bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recent advances in interpenetrating polymer networks
Authors: Frisch K. C. , Klempner D. , Frisch H. L. 
Published: December 2004

AbstractWe review the synthesis, morphology, and physical and mechanical properties of IFNs as well as the related pseudo‐IPNs, in which only one of the polymers is crossliriked. Recent studies have shown that the degree of phase separation achieved in these materials is strongly dependent on the compatibility of blends of the linear polymer constituents of the IPN components as well as the kinetics of chain extension and the presence of grafting between component polymers. We illustrate this by a series of IPNs consisting of a polyurethane and an acrylic copolymer. The acrylic is a typical automotive enamel. An enhancement in properties results, which is dependent on the amount of grafting and the kinetics of polymerization. Also discussed are IPNs of a polyurethane and an epoxy, which exhibit a synergism in adhesive properties, and IPNs of a RIM polyurethane with several epoxies and unsaturated polyesters. In addition, also reported are the preliminary studies on the first successful preparation of a three‐component IPN, consisting of a polyurethane, an epoxy, and an acrylic.
Pressure drop of polymeric melts in conical converging flow: Experiments and predictions
Authors: Kwon T. H. , Shen S. F. , Wang K. K. 
Published: December 2004

AbstractIt is of importance to estimate the pressure drop of polymeric materials in a converging die with an abrupt change in geometry for many polymer processes. In the present study, experiments have been conducted with an extruder and conical dies of four different converging angles for two different polymeric melts under various processing conditions. As part of the analysis, numerical calculations have been carried out using a finite element method (FEM) for a power‐law fluid model, A simple formula for estimating pressure drops has also been derived based on a power‐law fluid model with normal‐stress effects incorporated. In particular, the formula with the normal‐stress term excluded underpredicts pressure drops systematically at high flow rates, giving very similar results to those by the FEM calculation. When the normal‐stress term is included, the formula is in bettor agreement with the experimental data, confirming that the normal stress effect is important at high flow rates. Other formulae in the literature have been also compared with the present experimental data.
Multidimensional control of profile extrusion
Authors: Stevenson James F. , Lee L. James , Griffith Richard M. 
Published: December 2004

AbstractDimensional changes in complex profile extrusions are classified as overall size and local shape changes which can be related naturally and systematically to changes in operating conditions. The theoretical basis and supporting experimental data for simultaneous, independent control of certain classes of extrudate dimensions are presented for the following strategies: (1) size control by manipulating line speed relative to extruder output rate, (2) shape control by manipulating extrudate swell through adjustments in stock temperature, and (3) shape control by manipulating local die flow by adjusting the die temperature set point.
Solid state extrusion of polytetrafluoroethylene fibers
Authors: Mc Gee Robert L. , Collier John R. 
Published: December 2004

AbstractPolytetrafluoroethylene (PTFE) was solid state extruded to fiber form at temperatures between 250 and 300°C and at pressures between 7000 and 15,000 psi. The PTFE fibers had a diameter of 0.0502 inches and the reduction ratio for extrusion was 55.8. The fibers were tested for mechanical strength, and examined with a scanning electron microscope, which revealed a fibrous structure at high magnifications. The melting point of the fibers was 342°C by differential scanning calorimetry. The tensile properties were enhanced with an increase in processing temperature and pressure, the highest properties resulting from an extrusion temperature of 300°C and pressures greater than 10,000 psi. A tensile strength of 5500 psi and a secant modulus of 250,000 psi were obtained.
The effect of flow on cavity surface temperatures in thermoset and thermoplastic injection molding
Authors: Frutiger R. L. 
Published: December 2004

AbstractIn the Injection molding process, nonuniform heat transfer between the polymer and the mold caused by flow during the cavity filling stage can lead to spatial variations in the cavity surface temperature. This can result in an increase in cycle time or poor part quality. An investigation of the flow‐induced, nonuniform, cavity surface temperature is reported here. A flow model for a thin, rectangular, end‐gated cavity and a model for the steady‐state temperature distribution in a simple mold are developed. These are applied to some thermosetting and thermoplastic systems. For both filled and unfilled thermosets, it is found that a simple plug flow model gives a good approximation for the heat transfer during flow. For thermoplastics, however, the full flow solution must be used. For the cases considered in this study, the steady‐state temperature variation along the cavity surface is less for the thermoplastics than for the thermosets.
Physical aging and biaxial creep in cellulose acetate butyrate
Authors: Questad D. L. 
Published: December 2004

AbstractTorsional and tension‐torsion creep studies have been performed on cellulose acetate butyrate at 65°C. The aging shift factor, μ, at this temperature has been determined to be 0.85. This is somewhat higher than 0.75 which was suggested as a maximum value for cellulose acetate butyrate (5). Axial stresses cause the torsional retardation times to become shorter. The change in retardation time is mainly determined by the magnitude of the axial stress and not by the length of time during which the axial stress is applied. Torsional stresses cause the axial retardation times to shift in a similar manner. The shifting of retardation times follows a maximum shear stress criterion.
Elastomeric properties of networks prepared from high‐cis and high‐trans 1,4‐polybutadienes
Authors: Sharaf M. A. , Mark J. E. , Cesca S. 
Published: December 2004

AbstractNetworks were prepared from a sample of 1,4‐polybutacliene having an extremely high cis content (98.5 mol percent) and from other samples having relatively high trans contents (72 to 80 mol percent). The cross‐linking techniques employed were gamma irradiation, ultraviolet irradiation, and peroxide thermolysis. The resulting elastomers were studied in elongation in the unswollen state at several temperatures, to their rupture points, and in swelling equilibrium in a good solvent. Values of the elasticity constant 2C1 obtained from the stress‐strain isotherms at low and moderate elongations gave values of the molecular weight M, between cross‐links in at least approximate agreement with those obtained from the swelling equilibrium data. The other elasticity constant 2C2 generally had relatively large values, suggesting inhomogeneous cross‐linking, but approached zero for small Mc as expected from reduced configurational interpenetration. At high elongations, the reduced stress for the high‐cis polymer showed marked upturns due to strain‐induced crystallization.
The effect of melt compressibility on a high‐speed wire‐coating process
Authors: Chung Tai‐Shung 
Published: December 2004

AbstractThe effects of melt compressibility on a wire‐coating process have been investigated, assuming that the compressible behavior of a polymeric melt obeys the Spencer‐Gilmore equation of state. The compressible model is distinctly different from the incompressible model in two ways: (1) it has substantially lower pressure build‐up within the die, and (2) the location of the maximum velocity is closer to the traveling wire position. As a result, the velocity profile within the die may change from a parabolic shape to a shape somewhat similar to that observed in a drag‐flow case; and the shear stress generated by the fluid on the moving wire is no longer constant. Calculations indicate that the effect of melt compressibility during wire coming may not be neglected if the wire speed Ls greater than 50 cm/s (100 ft/min). In addition, the relationships between processing parameters and product coating thickness for both compressible and incompressible fluids are quite different.
A study on polymer blending microrheology
Authors: Elmendorp J. J. 
Published: December 2004

AbstractIn this paper it is shown that the formation and subsequent breakup of threadlike particles are important disperging mechanisms and largely govern the morphology resulting from a polymer blending process. Experiments on the breakup of Newtonian threads surrounded by a second Newtonian fluid have been carried out and good agreement with Tomotika's theory is achieved. Experiments on the breakup of viscoelastic fluid threads showed the influence of shear thinning and stretch thickening effects of the fluids used. To investigate the influence of non‐Newtonian behavior of molten polymers on capillary instabilities, experiments were carried out on the breakup of molten polymer threads embedded in a second polymer melt. Surprisingly an absence of shear thinning and stretch thickening effects was noticed and good agreement with Tomotika's theory was obtained. Finally, the stability of threads of fluids exhibiting a yield stress was studied. A criterion predicting the stability of such threads was established and verified experimentally. On the basis of this criterion a possible explanation is given for the stability of a certain class of co‐continuous morphologies.
Rheology of curing thermosets: A review
Authors: Roller M. B. 
Published: December 2004

AbstractOver the past decade great strides have been made in the measurement, modeling and application of the rheology or viscosity history of curing thermosets. This paper will review the work that lead to the formulation of a simple predictive model to simulate the viscosity path of curing epoxies and to the use of the model in the understanding of the epoxy lamination process. Subsequent work by others that has clearly refined, extended, and simplified the method will be discussed.
Two directional coextrusion flow of two molten polymers in flat dies
Authors: Sornberger G. , Vergnes B. , Agassant J. F. 
Published: December 2004

AbstractA theoretical study has been carried out of the two directional isothermal flow of two molten polymers in a flat die. The viscous behavior of each fluid is described by a power‐law. Using an iterative finite difference method, a numerical program predicts the influence of geometrical and Theological parameters on the variations of the interface position. Theoretical values are in good agreement with experimental results obtained on a fish‐tail die. In the case of a coat hanger‐die, the mean value of the interface position is correct, but the general shape may be quite different.
Pressure‐Induced densification in injection molding
Authors: Greener J. 
Published: December 2004

AbstractThe effect of pressure on the densification of amorphous polymers in the Injection‐molding process is examined. Density distributions in molded polystyrene slabs were measured for several well‐defined molding histories. In all cases the density of the molded part was spatially inhomogeneous, and its distribution in the slab was closely related to the pressure and temperature histories that prevailed in the molding cavity during the process cycle. The density profile in the gapwise direction followed a characteristic “parabolic” pattern with a minimum at the midplane of the slab. A simple phenomenological model, based on the pressure‐induced densification effect, was constructed to explain the observed density profiles, and close agreement with experimental data was found. Annealing of the molded article at a high temperature (<Tg) caused the density to decrease overall and become more uniform across the part. This is generally consistent with volume‐recovery data for the densified material, which were generated independently in a controlled pressure‐densification experiment.
Tensile yield in polyethylene
Authors: Hartmann Bruce , Lee Gilbert F. , Cole Richard F. 
Published: December 2004

AbstractUniaxial tension tests to the yield point were performed on polyethylene as a function of temperature from 21 to 117°C at a strain rate of 2 min−1. At 21, 45, and 69°C, measurements were also made at strain rates from 0.02 to 8 min−1. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (140°C). The ratio of thermal to mechanical energy to produce yielding is about three times smaller than for glassy amorphous polymers. The ratio of yield stress to (initial) Young's modulus is 0.021 at room temperature and increases to 0.059 at 117°C. Also this ratio was found to decrease with log strain rate. For instance, at 21°C for a strain rate of 0.02 min−1 the value was 0.023, while at 8 min−1 this value decreased to 0.020.
Correlation of blown film optical properties with resin properties
Authors: Pucci M. S. , Shroff R. N. 
Published: December 2004

AbstractThe optical properties of conventional, free‐radical polymerized low density polyethylene (LDPE) blown films are due essentially to surface irregularities that develop during fabrication. Past studies have shown that the extent to which these irregularities occur (and therefore optical properties) correlates well with the melt elasticity of the resin. Specifically, it has been shown that resins with higher melt elasticity result in films with poorer optical properties. However, it was recently reported that the optical properties of film blown from a Sci of three generically similar LDPE resins were found to correlate with the crystallization kinetics of the resins. Specifically, it was reported that the resins that exhibited faster crystallization rates produced films with better optical properties. This present work shows, however, that this apparent correlation is only coincidental. It has been shown that resins exhibiting faster crystallization rates do not necessarily result in films with better optical properties. On the other hand, it has been shown that resins with higher melt elasticity consistently result in films with poorer optical properties.
Phase structure of polyetherpolyol‐4,4′‐diphenylmethane diisocyanate‐based reaction injection molded (RIM) polyurethanes
Authors: Nishimura H. , Kojima H. , Yarita T. , Noshiro M. 
Published: December 2004

AbstractA series of polyetherpolyol−4,4/‐diphenylmethane diisocyanate based polyurethanes were prepared by reaction injection molding (RIM). The degree of phase separation and morphology, which govern the mechanical properties, was investigated by X‐ray scattering, dynamic mechanical spectroscopy, and electron microscopy. The phase reversion occurred at just a 70 weight percent concentration of the based reagent. The degree of phase separation increased with the molecular weight of polypropyleneglycol and decreased with the ethyleneoxide capping content. Morphology was influenced by injection rates.
Crystallization of poly(etheretherketone) (PEEK) in carbon fiber composites
Authors: Lee Youngchul , Porter Roger S. 
Published: December 2004

AbstractThe tendency of carbon fiber to nucleate the zation of poly(etherettterlcetone) (PEEK) has been evaluated by DSC and other techniques. As the carbon fiber content was increased, the supercooling necessary for PEEK crystallization decreased. The repeated melting (at 396°C) of the same PEEK sample results in a decrease of the number of nuclei for crystallization. At equivalent thermal histories, PEEK with carbon fiber was found to have a higher nucleation density than PEEK itself. The surface of carbon fibers and nuclei in the PEEK matrix compete for crystallization growth. As the holding time in melt was increased, the number of matrix spherulites formed on cooling decreased, hence a more pronounced transcrystalline region was developed. Correspondingly, the composites preheated in the melt for 100 min showed about two times the transverse tensile strength and strain‐to‐failure of those preheated for only 30 min. Corresponding fracture surface produced in tension showed that the former samples had a greater matrix adhesion to the carbon fiber than the latter.A strong interfacial bond is thus developed by crystallization on carbon fiber surface. Destroying nuclei in the PEEK matrix by long preheating enhances crystallization on the carbon fiber.
Measurements of cycle time in injection molding of filled thermoplastics
Authors: Boldizar Antal , Kubát Josef 
Published: December 2004

AbstractThis study presents the results of measurements of the sealing and cooling periods of the injection molding cycle of filled thermoplastics, both periods constituting a major part of the cycle. The compounds used were based on HDPE, PP, and PS. The fillers were calcium carbonate, carbon black, and magnesium oxide. The latter two materials were chosen for their high thermal conductivity. The sealing time was determined by a gravimetric method, while the measurement of the cooling time was based on the assessment of the recovery of the ejector marks for samples ejected after varying times of cooling. Increasing filler content produced significant and reproducible reductions of the cycle time. Such effects were especially pronounced with the high thermal conductivity fillers. The cooling process was also treated theoretically, starting from the heat conduction equation and producing a fully satisfactory description of the experimental data. Furthermore, the value of the thermal diffusivity, exemplified by the HDPE/MgO compounds, was in good agreement with the values obtained from current composite expressions.
General consequences of the packing phase in injection molding
Authors: Greener J. 
Published: December 2004

AbstractThe post‐filling phase in injection molding was analyzed via simple heat‐transfer and P‐v‐T models. An expression for the evolution of (volume‐averaged) pressure in a molding cavity during the cooling phase of the process was derived from the empirical Tait model combined with the transient heat‐conduction equation. This expression was used to establish general optimization criteria for the packing phase in injection molding, based on simple heuristics, and to assess the effects of various process and material parameters on the packing response of the system. The effects of gate geometry, part geometry, mold temperature, and melt temperature on the packing characteristics of a simple part are examined, and the general implications to the dimensional integrity of the part are discussed.
The recent developments of thermotropic liquid crystalline polymers
Authors: Chung Tai‐Shung 
Published: December 2004

AbstractThe historical development of both main‐chain (M.C.) and side‐chain (S.C.) liquid crystalline polymers (LCPs) is presented. Synthetic routes and characterization techniques for LCPs are introduced. Various approaches to reduce the melting points of M.C. LCPs and to increase the mesogenic order of S.C. LCPs are reviewed and evaluated. The criteria to form a liquid crystalline phase are then discussed. Comparisons among thermotropic, lyotropic, and low‐molecular‐weight liquid crystals are also made. It is concluded that the preparation of LCPs has been well developed by the industry, but that the understanding of the formation of LC domains has not been completely understood. The theoretical explanations for some unexpected results are still not available. These anomalies are detailed in this work. Future research activity en LCPs for plastics engineers is also mentioned in this article.
The biaxial deformation and yield behavior of bisphenol‐a polycarbonate: Effect of anisotropy
Authors: Carapellucci L. M. , Yee A. F. 
Published: December 2004

AbstractThe biaxial tension stress‐strain‐yield behavior of glassy bisphenol A‐polycarbonate has been investigated at constant octahedral shear stress rate and at 25°C and −40°C. The specimens possess a small amount of anisotropy. Hill′s criterion for yielding of anisotropic materials is modified to take into account the sensitivity of the yield locus to the hydrostatic stress component. This modified yield criterion fits the 25°C data quite well. However, the data at −40°C cannot be fitted using reasonable parameters.
Analysis of steady state of free radical solution polymerization in a continuous stirred tank reactor
Authors: Choi K. Y. 
Published: December 2004

AbstractThe steady state structure of non‐isothermal free radical solution polymerization in a continuous stirred tank reactor is analyzed. With mean residence time as a bifurcation parameter, five regions of steady states are identified. The effect of reactor operating conditions on the structure and the stability of steady state is discussed.
Evaluating screw performance: Extrusion process stability and the degree of mixing from melt rheology data and from measurement on an instrumented extruder
Authors: Plochocki A. P. , Dey S. K. , Wilczynski K. 
Published: December 2004

AbstractA comprehensive study of polyethylene extrusion was carried out with an instrumented extruder on several screws differing in geometry and paralleled with capillary rheometry of the extrudate leading to melt viscosity and elasticity functions. Assuming Oldroyd's constitutive equation for molten polyethylene and the extrudate melt temperature oscillation (ΔTm) as a measure of the process stability and an indication of melt mixing quality, it was found that the product of the dimensionless numbers (Deborah, De and Brinkman, Br) correlates well (r = 0.93) with ΔTm. Since the Br and De groups follow from the rheological characteristics of the melt and the extrusion process parameters, a relationship of type: ΔTm = a + b (De) (Br) appears useful in designing an extrusion process (for a polymer of known rheology) with respect to its stability, and indirectly, its mixing efficiency.
Simulation of welding flows in a slit. Part I: Kinematics
Authors: Wei K. H. , Malone M. F. , Winter H. H. 
Published: December 2004

AbstractThe kinematics of ideal welding flows generated by a thin‐plate divider, a cylinder, or a slab in a slit channel are studied by using a finite element analysis. The analysis includes simulations of Newtonian and Carreau fluids. There are two flow configurations. First, a single plate‐divider or an obstacle was positioned symmetrically in a slit channel with no‐slip at the walls. In the second, an infinite number of plate‐dividers or obstacles were positioned in parallel, and the boundary walls were infinitely far away. It was found that extensional flow dominates the region near the stagnation points of obstacles and plate‐dividers, and that the fluid elements near the weld interfaces have a strain history of both high stretching and shearing. The thickness of the elongated region is reduced as the thickness of the plate‐divider increases. Shear‐thinning tends to increase the rate of extension. However, its influence on the flow field tends to lessen as the width of the flow channel or the obstacle size increases. A no‐slip condition at walls causes slightly stronger elongational flow in the weld interface than does the symmetric condition of perfect slip at walls.
Using the optical microscope to characterize molecular ordering in polymers
Authors: Viney C. 
Published: December 2004

AbstractThis review aims to encompass various situations where optical microscopy—particularly observation and measurement of birefringence—can be used to deduce the nature of intermolecular correlations in polymers. The necessary background dealing with light propagation in anisotropic media is summarized in practical terms. The review is especially concerned with illustrating how unjustified assumptions and ambiguous terminology can cause erroneous interpretation of results. Many references cited are themselves reviews or even textbooks; they afford detailed access to the wide and diffuse literature that full coverage of this subject demands, but would constitute an unwieldly bibliography if listed as individual publications.