bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of void growth in the partial frame process
Authors: Ahn Kyung Hyun , Kim Dong‐Hak 
Published: April 2004

AbstractThe Partial Frame Process (PFP) is a kind of gas‐assisted injection molding, in which the void core is generated by imposing low pressure air into the molded part just after the resin is completely filled, after which the void grows as it compensates the volume shrinkage of resin. It resembles a secondary gas penetration step of gas‐assisted injection molding, but has more advantages, such as its simplicity, design flexibility, ease of control, and cheap utilities. In this study, modeling of the void growth in PFP was carried out. By comparing the results with the experimental data, basic assumptions have been justified and the mechanism of the void growth could be explained in terms of the process parameters such as mold temperature, melt temperature, and the channel size. An experimental approach was also taken. As there are many factors affecting the process, the method of design of experiments was adopted, and the effects of the process parameters on the void growth length and the mechanism of the void growth were investigated. The results are expected to help in mold design and the determination of the operating conditions, as well as our understanding of this new process.
A three‐dimensional analysis of the effect of die body deflection in the design of extrusion dies
Authors: Gifford W. A. 
Published: April 2004

AbstractFlat extrusion dies operating under high pressure often experience a significant amount of distortion. Satisfactory designs of such dies require an accurate prediction of the deflection of the die body as well as the flow in the internal channels of the die. Here a three‐dimensional deflection analysis is coupled to a three‐dimensional flow analysis. Such analyses are now being used by design engineers on personal computers for routine design of deflecting dies.
The use of birefringence for predicting the stiffness of injection molded polycarbonate discs
Authors: Neves N. M. , Pouzada A. S. , Voerman J. H. D. , Powell P. C. 
Published: April 2004

AbstractPolycarbonate discs were injection molded with different sets of molding conditions. The parameters studied were the flow rate, melt‐ and mold‐temperature. The discs were subjected to three point support flexural tests. Those tests are specially intended for injection molded discs because of their inherent non‐flatness. The through‐thickness molecular orientation was assessed by birefringence measurements along and across the flow direction using the wedge method. This method is ideal to measure the birefringence of materials that are difficult to cut with a microtome. The through‐thickness stiffness of the discs was calculated from the measured birefringence distributions. A composite model of the disc was used in the Algor finite element method (FEM) package to simulate the flexural tests.
Squeezing flow of viscoplastic fluids subject to wall slip
Authors: Lawal Adeniyi , Kalyon Dilhan M. 
Published: April 2004

AbstractPolymer processing operations such as compression molding, sheet forming and injection molding can be modeled by squeezing flows between two approaching parallel surfaces in relative motion. Squeezing flows also find applications in the modeling of lubrication systems, and in the determination of rheological properties. Here, analytical solutions are developed for the constant‐speed squeezing flow of viscoplastic fluids. It is assumed that the fluid is purely viscous, and hence viscoelastic effects unimportant. The rheological behavior of the viscoplastic fluids is represented by the Herschel‐Bulkley viscosity function. The deformation behavior of commonly encountered viscoplastic fluids is generally complicated by the presence of wall slip at solid walls, which is a function of the wall shear stress. The slip coefficient that relates the slip velocity to the shear stress is affected by the material of construction and also the roughness of the solid surfaces, leading to the possibility of different slip coefficients at various solid surfaces. The model developed in this study accommodates the use of different slip coefficients at different solid surfaces. The accuracy of the solutions is established, and the effects of various parameters such as slip coefficient and apparent yield stress are examined. The solutions provide useful design expressions that can be utilized for squeezing flows of viscoplastic fluids, with or without wall slip at the solid boundaries.
Continuous extrusion of self‐reinforced high density polyethylene
Authors: Huang Han‐Xiong 
Published: April 2004

AbstractContinuous extrusion was studied of self‐reinforced high density polyethylene (HDPE) sheets from flow‐induced crystallization at die pressures varying from 30 to 60 MPa. Their morphology, thermal behavior, tensile strength, and light transmittance were tested. Flow fields of a polymer melt through a converging wedge channel were also investigated by direct visual observations in conjuction with a theoretical analysis. The extensional strain rate increased abruptly as the melt approached the exit of the converging channel, this resulting in a higher crystallization rate. So, achieving the crystallization of molecular chains just in front of the exit of the converging channel may favor to extrude the bulk polymeric materials having high properties under lower pressures (e.g., 40 MPa or lower), this having been realized in the present work. The tensile strength of the self‐reinforced HDPE sheet prepared at a 40 MPa pressure was enhanced by a factor of 8.
Low density microcellular foam processing in extrusion using CO2
Authors: Park Chul B. , Behravesh Amir H. , Venter Ronald D. 
Published: April 2004

AbstractA continuous extrusion process for the manufacture of low‐density microcellular polymers is presented. Microcellular polymers are foamed plastics characterized by a cell density greater than 109 cells/cm3 and a fully grown cell size on the order of 10 μm. Previous research on continuous processing of microcellular polymers has focused on control of microcell nucleation in extrusion. This paper presents an effective means for control of cell growth to achieve a desired expansion ratio with CO2 as a blowing agent in microcellular foam processing. Also, a strategy to prevent deterioration of the cell‐population density via cell coalescence during expansion is presented. Promotion of a desired volume expansion ratio and prevention of cell coalescence in microcellular foam processing were experimentally verified. By tailoring the extrusion processing parameters, microcellular HIPS foams with a cell density of 1010 cells/cm3 and a controlled expansion ratio in the range of 1.5 to 23 were obtained.
Hot compaction and consolidation of polycarbonate powder
Authors: Vick Linda W. , Kander Ronald G. 
Published: April 2004

AbstractIn order to take advantage of the potential benefits provided by solid‐state processing of thermoplastic polymers (1–3), conventional compaction and sintering techniques must be modified to prevent large‐scale recovery (or dimensional changes) that occur upon heating polymeric compacts above their respective glass transition temperature (Tg). Two solid‐state processing techniques that have the potential for reducing recover, hot compaction and consolidation (sintering polymeric compacts under applied pressure), were investigated in this study. The results presented in this paper show that while hot compaction (below Tg) does not prevent large‐scale recovery, consolidation using pressures as low as 50 kPa (7.3 psi) did significantly reduce recovery in polycarbonate compacts.
Crystallization morphology of a thermotropic liquid crystalline polymide
Authors: Liu S. L. , Chung T. S. , Goh S. H. , Torii Y. , Yamaguchi A. , Ohta M. 
Published: April 2004

AbstractCrystallization morphology of an aromatic thermotropic liquid crystalline polyimide was studied by means of polarized light microscopy. The polyimide was synthesized from 1, 2, 4, 5‐benzenetetracarboxylic dianhydride (PMDA) and 1, 3‐bis[4'(4′ aminophenoxy) cumyl] benzene (BACB), which exhibited three exothermic peaks at onset temperatures of 292, 279, and 250°C in the DSC cooling curve. The results of polarized light microscopy revealed that the polyimide quenched from 350°C in air exhibited fine structure, frozen liquid crystalline texture. The liquid crystalline texture disappeared when the sample was heated to 298°C. However, the polymer melt still exhibited, to some degrees, birefringence until the temperature reached 340°C, where the polyimide was in the truly isotropic state. Isothermal crystallization experiments were carried out at both the isotropic temperature range and the non‐isotropic temperature range. Two types of negative spherulites with lamellar structure and positive needle‐like crystals formed from the isotropic melt have been observed. Interestingly, with a further decrease of the crystallization temperature to the liquid crystalline state temperature, the whole field was covered by the liquid crystalline texture. However, if the sample was kept at 286°C for a long time, and then reheated to 305°C to melt the liquid crystalline phase, negative spherulites with loose structures formed from the liquid crystalline state could be observed. Surprisingly, if the sample was kept at 305°C for a period of time, further crystallization could be observed using the spherulites formed at 286°C as nuclei. Composite spherulites were developed if the low‐high temperature crystallization process was repeated.
Solid state and mechanical properties of injection molded poly(ether ether ketone)/polyarylate blends
Authors: Arzak A. , Eguiazábal J. I. , Nazábal J. 
Published: April 2004

AbstractBlends of poly(ether ether ketone) (PEEK) and bisphenol‐A polyarylate (PAr) were directly prepared during the plasticization step of an injection molding machine and their solid‐state and mechanical behaviors were studied. Despite the fact that PEEK‐rich blends were apparently miscible by differential scanning calorimetry (DSC), from the dynamic‐mechanical analysis (DMTA) results all the blends were composed of (a) a crystalline PEEK phase, (b) a practically pure amorphous PEEK phase, and (c) a PAr‐rich phase richer in PEEK as the PEEK content in the blends increased. Annealed blends showed a poor mechanical performance in the PAr‐rich region, but the PEEK‐rich blends showed additive modulus of elasticity and tensile strength, and ductility and impact strength values similar to those of the highest of the two pure components. All the as‐molded low‐crystalline blends presented a synergistic behavior in the modulus of elasticity, as well as, surprisingly, in ductility and impact strength in the intermediate and slightly majority PEEK compositions. The different mechanical response of the components in fine dispersed phases and in macroscopic tensile specimens may account for the observed results.
Cell morphology and property relationships of microcellular foamed pvc/wood‐fiber composites
Authors: Matuana Laurent M. , Park Chul B. , Balatinecz John J. 
Published: April 2004

AbstractWood‐fiber composites make use of cellulose fibers as a reinforcing filler in the polymer matrix and are known to have a lower material cost and a higher stiffness than neat polymers. However, the lower material cost and enhanced stiffness of wood‐fiber composites are achieved at the expense of other properties such as the ductility and impact strength. Since microcellular plastics exhibit a higher impact strength, higher toughness, and increased fatigue life compared to unfoamed plastics, microcellular foaming of wood‐fiber composites will improve the mechanical properties of the composites and therefore increase the usefulness of the materials. In this paper, microcellular foamed PVC/wood‐fiber composites with unique cell morphology and material composition are characterized. Microcellular structures are produced in PVC/wood‐fiber composites by first saturating the composite samples with CO2under high pressure followed by rapidly decreasing the solubility of gas in the samples. The void fraction of the microcellular foamed PVC/wood‐fiber composites is controlled by tailoring the composition of materials and the foaming process parameters. The results indicate that tensile and impact properties of microcellular foamed PVC/wood‐fiber composites are most sensitive to changes in the cell morphology and the surface modification of fibers.
Physical and relaxation properties of flame‐sprayed ethylene‐methacrylic acid copolymer
Authors: Brogan Jeffrey A. , Berndt Christopher C. , Simon George P. , Hewitt David 
Published: April 2004

AbstractA range of physical and chemical properties of flame‐sprayed ethylenemethacrylic acid copolymer (EMAA) were assessed, following different processing conditions. Coatings were produced at a range of specific temperatures by varying the propane flow rate and gun traverse rate. The flame spraying process oxidizes the EMAA copolymer during processing, the extent of oxidation increasing with greater deposition temperatures. Coatings were scanned using dielectric relaxation spectroscopy at a frequency range from 102 to 106 Hz over a temperature interval of ‐20 to 85°C. The glass transition temperature (usually denoted as the β′ relaxation in this system), is attributed to the microBrownian motion of long chain segments in the amorphous phase and is found to decrease with increasing deposit temperature. The oxidation process appears to reduce the position of the β relaxation due to chain scission. The molecular weight for the EMAA powder was reduced from 22,693 g/mol to 9302 g/mol when deposited at 271°C as shown by gel permeation chromatography. Despite the decrease in chain length, the activation energies for β′ relaxation increased with increasing coating temperatures. This is attributed to the increased polarity of the oxidized coatings resulting in greater intermolecular association, which outweighs the decreased chain length.
Fibrillar morphology development of PE/PBT blends: Rheology and solvent permeability
Authors: Monticciolo A. , Cassagnau P. , Michel A. 
Published: April 2004

AbstractMorphology, rheology, and permeability studies were carried out for blends of polyethylene (PE) and polybutylene terephthalate (PBT). The effect of draw ratio at the die exit of the extruder on blend morphology was investigated, and thus isotropic fibrillar morphology with different aspect ratio was obtained. The solvent barrier properties of these blends improve as the aspect ratio of the PBT fibrils increases. Rheological experiments showed that these properties can be closely related to the development of a physical network structure of the PBT fibrils. Furthermore, the elaboration of a composite polymer system PE/PBT has been made by a second extrusion processing step. This system led to anisotropic oriented PBT fibrils in the PE matrix. Thus, random oriented PBT fibrils appeared to be an effective way of improving the barrier properties of PE/PBT blends.
Partially miscible EVOH/copolyamide‐6/6.9 blends: Thermal, dynamic‐mechanical and shear rheology behavior
Authors: Nir Y. , Narkis M. , Siegmann A. 
Published: April 2004

AbstractBinary blends of two random copolymers, ethylene‐vinyl‐alcohol (EVOH) consisting of different ethylene contents, and copolyamide‐6/6.9 with an approximate 1:1 comonomer ratio, have been prepared via blown film extrusion as films, 20 μm thick. Thermal, dynamic‐mechanical, and rheological properties were determined. It was found that these blends are partially miscible. The‐EVOH‐rich blends exhibit much lower miscibility than the copolyamide‐rich blends. The ethylene content in the EVOH affects the miscibility of the blends: a higher ethylene content results in a lower miscibility. This is due to fewer intermolecular hydrogen bonds between the OH group of the EVOH and the amide group of the copolyamide. The interactions between the blends' components affect their thermal, dynamic‐mechanical and their rheological behavior.
Shear rate effect on the resistivity of HIPS/LLDPE/carbon black extrudates
Authors: Breuer O. , Tchoudakov R. , Narkis M. , Siegmann A. 
Published: April 2004

AbstractThe effect of shear level on the structure and resultant resistivity of CB‐containing high impact polystyrene/linear low density polyethylene (HIPS/LLDPE) extrudates produced by a capillary rheometer, as a function of blend composition and CB content, was studied. The data were compared with results obtained by various processing methods such as compression molding, extrusion, and injection molding. The conductivity of systems consisting of a single polymer matrix is more sensitive to shear rate than are those with HIPS/LLDPE matrices. Increased temperature tends to increase resistivity at high shear rates, and has practically no effect at low shear rates. Capillary entrance effects determine the CB structure and resultant resistivity of the extrudates. Apparently, the combined effects of CB location and flow‐induced structuring may explain the enhanced conductivity of some of the extrudates.
Melt strength of polypropylene: Its relevance to thermoforming
Authors: Lau H. C. , Bhattacharya S. N. , Field G. J. 
Published: April 2004

AbstractThe melt strength of homopolymer, copolymer and high melt strength (HMS) grades of polypropylene (PP) was measured to assess the sagging resistance of PP for thermoforming applications. Acrylonitrile‐butadiene‐styrene (ABS), which can be easily processed during thermoforming, was also studied in this work. A polymer with high melt strength is considered to have a better sagging resistance. The melt strength measurements were carried out using a Gottfert “Rheotens” melt strength tester. The melt strength of the polymers increased with decreasing temperature and increasing extrusion rate. ABS generally had the highest melt strength in the low extrusion temperature region approaching the thermoforming region, indicating that it has a good sagging resistance during thermoforming. The HMS PP had significantly higher melt strength than conventional PP grades; therefore HMS PP is expected to have an improved sagging resistance. For conventional PP, melt strength was higher for the lower melt flow index (MFI) grades. A sharp increase in the melt strength was observed for conventional PP at low extrusion temperature, probably due to flow‐induced crystallization of the PP. These results indicate that to minimise the sagging problem with conventional PP, low MFI grades should be used and thermoforming should be performed at temperatures close to the melting point of PP.
Effect of holding time on high strain hysteresis loss of carbon black filled rubber vulcanizates
Authors: Kar Kamal K. , Bhowmick Anil K. 
Published: April 2004

AbstractHysteresis loss has been measured at constant stress and constant strain, at various holding times under tensile deformation of natural rubber (NR) and styrene‐butadiene rubber (SBR) vulcanizates filled with various loadings of carbon black filler. The effects of temperatures (25°C to 150°C), strain rates (3.78 × 10−5 sec−1 to 210 × 10−3 sec−1) and strain levels (20% to 300%) have been studied. Hysteresis loss and hysteresis loss ratio increase with an increase in strain rate, filler loading, strain level and holding time. It decreases with an increase of temperature. However, higher hysteresis loss and hysteresis loss ratio are observed at constant stress than at constant strain. NR and SBR vulcanizates show similar behavior. Evidence has been produced for the existence of a distinct relaxation process that occurs within first 120 second of holding time at room temperature. This process becomes less important as the strain or the temperature is increased. However, at high temperature another distinct relaxation process has been observed. The activation energy has been found to be 66.3 kJ/mole for the rates at the higher holding time, while it has been found to be 17.3 kJ/mole for the rates at the lower holding time using the data of hysteresis loss at first cycle of 40 phr black filled NR vulcanizates.
On‐line density and crystallinity of polyethylene terephthalate during melt spinning
Authors: Bansal Vishal , Shambaugh Robert L. 
Published: April 2004

AbstractThe density and crystallinity of polyester fiber were measured on the moving threadline during the melt spinning process. The density was calculated by applying the continuity equation at points along the length of the threadline. Experimental inputs to the equation included paralle, on‐line measurements of fiber diameter, fiber velocity, polymer mass flowrate, fiber temperature, and fiber birefringence. When spinning speeds exceeded 4500 m/min, a distinct rise in density occurred along the threadline. This rise corresponded with the rise in birefringence.
Hydrosilylation of terminal double bonds in polypropylene through reactive processing
Authors: Malz Hauke , Tzoganakis Costas 
Published: April 2004

AbstractThe melt‐phase hydrosilylation of terminal double bonds in polypropylene (PP) was investigated. The double bonds were generated by peroxide initiated degradation of PP in an extruder or a batch mixer. For this purpose, an organic peroxide, Lupersol 101, was employed in concentrations of 0.5–5 wt%. A hydride‐terminated polydimethylsiloxane was employed as a model substance to investigate the feasibility of hydrosilylating the terminal double bonds of the degraded polypropylene. Reactive processing experiments were carried out in a hot press, a batch mixer, and a single screw extruder. Two different reaction mechanisms were used to initiate the hydrosilylation reaction: a radical chain addition mechanism and a platinum catalyzed mechanism using Karstedt's catlyst. For the radical mechanism, it was shown that catalytic amounts of a peroxide could initiate the addition of silanes to the double bonds of the degraded polypropylene. Furthermore, it was found that both reactions, degradation and hydrosilylation, could be performed simultaneously. For the catalytic mechanism, the required stabilization of the platinum colloid formed in this mechanism was accomplished by adding t‐butylhydroperoxide as a cocatalyst. This melt‐phase hydrosilylation route may be used to produce terminally functionalized polypropylenes, and a case study involving the terminal attachment of a styrene functionality was examined.
Pressureless sintering of polycarbonate powder compacted at ambient temperature
Authors: Vick Linda W. , Kander Ronald G. 
Published: April 2004

AbstractSolid‐state processing of polymer powders through compaction and sintering has potential advantages over conventional polymer processing methods. However, pressureless sintering of compacted polymer powders has been unsuccessful. In a previous paper (2), room temperature compaction of polycarbonate powder was studied to better understand the fundamental mechanisms that control polymer compaction. This paper focuses on the pressureless sintering of room temperature compacted polycarbonate powder. Thermomechanical analysis was used to characterize the dependence of dimensional recovery on time, temperature, and compaction pressure for compacts formed from both aged and unaged polycarbonate. It was found that all polycarbonate compacts exhibited irreversible expansion when heated to relatively low temperatures (∼ 50°C), with large‐scale expansion occurring near its glass transition temperature. It was concluded that irreversible expansion of polymer compacts is driven by entropic factors. Therefore, parameters that affect the degree of particle deformation during compaction also affect the degree of dimensional recovery that occurs during pressureless sintering.