bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheology of short glass fiber‐reinforced thermoplastics and its application to injection molding. III. Use of a high shear rate capillary rheometer in the injection molding shear rate range
Authors: Crowson Roger J. , Scott Anthony J. , Saunders Derek W. 
Published: December 2004

AbstractA capillary rheometer has been designed and built which is capable of making measurements in the shear rate range: 100 s−1 < \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document} < 3 × 106 s−1. The rheometer uses the injection unit of an injection molding machine. A modification of this rheometer has been built which consists of two dies in series. Both dies may be used for rheometric purposes, but the second die is intended primarily to act as a valve to allow the mean pressure to be varied in the first die, while keeping the pressure drop constant. In this way the pressure dependence of viscosity may be measured in the injection molding shear rate range. Measurements have been made on unfilled and short glass fiberreinforced polypropylene melts and flow curves covering seven decades of shear rate are presented for the unfilled material. The temperature of the extrudate may be as much as 70°C higher than the barrel temperature. Two effects, shear heating and compression heating, contribute towards this temperature rise, and calculations of the extrudate temperature are in good agreement with measured values. At high shear rates the viscosity is affected by the pressure needed to drive the flow. The effect of pressure on the viscosity outweighs the effect of temperature on the viscosity at high shear rates. A value for the pressure coefficient of viscosity of unfilled polypropylene β = 0.0058 m2 MN−1 has been obtained.
The rheology of thermoplastics under conditions of spiral flow and vibrations on extrusion
Authors: Fridman M. L. , Peshkovsky S. L. , Vinogradov G. V. 
Published: December 2004

AbstractThis paper describes the results of a theoretical and experimental study on the rheology of thermoplastics subjected to mechanical effects at extrusion conditions. The spiral flow of non‐Newtonian systems has been studied and quantitative relationships obtained for its description, which are suitable for engineering. The effect of rotational low‐frequency large‐amplitude vibrations on the flow of melts in the extruder's head of simple (circular) and complex cross sections has been studied and an analysis provided for flow with small‐amplitude high‐frequency (ultrasonic) superimposed vibrations. The energy efficiency of cyclic deformation upon extrusion has been estimated. The investigation has provided recommendations for the application of complex shear as a method of directed action on the relaxation and, hence, rheological characteristics of polymers. This opens up new possibilities for the intensification of the extrusion processes and compositions based on thermoplastics.
Relation between kneading behavior and flow instability of a high molecular weight high density polyethylene, applications to extrusion
Authors: Torregrosa J. M. , Weill A. , Druz J. 
Published: December 2004

AbstractNon‐monotonic continuous curves of torque as a function of shaft speed, M(N), have been obtained for a high molecular weight high density polyethylene (HDPE) from measurements obtained with a torque rheometer (Haake Rheocord). Previous papers have given theoretical demonstration of the non‐monotonic character of the shear stress‐shear rate function, s(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}), which makes it possible to explain the extrusion behavior of a high molecular weight HDPE. In capillary rheometry, it is not possible to obtain the values of s(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}) into the “well zone” of this function because the compressibility of the polymer creates a phenomenon of oscillation in the barrel affecting the die output flow rate and the pressure loss. The M(N) function measured by the Haake Rheocord is a complete representation of the s(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}) function, although the capillary rheometer only gives a partial representation of this function. The transformation of the M(N)function into s(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}) is quite difficult because of the complex geometry of the Haake Rheocord measuring head. The “critical points” of the s(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}) function in the capillary rheometer (appearance of oscillations), can be correlated to the maximum points of the M(N) function in the Haake Rheocord at constant temperature. The non‐monotonic aspect of the s(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}) function provides an important technological application: extrusion of a high molecular weight HDPE at an increased flow rate at low temperatures.
Evaluation of cushioning properties of plastic foams from compressive measurements
Authors: Miltz Joseph , Gruenbaum Gad 
Published: December 2004

AbstractEvaluation criteria for the cushioning properties of plastic foams were developed on the basis of their stress‐strain curves. The energy‐absorption efficiency and ideality parameters have maxima when plotted against stress. The maximum in the efficiency curve represents the strain range where maximum energy is absorbed by the foam at the corresponding stress; the higher and flatter this maximum, the better the cushioning properties of the foam. The maximum in the ideality curve represents the range where the foam transmits a constant force to the packaged product. Two flexible polyurethane foams and two semirigid bonded polyurethane chipfoams were evaluated by the proposed method.
A critical review of dynamic modeling and control of plasticating extruders
Authors: Costin M. H. , Taylor P. A. , Wright J. D. 
Published: December 2004

AbstractThis is a critical review of the recent literature on plasticating extruder dynamic modeling and control, The papers reviewed are divided into three categories: extruder disturbance studies, classical control and modeling studies, and stochastic control studies. It was found that most researchers have concentrated on modeling the long‐term disturbances associated with the extruder melt temperature, melt pressure or extrudate thickness. The control problem for these variables has been treated to a much lesser extent. The difficult to control and industrially important high frequency disturbances have been, in the most part, neglected. Recommendations are made for the future direction of research into extruder control.
Structure and morphology of thermally oxidized high density polyethylene pipes
Authors: Terselius B. , Gedde U. W. , Jansson J‐F. 
Published: December 2004

AbstractThe effects of thermal oxidation on the‐ molecular structure and on the morphology of a series of high‐density polyethylene pipes have been studied “as received” or after service. The existence of a 40 to 170 μm thick oxidation skin was established, the structure and morphology of which were characterized by gloss measurements, scanning electron microscopy, polarized microscopy, infrared spectroscopy, gel measurements, and differential scanning calorimetry. The skin surface frequent contained craterlike structures, 25‐50 μm in diameter, whereas small‐scale structures occurred much less frequently than in non‐oxidized surfaces, and the gloss increased significantly. The presence of a carbonyl concentration gradient through the skin was established, and the gel measurements also indicated a crosslink gradient. The skin was found to be composed of a top layer with a mainly non‐spherulitic structure of very low crystallinity and melting point and a large‐scale spherulitic layer with a crystallinity and melting point slightly below the corresponding bulk values. The formation of this brittle surface layer and its effect on the long‐term fracture performance of the pipe are discussed.
Studies of poly(2,6‐dimethyl‐1,4‐phenylene oxide blends): I. Copolymers of styrene and maleic anhydride
Authors: Fried J. R. , Hanna G. A. 
Published: December 2004

AbstractBlends of poly(2,6‐dimethyl‐l,4‐phenylene oxide) and copolymers of styrene and maleic anhydride have been characterized by differential scanning calorimetry, dynamic mechanical analysis, and tensile measurements. Differential scanning calorimetry measurements indicate a single broadened glass transition for each blend of a 8 wt.% maleic anhydride copolymer, P(S‐8MA), but two glass transitions when the copolymer composition is 14 wt.% MA, P(S‐14MA). The glass transition temperatures of the former blends follow a sigmoidal dependence on blend composition, which is explained on the basis of evidence for phase separation from their dynamic mechanical tan 8 spectra. Tensile moduli of both blends reach a maximum at intermediate blend compositions; however, large‐strain mechanical properties are highly dependent on blend compatibility and the method of sample preparation. The more homogeneous P(S‐8MA) blends yield at low‐to‐intermediate copolymer compositions but fail in a brittle mode at higher compositions. All heterogeneous P(S‐14MA) blends undergo brittle failure, but comparison of experimetal values of ultimate stress and strain with predictions from empirical relationships developed for composites indicate that interfacial adhesion is strong in these systems.
Fatigue crack propagation in amorphous poly(ethylene terephthalate)
Authors: Ramirez Alvaro , Manson John A. , Hertzberg Richard W. 
Published: December 2004

AbstractEarlier studies of fatigue crack propagation (FCP) in polymers have shown a general superiority of crystalline relative to amorphous polymers in terms of FCP resistance. In order to study in detail the effect of crystalline content and character on FCP rates, poly(ethylene terephthalate) (PET) was selected as a convenient material in which a wide range of crystallinity can be obtained. To provide a baseline for comparison, FCP rates were determined for essentially amorphous polymers covering a range of molecular weight. Surprisingly, the essentially amorphous PET turned out to be as resistant to FCP as the best crystalline polymers so far observed. In this paper, several observations about FCP rates and fracture topography are reported: FCP rates agree well with the Paris equation over a wide range of ΔK; in any case, the higher the molecular weight, the greater the crack growth resistance according to the Manson‐Hertzberg relationship previously established. Fracture surface analysis revealed evidence of softening and drawing, as well as extensive plastic deformation. We suggest that PET can undergo, under cycling loading, both extensive drawing and actual crystallization at the crack tip to form an efficient, crack‐resistant network. Thus, PET appears to be the first thermoplastic observed to be self‐reinforcing in fatigue.
Some aspects of the miscibility behavior of polyester/halogenated polymer blends
Authors: Prud'Homme R. E. 
Published: December 2004

AbstractGlass transition temperature and depression in melting point methods are commonly used to determine the miscibility behavior of polymer/polymer blends, where at least one component of the mixture is semicrystalline. However, these methods often lead to ambiguous and even contradictory results, as can be shown by several examples. Furthermore, a comparison of the miscibility behavior of poly(vinyl chloride), poly(vinyl bromide), and poly(vinyl fluoride) with linear and branched polyesters indicates that small changes in the structure of the halogenated polymer and/or of the polyester lead to major changes in miscibility, indicating the subtle nature of the miscibility phenomenon and emphasizing difficulties in its control.
Fractography of polyethylene glycol dimethacrylate doped with polymethyl methacrylate
Authors: Atsuta M. , Turner D. T. 
Published: December 2004

AbstractThe presence of polymethyl methacrylate (PMMA) can greatly affect the properties of materials made by polymerization of ethylene glycol dimethacrylate (EGDM). Fracture surfaces, examined by scanning electron microscopy, show a much wider range of morphologies in mist regions than observed in previous work on PEGDM alone. These morphologies are attributed to the moderation of brittle fracture by localized plastic deformation. It is suggested that the effect of PMMA is due to its segregation around clusters of highly cross‐linked particles of PEGDM that, as a result, become more discrete and, hence, more susceptible to interparticle displacements during fracture. In agreement With this suggestion, the mist regions usually exhibit a particulate microstructure.
Copolymer composition as a function of molecular weight for poly(styrene‐methyl methacrylate) initiated by ethylaluminum sesquichloride
Authors: Nunes R. W. , Huang S. J. , Johnson J. F. 
Published: December 2004

AbstractThere is an increasing body of evidence showing that, for a variety of copolymers, there are significant changes in the copolymer composition over the molecular weight distribution of the polymer. In this work, we have polymerized the copolymer poly(styrene‐methyl methacrylate) using ethylaluminum sesquichloride as the initiator. The copolymers produced were fractionated using a semiprep gel permeation chromatograph. The composition of the fractions was determined using infrared spectroscopy. Results show that the percent methyl methacrylate of the copolymers was higher at both the low‐ and high‐molecular‐weight regions of the polymers.
Analysis of mixing in modified single screw extruders
Authors: Erwin Lewis , Mokhtarian Farzad 
Published: December 2004

AbstractA numerical model of mixing in single‐screw extrusion is developed which uses a two‐dimensional unsteady analogue to three‐dimensional continuous mixing. This two‐dimensional unsteady analogue uses the transverse and axial velocities to calculate an apparent tránsverse streamline velocity which is used to simulate mixing. The mixing calculations are rigorously correct for continuous mixing of well‐metered streams of equal‐viscosity Newtonian fluids in continuous mixers of constant envelope. This scheme is applied to the analysis of singlescrew extruders with stepwise varying cross‐section, particularly beginning and ending flights. The numerical simulation produces patterns qualitatively similar to those observed in mixing experiments and predicts behavior for unmodified extruders in close quantitative agreement with experiments.
Melt viscosity behavior of some engineering thermoplastics
Authors: Mendelson R. A. 
Published: December 2004

AbstractFrequently, the enhanced elevated‐temperature rigidity of engineering thermoplastics (ETPs) is a consequence of high glass‐transition temperature, and many ETPs contain aromatic ring structures in the backbone chain. These factors can lead to difficulty in melt processing, or fabrication, of parts. Thus, the definition of the melt rheology of such systems is of considerable technological, as well as scientific importance. The investigation reported here first defines the viscosity‐temperature dependence of five ETPs over a relatively narrow range of temperatures appropriate to melt processing in terms of superposition methodology. The five ETPs studied were bisphenol A polycarbonate, polysulfone, the condensation polymer of bisphenol A and mixed iso‐ and terephthalic acids, and two experimental condensation polymers: bisphenol A/isophthalic acid and 1,2 bis(4,4′‐hydroxy phenyl) ethane/isophthalic acid. Viscous flow energies of activation are examined in terms of polymer chain structure. In the second portion of the investigation it is shown that, for the latter two condensation polymers, the molecular weight, temperature, and shear rate dependence of the viscosity may be expressed in terms of a modified Carreau model. The Newtonian limiting low‐shear viscosity dependence on molecular weight and that of the shear rate shift factor (relaxation time) are found to be somewhat greater than that normally observed.
Effects of protonation on the conformational characteristics and geometry of the rod‐like benzobisoxazole polymers
Authors: Welsh W. J. , Mark J. E. 
Published: December 2004

AbstractRecent experiments on model compounds suggest that rodlike polybenzobisoxazole (PBO) and polybenzobisthiazole (PBT) chains are protonated when dissolved in highly acidic solvent. The PBO model compound can exist as a 2H+ ion, with one proton on each nitrogen atom, or (depending on the acidity of the medium) as a 4H+ ion, with two additional protons on the oxygen atoms. The PBT model compounds generally form 2H+ ions, owing to the lower basicity of sulfur atoms relative to oxygen atoms. In the present study, geometry‐optimized CNDO/2 calculations have been carried out in an attempt of predict the effect of protonation on the conformational characteristics and geometry of PBO model compounds. Values of the conformational energy vs. rotation of the endphenylenes about the heterocyclic group are calculated for cis‐PBO model compounds in the unprotonated form and as 2H+ and 4H+ ions. All three species prefer the coplanar conformation with maximum barriers, occurring at the perpendicular conformation, of approximately 8.4, 33.6, and 84.0 kJ mol−1 for the unprotonated form, the 2H+ ion, and the 4H+ ion, respectively. Steric arguments would suggest that repulsions between the acidic protons and the ortho hydrogens on the phenylenes would render the coplanar conformation more repulsive than other orientations. However, detailed analysis of the optimized geometries reveals that the rotatable bond shortens with protonation, indicating an increased bond strength and, hence, increased conjugation energy.
Rheological behavior of highly filled polymer melts
Authors: Bigg D. M. 
Published: December 2004

AbstractThe rheological behavior of highly filled polymer melts has been examined. At concentrations near the maximum packing fraction, strain‐dependent behavior was observed at strains as low as 1 percent. Selected surface treatments were shown to reduce particle agglomeration. This produced composite melts with lower viscosities and higher maximum loadings. While η* – ω plots provide information on the shear strength of the interparticle network, G′ – ω plots show evidence of phase separation.
Head‐to‐head polymers 27: Thermal degradation of head‐to‐head polyisobutylene
Authors: Malanga M. , Xi F. , Vogl O. 
Published: December 2004

AbstractHead‐to‐head polyisobutylene degrades at a maximum rate at 320°C, a temperature about 65°C lower than head‐to‐tail polyisobutylene. Under our conditions, head‐to‐tail (the regular polyisobutylene) degrades (as do many other disubstituted vinyl monomers) to a high yield of the monomer isobutylene. Surprisingly, head‐to‐head polyisobutylene also degraded, primarily to isobutylene. Liquid, low‐molecular compounds, probably dimers, were also obtained from head‐to‐tail and head‐to‐head polyisobutylene. A mechanism of this degradation is proposed.
Steady‐shear rheological behavior of the suspension of spherical particles in a second‐order fluid
Authors: Kaloni P. N. , Stastna V. 
Published: December 2004

AbstractIn this paper we study the rheological behavior of a dilute suspension of rigid spherical particles in a second‐order fluid. We extend the results of viscous fluids to discuss the expression for the bulk stress tensor of a second‐order fluid and also obtain an approximate solution to the shear flow problem of this fluid. By combing these results, we write an approximate constitutive equation for the bulk stress tensor for such a suspension and study it in a shear flow. It is found that the new equation predicts no variation in the shear viscosity, but predicts enhancement of the pre‐existing non‐Newtonian nature of the suspending fluid with regard to the normal stress functions.
Extrusion and melt spinning characteristics of thermally degraded polypropylene
Authors: Yamane Hideki , White James L. 
Published: December 2004

AbstractA basic study of the influence of thermal degradation of polypropylene on its extrudate swell and melt spinning characteristics is reported. The degradation reduces swell, changes the shape of the spinline diameter/velocity profile (i.e., the spinline apparent elongational viscosity function), and stabilizes the melt spinning process. The importance of molecular weight distribution narrowing during the degradation process is noted in these studies.
Vibrational spectroscopic characterization of rigid rod polymers: IV. Crystalline modifications of poly(p‐phenylene terephthalamide)
Authors: Shen D. Y. , Molis S. E. , Hsu S. L. 
Published: December 2004

AbstractInfrared spectroscopy (4000–50 cm−1) was used to characterize the two crystalline modifications of poly(p‐phenylene terephthalamide). Polarized studies revealed that hydrogen bonds are oriented primarily perpendicular to the film plane in both forms. We also found that the crystalline modification coagulated in water could be transformed into the other form by annealing at high temperatures.
On the application of fourier transform infrared spectroscopy to the elucidation of specific interactions in miscible polyester‐poly(vinyl chloride) blends
Authors: Varnell Daniel F. , Moskala Eric J. , Painter Paul C. , Coleman Michael M. 
Published: December 2004

AbstractFT‐IR spectroscopic studies have been performed in an attempt to elucidate the nature of the specific interactions occurring in miscible poly(ϵ‐caprolactone) (PCL)‐poly (vinyl chloride) (PVC) blends. Studies of low molecular weight analogues, polymer/solvent mixtures and blends of PCL and α‐deuterated PVC are presented. The results strongly suggest that a hydrogen bonding type of interaction between the carbonyl bond of PCL and the α‐hydrogen of PVC exists in compatible PCL‐PVC blends.
Viscoelastic properties of polyamic acid solutions—precursors of polyimides
Authors: Jenekhe S. A. 
Published: December 2004

AbstractThe rheology of polyamic acid (PAA) solutions, precursors of polyimides used in microelectronic device applications, has been investigated by dynamic (oscillatory) shear flow measurements. Frequency dependent storage and loss moduli and dynamic viscosity were measured in the frequency range 10−1 to 103 rad/s at 23°C. The storage modulus G′ (ω) and loss modulus G″ (ω) exhibited quadratic and linear dependence in frequency at low frequencies respectively, the viscoelastic fluid behavior commonly predicted for polymer solutions from many molecular theories. At high frequencies both dynamic moduli become proportional to ω2/3. The results show that PAA solutions are very high loss viscoelastic fluids, judging from the loss tangent values which far exceed unity. It is suggested that dynamic viscoelastic properties could be used to monitor the degree of imidization since there is a gradual change from viscoelastic fluids to soft viscoelastic solids to hard viscoelastic solids as PAA is converted to polyimides. Onset of non‐Newtonian flow as shown on the frequency dependent dynamic viscosity was in the range 30 to 200 rad/s. The viscoelastic constants, zero‐shear rate viscosity ηo and steady‐state compliance Je0, where also determined from the dynamic data and compared to previous steady shear flow results.