bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of the performance of plasticating single‐screw extruders with a new concept of solid‐bed deformation
Authors: Lee Kee Yoon , Han Chang Dae 
Published: December 2004

AbstractThe performance of plasticating single‐screw extruders is analyzed by combining three functional sections: (a) solids‐conveying section, (b) melting section, and (c) melt‐conveying section. In the analysis of the melting section, we have incorporated a new concept of solid‐bed deformation (i.e., the rheology of the solid bed) into Lindt‐Elbirli's analysis and included convective heat transfer in the energy equation. Specifically, we have computed stresses on the surfaces of the solid bed, which is surrounded by thin melt films and a melt pool, and, also, computed the apparent modulus of the solid bed in the bulk state as a function of temperature and position within the solid bed, along the extruder axis. From this information, we were able to compute the extent of solid‐bed deformation, by assuming a linear stress‐strain relationship as the constitutive equation of the solid bed. In this approach, we do not assume a priori whether the solid bed is rigid or freely deformable. The solution of the system equations gives us the following information: (a) whether or not the solid bed deforms and if it does, then, how much; (b) the solid‐bed velocity along the extruder axis; (c) pressure profiles along the extruder axis; (d) solid‐bed profiles in the melting zone along the extruder axis; (e) temperature profiles along the extruder axis; (f) velocity and temperature distributions in the melt pool along the extruder axis; and (g) thicknesses of thin melt films surrounding the solid bed. Theoretically predicted solid bed and pressure profiles along the extruder axis are compared with experimental results reported in the literature. We have pointed out an urgent need for measurements of the apparent modulus of the solid bed in the bulk state as a function of temperature and pressure, under a combined shear/drag flow field.
Chain structure, phase morphology, and toughness relationships in polymers and blends
Authors: Wu Souheng 
Published: December 2004

AbstractWe present chain structure, phase morphology, and toughness relationships in thermoplastic polymers and polymer/rubber blends. In neat polymers, molecular aspects of craze/yield behavior are controlled by two chain parameters: entanglement density νe and characteristic ratio C∞. The crazing stress is proportional to ν, and the yield stress is proportional to C∞. The dispersed rubber toughens a polymer/rubber blend mainly by promoting energy dissipation of the matrix. The toughening efficiency correlates with the rubber phase morphology and the chain structure of the matrix.
Low density foams produced from sheared ultra‐high‐molecular‐weight polyethylene gels
Authors: Matthews Flori'da M. , Hoffman D. Mark 
Published: December 2004

AbstractLow‐density foam (0.02–0.09 g/cc) was produced from gels of ultrahigh molecular weight (UHMW) polyethylenes in solvents with melting points above ambient. The hot PE solutions were stirred at high speed to induce extended chain crystalline gels. These gels were subsequently cooled to allow the solvent to solidify and then the solvent was extracted with alcohol or sublimed. This resulted in a tough, low density foam or a collapsed mass depending mainly on the concentration of the polymer. Shrinkage was significant until polymer concentrations reached 4–5%. Foam cell size varied between 5–30 μm, or 25–75 μm depending on the method of preparation. Polarizing microscopy revealed both spherulitic and row‐nucleated structures depending on the thermal history followed during the sample preparation. We were also interested in whether or not small particles could be used to influence the nucleation and growth of the solution crystallization process. These particles could be suspended in the gel and stabilized in something like a colloidal necklace as has been proposed recently. We successfully incorporated small (0.5 μm) tungsten particles in UHMWPE gels which remained in the foam on extraction of the solvent. Polyethylene containing carbon black particles produced less successful results. These effects may be related to absorption associated with gelation of UHMWPE.
Thermorheological analysis of glass beads‐filled polymer melts
Authors: Lepez Olivier , Choplin Lionel , Tanguy Philippe A. 
Published: December 2004

AbstractThe complex viscosity of two thermoplastic polymer melts (high density polyethylene and polystyrene) filled with polydisperse glass beads (10–53 μm) has been studied in the domain of linear viscoelasticity as a function of frequency, temperature, and filler concentration. In the experimental windows examined, the complex viscosity can be well described by a new empirical model, which contains a Cross‐type viscosity model for the frequency dependence, a Quemada‐type model for the filler concentration dependence, and a compensation effect for the temperature dependence. This model allows the prediction of the complex viscosity of a glass bead‐filled thermoplastic melt provided only four parameters are known, namely: the average maximum packing volume fraction characteristic of the filler geometry and size distribution, the flow activation energy of the thermoplastic, the shear‐thinning parameter, and an adjustable parameter, also characteristic of the thermoplastic.
Effect of dispersion of particles on viscoelasticity of CaCo3‐filled polypropylene melts
Authors: Li Lin , Masuda Toshiro 
Published: December 2004

AbstractViscoelastic properties of polypropylene melts filled with small (0.15 μm) and large (4.0 μm) CaCO3 particles have been measured. The effects of particle size, loading, and rheological history on the dispersion of particles have been investigated. The dispersion of particles was found to decisively influence the viscoelastic properties of these filled polymers. The systems filled with large particles exhibit a relatively stable viscoelastic behavior. The small particle‐filled polymers with low loading are stable similarly to the large particle‐filled system. For the system filled with 30 wt% small particles, there appears a “second plateau” in the storage modulus G′ curve in low frequency region and the height of the second plateau depends strongly on the rheological history. The results are interpreted in terms of the formation of an internal structure of particles. It was found that the internal structure of particles is broken up by a steady shear flow and the dispersion of particles is changed.
Numerical prediction of three‐dimensional fiber orientation in Hele‐Shaw flows
Authors: Altan M. Cengiz , Subbiah S. , Güçeri Selçuk I. , Pipes R. Byron 
Published: December 2004

AbstractA numerical technique is developed to determine the three‐dimensional fiber orientation in complex flows. The fiber orientation state is specified in terms of orientation tensors, which are used in several constitutive models. This method is applied to quasi‐steady state Hele‐Shaw flows in order to predict the flow‐induced fiber orientation during injection molding at zero volume fraction limit. At the inlet, a number of fibers are introduced at a specified rate into the flow and each fiber location is traced during the mold filling. Along these determined paths, the independent components of fourth order orientation tensors are solved, describing the orientation state. The numerical grid generation technique, which is suitable for complex mold shapes, is employed for the flow solution. Orientation ellipsoids are calculated from the second order tensors and are used to present the fiber orientation results. The numerical solutions are obtained for channel and converging flows. Planar, longitudinal, and transverse orientation results are generated from the orthogonal projections of the orientation ellipsoids.
Dynamic behavior of continuous vinyl chloride suspension polymerization reactors: Effects of segregation
Authors: Pinto J. C. 
Published: December 2004

AbstractAssumed is that there is no mass transfer among the droplets of reacting organic phase in a continuous vinyl chloride (VCM) suspension polymerization reactor. A mathematical model is thus developed to allow the calculation of steady states and the analysis of their dynamic stability. The results obtained are compared with those obtained with the hypothesis of perfect micromixing. It Is shown that both assumptions lead to similar dynamic structures, which confirms the complex behavior of these reactors. There are major differences, however, that can be exploited in future experimental work.
Internal stress, molecular orientation, and distortion in injection moldings: Polypropylene and glass‐fiber filled polypropylene
Authors: Hindle C. S. , White J. R. , Dawson D. , Thomas K. 
Published: December 2004

AbstractResidual stress measurements and distortion analyses have been conducted on injection molded plaques made from polypropylene (PP) and a short glass‐fiber filled polypropylene (GFPP). The residual stress analyses include measurements both parallel and perpendicular to the direction of flow during mold filling. Residual stresses are very anisotropic in GFPP, but not in PP. The residual stress levels in PP fall on aging at room temperature, whereas in GFPP the proportion of stress relaxation is smaller, and significant stresses remain even after heating to elevated temperatures. A significant contribution to distortion has been linked to the ejection process, and the long‐ and short‐term distortion of moldings is discussed within the framework of the properties of the materials measured here.
A general non‐isothermal model for one‐dimensional multilayer coextrusion flows
Authors: Puissant S. , Vergnes B. , Demay Y. , Agassant J. F. 
Published: December 2004

AbstractA general computation of multilayer coextrusion flow in a flat die geometry is presented. For any given number of layers of different polymers, characterized by their thermal and rheological behaviors, the model permits computation of velocity and temperature fields along the flow in constant or slightly varying geometries. The influence of different operating parameters (wall regulation temperature, flow rate, initial temperatures) on the interface positions and temperature evolutions is evaluated. Theoretical predictions of interface positions are in agreement with experiments carried out on an industrial multimanifold flat die.
Temperature dependence of the interfacial dielectric loss process in glass bead‐filled polyethylene
Authors: Steeman P. A. M. , Baetsen J. F. H. , Maurer F. H. J. 
Published: December 2004

AbstractThe temperature dependence of the interfacial dielectric loss process in glass bead‐filled high density polyethylene (HDPE) due to an interfacially adsorbed water layer has been studied. The frequency of maximum dielectric loss shifts to lower frequencies with decreasing temperature. This is thought to be due to decreasing mobility of the free charge carriers in the adsorbed water layer, resulting in the reduced conductivity of the layer. The shifting of the loss peaks with temperature can be described with the well‐known Arrhenius relation. The energy of activation, as obtained from this relation, shows a stron dependence on the thickness of the adsorbed layer. For thinner layers a higher activation energy is found, indicating that the charge carriers are increasingly affected by the presence of a layer of bound charges on the glass surface. This thickness dependence of the activation energy offers some possible applications. First, information on the water layer thickness can be extracted from the energy of activation, and second, it becomes possible to study the effect of interfacial modifications such as the application of coupling agents.
Gear pump assisted extrusion
Authors: Pham Hoang T. , Hyun Kun S. 
Published: December 2004

AbstractGear pump assisted extrusion is becoming popular in the plastics processing industries. The growth has been tremendous since 1980. In this study, the benefits of gear pump assisted extrusion, especially in single screw applications, is critically reviewed, and a method of predicting the operational conditions of the gear pump assisted extrusion system is discussed. Further, shortening the length to diameter ratio of the extruder in gear pump assisted extrusion was analyzed and found to produce a reduction in energy consumption, provided melting is completed.
The measurement of thermal stress distributions along the flow path in injection‐molded flat plates
Authors: Hastenberg C. H. V. , Wildervanck P. C. , Leenen A. J. H. , Schennink G. G. J. 
Published: December 2004

AbstractInternal stresses in injection‐molded parts are the result of thermal, flow, and pressure histories. Internal stresses can be roughly divided into thermal and flow‐induced stresses. In this paper, a modified layer‐removal method is presented to determine thermal stress distributions in injection‐molded flat plates. With this method, the curvature of a rectangular specimen is determined after the removal of a layer from one surface. This curvature is converted into a stress via a mathematical relation, originally derived by Treuting and Read. By determining the local curvatures after successive layer removals, stress distributions along the flow path were obtained within a single specimen. Validation of this modified layer‐removal method is described. A good reproductibility was obtained. The method can be regarded as semi‐quantitative. Flat plates were injection‐molded from three amorphous polymers: polystyrene, polycarbonate, and a polyphenylene ether/high‐impact polystyrene blend. In general, the flat‐plate cross‐section shows a three‐region stress distribution with a tensile stress region both at the surface and in the core of the flat plate and an intermediate region with compressive stresses. The modified layer‐removal method was used to determine influences of mold temperature, annealing treatment, and pressure history on the thermal stress distributions. Increasing mold temperature results in a decreasing overall stress level, while the compressive stress region shifts to the surface. An annealing treatment significantly reduces the overall stress level, without affecting the stress pattern. Stress distributions along the flow path were influenced by the varying pressure histories from the entrance to the end of the mold cavity. The various features of the stress profiles are explained by the influence of the pressure decay rate in the injection‐molding process.
A microdielectric analysis of moisture diffusion in thin epoxy/amine films of varying cure state and mix ratio
Authors: Day David R. , Shepard David D. , Craven Kelly J. 
Published: December 2004

AbstractRecent work has shown that moisture diffusion coefficients can be measured in thin polymer films through monitoring changes in permittivity with microdielectric sensors. The sensor is constructed in silicon and consists of an interdigitated electrode and two depletion mode field effect transistors. When operated in conjunction with appropriate external circuitry, the sensor measures dielectric constant and loss factor of any material placed on the SiO2 insulator and aluminum electrodes. The dielectric properties are measured locally within the first 10 microns of the film in contact with the sensor. As a thin polymer film on the sensor is exposed to a high relative humidity, the dynamically measured dielectric constant can be used to determine exactly when the moisture arrives at the polymer‐SiO2 interface and the rate at which the concentration increases. The magnitude of the change in permittivity after equilibration has also been related to total amount of moisture uptake. In this investigation, several epoxy/amine films of varying mix ratios and cure state are cured on microdielectric sensors. The films, approximately 100 microns thick, are alternately exposed to wet and dry environments. Diffusion coefficients for both absorption and desorption are determined from the dielectric data as a function of cure state and epoxy/amine mix ratio. In addition, relative changes in amount of moisture uptake after equilibration is monitored.
Analysis of gel formation in imidazole‐catalyzed epoxies
Authors: Heise M. S. , Martin G. C. , Gotro J. T. 
Published: December 2004

AbstractThe network formation processes for imidazole‐cured epoxy resins were examined by relating the reaction chemistry and the physical properties during cure. Network formation models were developed based on kinetic studies and the laws of conditional probability. These models were used to predict the weight‐average molecular weight, the gel point, and the sol fraction as a function of the resin composition and the processing conditions. Rheological and extraction experiments were conducted to confirm the model results and to develop criteria for identifying the gel point.
Free volume theory and nonlinear thermoviscoelasticity
Authors: Losi Giancarlo U. , Knauss Wolfgang G. 
Published: December 2004

AbstractThe rheological behavior of polymers in the neighborhood of the glass transition is investigated in the framework of the free volume theory of nonlinear viscoelastic behavior. Free volume theory as normally applied above the glass transition is modified to account for the effect of the residual volume of vacancies below the glass transition; this modification is accomplished by modeling the changes in the state of the polymer as the sum of viscoelastic changes and a random disturbance deriving from the thermal collisions between molecule segments. The changes in mechanical properties in passing across the glass transition follow from the freezing‐in of relaxation mechanisms and of free volume; the model, which also incorporates a time‐dependent coefficient of thermal expansion under isobaric conditions, does not require additional parameters other than those characterizing the rubbery state. The pressure dependence of the glass transition is found to be in qualitiative agreement with measurements on PVAc, while the ratio of the glassy and rubbery heat capacities is found to coincide with the ratio of the equilibrium bulk compliances in the glassy and rubbery domains.
Analysis of the deformation of polypropylene hot‐tool butt welds
Authors: Gehde M. , Bevan L. , Ehrenstein G. W. 
Published: December 2004

AbstractThin microtomed samples from hot‐tool butt welds of polypropylene pipes are subjected to uniaxial tensile stress using a specially built instrumented microtesting machine. The deformation of the interface between the weld and the bulk polymer is measured by an optical method. An analysis of these measurements is carried out using the finite element method, and contours of the effective stress are obtained. There is a steep stress gradient at the junction of the weld flash and the bulk polymer, although the stress concentration factor is relatively low. The stress is essentially constant in the bulk polymer apart from the region near the weld zone. Tests on samples without the weld flash show that the maximum stress occurs within the weld zone. This is consistent with long‐term tests on larger samples, where the fracture is found to initiate within the weld. The method of analysis enables the stress‐strain response of the weld material to be determined.
Polypropylene composites. II: Structure‐property relationships in two‐ and three‐component polypropylene composites
Authors: Chiang Wen‐Yen , Yang Wen‐Der , Pukánszky Béla 
Published: December 2004

AbstractTwo‐ and three‐component polypropylene (PP) blends and composites were prepared to study their structure/property relationships. Butadiene‐styrene (BDS) copolymers of low compatibility formed large particles of poor adhesion in PP resulting in inferior mechanical properties. Better miscibility of ethylene‐propylene‐diene (EPDM) elastomer results in more finely dispersed particles and the experimental results indicate a transition to an interpenetrating network (IPN)– like structure with increasing elastomer content. Effective impact modification can be achieved only with EPDM elastomers of sufficient miscibility. Mutual wettability and adhesion of the components determine the structure and properties in PP/elastomer/filler systems. Modification of PP by acrylic acid grafting promotes PP/filler adhesion which, in turn, results in the separate dispersion of the components. In an unmodified PP matrix, a significant amount of the filler is encapsulated by the elastomer. At low filler content, better low temperature impact strength is achieved in the case of separately dispersed components, while encapsulation is more advantageous at high filling grades.
Rheology of phase separated blends of two thermotropic liquid crystalline copolyesters
Authors: Lin Y. G. , Winter H. H. 
Published: December 2004

AbstractThe melt rheology of phase separated blends of two thermotropic liquid crystalline polymers (LCPs) have been studied. The two components are a random copolyesters consisting of 73 mol% 4‐hydrobenzoic acid (HBA) and 27 mol% 6‐hydroxy‐2‐napthoic acid (Vectra A900 of Hoechst Celanese Corp.) and a poly(ethylene terephalate‐co‐4‐oxybenzoate) containing 60 mol% HBA units (PET/60HBA of Eastman Kodak Corp.). Most striking is the effect of adding 10% PET/60HBA to Vectra A900: The viscosity at 290°C drops by a factor of 4 and the terminal zone of the relaxation time spectrum is shifted to much shorter times. This is an interesting effect that could be used for LCP processing even if its origin is not yet understood. Differential scanning calorimetry measurements support the hypothesis that the blend is phase separated and that no transestification reaction occurs during the experiments.
Toughening behavior of elastomer‐modified polycarbonates based on thej‐integral
Authors: Lee Chang‐Bing , Chang Feng‐Chih 
Published: December 2004

AbstractTheJ‐integral method to determine the fracture toughness of tough and ductile polymeric materials previously developed has been applied to the elastomer‐modified polycarbonates. This investigation compares three different methods to obtainJc: the conventional crack growth length, the stress whitening zone, and the newly developed hysteresis method.Jcvalues obtained from these three comparative methods are fairly close. The hysteresis method has the advantage over the other two methods of obtainingJcwithout requiring the measurement of the crack growth length or the stress whitening zone, therefore avoiding the controversy in defining crack blunting. Results also indicate that the effect of elastomer quantity in polycarbonate onJcis insignificant as long as the crack is in a stable condition. Higher elastomer contents in polycarbonate result in higherdJ/dΔa,dJ/dΔl, and tearing modulus (Tm). This indicates that the elastomer toughening mechanism is due to the increase of the energy required for crack growth extension. The hysteresis loss energy is directly related to the size of the crack tip plastic zone, and the presence of more elastomer indeed increases the crack tip plastic zone, thus making the polycarbonate tougher. Besides, the presence of elastomer tends to increase the crack initiation displacement and shift the failure modes from an unstable fracture.Jcand the criterion for crack initiation based on rate change of hysteresis energy are discussed in detail.