bluuebunny/crossref_metadata_2025_split huggingface dataset:
Critical parameters for thermoset curing in heated molds
Authors: Adabbo Humberto E. , Rojas Alfredo J. , Williams Roberto J. J. 
Published: December 2004

AbstractThe change in temperature and conversion during the curing of a thermosetting resin in a slab‐shaped heated mold is analyzed theoretically. Results show that there is a critical value of β = AL2/k, for which the maximum center exotherm takes place (A = Arrhenius pre‐exponential factor, L = slab thickness, k = thermal conductivity). Beyond this value, increasing β decreases the center exotherm. The temperature rise at the slab center may be substantially greater than under adiabatic conditions. Wall temperature has a great effect on the process behavior, implying the need of an adequate control system. A description of the temperature profiles and conversion rates is provided and some criteria for the process design are stated.
On the linear viscoelastic limit of polymers—exemplified on poly(methyl methacrylate)
Authors: Brüller O. S. , Schmidt H. H. 
Published: December 2004

AbstractThe linear viscoelastic limit of poly(methyl methacrylate) (PMMA) is established on the basis of the Reiner‐Weissenberg criterion of strength. The obtained limit is not simply a “strainlimit” or a “stress‐limit” but a function of both strain and stress, an energetical limit. In stress‐strain representation the limit is independent of time and temperature, which means that the linear or non‐linear behavior of the material depends only on the actual values of strain and stress. Some experimental data obtained on PMMA confirm the theory.
Cavity temperature—an important parameter in the injection molding process
Authors: Čatić Igor J. 
Published: December 2004

AbstractThe paper stresses the importance of cavity temperature in the injection molding process of thermoplastics. From the study of the temperature field in the mold, it follows that there is no such thing as a uniform mold temperature. The heat balance equation for the injection mold is discussed in detail. It shows that the sum of the heat exchanges during the cycle equals zero. There is an extensive explanation of the heat transfer from the melt to the mold, the heat exchange with the environment, and between the heat exchange medium and the mold. New criteria are given for the cavity material selections. The cavity temperature is a complex function of static and dynamic parameters and should be kept constant in the equal parts of the cycle. This demands a new way of regulating the temperature.
Determination of the structure of the noncrystalline regions in isotropic and oriented poly(ethylene terephthalate)
Authors: Zachmann H. G. 
Published: December 2004

AbstractThe mechanical properties of polymers are influenced strongly by the structure of the noncrystalline regions. The different methods for characterization of these regions are reported and the results obtained on polyethylene terephthalate, are discussed. The orientation function of the noncrystalline chains can be determined by measurements of the X‐ray scattering and the birefringence. The fraction of taut noncrystalline chains is obtained from NMR measurements combined with a determination of the degree of crystallinity. For a further evaluation of the results it is also necessary to use calculations of the NMR‐ line‐width and the birefringence of chains with fixeu ends. With help of such calculations the end‐to‐end distance of the taut and mobile non‐crystalline chains can be determined, It is also possible to distinguish between tie molecules and loops. With increasing orientation, the amount of taut noncrystalline chains increases. The taut chains are tie molecule rather than taut loops. The end‐to‐end distances increase with increasing crystallization temperature.
Non‐isothermal phenomena in polymer engineering and science: A review. Part I: Non‐isothermal polymerization
Authors: Stolin A. M. , Merzhanov A. G. , Malkin A. Ya. 
Published: December 2004

AbstractThis paper reviews non‐isothermal polymerization processes in which the chemical reaction occurs with thermal selfacceleration. A macrokinetic approach to the description of these processes, with consideration of their specific characteristics, allows the study of the thermal operating behavior of periodic and continuous reactors utilized in polymer engineering. Development of non‐isothermal methods for the determination of chemical kinetics in polymerization processes is discussed.
Simulation of extrusion coating by tape drawing
Authors: Shaw M. T. , Miller J. C. 
Published: December 2004

AbstractNeck‐in and maximum stress were studied in a tape‐drawing experiment using a 3.5 MI low density polyethylene at 300°C. The conditions of the experiment were designed to reproduce closely those found in extrusion coating lines. The maximum stress was found to increase roughly with the 1.6 power of the drawdown ratio and the 1.0 power of the extrusion speed over a stress range of 4 × 103 to 5 × 105 Pa produced by drawdown ratios ranging from 2 to 22 and extrusion speeds of 2.3 to 6.1 cm s−1. The neck‐in decreased weakly with drawdown ratio at low extrusion speed and with extrusion speed at constant drawdown ratio. After carefully characterizing the test resin in shear and extension, the similarities between predicted pure‐shear (planar extension) transients and the tape experiments were studied. It was found that the trends, but not the magnitude of the experimental maximum stress were quite similar to the calculated longitudinal stress in pure shear. The behavior of the transverse to longitudinal stress ratio in pure shear was similar in behavior to the neck‐in results, but considerable improvement was achieved by adding in a decayed stress from a simple‐shear transient to simulate the conditions produced by the extrusion die. The philosophy of purposefully studying similarities between transient, pure or simple deformations and steady, complex processes is discussed.
An investigation of spin coating of electron resists
Authors: Lai Juey H. 
Published: December 2004

AbstractThis paper reports the results of spin coating studies of an electron resist using several different solvents. Two problems which were frequently observed during the spin coating studies were the appearance of orange peel coatings and the formation of cloudy films. The appearance of orange peel is attributed to the rapid drying of low‐boiling solvents. The formation of a cloudy film is believed to be caused by the hygroscopic nature of the solvents used. The resist film thickness can be approximated by the relationship l = KC2.1/ω0.5, where l is film thickness, C is volume fraction of polymer resist, K is a constant and ω is the rotation speed. The results are compared with the theoretical modelings of Washo (1) and Meyerhofer (2).
Effect of hydrostatic pressure on the deformation behavior of polyethylene and polycarbonate in tension and in compression
Authors: Spitzig W. A. , Richmond O. 
Published: December 2004

AbstractThe stress‐strain response of crystalline high density polyethylene and of amorphous polycarbonate has been determined in tension and in compression at superimposed pressures up to 1104 MPa(160 ksi). Strain softening occurred in the polycarbonate at low pressures but was inhibited by pressure. Tensile necking occurred in both materials, but was promoted by pressure in polyethylene and inhibited in polycarbonate. The initial modulus,E, and the flow stress, σ, at a given offset strain varied linearly with the mean pressure,P, with essentially the same pressure coefficient, α. Thus,E= (1+αP)E0and σ = (1+αP)σ0, whereE0and σ0are values at zero mean pressure. In polyethylene, the coefficient, σ0, was the same in tension and compression, indicating that the strength differential between tension and compression was a simple manifestation of pressure‐dependent yielding. In polycarbonate the coefficient, σ0, was different in tension and in compression, implying an effect due to the third stress invariant or to anisotropy. The results suggest a constitutive model for polymers in which the flow stress is linearly dependent on mean pressure, but in which inelastic volume change is negligible. The results also suggest that the pressure dependence of flow stress in polymers is the same as that of the initial modulus.
Superposition of the notched strength of composite laminates
Authors: Pipes R. Byron , Gillespie John W. , Wetherhold Robert C. 
Published: December 2004

AbstractAn improved macroscopic model for predicting the strength of a composite laminate containing a circular notch is developed. Two constants are introduced which uniquely determine the notch sensitivity of a given material. A superposition method for the notched strength of composite laminates is developed which allows data for arbitrary materials and laminate configurations to be superimposed upon a single master curve. The influence of material orthotropy upon notched strength is discussed. A relative notch sensitivity parameter is introduced which allows quantification of the notch sensitivity of a given composite material system, stacking sequence, or laminate configuration.
Theoretical prediction of the pressure gradients in coextrusion of non‐newtonian fluids
Authors: Han C. D. , Chin H. B. 
Published: December 2004

AbstractIn previous publications we have reported our experimental observations that, when the less viscous component flows outside the more viscous component in sheath‐core coextrusion through a cylindrical die, or in sandwich three layer film coextrusion through a slit die, the pressure gradients in a two‐phase system can be lower than those in the two components flowing individually. The experimental observations suggest that the energy requirement for extrusion can be decreased, and the throughput increased, when one judiciously chooses proper combinations of materials and/or optimal processing conditions. In this paper, we present a theoretical analysis, which shows that the seemingly anomalous behavior of the experimentally observed pressure gradient reduction is indeed possible, depending on the rheological properties of the individual components involved in coextrusion.
High‐strength polyethylene
Authors: Wu W. , Black W. B. 
Published: December 2004

AbstractPolyethylene (PE) continuous filaments having high tensile strength as well as high Young's modulus have been obtained from several linear polyethylene materials by stretching a partially oriented spun yarn to a draw ratio of ≃30. The high draw ratio was readily attained for linear PE fiber extruded at a temperature of at least 250°C and quenched in air while under some intermediate tension. The number average molecular weight of the polymer was found to have the predominant effect on the ultimate tensile strength of the drawn fiber. Yarn with a tensile strength of 19 gpd (167 kg/mm2) and a Young's modulus of 854 gpd (7380 kg/mm2) was produced. Yarn with a Young's modulus of 1145 gpd (9890 kg/mm2) was made by sacrificing some tensile strength.
Residence time distribution of polymer melt in the T‐die
Authors: Matsubara Yutaka 
Published: December 2004

AbstractTheoretical or rheological calculations for crosshead die geometry were thought not worthwhile until recently, and restrictor, or choker, bars were often excessively relied upon for film uniformity. Thus, the residence time distribution of a polymer melt was infrequently calculated especially in the T‐die, because it was assumed to be very wide in T‐dies. This report provides a general equation expressing the residence time distribution of polymer melts in T‐dies, and indicates how to take an optimum combination of the flow‐path dimensions in order to obtain both a high flow uniformity and a comparatively narrow residence time distribution across the die width. Such a T‐die designed by the above considerations will produce a shorter heat history and improved physical properties of the sheet or film produced.
Residual stresses and aging in injection molded polypropylene
Authors: Coxon L. D. , White J. R. 
Published: December 2004

AbstractThe residual stresses in injection molded bars of polypropylene have been examined using a stress relaxation method and by the layer removal technique. A positive value for the internal stress parameter was obtained with newly molded specimens and was found to be retained by specimens stored at liquid nitrogen temperature. The stress relaxation parameter reduced to zero both for specimens aged at room temperature and also for those aged at −40°C. Nevertheless the relaxation behavior of specimens aged at all three temperatures was quite distinct. The layer removal technique showed that the stresses near to the surface were compressive and those in the interior tensile, in apparent contradiction to the interpretation of Kubat and Rigdahl for the meaning of a positive internal stress parameter. A marked reduction in stress levels on aging at room temperature was confirmed, however. The relevance of the relaxation spectrum of polypropylene to these observations is discussed.
Sorption and diffusion of ionic dyes in anionic cellophane membranes
Authors: Hori T. , Ott R. J. , Rys P. 
Published: December 2004

AbstractExperimental steady‐state permeability studies have been made with non‐ionic, anionic and cationic dyes using carboxy cellulose membranes as anionic substrates. The experimental results show that with increasing bulk ionic strength the diffusion velocities of anionic and cationic compounds increase and decrease, respectively. The diffusion behavior of non‐ionic compounds is independent of the ionic strength. Empirical relationships have been deduced which fit the permeation data of the anionic compounds. A new concept is introduced which postulates that the diffusion behavior of colons within an anionic membrane is dependent on the basicity of the fixed ionic groups. In substrates with matrix‐bound anionic groups of high basicity, such as carboxy cellulose, the permeability behavior is described in terms of a new diffusion mechanism referred to as the “fluctuating” charge mechanism. This concept can provide a semi‐quantitative understanding of the different electrostatic obstruction effects which matrix‐bound carboxylate and sulfonate groups have on the permeability of colons. The measured permeability of the counter ions is in qualitative agreement with the proposed diffusion model.
Oxidation of polypropylene powder
Authors: Frank H. P. 
Published: December 2004

AbstractFour polypropylene powders were prepared under different drying conditions. They were tested with respect to their oxidation induction period (120°C) which ranges between 75 and 347 min. The effect of these differences on processing stability was investigated. Also studied was the oxidation behavior of powder in a fluidized bed (air) in the temperature range 80–140°C.
Cold compaction molding and sintering of ultra high molecular weight polyethylene
Authors: Truss R. W. , Han K. S. , Wallace J. F. , Geil P. H. 
Published: December 2004

AbstractCold Compaction Molding and Sintering of Ultra High Molecular Weight Polyethylene (UHMWPE) has been examined as a function of particle size, sintering time and temperature, and cooling rate. Properties nearly equivalent to those obtained by compression molding can be obtained from samples with a fibrous particle morphology, sintered just above the melting point, with further improvement possible by control of particle size and addition of fine particles of normal molecular weight linear polyethylene. UHMWPE with a nodular particle morphology sintered poorly.
Infrared studies of deformation in semicrystalline polymers
Authors: Wool R. P. 
Published: December 2004

AbstractInfrared (IR) spectroscopy was used to study molecular deformation processes in polymers as a function of stress, strain, time and temperature. Stress‐induced frequency shifts were found to depend on temperature and morphology. Deformation of viscoelastic polypropylene was examined in terms of time dependent molecular stress distributions, orientation changes, conformational variations, and chain fracture. A tie chain length distribution model was used to quantitatively interpret the IR data. Molecular deformation processes of creep and stress relaxation were found to be opposite in nature, Observed long lifetimes of highly stressed chains suggest a reappraisal of existing fracture theories.
Mixing for reaction injection molding II. Impingement mixing of fiber suspensions
Authors: Tucker Charles L. , Suh Nam P. 
Published: December 2004

AbstractThe performance of confined impinging jet mixers on suspensions of milled glass fibers in Newtonian liquids is investigated experimentally. Also studied are the performance of these devices in conjunction with an impingement aftermixer and a rotating mechanical mixing aid. In contrast to the behavior of unfilled liquids, fiber suspensions exhibit significant large‐scale mixing defects. Over the range of fiber lengths and loadings tested, large‐scale mixing quality is found to be dependent on an effective Reynolds number based on the shear viscosity of the suspension at a strain rate characteristic of the length of fibers. Both mixing aids are shown to provide improved mixing quality and could be useful in situations where length of fibers. Both mixing aids are shown to provide improved mixing Quality. and could be useful in Situations where an impingement mixer alone is not adequate.
Some considerations of heat‐transfer problems in thermoforming
Authors: Brinken F. , Potente H. 
Published: December 2004

AbstractDetails are given below of how the heat‐up process for radiation methods may be expressed mathematically. In order to fulfill practical requirements, a process must ensure calculation of necessary heating time using process‐specific characteristic curves with a minimum of mathematical effort. To this end the amount of heat actually absorbed by the surface of the O product must be known when sheets are heated by radiation. This can easily be determined through measurement of sheet surface temperature. It will be shown that if certain preconditions are satisfied, then variations in the distance of the IR‐heaters have no effect on the temperature profile of the sheet. With poly(methyl methacrylate) (PMMA) the nature of coloration does not play a significant role. Investigations into the cooling process centered on a number of cooling methods and tool materials. The dynamic behavior of tempered and untempered thermoforming tools showed similarities to work already carried out in the injection molding sector. Consideration was given to possible ways of using the “Thermolog” analog computer, developed at IKV, to calculate the necessary cooling times in the production of thermoformed parts. Input values and basic data on temperature‐time curves, necessary for the compilation of cooling curves using the analog simulator, were derived from appropriate tests on a thermoforming machine.
Viscoelastic properties of linear polymers in the fluid state and their transition to the high‐elastic state
Authors: Vinogradov G. V. , Yanovsky Yu. G. , Titkova L. V. , Barancheeva V. V. , Sergeenkov S. I. , Borisenkova E. K. 
Published: December 2004

AbstractThe experimental results of the Viscoelastic properties of linear polymers of narrow molecular weight distribution (MWD) and of their mixtures have been analyzed and generalized. Based on the study of the properties of polymers of narrow MWD, we propose a classification of high molecular weight compounds. It specifies a distinct boundary between oligomers and polymers, assuming that the most important feature of polymers is the manifestation of large high‐elastic recoverable deformations of entropy character. For polymers to be characterized, not the absolute molecular weight is essential, but the molecular weight referred to the boundary values. The corresponding state for polymers is attained at temperatures 100°C away from the glass temperature. The transition from the fluid to the high‐elastic state with increasing deformation rate (or frequency for cyclic deformation) has been studied. Transition to the high‐elastic state takes place over a narrow stress range (0.1‐1.0 dynes/cm2), independent of molecular weight, whereas the critical deformation rates (frequencies), like viscosity, depend greatly on molecular weight. An increase in the amount of deformation shifts, to u certain extent, this transition to lower Kites of deformation (frequencies). In the region of deformation rates (frequencies) corresponding to the high‐elastic state, the effect of large deformations during shear manifests itself largely in the tear‐off of polymers Iron, the confining surfaces and in specimen rupture. Polydispersity has a strong effect on the properties of polymeric systems. As the rate of deformation is increased, the transition proceeds successively from the higher molecular weight components. This relaxational transition is tantamount to a change of the structure for polymeric systems. It is responsible for non‐linear, particularly, non‐Newtonian behavior of such systems. The transition to the high‐elastic state and all the related phenomena are observed also in concentrated solutions of high molecular weight polymers. The long‐term durability of un‐cured rubbers in the high‐elastic state is described by the same relationships.
A trilogy on surfaces. I. The temperature‐surface tension coexistence curve
Authors: Legrand D. G. 
Published: December 2004

AbstractExperimental data and theoretical considerations on the shape of the temperature‐surface tension coexistence curve are presented for binary mixtures. It is found that the interfacial tension is proportional to the difference between the surface tensions raised to the nth power where n is of the order of 4.0.
A trilogy on surfaces. II. On Gibb's adsorption equation and Antonow's law
Authors: Legrand D. G. 
Published: December 2004

AbstractThe Gibb's adsorption equations for a multicomponent multiphase system are used to discuss the relationship between the surface tensions and interfacial tension. It is shown for binary systems that when the terms involving the surface excesses vanish, Antonow's rule is obtained.
The change in mechanical behavior of linear polymers during photochemical aging
Authors: Pabiot José , Verdu Jacques 
Published: December 2004

AbstractFilms of low‐density polyethylene, polypropylene, and rigid poly(vinyl chloride) were exposed for 1700 h to artificial aging in a Weather‐O‐Meter. Photochemical aging was characterized by tensile measurements. We noted that only ultimate properties are affected, whereas properties defined in the low strain range remain unchanged. The kinetics of strain and stress at break depend as much on the polymer's initial rheological characteristics as on the rate of the chemical degradation. The results show that aging results in localized chain breaking leading to defects at the supermolecular level. The average decrease of molecular weight does not seem to influence the mechanical behavior.