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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Anisotropic Shrinkage in Injection Moldings of Semicrystalline Polymers: Simulation and Experiment
A novel approach to predict anisotropic shrinkage of semicrystalline polymers in injection moldings was proposed using the flow-induced crystallization, frozen-in molecular orientation, elastic recovery and PVT equation of state. The anisotropic thermal expansion and compressibility affected by the frozen-in orientation function and the elastic recovery were used to obtain the in-plane anisotropic shrinkages. The elastic recovery and frozen-in stresses and birefringence were obtained by a non-linear viscoelastic model. The flow-induced crystallization was described via the elevated melting temperature affected by entropy production with modified kinetics of the crystallization. Numerous injection molding runs on polypropylene were carried out by varying packing time, flow rate, melt temperature and mold temperature, and anisotropic shrinkage of moldings were measured. The experimental results were compared with the simulated data.
Modeling the Infrared Sheet Heating in Roll-Fed Thermoforming
The heating stage is of primary importance in the thermoforming process. Computational methods using the finite element technique for modelling the radiation heating stage of thin gauge, roll-fed plastic sheet is presented and discussed. The theoretical approach as well as the experimental validation is also presented. The proposed approach takes into account the dynamic effects of sag and the displacement of the sheet inside the oven. The volumetric power absorption representing a heat generation term, which is critical in the case of semitransparent materials, is also integrated by using Beer’s absorption law.
Control of Thixotropicity of Polymer Melts by Disentanglement Processing
It is well known that thixotropicity of polymer melt is determined by the chemical nature of the bonds and the length of the macromolecules, more specifically the molecular weight distribution. Little is known of the influence of processing on thixotropicity. As a matter of fact, governing theories predict that processing variables (temperature, pressure, strain rate) should have no visible influence on melt pseudoplasticity or thixotropicity. The Carreau’s equation of viscosity describes well this tendency for a polymer melt to shear-thin at higher strain rate, and also incorporates the effect of temperature and pressure (via the pressure dependence of Newtonian viscosity). In terms of the simpler power law model, pseudoplasticity is described by the melt index, which is found from the slope of Log (Stress) vs Log (Strain Rate). As already said, it is generally accepted that neither the melt index, nor the Carreau’s parameters, are a function of the processing conditions.
Exfoliation of Nanoclays in Concentrates of LDPE
Masterbatch concentrations of nanoclay filled polymers are in high demand, but they have proven to be difficult to produce because of difficulties achieving homogeneous dispersion, exfoliation, and intercalation, especially in the case of polyolefins. This paper covers the use of disentanglement processing technology [1,2,3] to mix and disperse nanoclay concentrates (up to 30%) into LDPE resins. The prescribed treatments employed for the experiments covered by this paper were TekFlow technology by Stratek Plastic Ltd. These treatments extensively shear-thin polymeric melts, under conditions of non-linear viscoelasticity, producing disentanglement. Also, the high success in obtaining fully intercalated, exfoliated high concentration nanoclay blends is assumed to arise from the unique ability of the disentanglement processors to laminate the melt at very low temperature without rising pressure.
Cure Optimization of Layered Silicate Polynanomers
The mechanism of exfoliation in layered silicate - epoxy nanocomposites has been investigated using ex-situ x-ray diffraction (XRD) measurements taken during dynamic and isothermal curing cycles. Cure temperature ranges have been determined by differential scanning calorimetry (DSC) to coincide with the termination of the exotherm peak observed during cure. During cure, samples are sequentially removed from the heating system and immediately quenched to slow the polymerization reaction and lock-in the layered silicate morphology. The quenched samples are exposed to XRD analysis so that silicate d-spacing may be determined as a function of cure advancement. The changes in silicate morphology are correlated to the thermal events measured using DSC. Ultimately this approach is being used to develop specific cure cycles to control and optimize the properties of montmorillonite filled nanocomposites.
Implant Induction Welding of Nylon 6/6
The implant induction welding technique utilizes a heating element material at the joint interface to generate the heat. In this study, three factor two level full factorial design of experiments were performed to evaluate two different types of Nylon 6/6, denoted as A and B, in a lap shear joint geometry. It was found that weld time was the most dominant factor in affecting the weld strength followed by power and pressure. It was also found that the weld strength was proportional to the heating time at constant power and constant pressure. In addition, final sample thickness was inversely proportional to the lap shear strength. Bending of the joint during testing was the major failure mode. The maximum achievable strength for material B is 15% higher than that of material A. Furthermore, vibration welding of these two materials was also performed for comparison. It was found that material B achieved 80% higher weld strength than material A using vibration welding.
Novel Phillips Loop-Slurry Based Polyethylene Resins Using Modified Chromium Oxide Catalysts for High Performance Pipe Applications
Novel high density polyethylene resins made in the Phillips Loop-Slurry Process (single-reactor), using a catalyst of chromium on modified aluminophosphate, were developed with unique structural attributes that make them especially suitable for high performance pipe applications. These structural attributes include high molecular weight (MW), very broad molecular weight distributions (MWD), effective levels of short chain branching in polymer chains with MW > 1,000,000 g/mol, and reduced levels of long chain branching (LCB). In particular, pipes made from these ethylene 1-hexene copolymers satisfy the performance requirements of PE100 specifications; in addition, these resins also offer outstanding slump (or sag) resistance for large diameter (> 24 inch) pipe processing. In this paper, a brief description of these catalyst systems is presented along with the unique molecular aspects of the resins. The physical properties of these resins and their fabricated pipe processing/performance properties are compared to several “bimodal” type resins.
Continuous Process for Melt Intercalation of PP-Clay Nanocomposites with Aid of Power Ultrasound
A continuous ultrasound assisted process using a single screw extruder with an ultrasonic attachment was developed to prepare PP/clay nanocomposites of varying clay concentrations. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. An intercalation of polymer molecules into clay galleries and a partial exfoliation, which occur at short residence times (on the order of seconds), were observed as evident from measurements by X-ray diffraction and transmission electron microscopy. The obtained results indicate a possibility of the rapid intercalation and partial exfoliation of PP/clay nanocomposite without the matrix being chemically modified.
What Every Plastics Professional Should Know about Patents and Patenting Part 1: An Overview of Patents and the Role of Claims in Defining Intellectual Property Rights Granted in Utility Patents
In this article, the legal right to exclude others, granted in a patent, and the commercial significance of patent protection are discussed as they relate to plastic materials, processes, processing equipment and products. Also, presented are subject matters that may be patented and who may apply for a patent. The article also deals with the requirements that every patent application must meet in order to be allowed. The anatomy of a typical patent and the role of the claims(s) in defining intellectual property rights are also discussed.
Polymeric Fuel Cell Membranes: Mechanical Properties and Durability
Polymers are essential materials for low temperature fuel cells. Proton Exchange Membrane (PEM) fuel cells typically feature a polymer electrolyte and usually include other polymer components as well. Design of PEM cells for high performance and (especially) for durability requires that the physical and mechanical properties be known, as a function of the operating conditions.The present paper reviews the nature of the applications of polymers in PEM fuel cells, discusses the required properties and related environments, and provides some sample results of investigations of the behavior of polymers typically used for these applications. The discussion includes linear, nonlinear, and fracture behavior.
A Study on the Crystallization Behavior and Morphology of PP/EPR Blends
The morphology and crystallization behavior of polypropylene/ethylene-propylene rubber blends were studied in this paper. The crystallization effect of the addition of EPR in PP was discussed via observation using a polarized optical microscope. The result shown that, with the addition of EPR in PP, the rate of crystallization became slower, the Maltese cross formation gradually disappeared and bead dispersion became evident. Through wide-angle X-ray diffraction analysis, with the addition of EPR in PP, the crystal size was smaller, and differential scanning calorimeter analysis showed that the melting point moved to a lower temperature. This paper also discuss the effect of different take-off temperatures on crystallization for different ratios of PP/EPR in the PP/EPR blend in the flat-film extrusion process. It was found that the crystallization degree and crystalline lamella size were greater at higher take-off temperatures than those at lower take-off temperatures.
Enhancing Mixing Performance of Extrusion Process via Vibration Force Field
Effects of vibration force field on dispersive mixing have been investigated during extrusion of a calcium carbonate filled LDPE system using a split barrel electromagnetic dynamic extruder, which introduce vibration force field into the whole extrusion process. The samples are collected along the length of the screw by barrel opening experiments and subsequently examined by means of scanning electron microscopy (SEM). The quantitative image analyses of SEM micrographs show that the introduction of vibration force field improves dispersion of calcium carbonate in LDPE matrix. With the same vibration amplitude, a higher vibration frequency leads to a smaller average particle size and a narrower particle distribution.
Thermal and Mechanical Properties of Recycled PET and its Blends
This paper discusses the thermal and mechanical properties of virgin PET, recycled PET and their blends. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the thermal properties. The tensile tests at ambient and elevated temperature were used to study the mechanical properties. There were significant differences in the recrystallization behaviour as far as the thermal properties were concerned. In the case of mechanical properties, the tensile test at elevated temperature showed that the strength of the blends of recycled PET/virgin PET were lower than those ones of virgin PET.
True 3D CAE Visualization of Filling Imbalance in Geometry-Balanced Runners
The filling imbalance in geometrically balanced runner system of multi-cavities is always difficult to handle in injection molding. Previous researchers revealed that the flow imbalance problem is related to the three-dimensional thermal history and shear rate distribution of melt flow in the runner, and accordingly proposed a novel apparatus to overturn the melt to avoid this problem. However, the design parameter of this apparatus is different to realize, and it is only performed by trial-and-error. In this paper, we have proposed a new methodology to analyze this injection process. Firstly, a flexible meshing methodology comprising different element topologies is proposed to provide high-resolution mesh for the runner system and cavity. Further, to demonstrate and verify our idea, the comparison between simulation and experiments has been performed. From the numerical experiments, we have proven that the proposed methodology is a highly valuable tool to help understand and further optimize the melt flipping apparatus.
Development of PP/Clay Nanocomposite using scCO2 in Twin Screw Extruder
In this study, as a continuous processing method for the fabrication of polypropylene/clay nanocomposite, supercritical carbon dioxide (scCO2) was introduced in twin screw extrusion process. Supercritical CO2 was used for the purpose of improving dispersion of clay layers in PP matrix and diffusion of polymer chains into silicate layers. PP/clay nanocomposite was produced by two step extrusion processes. In first step, CO2 was injected into the barrel of extruder by CO2 metered injection system and the foamed extrudate was pelletized after solidification in water bath. In second step, CO2 in the foamed product was vented by vacuum pump. Finally, PP/clay nanocomposite without CO2 was produced. In this study, for the development of nanocomposite, the investigations were made for various cases such as variations in CO2 concentrations, maleic anhydride grafted polypropylene (PP-g-MA) concentrations and processing conditions. To confirm scCO2 effect, the comparison was made for the nanocomposites processed with and without scCO2 injection. The structures of the nanocomposites were investigated with X-ray diffraction and transmission electron microscopy. Mechanical properties were also evaluated.
Processing Effects on the Tribological Properties of Thermoplastics
An important demand on engineering-technology is the optimization of materials for tribological stressed parts with regard to friction- and wear-behavior. To be able to use the full potential of improvement an optimum in processing is necessary. The morphology especially of the tribologically stressed surface-regions is influenced by the variation of mold- and melt-temperature. The dependence of tribological properties on processing conditions is shown for POM and PA66 in sliding contact against steel. The results of wear-tests are correlated with mechanical, morphological, and thermodynamic results.
Measurement of Strain Rate Dependent Material Properties for Polymers and Their Prediction from Normal Tensile Tests
Present market forces dictate that the automotive industry must increase passenger safety. Since polymer material behavior are sensitive to speed, the determination of material data at crash relevant strain rates is of great importance.This study is concerned with a new method to predict the material behavior of polymers at high strain rates. The material data is determined with normal tensile tests and this material data is subsequently extrapolated to high strain rates. The results are compared and evaluated with those from high speed tensile tests.
Ranking of PP Pipe Grades by Their Failure Behavior under Impact Loads
In this work the influence of different test specimen configurations (different local and global stress states) on the brittle/ductile transition temperature TBD in PE pipe grades (PE 80 and PE 100) was characterized under impact loads at 1 m/s. It was found that TBD determined based on an energy criteria and fracture surface analyses was highly dependent on the stress state prevailing in the different test specimens. For all test specimens lower values for TBD were found for PE 100 in comparison to PE 80, corroborating the better performance of PE 100 under the different test conditions (from near plain stress to near plain strain conditions).
Through-Thickness Process Zone Characterization at Fatigue Cracks in PE-HD
Fatigue crack growth (FCG) experiments were conducted on different PE-HD pipe grades with CT specimens. All tests were interrupted in the region of stable crack propagation. The crack front and the front of the process zone ahead of the crack were systematically characterized via microscopic methods in the thickness direction of the specimen. The effects of stress intensity factor and frequency were systematically investigated. The experimental data are employed to study the mechanisms of process zone development and to determine the effective crack length by compliance relationships (instead of using optical methods).
PEO-Na+/MMT Nanocomposite Film as Polymer Electrolytes
A polymer-clay nanocomposites of Polyethylene oxide (PEO) and Na+/montmorillonite (MMT) was prepared by a conventional melt blending method in an internal mixer. The level of intercalation of the composites of PEO with Na+/MMT layered silicates was crucial to influence the conductivity and mechanical properties as well as the thermal stability, which were studied by thermal analysis, FTIR and Wide Angle X-ray Diffraction. Thermal stability was also studied by using Thermogravimetric Analysis. The ionic conductivity and the impedance plots were measured by using an alternating current meter. It was found that PEO-Na+/MMT could be an alternative system for polymer electrolytes with high thermal stability, high tensile modulus and moderate ionic conductivity (10-6 Siemen cm-1).
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