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.
A novel device for characterization of profile flexural properties is presented. The device is called the Vibration Decay Evaluator (VDE). Flexural modulus, profile stiffness, and damping response characteristics of profiles are determined. The characteristics are determined by digital observation of the naturally damped free vibration of a profile. The characteristics are determined from the vibration response through the use of computational algorithms based in structural mechanics and system dynamics theory. The VDE has been validated as an effective tool for rapid evaluation of full profile characteristics to support extrusion operations. A patent is pending on the device.
Melt temperature and screw rotational speed are important parameters in the injection molding process since they affect other injection molding processing conditions, cycle time and product quality. It has been shown that in injection molding, predictive control in comparison to the conventional control provides better close loop process dynamics. However, the magnitudes of controller parameters were non-optimal, and were generally chosen after several iterations. A simple and effective tuning strategy was developed for predictive control, and was implemented for controlling melt temperature and screw speed. Better temperature and screw speed responses were obtained when using this new tuning method.
The in-situ compatibilization of polymer blends in melt state was found to occur during ultrasonic assisted extrusion without use of any chemicals. Plastic/rubber blends were ultrasonically treated during continuous extrusion at high pressures and temperatures. The tensile strength, elongation at break, Young's modulus, toughness and impact properties of ultrasonically treated blends were significantly improved as compared to the untreated blends. The results of extraction experiments pointed towards copolymer formation during the ultrasonic treatment of the blends at a very short time (in the order of seconds). This in-situ ultrasonic copolymerization at the interface nanolayers enhanced intermolecular interaction, improved adhesion at the interface and stabilized morphology of the blends. The copolymers created at the interface nanolayers are believed to be a major reason for enhancing mechanical properties. This novel process can be applied for preparing plastic/rubber blends to make thermoplastic elastomers or plastic/plastic and rubber/rubber blends, and for making novel copolymers from practically any pairs of existing polymers to achieve desirable chemical and physical properties.
Recent progress in computer-aided polymer processing analysis demonstrates the need for accurate description of the material behavior under the conjugated effect of applied stress and temperature. Using the bubble inflation experiment and solving for non-linear governing equations of the inflation process, material constants for Mooney-Rivlin and Lodge models are determined. The results for ABS at a typical thermoforming temperature (143C) are presented. Also, the inflation process of thermoplastic polymers was numerically investigated by using the finite element method. A 3 node membrane element based incompressible formulation is analyzed to predict the deformations encountered during the inflation of the membrane. The predicted bubble height at the pole corresponds well to the experimental measurements.
Reactive extrusion is an efficient and environment-friendly technique for both continuous polymerizing monomers and chemical modification of polymers. In the present study, the process of bulk polymerization of ?-caprolactone was simulated by Finite Element Method (FEM), with considering different operational factors and reactive conditions. Two unwrapped channel models, 1-D model and 2-D model, are tried in the simulation. Temperature in the cross section of channel were assumed to be equal (to average temperature Tave) in 1-D model whereas temperature were locally different in 2-D model. The calculation shows that the 2-D model gives good results for the reactive process.
Nylon 12-layered silicate nanocomposites based on synthetic tetrasilisic fluoromica were prepared by melt compounding using a conventional single screw extruder. Wide-angle X-ray diffraction (WAXD), transmission electron microscopy (TEM) and scanning electron microscopy were used for characterization of the morphologies obtained. Predominantly disordered exfoliated morphologies were produced when quaternary alkylammonium modified organoclay was blended with Nylon 12. The mechanical properties of this nanocomposite were enhanced significantly, most noticeably the percentage elongation at break which exceeded 500% compared to 180% for neat Nylon 12, while tensile strength and flexural modulus increased by over 50%. Thermal analysis showed the nanocomposites exhibited glass transition temperatures up to 12 degC higher, and marked reduction in the melt viscosity compared to the pristine Nylon 12.
We present observation of a cavitation phenomenon in LLDPE extrusion. In the gross melt fracture regime, cavitation was always observed in the first 0.5 ~ 1.5 mm upstream of the exit. We saw cavities at the wall form (seemingly out of nothing) grow to a length and width of about 150 ?m, then shrink down and disappear. From velocity measurements of these structures, we conclude that their width in the radial direction is much smaller than those in the axial and lateral direction and that they are in contact with the wall. The process for the growth and disappearance is approximately 20 ~ 25 ms. The shape of the cavities is highly irregular. From several precise investigations, we concluded that the unstable flow and melt fracture in the entrance region is main source for the cavitation phenomenon, and the cavitation was initiated from the unstable flow by the extensional flow at the die exit.
This paper describes a new, simple and automated procedure for detecting, characterizing and counting otherwise invisible impurities such as black specs and yellow degraded residues in polymer resins and blends, or structural defects such as gels, fisheyes and flow lines in finished products such as calandered film and extruded profile.The method is based on the computer assisted Color Image Coding (CIC) analysis of a sample's digital image acquired from a high resolution flatbed scanner. The analytical results, stored on a relational database management system, are easily archived on customary data media for later retrieval.
Guaranteeing the quality of technical parts made by injection molding implies a precise characterization of the processing phase. In the case of parts with deep cores, the ejection step of the molding cycle is often critical. The prediction of the ejection force may contribute to optimizing the mold design and guaranteeing the integrity of the moldings. Data obtained from a fully instrumented mold (pressure, temperature and force) producing a tubular molding are compared with predictions from a simulation algorithm based on a thermo-mechanical model. Semi-crystalline (iPP) and amorphous (PS) materials were used to expand the amplitude of the research.
Real time measurements of diameter, velocity, temperature and crystallinity during the blown film extrusion of a linear low-density polyethylene (LLDPE) film are reported. The micro structural variation along the machine direction of the film was observed with online Raman spectroscopy. Based on these measurements, the variation of heat transfer coefficient along the machine direction was calculated from the energy equation governing the process. Experimental values for the coefficient indicate a maximum in the vicinity of the freeze line and match with trends from recent computational fluid dynamics studies  but not with conventional model predictions reported in literature .
Intrinsic or relative solution viscosities and melt flow index are widely used in the specification of many polymer resins used in the fiber industry. The solution viscosities provide a measure of the molecular weight of a polymer that is based upon theory, however, the precision of these measurements can be relatively poor. A relationship exists between solution viscosities and the zero shear rate melt viscosity of a polymer, where the latter is four times as sensitive to the molecular weight as the former. This paper discusses the practical application of this relationship using an on-line rheometer to monitor the fiber forming polymers. It will be shown that polymers that are indistinguishable by solution or MFR measurements can be easily differentiated in real time" and in the process from melt viscosities measured by the on-line rheometer."
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.
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.
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.
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.
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
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.
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.
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.
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.
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