and the lubrication approximation applied. For three-dimensional analysis, a mesh is generated which describes accurately the geometrical screw configuration without any unwrapping. For both the two- and three-dimensional analyses, the Galerkin Finite Element Method is utilized in the solution of the governing equations of conservation of mass, and momentum. In this study, the different analyses will be described for the flow of Heschel-Bulkley fluids with wall slip, and simulation results presented and compared for the special case of a Newtonian fluid for three different screw geometries. The limits of application of the different analyses will be discussed.
Twin screw co-rotating kneaders are popularly used as plasticating compounding extruders for a broad range of technical plastics and commodity polymers at high rates. Melting in these devices is always initiated by a combination of kneading disks which effect repeated bulk deformations of the plasticating mass. The resulting melt quality is sensitive to size, shape, and physical properties of the feedstocks, to the configuration of the melting screw, and to operating conditions. Four pelletized polymers were each plasticated using a split barrel ZSK40 configured with two screws and run at two operating conditions. Carcasses were examined in place and by dissection for overall melting lengths and residual particle shape and melt texture.
Fiber length retention during incorporation of glass fibers into a polymer matrix has re-gained importance over the past few years. This can be attributed to the introduction of injection moldable long fiber reinforced thermoplastics. The longer fiber length in the feed material results in 5 – 20 times longer fiber in the molded part with significant improvements in final product properties when compared to its short fiber counterparts . Long-fiber composites have been found to exhibit overall higher physical properties compared to their short-fiber analogs. Mechanical properties, elevated temperature performance and creep and fatigue endurance are all higher for long-fiber composites . An indication of how increased fiber length translates into better properties can be seen by burning off the matrix resin from a molded part (see Figure 1). The residue is a three dimensional structure formed by a network of long fibers that retains the original shape of the part. This allows better distribution of stresses throughout the part.
Microelectronics is a field currently in high demand considering its many applications. Concerns are raised to improve reliability and performance of high performance packages. To do this, one must first understand the physics behind the failures of these small packages. To do this, non-destructive testing and the use of microscopy to identify the location of failure can be employed. By identifying the mode of failure in these packages, a micromechanics and materials approach can be used to implement a new package that shows a significant improvement in both the reliability and performance.
The linear and nonlinear viscoelastic responses of concentrated solutions of polystyrene in ortho-terphenyl are being investigated. Three aspects of behaviour are being addressed: 1) the time-temperature and 2) the time-concentration dependence of this material system and 3) the time-strain separability of the response in the non-linear regime. Linear viscoelastic responses are being measured using an ARES rotary rheometer and the non-linear response will be investigated using an RMS7200 where both the torque and normal force response in torsional deformations will be measured. The polymer is a commercial specimen having a weight average MW of 192,000 g/mol. Concentration is being varied between 0.2 and 0.7 mass fraction of polystyrene. Since time-strain separability is fundamental to the tube theory of reptation, the non-linear response will be discussed in the reptation framework.
The swelling of cross-linked elastomers is generally treated with the Flory-Rehner[I] theory. One aspect of the common use of the theory is the simplification of the form of the elastic strain energy function such that it appears as the shear modulus G(?) in the swelling equilibrium equations. A more general form of the relevant equations would be to use ??A(?)/?(?1/3) where A is the Helmholtz free energy of the network, ? is the volume fraction of polymer in the swollen system. Here we examine the limitations put on the form of the strain energy density function (A) when the shear modulus is observed to scale as ?1/3.
Recently, we extended a thermo-viscoelastic model  to describe the development of isotropic residual stresses for a commercial thermosetting material during cure . In this paper, we extend this model to study residual stresses in novel thermosetting resin systems, such as spiro orthocarbonate/bismaleimide (SOC/BMI) which are under consideration by the Air Force for use as polymer matrix composites. In these systems, cure shrinkage and isotropic residual stresses are reduced through a ring-opening reaction which occurs independently of the addition reaction. The modeling effort includes a parametric analysis of the effects of various parameters, including the volume changes involved in the reactions, the relative rates and orders of the reactions, and the dependence of the glass transition on the network formed.
Data are presented from tests of the stress relaxation response of a glassy polycarbonate under torsional deformations. Tests were performed on samples over a range of strains from 0.0025 to 0.07 and at temperatures from 30 EC to 135 EC, all at a fixed aging time of 64800 s. Individual data sets at each strain and temperature could be described using a stretched exponential form relaxation function. Over the range of temperatures studied the data at each strain could be superimposed using conventional time-temperature superposition. For strains up to the yield strain the data at each temperature could also be superimposed to form a master curve following the principle of time-strain superposition. Interestingly, the master curves found from time-strain superposition at each temperature did not have the same form. Similarly, the master curves found from time-temperature superposition at each strain did not have the same form.
Linear low density polyethylenes (LLDPE's) polymerized using metallocene and Ziegler-Natta catalyst were used to study the shear-induced crystallization in injection moldings. The gapwise distributions of crystallinity, spherulite size and thickness of the shear-induced crystallization layer in moldings were measured along with the mechanical properties of the moldings. The effects of processing conditions on these properties were determined. Metallocene based LLDPE shows higher thickness of skin layer, lower spherulite size and higher degree of crystallinity than Ziegler-Natta based LLDPE.
This paper introduces the viscosity regulation problem for polymer extruders, through viz breaking of polypropylene with injected peroxide. A simple, physically motivated model dependent on plant operating conditions is presented, the sensors used are characterized, and the results of experiments demonstrating the disturbance rejection capacity of the control system are shown. Low frequency disturbances, that is, disturbances with volume scale greater than the filled volume of the extruder, are of primary interest. The dynamic behavior of the plant varies as a function of the operating condition, and together with the sensor create significant if structured uncertainty. For this reason, adaptive control is applied.
Polymer nanocomposites consist of highly purified inorganic material with at least one dimension in the nanometer scale and with an organic surface treatment to help their dispersion into a polymer matrix. The interest for the production of such materials has been growing because they exhibit greatly improved properties, even with a small addition of nanoclays. This work deals with the epoxy-clay nanocomposites. The state of dispersion and the fracture behavior of the system are studied. Core-shell rubber (CSR) particles are used to improve the toughness of such a system and found to be effective.
The blending process of two blend systems, polystyrene/polypropylene (PS/PP) and poly(ether imide)/polycarbonate (PEI/PC), are studied by visualization of blending in an internal mixer. The study shows that higher RPM and higher barrel temperature accelerated the melting and blending process. For PEI/PC blends, the composition of PEI has no effect on the time for melting of PEI pellets. Times for softening PEI to a dough-like material at 340°C and 50rpm is 30s and to completely melt it is 40s. SEM photos and DSC data verify the visualization result that PEI/PC blends are partially miscible at higher PEI compositions.
The most common commercial processes for manufacturing pre-pregs for electronic applications use solvent-based epoxy systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. Voids cause product variability, which is a major source of scrap in board shops. In this paper, we use chemo-rheological and kinetic measurements to identify a potential epoxy-based resin system for a solventless process, based on injection pultrusion. DSC and rheological data show that the candidate system does not react appreciably without catalyst to temperatures of 170°C or with catalyst at temperature below 110°C. The system solidifies below 105°C. It was found that the overall viscosity of the resin system is dependent upon the temperature, degree of cure, and filler content. Kinetic rate and viscosity rise expressions to be used in process modeling and optimization have been developed. A preliminary process window for the process has been established.
The standard practice when compression molding Sheet Molding Compound (SMC) panels is to in-mold coat (IMC) the parts, when surface appearance is important. Thus IMC needs to be considered an integral part when improving the process. Selecting the proper injection gate location is key to obtaining a defect free coating. In the present work, we present an optimization method to select the injection gate location that minimizes the potential for surface defects. We will also describe a process for the optimization of cycle time by minimizing curing time by either increasing the mold wall temperature or adding more catalyst. The approach is illustrated for typical IMC coating material.
This paper investigates the structure development in conventional molding and shear controlled orientation in injection molding (SCORIM) of HDPE/hydroxyapatite (HA) composites. The effect of a zirconate and a titanate coupling agents aimed to improve the interfacial interaction between the filler and the matrix is also described. The mechanical characterization of the composites included tensile testing and microhardness along the part thickness. The structure variation of the composites across the molding thickness was inferred from X-ray diffraction patterns. The tensile fracture surfaces and interfaces between the filler and the matrix were observed by scanning electron microscopy (SEM).
This communication describes a preliminary study based on the use of carbon (C) fibers as reinforcement of a HDPE matrix, using a non-conventional processing approach that integrates compounding and injection molding during the processing cycle. The mechanical performance of the short fiber reinforced composites produced was assessed by tensile tests and compared with the respective structure development and fiber orientation and length properties. Composites based in HDPE and C fibers with high stiffness were developed. Nevertheless, the mechanical performance is limited by fiber length degradation and final fiber orientation pattern across the molding thickness.
It is well known that a certain amount of volatile material can be produced during polymer extrusion or compounding operations. Even with proper venting of the equipment, volatiles can still collect and condense in unwanted areas of the equipment causing vent plugging, die drip and buildup on chill rollers. In an effort to control these problems, laboratory methods for studying the kinetics and composition of the volatiles produced during extrusion have been developed. These methods include thermal gravimetric analysis (TGA), low temperature pyrolysis and other thermal techniques. The main disadvantage of these techniques is that the sample is subjected to thermal conditions in a static manner during analysis. In an extruder, the volatiles are produced while the polymer is in a dynamic melt state subjected to both heat and shear. This paper will focus on methods developed for the trapping and analysis of volatiles during extrusion. The main advantage of these methods is that the volatiles collected are a function of the heat and shear of the extrusion process providing a more realistic assessment of the composition and quantity of the volatiles. Other advantages of these techniques are increased sensitivity of analysis, the option of analyzing for a broader molecular weight range of the volatiles and the ability to use larger, more representative samples.
Conventional pipe dies normally have no means to get rid of unsymmetrical differences of the local melt stream around the circumference of the die. Solutions to locally change the die temperature in order to influence the flow distribution are limited to dies with great diameters. But this creates undesirable differences in the temperature of the melt and causes trouble concerning straightness of the pipes. Integrating an elastic outer tubing into the die allows to locally alter the gap of the flow channel at the die exit. The theory of the technique and first practical results attained on a production line are described.
In respect of weight reduction an increasing request for light weight materials exists in the automotive industry. The compression molding of sheet molding compounds (SMC) has been established as a cost-efficient and widely applied process for semi-structural automotive components, especially in commercial vehicles. The deficiency of this material is the relatively low Young's modulus, which prevents these materials from being used in loaded structures. Therefore the idea was to increase the performance of these materials by forming a sandwich, but in principle use the same fast and cost-effective process of conventional SMC. The principle of this new technology is based on a one-step process using one sheet containing a blowing agent disposed between two conventional SMC sheets in the mold. By closing the mold the three layers are compressed and heated up until the expansion of the core material starts. The foaming process resulting from the expansion of the core material is controlled by a defined opening motion of the mold according to the requested sandwich height. After the foaming process the curing of the part is completed. The result is a rigid lightweight sandwich structure. The advantages of the One Step Sandwich-SMC in comparison to typical sandwiches are the decrease in production cost and the recycling properties, since no separation of the single layers is required (single material system) and since additionally the core layer may contain a high amount of SMC scrap material. The developing process of this technology was conducted by the simultaneous integration of fundamental research (material development, testing, processing technology) and by the development of the structural part (part conception/design). This demonstrator component is the front hood of a commercial vehicle, the Mercedes-Benz Actros, which was produced with optimized processing parameters. For the demonstrator chosen a cost potential of 30 % and a weight reduction potential of 10-1
A predictive model based controller is used for dynamically controlling the mold wall temperature in injection molding. The reference model is a physics based model developed using one-dimensional heat transfer analysis. The process involves preheating the inner mold surface and then rapidly cooling it to achieve faster cycle times and better part quality. The controller attempts to track a desired reference surface temperature profile by regulating the preheat time, preheat temperature, and coolant temperature. The state variables are monitored online and control set points are generated using the model as reference.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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