bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combined reactive extrusion–orientation of polyethylene
Authors: Suwanda D. , Balke S. T. 
Published: May 2005

AbstractThe objective of this work is to combine reaction, extrusion, and orientation together in a process so as to provide product in a form which is not limited to fiber or film. Three coupled problems form the focus of the work: (i) devising a practical, continuous extrusion‐orientation method; (ii) generating low concentrations of free radicals in the polymer to tailor molecular weight distribution before orientation; (iii) generating high concentrations of free radicals in the polymer to form a network in the oriented polymer without destroying its superior properties after orientation. A continuous extrusion method for orienting polymer in forms other than fibers and films was devised based upon two melt pullers. Operation of a prototype of the equipment showed it capable of providing draw ratios of greater than ten. Injection of low initiator concentrations during extrusion (i.e., before orientation) directed at solving the second problem had an effect which depended upon the degree of branching, the molecular weight, and the degree of unsaturation of the polyethylene. Large increases in molecular weight could be obtained. However, in agreement with previous work, formation of branched molecules drastically limited draw ratios attainable by the extrusion‐orientation process. To obtain high concentrations of free radicals, bench scale experiments demonstrated that a recently published method involving the use of a UV sensitizer and crosslinker followed by irradiation was directly adaptable to this process (with the irradiation applied after orientation) and provided significant improvements in creep resistance. Various attempts involving die design to obtain orientation and high initiator concentrations as well as gamma radiation to induce crosslinking after orientation were attempted and appear far less promising than the above methods.
Influence of processing conditions on shrinkage behavior of low profile unsaturated polyester resins. I: Systems without fillers
Authors: Ruffier M. , Merle G. , Pascault J. P. 
Published: May 2005

AbstractBlends of unsaturated polyester resin and polyvinylacetate (PVAc) were molded with a new instrument called the Plastoreactomat (PRM). The shrinkage and exothermic peak of polymerization were recorded during moding, and the influence of the processing conditions (pressure and temperature) on these phenomena and on the morphology was investigated for various PVAc contents. Within the limits of this study, it was found that shrinkage increases as the temperature and pressure increase. These results are discussed in terms of a competition between the phase separation and the reaction rates. In addition, it was verified that a co‐continuous two‐phase system consisting of the PVAc and the polyester network enhances the low‐profile behavior.
Modeling viscoelastic behavior of glasses during physical aging
Authors: Espinoza Abel , Aklonis J. J. 
Published: May 2005

AbstractThe generalization of a multiordering parameter model to treat physical aging in polymeric glasses is more fully explored. In the past, this model has successfully rationalized most aspects of time dependent volume and enthalpy behavior; however, only qualitative agreement between predictions of the generalized model and experiment were previously achieved for physical aging. Now, by paying strict attention to the specific analytical form of the shift factor expression, quantitative predictions have been realized for physical aging behavior based on evaluations of the shift factor parameters using volumetric data. The model also reproduces the observed behavior of glasses subjected to more complex thermal treatment such as those which evoke “memory” in glasses, e.g., shift reversal and nonmonotonic variations of the steepness of relaxation curves in the primary transition region.
The cook‐gordon mechanism in polymeric materials
Authors: Raab Miroslav , Schulz Eckhard , Sova Miloš 
Published: May 2005

AbstractThis review article, supported by some original experimental results, explains the nature of the Cook‐Gordon (C‐G) mechanism of crack blunting. Examples are given of how the C‐G mechanism influences the toughness of several anisotropic materials: fibrillated polymeric films, composites based on oriented polymers, and beech and spruce woods. Moreover, the C‐G mechanism can explain the effects of orientation on anisotropic photo‐oxidative degradation of semicrystalline polymers, and also the sudden embrittlement of polymeric films exposed to UV light under stress.
Distortion of nylon 6,6 moldings caused by asymmetric water absorption
Authors: Paterson M. W. A. , White J. R. 
Published: May 2005

AbstractDistortion of nylon 6,6 molded bars caused by one‐sided absorption of water has been investigated experimentally and the results have been compared with the predictions of an analysis based on data measured on dry bars or bars that were immersed completely in water. Account is taken of swelling, secondary crystallization, variations in Young's modulus, and the original residual stress distribution prior to the absorption of water. The major influences on distortion are (i) swelling and (ii) secondary crystallization. A much smaller effect is caused by the change in the residual stress distribution resulting from the change in the distribution of Young's modulus that develops when water is absorbed. The two major effects normally act in opposite directions, and may sometimes balance out. Differences in distortion obtained when moldings that had different aging histories were exposed to water absorption from one surface only are discussed.
Solid state extrusion of vinylidene fluoride (VF2)/vinylidene trifluoride (VF3) copolymers. I: Dynamics of solid state extrusion
Authors: Lee J. S. , Cakmak M. 
Published: May 2005

AbstractSolid state extrusion dynamics of poly(vinylidene fluoride) and its copolymers have been studied using an Instron capillary rheometer with specially designed die set. At and above the Curie transition temperatures, the copolymers rapidly soften while preserving the semicrystalline structure. This allows them to be solid state extruded between this temperature and melting temperature. The processing windows within which high quality extrudates can be obtained were established for two copolymer compositions and they were found to be much wider than those typically observed in semicrystalline homopolymers such as polyethylene and polypropylene. Extrudate swell under all solid state extrusion condition remains constant and is always less than 1 and it was found to increase above this value as the extrusion temperature increased through the melting region which is typical of melt extrusion of these polymers.
Residual stresses in injection molded polycarbonate rectangular bars
Authors: Pham H. T. , Bosnyak C. P. , Sehanobish K. 
Published: May 2005

AbstractThis study deals with the quantification of the residual stress profiles of injection molded rectangular bars with polycarbonate of various molecular weights. Determinations via the layer removal technique indicated that these bars can possess compressive stress of up to 10 MPa at the surface and up to 9 MPa in tension in the interior. The residual stress profile showed a shape similar to that observed in thermal quenching experiments, i.e., parabolic, for locations far away from the gate of the cavity. At locations near the gate of the cavity and for injection molding at high speed, the residual stress profile changed sign, going from compressive to tension at the surface and vice versa in the interior. These residual stress profiles were very dependent on gating geometry and location.
Thermoplastic starch blends with a poly(ethylene‐co‐vinyl alcohol): Processability and physical properties
Authors: George E. R. , Sullivan T. M. , Park E. H. 
Published: May 2005

AbstractWe investigated the effect of poly(ethylene‐co‐vinyl alcohol) (EVOH) concentration on the processability and physical properties of thermoplastic starch plasticized with glycerine and water. Waxy maize starch (Amioca), native corn starch (Melogel), and a treated high amylose corn starch (Hylon VII) were employed to explore the effect of starch type on blend properties. All the starches exhibited similar changes in properties with increasing EVOH content. The minimum injection pressure required for filling a standard test specimen (a measure of processability) decreased with increasing EVOH concentration and provided an indication of improved processability. Blends with high amylose corn exhibited higher injection pressures than the corresponding waxy maize or native corn starch blends. The ductility of all the thermoplastic starches was significantly increased upon the addition of EVOH. The waxy maize blends were stiffer and the high amylose corn blends exhibited higher elongation at low EVOH concentrations, but all the starch/EVOH blends exhibited similar physical properties when the EVOH concentration was ≥ 50 wt%. An investigation of physical properties of this blend series after long term aging from 10% to 90% relative humidity is in progress. Future studies include rheology, electron microscopy, and thermal analysis to more fully elucidate phase behavior in these binary blends.
The fracture probability of high impact polystyrene
Authors: Sjoerdsma S. D. , Boyens J. P. H. 
Published: May 2005

AbstractA theory is developed to describe the fracture probability of high impact polystyrene. By assuming that fracture initiation is a consequence of the impingement of crazes due to the craze thickening process, an equation for the fracture probability as a function of the strain is derived. Experiments support the validity of this equation qualitatively while the stress and temperature dependence of the fracture probabilty correlate in the expected manner with the strain rate. An approximation allows the calculation of the fracture probability as a function of time.
Experimental study on the dynamics of thermoforming of polystyrene
Authors: Parisi M. J. , Ryan M. E. , Charrier J.‐M. 
Published: May 2005

AbstractAn experimental study of the dynamics of thermoforming a high‐impact polystyrene sheet was undertaken to evaluate the effect of evacuation rate and temperature on the rate of sheet deformation and the wall thickness distribution of the molded part. The studies were conducted using an instrumented cylindrical mold having an adjustable bottom insert to vary the depth of draw. The evaculation rate was varied by introducing a flow restriction in the form of an orifice plate in the base of the mold. The deformation rate of the sheet was determined by means of fiber‐optic infrared detectors located at various depths within the mold. Mold contact sensors also provided information with regard to the deformation process after contact with the mold surface had been achieved. The evaluation characteristics were monitored by a pressure transducer. A three‐level, two‐variable factorial design was conducted to provide information of the influence of the principal operating conditions and their interactions on the measured response variables. Reliable predictive expressions were derived for the minimum pressure, time to reach minimum pressure, overall forming time, and wall thickness near the lip of the mold. The wall thickness at other locations around the periphery of the mold contour was found to be relatively insensitive to the rate of evacuation and material temperature.
Radiation pyrometry on semitransparent sheets. II: Media with wavelength dependent absorption coefficient
Authors: Hajji N. , Spruiell J. E. 
Published: May 2005

AbstractThe apparent temperature of nonisothermal sheets with a wavelength dependent absorption coefficient was investigated. A polypropylene sheet with a parabolic temperature distribution across its thickness was used as an illustration of apparent temperature calculations. It was found that the variation of the apparent temperature of polypropylene with thickness was different from that of gray media (with absorption coefficient independent of wave length). This difference was attributed to the effect of thickness on the spectral distribution of the radiation emitted by the sheet.
Structure‐thermal expansivity relation for isotropic polyoxymethylene sheets
Authors: Zahran R. R. , Abolmagd A. A. 
Published: May 2005

AbstractA detailed parametric mapping analysis of the thermal expansion coefficient for isotropic polyoxymethylene is presented. The molecular composite model has been computerized to investigate the variation of the thermal expansivity of isotropic polyoxymethylene sheets with some typical morphological and structural parameters. The results are reported and analyzed in terms of three‐dimensional structure‐property maps. The thermal expansion coefficient is found to be significantly dependent on the crystallite content, in the first place, followed by the transverse aspect ratio of the crystallites and the amorphous phase stiffness. It is only at relatively low levels of crystallinity that the thermal expansivity is sensitive to the variation of the amorphous phase tensile modulus. The longitudinal aspect ratio is slightly effective in altering the expansion coefficient as long as it is kept below 25; otherwise it is ineffective.
Entrance effects for power‐law fluid
Authors: Gupta Mahesh , Hieber C. A. , Wang K. K. 
Published: May 2005

AbstractEntrance pressure losses for the creeping flow of a power‐law fluid are calculated for an abrupt contraction of ratio 2, 4, 8 and ∞ for both the axisymmetric and planar cases using P2P1 and PP1 finite elements. Contrary to some earlier findings in the literature, the entrance pressure loss obtained by using the two different types of finite elements, both of which satisfy the Babus̆ka‐Brezzi condition, are found to converge to the same results. The present results also confirm that the variational method of Duda and Vrentas gives excellent upper bounds for both the axisymmetric and planar cases with infinite contraction ratio.
Simulation of non‐isothermal flow in modular co‐rotating twin screw extrusion
Authors: White James L. , Chen Ziyun 
Published: May 2005

AbstractNon‐isothermal flow is simulated in the screw and kneading disc elements in a modular co‐rotating twin screw extruder. Methods of calculating mean temperature rises for individual elements are discussed and results are presented. The implications of non‐isothermal operation for scale‐up is discussed. A method is then described for making calculations in a modular co‐rotating machine, that contains many different elements. Example calculations are given showing the tendency of larger machines to buildup greater temperatures when viscous heating is included.
A computer‐aided analysis of automatic degating molds for injection molding of plastic balls
Authors: Tseng Ampere A. , Kaplan Jeffrey D. 
Published: May 2005

AbstractA computer software has been developed to speed up the design process of automatic degating molds used for injection molding of plastic balls. Following an introduction to the ball making process and the associated mold design consideration, the algorithm and formulation of the software are presented. To demonstrate its versatility, the software developed is adopted to design both testing and production molds that best meet the design and production requirements. Two testing molds were built. While one was used to verify the gate size predicted, the other was built to confirm the workability of the automatic degating design. The results of testing runs have also been used to finalize the details for designing the production mold. The software developed is compact enough to be run on an IBM/PC compatible and has the capability to communicate with commercial CAD/CAM systems to provide necessary drawings or CNC files for mold fabrication.
Double coated optical fibers undergoing temperature variations: The influence of the mechanical behavior on the added transmission losses
Authors: Cocchini Franco 
Published: May 2005

AbstractA model to predict the temperature‐induced added loss in dual‐coated optical fibers is presented. Longitudinal and lateral temperature‐induced forces, originating from fiber irregularities and from the mismatch among the expansion coefficients of the glass fiber and of the coatings, are consistently included in the model. Both the bendings of the glass fiber and of the coating are considered. Transmission losses are explicity computed according to Petermann's theory on the microbending of single‐mode fibers.
Quiescent polymer crystallization: Modelling and measurements
Authors: Chan T. W. , Isayev A. I. 
Published: May 2005

AbstractThe problem of predicting nonisothermal crystallization kinetics based on isothermal data is considered, with reference to the difficulties involved, both experimental and theoretical. The kinetic model used is the differential form of the Nakamura equation which is an extension of the Avrami equation so as to apply to nonisothermal crystallization. Nonisothermal induction times are obtained from isothermal induction times according to the concept of induction time index. The theory of Hoffman Lauritzen is used to extrapolate the limited isothermal crystallization rate data. Good agreement between DSC (differential scanning calorimetry) nonisothermal crystallinity results and model predictions is obtained for our own data on poly(ethylene terephthalate) (PET) and some literature data on nylon‐6, if the temperature lag between the sample and the DSC furnace is taken into account. The advantages of the present approach in process modeling are pointed out. Quenching experiments have also been performed in which PET slabs are allowed to cool and crystallize from the melt under quiescent conditions. The resulting crystallinity distributions in the thickness direction are measured and predicted by using kinetic parameter values obtained from isothermal DSC measurements alone.
Polypropylene composites. III: Chemical modification of the interphase and its influence on the properties of PP/mica composites
Authors: Chiang Wen‐Yen , Yang Wen‐Der , Pukánszky Béla 
Published: May 2005

AbstractA surface treatment technology was developed for PP/mica composites that produces a diffuse interlayer with excellent adhesion between the components. The interlayer is created by the silane treatment of the filler and the chemical modification of the polymer components, and its polarity gradually decreases from the surface of the filler to the matrix. Properties of the composites depend on the characteristics of the interphase. With changing chemical composition, the characteristics of the interphase change from a thin, rigid layer to a more diffuse, elastic one. Properties of the composites change accordingly, optimum properties are achieved with a thick interlayer ensuring good stress transfer, strength, hardness, acceptable impact properties, and low mold shrinkage.
Residual stress development in neat poly(etheretherketone)
Authors: Eduljee Rushad F. , Gillespie John W. , McCullough Roy L. 
Published: May 2005

AbstractMaterial property models for poly(etheretherketone) (PEEK) have been combined with a residual stress model to provide a means for investigating the effect of crystallization process on the residual stress development in semicrystalline materials. The analysis shows that crystallization causes an increase in the residual stress levels. This increase is affected through an increase in the resin modulus values and through the resin modulus build‐up at higher temperatures. The shrinkage due to crystallization was found to have no effect on the residual stress development in neat PEEK.
Flow field analysis of an intermeshing counterrotating twin screw extruder
Authors: Li Tao , Manas‐Zloczower Ica 
Published: May 2005

AbstractThe intermeshing counterrotating twin screw extruder is widely used for compounding, devolatilization, blending, and reactive extrusion. A fluid dynamics analysis package‐FIDAP, using the finite element method, was implemented to simulate the 3‐D flow patterns in the region of conveying elements and shearing discs of a Leistritz LSM30.34 twin screw extruder. The rheological behavior of the fluid was described by a power law model. The flow fields were characterized in terms of velocity profiles, pressure distributions, shear stresses generated, and a parameter λ quantifying the elongational flow components. The influence of screw rotational speed and axial pressure difference on the flow characteristics was also analyzed. A comparison between the flow characteristics in the shearing discs operated in a corotating or counterrotating mode was also presented.
Optimization of the structure of integral skin foams for maximal flexural properties
Authors: Khakhar D. V. , Joseph K. V. 
Published: May 2005

AbstractThe effective flexural properties of integral skin foams (ISF), are modeled using Euler‐Bernouli beam theory along with a power law empirical equation relating the properties of a homogeneous foam to its density. The optimal density profile that maximizes the effective flexural modulus of an ISF beam of fixed overall density, and with the density constrained to lie in a given range, is continuous when the power law exponent (n) is less than 1. For n > 1, the optimal density profile is discontinuous with a low density core and a high density skin. The effective flexural modulus of such sandwich beams is maximized for a fixed density ratio (ratio of the core density to the skin density) and fixed overall density. The maximal flexural modulus is found to increase monotonically with decreasing density ratios and increasing values of n. The flexural strength of the sandwich beam is also maximized considering failure to occur by tensile fracture or buckling of the skin. In this case an optimal skin thickness and an optimal density ratio are obtained for a fixed overall density. The results are useful for the design and evaluation of flat ISF panels.
On the rheological behavior of latex polystyrene blends
Authors: Nemirovski N. , Narkis M. 
Published: May 2005

AbstractThe synthesis of latex two‐phased polystyrene blends has been accomplished by three different mixing routes: (1) PS‐b‐XPS system consisting of a physical blend of polystyrene (PS) and crosslinked polystyrene (XPS) lattices, the latter being lightly crosslinked with divinylbenzene (less than 1% DVB), (2) (XPS‐s)‐PS system obtained by styrene polymerization in presence of a XPS seed latex, and (3) (PS‐s)‐XPS system, in which styrene and DVB are copolymerized in presence of a PS seed latex. Structuring of these PS/XPS systems resulted in different microstructures by each of the procedures. Different rheological behaviors have been noticed, along with a rather interesting property dependence on XPS content and DVB concentration. The polymerization method appears to be critical to the development of well‐characterized, tailor‐made latex microstructures, insofar as the order of monomers addition determines much of the polymerizations sites.