bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological properties of linear low density polyethylene/polypropylene blends. Part 2: Solid state behavior
Authors: Dumoulin M. M. , Carreau P. J. , Utracki L. A. 
Published: December 2004

AbstractThis second paper of a series continues the examination of the tensile properties of two series of linear low density polyethylene/polypropylene, (LLDPE/PP) blends. The blends were prepared using a twin‐screw extruder and cover the whole concentration range, An Instron Universal Tensile Tester was used to measure the tensile properties of the blends between 10 and 70°C, and the temperature and composition dependences of the modulus were examined. A comparison is established between the solid state and melt properties to underline the behavior in the PP rich region. Results of dynamic mechanical experiments and differential scanning calorimetry on the same materials are also given, and the mechanical behavior is discussed in terms of the variation of the system's crystallinity.
Effect of a separator in a sheet die on the anisotropy of tear strength of extruded medium density polyethylene
Authors: Gent A. N. , Gregory B. L. , Jeong J. , Charrier J.‐M. , Hamel F. 
Published: December 2004

AbstractSheets of medium density polyethylene (MDPE) were extruded through a slit die containing an internal separator. Thus, the melt stream was momentarily split before emerging from the die. A line of separation was evident in the extruded sheets. It is attributed to incomplete welding or healing. Measurements of tear energy Gc revealed that the extruded sheets were anisotropic and that the weld line was extremely weak after extrusion start‐up, only about 1/5 of the strength elsewhere. As extrusion continued, the strength of the weld line increased to reach that of the bulk material after about 10 min. This is attributed to an increasing temperature of the melt in the die region, aiding interdiffusion. A sample containing 30% by weight of short glass fibers showed less initial weld‐line weakness but the weld line remained weak in this case, even after long extrusion times.
The formation of polymer fibers from the rapid expansion of supercritical fluid solutions
Authors: Petersen Robert C. , Matson Dean W. , Smith Richard D. 
Published: December 2004

AbstractFibers of organic polymers (polystyrene, cellulose acetate, and polypropylene) were formed by the rapid expansion of supercritical fluid solutions through a small diameter nozzle to ambient temperature and pressure. Solutions were prepared either by dissolving the polymer directly in room temperature pentane, or in an autoclave at elevated temperatures and pressures for less soluble polymers. The fibers were collected on substrates mounted in the expansion jet. The diameters of the fibers formed (typically 1‐5 μm) were much smaller than the opening of the nozzle, although fiber diameter was observed to generally increase with nozzle diameter. The aspect ratios of the fibers, produced by this process were on the order of 103 or larger. Optimum conditions for fiber formation occurred at fluid expansion temperatures near the melting point of the polymer, with particle formation mechanisms favored at higher and lower temperatures.
Testing of a kinetics equation of mechanical degradation
Authors: Mantia Francesco P. La 
Published: December 2004

AbstractA modification of the kinetics equation of mechanical degradation of Harrington and Zimm is proposed to fit experimental data taken on a molten polystyrene. This equation is applied to each molecular weight of the discretized molecular weight distribution curve, and the limiting molecular weight is determined for each molecular weight. With this modification the theoretical curves fit both Mw and Mn curves well.
Physical aging in thermosets of differing degrees of cure—master curve generation and the relation to mechanical properties
Authors: Schwartz S. A. , Bubeck R. A. 
Published: December 2004

AbstractPhysical aging of a thermoset system based on bisphenol‐A epoxy (DERTrademark of The Dow Chemical Company.
383) and tetrabromobisphenol‐A cured with sulfanilamide and diaminodiphenylsulfone was studied as a function of cure history. Changes in the dynamic mechanical spectra for the thermoset system were correlated to changes in relative toughness associated with physical aging as determined by plane‐strain biaxial tension‐compression yield measurements. It was found that master curves, generated by using tan δ data obtained in the β relaxation temperature regime, are well related to the corresponding changes in mechanical properties and, hence, have predictive value. Relative toughness decreases and compressive yield increases with decreasing tan 5 because of decreased molecular segmental mobility. The relative extent of physical aging for the as‐cast thermosets was shown to be linearly related to the cure time.
Strain‐induced crystallization behavior of poly(ether ether ketone) (PEEK)
Authors: Chien Ming C. , Weiss R. A. 
Published: December 2004

AbstractStrain‐induced crystallization of poly(ether ether ketone) (PEEK) was studied by the use of a parallel plate rheometer. The experimental variables included preheating time, crystallization temperature, and shear rate. The crystallization kinetics were characterized by means of an induction time defined as the time elapsed from the start of shearing to the onset of crystallization. The experimental results showed that the induction time for strain‐induced crystallization of PEEK was significantly shorter than that for crystallization under quiescent condition, and that strain‐induced crystallization was much less temperature dependent than quiescent crystallization. The activation energy for strain‐induced crystallization was found to be 0.035kcal/mole, which was considerably smaller than the reported activation energy for quiescent crystallization. Photomicrographs of the sheared specimens indicated that PEEK crystallites orient along the flow direction.
Polymer welding relations investigated by a lap shear joint method
Authors: Kline D. B. , Wool R. P. 
Published: December 2004

AbstractA lap shear joint method was used to study strength development during welding of polystyrene surfaces‐ The surfaces previously had not been in contact and care was taken to insure rapid wetting of the interface. The shear stress at failure, τf was measured at room temperature as a function of contact time, t, at constant welding temperatures up no 20°C above the glass transition temperature, Tg. The time dependence of welding could be well described by τfαt1/4. This result is in agreement with predictions of the reptation molecular dynamics model applied to inter‐diffusion at a symmetric amorphous polymer‐polymer interface. The activation energy for the thermally activated increase in strength development was determined as E = 96 kcal/mol at T = 113.5°C, which compares with E = 93,2 kcal/mole as predicted by the W‐L‐F theory using C1 = 13.7, C2 = 50 and Tg = 100°C. The polystyrene samples had molecular weights, Mn = 143,000 and Mw = 262.000. The time to achieve complete healing, t∞ ≈︁ 256 min at 118°C, was found to be of the same order of magnitude as the viscoelastic relaxation time and also with the time required for a polymer chain to diffuse a distance equal to its root mean square end‐to‐end vector.
Electrical conductivity of polymers containing carbon black
Authors: Ghofraniha Mehrdad , Salovey R. 
Published: December 2004

AbstractChanges in volume resistivity with temperature of carbon‐black‐filled polymers and a random copolymer of styrene and butyl methacrylate were measured. For polystyrene containing 20 wt % carbon black, of surface area 24 m2/g, the resistivity changes abruptly from 1013 to 106 ohm‐cm above 150°C. Poly(butyl methacrylate) did not show well‐defined changes in resistivity on heating. The random copolymer containing 16.7 or 28.6 wt % carbon black, of surface area 24 m2/g, showed a resistivity exceeding 1013 ohm‐cm, that decreased to about 107 ohm‐cm on heating above 120°C. This Copolymer containing 16.7 wt % carbon black, of surface area 625 m2/g, shows a resistivity of about 108 ohm‐cm that decreases sharply to 103 ohm‐cm by 150°C. Decreases in resistivity on increasing the temperature in the quiescent state are correlated with the observation of a yield stress at low shear rates in rheological studies. It is suggested that carbon black agglomerates at elevated temperature and forms an independent conductive network that prevents flow.
Multiple melting endotherms of poly(ethylene terephthalate)
Authors: Zhou Chixing , Clough S. B. 
Published: December 2004

AbstractPoly(elhylene terephthalate) samples were isothermally crystallized from the melt on a differential scanning calorimeter. Subsequent fusion showed three endotherms under many crystallization conditions. These three peaks are attributed to melting of crystallites formed daring primary and secondary crystallization processes and to fusion of crystals formed during recrystallizatlon during the melting scan.
Elongational behavior of low density/linear low density polyethylenes
Authors: La Mantia F. P. , Valenza A. , Acierno D. 
Published: December 2004

AbstractRheological data have been collected in isothermal elongational flow for three different types of blends, made from one low density polyethylene and three linear low density samples. In addition to the transient curves, elongation at break data are also reported. The influence of the composition and of the molecular weight of the linear low density polyethylene is discussed.
Morphological studies of polycarbonate‐poly(butylene terephthalate) blends by transmission electron microscopy
Authors: Delimoy Didier , Bailly Christian , Devaux Jacques , Legras Roger 
Published: December 2004

AbstractThe morphology of polycarbonate (PC)‐poly(butylene terephthalate) (PBT) blends prepared by melt‐processing in an extruder or a Brabender Plastograph was studied by Transmission Electron Microscopy. Transesterification during blending was avoided by the use of di‐n‐octadecyl phosphite, an efficient transesterification inhibitor. Ruthenium tetraoxide was used to selectively stain the PC fraction. Observation of ultrathin sections revealed the biphasic nature of the blends and the partial compatibility of the polymers in the molten state. The most striking consequence of this Is the presence, of PBT crystalline lamellae growing inside the PC‐rich phase for samples annealed in the proper temperature range. A preliminary study of the morphology as a function of composition and thermal annealing was undertaken. The RuO4 staining technique was also applied to the commercial blend Xenoy CL 100 from General Electric, which was shown to contain an MBS impact modifier (a methylmethacrylate butadiene‐styrene copolymer) exclusively located In the PC‐rich phase.
Observers for optimal anticipatory control of ram velocity in injection molding
Authors: Agrawal A. R. , Pandelidis I. O. 
Published: December 2004

AbstractThe application of optimal anticipatory control assumes that the entire stare is available for feedback. However, in the case of injection molding this assumption is viola red due to economic considerations. For that purpose, this paper discusses the effectiveness of optimal anticipatory control using estimates of the states obtained from a dynamic system, called observer. State estimation is essential to optimal control techniques since in general the states are used in some form of feedback and the number of measurable states is usually much Jess than the actual number of state variables, limited by the availability of cheap and rugged sensors and the ease of installation. Furthermore the measurements from the existing sensors may be corrupted by significant noise. In the present paper both the stochastic and the deterministic cases are investigated for application to optimal control of ram velocity in injection molding.
Development of a mathematical model for the pultrusion of unsaturated polyester resin
Authors: Han C. D. , Chin H. B. 
Published: December 2004

AbstractA mathematical model is developed for simulating the pultrusion process of unsaturated polyester resin, using a mechanistic kinetic model based on free radical polymerization. In their previous publications (Refs. 1 and 7), Han and Lee used the mechanistic model to simulate the curing behavior of unsaturated polyester resins under isothermal conditions, employing the differential scanning calorimetry data obtained for a range of single initiators and multiple initiator systems. For the sake of mathematical convenience, a pultrusion die of cylindrical geometry was considered. The mathematical model developed permits one to choose any number of initiators when predicting the distributions of the degree of cure and temperature in both the radial and axial directions of the die. The effects of material variables (e.g., the type and concentration of mixed initiators) and processing conditions (e.g., pulling speed and die temperature distribution) on the performance of the pultrusion are evaluated.
Measurement of the melting points of oligomers obtained in the manufacture of poly(ethylene terephthalate)
Authors: Yamada T. , Mizuno Y. , Imamura Y. 
Published: December 2004

AbstractThe melting points (Tm) were measured for oligomers obtained by a direct continuous esterification process between terephthalic acid and ethylene glycol. Multiple regression analyses of data were carried out, and an equation was obtained for predicting melting points with correlation coefficient of ∼0.99.
Molding by reactive injection of reinforced plastics
Authors: Reboredo M. M. , Rojas A. J. 
Published: December 2004

AbstractA model for the molding by reactive injection of reinforced plastics for systems in which fiber glass reinforcements are placed into the molds, is proposed. It allows for the determination of processing parameters and their influence on dependent variables: conversion, temperature, and pressure. Moldability areas, where premature gelling is avoided, are defined. Operating conditions are selected to reduce cycle time, produce small load losses, and provide a fairly uniform curing stage throughout the product.
A predictive model for the mechanical behavior of particulate composites
Authors: Anderson Lori L. , Farris Richard J. 
Published: December 2004

AbstractA method for predicting the stress‐strain and volumetric behavior of particulate composites from constituent properties has been developed for large values of strain. This approach allows a simple model for systems in which damage occurs without resorting to complicated constitutive equations. An energy balance derived from the first law of thermodynamics and the equations of linear elasticity calculates critical strain values at which filler particles will dewet when subjected to uniaxial tension and superimposed pressure. Calculations of critical strains over the entire strain history using reevaluated material properties accounting for the damage yield highly nonlinear stress‐strain and volumetric curves. Experimentally observed dependences on particle size, filler concentration, matrix and filler properties, and superimposed pressure are correctly predicted. The method has no adjustable parameters, and allows several idealized models of the dewetting process to be examined. Comparisons of model predictions to experimental data show good agreement.
Analysis of interfacial stresses for elastomeric disks in compression
Authors: Thornton J. S. , Montgomery R. E. , Thompson C. M. , Dillard D. A. 
Published: December 2004

AbstractRelatively simple forms have been derived for obtaining the total force required to deflect a circular rubber disk of arbitrary dimensions between two rigid platens which offer Coulomb frictional resistance to flow of the rubber. The calculation of the critical radius which separates the regions of frictional adherence and restrained flow is a necessary step in the solution process. Although it cannot be solved for explicitly, an implicit form given herein converged rapidly. The solutions for force can involve differences between very large numbers as the coefficient of friction becomes small. Care should be used to evaluate these quantities in order to avoid round off errors.
Reaction kinetics of a polyurea reaction injection molding system
Authors: Pannone Mary C. , Macosko C. W. 
Published: December 2004

AbstractPolyureas have the potential for Improving reaction Injection molding (RIM) productivity through shorter demo Id times and elimination of external mold release agents and post‐cure. Kinetics of urea formation are necessary for process modeling of polyurea RIM systems. Adiabatic temperature rise measurements were used to monitor the extent of reaction of an aliphatic diamine and an aromatic diamine reacting competitively with a single diisocyanate. The aliphatic diamine reacted much faster; essentially complete polymerization occurred in the RIM mixhead. A similar three‐component system was studied in dimethylacetamide and diethylene glycol dimethyl ether, and the sequential nature of the two competing reactions was confirmed. The RIM polymerization of the aromatic diamine, 3,5 diethyltoluene (2,4 and 2,6) diamine and;4,4′‐diphenylmethane diisocyanate was studied using an unreactive poly ether as the solvent. The exotherms could be fit with a third order model. Adiabatic temperature rises for all RIM experiments were in good agreement with the values predicted by heats of reaction measured in solution.
Properties of segmented block copolyurethane I. Adhesion between PET cord and rubber by polybutadiene‐polyethylene terephthalate block copolyurethane
Authors: Yamashiro Seiichi 
Published: December 2004

AbstractA block Copolyurethane was synthesized by using a hydroxy‐terminated 1,2‐polybutadiene (HPBD) having vinyl side chains and a molecular weight of 2000 to 5500 as a rubber‐affinitive component, a hydroxy‐terminated poly(ethylene terephthalate) as a PET‐affinitive component, and 4,4′‐diphenylmethane diisocyanate as a chain extender. The block copolymer was mixed with a curing agent and used for the adhesion of PET cord of 1100 denier and rubber. The peak of adhesive strength was observed at the HPBD molecular weight of 4500 within the molecular weight range of 2000 to 5500.
The effects of fluids in the aircraft environment on a polyetherimide
Authors: Long Edward R. , Collins William D. 
Published: December 2004

AbstractFluid absorption studies have been made for a polyetherimide thermoplastic film and a unidirectional composite of the thermoplastic with graphite fibers immersed in water, JP4 jet fuel, ethylene glycol, and hydraulic fluid. The changes in the weight, thickness, and tensile properties were measured for the film. The changes in the flexural properties of the composite were measured for specimens whose fiber orientation was transverse to their length. Only the hydraulic fluid, which caused an erosion or dissolving of the resin at the specimen surface, affected the film's properties. Both the water and the hydraulic fluid affected the flexural properties of the composite, due to capillary absorption along the fiber‐resin interface.
New horizons in advanced oriented fiber
Authors: Tam T. Y. , Boone M. B. , Weedon G. C. 
Published: December 2004

AbstractAchievement of exceptional properties in films/fibers generally requires very high to ultra high molecular weights and very high degrees of orientation. A brief description of the fiber related technologies‐used to maximize orientation in high performance fibers, e.g., solid state extrusion, special drawing methods gel spinning, and liquid crystal spinning are reviewed. A detailed comparison of the fiber properties resulting from these technologies is also shown. Particular emphasis is.placed on describing the upgrading of polyethylene to a high performance fiber product through several of these technologies. Gel/solution spinning of ultra high molecular weight polyethylene (UHMWPE) is especially highlighted. The latest worldwide efforts to commercialize gel spun fibers are discussed as well as the applicability of the process to other thermoplastics. Applications illustrating the use of high performance fibers in various end use areas are summarized. The primary properties critical to each are also outlined.
Vibration welding of thermoplastics. Part IV: Strengths of poly(butylene terephthalate), polyetherimide, and modified polyphenylene oxide butt welds
Authors: Stokes V. K. 
Published: December 2004

AbstractIn vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time or weld penetration.; The effects of these parameters on weld quality were systematically studied by first butt welding thermoplastic specimens under controlled conditions, over a wide range of process parameters, and by then determining the strengths and ductilities of these welds by tensile tests. The three thermoplastics investigated are poly (butylene terephthalate), polyetherimide, and modified polyphenylene oxide. Changes in the weld pressure are shown to have opposite effects on the strengths of polyetherimide and modified polyphenylene oxide welds; Also, the weld frequency is shown to have a significant effect on the weldability of polyetherimide. The weldability data for these three thermoplastics are compared with data for polycarbonate. Under the right conditions, the strengths of butt welds in these materials are shown to equal the strength of the virgin polymer.
Comments and recommendations on the use of the Avrami equation for physico‐chemical kinetics
Authors: Khanna Y. P. , Taylor T. J. 
Published: December 2004

AbstractOver the last four decades, numerous reports have appeared on the physico‐chemical kinetics, especially crystallization kinetics, based on the Avrami equation, ϕ = exp [−Ktn] where ϕ is the fraction of material unchanged at time t, K is an overall rate constant and “n” is the Avrami exponent indicative of process mechanism. The usage of the Avrami equation has been limited to the determination of “n” and its temperature dependence. It is shown that the evaluation of K and the activation energy (E) using this equation is erroneous since K and E are both influenced by “n” although such would be unexpected from the Avrami equation. On the other hand, if one uses a modified expression, ϕ = exp[−Kt]n, then in addition to the value of “n”, correct values of K and E are obtained. This retains the original correspondence of the Avrami equation to nuclea‐tion and crystal growth processes but extends its applicability to (i) correctly evaluate K and E parameters, and (ii) correctly compare transformation rates when the systems differ in their n values. Experimental data are presented to support these conclusions.
Chemorheological characterization of thermoset cure
Authors: Tungare A. V. , Martin G. C. , Gotro J. T. 
Published: December 2004

AbstractThermosetting resin/glass cloth composites find extensive use in the packaging of electrical circuits into multi‐layered circuit boards. To determine optimum processing conditions, it is necessary to understand the rheology of the resin as it cures. In this study, a squeezing flow geometry was used to determine the shear viscosity of a high performance epoxy resin during cure; Viscosity profiles were obtained during rising temperature cure. The results were compared with the complex viscosities obtained using the dynamic oscillatory parallel plate geometry. A numerical optimization algorithm was used to obtain the dual Arrhenius viscosity model parameters from the experimental viscosity data. The sensitivities of the model parameters and their effects on the predicted viscosity profiles were also determined.