bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase separation and mechanical properties of poly(methyl methacrylate)/polycarbonate blends
Authors: Kodama Minekazu 
Published: December 2004

AbstractDynamic mechanical properties, tensile properties, and scanning electron microscopy of blends of poly(methyl methacrylate) and polycarbonate were investigated after phase separation above their cloud point temperature by annealing in a hot press. The dynamic mechanical properties show that phase separation proceeds more distinctly for the blends annealed at higher temperature and for longer time. The scanning electron micrographs show that the morphology of phase separated blends varies with the conditions of heat treatment. The tensile properties of phase separated blends deteriorate on account of the coarsening of the brittle dispersed phase over the optimum size and the occurrence of voiding during the heat treatment.
Analysis of the packing stage of a viscoelastic melt
Authors: Nguyen Ky T. , Kamal Musa R. 
Published: December 2004

AbstractThe packing stage starts at the end of mold filling. During this stage, additional material is forced into the mold to compensate for the shrinkage during subse‐quent cooling. Underpacking results in molded parts with dimensional variation. Overpacking causes flash at the parting lines, stick during ejection, and excess residual stresses resulting in warpage. The packing stage is thus extremely important in the determination of the final quality of the product. Despite its importance, analysis of the packing stage has been relatively ignored, particularly the viscoelastic effect. In this work, the analysis of the isothermal packing stage is presented for a Maxwell fluid. A set of governing equations is derived for a two‐dimensional mold and solved using the Galerkin finite element method. In addition to the distribution of velocity and pressure, the model predicts the stresses in the planar direction, which could be used for subsequent calculation of the residual stresses.
Controlling morphology of polystyrene/poly(vinyl methyl ether) blends undergoing spinodal decomposition process by photo‐crosslinks
Authors: Tran‐Cong Q. , Imura M. , Soen T. , Shibayama M. 
Published: December 2004

AbstractThe morphology developing during the spinodal decomposition process of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends was successfully controlled by photo‐crosslink reactions between PS chains. The crosslink reaction was carried out by taking advantage of the photodimerization of anthracene moieties that are labeled on PS chains. Effects of photo‐crosslinks on the morphology induced by temperature jumps (T‐jump) from the one‐phase region into the spinodal region were examined under several experimental conditions such as T‐jump depths and irradiation times. It was found that the concentration fluctuations developing during the spinodal decomposition process were efficiently frozen upon irradiation using a XeF excimer laser as well as a mercury (Hg) lamp. Furthermore, these ordered structures are quite stable upon annealing. These results demonstrate that the morphology developing during the spinodal decomposition process can be well controlled by easily accessible light sources such as high pressure mercury lamps. Thus the photo‐crosslink reaction described in this work can provide the basis for a potential technique to design multiphase polymer materials with controllable ordered structures.
Liquid crystal polymer/polyethylene blends for thin film applications
Authors: Hsu T. C. , Lichkus A. M. , Harrison I. R. 
Published: December 2004

AbstractA series of liquid crystal polymer/polyethylene (LCP/PE) blends have been studied to determine the potential of such a system to produce a high modulus film material which retains fabrication and low temperature characteristics of some current PE films. The subject of liquid crystalline polymer blends has been the focus of significant attention for the last decade due to the novel rheological and mechanical properties of this class of polymers. It has been demonstrated that if an LCP blend is processed under elongational flow conditions, the partially ordered LCP meso‐phase intermediate allows the development of an oriented fibrillar morphology which is retained upon solidification. In this study, blown films of blends of 5 and 15% LCP in PE have been produced which show an enhancement in modulus over the neat PE matrix. These results are discussed in terms of processing conditions, LCP reinforcement aspect ratio, fibril diameter, and LCP/PE modulus ratio.
Stress analysis around a three‐dimensional craze in glassy polymers
Authors: Xiao Z. M. , Pae K. D. 
Published: December 2004

AbstractStress analysis around a three‐dimensional craze and a three‐dimensional craze containing a penny‐shaped crack has been made. The craze is treated as a transversely isotropic, oblate spheroid embedded in an isotropic glassy polymer. The craze is assumed to consist of primary fibrils and cross‐tie fibrils, such that a penny‐shaped crack may form at the central regime of the craze. The craze surface stress, the stress field near the craze tip outside the craze region, and the stress intensity factor in the crack tip are determined by using Eshelby's equivalent inclusion method. Numerical values of the fracture toughness and the stress needed to sever a craze fibril at the crack tip are calculated and the results appear to be in good agreement with the data given in the literature.
Melt blending of ultra high molecular weight and high density polyethylene: The effect of mixing rate on thermal, mechanical, and morphological properties
Authors: Tinçer T. , Coşkun M. 
Published: December 2004

AbstractThe blends of two different ultra high molecular weight polyethylenes (UHMWPE) and high density polyethylene (HDPE) were prepared in melt at different compositions and mixing rates in Brabender Torque Rheometer. The temperature build‐up due to the internal friction during melt blending was recorded and evaluated with respect to the change in the torque. The temperature at maximum torque was considered the fusion point temperature of the UHMWPE in the blend. This fusion point temperature was found to depend on the composition, mixing rate, and molecular weight. The effect of mixing rate on the mechanical properties (measured as yield and tensile strengths and elongation at break), thermal oxidative degradation and melting behavior were studied. The morphology of the blends were investigated by optical microscopy.
Rheokinetic studies for the reaction injection molding of polydicyclopentadiene
Authors: Ng Hendra , Manas‐Zloczower Ica , Shmorhun Mark 
Published: December 2004

AbstractDicyclopentadiene (DCPD) based liquid engineered resins are emerging among the newest commercial reaction injection molding (RIM) systems. Since the filling stage is coupled with chemical reaction, an understanding of the chemorheological changes is critical for establishing moldability criteria. An adiabatic reactive viscometry technique which involves the simultaneous measurement of viscosity and temperature changes was used to investigate the chemorheological changes during the adiabatic copolymerization of a DCPD based RIM system. The influence of impingement mixing conditions and initial material temperature on the reaction kinetics, rheology, as well as the resulting final physical properties of the system were investigated. The “apparent gel time” under adiabatic conditions is estimated from the intersection of the tangents to the initial and final portions of the viscosity curve. An autocatalytic kinetic model with an Arrhenius rate constant was used to model the reaction kinetics.
The effects of physical aging on the brittle fracture behavior of polymers
Authors: Arnold J. C. 
Published: December 2004

AbstractThe effects of physical aging on the failure behavior of a typical brittle polymer, polystyrene, have been studied. Properties examined were creep rupture lifetimes, fatigue lifetimes, and environmental stress cracking in ethanol. Fractured samples were examined both optically and by scanning electron microscopy to determine the degree of crazing. It was found that a longer physical aging time produced shorter lifetimes in all cases. The main reason for this is the reduction in craze strength caused by a reduced toughness due to physical aging. A long aging time was found to delay craze formation, but once formed, these crazes were much less stable than those formed with a short aging time. The effects of aging are important on failure prediction criteria and on testing methodologies, and the implications are discussed.
A preliminary investigation of flash formation during injection molding of polyphenylene sulfide and liquid crystalline polymer blends
Authors: Shonaike G. O. , Yamaguchi S. , Ohta M. , Hamada H. , Maekawa Z. , Nakamichi M. , Kosaka W. , Toi K. 
Published: December 2004

AbstractFlashing in pure polyphenylene sulfide (PPS) and a blend containing PPS and liquid crystalline polymer (LCP) during injection molding was investigated by differential scanning calorimetry and scanning electron microscopy. The shape of the flash was observed by use of a projector. Flashing was detected in pure PPS and 90/10 PPS/LCP blend but was not found in other compositions, including pure LCP. The DSC thermograms of the flash revealed both exothermic and endothermic peaks at around 120° and 285°C. The first peak, known as crystallization temperature on heating, occurred as a result of early crystallization of PPS. The observed double peaks indicated that the degree of crystallinity was lower in the flash than in the molded part. The morphological studies revealed the presence of LCP fibrils in the skin region and droplets in the core region of 90/10 PPS blend. The absence of flash was attributed to the diameters of the fibrils and droplets, which were found to increase with increasing LCP component.
Modeling the dielectric response of unsaturated polyester resin during cure
Authors: Alperstein D. , Narkis M. , Siegmann A. 
Published: December 2004

AbstractThe dielectric relaxation of unsaturated polyester resin during cure was modeled using a modified Williams–Watts decay function. The dielectric response was studied using dielectric measurements coupled with two dynamic mechanical measurement methods. It was found that the variation of the relaxation time during cure is a WLF process using Tg (α) (α‐conversion) as the varied temperature. It was shown that this process fits the Williams‐Watts decay function Φ(t)=exp(‐(t/τ)β) where τ‐relaxation time and β‐empirical parameter are time dependent. It was found that τ obeys a time dependent power law rule and β depends linearly on log(time). Using this modified decay function, it was shown that the experimental dielectric response measured during cure agrees well with the computed response. Relaxation times above and below the dielectric measurement system capability were computed thus, demonstrating the capability of yielding the entire relaxation times spectrum during cure, out of a single limited frequency dielectric measurement.
Effect of the pressure drop rate on cell nucleation in continuous processing of microcellular polymers
Authors: Park Chul B. , Baldwin Daniel F. , Suh Nam P. 
Published: December 2004

AbstractMicrollular plastics are cellular polymers characterized by cell densities greater than 109 cells/cm3 and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth.
Morphology and mechanical properties of liquid crystalline copolyester and polyester elastomer blends
Authors: Jang Sang Hee , Kim Bong Shik 
Published: December 2004

AbstractBlends of a polyester elastomer (PEL) having a hard segment of polyester (PBT) and soft segment of polyether (PTMG) and a liquid crystalline copolyester (LCP), poly(benzoate‐naphthoate), were prepared in a twin‐screw extruder. Specimens for mechanical testing were prepared by injection molding. The morphology of the LCP/PEL blends was characterized under different processing conditions. To determine what conditions were necessary for the development of a fibrillar morphology of LCP, we have studied the effect of processing method (extrusion and injection molding), injection molding temperature (below and above the melting point of LCP), and gate position in the mold (direct gate and side gate). SEM studies revealed that some extensional flow was required for the fibrillar formation of LCP and the fibrillar structure of LCP was controlled by the processing method. The morphology of the blends was found to be affected by their compositions and processing conditions. SEM studies revealed that finely dispersed spherical domains of LCP were formed in the PEL matrix and the inclusions were deformed in fibrils from the spherical droplets with increasing LCP content and injection temperature. The mechanical properties of the LCP/PEL blends were also found to be affected by their compositions and processing conditions. The mechanical properties of LCP/PEL blends were very similar to those of polymeric composite. An attempt was made to correlate the structure of the blends from the scanning electron microscope with the measured mechanical properties. All of the aspects of the morphology were possible to explain in terms of the mechanical properties of the blends. A DSC study revealed that the crystallization of PEL was accelerated by the addition of LCP in the matrix and a partial compatibility between LCP and PEL was predicted. The rheological behavior of the LCP/PEL blends was found to be very different from that of the parent polymers, and significant viscosity reductions were observed in the blend consisting of only 5 wt% of LCP.
The effect of curing of unsaturated polyester resin on the dynamic relaxation time
Authors: Alperstein D. , Narkis M. , Siegmann A. , Binder B. 
Published: December 2004

AbstractThe effect of hot curing of unsaturated polyester resin on the dynamic relaxation time was studied using dielectric measurements along with two dynamic mechanical measurement methods. It was found that the dynamic response during cure was a material frequency dependent property and did not depend on the measurement method. All relaxation times, measured during cure, by all three measurement methods used, converged to a single equation: τ(t)av=atbwheret= curing time,a, b=constants. The increase of the relaxation time during cure followed the same trend as a friction factor, which was found to increase with conversion. The crosslinking density was found to increase slowly with conversion, while the relaxation time increased exponentially. These two different modes of behavior during cure explain the high resolution of dynamic measurements as a cure monitoring tool, which can easily detect small curing changes. This behavior of the relaxation time was explained by the sharp rise of activation energy due to a parallel decrease of free volume at high conversion.
Effect of extensional viscosity and wall quenching on modeling of mold fillings
Authors: Moller James C. , Lee Daeyong , Kibbel Bradley W. , Mangapora Leslie 
Published: December 2004

AbstractA combined finite element and finite difference approach has been developed to include the capability to model fluid and thermal transport for the filling of a die cavity by a fluid that has differing sensitivities to extensional and shear deformation rates. This is referred to here as a dual viscosity fluid. For the case of mildly convergent or divergent quasi two‐dimensional flows, a viscosity model is described that has such a dual‐viscosity character and in which shear and extension rate sensitivities are nearly separated. Filling simulation results can be generated rapidly in a modest computational environment. The range of cavities and molding materials that may be modeled realistically is widened by the inclusion of a dual viscosity model. The effect of wall quenching (freezing) increased with decreasing filling rate, while the effect of dual viscosity increased with increasing filling rate.
Principal directions as a basis for the evaluation mixing
Authors: Bigio David I. , Conner James H. 
Published: December 2004

AbstractMeasures of mixing for laminar flow are developed from basic principles of continuum mechanics for infinitesimal rates of stretch. The entire analysis is performed from the basis of the eigenvalues and principal directions of the appropriate flow tensors. Measuring the rate of line growth, where the line marks the interface between two miscible fluids, in terms of the major eigenvalue provides a direct measure of the maximum rate of mixing. Two efficiency measures for mixing are derived in terms of the eigenvalues and their directions. The creation efficiency of the magnitude of the major eigenvalue as a function of the energy input into the flow field is evaluated. The orientation of the interface to the principal direction qualifies the mixing efficiency in laminar flow. The new theory is used to analyze two‐dimensional and three‐dimensional channels. The results demonstrate not only the continuum measures for mixing but also extend our present understanding on mixing and provide future directions.
The self‐wiping co‐rotating twin‐screw extruder as a polymerization reactor for methacrylates
Authors: Jongbloed H. A. , Kiewiet J. A. , Van Dijk J. H. , Janssen L. P. B. M. 
Published: December 2004

AbstractThe self‐wiping co‐rotating twin‐screw extruder was studied as a reactor for two polymerizations in bulk: the homopolymerization of n‐butylmethacrylate and the copolymerization of n‐butylmethacrylate with 2‐hydroxypropylmethacrylate. The influence of the extrusion parameters on the product was analyzed. With both reactions, conversions up to 95% were obtained. Nevertheless, a significant difference was observed in the working domain of both polymerizations, in which a stable reactive extrusion process could be attained wherein the discharge rate is constant and equals the feed rate. In the case of the relatively fast copolymerization, both the throughput and the screw rotation rate could be raised without endangering the stability of the process. This was not the case for the homopolymerization studied. It was determined that the stability of the process depends on the reaction velocity and the product viscosity. Within the boundaries of the working domain, the molecular weight could be influenced by adjustments of the extrusion parameters.
Determination of fracture toughness in rubber modified glassy polymers under impact conditions
Authors: Bernal Celina R. , Frontini Patricia M. 
Published: December 2004

AbstractThis paper analyzes the applicability of simple indirect methods for determining the impact fracture toughness of ductile polymers. Commercial rubber‐modified thermoplastics were assayed. Tests were carried out in a Charpy impact pendulum on sharp notched samples at room temperature and at 80°C. Specimens of different geometric relationship, were considered. Thickness, side grooving and span effects were investigated. Reslts appear to be geometrically and strain rate independent.ABS and high impact polystyrene samples exhibited a whitening effect due to craze formation through the whole fracture surface, indicating that stable crack propagation was occurring. Medium impact polystyrene, however, exhibited combined stable and unstable crack propagation mode, displaying shiny and dull zones on the surfaces of the broken samples. Data were analyzed following the corrected elastic and the Jc methods. The fit quality was evaluated by statistical analysis. In addition, two new methods were tried: the methods proposed by Vu‐Khanh and De Charentenay for semiductile behavior and by Vu‐Khanh for ductile behavior. The equivalencies between the different critical parameters that arose from the methods are compared and analyzed.
Dynamics of liquid‐liquid mixing: A 2‐zone model
Authors: Janssen Jos M. H. , Meijer Han. E. H. 
Published: December 2004

AbstractThe development of multiphase liquid‐liquid morphologies during mixing at small Reynolds numbers has been modeled. The mixing process is divided into (i) stretching of dispersed drops. (ii) breakup of the liquid threads formed, and (iii) coalescence of the final droplets upon collision. Rules and criteria of the distinct processes are presented and combined to a general 2‐zone mixing model simplifying the flow field into a sequence of alternating “strong and weak zones.” In a “strong zone,” dispersed drops and threads are stretched unless their radius is too small; meanwhile, the stretching threads might break up into droplets. In the subsequent “weak zone,” the remaining threads may disintegrate while any drops present may coalesce. After passing a number of zones, stretching, breakup, and coalescence lead to a dynamic equilibrium that could be considered as the “final” morphology. Using the 2‐zone mixing model, the influence of material parameters and processing conditions on the morphology has been studied. Interestingly, increasing either viscosity (dispersed or continuous phase) yields a finer morphology due to the delay of thread breakup, allowing for further stretching and suppression of coalescence.
A hybrid numerical technique to model 3‐D flow fields in resin transfer molding processes
Authors: Friedrichs B. , Güçleri S. I. 
Published: December 2004

AbstractA hybrid two‐/three‐dimensional solution technique is presentedto model 3‐D flow fields in resin transfer moeling using Darcy's low. The 3‐D flow field is only solved for regions where all three velocity components are significant, thus largely reducing the number of unknowns. Elsewhere, the commonly used 2‐D approximation for flow in thin gaps between plates is employe.d The method is applied to regions where the flow splits, such as T‐joints. Because of the uncertainties associated with an accurate determination of the permeability in these regions, a simplified decompled procedure is procesed, which reduces the computational complexity. In this procedure, the flow front is advanced using the 2‐D formulation. The 2‐D formulation also provides the boundary conditions for the subsequent computation of the 3‐D flow field without feedback of flow field information to the 2‐d model. The governing equations are solved using boundary fitted coordinate systems (BFCS) together with the finite difference method (FDM). Numerical as well as algebraic grid generation and domain decomposition are employe dto generate grids that always concide with the continuously deforming and enlarging flow domain. Results that include the trackingof numerical tracer particles to visualize the three‐dimensionality of the flow field are presented for isothermal flow of a Newtonian fluid through a T‐joint. This detailed flow field description is expected to form the basis for a rather accurate simulation of quantitities that largely depend on the fluid particle pathlines, such as the degree of cure. The method is also extendable to shear‐thinning fluids as well as to 3‐D flow in the vicinity of the flow front.