bluuebunny/crossref_metadata_2025_split huggingface dataset:
A model for the transient flow of thermoplastics in annular hot runners
Authors: Lord H. A. 
Published: December 2004

AbstractAnnular hot runner systems, in which the inner surface is heated and the outer surface cooled, are being used increasingly in the injection molding of thermoplastics. In this paper a computer model which has been developed to calculate transient pressure, temperature, and velocity fields is described. Using the properties of acrylonitrile‐butadiene‐styrene for illustration, some detailed temperature and velocity profiles computed with the model are presented for atypical hot runner section. The effects of a number of design and operating variables on the pressure drop are also presented.
The effect of additives on the crystallization of poly (butylene terephthalate)
Authors: Pi Chang Eng , Kirsten Rudolf O. , Slagowski Eugene L. 
Published: December 2004

AbstractThe effect of glass fibers and some fire retardant additives on the kinetics and mechanism of crystallization of poly(butylene terephthalate) (PBT) has been investigated. Shorter half times of crystallization and higher optimum crystallization temperatures of the filled samples are attributed to the nucleating ability of the additives. Based on the percent crystallinity determined, the efficiency of the different quenching media studied can be arranged in the order: ice water > 25°C water ⩾ dry ice/ethanol > liquid nitrogen. The inefficient quenching of dry ice/ethanol arid liquid nitrogen media is attributed to their poor heat transfer. The Tg of these quenched samples is, however, independent of the percent crystallinity.
Application of small system thermodynamics to polymer molecules. I. The entropy barrier between liquid and crystalline state
Authors: Lindenmeyer P. H. , Beumer H. , Hosemann R. 
Published: December 2004

AbstractThe methods of small systems thermodynamics have been applied to the calculation of the entropy barrier to the growth of polymer crystals. The height of this barrier at the equilibrium melting point of polyethylene molecules of typical lengths (X = 4,000 to 10,000 segments) is estimated to be of the order of 4 to 5 Kcal per molecule. This barrier increases linearly with ln X if the crystal is very large but retains the approximate values mentioned for crystals with the lamella thicknesses usually found. This entropy change causes the free energy to go through a maximum as in a nucleation phenomena but no new surface formation is involved. The existence of such a barrier explains why crystallization (or melting) never occurs at the equilibrium melting temperature.
Elastic modulus and strength of fibrous material
Authors: Peterlin A. 
Published: December 2004

AbstractAs a rule, the large increase of elastic modulus with increasing draw ratio obtainable in highly‐drawn or extruded semicrystalline polymers is not reflected in a similarly large increase of strength. This is closely connected with the wellknown fact that with increasing plastic deformation one obtains fibrous material with decreasing strain to break. The axial elastic modulus is mainly caused by the taut tie molecules which bridge the amorphous layers between consecutive crystal blocks and thus provide an efficient axial force transmission through the sample. The defects at the ends of microfibrils interrupt this transmission because they contain few if any taut tie molecules connecting the end of microfibril with adjacent fibrillar elements. As a consequence of the small number of such ends, they only marginally reduce the elastic modulus. But as the mechanically weakest areas of the fibrous material, they drastically depress the strength. They fail as soon as the strain concentration upon them reaches their strain to break. The growth and coalescence of resulting microcracks finally lead to bulk fracture as the growing crack reaches critical dimensions.
Stress‐strain isotherms for polymer networks at very high elongations
Authors: Mark James E. 
Published: December 2004

AbstractSome polymer networks show an anomalous increase in the modulus or reduced stress at very high elongations. This behavior has now been investigated definitively by determining stress‐strain isotherms for both crystallizable and noncrystallizable networks, prepared using several curing techniques (carried out so as to yield a wide range in degree of cross‐linking). The networks were studied unfilled at a number of temperatures, and at several degrees of swelling. The results clearly implicate strain‐induced crystallization as the origin of the upturn in the modulus, and thus demonstrate that the wide spread interpretation of this upturn in terms of limited chain extensibility is incorrect.
Determination of fiberglass lengths: Sample preparation and automatic image analysis
Authors: Sawyer L. C. 
Published: December 2004

AbstractThe optimization of end product properties of fiberglass reinforced engineering thermoplastics must be based upon knowledge of the constituents, including the fiber length distribution. This paper presents the techniques developed for the recovery, dispersal and length distribution analysis of glass fibers recovered from filled engineering resins. An automatic image analyzing computer system is used for the determination. The tedious manual method of measurement from optical photomicrographs is replaced by a rapid, quantitative and reproducible analysis.
Strain‐induced crystallization, Part IV: Induction time analysis
Authors: Yeh G. S. Y. , Hong K. Z. , Krueger D. L. 
Published: December 2004

AbstractThe empirical equation, 1/ti = AeEi/RT, which expresses the exponential dependence of the reciprocal of crystallization induction time, ti, has been analyzed and shown to be equivalent to the nucleation rate equations derived earlier in Part III (1). Consequently we have used the ti measurements obtained earlier by Krueger and Yeh to calculate not only the nucleation rate enhancements but also the melting point elevations, the relative crystal thickness changes and molecular coil extension ratios of shear‐crystallization polyethylene. It is shown that polyethylene when crystallized between 129 and 131°C at shear rates between 1.56 and 9.70 sec−1 can have melting point increases of 4.2 to 7.2°C and crystal thickness decreases of 20 to 25 percent, when compared to those crystallized at 130°C in the quiescent state. The predicted “coil” extension in the melt just prior to shear‐induced crystallization ranges between 21 and 36 percent. The results of these analyses as well as those on nucleation rates of polyethylene oxide are discussed in detail.
Glass transitions of organic compounds. III. Cellulose substrate technique and aliphatic alcohols
Authors: Koleske J. V. , Faucher J. A. 
Published: December 2004

AbstractThe cellulose blotter/torsion pendulum technique used for the determination of relaxations that occur in low molecular weight compounds, oligomeric materials, and amorphous polymers is discussed. The glass transition temperature of a number of aliphatic alcohols and hydrocarbons have been determined and correlated with a method proposed by Gorskii in 1934. The glass transition temperature and molecular weight of these compounds follow the relationshipTg=BMarather thanTg=Tg(∞) ‐K/M. Although differences exist between the primary, secondary, and tertiary alcohols, they appear to follow a similar general pattern. In contrast, the hydrocarbons investigated have markedly different behavior.
Volume fraction determination of Kevlar 49/epoxy composites
Authors: Allred Ronald E. , Hall Nancy H. 
Published: December 2004

AbstractA knowledge of filament, matrix, and void content is generally required in order to characterize and study composite materials. It is difficult to obtain such data for Kevlar 49/epoxy composites due to chemical attack of the Kevlar filaments when techniques developed for other composite systems are used. This paper presents a chemical dissolution technique for Kevlar 49/epoxy composites by which less than one percent loss of the filament weight occurs. The procedure involves swelling the epoxide matrix in hot dimethylsulfoxide and then rapidly dissolving the degraded epoxide in a nitric aciddimethylsulfoxide solution. This technique allows the determination of filament, matrix, and void volume fractions of Kevlar 49/epoxy composites with a single procedure and has been successfully applied to fabric and filament‐wound composites and to a variety of epoxides. Results obtained with this dissolution technique show excellent agreement with those from optical and weight‐difference methods.
The effect of hot drawing on the properties of short fiber reinforced extruded sheets
Authors: Nicolais L. , Nicodemo L. , Masi P. , Dibenedetto A. T. 
Published: December 2004

AbstractThe hot drawing of extruded composite sheets can be used to control the orientation of both matrix and reinforcing fibers. A study was made of the effect of draw ratio on the properties of an extruded polystyrene sheet containing 0 to 1 percent of short glass fibers. An increase in draw ratio resulted in an increase in fiber orientation. A model of a rigid fiber rotating in an elongational flow field was used to describe the effect of draw ratio on the final orientation distribution. An increase in draw ratio also caused an increase in the amount of fiber breakage. A shear‐lag analysis was used to estimate the extent of damage as a function of draw ratio. It was also found that the mechanical properties were dependent upon both the draw ratio and fiber concentration.
Measurement of the elastic properties of polymer melts
Authors: Maxwell Bryce , Nguyen My 
Published: December 2004

AbstractA method and apparatus for measuring the elastic and other properties of polymers in the melt state is presented. The recoverable strain magnitude and the rate of strain recovery have been measured as a function of: applied shear rate, applied shear magnitude, temperature and molecular weight. The elastic properties indicate that there is an abrupt change or “transition” in the response of polystyrene melts at temperatures well above the glass transition. This abrupt change is found to be molecular weight dependent. The results are interpreted qualitatively in terms of molecular structure and practical processing operations. The possible relationship of this “transition” to Tu, is briefly discussed.
An improved concept in solubility parameter theory applied in amorphous polymers. I. Poly(ethyl methacrylate)
Authors: Karim K. A. , Bonner D. C. 
Published: December 2004

AbstractGas‐liquid chromatography has been used to estimate thermodynamic parameters of a variety of aromatic and aliphatic solvents at infinite dilution in poly(ethyl methacrylate). Heats of solution, Flory‐Huggins interaction parameters, and specific interaction parameters were calculated from specific retention volumes. Comparative interpretation of these thermodynamic quantities has led to the establishment of a solvent selectivity scale for poly(ethyl methacrylate). Limitations of the threedimensional solubility parameter theory on the systems tested here are demonstrated. A significantly improved concept is developed and tested.
Transitions, relaxations, and thermodynamics in the glassy state
Authors: Simha Robert 
Published: December 2004

AbstractThe PVT properties of polymer glasses are discussed from two points of view. First, as a low frequency tool in the study of sub‐glass relaxations. Dilatometric results illustrate the sensitivity of the thermal expansivity and its temperature coefficient to dynamic processes occuring in the glass. The second point of view considers the quasi‐thermodynamics of the non‐equilibrium system, under conditions where the rates of relaxational processes are small in comparison with experimental rates, and time dependent processes are practically absent. The starting point is a theory of the equilibrium melt which describes the characteristic liquid disorder in terms of a temperature and pressure dependent hole or loosely, free volume fraction. This function is obtained by the minimization of a configurational free energy. Upon reaching the glass transition, this dependence is reduced, and further so in a sub‐glass relaxation region. However, it is not eliminated until temperatures of the order of 50 to 70 K are reached. While this picture is qualitatively universal, significant quantitative differences are observed with different chemical structures and different thermal and pressure histories. A comparison of thermal expansivities of high and low Tg systems indicates that in the former the free volume retained upon reaching Tg is comparatively large and the departure from equilibrium or degree of freeze‐in comparatively small. Similarly, it appears that the glassy densification generated by cooling the melt under pressure is more extensive in high Tg glasses. Such results imply structural differences. These should be investigated by comparative studies of (a) time dependent processes in terms of the free volume functions, (b) sorption and transport, and (c) the temperature dependent dynamics of density fluctuations.
Synthesis of permselective membranes by radiation induced grafting of hydrophilic monomers into poly(tetrafluoroethylene) films
Authors: Chapiro A. , Jendrychowska‐Bonamour A.‐M. 
Published: December 2004

AbstractA large variety of permselective membranes were prepared by radiation grafting techniques. Grafting of styrene into poly‐(tetrafluoroethylene) films followed by sulfonation led to strong anionic membranes showing good performance in reverse osmosis. Carboxylic membranes were prepared by grafting acrylic and methacrylic acids. Cationic membranes were obtained via grafting 4‐vinylpyridine. These membranes were tested in various fractionation processes including reverse osmosis. N‐vinylpyrrolidone grafts exhibited high selectivity for separating water from organic solvents by pervaporation. Bifunctional membranes containing both carboxylic and pyridine groups were obtained by two successive grafting steps either in bulk giving rise to “homogeneous” membranes with unusual swelling properties, or into localized areas generating mosaic membranes which exhibit negative osmosis and increased rates of ion‐pair diffusion.
Performance of extrusion crossheads in multi‐layer cable covering
Authors: Nadiri F. , Fenner R. T. 
Published: December 2004

AbstractExperiments are reported concerning the performance of an extrusion crosshead used in the three‐layer covering of high voltage electrical cables. Both extrusion pressure requirements and circumferential distributions of polymer layer thicknesses in the finished cable were measured and compared with the results of a previously published finite element method of melt flow analysis within the crosshead. While agreement on pressure is good, it is necessary to allow for the effects of both gravity and slight misalignments of crosshead components if the thickness distributions are to be correlated satisfactorily. The latter effect emphasizes the need for a high degree of accuracy in crosshead design and manufacture.
The degradation of an aromatic polyamideimide in an NO2 atmosphere
Authors: Kambe Hirotaro , Yokota Rikio 
Published: December 2004

AbstractFilms of an aromatic polyamideimide showed a significant degradation in an NO2 atmosphere at 100 mm Hg at 50°C. The degradation was followed by the dynamic tensile measurements. In the curves of temperature dependence of dynamic loss modulus of degraded films, a separate mechanical absorption α′ peak appeared below the glass transition α peak. In the course of degradation, the α′ peak grew and shifted to lower temperature. On thermal treatment of degraded films, the α′ peak shifted to higher temperature and finally merged into the α peak. The formation of reacted surface layers by the diffusion of NO2 was confirmed by scraping off and by solvent extraction. Infrared spectroscopy showed that most amide linkages were destroyed by NO2. The gel permeation chromatography of extracted products showed that the low molecular products were occluded in degraded layers. The influence of these components caused the α′ absorption in dynamic loss curves.
Cushioning energy dissipation in foam polymers
Authors: Peleg Kalman 
Published: December 2004

AbstractDerivation of dynamic hysteresis loops (force deflection curves) of shock absorbing bushing materials by means of double integration of accelerometer signals is described. The significance of energy dissipation capability of expanded polymers with associated peak deceleration and maximal strain is discussed along with damping characteristics. A “Cushion Efficiency Factor” is introduced, in terms of the ratio of peak acceleration transmitted by a cushion to the energy dissipated per unit cushion area. Three types of expanded polymers commonly used as cushioning materials are evaluated accordingly. Expanded polyethylene (2,2 lb/cu ft), expanded polyurethane (2.1 lb/cu ft) and polystyrene filled polyurethane (1.7 lb/cu ft), all conditioned at 73°F and 50 percent RH. For each of these, two effective drop height tests were conducted, with heights of 12 in. and 42 in. Depending on the polymer type, peak product accelerations were between 33–38 g's in the 12 in. drops and 65–118 g's in the 42 in. drops, with corresponding maximal cushion strains of 0.15–0.20 and 0.39–0.47, respectively. Energy dissipating capabilities of polymers tested during first half cycle following drops were 148–179 lb in. and 477–708 lb in., respectively, depending on polymer type. This approach may facilitate optimal selection of cushioning materials for shock protection in packaging, as well as enable development of improved polymers for cushioning applications.
The interpretation of dynamic mechanical behavior in ultra high modulus polymers
Authors: Gibson A. G. , Davies G. R. , Ward I. M. 
Published: December 2004

AbstractRecent studies of the dynamic mechanical behavior of ultra high modulus polyethylene? are discussed in the context of our present understanding of the structure of these materials. In particular, the Takayanagi model is shown to achieve a new status in the light of direct measurements of crystal continuity from wide angle X‐ray diffraction data. It is further shown that the Takayanagi model in one formulation is compatible with the Cox model for a short fiber reinforced composite. The fiber composite model offers a simple physical understanding of the fall in modulus due to the α‐relaxation in terms of shear lag. This reduces the effectiveness of the continuous crystal fraction postulated in the Takayanagi model. The γ‐relaxation is considered to be associated primarily with an amorphous relaxation, consistent with the conclusions of previous workers for materials of lower draw ratio.
Crystalline and amorphous orientations in injection molded polyethylene
Authors: Moy Francis H. , Kamal Musa R. 
Published: December 2004

AbstractThe techniques of density, birefringence, and wide X‐ray diffraction were employed to characterize the microstructure of injection molded polyethylene parts. Generally, maximum crystallinity (density) occurs at the center of the molding, while the minimum crystallinity occurs near the surface. Higher densities are observed near the gate. Raising the injection temperature tends to cause a marginal increase in the crystallinity throughout the molding. Birefringence measurements suggest that the maximum orientation occurs near the surface and that the relative orientation distribution is independent of the injection temperature. X‐ray diffraction indicates that the crystallographic a‐axis tends to orient in the flow direction while the b and c axes vary symmetrically about that direction. Increasing the injection temperature creates c‐axis orientation near the surface, while towards the core region a‐axis orientation is observed. Generally, near the surface it is the amorphous phase that makes the major contribution to the total orientation as measured by birefringence. Increasing the injection temperature tends to decrease the amorphous phase orientation near the surface. The crystalline phase contribution to the total orientation increases as distance from the surface increases, regardless of injection temperature.
Recent advances in the photodecomposition mechanisms of diazo‐oxides
Authors: Pacansky J. 
Published: December 2004

AbstractIn 1902, Wolff proposed a mechanism to explain the formation of carboxylic acids from diazo‐oxides; Süs in 1944 invoked this same mechanism for the formation of indene carboxylic acid from diazo‐oxides. Since these materials are currently used in the well known class of AZ photoresists, the Süs mechanism has been referred to many times to explain the positive working nature of the photoresists. In spite of the widespread use and industrial importance of the AZ resists, the validity of the Süs mechanism had not been unequivocally demonstrated to any degree of satisfaction. For these reasons, photochemical studies were initiated to establish the following: (1) Obtain direct spectroscopic evidence for ketene intermediates in the Wolff rearrangement of diazooxides. (2) Determine the reactivity of the ketene towards water and hydroxyl containing organic compounds. (3) Determine the reactivity of the ketene in the AZ resists. Fundamental photochemical decomposition mechanisms have been established for the AZ‐type photoresists; these and recent theoretical results on the Wolff rearrangement are used to convey the technological implications of the studies.
Electron sensitive negative resists of vinylaromatic polymers
Authors: Jagt J. C. , Sevriens A. P. G. 
Published: December 2004

AbstractElectron resist properties of three vinylaromatic polymers, polystyrene, polyvinylcarbazole and poly(3‐bromo‐N‐vinylcarbazole) have been examined. Polystyrene and polyvinylcarbazole are high contrast resists of high dry etch resistance, but for adequate sensitivity (D ⩽ ca. 10 μC/cm2 at 25 kV) high molecular weights are needed (Mw ⩾ 106). Poly(3‐brotno‐N‐vinylearbazole) has a much higher sensitivity (D = ca. 2 μC/cm2) than the unsubstituted polymer. The sensitivity of polystyrene and polyvinylcarbazole is increased appreciably by addition of organic bisazides as crosslinking agents, e.g. a sensitivity increase of almost an order of magnitude was found upon addition of 3% 4, 4′‐diazidostilbene to polystyrene, high contrast being maintained.
Device processing using the trilevel technique
Authors: Moran J. M. , Maydan D. 
Published: December 2004

AbstractThree front runners for the next generation of devices for fine line lithography are photo, electron, and X‐ray lithography. Each of these techniques has both advantages and disadvantages when considered for direct wafer processing. This paper discusses the problems encountered using each of these techniques and how a trilevel technique can be applied to make each of these techniques more viable.
Impact strength of polymers. 3: The effect of annealing on cold worked polycarbonates
Authors: Thakkar B. S. , Broutman L. J. 
Published: December 2004

AbstractCold working (rolling) of polycarbonates introduces residual stresses and molecular orientation both of which can improve, the notched Izod impact value. Annealing relieves both residual stresses and orientation. Annealing for various time periods established the critical level of residual stress necessary for the ductile failure mode of polycarbonate in the Izod impact test. The relaxation of both residual stress and molecular orientation was measured as a function of annealing temperature, for annealing times of 2 hs, and the relative changes have thus been determined. It is shown that residual stresses cannot be entirely removed without significantly influencing orientation for 2 h annealing times.