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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Optimisation of Plastic Boxes Accounting for Visco-Elasticity
The load carrying capacity of plastic boxes diminishes with time, due to the visco-elastic behaviour of plastics. Structural optimisation of boxes is possible by applying Multipoint Approximation Response Surfaces (MARS) in combination with Finite Element Method pro-grams like MSC/MARC. The MARC program has an open structure and the non-linear viscoelastic constitutive relationships can be accounted for, using the user subroutine HYPELA.Results from structural optimisation calculations will be presented, with the mass as the objective function and the load carrying capacity determined by buckling as the major constraint.Results from experimental verification of buckling loads will be given as well.
Optimisation of the Flow Distribution in Profile Extrusion Dies
The current state of a computational code that is being developed to aid the design of extrusion dies for thermoplastic profiles is presented. This code encompasses three main parts: i) flow modelling routines based in the finite volume method, to calculate the 3D flow field using non-isothermal models; ii) geometry and mesh generators; ii) optimisation algorithm based on the non-linear simplex method.Currently the code solves the flow balancing problem using simultaneously different strategies: length and thickness control of the die flow channel. Its application is illustrated using one case study.
Optimization of a Thermal Sprue for Hot Runner Mold
Recently, Husky sought to investigate further optimization of the performance of their Thermal Sprue TS 750 series. A test rig for evaluating the sprue performance was constructed for that purpose. The temperature distribution was measured along the nozzle tip to track the thermal profile of the sprue with various settings and design parameters. The comparison between measurements on the test rig and on a mold validated the simulated thermal environment created in the test rig. While this approach proved to be useful, there is still a need for trial and error procedures because each set of parameters has to be adjusted to obtain the corresponding thermal profile of the sprue. Furthermore, no prediction of the thermal profile could be done using only the processing conditions or changes in the sprue geometry.
Optimize Injection Molding Cycles for HDPE by Considering the Effect of Cooling times on Part Performance
Many different grades of high-density polyethylene (HDPE) are used in the production of injection molded rigid containers that are widely used in food packaging and promotional drink cups.1 These grades are differentiated from each other by their physical properties, such as molecular weight, molecular weight distribution, density, comonomer type, and antioxidant level. Material physical properties and processing conditions often dictate end-use part performance. This paper investigates the relationship between injection molding cycle time manipulation via cooling time selection and the part performance of two grades of HDPE.
Organic Colors and the Food & Drug Administration...What is Acceptable in Today's Marketplace
Natural colors such as paprika, beets, carrot oil, dried algae, grape skins and saffron have been around since the time of the Egyptians (5000 BC). However, it was not until the late 1800’s, during the “Dyestuffs Era” that colors were produced synthetically, beginning with Perkin’s historic discovery of Mauve in 1856. These chemically synthesized colors were more economical, easier to obtain, easier to incorporate and offered greater tinting strength than their natural counterparts. However, many of these colors, being used at the time to color foods such as ketchup, mustard, jams and wine, had never been tested for their toxicity to humans.As a result of safety concerns, in 1906, Congress passed the Pure Food and Drugs Act covering the use of colors in food. The 1906 act was to be followed in 1938 by the passage of the Federal Food, Drug and Cosmetic Act, making certification mandatory. The Food and Drug Administration (FDA) was empowered by Congress to adopt and enforce the regulations promulgated by the Federal, Food, Drug and Cosmetic Act. It was as a result of this act that the designations “FD&C Blue No. 2, D&C Red No. 17, etc.” came into existence. The Food Additives Amendment of 1958 required a user to obtain pre-market approval of any new food additive. In 1960, as a result of a major outbreak of diarrhea caused through children eating candy colored with excessive amounts of FD&C Orange No. 1, the 1938 law was broadened to allow the Agency to set limits on the levels at which colorants could safely be used in food. It was at this time that the FDA began a review of over 200 chemicals then being used to color foods to determine if they were indeed safe in this application. These colors were placed on a “provisional” list until their safety could be confirmed or the colors delisted. From this original list have come a small group of colors that are “permanently” listed.The Code of Federal Regulations (CFR) is the embodiment of all the laws adopted by the agen
Orientation-Induced Crystallization in Isotactic Polypropylene
In-situ synchrotron small-angle x-ray scattering (SAXS) and wide-angle x-ray diffraction (WAXD) techniques were used to study the effects of step-shear fields on orientation and crystallization in isotactic polypropylene. The results suggest that the orientation affects the molten chains both thermodynamically and hydrodynamically. The thermodynamic effect involves entropy reduction of oriented chain segments and favors formation of primary nuclei. The hydrodynamic effect generates a network of primary nuclei through the relaxation time difference in chains and also causes realignment of the nuclei, which leads to a scaffold (or network) of primary nuclei in the melt at the very early stages of crystallization that dictates the morphology of the crystallized polymer.
Outdoor Weathering of LLDPE Modified with Peroxide
In order to use linear low density polyethylene (LLDPE) modified with dicumyl peroxide (DCP) as a protective coating to the interior or exterior of pipes, we have investigated its resistance to outdoor weathering.We have prepared mixtures of LLDPE with DCP in selected conditions. The mixtures were put onto a hot metallic plate and spread with a spatula to produce coating with regular thickness. Specimens in a form of dumbbell were cut from the plates and submitted to exposure to outdoor condition at IMA (UFRJ) for three months. The effects of degradation of LLDPE were studied based on changes on its mechanical properties.The outdoor weathering causes a decrease on mechanical properties mainly in the strain at break. The samples without DCP showed the highest decrease of this parameter.
Parametric Study of Mixing Efficiency in a Kneading Block Section of Twin-Screw Extruder
In polymer extrusion, the mixing of several compounds is often a critical point: the quality of the final material depends on the efficiency of the mixing step. In order to perform this function, several kneading block elements (KBE) are placed along the screw in a so-called mixing section. Furthermore, the shape of each KBE significantly affects the efficiency of the mixing.In this paper, the effect of the geometrical parameters of KBE on distributive mixing is studied using numerical simulation. First, we check the convergence and the accuracy of our results: influence of mesh refinement and interpolation is determined. Next, we perform several 3D transient simulations using different geometries of KBE.For each case, we determine its mixing capability by using statistical tools performed on a large set of material points trajectories: residence time, shear rate and total shear distributions are compared.
Parison Verification for Extrusion Blow Molding Simulation Software
Constructing a parison for extrusion blowmolding simulation analysis is typically done assuming a cylindrical shape and uniform wall thickness. Some simulation software packages don't take die swell and sag into account. As these two phenomena always occur during extrusion, the results of an analysis of a parison with a cylindrical shape and uniform wall thickness will lack accuracy when utilized in the real world situations. This inaccuracy leads to higher mold costs and lost time in the development of new molds. In an attempt to obtain more accurate results, a 2D axisymmetrical model was used to simulate the extrusion of the parison. This process will take into account die swell and sag. To test the accuracy of the software being used, the process was replicated on a blowmolding machine. By proving its accuracy, it is hoped that the software will gain acceptance within the blowmolding industry.
The Part Quality Prediction from Ultrasonic Wave and Artificial Neural Network in Injection Molding Process
Until now, Several method of part quality prediction have been used to generate useful information for injection molding process, where more precise methods based on physical laws and linear relations are not available. Traditional prediction methods have resulted in creation of many problems, due to the selection of experimental variables from the machine rather than the cavity mold. Injection molding process has plenty of variables to be carefully observed concerning parts quality. Among these, cavity pressure and temperature are the ideal candidates for part quality prediction, thanks to their capability to present the dramatic changes inside the mold. But these methods were not able to predict part modulus and strength. One needs other sensor system that directly reflects not only external or physical changes of the parts, but also interior molecular status or density. We must note that pressure-volume-temperature-related variables emerged as important effects in this case.
Performance and Properties of Modified Pet Produced by Solid State Polymerization of Low IV PET Prepolymer
A PET production process that uses mostly solid state polymerization to give PET with the desired MW or IV may have economic advantages. However, PET copolyesters produced from low IV prepolymers with IV's in the range of 0.30 to 0.36 gives PET copolyesters with higher melting ranges compared to conventional PET copolyester with similar composition. This requires higher injection molding temperatures to produce PET bottle preforms relative to conventional PET. Higher comonomer content is required to give comparable injection molding performance relative to commercially available PET resins.
Perspectives on Durability of Composite Materials - Status and Promise
The field of durability of composites has made remarkable strides in the last ten years. The Failure Analysis and Prevention Special Interest Group in SPE is evidence that this progress is now impacting the applied community. It is appropriate that we assess the status of the field and set directions for the future growth and application of this important field. The present discussion will attempt to outline the current capabilities and approaches that have shown promise, and to discuss the related experimental techniques that are available to support them. Then, comments on the gaps in those modeling and experimental capabilities ill be identified and possible directions for future research and development will be suggested.
PET/Epoxide Reactive Extrusion Process Requirements from Batch Kinetic Data
The complex chain extension/degradation reactions occurring in a polyethylene terephthalate (PET) melt, in the presence of triglycidyl isocyanurate (TGIC) as a chain extension additive, were followed in an intensive batch mixer by torque changes, analyzing the products for residual carboxyl content, and by dynamic mechanical testing. Valuable information was obtained from the batch mixer data about the effects of various process parameters on the kinetics of the reactive modification. The preliminary results indicate an overall decrease in carboxyl content and increase in melt viscosity and storage modulus values depending on mixing conditions and concentration of the additive. The batch kinetic data were used to define the process requirements to carry out continuous reactive modification in an extruder. Modified PET extrudates were characterized by high die swell, low melt flow index (MFI), and higher melt strength, as compared to unmodified PET control.
Phase Equilibrium in Blends of Polypropylene and Linear Low Density Polyethylene
Blends of polypropylene and polyethylene are reported to be immiscible in the solid state, and partly miscible in the melt. Blends with excellent mechanical properties made without a compatibiliser have been reported. The miscibility is of interest in predicting suitable processing conditions to achieve good quality products with various processing equipment, even though cooling rates may vary significantly. Blends of polypropylene and linear low density polyethylene were compounded and then their dynamic shear behaviour, and thermal behaviour were characterised. Blends with low levels of PP were found to be miscible above 120°C; other blends were immiscible. The data were correlated with a previously reported morphology study and the sensitivity of the blend morphology to processing variables was deduced.
Phase Separation in a Homogeneous Shear Flow
Computational results of phase separation in a homogeneous shear field, based on a Galerkin type spectral element method have been obtained. The theory of Cahn and Hilliard, describing the free energy of a non-uniform system with local and non-local terms, is used in the framework of the theory of the non-classical thermodynamics described by de Groot and Mazur (1) to derive a complete set of equations that governs phase separation and hydrodynamic effects such as coalescence. This work is compared with results in which the velocity field is inserted directly into the convective term of the time-dependent Ginzburg-Landau equation. Logically the results of a coupled solution with high capillary number closely resemble those of a directly imposed velocity field. However, as a smaller capillary number is chosen the interfacial forces become more dominant over the viscous forces which results in different morpologies.
Phota Degradation Mechanisms of Layered Silicate-Polycarbonate Nanocomposites
The use of advanced lightweight materials to improve combat survivability has been of crucial interest to the U.S. Army for a number of years. The design, development, and performance testing of these advanced materials is critical for enabling Future Combat Systems and the Objective Force Warrior. Specifically, hybrid organic/inorganic polymer matrix nanocomposites show promise in providing many of the physical properties required (i.e. lightweight structure, rugged abrasion resistance, high ballistic impact strength). However, as with any polymer system, these materials are susceptible to degradation over time when exposed to various environmental (i.e. sunlight, moisture, temperature) conditions. This structural degradation (1-5) will eventually comprise the original integrity of the materials’ desired properties.Polycarbonate (PC) has outstanding ballistic impact strength, good optical clarity, and high heat distortion resistance. The Army has a continuous interest in research on PC for better chemical resistance and enhanced resistance to abrasion. The focus of our research is to exploit nano-technology through incorporation of layered silicates for property enhancement. Typical mica-like clays consist of stacked platelets with the thickness of each individual platelet on the order of 1 nm. (1-5) Because of the nanometer size and high aspect ratio characteristics, polymer-layered silicate nanocomposites with much lower volume fraction of clays exhibit properties significantly better than the conventional mineral-filled micro- or macro-composites.In this study, the impact of accelerated weathering upon newly developed polycarbonate-layered silicate nanocomposites materials was investigated. The silicate loading varied from 0-3.5 % by weight. 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 carbonate linkages
Photoelastic Measurement of Residual Stresses in Hot Plate Welded Polycarbonate
Formation of thermal and residual stresses during thermoplastic welding can have detrimental effects on the joint quality under both dynamic and static loading conditions. Residual stresses can reduce the solvent resistance of the polymers as well as the tensile strength and fatigue life. Therefore, it is important to be able to measure and predict the residual stresses that develop during welding and to relate process parameters to the stress level. Photoelasticity was used to measure the residual stresses in hot plate welded polycarbonate. It shows that stresses in the direction parallel to the weld are highest.
Photostabilization of Wood Flour Filled HDPE Composites
Wood/plastic composites are increasingly examined for non-structural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, resulting in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. This study examines the performance of photostabilized HDPE/wood flour composites after accelerated weathering. A full factorial experimental design was used to determine the effects of hindered amine light stabilizers (HALS), a UV absorber (UVA), a colorant, and their interactions on the photostabilization of the composite. After 250, 500, 1000, and 2000 hours of accelerated weathering, color change and flexural properties were determined. The experimental results indicate that both colorant and UVA are more effective photostabilizers for wood flour/HDPE composites than HALS.
Physical Aging during Creep and Recovery of PET Bottle Grade Material
The effect of physical aging on long-term creep and recovery of PET bottle grade material was investigated at temperatures below glass transition temperature. Long-term experiments (time duration -840 hrs) were performed to probe the significance of temperature on the intensity of aging and its effect on the rate of creep and recovery. It was found that the effect of aging during the creep and recovery is significant at elevated temperature. This investigation is important for the packaging application. The paper provides information regarding the collapse of PET bottles over time and temperature and also provides quantitative design information for the assembly of the package. Furthermore, comparative study of recovery responses of PP (material for the closure) and PET (bottle grade material) over time and temperature was made.
Pipes from Recycled High Density Polyethylene Blends
This paper presents the results of the development of recycled HDPE blends with improved SCR for low pressure pipe containing the maximum possible portion of post consumer recycled HDPE. A post consumer recycled High Density Polyethylene (R-HDPE) was blended with virgin Medium Density Polyethylene (MDPE), over the composition range of 0-100%. The recycled HDPE has limited post-consumer applications due to its poor stress crack resistance (SCR). Resistance to SCR of the compositions was determined by the Notched Constant Tensile Stress Test (NCLS). Results indicate that there is potential to incorporate the use of Post consumer HDPE in low pressure pipe applications at composition greater than 50%.
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