bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of crystallinity and morphology in the preparation of ultra‐highly oriented polyethylene
Authors: Capaccio G. , Crompton T. A. , Ward I. M. 
Published: December 2004

AbstractThe influence of the degree of crystallinity and morphology on the drawing behavior of linear polyethylene (LPE) has been investigated on three polymers with molecular weights ranging from 67,000 to over 300,000. Samples of similar crystallinity, but different morphology, were obtained by subjecting the polymers to two distinct preparations: slow cooling from the melt in one case and rapid quenching followed by annealing at 120°C in the other. The resulting isotropic products, characterized by optical microscopy and density measurements were drawn at constant speed and the deformation process monitored by recording the draw ratio/draw time relationship and the stress/strain curves. The results indicate that crystallinity per se does not have a primary effect in determining the rate of local deformation except in the case of polymers of very low weight average molecular weight and narrow molecular weight distribution. A dominant role seems to be played by the broad features of the sample morphology as detected by optical microscopy. A comprehensive explanation of these results is based on the concept of a network structure whose nature is affected by the annealing treatment to an extent which depends on the degree of coupling between adjacent crystalline regions in the isotropic undrawn polymer.
Time and strain dependent thermal expansion of carbon‐black filled SBR elastomers
Authors: Caruthers J. M. , Hooley C. J. , Cohen R. E. 
Published: December 2004

AbstractLength‐temperature measurements were made on unfilled and carbon‐black filled vulcanizates of styrene‐butadiene rubber. As in earlier experiments on polybutadiene, transients in thermal expansion behavior were observed following abrupt changes in the temperature. The nature of this time dependence was not dramatically affected by either the level of equilibrium strain or the structure and loading of the carbon‐black filler. Both the magnitude of the linear coefficient of thermal expansion and the point of thermoelastic inversion were sensitive to the presence of carbon‐black. A model based on considerations of occluded rubber and strain amplification in the free rubbery matrix was used successfully to rationalize the observed behavior of the filled compounds.
Polymer blends containing poly(vinylidene fluoride). Part I: Poly(alkyl acrylates)
Authors: Wahrmund D. C. , Bernstein R. E. , Barlow J. W. , Paul D. R. 
Published: December 2004

AbstractThe transitional behavior of poly(vinylidene fluoride) (PVF2) blends with poly(methyl acrylate) and with poly(ethyl acrylate) was examined by differential thermal analysis and dynamic mechanical testing. Both blend systems were judged to be miscible on the bases of the presence of single, composition dependent glass transitions and of the strong melting point depression of the PVF2 component, Blends of poly(isopropyl acrylate) with poly(vinylidene fluoride) were found to be immiscible. These results suggest that miscibility of the acrylate series depends on a specific attractive interaction between the PVF2 and oxygen within the acrylate and the effect of this interaction is diminished as the hydrocarbon content of the ester is increased.
Studies on structural foam processing I. The rheology of foam extrusion
Authors: Han Chang Dae , Villamizar C. A. 
Published: December 2004

AbstractAn experimental study was carried out to investigate the flow behavior of gas‐charged molten polymers in foam extrusion. For the study, a rectangular slit die with glass windows was constructed to permit visual observations, from the direction perpendicular to flow, of the dynamic behavior of gas bubbles when a gas‐charged molten polymer flows between two parallel planes. Pictures were taken of gas bubbles in the flow channel with the aid of a camera attached to a microscope, and these were later used to determine the position at which gas bubbles start to grow. Using three melt pressure transducers mounted on the short side of the rectangular slot, pressure distributions were measured along the longitudinal centerline of the die. The polymeric materials used were high‐density polyethylene and polystyrene, and the chemical blowing agents used were a proprietary hydrazide which generates nitrogen, and sodium bicarbonate which generates carbon dioxide. It was observed that the gas‐charged molten polymer shows a curved pressure profile as the melt approaches the die exit, whereas the polymer without a blowing agent shows a linear pressure profile. The visual observations of the bubble growth in the flow channel, together with the pressure measurements, permitted us to determine the bubble inflation pressure, often referred to as the critical pressure for bubble inflation. It was found that the critical pressure decreases with increasing melt extrusion temperature, and increases with increasing blowing agent concentration. It was also found that the bulk viscosity of gas‐charged molten polymers decreases with increasing blowing agent concentration and with increasing melt temperature. A general remark is made concerning the precaution one should take when an Instron rheometer is used for determining the bulk viscosity of gas‐charged molten polymers.
Viscoelasticity of ABS samples differing in thermal history
Authors: Booij H. C. , Palmen J. H. M. 
Published: December 2004

AbstractAn important parameter in the various molding techniques used in polymer processing is the rate of cooling the object. The effect of the thermal history on the linear viscoelastic properties was studied, mainly by means of stress relaxation experiments on ABS samples in which the influence of other process variables was eliminated. In agreement with recent literature data, it appeared that the time dependence of the stress can be represented by a universal formula, provided that no perceptible change in temperature or relaxation of volume takes place during the experiment. The position of the momentary relaxation curve along the time scale can therefore be described by one characteristic mechanical relaxation time tr. The value of tr is affected by the temperature T, but even more by the thermal history, i.e., by the rate of cooling, q, and the annealing time, ta, at the measuring temperature previous to recording of the relaxation curve. In the case of very rapidly quenched samples, exact proportionality was found to exist between tr and ta at temperatures below Tg −15°C. In slowly cooled samples tr can be longer by a factor of ten than in quenched samples, at the same T and at annealing times of about 1 h. The difference decreases with increasing ta, but remains substantial up to ta values much longer than the total cooling time.
Kinetic studies on shear degradation of polystyrene during extrusion
Authors: Shur Young J. , Rånby Bengt , Chung Ki‐Hyun , Kim Sang‐Dae 
Published: December 2004

AbstractKinetic studies on shear degradation of a polystyrene (M̄n = 115,700 and P̄n = 1113) during extrusion in a model extruder were made at different temperatures (170, 190, 210, and 230°C) and shear stresses (340,406, and 472 g/cm2) for determination of rate constants for degradation, reaction order, and effects of temperature and stress on the rate constants. Mechanical energy and effective activation energy (E*) of bond rupture were related to temperature and applied stress. The following results were obtained. The degradation process is found to be satisfied by a second order reaction over the temperatures and stresses studied with respect to the changes in number average chain length (Pt – P∞), thus –dP/dt = k(Pt – P∞)2, where k is a reaction rate constant and t and ∞ refer to degradation times. The mechanical energy of bond rupture has a maximum and the rate constant a minimum at about 180°C, indicating that the least effective temperature for mechanical degradation is about 180°C. E* decreases with increasing applied stress (τ) as a linear relationship, i.e., E* = EA – ατ. At τ = 0, E* becomes equal to the activation energy for thermal degradation with the value EA = 48.6 kcal/mole which agrees well with literature data. Temperature and stress effects on the rate constant are well expressed for our study by the Arrhenius equation proposed by Zhurkov, et al., i.e., k = A exp[–(Ea – ατ)/RT] where A and α are coefficients.
The influence of morphology on the tensile properties of polyethylenes
Authors: Phillips P. J. , Patel J. 
Published: December 2004

AbstractThe tensile properties of high and low density polyethylene specimens produced under careful crystallization and annealing procedures have been determined. A morphologically controlled brittle‐ductile transition has been observed for high density polyethylene. Although the lamellar thickness appears to determine the transition, a postulate involving molecular fractional on during crystallization as the cause is offered. For ductile materials, dependence of the Young's Modulus on morphology is interpreted using the fiber‐composite analogy of Halpin and Kardos. Yield stress varies as modulus and achieves maximum values consistent with estimates of the critical resolved shear stress of polyethylene crystals.
Mechanical properties of selected injection‐molded thermosets
Authors: Kleinemeier B. , Menges G. 
Published: December 2004

AbstractPractical ways of processing thermoset materials by injection molding have been developed. These methods have been used particularly in the automotive and electrical industries. The tensile behavior is discussed for specimens which were injection molded from reinforced and filled phenolic unsaturated polyester and epoxy resin. This behavior aids the layout of flow paths. Under static loads the materials show less creep than most thermoplastics. “Post shrinkage” was observed as a shortening of specimens under prolonged heating. Because of brittleness, the materials failed under dynamic load at low strain. The first microcracks directly initiate the final failure. Before the final failure, the materials craze at a certain strain. By means of different testing methods these strain values were determined. For practical applications, these values should be considered in the designing of thermoset parts.
The effects of thermal treatment, residual solvent, and preswelling on the thermal properties and sorption behavior of poly(2,6‐dimethyl, 1,4‐phenylene oxide)‐polystyrene blends
Authors: Apicella A. , Drioli K. , Hopfenberg H. B. , Martuscelli E. , Nicolais L. 
Published: December 2004

AbstractThe effects of thermal treatment, residual solvent, and preswelling on the thermal properties and swelling behavior of solution cast polyblend films of poly(2,6‐dimethyl,1,4‐phenylene oxide) (PPO) and polystyrene (PS) were determined. Repeated cycling in the DSC analysis of the “as cast” films suggested that the original films contained residual casting solvent and that solvent‐induced crystallization occurred in the PPO‐rich compositions. Crystallinity was, apparently, eliminated by the first heating cycle in the differential scanning calorimeter. Sorption kinetics and apparent equilibria, characterizing the penetration of these films by n‐hexane from the vapor phase, indicated that both the sorption rate and apparent equilibria are significantly affected by the prior history of the film samples. The sorption results presented here are quantitatively consistent with earlier studies of the PPO‐PS system. The increased rate and amount of sorption observed in preswollen samples, and the reduced rate and amount of sorption observed in annealed samples are consistent with recent descriptions of sorption behavior in diverse glassy homopolymer systems.
Theory of laminar mixing
Authors: Erwin Lewis 
Published: December 2004

AbstractAn expression is derived for the increase in mixedness due to an arbitrary deformation of a material. For mixtures having initial orientation this expression is a function of the principal values of the strain tensor and the orientation of the fluid. For mixtures without initial orientation, this expression is simply a function of the principal values of the strain tensor. Mixing in pure shear, simple shear, and pure elongation is determined. The rate of mixing for each of these deformations in steady flow is derived. A comparison of these rates of mixing with the energy consumed in the deformation shows that simple shear flow is a very inefficient way to accomplish mixing. For the example cited, five orders of magnitude greater energy is required to accomplish mixing in shear flow as opposed to extensional flows.
The coating of Newtonian liquids onto a roll rotating at low speeds
Authors: Tharmalingam S. , Wilkinson W. L. 
Published: December 2004

AbstractA theoretical treatment is presented for the prediction of the rate at which a liquid is entrained by a roll which is rotating partially submerged in a Newtonian liquid, and also for the prediction of the variation in the thickness of the film around the roll. The method involves the integration of the momentum equation after neglecting inertia forces in the dynamic meniscus region and the matching of the surface curvature with that derived for the static meniscus region near the liquid surface. The resulting equation allows the prediction of the relationship between a dimensionless film thickness parameter, T, and the capillary number, Ca, as a function of the radius of the roll, the withdrawal angle and the position of the roll periphery. The liquid flux on the roll can also be predicted.
Dynamic Poisson's ratio: A novel technique to study interfacial adhesion
Authors: Takemori M. T. 
Published: December 2004

AbstractA novel technique utilizing the dynamic Poisson's ratio to measure the strength of adhesion in fiber‐filled polymeric composites is described. This technique is based on the observation that glass‐filled composites exhibit a large drop in Poisson's ratio as a function of prestrain at very low prestrains. This drop, which indicates additional volume dilation, is interpreted as due to debonding or void formation at the filler‐matrix interface. This interpretation is consistent with the results obtained by using three very different glass surface treatments, with a description of the debonding process using two simplified models and with mechanical properties data. The dynamic Poisson's ratio technique is insensitive to filler orientation and has high resolution, since very small volume changes are reflected as large drops in Poisson's ratio.
An anomaly in the necking behavior of polyethylene
Authors: Gedde U. W. , Jansson J. F. 
Published: December 2004

AbstractTensile creep measurements at constant load on nonoriented polyethylene have shown a marked transition at a certain stress level from a neck formation followed by instantaneous fracture to the formation of a neck which resists fracture for a considerable time. The transition, which shifts towards shorter time and higher nominal stress with increasing molecular weight, has been studied for 16 polyethylenes of different molecular weights, degrees of branching and crystalline structures. The marked. transition has only been observed for high density polyethylene of high molecular weight. Deformation measurements show a more distinct necking for the high density than for the medium density polyethylenes. This is consistent with current molecular deformation theories. A hypothesis for the transition is proposed based on the distinctness of the neck process in the high density polyethylene and the large difference in strength between the spherulitic structure and the fibrillar structure. The dependence of the transition on molecular weight is expected since the number of tic chains incrcrtses with increasing molecular weight.
Role of bond thickness on adhesive failure
Authors: Fourney M. E. , Muki R. , Stone S. F. , Westmann R. A. 
Published: December 2004

AbstractAn analytical, numerical and experimental program is described which establishes the basic fracture mechanics properties of an adhesive joint. A finite element analysis of a homogeneous finite tapered double cantilever beam is first presented and the results compared with elasticity and strength of materials solutions. Using analytical results developed in another paper, a finite bond line thickness correction factor is introduced to determine the crack tip stress intensity factor as a function of crack length. An experimental program is described wherein the crack tip stress intensity factor for the cantilever beam adhesive joint is measured by the compliance method and the results compared with those obtained by analytical and numerical methods. Finally, the critical value of the adhesive crack tip stress intensity factor is determined using the analytical and experimental techniques presented.
Further developments of a damage theory for filled polymers
Authors: Rubinstein R. , Fitzgerald J. E. 
Published: December 2004

AbstractThis paper investigates matrix debonding from filler particles as a mechanism for weakening of a filled polymer. We analyze several simplified models of debonding. Our main concern is its effect on the overall elastic instants; for each debonding model, we calculate the change ΔW in overall strain energy density due to debonding. The resulting formulas for ΔW are all special cases of one general expression. Accordingly, we propose that this expression describes a broad class of debonding models, including some for which a detailed stress and strain analysis is not possible.
Evaluation of resin‐glass fiber interface under environmental stress
Authors: Haarsma John 
Published: December 2004

AbstractA test method has been developed to evaluate resin‐glass composite materials for their resistance to environmental, thermal and hydrolytic stresses, humidity, radiation, and immersion in aggressive fluids. The advantages this method offers are ease of specimen preparation, small specimen size, and maximum exposure of resin, glass and interface to the test environment.
Selection and sensitivity of pellet dimensions and operating parameters to maximize production rate
Authors: Johnson Glen E. , Townsend Miles A. 
Published: December 2004

AbstractThe manufacture of pellets from extruded plastic strands is modeled as a constrained nonlinear programming problem. The objective is to maximize the production rate by choice of pellet dimensions and pelletizing machine operating parameters. A general solution strategy leading to identification of a globally maximum production rate for any numerical case is given. It is shown that increases in the maximum production rate can be obtained by selective relaxation of the constraints. A numerical example is presented and discussed.
Effects of extrusion on the structure and properties of high‐impact polystyrene
Authors: Kalfoglou Nikos K. , Chaffey Charles E. 
Published: December 2004

AbstractA commercial heat‐resistant polystyrene (M̄n = 7 × 104, M̄w = 3 × 105), containing 9 percent cis‐1, 4‐polybutadiene, was extruded either repeatedly (2 to 8 times) at 220°C, or else only once at a higher temperature (up to 290°C). Neither treatment significantly altered the melt rheology at 220°C (pseudoplastic, with n = 0.39), or the tensile modulus (1.5 GPa) and yield stress (20 MPa), or the material's rubber content, determined by both infrared spectrophotonietry and Wijs iodometry. Other properties, only slightly affected by recycling at 220°C, were changed after one extrusion at 290°C: elongation at tensile failure was reduced by 57 percent; in impact testing the strength was 29 percent less, and the mode of fracture (revealed by scanning electron microscopy of the surfaces) became brittle instead of ductile; the rubber particles seen in the transmission electron microscope had agglomerated and lost sphericity; and the ratio of weight‐to‐number‐average molecular weight of the polystyrene component, calculated from gel permeation chromatograms, increased by 93 percent. Mechanical spectra (Rheovibron), from −120 to + 120°C at 110 Hz, changed gradually with increasingly harsh treatment of the material, a peak emerging at ∼50°C due to a beta relaxation of the polystyrene. Thus, good properties were retained after normal processing, but were lost after shearing at too high a temperature, probably because of destruction of entanglements and of the bonds between polystyrene and rubber.
Impact behavior of nylon‐66 compositions: Ductile‐brittle transitions
Authors: Flexman Edmund A. 
Published: December 2004

AbstractThe ductile‐brittle transitions of nylon‐66 compositions were studied by Izod and falling weight tests. Samples included unmodified and impact modified compositions. Brittle breaks did not occur in the toughest resin with changes in rate of loading, notch radius, thickness, or distance and orientation to the gate. A fracture mechanism is proposed.
Investigation of the Tu(>Tg) relaxation in homopolymers and block copolymers of styrene by torsional braid analysis
Authors: Gillham J. K. 
Published: December 2004

AbstractInvestigation of the Tu (>Tg) relaxation in amorphous polymers of styrene by the technique of torsional braid analysis is reviewed. For the most part the relaxation behaves like the glass transition (Tg) in its dependence on molecular weight, on average molecular weight in binary polystyrene blends, and on composition in a polystyrene homogeneously plasticized throughout the range of composition. Diblock and triblock copolymers also display a T > Tg relaxation above the Tg, of the polystyrene phase. Two results in particular suggest that the Tu relaxation is molecularly based. (1) The Tu temperature is determined by the number average molecular weight for binary blends of polystyrene when both components have molecular weights below Mc. (the critical molecular weight for chain entanglements). (2) Homopolymers, and diblock and triblock copolymers of styrene, have a T > Tg relaxation at approximately the same temperature when the molecular weight of the styrene block is equal to that of the homopolymer.
Effect of cure cycle on mechanical properties of thick section fiber‐reinforced poly/thermoset moldings
Authors: Mallick P. K. , Raghupathi N. 
Published: December 2004

AbstractOne of the major factors of concern in compression molding of fiber‐reinforced thermosets is the mold cycle time which directly affects the processing cost. An ideal system would be the one which cures in a relatively short time resulting in excellent mechanical and physical properties. However, in practice, a compromise has to be made between the mold cycle time and ultimate property requirements. The effects of cure cycle time, temperature, preheating and post‐cooling on mechanical properties of continuous as well as chopped glass fiber reinforced polyester and vinyl ester systems involving 1/4 to 1 in thick sections have been studied. Mold cycle time is strongly influenced by the part thickness and mold temperature. Internal heat generation due to curing reaction causes high thermal gradients across the thickness. Preheating offers advantages of reducing both the mold cycle time and the thermal gradient. The flexural and interlaminar shear strengths are strongly dependent or, the mold cycle time. Maximum strengths are obtained when the mold is opened at the instant when there is no thermal gradient across the thickness.