bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of drawing on structure and properties of a liquid crystalline polymer and polycarbonate in‐situ composite
Authors: Lin Qinghuang , Jho Jaeyoung , Yee Albert F.
Published: December 2004

Fibers (strands) with various draw ratios were spun from the liquid crystalline state of a pure aromatic liquid crystalline copoly(ester amide) and the melts of its blend with polycarbonate. Scanning electron microscopy (SEM), wide angle X‐ray scattering (WAXS), and differential scanning calorimetry (DSC) were employed to investigate the structure and properties of the resulting fibers. Mechanical properties of the fibers were also evaluated. It was found that both the crystallite size and heat of fusion of the liquid crystalline polymer (LCP) increase steadily with draw ratio. However, the crystal‐nematic transition temperature of the LCP is virtually unaffected by drawing. Moreover, heat of fusion of LCP is much smaller than that of isotropic condensation polymers despite the presence of very sharp diffraction peaks in WAXS measurements. These results are ascribed to the (semi)rigid rod nature of the LCP chains and the persistence of an ordered structure in the LCP melt, i.e., entropy effect. It was further observed that tensile modulus and tensile strength along fiber axis rise with draw ratio for the composite fibers. The elastic modulus of the composite fibers were found to be as high as 19 GPa and tensile strength reached 146 MPa with draw ratios below 40 and an LCP content of 30 wt%. Compared with the thermoplastic matrix, the elastic modulus and tensile strength of the in‐situ composite have increased by 7.3 times and 1.4 times, respectively, with the addition of only 30 wt% LCP. This improvement in mechanical properties is attributed to fibrillation of the LCP phase in the blend and the increasing orientation of the LCP chains along the fiber axis during drawing.
Modification and compatibilization of nylon 6 with functionalized styrenic block copolymers
Authors: Modic M. J. , Pottick L. A.
Published: December 2004

Much work in recent years had focused on the improvements of the impact properties of engineering thermoplastics by the addition of a low modulus modifier that contains polar moieties as a result of polymerization or that has been modified to contain polar moieties as a result of various grafting techniques. Styrenic block copolymers (styrene‐ethylene/butylene‐styrene) functionalized with maleic anhydride have proved useful as impact modifiers and compatibilizers in blends with engineering thermoplastics. This paper focuses on the use of these functionalized elastomers to modify nylon 6. In such compositions, a nylon material with unique mechanical performance may be achieved using the functionalized elastomer either alone or in combination with an unfunctionalized styrenic block copolymer. The optimization of performance in these rubber toughened polyamide blends using various types of styrenic block copolymers is discussed. The morphology as it pertains to performance is also reviewed. The information contained herein may prove useful in obtaining a better understanding of the mechanisms of compatibilization and modification of nylon 6 systems.
Suspension, dispersion, and interfacial polycondensation: A methodological survey
Authors: Arshady Reza , George Maurice H.
Published: December 2004

This review presents a general picture of suspension, dispersion, and interfacial polycondensation processes employed for the preparation of beaded resins, dry powders, and high solid dispersions. The polymer systems covered include polyamides, polyesters, polycarbonates, polyurethanes, and phenol‐formaldehyde and urea‐formaldehyde resins. Basic features of heterogeneous polycondensation processes are outlined, and different mechanisms of particle formation in suspension, dispersion, and interfacial polycondensation are discussed. Effects of manufacturing parameters such as feed ratio, droplet/particle stabilizer, and stirrer speed on product characteristics are also briefly covered.
Semi‐interpenetrating polymer networks composed of poly(ethylene terephthalate) and castor oil: Synthesis, structure, and properties
Authors: Barrett L. W. , Sperling L. H.
Published: December 2004

Semi‐interpenetrating networks have been produced from castor oil and poly(ethylene terephthalate) (PET). Bond interchange between PET and castor oil plays a major role in the development of initial miscibility, also affecting morphology and chemical structure. Microheterogeneous morphology is developed for materials of intermediate composition, which have much greater toughness than the polymers from which they were made.
Numerical simulation of profile extrusion dies without flow separation
Authors: Hurez P. , Tanguy P. A. , Blouin D.
Published: December 2004

Lubrication theory has been applied to solve flow problems in profile extrusion dies without flow separations, for Newtonian and power law type fluids. The method is based on velocity calculation within cross sections perpendicular to the flow. Pressure drop can also be obtained from a macroscopic balance, if the flow rate is known. Comparison of pressure drops in 2‐D and 3‐D geometries has been made with numerical simulation obtained by a finite element method. Results show a good accuracy of the proposed method.
The application of reactive processing to stampable sheet of toughness improved unsaturated polyester
Authors: Sakai Tadamoto , Nakamura Kazuyuki , Inoue Shigeki
Published: December 2004

Using twin screw extrusion and stampable sheeting processes, we have investigated the application of reactive processing technology to fiber‐reinforced stampable sheet made of an unsaturated polyester (UP) alloy with high toughness. As a result, we obtained a stampable sheet composed of a UP/nitrile butadiene rubber (NBR) polymer alloy matrix and glass fiber mats with physical properties equivalent to those of polypropylene (PP) stampable sheet, and moreover, with higher heat resistance than PP.
The laminate‐bending process for long fiber‐reinforced plastics
Authors: Machida Terufumi , Schott Nick R.
Published: December 2004

In order to form long fiber‐reinforced plastic sheets into angled parts, a new process called the Laminate‐Bending Process was recently developed. The process consists of preforming a prepreg into semi‐cured stable shapes having various sharp bending radii, followed by laminating the preforms into a fully cured thick angle product having high strength and rigidity. A sharp 90°V‐angled product of five lay‐ups of preform was test fabricated under various preforming and laminating conditions by using a continuous glass fiber reinforced epoxy resin, and it was confirmed to be excellent in delamination resistance and specific strength. Also, the process is quite practical in productivity, handling, and applicability to other advanced composite materials, and it can expand the use of such brittle materials for wider applications.
Fusion simulation of electrofusion polyethylene joints for gas distribution
Authors: Nakashiba Akio , Nishimura Hiroyuki , Inoue Fumio , Nakagawa Tomokazu , Homma Katsuhiko , Nakazato Hideo
Published: December 2004

Fusion simulation is one of the key techniques used in designing and producing electrofusion joints for gas distribution and in evaluating fusion joint integrity. This paper describes the results of numerical simulation of the thermal fusion process, using the finite element method. A nonlinear heat transfer computer program was used to obtain the temperature profile of an electrofusion joint at fusion. It was found that the temperature experimentally measured at the fusion interface by insertion of a thermocouple agreed with the temperature computed by fusion simulation. In addition, as both the temperature at the fusion interface and the resin temperature close to the wire corresponding to the mechanical strength of the fusion part were measured, it was confirmed that the proper heating conditions for each joint could be determined based on the results of the fusion simulation.
Effect of molecular weight on spherulite growth rate of poly(ethylene terephthalate) via real‐time small angle light scattering
Authors: Tant Martin R. , Culberson Wayne T.
Published: December 2004

The effect of molecular weight on the spherulite growth rate of poly(ethylene terephthalate) (PET) has been determined using a real‐time small angle light scattering (RTSALS) device equipped with a two‐dimensional position‐sensitive detector. This detector, the design of which was previously reported, incorporates a CCD camera, a personal computer, and an imaging board as the major hardware components. The device performs real‐time analysis of the light scattering pattern and calculates the average spherulite radius as a function of time during the crystallization experiment. Growth rate data were obtained for PET having number‐average molecular weights of 18,000, 24,700, and 33,100. Samples were crystallized isothermally following a temperature jump from the glass at room temperature to the desired crystallization temperature, which ranged from 130 to 200°C. Both the temperature and molecular weight dependence were found to be well described by the Hoffman equation. The temperature dependence agrees well with that found by previous workers, but the molecular weight dependence is somewhat different.
Prepreg processing science and engineering
Authors: Ahn K. J. , Seferis James C.
Published: December 2004

Resin flow and fiber spreading during the prepregging process were investigated experimentally using a scale‐down version of a commercial hot‐melt prepregger with bismaleimides and carbon fibers as model systems. Specifically, several dimensionless parameters such as the Prepreg Flow Number, fractional resin uptake, resin distribution function, fractional width change, and prepregging efficiency were defined to characterize the prepregging process as well as the quality of the prepreg. Fiber spreading during the prepregging process was observed to be a viscoelastic phenomenon depending on the impregnation temperature. For resin impregnation into collimated fiber tows, all the experimental data points obtained at different operating conditions were superimposed onto a single line showing a temperature‐pressure‐velocity superposition for the prepregging process as predicted by the definition of the Prepreg Flow Number (PFN). Finally, three fundamental steps of the prepregging process were identified and confirmed with cross‐sectional micrographs of unaged prepregs produced at different temperatures.
Friction and its effect on the mechanical‐ to‐thermal energy conversion during extrusion of poly(vinylidene chloride)
Authors: Kirkpatrick Donald E. , Hyun Kun S. , Chung Chan I.
Published: December 2004

Solid state friction reduction has been found to be an effective method for extrusion stabilization of a high coefficient of friction (COF) thermally sensitive polymer. A poly(vinylidenechloride) copolymer (PVDC) was studied alone and blended with various polyolefins to change its frictional behavior. COF of the polymer rubbing on a metal surface was measured under conditions typical of an extrusion process. These results correlated well with the measured mechanical energy consumed during extrusion. Of the polyolefins studied, high and low density polyethylene were found to be very effective for lowering friction and improving extrusion performance of the PVDC. Polypropylene was found to be much less effective. Interface temperature where melting occurs due to frictionally generated heat has been experimentally shown to be a function of COF and the bulk metal temperature.
The effect of fluid decoupling on viscous mixing
Authors: Bigio David I. , Young Dave
Published: December 2004

Flow in a three‐dimensional channel with a sinusoidally‐wavy, vertical wall is examined for the case of applied down‐ and cross‐channel velocity components. An important parameter for the analysis of the nature of laminar mixing in the flow field occurs when the changes in the downstream direction can be decoupled from the changes in the cross‐channel direction, thereby allowing for a two‐dimensional solution of the system of equations. This paper shows the effect on the nature of laminar mixing when the decoupling of the momentum equations from a fully three‐dimensional case to one where a two‐dimensional solution can be performed. Experiments are performed on a channel with sinusoidally varying vertical walls that cover the range of decoupling criteria. Silicone pigmented either white or black was run in the apparatus, cured, and cross‐sectioned. The cross sections embody a local, detailed history of the state of mixing as it proceeds down the mixer. The amount of mixing is presented as a function of position at each cross section for the different channel configurations. The nature of mixing changes from a linear growth rate in the amount of interfacial area to an exponential rate as the amplitude of the wave is increased. Results demonstrate the existence of chaos, islands, and the factors affecting the mixing behavior.
Analytical and experimental study of the die drawing of circular rods through conical dies
Authors: Motashar F. A. , Unwin A. P. , Craggs G. , Ward I. M.
Published: December 2004

An analysis is presented of the process of die drawing isotropic polymers, in the form of circular rods, to produce highly oriented materials with enhanced mechanical properties. The stresses in a small element of material undergoing the drawing process have been analyzed using a force‐equilibrium approach and the initial yield and flow stresses in the material have been predicted from the von‐Mises yield criterion. The stress‐strain‐strain rate characteristics of the polymer used in the analysis were deduced from uniaxial tensile test data obtained at the same temperature at which the die drawing occurred. Experimental results are presented of the stress in polypropylene GSE‐108 rods when die drawn at 90°C in a purpose‐built die drawing facility. Novel techniques were used to determine the stress and strain distributions along the die. A comparison of the experimental results and the analytical predictions shows good agreement.
Flow induced phase inversion agglomeration: Fundamentals and batch processing
Authors: Akay G.
Published: December 2004

A novel agglomeration technique, based on flow induced phase inversion (FIPI) is described and applied to the batch preparation of polyethylene‐bound abrasive calcite agglomerates. Water soluble polymers are used to agglomerate the needle‐like crystals of tetraacetylethylene diamine and also sodium chloride crystals. In a typical isothermal FIPI agglomeration process primary particles are dispersed in the molten binder, which is subsequently inverted by the addition of sufficient amount of primary particles, which also defines the critical filler concentration at phase inversion, Cc. Agglomerate particle size is primarily a function of Cp – Cc where Cp is the mean concentration of filler. Cc decreases with increasing binder molecular weight and primary particle surface area. Agglomerate size distribution is affected by processing, mainly by the mixing time after phase inversion. For the non‐isothermal FIPI agglomeration process, phase inversion is induced locally, by the addition of fine particles in the molten binder. Phase inversion is then propagated by cooling the dispersion during mixing. Agglomerate characteristics such as particle size, particle size distribution, binder concentration distribution in each agglomerate size range, agglomerate topology, binder morphology in the agglomerates, agglomerate strength, and agglomerate dissolution rate in water were evaluated. These agglomerate characteristics are related to the binder and filler properties as well as to the processing conditions.
A nonlinear dynamic model of a servo‐pump controlled injection molding machine
Authors: Wei Jong‐Hwei , Chang Chian‐Chiunn , Chiu Cheng‐Ping
Published: December 2004

This paper presents the development of a nonlinear mathematical model and a microcomputer controlled servo‐pump system for the study of the dynamics of a servo‐pump controlled injection molding machine (IMM). The model is formulated by the Reynolds transport theorem which is applied to describe the polymer flow dynamics in the nozzle. The comparison between the simulation results and experimental investigations indicated that the nonlinear dynamic model is a reasonable representation of a servo‐pump controlled IMM. The output flow rate and working pressure of a servo‐pump controlled IMM can be reasonably represented by the nonlinear model when the acrylonitrile‐butadiene‐styrene (ABS) is injected.
The influence of surface heating on the birefringence distribution in injection molded parts
Authors: Jansen K. M. B. , Flaman A. A. M.
Published: December 2004

In order to reduce the frozen‐in orientation, which is usually present in injection molded products, the effect of high‐performance mold surface heaters was investigated. The heaters are capable of changing their surface temperature by 70°C within a few tenths of a second typically, which minimizes their effect on the cooling time. The effects of the heating time, the instant of heating, and the heating power on the birefringence distribution of a polystyrene resin were studied. Reductions of the birefringence peak by a factor 4 to 7 were observed. The birefringence is removed most effectively by heating briefly before and during the injection stage. A heating pulse of about one second and with a power density of 20 W/cm2 then seems to be sufficient. A minimum power density of 10 W/cm2 is needed for the relaxation to occur in this specific system.
Investigation of cure in epoxy acrylate resins using rheological and dielectric measurements
Authors: Hayward D. , Mackinnon A. J. , Radhakrishnan S. , Pethrick R. A.
Published: December 2004

Dielectric and rheological measurements are reported for the cure in a series of mixtures of an epoxy‐acrylate with n‐butyl methacrylate. The level of the initiator and properties of the epoxy acrylate and n‐butyl methacrylate influence the cure characteristics and morphology of the film formed. Analysis of the rheological data indicates that during the curing process, microphase separation occurs within the mixture. The changes in the dielectric relaxation behavior with composition of the completely cured material is also consistent with microphase separation occurring in these resins while they are cured.
Screw optimization of a co‐rotating twin‐screw extruder for a binary immiscible blend
Authors: Vainio Tommi P. , Harlin Ali , Seppälä Jukka V.
Published: December 2004

The effect of the screw configuration of a closely intermeshing co‐rotating twin‐screw extruder on residence time and mixing efficiency was studied for an uncompatibilized immiscible PA6/PP (80:20) bend. Alternative screw configurations were investigated systematically. The residence time distribution (RTD) was found to be a poor indicator of the total mixing efficiency, whereas the mixing intensity function yielded considerably better information. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good dispersion of the minor phase. The evolution of morphology along the screw axis depended strongly on the screw configuration. The downstream flow characteristics after the screw end determined the final morphology of the blend.
Effects of inserts on the injection molding process
Authors: Rezayat Mohsen , Jantzen Brian
Published: December 2004

Injection molds often contain blocks of dissimilar material for improved cooling; they may also contain blocks of movable metal as a means of ejecting large parts from the mold. In this case, the blocks of metal are made of the same material, but the resistance at the interface between them has a marked influence on the cooling in the local area near the interface. In many other cases, inserts may be required because of wear in a particular mold section, or because efficient mold design is needed to produce similar parts. Hence, any mathematical model for analysis of heat transfer in injection molds must be general enough to apply to interfaces with and without gaps (i.e., with and without resistance to the flow of heat at the interface) for similar, as well as dissimilar, materials. A new and accurate model for prediction of heat transfer in heterogeneous (zoned) molds is presented in this paper. Through the solution of real problems with this model, the effects of differing material properties and interfacial thermal resistance are studied and the results are reported. It is observed that inserts have both local and global effects on the injection molding process; the overall ejection time for a part may be shortened, and the surface appearance of a part may be improved by correct placement of inserts.
Nonisothermal bubble growth in polymeric foams
Authors: Arefmanesh A. , Advani S. G.
Published: December 2004

The dynamics of a large number of bubbles separated by distances of the order of their radii in highly viscous fluids with specific application to foams is investigated. The growth of bubbles is due to diffusion of gas from the fluid and the momentum transfer between the fluid and the bubbles. Equations governing the growth of a single bubble in a shell of fluid containing limited dissolved agas are coupled with the transport equations for the fluid under non‐isothermal conditions. The resulting set of equations are solved numerically for a system of bubbles growing along the axial direction in a mold. The results predict a bubble size distribution along the axial direction with large bubbles close to the melt front and smaller bubbles close to the gate, which results in a density distribution in the molded article. Experimental studies on structural foam under nonisothermal conditions are performed. The transient bulk foam density is measured by monitoring the melt front as the foam expands. The predicted values of the foam density are compared with the experimental results and the sources of error are discussed.
Mechanical response of beams of a nonlinear viscoelastic material
Authors: Wineman Alan , Kolberg Raymond
Published: December 2004

A constitutive equation for nonlinear viscoelasticity is used to model the mechanical response of solid polymers such as polycarbonate. The nonlinearity arises from a reduced time which causes stress relaxation to accelerate with increasing strain. The constitutive equation can account for the occurrence of yield in a homogeneous uniaxial constant strain rate test. The constitutive equation is used in a study of the pure bending of beams. It is assumed that the classical assumption of beam theory is valid, i.e., plane sections remains plane. At each fixed time, the strains vary linearly through the depth of the beam. At a fixed material element the strain varies in time with the curvature. This spatial variation of the strains combined with the nonlinear dependence of the reduced time on strain leads to a significantly different response from that given by traditional beam theory. The implications of this for the bending moment history, stress distributions, and other factors that relate to beam design are discussed.
An investigation into the three‐dimensional stress‐birefringence‐strain relationship in elastomers
Authors: Arruda Ellen M. , Przybylo Phillip A.
Published: December 2004

The statistical theory of the birefringence of an individual non‐Gaussian elastomer chain is used together with a chain network description of rubber elasticity to develop a relationship among the strain, birefringence, and stress in elastomers, valid for large deformations under generalized strain states. The result is a fully three‐dimensional internal variable based constitutive model of rubber elasticity in which measurement of the elastomeric birefringence during straining in one deformation state characterizes the optically anisotropic response of the elastomer. Simultaneous measurement of the stress vs. strain response provides the rubbery modulus and limiting network extensibility properties needed to completely characterize the mechanical anisotropy of the material. Once characterized using the single, large deformation experiment, the birefringence and stress responses of the elastomer in other deformation states may then be predicted without adjusting any model parameters. The theory is compared to experimental studies from the literature of large strain deformations of elastomers in uniaxial tension and compression for which the exhibited birefringence and stress responses of deforming elastomers have been simultaneously recorded.
Kinetics modeling and time‐temperature‐transformation diagram of microwave and thermal cure of epoxy resins
Authors: Wei Jianghua , Hawley Martin C. , Demeuse Mark T.
Published: December 2004

Stoichimetric mixtures of a diglycidyl ether of bisphenol A (DGEBA)/ diaminodiphenyl sulfone (DDS) and a DGEBA/meta phenylene diamine (mPDA) were cured using both microwave and thermal energy. Fourier transform infrared (FTIR) was used for the measurement of the extent of cure and thermal mechanical analysis (TMA) was used for the determination of the glass transition temperature (Tg). The cure kinetics of the DGEBA/mPDA and DGEBA/DDS systems were described by an autocatalytic kinetic model up to vitrification in both the microwave and thermal cure. For the DGEBA/mPDA system, the reaction rate constants of the primary amine‐epoxy reaction are equal to those of the secondary amine‐epoxy reaction, and the etherification reaction is negligible for both microwave and thermal cure. For the DGEBA/DDS system, the reaction rate constants of the primary amine‐epoxy reaction are greater than those of the secondary amine‐epoxy reaction and the etherification reaction is only negligible at low cure temperatures for both microwave and thermal cure. Microwave radiation decreases the reaction rate constant ratio of the secondary amine‐epoxy reaction to the primary amine‐epxy reaction and the ratio of the etherification reaction to the primary amine‐epoxy reaction. Tg data were fitted to the DiBenedetto model. A master curve and a time‐temperature‐transformation (TTT) diagram were constructed. The vitrification time is shorter in microwave cure than in thermal cure, especially at higher isothermal cure temperatures. For the DGEBA/mPDA system, the minimum vitrification time is two to five times shorter in the microwave cure than in the thermal cure. For the DGEBA/DDS system, the minimum vitrification time is 44 times shorter in the microwave cure than in the thermal cure.
Enhanced polycarbonate toughness. II: Mechanisms
Authors: Kim S. W. , McGarry F. J. , Riew C. K.
Published: December 2004

Glassy shell‐rubbery core polymer particles, 0.1 to 0.2 μm in diameter, increase the plane strain JIC values of 3.175 mm thick polycarbonate from 3.05 kJ/m2 (no particles) to 9.5 kJ/m2 (7.5 phr particles) at 23°C. Some modest decreases in these values are caused by tests at −20°C in samples 9.525 and 3.175 mm thick. If only the particle concentration is varied, JIC increases monotonically to 7.5 phr (by wt), then levels off or decreases slightly at 10.0 phr. The total volume of 1 to 2 μm diameter cavities formed in the matrix by the apparently unbonded particles behaves similarly; cavity volume and JIC are directly related. With increasing particle concentration the tensile modulus is unchanged, the yield stress and strain decrease modestly, the strain at fracture decreases appreciably, and the heat recoverable orientation in the fractured samples decreases. Few cavities are formed. The particles reduce the extent of shear deformation in the tensile samples.
The copolymerization of methacrylates in a counter‐rotating twin‐screw extruder
Authors: Jongbloed H. A. , Mulder R. K. S. , Janssen L. P. B. M.
Published: December 2004

The copolymerization of n‐butylmethacrylate with 2‐hydroxypropylmethacrylate was studied in a closely intermeshing counterrotating twin‐screw extruder. The average molecular weight of the product can be increased by increasing the screw rotation rate or the die resistance or by decreasing the throughput or the barrel temperature. The conversion can be improved by decreasing the throughput, increasing the die resistance, and (within limits) increasing the barrel temperature, as well as through post‐initiation. Compared with various classical polymerization processes, this situation requires that particular attention be paid to the occurrence of a gel effect, the existence of a thermodynamic ceiling temperature, and the reactivity ratio of the monomers used.
Residence time distribution in non‐intermeshing counter‐rotating twin‐screw extruders
Authors: Chen L. , Hu G. H. , Lindt J. T.
Published: December 2004

This paper deals with the residence time distribution (RTD) in a non‐intermeshing counter rotating twin screw extruder.

The RTDs were measured in three vent zones of the extruder sparately, and in the adjacent zones combined, using a soluble dye as the tracer. Assuming that the RTDs in the adjacent zones are independent of each other, the overall RTD was also calculated using a previously developed statistical theory. The theory has also confirmed the consistency of the present measurements.

A predictive RTD model for the non‐intermeshing twin screw extruder, based on the flow analysis of the individual screw zones and their statistical superposition, was also developed. The predictions are in good agreement with experiment.
The flow‐induced phase morphology of fluoroelastomer and polycarbonate blends during extrusion
Authors: Tsai Hsien Yin , Min Kyonsuku
Published: December 2004

The flow‐induced phase morphological development under different extrusion conditions was studied in terms of the rheological property and interfacial tension of various elastomers and thermoplstics. The interfacial tension for elastomers and thermoplastics was investigated by using a breaking thread method (1‐4). We found that the method is suitable for measuring interfacial tension without degradation. The droplet‐fibrillation transition phenomenon was observed in various extrudates of fluoroelastomer/polycarbonate blends. The criteria for the flow‐induced morphology, in particular the droplet‐fibrillation transition, are critically discussed in this paper.
Master curve approach to polymer crystallization kinetics
Authors: Chan T. V. , Shyu G. D. , Isayev A. I.
Published: December 2004

Nonisothermal crystallization kinetic data obtained from differential scanning calorimetry (DSC) for a poly(ethylene terephthalate) are corrected for the effects of temperature lag between the DSC sample and furnace using the method of Eder and Janeschitz‐Kriegl which is based on experimental data alone without resort to any kinetic model. A method is presented for shifting the corrected nonisothermal crystallization kinetic data with respect to an arbitrarily chosen reference temperature to obtain a master curve. The method is based on experimental data alone without reference to any specific form of kinetic model. When the isothermal crystallization kinetic data for the same material are shifted with respect to the same reference temperature, a master curve is also obtained which overlaps to a large extent the corresponding master curve from nonisothermal data. It follows that nonisothermal DSC measurements provide the same crystallization kinetic information as isothermal DSC Measurements, only over a wider range of temperatures. The shift factors obtained from experimental data alone are compared in turn with the corresponding values calculated from the Avrami equation, the Hoffman‐Lauritzen expression, and the Nakamura equation as a means of evaluating these models individually. It is concluded that the Avrami equation is very good at describing isothermal crystallization kinetics, the Hoffman‐Lauritzen extrapolation of the limited isothermal data to a wide range of temperatures is quite good, and the Nakamura equation yields reliable crystallization kinetic information over a narrower range of temperatures than nonisothermal data alone without using any specific model.
Finite element analysis modeling of powder injection molding filling process including yield stress and slip phenomena
Authors: Kwon T. H. , Park J. B.
Published: December 2004

For a science‐based design of the Powder Injection Molding (PIM) process, it would be desirable for designers to have a numerical analysis tool capable of predicting the PIM filling process as a design aid. In this regard, the present study is aimed at developing a numerical analysis system to simulate the PIM filling process based on a new physical modeling taking into account rheological characteristics of powder/binder mixtures, namely the yield stress and the apparent slip phenomena. In particular, two different slip models were employed to represent the apparent slip phenomena. In accordance with the new physical modeling, the numerical simulation of the PIM filling process was accomplished by combining a finite element method and a finite difference method. It was found that the slip layer plays a role of not only a lubricating layer but also a thermal insulation layer. In this aspect, the slip layer model seems to represent the apparent slip phenemena better than the slip velocity model with regard to both the momentum and the thermal transport phenomena. The present paper presents the physical modeling, numerical scheme, and some numerical analysis results showing the effect of the yield stress and slip phenomena.
Effect of matrix ductility on the fracture behavior of rubber toughened epoxy resins
Authors: Chen Teng Ko , Jan Yi Hung
Published: December 2004

This paper investigates the effect of matrix ductility on toughness in a carboxyl‐terminated butadiene‐acryionitrile copolymer (CTBN) toughened diglycidyl ether of bisphenol‐A (DGEBA)‐piperidine system. Two kinds of epoxides were blended separately into this system to change the matrix ductility. One was a rigid and polyfunctional 4,4′‐diaminodiphenol methane (MY720), and the other was a flexible diglycidyl ether of propylene glycol (DER732). The matrix Tg was significantly changed, but without alteration of the microstructure of the dispersed rubbery phase. The result of fracture energy tests reveals that the toughness of the neat epoxy resins increases slightly with the increase in the resin ductility. The toughness of the rubber‐modified epoxy resins increases strongly with matrix ductility. Studies on the morphology of the toughened systems and their fracture surfaces indicate that the size of the plastic deformation zone under constant rubbery‐phase morphology is determined by the multiple but localized plastic shear yielding. Increasing matrix ductility increases the size of the plastic deformation zone by inducing more extensive shear yielding. In addition, fracture surfaces reveal that as the matrix rigidity is increased, an increasing proportion of the fracture energy is dissipated by rubber cavitation during crack initiation.
Fracture toughness of acrylonitrile‐butadiene‐styrene byJ‐integral methods
Authors: Lu Ming‐Luen , Lee Chang‐Bing , Chang Feng‐Chih
Published: December 2004

The fracture toughness of acrylonitrile‐butadiene‐styrene (ABS) was determined by threeJ‐integral methods, ASTM E813‐81, E813‐87, and by hysteresis. The criticalJvalues (J1c) obtained are fairly independent of the specimen thickness, ranging from 10 to 15 mm. ASTM E813‐81 and hysteresis methods result in comparableJ1cvalues, whereas the ASTM E813‐87 was ∼40% to 50% higher. The critical displacement determined from the plots of hysteresis (energy or ratio) and the true crack grow length vs. displacement are close. This indicates the critical displacement determined by the hysteresis method is indeed the displacement at onset of crack initiation, and the correspondingJ1crepresents a physical event of crack initiation. The elastic storage energy. The input energy minus the hysteresis energy, is the most important factor in determining the onset of crack initiation. The critical elastic storage energy (at the beginning of crack growth) was found close to theJ1cobtained from the E813‐81 or the hysteresis method.
Interfacial structure in reacting poly(methyl methacrylate)/polycarbonate polymer blends
Authors: Yoon H. , Han C. C.
Published: December 2004

The snall angle neutron scattering (SANS) technique has been used to study the interfacial structure development in poly(methyl methacrylate)/polycarbonate (PMMA/PC) blends through transesterification. We found: (1) Development of interfacial structure through transestrification at the phase separated domain interfaces are observed at T ≤ 200°C. At T ≥ 215°C, because of a higher transesterification rate, the melting of domains is observed together with very weak scattering by interfacial structure. (2) Interfacial thickness ti increases with time and reaches a plateau value of ti at 32.5 ± 2.4 Å and 29.6 ± 3.7 Å for 180°C and 200°C, respectively. (3) The internsity profiles at 190°C and long times shows the formation of spherical domains similar to those reported by Rabeony et al. (1). These may be caused by the crosslinking effect of the transesterification reaction between PMMA and PC.
Curing of thermosetting polymers by an external fluid
Authors: Reboredo M. M. , Vazquez A.
Published: December 2004

A theoretical model is proposed for curing thermosetting polymers. The following heat transfer mechanisms are taken into account: convection through the heated fluid‐mold interface, conduction through the resin, and heat generated by chemical reaction. To study the influence of the convective heat in the curing step of the polymers, different external heating fluids are considered. Several chemical systems are used in the simulation. The results show that an apoxy requires precise control of thermal runaway. Criteria for processability are established and they provide a cycle time without promoting a damaging exotherm.
Mixing in reactive extrusion of low‐density polyethylene melts: Linear vs. branched
Authors: Polance R. , Jayaraman K.
Published: December 2004

The melt flows of linear low‐density polyethylene (LLDPE) and branched low‐density polyethylene (LDPE) have been compared in a fully intermeshing co‐rotating twin‐screw extruder. The polyethylene melts were selected in order to investigate the effects of the melt rheology on the mixing. Their shear vicosity curves are quite similar, but the LDPE has a markedly higher apparent extensional viscosity over a wide range of stretch rates. The stagger of the paddles in the mixing zone of the extruder creates axial pressure‐driven axial flow can have significant extensional strain components. Residence time distributions obtained in the melt zones of the extruder with tracer dye reveal that the LDPE has a narrower residence time distribution than the LLDPE over a wide range of operating conditions. The axial dispersion for the LDPE is significantly lower than the axial dispersion for the LLDPE. This is attributed to the greater extensional viscosity of the LDPE. During the reactive extrusion process, solid maleic anhydride and polyethylene were added at the feed port but the peroxide provides better control of the crosslinking reaction. Residence time distributions measured for the chemically more reactive LLDPE melt indicate reduced levels of axial mixing with reaction. The reduction in mixing is due to a crosslinking reaction that occurs in parallel to the grafting reaction. This change in mixing is smaller than the difference in mixing between LDPE and LLDPE.
The control of miscibility of PP/EPDM blends by adding lonomers and applying dynamic vulcanization
Authors: Kim Youngkyoo , Cho Won‐Jei , Ha Chang‐Sik , Kim Wonho
Published: December 2004

The control of miscibility for isotactic polypropylene (PP) and ethylene‐propylene‐diene terpolymer (EPDM) has been attempted by adding poly(ethylene‐comethacrylic acid) (EMA) ionomers and by applying dynamic vulcanization. The rheological properties, crystallization behavior, and morphology of the dynamically vulcanized EPDM/PP/ionomer ternary blends were investigated with a Rheometrics dynamic spectrometer (RDS), a differential scanning calorimeter (DSC), and a scanning electron microscope (SEM). Two kinds of EMA ionomers neutralized with different metal ions (Na+ and ZN++) were investigated. Blends were prepared on a laboratory internal mixer at 190°C. Blending and curing were performed simultaneously, i.e., EPDM was vulcanized with dicumyl peroxide (DCP) in the presence of PP/ionomer. The composition of PP and EPDM was fixed at 50/50 by wt% and the contents of EMA ionomer were vaired from 5 to 20 parts based on the total amount of PP and EPDM. It was found that the addition of ionomers and the application of the dynamic vulcanization were effective in enhancing the miscibility of PP and EPDM. The structure of the blends was controlled by the following three component phases, i.e., the phase of the dynamially valcanized EPDM, PP, and Zn‐neutralized ionomer. The ternary blends showed more miscibility than the PP/EPDM binary blend. This is due to the thermoplastic interpenetrating polymer network (IPN) of the ternary blends. The structure and properties of the ternary blends differed, depending on the types and contents of ionomer, i.e., the ternary blend containing Na‐neutralized ionomer did not show a thermoplastic IPN structure clearly, even though the blend was prepared by dynamic vulcanization. The ternary blend containing Zn‐neutralized ionomer clearly showed the behavior of a thermoplastic IPN when the contents of ionomer and DCP were 15 parts and 1.0 part, respectively.
Transesterifications in a polyblend of poly(butylene terephthalate) and a liquid crystalline polyester
Authors: Jo Byung‐Wook , Chang Jin‐Hae , Jin Jung‐Il
Published: December 2004

Transesterfication between a liquid crystalline polyster and poly(butylene terephthalate) was followed quantitatively by analyzing 13C‐NMR spectra of the 50:50 blend after heat treatmetn at 290°C for varying lengths of time. Differential scanning nalysis was employed to follow the interchange reactions. From analysis of triad sequences of the transesterified blends, it was clear that measurable exchange reactions occurred when the blend was kept at 290°C for 20 min. The distribution of sequences tends to approach that of a statistical binary copolymer as the heat treatment period is increased. The results ontained from this investigation show that polyblends between an LC polyesterand conventional polyesters must be handled carefully. Otherwise, ester interchange reactions are inevitable.
Effect of die geometry on the structural development of a thermotropic liquid crystalline polymer in a thermoplastic elastomer matrix
Authors: Seo Yongsok , Hwang Seung Sang , Hong Soon Man , Park Tae Suk , Kim Kwang Ung
Published: December 2004

This study investigates deformation of a thermotropic liquid crystalline polymer (TLCP) in different die geometries. Blends of aTLCP with a thermiplastic elastomer of EPDM were made in a twin‐screw extruder. Morphological observation of the extruded blends demonstrates the complimentary effect of shear in the die exit on dispersed phase deformation and fibril formation. Shear strain can affect fibril formation for a relatively large dispersed phase in the region close to the die wall. However, the main role of shearing is in breaking up the larger particles and initial polydomain structure. A strong elongational deformation on the blended melt after the die exit is required, and fine microfibrils normally obnserved in in situ composites were not easily formed by shear deformation only in the die.
Mixing and morphological transformations in the compounding process for polymer blends: The phase inversion mechanism
Authors: Shih Chi‐Kai
Published: December 2004

This study reports on the progression of processes occurring in polymer blends during mixing. For the polymer pellet blends studied, an abrupt phase inversion was observed simultaneous with attainment of maximum torque in the batch mixer. A four‐step phase inversion mechanism is described as predominant where dissipative mix‐melting of the polymer system occurred in the mixing process.
A simple model for heat transfer inside an extrusion die
Authors: Wu Ping‐Yao , Huang Lee‐May , Liu Ta‐Jo
Published: December 2004

A simple model based on the lubrication approximation has been developed to analyze heat transfer of power‐law fluids inside an extrusion die. This model can effectively predict the influence of temperature variations and other production alterations on flow uniformity. The predictions of this model are compared with those based on three‐dimensional finite element simulation, and the agreement is satisfactory. The optimal design concept can be incorporated into this model so that a specially designed choker bar can be inserted into the extrusion die to reduce flow nonuniformities. The shape of the choker bar is initially suggested by the lubrication model; minor corrections through the three‐dimensional finite element simulation are then introduced so that a choker bar can be properly constructed to eliminate flow nonuniformities.
A unified K‐BKZ model for residual stress analysis of injection molded three‐dimensional thin shapes
Authors: Chang Rong‐Yeu , Chiou Shiaw‐Yuh
Published: December 2004

The flow‐induced and thermally induced residual stresses during injection molding of a thin part with complex geometries are predicted. The injection molding precess was considered to consist of a filling and a post‐filling stage (packing coupled with cooling). Additionally, the analysis were applied to successive stages of the process. The model takes into account the viscoelasticity of the molding polymer, which has been neglected in most previous works, because of the complexity of its inclusion. A unified K‐BKZ viscoelastic constitutive model, capable of modeling both the fluid‐rubbery state and the glass state of amorphous polymers, was employed for simulating this problem. For the flow‐induced residual stress predictions of the filling stage, a quasi‐steady state approximation was employed for each element of the part, for the calculation of stress profile and subsequent stress relaxation after cessation of flowf. Stress calculations were provided for the thermally induced residual stress predictions of the post‐filling stage. These explicit calculations led to the results of pressure and temperature distributions of the part during the post‐filling stage into the viscoelastic constitutive model. Additionally, the pressure and asymmetric temeprature profiles of the post‐filling stage were based on finite element packing analysis coupled with a boundary element cooling analysis of the molding process. Finally, the total residual stress in the part was obtained via superposition of the flow‐induced and thermally induced residual stresses. An example is provided to demonstrate the entire concept. The results indicate that thermally induced residual stress is higher than the flow‐induced residual stress by one to two orders of magnitude.
Stretch and inflation of hyperelastic membranes as applied to blow moldiing
Authors: Khayat R. E. , Derdouri A.
Published: December 2004

The free and confined inflation of isotropic homogeneour membranes of general shape are considered. The material is assumed to obey the Mooney‐Rivin constitutive model, and the resulting partial differential equations, governing the deformation field, are solved using a Galerkin based finite‐element procedure. The method is illustrated through examples of both free and conflined inflation, as well as simulationeus stretch and inflation. Measurements were carried out on the final thickness distributionof containers blow‐molded inour laboratory. These containers typically cover a wide range of geometry adn size, including bottles with handles. Comparison between theory and experiment leads generally to good agreement, despite the limitation of the membrane hypothesis.