bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interfacial instabilities in coextrusion flows of low‐density polyethylenes: Experimental studies
Authors: Tzoganakis Costas , Perdikoulias John 
Published: April 2004

AbstractA fundamental investigation into the interfacial instability phenomenon was performed. Coextrusion experiments were carried out using well‐characterized low‐density (LDPE) resins in an effort to gain a better understanding of interfacial instability phenomena. The resins used were chosen carefully and included materials of high and low viscosity as well as broad and narrow molecular weight distributions (MWD). The experiments involved the coextrusion of either the same material in both layers or various combinations of the four materials and the focus of the work was to elucidate the effects of flow rates, molecular weight (MW) and MWD on interfacial instability. The effect of the geometry at the point where the materials merged was also investigated. It was concluded that there are essentially two types of interfacial instabilities and that the MW had the strongest effect on the occurrence of the “zig‐zag” instability due to high interfacial stress while the breadth of the MWD had a strong effect on the appearance of the “wave” instability. Broad MWD materials had a greater tendency to exhibit interfacial instability, which is more due to layer ratio than processing conditions or die geometries. The results suggest that the origin of the “wave” type of interfacial instability is due to an extreme extensional deformation of the minor layer at the merge point and that the viscoelastic properties of adjacent layers determine the instability development.
Experimental study on extrudate swell and die geometry of profile extrusion
Authors: Lee Woei‐Shyong , Ho Hsueh‐Yu 
Published: April 2004

AbstractThe objective of this study was to determine the die swell behavior of a polymer melt and to design a die for forming a polymeric extrudate with a desired shape using profile extrusion. Polystyrene pellets were chosen to perform the profile extrusion experiments. First, the polystyrene pellets were melted and pushed through a quarter ring profile. The profile of the swelled extrudate agreed with the numerical predictions. A modified die was designed to produce a quarter ring profile extrudate based on the direct extrusion problem (DEP) prediction. Polystyrene pellets were also melted and pushed through the modified die. The experimental results were close to the computational results. The melting temperature, die length, and melting residence time affect die swell behavior. The die swell ratio becomes smaller as the melting temperature and melting residence time are increased. As the die length is increased, the die swell ratio is lowered. According to the die geometry predictions, an extrudate with the desired profile can be made precisely.
The effects of kneading block design and operating conditions on distributive mixing in twin screw extruders
Authors: Shearer Gifford , Tzoganakis Costas 
Published: April 2004

AbstractA mixing limited interfacial reaction between polymer tracers was used to directly measure the distributive mixing performance of a co‐rotating twin screw extruder during melt‐melt blending of polypropylene. The reaction between the polymer tracers, which are low molecular weight succinic anhydride and primary amine terminally functionalized polymer chains, was followed using Fourier‐Transform Infrared Spectroscopy (FT‐IR). Experiments were completed to determine the effects of flow rate, screw speed, and kneading block design on the distributive mixing performance and the residence time distribution (RTD). The only RTD variable that was significantly affected by the experimental factors was the average residence time. Distributive mixing with neutral and reverse kneading blocks was controlled by the average residence time, the fully filled volume, and the shear rate. Conversely, the mixing performance of a forward kneading block did not follow the same trends.
In‐line monitoring of polyethylene density using near infrared (NIR) spectroscopy
Authors: Nagata Takefumi , Ohshima Masahiro , Tanigaki Masataka 
Published: April 2004

AbstractDensity and melt index are two key properties in grading commercial polyolefin polymers. For quality assurance, these properties must be controlled as accurately as possible in the production plant. However, the lack of suitable in‐line sensors for these properties makes feedback quality control difficult. In this study, an in‐line density sensor using near infrared (NIR) spectroscopy is developed. The NIR spectra of molten polyethylene in flow are collected by a fiber‐optic device attached to a single screw extruder. By the ratio of the absorption intensity at 1170 nm to that at 1213 nm, the densities of 14 grades of polyethylene were successfully measured. The results were very promising for quality control in the polyethylene production process.
Kinetic study of the degradation of a new aromatic polyethersulfone
Authors: Abate L. , Pappalardo A. , Recca A. 
Published: April 2004

AbstractThe degradation of a new thermoplastic polyethersulfone containing more than one SO2 group in the repeating unit was carried out in both dynamic and isothermal heating conditions, under N2 flow and in a static air atmosphere. The experiments indicated that the polymer degraded by initial random chain scission, followed by branching and crosslinking in an inert atmosphere and complete degradation in an oxidative environment. Apparent activation energy values associated with the first degradation stage were calculated and suggested that the first degradation stage was not affected by the experimental conditions. Results indicated for the investigated polymer a thermal stability higher than those of some previously investigated polyethersulfones containing only one SO2 group in their repeating units.
Single and double bubble tubular film extrusion of polyethylene 2, 6‐naphthalate (PEN)
Authors: Song Kwangjin , White James L. 
Published: April 2004

AbstractAn experimental study of film formation and structure development of polyethylene 2,6‐naphthalate (PEN) in single and double bubble tubular film extrusion is presented. PEN was largely stable in film blowing. The films produced were characterized with wide angle X‐ray diffraction, DSC, and Abbe refractometer techniques. The structure and orientation in the films varied substantially with process and film formation history. Single bubbles exhibited polymorphs with considerable levels of orientation, while double bubbles possessed only the extended α‐modification. With increasing planar strain, the naphthyl rings on the chain backbone became increasingly aligned parallel to the film surface. The mechanism of structure evolution in PEN was related to its behavior during the inflation period and compared with that found in polybutylene terephthalate (PBT) and polyethylene terephthalate (PET).
Blends of linear and branched polyethylenes
Authors: Lee Heon Sang , Denn Morton M. 
Published: April 2004

AbstractWe employ rheological measurements of polyethylene blends in the melt and solid state, together with thermal analysis, to infer phase behavior. Partial‐miscibility in the melt is characterized by use of the double‐reptation model to define the complex modulus of the continuous phase for input into the emulsion model for the blend; this approach introduces a new fitting parameter, the fraction of the minor component contained in the continuous phase. The results on binary systems suggest the use of HDPE as a compatibilizer for LLDPE/LDPE blends, apparently creating a fully miscible ternary system.
Blending of immiscible polymers in a mixing zone of a twin screw extruder—effects of compatibilization
Authors: Franzheim O. , Rische T. , Stephan M. , MacKnight W. J. 
Published: April 2004

AbstractThe dependence of the morphology development of physical as well as of reactive compatibilized polypropylene/polyamide 6 (PP/PA6) blends in a mixing zone of a co‐rotating twin screw extruder on blend composition and screw rotational speed was investigated. A special process analytical set‐up based on a co‐rotating twin screw extruder was used, which allowed melt sampling from different positions along the operating extruder in time periods less than 10 seconds. It has been shown that the disperse particle sizes in physical blends depend crucially on the blend composition because of the increasing influence of coalescence with an increasing concentration of the disperse phase. Furthermore, the morphology of physical PP/PA6 blends depends strongly on their rheological properties. In contrast, the influence of the screw rotational speed on the morphology is minor. The resulting particle size in a mixing zone is achieved already after a short screw length. The particle size of compatibilized blends is significantly smaller than in physical blends because of the better conditions for drop break‐up and the suppression of coalescence effects. Due to this, compatibilization has a stronger influence on the blend morphology than a variation of process or rheological conditions with physical blends. Furthermore, the compatibilization leads to a concurrent crystallization of the PA6 phase with the PP phase.
Co‐injection molding: Effect of processing on material distribution and mechanical properties of a sandwich molded plate
Authors: Seldén R. 
Published: April 2004

AbstractThe effect of molding parameters on material distribution and mechanical properties of co‐injection molded plates has been studied using experimental design. The plates were molded with a polyamide 6 (PA 6) as skin and a 20% glass fiber‐reinforced polybutyleneterephtalate (PBTP) as core. Five molding parameters—injection velocity, mold temperature, skin and core temperature, and core content—were varied in two levels. The statistical analysis of the results showed that three parameters—Injection velocity, core temperature, and core content—were the most significant in affecting skin/core distribution. A high core temperature was the most significant variable promoting a constant core thickness, while core content was the most significant factor influencing a breakthrough of the core. Mechanical properties, such as flexural and impact strength showed a high correlation with the skin/core distribution. The slight increase in falling weight impact strength of the sandwich molded plates, compared to similar plates molded from PBTP only, could be explained from the failure process, which initiates in the brittle core and propagates through the ductile skins.
Post‐yield behavior of thermoplastics and the application to finite element analysis
Authors: Fesko Donald G. 
Published: April 2004

AbstractThis report delineates the rate sensitivity of three commodity thermoplastics and assesses the appropriateness of assuming simple rate dependence in finite element analysis. Polycarbonate does indeed show simple rate dependence in the plastic region with very rapid adjustment from one rate to the next; thus, a rate dependent model is an accurate representation. Acrylonitrile/Butadiene/Styrene (ABS) does not exhibit such large plastic strains and is a bit more complex with a process of craze formation leading to more variable necking and failure. It also shows a rapid transition from one rate to another, but superimposed failure processes impart considerable variability. Assuming simple rate dependence is a reasonable approximation and directionally correct. An impact‐modified polypropylene exhibits craze formation, a very low Poisson's ratio to large extensions and simple rate dependent behavior before failing. At elevated temperature, it draws and forms a stable neck and again shows simple rate dependence. However, the processes of failure and transition to necking are not simply rate dependent and this will keep this assumption from being generally valid.
An experimental matrix design to optimize the weldline strength in injection molded parts
Authors: Liu Shih‐Jung , Wu Jun‐Yu , Chang Jer‐Haur , Hung Shiu‐Wan 
Published: April 2004

AbstractThe forming of weldlines wherever polymer flow fronts meet is one of the problems that confound the overall success of injection molding technology. In this study, an L'18 experimental matrix design based on the Taguchi method was conducted to optimize the weldline strength of injection molded thermoplastics. Experiments were carried out on a 4.1 oz injection molding machine. A plate cavity with an obstacle at the center was used to create a weldline. After molding, the weldline strength of the parts was measured with a tensile tester. Of the factors selected in the main experiments, melt temperature and mold temperature were found to be the principal factors affecting the weldline property of injection molded thermoplastics. Weldline strengths of injection molded parts increase with the size of the obstacles.
Non‐isothermal crystallization kinetics of PET
Authors: Piccarolo S. , Brucato V. , Kiflie Z 
Published: April 2004

AbstractThe crystallization kinetics of poly(ethylene terephthalate) was studied using constant cooling rate, isothermal and quenching experiments. A non‐isothermal crystallization kinetics equation based on a single mechanism was used to analyze the data. Different mechanisms of crystallization at low, intermediate, and high cooling rates were hypothesized based on deviation of the experimental data from the single mechanism model.
Cavity balance for plastic injection molding
Authors: Lam Y. C. , Seow L. W. 
Published: April 2004

AbstractCavity balancing is the process of altering the flow front within a cavity through thickness and design changes such that a desired fill pattern is achieved. This paper reports the preliminary research undertaken in developing an automated method for cavity balancing of two‐dimensional cavities. The aim of the automated cavity balancing routine is to reduce product development time and to improve product quality. This will lower the level of prerequisite expert knowledge necessary for successful mold and part design. The automated cavity balancing routine has been developed using the concept of flow paths. The hill‐climbing algorithm was employed on the cavity fill pattern for generation of the flow paths. Replacing the flow paths generated using the straight flow path assumption in previous work, this method was found to be more versatile and suitable to automation. No special considerations or routines were required to overcome the presence of inserts within the cavity. The method has been implemented in a computer program running as an external loop to the Moldflow software. The models analyzed demonstrate that the proposed method is viable and robust.
On mechanical properties of sago starch/poly(ε‐caprolactone) composites
Authors: Odusanya O. S. , Ishiaku U. S. , Azemi B. M. N. , Manan B. D. M. , Kammer H. W. 
Published: April 2004

AbstractFour types of sago starch were incorporated into a poly(ε‐caprolactone) (PCL) matrix, native, predried, thermoplastic starch (TPS) granules and TPS. All systems were found to be phase‐separated. Tensile properties were obtained after formulation of various mixtures and processing of suitable test specimens. It was found that elongation at break of composites comprising native starch and thermoplastic starch decreases almost linearly with volume fraction of starch whereas tendencies to nonlinear dependencies were observed for predried and thermoplastic starch granules. Except for composites containing native starch, tensile strength was found to decrease linearly with volume fraction of starch. However, statistical analysis of the corresponding regression coefficients shows that the coefficients ruling the compostion dependence of tensile properties are not significantly different for the four starch types. One may conclude that in all cases, tensile properties decrease almost linearly with volume fraction and maximum volume fraction of starch loading is around 0.6. Scanning electron micrographs of fracture surfaces revealed weak interfacial adhesion between sago starch and the polymer matrix.
Synthesis and properties of fluoro‐polyetherimides
Authors: Vora Rohitkumar H. , Goh Suat Hong , Chung Tai‐Shung 
Published: April 2004

AbstractA series of amorphous fluoro‐polyetherimides based on 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and di‐ether‐containing diamines 4,4′‐bis(3‐aminophenoxy)diphenyl sulfone (m‐SED), 4,4′‐bis(4‐aminophenoxy)diphenyl sulfone (p‐SED), 4,4′‐bis(4‐aminophenoxy)diphenyl propane (BPADE) were synthesized. These melt processable polyetherimide polymers fromp‐SED and BPADE showed excellent electrical properties. The dielectric constants, 2.74 and 2.65 at 10 MHz respectively, are lower than commercially available polyetherimide ULTEM® 1000, and polyimide Kapton® H films. In addition, we found that trifluoromethyl groups‐containing polyimides not only show extraordinary electrical properties, but they also exhibit excellent long‐term thermo‐oxidative stability and reduced water absorption relative to non‐fluorinated polyimides. The weight retention of these fluoro‐polyetherimides at 315°C for 300 h in air varies from 93% to 98%. Whereas, their moisture absorption at 100 RH at 50°C was in the range of 0.3% to 1.05%, which is much lower than those of Ultem 1000 and Kapton H. In the case of fluoro‐polyetherimides fromp‐SED andm‐SED (paraandmetaisomers) diamines with ‘ether’ and sulfonyl (‐SO2‐) spacer groups, thed‐spacing andTgvalues decreased from 4.72Å to 4.56Å and 293°C to 244°C respectively. Similarly, the transparency of these polymer films (in the range of 80% to 90%) at 500 nm solar wavelength was higher than Ultem 1000 and Kapton H.
Prediction of the nonlinear poisson function using large volumetric strains estimated from a finite hyperelastic material law
Authors: Kakavas P. A. 
Published: April 2004

AbstractThe aim of this study is to evaluate the transverse strain of hyperelastic solids as a function of its longitudinal using a special constitutive equation for compressible hyperelastic materials. In addition, the nonlinear dependence of the Poisson ratio on longitudinal strain was derived. Experimental data from EPDM elastomers subjected to uniaxial tension were used in order to determine the material parameters, which are incorporated in the constitutive law.
A visual barrel system for study of reciprocating screw injection molding
Authors: Gao Furong , Jin Zhiming , Chen Xi 
Published: April 2004

AbstractA “visual” barrel system has been developed to promote the understanding of polymer behavior in a reciprocating screw injection molding machine. This system allows the dynamic status of the polymer inside the injection barrel to be conveniently visualized though photography and video recording, and the corresponding material conditions can be measured via a computerized data acquisition system. High density polyethylene (HDPE), a commonly used thermoplastic, is chosen to demonstrate the polymer melting behavior in injection molding. Effects of processing conditions on the melting behavior are analyzed, suggesting that the modeling of the plastication phase should not be treated simply as an extrusion process. The system, therefore, can not only assist in the understanding of the process but also can be used to verify quantitatively the modeling and optimization of an injection molding system.
Rubber modification of low temperature cure cyanate ester matrices and the performance in glass fabric composites
Authors: Hayes Brian S. , Seferis James C. , Parker George A. 
Published: April 2004

AbstractLow temperature cure cyanate ester resin systems were developed and modified with epoxy‐terminated butadiene acrylonitrile rubber (ETBN) and impregnated into woven glass fabric. Mode I and mode II interlaminar fracture toughness values of the cured laminates were evaluated as a function of rubber concentration. Mode I fracture toughness increased to almost twice that of the unmodified system, while mode II fracture toughness remained essentially unchanged. Composite samples were subjected to aging experiments in water and the absorption/desorption behavior was investigated as was the effect on thermal performance. The presence of rubber was found to reduce the rate of matrix deterioration but also caused a substantial increase in water uptake. It was found that although the addition of rubber to the matrices decreased the unconditioned (dry) Tg all specimens showed the same reduction in Tg, after equilibrium water absorption.
On the growth of a non‐ideal gas bubble in a solvent‐polymer solution
Authors: Favelukis Moshe , Zhang Zhihui , Pai Vivek 
Published: April 2004

AbstractA model for the growth of an ideal and a non‐ideal spherical gas bubble in a quiescent viscous liquid is presented. The growth of the bubble is assumed to be controlled by both mass transfer and viscous forces. Using the integral method, the differential momentum and binary mass balances were transformed into ordinary differential equations, which were numerically solved. Some analytical solutions for simple cases are also presented. The relevance of this work to the process of polymer melt devolatilization is discussed.
Morphology of injection molded modified poly(phenylene oxide)/polyamide‐6 blends
Authors: Son Younggon , Ahn Kyung Hyun , Char Kookheon 
Published: April 2004

AbstractThe morphology of injection molded poly(phenylene oxide)/polyamide‐6 blends was investigated. A distinct skin layer, subskin layer, and core region were found across the part thickness, and the morphology of the skin layer was clearly observed. The shape and size of the dispersed phase depended on the position across the part thickness and the viscosity ratio of the component polymers. For low viscosity ratios, small and large particles coexisted in the subskin layer, implying that both coalescence and breakup of the dispersed phase occurred in that layer. For high viscosity ratios, an intermediate zone, in which little deformation of the dispersed phase occurred, was found between the skin layer and the subskin layer. These findings are expected to help foster understanding of the mechanism of morphology evolution during the filling and cooling stages of the injection molding process.
Failure mechanisms in stereolithography injection molding tooling
Authors: Palmer A. E. , Colton J. S. 
Published: April 2004

AbstractStereolithography tooling is a form of rapid tooling that has been used to injection mold limited runs of prototype parts. However, the process is not well understood and tooling life for fine mold features is difficult to predict. Injection molding processing conditions and feature geometry affect the number of parts that can be made before a mold fails. To study the effects of feature geometry, general purpose polystyrene parts were injection molded in molds made of DSM Somos 7110 stereolithography resin. The ACES build style was used, and no polishing was performed on the mold. The experimental results were compared with theoretical models developed for the two failure mechanisms for raised features in a stereolithography mold—failures during injection due to the flow pressure of the injected polymer; and failures during ejection, whereby the part pulled out a feature of the mold. Injection failures occurred in taller mold features due to the force of flow and the feature's geometry. Ejection failures occurred in the shorter features when the stress from the ejection force (distributed over the bond area) exceeded the yield strength of the mold material. Models were developed to predict the number of parts that a mold could make before mold features break off and were validated through experimental results.