bluuebunny/crossref_metadata_2025_split huggingface dataset:
The dynamic properties of elastomers above the limit of linear viscoelastic response
Authors: Lidor Gershon , Maxwell Bryce 
Published: December 2004

AbstractA method of measuring the dynamic viscoelastic properties of polymers at large strain magnitudes, well above the limit of linear viscoelastic response, has been developed. A straight line relationship has been found between the dynamic stress and the dynamic strain above the limit of linear viscoelastic response. This straight line relationship can be described by a dynamic in‐phase modulus that is a function of the maximum strain applied and the frequency of the applied dynamic strain. This rheological characterization method is demonstrated for a series of synthetic elastomers with various carbon black loadings.
Crystallization studies of semi‐crystalline polymers under oscillatory shear using the rheometrics mechanical spectrometer
Authors: Chang Eng‐Pi , Kushner Brian 
Published: December 2004

AbstractA method has been developed on the Rheometrics mechanical spectrometer using the eccentric rotating disks mode to study the crystallization kinetics of different semi‐crystalline polymers (polyethylene, polypropylene, poly(butylene terephthalate) and Nylon 11) under oscillatory shear. Dynamic shear moduli (storage G′ and loss G″), loss tangent (tan δ), and dynamic viscosity (η′) were simultaneously, monitored during the crystallization process. The onset and completion of crystallization were characterized by the initial rise and final levelling off of G′, while the peak time, of crystallization (tp) is calculated from the time elapsed between the onset and peak of crystallization which is indicated by the G″ or η′ maximum. In the case of polypropylene, going from a low frequency of ≃0.1 rad/s, to higher frequencies of up to 10 rad/s, there is a monotonic decrease in peak time of crystallization (tp) together with a progressive decrease in spherulitic morphology. The observed acceleration in crystallization is due predominantly to the increase in nucleation rate and orientation of chains in melt crystalline aggregate. The progressive disappearance of the spherulitic morphology is attributed to the disruption of the spherulite superstructure at higher frequencies of shear.
Realistic analysis of flow in wire‐coating dies
Authors: Carley James F. , Endo Tadakazu , Krantz William B. 
Published: December 2004

AbstractWe have constructed a rigorous numerical solution of the equations of flow and energy within a general wire‐coating die that provides a far more accurate and detailed description of the flow than any previously available. The program* can accommodate uni‐ or multi‐sectional dies, in which the sections have conical or cylindrical shapes. Melt rheology was satisfactorily represented over the full range of shear rate at processing temperatures by a model with three regions for each isotherm, requiring six constants evaluated from rheometric data. Thirty‐three cases have been run, all of them in the domain of moderate‐to‐high wire speeds, with the two most important wire‐coating resins, low‐density polyethylene (LDPE) and plasticized polyvinyl chloride (PVC). Although the radialconvection term was omitted from the energy equation to overcome calculational instability, we believe the accuracy of our calculated results is chiefly limited by knowledge of melt properties. Temperature profiles typically exhibit two maxima, the more pronounced one being found close to the die wall. In coating a No. 22 AWG wire with LDPE at 2000 ft/min in one cylindrical die, the maximum rise, occurring at the die exit, was 100 K. Profiles of axial velocity across the stream exhibited maxima in some cases, not in others. Shear rates ranged from zero to about 106 s−1 and viscosity profiles were highly variable. Because the melt passes through the die so quickly, the calculated results for isothermal and adiabatic walls were not very different, even though the melt streams were only about 0.3 mm thick. While the investigation was focused on high‐speed wire coating, in which viscous dissipation is extreme, the program can also be used for analysis and design of dies for making pipe and blown film.
Melt spinning and draw resonance studies on a poly (α‐methyl styrene/silicone) block copolymer
Authors: Blyler L. L. , Gieniewski C. 
Published: December 2004

AbstractFiber spinning experiments were carried out with an α‐methyl styrene/silicone block copolymer under various sets of spinning conditions. The behavior observed was very sensitive to the ambient axial temperature profile employed along the spinline and to the initial melt temperature at the die. By optimizing these parameters, very high draw ratios (>400 to 1) could be achieved. Under less optimum conditions, filament rupture and instabilities such as draw resonance, accompanied by periodic diameter and spinline tension fluctuations, were noted. Tensile stress and axial velocity gradient profiles were obtained along the spinline under a variety of spinning conditions. These profiles, together with an independent: rheological characterization of the polymer, provide insights into the mechanisms giving rise to the various types of behavior observed.
Topomorphic states and phase transitions connected with the crystallization of polymers
Authors: Poddubny V. I. , Elyashevich G. K. , Baranov V. G. , Frenkel S. 
Published: December 2004

AbstractThe crystallization of flexible‐chain molecules of different degrees of coiling is considered. The nature of the phase transition during crystallization is discussed. The revision of established notions on phase transitions in polymers leads to the concept of crystalline topomorphism, i.e., the existence of two crystalline types with different modes of packing of macromolecules in the macroscopic crystal though they belong to the same lattice class: folded‐chain crystal (FCC) and extended‐chain crystal (ECC). Phase diagrams in coordinates of degree of coiling vs temperature are plotted. The values of molecular orientation and temperatures at which each of both mechanisms of crystallization takes place are evaluated. The mechanisms of ECC growth under equilibrium conditions and under conditions of molecular orientation are discussed. It is shown that the melting of ECC obtained by the process of orientational crystallization is a second order phase transition, being analogous to a crystal‐nematic phase transition. At the same time the melting of FCC provides all the features of a first order transition.
Plane stress and plane strain fractures in polypropylene
Authors: Fernando P. L. , Williams J. G. 
Published: December 2004

AbstractThe concepts of Linear Elastic Fracture Mechanics (LEFM) are applied to polypropylene, a homopolymer and two copolymers, with a view to characterizing their brittle behavior at slow rates (0.5 cm/min) in terms of a fracture toughness, KIc. The effect of thickness, notch sharpness, and the mode of loading on KIc have been investigated in order to determine the plane strain toughness values, KcI for the materials. The two types of material are compared in terms of their toughness values over a range of temperatures between +30 and −160°C. Evidently, the small amounts of ethylene added to the copolymers show plasticizing effects, suppressing the yield stress and the ductile‐brittle transition temperature. In addition, the copolymers exhibit a ductile‐brittle region between −100 and −45°C where notch strengthening is apparent in the tension mode and a slow crack growth region between −45 and −30°C where slow growth precedes unstable fracture. The homopolymer, however, shows no clear evidence of such intermediate regions, except for slight amounts of slow growth above 0°C, and becomes ductile around 30°C.
Diffusion with discontinuous swelling. IV. Type II diffusion into spherical particles
Authors: Peterlin Anton 
Published: December 2004

AbstractIn the last few years some new features of the so‐called type II diffusion have been established which confirm the first theoretical description of such a material transport into a semi‐infinite glassy medium which at a certain concentration of the sorbate is transformed into a gel. The boundary between the glass and the gel progresses at a constant velocity into the interior of the sample thus yielding a linear term in the weight gain. The gradual establishment of the concentration profile in front of this boundary yields at the beginning a square root term in the weight gain. A detailed analysis of the extensive measurements of Hopfenberg, et al. of the diffusion of n‐hexane into extremely small polystyrene spheres demonstrates that the weight gain always starts with a square root of time term. In sufficiently large spheres this contribution is soon completely overridden by the term linear in time. The spherical geometry substantially modifies the concentration profile and the weight gain. In particular the weight gain divided by the square root of time vs the square root of time shows a maximum as soon as the geometrical factors prevail over the effect of the constant velocity progression of the boundary between the glass and the gel.
Concentration dependence, boundary layer resistance, and the “time‐lag” diffusion coefficient
Authors: Skaarup Klemen , Hansen Charles M. 
Published: December 2004

AbstractDiffusion coefficient measurements have been shown to be strongly influenced by boundary layer resistance and concentration dependence. When half‐times for desorption or absorption are used to find diffusion coefficients from the equation for a constant coefficient (T½ = Dt/L2 = 0.049), the values so obtained require correction. Diffusion coefficients found by the “time‐lag” method are also influenced strongly by surface resistance and concentration dependence. The usual equation for a constant diffusion coefficient gives a break‐through curve with an extrapolation to the time‐lag, TL = Dt/L2 = 1/6. This factor can rise to ½ for concentration dependence. Where boundary layer resistance is encountered, (a situation which appears to be quite common), TL is significantly increased and the slope at steady state is decreased.
Sorption and diffusion of weak acids in nylon—dual sorption and diffusion model
Authors: Iijima Toshiro , Miyata Eiji , Komiyama Jiro 
Published: December 2004

AbstractThe sorption and diffusion of fluoro‐substituted acetic acids in nylon‐6 were measured. Hydrochloric acid was also used for comparison purposes. The results were successfully interpreted quantitatively by a dual sorption model, namely by contribution of associated and dissociated species of the acids concerned. As was expected in the case of the sorption of the weakest acid among the acids used, acetic acid, the contribution of associated species is large. The analysis of the diffusion behavior of acetic acid has shown that the contribution of associated species plays a dominant role in the diffusion process in nylon.
The glass point of elastin as a function of diluent concentration
Authors: Hoeve C. A. J. , Hoeve M. B. J. A. 
Published: December 2004

AbstractElastin shares the properties of rubberlike elasticity and its capability to form a glass with crosslinked polymers in general. The glass transition temperature of dry elastin at 200°C is strongly depressed by water, as well as by ethylene glycol. On a volume fraction basis, both diluents depress the glass point equally. This result is strong evidence against any specific binding of diluent molecules and indicates relatively high mobility of diluent molecules in glassy elastin. This deduction is in agreement with the conclusions reached on the basis of heat capacity and dielectric measurements. Proposed small sections of β turns in the elastin chain are compatible with the concept of naturally occurring elastin chains in the amorphous state. Our results, however, do not confirm the existence of proposed β spirals with periodicities of 100 Å which were suggested to be the basis for the banded filaments observed in electron micrographs.
Effects of sorption modes on the transport and physical properties of nylon 6
Authors: Sfirakis Alexander , Rogers C. E. 
Published: December 2004

AbstractThe presence of low molecular weight molecules in a polymeric matrix often has a marked effect on material properties. Knowledge of specific penetrant distributions and component interactions is important for an elucidation of structure‐property relationships, plasticization phenomena, and any modification of structure induced by the presence of penetrants. The sorption‐mode characteristics of water, methanol, and ethanol in Nylon 6 films have been investigated by the application of the differential sorption method. The sorption and diffusion behavior were interpreted in terms of clustering theory with suitable account being made for penetrant molecular size and hydrogen‐bonding capability. The examination of transport and mechanical properties of these films indicates a pronounced dependence of those properties on the concentration of penetrants. The effect of penetrant cluster formation at characteristic concentrations of sorbed penetrant is to decrease the concentration dependence of both diffusion and mechanical relaxation processes in the case of alcohols. The onset of water clustering apparently only affects the mechanical relaxation process. The samples were further characterized by DSC, X‐ray diffraction and density measurements to detect any significant changes in the structure of Nylon 6 induced by the penetrant conditioning.
A rheometer for measuring the viscoelastic response of polymer melts in arbitrary planar and biaxial extensional flow fields
Authors: Denson C. D. , Hylton D. C. 
Published: December 2004

AbstractIn this paper we describe the operation of a rheometer that is capable of measuring the viscoelastic response of a polymer melt in a biaxial or planar extensional flow field under circumstances wherein the deformation history can be varied in an arbitrary manner. The principal feature of this rheometer is the use of a closed loop feedback system to control the inflation of a flat, molten polymer sheet clamped around its periphery. The feedback system is especially designed so that either stress or strain can be used as the reference point, thus permitting the deformation history to be varied arbitrarily. Illustrative data are presented on the viscoelastic response of a molten acrylonitrile‐butadiene‐styrene copolymer subjected to a planar extensional flow for the following deformation histories: constant stress, constant strain, constant strain rate, oscillatory stress and oscillatory strain.
An anomaly in the necking behavior of polyethylene, Part 2
Authors: Gedde U. W. , Jansson J.‐F. 
Published: December 2004

AbstractDumb‐bell shaped specimens of three polyethylenes were subjected to constant uniaxial tensile loads at test temperatures from 298 to 353 K. For the high density polyethylenes, a marked transition appeared in the neck/fracture behavior. At a certain stress level, the instantaneous fracture of the neck formed at high loads was replaced by the formation of a neck that resisted fracture for a considerable time. This transition was more gradual for the medium density polyethylene. Furthermore, at all test temperatures the transition shifts towards higher nominal stresses with increasing molecular weight. Mainly on the basis of measurements of the local strain rate in the neck forming region, a hypothesis is proposed which explains the appearance of the marked transition. The draw ratios and the densities of the fractured neck fibers were also measured and are in accordance with current molecular deformation theories.
Estimation of the shear deformation exerted by a roll‐mill upon a rubber compound
Authors: Ng T. S. , Angerer G. 
Published: December 2004

AbstractThe shear deformation which a rubber compound undergoes when passing through a mill nip was calculated. For this purpose the pressure distribution was measured using a strain gauge mounted in the table of a RAPRA micro‐mill. The method has been applied to black‐loaded master batches of natural rubber and styrene‐butadiene rubber, where the shear deformation was estimated as a function of the mill nip opening. Furthermore, the physical properties of a latex‐mixed powder vulcanizate was measured as a function of the estimated shear deformation.
Manufacture of high stiffness solid rods by the hydrostatic extrusion of linear polyethylene. Part I: Influence of processing conditions
Authors: Hope P. S. , Parsons B. 
Published: December 2004

AbstractHigh stiffness solid rods, up to 25 mm diameter, have been produced by the solid phase hydrostatic extrusion of a single linear polyethylene grade. Factors affecting the processing behavior and the product properties, as characterized by the enhanced axial Young's modulus and long term creep behavior, have been examined and sources of product flaws have been identified. At high product diameters extrusion occurred in a predominantly adiabatic thermal régime, for which the magnitude of the temperature rise was estimated by measurement of the long periods of the products. This adiabatic regime allowed high production rates to be obtained at lower extrusion pressures, but caused a reduction in the Young's modulus of the products and limited the maximum degree of deformation which could be obtained in stable extrusions.
Radiation degradation behavior of chlorine‐containing vinyl copolymers. Search for improved electron‐beam resists
Authors: Helbert John N. , Poindexter Edward H. , Pittman Charles U. , Chen Chi‐Yu 
Published: December 2004

AbstractVinyl copolymers with high radiation degradation sensitivity have been synthesized by copolymerizing vinylidene chloride (VDC), CH2 = CCl2, with methyl methacrylate (MMA), methacrylonitrile, methyl α‐chloroacrylate, and dimethyl itaconate using emulsion techniques. In addition, copolymers of methyl α‐chloroacrylate with methyl methacrylate and poly(α‐chloroaerylonitrile) were studied. Introduction of vinylidene chloride into methyl methacrylate polymers caused a sharp increase in Gs even at relatively low VDC incorporation. Upon 29 percent VDC incorporation, the Gs value increased from 1.3 (homopolymer of MMA) to 3.4. Gs was found to be a linear function of copolymer content for several systems, but Gx was not. At higher VDC levels, the increase in Gs was countered by increases in Gx. At lower VDC levels, Gx was suppressed below the values predicted by a linear Gx dependence on composition for such systems as VDC/MMA, MCA/MMA, and α‐chloroacrylonitrile/MMA. The VDC/MMA co‐polymer(29 percent VDC) gavea sensitivity of 4.0 × 10−5C/cm2 to electron beam exposure using the 0 percent unexposed resist thickness loss criterion and is 2–3 times more sensitive than PMMA. Poly(α‐chloroacrylonitrile) is a negative resist with a sensitivity of 5 × 10−5 C/cm2 using one‐micron line images for testing.
Rapid response of a growing environmental craze to a stress pulse
Authors: Conners Andrew , Kramer Edward J. 
Published: December 2004

AbstractDouble exposure holographic interferometry has been used to measure the response of a growing craze to a pulsed stress. The craze was grown in situ by application of methanol to a crack in a poly (methyl methacrylate) (PMMA) strip under tension (K1 = 0.4 MN/m3/2). An incremental stress, approximating 15 percent of the overall crazing stress, is applied to the growing craze in a 1 s pulse. Incremental strain and stress profiles are measured along a line parallel to, but displaced 1.0 mm from, the growing craze, from a double exposure hologram triggered just before and during the pulse. The craze deforms rapidly, relieving the incremental stress concentration that can be shown to exist before craze growth. In a second set of experiments one holographic exposure is triggered during the incremental stress pulse, and a second exposure is triggered afterward. The results of such experiments indicate that the craze deformation is primarily plastic, and corresponds to a plastic strain rate of not less than 0.2 s−1. Consideration of the diffusion limitation of the rate of craze thickening leads to the conclusion that this plastic deformation is attributable to fibril creep rather than a surface drawing mechanism.
The effect of variations in light intensity on the photo‐oxidation of polypropylene
Authors: Kollmann T. M. , Wood D. G. M. 
Published: December 2004

AbstractWhen polypropylene foil was photo‐oxidized in a laboratory UV aging apparatus, the rate of photo‐oxidation was proportional to various fractional powers of the light intensity depending on the type of lamp(s) used and whether the polymer was stabilized or unstabilized.
Degradation of polycarbonate during recycling in a capillary rheometer
Authors: Abbås Kent B. 
Published: December 2004

AbstractPolycarbonate was recycled in a capillary rheometer at high constant shear stresses (0.15–0.95 MPa) and at temperatures between 275 and 320°C. Changes in melt viscosity and molecular weight were evaluated. Significant polymer degradation was observed on repetitive extrusion. An activation energy of 113 kJ/mol was determined for the initial stages of the process. The degradation kinetics were in agreement with a non‐random chain scission. It was concluded that bonds were more susceptible to scission the closer they were to the middle of the polymer molecule and that the extent of degradation increased with an increase in molecular weight.
Preparation of aligned discontinuous fiber pre‐pregs by deposition from a suspension
Authors: Salariya A. K. , Pittman J. F. T. 
Published: December 2004

AbstractIn a process for production of aligned short fiber pre‐pregs, fiber suspension passes through a converging channel to emerge as a thin free‐surf ace sheet which is laid down onto a reciprocating horizontal filter surface. Following our previous work on fiber alignment in the channel, detailed studies are reported of the suspension sheet falling under gravity, and of the deposition stage. Close agreement is found between computed and experimental velocity profiles for sheets of fiber‐free liquid. Modification of the velocities resulting from the presence of fibers aligned in the flow direction is taken into account using an increased extensional viscosity. This is evaluated using pre‐existing theory which is tested experimentally and found satisfactory. A simple relationship between velocity and fiber alignment change in the falling sheet is derived and tested experimentally. Alignment is marred by surface disturbances to the sheet. Comments are made on the stability of the free‐surface sheet. An experimental study is made of alignment changes as fibers are deposited on the filter, and the results related qualitatively to operating conditions. In general there is little difference in alignment before and after deposition, except close to the leading edge of the filter where alignment loss occurs. Previous work is reviewed and recommendations made on optimum operating conditions.
Bulk polymerization of styrene in plate and frame batch reactors
Authors: Kovenklioglu Suphan 
Published: December 2004

AbstractThermal bulk polymerization of styrene in the plate and frame batch reactor i.s simulated with a mathematical model which accounts for chain transfer to monomer and gel effect. The design parameters are: the frame thickness, the temperature policy, and the level of prepolymerization in the feed. The recommended frame thickness with 27% prepolymerization is 5 in. The resulting polydispersities and number average chain lengths range from 2.2–2.3 and 2000–2100 respectively. The implementation of temperature policy, particularly the timing of the application of the coolant, is critical to obtain satisfactory polymer quality. When pure styrene feed is used the reactor displays thermal ignition unless the frame thickness is less then 2 in. For a 5 in. frame prepolymerization should be at least 25 percent to permit adequate temperature control.