bluuebunny/crossref_metadata_2025_split huggingface dataset:
Critcal stress and recoverable shear for polymer melt fracture
Authors: Vlachopoulos J. , Alam M. 
Published: December 2004

AbstractThe phenomenon of extrudate distortion, which is called melt fracture, was studied for polystyrene samples of narrow and broad molecular weight distribution, and commerical samples of polypropylene and linear and branched polyethylene. It was experimentally found that the shear stress at the onset of melt fracture (τcr) is of the order of 106 dynes/cm2 and independent of the distribution of molecular weights. As the weight average molecular weight increases the shear stress τcr decreases. For polystyrene extruded at τcr the recoverable shear strain, which is defined to be half the ration (first normal stress difference/shear stress), was found proportional to the factor MzMz+1/Mw2 which represents the distrubution of molecular weights. The proportionality is expected to hold for other polymer systems. The polymer behavior at the onset of melt fracture was explained in terms of Graessley's entanglement theory and his correlation between true and Rouse shear compliance.
Fusion of particulate structure in polyvinyl chloride during powder extrusion
Authors: Hattori T. , Tanaka K. , Matsuo M. 
Published: December 2004

AbstractIt has been recognized recently that suspension polyvinyl chloride granules consist of particles ca 1μ in diam which are linked together to form a three‐dimensional, sponge‐like lattice. This paper deals with the fusion process of this particulate structure of PVC resin during powder extrusion. Extrudates prepared under various extrusion conditions are investigated through the electron microscope using a methyl methacrylate (MMA) embedding method followed by ultrathin sectioning. The MMA embedding method has been proven to be an effective means of revealing the detailed structure of molded PVC. Results showed that the 1μ‐particles were subjected to breakdown due to heat and shear into fibrils 100‐300 Å in thickness, which were the final structure attainable by extrusion. Discussion was focused on the fibrillar structure especially in relation to the elasticity in plasticized PVC.
An analysis of fiber buckling
Authors: Hackett R. M. , Tarpy T. S. , Wood J. L. 
Published: December 2004

AbstractThis paper presents results obtained by the experimental technique of photoelastic stress analysis and by finite or discrete element analysis, applied to the case of buckling of a single, axially‐loaded metal fiber embedded in a plastic matrix. The program was conducted utilizing a mild steel fiber embedded in an epoxy resin system. The fiber was loaded axially with an increasing compressive force until buckling occurred. Along with determination of the critical load for the fiber, the maximum shearing stress at any point in the epoxy matrix was determined using two‐dimension photoelastic stress analysis. In the analytical study, the fiber was modeled by a series of bending elements and the matrix by an assemblage of constant‐strain triangular elements. The total system was thus modeled by the two types of elements connected at common nodal points. The instability was solved as a standard eigenvalue problem and the stress tensor was obtained by finite element stress analysis.
The elastic, anelastic and plastic components of strain in the load‐extension curve for bisphenol‐A polycarbonate
Authors: Robertson Richard E. , Patel Ashwin M. 
Published: December 2004

AbstractA procedure has been developed for analyzing the elongation of a specimen in a tensile test for the elastic, anelastic, and plastic components of strain. The procedure was applied to bisphenol‐A polycarbonate, which showed the division between the anelastic and plastic components to be justified and gave the following results. First, the elastic modulus was found to be essentially constant, independent of stress up to at least 7,000 psi. Second, the strain accumulated at the yield point was found to be mainly anelastic and recoverable with release of the stress. Third, plastic or non‐recoverable strain was mainly accumulated only beyond the yield point. These latter two results suggest that anelasticity is important for ductility. The relatively large anelastic response at low stresses that contribute to the ductility of polycarbonate probably arises from both the large size of the moving segment and the large low temperature loss process.
Fracture mechanics and relaxation processes in polyvinyl chloride
Authors: Radon J. C. 
Published: December 2004

AbstractLinear elastic fracture mechanics has been applied to investigate the strain rate sensitivity of polyvinyl chloride over a range of temperatures (−197 to +80°C). Three‐point bend tests have been carried out at two widely different strain rates; in “static” (slow bend) conditions and in a “dynamic” (impact) situation. A specially instrumented Charpy impact hammer has been used to analyse the record of transient loads.The fracture toughness results show a close relationship to the relaxation phenomena between −60 and +75 °C; it was observed that in this region the maximum toughness correlated with the maximum β‐relaxation. It was also found that, while in the region of low temperatures the material showed a considerable degree of strain rate sensitivity, at +50° the dynamic and static toughness were of the same order of magnitude; this behavior differs substantially from that observed in metals.
Unsteady‐state heat transfer in a crystallizing polymer
Authors: Sifleet William L. , Dinos Nicholas , Collier John R. 
Published: December 2004

AbstractThe processing of polymers typically includes steps involving heat transfer, such as quenching and crystallization. The mechanical properties of a polymer are thus affected by processing conditions, such as the amount of time spent by each portion of the polymer at each temperature in the processing sequence.This paper presents the results of a mathematical modeling study of the unsteady‐state temperatures inside a crystallizing polymer during quenching. This model differs from usual methods in including temperature dependence of induction times and kinetic processes, and in not treating the polymer as a simple, small molecule system. The model permits the prediction of the final morphological distribution within the polymer. Use of the model will aid in tailoring processing conditions to produce a product with specified morphology. The method is applicable to a wide variety of problems in polymer processing, particularly for those polymers which exhibit crystallization.
Physical properties of polymers–an introductory discussion
Authors: Smith Thor L. 
Published: December 2004

AbstractPhysical characteristics of isolated molecules and bulk polymers are discussed briefly. The broad spectrum of mechanical properties resulting from changes in temperature and experimental time‐scale is introduced by first considering the time‐independent properties of elastomers under large deformations and then the effect of a progressive decrease in segmental mobility, leading eventually to glassy characteristics. The phenomenological theory of linear viscoelasticity along with time‐temperature superposition is outlined, and illustrative data are presented. Finally, phenomena resulting from volumetric relaxation processes are considered briefly.
Effect of gas diffusion on creep behavior of polycarbonate
Authors: Hojo Hidemitsu , Findley William N. 
Published: December 2004

AbstractBiaxial tension‐tension creep experiments were performed to study the effect of gas diffusion on creep behavior of polycarbonate. Experiments were conducted on a thin‐walled tubular specimen by applying both gas pressure and axial tension at room temperature, and measuring axial strain and gas absorption. Experiments were performed with helium, nitrogen, air, carbon dioxide and Freon‐22Registered trademark, E. I. duPont de Nemours Co., Inc.
. It was found that the creep deformation was highly affected by the solubility controlled gases, carbon dioxide and Freon. The absorption measurements showed that the gas absorption behavior was clearly affected by the creep deformation of the material. Also an anomalous diffusion‐type behavior appeared even in permanent gas‐polymer systems under creep conditions. The modified superposition principle satisfactorily predicted the recovery following creep. The axial creep for the biaxial tension‐tension experiments was also computed from data previously reported for creep under combined tension and torsion of a different sample of polycarbonate.
Effects of gamma radiation on the dynamic mechanical and swelling behavior of styrene butadiene block and random copolymers
Authors: Samuels Sam L. , Wilkes Garth L. 
Published: December 2004

AbstractThe physical structure of a number of styrene‐butadiene copolymers were investigated via dynamic mechanical and swelling studies on uncrosslinked and gamma‐radiation cross‐linked films that had initially been solvent cast from toluene or methyl ethyl ketone. The mechanical behavior of these films before and after crosslinking was found to depend on the material history as well as the chemical structure of the copolymer, in agreement with observations made by other experimental techniques. A simple morphological interpretation was given to the dynamic mechanical spectra as a function of radiation dosage and a limited discussion of the swelling behavior is included.
Design of certain fluted mixing sections of extruder screws
Authors: Tadmor Zehev , Klein Imrich 
Published: December 2004

AbstractA theoretical model is proposed, for certain barrier type fluted mixing sections of extruder screws. Screws with such mixing sections are occasionally used in plasticating extruders. With the aid of this model, these screws can now be quantitatively simulated in the design stage. Specifically the model enables the calculation of pressure change across the section as a function of geometrical configuration of the mixing section and operating conditions.A generalized set of curves, plotted in dimensionless form, for quick manual computation is also given. With its aid, the effect of the design variables on the pressure change is discussed.Finally, mixing section‐zones, in reference to the plasticating extrusion theory, and the state of the art of extrusion theory are very briefly discussed.
Investigation of the ductility of rolled polymers
Authors: Bahadur S. , Henkin A. 
Published: December 2004

AbstractThe effect of cold rolling on the mechanical properties of polymers, viz., acetal, nylon 66, poly(vinyl chloride) and polycarbonate has been studied. The yield strength, Young's modulus, and hardness increase with increasing cold work, except for a slight drop in these properties at low values of cold work. The ductility increases with rolling to a maximum and drops with further reduction. At the same time, the tensile strength increases continuously with rolling. This conspicuous occurrence of the increase in ductility with a simultaneous increase in tensile strength for polymers, unlike that in metals, is explained considering the morphological changes produced in polymers upon cold rolling. It is shown that this typical behavior is not due to the unique loading or heating and cooling cycle involved in the rolling process.
Tailoring the interface in graphite‐reinforced polycarbonate
Authors: Kardos J. L. , Cheng F. S. , Tolbert T. L. 
Published: December 2004

AbstractPronounced effects of thermal treatment on the properties of graphite fiber/polycarbonate and glass fiber/polycarbonate composites have been demonstrated and explained. At 20 volume percent loading of random‐in‐a‐plane, discontinuous fibers, both specimen strength and modulus in both fiber systems were found to increase dramatically upon molding above 260–265°C, whereas only the graphite system was further improved by subsequent annealing. In the latter case, property improvement is due to generation of a crystalline innerlayer at the interface, which apparently transfers the stresses more effectively from fiber to fiber. Regardless of the type of fiber, molding at 275°C (slightly above 260–265°C, the melting point of crystalline polycarbonate) results in improved properties due to better wetting of the fibers by the resin. Hot forming of graphite reinforced polycarbonate composites between the molding and annealing steps takes advantage of the higher processability of the unannealed material in addition to providing increased modulus and strength in the final molded article.
A rheological study of aqueous separan solutions
Authors: Blanks R. F. , Park H. C. , Patel D. R. , Hawley M. C. 
Published: December 2004

AbstractThe concentration dependence of the rheological response of aqueous Separan solutions was measured. The shear and primary normal stress response in steady shearing flow, and the relaxation of shear stress following cessation of steady shear flow, were measured with four different polymer solution concentrations. Two different nonlinear constitutive equations, Bird‐Carreau and Meister, were used to analyse the data. The Bird‐Carreau model fit the steady shear data very well and the parameters obtained from steady shear data allow reasonable estimates of the stress relaxation of these systems. The Meister model provided a fit of the transient stress relaxation data and could be used to estimate the steady shear response. No quantitative molecular theory was developed in this work. However, the nature of the concentration dependence of the Bird‐Carreau parameters suggests that as the polymer concentration of aqueous Separan solutions decreases from 2.0 to 0.05 weight percent the solutions should be modeled less by an entangled network theory and more as slightly overlapping hydrodynamic units. The concentration where this behavior seems to be changing appears to be about 0.25 percent by weight of polymer.
A new thickness sensor based on the Hall effect
Authors: Okuyama M. , Yagii K. , Sharda S. C. , Tschoegl N. W. 
Published: December 2004

AbstractA highly sensitive thickness sensor has been developed which may be used as a continuously recording extensometer for rubbery materials. The application of the sensor for measuring volume changes in dewetting filled rubbers is also discussed. Further possible applications include the determination of Poisson's ratio on plastics.
Rheological analysis of stabilizing forces in wire‐coating dies
Authors: Tadmor Z. , Bird R. B. 
Published: December 2004

AbstractA rheological analysis of a wire‐coating die is presented. The rheological forces which might play a role in the stability of the wire are estimated. In particular, consideration is given to lateral forces related to the secondary normal stress function acting on the wire which is in an eccentric position, and the hydrodynamic force related to the viscosity function acting on the wire which moves at an angle to the die axis. For the former a simple, yet general, expression was derived by solving the flow problem (without axial pressure gradient) with the Ericksen equation in bipolar coordinates. Results indicate that normal stresses stabilize the wire, i.e., tend to restore it to the central location, provided the secondary normal stress function is negative. The hydrodynamic effect tends to reduce the angle between wire and die axes, thus drawing attention to the need of perfect mechanical centering of the guider tip, since in this case this effect also reduces eccentricity. The need is stressed for further work, in particular, experimental measurement of the secondary normal stress function.
A method for estimating both the solubility parameters and molar volumes of liquids
Authors: Fedors Robert F. 
Published: December 2004

AbstractThe solubility parameters and molar volumes of substances can be used, in conjunction with suitable theory, to provide estimates of the thermodynamic properties of solutions; the solubility characteristics of polymer‐solvent systems and the estimation of the equilibrium uptake of liquids by polymers are examples of the type of practical problems that are amenable to treatment.For low molecular weight liquids, the solubility parameter, δ, is conveniently calculated using the expression δ = (ΔEv/V)½, where ΔEv is the energy of vaporization at a given temperature and V is the corresponding molar volume which is calculated from the known values of molecular weight and density.For high molecular weight polymers, the volatility is much too low for ΔEv to be obtained directly and hence recourse must be made to indirect methods for estimating δ for these materials. One such widely used method is based on Small's additive group “molar‐attraction constants” which when summed allow the estimation of δ from a knowledge of the structural formula of the material; however, the density must still be determined experimentally.The proposed method of estimating δ, also based on group additive constants is believed to be superior to Small's method for two reasons: (1) the contribution of a much larger number of functional groups have been evaluated, and (2) the method requires only a knowledge of the structural formula of the compound.
The solution of plastics prediction problems by thermoanlytical techniques
Authors: Bair H. E. 
Published: December 2004

AbstractOften the first step in the solution of problems concerning the use of plastics involves the detailed characterization of a particular resin. Typically, a commercial plastic is composed not only of the basic resin but also of many additional additives. These additives may be such things as impact modifiers, plasticizers, flame retardants, and molding lubricants. In our laboratory we have developed thermoanalytical techniques for the determination of the morphology and composition of these multiphase materials. Specifically, we have quantitatively analyzed an ABS resin for not only the amount of SAN and BD but also the concentration of a molding lubricant (ML) in the resin. The concentration of BD and SAN was estimated calorimetrically from ΔCp measurements at Tg, and the ML level was calculated from ΔHf determinations. In addition, the shifts in Tg of both the BD and SAN phases of the ABS were studied as a function of diluent concentration. The diluents in these resins are residual monomers or other “impurities”.
A sliding scale method for rapid interpretation of rheological measurements
Authors: Ziabicki Andrzej , Szenberg George 
Published: December 2004

AbstractA simple method has been developed for interpreting rheological data from virtually any of the common rheometers. The method involves the use of an overlapping scale to provide a direct readout of apparent viscosity. The procedure can accommodate data from either rotational or capillary instruments and for the conditions of either shear rate or shear stress control. The method is fully described along with several examples of its application.
Melt viscosity of poly(vinyl chloride) formulations
Authors: Utracki L. A. 
Published: December 2004

AbstractCommercial, suspension‐type PVC resin, poly (vinyl chloride), molecular weight Mw × 10−4 = 8.6 ± 0.9, polydispersity Mw/Mn = 2.26, was mixed with plasticizer di(2‐ethyl hexyl)phthalate (DOP) and organo‐tin stabilizer in four different proportions. The mixtures were milled and pressed into sheets for testing. The polymer content in these samples was 97, 80, 60, and 40 wt percent. The viscoelastic properties of the materials were investigated using a Weissenberg rheogoniometer in a cone‐and‐plate, steady‐state shearing mode. The viscosities and primary normal stress difference coefficients were measured at shear rates of 10−2 ≤ \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^. $\end{document} (sec−1) ≤ 102 and at temperatures from 151 to 246°C. The zero shear viscosities, plotted as log η0 vs 1/T (T is the absolute temperature) did not follow either a straight line dependence, reported for PVC melts at low shear rates at 170–190°C, nor was any discontinuity found near 195°C as by others; the data follows a continuous concave curve. The apparent activation energy of flow increases steeply with decreasing temperature. The data can be represented by a WLF type of equation, but the magnitudes of the parameters of this relation differ from expected values. A crossplot of log η0 (T = const.) vs log w (where w is the polymer content) also demonstrates a faster increase of η0 with w than expected from the straight line dependence. The primary normal stress difference coefficient was found to increase with w and decrease with T, paralleling the observed dependencies of η0.
The influence of crystallinity on the beta‐transition in poly(vinyl chloride)
Authors: Harrell E. Ray , Chartoff Richard P. 
Published: December 2004

AbstractThe effect of changes in crystallinity on the β‐transition in poly(vinyl chloride) was studied by dynamic mechanical measurements of loss tangent (tan δ) and storage modulus (E′) over the temperature range −160° to 85°C. Four frequencies were covered, 3.5, 11, 35, and 110 Hz. The data presented demonstrate that crystallinity has a significant influence on the relaxation processes involved in the β‐transition. The restrictions on segmental mobility imposed by crystallinity are most pronounced in the region between Tβ and Tg, with Tβ tending to shift to lower temperatures, Tg shifting to slightly higher temperatures, the magnitude of tan δ decreasing, and engineering tensile strength increasing. Our data also show that individual PVC resins have mechanical and physical properties which differ enough so that comparisons which are often made between them may be inconclusive. Moreover, the properties of one resin may be more sensitive to thermal treatment than those of another. We are continuing this study to establish correlations between the observed trends and other important mechanical properties such as impact strength, toughness, tensile, and compressive strength.
Crystallization of polyethylene oxide under shear
Authors: Fritzsche A. K. , Price F. P. 
Published: December 2004

AbstractA concentric cyclinder dilatometer was designed and built to study the influence of shear on the crystallization kinetics of polymers. This instrument allows crystallization to be followed at both constant temperature and shear rate. Several samples of polyethylene oxide (Carbowax 4000, Carbowax 20‐M, and WSR‐205) were used. A low molecular weight fraction of the Carbowax 20‐M, as well as the unfractionated material, was crystallized under shear. The WSR‐205 was studied only in a mixture with Carbowax 4000. It was shown that the kinetics of crystallization of uncrosslinked melts of polyethylene oxide are altered by shear. The induction times for the appearance of crystallinity are shorter in the sheared systems than in the quiescent melts. The Avrami exponents are also higher for crystallization in sheared melts than in quiescent systems and increase with decreasing supercooling. The high values of the Avrami exponent are attributed to the disruption of crystalline aggregates into particles larger than the critical sized nucleus. These particles will persist in the melt and continue to grow spontaneously. A continuous infusion of growing particles into the melt occurs.At constant temperature and shear rate, the induction time of the crystallization curve is influenced by polymer molecular weight. In moderate to high molecular weight samples, the effect of shear becomes saturated at very low shear rates. Decreasing the molecular weight separates the crystallization curves. The curves from the higher shear rates appear at the shorter induction times. However, decreasing the molecular weight below that at the critical entanglement molecular weight allows the nucleation rate, strongly dependent upon the supercooling, to influence the relative positions of the sheared crystallization curves.