bluuebunny/crossref_metadata_2025 huggingface dataset:
Fiber reinforced polypropylene: Influence of iPP molecular weight on morphology, crystallization, and thermal and mechanical properties
Authors: Avella Maurizio , Dell'Erba Ramiro , Martuscelli Ezio
Published: April 2004

The influence of molecular weight and its distribution on the nucleation density, crystallization, thermal and mechanical behavior of isotactic polypropylene based composites has been investigated. The composites were prepared by compression molding. The ability of carbon and Kevlar fibers to nucleate the polypropylene has been studied during isothermal and nonisothermal crystallization, by optical microscopy and differential scanning calorimetry (DSC), as function of crystallization temperature Tc and iPP molecular weight. Two extreme crystallization conditions were tested: quenching and slow crystallization to obtain crystals and amorphous phases of different structure. The ability of fibers to enhance mechanical properties in polypropylene based composites was examined by tensile tests at room temperature. It was found that nucleation density, crystallization parameters, and the results of tensile tests strongly depend on the molecular weight Mw of iPP, molecular weight distribution, and thermal history of polypropylene. The numerical values of the nucleation density have been found to strongly depend on the nature of fiber. In fact, Kevlar fiber has shown a better nucleating ability than carbon fiber. The results of tensile tests have been related to the sample morphology. The analysis of fractured specimens also provided useful information about fiber‐matrix adhesion.
Optimization of elastic properties in the design of textile composites
Authors: Vaidyanathan Ragavan , Gowayed Yasser A.
Published: April 2004

The elastic behavior of textile composites depends on a number of factors, including fiber and matrix properties, fabric architecture, and relative and total fiber volume fractions. The optimum design of a textile composite is, therefore, a highly combinatorial problem. In this work, the problem of predicting the optimum fabric architecture and fiber volume fractions to achieve a set of target elastic properties is formulated as a constrained nonlinear optimization problem. The design procedure uses the Stiffness Averaging Technique for the prediction of composite elastic properties. Two standard routines for solving optimization problems are employed to identify optimum design parameters. Several case studies are presented to illustrate the applicability of this novel design procedure.
An experimental and theoretical study of creep of a graphite/epoxy woven composite
Authors: Govindarajan S. , Langrana N. A. , Weng G. J.
Published: April 2004

The creep behavior of woven fiber polymer composites has been investigated through both an experimental study and analytical modeling. In the modeling, the matrix is assumed to be a 4‐parameter model (a Maxwell‐Voigt combination) and the fibers to be elastic. The fiber undulation model developed by Ishikawa and Chou for elastic behavior of woven fiber composites has been extended to the viscoelastic system by the correspondence principle. This considers the longitudinal and transverse fibers separately. The weave geometry and dimensions are accounted for, thus bringing the model closer to the actual composite. While this model has been used previously to predict the composites elastic behavior, this is the first time it is considered as a viscoelastic solid, which helps determine its time dependent behavior. The resultant model takes into account the different parameters associated with the weave (the density of the fibers in the weave, the radius of the fibers and the profile of the fill and warp fibers), volume concentration of the fiber and matrix in the composite, and the elastic moduli of the fill and warp fibers and the viscoelastic properties of the polymer matrix. We have conducted creep tests on graphite fiber/epoxy composites to evaluate our model. Experiments have been conducted from room temperature (22°C) to 200°F (93°C). The results from experiments have been analyzed and an inverse simulation has been performed to obtain the unknown parameters of the matrix and fibers in the composite. The model is then used to predict the creep behavior of the woven fiber composite under other loading conditions and temperature levels, showing satisfactory agreement with the data.
Numerical simulation of the resin transfer mold filling process using the boundary element method
Authors: Yoo Yeong‐Eun , Lee Woo Il
Published: April 2004

A numerical simulation of the mold filling process during resin transfer molding with a heated die was performed using the boundary element method. The governing differential equation with a variable coefficient was rearranged into a system of Poisson equations using the perturbation technique. The boundary element method was employed to solve the resulting equations. The resin viscosity was calculated by introducing markers at the resin inlet and tracing them. As the calculation domain changes because of the proceeding resin front, numerical calculation nodes on the boundary were rearranged for each time step and integration was performed only for the meshes in the calculation domain among the fixed meshes over the mold. Sample calculations were performed for two molds with different shapes. To check the validity of the numerical scheme, the calculated mass flow rate at the resin front was compared with the mass flux at the inlet. Close agreement was observed.
Improved interfacial shear strength and durability of single carbon fiber reinforced isotactic polypropylene composites using water‐dispersible graft copolymer as a coupling agent
Authors: Park Joung‐Man , Lee Jang‐Oo , Park Tchun‐Wook
Published: April 2004

A synthesized water‐dispersible graft copolymer (WDGP) was evaluated as a coupling agent in carbon fiber/isotactic polypropylene composites. Measurements of the interfacial shear strength (IFSS) were made using single fiber composite (SFC) specimens. A graft copolymer of isotactic polypropylene backbone grafted with polyacrylamide (PAAm) was synthesized for testing as a coupling agent. Optimal conditions for the coupling agent treatment and SFC specimens preparation were established. Improvement in the IFSS was 18% at room temperature, whereas improvement was >60% under wet conditions, after 1 h in boiling water. This improvement is due to chemical bonding in the interphase between functional groups in carbon fiber and PAAm in WDGP coupling agent, and interdiffusion in the interphase between IPP in WDGP coupling agent and matrix IPP. The hydrophobic nature of the interfacial region and crosslinking between amide groups in grafted PAAm chains based on inter‐ and intramolecular interactions may be the reason for the high improvement of the IFSS under wet conditions. In addition, the spherulite size and transcrystallinity seem to correlate with the IFSS of SFC specimens.
Tensile behavior of nanocomposites from latex and cellulose whiskers
Authors: Hajji P. , Cavaillé J. Y. , Favier V. , Gauthier C. , Vigier G.
Published: April 2004

Cellulose whiskers have been used as reinforcement in a copolymer matrix prepared from a latex phase. If a water suspension‐mixing procedure is adopted, the fibril breakage that usually occurs during the mixing with a molten polymer can be avoided, and an enhanced filler dispersion can be expected. In this study, different processing methods have been used to prepare composite films, either by film casting (water evaporation) or by freeze drying, followed by classical compression or extrusion processes. The thermomechanical properties of these nanocomposites have been investigated, and the influence of processing conditions and the effect of whisker content have been considered. Processing conditions have a large influence on the mechanical behavior and can be classified in ascending order of their reinforcement efficiency: It can be attributed to a decrease of the apparent whisker aspect ratio, due to gradual breakage and/or orientation of the whiskers when hot pressing or extrusion is used. Below Tg, good agreement is found between experimental moduli and the theoretical predictions of the Halpin‐Kardos equation. On the other hand, above Tg, a spectacular reinforcing effect is observed, which is widely underestimated by this short fiber composite model. This is related to the presence of a rigid cellulose network, linked by hydrogen bonds, when the whisker content is above its percolation threshold. The quality of this network (i.e., density and homogeneity) and thus, the magnitude of the reinforcing effect, depend on processing conditions.
Fiber coiling during bladder molding of thermoplastic composites
Authors: Colton Jonathan S. , Beeson Margaret S.
Published: April 2004

An investigation is presented into fiber movement during the consolidation of cylindrical, filament‐wound preforms when pressure is applied internally (bladder molding). It is necessary to characterize the fiber movement to predict the final fiber orientation of successful parts as well as to predict which parts will not be successful. Unsuccessful parts have fibers that clump together in thick coils at the interior surface of a part, resulting in an uneven wall thickness and poor mechanical properties. Cylindrical preforms (∼7.5 cm in diameter) made from glass fiber (20 μm in diameter, ∼50 vol%) coated with polypropylene powder (powder‐coated towpregs) were filament‐wound in a range of angles, interweaving patterns, and diameters. Trellising, a mode of fiber movement in which the fibers rotate as if they are pinned at the interweaving points, occurs first as the preforms expand. If the preforms “trellis” as much as possible without reaching the mold wall, shearing between adjacent fibers must occur to complete the expansion. Coiling occurs when a large amount of shearing is necessary to provide the final expansion needed to bring the preform to the mold diameter. A dimensionless “coiling” number is presented that predicts coiling.
Estimation of diffusion and solubility coefficients for water and CO2 in reaction injection molded parts
Authors: Mielewski Deborah F. , Anturkar Nitin R. , Bauer David R.
Published: April 2004

The evolution of gases from Reaction Injection Molded (RIM) parts during painting causes “pinhole” surface defects, which result in scrap. The transport of gases plays a major role in this outgassing. The diffusion rates of CO2 and water through reaction injection molded parts is measured in this work. Despite the presence of glassy hard domains and dispersed microbubbles of size <25 μm (nucleated parts), the diffusion showed Fickian characteristics, and diffusion coefficients were independent of the concentration of water and CO2 in nucleated and non‐nucleated RIM parts. The presence of microbubbles enhances diffusion, which could be predicted from the diffusion rate through the non‐nucleated material by using a simplistic one‐dimensional model. The diffusion coefficients of water and CO2 follow an Arrhenius relationship. The solubility coefficients follow a van't Hoff relationship over a wide range of 20 to 150°C. Apart from predicting diffusion and solubility coefficients, for various RIM materials and processing conditions, the estimated parameters will be used to interpret the outgassing phenomenon in a subsequent paper.
Viscoelasticity of polymers filled by rigid or soft particles: Theory and experiment
Authors: Alberola N. D. , Mele P.
Published: April 2004

An improved modeling for the viscoelasticity of polymers filled by rigid or soft inclusions is proposed. Such a self‐consistent scheme can predict the strong increase in the reinforcement effect of the polymer matrix observed for large volume fractions of fillers. Then, it is based on both (i) the percolation concept and (ii) the definition of an original “representative morphological motif” accounting for local phase inversions due to the presence of clusters of particles. To illustrate the validity of such an approach, the predicted viscoelasticity of polystyrene filled either by glass beads or by rubbery inclusions is compared with experimental data and/or theoretical results that issue from other modelings.
Effects of hygrothermal aging on the fracture and failure behavior in short glass fiber‐reinforced, toughened poly(butylene terephthalate) composites
Authors: Czigány T. , Ishak Z. A. Mohd , Heitz T. , Karger‐Kocsis J.
Published: April 2004

The fracture response of injection molded short glass fiber (GF) reinforced and rubber‐toughened poly(butylene terephthalate) (PBT) composites has been characterized by the fracture toughness (Kc) and energy (Gc), measured on static‐loaded compact tension (CT) specimens. The related failure of the composites with 30 wt% GF reinforcement in as‐received (AR), hygrothermally aged (HA) and re‐dried (RD) states, respectively, was studied by acoustic emission (AE) and fractography. Tougheners were functionalized ethylene/acrylate (EAF), crosslinked acrylate (XAR) and core‐shell type (CSR) rubbers, at 20 wt% in the composites. It was shown that both Kc and Gc decrease with hygrothermal aging at 90°C, and their values cannot be restored by subsequent drying. This is attributed to severe hydrolysis degradation of the PBT matrix. Deterioration in the fracture parameters was affected by the composition of the rubbery toughener: The toughness retention by EAF was superior to the other modifiers. The difference in the failure mode of the GF‐PBT composites before and after hygrothermal aging was revealed by viewing the fracture surface of the CT‐specimens in scanning electron microscope (SEM). Based on the fractographic results, changes in the AE amplitude envelopes are interpreted and discussed.
Using the essential work of fracture method for studying physical aging in thin, ductile, polymeric films
Authors: Liu Chun‐Hsin , Nairn John A.
Published: April 2004

Water‐filled, drop impact tests on full‐scale, blow‐molding polyester bottles showed that impact properties change significantly after 30 days of aging at 50°C. To quantify this deleterious effect of aging, we did small‐scale laboratory experiments using the essential work of fracture method (EWFM). We measured the essential work of fracture of thin specimens cut from the sides of blow‐molded bottles and aged under various conditions. Similar to the impact results, significant drops in essential work occurred after relatively short amounts of aging. Additional experiments confirmed that the decreases in essential work were due to physical aging and not to chemical degradation. A comparison of the essential work results to the full‐scale, bottle‐drop impact tests showed some inconsistencies that need to be resolved before EWFM can be recommended as a quantitative method for studying physical aging of blow‐molding polyester resins.
Semicrystalline thermoplastic polyimide + polymer liquid crystal blends: Nonisothermal calorimetry and thermogravimetry
Authors: Brostow Witold , D'Souza Nandika Anne , Gopalanarayanan Bhaskar
Published: April 2004

Blends of a thermoplastic polyimide (TPI) and a polymer liquid crystal (PLC) were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The presence of PLC enhances orientation in the system and lowers the crystallization temperature‐—a manifestation of the channeling effect predicted theoretically (38). The degradation studies show high temperature stability of all blends with the degradation onset consistently above 520°C. The onset decreases with PLC concentration but reaches a plateau above 30 wt% PLC when the PLC‐rich islands are formed. The amount of moisture absorbed decreases with the PLC concentration while the moisture does not affect the degradation of the samples significantly. A phase diagram is constructed for the PLC + TPI blends from the DSC and TGA data. A comparison of amorphous and semicrystalline TPI and the characterization of amorphous TPI + PLC blends will be reported later.
Effect of epitaxial crystallization on adhesive strength in impact‐toughened isotactic polypropylene
Authors: Kestenbach Hans‐Jürgen , Loos Joachim , Petermann Jürgen
Published: April 2004

The influence of the epitaxial crystallization of the polyethylene (PE) content on the adhesive interface strength of impact‐toughened isotactic polypropylene (iPP) has been investigated. The morphologies and crystal arrangements of four different matrix/rubber combinations were observed by transmission electron microscopy (TEM) and were correlated with the interface strengths measured by a peel test. It was found that the adhesion is best at interfaces, where an epitaxial morphology of the PE was observed.
Development of a helical coordinate system and its applications to analysis of polymer flow in screw extruders. Part II: A helical channel model for single screw extruders
Authors: Yu Quanping , Hu Guo‐Hua
Published: April 2004

Because of its simplicity and originality, the parallel plates model (PPM) is often used to analyze flow in a single screw extruder. This model is developed in a rectangular coordinate frame and approximates the geometry of the screw as a hollow rectangle. As such, the geometrical features of the screw channel (curvature and helicity) are lost. In this paper, we present a helical channel model (HCM). It is developed in a helical coordinate frame that takes the real screw geometry into full consideration. A comparison is made between the HCM and PPM to better appreciate the effects of these inherent geometrical parameters of a screw channel on flow in terms of velocity profile, flow rate and shape factors. In order to obtain analytical solutions, a one‐dimensional flow of an isothermal, incompressible and Newtonian fluid is considered. It is concluded that the PPM is a special case of the HCM. In other words, the HCM reduces to the PPM when the channel depth‐to‐screw diameter ratio approaches zero.
Studies on high density polyethylene/polycarbonate blend system compatibilized with low density polyethylene grafted diallyl bisphenol A ether
Authors: Yang Mingbo , Li Zhongming , Feng Jianming
Published: April 2004

Blends of a high density polyethylene (HDPE) matrix and a polycarbonate (PC) minor phase were investigated through their morphology, heat resistance, mechanical properties, crystallizing behavior, rheological measurement and especially the compatible effect of a compatibilizer: low density polyethylene grafted diallyl bisphenol A ether (LDPE‐g‐DBAE). The blends without compatibilizer exhibited a phase growth and no adhesive between the HDPE matrix and the dispersed phase. In the presence of 10% by weight of LDPE‐g‐DBAE as a compatibilizer, more fine particles and a dim phase interface were observed, and the blends showed a remarkable increase in heat distortion temperature and mechanical properties. The compatibilized blends possessed a high apparent viscosity as compared with the noncompatibilized ones. However, the apparent viscosity of the blends, with or without the compatibilizer, was lower than that of the neat HDPE and PC. Exploration by DSC found that the melting point and the crystallinity of HDPE in the blends decreased, and especially for the blends with the compatibilizer. These facts could be interpreted in terms of the efficient compatible effect of the LDPE‐g‐DBAE, which resulted from the interaction between the diallyl bisphenol A ether unit of LDPE‐g‐DBAE and polycarbonate, and the miscibility of the LDPE unit and HDPE.
Effects of surface functional groups on film formation and tensile strength development in reactive latex systems
Authors: Park Young‐Jun , Kim Jung‐Hyun
Published: April 2004

The effect of surface functional groups on chain interdiffusion at the interfacial zone of reactive latexes was investigated. A series of latexes with different surface functionalities was prepared by batch or shot‐growth emulsion polymerizations. The particle surface properties were varied by changing the number density of functional groups. The rate of tensile strength development decreases with the increasing number density of surface functional groups, which indicated that inter‐particle crosslinking restricted the interdiffusion of polymer chains during film formation and annealing. The average diffusion coefficient D of polymer chains across particle interfaces was obtained from dynamic mechanical analysis and compared well with the results from the rate of tensile strength development. The magnitude of D of the reactive latex film was lower than that of the homopolymer film. The lower chain mobility of reactive latexes prevented mechanical strength development.
Thermomechanical properties of a magnetically and mechanically oriented liquid crystalline copolyester, xydar
Authors: Kossikhina Svetlana A. , Kimura Tsunehisa , Ito Eiko , Kawahara Masanori
Published: April 2004

Elastic moduli and linear coefficients of thermal expansion (CTE) of a random thermotropic liquid crystalline copolyester, oriented in a magnetic field and by mechanical methods were measured in the directions parallel and perpendicular to the orientation direction. The axial elastic modulus of the magnetically oriented film was lower than that of the uniaxially stretched film. The elastic modulus measured in the transverse direction was higher for the magnetically oriented film. In the axial direction, both the mechanically stretched and magnetically oriented films exhibited shrinkage at low temperatures (CTE ≈ ‐2 · 10−5 K−1) and exhibited expansion at elevated temperatures. In the transverse direction, expansion was observed except for the biaxially stretched film at low temperatures. The magnetically oriented film showed the lowest axial CTE at elevated temperatures.
A rheo‐infrared‐dichroism study of sheared molten polystyrene fractions
Authors: Skytt M.‐L. , Jansson J.‐F. , Gedde U. W.
Published: April 2004

The development of orientation in molten narrow molar mass fractions of polystyrene during shear flow in the non‐Newtonian shear rate range (11–24 s−1) at temperatures between 225 and 275°C has been assessed by measurement of the infrared dichroism. Deviation from linearity between shear stress and orientation was found at high shear stresses in the steady state region. A sudden change in the shear rate caused a change in the shear stress that was one to two orders of magnitude‐state level of the Hermans orientation function (fss) was dependent on temperature, shear rate and molar mass (M): fss = C1–C2/M (where C1 and C2 are constants). The time to reach steady state on the inception of shear was proportional to M1/2. The recovery of the isotropic state after the cessation of shear followed initially a simple exponential law: f ∝ e−t/τ, where t is the time and τ is the relaxation time. The relaxation time showed only a weak molar mass dependence (τ ∝ M0.8), indicating that the decay of orientation was initially governed by processes other than reptation.
The precision of dynamic oscillatory measurements
Authors: Bafna Sudhir S.
Published: April 2004

This paper examines the precision of complex viscosity measurements in the constant stress and constant strain modes. A Bohlin Controlled Stress Melt Rheometer was used to make the measurements, which cover a stress range of 400 to 3227 Pa and a frequency range of 0.01 to 30 hertz. In principle, oscillation in the linear region should give the same values regardless of how it is done. In reality, various measurement modes exhibit different precision. A wide range of parameters encompassing three decades in complex viscosity and over three decades in frequency are considered. Contrasting frequency dependence, i.e., shear‐thinning and Newtonian plateau, are also considered. Constant stress measurements are found to provide improved precision at lower frequencies, while constant strain measurements provide improved precision at higher frequencies. This is significant because low frequency data are often used to estimate the zero‐shear viscosity, which correlates with the weight‐average molecular weight. The “between‐sample” and “within‐sample” components of the total variation are examined separately for poly(dimethyl siloxane) and polyethylene. To do this for polyethylene, a new technique (moving range average) had to be used. Initial attempts at modeling are discussed. The discussion is limited to isotropic polymeric melts. This paper provides guidance in determining the most appropriate way to perform oscillation.
Compatibilizing effect of natural rubber‐g‐poly(methyl methacrylate) in heterogeneous natural rubber/poly(methyl methacrylate) blends
Authors: Oommen Zachariah , Gopinathan Nair M. R. , Thomas Sabu
Published: April 2004

The morphology and properties of heterogeneous poly(methyl methacrylate)/natural rubber blends have been modified by the addition of a graft copolymer of natural rubber and poly(methyl methacrylate) (NR‐g‐PMMA). The morphology has been studied as a function of copolymer concentration. A sharp decrease in the dispersed domain size was observed by the addition of a few per cent of the copolymer followed by leveling off at higher concentrations. The compatibilizer increases the interfacial adhesion by the formation of micro‐bridges with the matrix. The effects of homopolymer molecular weights, processing conditions, and mode of addition on the morphology of the dispersed phase have been investigated. The experimental results are compared with the theoretical predictions of Noolandi and Hong. Attempts have been made to explain the conformation of the graft copolymer at the interface. The changes in mechanical properties of the blends as a result of the addition of the compatibilizer were related to the morphology of the blends.
Henry constants in polymer solutions with the van der waals equation of state
Authors: Bithas Sotiris G. , Kalospiros Nikolaos S. , Kontogeorgis Georgios M. , Tassios Dimitrios
Published: April 2004

The simple der Waals equation of state, as extended to polymer systems, is applied to the correlation and prediction of Henry constants in polymer solutions comprising five polymers and many nonpolar and polar solvents, including supercritical gases. The correlation achieved with one adjustable parameter is satisfactory, with typical errors within the experimental uncertainty and comparable to those with the more complex Perturbed Hard Chain Theory‐based equations of state with the same number of adjustable parameters. A predictive scheme for calculating Henry constants is also presented, which is a corresponding‐states correlation for a dimensionless Henry constant defined based on the van der Waals equation of state. Satisfactory results—often close to the ones from the one‐parameter correlation—are obtained for all systems investigated in this work. Compared with literature models that have been applied to the prediction of Henry constants in polymers, this scheme is simpler and applicable to supercritical gas‐containing systems.
Elastomer‐toughened poly(phenylene sulfide)
Authors: Masamoto Junzo , Kubo Kimihiro
Published: April 2004

For use as electrical and electronics parts, or automobile and mechanical parts, toughened poly(phenylene sulfide) (PPS) is desired. For these applications, our investigation centered on improving the toughness of PPS and developing elastomer‐toughened PPS and elastomer‐toughened compounds of PPS. Using chemically treated PPS and an olefinic elastomer with a functional group, we developed elastomer‐toughened PPS using a reactive processing method. In the PPS matrix, the elastomer is finely dispersed. While the notched Izod impact strength of the original PPS is about 1 kg · cm/cm. clastomer‐toughened PPS has a notched impact strength around 50 kg · cm/cm. The notched fracture surface of elastomer‐toughened PPS is observed using a scanning electron microscope. We concluded that the mechanism for the toughening is attributed to energy dissipation by matrix yield.
Extrusion blow molding of microcomposites based on thermotropic liquid crystalline polymers and polypropylene
Authors: Handlos A. A. , Baird D. G.
Published: April 2004

This work is concerned with the extrusion blow molding of bottles from pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The TLCPs used are HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties observed for in situ composites in which the TLCP fibrils are generated in elongational flow fields that occur in polymer processing operations and to determine if TLCP reinforced bottles could be produced by extrusion blow molding of microcomposites. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors considered include the effect of TLCP concentration and in situ composite strand properties on the mechanical properties and anisotropy of bottles made from microcomposites. Specifically, strands having three different draw ratios are used to produce bottles at 10 and 20 wt% TLCP. Increasing the in situ composite strand modulus is shown to cause an increase in both the machine and transverse direction moduli of the composite bottles. The mechanical properties of the bottles increase with increasing TLCP composition. Finally, the machine and transverse direction properties are not balanced in the composite bottles produced in this study (degrees of anisotropy ranging from 1.5 to 1.8). The mechanical anisotropy is probably the result of a low blow up ratio (2) in the bottles and the TLCP fibers being oriented primarily in the machine direction due to the shear flow in the die.
Swell and distortions of high‐density polyethylene extruded through capillary dies
Authors: Eggen Svein , Hinrichsen Einar L.
Published: April 2004

The effect of varying the die entrance angle and the die length on extrudate swell and on the onset of extrudate distortion in capillary extrusion has been studied. Using theory from the literature, we have analyzed the contribution to the total pressure drop from the elongational and shear deformation in the entrance region, and from the capillary pressure drop in the land region of the die. From the contribution of the elongational deformation, we obtained an estimate for the elongational viscosity of the polymer. The same analysis was used to study the influence of the die geometry on the stick‐slip instability. It is found that the elongational component at the inlet region mainly influences the extrudate distortions. The onset of the stick‐slip instability occurs within 10% at a wall stress τw of 0.3MPa, where τw is calculated from expressions assuming fully developed flow. The variation around this average value is systematic with changes in die geometry, and the observed variations are probably due to the non‐homogeneous pressure field in the die. We also propose a model for predicting extrudate swell. Input to the model are material parameters obtainable from oscillatoric measurements of the loss and storage modulus and residence times calculated from the geometry of the die. The swell model includes a fitting parameter that sets the overall scale of the swell.
A cell model to describe the spherulitic growth in semicrystalline polymers
Authors: Bénard André , Advani Suresh G.
Published: April 2004

The evolution of the spherulitic morphology, commonly encountered during the solidification of semicrystalline materials, is modeled by taking into account the transport of the solute (the noncrystallizing species) and the crystallization kinetics. In this paper, a microscopic cell model is presented that incorporates the influence of these phenomena. The growth of the spherulite in the cell is represented by defining three concentric zones within the unit cell: a liquid zone, a dendritic zone, and a solid zone. The governing equations that describe the process are solved simultaneously with an integral method and a time‐stepping scheme to obtain a description of the growth of a spherulite within the cell. Five dimensionless parameters are identified that affect the cooling profile and the microstructure. Also, the concentration profiles of the noncrystallizing species, the cooling history of the spherulite, and the evolution of the grain envelope and the dendritic zone are calculated during the solidification process. These results are obtained for boundary conditions of prescribed heat flow, prescribed cooling rate, and isothermal crystallization. The development of a significant interdendritic region is observed under prescribed heat flow, along with the rise in temperature associated with the self‐heating of the polymer due to the latent heat. No interdendritic region developed with the prescribed cooling rate, and a much smaller one appeared under isothermal conditions. The solid fraction, in the last case, also reached a plateau below unity due to the choice of cooling conditions. These results are consistent with experimental observations.
Diffusion of moisture in poly(p‐phenylene terephthalamide) film: Analysis by the adsorption‐controlled diffusion equation
Authors: Fukuda Mitsuhiro
Published: April 2004

Diffusion of moisture in poly(p‐phenylene terephthalamide) films was observed using a gravimetric method at various vapor pressures at 25°C. The equilibrium moisture regain was 4.9% (g/g) and 4.2% (g/g) at 65% relative humidity for the 16‐μm and 50‐μm thick film, respectively. These values are slightly larger than regular Kevlar or Kevlar 49 that have the same chemical structure of poly(p‐phenylene terephthalamide) (PPTA). The sorption and desorption curves were satisfactorily analyzed by the adsorption‐controlled diffusion equation assuming reversible bimolecular kinetics. These results strongly indicate that the interaction between the water molecules and amide groups of polymer plays an important role in the diffusion process and has much effect on the shape of sorption/desorption curves. The diffusion coefficients for the films were in the order from 10−‐11 to 10−‐10 cm2/s, which were also larger than those for Kevlar fibers of 10−‐12 cm2/s. The higher moisture diffusivity in the film reflects sparser molecular packing and existence of interstitial microvoids due to the lower molecular orientation in the noncrystalline region in the PPTA film than in the fiber (Kevlar).
Epoxidation reaction of trimethylolpropane with epichlorohydrin: Kinetic study of chlorohydrin formation
Authors: Quintela Arturo Lopez , Pellin Mercedes Pazos , Abuin Senen Paz
Published: April 2004

The kinetics of the reaction between trimethylolpropane (TMP) and epichlorohydrin (ECH) were studied. A mechanism is proposed which involves the synthesis of chlorohydrins, a previous stage which then leads to epoxy resin formation. From this mechanism a set of three coupled non‐linear differential equations, (each equation corresponds to each chlorohydrin) was derived and numerical solutions were obtained using a Monte‐Carlo method. The concentrations of chlorohydrins determined by this method (41.7, 35.7, and 22.5%) compare well with the experimental GPC results (42.7, 34.7, and 22.6%). The corresponding rate constants for the formation of the chlorohydrins were obtained.
Liquid crystalline polymer blends with stabilized viscosity
Authors: Wei K. H. , Kiss G.
Published: April 2004

The rheology of blends of thermotropic liquid crystalline copolyester co(hydroxybenzoate‐isophthalate‐hydroquinone) (HIQ) and polyetherimide were studied at different temperatures. As a result of the anisotropic‐to‐isotropic transition, the viscosity of the biphasic HIQ was found to be able to compensate that of the host polyetherimide at proper composition when the temperature increased or decreased in the capillary rheometer study. The 33% HIQ blend had almost stabilized viscosity between 350 and 370°C, whereas the 15% HIQ blend did not have stabilized viscosity. For the nonisothermal spiral molding trial, the 33% HIQ blend stabilized at a mean length of 21 inches (53 cm) with a standard deviation of 2.1 inch (5.3 cm) when the melt temperature increased by 30 Celsius degrees from 340 to 370°C.
Injection molding of PC/PBT/LCP ternary in situ composite
Authors: Xu Qianwei , Leng Yang , Mai Yiu‐Wing
Published: April 2004

A liquid crystalline polymer (LCP), Vectra B950, reinforced polycarbonate (PC) 60 wt%/polybutylene terephthalate (PBT) 40 wt% blend was studied using the injection molding process. Morphology and mechanical properties of ternary in situ LCP composites were investigated and compared with binary polycarbonate/Vectra B950 LCP composites. Good in situ fibrillation of LCP was observed in the direct injection‐molded LCP composites. Preliminary results of this work indicate that addition of PBT improves skin‐core distribution of LCP microfibrils in the matrix and also enhances adhesion between the matrix and Vectra B950, which contains terephthalic acid. The PC/PBT/LCP ternary system also exhibits lower viscosity than the PC/PBT blend and pure LCP. In a ternary system with 30 wt% of Vectra B950, tensile modulus and strength increase approximately threefold and twofold, respectively. The rule of mixtures (ROM) for continuous reinforcement can accurately represent the strengthening effects for the ternary LCP in situ composites. Generally, LCP reduces the ductility and impact strength of the thermoplastic blends; however, the relative loss is less in the ternary system than in the binary system.
Note: Micromechanical testing of toughness in nylon 6/PDMS block copolymers and blends
Authors: Mukai U. , Argon Ali S. , Cohen R. E.
Published: April 2004

Small specimens of nylon 6/PDMS compositions were screened for relative levels of toughness using a micromechanical testing device. Measurements were made of the total crack length emanating from pre‐cut notches in a specially designed specimen. At room temperature, cracks propagated readily in nylon 6 homopolymer and somewhat more slowly in a composition containing 4 wt% PDMS; at 10 and 28 wt% PDMS the cracks were blunted in a diffuse whitened zone and did not propagate through the specimens. At −40°C, the 10 wt% blend appeared to be as tough as the 4 wt% blend at room temperature.
Estimates for process conditions during the ultrasonic welding of thermoplastics
Authors: Nonhof C. J. , Luiten G. A.
Published: April 2004

Order of magnitude estimates are presented for processes that play a role in ultrasonic welding. The fact that the sonotrode may not always be in contact with the product being welded, which results in the sonotrode repeatedly hammering the product, is accounted for in this study. The calculations do not use estimates for loss or storage modulus of plastics at 20 kHz around the glass or melting point for amorphous or semicrystalline polymers respectively. The flow of molten polymer in the weld zone is shown to be a laminar viscous squeeze flow driven by the welding pressure. An energy balance is used to show that the heat generated by the internal damping is, in part, used in heating cold material and is squeezed out into weld flash. The theoretical findings are correlated with existing practical pointers on ultrasonic welding in series and mass production in industry.
Optimization of hot plate welding for series and mass production
Authors: Nonhof C. J.
Published: April 2004

A single optimal parameter setting for hot plate welding is not possible because of the large number of plastics and fillers, different types of parts, and different demands on joints. Results of a program aimed at finding an optimization procedure are presented. It is shown that one of the procedures proposed in the past is not always valid. After considering alternative approaches, the general method of a statistical process optimization is shown to be best. A complete factorial experimental design with welding machine parameters is employed.
Moldable thermoplastic elastomers: Electrical worker gloves and sleeves
Authors: Bigg D. M.
Published: April 2004

A series of blends of styrene‐isoprene‐styrene block copolymers and ultralow density polyethylenes were evaluated for mechanical and electrical properties. A number of these blends were found to be suitable for use as moldable gloves for electrical workers. The mechanical properties exceeded those required of natural rubber solvent dipped gloves. The electrical properties were also found to satisfactorily meet the required levels of voltage and current resistance. Of particular importance were the blends in which the SIS component comprised the matrix phase. These blends exhibited low values of hardness, which made the resulting material highly flexible and compliant. The addition of polyethylene to the SIS elastomer reduced the surface tack to an acceptable level, without negatively affecting the other key properties of the elastomer. Good interfacial compatibility was found at low levels of each component in the other.
Transport in a twin‐screw extruder for the processing of polymers
Authors: Chiruvella Raman V. , Jaluria Y. , Karwe M. V. , Sernas V.
Published: April 2004

The fluid flow and heat transfer in polymer extrusion in a twin‐screw extruder was studied numerically by using the finite volume method. In the mathematical model, the coordinate system is fixed to the screw so that it is held stationary and the barrel is moved to simplify the complicated geometry. The screw channel of a twin‐screw extruder is approximated as two regions: translation and intermeshing. The flow in the translation region is similar to that in a shallow single screw extruder and is treated by the numerical methods given in the literature. In the nip or intermeshing region, strong mixing effects are expected, along with the diffusion of energy and momentum. The full governing equations are solved in this region to determine the velocity components in all the three coordinate directions. The energy equation is coupled with the equations of motion through viscosity, since the viscosity of the polymeric, non‐Newtonian, fluids considered here is dependent upon the shear rate and temperature. There is no clear physical demarcation between the nip region and the translation region. Therefore, a domain matching was employed at an arbitrary location that was varied numerically to ensure that the results were independent of this location. The variation of pressure and bulk temperature along the helical channel of the twin‐screw extruder is obtained, along with the shear rate. An experimental investigation of the velocity profiles in the translation region of a self‐wiping twin‐screw extruder, which is often used in practical applications, was carried out using a Laser Doppler Anemometer. The numerically predicted velocity profiles are compared with those from the experiments, yielding fairly close agreement.
Throughput calculation with considerations of leakage flow on injection molding plasticizing units
Authors: Potente H. , Effen N. , Liu J.
Published: April 2004

The metering time or melt throughput frequently dictates the cost efficiency of the injection molding process, which means that as accurate as possible an advance calculation must be guaranteed. In the past, leakage flow via the screw flights was neglected in pressure/throughput calculations for plasticizing units on injection molding machines. This paper presents equations for the melt throughput calculation of isothermal/non‐isothermal Power Law fluid in multi‐zone screws when considering the leakage flow over the screw flights. The concluding comparison of experimental and calculated throughputs shows a good level of agreement.
Generation of fibrillar morphology in blends of block copolyetheresteramide and liquid crystal polyester
Authors: Champagne M. F. , Dumoulin M. M. , Utracki L. A. , Szabo J. P.
Published: April 2004

Polymer blends comprising liquid crystal polymers, LCP, as a minor component can be formed into fibrillar‐type morphology. This morphology enables the generation of improved mechanical properties in the draw direction, in a manner comparable to unidirectional composites: In this paper, the results obtained for blends of a polyetheresteramide block copolymer, PEBA, with a liquid crystalline copolyester are presented. Films prepared using a single‐screw extruder were melt drawn on calendering rolls. The blends' storage modulus increased with draw ratio, λ, reaching a maximum value for λ = 3–4. The storage modulus of blends containing 30 wt% LCP, and drawn to λ = 4 to 12, was found to increase nearly 50‐fold in comparison to neat PEBA (from 18 MPa to almost 1 GPa). The blends' morphology was characterized by dissolving the PEBA matrix, followed by gravimetric and microscopic analysis of the LCP phase. As expected, the average fiber diameter decreased as a function of λ−0.5. The fiber content as a function of λ followed a trend parallel to that of the modulus. Longitudinal and transverse moduli followed the Halpin‐Tsai predictions for unidirectional composites. Properties of compression molded specimens prepared from these blends compared favorably with glass fiber composites.
Contribution of polyalkyl(meth)acrylates to the design of PVC melt viscosity
Authors: Vankan R. , Fayt R. , Jérôme R. , Teyssié Ph.
Published: April 2004

The shear viscosity of poly(vinylchloride) (PVC) at 200°C can be decreased by at least one order of magnitude by the addition of as little as 5 wt% poly n‐alkyl‐(meth)acrylates (PMA) of a much lower dynamic viscosity than PVC. For this effect to be observed, the polymeric additive must be immiscible with PVC at 200°C. The average size of the dispersed phases is observed in the range of 0.5 to 5 μm; size fluctuation in this domain has no significant effect. When these conditions are met, there is a linear increase in the shear viscosity ratio ηblend/ηPVC from 0.2 to 1.0 with increasing logarithmic values of the dynamic viscosity ratio of the additive over PVC [(log(η/η)) from −4 to −1].
Diffusivity of a drug preservative in bromobutyl rubber
Authors: Hoyt Michelle A. , Balik C. M.
Published: April 2004

Sorption of phenylethyl alcohol (a model drug preservative) by bromobutyl rubber (a polymer used in drug packaging) is characterized by relatively low apparent diffusivities at room temperature (D ≈︁ 10−10 cm2/s) and a high solubility that leads to considerable swelling of the polymer. The sorption curves for thin samples exhibit non‐Fickian anomalies, which are normally observed only in glassy polymers, including two‐stage sorption and sorption overshoot. The desorption curves were much more Fickian. The swelling kinetics were very slow, and true equilibrium was not reached in the time frame of most of the experiments, which ranged up to 78 days. This produced lower apparent diffusivities and higher activation energies for sorption compared to desorption.
Rheological and thermal properties of blends of low‐density polyethylene and its ionomers
Authors: Horrion J. , Agarwal P. K.
Published: April 2004

Melt rheology and DSC studies of blends of two ionomers′ ethylene‐acrylic acid copolymers are reported, EAA (4.6 mole % AA) and EAA (6.5), as a function of their concentration and counter ion types with their precursor, a low‐density polyethylene. Various isothermal dynamic measurements in the frequency range of 0.01 to 10 rad/sec, from 120 to 200°C, were made; and partial master curves of G′ and G″ were generated. Although the melts appeared to follow the conventional superposition principle, the Cole‐Cole plots were found to be unsatisfactory in describing the miscibility of such blends. The analysis based on the calculations of activation energies and other supporting measurements such as Vicat softening and DSC thermal analysis indicate that such blends are immiscible and perhaps do not have LCST. The blends failed to follow the additivity rule. The Vicat softening measurements indicated variations in the morphology of blends. The DSC studies performed on various 50/50 blends clearly demonstrated phase immiscibility.