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Polymer Melt (polymer + melt)
Terms modified by Polymer Melt Selected AbstractsLinear and Nonlinear Viscoelasticity of a Model Unentangled Polymer Melt: Molecular Dynamics and Rouse Modes AnalysisMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006Mihail Vladkov Abstract Summary: Using molecular dynamics simulations, we determine the linear and nonlinear viscoelastic properties of a model polymer melt in the unentangled regime. Several approaches are compared for the computation of linear moduli and viscosity, including Green-Kubo and nonequilibrium molecular dynamics (NEMD). An alternative approach, based on the use of the Rouse modes, is also discussed. This approach could be used to assess local viscoelastic properties in inhomogeneous systems. We also focus on the contributions of different interactions to the viscoelastic moduli and explain the microscopic mechanisms involved in the mechanical response of the melt to external solicitation. [source] Numerical simulation of the microscale impregnation in commingled thermoplastic composite yarnsADVANCES IN POLYMER TECHNOLOGY, Issue 2 2010R. Gennaro Abstract The impregnation of a glass woven fabric with an amorphous polyethylene terephthalate copolymer (PET- g) matrix was investigated using a finite element (FE) model for interbundle and intrabundle flow of the matrix. Micrographs of samples obtained by film stacking of PET- g to impregnate the glass fabric have confirmed the occurrence of interbundle and intrabundle flow, taking place as separate steps. On the basis of this evidence, two different mechanisms for the fiber impregnation were postulated. The first flow process is associated with a macroscale interbundle impregnation, whereas the second is associated with microscale intrabundle impregnation. Two different FE models were developed to simulate the microscopic and macroscopic flow of the matrix, considering a large number of different random fiber arrangements. Both models could account for the non-Newtonian rheological behavior of the thermoplastic matrix. The microscale impregnation of fibers was simulated by using randomly spaced and nonoverlapping unidirectional filaments. The effect of the number of filaments and the number of random distributions necessary to achieve an adequate accuracy of the method was assessed. The results obtained from the simulation showed that at low pressures, the polymer melt exhibits Newtonian behavior, which makes it possible to predict the tow permeability by the Darcy law. A more difficult situation arises at high pressures because of the non-Newtonian behavior of the melt. This requires the introduction of a value for the permeability that is also dependent on the rheological properties of the melt. The same non-Newtonian behavior of the matrix was observed for macroscale impregnation of bundles. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:122,130, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20179 [source] Parameters affecting the full-shot molding of gas-assisted injection-molded partsADVANCES IN POLYMER TECHNOLOGY, Issue 1 2003Shih-Jung Liu Abstract Full-shot gas-assisted injection-molding has the advantage of eliminating the switchover mark that usually occurs on the surface of short-shot gas-assisted molded parts. The purpose of this report was to study the effects of processing parameters on the moldability of the full-shot gas-assisted injection-molding process. Experiments were carried out on an 80-ton injection-molding machine equipped with a high-pressure nitrogen-gas injection unit. The materials used were general-purpose polystyrene and polypropylene. A plate cavity with a gas channel of various geometries (trapezoid, semicircle, and rectangle) across the center was used to mold the parts. After molding, the lengths of gas penetration were determined. The hollowed core ratio by the gas was also determined. A numerical analysis was carried out to find out the temperature distribution of the polymer melt inside the gas channel. It was found that the sink mark of molded parts decreases with the length of gas penetration. Molded parts using trapezoidal gas channel had the longest gas penetration length. In addition, a thermal contraction model was proposed to predict the gas penetration volume inside the parts. Good agreement was reached between the experimental data and the calculated result. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 1,14, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10036 [source] Effect of screw element type in degradation of polypropylene upon multiple extrusionsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2002Sebastião V. Canevarolo Abstract The screw profile of a twin-screw extruder can be designed to contain kneading and conveying elements inducing different levels of degradation in the polymer melt. In this work, the level of degradation in polypropylene has been measured after multiple extrusions,for various screw profiles,using size exclusion chromatography and IR spectroscopy. The average molecular weight and the polydispersity have been reduced and the carbonyl and unsaturation indexes increase as the number of extrusions and the aggressivity of the screw profile increase. The kneading element with 90° caused the greater level of degradation. On the other hand, the addition of left-hand conveying elements reduces the level of degradation because of the extra volume of molten polymer held in the screw, reducing the viability of oxygen inside the barrel. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 243,249, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10028 [source] Rheological behavior of a polymer melt under the impact of a vibration force fieldJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2007Guang-sheng Zeng Abstract A model for the molecular motion of a polymer melt under the impact of a vibration force field was developed. From complicated theory deduction, an expression of the relaxation time and dynamic apparent viscosity were obtained. The effect of a vibration frequency and amplitude on the melt's dynamic apparent viscosity is explained in terms of shear-thinning and untie-tangle criteria. The model is supplemented by a calculation sample and experiment, which show that dynamic apparent viscosity of a melt will tend to decrease as the vibration frequency or amplitude increases. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Measuring anisotropic thermal conduction in polyisobutylene following step shear strainsAICHE JOURNAL, Issue 3 2000Hadjira Iddir The connection between polymer chain orientation and several macroscopic properties in a polymer melt was studied using mechanical and optical techniques. Anisotropic thermal conductivity following shear deformation was measured using forced Rayleigh light scattering, the refractive index tensor is followed using birefringence measurements, and the stress was measured mechanically in a parallel-plate rheometer. The thermal diffusivity measured in the flow and neutral directions increased and decreased, respectively, immediately following the deformation. These quantities then relaxed to the equilibrium value on the time-scale of the stress-relaxation memory. Comparison of the difference between measured flow and neutral direction thermal diffusivities with the analogous flow-induced birefringence in the same deformation provided indirect evidence for a linear relation between stress and thermal diffusivity at two different values of strain. Mechanical measurements were used to characterize the memory of the fluid. [source] Additive interactions in the stabilization of film grade high-density polyethylene.JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2002Part I: Stabilization, influence of zinc stearate during melt processing The melt stabilization activity of some of the most commercially significant phenolic antioxidants and phosphites (alone and in combination), without and with zinc stearate, was studied in high-density polyethylene (HDPE) produced by Phillips catalyst technology. Multiple pass extrusion experiments were used to degrade the polymer melt progressively. The effect of stabilizers was assessed via melt flow rate (MFR) and yellowness index (YI) measurements conducted as a function of the number of passes. The level of the phenolic antioxidant remaining after each extrusion was determined by high-performance liquid chromatography (HPLC). Phenolic antioxidants and phosphites both improved the melt stability of the polymer in terms of elt viscosity retention; the influence of zinc stearate was found to be almost insignificant. However, phosphites and zinc stearate decreased the discoloration caused by the phenolic antioxidants. A correlation was found between the melt stabilization performance of phosphites and their hydroperoxide decomposition efficiency determind via a model hydroperoxide compound. Steric and electronic effects associated with the phosphorus atom influenced the reactivity towards hydroperoxides. Furthermore, high hydrolytic stability did not automatically result in lower efficiency. Besides phosphite molecular structure, stabilization activity was also influenced by the structure of the primary phenolic antioxidant and the presence of zinc stearate. [source] Synthesis and Structure,Efficiency Relations of 1,3,5-Benzenetrisamides as Nucleating Agents and Clarifiers for Isotactic Poly(propylene),MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2010Frank Abraham Abstract This paper presents the synthesis and properties of 1,3,5-benzenetrisamides with a particular focus on structure-efficiency relationships of nucleation and optical property enhancement of isotactic poly(propylene) (i -PP). A family of twenty 1,3,5-benzenetrisamide derivatives was synthesized, in which the direction of the amide linkage between the core and the peripheral substituents, as well as their length (C-3 to C-6) and flexibility were systematically varied. Dissolution- and recrystallization temperatures of the additives in the polymer melt, the crystallization temperature of i -PP, and the optical properties clarity and haze were determined in the additive concentration range from 200 to 2,500,ppm. Within the reported series of compounds, few exhibited very good nucleating and clarification abilities, only one with outstanding characteristics, whereas other, very closely related derivatives were found to be incapable to nucleate or clarify i -PP, although, intriguingly, most are structural isomers. We conclude that it is the particular chemical structure of the additive that determines its crystallization/self-assembly process, and, therewith, the structure of the heterogeneous nuclei, and at a higher hierarchical level the morphology of the poly(propylene) solid state and its final properties; and, hence, that a predictive understanding is still elusive. [source] Polymer Foams Stabilized by Particles Adsorbed at the Air/Polymer InterfaceMACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2008Prachi Thareja Abstract In aqueous systems, partially hydrophobic particles are known to stabilize foams even in the absence of any added surfactant. This paper shows that the same principle can be applied to polymeric systems: particles that are partially wetted by a polymer melt can stabilize a foam of that polymer. The foam stability is attributable to the adsorption of the particles at the air/polymer interface. Remarkably, stable foams are realized even from polymers that are liquid at room temperature, and hence are otherwise unfoamable. The implications of this result to practical foaming operations are discussed. [source] Linear and Nonlinear Viscoelasticity of a Model Unentangled Polymer Melt: Molecular Dynamics and Rouse Modes AnalysisMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006Mihail Vladkov Abstract Summary: Using molecular dynamics simulations, we determine the linear and nonlinear viscoelastic properties of a model polymer melt in the unentangled regime. Several approaches are compared for the computation of linear moduli and viscosity, including Green-Kubo and nonequilibrium molecular dynamics (NEMD). An alternative approach, based on the use of the Rouse modes, is also discussed. This approach could be used to assess local viscoelastic properties in inhomogeneous systems. We also focus on the contributions of different interactions to the viscoelastic moduli and explain the microscopic mechanisms involved in the mechanical response of the melt to external solicitation. [source] The occurrence of surface roughness in gas assist injection molded nylon compositesPOLYMER COMPOSITES, Issue 2 2000Shih-Jung Liu Gas assist injection molding has increasingly become an important industrial process because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that limit the overall success of this technique. The purpose of this report was to study the surface roughness phenomenon occurring in gas assist injection molded thermoplastic composities. The materials used were 15 % and 35% glass-fiber filled nylon-6 composites. Experiments were carried out on an 80-ton injection molding machine equipped with a high-pressure nitrogen-gas injection unit. Two "float-shape" axisymmetric cavities were used. After molding, the surface quality of molded parts was measured by a roughness meter. Various processing variables were studied in terms of their influence on formation of surface roughness: melt temperature, mold temperature, melt filling speed, short-shot size, gas pressure, and gas injection delay time. Scanning electronic microscopy was also employed to characterize the composites. It was found that the surface roughness results mainly from the exposure of glass fiber in the matrix. The jetting and irregular flows of the polymer melt during the filling process might be factors causing the fiber exposure. [source] The draw ratio,Deborah number diagram: A useful tool for coating applicationsPOLYMER ENGINEERING & SCIENCE, Issue 3 2006S. Bourrigaud The understanding of the basic physical effects of viscoelasticity on drawing performances in the coating process leads to a useful approach to link the rupture of the polymer melt to critical processing conditions. In particular, we show that when solving the drawing problem in the air gap with a simple constitutive equation,like the upper convected Maxwell model,a mathematical inconsistency appears for some drawing parameters. This mathematical instability may be experimentally correlated to the occurrence of melt-rupture, giving rise to a discussion on the effect of viscoelastic properties on drawing performances. Results are given in terms of a diagram representing the maximum drawing ratio Dr with respect to the Deborah number De. A master curve, obtained form experimental results, accounts for the temperature, melt-index, air-gap height, and extrusion output dependences. The limitations of the "universality" of the concept are discussed later. POLYM. ENG. SCI. 46:372,380, 2006. © 2006 Society of Plastics Engineers [source] A parallel coextrusion technique for simultaneous measurements of radial die swell and velocity profiles of a polymer melt in a capillary rheometerPOLYMER ENGINEERING & SCIENCE, Issue 10 2004N.-T. Intawong This article proposes a new experimental technique to simultaneously measure radial die swell and velocity profiles of polystyrene melt flowing in the capillary die of a constant shear rate rheometer. The proposed technique was based on parallel coextrusion of colored melt-layers into uncolored melt-stream from the barrel into and out of the capillary die. The size (thickness) ratio of the generated melt layers flowing in and out of the die was monitored to produce the extrudate swell ratio for any given radial position across the die diameter. The radial velocity profiles of the melt were measured by introducing relatively light and small particles into the melt layers, and the times taken for the particles to travel for a given distance were measured. The proposed experimental technique was found to be both very simple and useful for the simultaneous and accurate measurement of radial die swell and velocity profiles of highly viscous fluids in an extrusion process. The variations in radial die swell profiles were explained in terms of changes in melt velocity, shear rate, and residence time at radial positions across the die. The radial die swell and velocity profiles for PS melt determined experimentally in this work were accurate to 92.2% and 90.8%, respectively. The overall die swell ratio of the melt ranged from 1.25 to 1.38. The overall die swell ratio was found to increase with increasing piston speed (shear rate). The radial extrudate swell profiles could not be reasoned by the shear rate change, but were closely linked with the development of the velocity profiles of the melt in the die. The die swell ratio was high at the center (,1.9) and low (,0.9) near the die wall. The die swell ratio at the center of the die reduced slightly as the piston speed was increased. Polym. Eng. Sci. 44:1960,1969, 2004. © 2004 Society of Plastics Engineers. [source] The effect of surface energy of boron nitride on polymer processabilityPOLYMER ENGINEERING & SCIENCE, Issue 8 2004Nimish Rathod Flow instabilities manifest themselves as distortions on the extrudate surface (melt fracture). They are usually observed at high production rates in many polymer processing operations. Certain fluoropolymers/fluoroelastomers have long been used as processing aids for surface melt fracture elimination. Recent developments have shown that a small amount of boron nitride (BN) powder may successfully eliminate surface melt fracture and also delay the onset of gross melt fracture to higher rates. It has also been reported that a combination of BN and fluoropolymer/fluoroelastomer enhances the effectiveness of the polymer processing even further. The main objective of the present work was to measure the surface properties of a number BN powders, mainly surface energy, in order to gain a better understanding of its performance as a processing aid. Based on this study, it can be concluded that surface energy plays an important role in deciding the possible interactions between the processing aid, polymer melt and the extruding surface. It is observed that the lubricious nature of BN along with an optimum balance of its polar (non-dispersive) and non-polar (dispersive) components of surface energy renders BN a successful processing aid in eliminating both sharkskin and gross melt fracture phenomena. Polym. Eng. Sci. 44:1543,1550, 2004. © 2004 Society of Plastics Engineers. [source] The influence of power-law rheology on flow distribution in coathanger manifolds,POLYMER ENGINEERING & SCIENCE, Issue 3 2003J. D. Reid Coathanger dies are effective in delivering uniform flow if a polymer melt; however, when the fluid flow index varies from the design values, the flow is not uniform. Although mechanisms such as die lip adjustments have been effective tools for adjusting flow profiles, the issue of a variable flow index has not been fully addressed at the design stage. An analytical solution, based on the assumptions present in the 1-D design equation, has been developed for the flow distribution in a coathanger manifold. This solution determines the flow distribution for a power-law fluid with a flow index n* in a manifold designed for a separate flow index n*. From this solution, a uniformity index and a critical design angle are defined. The critical design angle is the angle at which the local derivative of the uniformity index with respect to n* approaches a maximum (for n* < n) or a minimum (for n* > n) as a function of the design angle. The critical design angle is independent of n and is presented as a function of the manifold aspect ratio. [source] Numerical analysis of polymer melt flow in the nipping regionPOLYMER ENGINEERING & SCIENCE, Issue 4 2002M. Takase In the extrusion coating process, it has never been revealed how a polymer melt flows near the nipping region and how the cooling process occurs. We created a numerical simulation program for the polymer melt flow near the nipping region using the finite element method. Numerical results showed the effects of many individual factors (e.g. line speed, melt thickness, extrusion temperature, shear-thinning property, etc.) on the cooling process and polymer melt flow near the nipping region. It was found that a polymer melt buildup that can be observed between two calender rolls in the sheet forming process also formed in the extrusion coating process, and that the amount of polymer melt buildup (bank) depended upon the coating condition. It was found that not only line speed and melt thickness contribute to the extrusion coating process significantly, but also the rheological property has an effect on the process. [source] Experimental investigation of the energy balance for the metering zone of a twin screw extruderPOLYMER ENGINEERING & SCIENCE, Issue 2 2000Stephan Tenge The object of this study is to investigate experimentally the mechanical power transported from the screws to the polymer melt, the heat dissipated in the polymer melt, and the heat transferred to the barrel of the metering zone of a co-rotating twin screw extruder. For the experimental investigations, different screw elements, mixing elements, and kneading discs are used. The experimental results for the dissipation show good agreement with known calculation models. For the calculation of the heat transfer, a new equation is used to calculate the mean temperature difference under consideration of the dissipation. The Nusselt-number can be calculated in good agreement with the experimental results as a function of the Brinkmann-number. [source] PY181 Pigment Microspheres of Nanoplates Synthesized via Polymer-Induced Liquid PrecursorsADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Yurong Ma Abstract Organic pigments are important crystalline substances, and their properties and applications rely on size and shape control. Pigment Yellow 181 (PY181) is an industrial azo pigment that is light and weatherfast and suitable for high temperature processing. One disadvantage is its needle-like shape in the default , -phase, which makes the pigment difficult to process in industry, e.g., in polymer melts, where a spherical structure would be ideal. Here, we show for the first time, that polymer-induced liquid precursor structures can be formed even in association to a chemical reaction. Furthermore, it is demonstrated that biomineralization principles can be exploited for the generation of advanced functional materials, such as pigments with novel complex morphology and different properties. Stable PY181 microspheres of nanoplates in the , -phase were obtained in mixed solvents of water and isopropanol by direct azo coupling under the directing influence of a designed copolymer additive aminobenzoylaminobenzamide-acetoacetyl-poly(ethylene imine)- block -poly(ethylene glycol) (ABABA-acetoacetyl-PEI- b -PEG). [source] A comprehensive 3-D analysis of polymer melt flow in slit extrusion diesADVANCES IN POLYMER TECHNOLOGY, Issue 2 2004Yihan Huang Abstract An understanding of flow behaviour of polymer melts through a slit die is extremely important for optimizing die design and, consequently, for die performance in processing polymer sheets and films. In view of the complex nature and the physical properties of polymer melts as well as of die geometries, such as coat-hanger dies, no simple mathematical formulae can be used to compute the flow regimes within dies. This paper illustrates the development of a three-dimensional (3-D) computer model of an example of a coat-hanger die design using the computational fluid dynamics package, FIDAP, based on the finite element method. A difference of only 3.7% was found when comparing the velocity distribution at the die exit obtained from the 3-D simulation with that calculated using a two-dimensional analytical design procedure, indicating that full 3-D analysis seems to be unnecessary. However it has been shown that unwanted flow phenomena and production problems can be ameliorated by means of visualization and the detailed information obtained from computer simulations. Comparative simulation results with polymers of different rheological properties in the same die are also described. The comprehensive analyses provide a means of interpretation for flow behavior, which allows modification of the die geometry for optimal design. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 111,124, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20002 [source] Rheological behavior of polymer melts in monodimensional flow through low-angle convergence and spiralling diesADVANCES IN POLYMER TECHNOLOGY, Issue 2 2001L. Mascia An experimental study was carried out to examine the rheological behavior of polymer melts in laminar flows through channels with small-angle convergences (2,3°) and spiralling walls (6°/mm along the flow direction), using an extrusion grade of low-density polyethylene. The results show that convergence is the main factor responsible for the observed deviations from steady state laminar shear flow, particularly with respect to additional pressure requirements to maintain a constant mass output. The swell ratio, calculated from the dimensions of the channel at the exit, was found to be considerably higher for flow-through converging channels. Only a small increase in swell ratio could be attributed, on the other hand, to the rotational elements of the die configuration. It is inferred that even for small angles of convergence the increased level of swelling is associated with elongational stress components, which were grouped together and denoted as the "additional stress." This was obtained from the difference between the calculated average shear stress at the wall, using the recorded pressure at the die entry, and the value of the average shear stress at the wall calculated from the shear viscosity data for the melt. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 99,107, 2001 [source] Elongational rheology by different methods and orientation numberJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007John R. Collier Abstract The elongational rheology of polymer melts was measured by the authors using the hyperbolic convergent die technique and the results were compared with the same samples measured using a Meissner type device or an Instron tensile tester. Polyethylene and polystyrene samples were tested at Eidgenössische Technische Hochschule-Zürich or Virginia Polytechnic Institute, and the polyisobutylene was part of a world wide "Round Robin" comparison. A modified Weissenberg number, i.e., an Orientation number, is suggested to explain the agreement between techniques for some samples and lack of agreement for others. The Orientation number is the product of Hencky strain, elongational strain rate, and average relaxation time. When it is less than one a relaxation dominant regime results, when greater than one an orientation dominant regime results, and near one a transition occurs. For the hyperbolic convergent die technique, in which the polymers are transversely constrained by the walls, the extrudates in the transition regime have slight surface defects and the pressure fluctuates more than in the other regimes. If the transition occurs after significant time, i.e., lower elongational strain rates, in the free boundary Meissner and Instron devices, the samples apparently experience more relaxation since unconstrained transversely (and perhaps differential thinning) leading to disagreement with the hyperbolic die measurements. The orientation related body forces are magnitudes larger than the shearing forces and cause slip at the wall in the hyperbolic dies in the orientation dominant regime. Even in the relaxation dominant regime, shear near the wall is a minor contributor to the necessary pressure force. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Structure and dynamics of silica-filled polymers by SANS and coherent SAXSMACROMOLECULAR SYMPOSIA, Issue 1 2002Erik Geissler Random crosslinking in elastomers gives birth to local variations in the crosslink density. When the network is swollen in a low-molecular-weight solvent, competition between the osmotic pressure and the local elastic constraints transforms these variations into differences in polymer concentration, the range and amplitude of which can be measured by small-angle X-ray or neutron scattering (SAXS or SANS). In filled systems, the distribution both of the polymer and of the elastic constraints is modified. By varying the proportion of deuterated solvent in the network, the scattering function of the polymer can be distinguished from that of the filler using SANS. Such measurements yield not only the internal surface area of the filler particles but also the fraction of that surface in contact with the polymer. The recently developed technique of quasi-elastic SAXS detects slow dynamic processes at wave vectors larger than those accessible with visible light lasers. This technique is used to investigate the dynamics of filler particles in uncrosslinked polymer melts. It is directly shown that the structural reorganization process of the filler following an external mechanical perturbation is diffusion-controlled. [source] Shear-stimulated formation of multi-wall carbon nanotube networks in polymer meltsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009T. Skipa Abstract We report on shear-induced nanotube network formation in multi-wall nanotubes/polycarbonate (MWNT/PC) composite melts which was directly monitored by the time-resolved DC-conductivity measurements during steady shear. A small steady shear applied for 1,h to a non-conductive composite with initially well-dispersed nanotubes was found to induce the insulator-to-conductor transition resulting in a conductivity increase by about six orders of magnitude. Similar composite melt annealed without steady shear demonstrates much slower process of the network formation what can be attributed to an agglomeration of attractively interacting nanotubes in polymer melts. The rheologic properties were also measured for shear-stimulated agglomeration. Unexpected difference between the electrical and mechanical networks in MWNT/PC composites was found. For the modeling of the network formation a shear-dependent kinetic equation for the nanotube agglomeration was coupled with empirical formula for insulator-to-conductor transition. Electric DC-conductivity and shear modulus (G, and G,) of MWNT/PC melt (230,°C) measured simultaneously during shear-stimulated network formation. [source] An investigation on the correlation between rheology and morphology of nanocomposite foams based on low-density polyethylene and ethylene vinyl acetate blendsPOLYMER COMPOSITES, Issue 10 2010M. Riahinezhad This article presents the correlation between rheology and morphology of nanocomposite foams of low-density polyethylene (LDPE), ethylene vinyl acetate (EVA), and their blends. LDPE/EVA nanocomposites were prepared via melt mixing and then foamed using batch foaming method. To assess the rheological behavior of polymer melts, frequency sweep and creep recovery tests were done. Morphology of the samples was also studied by scanning electron microscopy and X-ray diffraction. The results showed that with increase in clay content, storage modulus, complex and zero shear viscosities will be increased, which affect the foam morphology. In addition, elasticity plays an important role in foaming process, in a way that samples with more elasticity percentage have the highest cell density and the lowest cell size. POLYM. COMPOS., 31:1808,1816, 2010. © 2010 Society of Plastics Engineers. [source] Visual perception and measurements of texture and gloss of injection-molded plasticsPOLYMER ENGINEERING & SCIENCE, Issue 2 2009Sofie Ignell The effect of an imposed texture on the gloss of injection-molded polymeric surfaces was evaluated as well as the way in which these properties are visually perceived. Specimens having small differences in surface topography were produced using two mold cavities with slight differences in texture and three different polymers. The texture and gloss were characterized using laser profilometry, gloss measurements, and by means of psychometric evaluations. The measured surface topography parameters and gloss were determined mainly by the texture of the mold surface and the gloss also by the processing conditions. Variations in surface topography due to differences in the rheological properties of the polymer melts were, in most cases, too small to be reflected in the measurements. The visual assessments of the texture and the gloss of specimens from the same cavity were in fair agreement with the measurements, although the observers could discern differences between some specimens not revealed by the measurements. When the specimens molded in the two cavities differing significantly both in gloss and texture were compared, the agreement between the measured topography parameters and the perceived roughness was poorer. It is suggested that higher gloss of a textured surface enhances the perception of a higher roughness. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source] In-line near infrared monitoring of esterification of a molten ethylene,vinyl alcohol copolymer in a twin screw extruderPOLYMER ENGINEERING & SCIENCE, Issue 11 2006Claire Barrès Near infrared spectroscopy has developed in the polymer industry as a tool for in-line monitoring of processes, particularly extrusion. However, little work is dedicated to the monitoring of chemical reactions involving polymer melts. In this paper, we examine the suitability of NIR spectroscopy for monitoring the chemical modification (catalyzed esterification) of a molten ethylene,vinyl alcohol copolymer by octanoic acid in a twin screw extruder. Extrusion samples are characterized off-line, for calibration purposes, for the three species of interest (i.e. unreacted acid, OH groups, and ester functions formed on the polymer backbone) by means of two techniques: 1H NMR, allowing all three species to be quantified, and residual (free) acid titration. However, the mass balance of free acid is not straightforward, due to loss of mass by volatilization at the vent. Therefore, 1H NMR analysis and acid titration have to be combined to allow for determination of all concentrations. Multivariate calibration is implemented here to quantify and subsequently predict the analyte concentrations by using the NIR spectroscopic data. Our calibration, based on a partial least squares regression software, provides satisfactory results in terms of correlation between actual and predicted concentrations. This work demonstrates the potential of in-line NIR spectroscopy for monitoring chemical reactions with polymer melts in extrusion. POLYM. ENG. SCI. 46:1613,1624, 2006. © 2006 Society of Plastics Engineers [source] On the effect of pressure on the shear and elongational viscosities of polymer meltsPOLYMER ENGINEERING & SCIENCE, Issue 7 2004Tomas Sedlacek The effect of pressure and temperature on the shear and elongational deformation rate,dependent viscosities has been experimentally investigated for several polymers (HDPE, LDPE, LLDPE, PP, PC, PMMA, and PS) on a capillary rheometer with a back-pressure device. Pressure, ,, and temperature, ,, coefficients have been determined through simultaneous fitting of the shear and extensional viscosity data by the modified White-Metzner model. The dependence of , and , on temperature and pressure, respectively, was investigated and it has been found that simple relationships exist between pressure and temperature sensitivity coefficients for individual polymers. Polym. Eng. Sci. 44:1328,1337, 2004. © 2004 Society of Plastics Engineers. [source] Thickness uniformity of HDPE blown film: Relation to rheological properties and densityPOLYMER ENGINEERING & SCIENCE, Issue 5 2004Hiroyuki Higuchi Previous work has elucidated that the wall slip velocity and viscosity of polymer melts influence the thickness uniformity of blown film. The present study investigates the effects of the stress dependence of wall slip, the shear thinning and the density on the uniformity. We have prepared high-density polyethylenes with a variety of molecular weight distributions, which have different rheological properties. Examination of the thickness uniformity of their blown film has shown that the uniformity is correlated with wall slip velocity, the stress dependence of the velocity, melt viscosity, shear thinning and density; the coefficient of the correlation is determined to be 0.990. The reason why the stress dependence of wall slip and the shear thinning affect the uniformity is explained in terms of polymer melt flow behavior in a die, while the effect of density is interpreted considering bubble fluctuation in the blow-up process. Polym. Eng. Sci. 44:965,972, 2004. © 2004 Society of Plastics Engineers. [source] Analysis and measurement of carbon nanotube dispersions: nanodispersion versus macrodispersionPOLYMER INTERNATIONAL, Issue 10 2010Micah J Green Abstract Because of their unique mechanical, optical, thermal and electrical properties, carbon nanotubes (CNTs) form the basis for a wide variety of multifunctional devices and materials; many of these applications require that CNTs be dispersed and processed in liquids such as organic solvents, polymer melts or surfactant solutions. One of the most problematic issues affecting the CNT research community is the lack of standards and uniform characterization methods for CNT dispersion. A 2005 NASA-NIST workshop aimed to address this issue and made a clear distinction between ,nanodispersion' of individual CNTs and ,macrodispersion' of CNT bundles. Unfortunately, this distinction has yet to percolate through the CNT dispersion literature. The present article seeks to elucidate and commend these concepts, identify the situations where this difference is most critical, note some scenarios where these concepts have been underutilized and posit experimental and computational characterization methods for quantifying the degree of nanodispersion. Particular attention is devoted to the controversial claims of complete nanodispersion and how such claims may be verified. Copyright © 2010 Society of Chemical Industry [source] Viscoelastic properties of branched polyacrylate meltsPOLYMER INTERNATIONAL, Issue 6 2001Nasir M Ahmad Abstract The viscoelastic properties of poly(n-butyl acrylate), poly(ethyl acrylate) and poly(methyl acrylate) melts have been studied using samples that varied in both molar mass and the mol% branched repeat units, these properties having been previously determined by gel permeation chromatography and 13C NMR spectroscopy, respectively. Poly(n-butyl acrylate) was studied most extensively using seven samples; one sample of poly(n-butyl acrylate), two samples of poly(ethyl acrylate) and one sample of poly(methyl acrylate) were used to study the effect of side-group size. Storage and loss moduli were measured over a range of frequency (1,×,10,3 to 1,×,102,rad,s,1) at temperatures from Tg,+,20,°C to Tg,+,155,°C and then shifted to form master curves at Tg,+,74,°C through use of standard superposition procedures. The plateau regions were not distinct due to the broad molar mass distributions of the polyacrylates. Hence, the upper and lower limits of shear storage modulus from the nominal ,plateau' region of the curves for the seven poly(n-butyl acrylate) samples were used to calculate the chain molar mass between entanglements, Me, which gave the range 13.0,kg,mol,1,<,Me,<,65.0,kg,mol,1. The Graessley,Edwards dimensionless interaction density and dimensionless contour length concentration were calculated for poly(n-butyl acrylate) using the mean value of plateau modulus (1.2,×,105,Pa) and three different methods for estimation of the Kuhn length; the data fitted closely to the Graessley,Edwards universal plot. The Williams,Landel,Ferry C1 and C2 parameters were determined for each of the polyacrylates; the data for the poly(n-butyl acrylate) samples indicate an overall reduction in C1 and C2 as the degree of branching increases. Although the values of C1 and C2 were different for poly(n-butyl acrylate), poly(ethyl acrylate) and poly(methyl acrylate), there is no trend for variation with structure. Thus the viscoelastic properties of the polyacrylate melts are similar to those for other polymer melts and, for the samples investigated, the effect of molar mass appears to dominate the effect of branching. © 2001 Society of Chemical Industry [source] | |||||||||||||||||||||||||