bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental study of the thermoforming of a blend of styrene‐butadiene copolymer with polystyrene
Authors: Stephenson M. J. , Ryan M. E. 
Published: April 2004

AbstractMaterial characterization and thermoforming studies were completed using a blend of a styrene‐butadiene copolymer with polystyrene used commercially for the production of cups and dishes. This composition was thermoformed between 135 and 152°C. Studies consisted of forming 30‐mil and 46‐mil sheets at 130, 140, and 150°C at three evacuation rates in an aluminum cylindrical mold. The mold was instrumented with a pressure transducer to follow the change in pressure during forming and two Linear Voltage Displacement Transducers, which served as mold wall contact sensors. The results indicated that the process is extremely rapid (0.25–0.60 sec) for the high and medium evacuation rates. The process was found to require a low pressure differential for forming (typically <4 psi). The final part thickness distribution and extension ratio data indicated that the material stretches into the approximate shape of a spherical segment, contacts the bottom/ center of the mold, contacts the sides, and finally stretches into the corners. The tensile strength and modulus of elasticity measurements of the final part were slightly less than the original sheet properties for samples measured in the machine direction but slightly greater for samples taken in the transverse direction. However, the percent elongation at break increased significantly in both the machine and transverse directions.
Evaluation of data on the kinetics of isothermal polymer crystallization: Part II
Authors: Lambrigger Markus 
Published: April 2004

AbstractThe kinetic crystallization model of Avrami is generally accepted as a starting point for the analysis of isothermal polymer crystallization. In a previous communication, the author has shown that data of isothermal crystallization experiments can be evaluated together with the help of Avrami master curves, if the Avrami index n is larger than one. These Avrami master curves have been obtained by scaling the three‐parameter Avrami equation functions θ(t) with the time‐values of its inflection points. In this work, alternative Avrami master curves will be displayed; they are obtained by scaling θ(t) with the mean‐time t̄ = ∫ t dθ. These alternative Avrami master curves can be constructed for every Avrami index n > 0.
Laminar morphology development and oxygen permeability of LDPE/EVOH blends
Authors: Lee Sang Young , Kim Sung Chul 
Published: April 2004

AbstractMorphology and oxygen barrier properties of LDPE/EVOH blends have been studied. Laminar dispersion of ethylene‐vinyl alcohol copolymer (EVOH) with high oxygen barrier properties was obtained in the matrix of low density polyethylene (LDPE) when extruded through an annular blown film die. Various laminar morphologies were observed and the main factors determining the morphology of the blends were viscosity ratio of the components, processing conditions, and compatibilizer level. Oxygen permeation tests have shown that thinner and longer EVOH layers in larger numbers were more effective in reducing the oxygen permeability. The oxygen permeability of the compatibilized blend having 6 phr of LLD‐g‐MAH was reduced by a factor of 740. The correlation between morphology and oxygen permeability was explained as a function of the EVOH layer size (L × R) and the number of EVOH layers (N), which were closely related to the predeformed domain size (Lo × Ro). The high Weber number (resulted from large Lo × Ro and low interfacial tension) and low viscosity ratio yielded large L × R. However, small Lo × Ro produced high N. Experimental results of oxygen permeability were well correlated with (L × R) × N.
Biofiber‐reinforced polypropylene composites
Authors: Karnani Rajeev , Krishnan Mohan , Narayan Ramani 
Published: April 2004

AbstractBiofibers, natural lignocellulosics, have an outstanding potential as a reinforcement in thermoplastics. This study deals with the preparation of lignocellulosic composites by reactive extrusion processing in which good interfacial adhesion is generated by a combination of fiber modification and matrix modification methods. PP matrix was modified by reacting with maleic anhydride and subsequently bonded to the surface of the modified lignocellulosic component, in‐situ. The fiber surface was modified by reacting it with a silane in a simple and quick aqueous reaction system, similar to that employed for glass fibers. The modified fibers are then extruded with the modified polymer matrix to form the compatibilized composite. The various reactions between the lignocellulosic fiber/filler and modified polymer chains, is expected to improve the interfacial adhesion significantly as opposed to simple mixing of the two components, since new covalent bonds between the fiber surface and matrix are created in the former case. These composite blends were then injection molded for mechanical characterization. Typical mechanical tests on strength, toughness and Izod impact energy were performed and the results are reported. These findings are discussed in view of the improved adhesion resulting from reactions and enhanced polar interactions at phase boundaries.
Kinetics of isothermal and nonisothermal crystallization of novel poly(arylene ether ether sulfide)s
Authors: Srinivas Srivatsan , Babu J. R. , Riffle J. S. , Wilkes Garth L. 
Published: April 2004

AbstractThe kinetics of crystallization have been studied for a series of novel poly(ether ether sulfide)s based on a biphenyl moiety in the backbone (Mn = 14.3K, 19.1K), referred to as biphenyl sulfide (Tg = 142°C, Tm = 347°C) and phenyl moieties in the backbone (Mn = 8.1K, 19.9K, 34K), referred to as phenyl sulfide (Tg = 100°C, Tm = 243°C). Isothermal melt crystallization kinetics were analyzed based on the Avrami equation. Avrami exponents close to three were obtained for the phenyl sulfides, independent of molecular weight or crystallization temperature, which implies growth of three‐dimensional spherulitic superstructures following heterogeneous nucleation. For the biphenyl sulfides, values closer to 2 were obtained for the exponent, also independent of molecular weight or crystallization temperature, which could imply the incomplete development of three‐dimensional superstructures following heterogeneous nucleation. Nonisothermal crystallization kinetics were also studied by cooling from the melt; in all cases studied, the Ozawa analysis could not well describe the evolution of crystallinity, probably because of the inapplicability of some of the inherent assumptions in this type of analysis. The data were analyzed using the conventional form of the Avrami equation, which yielded good fits. This semiquantitative method of analysis yields a reduced rate constant that was found to increase with increasing cooling rate and decreasing molecular weight. The results of the isothermal and nonisothermal crystallization studies carried out on the poly(ether ether sulfide)s have been compared wherever possible to the results available for PPS and PEEK.
Mathematical modeling and computer simulations of the flow, nematic phase orientation, and heat transfer in thermotropic liquid crystalline polymers
Authors: Lekakou C. 
Published: April 2004

AbstractThis study includes a mathematical analysis and computer simulations of the injection molding of thermotropic liquid crystalline polymers (LCPs). The particular area of interest is the modeling and numerical evaluation of the orientation of the rigid rods in the nematic phase of LCPs during the filling stage of injection molding. The model is based on a continuum mechanics approach in order to derive the orientation distribution function of rigid rods for different orientation angles. Numerical distributions of average orientation factors are also derived. Computer simulations have been conducted in case studies that investigate the effects of changes in the processing conditions.
Aromatic copolyester thermosets: High temperature adhesive properties
Authors: Frich Dan , Economy James , Goranov Konstantin 
Published: April 2004

AbstractThe adhesive properties of a new family of crosslinkable aromatic copolyester resins are described in this paper. A unique method for forming an adhesive bond in the solid state through high temperature interchain transesterification reactions (ITR) between cured thin films of these copolyester thermosets is indicated. Bonds formed via this procedure yield average lap shear strengths of roughly 13 MPa to titanium adherends and invariably exhibit failure at the polymer‐metal interface and not within the polymer. Various procedures to increase the strength of the bond at the interface between the polymer and the metal were tested such as the effect of surface pretreatments, primers, fillers, and the role of bondline thickness on the lap shear strength of the joints. Of these, the use of surface pretreatments and thinner bondlines has the greatest effect, raising the observed average lap shear strength of the joints to 16.5 and 20.7 Mpa, respectively. Some of the adhesive properties pertaining to the use of this new thermoset as a matrix in a graphite fiber composite are also presented.
Finite element analysis for the flow characteristics along the thickness direction in injection molding
Authors: Lee Ho‐Sang 
Published: April 2004

AbstractA numerical simulation of the filling stage along the thickness direction is proposed by combining the free‐surface boundary condition with the relevant governing equations. The mathematical model is based on the equations of continuity, momentum, and energy along with the inelastic power‐law model and relevant boundary conditions. Because of the significant implications for microstructure development in the product, the fountain effect at the advancing free surface is explicitly taken into consideration in the simulation. The model yields data on free‐surface shape and velocity, pressure, temperature, and shear stress distributions within the mold cavity. The rearrangement of the velocity and temperature profiles in the vicinity of the melt front is considered in detail.
Nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone)
Authors: Liu Tianxi , Mo Zhishen , Wang Shanger , Zhang Hongfang 
Published: April 2004

AbstractAnalysis of the nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK. And, the Ozawa analysis, when applied to this polymer system, failed to describe its nonisothermal crystallization behavior. A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation. By evaluating the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed. According to the Kissinger method, the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization, respectively.
Simulation of thermal degradation, peroxide induced degradation, and maleation of polypropylene in a modular co‐rotating twin screw extruder
Authors: Kim Byoungjoo , White James L. 
Published: April 2004

AbstractThe characteristics of thermal degradation, peroxide induced degradation, and maleation of polypropylene have been modeled in a modular intermeshing twin screw extruder for a range of screw configurations and screw speeds. The models use the Akro‐co‐Twin Screw® formulation and account for starvation and fully filled pressurized regions including the effects of viscosity reduction along the screw axis by both degradation and viscous heating. The results are compared with experiments.
Numerical analysis of injection molding of glass fiber reinforced thermoplastics. Part 1: Injection pressures and flow
Authors: Greene Joseph P. , Wilkes James O. 
Published: April 2004

AbstractNumerical calculations of flow and injection pressures during injection molding of fiber‐filled thermoplastics are compared to experimental measurements. The flow is modeled as a 2–D, nonisothermal, free‐surface flow with a new viscosity model dependent upon temperature, pressure, and fiber concentration. The steady‐state viscosity model is developed to account for the fiber‐concentration and shear‐thinning viscosities of the polymer based upon combining the Dinh‐Armstrong fiber model with the Carreau viscosity model. The new model has four parameters, three from the Carreau model and one from Dinh‐Armstrong for fiber concentrations. The new model calculates reasonably well the steady‐state viscosity of fiber‐filled polypropylene over the shear rate range of 0.01 s−1to 20 s−1. The numerical work successfully describes the flow of fiber‐filled polymers during injection molding using finite‐difference solutions for the transport equations and marker particles to track the flow front. The comparisons between the calculated and measured pressure drops for an injection molded part were reasonable for the unfilled and fiber‐filled polypropylene materials. The pressure drop comparison is very good for slow fill of a base case resin, Himont polypropylene, but not as good for fast fill of the resin. The pressure drop comparison is very good for fast fill of glass‐filled resin, DSM polypropylene with 10% and 20% short fibers, but not as good for slow fill of the resin and resin plus fibers.
Properties of poly(butylene terephthalate)/functionalized polyolefin blends
Authors: Kang Tae‐Kyu , Kim Yang , Kim Guehyun , Cho Won‐Jei , Ha Chang‐Sik 
Published: April 2004

AbstractThe object of this study was to investigate the physical properties and morphology of melt‐mixed blends containing poly(butylene terephthalate) (PBT) with several functionalized polyolefins such as ethylene/vinyl acetate copolymer (EVA), EVA‐g‐maleic anhydride (EVA‐g‐MAH), EVA‐g‐ACID, EVA‐g‐ACID/ACRYLATE, ethylene methacrylate‐g‐MAH (EMA‐g‐MAH), ethylene/ethyl acrylate copolymer (EEA) and an ethylene ionomer. Special focus was made on PBT/EVA‐g‐MAH and PBT/EMA‐g‐MAH blends compared with PBT/EVA and PBT/EMA blends. Blends were prepared in a counter‐rotating twin‐screw extruder. Mechanical and thermal properties, glass transition temperature and morphology were examined using a tensile testing machine, differential scanning calorimeter (DSC), dynamic mechanical analysis and Scanning Electron Microscope (SEM). PBT/EVA‐g‐MAH and PBT/EMA‐g‐MAH blends exhibited better impact strength than PBT/EVA and PBT/EMA blends because of the larger interfacial adhesion of EVA‐g‐MAH and EMA‐g‐MAH with PBT than EVA and EMA.
Simulation of linear viscoelastic flow behavior in the Buss Kneader
Authors: Lyu Min‐Young , White James L. 
Published: April 2004

AbstractViscoelastic flow in a Buss Kneader in which the screw has both rotating and oscillating motions is simulated. Linear viscoelastic responses are considered using both the Maxwell model and the Boltzmann superposition model. Calculations are made first in a basic screw element and subsequently in Kneader screw modules where we consider leakage flows through the interrupted screw flights. Our study includes filled length variation in the crosshead screw extruder, screw characteristics of Kneader screw elements, and pressure profiles along the modular Kneader machine.
The effect of temperature on the interfacial tension of polycarbonate/polyethylene blends
Authors: Pham H. T. , Carriere C. J. 
Published: April 2004

AbstractControlling interfacial tension during the processing of blends is critical to developing morphologies that will yield consistent and acceptable mechanical properties. Determination of the interfacial tension is important in developing a predictive understanding of the effects of processing conditions on the morphology and the physical properties of multicomponent systems. The focus of the research reported herein was to investigate the temperature dependence of the interfacial tension for blends composed of polycarbonate (PC) and polyethylene (PE). The effects of temperature were characterized by direct measurements of the interfacial tension using the imbedded fiber retraction (IFR) method. The interfacial tensions of PC/PE were measured at 210, 220, 230, and 240°C. The temperature dependence of the interfacial tension was found to be −0.018 ± 0.006 dyn/cm‐°C. In general, the interfacial tension, evaluated for low‐viscosity simple fluids, is commonly a weak function of temperature (on the order of 0.01 dyn/cm‐°C). The results found in this study are in accord with those findings.
Interferometric measurement of the apparent longitudinal electrostrictive effect in isotactic polypropylene
Authors: Kloos Gerhard 
Published: April 2004

AbstractBy the application of high electric fields, small dilatations are induced in samples of polypropylene. These strains are detected at double frequency using a Michelson interferometer. This corresponds to the measurement of the proportionality factor between strain and the square of the electric field strength. Experimental results and a macroscopic discussion based on thermodynamics are presented. From X‐ray experiments it is concluded that the majority of the investigated polymers can be regarded as isotropic, while two polymers show a slight anisotropy. With the exception of one material, the different isotactic polypropylenes show quite similar electrostrictive behavior. The purpose of the thermodynamic considerations is to study how the viscoelastic response of polymeric materials might influence the observed values.
Polymer flow length simulation during injection mold filling
Authors: Buchmann M. , Theriault R. , Osswald T. A. 
Published: April 2004

AbstractThe maximum flow length of a polymer for a given set of processing conditions is important in injection molding to avoid incomplete mold filling. Experimental analysis, using various processing conditions, can generate the actual influence of processing conditions on the maximum flow length. However, the experimental determination of the flow length for all known industrial polymers would be time consuming and expensive. A non‐Newtonian, nonisothermal model of mold filling was developed to evaluate the flow length without requiring large amounts of computation time. The model implements the use of both a temperature and shear rate–dependent viscosity as well as viscous heating. This paper presents the model and its numerical implementation, followed by simulation results. The model is compared with other simulation programs and experimental results using both an amorphous Styron 484‐27 polystyrene and a semicrystalline 640I polyethylene in a spiral mold geometry. Good agreement between the three is observed.
A review of the electrofusion joining process for polyethylene pipe systems
Authors: Bowman Jeremy 
Published: April 2004

AbstractElectrofusion joining is now an essential and widely used method to assist in the creation of polyethylene pressure pipe systems. The process of electrofusion joining is reviewed by examining the experimental and some computer simulation literature relating to the temperature and melt pressure changes during the fusion process, and on how varying fusion time and pipe/fitting gap influences the strength of electrofusion joints. From this literature review, four key stages in the joining process are identified. First, an incubation period where the joint has no strength. Second, a joint formation and consolidation stage where an increasing joint temperature aids molecular diffusion to both increase the joint strength and promote a more ductile mode of failure. A plateau region then follows where the joint strength, and ductility, remain reasonably constant despite the fusion time increasing. This plateau is thought to allow some welding variables, such as gap, to have only a small influence on joint strength (for gap maintained within reasonable limits). Finally there is a cooling stage where the joint bridging “tie molecules” become locked into either side of the joint. It is these tie molecules that give the joint its ductility and strength. The concluding section of the review notes some of the important on‐site practices that, if followed, allow electrofusion joints to acquire their good strength properties, and hence give polyethylene pressure pipe systems of a high integrity.
Cross‐thickness vibration welding of polycarbonate, polyetherimide, poly(butylene terephthalate), and modified polyphenylene oxide
Authors: Stokes Vijay K. 
Published: April 2004

AbstractIn vibration welding of thermoplastics, frictional heat generated by vibrating two parts under pressure, along their common interface, is used to effect welds. In the normal, well‐understood mode, the vibratory motion is along the weld seam, which is at right angles to the thickness direction for straight boundaries. But in many applications, such as in the welding of closed seams of box‐like parts, this vibratory motion occurs in the part‐thickness direction, so that a portion of the molten layer along the seam is exposed to the ambient air during each vibratory cycle. The resulting reduction in temperature can affect weld quality. The process phenomenology and the weld strengths of such cross‐thickness vibration‐welded butt joints are investigated for four neat resins. Weld amplitudes and weld pressures are shown to affect the strengths of 120‐Hz welds differently. It is shown that strengths on the order of the strengths of the neat resins can be achieved in 250‐Hz butt welds.
Microwave welding of high density polyethylene using intrinsically conductive polyaniline
Authors: Wu Chung‐Yuan , Benatar Avraham 
Published: April 2004

AbstractThe use of intrinsically conductive polymers in welding of plastics and composites offers the possibility of developing new welding methods. Intrinsically conductive polyaniline (PANI) composite gaskets were used to microwave weld high density polyethylene (HDPE) bars. Two composite gaskets were made from a mixture of HDPE and PANI powders in different proportions. Adiabatic heating experiments were used to estimate the internal heat generation and electric field strength in the gasket. During welding, the effects of heating time, heating pressure and welding pressure were evaluated. It was found that increasing the heating time and the welding pressure increased the joint strength. The maximum tensile joint strength was achieved using a 60 wt% PANI gasket with a heating time of 60 sec and a welding pressure of 0.9 MPa; this resulted in a tensile weld strength of 24.79 ± 0.34 MPa, which equals the tensile strength of the bulk HDPE.
Threaded joints in glass fiber reinforced polyamide
Authors: Dratschmidt Frank , Ehrenstein Gottfried W. 
Published: April 2004

AbstractThreaded joints can be used to join different polymers or polymers to metals at high loads. Design with self‐threading screws or threaded inserts requires dynamic mechanical properties. Results are presented on threaded joints of glass fiber reinforced polyamide 6 under static and dynamic loads. Dynamic load limits are determined by using the hysteresis measurement method with stepwise load increment experiments and single load level experiments. The failure and fatigue behavior of threaded joints is characterized by several parameters calculated from the hysteresis loop. These parameters change in a characteristic manner as a function of load and time. Significant changes exhibited by the damping and stiffness curves in stepwise load increase experiments can be used to determine the loss of preload on the screw and the beginning of screw pull out. Specially designed self threading screws for threaded joints capable of bearing high dynamic loads are discussed. These joints can attain a life in the endurance range (106 cycles) without loss of preload. In comparison with S‐N curves, the dynamic load limits for threaded joints can be determined more quickly by the hysteresis measurement method.