bluuebunny/crossref_metadata_2025_split huggingface dataset:
Advances in calculating thermally induced stresses in nonlinear viscoelastic materials
Authors: Schmachtenberg E. , Schoeche N. 
Published: April 2004

AbstractTemperature change can build up tensile stresses into thermoplastic materials, if their thermal expansion is hindered. This paper describes how to calculate those stresses. Because thermoplastic materials are time dependent with respect to temperature and strain, a nonlinear viscoelastic material model is necessary for the prediction of thermal stresses. This paper presents a numerical model that is able to predict thermally induced stresses in dependency on the load history. The calibration as well as the numerical procedures are described. The model is evaluated with a semicrystalline high density polyethylene (HDPE). Finally, a simulation of a screwed joint reveals the importance of this modeling for a more effective use of thermoplastics in the future.
Thermal analysis characterization of fiberglass epoxy prepreg used to join composite pipes
Authors: Mensah Patrick F. , Stubblefield Michael A. , Pang Su‐Seng , Wingard Doug 
Published: April 2004

AbstractThermal characterization of a fiberglass/epoxy prepreg fabric used as the bonding material to join composite‐to‐composite pipes by curing has been investigated. The prepreg material and composite pipes have temperature dependent thermal properties. Thus the resulting boundary value equations are nonlinear and analytical solutions cannot be easily obtained. Finite difference modeling (FDM) and numerical computational techniques were used to solve the one‐dimensional heat conduction with chemical kinetics in the thermosetting material. Temperature distributions and degree of cure within the composite pipe joint are predicted. A Differential Scanning Calorimeter (DSC) in both isothermal and dynamic modes was used to characterize the curing kinetic properties of the prepreg. The result of this characterization is necessary for optimizing the curing process to produce a superior heat activated coupled joint. In addition, to assess the effects of induced thermal stress in the joint, the temperature profile is needed. The methodology employed in this analysis compares favorably with data from experimentation.
Anhydride chain ends functionalization of poly(ethylene terephthalate)
Authors: Sclavons M. , Carlier V. , Legras R. 
Published: April 2004

AbstractThis paper aims at the end‐capping of poly(ethylene terephthalate) (PET) chainends in order to introduce anhydride moieties on this polymer. An acid chloride reactive carrier of anhydride was chosen because it selectively reacts by alkoxy‐dehalogenation with the hydroxyl chain ends of PET. This type of functionalization has already been described and claimed (1–3) on various polymers. However, in the present paper, a solid‐liquid synthesis is reported for the first time: The reaction was performed on solid PET powder swollen in a solvent of the trimellitic anhydride chloride. This new reaction method prevents the polymer from degrading. This point is supported by parallel studies of similar reactions performed in the melt and in solution.
Influence of molecular structure on the rheological and processing behavior of polyethylene resins
Authors: Kazatchkov I. B. , Hatzikiriakos S. G. , Bohnet N. , Goyal S. K. 
Published: April 2004

AbstractThe rheological and processing behavior (melt fracture performance) of linear lowdensity polyethylenes (LLDPEs) is studied as a function of both the weight average molecular weight (Mw) and its distribution (MWD). A number of LLDPE resins having different molecular characteristics were tested, with essentially one characteristic (Mw or MWD) changing at a time. The first series of resins consisted of nine samples having a wide range of polydispersities (3.3–12.7) and nearly constant Mw and short chain branching. The second series had six resins with varying Mw (51,000–110,000) but fixed MWD (about 4). The influence of Mw and MWD on the viscosity profiles, linear viscoelastic moduli as expressed by means of a discrete spectrum of relaxation times, extrudate swell, and melt fracture behavior for these resins is reported. Correlations between the molecular characteristics of the resins and their rheological and processing behavior are also reported. It is found that for a given molecular weight, the optimum melt fracture performance is obtained at a specific polydispersity value, and it is characterized by a minimum relaxation time for the resin defined in terms of recoverable shear.
Shear viscosity of nylon 6 melts reinforced with microfibrous calcium silicate hydrate
Authors: Tanaka Hideho , Watanabe Kunio 
Published: April 2004

AbstractSteady shear viscosity of nylon 6 melts reinforced with xonotlite, microfibrous calcium silicate hydrate (6CaO · 6SiO2 · H2O), is investigated. The highly filled nylon 6 melt tends to exhibit a yield value, resulting in remarkable viscosity increase particularly at low shear rates. Addition of the xonotlite significantly increases activation energy of viscous flow of the nylon 6 melt, leading the viscosity to be strongly temperature dependent. Comparisons with the melts filled with glass fibers and wollastonite are made. Flow‐induced orientation becomes more important at low volume fractions. Shortening of the xonotlite during shear flow measurement can also be observed.
Optical and acoustical investigation for plastic deformation of isotactic polypropylene/ethylene‐1‐hexene copolymer blends
Authors: Yamaguchi Masayuki , Nitta Koh‐Hei 
Published: April 2004

AbstractThe effects of morphology on mechanism of plastic deformation are investigated for binary blends of isotactic polypropylene and rubbery ethylene‐1‐hexene copolymers. In this work, plastic deformation developed during elongation is investigated by measuring light transmittance, electron microscopy, and ultrasonic propagation in the temperature region between 298 K and 353 K. It is found that the compatible blends hardly show stress‐whitening at any temperature, whereas the incompatible blends show distinct stress‐whitening below 333 K. Furthermore, microscopic defects such as microvoids and crystalline defects are found to be precursors for crazing which are origin of the stress‐whitening.
Polybenzimidazole nanofiber produced by electrospinning
Authors: Kim Jong‐Sang , Reneker Darrell H. 
Published: April 2004

AbstractNanofibers of aromatic heterocyclic PBI (poly(2,2′(m‐phenylene)‐5,5′ bibenzimidazole)) polymer were made by an electrospinning process. The diameter of the fibers was around 300 nanometers. A liquid jet of a polymer solution, formed when electrical force overcame surface tension, stretched and dried as the solvent evaporated. The resulting electrically charged nanofibers were attracted to and collected on a rotating cylinder covered with aluminum foil that was electrically grounded. The fibers were collected in non‐woven sheets about 20 centimeters wide and 100 centimeters long, with a compressed thickness of a few tens of microns. The mass per unit area of the nonwoven sheets was 15 to 50 g/m2. The nonwoven fabric of PBI nanofibers was treated with sulfuric acid, and then washed, dried and heated to improve its strength. Optical microscopy showed that electrospun PBI nanofibers fibers were birefringent. Other morphological features of these fibers were observed with scanning electron microscopy, transmission electron microscopy and atomic force microscopy.
Drawing of high density polyethylene tube: Effect of different cooling conditions
Authors: Ulas I. 
Published: April 2004

AbstractA method of producing biaxially oriented high density polyethylene tube is described where some of the deformation parameters may be controlled by a post mandrel cooling bath application. Experimental results show that dimensional stability of the drawn products primarily depend on uniform temperature distribution around the tube circumference. This research gives a clear understanding of the post mandrel deformation process and shows that natural cooling conditions may lead to inhomogeneous products having properties significantly different from water cooled products.
Solvent‐free generation of poly(vinyl acetals) directly from poly(vinyl acetate)
Authors: O'Neill Mark L. , Newman Deborah , Beckman Eric J. , Wilkinson Steve P. 
Published: April 2004

AbstractThe simultaneous methanolysis and butryalization of poly(vinyl acetate) was conducted via the reaction of methanol and butyraldehyde with polyvinyl acetate under batch conditions at temperatures from 70°C to 90°C at the vapor pressure of the reactants. It was found that use of an acid catalyst allowed for the methanolysis to be the rate limiting step of a simultaneous methanolysis‐butyralization reaction, minimizing the buildup of alcohol repeat units in the polymer during the reaction. As such, use of an excess of aldehyde was counterproductive in that it served to dilute both the methanol and the acetate groups in the polymer phase, lowering the overall rate of the reaction. With 20% stoichiometric excesses of methanol and butyraldehyde, it was possible to produce poly(vinyl butyral) directly from poly(vinyl acetate) with very low residual acetate and overall conversions equivalent to commerical samples. Further, carbon dioxide was evaluated as a reversible plasticizer for polyvinyl acetate during methanolysis. Results at various pressures were consistent with the expectation that the presence of CO2 would lower the reaction rate, primarily because of dilution of reactants in the CO2‐swollen polymer phase. Finally, it was shown that the simultaneous reaction procedure can be used to generate polyvinyl acetals from a variety of aldehydes.
Reinforcement of polyamide 6 with thermotropic liquid crystalline polymer
Authors: Kurokawa M. , Nagai S. 
Published: April 2004

AbstractThe in‐situ composites of polyamide 6 (PA 6)/liquid crystalline polymer (LCP) were investigated from the standpoint of fibrillation of LCP to develop a new high performance gear material for heavy load use that is superior to conventional plastic gears made of polyacetal (POM). LCP used was a wholly aromatic copolyester. PA 6 was chosen as the matrix polymer because of its excellent fatigue resistance. Extrusion of PA 6 added with LCP from 10 to 30 vol% was carried out at a temperature between 260 and 290°C by a twin screw extruder and take‐up equipment. Insitu fibrillation of LCP droplets, which were dispersed in PA 6 matrix, took place during the process. Injection molding of the composites was followed at a temperature below the softening point of LCP fibrils so as to keep the fibrils as extruded. Key factors for fibrillation of LCP were found as follows: (1) control of stress relaxation of LCP when the melt passes through the die‐head, (2) the optimum temperature of nent, (3) the optimum LCP content, and (4) addition of a small amount of 3rd component. A gear made of in‐situ composite of PA 6/LCP (30 vol%) added with 2‐functional epoxy resin (2.5 phr) was found to bear a load about 1.2 times heavier than a POM gear.
Influence of molecular parameters on material processability in extrusion processes
Authors: Nichetti D. , Manas‐Zloczower I. 
Published: April 2004

AbstractA viscosity model showing a direct correlation between molecular weight distributions and shear thinning behavior of polymeric melts was used in 3D numerical simulations of an extrusion process. The equipment analyzed was a single screw extruder with an annular die attached. The material of choice in the simulations was polystyrene in a range of molecular weights and degrees of polydispersity. The influence of material parameters (molecular weight and polydispersity) on the system operating point, power consumption and residence time distribution was analyzed. The results were generalized and a window of processing conditions for resins with different properties was analyzed. The effect of blending homologous polymers with different molecular parameters on material processability was also presented. The model can be extended to other materials and various processing equipment.
A new method for estimating the cellular structure of plastic foams based on dielectric anisotropy
Authors: Nagata Shinichi , Koyama Kiyohito 
Published: April 2004

AbstractThe characterization of the cellular structure of plastic foams has long been of importance to investigate their physical properties. We have been developing an instrument that measures the orientation of seat materials based on their dielectric anisotropy. It is demonstrated by electromagnetic theory that composite materials with an island‐sea structure show a macroscopic anisotropy of dielectric constant because of the shape of islands, even if both the islands and sea are dielectrically isotropic themselves. The orientation based on the dielectric anisotropy caused by the shape of cells was investigated for the polystyrene by using our microwave cavity resonator method. From this data, a better manufacturing condition to minimize the thermal shrinkage was derived. The manufacturing condition was taken as extrusion rate, foaming temperature and die gap. The shape of cells of polystyrene foams was estimated using the derived equations, which express the maximum and minimum dielectric constant of whole composite materials as a function of the eccentricity of their ellipsoidal islands and the volume fraction and the dielectric constant of each materials in the islands‐sea structure.
Polypropylene reactor blends: Composition evaluation by analytical TREF
Authors: Zacur R. , Goizueta G. , Capiati N. 
Published: April 2004

AbstractThe molecular structure of a polypropylene (PP) blend, of the type referred to commercially as “impact polypropylene copolymer” (IPC), was studied and a procedure to determine its main component composition developed. The constituent species of the whole IPC, PP and ethylene‐propylene copolymers (EPC), were separated by step elution analytical Temperature‐Rising Elution Fractionation (TREF). The corresponding fraction compositions were calculated as percent areas of the fractogram. Since the EPC elution signal overlaps that of the homopolymer, an independent determination of pure PP fractions has to be performed in order to subtract its effect from the IPC profile. Thermal and molecular analysis of the recovered fractions by Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC), and spectroscopic analysis by FTIR and 13C‐NMR supported the necessary assumptions for a good estimation of the composition.
One‐line measurement of the residence time distribution in screw extruders
Authors: Hu Guo‐Hua , Kadri Ilham , Picot Claude 
Published: April 2004

AbstractA fluorescence monitoring device was constructed to measure in real time the residence time distribution (RTD) function in screw extruders. Its centerpiece was an optical fiber probe capable of transmitting optical excitation energy to the processed flow stream and detecting the subsequent fluorescence emission. The source of fluorescence emission was an anthracene‐bearing substance that was injected to the flow stream as a pulse (tracer) in very small amounts. This device was validated against an off‐line ultraviolet spectrophotometer and self‐checked as well. In addition to its great sensitivity to fluorescence emission and ease of implementation on an extrusion line, this device could be used to monitor in real time subtle variations of an extrusion operation. The influence of the nature of anthracene‐bearing compounds on the measured distribution and the effects of processing parameters on the RTD function were also investigated.
Thermal analysis of vectra B950 liquid crystal polymer
Authors: Chung Tai‐Shung , Cheng Min , Pallathadka P. K. , Goh Suat Hong 
Published: April 2004

AbstractThe melting and crystallization behavior of Vectratm B950, a random liquid crystalline copoly(ester amide), was studied by differential scanning calorimetry (DSC). Nonisothermal experiments showed the existence of some interesting and peculiar transition behavior, which may depend on the crystallization conditions (cooling rate). In isothermal experiments, both the thermal and crystallization behavior have been studied as functions of annealing temperature and annealing time. Different thermal behaviors were observed, indicating the possibility of multiple states of mesophase aggregation In addition, the thermal decomposition of Vectra B950 was also studied by TGA‐FTIR in both nitrogen and air environments. A single‐stage decomposition process was found when heating in nitrogen atmosphere, and the decomposition is due to the easter linkage rupture. A double‐stage decomposition process was found when heating in air, and the decompositions are mainly due to the ester linkage rupture for the first decomposition step and the oxidative reaction for the second decomposition step. Annealing slightly changes the decomposition composition occuring in the early stage of thermal degradation.
Influence of the additive type and modification on the properties of blends of polyamide‐6 with poly(styrene‐co‐maleic anhydride)
Authors: Kelnar I. , Fortelný I. , Stephan M. , Jakisch L. 
Published: April 2004

AbstractAddition of rigid poly(styrene‐co‐maleic anhydride) (SMA) to a polyamide‐6 (PA‐6) matrix leads to a system with increased stiffness and unchanged toughness as a consequence of absorption of deformational energy by the plastic deformation of brittle inclusions together with the matrix. The range of properties of both components, where this effect occurs, was studied. In addition to the use of various PA‐6 and SMA types, PA‐6 was also modified with epoxy resin, as well as SMA with liquid rubber bearing amino groups. Owing to the crosslinking ability of both modifiers, the influence of the changed deformability of blend components was demonstrated. Simultaneous influencing of rheological properties and reduction of the amount of reactive groups usable for the in situ compatibilizer formation make it possible to vary the size of dispersed SMA particles and the interfacial adhesion. Thus, a more comprehensive insight into the behavior of ductile‐brittle blends is gained. As SMA and modifiers have negative effect on the PA‐6 crystallinity, comparison of the obtained data with model calculations is difficult.
Morphology development of in situ compatibilized semicrystalline polymer blends in a co‐rotating twin‐screw extruder
Authors: Cartier Hervé , Hu Guo‐Hua 
Published: April 2004

AbstractThis paper concerns the morphology development of in situ compatibilized semicrystalline polymer blends in a co‐rotating, intermeshing twin‐screw extruder, using polypropylene (PP) and polyamide 6 (PA‐6) blends as model systems. The morphology of in situ compatibilized blends develops much faster that of mechanical ones. The size of the dispersed phase (PA‐6) undergoes a 104 fold reduction from a few millimeters to sub‐micron during its phase transition from solid pellets to a viscoelastic fluid. The final morphology is reached as soon as the phase transition is completed, which usually requires only a small fraction of the screw length in a co‐rotating twin screw extruder. Screw profiles and processing conditions (screw speed, throughput and barrel temperature) control the PA‐6's melting location and/or rate, but do not have significant impact on the ultimate morphology and mechanical properties of in situ compatibilized blends. The finding that morphology of PP/PA‐6 reactive blend develops rapidly makes it possible to produce compatibilized PP/PA‐6 blends by the so‐called one‐step reactive extrusion. It integrates the traditionally separated free radical grafting of maleic anhydride onto PP and the compatibilization of PP/PA‐6 into a single extrusion step.
Coalescence in blends of thermoplastic polyurethane with polyolefins
Authors: Wallheinke Katrin , Pötschke Petra , Macosko Christopher W. , Stutz Herbert 
Published: April 2004

AbstractThe coalescence behavior of immiscible blends was determined by annealing the melt without shear. The kinetics and the mechanism of coalescence were observed for blends of thermoplastic polyurethane (TPU) and polyolefins. Two different types of measurements were used to observe coalescence in quiescent melt at the processing temperature. On the one hand, the blend granules were annealed in bulk. The resulting particle sizes were determined by light microscopy and by SEM on particles separated from the blend. On the other hand, thin samples were annealed on a hot stage. Coalescence was observed in situ by light microscopy or static laser light scattering. It was found that the higher viscosity and elasticity ratios between polyethylene and TPU lead to a more pronounced coarsening of the morphology of 80/20 blends than in TPU/polypropylene. It has been shown that the process of reshaping coalescence is one mechanism of coalescence that occurs in quiescent melt. Another mechanism that was directly observed is a “domino effect” where one coalescence process causes the next one.
Modeling of structured polyblend flow in a laminar shear field
Authors: Bousmina M. , Palierne J. F. , Utracki L. A. 
Published: April 2004

AbstractA new model is proposed for describing the negative deviating behavior, NBD, of polymer blends. The model was derived for a telescopic flow of two Newtonian liquids, flowing through a capillary at vanishing Reynolds numbers. The stress field was considered continuous along the radial position, while the velocity field, due to the slippage, was assumed to be discontinuous at each interface between the two adjacent polymeric layers. A special case of an interphase with its own characteristics, thickness and viscosity, was also considered. The model derived here is applicable for Newtonian fluids or for generalized Newtonian fluids (non‐Newtonian) but at constant stress and for morphologies where the phases are structured in oriented layer in the direction of flow or for sheared sandwiches. The capability of the model for describing the NDB behavior was shown on some experimental data of the literature. The main future of the results is that the interlayer slip is caused by the interfacial lubrication due to low viscosity of the narrow interphase. The proposed model was compared with Heitmiller's and Lin's models. Some inconsistencies of Lin's approach have been indicated.
Flow induced deformation of dual‐phase continuity in polymer blends and alloys. Part I
Authors: Lyngaae‐Jørgensen J. , Rasmussen K. Lunde , Chtcherbakova E. A. , Utracki L. A. 
Published: April 2004

AbstractA hypothesis for formation of bi‐continuous phase structures in immiscible polymer blends is proposed. It is based on the observation that a critical volume fraction φcr for the dual continuity of phases may be calculated considering the geometry of the dispersed phase. The knowledge of the form of discrete domains at the volume fractions φ < φcr and the probability that two close neighbor domains will form a strongly fused connection are sufficient to calculate φcr. Furthermore, it can be predicted that φcr should increase with stabilization of the interface. A comparative study showed that an addition of block copolymer may narrow the volume fraction range where bi‐continuous phase structures are formed. Both annealing in the molten state and shearing history influence the measured φcr for the formation of bi‐continuous phase structure in amorphous immiscible polymer blends.