bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experience with a full notch creep test in determining the stress crack performance of polyethylenes
Authors: Fleissner M. 
Published: April 2004

AbstractA laboratory method to measure the stress crack resistance of polyethylenes was developed and has since been applied in our laboratory for more than twelve years. The experience gathered since our first paper is herewith reported. The creep rupture test of circumferentially notched specimens cut from plaques or pipes has proven to be a rapid and reliable method to evaluate the stress crack performance. Surfactant‐assisted stress cracking was employed to accelerate testing. The stress crack resistance of several polyethylene samples was studied with respect to its dependence on stress, temperature, and environment. The creep rupture behavior at different temperatures could be superposed by horizontal shifting when the stresses were normalized in proportion to the respective bulk yield stresses. The notch tip radius turned out not to be very crucial, and variation of the nominal concentration of the surfactants, nonylphenolpolyglycolethers, scarcely affected slow crack growth. Acceleration of testing by surfactants equalized property differences to a noticeable extent but did not influence the ranking of the materials. The activation energy of crack growth was in the expected range. Defects introduced into the line by butt joint welding were precisely modeled by the full notch creep test.
Cure processing modeling and cure cycle simulation of epoxy‐terminated poly(phenylene ether ketone). V: Estimation of temperature distribution during cure process
Authors: Wang Qiang , He Tianbai , Xia Ping , Chen Tianlu , Huang Baotong 
Published: April 2004

AbstractA numerical method to estimate temperature distribution during the cure of epoxy‐terminated poly(phenylene ether ketone) (E‐PEK)‐based composite is suggested. The effect of the temperature distribution on the selection of cure cycle is evaluated using a suggested alternation criterion. The effect of varying heating rate and thickness on the temperature distribution, viscosity distribution and distribution of the extent of cure reaction are discussed based on the combination of the here‐established temperature distribution model and the previously established curing kinetics model and chemorheological model. It is found that, for a thin composite (< = 10mm) and low heating rate (< = 2.5K/min), the effect of temperature distribution on cure cycle and on the processing window for pressure application can be neglected. Low heating rate is of benefit to reduce the temperature gradient. The processing window for pressure application becomes narrower with increasing thicknesses of composite sheets. The validity of the temperature distribution model and the modified processing window is evaluated through the characterization of mechanical and physical properties of E‐PEK‐based composite fabricated according to different temperature distribution conditions.
Modeling of the relationship between morphology and viscoelastic behavior of unidirectional fiber‐reinforced polymers
Authors: Alberola N. D. , Benzarti K. 
Published: April 2004

AbstractA new approach is proposed to predict the relationship between geometric arrangement of fibers within the polymer matrix and viscoelastic behavior displayed by unidirectional fiber‐reinforced polymers. Based on a quantitative morphology analysis of epoxy/glass fibers composites, a four‐phase model taking into account the fiber spatial distribution is developed to rigorously express the reinforcement effect of the polymer matrix over a wide range of fibers and temperatures. Comparisons with other modelings and experiment illustrate the validity of the proposed approach. In addition, changes in the viscoelastic behavior of the epoxy matrix in composite materials resulting from a decrease in the crosslinking degree of such a kind of polymer are, subsequently, assessed through such an approach.
A multiscale model for polymer crystallization. II: Solidification of a macroscopic part
Authors: Charbon Christian , Swaminarayan Sriram 
Published: April 2004

AbstractIn part I of this paper, we presented two efficient front‐tracking methods to simulate the growth of a spherulite within an imposed temperature field. In this second part we present a method that predicts the final microstructure in a macroscopic part by coupling these front‐tracking techniques with (a) a stochastic model for the nucleation of individual spherulites, (b) a cellular model for spherulite impingement and solid fraction evolution and (c) a Finite Difference Method (FDM) for latent heat release and heat diffusion. The method tracks the physical phenomena on several length scales: a course grid for the heat diffusion, a fine grid for solid fraction evolution and a very fine grid for the shape of the individual spherulites and the lamellae within them. To our knowledge this is the first time that fully coupled multiscale model has been applied to the solidification of polymers which gives realistic microstructure evolution, orientation of the different lamellae within spherulites and maps of the solid fraction and temperature fields during solidification. The model provides us with a quantitative predictive tool that can be used to optimize industrial processes.
Microcellular sheet extrusion system process design models for shaping and cell growth control
Authors: Baldwin Daniel F. , Park Chul B. , Suh Nam P. 
Published: April 2004

AbstractThe feasibility of shaping a nucleated polymer/gas solution represents a significant advancement for microcellular plastics process technology. Through proper design of the foaming die, nucleated solution flows can be shaped to arbitary dimensions while maintaining the functional independence of cell nucleation, cell growth and shaping. To maintain funcational independence, stringent pressure and temperature design specifications, which supersede those of conventional foam processing, must be met by the foaming die design. As a means of aiding the design process, a model is developed for predicting pressure losses and flow rates of nucleated polymer/gas solutions. A comparison of the model predictions and the actual foaming die design performance shows good agreement for limited data. These relatively simple models capture the major physics of the complicated two‐phase flow field and provide a sound base from which scale‐up of the foaming die concept can be achieved. The nucleated polymer/gas solution flow models predict highly nonlinear volumetric flow rates contrasting constant flow rates predicted for the neat polymer flow. In addition, a convenient method for classifying nucleated polymer/gas solution flow is presented based on a dimensionless ratio of the characteristic flow rate to the characteristic gas diffusion rate.
The recovery behavior of crosslinked closed cell polyolefin foams
Authors: Rodríguez‐Pérez M. A. , Díez‐Gutiérrez S. , De Saja J. A. 
Published: April 2004

AbstractIn this work an experimental study on the short term creep‐recovery response of a collection of crosslinked low density polyolefin foams, with closed cell structure and different chemical composition, is presented. The effect of the maximum creep strain and the relationships between the chemical composition, the morphology of the foams, and their recovery response are examined. The experimental results show that the main mechanism that controls the behavior of these materials is the viscoelastic recovery of the cell walls.
Thermoplastic bonding to metals via injection molding for macro‐composite manufacture
Authors: Ramani Karthik , Moriarty Brendan 
Published: April 2004

AbstractIn this work, we explore a new method of in‐situ joining of polymers to metals in injection molding to allow direct bonding between thermoplastic and metal parts. Such a method can integrate several downstream steps in product manufacture, allow optimal design of products and joints, and avoid adhesive application, assembly, and associated difficlties. A variety of process parameters and their effects upon the interface tensile strengths were examined. A full factorial experiment was conducted involving four of the critical process parameters identified. The effects upon tensile strength at break of the following process parameters were studied: (1) adherend surface temperature, (2) screw linear velocity, (3) bondline thickness, and (4) pack and hold pressure. The fracture surfaces and the thermoplastic metal interfaces were analyzed. The bonds fabricated with higher adherend surface temperatures have increased mean tensile strength and less adhesive failure. This increase in mean bond tensile strength and less adhesive failure was due to increased polymer penetration of the adherend surface roughness, at the micrometer level, as shown in the analysis of the polymer‐metal interface by a scanning electron microscope (SEM).
Identification of off‐flavor compounds in high‐density polyethylene (HDPE) with different amounts of abscents
Authors: Villberg Kirsi , Veijanen Anja , Gustafsson Irma 
Published: April 2004

AbstractThe use of synthetic pipes for drinking water distribution has increased. High desnity polyethylene (HPDE) is preferred because of its favorable mechanical properties, ease of handling during manufacturing, and low permeability to external contaminants. Off‐flavor drinking water is a problem with plastic pipes. The compounds causing off‐flavors are mainly carbonyl compounds. A combined zeolite called Abscents is used to eliminate odors and to remove odor‐causing compounds. In this study, four different amounts of Abscents were added to raw HDPE pellets, and the influence on the off‐flavor properties were analyzed. When the maximum amount of Abscents was added, almost all the carbonyl compounds disappeared, and the intensities of odors also decreased. The use of Abscents notably increased the acceptability of HDPE pipes. The system used for analysis of volatile organic compounds was a gas chromatographic/mass spectrometric/sniffing system. Purge and trap techniques were used to introduce the volatile, off‐flavor components into the gas chromatograph.
Influence of design on dispersive mixing performance in an axial discharge continuous mixer—LCMAX 40
Authors: Yao Chih‐Hsiang , Manas‐Zloczower Ica 
Published: April 2004

AbstractThe axial discharge continuous mixer combines the features of a continuous mixer and a twin screw extruder, expanding the flexibility of this compounding machine. In this work we analyzed the influence of rotor design on the dispersive mixing performance of a LCMAX 40 unit. Specifically we looked at various arrangements for the pushing and counter pushing units in the design of the LCMAX 40. A fluid dynamics analysis package—FIDAP, based on the finite element method, was used to model the flow behavior of a power law model fluid under different pressurization conditions. Dispersive mixing efficiency was quantified in terms of shear stresses and elongational flow components generated in the flow field. We found that the counter‐pushing unit generally contributes more in building up high shear stresses. However, the generation of elongational flow components, which is beneficial for dispersive mixing, is not solely dependent upon the pushing–counter pushing configuration but rather on the overall rotor geometry. We found that the maximum number of counter‐pushing units in the rotor design of the LCMAX 40 should not exceed two in order to provide adequate material pumping. Rotor designs with alternating arrangements of pushing and counter‐pushing units provide overall better dispersive mixing conditions.
Heat transfer coefficient in a high pressure tubular reactor for ethylene polymerization
Authors: Lacunza Marta H. , Ugrin Pedro E. , Brandolin Adriana , Capiati Numa J. 
Published: April 2004

AbstractHeat transfer in tubular reactors for the high pressure polymerization of ethylene is very complex, since these tubular reactors are usually divided into several zones that exhibit different flow patterns and critical fouling behavior. The correct estimation of the overall heat transfer coefficient along the reactor axial distance is a major issue when assessing the predictive capabilities of a mathematical model for the process. In general, previous models employed either constant heat transfer coefficients or the usual correlations for the Nusselt number. Neither of these two approaches is accurate enough to allow a correct prediction of the reactor behavior with respect to temperature profiles and product molecular properties. The present work performs a more comprehensive estimation of the heat transfer coefficient in these reactors. At a first stage the overall heat transfer coefficients were estimated by using approapriate energy balances and a good set of experimental data. Then, a predictive model was proposed for the overall heat transfer coefficient. All flow regimes, as well as fouling effects, were taken into account, and the parameter estimation was based on temperature profiles obtained from an industrial reactor. The temperature profiles, conversions, pressures and molecular properties calculated by means of the experimentally fitted heat transfer coefficients or with the predictive model showed good agreement with plant data.
Assessment of lifetime of hot‐water polyethylene pipes based on oxidation induction time data
Authors: Viebke J. , Gedde U. W. 
Published: April 2004

AbstractA method is presented for assessment of lifetime of polyethylene pipes undergoing thermal oxidation (Stage III failure) based on oxidation induction time (OIT) data obtained by DSC. The method requires pressure testing for limited time periods, sampling from unexposed and exposed pipes, the establishment of a linear relationship between the OIT and the antioxidant concentration, and the taking of OIT profiles through the pipe wall. The method is not applicable to pipes with improper dispersion of the antioxidant. A mathematical procedure based on a model for the migration and chemical consumption of the antioxidant system is used to extrapolate short‐term OIT profiles to obtain the OIT profiles after extended exposure. The lifetime prediction is also based on the empirical establishment of a criterion, a critical OIT value, for the onset of thermal oxidation of the polymer (Regime C). The total lifetime is then obtained under the assumption that the time period of Regime C constitutes 10% of the total lifetime. The pressure testing time required to obtain adequate data for modeling is only a fraction (20% to 70%) of the failure times of the pipes studied. The average difference between the actual and predicted times was 15% for the MDPE pipes studied.
Bulk moduli from physical aging and stress relaxation data
Authors: Kubát M. J. , Vernel J. , Rychwalski R. W. , Kubát J. 
Published: April 2004

AbstractThe process of physical aging is accompanied by a gradual change in a number of physical parameters of the solid under study. In this paper we show that by correlating the excess enthalpy with the excess volume, bulk modulus, K, data of reasonable magnitude are obtained for polystyrene, PS, and poly(vinyl acetate), PVAc. The underlying reasoning is based on standard equilibrium thermodynamics. For PVAc the time dependence of K during the aging process is discussed in terms of corresponding data calculated from dynamic mechanical measurements at varying frequency. Examples are also given of calculations of K from uniaxial stress relaxation data obtained with polyethylene samples where both the volume and the con comitant stress changes were determined. The calculation of K was based on the usual formula relating pressure (1/3rd of the uniaxial stress) to the corresponding volume change. The K data obtained were somewhat lower than those normally reported, an effect likely to be related to the time scale involved.
Microstructure and stiffness analysis of a new ternary melamine‐formaldehyde composite
Authors: Hagstrand P.‐O. , Rychwalski R. W. , Klason C. 
Published: April 2004

AbstractA new ternary planar random fiber composite manufactured under the name RMC (Reinforced Melamine Compound) is studied. Microstructure and stiffness of the random glass fiber‐reinforced and particulate‐filled melamine‐formaldehyde composite processed by compression molding from RMC molding compounds are analyzed. Glass fiber bundles in a mixture of melamine‐formaldehyde resin with various size of filler particulates outside the bundle space, and small size particulates inside the bundle space are found from scanning electron microscopy (SEM) and optical micrographs. The tensile modulus of the particulate‐filled matrix is modeled using equations of Halpin and Tsai, and Lewis and Nielsen. The tensile modulus of the resin/filler/fiber composite is calculated using the Halpin‐Tsai equation followed by a randomization procedure employing the averaging concept of Nielsen and Chen. Fiber bundles rather than single fibers are assumed as the reinforcing unit. Parameter ϵ representing the reinforcing efficiency is discussed for the case of stiffness in the direction transverse to the bundles orientation. Predicted values of the tensile modulus are in good agreement with experimental results for various compositions. Different resin/filler/fiber compositions are characterized using the calculated tensile modulus values together with merit indices introduced for the purpose of tailoring the composite toward minimized weight and material cost.
Process studies in precision injection molding. I: Process parameters and precision
Authors: Liu C. , Manzione L. T. 
Published: April 2004

AbstractPrecision injection molding is an important technology for improving productivity and lowering costs in fields such as electronics, photonics, and medical plastics by allowing the substitution of molded plastics for more expensive metals and ceramic parts. This work is part of an effort to develop a molding technology that can deliver the micron‐level precision required for these applications. Two engineering thermoplastics with glass and/or mineral fillers, poly(etherimide) (PEI) and poly(benzoate‐naphthoate) liquid crystal polymer (LCP), were studied. Precision was defined as the standard deviation of part mass and part dimensions as measured on a coordinate measuring machine. Robust design, or design of experiments (DOE), principles were used to determine optimal injection molding parameters. The results showed that ram position and hydraulic pressure were the most effective injection phase cut‐off control methods of those studied. With regard to process parameters, those that increase melt fluidity had the greatest effect on improved precision with PEI. For LCP, the effect of process parameters was far more complicated. The cross‐sectional morphology of the liquid crystal parts was investigated in the second phase of the study to assess the influence of morphology on part precision.
Izod impact fracture morphology of rubber‐toughened polysulfone and poly(phenylene sulfide) blends
Authors: Cheung M.‐F. , Plummer H. K. 
Published: April 2004

AbstractBlends of polysulfone (PSF) and poly‐phenylene sulfide (PPS) exhibit ductile behavior, below 35% by weight PPS, under tensile loading conditions. However, the blends are notch sensitive to Izod impact. The use of a core‐shell type rubber‐modifier effectively toughens the blends. Notched Izod impact strength rises, from ∼ 50 J/m to about 900 j/m, by increasing rubber content from 0% to 10–15%. It remains constant at a rubber content > 10–15%. Scanning electron microscopy (SEM) is used to study the morphology of the fracture surfaces. At low modifier content (5%), smooth or mesa‐like fracture surfaces are observed. Voids and interfacial debonding are revealed. With a higher concentration of toughening agent (> 10%), some crazing is evidence but not consistent. However, matrix yielding and extensive plastic flow of the PSF/PPS matrix are seen throughout, with a higher level of rubber modifier.
Extrusion of polypropylene. Part II: Process analysis of the metering zone
Authors: Lekakou C. , Brandao J. 
Published: April 2004

AbstractThis is a study of the extrusion of thermoplastics with special focus on the extrusion of polypropylene. A multidimensional numerical model is presented for computational simulations of the extrusion in the metering zone. The model contains a non‐isothermal analysis of the extrusion of non‐Newtonian melts in single‐screw extruders. The computer code developed is tested against an analytical solution and against literature data for the case of a high density polyethylene. Computer simulations are carried out for the extrusion of two grades of polypropylene at two different screw rotation speeds. Special attention is paid to the evaluation of variables of practical interest, such as residence times and measures of mixing quality.
Estimating liquid transport properties by a free volume method
Authors: Guo C. J. , De Kee D. 
Published: April 2004

AbstractA reduced free volume has been used to represent the viscosities as well as the self‐diffusion coefficients of different hydrocarbon liquids with viscosity less than 1 × 10−3 Pa.s at 298K by a master curve. Such correlations allow for the estimation of liquid viscosities as well as the self‐diffusion coefficients of a binary liquid mixture at infinite dilution using only density and occupied volume data of the liquids.
Fracture toughness and mechanical properties of poly(n‐pentyl‐n‐alkylsilanes)
Authors: Klemann Bruce M. , DeVilbiss Tad , Koutsky James A. 
Published: April 2004

AbstractThe mechanical properties and fracture toughness of thin films of a series of poly(n‐pentyl‐n‐alkylsilanes) were investigated. Poly(n‐butyl‐n‐pentylsilane) is the strongest of these polymers with an elastic modulus of 2.96 × 108Pa and a fracture strain of 85% at 25°C. The hexagonal mesophases of these polymers generally show elastic moduli on the order of 107Pa and are often quite extensible. AJ‐integral analysis of the ductile tearing of thin films of poly(n‐butyl‐n‐pentylsilane) and poly(n‐propyl‐n‐pentylsilane) using an Instron tensile testing machine and specimens in the single edge notch (SEN) geometry yielded plane stressJ1c(critical value ofJfor fracture initiation) of 1745 J/m2and 205 J/m2, respectively. Both values are significantly higher than the plane stressG1c(critical energy release rate) value of 109 J/m2obtained for poly(di‐n‐hexylsilane) with a residual stress analysis using the same apparatus and testing procedure.
Fracture behavior of high‐impact polystyrene under an aggressive environment
Authors: Corleto Carlos R. , Sosa Jose , Bradley Walter L. , Hurtado Jose , Daumerie Michael 
Published: April 2004

AbstractThe fracture behavior of three high‐impact polystyrene (HIPS) materials has been investigated using constant load at 1/2 h interval tests of margarine‐exposed compact tension fracture mechanics specimens. Scanning electron microscopy has also been done on the fracture surfaces to correlate the micromechanics of fracture to the fracture test results. The results indicate that the proposed tests provide a useful approach to study the environmental fracture resistance (EFR) of HIPS under the influence of an aggressive environment. It was found that the EFR of HIPS under margarine, with comparable rubber content, improves with decreasing rubber particle size and increasing molecular weight.