bluuebunny/crossref_metadata_2025_split huggingface dataset:
AC and DC dielectric properties of some polypropylene/calcium carbonate composites
Authors: Bánhegyi György , Karasz Frank E. , Petrović Zoran 
Published: May 2005

AbstractAC dielectric properties and thermally stimulated polarization (TSP) and depolarization (TSD) currents were studied in a series of CaCO3‐filled polypropylene composites. The filler content (0 to 50 weight percent) and the average particle size (3.0 to 16.1 μm) at constant filler content (30 weight percent) were varied in separate groups of samples. In a third group of samples the filler (20 to 40 weight percent) was surface treated with stearates. The AC dielectric behavior of composites containing untreated fillers is largely determined by a small amount of adsorbed water. Upon heating, the dielectric properties show maxima (increasing with decreasing frequency) which disappear on cooling. In the case of stearate‐treated fillers the dielectric loss level is higher, the dispersion and loss curves on heating reflect a combination of dipolar and protonic processes with water desorption. In the dry state the onset of an audio frequency relaxation process is observed in the pre‐melting zone. The thermally stimulated currents of the composites containing treated and untreated fillers are also different. In the case of the untreated fillers the TSP curves show maxima indicating water desorption which are increasingly intense and roughly exponential with filler content. The high temperature conductivity and the intensity of the pre‐melting depolarization peak pass through a minimum as a function of filler content. Above 20 weight percent filler content the activation energy of high temperature conductivity decreases. In the case of the surface treated samples, the thermally stimulated response is different for “wet” and dried samples. The dry samples exhibit a relaxation between the amorphous and crystalline transitions of the matrix polymer which is probably due to interfacial relaxation caused by the enhanced surface conductivity of the stearate‐treated fillers.
Component interactions and properties of crosslinked vinyl systems
Authors: Schreiber H. P. , Degrendele C. , Bataille P. 
Published: May 2005

AbstractCompositions based on poly(vinylchloride) (PVC) containing diisodecyl phthalate (DIDP) or trioctyl trimellitate (TOTM) plasticizers and, in several cases, also containing chlorinated polyethylene (CPE) as property modifier were cross‐linked by γ irradiation, using a trifunctional acrylic cross‐linking agent. Cross‐linking effectiveness was analyzed by solvent swelling data, and the effects of irradiation up to dosages of about 10 Mrad on the mechanical properties of the systems were recorded. The interaction potential of components used in these systems was determined by recently developed methods of inverse gas chromatography (IGC). These classify PVC and CPE as electron acceptors and the plasticizers as donors. Expectedly, increased moduli and decreased elongational properties follow exposure to γ‐rays. The plasticizers reduce the effectiveness of cross‐linking, the magnitude of the reduction being related to the degree of acid‐base interaction between PVC and plasticizing fluids. Interference with cross‐linking mechanisms thus is a function of the solvent power of the plasticizers. CPE competes with PVC for plasticizer so that for given quantities of DIDP or TOTM, the fraction available to solubilize the host polymer is reduced. In compounds with CPE, therefore, the cross‐linking effectiveness of irradiation is raised, consistent with the acid‐base balance of Interactions, as given by the IGC results. Twin yield points have been observed in the stress‐strain curves of compounds containing CPE. It is postulated that distinct, interpenetrating cross‐link networks are formed when these polymers are subjected to γ irradiation.
Rheology of polycarbonate/linear low density polyethylene blends
Authors: Utracki L. A. , Sammut P. 
Published: May 2005

AbstractThe flow behavior of linear low density polyethylene blended with polycarbonate (LLDPE/PC) was studied at 245°C using an Instron Capillary Rheometer and a Rheometrics Mechanical Spectrometer. The capillary measurements were repeated several times for each crosshead speed and capillary. The averaged values were corrected for shear heating as well as the pressure, entrance‐exit, and power‐law fluid effects. In spite of the utmost care, blend results were erratic with a standard deviation of 25 to 35 percent. Analysis of the capillary data suggested a telescopic flow with the lower viscosity component of the blend migrating toward the capillary wall. The experimental difficulties resulted from the flow and time induced variations of blend morphology. By contrast, the dynamic shear test results were found to be rapid and reproducible with a standard deviation for the complex viscosity of blends not exceeding four percent. The shear moduli of blends indicated the presence of an apparent (time dependent) yield stress, originating from interaction between domains of the dispersed phase. At frequencies exceeding a critical value, shear coalescence of the dispersed phase was observed near the rim of the rheometer plates.
Dynamic mechanical properties of VAMAS polycarbonate/polyethylene blends
Authors: Wippler C. 
Published: May 2005

AbstractAs part of the Versailles Project on Advanced Materials and Standards Technical Working Party on Polymer Blends, the dynamic mechanical properties of polycarbonate/linear low density polyethylene (PC/LLDPE) blends were measured. Ten laboratories participated in the round robin tests. As a whole, the inter‐laboratory agreement of data is good, particularly when results are obtained using the same apparatus (especially a Rheovibrom DDV‐III EA). The results clearly show the nonmiscibility of the parent components. The influence of frequency is also obvious but difficult to characterize because of the narrowness of the frequency range explored. The Takayanagi model applies very well for the calculation of the storage moduli as a function of composition and morphology. The most specific result is probably that of the processing orientation effect: There is no visible influence of flow orientation on dynamic tensile moduli of the parent polymers, but there is a significant difference in the moduli measured in the direction of extrusion and in the transverse direction for the blends at temperatures above 0°C. The difference is greatest for the high PE‐concentration blend.
Criteria for selecting cure cycles in autoclave processing of graphite/epoxy composites
Authors: Williams R. J. J. , Benavente M. A. , Ruseckaite R. A. , Churio M. S. , Hack H. G. 
Published: May 2005

AbstractRoom temperature mechanical properties, such as flexural strength and impact resistance, of epoxies and graphite/epoxy composites go through a maximum as a function of epoxy conversion. For tetraglycidyl 4,4′‐diaminodiphenylmethane (TGDDM)‐4,4′‐diamlnodiphenylsulfone (DDS) formulations, the recommended cure cycle prescribes a maximum temperature close to 177°C. The maximum extent of reaction that may be obtained at this temperature is determined from the vitrification curve. At this maximum conversion, balanced mechanical and physical properties are attained in the partially cured specimen. However, if the standard cycle is used to cure thick parts, the maximum temperature inside the sample increases beyond 177°C. This leads to a complete conversion in most of the part and a consequent impairment of resulting physical and mechanical properties. It is shown how numerical solutions of differential energy and mass balances may be used to propose alternative cure cycles such that the maximum conversion at every point remains bounded by the vitrification curve. An illustration for a particular thickness is provided.
Flow‐drawing of poly(ethylene terephthalate)
Authors: Gupta V. B. , Sett S. K. , Venkataraman A. 
Published: May 2005

AbstractThe drawing characteristics of poly(ethylene terephthalate) (PET) yarns spun at 1000 and 3000 m/min and film cast at 10 m/min have been studied as functions of drawing temperature up to 200°C and drawing rate up to 50 min−1. The fiber spun at 1000 m/min and the film had very low degrees of pre‐orientation and flow‐drawing occurred 20 to 30°C above their respective glass transition temperatures, for which the drawing tension dropped to almost zero and the resulting drawn samples were found to be amorphous and isotropic. In these samples, flow‐drawing could be prevented if they were drawn at relatively low temperatures or high strain rates. The partially‐oriented yarn spun at 3000 m/min, which had higher pre‐orientation, did not exhibit flow‐drawing under the conditions used. Flow‐drawing apparently occurs due to molecular relaxation processes, which predominate if the drawing temperatures are high, the strain rates are low, and the PET precursor has a low degree of orientation.
A process for making microcellular thermoplastic parts
Authors: Kumar Vipin , Suh Nam P. 
Published: May 2005

AbstractA novel process to produce microcellular thermoplastic parts is described. This is achieved by integrating the deformation process in the foaming cycle in such a way that the cell nucleation and growth processes are effectively uncoupled from deformation. The nitrogen‐polystyrene system is studied and the relationships between the essential process parameters are established. It is experimentally shown that the pressures associated with deformation do not reduce the number of bubbles nucleated. The process synthesized is demonstrated by making a microcellular polystyrene container.
Mechanical behavior related to the phase morphology of PC/SAN polymer blends
Authors: Quintens D. , Groeninckx G. , Guest M. , Aerts L. 
Published: May 2005

AbstractThe phase morphology of intensively melt mixed and injection moulded bisphenol‐A polycarbonate (PC)/styrene‐acrylonitrile copolymer (SAN) blends changes on annealing above the glass‐transition temperature (Tg) of both components. For the selected PC and SAN resins, the phase morphology of the 60/40 PC/SAN blend changes from a fine dispersion of the PC phase in a SAN matrix to a coarse co‐continuous phase network, whereas a co‐continuous 70/30 PC/SAN blend changes to a dispersion of SAN domains in a PC matrix. The effect of the blend morphology on dynamic mechanical properties and ambient tensile stress‐strain properties have been studied thoroughly. An increase of the storage modulus between Tg(SAN) and Tg(PC) is observed with increasing coarsening of the phase structure until a continuous PC matrix is formed. The coarsening of the phase structure of the blends gives rise to a transition from ductile to brittle fracture. The loss in ductility is related to a decrease in relative amount of interface and a transition in the type of dispersion.
Devolatilization of polymer melts: Machine geometry and scale factors
Authors: Biesenberger J. A. , Dey S. K. , Brizzolara J. 
Published: May 2005

AbstractThis study was aimed at comparing vented extruder geometries and identifying scale‐up parameters for melt devolatilization. Data are presented comparing single‐ and corotating twin‐screw extruders for devolatilization of methyl methacrylate from poly(methyl methacrylate), and parameters are identified which characterize dynamic similarity for potential use in design and scale‐up. These parameters include conventional process variables such as temperature, throughput, screw RPM, and degree of fill.
The oscillating die: A useful concept in polymer extrusion
Authors: Casulli J. , Clermont J. R. , Von Ziegler A. , Mena B. 
Published: May 2005

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractRecently, 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

AbstractHydroxyl 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

AbstractMelt 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

AbstractThe 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

AbstractThis 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

AbstractAn 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

AbstractSolid‐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.