bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientation in amorphous polymers I. Preparation and testing of oriented samples
Authors: Vrentas J. S. , Vrentas C. M. , Bhombal A. H. , Lahalih M. S.
Published: May 2005

Orientation effects in amorphous polystyrene are studied using a uniaxial stretching experiment. The rheological properties of the polymer are determined from an analysis of creep data obtained from the tensile apparatus, and oriented polymer samples are prepared at different extension ratios and rates of stretching. From birefringence and tensile strength measurements on oriented samples of polystyrene, it is shown that the tensile strength is not a unique function of the birefringence. It is proposed that the tensile strength may depend not only on the average orientation, as reflected by the birefringence, but on which portion of the relaxation spectrum is preferentially oriented.
Polymer blends from polyurethane and poly(methyl methacrylate) by reaction injection molding
Authors: Kircher K. , Mrotzek W. , Menges G.
Published: May 2005

The simultaneous production of polyurethane (PUR) and polymethyl methacrylate (PMMA), starting from a mixture of polyol, polyisocyanate, and vinyl monomer, results in 2‐phase polymer alloys. A simultaneous crosslinking of the PMMA is unable to prevent phase separation during the curing reaction; interpenetrating polymer network (IPN) structures were not found, Grafting the PMMA onto the PUR through the incorporation of 2‐hydroxyethylacrylate resulted in single‐phase systems. Various material combinations did not show, with a relatively high PMMA content, any poorer properties than the straight PUR. A major advantage of incorporating low‐viscosity vinyl monomers lies in the fact that high‐viscosity polyurethane starting components that are otherwise difficult or impossible to process can be processed here without problem.
Thermal stability of polyethylene terephthalate
Authors: Jabarin S. A. , Lofgren E. A.
Published: May 2005

The kinetics of thermal and thermal‐oxidative degradation of polyethylene terephthalate (PET) have been investigated as a function of melt temperature, melt residence time, melt environment, and drying environment. Rates of thermal and thermal‐oxidative degradation were measured in terms of: weight loss of volatile degradation products, decreasing inherent viscosity, and increasing carboxyl end group concentration. Thermal‐oxidative degradation was also investigated by Differential Scanning Calorimetry. Calorimetric results show that thermal‐oxidative degradation of PET is an exothermic reaction, with an apparent activation energy of 117 kJ/mol. Melt temperature, melt residence time, melt environment, and drying environment have all been found to affect the degradation of PET. Analysis of inherent‐viscosity kinetic data has been carried out, utilizing existing theories based on a random chain scission mechanism. Activation energies of 117 and 159 kJ/mol have been calculated for air‐dried and vacuum dried samples respectively.
New model of physical aging effects in enthalpy recovery
Authors: Rendell R. W. , Lee T. K. , Ngai K. L.
Published: May 2005

A new model of enthalpy recovery is presented which is based on a microscopic‐relaxation theory. The microscopic basis and manner of construction of the enthalpy‐recovery model are discussed in detail. The qualitative features of the model are illustrated using numerical simulations. In particular, the way in which the effects of physical aging are produced is discussed. The qualitative features observed in differential‐scanning‐calorimetry experiments are reproduced, and a program of extensive simulations is proposed and outlined. The present microscopically based model is also used to suggest interpretations and possible modifications of currently used phenomenological enthalpy recovery models.
Physical aging of poly(methyl methacrylate) in the nonlinear range: Torque and normal force measurements
Authors: McKenna G. B. , Kovacs A. J.
Published: May 2005

Cylindrical specimens of poly(methyl methacrylate) (PMMA) were quenched from above the glass transition and subsequently tested in torsion. Torque and normal‐force relaxation responses were recorded simultaneously. The experiments were performed at 40, 60, and 80°C, at increasing aging times and at deformations ranging from γ = 0.0027 to γ = 0.074. It was found at 40 and 60°C, that, contrary to the classical picture of aging, the small‐deformation torque‐relaxation curves could not be superposed by any combination of vertical and horizontal shifts. On the other hand, at 80°C, and in the nonlinear deformation range even at lower temperatures, the relaxation curves are superimposable simply by horizontal shifts, but as γ increases they involve decreasing values of the double‐logarithmic shift rate. At the same deformation level, however, the shift rate for the normal force is significantly higher than is that for the torque over most of the γ range investigated.
Kinematics, dynamics and stability of the tubular film extrusion of various polyethylenes
Authors: Kanai Toshitaka , White James L.
Published: May 2005

A basic study of the kinematics, dynamics, and heat transfer occuring during tubular film extrusion of polyethylene is outlined. Three rheologically characterized polyethylenes, a low‐density polyethylene (LDPE), a linear‐low‐density polyethylene (L‐LDPE), and a high‐density polyethylene (HDPE) were used in this study. The kinematics and stability of the tubular film process were investigated over a wide range of blow‐up ratios, drawdown ratios, and frost‐line heights. Local deformation rates along the bubble have been determined. Regions of stability and instability are described. Tensions and inflation pressures have been measured and expressed in terms of locol elongational viscosities. Temperature profiles along the bubble were determined and interpreted in terms of local heat transfer coefficients. Positions of crystallization and temperature profiles have been noted and used to estimate rates of crystallization. The characteristics of the LDPE, LLDPE, and HDPE are contrasted.
Thermal catalytic polymerization of mortars impregnated with styrene‐acrylonitrile
Authors: Gadalla Ahmed M. , El‐Derini Mohamed E.
Published: May 2005

Standard test specimens of mortar were cured under water for 15 days to achieve satisfactory strength. They were dried without allowing dehydration reactions to occur, evacuated to 40 millimeters (mm) Hg, and impregnated with a styreneacrylonitrile comonomer, which gives the highest strength after polymerization. Positive pressure of 0.6 N/mm2 was applied and thermal catalytic polymerization was carried out. Optimum initiator concentration was found to be 2 percent. Strength (compressive and tensile) increases with polymerization temperature up to 120°C, above which rapid deterioration occurs due to monomer loss, production of short chains with high polymerization rates, and the possibility of polymer degradation at high temperature. Optimum polymerization period of' 10 hours was selected. Inexpensive methods for field polymerization were tried at 95°C. Hot water yields a strength more than double that obtained with a, flow of hot air and about 80 percent of that obtained radiolytically. While hot air accelerates evaporation, hot water forms a hydraulic head above the capillaries and decreases the monomer losses tremendously.
A note on the role of diffusion during the inflation of a tubular viscoelastic film
Authors: Chung Tai‐Shung
Published: May 2005

A mathematical simulation of the effect of diffusion on the inflation of a cylindrical polymer film has been developed. The rheological constitutive equation of polymer was assumed to obey an Oldroyd fluid B type. Calculated results indicate that the diffusion coefficient and solubility of the gas have a profound influence on the film or membrane expansion.
Free radical solution oligomerization of styrene in a continuous‐stirred tank reactor train
Authors: Hsu Keh‐Ying , Chen Show‐An
Published: May 2005

For free radical oligomerization of styrene, a scheme for calculating the molecular weight distribution and conversion in a continuous‐stirred tank reactor (CSTR) train is developed, which also allows the calculation of molecular weight distribution (MWD) for batch reaction. Calculations show that under conventional or near dead‐end condition: (1) increasing initial initiator concentration, reaction time and reaction temperature, and decreasing initial monomer concentration cause P̄n and P̄w to decrease and MWD to narrow; (2) increasing initial initiator concentration, reaction time and reaction temperature, and increasing monomer concentration cause monomer conversion to increase; (3) a single CSTR gives a lower rate of oligomer production, but a narrower MWD than does a batch reactor.
Measurement of mixing in polymer melts by focused ultrasound
Authors: Erwin Lewis , Dohner Jeffery
Published: May 2005

This paper outlines the development of an acoustical technique for measuring the dispersion of an additive in a polymer melt. It included a justification of the use of sound over other interrogating methods and an analysis of the acoustical system's operation. Results for dispersions of liquid or solid additives were shown. It was demonstrated that this system could detect the presence or absence of large particles in melts filled with small particles.
Radiation‐degradation susceptibility studies of vinyl terpolymers: Search for improved electron beam resists
Authors: Wallace Easley , Chen Chi‐Yu , Pittman Charles U. , Kwiatkowski Joe H. , Cook Charles F. , Helbert John N.
Published: May 2005

To develop polymer systems with improved lithographic resist properties, terpolymers of methyl methacrylate/methacrylonitrile/methyl α‐chloroacryate (MMA/MCN/MCA), methyl methacrylate/methacrylonitrile/α‐chloroacrylonitrile (MMA/MCN/ACAN), and methyl methacrylate/methacrylonitrile/vinylidene chloride (MMA/MCN/VDC) were prepared by emulsion polymerization. Also one methyl methacrylate/ methyl α‐chloroacylate/α‐chloroacrylonitrile (MMA/MCA/ ACAN) terpolymer was prepared. The radiation susceptibilities of these terpolymers were measured using the 60Coγ‐irradiation method. Molecular weights were determined both by membrane osmometry and gel permeation chromatography. All terpolymers exhibited higher radiation‐degradation susceptibilities than poly(methyl methacrylate). The Gs values did not follow the general trend, previously observed with MCN/MCA copolymers, of being directly proportional to the respective terpolymer compositions. In some cases, the addition of small quantities of α‐chlorine‐containing monomers caused Gx to increase. This observation greatly differs from those observed for copolymer systems such as MMA/MCA, MCN/MCA, MMA/ ACAN, etc. studied previously. Terpolymerization gives highly soluble polymers especially suitable for wet development by many solvents. This is an important consideration for polymers with high mole fractions of methacrylonitrile (MCN) or vinylidene chloride (VDC) which are rendered soluble in development solvents. The electron‐beam sensitivities were obtained for samples of three classes of the terpolymers and they were higher than that of PMMA. For example, at 20Kev a 62/34/4 MMA/MCN/MCA terpolymer exhibited a sensitivity of 1.3 × 10−5 coulombs cm−2 at l/lo = 1. The introduction of ACAN narrows the working range for positive resist behavior. For example MMA/MCN/ACAN(41/40/19) has a sensitivity of 8.3 × 10−6 coulombs cm−2 at l/l0 = 0.6 but it crosslinks at 1 − 1.3 × 10− coulombs cm2. The MMA/MCN/VDC(21/76/3) polymer was about 25 times more sensitive than PMMA (7 × 10−6 C cm−2 at l/l0=1).
Damping modulus studies of poly(dimethylsiloxane)‐bisphenol‐a‐polycarbonate block copolymers
Authors: Maung W. , Williams H. Leverne
Published: May 2005

Random multiblock copolymers of bisphenol‐A‐polycarbonate and poly(dimethylsiloxane) were hot‐pressed or solvent cast into films which were studied by dynamic mechanical methods over the range 11 to 110 hertz (Hz) and 100 to more than 2200 Hz, respectively. The samples were studied also by differential‐scanning calorimetry. The two phases are separated well in spite of the low‐molecular weights of the blocks. This separation is altered by thermal history and by the solvent medium when solvent casting is used to prepare the films. The damping properties do not vary greatly with frequency. Damping is greatest near the glass‐transition temperatures of the two components. The expansion of the block copolymer with heat appears to be retarded by the polycarbonate phase until the glass transition of that phase is approached.
Polymer molecular‐weight distribution from dynamic melt viscoelasticity
Authors: Wu Souhenc
Published: May 2005

A method is developed by which polymer molecular weight and its distribution can be accurately determined by deconvolution of dynamic melt viscoelastic properties in the terminal and plateau zones. The method is illustrated with a series of monodisperse (narrow‐distribution) and polydisperse (broaddistribution) polystyrenes. The Mn, Mw, and Mn/Mw values obtained are in excellent agreement with those determined by light scattering, osmometry and gel permeation chromatography with less than 5 to 10 percent error. The differential molecular‐weight distribution curves obtained coincide wall with those obtained by gel permeation chromatography. The method is applicable to insoluble as well as soluble polymers.
Surface embrittlement of ductile polymers: A fracture mechanics analysis
Authors: Roliand L. , Broutman L. J.
Published: May 2005

The embrittlement of ductile polymers resulting from outdoor weathering or aging or from the application of brittle surface coatings is explained using fracture mechanics principles. It is shown that in order for surface embrittlement to occur, the brittle surface should have a dynamic stress intensity factor at the brittle/ductile interface that exceeds the arrest toughness of the ductile polymer. This phenomenon is modeled using duplex tensile specimens fabricated from poly(methylmethacrylate) (brittle layer) and polycarbonate (ductile substrate) as well as from styrene‐acrylonitrile and acrylonitrile‐butadiene‐styrene copolymers.
Free radical polymerization of methyl methacrylate at high temperatures
Authors: Baillagou Pierre E. , Soong David S.
Published: May 2005

Free‐radical polymerization of methyl methacrylate in a tubular reactor has been conducted at above‐Tg temperatures. A salient feature of these experiments is the very efficient control of reactor temperature by vapor‐liquid equilibrium of the polymerizing mixture via monomer evaporation. The system pressure thus provides a powerful control variable, restricting the temperature in the entire reactor by changing the monomer evaporation rate. In the range of our experimental conditions, the temperature and pressure in the reactor follow the Antoine equation closely. High temperature runs also reduce the length requirement of the reactor. However, molecular weight averages of the products are not impressive, unless slow‐burning initiators are used. Modeling of above‐Tg reactions has been attempted at two‐levels of sophistication. A plug‐flow model gives predictions in good agreement with our experimental temperatures and conversion data. The predicted molecular weights are also consistent with the experimentally observed values. However, the more elaborate rheokinctic model suggests that the superficial agreement between model and experiment is due to initiator burn‐out, which limits the final conversion to within 40 percent. The liquid layer next to the reactor wall can never be so viscous as to form a stagnant deposit, due to this conversion limitation. The velocity profiles are thus not very much distorted, and a plug‐flow model is adequate. With a slow‐burning initiator and a sufficiently long reactor, skewing of velocity profile and reactor channeling will eventually emerge. Hence, the rheokinetic model must be evoked to model the system under such conditions.
Shear deformation under impact conditions
Authors: Sjoerdsma S. D. , Boyens J. P. H. , Mooij J. J.
Published: May 2005

The deformation behavior that results from falling weight impact testing with flat‐headed darts is analyzed in terms of elasticity and plasticity. From a comparison of the time and temperature dependence of the yield stress that is observed during a falling weight test with the same dependences of the yield stress during simple shear tests, it is concluded that the use of flat‐headed darts results in strong shear loading. Consequently most of the plastic deformation takes place by shear flow. Of practical interest is that this leads to a simple dependence of the yield stress during the impact test and the impact energy on the plate thickness. Furthermore, for a number of cases this result allows a direct conversion of temperature effects to time effects. In practice this means that it is possible to simulate the impact behavior at very high impact rates simply by performing impact tests at lower temperatures.
Flow of polymeric melts in short tubes
Authors: Isayev A. I. , Chung B.
Published: May 2005

In an attempt to further understand the flow of polymeric melts through gates in injection molding, the present investigation deals with measurement of pressure drops during isothermal extrusion of fiber‐filled and unfilled polystyrene, polypropylene, and polycarbonate melts in short tubes with sudden contraction at high shear rates typical of injection molding. Flow curves for these materials have been determined over a wide range of shear rates at various temperatures by using a capillary rheometer and extruder. Measurements indicate that rheological properties of fiber‐filled melts after injection molding differ from those of fresh samples. Moreover, it has been found that decreasing the tube length increases the slope of the curve for pressure drop vs. Volumetric flow rate. Extra pressure losses due to end effects have been determined which show that at high shear rates these losses can reach levels as high as 100 bar, with the effect being higher for the fiber‐filled melts. By using a viscoelastic consitutive equation, the extra pressure losses have been separated into entrance and exit losses. Model parameters required for this calculation have been determined from viscosity‐shear rate curves for the melts. For various polymers, master curves useful for industrial applications have been constructed for the extra pressure losses.
Influence of the molecular structure on the melt strength and extensibility of polyethylenes
Authors: La Mantia F. P. , Acierno D.
Published: May 2005

Melt strength (MS) and breaking stretching ratio (BSR) data relative to polyethylenes with different molecular structure (high density (HDPE), low density (LDPE), and linear low density (LLDPE)) are shown. HDPE and LLDPE samples show high breaking stretching ratio and low melt strength values. The LDPE samples exhibit very large melt strength values but low breaking stretching ratio values. For the last mentioned samples, differences are shown in the non‐isothermal elongational behavior between samples polymerized with tubular and vessel technology. For all the samples, MS decreases with increasing melt index while BSR increases with melt index.
The effect of tension during drying on the structure and mechanics of poly(p‐phenylene benzobisthiazole) fibers
Authors: Pottick L. A. , Farris R. J.
Published: May 2005

The effect of tension during drying on the structure and mechanics of poly(p‐phenylene benzobisthiazole) (PBT) fibers has been investigated. The application of tension during drying on PBT fibers spun from anisotropic solutions of PBT/Polyphosphoric acid (PPA) results in an enhancement of tensile modulus and yield strength with a reduction in strain to break. The alterations in the tensile properties can be attributed to the straightening of the wet fibrillar network and the reduction in the axial compressive stresses which develop during drying. Modifications in the mechanical behavior of PBT fibers through tension drying can be achieved regardless of the initial spin draw ratio of the fiber. Additionally, tension drying provides a means to maximize the potential stiffness of PBT fibers which have a low spin draw ratio. Lastly, these investigations show that in the processing of PBT fibers, preventing the onset of buckling and aligning the wet fibrillar network with tension during drying is more effective in enhancing the tensile properties than straightening the dried buckled fibers.
Smoothing the electromagnetic heating pattern in polymers
Authors: Inkpen S. L. , Melcher J. R.
Published: May 2005

In the production of polymers, particles and fibers are often added for coloring and/or improvement of mechanical, electrical, and thermal properties. Carefully choosing the electrical properties and size of these additives can allow manipulation of the electrical properties of the composite so that the material can then be heated in both the electric and magnetic fields. Heating can be induced by fields at microwave frequences, where the electric and magnetic fields tend to be concentrated in different regions, or by fields that are quasistatic. These features add a degree of freedom in smoothing the total heating pattern. Models for predicting the electrical properties with the addition of particles or fibers are developed and verified experimentally. Engineering guidelines are established in choosing the electrical properties and size of the additives. Experimentally, a rectangular cavity at 2.45 GHz is used to heat a casting resin with a 5.7 micrometer aluminum powder additive, demonstrating the dramatic smoothing in the heating, pattern made possible by using these additives. Some examples are also suggested to indicate the use of this technique in quasistatic heating configurations.
Experimental and theoretical evaluation of a spiral disc extruder
Authors: Krein H. L. , Plumtree A. , Rudin A.
Published: May 2005

A 5‐inch diameter disc extruder was operated with a commercial polypropylene polymer to provide comparison data and the model predictions were compared to machine performance as a function of extrusion conditions and polymer characteristics. The mathematical model used for comparison has been described previously by the authors.
Solid‐phase flow behavior of polymers
Authors: Halldin G. W. , Lo Y. C.
Published: May 2005

The solid‐phase flow behavior of polymers is very important in the mechanical performance and testing of solid polymers and in solid‐phase forming. This paper includes an extensive characterization of the solid‐phase flow curve for a wide range of commercially important polymers. Rigid semicrystalline, ductile semicrystalline, tough ductile amorphous, and two‐phase ductile amorphous resins were studied in both tension and compression. It is clearly shown that semicrystalline polymers normally exhibit a load drop upon yielding due only to geometrical strain softening while the amorphous polymers exhibit yield drops due to material strain softening. New flow equations are given that closely model the observed behavior for all types of materials, over the entire range of strain.
Polymerization and crystallization behavior of anionic nylon 6
Authors: Iobst Stanley A.
Published: May 2005

The kinetics of the activated anionic polymerization of caprolactam to nylon 6 was studied by the adiabatic temperature rise technique. This allowed very rapid reaction conditions to be studied. The polymerization was activated by diisocyanate and catalyzed by sodium caprolactamate, produced in situ by the addition of sodium hydride. The temperature rise measurements were used to generate Arrhenius curves of the rate data. Several isocyanates were investigated, all giving similar rate curves. The reaction rate was reduced, however, when the activator concentration exceeded the catalyst concentration. To model the actual rapid molding conditions, time vs. temperature reaction profiles were measured for thin plaque castings. In these reaction profiles, two successive exotherms were observed. The first was the polymerization exotherm, and the second was determined to be the crystallization peak. This second exotherm allowed the direct observation of crystallization times within the closed molds. The crystallization times were found to depend strongly on the mold temperature and to a lesser extent on the monomer temperature. The crystallization times were minimized at a 150°C mold temperature. At higher temperatures, the crystallization rate was significantly slower, while at lower temperatures, the slow rate of polymer formation delayed the onset of crystallization. This study has demonstrated the value of using temperature monitoring as a means of studying the polymerization and crystallization behavior of nylon.
Rheological properties of a liquid crystalline copolyester
Authors: Bhattarcharya S. K. , Misra A.
Published: May 2005

Rheological studies of an experimental liquid crystalline (LC) copolyester were carried out using a capillary rheometer and a cone and plate rheometer. Rheological characteristics of the polymer in the nematic state were observed. The nematic melt was found to be pseudoplastic and the degree of pseudoplasticity varied with shear rate. Melt viscosity was found to decrease with shear rate. Negative die swelling was observed at the exit of the capillary rheometer at temperatures marginally above the solid‐nematic transition temperature of the polymer and was also found to be a function of shear rate. The dynamic mechanical properties of the polymer were studied as a function of temperature. The activation energies of flow and of dynamic mechanical deformation were calculated.
Ultrasonic processing of thermoplastic foam
Authors: Byon Sung K. , Youn Jae R.
Published: May 2005

Ultrasonically induced bubble formation for the production of thermoplastic foam was investigated experimentally and theoretically as a basic study. A general purpose polystyrene and blends of low density polyethylene and polyethylene wax were saturated with nitrogen gas under various pressures and the ultrasonic excitation was applied to the polymer system upon release of gas pressure. The ultrasonic nucleation of bubbles in the polymer matrix was modeled by utilizing the classical nucleation theory. The negative pressure generated by the ultrasonic excitation was considered as the environmental pressure at the moment of nucleation. The experimental results showed that the heterogeneous nucleation must be used for ultrasonic foaming of the viscous fluid and the homogeneous nucleation for the low viscosity fluid. The theoretical analysis also indicated that the ultrasonic nucleation can be applied to the production of thermoplastic foam if the ultrasonic excitation generates large enough negative pressure.
Measures of mixing in laminar flow
Authors: Bigio David , Stry William
Published: May 2005

The general domain in which this work resides is that of mixing in creeping flows. Mixing, in this context, refers to the stretch of an interfacial line, or area in a strain field. The advancement of mixing technology is applied to the design of continuous mixers used in polymer processing. The geometric designs included single screw extruders, static motionless mixers, and co‐ and counter‐rotating twin screw extruders. The co‐rotating twin screw extruder was chosen to be studied in detail since it enjoys wide applications and, for which, little understanding of the contribution to mixing in the different screw geometries is known. In order to evaluate the rate of mixing for the non‐uniform strain history flows, the method for measuring mixing had to be reexamined and broadened. An automated method has been developed which incorporates a digital camera and a computer to analyze the cross‐sections of interest. Two measures of mixing—the correlation function and the distribution function—are developed to describe mixing in these regimes. These measures are applied successfully to the mixer geometries revealing subtle differences as to the nature of mixing in each.
Dynamic‐mechanical and dielectric characterization of PEEK crystallization
Authors: D'Amore A. , Kenny J. M. , Nicolais L. , Tucci V.
Published: May 2005

Dynamic‐mechanical and dielectric characterization of the cold crystallization of PEEK has been performed in order to develop a non‐destructive evaluation method of crystallinity in thermoplastic matrices. The Avrami approach is applied here to describe the Poly(ether ether ketone) (PEEK) crystallization kinetics after an appropriate reduction of dynamic‐mechanical and dielectric parameters. Avrami exponents obtained from dielectric characterization are comparable with those obtained with DSC measurements reported in literature, while the exponents obtained from the dynamic‐mechanical characterization are higher, reflecting also changes in the aspect ratio of the growing crystals. Variations in the glass transition temperature detected during cold crystallization are analyzed and analogies between PEEK and PET are discussed.
Polymer blends containing liquid crystals: A Review
Authors: Dutta D. , Fruitwala H. , Kohli A. , Weiss R. A.
Published: May 2005

This paper reviews the literature of polymer blends containing low and high molar mass liquid crystals. Low molar mass liquid crystals have been used as plasticizers for thermoplastic polymers and in applications such as electrooptics, optical recording media, and membranes. High molar mass liquid crystalline polymers have been primarily used in polymer blends as processing aids and as an incipient reinforcing phase for “self‐reinforced” materials. This review discusses the phase behavior, rheology, and mechanical properties of these blends.
On the uniaxial extensional flow of polystyrene/polyethylene blends
Authors: Utracki L. A. , Sammut P.
Published: May 2005

The uniaxial extensional flow behavior of polystyrene/low density polyethylene blends (PS/LDPE) was studied using a Rheometrics Extensional Rheometer, Model RER‐9000, at 150°C within the range of the extension rates \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} = 0.0005 to 1.0 (s−1). The measurements were repeated several times at each deformation rate to ascertain reliability. The effect of the suspending silicone oil was found to be negligible.
Reactive processing of polystyrene‐co‐maleic anhydride/elastomer blends: Processing‐morphology‐property relationships
Authors: Willis J. M. , Favis B. D. , Lunt J.
Published: May 2005

The morphology and impact properties of polystyrene‐maleic anhydride/bromobutyl rubber blends have been studied as a function of interfacial modification and melt processing conditions. It is found that dimethylaminoethanol (DMAE) serves as a reactive compatibilizing agent for these blends and that the addition of DMAE results in a five‐fold reduction In the size of the dispersed phase. Evidence for covalent bond formation between the DMAE and the elastomer and reactive polystyrene phases is presented. The volume average diameter of the minor phase increases significantly as the screw rotation speed and the material throughput increase. In fact, control of various material and processing parameters can be used to effectively control the particle size distribution during compounding. Impact strength measurements are shown to be clearly dependent on the quantity of DMAE in the system as well as the concentration of elastomer. Saturation of the interface with DMAE is shown to be an important consideration.
Reflection methods for the study of polymer interfaces
Authors: Walsh David J. , Sauer Bryan B. , Higgins Julia S. , Fernandez Marisa L.
Published: May 2005

The direct study of polymer Interfaces is very difficult. Small angle scattering methods have been most successfully applied to block copolymer Interfaces where the morphology is well known. Other techniques such as electron microscopy, Rutherford back scattering, and forward recoil spectroscopy generally only give resolution of the order of 10 nm. Here we describe two techniques which have only recently been applied to polymer interfaces, neutron reflection, and spectro‐scopic ellipsometry. Both reflection techniques examine planar samples and give compositional information in the depth direction. Neutron reflection gives a resolution of 0.5 nm and spectroscopic ellipsometry may give better than 5 nm. We will describe experiments using neutron reflection which measure the inter‐facial thickness between two immiscible polymers and experiments using both techniques which measure the interdiffusion of miscible polymers. Other applications and limitations of the techniques will also be discussed.
Poly(ethylene terephthalate) crystallization as a method for microlithography
Authors: Sonnenschein M. F. , Kotliar A. M. , Roland C. M.
Published: May 2005

Thermal lithography on poly(ethylene terephthalate) (PET) is carried out by inducing crystallization through selective exposure of amorphous films to Infrared radiation. The obtained images can be smaller than the wavelength of the CO2 laser light. This circumvention of the diffraction limit is accomplished by taking advantage of the non‐linear temperature dependence of the crystallization rate. The optical marking process is reversible through simple melting of the crystalline images. The complementary process, selective melting of an initially crystalline film, can also be accomplished. The use as a heat sink of a mask which forms the image pattern is demonstrated.
Accelerated test for evaluating slow crack growth of polyethylene copolymers in igepal and air
Authors: Ward Andrew L. , Lu Xici , Brown Norman
Published: May 2005

The time for brittle failure by slow crack growth for 22 polyethylene copolymers was measured in Igepal and air. The notched tensile tests were conducted in Igepal and air at 50°C and 4.2 MPa and in air at 80°C and 2.4 MPa. For failure times less than 103 min, the difference between the Igepal and air environments was not measurable. As the failure time increased beyond 103 min, the ratio of failure in air compared to that in Igepal increased so that for the very highest failure times of 5 × 105 to 108 min in air, the failure time in Igepal was reduced by 25—50 times. The correlation between the Igepal and air tests was generally good with respect to all types of polyethylene. However, a separation of the polyethylenes with respect to their comonomer, butene, hexene, or octene improved the correlation. The resistance to slow crack growth of all the current commercial polyethylene copolymers can be assessed by a notched tensile test in Igepal in about a week or less.
The manufacture of continuous polymeric filaments by the melt‐blowing process
Authors: Kayser John C. , Shambaugh Robert L.
Published: May 2005

This paper presents an experimentally‐based analysis of the continuous filament regime of the melt‐blowing process. The experiments were performed with a versatile air‐polymer die, several die operating temperatures, and three different polymer feed resins. The measurements discern the effects upon the final fiber diameter of the following input parameters: die dimensions, die temperature, polymer feed resin, and both the air and polymer mass flow rates. An empirical model equation is developed which relates these input parameters to the final fiber diameter. In addition, the conditions which result in a transition of the filament from continuous (or stable) to discontinuous (or unstable) are quantified. The model equation and the transition or stability information are then used to predict the behavior of the melt‐blowing process for a wide range of case studies involving the input parameters noted above. The data and empirical model are of considerable utility for developing new die designs, for comparison with theoretical models, for predicting fiber stability, and for explaining the behavior of current industrial melt‐blowing processes.
Mathematical model and experimental investigation of polycarbonate pellet drying
Authors: Munjal Sarat , Kao Che‐I
Published: May 2005

An easy to use, spreadsheet based, mathematical model for drying of strand cut polymer pellets has been developed and experimentally verified. This particle‐scale model is based on internal mass‐transfer controlled diffusion in the pellet. Examples of its usage in correlation and prediction of the effects of the drying‐gas temperature, humidity, and pellet dimensions are presented. Application of the particle‐scale model to the design of a countercurrent hopper drier is discussed. Even though examples are limited to water removal from poly(bisphenol‐A)carbonate pellets, the model is general and may be used for the removal of other non‐solvating low‐concentration molecules from polymers with isotropic morphology.
Impact modification of styrene‐acrylonitrile copolymers by methyl methacrylate grafted rubbers
Authors: Keskkula H. , Kim H. , Paul D. R.
Published: May 2005

Monodisperse methyl methacrylate grafted latex rubber (MMA‐g) particles (0.12‐0.13 µm) have been used for the impact toughening of a series of styrene‐acrylonitrile (SAN) copolymers of varied AN content. It was found that the MMA‐g particles are most effective in toughening SANs containing about 25 to 34% AN. Mechanical properties, interphase adhesion, mechanical dilatometry, and phase morphology by transmission electron microscopy were determined on blends containing 20‐30% rubber. Also, the miscibility range of SANs and poly(methyl methacrylate) (PMMA) graft was considered in attempting to analyze the relationships between the mechanical properties and the characteristic features of the blends. Issues relating the impact strength and deformation mechanisms, interphase adhesion, and particle morphology are discussed. It appears that the high impact strength of some of the blends may be caused primarily by certain morphological features such as particle clustering or small interparticle distances. Thus, craze initiation, shear yielding, and significant matrix deformation may all contribute to the overall ductility of the blend.
Fluidity and optimum packing in suspensions of mixed dissimilar particles
Authors: Tsenoglou Christos , Yang Soohyeon
Published: May 2005

This is a study on the rheological properties and packing efficiency of a fluid suspension, composed of a mixture of two dissimilar particulate species. A generalized analytic expression for the viscosity of the blend is first developed, and then utilized to derive quantitative ways of maximizing the fluidity and optimizing the filling capacity of the composite system. These, results are compared with earlier experimental and theoretical findings, and with the rheological measurements performed in the course of this work on a series of calcium carbonate‐carbon black suspensions in poly‐dimethylsiloxane.
Structure and filtration properties of melt blown polypropylene webs
Authors: Lee Youngchul , Wadsworth Larry C.
Published: May 2005

Polypropylene melt blown webs have been studied in terms of the relationships among the processing conditions, structure, and filtration efficiency. The effects of the processing conditions on filtration efficiency to aerosolized latex particles, pore size, fiber diameter, and air permeability have been investigated. The melt blowing process conditions investigated in this study were die and air temperatures, die‐to‐collector distance, and attenuation air flow rate at the die. The filtration efficiency has been found to increase linearly as mean pore size decreased. The degree of fiber‐entanglement increased, therefore, the pore size and air permeability decreased with increasing processing temperature, increasing air flow rate at the die, or decreasing die‐to‐collector distance. Average fiber diameter appeared to change little with die‐to‐collector distance, but decreased with increasing die temperature or with increasing air flow rate.
A direct injection gas‐liquid chromatographic method to monitor polymer melt devolatilization: Methyl methacrylate in poly(methyl methacrylate)
Authors: Edkins T. J. , Notorgiacomo V. J. , Biesenberger J. A.
Published: May 2005

A new capillary gas chromatography method to monitor a residual monomer in a polymer is described. A short (5 m) crosslinked methyl silicone fused silica capillary column with flame ionization detection gave good separation efficiency and parts‐per‐million detection limits. Capillary gas‐liquid chromatography was superior to packed column analysis (SP 1000) in terms of both analytical utility and ease of use. This technique may prove useful for monitoring other monomer/polymer systems.
Migration of polymer blend components during melt compounding
Authors: Dekkers M. E. J. , Hobbs S. Y. , Bruker I. , Watkins V. H.
Published: May 2005

In this paper it is shown that a core‐shell impact modifier which is predispersed in one phase of a complex blend may migrate to another phase during melt compounding. The migration process appears to be driven by differences in the spreading behavior of the individual blend components. The details of the migration are analyzed by electron microscopy studies of partially compounded samples which were quenched, extracted, and separated from the extruder screw.
Environmental effects on the water absorption and mechanical properties of carbon fiber reinforced PPS and PEEK composites. Part II
Authors: Ma Chen‐Chi M. , Yur Shih‐Wen
Published: May 2005

Research has been conducted to investigate the water absorption in carbon fiber reinforced poly(ether ether ketone) (PEEK/CF) and poly(phenylene sulfide) composites (PPS/CF). Effect of humidity and temperature on tensile, flexural, and impact strength of these composites were also studied. Results indicated that the water absorbed in PPS/CF and PEEK/CF are 0.059 %wt, 0.130 %wt, 0.138 %wt, and 0.153 %wt at 80°C. 75 %RH and 85 %RH, respectively. The diffusion process is a classical Fickian diffusion in the temperature range investigated. The activation energies of diffusion are 667 cal/g‐mole (for PPS/CF) and 8934 cal/g‐mole (for PEEK/CF) at 80°C and 75 %RH. The retention of mechanical properties of these composites is very good under hot‐wet conditions. These composite materials can be served as high performance materials even in the hostile environment. PEEK/CF composites shows excellent mechanical properties retention even at 80°C, 75 %RH, and 85 %RH.
Mechanical properties in multidimensional composites
Authors: Jang B. Z. , Cholakara M. , Jang B. P. , Shih W. K.
Published: May 2005

The mechanical properties of three dimensional stitched composites were compared against those of the traditional two dimensional laminates. An attempt was made to correlate the change in properties to the change in the third directional fiber density. Tests conducted were the impact, three‐point bending, damage tolerance, end notched flexure, and bending fatigue test. The results of these tests show that the third directional fibers can effectively inhibit delamination by increasing the interlaminar shear strength. Three dimensional composites also possess better damage tolerance, fracture toughness, and fatigue life. However, a high stitching density can degrade the in‐plane properties of the composites.
The coupled relaxation model for toner melt rheology
Authors: Karis T. E. , Seymour C. M. , Jhon M. S.
Published: May 2005

Process changes aimed at improving printer engine performance must take into consideration not only the process variables (such as nip temperature and pressure and process time to), but also the melt rheological variables (such as the characteristic time scale of the toner Tc). The melt rheology relevant to the electrophotographic toner fusing process is discussed. One criterion for toner quality can be conveniently measured through the Deborah number De, which is the ratio of Tc to to. Modification of the melt rheology by matrix polymer composition and carbon black size and concentration has previously been explored. Here, the melt rheology of toners with a range of gel content was studied using a step shear test. The coupled relaxation model was employed to fit the stress relaxation data. The viscoelastic properties were calculated from the melt data with this model. These properties were then used to estimate the strain deformation of the toner as it passes through the nip with arbitrary residence time and nip pressure as a function of gel content. This method can be used to match the toner melt properties with the processing conditions.
Rubber toughening of poly(methyl methacrylate). Part I: Effect of the size and hard layer composition of the rubber particles
Authors: Wrotecki C. , Heim P. , Gaillard P.
Published: May 2005

Poly(methyl methacrylate) (PMMA) is a brittle material which can be reinforced by the incorporation of acrylic particles, which do not spoil the transparency but which considerably increase the toughness of the material. In that study, we have varied the particle size and the outer layer for anchoring with the matrix. The proportion of reinforcing material is kept constant and the particles have an elastomeric core structure and a hard outer layer of PMMA. Monitoring of the two parameters, the critical stress intensity factor KIC and the critical energy release rate GIC, which are given by the fracture mechanics under static and dynamic (impact) loading, has made it possible to establish an optimum size of the reinforcement of the order of 200 to 250 nanometers. This optimum size can be explained as being the best compromise between the initiation of the damage and the control of its propagation, and that makes it possible to avoid a premature catastrophic failure. It also appears that a higher degree of grafting and a higher molecular mass of the hard layer result in an improved toughness.
Rubber toughening of poly(methyl methacrylate). Part II: Effect of a twin population of particle size
Authors: Wrotecki C. , Heim P. , Gaillard P.
Published: May 2005

Rubber toughened poly(methyl methacrylate) (PMMA) is reinforced efficiently by particles of a size of the order of 200 to 250 nm in the case of acrylic particles of core‐shell structure. In this study we have attempted to detect a possible synergy effect related to the presence of a twin population of particle sizes, as has already been observed, for example in high impact polystyrene. Two pairs of particle sizes were studied: (82,203) and (130,520) nm. The determination of the fracture mechanics parameters KIC and GIC under static and dynamic loading has enabled us to demonstrate a synergy effect in the case of the critical energy release rate GIC at a proportion of 50/50. Furthermore, this effect is verified in the case of the two pairs of particle sizes and in the case of the two speeds of loading. Nevertheless, this effect remains smaller than those observed in the case of materials which deform by crazing (HIPS, ABS). The rubber toughened PMMA deforms by shear bands and this mode of deformation seems to be less adapted to promote a synergy effect due to a twin distribution of particle sizes.
Measurement of the equibiaxial elongational viscosity of polystyrene using lubricated squeezing
Authors: Hsu T. C. , Harrison I. R.
Published: May 2005

The equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Test results from controlled stress and controlled strain rate measurement were consistent and yielded well‐defined steady‐state viscosities. Measurements appeared to be unaffected by sample geometry, although proper lubrication is important in achieving steady state. The measured biaxial viscosity appeared to be strain rate thinning above a biaxial strain rate of ≈ 0.01 s−1 at 160°C. As anticipated in the Newtonian region, biaxial elongational viscosity was approximately six times the shear viscosity. Thinning indices of both shear and biaxial elongational viscosities were 0.75. Data obtained at various temperatures were shifted following the timetemperature superposition principle. The resulting master curve could be fitted by a Carreau model with n ≈ 0.3 and a time constant of 110 s.