bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulation of reactive injection molding in a radial flow geometry
Authors: Lack C. D. , Silebi C. A.
Published: December 2004

The radial flow of a chemically reactive fluid between two parallel circular disks during the process of Reactive Injection Molding (RIM) has been simulated in a decelerative, non‐isothermal, transient flow environment. The effects of key operating and system parameters (feed temperature, volumetric flow rate, reaction rate, and cavity thickness) on velocity, conversion, and temperature profiles which occur in this decelerative flow environment were determined. A catalyzed, unfilled polyurethane RIM system was modeled by a linear step polymerization scheme using average literature values for the reaction rate, and thermodynamic and constitutive parameters. The numerical solution was achieved using the method of lines and upwind approximations of the spatial derivatives. The geometry studied (two parallel, center gated circular disks) models flow patterns in commercial RIM processes more realistically than the rectangular flow between two parallel surfaces (studied by previous workers) in which the average velocity is constant along the length of the mold. This simulation predicts the accumulation of high polymer near the entrance to the mold and near the outer edge of the cavity in fast reactive systems. The accumulation of material near the gate results in viscous heat generation and a maximum in temperature in the region immediately downstream from the restriction.
Extrusion behavior of filled polymeric systems exhibiting an apparent yield stress
Authors: Poslinski A. J. , Ryan M. E. , Gupta R. K. , Seshadri S. G. , Frechette F. J.
Published: December 2004

An investigation was undertaken to study the extrusion behavior of composite systems. A compound made up of approximately 50 percent ceramic particulates by volume dispersed in a high molecular weight thermoplastic polymer was characterized by measuring the shear viscosity on an Instron capillary viscometer. The experimental data indicated that the ceramic composite exhibited an apparent yield stress. As a result, an expression that was previously shown to provide flexibility for describing a yield stress at low rates of deformation could explain the viscosity of the ceramic composite. The expression was then applied to the flow analysis of both a “rod” and a “slit” die in an extrusion process, and the derived equations adequately correlated experimental volumetric flow rate us. Pressure drop data obtained on a laboratory extruder.
The effect of sizing on composite properties for materials used in the shuttle filament wound case
Authors: Cagliostro D. E.
Published: December 2004

An epoxy resin and a sized carbon fiber have been used to produce a light‐weight filament wound case for the Space Shuttle. The sizing facilitates fiber handling during winding but may affect the amount of resin absorbed by the fiber during impregnation and the final mechanical properties of the composite. Naval Ordnance Lab rings were wound to study the effect of the sizing content on the resin absorption by the fiber bundles, the final tensile properties of the composite, and the type of failure observed at burst. The resin content of the rings studied was between 20 to 40 percent, and the sizing content, 0 to 1.6 percent by weight. Results showed that the sizing content was a critical parameter which determined the amount of resin absorbed by the fibers. The final tensile strength was dependent on the amount of sizing present. The tensile strength decreased by as much, as 60 percent when a low resin and high sizing content were present. The type of failure at burst was a function of resin content rather than size content.
The mechanical behavior of polymer coatings: Solvent removal in polyamic acid films
Authors: Bauer Charles L. , Farris Richard J.
Published: December 2004

The development of the mechanical properties and stresses during the formation of polyamic acid (PAA) coatings has been studied using methods such as a “propagating wave technique.” The shrinkage stress due to solvent removal in PAA coatings under a one dimensional constraint was determined to be 8 MPa. A coupling between the residual stress and solvent removal process has been observed.
Process control of profile extrusion using thermal method. Part I: Mathematical modeling and system analysis
Authors: Yang B. , Lee L. J.
Published: December 2004

An analytical model based on the heat penetration through the die wall was preposed to calculate the effect of die wall temperature on the flow of polymer melt in profile dies. Model prediction matched well with the experimental data measured from a modified Instron capillary rheometer. The model was applied to an extrusion line with an L‐shaped profile die. Dynamic responses of the profile extrusion line based on this die were measured and modeled. The pairing of manipulated variables and controlled variables was analyzed.
Residual stresses in polymeric passivation and encapsulation materials
Authors: Noyan I. C. , Nguyen L. T.
Published: December 2004

The residual stresses caused by polyiinide (Pi 5878 and PI 2566), and silieone (3‐6550 and 1‐2577) films used as passivation/encapsulation layers in microelectronic circuit manufacturing are investigated by X‐ray curvature measurements. For both PI types, the maximum stress is between 20–40 MPa. This stress is independent of film thickness for films thinner than 10 μm. For films thicker than this value, however, some dependency of the film stress on film thickness is observed. The variation of stress during the cure cycle is significantly different for PI 5878 and PI 2566. This is due to void nucleation and growth in the 5878 films during solvent volatilization. The silieone films have no residual stress at room temperature for all thicknesses. The compensating stresses in the Si wafer are insignificant for all cases studied.
Lateral strain effects during the large extension of thermoplastics
Authors: Stokes Vijay K. , Nied Herman F.
Published: December 2004

A noncontacting experimental procedure is used for characterizing lateral strain effects during the large‐strain uniaxial stretching of flat sheet‐like specimens of polycarbonate, polyetherimide, and poly(butylene terephthalate), both at room and elevated temperatures. It is shown that the in‐plane lateral stretch, λ2, is related to the longitudinal stretch, λ1, through the relation λ2 = λ. Depending on the temperature, the “Poisson's ratio” for incremental strains, n, is shown to lie between n = 0.4 and n = 0.5. While the lateral stretch in the thickness direction, λ3, is smaller than λ2 at room temperature, it is shown that λ3 = λ2 at higher temperatures. Stretch data have been used to infer the volumetric strains in these materials.
Molecular orientation of polypropylene by rolling‐drawing
Authors: Tate K. R. , Perrin A. R. , Woodhams R. T.
Published: December 2004

Rolling‐drawing is a simple, effective, solid state processing technique for manufacturing high strength and high modulus oriented polymer sheet products. The process is capable of increasing the tensile modulus and strength of polypropylene by more, than an order of magnitude with inexpensive equipment and straight forward controllable techniques. This paper gives an overview of the rolling‐drawing of polypropylene. It is intended to answer the following questions. What is rolling‐drawing? What changes in tensile properties can be expected as a result of this process? What deformation processes occur during rolling‐drawing? What are the processing variables and how do these variables relate to the deformation ratio achieved by rolling‐drawing? A tensile flow stress relationship was formulated from experimental data for oriented polypropylene. This constitutive equation, estimates the flow stress (or yield stress) of the polymer as a function of deformation ratio, strain rate and temperature. Since stretching was found to provide a significant portion of the deformation during the rolling‐drawing process a Hoffman‐Sachs computer analysis was written to predict plastic deformation and drawing forces in the stretch zone. The results of experimentation and the analysis are briefly compared in this paper.
Evaluation of residual thermally induced stresses in the cooling of polymer melt via transfinite element computations
Authors: Tamma K. K. , Railkar S. B.
Published: December 2004

The present paper describes the evaluation of nonlinear thermally induced residual stresses in the cooling of polymer melt during injection molding of plastic components. The computational methodology adopted is based on the transfinite element approach, which is a hybrid scheme as it combines transform methods and classical Galerkin schemes with finite element formulations to preserve the modeling versatility. The applicability of the proposed formulations for understanding the physics and the nature of the nonlinear thermally induced stresses in the solidifying process of a sample amorphous polystyrene specimen demonstrates the basic capabilities and potential of the methodology. Results obtained agree qualitatively well with earlier research studies and experimental findings relevant to thermally induced residual stresses in the injection molding of plastic components.
On the accuracy of the calculated stress field around a craze
Authors: Warren W. E. , Chudnovsky A. , Mullen R. L.
Published: December 2004

Several recent calculations of the stress field around crazes in glassy polymers have been based on experimentally obtained craze opening displacements. Although various techniques for performing these calculations have been presented (i.e., Fourier transform, boundary integral, and finite element methods), all are based on the solution of the same ill‐conditioned boundary value problem. Specific boundary conditions required to calculate the stresses around a craze lead to a large change in the stress field with small changes in the craze profile which are within the reported experimental tolerance.
Vitrification effect during the reaction injection molding (RIM) process of epoxy resin
Authors: Kim Do Hyun , Kim Sung Chul
Published: December 2004

Vitrification occurs during the reaction injection molding (RIM) of epoxy resin, and the curing reaction rate is reduced as the Tg of the reacting mixture exceeds or approaches the local reaction temperature inside the mold cavity. The effect will be manifested in the distribution of the glass transition temperature across the thickness direction of the molded product. The reaction kinetic equation which includes the vitrification term in the form of the WLF equation is used in the computer simulation of the epoxy RIM process and the effect of the vitrification is shown by comparing with models with no vitrification considerations.
The effect of mesh refinement on the computation of entrance effects for shear‐thinning fluids
Authors: Robichaud M. P. , Tanguy P. A.
Published: December 2004

The effect of mesh refinement on the finite element computation of velocity and pressure is assessed for the creeping flow of a power law fluid and a Carreau fluid through an axisymmetric sudden contraction. The emphasis is placed on the determination of the entrance pressure correction nent. The augmented Lagrangian formalism is used and the discretization of the variational problem is based on the Crouzeix‐Raviart triangular element. For power‐law fluids, it is found that fine meshes yield values of nent which are significantly lower than those obtained in previous numerical studies, especially for high shear‐thinning fluids. A similar trend is observed in the Carreau model.
The effect of extrudate swell on modeling the film blowing process
Authors: Seo Yongsok , Wissler Eugene H.
Published: December 2004

The extrudate swell effect has not received sufficient attention in modeling the film blowing process. This effect is addressed in this paper, and as an ab initio study, only viscous fluids were considered. The problem region was separated into two zones; the extrudate swell zone and the film blowing zone. The annular extrudate swell problem was solved using a finite element method. The film blowing process was modeled following Pearson and Petrie's (4) work. Although only viscous fluids were considered, the simulation results show a remarkable difference when swelling was included in the modeling. Viscoelastic fluids, which are more realistic for polymer melts, were not investigated here because of the so called high Weisenberg number problem. This is an open area still under investigation.
Measurement and correlation of mutual diffusion coefficients for polybutadiene‐hydrocarbon systems
Authors: Iwai Yoshio , Maruyama Shunsuke , Fujimoto Mitsuki , Miyamoto Shinji , Arai Yasuhiko
Published: December 2004

The mutual diffusion coefficients for polybutadiene‐ethylbenzene and polybutadiene‐n‐nonane systems were measured by using a sorption apparatus with a quartz spring in the temperature region from 80 to 130°C and for mass fraction of hydrocarbon ranging from 0 to 0.27. The mutual diffusion coefficients were correlated with good agreement by the free‐volume theory.
Effect of methylmethacrylate‐butadiene‐styrene modifier level on the viscoelastic beta process in poly(vinyl chloride)
Authors: Havriliak S. , Shortridge T. J.
Published: December 2004

Viscoelastic measurements were made on test specimens cut from plaques made from milled, compression molded blends of poly(vinyl chloride) (PVC) and methylmethacrylate‐butadiene‐styrene modifier (MBS). The experimental frequency range was from 0.0159 to 79.6 Hz. and the temperature range was from −140 to 20°C. The MBS modifier level studied was 8.26, 10.71, and 13.04 weight percent. This experimental range covers the beta relaxation process of PVC and the alpha relaxation process of the rubbery regions of the modifier. The complex compliance was represented in terms of a function originally proposed by Havriliak and Negami to represent the dielectric relaxation processes in polymers. The parameters of this expression as well as their dependence on temperature were determined by the multi‐response statistical techniques developed by Havriliak and Watts. Addition of MBS modifier to PVC appears to enhance the already present beta relaxation process in PVC. In addition the temperature dependence of the relaxation time has been increased so that the process is faster at room temperature. The α and β parameters of the relaxation function have changed so that the process is narrower at room temperature. There is no significant viscoelastic evidence supporting a second phase. This observation suggests significant impedance matching of the two phases which may be an important criteria for impact modification. Similarity of the two processes suggests a possible mechanism for the PVC beta process.
Water‐Soluble contrast enhancing materials—new photobleachable dyes
Authors: Yonezawa T. , Kikuchi H. , Hayashi K. , Tochizawa N. , Endo N. , Fukuzawa S. , Sugito S. , Ichimura K.
Published: December 2004

Many styrylpyridinium compounds (SPC), which are very stable in the dark, were prepared and evaluated as photobleachable dyes for contrast enhanced lithography (CEL). The photobleaching characteristics of water‐soluble contrast enhancing materials composed of SPC and water‐soluble polymer depend on the structure of the SPC and the kind of polymers used. The technique using SPC‐based CEL proved to be very effective for the resist pattern profiles.
Effect of extensional and shearing strains on molecular orientation of a polymer melt
Authors: Picot J. J. C. , Santerre J. P. , Wilson D. R.
Published: December 2004

The flow of two grades of polydimethysiloxane (Dow Corning type 200 grades 60 Pa's and 300 Pa's) was studied in a 60° wedge flow cell. The stress‐optical law was validated along the center‐line (extensional strains only) and at off centerline locations (extensional and shearing strains combined). Values for stressoptical coefficient were 8.01 × 10−11 Pa−1 and 9.61 × 10−11 Pa−1 respectively, the differences apparently being due to experimental error. Orientation angles along a fixed radius at 20° to the cell center‐line were almost constant. Center‐line orientation angles were zero, as expected. Orientation angles at a constant radius for various angular positions varied from zero at the centerline to 54° near the wall. A method for testing constitutional relations for stress is presented. The power law model and linear viscoelastic models are shown to be inadequate in describing orientation effects caused by rotation in the flow. The Goddard‐Miller model was shown to express this but accuracy was not very good, perhaps because of the single Maxwell unit used.
Optimum heating system design for compression molds
Authors: Kwon T. H. , Forcucci S. J.
Published: December 2004

Compression molding is a widely used method of forming composite materials where long fibers are necessary for strength requirements. Compression molding involves putting the charge through a specific, material dependent temperature and pressure path to induce thermochemical cure. During cure, certain temperatures are required for a time. Spatial variation of the cavity temperature can lengthen time needed for curing and cause voids and residual stresses in the part. Towards the goal of uniform cavity surface temperature, an interactive graphics based computer aided system for compression mold heating design has been developed. The system employs a boundary element method treating long, thin cylindrical electric heating elements as singular line sources. It is coupled with a CONMIN algorithm, a nonlinear constrained minimization procedure to, optimize the heating system for uniform temperature over the cavity surface. Realistic constraints are featured to insure design feasibility. The problem is also decomposed in such a way to allow easy redesign and a sensitivity study. Through the optimization process, it was found that uniformities can be obtained which are far better than anything that could be achieved through common sense.
Determination of poisson's ratio for polyimide films
Authors: Bauer C. L. , Farris R. J.
Published: December 2004

The Poisson's ratios of polyamic acid and polyimide films were determined using a high pressure gas dilatometer. In this technique, a sample is held at constant length and a hydrostatic pressure is applied to the sample. The resulting change in stress on the sample with applied pressure provides a measure of Poisson's ratio. For fully cured polyimide films based on pyromellitic dianhydride and oxydianiline, Poisson's ratio was measured to be 0.34 at approximately 1% strain. This value increases to 0.48 as the strain is increased to 5%.
The processing and use of organosilicon polymers for photonic applications
Authors: Bagley B. G. , Quinn W. E. , Kurkjian C. R.
Published: December 2004

Three potential applications for the “ladder” siloxanes in photonic technologies are discussed. These are: (1) as a silica fiber cladding material for which a silica fiber core‐siloxane cladding index depression (Δn) of 0.04 is observed; (2) as a fiber coating material to provide mechanical and environmental protection for which a siloxane coated silica core fiber is observed to have improved properties over a fiber coated with an epoxy‐acrylate or linear siloxane. Thus, the ladder siloxane can serve a dual coating/cladding function; and (3) as the passive lightguiding element in planar optoelectronics for which the index depression (Δn), as compared to silica, is 0.04 for the cured siloxane. 0.02 for a fenestrated silica obtained by removing the organic component from the siloxane, or values between 0.02 and 0.0 obtained by sintering this fenestrated silica.
Parametric sensitivity of chain polymerization reactors exhibiting the trommsdorff effect
Authors: Kapoor Bir , Gupta Santosh K. , Varma Arvind
Published: December 2004

The recently developed mathematical technique for studying the parametric sensitivity of reactors is extended to include chain polymerization systems exhibiting the gel and glass effects, as well as physical property variations. The sensitivities of the two temperature maxima with respect to various parameters are computed. It is found that, for a sample system, poly(methyl methacrylate), all the sensitivities of the gel effect induced temperature peak attain their maxima at the same conditions—this leads to a generalized temperature sensitivity constraint applicable to reactor design or operation. This sensitivity boundary is associated with high conversions and high molecular weights. The analysis shows that the dimensionless propagation activation energy, ϵp, and the dimensionless initiation activation energy, ϵd, are the two most important parameters governing the system performance. Sensitivities of the gel effect‐induced number average chain length peak with respect to various parameters are also obtained. Again, all of these chain length sensitivities show maxima at the same condition, leading to the concept of a generalized chain length sensitivity criterion of constraint. Most importantly, the temperature and chain length sensitivity boundaries are virtually identical.
Recent developments in hot plate welding of thermoplastics
Authors: Watson M. N. , Murch M. G.
Published: December 2004

This paper considers the hot plate welding process applied to three injection molded thermoplastic materials: polypropylene, high impact polystyrene, and poly(phenylene oxide). Weld quality was assessed by tensile testing. The process was found to be suitable for all three materials, although tolerance to variations in process parameters varied. The parameters in the heating phase, i.e., hot plate temperature and time, were the most important for achieving good welds, whereas parameter variations in the consolidation phase were relatively unimportant.
Grafting of unsaturated acids and silanes to ethylene polymers: A kinetic model
Authors: Motha Kshama , Seppälä Jukka , Bergström Christer
Published: December 2004

A general kinetic model was developed to simulate the grafting of monomers such as unsaturated carboxylic acids and silanes to ethylene polymers. The polymers considered were ethylene‐co‐vinyl acetate (EVA), ethylene‐co‐butyl acrylate (EBA), and low‐density polyethylene (LDPE). Grafting was assumed to proceed by a free‐radical mechanism involving chain transfer. Organic peroxides having a strong tendency for hydrogen abstraction were selected as the source of primary radicals. The model simulated the grafting reaction as taking place in a single screw extruder. The residence time distribution in the extruder was experimentally determined by tracer analysis, according to which the extruder was a plug‐flow reactor connected to two mixed reactors in parallel. The model is able to predict the extent of grafting in terms of predefined parameters. Comparison of model predictions with available experimental data showed slight deviations, the possible causes of which are discussed. However, the kinetic behavior expected on the basis of the input parameters was observed, and, as such, the model allowed study of the effect of process variables on grafting kinetics and provided insight into the reaction mechanism.
Effect of processing on uniaxial creep behavior and environmental stress‐crack resistance of a linear low‐density polyethylene
Authors: Crissman J. M.
Published: December 2004

This paper describes characterizations performed on two types of polyethylene T‐Joints as well as the starting resin from which they were manufactured. It was found that the melt flow rate of material taken from the two types of joints differed from that of the starting resin and differed from each other by as much as a factor of two. Investigation of the environmental stress‐crack resistance (ESCR) and uniaxial creep behavior of material from the two joints revealed further significant differences in behavior between the two joints. These observations lead to the conclusion that subtle differences in the processing conditions can result in significant differences in the long‐term mechanical behavior.
Melt immiscibility in crosslinked polyethylene
Authors: Phillips P. J. , Vatansever A.
Published: December 2004

Low density polyethylene crosslinked by decomposition of dicumyl peroxide shows evidence for two phases being present in the melt in a narrow temperature range just above the melting point. The effect has been studied in detail using differential scanning calorimetry, transmitted light intensity, and wide angle X‐ray diffraction studies at 107°C. It is believed that the effect is caused by the presence of relatively low molecular weight molecules which remain as an extractable fraction after crosslinking.
Measurement and correlation of mutual diffusion coefficients for styrene‐butadiene rubber (SBR)‐ethylbenzene systems
Authors: Iwai Yoshio , Miyamoto Shinji , Nakano Katsuyuki , Arai Yasuhiko
Published: December 2004

The mutual diffusion coefficients for styrene‐butadiene rubber (SBR)‐ethylbenzene systems were measured using a sorption apparatus with a quartz spring at 100 and 130°C for mass fractions of ethylbenzene ranging from 0 to 0.17. The mutual diffusion coefficients were correlated with good agreement by the free‐volume theory.
Modality of molecular weight distributions
Authors: Friedman Emil M.
Published: December 2004

Even restricting attention to weight distributions, it is ambiguous to merely say that a polymer is “not bimodal.” A simple example is shown wherein the weight distribution of log (molecular weight) is bimodal, but the weight distribution of molecular weight is not bimodal.
Isothermal volume relaxation in aged polycarbonate measured by positron annihilation lifetime spectroscopy
Authors: Hill A. J. , Katz M. , Jones P. L.
Published: December 2004

The positron annihilation lifetime spectroscopy (PALS) technique is used to measure volume relaxation in physically aged glassy polycarbonate. The relaxation times and activation energy calculated for the isothermal relaxations in the aged polycarbonate are greater than those parameters calculated for unaged polycarbonate. The activation energy of 8.2 kcal/mol in the aged polycarbonate is used to identify the phenyl group motion or the cooperative carbonate‐phenyl interaction as the molecular features responsible for the thermally induced open volume relaxations. It is postulated that the open volume relaxation kinetics as measured by PALS can be used as a nondestructive indication of property differences between aged and unaged polycarbonate.
High pressure tubular reactors for ethylene polymerization optimization aspects
Authors: Brandolin A. , Valles E. M. , Farber J. N.
Published: December 2004

Optimal policies for operation of high pressure tubular reactors for ethylene polymerization are presented. The work is based on a previously developed model, allowing accurate representation of different configurations and operation conditions of industrial relevance. Several policies based on temperature and initiator concentration as control parameters are evaluated and compared.
Impact resistance performances of polyamide 6 blended with different rubber phases
Authors: Crespy A. , Caze C. , Coupe D. , Dupont P. , Cavrot J. P.
Published: December 2004

We have studied the impact strength, by Charpy and Izod tests, of blends of polyamide 6 with different rubbers, 10 wt% of each, or rubbers and glass fibers (8.5 wt% and 15 wt% respectively). The rubbers are from three different families: (i) a nonreactive cross‐linked terpolymer, methyl methacrylate/butadiene/styrene (17/64.5/18.5); (ii) two block copolymers compatible with the matrix, poly(tetramethylene glycol)/polamide 12 (70/30 or 34/66); and (iii) two polymers containing reactive functionality, a terpolymer ethylene/ethyl acrylate/maleic anhydride (68/30.5/1.5) and a copolymer ethylene/acrylic acid (90/10). The classification of additives in regard to improved impact depends on the procedure used for the impact strength measurement, particularly on whether the samples are notched or unnotched. The results are discussed in relation to the dimensions and the adhesion of the rubber particles. The level of adhesion has been estimated from observations in scanning electron microscopy of cavities due to pullout nodules and of nonextracted rubber after treatment in boiling xylene. Strong variations in the morphologies are found, depending on the chemical nature of the rubber. The crystalline state of the polyamide in the blends has also been evaluated from differential scanning calorimetry.
Fatigue strength of vibration welded thermoplastic butt joints
Authors: Stokes Vijay K.
Published: December 2004

Fatigue data are presented for the strengths of 120‐Hz vibration‐welded butt joints of four resins: the three amorphous polymers polycarbonate (PC), polyetherimide (PEI), and modified polyphenylene oxide; and the semicrystalline polymer poly(butylene terephthalate). Data are also presented for the fatigue strength of 250‐Hz vibration welds of the high‐temperature polymer PEI. For all the welds, fatigue strength was evaluated through 10‐Hz, tension‐tension, load‐controlled tests at an R value (ratio of minimum stress) of 0.1. Surprisingly, for all the stress levels studied, none of the PC test specimens failed at the welds, indicating that the fatigue strength of PC welds equals that of the base resin. This is not true of the other three resins, except at relatively low stress levels. For each of the four resins, macrographs are used to highlight the differences between the failure surfaces of monolithic specimens and specimens that failed at the welds.
Extension behavior and morphology in polypropylene extended under hydrostatic pressure
Authors: Ariyama Takashi , Takenaga Mitsuru
Published: December 2004

The effect of hydrostatic pressure on molecular deformation of polypropylene extended under hydrostatic pressure is investigated by using internal friction measurements, wide angle X‐ray diffraction, and polarizing microscopy. A homogeneously transparent straight part is obtained by extending samples in the pressure range from 78 to 128 MPa. The overall mechanical properties of a sample extended under P = 102 MPa is significantly different from that of a sample extended under P = 128 MPa. The difference is related to the magnitude of hydrostatic pressure, the extension ratio, and the extent of transparency. The observed results on the β relaxation in the extended samples is found to be related to the morphological reorganization from a coarse spherulitic to a fine spherulitic structure. The cold‐drawn sample at atmospheric pressure has the γ‐peak at around °50°C, while the hydrostatically extruded samples and the extended samples have no γ‐peak. Consequently, the hydrostatic pressure suppresses the formation of the molecular structure relevant to the γ relaxation.
On the solution of fiber orientation in two‐dimensional homogeneous flows
Authors: Akbar Sameer , Altan M. Cengiz
Published: December 2004

This work presents an analytical technique to describe the orientation behavior of short fibers in arbitrary two‐dimensional homogeneous flows. It is shown that the fiber orientation, specified by a unit vector, can be analytically calculated at any instant using any initial orientation and flow kinematics. The rotation of a fiber with the bulk fluid deformation is expressed in terms of orientation vector components by utilizing an equivalent strain tensor calculated from the fluid kinematics. This technique is then used to evaluate the orientation behavior of a large number of fibers starting from different initial orientations, representing an orientation state. The orientation distribution function is generated statistically by considering the frequency distribution curve of the orientation of the large number of fibers. It is shown that using a combination of analytical solutions and statistical methods provides a convenient description of fiber orientation behavior. The accuracy of the generated orientation distribution function is found to be dependent on the number of fibers used in the analytical solution. The statistical orientation distribution function is compared with the exact solutions for certain homogeneous flows and found to be in close agreement.
Studies on poly(vinylchloride)‐based polymer blends intended for medical applications. Part II: Mechanical properties
Authors: Pal S. N. , Ramani A. V. , Subramanian N.
Published: December 2004

Binary polyblends of plasticized poly(vinylchloride) (PPVC1) with acrylonitrile‐butadiene rubber (NBR1), compounded graft polymer of vinyl chloride and ethylene‐vinyl acetate copolymer (EVAPVC) and ternary blends of PPVC1, NBR1, and EVAPVC were formulated to study mechanical properties. For the “pure” components, elongation at break was found to be in the order PPVC1 < EVAPVC < NBR1. Addition of both EVAPVC and NBR1 resulted in improvement of ultimate elongation and tensile energy to break. PPVC1‐NBR1 binary blends exhibited synergistic behavior for both ultimate tensile stress and elongation at break, indicating the presence of appreciable specific interactions between the polymers. About 30% replacement of PPVC1 by NBR1 or EVAPVC resulted in marginal fall in modulus and significant improvement in elongation at break. EVAPVC or blends containing EVAPVC had a tendency to creep. A simple generalized equation suggested for various mechanical properties works satisfactorily. The results obtained have practical implications and indicate that PVC‐based polyblends can be investigated further for potential applications in medicine.
Phase transformations in a thermotropic liquid crystalline copolyester and its blends with polyether sulfone
Authors: Zheng Johnny Q. , Kyu Thein
Published: December 2004

Mesophase transitions in a thermotropic liquid crystalline polymer comprising p‐hydroxybenzoic acid (PHB) and polyethylene terephthalate (PET) in a copolymer ratio of 60/40 were studied by means of optical microscopy, light scattring, and wide‐angle X‐ray diffraction (WAXD). According to time‐resolved light scattering and optical microscopic studies, at about 250°C, a mesophase transition was evident in which Schlieren texture developed with elapsed time. This transition has been identified as a solid crystal‐nematic mesophase transition associated with the melting of PHB‐rich crystals. It is concluded that the copolymer sequence may not be random. An isotropic, amorphous blend of PHB‐PET/polyether sulfone (PES) was prepared by solvent casting from hexafluoro‐2‐propanol solution. However, this homogeneous blend appears to be kinetically entrapped during solvent removal. Thermally induced phase separation takes place upon heating slightly above the glass transition temperature of PES. Morphology development within phase‐separated domains has been qualitatively examined by light scattering and optical microscopy.
Optical waveguiding as a method for characterizing the effect of extended cure and moisture on polyimide films
Authors: Noe Susan C. , Pan Jeffrey Y. , Senturia Stephen D.
Published: December 2004

Integrated optics techniques (i.e., guiding light through a thin film) have been used to study the effects of extended cure and moisture exposure on polyimide films as manifested in changes in the TE (in‐plane) and TM (out‐of‐plane) refractive indices and in their difference (birefringence). Mechanical testing of these films has been done using the load‐deflection technique. Du Pont polyimide Pyralin 2555 and 2556 (benzophenone tetracarboxylic dianhydride‐oxydianiline/metaphenylene diamine), cured repeatedly at 400°C and 375°C respectively, show an increase in refractive index as a function of cure (possibly due to densification), as well as an increase in birefringence (due to increased residual stress). Upon exposure to moisture, the TM and TE refractive indices both increase (absorption of the polar water molecule), but the TE index does not increase as much. Mechanical testing has shown that the residual stress in the polyimide film increases with extended cure and decreases with moisture exposure due to moisture‐induced swelling of the film. A model is proposed which relates the optical results to the mechanical measurements. Based on our data, a preliminary stress‐optic coefficient is reported.
The structure of highly oriented high modulus polyethylene
Authors: Zubov Y. A. , Chvalun S. N. , Selikhova V. I. , Konstantinopolskaya M. B. , Bakeev N. Ph.
Published: December 2004

A comparative study of the structure of uniaxially‐oriented bulk samples of linear PE of various molecular weights over a wide range of draw ratios has been carried out by means of small and wide angle X‐ray analysis, NMR‐spectroscopy and DSC. The structure of oriented high molecular weight PE samples, prepared by drawing single crystal mats to draw ratios up to 200, have also been studied. A large number of unfolded tie‐molecules have been found to exist in the trans‐conformation in PE amorphous regions. These tie‐molecules, which connect the adjacent crystallites along the axis of orientation, and are not large crystals, account for the high mechanical properties of these samples. It has been shown that in the course of the orientation process, chain unfolding in the amorphous regions is accompanied by the formation of continuous linear systems consisting of several coherent crystallites and tie‐molecules. These are coherently aligned along the macromolecular axis.
Emulsion copolymerization: Kinetics model and reactor performance
Authors: Quarderer George J. , Katti Sanjeev S.
Published: December 2004

The Dow process for producing perfluorinated ionomeric membranes includes several emulsion copolymerizations involving gaseous tetrafluoroethylene and a second liquid phase monomer. The choice of the organic phase monomer depends on the desired product. The emulsion copolymerization reactor model was developed by extending the Smith‐Ewart‐Gardon theory for emulsion polymerization processes. Population balance techniques and Flory‐Huggins solution theory were applied. The resulting coupled partial differential equations were solved using the method of characteristics. The reactor model, with minimal adjustable parameters, predicts most polymerization results, including molecular weight, reaction rates in the three process stages, latex particle size, polymer composition, and the composition drift as a function of reaction time. The analysis and reactor model is used in the manufacturing process to set process conditions to obtain the desired properties in the polymer product.
Synergism on tensile properties of injection molded polybutene‐1 /polypropylene blends
Authors: Lee Mao‐Song , Chen Show‐An
Published: December 2004

Blends of polybutene‐ 1 (PB‐1) and polypropylene (PP) have been injection and compression molded. A synergism appears in the ultimate elongation and the tensile strength for the injection moldings. The maximum point of the synergism at the composition of 25 wt% PB‐1 shifts to 50 wt% PB‐1 after annealing at 145° C for 1 h. A linear relation and negative deviation from the additivity rule for these two properties are observed for the compression moldings with quick cooling and slow cooling, respectively. Thermal analysis, polarized optical microscopy, and scanning electron microscopy (SEM) are used to study the occurrence of the synergism. The mutual interference between the two components on the crystal formation and the plasticization effect of PB‐ 1 on PP result in the synergism. An increased phase separation probably occurs during the compression molding with slow cooling. So, the blends compression‐molded with slow cooling having a higher amount of PP have brittle breaks, similar to pure PP.
Three‐dimensional path line tracking and residence time distribution in fishtail dies
Authors: Huang Chin‐Ching , Tsay Sun‐Yuan , Wang Yeh
Published: December 2004

The flow kinematics of power‐law fluids in fishtail dies is studied. A general isothermal three‐dimensional finite element code developed by the authors is used for the flow analysis purpose. The basic geometry of the fishtail die is defined by simple super‐elliptical curves, which allows a smooth transition from a circle to a slit. The three‐dimensional path line and the residence time distribution (RTD) are calculated from the velocity field obtained from the finite element solution of the conservation equations. The effects of the rheological properties and the die geometry on the path line pattern and the residence time distribution are investigated. The results indicate that as both the length of the transition zone and the fishtail angle increases, the residence time distribution becomes more uniform. However, the power‐law index does not affect the residence time distribution significantly.
Fracture behavior of poly(vinyl chloride)/methyl methacrylate/butadiene/styrene polymer blends
Authors: Takaki Akira , Hasegawa Toshihiko , Isogawa Masataka , Narisawa Ikuo
Published: December 2004

The fracture mode of poly(vinyl chloride)/methyl methacrylate/butadiene/styrene (PVC/MBS) polymer blends can change from ductile to brittle in accordance with the changes in shape of the test specimen or test conditions. Therefore, the mechanisms of impact energy absorption and the main cause of stress whitening are complicated. The following results on PVC/MBS blends were obtained by carrying out fracture experiments at different test speeds and temperatures:

The ductile/brittle fracture mode of the PVC and PVC/MBS blends can be explained by σ (the craze initiation stress)/σy (the shear yield initiation stress), which depends on the strain rates and temperature.

The fracture behavior of the PVC/MBS blends can be classified into the following types from the standpoints of fracture mode and whitening degree: Fracture I: ductile fracture without whitening;

Fracture II: ductile fracture with whitening; and

Fracture III: brittle fracture without whitening.

The following concepts can be estimated from the measurements of yield stress, specific gravity and SEM, TEM and visual observations. In Fracture I, shear yield occurs mainly. In Fracture II, both shear yield and crazing occur. In Fracture III, deformation of the rubber and local crazing occur.

The main cause of stress whitening in PVC/MBS blends is light scattering by cavities in the rubber particles.

In Fracture II, at first, crazes with cavities in the rubber particles occur. Then, shear yield occurs. Finally, crazes are healed by the heat, and only the cavities in the rubber remain.
Performance blends based on recycled polymers
Authors: Akkapeddi M. K. , Van Buskirk B. , Mason C. D. , Chung S. S. , Swamikannu X.
Published: December 2004

The recent growth in the post‐consumer recycling of plastics presents an opportunity for developing new, value‐added blend products from the recycled polymers. However, in order to develop blends with useful performance characteristics, suitable techniques of compatibilization and impact modification must be employed. In this study, reactive toughening and compatibilization techniques have been found to be particularly useful in achieving high thermal embrittlement resistance in the blends of recycled poly(ethylene terephthalate) containing functionalized ethylene copolymers and polycarbonate. Reactive compatibilization of recycled polyolefin blends with poly(ethylene terephthalate) and polyamide has also been investigated.
Stress‐strain behavior and dynamic mechanical properties of poly(1,1‐dimethyl‐1‐sila‐cis‐pent‐3‐ene), poly(1‐methyl‐1‐phenyl‐1‐sila‐cis‐pent‐3‐ene) and of these polymers after crosslinking with sulfur
Authors: Chen Min Wei , Liao Charles X. , Weber William P.
Published: December 2004

Mechanical properties of polymers can be described by their stress/strain curves and by their behavior under dynamic mechanical thermal analysis (DMTA). The purpose of this paper is to report such mechanical properties for two unsaturated polycarbosilanes: poly(1, 1‐dimethyl‐1‐sila‐cis‐pent‐3‐ene) (I) and poly(1‐methyl‐1‐phenyl‐1‐sila‐cis‐pent‐3‐ene) (II). Tensile strength, elongation at break, modulus, bending modulus, Tg, and tan δ for I, II and for sulfur crosslinked I and II have been measured. The influence of polymer molecular weight, quantity of crosslinking agent, cure time, presence of carbon black filler, the effect of crosshead speed, and frequency on these properties was investigated.
Monomer chain cross‐transfer constants and cross termination factor evaluations on styrene‐acrylonitrile copolymerization
Authors: Mendizabal E. , Velazquez S. , Gonzalez V. , Jasso C. F.
Published: December 2004

Using low conversion bulk copolymerization experimental data and the apparent rate constant model, the monomer chain cross‐transfer rate constants and the cross‐termination coefficient were evaluated. It was found that the dependence of the cross‐termination coefficient on composition is a function of initiator efficiency and that monomer chain cross‐transfer rate constant are relevant for the theoretical estimation of the molecular weights and molecular weight distributions.
Comparison of microwave and thermal cure of an epoxy/amine matrix
Authors: Jordan Catherine , Galy Jocelyne , Pascault Jean‐Pierre , Moré Claude , Delmotte Michel , Jullien Henri
Published: December 2004

An investigation was carried out into the effect ofa microwave cure on an epoxy prepolymer with a cycloaliphatic diamine mixture, as compared to a standard thermal cure. The microwave waveguide and process (propagation mode TE01) were adjusted to obtain large homogeneous samples. The extent of reaction, x, was measured during the microwave processing by size exclusion chromatography and differential scanning calorimetry. A good estimate of x was found using a modified DiBenedetto equation correlating x and the glass transition temperature Tg. The homogeneity of the samples was checked during the last steps of cure, showing the efficiency of the microwave processing and waveguide. The influence of the nature of the mold (metallic or dielectric) on the reaction kinetic was also investigated. Samples cured by both thermal and microwave processing were characterized by dynamic and static mechanical properties and then compared with those of fully crosslinked networks, i.e., postcured at a high temperature.
Molecular weight dependence of the fracture toughness of glassy polymers arising from crack propagation through a craze
Authors: Hui C. Y. , Kramer E. J.
Published: December 2004

We investigate criteria for craze failure at a crack tip and the dependence of craze failure on the molecular weight of the polymer. Our micromechanics model is based on the presence of cross‐tie fibrils in the craze microstructure. These cross‐tie fibrils give the craze some small lateral load bearing capacity so that they can transfer stress between the main fibrils. This load transfer mechanism allows the normal stress on the fibrils directly ahead of the crack tip in the center of the craze to reach the breaking stress of the polymer chains. We solve for stress field near the crack trip and use it to relate craze failure to the external loading and microstructural quantities such as the craze widening (drawing) stress, the fibril spacing, the molecular weight, and the force to break a single polymer chain. The relationship between energy flow to the crack tip due to external loading and the work of local fracture by fibril breakdown is also obtained. Our analysis shows that the normal stress acting on the fibrils at the crack tip increases linearly as the square root of the craze thickness, assuming that the normal stress distribution is uniform and is equal to the drawing stress acting on the craze‐bulk interface. The critical crack opening displacement, and hence the fracture toghness is shown to be proportional to [1–(Me/qMn)]2, where Me is the entanglement molecular weight, Mn is the number average molecular weight of polymer before crazing, and q is the fraction of entangled strands that do not undergo chain scission in forming the craze.