bluuebunny/crossref_metadata_2025_split 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractCellulose 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

AbstractAn 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

AbstractThe 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

AbstractAn 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

AbstractThe 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

AbstractWater‐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

AbstractBlends 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

AbstractThe 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

AbstractBecause 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

AbstractBlends 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

AbstractThe 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

AbstractElastic 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

AbstractThe 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.