bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of chemical composition upon the radiation and electron beam resist behaviors of vinyl polymers
Authors: Helbert J. N. , Iafrate G. J. , Pittman C. U. , Lai J. H.
Published: December 2004

Chemical composition effects upon polymer electron energy absorption and radiation chemistry have been identified to develop resist design criteria. By use of Bethe's theory for electron scattering in solids, chemical incorporation of higher atomic‐numbered substituents is predicted to decrease energy absorption and increase scattering. Incorporation of chlorine or fluorine into vinyl polymers at the possible substituent sites is empirically found to have a large effect upon radiation G (scission) and G (crosslink) values. G (scission) values determined for several copolymers over a large range of compositions are found to vary linearly with composition. In contrast, G (crosslink) values are found to be generally less than those predicted from a linear extrapolation between the homopolymer values. Electron beam resist behavior is found to correlate well with the Gs/Gx ratio.
Mechanism of formation of fluted void superstructures in the coagulation of wet spun fibers and application to membranes
Authors: Hancock Tony A. , White James L. , Spruiell Joseph E.
Published: December 2004

An experimental study is reported of the origins of fluted void structures in wet spun fibers. Optical microscopy studies of the interaction of spinning solutions and coagulating bath liquids suggest these voids originate in a fingering phenomenon occurring at the interface. Further studies show that this fingering effect is generally independent of the presence of the polymer and dependent on the two low molecular weight liquids alone. In the systems investigated it is found that the occurrence of the fingering is associated with a critical value of the heat of solution. It is argued that the fingering and associated fluted void structures in wet spun fibers are due to a “Thomson‐Marangoni” type interfacial instability. This can be justified using the theory of hydrodynamic stability. Fluted void structures produced in asymmetric membranes probably have a similar origin.
Biaxially oriented poly(ethylene terephthalate) bottles: Effects of resin molecular weight on parison stretching behavior
Authors: Bonnebat C. , Roullet G. , de Vries A. J.
Published: December 2004

Uni‐ and biaxial stretching of poly(ethylene terephthalate) (PET) specimens of appropriate geometry at temperatures near the glass‐rubber transition may lead to non‐uniform deformation unless the draw ratio exceeds a critical value, the natural draw ratio, characteristic of the onset of strain hardening due to stress‐induced crystallization. Experimental results obtained in the present investigation show that natural draw ratios in uni‐ and biaxial stretching decrease with increasing resin molecular weight and with decreasing temperature. Undesirable uneven wall thickness distribution in biaxially stretched cylindrical parisons can only be prevented if draw ratios in both orthogonal principal stretching directions exceed the corresponding natural values. The minimum thickness reduction required for uniform biaxial stretching of a cylindrical parison at 95°C may vary between 12 and 5 depending on the resin's molecular weight or viscosity and this will affect the optimum design of parison geometry. The degree of unbalanced biaxial molecular orientation in the wall of cylindrical parisons stretched up to or beyond the natural draw ratios also depends on the resin molecular weight. Unbalanced biaxial orientation has been investigated by means of wide angle X‐ray diffraction and birefringence measurements as well as its effect on various properties: rigidity, yield stress, creep compliance, and dimensional stability.
Effect of aging and moisture on the reactivity of a graphite epoxy prepreg
Authors: Sanjana Z. N. , Schaefer W. H. , Ray J. R.
Published: December 2004

The effect of moisture on the curing reaction of Hercules 3501‐6/AS graphite‐epoxy prepreg was investigated. Test samples of prepreg were aged under humid conditions, while control samples were aged under identical temperature conditions but with negligible humidity. Determinations of the amounts of moisture absorbed and desorbed fom the samples were accomplished gravimetrically. Dielectric analysis was used to monitor the relative reaction rates and overall activation energies of the prepreg after various aging periods. Changes taking place in monomer concentrations were observed using high performance liquid chromatography (HPLC). As aging continued, samples aged under humid conditions displayed, significant decrease in the overall activation energy accompanied by increased reaction rates. This change did not occur in the control samples. Samples aged in high humidity showed increased conversion of monomers to polymer when compared to dry aged samples. The aging time required before the above changes became apparent was temperature dependent; the higher the aging temperature, the sooner the changes in reactivity occurred.
Predicting the shock mitigating properties of thermoplastic foams
Authors: Bigg D. M.
Published: December 2004

A procedure is presented by which the impact response of polymer foams can be predicted from basic compressive stress‐strain data. The effect of strain rate is accounted for by dividing the cushion into incremental thicknesses. The changing velocity in each increment is related to a changing strain rate by an iterative procedure incorporating experimental data taken over a wide range of strain rates. This procedure represents a considerable savings in the time required to evaluate a cushion over the currently used drop test method.
Influence of crosslinking on the moduli and impact strength of methacrylate polymers
Authors: Gomes A. S. , Timbó A. M. P.
Published: December 2004

Glassy crosslinked networks were prepared by copolymerization of methyl methacrylate with up to 5.2 mole‐percent of ethylene and triethylene dimethacrylates. The moduli of these materials were measured by tensile and two dynamics methods: forced resonance vibration and ultrasonic. Impact strength were measured using the Izod geometry and Sharpy notched samples to induce brittle fracture. The increase in the length of the crosslinking agent caused an increse in the deformability and impact strength of these materials without any effects in the moduli.
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

A 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

This 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

Non‐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

Evaluation 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

This 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

The 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

Blends 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

Earlier 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

Glass 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

The 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

There 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

A 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

Frequently, 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

Recent 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

The 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

Head‐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

In 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

A 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

Infrared 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

FT‐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

The 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.
Fracture toughness of a short‐fiber reinforced thermoplastic
Authors: Haskell W. E. , Petrie S. P. , Lewis R. W.
Published: December 2004

Thin plates of carbon short‐fiber reinforcement polycarbonate were injection molded. The mold was designed to produce a uniform melt flow across the cavity and an extended knock‐out pin was incorporated to form a circular hole at the center of the molded plate. The elastic constants of the plaques were determined using sections cut from the plate at different angles to the direction of flow. Analysis of the data showed that the plates could be treated macroscopically as being orthotropic. Microscopic observations revealed that the fiber orientation was primarily in the flow direction and was tangential in the vicinity surrounding the hole. The fracture toughness, as measured by the stress intensity (K), was determined using the compliance method. Experimental calibration curves were constructed at 0° and 90° to the axis of flow by loading specimens containing saw cuts of varying length. The resultant curves were non‐dimensionalized by incorporation of the elastic moduli, thickness, and width. The fracture toughness values were determined using a razor notch as a starter crack. The crack growth during testing was found to be stable, which could allow several determinations to be made on each plate. The effects of crack length, flow in the cavity, and fiber orientation around the hole were investigated. The fracture toughness was found to decrease with increasing crack length, but was not found to reach a limiting value within the practical range of testing. The effect of flow was also found to be significant. Specimens oriented 90° to the axis of flow showed higher toughness values. This was attributed to the fibers being oriented perpendicular to the axis of the crack. The samples tested with razor notches cut at the edge of the molded holes had still higher apparent toughness values. Similarly, this effect was explained by the higher fiber orientation shown with photomicrographs of specimens cut near the edge of the hole.
Phase relationships of rigid rod polymer/flexible coil polymer/solvent ternary systems
Authors: Hwang W‐F. , Wiff D. R. , Verschoore C.
Published: December 2004

Phase diagrams of two types of rigid rod polymer/flexible coil polymer/methanesulfonic acid (MSA) ternary systems were determined by polarized optical microscopy at ambient conditions. The rigid rod polymer is a wholly aromatic high temperature resistant (no measurable Tg) poly (p‐phenylenebenzobisthiazole) (PPBT). One of the flexible coil polymers is a wholly aromatic high temperature resistant poly (2,5′(6′) benzimidazole) (ABPBI), the other is a thermoplastic poly[2,2′ ‐(1–4‐phenylene)‐6,6′ ‐bis (3‐phenyl‐quinoxaline)] (PPQ) with Tg of 359°C. The solvent is methane‐sulfonic acid (MSA). The experimentally determined critical concentration points, Ccr, are in excellent agreement with Flory's recent theory. Total phase segregation between the polymer pair in ternary solution was predicted and observed at C > Ccr. Different decomposition mechanisms of phase separation were observed as a function of concentration.
Morphology—properties relationships in binary polyamide 6/rubber blends: Influence of the addition of a functionalized rubber
Authors: Cimmino S. , D'Orazio L. , Greco R. , Maglio G. , Malinconico M. , Mancarella C. , Martuscelli E. , Palumbo R. , Ragosta G.
Published: December 2004

The modification of an amorphous random ethylene‐propylene rubbery copolymer (EPM) has been accomplished by solution grafting of maleic anhydride molecules promoted by radical initiators, The resulting EPM‐g‐succinic anhydride (EPM‐g‐SA) and EPM have been used to obtain binary polyamide 6/EPM or polyamide 6/EPM‐g‐SA and ternary polyamide 6/EPM/EPM‐g‐SA blends by melt mixing. The formation of an EPM‐g‐PA6 graft copolymer during the blend preparation has been assumed. Different blend morphologies were observed by scanning electron microscopy (SEM) according to the nature and content of the rubber used. The tensile mechanical properties and the impact behavior of the prepared blends were investigated and correlated with the SEM analysis of the fracture surfaces. Binary and ternary blends containing 20 percent by weight of total rubber show a significant improvement of the impact properties at low temperature (−20°C) when the rubber is partly or entirely EPM‐g‐SA. In the case of PA6/EPM‐g‐SA (80/20) blend these results are related to the presence of rubbery domains of very small size strongly adherent to the PA6 matrix. In the case of 80/10/10 ternary blends, a much more complicated overall morphology is observed. Such morphology is characterized by the presence of large EPM domains, likely containing some EPM‐g‐PA6 graft molecules acting as an interfacial agent, and domains of EPM‐g‐PA6 of smaller size strongly adherent to the matrix as in the previous case.
Rheological and mechanical behavior of the UHMWPE/MDPE mixtures
Authors: Dumoun M. M. , Utracki L. A. , Lara J.
Published: December 2004

An attempt was made to melt incorporate ultra high molecular weight polyethylene, UHMWPE, into medium density polyethylene, MDPE. The behavior of the mixtures, containing up to 6 wt percent of UHMWPE, was examined using mechanical and rheological testing. The mechanical test results were found to contain large experimental errors, which makes interpretation very difficult. On the other hand, melt rheology studies, using dynamic and extensional deformations, gave direct insight into the extent and effect of blending. Degradation during the processing was evaluated by size exclusion chromatography. The degree of dispersion of the UHMWPE was examined under the optical microscope.
Thermally stimulated creep of polyethylene, polypropylene, copolymers, and blends
Authors: Demont P. , Chatain D. , Lacabanne C. , Ronarc'h D. , Moura J.‐L.
Published: December 2004

The technique of Thermo Stimulated Creep (TSC) has been applied to the study of anelastic properties of polyethylene, polypropylene, their copolymers and blends. In the temperature range −200 to 100°C, complex TSC peaks were observed in all samples, namely around 0°C, about the same temperature as for the homopolypolymer polypropylene. By applying “fractional stresses”, with a convenient choice or the loading program, these peaks have been experimentally resolved. Two components can be distinguished: 1. The “low temperature” component is characterized by mechanical retardation times following a compensation law. It has been attributed to microbrownian motions of polypropylene sequences liberated at the glass transition of the “true” amorphous regions. 2. The “high temperature” component which is influenced by thermal treatment has been assigned to microbrownian motions of polypropylene sequences liberated at the glass transition of the “constrained” amorphous regions. In block polymers, an additional TSC peak is observed around −50°C: it has been associated with the glass transition of ethylene‐propylene‐rubber (EPR) interphase. The coupling of this interphase with polyethylene and polypropylene phases is insured by diffusion of some ethylene and propylene sequences in‐EPR. At about −140°C, a TSC peak associated with the low temperature component of the glass transition of polyethylene can be distinguished in all the materials studied.
Thermokinetics of unsaturated polyester and vinyl ester resins
Authors: Lem Kwok‐Wai , Han Chang Dae
Published: December 2004

An experimental study was carried out to investigate the isothermal and non‐isothermal curing kinetics of unsaturated polyester and vinyl ester resins, using differential scanning calorimetry (DSC). Emphasis was put on investigating the effect of low‐profile additives on the curing kinetics of the thermo‐setting resins. For the study, a general‐purpose polyester resin and a vinyl ester resin were used, together with polyvinyl acetate (PVAc) as low‐profile additive, benzoyl peroxide as initiator, and N,N‐dimethyl aniline as promoter. It has been found that (1) the addition of the low‐profile thermoplastic‐additive decreases the rate of cure and, also, the final degree of cure of the resins, (2) the total heat of cure generated by isothermal cure is lower than that generated by non‐isothermal cure, and (3) the resin/initiator mixture with promoter exhibits two major exotherm peaks during non‐isothermal cure, but only a single exotherm peak during isothermal cure.
Concerning voids in polyimide
Authors: Russell T. P.
Published: December 2004

Small angle X‐ray scattering (SAXS) has been used to evaluate the size and concentration of voids in poly(N,N′‐bis‐(phenoxyphenyl)pyromellitimide), PMDA‐ODA. Analysis of the angular dependence of the scattering indicates the presence of voids ranging from 50 to 150 Å in radius. Integrated SAXS demonstrated that the volume fraction of voids was 7 × 10−4. These results were supported by measurements of the attenuation factor as a function of the sample thickness.
A study of aromatic polyester/chlorinated polymer blends
Authors: Aubin Madeleine , Prud'Homme Robert E.
Published: December 2004

A large number of studies have been devoted in recent years to the miscibility behavior of linear polyesters with chlorinated polymers, including poly(vinyl chloride) (PVC), chlorinated PVC, chlorinated poly(ethylenes), and copolymers of vinylidene chloride (Saran). However, similar studies with aromatic polyesters are lacking. It is the purpose of this paper to compare the properties of blends made of poly(ethylene terephthalate), poly(butylene terephthalate) or poly(hexamethylene terephthalate) and of various chlorinated polymers. It is shown that a high concentration of chlorine atoms is required to achieve miscibility. Moreover, there is a “miscibility window” in terms of the carbonyl concentration of polyesters, immiscibility being found for carbonyl concentrations outside this window, A similar behavior was observed before for linear polyester/chlorinated polymer blends and for polyester/polycarbonate blends. Solid state small‐angle light scattering experiments were also conducted to follow the morphology of the blends as a function of composition. Spherulites were found but their size vary with composition.
Small angle scattering from ampholytic styrene ionomers
Authors: Clough S. B. , Cortelek D. , Nagabhushanam T. , Salamone J. C. , Watterson A. C.
Published: December 2004

Small angle neutron scattering experiments were made on an ionomer synthesized from perdeuterostyrene and an ion pair comonomer. A Debye plot based on data from the sample with lower ion concentration gave a correlation length of 5.3A. Clustering is not significant in this sample. With a higher concentration of ionic groups a peak in the scattering curve is interpreted as due to clusters about 20A in diameter. These studies along with X‐ray scattering and electron microscopy also indicate the presence of larger ion rich domains.
Tensile behavior of high‐density thermosetting polyester foams
Authors: Masi P. , Nicolais L. , Mazzola M. , Narkis M.
Published: December 2004

This paper shows that the tensile properties of high‐density stiff foams having cellular structures consisting of spherical voids can be described and predicted by simple rules. These rules are derived from other known and experimentally established relationships describing particulate systems of continuous glassy matrices containing a uniform dispersion of solid glass beads.
General treatment of polymer crystallization kinetics—Part 2. The kinetics of nonisothermal crystallization
Authors: Malkin A. Ya. , Beghishev V. P. , Keapin I. A. , Andrianova Z. S.
Published: December 2004

The isothermal macrokinetic equation of polymer crystallization has been generalized to cover nonisothermal situations as well. The process of nonisothermal crystallization of poly(caproamide) has been studied experimentally. It is shown that the macrokinetic equation of the autocatalytic type can be used to solve both direct and inverse problems of nonisothermal polymer crystallization. Use of the inverse approach has made it possible to establish the value of the constants of the new kinetic equation. The general statement of the problem of nonisothermal crystallization of polymers in an inhomogeneous temperature field is considered. Inhomogeneous temperature and conversion fields have been calculated for model products of different sizes and configurations.
Elastomeric properties of bimodal networks prepared by simultaneous curing‐filling technique
Authors: Tang M.‐Y. , Mark J. E.
Published: December 2004

If the tetraethylorthosilicate (TEOS) used to end link hydroxyl‐terminated poly(dimethylsiloxane) chains is present in excess, there are two effects on the resulting network structure. First, some of the excess TEOS hydrolyzes to give in situ precipitation of reinforcing silica particles. In addition, some can cause extension of the polymer chains, particularly of the shorter chains in the case of a bimodal network. In the present investigation, the ultimate strength and toughness of such bimodal networks was found to go through a maximum with increase in the amount of excess TEOS used in the curingfilling procedure.
History and development of engineering resins
Authors: Woodhams Raymond T.
Published: December 2004

A brief perspective of the history and development of the plastics industry is outlined with special reference to engineering plastics and high performance resins. Since the birth of the synthetic plastics industry just over half a century ago, a myriad of polymeric structures have been created of which only a few generic types have attained commercial status. These basic resin types are combined in many ways as composites or blends to make available to industry over 6000 grades for use in fibers, films, coatings, adhesives, or molded shapes. Although plastics are characterized by their mechanical, electrical, chemical, or physical properties, it is their selling price that tends to dominate the volume production of each resin. Today, the modern plastics engineer employs remote‐access interactive computer databanks to conduct design and feasibility studies employing the full inventory of resin grades in his assessment. A final section reveals current attempts by researchers to impart extraordinary strength and modulus to conventional plastics by means of solid phase processing, whereby polymeric chains are uncoiled and aligned to produce remarkably tough materials which are likely to challenge the supremacy of steel.
Kinetics of acetylene polymerization and structures of polyacetylene
Authors: Chien James C. W.
Published: December 2004

The kinetics of acetylene polymerization have been studied as a function of monomer pressure, catalyst aging and concentration, Al/Ti ratio, and temperature. The rate constants of chain propagation and termination and their activation energies have been determined, The Mn of polyacetylene has been obtained using a radioquenching technique, and was found to vary from 500 to 250,000. Wide angle X‐ray diffraction showed the polymer to be highly crystalline but the crystallites are disordered. The crystal structures of cis and trans polyacetylene have been obtained from the fiber electron diffraction patterns. The c‐axis is the polymer chain axis which is along the fiber axis. The basic morphological entity is the microfibrils of 2 to 3 nm diameter which aggregate to form 20 to 30 nm fibrils.
The development of molecular orientation and morphological texture in thermotropic copolyesters
Authors: Viola G. G. , Baird D. G. , Wilkes G. L.
Published: December 2004

Liquid crystalline polymers can be processed to form high strength/modulus materials. In processing these materials, it is apparent that molecular orientation is an important factor in determining the physical strength of the processed materials. In this study a systematic investigation was carried out to determine how a thermotropic copolyester of parahydroxybenzoic acid (PHB) and polyethylene terephthalate (PET) responds to two basic types of flows: shear and extensional flow. This was accomplished by preparing sheared and extended samples under controlled conditions of temperature and flow history. Sheared disks were prepared using a disk and plate geometry of a Rheometrics Mechanical Spectrometer (RMS model 605), while extended ribbons were prepared using a slit die attached to an Instron capillary rheometer. Two copolymerer compositions of 60 mole percent and 80 mol percent PHB were investigated. The sheared disks and extended ribbons were investigated for molecular orientation and morphological textures using wide angle x‐ray scattering (WAXS) and scanning electron microscopy (SEM) analysis, respectively. It was found that extensional flow has a greater capacity for orienting such materials than shear flow. Samples annealed at their softening points for 1 minute (240°C for the 60 mole percent PHB/PET copolymer and 300°C for the 80 mole percent PHB/PET copolymer) showed no significant loss of orientation, indicating that once orientation is produced it may remain in the melt for a long period of time. Sheared samples prepared by shearing the sample while cooling showed significantly higher degrees of orientation than those not cooled while being sheared. This may indicate that a minimum stress level exists for the production of orientation in shear flow.
An empirical correlation for polymer self‐diffusion data in the dilute and semidilute concentration regimes
Authors: Hanley Brian , Tirrell Matthew
Published: December 2004

An expression is presented which can be used to correlate and predict, in an empirical fashion, polymer self‐diffusion coefficients in solution over a wide range of concentrations and molecular weights, and whose parameters can be established with a minimal amount of data. Predictions thus made have been found to agree well with the limited amount of available experimental data over the entire concentration‐molecular weight spectrum studied to date. This is in marked contrast to other available expressions, whose validity is confined to a narrow range of concentrations and/or molecular weights.