bluuebunny/crossref_metadata_2025_split huggingface dataset:
A step towards understanding the heating phase of laser transmission welding in polymers
Authors: Becker F. , Potente H. 
Published: April 2004

AbstractIn recent years, laser transmission welding has gained in significance by displaying its specific advantages among the established welding processes for thermoplastics. However, a deep understanding of the developed process variants is so far missing. Useful results for temperature development were obtained in cases of high absorption constants by setting up an analytical model by analogy to single‐sided heat impulse welding. Yet there is no physico‐mathematical model considering the different energy conditions for joining parts with various absorption properties. This investigation is a first step towards a deep and detailed insight into the heating phase of the laser transmission welding process. Experimental data for temperature progression was collected for polypropylene. In addition, an analysis of the heat transfer problem using the finite element method showed a good level of agreement with the experimental results.
Particle motion in the fountain flow region during filling of a tube with a viscoelastic fluid
Authors: Kolli Venkata Giri , Ogadhoh Shem O. , Abel Steve M. , Gadala‐Maria Francis , Papathanasiou Thanasis D. 
Published: April 2004

AbstractWe present the results of an investigation of particle motion behind the advancing free surface during the filling of an initially empty tube with a viscoelastic fluid. Particle motion in the vicinity of an advancing free surface (the fountain flow region) is of significance in a number of processes used to form composite materials, notably injection and compression molding. This motion determines, to a large extent, the distribution of the reinforcing phase in the molded part. We show experimentally that an isolated spherical particle moves behind the interface in characteristic orbits, remaining in close proximity to the advancing free surface. This is in stark contrast to what happens in a Newtonian fluid. In that case, the particle is deposited on the tube walls by the fountain flow and never again reaches the faster moving free surface. The particle motion behind the interface is modeled with a combination of equations that describe the advection of the particle due to convective/fountain flow and its lateral migration due to viscoelasticity. This model neglects the finite size of the particle and is thus unable to capture the full details of the observed motion. However, the qualitative agreement between the experimental results and the modeling predictions suggests that the observed particle motion is the result of the combined effect of viscoelasticity and fountain flow.
Structure and mechanical properties of blends of an amorphous polyamide and a liquid crystalline polymer
Authors: García M. , Eguiazábal J. I. , Nazábal J. 
Published: April 2004

AbstractThe structure and the mechanical properties of blends of an amorphous polyamide (PA) and a thermotropic copoly(ester‐amide) (VB) obtained both by direct injection molding (DI) and also by extrusion and subsequent injection molding (EI) have been studied. Besides the usual fibrillar morphology of the skin, fibrillation was also observed in the core of most of the blends. The important synergisms in the modulus of elasticity (20% positive deviations in both blends with 30% and 40% VB contents) and also in the tensile strength (30% and 55% positive deviations in the EI blends at the same compositions) were obtained without the presence of compatibilizer.
A theoretical approach to solid filler dispersion in a twin‐screw extruder
Authors: Berzin F. , Vergnes B. , Lafleur P. G. , Grmela M. 
Published: April 2004

AbstractCompounding of highly filled minerals in a polymeric matrix has never been an easy task. The objective of this work was to build a theoretical model to predict the evolution of dispersion of an inorganic filler in a polymer matrix along a twin‐screw extruder as a function of the screw geometry and processing conditions. We developed a general kinetic model of agglomeration/breakup of the fillers, based on chemical‐like equations. It allowed us to describe the evolution of a population of agglomerates, taking into account the deformation field. When implemented in a flow model of a twin‐screw extrusion process, the model can be used to pinpoint the main effects of twin‐screw operating conditions on dispersion.
Gross melt fracture of polyethylene. II: Effects of molecular structure
Authors: Kim Seungoh , Dealy John M. 
Published: April 2004

AbstractThe effect of molecular structure (MW, MWD and LCB) on the critical tensile stress (σc) for the onset of gross melt fracture (OGMF), proposed in Part I (1) as a material‐dependent criterion for fracture, was determined for a group of polyethylenes varying in structure. These included linear low and high‐density polyethylenes and several materials produced using metallocene and constrained geometry catalysts. It was found that the critical stress is independent of MW, for constant polydispersity but increases with increasing long chain branching and polydispersity. The addition of boron nitride particles had no effect on the σc up to a level of 0.5% by weight.
Combined effect of temperature and thickness on work of fracture parameters of unplasticized PVC film
Authors: Arkhireyeva A. , Hashemi S. 
Published: April 2004

AbstractThe combined effect of temperature and thickness on the essential work of fracture (EWF) parameters for an unplasticized poly(vinyl chloride) (uPVC) film was investigated using double edge notched tension specimens. It was found that for the range of temperatures (23°C to 60°C) and thicknesses (0.15 mm to 0.40 mm) studied here, specific essential work of fracture (we) was independent of temperature at each thickness but increased with thickness at each temperature. It was found that at each temperature, we and its yielding (we,y) and necking/tearing components (we,nt), all increased linearly with increasing thickness. However, whilet we showed no significant variation with respect to temperature, its yielding component (we,y) decreased and its necking/tearing component increased (we,nt) with increasing temperature. It was found that estimated values of we and its components we,y and we,nt via crack opening displacement values were by and large unsatisfactory, being either much higher or lower than the directly measured values.
Hot embossing in microfabrication. Part II: Rheological characterization and process analysis
Authors: Juang Yi‐Je , Lee L. James , Koelling Kurt W. 
Published: April 2004

AbstractThe dynamic shear viscosity and the transient extensional viscosity of polycarbonate (PC), polymethyl methacrylate (PMMA), and polyvinyl butyral (PVB) were measured at temperatures near and far above their glass transition temperatures. The temperature sensitivity of rheological properties was used to explain the displacement curves during embossing. Numerical simulation of the embossing process was also carried out to compare with the observed polymer flow patterns. It was found that the simulated flow pattern during isothermal embossing agrees fairly well with the experimental observation. The deviation between the simulated and experimental results at the late stage of embossing may be due to air entrapment between the mold feature and the polymer substrate. For non‐isothermal embossing, the observed flow pattern can also be reasonably simulated, i.e. the polymer flows upward along the wall of the heated mold feature, and then compresses downward and squeezes outward. Temperature sensitivity of the dynamic shear viscosity and the transient extensional viscosity is similar for all three polymers. This correlates well with the initial displacement curves in isothermal embossing. Over a longer time, the strain hardening effect of the transient extensional viscosity seems to play a major role in the displacement curves.
Flow through a convergence. Part 1: Critical conditions for unstable flow
Authors: Meller Mika , Luciani André , Sarioglu Alp , Månson Jan‐Anders E. 
Published: April 2004

AbstractThe critical conditions leading to fracture in elongation and different types of flow instabilities were examined in uniaxial elongation and in a capillary rheometer equipped with dies having different entry profiles. Either ductile or brittle fracture may be observed, ductile being related to necking of material. The critical stress approach was used to predict fracture in elongation. All linear polymers studied in this work exhibited ductile fracture in uniaxial elongation, but the transition to brittle fracture is discussed in relation to existing experiments with other materials. In a ductile fracture regime, critical stress and work both increase with an increasing rate of deformation, whereas in a brittle regime the critical values remain constant. The converging flow studies indicated that two types of flow instability that have been previously related to each other, namely, pressure oscillations and voltions distortions, are of different origins. The critical flow rate for pressure oscillations is independent of entry profile, and the origin for this type of instability lies along the wall of the capillary. On the other hand, the critical flow rate for volume distortions increased with a decreasing entry angle, indicating that volume distortions are not a consequence of pressure oscillation, nor are their origin at the capillary wall. Numerical simulations were used to determine the stress profiles within the flow, and it was shown that the onset of volume distortions is directly related to the magnitude of elongational stress and work, and may therefore be considered to be caused by fracture in elongation. In dies with 90° entry profile, volume distortions were observed simultaneously with pressure oscillations, making it difficult to distinguish between the two phenomena.
3‐D numerical analysis on the mixing performance for assemblies with filled zone of right‐handed and left‐handed double‐flighted screws and kneading blocks in twin‐screw extruders
Authors: Funatsu Kazumori , Kihara Shin‐Ichi , Miyazaki Masaru , Katsuki Shingo , Kajiwara Toshihisa 
Published: April 2004

AbstractWe have calculated and visualized numerically the mixing performances of four kinds of assemblies in twin‐screw extruders that were composed of right‐handed or left‐handed double‐flighted full flight screws and neutral or left‐handed stagger angle kneading blocks, taking into consideration industrial usage. We have found that the mixing performance of a kneading block interposed between full flighted screws is strongly influenced by the flow of full flighted screws, in particular that of a neutral kneading block. Furthermore, we have proposed the simple mixing indices, which could describe both uniform mixing and heterogeneous mixing, and also applied them to our marker tracking results of four kinds of assemblies. We found that more uniform mixing is obtained for the assembly that has a neutral kneading block before the right‐handed full flight screw, and a more enhanced heterogeneous mixing is obtained for the assembly that has a left‐handed kneading block before the left‐handed full flight screw. The reason for the latter mixing ability will relate to the quasi‐channels of the left‐handed kneading block, through which marker clusters flow while elongating.
Thermal and dynamic mechanical characterization of polypropylene‐woodflour composites
Authors: Nuñez Adrián J. , Kenny José M. , Reboredo María M. , Aranguren Mirta I. , Marcovich Norma E. 
Published: April 2004

AbstractThe performance of wood particle/polypropylene (PP) composites with modified compatibilities was compared. Woodflour modification was performed by esterification with maleic anhydride (MAN) and a non‐commercial maleic anhydride‐polypropylene copolymer (PPMAN) was selected as compatibilizing agent. The thermogravimetric analysis indicates that the onset of thermal degradation of treated woodflour occurs at lower temperature than that of the untreated one, and the same behavior was found in the corresponding composites. Differential scanning calorimetry indicated that both woodflours acted as nucleating agents for PP, while only treated woodflour induced PP crystallization in β‐phase in the composites. X‐ray diffractometry demonstrated that the crystallization in β‐phase was a shear‐induced phenomenon favored by the chemical modification of the woodflour surface. Dynamic mechanical studies suggested that composite properties decreased at concentrations higher than 40 wt% of woodflour and that the overall performance of MAN‐treated woodflour composites was lower than that of the composites where a compatibilizing agent was added.
Metal injection molding: 3D modeling of nonisothermal filling
Authors: Ilinca Florin , Hétu Jean‐François , Derdouri Abdessalem , Stevenson James 
Published: April 2004

AbstractA three‐dimensional transient finite element flow analysis code that includes inertia and free surface modeling is used to predict uniform (axisymmetric) and nonuniform (nonaxisymmetric) filling patterns in a thick‐walled tool with a diaphragm gate. The simulation for a metal injection molding compound, which is strongly influenced by thermal effects, predicted several observed flow patterns: initial annular free surface flow (jetting), bypass and folding flow to form surface defects, and the transition from uniform (axisymmetric) flow to nonuniform (nonaxisymmetric flow) with increasing fill time and lower temperatures. Simulations of filling through a thicker diaphragm gate showed jetting and the associated problems were eliminated. Simulations also demonstrate the effects of filling time, mold temperature, inertia, yield stress, and wall slip on filling patterns, particularly the processing conditions that separate regions of uniform and nonuniform flow.
Influence of elasticity on dispersed‐phase droplet size in immiscible polymer blends in simple shearing flow
Authors: Lerdwijitjarud Wanchai , Sirivat Anuvat , Larson Ronald G. 
Published: April 2004

AbstractThe influence of elasticity of the blend constituent components on the size and size distribution of dispersed‐phase droplets is investigated for blends of polystyrene and high density polyethylene in a simple shearing flow. The elasticities of the blend components are characterized by their first normal stress differences. The role played by the ratio of drop to matrix elasticity at fixed viscosity ratio was examined by using high molecular weight polymer melts, high density polyethylene and polystyrene, at temperatures at which the viscosity ratios roughly equaled each of three different values: 0.5, 1, and 2. The experiments were conducted by using a cone‐and‐plate rheometer, and the steady‐state number and volume‐mean averages of droplet diameters were determined by optical microscopy. After steady‐state shearing, the viscoelastic drops were larger than the Newtonian drops at the same shearing stress. From the steady‐state dispersed‐phase droplet diameters, the steady‐state capillary number, Ca, defined as the ratio of the viscous shearing stress over the interfacial tension stress, was calculated as a function of the ratio of the first normal stress differences in the droplet and matrix phases. For the blend systems with viscosity ratio 0.5, 1 and 2, the values of steady‐state capillary number were found to increase with the first normal stress difference ratio and followed a power law with scaling exponents between 1.7 and 1.9.
Melt processed microporous films from compatibilized immiscible blends with potential as membranes
Authors: Xanthos M. , Chandavasu C. , Sirkar K. K. , Gogos C. G. 
Published: April 2004

AbstractMicroporous flat films with potential as membranes were produced via melt processing and post‐extrusion drawing from immiscible polypropylene/polystyrene blends containing a compatibilizing copolymer. The blends were first compounded in a co‐rotating twin‐screw extruder and subsequently extruded through a sheet die to obtain the precursor films. These were uniaxially drawn (100%–500%) with respect to the original dimensions to induce porosity and then post‐treated at elevated temperatures to stabilize the resultant structure, which consisted of uniform microcracks in the order of a few nanometers in width. The effects of blend composition and extrusion process parameters on surface and cross‐sectional porosity and solvent permeability of the prepared films are presented and related to specific microstructural features of the films before and after drawing. Finite element modeling of the stretching operation in the solid state yielded a successful interpretation of the blend response to uniaxial tension that resulted in microcrack formation. Comparison of some of the novel microporous structures of this work with commercial membranes prepared by solvent‐based phase inversion processes suggests comparable pore size and porosity ranges, with narrower pore size distribution.
Experimental investigation and numerical simulation of injection molding with micro‐features
Authors: Yu Liyong , Koh Chee Guan , Lee L. James , Koelling Kurt W. , Madou Marc J. 
Published: April 2004

AbstractInjection molding of thin plates of micro sized features was studied in order to manufacture micro‐fluidic devices for bioMEMS applications. Various types of mold inserts—CNC‐machined steel, epoxy photoresist, and photolithography and electroplating produced nickel molds—were fabricated and tested in injection molding. The feature size covers a range of 5 microns to several hundred microns. Issues such as surface roughness and sidewall draft angle of the mold insert were considered. Two optically clear thermoplastics, PMMA and optical quality polycarbonate, were processed at different mold and melt temperatures, injection speeds, shot sizes, and holding pressures. It was found that the injection speed and mold temperature in injection molding greatly affect the replication accuracy of microstructures on the metal mold inserts. The UV‐LIGA produced nickel mold with positive draft angles enabled successful demolding. Numerical simulation based on the 2D software C‐MOLD was performed on two types of cavity fillings: the radial flow and the undirectional flow. The simulation and experimental data were compared, showing correct qualitative predictions but discrepancies in the flow front profile and filled depth.
Effect of melt temperature and skin‐core morphology on the mechanical performance of nylon 6
Authors: Murthy N. Sanjeeva , Kagan Val A. , Bray Robert G. 
Published: April 2004

AbstractThe crystalline texture and mechanical (tensile and flexural) properties of injection molded nylon 6 were evaluated to understand the influence of the melt temperature (Tmlt), one of the key‐processing variables. The mechanical properties are found to be sensitive to Tmlt only below ∼ 250°C. Rapid quenching of the surface produces a skin with lower crystallinity than the core, which cools more slowly; because of this difference in the rate of cooling, the crystalline component in the skin is rich in γ and that in the core is rich in α. The thickness of this skin decreases from about 1.25 mm to 0.75 mm as Tmlt increases from 225°C to 310°C. Higher tensile strength at yield, lower elongation at break and higher flexural strength were observed in specimens molded at lower Tmlt. These characteristics are associated with thicker and less ordered skin, and a lower crystallinity core. The role of the Tmlt, on microstructure and mechanical properties of injection molded nylon 6, the development of skin‐core morphology, and the role of the residual stresses in the core are discussed.
Self‐reinforced polypropylene/LCP extruded strands and their moldings
Authors: Liang Y. C. , Isayev A. I. 
Published: April 2004

AbstractPolypropylenes (PP) of various molecular weights were mixed with a thermotropic liquid crystal polymer (LCP) and strands were prepared by extrusion and stretching. The strands were subsequently pelletized and then injection molded at temperatures below the melting point of LCP. The mechanical properties and the morphology of the strands and injection‐molded specimens were investigated as a function of draw ratio, LCP concentration, and PP molecular weight. The results for strands show that an increase in the draw ratio, LCP concentration and matrix molecular weight in general enhance the modulus and tensile strength. However, the tensile properties of injection‐molded specimens are found to be reduced compared with those of the original strands, in particular at high LCP concentration. The morphology of LCP changes from spherical or ellipsoidal droplets to elongated fibrils in the strands as the draw ratio increases, but this aligned LCP fibrillar morphology was not transferred to the injection‐molded specimens because of the disorientation of fibrils during injection molding. Compatibilization of PP/LCP blends was also studied by using various polymers. Maleic anhydride and acrylic acid modified PPs improved the tensile properties modestly, but maleic anhydride modified EPDM reduced the tensile properties.
Monitoring the reaction progress of a high‐performance phenylethynyl‐terminated poly(etherimide). Part I: Cure kinetics modeling
Authors: Bullions Todd A. , McGrath J. E. , Loos A. C. 
Published: April 2004

AbstractThe cure kinetics of a phenylethynyl‐terminated poly(etherimide) are examined via differential scanning calorimetry (DSC) measurements. Isothermal holds at temperatures ranging from 325°C to 360°C provided the necessary information to develop reaction kinetics models using both first‐order reaction kinetics and combination reaction kinetics. The first‐order reaction kinetics model works well for quick estimates of degree of cure versus time over the experimental temperature range. However, significantly more accurate predictions of degree of cure versus time were provided by the combination reaction kinetics model. The lack of accuracy in the first order model is due to the fact that the reaction cannot be described by a simple order. The experimental procedures followed to obtain the cure kinetics data and the construction of the models from this data are described; the predictions of these models are compared with the experimental results.
Improved properties of SBS‐modified asphalt with dynamic vulcanization
Authors: Wen Guian , Zhang Yong , Zhang Yinxi , Sun Kang , Fan Yongzhong 
Published: April 2004

AbstractStorage‐stable styrene‐butadiene‐styrene triblock copolymer (SBS)‐modified asphalt was prepared by dynamic vulcanization. The vulcanization characteristics of the asphalt/SBS/sulfur blend were studied using a strain‐controlled rheometer. The vulcanization of SBS in the asphalt resulted in a marked increase in the torque of the blend. In addition, the vulcanization of a butadiene rubber (BR)/sulfur blend was significantly influenced by the addition of asphalt through a curemeter. The existence of asphalt can accelerate the vulcanization of BR/sulfur blend and reduce its reversion. The preparation process of storage‐stable SBS‐modified asphalt by dynamic vulcanization was identified by a plot of the electric current versus time. The addition of sulfur to the SBS‐modified asphalts resulted in the formation of chemically vulcanized network structures in the modified binders. The physical properties of the SBS‐modified asphalt containing sulfur were compared to those of the modified binders without sulfur. The storage stability of the SBS‐modified asphalt was effectively improved by the addition of sulfur. The rheological properties of the SBS‐modified asphalts before and after adding sulfur were characterized by using dynamic shear rheometry and a rotational viscometer. As indicated by the monitored morphology, the compatibility and high‐temperature storage stability of SBS‐modified asphalts were improved by the addition of sulfur.