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.
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Flow Analysis in Single Screw Extruders
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.
Comparative Melting Trials in ZSK Extruders
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.
One-Step Blending and Molding of Glass Fiber Filled Polypropylene - Physical Property Measurements
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.
Improving the Reliability and Performance of Microelectronic Packaging
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.
TiO2 Photochemistry and Color Applications
TiO2 is one of the most commonly used pigments in the coloring of plastics. TiO2 not only provides opacity but it is an excellent UV absorber. Hence, the pigment provides opacity and protection for plastics. This paper reviews the sources of TiO2 photochemistry and methods to control photoactivity.
A Next Generation Color Management Tool
A knowledge-based system allowing for more effective use of color concentrates in plastics has been developed. Software and portable spectrophotometers utilized during processing present a color matching system that functions as a significant new color management tool to both injection molders and machine extruders. Used this way, as a quality or process monitor, the system can manage color consistency and product stability, because the deleterious effects of fluctuations in colorant loading on the physical properties of molded parts can be eliminated.
Modeling Structural Recovery: Analysis of the Peak Shift Method
Amorphous polymers below their glass transition temperature, Tg, are inherently not at equilibrium. As a consequence, their structures continuously relax in an attempt to reach the equilibrium state. Models of structural recovery can quantitatively describe this process. One of the parameters needed in the models is the non-linearity parameter x. It has been purposed that x can be obtained from experimental data using the peak-shift method. In this work, we use computer simulations to quantify the error in the value of x obtained from the peak shift method.
Rheological Response of Polystyrene/Ortho-Terphenyl Solutions
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.
Swelling as a Method of Discriminating among Strain Energy Functions
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.
Isotropic Residual Stresses in Thermosetting Resins: Modeling and the Effects of Resin Modification Properties
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.
Large Deformation Response of Polycarbonate: Time-Temperature and Time-Strain Superposition
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.
Comparative Study of Structure and Property of Ziegler-Natta and Metallocene Based Linear Low Density Polyethylene in Injection Moldings
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.
Biaxial Orientation of Blown Films Using an 80/20 LLDPE/LDPE Blend
The Hermans orientation function and the White-Spruiell biaxial orientation factors [1, 2] of blown films of blends constituted of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE), with 90%  and 80% of LLDPE, were calculated by infrared spectroscopy and differential scanning calorimetry. These films were produced by using a industrial equipment, controlling the following processing conditions: BUR=Rf/Ri, where Rf and Ri are the final and initial radius of the blown films, the temperature and the thickness of the sample.
Phenomenological and Morphological Characterization of Shear Induced Crystallization of Isotactic Polypropylene
The Flow Induced Crystallization (FIC) of polypropylene was studied in a slit die coupled to a twin screw extruder in several ranges of temperature and flow rate. FIC layers were measured and characterized and fitted to the Janeschitz-Kriegl model (1). A morphological investigation using TEM, SEM and WAXS were also done. Morphological results showed that the FIC layers are composed by extended lamellae in the ? phase. The ? phase was observed in the neighborhood of FIC layer generated probably by a transcrystallization effect.
Quantitative Evaluation of Feeding Different Physical Forms of Stabilizers
The principles of feeding dry materials and a mathematical correlation to rank their ease of flowing (flowability) or ease of creating feeding problems (floodability and archability) were first explained by Ralph Carr in 1965. These same principles applied to powders of antioxidants explain the feeding challenges associated with handling such materials. Granular and non-dusting forms of the same additives improve these handling characteristics. This model helps explain how appropriate feeder designs can alleviate the problem, while inappropriate ones can create a massive problem.
Viscosity Regulation for Polymer Extruders
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.
Preparation and Mechanical Properties of Epoxy-Clay Nanocomposites. Influence of Core-Shell Rubber Particles Addition to Epoxy-Clay Nanocomposites
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.
Application of Chemo-Rheology to Establish a Process Window for a New Solventless System to Manufacture Pre-Pregs and Laminates for Electronic Applications
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.
Optimizing Injection Gate Location and Cycle Time for the In-Mold Coating (IMC) Process
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.
Interfacial Interactions and Structure Development in Injection Molded HDPE/Hydroxyapatite Composites
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).
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