bluuebunny/crossref_metadata_2025 huggingface dataset:
The oscillating die: A useful concept in polymer extrusion
Authors: Casulli J. , Clermont J. R. , Von Ziegler A. , Mena B.
Published: May 2005

The effect of superimposing longitudinal and transverse oscillations on the die section at the exit of an extruder is examined. Longitudinal oscillations ranged from 0 to 30 mm in amplitude, and frequencies varied between 0 and 50 Hz. Transverse vibrations varied from 0 to 0.35 rad in amplitude and from 0 to 50 Hz in frequency. Experiments were performed in two types of extruders: a horizontal Brabender Plasticorder and a vertical Scamia both with similar characteristics of 7 Kw power output and 7.105 Pa maximum pressure. The polymers used were high and low density polyethylene and polystyrene. The overall effect of the oscillations is to increase the mechanical properties of the extrudate as well as to reduce the pressure drop in the die section. This pressure reduction results in a considerable saving of the total power consumption per unit weight of extrudate. Within a given range of amplitude‐frequency of oscillations, overall power savings of up to 25% are possible with respect to the stationary mode. Furthermore, the total flow rate through the die is enhanced by the vibrations and the die swell is diminished.
Flow of thermoplastics in an annular die under parallel oscillations
Authors: Wong C. M. , Chen C. H. , Isayev A. I.
Published: May 2005

A sound wave extrusion system has been developed. This system includes a single screw extruder and an annular die having an internal surface oscillating in the sound frequency range. Oscillating shear flow has been imposed in the direction parallel to the main pressure flow. The die characteristics and average melt temperature at the exit from the die for several thermoplastics have been measured with and without imposition of oscillations. Modeling of parallel superposition of sound oscillations upon pressure flow has been performed using the Leonov viscoelastic constitutive equation. Three cases are considered: (i) the process is isothermal and the change in die pressure is only due to a nonlinear interaction of oscillatory and pressure flow; (ii) the process is nonisothermal and adiabatic, and pressure reduction is due to the nonlinear interaction and the dissipation of oscillatory energy leading to the temperature rise in polymer melts; (iii) the process is nonisothermal with heat transfer due to transient heat conduction and the dissipation of oscillatory energy. Pressure reduction occurs due to both nonlinear interaction and temperature rise. It is found that case (i) cannot explain the observed die pressure reduction, while case (ii) describes those data only at high flow rates. The theoretical results from case (iii) are found to be in qualitative agreement with experimental observations. Generally, the theoretical results of case (iii) are better than those of cases (i) and (ii).
Characterization of network segment density from compression modulus measurements on swollen elastomers
Authors: Cooper Anthony R.
Published: May 2005

The characterization of network segment density of elastomers is discussed. Normally equilibrium solvent swelling is used as long as the polymer‐solvent interaction parameter χ is available. However, χ is often not known or may be a function of the network segment density, or composition for a polymer whose structure is changed upon aging. The technique of measuring the modulus in tension or compression on solvent‐swollen samples allows the network segment density to be calculated from the theory of rubber elasticity. This circumvents the problems associated with the solvent swelling technique. The modification of a commercially available thermomechanical analyzer is described, to enable compression modulus measurements on solvent swollen elastomers to be performed.
Interpenetrating polymer network approach to tough and microcracking resistant high temperature polymers. Part II. LaRC‐RP41
Authors: Pater Ruth H.
Published: May 2005

Recently, we reported on the interpenetrating polyimide network (IPN) approach to develop tough and microcracking resistant high temperature matrix resins for use in aircraft/aerospace structural components. One such polymer developed is designated LaRC‐RP40. This new simultaneous semi‐IPN was prepared from easy‐to‐process but brittle crosslinking PMR‐15 and tough but difficult‐to‐process linear NR‐150B2. Significantly improved toughness, microcracking resistance, and glass transition temperature over PMR‐15 were realized from the combination. These property improvements were achieved without compromising ease of processing, high temperature mechanical performance, and cost effectiveness compared to PMR‐15. These results encouraged us to further explore this approach for the development of a wider range of polymers of basic technological and economic interest. In the present work, we combine crosslinking PMR‐15 and linear LaRC‐TPI to provide a new sequential semi‐2‐IPN called LaRC‐RP41. The physical and mechanical properties of the neat resin and composite reinforced with graphite fibers are presented. The phase morphology and phase stability of the neat resin and composite studied by various techniques are also discussed.
Effect of temperature on the rheological behavior of hydroxyl terminated polybutadiene propellant slurry
Authors: Muthiah R. M. , Manjari R. , Krishnamurthy V. N. , Gupta B. R.
Published: May 2005

Hydroxyl terminated polybutadine (HTPB) based composite solid propellants have gained prominence in advanced missiles and launch vehicles including the Space Shuttle's Inertial Upper Stage (IUS) motor (1). To achieve a blow‐hole free well performing casting, the knowledge of the processability characteristics and rheological behavior of the propellant slurry are of vital interest. In our earlier communication (2) we had discussed the effect of compositional aspects, namely solid loading, oxidizer particle size distribution, and aluminum content on the rheology of HTPB propellant. For an optimized solid loading with corresponding oxidizer particle size distribution and aluminium content, the effect of temperature on the processability and the pot life are studied and reported in this paper. This study establishes the fact that the HTPB slurry shows a complex rheological behavior having thixotropy and yield stress. The thixotropic index and yield stress show minimum values at an optimum temperature. This optimum temperature shifts to lower values as time elapses. Activation energies have been calculated for the cure reaction based on yield stress and viscosity. It is observed that the activation energy values reach asymptotic levels after about three hours of curative addition.
Film casting of viscoelastic liquid
Authors: Alaie Seyed M. , Papanastasiou T. C.
Published: May 2005

Melt film‐casting is analyzed by means of a nonlinear integral constitutive equation that incorporates shear history effects, spectrum of relaxation times, shear thinning, and extension thinning or thickening. Film temperature and thickness profiles are predicted. The effects of shear‐thinning, relaxation time, and die‐design on the final film thickness are evaluated. Temperature variations are investigated by means of the pseudo‐time concept. The process dependence on the rheological characteristics of the viscoelastic fluid, the die‐design through the history effects, the conditions at the take‐up end, and the film temperature is discussed. Predicted film and temperature profiles of casting of polypropylene are compared with experimental data taken from the literature.
Study of rubber‐modified brittle epoxy systems. Part II: Toughening mechanisms under mode‐I fracture
Authors: Sue Hung‐Jue
Published: May 2005

The toughening mechanisms in grafted‐rubber concentrate (GRC), dispersed acrylic rubber (DAR), and Proteus rubber‐modified brittle epoxy (i.e., highly crosslinked) systems are examined using scanning electron microscopy, optical microscopy and transmission electron microscopy techniques. The toughening of the GRC‐modified brittle epoxy system is found to be due to cavitation of the GRC rubber particles, followed by formation of limited shear yielding when the crack propagates. Crack bifurcation and crack deflection are also observed in this system. Only crack bifurcation, crack deflection, and possibly crack/particle bridging mechanisms are operative in the DAR‐modified brittle epoxy system. In the case of the Proteus rubber‐modified system, the rubber appears to be rigid (Tg ≈ 28°C). As a result, the crack/particle bridging mechanism is not observed. Only crack deflection and crack pinning mechanisms are found. These observations are in agreement with the toughness measurement results (see Part I), which indicate that the GRC rubber provides the most effective toughening, followed by the DAR rubber, and then by the Proteus rubber. An approach for toughening brittle epoxies is also discussed.
On the long time creep and lifetime behavior in uniaxial extension of a linear low density polyethylene
Authors: Crissman J. M.
Published: May 2005

This paper describes uniaxial creep measurements done on a linear low density polyethylene over a wide range of temperatures and applied stresses. It is found that the creep behavior overall is quite complex and that the one quantity which can best be used to predict useful lifetime of this material is the time at which necking is observed. The time to neck data has been used to generate a composite curve which can serve as an upper bound to lifetime prediction.
Morphology and mechanical properties of rubber modified aromatic‐ether bismaleimide matrix resins
Authors: Chartoff Richard P. , Cho Jeongmi , Carlin Patrick S.
Published: May 2005

An aromatic ether bismaleimide (BMI) was modified by copolymerization with various CTBN and ATBN liquid elastomers. Dynamic mechanical (DMA), flexural, and SEM fractography studies indicate that cured specimens containing various amounts of the different elastomers have widely varying morphologies and properties. The experimental parameters of interest in this study included the type of elastomer reactive end group, elastomer acrylonitrile content, elastomer concentration, and cure reaction conditions. The ATBNs are clearly more compatible than CTBNs. CTBN modified compositions show a distinct, low temperature rubber phase mechanical loss dispersion, reduced modulus and ultimate strength values, and only slight improvements in elongation. Cured compositions with small amounts of ATBN elastomers (5 phr), however, show no reduction in modulus but improved elongation and ultimate strength values. The “rubber” domains in these systems are small, typically < 5 μm, and consist of copolymerized BMI and elastomer. DMA data for these systems show no distinct low temperature elastomer peak but a broad “interphase” loss dispersion covering a wide range of temperatures. Failure in the ATBN modified BMIs involves initiation of numerous microcracks with obvious crack deflection at the rubber particles. No cavitation of rubber particles occurs, as is frequently the case with the CTBNs.
Transverse orientation dies for solid‐state extrusion of polymers. Part I: Process mechanics
Authors: Mascia L. , Zhao J.
Published: May 2005

Solid‐state extrusion of crystalline polymers is a well‐known technique to produce monoaxial orientation in filaments and films. This is essentially achieved by extruding or drawing the polymer through a convergent die at temperatures below its melting point. Biaxial orientation in die drawing processes has been achieved by adding extensional forces in the transverse direction at the die exit, as in the case of tubular products. In the present study, billets of poly(tetrafluoropolyethylene) (PTFE) and ultrahigh‐molecular‐weight polyethylene (UHMWPE) were subjected to simultaneous deformations in the longitudinal and transverse directions, by means of dies featuring converging and diverging walls perpendicular to each other, to produce extrudates exhibiting a predominant orientation in the transverse direction. Two geometries, producing a nominal state of pure shear deformations, by maintaining constant the cross‐section area at entry and exit, were examined to determine the relationship between die geometry, yielding and frictional properties of the polymer and extrusion forces. The effects of die geometry and processing conditions are analyzed in Part 2.
Highly oriented polyacetylene: Structures and electrical conductivity of the compounds doped with alkali metals and selected oxidants
Authors: Billaud D. , Begin D. , Ghanbaja J. , Lelaurain M. , Saldi F.
Published: May 2005

Films of polyacetylene synthesized according to Akagi method present a high degree of crystallinity. A 6‐7 times stretching of these films results in the orientation of the polymer fibers: The mosaic was ± 5 degrees. Such highly oriented polyacetylene (HOPA) films were chemically doped by heavy alkali metals in the vapor state and electrochemically with GaCl anion in nitromethane medium. The evolution of the structures and the variation of the electrical conductivity upon doping were examined in both cases.

Doping with alkali metal leads to the appearance of different intercalated phases: The commensurability of these phases is discussed as a function of the nature and the concentration of the intercalated alkaline ion. The electrical maximum room temperature conductivity, which depends on the nature of the alkali metal, is maximum for K‐doped materials. In the case of GaCl doping, the unique intercalated phase observed is poorly organized except in the chain direction where a GaCl ion is found every 4.5 (CH) units. The room temperature electrical conductivity measured along the chain axis is equal to 15 000 S/cm, one order of magnitude higher than the value observed in Shirakawa unoriented polyacetylene.
Synthesis and characterization of polyamide‐imides
Authors: Dezern James F. , Gautreaux Carol R.
Published: May 2005

A series of thermally stable, tough, linear polyimides containing amide linkages was prepared. The new polyamide‐imides were synthesized by reacting a group of isomers of diaminobenzanilide (DABA) with various dianhydrides, such as 4,4′‐oxydiphthalic anhydride (ODPA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), and 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The resulting polyamide‐acids were thermally or chemically converted to the polyamide‐imide (PAI). Twelve polyimides were synthesized from unsubstituted and N‐methyl substituted amide diamines and their properties were compared with previously made polyamide‐imides and the polyimide LARC‐TPI. These polyimides exhibited high inherent viscosities and glass transition temperatures. They were made into tough, flexible films of which some showed good thermal stability and resistance to organic solvents. Overall, the mechanical properties of the PAI films were comparable to those of LARC‐TPI with the 4,4′‐systems exhibiting exceptional properties and crystallinity. These materials have potential as high temperature films, coatings and fibers, as well as molding and laminating resins.
Catalyst fragmentation during propylene polymerization. III: Bulk polymerization process simulation
Authors: Ferrero Monica A. , Chiovetta Mario G.
Published: May 2005

Fragmentation of support/catalyst particles during propylene bulk polymerization is analyzed by means of a mathematical model including energy and mass balances, with chemical reaction. The rupture phenomenon is specifically considered by the model and analyzed as it proceeds along time. Model predictions concerning the effects of fragmentation on polymerization are discussed. The influence of mass‐transfer resistances at the macroparticle and microparticle level, as well as the microparticle nucleus‐size effects over the polymerization process, are analyzed. Macroparticle mass‐transfer resistance affects both the rate of fragmentation and temperature excursions. Microparticle nucleus‐size exerts a strong influence over the whole polymerization process. A small micronucleus‐size produces both a delay in the fragmentation process and a greater value of she final catalyst yield. The effects of major critical parameters are evaluated via model simulation, and the results are discussed. The analysis shows that fragmentation depends on the combined effect of the parameters studied. Modeling of the process considering all parameters simultaneously is the proper way of predicting the fragmentation sequence for a given support/catalyst particle. Crystallinity of the produced polymer affects the rate of fragmentation, either increasing or decreasing the rupture rate depending on macroparticle porosity and compactness. Heat transfer conditions in the liquid‐phase system make the temperature runaway problem easy to predict and control, in spite of high polymer yields. The design of “tailor‐made” support/catalyst macroparticles in accordance with catalytic activity is necessary in order to obtain high yields and controlled process temperatures.
Ultralow density polyethylene blends with polypropylene
Authors: Lee Young Keon , Jeong Young Tae , Kim Kook Choong , Jeong Han Mo , Kim Byung Kyu
Published: May 2005

Two types of ultralow density polyethylene (ULDPE) of different melt viscosities were blended with a polypropylene (PP) in a twin screw extruder. Morphology, thermal, rheological, and mechanical properties of the blends were determined. Morphological observation from SEM showed a clean phase separation of PP/ULDPE blends. However, depending on the viscosity ratio, a significant difference in the extent of phase separation, as well as in the phase inversion composition, was demonstrated. The melting temperature of PP and ULDPE were respectively increased and decreased in the blend. Crystallization rate and the, crystallinity of PP and ULDPE were first increased and then decreased as the other component was increased. Yield at low frequencies was observed with 30 wt% ULDPE in PP. In ULDPE‐rich compositions, complex viscosities of the blends gave negative deviation from the additive rule of mixing. Mechanical properties such as flexural modulus, elongation at break and Vicat softening point were closely relatable to the morphology. The impact strength of PP is significantly improved by ULDPE addition.
The dynamic properties, temperature transitions, and thermal stability of poly (etherether ketone)‐thermotropic liquid crystalline polymer blends
Authors: Mehta Atul , Isayev A. I.
Published: May 2005

Differential scanning calorimetry, dynamic mechanical measurements, and thermal gravimetric analysis techniques have been used to thermally characterize blends of poly(etherether ketone)‐thermotropic liquid crystalline polymer (LCP) based on hydroxybenzoic and hydroxynaphthoic acid (HBA/HNA). Based upon differential scanning calorimetry and dynamic mechanical measurements, these blends have been shown to be incompatible in the entire range of concentration. For these blends the glass transition temperature of both components does not change much with composition. Dynamic mechanical measurements performed under torsional and flexural modes of testing and different samples geometries indicate that the dynamic properties depend a lot on the above two factors. Anisotropy in these blends was studied by performing dynamic measurements in flow and transverse directions. The effect of orientation is found to be predominant. Dynamic mechanical properties tend to improve in the flow direction, whereas in the transverse direction they are found to decrease with increasing LCP concentration.
The effect of free radical initiators and fillers on the cure of unsaturated polyester resins
Authors: Rodriguez Ernesto L.
Published: May 2005

The heats of polymerization for two unsaturated polyester resins are presented using two free radical initiator systems. The first was 1% methyl ethyl ketone peroxide/0.2% cobalt octoate (12%) and the second was 2% benzoyl peroxide/0.2% dimethylanyline. The heats of reaction were measured using a differential scanning calorimeter under dynamic and isothermal modes. Infrared spectroscopy and exotherm peak temperature test were employed to further establish the differences between the initiators and to determine the influence of three fillers (sand, clay, and fly‐ash) on the cure reaction.
Rubber‐toughening of glass fiber‐epoxy filament wound composites
Authors: Zhang H. , Berglund L. A. , Ericson M.
Published: May 2005

An attempt was made to improve the properties of filament wound glass fiber‐epoxy composites by addition of carboxyl‐terminated‐butadiene‐acrylonitrile (CTBN)‐rubber to the matrix. The interlaminarGIcof unidirectional glass fiber‐epoxy increased significantly with CTBN addition whereas the flexural strength decreased. The weepage stress in hoop loading of ±50 degree angle‐ply pipes was higher for unmodified as compared with 10 phr CTBN‐modified epoxy matrix pipes. However, the strain at weepage and the stress and strain at nonlinearity were higher for the pipes based on toughened epoxy. The reason for the lower weepage stress is that, although the toughened matrix pipes show higher resistance to cracking, their stiffness is lower. The addition of small amounts of CTBN‐rubber (about 5 percent by weight is suggested) to the present epoxy matrix for filament winding can be done with only a minor increase in viscosity. This is a way of toughness enhancement for applications where the matrix stiffness reduction and increased moisture absorption are of minor importance.
Adaptive model following control of the mold filling process in an injection molding machine
Authors: Chu Cheng‐Ping , Wei Jong‐Hwei , Shih Ming‐Chang
Published: May 2005

This paper is concerned with the practical application of the adaptive model following control (AMFC) theory on the cavity pressure control of the mold filling process in an injection molding machine. The experimental results indicate that the AMFC technique based on the modified Popov‐Landau method is very useful for the cavity pressure control. Two kinds of control algorithms are implemented on a 16 bit microcomputer to control the cavity pressure. The results also show that the AMFC algorithm is superior to the classical PI control in this system when the acrylonitrile‐butadiene‐stryrene (ABS) is injected into a test specimen mold which is designed according to the ASTM code.
Diffusion of benzene vapor in blends of poly(vinyl acetate) and poly(methyl acrylate)
Authors: Nunez Elizabeth M. , Myerson Allan S. , Kwei T. K.
Published: May 2005

Sorption and diffusion of benzene in miscible blends of poly(vinyl‐acetate), PVAc, and poly(methyl acrylate), PMA, have been studied. The polymer‐polymer interaction parameter values calculated from equilibrium vapor sorption data were all negative, indicating favorable interaction between the two polymers. The sorption of benzene vapor into these blends was measured at a temperature above the Tg's of the pure polymers and found to obey Fickian kinetics. The mutual diffusion coefficients were estimated from the initial slopes of the sorption curves. The concentration dependent diffusion coefficients were fitted to the empirical relation D = Do exp(αC) which satisfactorily correlated the data. Values of the constant Do were found to vary continuously with blend composition, while the α values did not. These experimental data were analyzed employing Fujita's free volume theory. It was found that the data was consistent with this theory. If the fo values for the blends are assumed to be the weighted average of the component polymers, then the β parameter values for the blends also obey the additivity rule.
Electrical conductivity in heterogeneous polymer systems. V (1): Further experimental evidence for a phase transition at the critical volume concentration
Authors: Wessling Bernhard
Published: May 2005

A new dispersion/flocculation phase transition model for the conductivity jump at the critical volume concentration of a conductive phase in an insulating matrix polymer is discussed. New experimental‐data including: SEM evaluations of the “seam” structure, excess pyrolytic residue analysis, BET measurements of dependence on conductive phase content, and temperature dependence of conductivity are presented for supporting the new model. Finally a first qualitative step towards a new non‐equilibrium thermodynamical description of these dissipative structures will be described.
On the application of micromechanics to the prediction of macroscopic thermal residual stresses in short‐fiber reinforced polyetheretherketone
Authors: Eduljee Rushad F. , Gillespie John W. , McCullough Roy L.
Published: May 2005

A micromechanics theory is outlined for predicting the elastic and thermoelastic properties of dispersed, short fiber systems. This micromechanics theory is then applied to the prediction of macroscopic thermal residual stresses in a poly(etheretherketone). (PEEK)‐glass. Fiber system, in an effort to determine the influence of crystallinity on residual stress development.
The onset of orientational crystallization in poly(ethylene terephthalate) during low temperature drawing
Authors: Roland C. M. , Sonnenschein M. F.
Published: May 2005

It is well known that crystallization can be induced in amorphous poly(ethylene terephthalate) (PET) by orientation below the isotropic crystallization temperature. The magnitude of the strain necessary for crystallization varies inversely with molecular weight because of relaxation. However, lower molecular weight PET might be expected to, crystallize at a lower extent of molecular orientation, since the crystallization rate also varies inversely with molecular weight. Chain conformations were measured during low temperature drawing of PET of various molecular weights. The molecular configuration associated with strain induced crystallization was found to be independent of chain length. The onset of orientational crystallization was associated with a particular conformation, and this critical trans/gauche ratio was equivalent for PETs of various molecular weights. The drawing behavior is thus in accord with theory concerning the transition of flexible chain polymes from isotropy to an ordered state. This result is congruent with previous studies suggesting the presence of extended chain crystallinity in amorphous PET after low temperature drawing.
Energetics of stress relaxation of glassy polymers at high pressure
Authors: Goldman A. Ya. , Maksimov V. L. , Kestelman V. N.
Published: May 2005

Kinetic changes of relaxation of the shift stress of glassy poly(methyl methacrylate) were studied when temperatures and pressures were changed in isobaric, isothermal, and isochoric conditions. In isochoric conditions the relaxation rate depends slightly on temperature. The volume of the polymer is the main parameter for the rate of stress relaxation. Isobaric and isochoric activation energies and activation vohime of stress relaxation were determined. The results are shown to satisfy the thermodynamic relation of the activation parameters of the relaxation process. The dimensions of elementary kinetic unit of the stress relaxation process were estimated.
Determining molecular weight distributions from viscosity versus shear rate flow curves
Authors: Tuminello William H. , Cudré‐Mauroux N.
Published: May 2005

Using the theoretical approach of Bersted and Slee, we developed a technique of determining the molecular weight distribution (MWD) from the viscosity vs. shear rate flow curve. Each molecular weight fraction was assumed to have a characteristic deformation rate. Below this rate, the viscosity was equal to the zero shear value. Above this rate, the viscosity was reduced to the zero shear viscosity of the molecular weight characteristic of the higher rate. The relationship between the weight fraction of each component and the viscosity/rate curve was derived from these assumptions. The flow curves of very well‐characterized polystyrenes were determined. MWDs were then calculated using the BerstedSlee approach and compared with results from size exclusion chromatography. Comparisons were also made with the results of Malkin and Teishev. They used the same assumptions as Bersted and Slee but chose a different methodology for determining the MWD.
High‐modulus polyaramide and polybenzimidazole blend fibers
Authors: Chung T. S. , Herold F. K.
Published: May 2005

Polymer blends from polybenzimidazoles (PBI) and high‐performance polyaramides were spun to give a PBI variant with better tensile properties than PBI itself. Infrared absorption spectra of a hot‐drawn fiber showed 10‐wavelength shift at the carbonyl band, CO, of high‐modulus polyaramide (HMA) due to an interaction of the CO with NH. Dynamic mechanical analysis (DMA) also confirmed the interaction is at a molecular level. The mechanical properties of hot‐drawn fibers from PBI/HMA polymer blends obey Halpin and‐Tsai's theory. Hot‐drawing “immediately after” dry‐spinning yielded fibers with impressive properties. Aging as‐spun PBI/HMA fibers was very harmful for fiber tensile properties. The effects of sulfonation and heat setting on fiber thermal and mechanical properties are also reported.
Study of the relationships between melt index, density, and blend ratio of binary polyethylene blends
Authors: Wong Anthony Chi‐Ying
Published: May 2005

Two relationships regarding various binary polyethylene blends were studied. The first was the relationship between melt index and blend ratio. The second was the relationship between resin density and blend ratio. The results revealed that melt indexes of the blended materials tested under standard testing conditions displayed an exponential decaying characteristic with the percentage of the base blending component. It was demonstrated that the melt indexes of the blended materials could be estimated by a modified Arrhenius Law of viscosity. The estimations showed good agreement with the experimental values. Resin density, on the other hand, exhibited a property that followed an additivity relationship. This indicated that the ability of one component to crystallize was not affected by the other component present in the same system.
Morphology of polyethylene blends. II: Formation of a range of morphologies in blends of polyethylene with increasing content of styrene‐isoprene‐styrene triblock copolymers during extrusion‐blowing
Authors: David C. , Getlichermann M. , Trojan M. , Jacobs R.
Published: May 2005

Blends containing polyethylene (LDPE, LLDPE, or LDPE‐LLDPE) with different weight percent of styrene‐isoprene‐styrene (SIS) triblock copolymers have been obtained by extrusion‐blowing. The morphology of the blends, investigated by scanning electron microcopy (SEM), has been related to composition but also to different parameters such as viscosity, nature of the polyethylene phase, and extrusion conditions. A large range of morphologies is observed and indicates that the main factors determining the morphology of the blends are the composition, the elongational fields at the exit of the die and, in certain limits, the relative viscosities of the components of the blends.
Buildup and relaxation of molecular orientation in injection molding. Part II: Experimental verification
Authors: Flaman A. A. M.
Published: May 2005

The numerical simulation of the injection molding process described in Part I is compared in the present paper with experimental results obtained with an instrumented test mold. Pressure and birefringence profiles are compared with corresponding predictions for an amorphous polymer. The influence of the melt temperature, the flow‐rate, and the packing pressure on the pressure profiles and the frozen‐in birefringence is investigated. It is demonstrated that the prescription of a specified packing pressure profile can reduce the frozen‐in birefringence. The shape and the tendencies of the predicted birefringence profiles agree well with the experimental ones. This leads to the conclusion that the, model can be used to optimize the processing conditions to mold high‐quality products with minimum frozen‐in orientation.
Study on the microphase structure of sodium sulfonated polystyrene lonomer by nuclear magnetic relaxation measurements
Authors: Park Jung‐Ki , Lim Jong‐Chul , Kim Chul‐Hwan , Ryoo Byung‐Kyu , Yoo In Suk
Published: May 2005

Nuclear magnetic relaxation techniques have been used to study the microphase structure of sodium sulfonated polystyrene ionomers. Microphase separation in the ionomers could be evidenced by the magnetization decays, which were resolved into two components. At lower temperature, 300K, the decay function for the ionomer was found to be a combination of two Gaussian functions that are indicative of more rapid dephasing of individual spins, while the magnetization decay at higher temperature, 413K, was composed of both a Gaussian function and a Lorentzian function. The relative portion of the ionic phase in the ionomer was seen to be significantly affected by the ion concentration or the temperature. From the comparison of the relative amounts of the ionic phases obtained from both the material's composition and the nuclear magnetic relaxation experiment, it is anticipated that the ionic domains contain a substantial amount of hydrocarbon segments.
The fracture behavior of oriented poly(methyl methacrylate)
Authors: Lin C. B. , Hu C. T. , Lee Sanboh
Published: May 2005

The fracture behavior of oriented poly (methyl methacrylate) (PMMA) has been investigated. The stress intensity factor KIC, characteristic distance a, and angle θ of switching propagation direction decrease with increasing draw ratio in the range of 1.25 and 3.25. The microstructures such as the plastic zone and the features of morphology are in good agreement with the variations of these three variables, i.e., KIC, a, and θ.
Temperature dependent dc dark conductivity in poly(n‐vinyl carbazole): Arrhenius and density of state model
Authors: Santos‐Lémus S. , Luna M.
Published: May 2005

DC dark conductivity (σ) has been measured in thin films of poly(N‐vinyl carbazole) (PVK). The dependence of σ on temperature (T) followed a typical Arrhenius relation but at the same time a relation σ(T)α exp(‐[T0/T]2) could be fitted to the experimental points. To reconcile this observation, it is suggested that the expression for the conductivity then is expected to contain in addition to the activation term, the factor exp[‐(T0/T)2] which is the behavior expected in a trap‐free molecular hopping system with a Gaussian distribution of sites energy, so that the DC dark conductivity would be of the functional form

.
Rubber toughened polyamide 6: The influences of compatibilizer on morphology and impact properties
Authors: Wu Chung‐Jen , Kuo Jen‐Feng , Chen Chuh‐Yung
Published: May 2005

In this study, styrene‐(ethylene‐co‐butylene)‐styrene (SEBS) triblock copolymer (Kraton G‐1652) was modified with maleic anhydride (MA). The maleated SEBS was used as compatibilizer for the blends of Nylon 6 (PA6) and SEBS. The morphology and impact strength of the blends were measured as functions of concentration and MA graft ratio of maleated SEBS. The compatibility and fracture mechanism of the blends were evaluated from the SEM micrographs of the xylene‐etched surfaces and of fractured surfaces. Some of the blends exhibited an impact strength up to about 30 fold greater than neat PA6. The fracture involved both both cavitation and shear yielding. The mechanism of compatibilization of maleated SEBS in the ternary components blends was proposed.
Orientational crystallization and orientational drawing as strengthening methods for polyethylene
Authors: Elyashevich G. K. , Karpov E. A. , Rosova E. Yu. , Streltses B. V. , Marikhin V. A. , Myasnikova L. P.
Published: May 2005

This paper reports on the theoretical and experimental studies of structure formation and strengthening (stiffening) of flexible‐chain polymers. Two techniques of strengthening relying on the melt extrusion, i.e., orientational crystallization (crystallization initiated by melt extension) and drawing (uniaxial stretching of a crystallized polymer) are analysed by theory. The experiments involved preparation and study of melt extruded films and film fibers of linear polyethylene formed by the two techniques mentioned above. The effect of the degree of orientation and other parameters of the formation processes on the mechanical characteristics and the factors limiting the ultimate values of these characteristics are discussed. It is shown that multistage drawing succeeds in achieving a higher tensile strength and elastic modulus (1.2 and 35 GPa, respectively) than the orientational crystallization, which gives 0.8 and 15 GPa. The strengthening by drawing is accompanied by microcrack formation. In contrast, no discontinuities are observed in orientationally crystallized samples up to their ultimate extension.
Creep/recovery behavior of toughened and untoughened graphite/epoxy systems
Authors: Tsotsis Thomas K.
Published: May 2005

A test program was developed to compare the viscoelastic behavior of an untoughened epoxy (R922) with a toughened epoxy (R6376). Creep/recovery tests were performed on neat resin as well as [ ± 40° ]2s composites using T500 or IM7 graphite fibers. The composite specimens were subjected to at least five cycles of load/unload at each stress level. The goal was to study the viscoelastic response of a flexibilized and unflexibilized epoxy and to try and observe any microstructural changes that might occur. Neat resin tests did not show a significant difference in behavior between the two systems. Single cycle behavior was found to differ significantly from multiple cycle behavior. Recovery strains were observed to be much higher than predicted from linear theory. Linear parameters were also seen to vary with stress level; however, when a plasticity‐based approach was used to model the creep behavior, the same parameters could then be used at all load levels. Creep and recovery behavior were seen to differ significantly. This observation leads to support for the theory of Schapery (1) that creep and recovery should be considered as different behavior in contrast to the assumptions of linear and nonlinear theory. In addition, the large difference between neat resin and composite data suggests that micromechanics models, which rely on constituent properties, will lead to large errors if neat resin properties are used to characterize composite viscoelastic behavior. Different fibers showed no influence on results. Scanning electron microscopy failed to reveal any microstructural changes.
Evaluating the fatigue resistance of notched specimens of polyethylene
Authors: Zhou Y. , Brown N.
Published: May 2005

The fatigue life of a linear low density polyethylene was measured as a function of stress, notch depth., and temperature under plane strain conditions. The fatigue life was precisely related to the stress intensity. The temperature dependence of the fatigue life corresponded to an activation energy of 72.5 KJ which was independent of stress level. A general equation for the fatigue lifetime was proposed for polyethylenes in terms of the material parameters, the mechanical parameters such as stress intensity, stress amplitude, frequency, and waveform.
Melting and solidification behavior of blends of high density polyethylene with poly(butylene terephthalate)
Authors: Yang L. Y. , Smith T. G.
Published: May 2005

This study focuses on the effect of various processing and cooling conditions upon the subsequent melting and solidification behavior of blends of poly(butylene terephthalate) (PBT) and high density polyethylene (HDPE). Differential scanning calorimetry (DSC) measurements have shown that the crystallization of reprocessed PBT is different from the crystallization behavior of virgin samples. Two melting endotherms for PBT were observed for reprocessed PBT and for PBT‐PE blends. The nature of each PBT peak is discussed in relation to processing history, solidification conditions, and composition. The presence of two crystallization peaks for the PE component in blends of PE and PBT are thought to be associated with the restriction of molecular motion of PE in the presence of the second component. The relative magnitudes of the two exotherms of PE vary with composition and cooling rate during solidification.
An assessment of crazing criteria for polyetherimide in three‐dimensional stress space
Authors: Woods J. T. , Delorenzi H. G.
Published: May 2005

Three point bend tests of notched, polyetherimide (PEI) beams are performed for varying notch radii and beam thicknesses. Finite element stress results including pressure sensitive yielding effects are correlated with experimental load‐to‐craze observations to determine the three‐dimensional stress state at craze initiation. Three crazing criteria; maximum principal stress, hydrostatic stress, and the critical strain criterion of Oxborough and Bowden are examined for consistency. Over the range of geometries studied, the critical strain criterion provides the best fit to the experimental data. This criterion could be used as a brittle failure criterion to help understand and prevent brittle failures.
A predictive model for the mechanical behavior of particulate composites. Part II: Comparison of model predictions to literature data
Authors: Vratsanos Lori Anderson , Farris Richard J.
Published: May 2005

The energy balance model presented in Part I is applied here to data taken from the literature. Care was taken to choose well‐characterized systems to give a true test of the model's predictive character, rather than its ability to curve‐fit the data. The effects of concentration, particle size, strain rate, and temperature on the stress‐strain and dilatation curves are examined. Good agreement is seen for each of these variables. This predictive approach will allow the design of particulate composites with given mechanical behavior, and analysis of material behavior in various geometries and conditions.
Experimental study of film thickness and free surface velocity around a rotating roll for non‐newtonian fluids
Authors: Chono S. , Iemoto Y. , Tomizawa T.
Published: May 2005

Measurements are performed on film thickness and free surface velocity around a rotating roll for Newtonian, non‐Newtonian inelastic, and viscoelastic fluids by using noncontact methods of a capacitance probe and a laser Doppler velocimeter probe. The film thickness decreases with increasing inspection angle for Newtonian fluids. For non‐Newtonian fluids, it retains an approximately constant value, owing to shear‐thinning of viscosity, except for a meniscus region development, which is dependent on fluid elasticity. Comparison of current results with the film thickness from a previous work is also made. With the increment of inspection angle, the free surface velocity increases rapidly in the meniscus region and maintains a constant value almost equal to a roll speed in the other region for viscoelastic fluids, while it increases linearly for Newtonian fluids. The shear rate at a roll surface is presented assuming that the velocity distribution in the liquid film is a polynomial equation. It is found that viscoelastic fluids exhibit different behavior from that of Newtonian and non‐Newtonian inelastic fluids. Evaluation of the force acting on the liquid film for Newtonian fluids implies that the velocity gradient at a roll surface in an ascending region may be steeper than the parabolic form assumed in this study.
The reactive modification of polyethylene. II: Mathematical modeling
Authors: Suwanda D. , Balke S. T.
Published: May 2005

In Part I of this work, experimental data showed that the effect of low concentrations of free radical initiator injected into polyethylene during extrusion depended upon the degree of unsaturation and branching in the feed as well as the molecular weight. This paper shows attempts to quantitatively explain these reactive extrusion results through development of two kinetic models based upon the rate equations for reactions considered dominant. The first model developed incorporated unsaturation via consideration of simultaneous crosslinking‐endlinking reactions. It contains two variable parameters: the overall initiator efficiency and a ratio of two rate constants reflecting the reactivity of the unsaturated bonds. The model was able to fit the changes in molecular weight distribution of both the low density and linear low density polyethylene but not the high density polyethylene samples. In addition to fitting the molecular weight distribution, this model also provided reasonable values of initiator efficiencies for crosslinking, endlinking, and chain extension reactions, as well as the number of terminal vinyls of the products. The second model is a special case of the first: it neglects the presence of unsaturation in the feed. This second model is actually the usual “crosslinking” model widely known from a derivation based upon statistical arguments. It was not able to fit most molecular weight distributions obtained. However, the model was shown to be useful for accounting for observed molecular weight distribution for a high density polyethylene sample of low initial unsaturation. Also, it was able to explain the amount of gel formed as a function of initiator concentration.
Jet impingement mixing in an L‐type mixhead: Comparison of mixing criteria
Authors: Baser S. A. , Shetty D. G. , Khakhar D. V.
Published: May 2005

High velocity jet impingement mixing is a unique operation of the reaction injection molding process. The quality of mixing depends on processing parameters for a given system, and can have significant effect on the properties of the product. We have compared three methods used for characterization of mixing quality reported in the literature for a cross‐linking polyurethane system processed on an industrial scale high pressure RIM machine, with an L‐type mixhead. The methods are based on, (i) visual appearance of a molded sample, (ii) adiabatic temperature rise during reaction and, (iii) flexural modulus of elasticity of a molded sample. The visual appearance test was made quantitative by using a color matching optical system. The adiabatic temperature rise increases rapidly with nozzle Reynolds number (Renzl) for polyol, up to a critical value (Renzl = 380) beyond which there is a slow increase. The latter is attributed to the geometry of the L‐type mixhead. A simple analysis is presented to explain the limiting extent of mixing at high Renzl. The flexural modulus and the visual appearance of molded samples are found to improve until Renzl = 500, implying a greater sensitivity to mixing as compared to the adiabatic temperature rise.
Compatibilization of immiscible blends with a mutually miscible third polymer
Authors: Machado J. M. , Lee C. S.
Published: May 2005

Four immiscible blend systems, styrene‐maleic anhydride/styrene‐acrylonitrile (SMA/SAN). styrene‐maleic anhydride/acrylonitrile‐butadiene‐styrene (SMA/ABS), poly(vinylidene fluoride)/SAN (PVF2/SAN), and PVF2/ABS, were investigated. The effect of adding up to about 10 wt% of a third polymer that is miscible with each blend component, poly(methylmethacrylate) (PMMA), was determined. In every case, the addition of PMMA led to the improvement of properties such as tensile strength, tensile elongation, and notched impact strength. Furthermore, the addition of PMMA resulted in finer, more uniform dispersions of the primary blend components. The experimental results are interpreted in terms of interfacial activity of the common phase component, PMMA.
A thermoanalytical study on solid‐state cure of poly(p‐phenylene sulfide)
Authors: Park Min , Lee Kwang Hee , Choe Chul Rim , Jo Won Ho
Published: May 2005

Differential scanning calorimetry (DSC) was used to investigate the solid‐state cure process of poly(phenylene sulfide)(PPS) resin. Virgin PPS resin in an open sample pan was cured in DSC cell. Either air or oxygen was used as a curing atmosphere. Cure temperatures were in the range of 200 and 250 °C, which are below the melting point of PPS resin. Cure temperature as well as atmospheric condition influenced the cure behavior of PPS in the solid state. Both the rate and the amount of cure increased with increasing cure temperature. On the other hand, the time to reach the maximum cure rate was independent of cure temperature. Changing the atmosphere from air to oxygen increased both the cure rate and the amount of cure. The size effect of PPS particles on the cure reaction was also discussed.