bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cavity pressure dynamics and self‐tuning control for filling and packing phases of thermoplastics injection molding
Authors: Gao F. , Patterson W. I. , Kamal M. R. 
Published: April 2004

AbstractBecause of its versatility, cost effectiveness, and ability to produce intricate shapes to tight specifications, the injection molding process is widely used in plastics processing. Mold cavity pressure plays an important role in determining the quality of the molded articles. The dynamic behavior and control of cavity pressure were studied for the filling and packing phases. The dynamics of cavity pressure during filling were investigated and found to be both nonlinear and time‐varying in relation to the hydraulic servo‐valve opening, which is the manipulated variable. A self‐tuning control system was designed and tested for a wide range of conditions. The transition from filling to packing was best detected by the change in the derivative of cavity pressure. The dynamics of cavity pressure during packing were studied and modeled similarly as for filling. The self‐tuning technique was successfully extended and implemented in the packing phase.
An investigation of the spatial and optical behavior of biaxially drawn PET film
Authors: Khan M. B. , Keener C. 
Published: April 2004

AbstractThe paper investigates the evolution of the spatial and optical properties of particle‐doped poly(ethylene terephthalate) PET film, as a function of the degree of biaxial extension. Mean surface roughness and peak particle concentration were the main spatial parameters studied. A sharp increase in the average asperity height has been recorded for early forward draw, followed by an abrupt decline that continues almost linearly through the remaining sideways draw. This behavior has been explained in terms of the unequal stress distribution and subsequent yielding in the polymer film surrounding the particles. The peak concentration drops initially due to stretching of the film surface, but remains constant through the transverse draw. The wide angle haze was found to be an exponential function of forward extension, similar to the stress/strain curve for PET. However, the surface haze followed the same trend as surface roughness, suggesting a probable correlation between the two. A consideration of the transversal particle migration suggests that the screw extrusion part of the process may be instrumental in the augmentation of the base surface roughness of the film leaving the slit die.
Conductive polymer blends with low carbon black loading: Polypropylene/polyamide
Authors: Tchoudakov R. , Breuer O. , Narkis M. , Siegmann A. 
Published: April 2004

AbstractThe electrical resistivity and morphology of polypropylene/nylon (PP/Ny) immiscible blends incorporated with carbon black (CB) were studied. CB was found to be preferentially located in the Ny phase or upon the Ny/PP interface. Blends with a co‐continuous phase morphology depicted especially low resistivity values, due to a “double percolation” effect. The blend preparation sequence tends to affect the phase morphology, thus influencing the system's resistivity. Polymer polarity and crystallinity are important factors determining the blend's morphology, which relates directly to the electrical resistivity obtained.
A microcellular processing study of poly(ethylene terephthalate) in the amorphous and semicrystalline states. Part I: Microcell nucleation
Authors: Baldwin Daniel F. , Park Chul B. , Suh Nam P. 
Published: April 2004

AbstractMicrocellular semicrystalline polymers such as poly(ethylene terephthalate) show great promise for engineering applications because of their unique properties, particularly at higher densities. Recent studies reveal some high density microcellular polymers have longer fatigue lives and/or equal strengths to the neat polymer. Relatively few microcellular processing studies of semicrystalline polymers have been presented. In general, semicrystalline polymers are relatively difficult to microcellular process compared to amorphous polymers. In this paper and a companion paper, the microcellular processing of poly(ethylene terephthalate) in the amorphous and semicrystalline states is studied in order to quantify the processing differences. The microcellular processing steps addressed in this paper include gas/polymer solution formation and microvoid nucleation. Particular emphasis is given to microvoid nucleation comparing the processing characteristics of semicrystalline and amorphous materials. Moreover, this study identifies a number of critical process parameters.In general, the semicrystalline materials exhibit ten to one thousand times higher cell nucleation densities compared with the amorphous materials, resulting from heterogeneous nucleation contributions. The amorphous materials show a strong dependence on cell density, while the semicrystalline materials show a weaker dependence. Moreover, classical nucleation theory is not adequate to quantitatively predict the effects of saturation pressure on cell nucleation for either the amorphous or semicrystalline polyesters. Both the semicrystalline and amorphous materials exhibit constant nucleation cell densities with increasing foaming time. Foaming temperatures near the glass transition are found to influence the cell density of the amorphous polyesters, indicating some degree of thermally activated nucleation. Furthermore, classical nucleation theory is not adequate to predict the cell density dependence on foaming temperature. Similar to the amorphous polyesters above the glass transition temperature, nucleation in the semicrystalline materials is found to be independent of the foaming temperature.
Measures of mixing for extrusion by averaging concepts
Authors: Kim S. J. , Kwon T. H. 
Published: April 2004

AbstractThis paper proposes modified Deformation Characteristics (DC) as a new deformation measure for three‐dimensional flows in extrusion. In contrast to the previous DC, the modified DC is defined by an averaged length stretch rate with the aid of two subsequent averaging concepts: firstly, average of length stretch rate of all the local elements in a shell, and secondly, average of a fluctuation of the averaged length stretch rate with time using a probability function. The modified DC was applied to the case of a two‐dimensional flow approximation based on the analysis of kinematics during one circulation including the “turning effect.” Consequently, we have proposed useful formulae to determine the modified DC for the two‐dimensional flow approximation. This involves extensive numerical calculations of the modified DC, both for the three‐dimensional flow and for the two‐dimensional flow approximation. Typical results are discussed with comparisons between the modified DC, the previous DC, and a strain proposed by Pinto and Tadmor. It is interesting to note that the Weighted‐Average Deformation Characteristics (WADC) obtained from the three‐dimensional analysis was found to be close to that from the two‐dimensional approximate analysis. Therefore, the formulae proposed for the modified DC of the two‐dimensional flow approximation seems to be useful in analyzing the mixing behavior on extrusion with a large aspect ratio, avoiding the complicated evaluation of the averaging process of the length stretch rate for the three‐dimensional flow.
Infrared temperature measurement of polymers
Authors: Maier Christian 
Published: April 2004

AbstractInfrared (IR) thermosensors that measure the temperature of polymeric melts in processing equipment by guiding the thermal radiation along optical fibers to the optovoltaic transducer are on the market. The fundamental concepts of thermal radiation must be viewed in a volumetric sense. In sequence, a model is presented to estimate the response of such IR thermosensors. It is dictated by the volumetric absorptivity of the polymer and the transmittance of the optical fiber. For typical commercial IR thermosensors, the entire wavelength range between 1.5 and 2.2 μm is relevant. Penetration depths can vary from magnitudes of mm to dm, since the IR probe is sensitive to the maximum temperatures in its acceptance volume. These findings were put to the test in two different experimental settings. In the first, the calculations overestimated the comparable experimental values by 10 to 20°C, but were reasonable given the relatively simple experimental apparatus. In the second setup, the maximum temperature of melt coming off the screws, measured by penetrating a small thermocouple into the stream, matched the IR temperature sensor's readings. The measurement of temperature excursions in different mixing geometries is demonstrated. No kneading section with forward staggered paddles gave significant increases in temperature. In contrast, maximum temperature excursions could be measured when reverse elements were in place.
Melt grafting of glycidyl methacrylate onto polypropylene and reactive compatibilization of rubber toughened polypropylene
Authors: Chen Li‐Feng , Wong Betty , Baker W. E. 
Published: April 2004

AbstractFree radical melt grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) was studied. The extent of GMA grafting and the molecular weight of the functionalized PP copolymers were controlled by carefully manipulating various reaction factors, such as monomer concentration, initiator concentration, reaction temperature, and molecular weight of the starting PP homopolymer. The use of a second monomer, styrene, in the grafting process helped to increase GMA grafting further and reduce chain scission. The GMA modified PP copolymer was found to be able to reactively compatibilize PP/acrylonitrile‐co‐butadiene‐co‐acrylic acid rubber (NBR) blends. Up to an eight‐fold increase in the impact energy of the PP/NBR blend was obtained. The compatibilizing capacities of the reactive copolymers, in terms of impact energy improvement of the PP/NBR blend, were found not to be exclusively dependent on the total concentration of reactive functionalities in the matrix of the blend. The characteristics of the reactive copolymers, i.e., the extent of functionalization and the molecular weight, were found to have significant influences on the compatibilizing capacity. A large amount of moderately functionalized copolymer offers better compatibilization performance than a small amount of highly functionalized copolymer. A significant drop in impact energy was observed with declining molecular weight of the copolymer.
Morphology development in immiscible polymer blends
Authors: Luciani André , Jarrin Jacques 
Published: April 2004

AbstractThis paper presents the results obtained using a new method for analyzing polymer blend morphologies. The method is based on the selective solubilization of the matrix followed by a separation of the dispersed phase in suspension by filtering. A suspension of the nodular part going through the filter is obtained and can be analyzed with a particle counter. The other part of the dispersed phase retained by the filter is constituted of fibers. The average droplet diameters were compared with those obtained using a Scanning Electron Microscope on fracture surfaces for different compositions and flow conditions. The average diameter obtained with the counter technique increases with the dispersed phase content up to an optimum where simultaneously a decrease in the mean diameter and an increase of the fibrillar part are observed, which means that there is a concentration range where these two types of morphologies are present in the blends. The results indicates that the stability of the fibrillar part seems to determine whether the blend morphology will evolve into nodules by the Rayleigh mechanism or into phase inversion by coalescence of stable fibers.
Computation of the morphological changes of a polymer blend along a twin‐screw extruder
Authors: Delamare L. , Vergnes B. 
Published: April 2004

AbstractThe control of the morphology of an immiscible polymer melt is of vital importance for the mastering of the final properties of the product. As polymer blends are produced using corotating twin‐screw extruders, understanding and modeling the changes experienced by the blend during this process is of great interest. In the present study, starting from Ludovic software, developed for computing flow parameters in the twin‐screw extrusion process, we present a computation of the droplet morphology development, based on the basic mechanisms of break‐up and coalescence. Depending on the value of a local capillary number and on local flow conditions, different changes may occur: affine deformation, drop splitting, break‐up by capillary instability, and coalescence. It is thus possible to follow, all along the screws, the changes in morphology, either for a single particle or for a particle distribution. Examples of these different computations are presented and compared with experimental results. Generally speaking, orders of magnitude of droplet size and tendencies when modifying processing conditions are correctly described, but the model still suffers from the absence of descrption of the melting process.
Asphalt modified by SBS triblock copolymer: Structures and properties
Authors: Adedeji A. , Grünfelder T. , Bates F. S. , Macosko C. W. , Stroup‐Gardiner M. , Newcomb D. E. 
Published: April 2004

AbstractMicrostructural transformation of a poly(styrene‐b‐butadiene‐b‐styrene), SBS, triblock copolymer blended with asphalt was studied as the asphalt composition was varied from 0 wt% to 96 wt%. Transmission electron microscopy (TEM), dynamic mechanical spectrometry (DMS), and differential scanning calorimetry (DSC) were used. The blends were made in batch mixers at 200°C, or by solution casting from a nonselective solvent (trichloroethane) at ∼28°C. Asphalt partially solubilizes the polybutadene (PB) midblock of the SBS producing saturated PB microdomains along with macrodomains of asphalt. When the asphalt concentration was varied from 10 to 90 wt%, the asphalt phase separated into a variable number of large domains, while the SBS‐rich regions formed a continuous matrix. Networks of SBS‐rich regions were observed at low magnification; these are referred to as macro‐networks. At higher magnification, networks that are stabilized by polystyrene (PS) microdomains (denoted micro‐networks) are also formed. The presence of a macro‐network is also confirmed by stress relaxation tests. The macro‐network broke down into microgel‐like structures when the asphalt composition exceeded 90 wt%. Examination of the interior of the SBS‐rich regions showed that the shape of the PS microdomains transformed from short cylinders to lamellae, hexagonally perforated lamellae (HPL), back to lamellae, short cylinders, and finally to spheres. DMS and DSC indicate a systematic increase in the PB glass transition temperature (Tg) and negligible change in the Tg of PS as the asphalt content increases. Triblock copolymers that can form a macro‐network at low concentration will be more desirable for highway pavement modification.
Effect of roughness as determined by atomic force microscopy on the wetting properties of PTFE thin films
Authors: Miller J. D. , Veeramasuneni S. , Drelich J. , Yalamanchili M. R. , Yamauchi G. 
Published: April 2004

AbstractThe influence of film roughness on the wetting properties of vacuum‐deposited polytetrafluorethylene (PTFE) thin films has been investigated using atomic force microscopy (AFM) and contact angle goniometry. Surface roughness has been characterized by atomic force microscopy in terms of RMS roughness (Rq) and fractal dimensions. A contact angle correlation with surface roughness, as determined by AFM, is evident from these results, which are discussed on the basis of wetting theory. The results also confirm that the high water contact angles (as high as 150°) recently observed at the surface of a new water repulsive coating material (mixture of PTFE and binder) are because of surface roughness. Such measurements clarify the effect of nanometer‐size surface asperities on the wetting properties of hydrophobic coating.
A constitutive model for nonlinear viscoelastic behavior of polymers
Authors: Drozdov A. D. , Kalamkarov A. L. 
Published: April 2004

AbstractA new constitutive model for the nonlinear behavior of noncrosslinked polymers with infinitesimal strains is derived. It generalizes a model of adaptive links for the viscoelastic behavior of crosslinked polymers. According to the model, a viscoelastic medium is treated as a set of elastic springs that replace each other. The springs model chemical links between polymer molecules, which arise and collapse because of the micro‐Brownian motion, a law for replacing the springs determines the stress relaxation in a viscoelastic medium. Unlike crosslinked polymers, noncrosslinked polymers demonstrate steady‐state creep flow after some transition period. To describe both the transition process and the steady creep, the model distinguishes two different types of adaptive links. Links of the first type are ruptured under loading, whereas links of the second type replace one another. Both these processes (destruction and replacement) are treated as kinetic, and equations of chemical kinetics are introduced for their description. The nonlinearity of the model arises because of a dependence of rates of kinetic processes on the stress intensity. The constitutive equations derived are testified by comparing theoretical results with data for polypropylene fibers. For the verification we use data presented by three independent sources. The results demonstrate good agreement between experimental observations and their theoretical predictions. Finally, the effect of molecular weight of polymers on parameters of the model is studied.
Prediction of cellular structure in free expansion polymer foam processing
Authors: Shafi Muhammad A. , Lee James G. , Flumerfelt Raymond W. 
Published: April 2004

AbstractA model is presented for free expansion polymer foam processing that includes simultaneous nucleation and bubble growth. The nucleation model includes dissolved gas, small critical cluster size, elastic, and non‐ideal solution effects. An influence volume approach, which couples nucleation and bubble growth, is used to account for the limited supply of dissolved gas. The resulting set of equations are solved using a combination of numerical techniques. A parametric study is conducted to examine the effects of key process variables on bubble growth, nucleation, and final bubble size distribution.
The effect of the packing parameters, gate geometry, and mold elasticity on the final dimensions of a molded part
Authors: Leo V. , Cuvelliez Ch. 
Published: April 2004

AbstractDespite a significant number of publications and the increasing use of numerical simulation, there is still a debate about the optimum gate design and packing conditions in the molding industry. Shrinkage uniformity for unfilled polymers is dominated by the time dependent pressure distribution in the cavity and the resulting volumetric shrinkage; gate freeze‐off is obviously important and difficult to predict; and pressure gradients during the packing phase, depend on process and design parameters and are also affected by the mold elasticity. Molding trials have been conducted on an instrumented mold (fan gated rectangular slab, 2 mm thick) under a variety of processing conditions and with different gate thicknesses using HDPE (Solvay Eltex A1050). Pressure decay during the molding cycle at different locations along the flow path have been correlated with sample thickness distribution. Overpacking at moderate packing pressure is shown to be a direct consequence of mold elasticity and to be related to both filling flow rate and gate thickness. The decay to a finite residual pressure can be computed by coupling the mold elasticity with the PVT behavior of the polymer. The results highlight the importance of gate design and processing parameters on the dimensional accuracy of the part and low internal stress level. When dealing with thick gates, packing pressure profiling appears to be the best way to avoid gate area overpacking. Mold elastic deformation can play a significant role in the cavity pressure‐time history, even for a seemingly stiff mold construction.
Estimates for process conditions during the vibration welding of thermoplastics
Authors: Nonhof C. J. , Riepen M. , Melchers A. W. 
Published: April 2004

AbstractThe aim of this work is to interpret experimental findings of Stokes and Schlarb on the basis of analytical formulas and finite element calculations. In the analytical approach, some simplifications that had to be made proved to be inappropriate. Only computer calculations may reveal the details of the processes involved in vibration welding. Comparison of the computer calculations with the experiments reveals that even transient effects in viscosity have to be considered. Viscosity is dependent not only on temperature and shear rate, but also on the frequency or amplitude of vibration. After correction for these effects, the correlation between theory and experiments proved to be excellent. Based on the calculations, some recommendations are presented to improve weld quality, as ascertained by the type of fracture in a tensile test, by changing the welding parameters.
A micromechanical model for the elastic properties of semicrystalline thermoplastic polymers
Authors: Guan X. , Pitchumani R. 
Published: April 2004

AbstractThis paper presents a micromechanical analysis of the elastic properties of semicrystalline thermoplastic materials. A lamellar stack aggregate model reported in the literature is used to derive tighter bounds and a self‐consistent scheme for the elastic modulus, and it is shown that the existing geometric models of the microstructures are not effective in predicting experimentally measured modulus of semicrystalline materials. Toward addressing this limitation, a model based on Mori‐Tanaka's mean field theory is developed by treating the semicrystalline materials as short‐fiber reinforced composites, in which the lamella crystalline phase is modeled as randomly embedded anisotropic ellipsoidal inclusions, and the amorphous phase as an isotropic matrix. The lamellae are characterized by two independent aspect ratios from three distinct geometric axes in general. Existing morphological studies on polyethylene (PE) and a syndiotactic polystyrene (sPS) are used to deduce the corresponding lamella aspect ratios, based on which the theoretical model is applied to predict the elastic modulus of the two material systems. The model predictions are shown to compare well with the reported measurements on the elastic moduli of PE and sPS. Polym. Eng. Sci. 44:433–451, 2004. © 2004 Society of Plastics Engineers.
Curing kinetics and chemorheological analysis of polyurethane formation
Authors: Dimier F. , Sbirrazzuoli N. , Vergnes B. , Vincent M. 
Published: April 2004

AbstractThe cross‐linking kinetics and the rheological behavior of a polyurethane system during curing are investigated by DSC and small amplitude oscillatory shear rheometry. In this study, isoconversional methods are applied to understand the reaction complexity. The activation energy depends on the extent of conversion. It can be shown that three parallel reactions occur during the evolution of the global reaction in non‐isothermal conditions. An original multi‐step model can involve these three parallel independent reactions. Dynamic viscosity is measured as a function of time and is found independent of shear rate. Isothermal viscosity rise is related to reaction extent by a phenomenological model. The gelation time is determined by the tanδ crossover at different frequencies. Polym. Eng. Sci. 44:518–527, 2004. © 2004 Society of Plastics Engineers.