bluuebunny/crossref_metadata_2025 huggingface dataset:
A predictive model for the effects of thermal history on the mechanical behavior of amorphous polymers
Authors: Shay R. M. , Caruthers J. M.
Published: May 2005

The effects of thermal history during formation on the mechanical behavior of amorphous polymer solids must be part of a constitutive description for polymers in order to enable efficient design of manufacturing processes. A nonlinear, thermoviscoelastic constitutive equation for amorphous polymers has been previously derived via the rational thermodynamics framework, where the dissipation is assumed to occur on a material timescale that is controlled by the non‐equilibrium entropy, In this paper we report on the predictions of this constitutive equation for poly(vlnyl acetate). The material properties required by the constitutive model were determined for poly(vinyl acetate) from PVT and linear viscoelastic shear and bulk moduli measurements. Predictions of specific volumes during isobarfc cooling from the rubber and nonlinear uniaxial stress‐strain curves just below Tg are in reasonable agreement with experimental data. The model predicts that samples cooled below Tg and then isothermally annealed for specified times will exhibit yield stresses that increase with Increasing annealing time, as well as the familiar effects of changes in temperature and strain rate on the uniaxial stress‐strain and yield behavior. Shortcomings and potential improvements in the model are discussed.
The morphology of extruded blends containing a thermotropic liquid crystalline polymer
Authors: Blizard Kent G. , Federici Carlo , Federico Olimpia , Chapoy L. Lawrence
Published: May 2005

Three different polymer blends consisting of an isotropic matrix and a ther‐motropic liquid crystalline polymer (LCP) as the reinforcement were extruded. Polycarbonate (PC) and polyetherimide (PEI) were the two matrices, and the LCPs used were Vectraw A950 of Hoechst‐Celanese, a copolyester of hydroxybenzoic and 2,6 hydroxynaphthoic acids and an LCP of Granmont Inc., a condensation polymer of terephthalic acid, (l‐phenylethyl)hydroquinone, and phenylhydroqui‐none. These extrudates were characterized by a quantitative morphological technique to determine the percentage of LCP present as fibrils and the average domain diameter. These experimental observations were then coupled with the component Theological behavior and a simple heat transfer analysis to explain the morphology and property differences between the blends. Blends with the Granmont LCP showed no appreciable increase In the quantity of fibrils with draw ratio, for example, whereas the amount of fibrils in Vectra® blends tended to increase to a plateau with draw. The tensile modulus of the blends agreed well with composite theory, with average fibril moduli of 24.6 GPa and 23,3 GPa for Vectra® and the Granmont LCP, respectively. These differences can be explained in terms of the cooling behavior of the LCPs.
Iterative boundary pressure reflection method for the simulation of injection mold filling
Authors: Lee Ho‐Sang , Sin Hyo‐Chol , Kim Sang‐Gook
Published: May 2005

An Iterative Boundary Pressure Reflection (IBPR) method has been developed to improve the accuracy of the flow front generation and transient mold filling simulation in injection molding. The method iteratively calculates the virtual pressure reflection, either positive or negative, at the impinging melt front nodes which are to be relocated subsequently according to the new pressure field. The scheme is formulated into a finite element program using a power‐law model and applied to the filling of polystyrene melts injected into an edge‐gated circular cavity and a variable‐gap‐thickness cavity with an insert. The calculated results show very good agreement with the experimental results of the previous study by others in the position of the advancing melt fronts at each time step, weldline location, and pressure distributions.
Predicting molding forces in SMC compression molding
Authors: Castro J. M. , Tomlinson G.
Published: May 2005

A model relating molding force, compression speed, and part thickness, to material properties, part size, and processing conditions (mold and charge temperature) is necessary, to determine the ranges of closing speed feasible, when molding a predetermined part with a press of given capacity (tonnage). The faster we can close, in principle, the faster reacting systems we can run in a given press. A model has been developed to predict the force required for compression molding of SMC under non‐isothermal conditions. The model requires two material rheological parameters, namely, the material resistance to extension η and a friction coefficient λ. A method has been developed to measure these coefficients. Preheating the charge is an attractive way of decreasing the molding force required. Also higher molding temperatures would give lower friction and thus lower molding force.
A barometer of crystallization rates of polymeric materials
Authors: Khanna Y. P.
Published: May 2005

A crystallization rate coefficient (CRC) parameter is introduced which has allowed a direct comparison of the crystallization rates of various polymers on a single scale for the first time. Basically, CRC represents a change in cooling rate required to bring about 1°C change in the supercooling of the polymer melt. For the polymers studied, this value varies between 35 h−1 (polyethylene terephthalate) and 155 h−1 (poly(tetrafluoroethylene)) and jumps to 295 h−1 for indium metal; the precision being better than ±5 percent. The reliability of CRC has been tested against the established trends e.g., (i) a large decrease in the crystallization rate of polyethylene terephthalate with increase in molecular weight, (ii) a lower crystallization rate of the “virgin” nylon 6 as compared to the processed nylon 6 resin, (iii) an increase in the crystallization rate of nylon 6 in the presence of nucleating agents, and (iv) a dramatic increase in crystallization rate as we go from poly(ethylene terephthalate) to poly(tetrafluoroethylene) and then from poly(tetrafluoroethylene) to the metals. The significance of the CRC barometer is discussed in the light of prior difficulties in directly comparing the crystallization rates of polymers.
Knit line fractures in injection molded liquid crystalline polymers
Authors: Engberg K. , Knutsson A. , Werner P.‐E. , Gedde U. W.
Published: May 2005

The microstructure and fracture behavior of Injection molded samples of unfilled and filled grades of liquid crystalline polymers (Vectra® and Ultrax®) containing cold and warm knit lines have been studied by scanning electron microscopy, X‐ray scattering, and Instron tensile tests. Four process parameters—melt temperature, mold temperature, injection time, and holding pressure—have been varied in accordance with a 24 factorial design experiment. In cold knit lines a 200 µm thick region with transverse orientation with Hermans orientation function f ≈ 0.12–0.18 is formed on both sides on the weld area. The strength of the cold knit lines is very low, 9.0–19.8 MPa corresponding to 15–20% of the full strength of the material. The strength of the warm knit lines increases markedly with increasing distance from the insert and is generally significantly greater (40–45 MPa, 48 mm from the insert) than in the cold welds. Annealing at 260–300°C of samples containing cold knit lines causes first a partial healing of the knit line and later extensive chemical degradation of the polymer.
Mechanical properties and mechanism of the degradation process of 316°C isothermally aged graphite fiber/PMR‐15 composites
Authors: Scola D. A. , Vontell J. H.
Published: May 2005

A series of graphite fiber/PMR‐15 polyimide composites, isothermally aged at 316°C in flowing air (100 cc/min) for time periods up to 2000 h, were investigated for mechanical property changes, fiber/resin interface changes, overall dimensional changes, and weight loss. The mechanism of the degradation process is suggested based on shear and flexural property measurements at room temperature and 316°C, optical micrographs of composite cross sections, and SEM analysis of fractured surfaces. The fiber materials investigated in composite form were Celion 6000 unsized and epoxy sized. G40‐700 unsized and epoxy sized, and T40R and IM6 both unsized.
Interpenetrating polymer network approach to tough and microcracking resistant high temperature polymers. Part III. LaRC‐RP71
Authors: Pater Ruth H.
Published: May 2005

A high performance semi‐interpenetrating polymer network (semi‐IPN) has been synthesized from Thermid‐600 and LARC‐TPI. Notable improvements in resin fracture toughness and graphite fiber reinforced composite microcracking resistance over the unmodified Thermid‐600 neat resin and composite have been realized. The chemistry, processing, physical and mechanical properties, and phase morphology of the neat resin and composite reinforced with graphite fibers are presented.
Vibration based non‐destructive evaluation of polymer composites
Authors: Shelby M. D. , Tai H. J. , Jang B. Z.
Published: May 2005

A feasibility study on the use of vibration spectrum analysis as a tool for nondestructive evaluation (NDE) of polymer composites was conducted. Material integrity of polymer composite samples was determined from the vibrational measurements by analyzing the resonant frequency and damping information. A number of important “states” in the composites tested could be characterized by this analysis. The vibration tehnique was found to be sensitive to physical flawing (fiber breakage, delamination, and matrix cracking). Vibrational NDE has many potential advantages that make it very attractive for composite applications. These include the ability to make global measurements of large structures in real‐time, no geometry restrictions, and high sensitivity to a wide variety of damage states.
Crystallization kinetics of poly(ethylene terephthalate). Part I: Kinetic equation with variable growth rate
Authors: Kim S. P. , Kim S. C.
Published: May 2005

A new crystallization kinetic equation has been derived considering the decrease in growth rate. The average linear growth rate of spherulite was assumed to be proportional to the m‐th order of the uncrystallized fraction of the crystallizing material. A modified Avrami equation, 1 − Vc = exp[‐Kf(t)n], was used where f(t) is the integral of the growth function, (1 − Vc)m. The validity of the equation was tested by analyzing the isothermal crystallization kinetic data of poly(ethylene terephthalate) from the melt using differential scanning calorimetry.
Models for the compressibility of layered polymeric sponges
Authors: Swyngedau S. , Nussinovitch A. , Peleg M.
Published: May 2005

The characteristic sigmoid compressive stress‐strain relationships of sponges and their layered arrays are described by two kinds of mathematical models having three experimentally determined parameters. Since sponge compression is not accompanied by a significant cross‐sectional area expansion, it was assumed that the stress in a multilayered array is the same in each layer. This enables prediction of the array's stress‐strain relationship from the parameters of the individual layers and their known thickness. The applicability of the method is demonstrated with experimental data of two kinds of double‐layered arrays of polyurethane sponges. It is shown that the arrays' compressive behavior can be satisfactorily predicted irrespective of the mathematical form of the model and whether the strain is expressed as engineering strain or Hencky's.
Study of rubber‐modified brittle epoxy systems. Part I: Fracture toughness measurements using the double‐notch four‐point‐bend method
Authors: Sue Hung‐Jue
Published: May 2005

The double‐notch four‐point‐bend (DN‐4PB) technique is known to produce fruitful information revealing the toughening mechanisms around the sub‐critically propagated crack tip. In this study, correlations among the single‐edge‐notch three‐point‐bend (SEN‐3PB), the single‐edge‐notch four‐point‐bend (SEN‐4PB), and the DN‐4PB toughness measurement techniques have been conducted using various modified‐epoxy systems. The toughnesses of both the neat and rubber‐toughened epoxy systems are found to be independent of the testing techniques used. Specifically, when the peak load is plotted against B. W1/2/Y (B: thickness, W : width, and Y: correction factor), the data obtained from SEN‐3PB, SEN‐4PB, and DN‐4PB all fall on the same line. The slope of this line is defined as the stress intensity factor. These results imply that with a single DN‐4PB test, it is possible to gain the information needed to describe both the toughening mechanisms and the fracture toughness value of relatively brittle (KIC ≤ 1.2 MPa. M1/2) polymeric materials.
Morphology and strength of polycarbonate to poly(butylene terephthalate) vibration‐welded butt joints
Authors: Hobbs S. Y. , Stokes V. K.
Published: May 2005

Under the right conditions, the strength of vibration‐welded butt joints of amorphous polycarbonate (PC) to semicrystalline poly(butylene terephthalate) (PBT) are shown to be as high as the strength of PBT, the weaker of the two materials. Optical, scanning and transmission electron microscopy are used to examine the morphology of the weld zone. Acoustic microscopy is used to visualize poorly bonded regions. The effects of the weld parameters on weld strength and weld morphology are considered in detail.
Strength of glass‐filled modified polyphenylene oxide vibration‐welded butt joints
Authors: Stokes Vijay K.
Published: May 2005

The strengths of glass‐filled modified polyphenylene oxide (GF‐MPPO) welds relative to the strengths of GF‐MPPO are shown to depend on specimen thickness. (Modified polyphenylene oxide is a blend of poly (2,6‐dimethyl‐1,4‐phenylene ether) and high‐impact polystyrene.) Relative strengths on the order of 70 and 87 percent can be achieved in 6.1 and 3.18‐mm‐thick specimens, respectively. Welds of GF‐MPPO to modified polyphenylene oxide (MPPO) can easily attain the strength of MPPO, the weaker of the two materials. In contrast to MPPO, in which weld strength decreases with increased weld pressure, the strengths of GF‐MPPO to GF‐MPPO welds and GF‐MPPO to MPPO welds, are not affected by weld pressure.
Quality assurance of computer controlled hot‐tool welding for mass production
Authors: Potente H. , Natrop J.
Published: May 2005

The hot‐tool welding process is commonly used for welding plastics, but high seam quality can be obtained only by optimizing weld parameters. Because of demand for better quality, the importance of quality control is increasing. At present, quality control is mainly performed by inspecting the end product, resulting in high scrap rates. An effective quality control system must therefore be able to recognize errors as they occur during the manufacturing process. For this, an FMEA (Failure Mode Effect Analysis) should be performed prior to mass production, and statistical quality control should be implemented during and after the process. This paper describes a quality control system for computer controlled hot‐tool welding that is based on an understanding of the physics of the process.
Dual polymer bonding of thermoplastic composite structures
Authors: Smiley A. J. , Halbritter A. , Cogswell F. N. , Meakin P. J.
Published: May 2005

This paper describes a process that facilitates fusion bonding of thermoplastic composite components without the need for complex fixtures and without disrupting the fiber alignment in the component laminates. The dual polymer bonding process, Thermabond, requires that an interlayer polymer be fused to the surface of each laminate prior to bonding. The characteristics of the interlayer polymer allow for joining of the components at a temperature below the softening/melting point of the reinforced polymer in the composite laminates. This leads to significant processing advantages without significant loss in mechanical performance. Discussions of resin compatibility, the effect of process conditions on mechanical performance, and the application of the APC‐2/PEI Thermabond system to various structural components are included.
Orientation studies of poly(vinyl chloride). Part I: Intrinsic birefringence
Authors: Jabarin Saleh A.
Published: May 2005

The intrinsic birefringence of rigid poly(vinyl chloride), PVC, was obtained from measurement of birefringence and infrared dichroism. Rigid PVC samples were stretched at temperatures above the glass‐transition temperature, Tg, to various stretch ratios. The measured intrinsic birefringence obtained in this study is consistent with theoretically calculated and previously measured values using other techniques and samples. From the intrinsic birefringence, the principal polarizability differences of the PVC monomer were also calculated, and the results are comparable with those estimated from flow birefringence measurements of PVC dilute solutions.
Study of birefringence character of injection‐ and compression‐molded polycarbonate and its interpretation
Authors: Wu Jong‐Pyo , White James L.
Published: May 2005

Birefringence development in molded polycarbonate is of great importance in the manufacture of optical discs. It is important in characterizing birefringence to realize that we are dealing not with a scalar but with the anisotropy of the refractive index tensor–and with the orientation and shape of the refractive index ellipsoid. This usually varies heterogeneously; i.e., point‐to‐point through the thickness of molded parts. We present here an experimental study of the shapes and orientations of refractive index ellipsoids in injection‐ and compression‐molded polycarbonate parts. We consider the variations in ellipsoid character as a function of molding conditions such as injection rate and quench. In injection‐molded parts, the refractive index ellipsoid is coaxial with the flow direction in the center of the parts, but varies with position in the direction of the mold walls. In some cases, the extinction angle reaches a maximum at the mold wall and in other cases, there is an intermediate maximum. In the central “flow‐thickness” direction plane, the transverse axis of the refractive index ellipsoid is perpendicular to this plane. The birefringence (in principal axis coordinates) in the flow‐thickness direction plane exhibits an intermediate maximum whose position and magnitude vary with molding conditions. In some cases, multiple maxima exist. In compression‐molded parts, a principal axis is normal to the mold wall. The results are interpreted in terms of the Rheo‐Optical Law using flow‐induced orientation and residual stress mechanisms. If the contribution of the residual stress to the birefringence can be subtracted, we may compute biaxial orientation factors. We do this for a case that has low residual quench stresses.
Theory of crystallization in high‐speed spinning
Authors: Schultz J. M.
Published: May 2005

Removal of the heat of fusion during steady‐state crystallization in a high‐speed spinline places restrictions on the morphology of the crystallites. An appropriate model is that of a thermal dendrite. It is shown that for this case there exists at each temperature along the threadline a limiting growth velocity, beyond which heat cannot be conducted away fast enough to permit growth. It is suggested that crystallization occurs when a fluid element reaches a temperature at which heat can just be conducted away rapidly enough. Comparison of dendrite theory predictions with experimental values of crystallite diameter and crystallization temperature shows satisfactory agreement. Poly(ethylene terephthalate) has been taken as the example.
Phase behavior and mechanical properties of poly‐p‐phenylene terephthalamide/amorphous nylon molecular composites
Authors: Yang Jen‐Chang , Fukai Tomohiro , Kyu Thein
Published: May 2005

Poly(p‐phenylene terephthalamide) (PPTA)/amorphous nylon (AN) molecular composites were prepared from sulfuric acid solution by rapidly coagulating in distilled water. The regenerated films appear homogeneous and transparent. However, the rod‐like and flexible macromolecules are probably entrapped in a single phase during rapid coagulation, thus thermodynamically unstable and undergoing phase segregation upon thermal treatment. The miscibility between PPTA/AN was identified by a dielectric relaxation method. Phase behavior and kinetics of phase separation in PPTA/AN mixtures were thoroughly investigated by time‐resolved light scattering as well as optical microscope. A pseudo phase diagram reminiscent of a lower critical solution temperature (LCST) was established by a cloud point measurement. Several temperature‐jump experiments were undertaken from ambient to a two‐phase temperature region. The low PPTA content molecular composites were prepared by coagulating in a non‐solvent, then by compression molding below the phase separation temperatures. The 30 wt% PPTA molecular composite exhibits over three‐fold increase in tensile modulus relative to that of the neat AN, however, there is little or no improvement in the tensile strength. On the other hand, by a slight addition of AN into PPTA, the tensile and compressive failures of spun fibers may be improved.
Parison swell—A new measurement method and the effect of molecular weight distribution for a high density polyethylene
Authors: Swan P. L. , Dealy J. M. , Garcia‐Rejon A. , Derdouri A.
Published: May 2005

The measurement of parison swell is difficult because swell is a time‐dependent phenomenon and because, for a parison, two independent swell ratios must be determined. A new technique has been developed that makes use of a video camera focused on the end of the parison. Unlike previous techniques designed to measure time‐dependent swell, no oil bath is required. The new technique was used to study the effect of molecular weight parameters on the parison swell of high density polyethylene. For a series of blends of two resins having significantly different weight‐average molecular weights, the blends exhibited larger swell ratios than the base resins.
Crystallization kinetics during polymer processing—Analysis of available approaches for process modeling
Authors: Patel Rajen M. , Spruiell Joseph E.
Published: May 2005

An analysis of available methods of dealing with polymer crystallization for process modeling is presented. Problems encountered in using isothermal data to predict nonisothermal results are discussed and illustrated using experimental data for nylon 6. A half‐time analysis is used to evaluate and extrapolate the isothermal crystallization rates. It is concluded that none of the available models are entirely satisfactory for computing nonisothermal crystallization from isothermal data, though the Nakamura model is shown to be more satisfactory for process modeling than other models discussed in the literature. A nonlinear regression method is presented for directly fitting nonisothermal crystallinity data using the Nakamura model to obtain crystallization rate equation parameters. Two empirical methods for including amorphous orientation effects are also considered and evaluated by comparing predicted results to online experimental data for melt spinning of nylon 6.
Rheological and morphological characterization of selected poly(organo)phosphazenes
Authors: Mujumdar A. N. , Kojima M. , Young S. G. , Chan E. K. , Magill J. H.
Published: May 2005

Rheological properties of selected poly(organo)phosphazenes have been studied using capillary rheometry. Melt viscosities of polymers were calculated as a function of shear stress and shear rate. Thermal stability was also studied. In the range of shear rate studied, all polyphosphazenes showed shear thinning behavior. The power law model was fitted to the data to get the power law index and the consistency index. Poly[bis(phenoxy)phosphazene] showed a Newtonian plateau at low shear rates whereas poly[bis(trifluoroethoxy)phosphazene] and poly[bis(p‐phenylphenoxy)phosphazene] which exhibited liquid crystalline character were shear thinning even at low shear rates. Solid state capillary extrusion of polyphosphazenes was found to be more successful in fiber formation than other “state‐of‐the‐art” processes, such as gel‐spinning. The molecular weights of all polyphosphazenes synthesized were found to be too low for, Couette fiber spinning. Chemical, physical, and morphological studies were made on all fibers prepared. Many investigative techniques, such as X‐ray diffraction, differential scanning calorimetry (DSC), density measurements, scanning electron microscopy (SEM), optical microscopy, solution nuclear magnetic resonance (NMR) spectroscopy, and gel permeation chromatography (GPC) analysis are featured in this paper as characterization tools.
An ultraviolet method for the determination of the residence time distribution in a twin screw extruder
Authors: Cassagnau P. , Mijangos C. , Michel A.
Published: May 2005

The stereoselective substitution of chlorine atoms was used to graft anthracene and phenyl groups onto the poly(vinyl chloride) (PVC) backbone as ultraviolet (UV) tracers for the assessment of the residence time distribution (R.T.D) of PVC chains during the extrusion of rigid and plasticized PVC. The residence time distribution obtained using these‐grafted tracers was compared with that obtained using a free UV tracer (anthracene). The polymeric tracer had a narrower R.T.D and a shorter mean residence time. This difference of behavior between a free and grafted tracers was attributed to the compatibility of these tracers with the PVC.
Mechanical modeling of initiation of localized yielding under plane stress conditions in rigid‐rigid polymer alloys
Authors: Sue H. J. , Pearson R. A. , Yee A. F.
Published: May 2005

Two‐dimensional Finite Element Method simulations, which involve consideration of the nonlinearity of a material, have been conducted to gain understanding about the rigid‐rigid polymer toughening concept we proposed. The simulation results for the plane stress condition indicate that as long as the inclusion phase possesses (i) a 60% difference in the tangent modulus from that of the matrix at any given strain level prior to failure or (ii) smaller yield or craze stain than the yield strain of the matrix, then, localized shear yielding will occur around the inclusion. A toughened rigid‐rigid polymer alloy system can then be obtained. The plain strain case is also discussed with an implementation of the rigid‐rigid polymer toughening concept.
A study on the performance of barrier‐screw extruders
Authors: Han Chang Dae , Lee Kee Yoon , Wheeler Norton C.
Published: May 2005

An experimental and theoretical study was conducted on the performance of barrier‐screw extruders. For the experimental study, an extruder (D = 63.5 mm and L/D of 24) with a Davis‐Standard barrier screw was used to extrude a low‐density polyethylene. The extruder had nine pressure transducers which were mounted, almost equally spaced along the extruder axis, on the wall of the extruder barrel, so that we could measure axial pressure profiles during extrusion. Also conducted were tracer experiments (i.e., screw ‘pushout’ experiments), which enabled us to examine the profiles of melt film thickness in the solid channel. For the theoretical study, the analysis of Elbirli, et at, was extended by making the following modifications: (a) the flow through the barrier flight clearance was treated separately from the flow of melt film above the solid bed; (b) the melt films surrounding the solid bed were assumed to circulate around the solid bed; and, (c) convective heat transfer was included in the energy equations for the melt channel and melt films surrounding the solid bed. Prediction of axial pressure profile was found to be in reasonable agreement with experiment. Predictions are presented of the effects of extrusion conditions on the thicknesses of the upper and lower films, and on the solid‐bed velocity. Practical implications of these results are discussed from the view of designing barrier screws and selenting barrier‐screw extruders.
A high resolution negative working resist, LMR‐UV, for g‐ and i‐line lithography
Authors: Yamashita Yoshio , Jinbo Hideyuki , Kawazu Ryuji , Asano Takateru , Umehara Hiroshi
Published: May 2005

LMR‐UV (“low molecular weight resist for uv lithography”), a naphthoquinone‐diazide sulfonic acid ester of a novolak resin, is a negative working resist. The mechanism of insolubilization of LMR‐UV is based on the facts that the naphthoquinone‐diazide moiety is decomposed to indenecarboxylic acid (polar compound) by photolysis upon UV irradiation and that the irradiated resist film insolubilizes in a non‐polar developer. LMR‐UV reliably forms 0.6 μm lines and spaces over a reflective substrate with steps by using a g‐line stepper having a 0.35 NA lens. 0.6 μm‐wide aluminum patterns over topography are obtained by use of g‐line exposure and reactive ion etching. By use of an i‐line aligner (NA = 0.42), LMR‐UV resolves 0.25 μm space patterns with overhang profiles. The profiles are due to the large absorption coefficient of 3.8 μm−1. 0.3 μm wide aluminum patterns are formed by i‐line exposure and lift‐off metallization.
Effect of drying conditions on the glass transition of poly(acrylic acid)
Authors: Park Jung‐Ki , Kim Dong‐Won , Kim Chul‐Hwan , Maeng Ki‐Suk , Hwang Taek‐Sung , Kim Young‐Chul
Published: May 2005

Systematic changes of drying conditions of poly(acrylic acid) were tested to study their effect on the glass transition of the material. The materials were synthesized in two different mediums of water and benzene, respectively. The glass transition temperatures of the samples were determined by thermal analysis using DSC. The samples were also characterized by IR spectra. The glass transition of poly(acrylic acid) was found to be significantly dependent on the drying conditions and also dependent on the medium in which poly(acrylic acid) was prepared. The anhydride formation in poly(acrylic acid) was increased as the drying temperature was raised, resulting in the increase of the glass transition temperature. The “bound” water involved in the preparation of poly(acrylic acid) in water medium could affect significantly the glass transition of the sample. A significant discrepancy in the previously reported values of the glass transition temperature of poly(acrylic acid) seems to be due to the differences in the drying conditions of the materials.
Determination of unblended chain dynamic parameters of a polar discontinuous phase in an immiscible polymer blend
Authors: Havriliak S. , Banhegyi G. , Karasz F.
Published: May 2005

A method is described by which the relaxation characteristics of a polar polymer in an included phase of an immiscible polymeric blend can be determined from those of the composite. The necessary prerequisite is that the relaxation regions of the matrix and of the dispersed phase do not overlap. First, the dynamic relaxation data of the composite is fitted to the Havriliak‐Negami function using a multi‐response fitting method. Next, the relaxation function for the included phase is determined using composite mixing equations and the data for the pure matrix. This method is demonstrated for dielectric data on a polypropylene/polyurethane (PP/PUR) composite containing 20 wt% polar additive. The resulting unblended relaxation function parameters of PUR are discussed and compared to other unblended PUR literature data. Blending PUR with PP did not change the shape of the relaxation process, did shift the maximum frequency by about half a decade, and significantly reduced the limiting values of the dielectric constants.
Studies on a diphenylether modified poly(phenyl‐1,4, phenylene terephthalate) liquid crystalline polymer and its blends with polycarbonate and polysulfone
Authors: Skovby M. H. B. , Kops J. , Weiss R. A.
Published: May 2005

Blends of a thermotropic liquid crystalline polymer, LCP, (4,4′‐dicarboxy diphenyl ether modified poly(phenyl‐1,4‐phenylene terephthalate)) with polycarbonate and polysulfone were prepared and characterized with respect to their thermal properties, viscoelastic behavior, processability and mechanical properties. The processability of the thermoplastics was significantly improved by the addition of small amounts of LCP. This was also reflected by decreases in the steady shear viscosities, though the dynamic complex viscosities of the blends were generally similar or higher than those of the individual component polymers. Composite fibers were spun from the blends and the tensile moduli and strengths were consistent with a morphology of highly oriented LCP microfibrils with high aspect ratios dispersed in the thermoplastic fiber. The properties increased with increasing draw ratio.
Ultrasonic velocity and attenuation of polymeric solids under oscillatory deformation. III: Drawn films of high density and linear low density polyethylene and their blends
Authors: Nitta Koh‐Hei , Tanaka Akira
Published: May 2005

Viscoelastic nonlinearity was examined on uniaxially drawn films of high density and linear low density polyethylenes and their blends using dynamic ultrasonic measurements. It was found that nonlinearity due to plastic deformations, such as slippage and dislocations, occurs in the fibrous structures. Plastic deformations were different from those in corresponding undrawn films. For undrawn films, the formation and/or deformation of crystal defects and voids were caused by the disruption of spherulitic structures. Nonlinearity was smaller for drawn films than for undrawn films, suggesting that the superstructure of drawn films is more uniform and more stable for mechanical deformations.
Graft copolymerization of gelatin with poly(methyl methacrylate) in aqueous medium
Authors: Roy Papia , Kumar Anil
Published: May 2005

The grafting of poly(methyl methacrylate) onto gelatin in aqueous medium has been studied experimentally. The polymerization system is heterogeneous and the temperature and the initial concentration of gelatin charged in the reactor have been found to be extremely important. It is found that the amount of graft polymer increases rapidly and the formation of homopolymers is suppressed for large times. The predominantly graft polymer for the large times is essentially free from homopolymers and needs no separation. A theoretical model has been proposed which accounts for the heterogeneity in the reaction mass. The numerical solution of mass balance equations and its validation against experimental data suggests that graft copolymers react at the waterdroplet interphase at considerably higher rate.
Elastic‐plastic analysis of the deformation mechanism of PP‐EPDM thermoplastic elastomer: Origin of rubber elasticity
Authors: Kikuchi Yutaka , Fukui Takayuki , Okada Tetsuo , Inoue Takashi
Published: May 2005

Polyolefinic thermoplastic elastomer (TPE) is a two‐phase material in which cured EPDM (ethylene‐propylene‐diene rubber) particles are densely dispersed in a PP (polypropylene) matrix. It can be melt‐processed at high temperatures and behaves like a vulcanized rubber at ambient temperature. The question is on its strain recovery, i.e., why the TPE can shrink back from the highly deformed states, even though the matrix consists of the ductile polymer. We constructed a two‐dimensional model with four rubber inclusions in ductile matrix and carried out the elastic‐plastic analysis on the deformation mechanism of the two‐phase system by FEM (finite element method). FEM analysis revealed that, even at the highly deformed states at which almost the whole matrix has been yielded by the stress concentration, the ligament matrix between rubber inclusions in the stretching direction is locally preserved within an elastic limit and it acts as an “in‐situ formed adhesive” for interconnecting rubber particles. It will provide a key mechanism of the strain recovery in the two‐phase system.
Effect of ultrasonic waves on foam extrusion
Authors: Isayev A. I. , Mandelbaum S.
Published: May 2005

The effect of ultrasonic waves upon foam extrusion has been investigated by using a special die attached to an extruder. The die consists of a special ultrasonic horn, having a circular channel, that vibrates at 20 KHz. Various ultrasonic amplitudes and flow rates were employed during extrusion of a foamed polystyrene. Ultrasonic waves were found to affect both die pressure as well as physical and mechanical properties of the foam. Increases in the amplitude of the ultrasonic waves resulted in a decrease of the pressure at the die entrance. The density of the foam was found to increase with an increase of the amplitude and a decrease of the flow rate. Extrudate swell was found to decrease with an increase in the amplitude. Ultrasonic waves also influenced cell size and distribution in extruded samples: increases in amplitude resulted in reduced cell size and in narrowing their distribution. These effects are likely caused by break up of large cells or by disruption of coalescence of small cells. The tensile strength and Young's modulus of samples of extruded foam were found to increase with ultrasonic treatment. A unique correlation of these mechanical properties with the density of the foam was established.
The permeability and compressibility of aligned and cross‐plied carbon fiber beds during processing of composites
Authors: Lam R. C. , Kardos J. L.
Published: May 2005

Two of the most important input parameters needed to simulate the processing of continuous fiber laminated composites are the fiber bed permeability and the portion of the autoclave load borne by the consolidating fiber network (compressibility). In this study we have experimentally examined how both these parameter change with resin volume fraction as pressure is applied and consolidation proceeds. For a unidirectional fiber bed, the Kozeny‐Carman equation can be used to predict both the transverse (perpendicular to the laminate plies) permeability (Kozeny constant, K′z = 11) and the axial (parallel to the fibers) permeability (Kozeny constant, K′X = 0.57). The axial permeability was found to be dependent on the surface tension of the permeant. For a unidirectionally aligned fiber, the measured transverse permeabilities varied from 1.1 × 10−10 cm2 to 12. × 10−9 cm2 while the axial values varied from 2.1 × 10−9 to 4.4 × 10−8 cm2 for a liquid volume fraction range of 0.25 to 0.5. Axial permeability measurements indicate that the permeability decreases with increasing off‐axis angle × (measured from the laminate axial direction). The off‐axis permeability behavior can be described by a modified Kozeny‐Carman equation. The fiber network compressibility can be described with a logarithmic relation which has been found valid for a large number of consolidated soils.
Pultruded fiber reinforced thermoplastic poly(methyl methacrylate) composites. Part II: Mechanical and thermal properties
Authors: Ma Chen‐Chi M. , Chen Chin‐Hsing
Published: May 2005

A novel process has been developed to manufacture poly(methyl methacrylate) (PMMA) pultruded parts. The mechanical and dynamic mechanical properties, environmental effects, postformability of pultruded composites and properties of various fiber (glass, carbon and Kevlar 49 aramid fiber) reinforced PMMA composites have been studied. Results show that the mechanical and thermal properties (i.e. tensile strength, flexural strength and modulus, impact strength and HDT) increase with fiber content. Kevlar fiber/PMMA composites possess the highest impact strength and HDT, while carbon fiber/PMMA composites show the highest tensile strength, tensile and flexural modulus, and glass fiber/PMMA composites show the highest flexural strength. Experimental tensile strengths of all composites except carbon fiber/PMMA composites follow the rule of mixtures. The deviation of carbon fiber/PMMA composite is due to the fiber breakage during processing. Pultruded glass fiber reinforced PMMA composites exhibit good weather resistance. They can be postformed by thermoforming, and mechanical properties can be improved by postforming. The dynamic shear storage modulus (G′) of pultruded glass fiber reinforced PMMA composites increased with decreasing pulling rate, and G′ was higher than that of pultruded Nylon 6 and polyester composites.
Studies on the theory of single screw plasticating extrusion. Part I: A new experimental method for extrusion
Authors: Zhu Fuhua , Chen Liqin
Published: May 2005

An extruder specially designed for the study of the single‐screw plasticating extrusion process was constructed. Its barrel is equipped with glass windows which are located on both sides of it so that the full process of plasticating extrusion, solid conveying, melting, and melt conveying, can be clearly observed and recorded with photos and video recordings through the transparent windows. The solid profile X/W, the velocity of the solid bed Vsz, the forming positions of the upper melt film and the melt pool, and the position at which the break‐up of solid bed occurs, was easily determined with good accuracy. Many dynamic characters of the plasticating extrusion, such as the non‐plug solid conveying, the process of the break‐up of the solid bed and the disappearance of the, broken pieces of solid, were also observed in the experiments.
Studies on the theory of single screw plasticating extrusion. Part II: Non‐plug flow solid conveying
Authors: Fang Shizeng , Chen Liqin , Zhu Fuhua
Published: May 2005

A non‐plug solid conveying theory for plasticating extrusion is proposed in this paper. The polymer granules are treated as‐bulk pellets which move down the screw channel at different speeds, rather than as a plug which never experiences deformation during extrusion. The pellets system is considered as a linear elastic system, and can only resist compressive forces but riot tensile forces. Based on elastic mechanics and virtual work principles, a mathematical model for non‐plug solid conveying is proposed. Finite element method (FEM) is used to determine the relationships between internal stress and velocity profiles of the pellets in the screw channel, the internal stress states at any point in the screw channel, etc. The prediction also proved the existence of the optimum depth of the screw channel and the optimum helix angle of the screw. Most of the experiments have been carried out on an extruder with glass windows it its barrel. The experiments confirm the validity of the theory.
Modeling of the impregnation process during resin transfer molding
Authors: Chan Albert W. , Hwang Sun‐Tak
Published: May 2005

A model has developed for simulating isothermal mold filling during resin transfer molding (RTM) of polymeric composites. The model takes into account the anisotropic nature of the fibrous reinforcement and change in viscosity of the polymer resin as a result of chemical reaction. The flow of impregnating resin through the fibrous network is described in terms of Darcy's law. The differential equations in the model are solved numerically using the finite element technique. The Galerkin finite element method is used for obtaining the pressure distribution. A characteristics based method is used to solve the non‐linear hyperbolic mass balance equation. The finite element formulation facilitates computations involving the motion of the polymer resin front characterized by a free surface flow phenomenon.
Thermal stress induced damage in a thermoplastic matrix material for advanced composites
Authors: Adams Mary Elizabeth , Campbell Gregory A. , Cohen Arie
Published: May 2005

In this paper, we analyze the basic physics of residual stress development during cooling of thermoplastic composite matrix materials. The analytical model presented here examines development of the stress field during cooling off a cylinder of thermoplastic matrix material. The residual stress field predicted by the model is compared to observations of the differences in microstructure of polymeric materials with different processing histories. The results of the investigation indicate that changes in the matrix related to processing conditions can contribute to damage formation in composites.
Influence of maleic anhydride as a coupling agent on the performance of wood fiber‐polystyrene composites
Authors: Maldas D. , Kokta B. V.
Published: May 2005

The lack of polar groups in thermoplastics (e.g., in polystyrene) provides low adhesion with cellulosic fibers. To improve compatibility between reinforcement and matrix, maleic anhydride (MA) was selected as a coupling agent for wood fiber‐filled polystyrene composites. In general, the mechanical properties improved along with increased concentrations of MA, initiator (e.g., benzoyl peroxide) and wood fiber up to a certain limit and then decreased. The concentrations of MA and fiber which produced maximum improvements in the mechanical properties varied according to wood species, pulping techniques and type of polystyrene. Moreover, properties were further enhanced when another coupling agent (e.g., isocyanate) was used in addition to the MA.
Reinforcing high density polyethylene with cellulosic fibers. I: The effect of additives on fiber dispersion and mechanical properties
Authors: Raj R. G. , Kokta B. V.
Published: May 2005

High density polyethylene (HDPE) was reinforced with 0‐40 wt% of wood flour (aspen). The effects of: stearic acid, mineral oil, maleated polyethylene wax, and sodium silicate on the tensile and impact strength of the composite were studied. The comparison of tensile properties of the composites showed that the addition of maleated polyethylene wax produced a significant increase in tensile strength, with the increase in filler concentration, while the tensile modulus remained relatively unaffected. Microscopic studies of the composites indicate a better dispersion of the fibers in the polymer matrix when stearic acid was used.
Computer simulations of crystallinity gradients developed in injection molding of slowly crystallizing polymers
Authors: Hsiung C. M. , Cakmak M.
Published: May 2005

A model is developed to simulate the crystallinity gradients developed in injection molding of slowly crystallizing polymers. In this model, effects of nonisothermal and stress‐induced crystallization kinetics are taken into account through phenomenological relationships. Computer simulations included calculations of the temperature, velocity, and pressure distributions as well as two dimensional crystallinity distributions in the final products. In addition, effects of various processing conditions: mold temperature, injection flow rate, and holding time are also included in the calculations. The crystallinity gradients obtained through computer simulations agree with the experimental results obtained with poly (p‐phenylene sulfide) under a variety of processing conditions.
Development of cracks in injection moldings of poly (2,6‐dimethyl‐1, 4 phenylene ether)
Authors: Wagner Alan H. , Kalyon Dilhan M.
Published: May 2005

Cracks in injection molded articles adversely affect their appearance as well as their ultimate properties. In this study, we have investigated the spontaneous development of cracks in samples molded from an engineering plastic in the absence of external loading. The specimens of a well characterized poly(2,6‐dimethyl‐1,4 phenylene ether), PPE, were injection molded employing a 40t Van Dorn injection molding machine and industrial practices. The initiation and development of cracks in the molded articles were monitored for a period of eighty weeks. The presence and the frequency of the cracks were found to depend on the operating conditions employed during the molding, the shape of the cavity, the presence of Irregularities at the mold surface, and the particular location observed. The results were elucidated under the light of the results of microstructural analyses including residual stress and birefringence distributions on both compression and injection molded specimens of the engineering plastic.