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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A New Formulation and Inerpretation of Shear-Thinning of Polymeric Melts. Effect of Temperature, Strain Rate and Frequency
Shear-thinning of polymeric melts is analyzed in this paper from dynamic viscosity data obtained in the non-Newtonian regime. Shear-thinning is expressed as a function of (G'/G*), where G' is the elastic modulus and G* the amplitude of the complex modulus. It is shown that viscosity depreciation, i.e. shear-thinning, is due to the cooperative coupling characteristic of the interactions between the polymer macromolecules which form a network , the EKNET network. The Newtonian character of viscosity at low strain rate is interpreted with the notion of structural re-localization of the conformers, without deformation of the potential energy of their interaction. It is purely a diffusion phenomenon. New equations are provided which define the mechanisms of shear deformation of the melt under different conditions of temperature and strain rate, and relate non-Newtonian viscosity to the number of interactive conformers stretching cooperatively versus those conformers which re-localize structurally. It is stipulated that viscous and viscoelastic effects can be interpreted from the EKNET model of interactive coupling kinetics [2-7].
Viewing Entanglements as a Two-Phase System in Polymeric Materials
All past statistical theories concentrate on the macromolecular aspect of polymeric materials, and try to determine the macroscopic properties from the characteristics of the individual macromolecules. In those theories a polymer molecule is identical to a spaghetti chain" which is able to "tie" other molecules or slip against another one creating flow and hysteresis effects. By necessity there is also place in the macromolecular theories for such a concept as chain entanglement. Accordingly two macromolecules can touch each other mechanically hook around each other in a static and stable fashion or transmit a stress as if there were a little nail pinning them together. More recently macromolecules reptate through imaginary tubes which represent the constraints imposed by neighboring chains. All those concepts are entirely directed by an approach of polymer physics around the properties of the individual singularizable macromolecules. The accent is put on determining the shape of the individual macromolecules called their configuration. The presence of neighboring and interpenetrating macromolecules is perceived as a disturbance to the ideal configuration of the chain. Macromolecules are able to rearrange their multiple configurations with the change of the thermal or mechanical energy input. This also yields a change in the conformational statistics of the bonds along the chains. For instance in the treatment of rubber elasticity it is said that the elongation of the end-to-end distance of the individual macromolecules results in a preferential orientation of the bonds in the direction of stretch."
Control of Viscosity of Polymer Melts Prior to Molding by Disentanglement Methods
Entanglement is responsible for the high viscosity of polymer melts and the molecular weight dependence of viscosity as M3.4. Disentangled polymers, at identical molecular weight, would have a much lower viscosity, proportional to M, providing a maximum viscosity reduction of (Mw/Mc)2.4. The objective of this work is to study methods to disentangle polymeric melts in order to achieve large viscosity reduction without breaking the polymer chains. We are also interested in the reverse process of re-entangling polymer melts which have been disentangled, in order to recover fully their mechanical performance after molding is performed. We first present the new concepts of interactive coupling kinetics of conformers, which naturally lead to the definition of an interface of penetration between adjacent macro-coil molecules in the melt, which we assign to entanglements". The stability of the entanglement phase depends on the potential energy of interaction between conformers. It can also vary with macroscopic variables such as temperature strain rate frequency and amplitude of melt deformation. We present a new method to increase cooperativeness between conformers in the melt to the extent that deformation occurs no longer by "reptation of the entanglement phase" which is dominated by entropic effects but by stretching resulting in disentanglement. We present viscosity reduction results for Polycarbonate and a metallocene PE obtained with a laboratory rheometer which might be proof that controlled disentanglement is indeed possible with potentially a large variety of applications for the plastic industry."
Prediction of Permeability Using Optical Coherence Tomographic Imaging of an Epoxy and Unidirectional E-Glass Composite
Knowledge of the permeability tensor in liquid composite molding is important for process optimization. Unfortunately, experimental determination of the permeability is difficult and time consuming. A rapid, non-destructive technique called optical coherence tomography (OCT) can image the microstructure of a composite in minutes. In this work, binary images were generated from the OCT data and input into a lattice Boltzmann model for permeability prediction. Calculated permeabilities agreed well with experimental values for the same fiber volume fraction.
Automated Search of the Optimal Robust Injection Molding Design against Process Validation
Injection molding optimization is unique since the injection molding process is a multifaceted process offering a number of technically feasible designs for the same optimum part quality. These solutions will vary in their quality robustness to the uncontrollable process variation. Therefore, it is of great importance to consider both response improvement and solution robustness. This paper introduces a methodology for automated search of the optimal robust design against process variability. Part warpage is chosen as the quality of interest. The warpage characteristics obtained from the proposed model are compared with those from other conventional optimization models. Each optimized design is then simulated for small plausible process fluctuations. It is seen that the optimal robust design obtained in this study exhibits the best warpage characteristics in terms of warpage mean and deviation against this mean.
Possible Applications for the Time-Temperature-Shift Principle to Describe the Impact and Long Term Materials Behavior of Thermoplastic Polymers
At the IKV a concept has been developed to describe the material behavior by means of spring/damper combinations using the time-temperature-shift principle and short-term test data. The concept called deformation model" has been used successfully to predict the uniaxial long term behavior of filled unfilled or reinforced thermoplastic polymers. In order to stimulate the dynamic material behaviour without the necessity of high speed tensile tests the deformation model is calibrated based on short-term tensile data at very low temperatures and common strain rates. To reduce the testing expenditure a concept has been developed to calibrate substitute spring/damper combination based on creep-curves from material databases (CAMPUS)."
Modeling and Experimental Validation of the Stretch Blow Molding of PET
In the two-stage stretch blow molding process for the manufacture of PET bottles, injection molded preforms are placed in an infrared oven, with axially profiled heating lamps. The subsequent inflation of the PET preform is strongly dependent on the preform geometry and the temperature profile, as hot zones will blow out faster and thin out more than colder and stiffer zones. In this work, the reheat and blowing stages of the process are both modeled and experimentally validated. The part considered is a water bottle produced at the Husky Bottle Development Center. The simulations were performed at the Industrial Materials Institute. Four oven operating settings are studied. The heat transfer in the oven is modeled by combining radiation and air convection. The preform stretching and inflation are modeled with a non-isothermal hyperelastic constitutive equation. Simulations are performed using experimentally measured temperature profiles as input.
Effect of Compounding Conditions on the Dispersion of Highly Filled CaCO3/PP Compounds in Twin-Screw Extruder
Highly filled CaCO3/PP blends (up to 60% wt) were compounded using an intermeshing corotating twin-screw extruder. The effects of screw configuration (4 geometries) and operating conditions such as RPM, total flowrate, filler feed position, temperature profile on the dispersion were investigated. A rapid and reliable method for evaluating the state of dispersion in the composites was developed. Falling weight impact and tensile tests were carried out. Composites' toughness and tensile properties (modulus, yield stress and strain), which are very sensitive to the dispersion, were correlated to the compounding conditions and to a dispersion index calculated by image analysis.
Crystallization Kinetics in Low Density Polyethylene Composites
The effect of a high electrically and thermally conductive filler on the crystallization kinetics of low-density polyethylene (LDPE) crystallites has been quantified. An increase in crystal growth rate was found which was consistent with the increase in composite thermal conductivity. However, an anomalous jump, not present in the bulk thermal conductivity, coincided with the end of the critical region in electrical conductivity. The cause of this jump is not absolutely clear; however, we believe the shift is due to the formation of a continuous network of particles causing an increase in local heat dissipation.
A Novel Test to Predict the Effect of Additives and Processing Conditions on Polypropylene Fiber Screen Pack Life
A mechanical component that is especially important in the extrusion of polymers for fiber and film applications is the screen pack. During processing this screen pack filters out material that can reduce product quality and productivity. This paper focuses on a new test method that can indicate whether a given additive/formulation or processing temperature will tend to contribute to screen pack pluggage in polypropylene. Some of the factors to be presented will be the additive formulation, melt temperature, type of neutralizer, and resin type. Key criteria for this test initially was the ability to run in a laboratory setting using normal additive loading levels and to have excellent correlation to real world" processing; these have been met with this test. Numerous resin producers worldwide have validated the results of this test in normal everyday production."
Novel All-Thermoplastic Composite (TPC) Sandwich Systems for Rapid Molding
Reinforced all-thermoplastic sandwich systems constitute a specific class of composites consisting of stiff faces and a thick and light core either porous or non-porous. They allow for a fast one-step and free of adhesive molding of continuously manufactured intermediates into complex parts (e.g. body panels, structural parts). Different all-thermoplastic sandwich systems were analyzed with respect to efficient processing techniques, manufacturing costs and mechanical performance. Furthermore, economical and technological benefits were exhibited and potential fields of application were derived. A significant potential for low-cost tooling was identified using self-expandable knitted cores whereas the application of a flowable core provided complex and stiff structures.
Characterisation of Polymers by Bubble Inflation
In order to characterise materials using a simple and relative inexpensive method, the bubble inflation technique was modified. A polymer plate is clamped between a Teflon coated heating plate and a heated cylinder. By applying air through the heating plate the polymer membrane deforms into the cylinder. The top position of the membrane is monitored by fibreoptic sensors positioned in the cylinder. The pressure difference across the membrane is measured as well. The deformation in this inflation device is non-uniform and is only equal biaxial in the top of the deformed membrane. Due to this, the response is modelled using a finite element method in 3D Cartesian coordinates. The K-BKZ constitutive equation is used to model the non-linear properties of the material. Using linear viscoelastic properties from oscillatory shear measurements and measurements of the bubble inflation, estimation of the strain dependence in the constitutive equation is possible.
Automating Online Quality Control by the Use of New Neural Network Algorithms and Neuro-Fuzzy Systems
Online quality control based upon empirical process models became a standard quality assurance tool for specific high complex and expensive parts produced in injection molding. The use of this control method is limited to special-educated engineers due to prerequisite knowledge in statistics and data analysis methods. At IKV algorithms based upon artificial intelligence have been developed to solve this problems and provide online quality control for each injection molded part without any specific education of the user. Well-known process knowledge modeled with Neuro-Fuzzy Algorithms reduces the design of experiments to a simple description of the molding. The new IKV Neural Network Algorithm enables a fully automated process modeling.
Closed Loop Fuzzy Control of Part Weight in Injection Molding of Liquid Silicone Rubber (LSR) Based on PVT-Behavior
The injection molding of Liquid Silicone Rubber (LSR) represents a cost-efficient process for the production of high quality elastomer moldings. Due to the extreme thermal conditions in the mold and the low material viscosity a precise undervolumetric filling of the cavity is required to avoid underfilling or flash formation. Since process disturbances lead to changes in the mass of material injected into the mold a closed loop control of the injected mass based on the pvT-behavior is developed and realized on an industrial injection molding machine. Dependent on the course of the cavity pressure and the mold temperature a fuzzy-based algorithm determines the required changes of the dosing volume in case of process disturbances.
Influence of mPE Grades on the Dynamic Properties of PP/mPE-Blends
Blending polypropylene (PP) with an elastomeric phase such as EPDM is often performed in order to increase its fracture toughness. With the availability of metallocene polymerized Polyethylene (mPE), a new modifier with interesting mechanical properties can be chosen for blending with PP. This research investigates the influence of different grades of mPE in PP/mPE-blends on the blend's properties. Special emphasis is placed on the dynamic characteristic quantities. The load limits of the blend for applications in which dynamic stresses are predominant are determined by using the hysteresis measurement method.
Stress Relaxation Profiles of Molded and Extruded Thermoplastics Using Dynamic Mechanical Analysis
The stress relaxation profiles across the skin-core-skin layers of injection molded polycarbonate and extruded polyethylene sheet are presented. The profiles were obtained by progressively removing the layers followed by stress relaxation tests using a Dynamic Mechanical Analyzer (DMA). The machined layers were characterized using the elastic modulus, Eo, and the relaxation time, ?o. It was found that the DMA was able to distinguish the differences in viscoelastic response across the thickness of the polymer samples. The variation in behaviour was consistent with the expected morphology and molecular orientation developed due to the processing method.
Computer Aided Design of Preforms for Injection Stretch Blow Moulding
Simulations of the injection blow moulding process have been performed using the Abaqus finite element package. The simulations have been developed using three different material models (creep, hyperelastic and Buckley) and the thickness predictions have been compared against those obtained experimentally. The Buckley model was found to be the most efficient material model to model the blow moulding process. This model is now being used to investigate the design and development of preforms. A methodology has been developed to use the material distribution produced by the simulation to predict the shelf life of the container. A FORTRAN subroutine has been written which accesses the properties of each element of the model and from these properties the shelf life can be found.
Sub-Inclusion Morphologies in HDPE/PS/PMMA Ternary Blends
Various ternary HDPE, PS and PMMA blends were prepared in one step using a brabender mixer. The morphology in this case consists of a PE matrix, a PS dispersed phase and PMMA sub-inclusions within the dispersed PS, the so-called composite droplet morphology. SEM observation and quantitative characterization were used to show that this complex morphology occurs within the first minute of mixing and remains stable thereafter. Furthermore, it is demonstrated that the presence of sub-inclusions generates a measurable change in PS droplet size. It is shown quantitatively that all the PMMA is present in sub-inclusion form.
Evaluation of the Thermal Degradation of Polymer Matrix Composites via Ultrasonic Spectroscopy and Fracture Toughness
Polymer matrix composites (PMC) are commonly exposed to excessive thermal gradients during service. Thermal degradation may not create distinct defects, yet will degrade the matrix modifying its behavior significantly. We have developed an ultrasonic spectroscopy method to characterize the thermal degradation of PMC. Ultrasonic spectroscopy utilizes the frequency spectrum of transmitted or reflected sound to characterize materials. Carbon fiber - epoxy laminate composite were exposed to short term - high intensity and long-term - low intensity thermal gradients. Frequency spectra were collected before and after thermal exposure. Changes in the frequency spectrum correlated with observed changes in mode I fracture toughness.
Mechanical and Thermal Properties and Leacheate Analysis of Carpet Residue/Polyethylene Prototypes for Building and Construction Applications
A complex carpet residue is obtained as a byproduct in the tertiary recycling of nylon-6 fibers from used carpets. It consists of mainly polypropylene, styrene-butadiene rubber and calcium carbonate, and is potentially a low cost, high volume waste stream with consistent properties. In this study, composites of carpet residue with polyethylene were evaluated for building and construction applications. As received carpet residue was first compounded with low density polyethylene, homogenized and devolatilized in a twin screw extruder. Later, blocks were prepared by the intrusion process and tested for their mechanical and thermal properties as well as the leaching characteristics of heavy metals and organic carbon. It was demonstrated that the prototypes of these blocks can be potential candidates for use in a novel thermal spacer application.
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