bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interpretation of the dynamic mechanical response of heterogeneous polymer blends in terms of continuum models
Authors: Dickie R. A. 
Published: December 2004

AbstractDynamic mechanical measurements have been widely used for characterization of polymer blends and composites. This paper discusses application of continuum models to interpretation of the dynamic mechanical response of isotropic microscopically heterogeneous polymer blends. The models typically predict shifts in apparent glass transition temperature (location of principal loss tangent maximum) for each blend constituent. Experimentally observed shifts in the apparent glass transition of heterogeneous blend constituents may thus arise at least partly for mechanical reasons rather than because of changes in the properties or glass transition temperature of the blend constituents. It is suggested that, for heterogeneous blends of well characterized phase morphology, changes in glass transition behavior of blend constituents be determined by comparison of measured and calculated loss tangent maxima. For two‐component blends, the loss tangent at the temperature at which the loss tangents of the blend constituents are equal may be useful as a further diagnostic tool for changes in loss mechanisius.
Non‐isothermal phenomena in polymer engineering and science: A review. Part II: Non‐isothermal phenomena in polymer deformation
Authors: Stolin A. M. , Merzhanov A. G. , Malkin A. Ya. 
Published: December 2004

AbstractThermal phenomena in deformation of solids and flows are reviewed. Regularities common to all these phenomena as well as their characteristic features and consequences important for science and engineering are reported. The analogy between thermal phenomena in polymer mechanics and in chemical reaction is noted.
Towards an understanding of the heat distortion temperature of thermoplastics
Authors: Takemori Michael T. 
Published: December 2004

AbstractA systematic understanding of the heat distortion temperature (HDT) of amorphous and semi‐crystalline polymers is possible through a direct correlation with the modulustemperature behavior. For amorphous polymers, the precipitous drop in modulus at the glass transition temperature makes the HDT a well‐defined, reproducible and predictable property. Furthermore, the addition of reinforcing fillers has a negligible effect on the HDT of the amorphous polymer. For semi‐crystalline polymers, however, the exact opposite may hold true. The modulus exhibits a “plateau” region between the glass transition and the melting transition. Hence the HDT often is difficult to predict, is sensitive to thermal history and may be greatly increased through the addition of fillers. More importantly, the HDT may not be an accurate measure of the upper use temperature for semi‐crystalline polymers in load bearing situations since considerable stiffness may still be retained even upon exceeding the HDT.
Thermal transition behavior of polybutadiene containing polyurethanes
Authors: Schneider N. S. , Matton R. W. 
Published: December 2004

AbstractThe thermal transition behavior of a series of hydroxy terminated polybutadiene (HTPBD) containing segmented polyurethanes has been studied by differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA). Four transition regions are observed; the soft segment Tg, at −74°C, two hard segment transitions T1, at 40°C and T2 at 103°C and a softening region by TMA at 180°C, presumed to arise from the dissociation of allophonate bonding, The low Tg, only 7°C higher than the Tg of free HTPBD, indicates nearly complete phase segregation despite the amorphous nature of the hard segment structure. The dependence of T1, on hard segment length and thermal cycling suggests that it represents domains consisting primarily of shorter hard segments units. Factors contributing to the rather low mechanical properties of HTPBD polyurethanes are also discussed.
Mechanical, thermal, and electrical properties of metal fiber‐filled polymer composites
Authors: Bigg Donald M. 
Published: December 2004

AbstractThe critical concentration at which a metal‐filled composite becomes electrically conductive can be dramatically reduced by adding the metal as randomly dispersed fibers. The higher the aspect ratio of the fibers, the lower the concentration needed to induce electrical conductance. Composites exhibiting resistivities below 20 ohm‐cm have been produced with less than 8 volume percent aluminum fibers, having an aspect ratio of 24:1. At low fiber loadings the tensile strength of the composites is similar to that of the unfilled polymer. The thermal properties of these composites are shown to increase monotonically in accordance with the theoretical development of Nielsen.
Studies on wire coating extrusion. II. The rheology of wire coating coextrusion
Authors: Han Chang Dae , Rao D. A. 
Published: December 2004

AbstractAn experimental and theoretical study of wire coating coextrusion through a pressure‐type die was carried out. For the experimental study, the wire coating apparatus employed was the same as that described in Part I of this series (14), except for the newly constructed coextrusion die. The die was provided with three melt pressure transducers along the axial direction, which permitted us to determine the pressure gradient in the die. It was found that a reduction in pressure gradient was realized when a lower viscosity polymer was coextruded with a high viscosity polymer. The materials used for the coextrusion were combinations of low‐density polyethylene, high‐density polyethylene, polystyrene, and two different commercially available thermoplastic rubbers (UniRoyal TPR‐1900 and Shell Kraton G 2701). The use of a high shrinking (crystalline) polymer inside a low shrinking (amorphous) polymer was found to give rise to distorted coatings (non‐circular cross section of the coated wire). The interface between the coextruded layers was examined under a magnifying lens, and it was found that under certain processing conditions, the interface was highly irregular. Experimental correlations were obtained to explain the onset of an unstable interface in terms of the rheological properties of the individual components being coextruded, and of the processing variables. It was found that interfacial instability occurs when the shear stress and the viscosity ratio (also elasticity ratio) of the two components at the interface exceed certain critical values. For the theoretical study, using a power‐law model, the equations of motion were solved numerically to predict the volumetric flow rate as functions of the pressure gradient in the die and the rheological properties of the polymers being coextruded. Solution of the system of equations permitted us to predict the velocity profile and shear stress distributions of two molten polymers inside a pressure‐type wire coating coextrusion die. Comparisons were made between the experimental and theoretically predicted volumetric flow rates. The comparison was found to be reasonably good with certain systems. The discrepancy between the experimentally obtained and the theoretically predicted volumetric flow rates was attributed to interface migration and interfacial instability.
Characterization and continuous extrusion of isotropic and anisotropic poly(p‐phenylene terephthalamide)/sulfuric acid solutions to form ribbons and blown film
Authors: Aoki Hiroshi , Onogi Yoshihiko , White James L. , Fellers John F. 
Published: December 2004

AbstractAn experimental characterization and processing study of redissolved Kevlar® and poly(p‐phenylene terephthalamide)/sulfuric acid solutions is reported. Polarized light microscopy studies show the development of an anisotropic phase. When two phases coexist, negatively birefringent spherulites are observed. At higher concentrations, a single phase of coalescing spherulites is seen and following melting and subsequent cooling, nematic (threadlike) structures are observed. Viscosity and normal stresses were measured at various concentrations and temperatures. A yield stress is exhibited at room temperature. Both room temperature and 60°C viscosity vs concentration curves display maxima. The solution in concentration ranges from 2 to 12 percent have been extruded as ribbons and as annular blown tubular film. Processing variables and problems are discussed. Wide angle X‐ray scattering patterns of films show orientation. Tensile properties have been measured on films.
Diffusion in polymers
Authors: Hansen Charles M. 
Published: December 2004

AbstractConcentration dependent diffusion coefficients explain Case II type diffusion. Solutions to the diffusion equation yield straight lines for weight gain vs time when the exponential variation of the diffusion coefficient is included. Boundary layer resistance together with concentration dependent diffusion coefficients explain Super Case II type diffusion. The increase in the rate of weight gain after a prolonged period is predictable. The surface concentration rises slowly to its equilibrium value in this case. Boundary layer resistance appears to be quite common, particularly where the penetrant has low affinity (not a true solvent) for the polymer, such as water in most polymers or hexane in polystyrene. Boundary layer resistance is quite significant for coatings (where film thicknesses are usually measured in microns), accounting for the majority of the resistance in some cases. A method to separate diffusional resistance from the surface resistance is suggested, but studies at different film thicknesses appear mandatory.
Modification to weld lines in extruded thermoplastic pipe using a rotating die system
Authors: Worth R. A. 
Published: December 2004

AbstractWhen a polymer melt flows around the cross head or past the fins of a torpedo in a pipe die, a weld line is produced where the separated melt streams rejoin. This weld line may result in an area of weakness in the extruded pipe, although in the case of unfilled materials the effect can be reduced by using a compression section in the die. However, With fiber reinforced polymers it is unlikely that fibers will cross the weld line, and a reduction in strength is inevitable. It is shown theoretically that by rotating the core of the extrusion die the weld line can be modified to form a spiral around the pipe wall, with a large‐surface area for improved strength. Experimental investigations, which employ photographs of thin sections of pipe containing carbon black particles, support these conclusions.
Solid state extrusion of ultra high molecular weight polyethylene. Processing and properties
Authors: Zachariades Anagnostis E. , Watts Michael P. C. , Porter Roger S. 
Published: December 2004

AbstractThe techniques of solid state coextrusion and powder extrusion have been employed for the deformation of ultra high molecular weight polyethylene. Chain folded and chain extended morphologies obtained under different crystallization conditions were coextruded within a nylon 11 casing acting as a processing aid at an extrusion draw ratio (EDR) of 5 at ≤ 120°C and 0.20 GPa. The powder was compacted and extruded at ≤ 128°C and 0.23 GPa up to an EDR of 24. The physical and mechanical properties of the extrudates were evaluated and found to be dependent on intial morphology. An extrudate from the chain‐folded morphology gave a low modulus of 0.71 GPa, the chain‐extended morphology a modulus of 6.7 GPa, and the compacted powder a modulus of 15 GPa.
Structure vs stability in polymer degradation
Authors: Stivala S. S. , Reich Leo 
Published: December 2004

AbstractAll materials are subject to aging, a process of long‐term degradation, but not at the same rate or affected in the same manner. The wide variation in susceptibility (or resistance) of polymers to various degradative agents, e.g., oxidative, thermal, mechanical, chemical, biological, depend on their chemical composition and structure. Accordingly, the chemical, physical, and energy considerations inherent in the pure polymer are discussed in relation to degradative stability.
Design of coat‐hanger sheeting dies based on ratio of residence times in manifold and slot
Authors: Matsubara Yutaka 
Published: December 2004

AbstractA new coat‐hanger die geometry with a uniform flow rate and optional ratio of residence times in manifold and slot is proposed. Such a die will be effective when thermal degradation in the die occurs, especially at die far end. This geometry is easily determined if the flow behavior index n of polymer is assumed. A suitable ratio greater than unity may be taken considering die‐height and cost, because lower height is attained as the ratio increases above unity. An example of a design calculation is shown.
Oriented monofilaments from blends of poly(ethylene terephthalate) and polypropylene
Authors: Rudin Alfred , Loucks D. A. , Goldwasser J. M. 
Published: December 2004

AbstractPoly(ethylene terephthalate) and polypropylene are considered, to be incompatible by the usual criteria for polymer blends. Sheath/core filaments of these polymers could not be oriented because of poor adhesion of the base polymers. Melt blends of the two polymers with 30 and 50 weight percent polypropylene produced useful, oriented monofilaments. Tensile and dynamic mechanical properties of these filaments indicate that the structures consist of interlocked microfibrillar domains of the polyester and polyolefim. The glass transition region of poly(ethylene terephthalate) is not affected by admixture with polypropylene. A fine mutual dispersion of the two polymers was possible because the melt viscosities of the ingredients were reasonably well matched under the conditions of mixing. The melt viscosity and elasticity of blends were lower than those of either component as expected if the two polymers are immiscible. Monofilament extrusion and melt flow measurements were made with a one‐half inch single screw extruder.
Impact strength of polymers 2: The effect of cold working and residual stress in polycarbonates
Authors: Thakkar B. S. , Broutman L. J. , Kalpakjian S. 
Published: December 2004

AbstractThe influence of cold working on the toughness improvement in glassy amorphous polycarbonates was studied. Cold working processes, namely rolling and. Steckel rolling were used to produce thickness reductions up to 40 percent in flat‐strip specimens. The notched Izod impact strength and tensile properties were measured as a function of strip thickness reduction. It was shown that the toughness enhancement in polycarbonates cold worked to low thickness reductions was due to the residual stress state present as opposed to molecular orientation which becomes significant at higher degrees of cold work. Residual stress measurements were made by using the layer removal technique. Residual tensile stresses as high as 2100 psi were present in 1/4‐in. cold‐rolled polycarbonate at the surface. The maximum stress in the center of the specimen was 1100 psi in compression. The residual stresses at the surface decreased with increasing thickness reduction. The residual stress state for Steckel rolled. 1/2‐in. polycarbonate was also measured and found to be more complex than for the thinner samples, The results demonstrated that surface tensile stresses and interior compressive stresses can produce large values of impact strength if the notch is to be machined after cold working. Thus, the values of impact strength measured from the notch Izod specimen are sensitive to the residual stress state in the polymer. This behavior is in contrast to earlier studies on thermally quenched material in which the material was quenched after notching. The thermal quenching produced surface compressive stresses which were also present at the notch tip. The presence of compressive residual stresses at the center of the notch suppressed the formation of a craze leading to toughness enhancement in cold worked polycarbonate strips. It is shown that by control of residual stresses in polycarbonate, strips at least 1/2 in. in thickness can be made to exhibit ductile failure in the notched Izod impact test.
Nodal positioning analysis (NPA)—A numerical method for determining flow behavior of thermoplastic materials
Authors: Echenagucia J. , Fricke A. L. , Hassler J. C. 
Published: December 2004

AbstractA finite difference method is presented for the solution of two dimensional flow problems in polymer processing. The method is applicable to narrow gaps of any shape and variable thickness. NPA was developed for analyzing the filling stage of the injection molding cycle, but it could be used in extrusion, blown film, and other polymer processing operations. In NPA the position of the flow front is calculated at the end of each time increment, and an axial node is placed at the newest location of the flow front. Each axial node is then divided into a determined number of radial nodes. The velocity and temperature profiles are obtained from the simultaneous solution of the momentum and energy equations. The use of finite differences transforms the continuity, momentum, and energy equations into a system of linear equations which can be solved by any direct or iterative technique. The procedure is repeated until axial nodes have been placed throughout the whole flow channel or until the flow front stops due to polymer solidification. The main advantage of this technique, when compared to the use of a fixed finite difference grid, is that computation time is saved by considering only nodes filled with the fluid. Empty nodes are not considered and corrections for partially filled nodes are not needed. No complications due to the parabolic‐shape of the flow front profile are introduced because the axial nodes are placed at average front locations determined by the average velocity at the particular time interval under consideration.
On the rheology of packed polymer powders
Authors: Umeya Kaoru , Hara Ryuichi 
Published: December 2004

AbstractThe rheology of polystyrene powder beds was examined by two kinds of experiments. From stress relaxation measurements during powder compaction, it was found that relaxation at the shorter times could be attributed to sliding between particles. This is followed by a relaxation attributed to the deformation of the polystyrene particles themselves. From dynamic mechanical measurements, an increase was found in the value of vibrational absorption coefficient (Q−1 value) at a temperature below that of the main relaxation dispersion of bulk polystyrene, attributed to the slipping around tight particle junctions. These phenomena appear characteristic of powder‐like materials.
Reactive polymer processing
Authors: Biesenberger J. A. , Gogos C. G. 
Published: December 2004

AbstractThis paper addresses some of the general engineering problems in reactive polymer processing: thermal effects on reactor stability and polymer properties due to rapid exothermic polymerization, the formulation of reaction viscosity relationships required in simulations, and the generation of flow and mixing via technology available from both ends of the viscosity spectrum, which is spanned in its entirety when going from monomer to molded polymer. Methods of analysis are discussed and general design concepts are suggested, which can be applied to the construction of innovative future processing equipment.
Impingement mixing in reaction injection molding
Authors: Lee Ly James , Ottino Julio M. , Ranz William E. , Macosko Christopher W. 
Published: December 2004

AbstractImpingement mixing is the unique feature of the reaction injection molding (RIM) process but mixheads are largely designed by trial and error. To visualize the impingement process we have taken high speed photographs. To characterize mixing quality we have followed adiabatic temperature rise of mixtures, varying Reynolds number, mixhead geometry and the reaction rate. These results are examined in terms of a simplified model which includes both fluid mechanical and polymerization aspects of the problem.
Polymer devolatilization: Theory of equipment
Authors: Biesenberger Joseph A. 
Published: December 2004

AbstractThe role of surface renewal and feedback phenomena in devolatilization equipment is clearly illustrated via staged models. A continuous model for the vented, single‐screw devolatilizer is developed, including barrel evaporation and bulk surface renewal as well as backmixing, which represents de‐volatilization data more accurately than previous models. Numerous sample computations are included. The models are used to demonstrate the sensitivity of devolatilization equipment to certain design parameters.
Mathematical analysis of transport properties of polymer films for food packaging. II. Generalized water vapor models
Authors: Peppas Nikolaos A. , Khanna Rohit 
Published: December 2004

AbstractDeterioration or spoilage of dehydrated food products stored in flexible packaging materials depends on the partial pressure of water vapor in the environment of the stored food. Mathematical analysis of the diffusion of water vapor through semipermeable polymer films using Nernst‐Planck equations is combined with non‐liner water sorption isotherms on food to establish criteria and optimum conditions for storage stability of dehydrated food. Langmuir, Brunauer‐Emmet‐Teller (BET), Halsey, Oswin and Freundlich isotherms are used for various ranges of water activity. It is shown that a single parameter, the permeability‐sorption constant, based on the physical properties of the polymer and the sorptive properties of the food, accounts for both diffusion and adostption and can be used to accurately determine maximum storage times and can be used to accurately determine maximum storage times and to optimize the selection of packaging films. The theory is extended to thermodynamically compatible solute‐polymer systems, where the polymer film is swollen appreciably by the diffusing species.
Relative influence of the mobility and the solubility parameters of fluids on the mechanical behavior of high impact polystyrene
Authors: Hoa S. V. 
Published: December 2004

AbstractAmong different fluid parameters having some effect on the environmental stress cracking of plastics, the surface tension and the solubility parameter are generally accepted as dominant ones. However, experimental evidence to date indicates that one single parameter can not be used as an index for predicting failure in all cases and a distinction of the conditions of their importance has not been made. This paper presents the results obtained from the creep and fatigue response of high impact polystyrene in different environments, especially those environments that do not show any effect on the unstressed polymer. The results indicate that at high stresses, the mobility of the fluid in penetrating into the polymer craze networks is more important and that at smaller stresses, the solubility parameter is more important.
Reaction injection molding (RIM) elastomers having superior high temperature performance
Authors: Rice D. M. , Dominguez R. J. G. 
Published: December 2004

AbstractReaction injection molding (RIM) elastomers are being seriously considered by major automotive companies as a substitute for metal in exterior body panels. One major consideration in this application is dimensional stability at a 325°F paint bake cycle. Reported here are formulations which via novel processing result in finished parts with excellent dimensional stability at 325°F. In addition, other properties such as impact resistance and flex modulus ratio improve parallel with high temperature performance. Mechanical properties as a function of processing and molding parameters are presented. Other studies are presented and a tentative explanation of the superior performance of these RIM elastomers is made.