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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Incompressible Model of Solids Conveying in a Single-Screw Extruder
Experiments in corn meal extrusion  have shown that the flow of solids in the screw channel of a single-screw extruder has a helical pattern. This observation implies that there is a cross-channel velocity component in the solids conveying zone of the extruder. Existing solids conveying models [2,5,6,9] treat the solids moving in the channel as a plug flow without a cross-channel velocity component. The two-dimensional powder conveying model proposed in this paper contains both a down-channel component and a cross-channel component. The stress generating mechanism is much more complicated in a powder flow than in a fluid flow. The incompressible model incorporates a constitutive equation for the powder flow with slip boundary conditions. The energy equation with appropriate boundary conditions is also included in the model. The numerically solved model shows that the predicted down-channel pressure development, velocity and temperature distributions are all reasonable.
The Effect of LDPE-g-AA by a Reactive Extrusion Process
Acrylic Acid (AA) was grafted onto LDPE to modify its properties by reactive extrusion process. In this study, a co-rotating twin screw extruder and Banbury were mainly used for the reactive grafting process. By changing the configuration of the screw elements, different degrees of shearing effects gave various degree of grafting. It was found that the ratio of LDPE/AA/DHBP=100/10/0.5 with a medium shearing in the extruder gave an optimal result, and the ratio of grafted AA was 4.7%, which was measured via a standard titration process.
Mechanical Performance of a Reinforced Unsaturated Polyester Resin Crosslinked with Divinyl Benzene/1,6 Hexanediol Diacrylate
Searching for an advance in mechanical performance, two monomers of high functionality with different spatial structure, were used in this study to crosslink a general purpose reinforced unsaturated polyester resin. Varying the concentration of Divinyl benzene (DVB) and 1,6 Hexanediol diacrylate (HDDA), different crosslinking structures and properties are expected.
Thermodynamic and Kinetic Analysis of Semicrystalline Recyclates by DSC
Pelletized curbside recyclate was analyzed using recently developed thermal analysis techniques. These techniques included stepwise DSC for accurate Cp determination even in the presence of difficult analytical conditions, rapid-scan crystallinity determination using the Gray-Mathot total enthalpy technique, and kinetics analysis of crystallization rates. These methods, which can be largely automated, offer a useful procedure for testing recyclate for possible processing, or end-use problems.
Modulus Properties of Triaxially Braided Carbon Fiber/Epoxy Spars
Traditionally, masts for sailboats were manufactured using a trial and error approach. The object of this work was to fabricate these structures using a computer code for design. In order to verify the code, specimens were fabricated and tested. Experimental flexural test properties obtained from flat coupons and cylinders were found on an average to be thirty percent lower than code predictions. Conversely, tensile properties from flat coupon tests were ten percent higher than predicted.
Carbon Black (CB) Distribution in Binary Immiscible Polymer Blends
Carbon Black(CB) distribution in binary immiscible polymer blends was elucidated by computer simulation and experimental observation (scanning electron microscopy (SEM) and optical microscopy (OM)). It has been found that the predictions of CB distribution by computer simulation based on a thermodynamic model are in agreement with microscopic observations when the viscosity of the two components is in a similar range. However, when the viscosity of one component in binary immiscible polymer blends is extremely high, the predictions are not valid due to incomplete wetting of CB particles by the high viscosity component.
Morphology Identification of a Polymer Blend by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) Chemical Imaging
The bulk morphology of a multi-component polymer blend of PC/PMMA/PVDF(50/20/30) was elucidated in detail by ToF-SIMS negative and positive chemical imaging. Based on the characteristic negative or positive secondary ions generated from different polymers under a 69Ga+ beam, bulk morphology can clearly be identified. A combination of negative and positive ion chemical imaging directly revealed that PMMA is distributed in the PVDF phase. Our results indicated that even though ToF-SIMS is a special technique used in surface and interface studies, it is also a powerful tool in the study of bulk morphology of polymer blends.
Relaxation of Residual Stress in a PPS High Precision Part
Glass filled polyphenylene sulfide (PPS) is a preferred material for many electronic applications because it is known to be dimensionally stable when exposed to elevated temperatures for short periods of time. The presence of residual stress, however, significantly affects the dimensional stability of this material. In this study, a new testing method, holographic interferometry, was used to monitor the relaxation of residual stresses in the molded actuator arm of a hard drive due to exposure to elevated temperatures. With this method, permanent deformation was detected in the arm at temperatures ranging from 40-80°C. This deformation is enough to cause significant problems in the high precision components of the hard drive.
Metal Injection Molding: Simulation of Three-Dimensional Flow with Free Surface Boundary and Experimental Comparison
A three-dimensional transient finite element flow analysis code that includes inertia and free surface boundary conditions is used to predict uniform (axisymmetric) and nonuniform (nonaxisymmetric) filling patterns in a thick-walled tool with a diaphragm gate. The simulation for a powder injection molding compound, which is strongly influenced by thermal effects, predicted several observed flow patterns: initial annual free surface flow, bypass and folding flow to form internal weld lines, and the transition from uniform (axisymmetric) flow to nonuniform (nonaxi-symmetric flow) with increasing fill time. The effects of inertia, yield stress, and wall slip on the filling patterns were assessed.
Influence of Temperature, Molecular Weight and Molecular Weight Dispersity on the Surface Tension of Polystyrene (PS): Experiment and Theory
In this work, the influence of temperature, molecular weight (Mn) and molecular weight dispersity (MWD) on the surface tension of polystyrene (PS) was evaluated using the pendant drop method. The discrete interface cell model (DICM) theory was used in conjunction with the Flory, Orwoll, and Vrij (FOV) equation of state theory to predict surface tension (?) with bulk pressure-volume-temperature (PVT) data. It was shown that surface tension of PS decreases with increasing temperature for all PS studied. The surface tension of PS increased when the molecular weight of polystyrene was varied from 3,000 to 40,000. When the molecular weight of PS was further increased the surface tension was shown to level off. The surface tension was shown to decrease with increasing molecular weight distribution. The theoretical predictions of DICM theory corroborated with the experimental results as far as the influence of temperature, molecular weight was concerned.
Ultrasonic Absorption in Rubber Filled Epoxies
Mechanisms of sound absorption in rubber toughened epoxies were studied. The general mechanisms of sound absorption in plastics were reviewed. Design of experiment principles were used to develop an experimental regime to investigate the impact of density, glass transition temperature of the rubber phase, and volume percent loading of rubber particulate on sound absorption. It was found that maximum sound absorption occurred in materials with high loadings of low glass transition temperature, rubber particulate whose acoustic impedance was very different from the host matrix.
Effects of Magnesium Hydroxides on the Physical Properties of a Semirigid PVC Used in Wire Coating
This is a study of ductility and smoke generation of Polyvinylchloride (PVC) with different smoke suppressants (SS). These smoke suppressants consisted of Magnesium Hydroxide (Mg(OH)2) and Alumina Trihydrate (ATH). It was found that the amount of smoke generated (SG) during the tests, decreased when the outer layer of the test samples were removed. The smoke generation and physical properties were analyzed to determine which smoke suppressant was best. No chemical versus physical correlations were found.
Simulation of CaCO3 Dispersion in a PP Matrix during Twin Screw Extrusion
Compounding of highly filled minerals in polymeric matrix has never been an easy task. This work deals with the simulation of CaCO3 (25 and 50 % wt.) dispersion in a PP matrix during twin screw extrusion. Based on a kinetic model of agglomeration/breakup of the filler, we were able to pin point the effect of twin-screw operating conditions on dispersion. Experimental work has been done to validate the model and evaluate kinetics constants.
Analysis of Polypropylene Behavior at Constant Load below the Elastic Limit
Polypropylene dog-bone samples have been tested using creep-recovery analysis at different stress values in order to determine the behavior of the material in the elastic region. It has been found non-linear behavior in the sample at values under the elastic modulus at the elastic region. It has been also found, by means of calorimetric analysis, that creep test affected the material, promoting changes in crystallinity in the tested samples. These effects are important in the performance of the material in time.
Computer Aided Design for Rotationally Molded Parts
3D Cad software is improving new product development in many plastic fields including rotational molding. These improvements are leading to better products that are developed faster with fewer down stream changes. Because a 3D Cad electronic file gives a more complete design that can be viewed as a 3-dimensional model or represented as a 2D drawing, everyone involved with the project has a better understanding of the final product. Some features of 3D Cad can improve the development process in ways that are unique to rotationally molded products. The use of 3D Cad is also creating new opportunities for the use of rotationally molded products because tighter tolerances can be achieved when the 3D electronic file is used to create the tooling models and/or molds.
The Role of Phosphites in Stabilization of Non-Polyolefin Polymers
The use of organophosphites as stabilizers for polyolefins has been well described and documented(1). This paper deals with the use of phosphites as stabilizers in non-polyolefin applications such as PVC and also in condensation polymers e.g. Polyesters, polyamides, and polycarbonates. A key point in understanding the application of phosphites in such materials is that the process of polyolefin thermooxidative degradation begins with thermomechanical scission of a carbon-hydrogen bond that yields a polymer based macroalkyl carbon-centered free radical. This free radical is highly reactive with molecular oxygen yielding a peroxy radical which can by interaction with the polymer substrate generate other free radical species such as alkoxy radicals and the highly detrimental hydroperoxides (see Figure 1).
Influence of Thermal History and Molecular Weight on the Mechanical Properties of High Density Polyethylene
Several variables affect the plastics solidification process, being the thermal history given to the polymer and its molecular weight the more important. Therefore, this paper is mainly aimed at establishing a relationship between thermal history, mechanical properties and molecular weight of HDPE based on mathematical models of the following type: mechanical property =f(molecular weight, crystallinity) through a multivariable non-linear regression method and three-dimensional views of the surfaces generated by the mathematical expressions were obtained to have a better view of the results and models developed, concluding that these models are very useful for the industry.
The Use of Thermomechanical Indices to Establish Straightforward Processing-Mechanical Properties Relationships
The thermomechanical environment imposed to the melt in injection molding is quantified by two thermomechanical indices estimated from computer simulations of the mould filling. These indices are associated to the onset conditions of the microstructure development, and aim at interpreting its final state. As the microstructure determines the mechanical properties, straightforward relationships between those and the thermomechanical indices can be obtained. In this work, axisymmetric specimens were injection molded with systematic variations on the melt and mold temperatures and the flow rate. The mechanical properties were assessed in tensile tests at cross-head velocities of 2, 10, 500 mm/min and 3 m/s. They were related to the thermomechanical indices. Their variations were interpreted in terms of the expectable microstructure of the moldings.
Rubbing Mechanisms of Polymers on Metal Surface Relevant to Extrusion
The processing behavior of a polymer inside an extruder largely depends on the rubbing mechanism of the polymer on the metal surfaces of the barrel and the screw. The rubbing mechanisms of five commercial polymers were investigated from a metal temperature below the thermodynamic melting (or glass transition) range of each polymer to a metal temperature well above the melting range. The rubbing mechanism was found to depend on the polymer properties and the metal temperature. For rigid, amorphous or highly crystalline polymers, the rubbing mechanism is friction" at low metal temperatures below the melting range and "melting" at high metal temperatures above the melting range. For soft crystalline polymers with a broad melting range the rubbing mechanism is complex exhibiting "friction" "tearing" and "melting" as the metal temperature is increased."
Through-Transmission Infrared Welding (TTIR) of Teflon TFE (PTFE)
Through-transmission infrared (TTIR) welding of Teflon®TFE using a Teflon®PFA interlayer was demonstrated to be a well-controlled process that resulted in strong joints. The interlayer was formulated with low levels of carbon black to increase its absorption of the infrared radiation. Designed experiments were used to provide some understanding of important factors.
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