bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase separation in epoxy resin‐reactive dendritic hyperbranched polymer blends
Authors: Plummer Christopher J. G. , Mezzenga Raffaele , Boogh Louis , Månson Jan‐Anders E. 
Published: April 2004

AbstractEquilibrium phase diagrams in composition‐conversion space have been calculated for stoichiometric blends of an epoxy resin with a diamine hardener and dendritic hyperbranched polymers, to which various numbers of epoxy groups have been grafted. An attempt has been made to incorporate both the effects of the polydispersity of the resin and the reactivity of the functionalized hyperbranched polymers for any given value of the interaction parameter. However, if the reactivities of all the epoxy groups are comparable, the presence of a highly functionalized modifier is expected to lead to a reduction of the gel point conversion and a narrowing of the composition‐conversion window available for cure induced phase separation. The experimental cloud point data are consistent with the model, although they sugget that the functionalized hyperbranched polymers may be significantly less reactive than the resin. Moreover, in the present system, the influence of functionalization on the phase behavior is also strongly linked to the accompanying changes in the interaction parameter.
Effects of inhibitors and retarders on low temperature free radical crosslinking polymerization between styrene and vinyl ester resin
Authors: Li Ling , Lee L. James 
Published: April 2004

AbstractMany composite manufacturing methods are room temperature processes, which require the resins to be cured at low temperatures. Examples are Seemann Composite Resin Infusion Molding Process (SCRIMP)—a vacuum assisted resin transfer molding (VARTM) process, hand lay‐up and spray‐up. Vinyl ester resins have been widely used in this type of processes because of their versatility as a composite matrix. Low temperature polymerization between styrene and vinyl ester tends to be complex because of the presence of different curing agents. This paper reports on (1) the effects of a promoter (cobalt naphthenate) on the initiatin at low temperatures, and (2) the effects fo a retarder (2,4‐pentanedione) and an inhibitor (1,4‐benzoquinone) on the pot life, gel time, and cure kinetics. A differntial scanning calorimeter (DSC) and a Fourier transform infrared (FTIR) spectrometer were used to investigate the reaction kinetics of vinyl ester resins. The influence of the retarders and inhibitors on the rheological changes of the resin during curing was also studied using a Rheometris Dynamic Analyzer (RDA).
Mechanical behavior of a semicrystalline polymer before necking. Part 1: Characterization of uniaxial behavior
Authors: Brusselle‐Dupend N. , Lai D. , Feaugas X. , Guigon M. , Clavel M. 
Published: April 2004

AbstractThe behavior of the semicrystalline polymer polypropylene (PP) was studied in the pre‐necking domain. Mechanical tests were performed to characterize its viselastic and its viscoplastic behavior. The usual approach for studying metals was adopted to investigate the effect of heterogeneities caused by spherulitic morphology. The macroscopic stress was split into an effectie stress and a back stress so that the interactions between crystalline lamellae and amorphous phases could be taken into account. An understanding of the relationship between microstructure and the macroscopic strain mechanisms was developed.
Reactive compatibilization and in‐line morphological analysis of blends of PET and a thermotropic liquid crystalline polymer
Authors: Qiao Fang , Migler Kalman B. , Hunston Donald L. , Han Charles C. 
Published: April 2004

AbstractThe reactive extrusion of a compatibilized polyethylene terephthlate and thermotropic liquid crystalline copolyester blend system is investigated via in‐line optical microscopy and light scattering. The reactivity, morphology, rheological behavior and mechanical properties were studied. It was found that a droplet‐fiber transition in the liquid crystalline polymer can occur, and this transition is dependent upon the reactivity, the viscosity ratio of the blend components and the shear fields. The fibers are strongly oriented along the flow direction when specific processing conditions are met. An enhancement in the mechanical properties correlates with the morphology. The formation, deformation and stability of the fiber microstructure under different flow conditions are discussed.
Molecular structural evolution in crosslinking low density polyethylene–trimethylolpropane trimethacrylate systems
Authors: Tai Horng‐Jer 
Published: April 2004

AbstractA Monte Carlo simulation algorithm for investigation the structural growth in a polymer‐polyfunctional monomer system and the method to obtain the required simulation parameters are proposed. Combining the Monte Carlo sampling technique and swell ratio experiments, the molecular structural evolution in crosslinking LDPE‐TMPTMA systems is explored. The crosslinking level can be effectively promoted at high TMPTMA concentrations and at high cure temperatures. With increasing overall crosslinking density, gelation occurs at lower degree of conversions; the gel corsslinking density, increases: the TMPTMA densities in both sol and gel fractions also increase; while the sol polymer molecular weights and the sol crosslinking density decrease. The implications of the simulated results to the processing of LDPE‐TMPTMA compounds are also discussed.
Improving polymer blend dispersion in mini‐mixers
Authors: Marić Milan , Macosko Christopher W. 
Published: April 2004

AbstractThe simple cup and rotor mini‐mixer, designed to blend very small polymer batches (0.3 g, MiniMAX), was compared to larger lab scale extruder (5 g, DACA): and a 16 mm co‐rotating twin screw (300 g/hr. PRISM). All were compared at the maximum shear rate in the cup and rotor mixer, 110 s−1. Particle sizes of poly(propylene) [PP] dispersed in poly(styrene) (80 wt% PS) were meausred by dissolving the PS, filtering and using scanning electron microscopy. The 16 mm twin screw gave somewhat smaller particle sizes than the lab scale mixers (102 μ vs 1.7 and 1.9 μ), but dispersion in the cup and rotor mini‐mixer was much poorer. Simply adding three steel balls to the cup as suggested by Maréchal et al. (Polym Networks Blends, 1997) greatly improved the dispersion (1.8 μm). Modifying the rotor design to allow recirculation yielded similar improvement. The benefit of adding three balls was confinmed in blends of low viscosity poly(dimethyl siloxane) PDMS in PS. When anhydride terminal PDMS was blended with amino terminal PS, the particle sizes were much smaller (10 vs. 0.3 μm) and the differences between the three versions of the cup and rotor were much less pronounced.
Drawing in high pressure CO2—a new route to high performance fibers in memory of late Roger Porter
Authors: Hobbs Terry , Lesser Alan J. 
Published: April 2004

AbstractIn this paper, we introduce a new draw technique for polymer orientation and apply it to different polymer fibers: poly(ethylene terephthalate) or PET, nylon 6,6, and ultra‐high molecular polyethylene (UHMWPE). In this technique, a polymer is drawn uniaxially in supercritical CO2 using a custom high‐pressure apparatus. This technique can be used in replacement of a traditional drawing process or as a post‐treatment process. With PET, the technique is not effective at temperatures at or below 130°. In contrast, the process is highly effective for nylon 6,6 where CO2 drawn fibers show significantly higher crystallinity and orientation along with improved mechanical properties. While the fibers are plasticized, the drawability of the fibers is only slightly dependent on temperature. High pressure CO2 drawing of ultrahigh molecular weight polyethylene (UHMWPE) fibers is equally effective. Commercial high performance fibers can be drawn up to a ratio of 1.9 in asecond stage, resulting in large increases in tensile modulus and small improvements in tensile strength.
Melting and densification of thermoplastic powders
Authors: Kontopoulou M. , Vlachopoulos J. 
Published: April 2004

AbstractThe present work focuses on the transformation of a loosely packed, low density powder compact, to a fully densified polymer part, when processed at temperatures above the melting (or glass transiton) point of the polymer. The purpose of this study is to dlucidate the mechanisms involved in the process and to examine the applicability of models available in the materials science literature for the description of the overall densification of molten polymer particles. The evolution of density as a function of time during sinter‐melting was measured experimentally using a heating oven. The results revealed that the overall process consists of two stages. The first stage involves particle coalescence, which depends on viscosity, surface tension and powder properties. During this stage air pockets, which eventually become bubbles, are entrapped inside the melt. The second stage involves the diffusion controlled shrinkage and eventual disapperance of the bubbles. The experimental results were compared to models commonly used for the densification of particulate compacts in the ceramics, glass and metals processing literature. Application of models based solely on viscosity and surface tension phenomena, can describe satisfactorily the process until the point where closed pores (bubbles) form. Abubble dissolution model has been successfully applied to provide predictions of density as a fuction of time for late stages of densification.
Toughened carbon fiber prepregs using combined liquid and preformed rubber materials
Authors: Hayes Brian S. , Seferis James C. 
Published: April 2004

AbstractModel epoxy resin formulations were modified with defferent concentrations of liquid rubber and preformed crosslinked rubber particles and impregnated into unidirectional carbon fibers. The liquid rubber was used to increase the mode I fracture toughness of the interlayer toughened prepreg systems, which already have high mode II fracture properties. In this paper it is shown that the mode II fracture toughness is not sacrificed by the incorporatiom of carboxyl terminated butadiene acrylonitrile rubber (CTBN) in the matrices, while mode I fracture toughness can be increased by as much as 100%.
In situ fibrillar reinforced PET/PA‐6/PA‐66 blend
Authors: Evstatiev M. , Fakirov S. , Schultz J. M. , Friedrich K. 
Published: April 2004

AbstractTernary fibrillar reinforced blends are obtained by melt‐blending of poly(ethylene terephthalate) (PET), polyamide 6 (PA‐6) and polyamide 66 (PA‐66) (20/60/20 by weight) in the presence of a catalyst, followed by cold drawing of the extruded bristles to a draw ratio of about 3.4 and additional annealing of the drawn blend at 220 or 240°C for 4 or 8 h. The blend samples are studied by DSC, X‐ray diffraction, SEM, and static and dynamic mechanical testing (DMA). SEM and DMA show that PA‐6 and PA‐66 form a homogeneous, continuous matrix in which PET regions are dispersed. X‐ray and DSC measurements of the drawn and annealed at 220°C samples suggest mixed crystallization (solid solubility) of PA‐6 and PA‐66, and cooperative crystallization of PET with the two polyamides. After annealing at 240°C (above the melting point of PA‐6 and below that of PET), the polyamide matrix becomes partially disoriented, while the oriented, fibrillar PET is preserved and plays the role of a reinforcing element. The DSC results for the same samples suggest in situ generation of an additional amount of copolymer. This additional copolymerization, together with that generated during blend mixing in the extruder, improves the compatibility of the blend components (mostly at the PET‐polyamide interface) and alters the chemical composition of the blend.
Thermo‐electric behavior (PTC) of carbon black–containing PVDF/UHMWPE and PVDF/XL‐UHMWPE blends
Authors: Mironi‐Harpaz I. , Narkis M. 
Published: April 2004

AbstractThis paper describes the structure and electrical performance of PTC/NTC (positive temperature coefficient/negative temperature coefficient) effects and their reproducibility upon healing/cooling cycles. The following three‐component blends were studied: PVDF/UHMWPE/CB, PVDF/XL‐UHMWPE/CB and γ‐irradiated compression molded plaques of these blends. Carbon black (CB) particles are attracted to the UHMWPE (ultra high molecular weight polyethylene) and XL (cross‐linked)UHMWPE particles, which constitute the dispersed phase in the PVDF (polyvinylidene fluoride) matrix, but practically cannot or only very slightly penetrate them because of their extremely high viscosity. A double‐PTC effect was exhibited by all unirradiated samples. Irradiation of compression molded PVDF/UHMWPE/CB plaques does not add to their already outstanding reproducibility, and it results In a wide single‐PTC effect. Irradiation of compression molded PVDF/XL‐UHMV/PE/CB plaque, slabilizes their structure upon heating/cooling cycles and thus makes them reproducible PTC/NTC materials, still exhibiting a double‐PTC effect. The carbon black concentrations studied in this report are extremely low (< 2 phr CB) in comparison to other literature reports.
Morphology of polymer blends in the melting section of co‐rotating twin screw extruders
Authors: Potente H. , Bastian M. , Bergemann K. , Senge M. , Scheel G. , Winkelmann Th. 
Published: April 2004

AbstractThe properties of polymer blends are largely determined by the morphological structure of the polymer combinations that are involved. In terms of extruder design, this means it is necessary to have models available for estimating the development of the morphology over the length of the screws. Since significant morphological changes are observed in the melting section, in particular, is it necessary to analyze not only the plasticizing process for binary material combinations but also the initial formation and further development of the morphology in this section of the extruder. In the framework of this study, experimental investigations were conducted into polypropylene/polyamide 6 (PP/PA6) blends with small components (by weight) of the disperse PA phase. Apart from varying the process conditions of screw speed and throughput, the viscosity ratio was also varied through the use of two different PP grades. The degree of melting and the development of the morphology over the length of the screws were determined for the individual tests. The study of blend morphology in the melting section reveals key findings that must be taken into account for modeling the initial formation and further development of the morphology. It is very clear that, on the second component, which melts at higher temperatures, a kind of melt film removal occurs at the surface of the granules as they melt. The drops of second component in the melting section, which are directly adjacent to components that have not yet fully melted in some cases, have already assumed dimensions (in the μm range) similar to those that are seen at the end of the extrusion process. This means that, in the melting section of the twin‐screw extruder, no volumes become detached from or are worn off the already‐molten granule surfaces. An evaluation of scanning electron micrographs also shows that, in the melting section of co‐rotating twin‐screw extruders, virtually all the degradation mechanisms that can essentially be distinguished, such as quasi‐steady drop breakup, folding, end pinching and decomposition through capillary instabilities, take place in parallel.
Superposed hydrodynamic disturbances from feeders in a starved flow modular intermeshing co‐rotating twin screw extruder
Authors: Kim Eung Kyu , White James L. 
Published: April 2004

AbstractA process dynamic model of surging in a modular self‐wiping co‐rotating twin screw extruder caused by superposed disturbances from feeders is developed. The changes of output flow rate with time (surging) are predicted for various time dependent input modes such as step function and sinusoidal function inputs into the hopper and other ports part way along the length of the machine.
Effects of rheological properties and processing parameters on ABS thermoforming
Authors: Lee Je Kyun , Scott Chris E. , Virkler Terry L. 
Published: April 2004

AbstractUnderstanding effects of material and processing parameters on the thermoforming process is critical to the optimization of processing conditions and the development of better materials for high quality products. In this study we investigated the influence of both rheological properties and processing parameters on the part thickness distribution of a vacuum snap‐back forming process. Rheological properties included uniaxial and biaxial elongational viscosity and strain hardening and/or softening while processing parameters included friction coefficient, heat transfer coefficient, and sheet and mold temperatures. The Wagner two parameter nonlinear viscoelastic constitutive model was used to describe rheological behavior and was fit to shear and elongational experimental data. The linear viscoelastic properties along with the Wagner model were utilized for numerical simulation of the thermoforming operation. Simulations of pre‐stretched vacuum thermoforming with a relatively complex mold for a commercial refrigerator liner were conducted. The effects of nonlinear rheological behavior were determined by arbitrarily changing model parameters. This allows determination of which rheological features (i.e., elongational mode, viscosity, and strain hardening and/or softening) are most critical to the vacuum snap‐back thermoforming operation. We found that rheological and friction properties showed a predominant role over other processing parameters for uniform thickness distribution.
Viscoelastic properties of reactive and non‐reactive blends of ethylene‐methyl acrylate copolymers with styrene‐maleic anhydride copolymer
Authors: Bayram G. , Yilmazer U. , Xanthos M. 
Published: April 2004

AbstractThe effects of compatibilizing reactions on the viscoelastic properties and morphology of ethylene‐methyl acrylate copolymers were studied. Potentially reactive blends of styrene‐maleic anhydride copolymer (SMAH) and a terpolymer of ethylene/methyl acrylate/glycidyl methacrylate (E‐MA‐GMA) were compared with a non‐reactive blend of SMAH and an ethylene/methyl acrylate (E‐MA) copolymer with similar rheological properties. Melt mixing was carried out in a batch mixer and in a co‐rotating twin screw extruder. The morphology of the reactive blends showed smaller domain sizes than the non‐reactive blends, and the viscoelastic properties of the blends were very different. The storage and loss moduli and the complex viscosity of the reactive blends were greater than those of non‐reactive blends. The reactive blends had a higher zero shear viscosity, plateau modulus and mean relaxation time than their non‐reactive counterparts, indicating a higher degree of melt elasticity. The melt elasticity was maximum at 25% functionalized ethylene‐methyl acrylate concentration.
Rheological analysis of polyvinyl butyral near the glass transition temperature
Authors: Juang Yi‐Je , Lee L. James , Koelling Kurt W. 
Published: April 2004

AbstractIn many polymer manufacturing operations, the material is processed near the glass transition temperature (Tg). Examples are thermoforming, blow molding, film blowing, hot embossing, forging, plastic welding, and de‐airing in safety glass lamination. In these processes, solid‐like behaviors such as strain hardening and yielding play important roles. These material properties cause the material to flow (or deform) in a way that substantially differs from a polymer melt. In order to understand the flow behavior near the Tg, polyvinyl butyral (PVB), a rubbery polymer used in safety glass lamination, was studied in this work. The flow properties of the polymer above the Tg were characterized by using both shear and elongational rheometers, and a tensile tester. The measured flow properties were described by a viscoelastic constitutive model.
Orthotropic elastic constants for polyimide film
Authors: Cho Seo Hyun , Kim Gene , McCarthy Thomas J. , Farris Richard J. 
Published: April 2004

AbstractThe orthotropic constants of polyimide film have been characterized using the theory of elasticity of an anisotropic material. Experimental techniques coupled with the mechanics of orthotropic materials are used to determine all 9 independent orthotropic elastic constants (3 tensile moduli, 3 shear moduli, and 3 Poisson's ratios) and 3 coefficients of thermal expansion. Vibrational holographic interferom‐etry is used to determine the orthotropic axes of symmetry. For this polyimide film, the two principal axes coincided with the machine and transverse directions. It is also used to evaluate the 2 in‐plane Poisson's ratios by measuring residual stresses in 2‐D and 1‐D square membranes. Using other instruments such as a high pressure gas dilatometry apparatus, a tensile tester, a pressure‐volume‐temperature apparatus, a thermornechanical analyzer, and a torsion pendulum, the 7 other orthotropic constants and the 3 coefficients of thermal expansion are determined.
Crystallization kinetics of poly(trimethylene terephthalate)
Authors: Chuah Hoe H. 
Published: April 2004

AbstractThe bulk isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) was studied using a differential scanning calorimeter. Avrami's theory was used to analyze the data. Based on crystallinity growth rate, Avrami rate constant, K, and crystallization half‐time, PTT's crystallization rate is between those of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) when compared at the same degree of undercooling. PBT has the highest crystallization rate with K in the order of 10−2 to 10−1 min−n. It is about an order of magnitude faster than PTT at 10−3 to 10−2 min−n, which in turn is an order of magnitude faster than PET with K of 10−4 to 10−2 min−n. Contrary to previous reports (PTT was not included in the study) that aromatic polyesters with odd numbers of methylene units were more difficult to crystallize than the even‐numbered polyesters, PTT did not fit in the prediction and did not follow the odd‐even effect.
The effect of talc on the crystal orientation in polypropylene/ethylene‐propylene rubber/talc polymer blends in injection molding
Authors: Obata Yutaka , Sumitomo Takashi , Ijitsu Toshikazu , Matsuda Masatoshi , Nomura Takao 
Published: April 2004

AbstractThe effect of tale on the b‐axis orientation of the polypropylene crystals in polypropylene (PP)/ethylene‐propylene rubber (EPR)/talc blends of injection moulding was examined using the X‐ray diffraction method. The b‐axes of the PP crystals were most strongly oriented in the thickness direction for the injection molded PP/EPR/talc blends. The b‐axis orientation in the thickness direction of injection moldings was promoted by increasing the concentration of talc, by reducing the particle size, or by purifying the tale. The dependence of the specimens' rigidity on talc content, particle size, and purity was also investigated. The rigidity depended on the degree of b‐axis orientation. The result of our investigated suggest that increasing the orientation of the PP crystals that are near talc particles may improve the rigidity.