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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Chlorine Resistance Testing of Cross-Linked Polyethylene Piping Materials
The chlorine present in potable water as a disinfectant has been reported to reduce the lifetime of some plumbing system components. In this study the nature of the failure mechanism of a commercial cross-linked polyethylene (PEX) pipe material exposed in the laboratory to chlorinated potable water is examined. Water quality, or more specifically, chlorine level, is seen to have a significant impact on material performance. Test lifetimes are seen to be noticeably lower for chlorinated potable water, even at chlorine levels as low as 0.1 mg/L (ppm), than for non-chlorinated water. Through accelerated testing at multiple temperature and pressure conditions and the use of the Rate Process Model, a model to estimate the test lifetime of the PEX pipe material at end use conditions is developed. Based on this analysis the PEX pipe material examined in this study appears to have good resistance to chlorinated potable water.
Development of a New TPV for Bonding to Rigid Thermoplastics
The development of a new flexible thermoplastic vulcanizate (TPV) that bonds to a number of different rigid polymeric substrates is introduced. Detailed bonding values will be given for this new material to ABS, polycarbonate, PC/ABS alloys, polystyrene, and polyester. Physical properties will be presented and compared to other bonding elastomeric materials. The processing recommendations are given for over molded or insert molded applications for this flexible bonding TPV. Potential applications for this flexible bonding material include bumpers for vacuum cleaners, soft touch grips for tools and utensils, and flexible housings for instruments.
The Use of Scanning Probe Microscopy to Determine the Surface Morphology and Mechanical Properties of Latex and Polymers
An overview of Scanning Probe Microscopy (SPM) and it applications to polymeric materials will be presented. The SPM is a mechanical technique capable of both imaging and making physical measurements. The images provide rapid comparison of surfaces, while image reduction to a surface roughness value (Ra) allows numeric comparisons. Additionally, the interaction of the imaging tip with the surface, using the phase modulated mode, provides details on relative compliance of the surface. Images of compliance can be used to differentiate the spatial location of the different materials that make up the materials surface. The combination of the two techniques, topography and phase modulated, provides a very powerful tool for surface characterization.
Modeling Drop Size Distribution in Polymer Blend Injection Molding
An approach for modeling the drop size distribution in the injection molding of polymer blends is developed. The simulation directly uses experimental data correlated to functional forms in the FIDAP fluid dynamics package. As an example, experimental data for droplet size and shape in a Polyisoprene /Polybutadiene system was measured using an in-situ optical microscopy instrument designed for studying complex fluids under simple shear flow. The data is collected in the flow-vorticity plane as a function of temperature and shear rate. Size and shape distributions were calculated from the digitized micrograph using standard image analysis software. The shear viscosity of the blends, as well as that of the pure components, was measured as a function of shear rate and temperature using a commercially available parallel-plate rheometer. From theoretical considerations, the simulation is expected to provide good estimates of drop size distribution for flows with large aspect ratios of flow length to thickness where entrance effects are expected to be negligible, and there are no regions of recirculation.
Investigation of Structure Development of Polyamide 11 and Polyamide 12 in Single Bubble Tubular Film Blowing
The processibility of single bubble PA11 and PA12 films was investigated. The development of crystalline structure and chain orientation of polyamide 11 and polyamide 12 films in single bubble film blowing was studied by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXS), infrared (IR) spectroscopy and birefringence. DSC measurements of both films exhibited a spontaneous increase in glass transition temperature (Tg) and cold crystallization temperature (Tc) during aging at room condition with crystallinity and melting point remained constant. Single bubble PA11 and PA12 films exhibited triclinic and monoclinic ? crystals, respectively. The level of biaxial orientation was evaluated by calculating White-Spruiell biaxial orientation factors with pole figure data.
Structure Development in Uni- and Bi-Axial Stretching of Extrusion Cast Polyamide 12 Film
Development of crystal structure, orientation and morphology in both uniaxial and biaxial stretching of extrusion cast polyamide 12 (PA12) films was carefully investigated. According to DSC measurements, aging of unstretched extrusion cast PA12 film at room condition raised both glass transition temperature (Tg) and cold crystallization temperature (Tc) without any considerable changes in crystallinity and melting point. The crystals of unstretched and stretched extrusion cast films were mostly monoclinic ? form. Stretching was carried out at various temperatures. By examining birefringences and WAXS flat films and pole figures, we found that the direction and level of molecular orientation was largely dependent on the extension ratios. SAXS showed that an increase in stretching temperature raised long spacings of lamellae. Annealing of PA12 films in formic acid solution raised crystallinity, melting point, level of chain orientation and long spacing of lamellae.
Drop Deformation and Breakup in Viscoelastic Polymer Blends
A three-dimensional finite element code is developed for simulating viscoelastic two-phase flows. The viscoelastic fluid is modeled via the Oldroyd-B model. The exact governing partial differential equations are solved using the Marchuk-Yanenko operator-splitting technique. The two-fluid interface is tracked using the level set method. The code is used to study the deformation of drops in simple shear flows and bubbles in gravity driven flow. The effects of Deborah Number (De) and capillary number (Ca) on deformation is analyzed for De values ranging from 0.0004 to 16, and Ca ranging from 0.06 to 1.2. The numerical results show that the viscoelastic stresses near the drop surface increase deformation of a Newtonian drop in a simple shear flow as compared against Newtonian shear flow. For the case of a viscoelastic drop in a Newtonian shear flow the deformation is smaller than that for the corresponding Newtonian drop. The effect of viscoelasticity on deformation is more pronounced when De<~O(1). For a Newtonian bubble rising in a quiescent viscoelastic fluid, the extensional viscoelastic stresses pull out the trailing edge and the bubble develops a cusp like trailing edge in one view and a broad edge in the orthogonal view. The trailing end of a Newtonian bubble rising in a Newtonian liquid, on the other hand, is pulled inwards which leads to the drop taking an umbrella-like shape.
Direct Simulation of Sedimentation of Solid Particles in Viscoelastic Fluids
The sedimentation of rigid spherical particles in viscoelastic fluids is studied by using 3D direct numerical simulations, in the simulation, a Galerkin finite element formulation is used to solve the fully coupled motion of the solid particles and the fluid that is governed by an Oldroyd-B model. The movement of the particles is handled with an arbitrary Lagrangian-Eulerian technique in conjunction with a mesh update strategy. Effects of the parameters controlling the particle motion, which are the flow/particle Reynolds number, the Deborah number, and the solid-liquid density ratio are investigated. This work was supported by NSF through grant CTS-9873236.
Rheological, Morphological and Interfacial Properties of PP/HDPE Blends
In this paper the linear viscoelastic properties of polypropylene (PP)/high-density polyethylene (HDPE) immiscible blends were measured as a function of frequency for different blend composition and temperatures. The morphology of the blends was studied by Scanning Electron Microscopy. The interfacial tension between the components of the blends was evaluated using small amplitude oscillatory shear analysis. The results seem to indicate that there is a range of compositions for which it is possible to use Gramespacher and Meissner analysis in order to calculate interfacial tension between polymers using small amplitude oscillatory shear measurements.
Predictive Model Helps Develop New High-Performance HDPE for Barrier Film Application
As the blown film industry has matured, the need for decreased cost has become paramount. The most attractive means of reducing cost is by down gauging film thickness, which inherently reduces the toughness of the film. This paper describes how a predictive model was used to develop a new homopolymer HDPE resin, which produces films with significantly improved mechanical properties without sacrificing barrier properties. The improved properties are the result of modifying the molecular weight and molecular weight distribution of the resin. Detailed blown film results demonstrate the performance improvement and the downgauging potential of the new resin compared to conventional HDPE.
Effect of Interdiffusion Regions on Barrier Properties of Multilayer Films
Barrier properties of polymer films can be improved in various ways, such as formation of multilayer structures by coextrusion, surface treatment, and coatings. This work explores the use of thousands of alternating layers of polymer (xyxy...) to alter the resistance to permeation. A model is presented to predict the number of layers needed in a laminate to change the flux of a permeant by a given amount. An important feature of the model is the species transport across the interdiffusion regions at the polymer-polymer interfaces where diffusivity of the penetrant is assumed to be a function of the volume fractions of the interdiffusing polymers. Our modeling results show that increasing the number of interfacial regions decreases the flux for a given condition, and a large number of layers are required to achieve appreciable barrier enhancement.
Temperature Monitoring of Capillary Rheometry Using a Fluorescence Technique
A non-contact temperature monitoring technique based on fluorescence spectroscopy was used to measure the temperature of a polymer resin during capillary rheometry testing. Polyethylene doped with a fluorescent dye, perylene, was used in experiments that were designed to measure resin temperature changes due to shear heating as shear rate in the capillary increased from 10 to 10000 s-1. Resin temperature at the exit orifice of a 1 mm diameter capillary die was found to increase monotonically with increasing strain rate reaching 25°C above the capillary set point temperature at the highest shear rates. The implications regarding rheometry testing are discussed.
New Solidification Models for the Simulation of the Injection Molding Process
In order to predict shrinkage and warpage in injection molded products, the thermal contraction and the residual stress have to be calculated. Therefore the temperature distribution in the injection mold has to be simulated during the fast cooling in the cavity. For semi-crystalline polymers this implies the incorporation of the latent heat of crystallization into the heat equation by means of an adequate crystallization model. Furthermore, properties such as the specific volume and the heat capacity and conductivity need to be modeled. The models for the crystallization and the thermal properties presented here are physically motivated. Simulations are presented of the temperature distribution during the fast cooling of semi-crystalline polymers with and without glass fibers. The calculations are compared to experimental results, which have been obtained with an apparatus designed especially for very high cooling rates.
A Preliminary Investigation into the Use of Wood Fibers as a Filler in the Rotational Molding of Polyethylene
There has been no known work carried out on the use of wood fibers as a filler in the Rotational Molding (herein also referred to as rotomolding) of Polyethylene. It is reported though that the extrusion industry has noticed a 100% increase in wood fiber profiles over the past two years. (1) It is only a matter of time before this diversity of materials will find itself being used in Rotational Molding. This paper presents investigative results of the characteristics of the molded parts in terms of molding conditions, percentages of wood fiber used and the type and size of wood used. Potential for novel product design and the uses for the wood/ plastic composite will also be discussed.
Natural Fiber Reinforced Polypropylene Composites – an Approach on Thermoforming Processing
This work has been performed at Mercedes-Benz of Brazil in a partnership with its suppliers aiming the replacement of fiberglass in polypropylene matrix composites by natural fiber reinforcements. The process that has been chosen for this purpose was Vacuum-forming. This choice took into account the large application that this technique represents in the company's commercial products. The results expected for this new material is cost and weight reduction besides the friendly environmental aspect that this change introduces. Jute fiber reinforced polypropylene sheets at constant thickness and fiber content were prepared in order to evaluate the feasibility of the application. The preliminary results have shown that this material has a great potential of application because of the low fiber costs.
Experimental and Analytical Verification of Plastics Material Models for Automotive Crashworthiness Applications
Plastics are widely used in automotive component applications, such as instrument panels, door panels, consoles and pillar garnishes. These components are subject to government-mandated impact tests for occupant safety. To overcome the traditional cut-and-try methods in designing automotive components, advanced CAE (Computer Aided Engineering)/FEA (Finite Element Analysis) analytical methodologies have been used to assist the design and manufacturing of the desired components. The objective of this paper is to investigate the effects of material model and impact speed of the drop weight on the response of an injection-molded plastic knee bolster part under a designed drop-silo impact test. FEA simulations on the knee bolster were conducted using both LS-DYNA3D and ABAQUS/Explicit. The analytical results are compared to the experimental data from the drop-silo impact test. Several engineering plastic materials are evaluated, and correlation is quantified. Observations are made with respect to materials characterization experiments, material constitutive models within the analyses, and general test and modeling procedures. Suggestions are made for improved correlation for the future.
The Effect of PP-MA and PP-GMA as Compatibilizers on Polypropylene/Nylon 6 Blends
Blends of polypropylene (PP) and nylon can combine good properties, however both polymer are incompatible. PP functionalized with maleic anhydride (PP-MA) has been used as compatibilizer for this system and the PP functionalized with glycidyl methacrylate (PP-GMA) should be a good alternative due to reactivity of the epoxy group with -NH2 and -COOH group. Blends of PP/PP- MA or PP-GMA/Nylon 6 were prepared using 30% of nylon (Ny6). The effect of the compatibilizer were evaluated by DSC, SEM micrograph and mechanical properties. The analysis indicate that PP modified with MA show the best compatibilizing effect in these systems.
Compatibilized Polypropylene/Polyamide Blends
When properly compatibilized PP/PA blends can offer a wide range of desirable characteristics, combining properties of both components. The aim of this work is to compare the effectiveness of the compatibilizing effects of different modified polyolefins on the properties of PP/PA blends. The blends were constituted by a PP matrix and they were obtained in a mixer chamber. PP modified with maleic anhydride and vinyltriethoxysilane (PP-MA and PP-VTES) and EPR modified with maleic anhydride (EPR-MA) were employed as compatibilizing agents. Products were characterized by SEM and DSC. Melt flow indexes and mechanical properties of the blends were determined.
Use of Pyrolised Oil Shale as Filler in Polyolefins
The pyrolysed oil shale originating from the pyrolysis of the bituminous rock was used as filler in mixture with poly(ethylene-co-vinyl acetate) (EVA) and high density polyethylene (HDPE). The effects of this addition were compared with the ones obtained with different vinyl acetate content and size of pyrolysed oil shale particle. The compounds were prepared on a Haake equipped with mixing head Rheomix, at 180°C. Samples were compression-molded and tensile testing ware performed on an Instron apparatus using a crosshead speed of 10 mm/min. Tension curves of samples were obtained. These curves showed the possibility utilization the pyrolysed oil shale without damaging the mechanical properties of the compounds, for low concentration of pyrolysed oil shale (1-5 wt%) if the particle of pyrolised oil shale is lower than 270 mesh. Besides of this behavior it was observed that the vinyl content of polymer is important to enhance the mechanical properties in the compound. Compounds of poly(ethylene-co-vynil acetate)/pyrolysed oil shale and high density polyethylene were obtained with concentration of pyrolysed oil shale up to 30%. The behavior of these materials were evaluated taking into account the concentration and the size of the used particle. It was observed that particles with the smaller diameters showed best effects on the mechanical properties of the final material if the concentration of the pyrolised oil shale used up 5% wt%. The mechanical properties, differential scanning calorimetry, and scanning electron microscopy results and dynamic mechanical thermal analysis are discussed.
Degradation Mechanisms of Thermoplastic Polyurethane Resins
The use of polymeric materials for transparent, lightweight armor has been of great interest to the U.S. Army for a number of years. Field items such as goggles, lens, face and windshields are currently manufactured using advanced polymeric plastics. These items are designed with polymers that provide excellent optical clarity, rugged abrasion resistance, and high ballistic impact strength. However, as with any organic polymer system, these materials are susceptible to degradation over time when exposed to various environmental (i.e. sunlight, moisture, temperature) conditions. This structural degradation (1-4) will eventually comprise the original integrity of the materials' desired properties. In this study, the impact of accelerated weathering upon newly developed polyurethane based thermoplastic materials was investigated. A fluorescent ultraviolet (UV)/condensation weathering tester was selected for the exposure study. The materials were characterized by UV/VIS spectroscopy and FT-IR spectroscopy. The results reveal that the urethane linkages undergo a scission reaction upon UV exposure drastically affecting the mechanical properties of the material. Furthermore, these urethane scissions produce a yellowing of the polyurethane which can inhibit its use where optical clarity in important.
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