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.
Using a factorial design approach, this study examined the effect of the component materials on the viscoelastic properties of PVC/wood-flour composites. Statistical analysis was performed to determine the effects of wood flour content, acrylic modifier content and plasticizer content on the die swell ratio and viscosity of the composites measured on a conical twin screw extrusion capillary rheometer. The experimental results indicated that both the wood flour content and acrylic modifier content have significant effects on the die swell ratio and viscosity of PVC/wood-flour composites.
This study focuses on the ability of U-PVC to be processed a number of times. Three different types of U-PVC were investigated: virgin lead stabilised and virgin calcium/zinc stabilised material and reground, 20 year old, post-consumer windows. Each material was extruded four times and samples taken at each stage for rheological and mechanical analysis.
Wire coating, based on the drag flow is a well-known process in the cable, wire or fibre-optic industry. It has been studied extensively in experimental and computational form over recent years. During the coating a polymer melt flows through an annular converging die and then meets a wire or cable that is usually traveling at high speed. This study is concerned with the numerical simulation of the complex flows that arise in the coating system with a thermoplastic polymer. The simulation study was performed in order to better understand the influence of the rheology parameters, the chosen processing conditions and the coating die geometry dimensions.
Nanocomposites based on nylon-12 and synthetic fluoromica were compounded using a single-screw extruder at different combination of shear and residence time and analysed with respect to their morphology, rheological, mechanical, and thermal properties. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) revealed unique structural arrays of the exfoliated layers which were found to be dependent on the extent of shear and residence time during processing. Rheological analysis showed that the melt viscosity of the nanocomposites was considerably lower compared to the unfilled polymer. Furthermore the melt viscosity and properties of each nanocomposite varied depending on orientation of the exfoliated layers. The results show that it may be possible to tailor the structures and properties of the nanocomposites using controlled extrusion conditions.
A study has been performed to examine the rheological impact of micropelletization on several polyethylene grades with melt index values between 1-5 g/10 min. The experiments were done on a 50 mm 30:1 L/D extruder with an underwater micropelletizer attached. A 2-D finite element simulation was used to assist in the analysis by comparing the observed results to the predicted shear stresses in the die. The average micropellet size collected was 0.525 mm diameter. Minor sharkskin was observed on the surface of micropellets due to the high stresses experienced in the pelletizer die. However, the rheological properties of the micropellets did not change in comparison to the virgin resins.
Fluctuations of the operating conditions or slight variations of the polymer rheology may occur during longterm productions, affecting the performance of the die in an extent dependent on its flow distribution sensitivity. In this work, four extrusion dies are optimised (balanced) using different design methodologies. These are compared in terms of their performance and stability to some operating conditions and polymer rheological properties. A finite-volume based computational code is used to perform the required simulations of the non-isothermal three-dimensional flows, under conditions defined by a statistical Taguchi technique. Correlation between the flow patterns developed and flow distribution sensitivity is also investigated.
In this study, the application of a finite volume discretization and volume-of-fluid method has been demonstrated to simulate three-dimensional gas-assisted injection molding processes. An effective fluid concept is employed to compute segregated multi-fluid flows. The modified Cross model and Arrhenius temperature equation are implemented in the numerical scheme in order to calculate the rheological properties of polymer flows. The numerical results successfully depict some important three-dimensional phenomena, such as the jetting effect, race-tracking effect, corner effect, and the flow asymmetry after the gas is injected, which could not be described by any two-and-half dimensional model commonly used in the current commercial CAE applications.
The design of injection molds can be accomplished by the state-of-the-art software available on the market. However, in daily practice where quick estimates of the parameters involved are needed, the application of sophisticated software can be time consuming and costly. This paper deals with straightforward solution procedures for optimizing the mold design by taking thermal, mechanical and rheological design criteria into account. Easily applicable analytical methods are given for calculating the heat transfer between the melt and the coolant. It is shown in these calculations how the geometrical layout of the cooling channels is related to the mechanical strength of the mold material. Furthermore, explicit relationships based on resin rheology are presented for balancing the melt flow in runner systems. These proven equations are illustrated by numerous worked-out examples.
In-Mold Coating (IMC) has been successfully used for many years with Sheet Molding Compound compression molded body panels for the automotive and heavy truck industries. The next logical step is to extend IMC technology to injection molded thermoplastic parts. The objective of this paper is to research the factors that affect IMC flow, cure, and final part appearance. We discuss the rheology of coating candidates for thermoplastic parts and show how it affects the coating process. We use 2D non-steady heat transfer computer code coupled with chemo-rheological analysis to predict cure time. Finally, we present a case study to demonstrate the effect of part thickness and initial molding conditions on cycle time.
In-mold coating (IMC) is carried out by injecting a liquid low viscosity thermoset material onto the surface of the thermoplastic substrate while it is still in the mold. The coating will then solidify and adhere to the substrate. IMC process is being integrated with conventional thermoplastic injection molding to improve the part surface quality and to protect it from outdoor exposure. This paper presents a Hele-Shaw based mathematical model to simulate the coating flow during the IMC process. Power-law viscosity model is employed to describe the rheological behavior of the coating material. The continuous deformation of the thermoplastic substrate caused by the coating injection is analyzed by means of the PVT relationship of the substrate. The corresponding computer code based on the Control Volume based Finite Element Method (CV/FEM) has been developed to predict the fill pattern and pressure distribution during the coating flow. The predicted results have been verified by experiments.
A number of metallocene and conventional LLDPEs, with different material properties, were injection moulded over four different mould temperatures. An assessment of the effect of cooling rate and polymer properties on the mechanical performance of the specimens was conducted to establish any significant correlations. Rheological studies of the materials under high shear rates experienced in injection moulding, was performed to determine flow characteristics of the materials. Differential scanning calorimetry (DSC) and dynamic mechanical thermal Analysis (DMTA) were used to study the influence of the comonomer type and degree of branching on the properties of the materials.
The most common commercial processes for manufacturing pre-pregs for electronic boards use solvent-based resin systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. The resin impregnation process is done in an open resin bath. This low-pressure impregnation is conducent to voids in the prepregs. Voids cause product variability, which is a major source of scrap in board shops. To eliminate the above mentioned drawbacks, a solventless process, based on the concept of injection pultrusion, is developed. The impregnation is done in a die under pressure to minimize voids.In previous work, chemo-rheological and kinetic measurements were used to identify a potential epoxy-based resin system. In addition, flow visualization using model fluids was used to establish the basic flow mechanism. Here, we use the previous results to develop a mathematical model for the B-staging process. Based on the mathematical model, three potential alternatives to produce prepreg are developed and analyzed. A prototype B-staging die is built and used to verify the mathematical model. The result shows that the model agrees well with the experimental data for low pulling speed and slightly under predicts the high pulling speed runs.
The aim of our study is to show that we can readily obtain a first estimate of the behavior of a tube in blow molding only using free software. From a numerical model of biaxial stretching and blowing of a parison with specific boundary conditions and thanks to a mathematical package freely available on internet : « Octave », we have studied some rheological laws of plastic materials in order to find the evolution of the radius and of the height of the tube during the blowing process. Finally, to prove that our method can be right, we check our analytical results against a complete Finite Elements simulation performed with « Polyflow ».
The microstructure evolution and corresponding transient rheological behavior of a thermotropic liquid crystalline polymer (TLCP), Vectran V400P, is reported. The structure was characterized by using a Linkam CSS- 450 shearing/hot-stage mounting on a polarized microscope. Rheological characterization in the transient mode revealed that the transient shear stress exhibited two overshoots. We believe that the domain and defect rearrangement leads to the first shear stress overshoot. The relative magnitude of the second shear stress overshoot increases with increasing shear rate and with decreasing temperature.
This work presents an overview on the role of process aids on the rheological properties of rigid PVC. A new rheological approach is introduced to allow a better assessment of the role of these additives. This system comprises a combination of a Couette-type cell and a capillary rheometer. The former allows a good control of the thermo-mechanical history of the compound prior to injection into the capillary barrel where a viscosity measurement is performed. The results showed that rigid PVC undergoes a fusion and gelation processes during the early stages of processing. In this step, the particles are agglomerated under the influence of heat and mostly shear. There seems to be an optimal morphological state where the best mechanical properties are obtained. Additional work showed that the addition of high molecular weight impact modifiers which also act as “binders” in the matrix promote the fusion and gelation of PVC. The results are supported by impact testing and microscopy.
A portable rheometer has been developed for characterizing plastic melts for different measurement purposes. The rheometer is intended particularly for use with rigid PVC processing, but can be used for other materials too. Measurements showing the accuracy of the instrument and its reproducibility are discussed. Comparisons are made between measurements on a conventional laboratory capillary rheometer and ones on the rheometer developed, using polypropylene. The practical application of the rheometer is also shown. This is used in combination with a twin-screw extrusion line to evaluate the rheological data of different pressure pipe and profile PVC formulations in order to develop new die geometries.
There is a demand for the development of techniques for viscosity measurements of very small polymer samples. Traditional rheological equipment and standard tools are limited in their capabilities to measure milligram samples of polymers. This paper outlines methods and tools used to measure the melt viscosity of polymer samples as small as 5 mg. Special, small diameter parallel plates are used to quantify the shear rheology of these samples. The data is fit to several GNF models, and the melt index is calculated from these parameters. Results from this technique are compared to results from actual melt index measurements.
The addition of small quantities of plate-like nanoclay can substantially increase the polymer melt viscosity, while adding dissolved gases such as CO2 can reduce the viscosity of a polymer melt. The combined effect of nanoclay and CO2 on polymer melt rheology was investigated for an extrusion process. The shear viscosities of polystyrene/CO2/nanoclay melts were measured using an extrusion slit die rheometer with a backpressure regulator. Our results show, without the presence of CO2, that the viscosity of the nanocomposite increases with nanoclay loading. However, when the nanocomposite melt is swelled by CO2, the nanoclay acts to reduce viscosity compared to the pure polystyrene/CO2 system. A possible explanation is that a significant amount of CO2 is adsorbed on the surface of the nanoclay to lubricate the flow due to the existence of surface modifier and a unique nanoclay particle layering structure.
A new rheological model of polymer melt was developed to describe viscosity-shear rate curves utilizing a four parameters equation based on Guassian processes approach for regression description of melt properties. Four parameters of the model (Newtonian viscosity at “zero” shear rate, viscosity and shear rate at inflection point, and dispersion of the rate of change of the viscosity) were found to be a function of polymer chain structure, molecular weight and temperature. The model provides precision description in a wide range of conditions of shear deformation of the polymer melts, solutions, blends and alloys.
Vibration welding is a joining technique to assembly thermoplastic components. Meltdown-time profiles and assessment of weld microstructure are commonly used to characterize the behavior of polymers during vibration welding. The aim of this work is to establish relationships between the rheological properties of molten polymers and their meltdown rate during vibration welding. Two polypropylene homopolymers with different molecular weights resulting in different rheological properties were studied. Vibration welding was carried out using a butt-weld geometry and meltdown-time profiles were measured. Significant discrepancies between experimental results and theoretical predictions based on the simple model developed by Stokes suggest the presence of significant elastic effects.
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