bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology and rheology relationships of epoxy/core‐shell particle blends
Authors: Nguyen‐Thuc Boi Huyen , Maazouz Abderrahim
Published: April 2004

The morphological and rheological behaviors of toughened epoxy resins modified with core‐shell rubber particles (CSR) were studied. These rubber particles were based on a poly (butadiene‐co‐styrene) core and a crosslinked poly (methyl methacrylate) shell. The effect of functionalized groups was performed on two types of CSR particles: first, those containing carboxyl‐functionalized groups (CSf), and second, particles containing no carboxyl‐functionalized groups (CSnf) in the PMMA‐shell. For these blends, the correlations between the morphology, particle dispersion state and their rheological behaviors before curing were investigated. Preliminary work using TEM micrographs indicated that the blends modified with CSf and CSnf exhibited the same particle size but differed with respect to the dispersion state. Rheological behavior of these blends was assessed in steady shear flow and dynamic viscoelastic experiments. Yield viscosity near‐zero shear rate occurred in the DGEBA/CSf blend presenting non‐Newtonian behavior at the particle volume fraction of 20% vol. The rheological behavior was clearly related to the state of particle dispersion and analyzed taking into account interactions between the particles‐particles and the particles‐matrix. The Williams‐Landel‐Ferry (WLF) shift procedure was used to construct modulus master curves G′ and G″ from the elastic solid state to molten polymers. A secondary plateau existed at low frequencies and was related to the presence of interactions leading to a physical network‐type structure. The deviation between theoretical G′ (Paleirne's model) and experimental G′ values was evaluated and exhibited high elasticity at the terminal zone, which correlated well with available literature.
Prediction of the creep of heterogeneous polymer blends: Rubber‐toughened polypropylene/poly(styrene‐co‐acrylonitrile)
Authors: Kolaříak Jan , Fambri Luca , Pegoretti Alessandro , Penati Amabile , Goberti Paolo
Published: April 2004

A previously proposed predictive format for elastic, storage and loss moduli is extended for the time‐dependent compliance Db(t) of polymer blends. The format employs a two‐parameter equivalent box model (EBM) and the data on the phase continuity of components in blends obtained by using modified general equations of the percolation theory. As input data, the compliances D1(t) and D2(t) and the critical volume fractions V1cr and V2cr (delimiting the interval of phase co‐continuity in blends) of components are sufficient. To describe the effect of time on D1(t), D2(t) and Db(t) within the linear stress‐strain region, a routinely used empirical equation was found suitable. Applicability of the proposed format is demonstrated on rubbertoughened polypropylene/poly(styrene‐co‐acrylonitrile) blends consisting of components with markedly different viscoelastic properties. The proposed predictive format fits fairly well the creep behavior of blends over the interval 0.1‐10,000 minutes.
An optical device to measure in‐line residence time distribution curves during extrusion
Authors: Mélo Tomás Jeferson A. , Canevarolo Sebastião V.
Published: April 2004

This paper proposes a setup for in‐line measurement of residence time distribution (RTD) curves during extrusion. The detection system is composed of a slit die with transparent borosilicate glass windows fixed at the extruder exit, an optical arrangement with an incandescent light microbulb with fixed luminescence, and a Light Dependent Resistor (LDR) photocell of CdS. As the tracer passes through the light path, the reduction in the transmitted light intensity is followed by changes in the voltage induced by the photocell to an electric circuit. The signal is collected by an external interface and sent to a computer. Software acquires the data, does all calculations, and presents all curves and calculated variables to the monitor. The validation of the system was done by checking for data reproducibility and linearity with tracer concentration. The response of the LDR sensor with respect to the concentration of the tracer was calibrated using a set of slight dark film, obtaining a logarithmic relationship. Thus the signal enhances any disturbance, if present, particularly in the tail‐region of the curves. Measurements were taken from a Werner‐Pfleiderer ZSK 30 twin‐screw extruder equipped with K‐Tron gravimetric feeders operating with various screw speeds, feeding rates and screw configurations. In this last case, the presence of kneading elements was taken into account.
Measurement of the residual mechanical properties of crazed polycarbonate. I: Qualitative analysis
Authors: Clay Stephen B. , Kander Ronald G.
Published: April 2004

A new technique to quantify the bulk craze density of transparent plates was used to characterize the craze growth behavior of polycarbonate at various stress levels. The craze growth rates were found to exponentially increase with an increase in stress, obeying the Eyring equation for thermally activated processes in the presence of an applied stress. The residual mechanical properties of crazed polycarbonate were then correlated to the crazing stress, relative craze density and strain rate. The results show that increasing the bulk craze density does not affect the yield stress but decreases both the failure stress and ductility of polycarbonate. Also, a crazing stress of 40 MPa was found to cause a much larger degree of degradation of failure properties than a crazing stress of 45 MPa. Correlating the crazing stress to the craze microstructure revealed that fewer, larger crazes form at the lower crazing stress. Therefore, flaw size has a greater effect on the failure properties of polycarbonate than flaw quantity.
Flow behavior of stratified viscoelastic laminar flow at junctions with different angles
Authors: Yamaguchi Hiroshi , Yamamoto Hideaki
Published: April 2004

Detailed study was carried out in order to investigate flow phenomena occurring at the junction of two incoming stratified flow layers with junction angles. Various combinations of fluids with Newtonian and non‐Newtonian rheological characteristics were tested in a relatively high‐speed stratification where the inertia of flow cannot be neglected. The flow characteristics at the junctions were classified into six main flow modes, which were arranged in mode maps by use of generalized Reynolds numbers and viscous ratios. From the resultant mode maps it was found that a mutual relation of inertial and viscous effects is essential for the determination of flow modes in the stratified flows.
Simulation of non‐isothermal melt densification of polyethylene in rotational molding
Authors: Bellehumeur C. T. , Tiang J. S.
Published: April 2004

Rotational molding involves powder mixing, heating and melting of powder particles to form a homogeneous polymer melt, as well as cooling and solidification. The densification of a loose powder compact into a homogeneous melt occurs over a wide range of conditions as the material passes from a solid state into a melt state. The numerical simulation of the non‐isothermal melt densification in the rotational molding process is presented in this work. The simulation combines heat transfer, polymer sintering and bubble dissolution models, and is based on an idealized packing arrangement of powder particles. The predictions are in general agreement with experimental observations presented in the literature for the rotational molding of polyethylenes. The simulation allows for systematic and quantitative studies on the effect of molding conditions and material properties on the molding cycle and molded part density. Results indicate that the densification process is primarily affected by the powder characteristics, which are accounted for in terms of the particle size and the particle packing arrangement. The material rheological properties become increasingly important as the powder characteristics lessen in quality. The simulation demonstrated that while certain combinations of processing conditions help reduce the molding cycle, they have a detrimental effect on the densification process.
Modeling of a Buss‐Kneader as a polymerization reactor for acrylates. Part I: Model validation
Authors: Troelstra E. J. , Van Lune J. , Van Dierendonck L. L. , Janssen L. P. B. M. , Renken A.
Published: April 2004

The Buss‐Kneader is generally known as a compounding device. Although a reasonable number of papers have been published on extruders as polymerization reactors, only little is known about the behavior of the Buss‐Kneader when used as a polymerization reactor. Its good mixing properties in the radial and axial directions make it a suitable reactor for exothermal polymerization reactions. This paper describes experiments with the co‐polymerization of n‐butyl acrylate and hydroxyethyl methacrylate in a Buss‐Kneader. For model calculations the Buss‐Kneader was treated as a plug flow reactor with axial dispersion. Experimental results on axial temperature profile, monomer conversion and molecular weight are compared with model calculations. Model parameters are based on independently measured data on the heat transfer coefficient, axial dispersion and polymerization kinetics.
Phase separation and gelation of epoxy resin/hyperbranched polymer blends
Authors: Mezzenga Raffaele , Luciani Andrè , Månson Jan‐Anders E.
Published: April 2004

The structural buildup during reticulation of thermoset systems containing reactive modifiers can strongly influence the final properties of such blends. This was studied by considering the rheological behavior during cure of an epoxy/amine thermoset system blended with reactive dendritic hyperbranched polymers (HBPs). Depending on the chemical structure of the HBP used in the blend, a phase separation could be observed. The onset and offset of the phase separation process could be detected by observing the evolution of the viscoelastic properties. The phase separation onsets obtained by rheological measurements were compared with the values obtained by traditional cloud point observations. Good agreement between the two techniques was observed. Hyperbranched polymers that did not phase separate during the curing process were used to study gelation phenomena and its dependence on the reactivity and functionality of the HBP. The gelation of the homogeneous blend system using the Flory‐Stockmayer theory was also modeled. This highlighted the influence of both functionality and reactivity of the components, and the appearance of co‐operative polymerization mechanisms in homogeneous blends.
Effect of polymer matrix on the rheology of hydroxyapatite‐filled polyethylene composites
Authors: Joseph R. , McGregor W. J. , Martyn M. T. , Tanner K. E. , Coates P. D. , Bonfield W.
Published: April 2004

The effect of matrix polymer and filler content on the rheological behavior of hydroxyapatite‐filled injection molding grade high‐density polyethylene (HDPE) has been studied. Studies of the flow curves revealed that the matrix and the composite exhibit three distinct regions in the flow curve, namely, a pseudoplastic region at low to moderate shear rates, a plateau and a second pseudoplastic region at high shear rates. The shear stress corresponding to the plateau (τc) is dependent on both the filler concentration and the melt temperature. Addition of HA in the HDPE matrix increases the value of τc and decreases compressibility of the melt. An increase in temperature also raises the value of τc. From the nature of flow curves it is concluded that the matrix polymer largely decides the rheology of the composite.
Extrusion blow molding of long fiber reinforced polyolefins
Authors: Garcia‐Rejon A. , Meddad A. , Turcott E. , Carmel M.
Published: April 2004

A 58% (by weight) long glass fiber reinforced (LGF)‐HDPE master batch was blended with a typical blow molding HDPE grade. HDPE composites having between 5% and 20% (by weight) long fiber content were extruded at different processing conditions (extrusion speed, die gap, hang time). The parison swell (diameter and thickness) decreased with increasing fiber content. Although the HDPE exhibited significant shear rate dependence, the LGF/HDPE composites were shear rate insensitive. Both the diameter and weight swell results also indicated very different sagging behavior. The LGF/HDPE parisons did sag as a solid‐body (equal speed at different axial locations) governed by the orientation caused by the flow in the die. Samples taken from blown bottles showed that fiber lengths decreased to 1‐3 mm, from the original 11 mm fiber length fed to the extruder. No significant difference in fiber length distribution was found when samples for different regions of the bottle were analyzed. SEM micrographs corroborate the absence of fiber segregation and clustering or the occurrence of fiber bundles (homogeneous spatial fiber distribution) as well as a preferential fiber orientation with the direction of flow. The blowing step did not change the orientation of the fibers. Five‐percent (5%) and 10% LGF/HDPE composites could be blown with very slight variations to the neat HDPE inflation conditions. However, 20% LGF/HDPE composites could not be consistently inflated. Problems related to blowouts and incomplete weldlines were the major source of problems.
A step towards understanding the heating phase of laser transmission welding in polymers
Authors: Becker F. , Potente H.
Published: April 2004

In 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

We 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

The 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

Compounding 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

The 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

The 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

The 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

The 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

We 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

The 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

A 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

The 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

Microporous 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

Injection 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

The 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

Polypropylenes (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

The 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

Storage‐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.
Residual thermal stresses in injection moldings of thermoplastics: A theoretical and experimental study
Authors: Kamal M. R. , Lai‐Fook R. A. , Hernandez‐Aguilar J. R.
Published: April 2004

Internal stresses in injection molded components, a principal cause of shrinkage and warpage, are predicted using a three‐dimensional numerical simulation of the residual stress development in moldings of polystyrene and high‐density polyethylene. These residual stresses are mainly frozen‐in thermal stresses due to inhomogeneous cooling, when surface layers stiffen sooner than the core region as in free quenching. Additional factors in injection molding are the effects of melt pressure history and mechanical restraints of the mold. Transient temperature and pressure fields from simulation of the injection molding cycle are used for calculating the developing normal stress distributions. Theoretical predictions are compared with measurements performed on injection molded flat plates using the layer removal method on rectangular specimens. The thermal stress development in the thinwalled moldings is analyzed using models that assume linear thermo‐elastic and linear thermo‐viscoelastic compressible behavior of the polymeric materials. Polymer crystallization effects on stresses are examined. Stresses are obtained implicitly using displacement formulations, and the governing equations are solved numerically using a finite element method. Results show that residual stress behavior can be represented reasonably well for both the amorphous and the semicrystalline polymer. Similarities in behavior between theory and experiment indicate that both material models provide satisfactory results, but the best predictions of large stresses developed at the wall surface are obtained with the thermo‐viscoelastic analysis.
Improved modeling for the reheat phase in thermoforming through an uncertainty treatment of the key parameters
Authors: Yousefi A. , Bendada A. , Diraddo R.
Published: April 2004

This work focuses on the treatment of parameter uncertainty in the simulation of the sheet reheat phase of the thermoforming process. The approach aims to improve the quality of predictions through more accurate evaluation of the input parameters. First, the modeling approach is employed to perform a sensitivity analysis on the reheat phase. Then, a series of specialized experiments with heat flux and temperature sensors are performed on a thermoforming machine. The key parameters identified through the sensitivity analysis are the subject of these experiments. The natural convective heat transfer coefficients are evaluated by two different approaches. Through treatment of the uncertainty associated with the input parameters, the prediction of sheet reheat phase is significantly improved.
Oxidative graft polymerization of aniline on Si(100) surface modified by plasma polymerization of glycidyl methacrylate
Authors: Chen Yongjun , Kang E. T. , Neoh K. G. , Zhang Yan , Tan K. L.
Published: April 2004

Modification of argon plasma‐pretreated Si(100) surfaces via plasma polymerization of glycidyl methacrylate(GMA), followed by reactive coupling of the epoxide groups of the plasma deposited GMA chains with aniline, and finally by oxidative graft polymerization of aniline was carried out. An alternative approach involved the modification of the argon plasma‐pretreated Si(100) surfaces via plasma polymerization of glycidyl methacrylate(GMA), followed by direct oxidative graft polymerization of aniline and thermal curing. The compositions and chemical states of the modified Si surfaces were characterized by X‐ray photoelectron spectroscopy (XPS). The two methods of surface modification of the Si(100) surfaces produced similar results. The protonation‐deprotonation behavior, the interconvertible intrinsic redox states, and the metal reduction behavior (the electroless plating of Pd from the Pd(II) ion solution) of the grafted polyaniline (PANI) chains on the Si(100) surface were grossly similar to those of the PANI homopolymer. The coupling of PANI to the covalently tethered GMA chains on the Si(100) surface was suggested by the cohesive failure inside the epoxy adhesive that was applied to the modified Si surface in an attempt to peel off the PANI layer from the GMA plasma‐polymerized Si (GMA‐pp‐Si) substrate.
Effect of addition protocol on mixing in miscible and immiscible polymer blends
Authors: Burch Heidi E. , Scott Chris E.
Published: April 2004

The effects of the addition protocol are investigated for very‐low‐viscosity‐ratio model miscible and immiscible blends consisting of two polyethylenes (PE) and polystyrene (PS)/polyethylene (PE), respectively, are investigated. Miscible and immiscible blends with a matched viscosity ratio of 0.003 are compounded using three different addition protocols: simultaneous solids addition; sequential solids addition; and sequential liquids addition. These protocols correspond to addition of a solid additive to the feed hopper of an extruder; addition of a solid additive into the melting zone in an extruder; and addition of a liquid additive into the melting zone of an extruder. Both of these blends are shown to exhibit phase‐inversion‐like behaviors using a simultaneous solids addition protocol, regardless of concentration. Using either of the sequential addition protocols results in macroscopic segregation of the minor‐phase material to high‐shear‐rate regions of the mixer, delaying mixing. At long mixing times, however, all three protocols achieve a similar dispersed droplet morphology. Furthermore, the simultaneous solids addition protocol is shown to be the least energetically intensive, and the simultaneous solids requires the least amount of time of the three protocols to achieve maximum mixing torque for blends consisting of 20 wt% minor phase.
Quantification of the slip phenomenon and the effect of shear thinning in the capillary flow of linear polyethylenes
Authors: Pérez‐González José , De Vargas Lourdes
Published: April 2004

The slip phenomenon in the capillary flow of linear polyethylenes and its relation to their shear‐thinning behavior was studied in this work. A simple macroscopic analysis that allows a description of the trend of the slip length and the contribution of slip to the average fluid velocity as functions of the shear stress is presented. From this analysis it is shown that an increase or decrease of the slip length for increasing shear stress is determined by the polymer architecture and the competition between slip and shear thinning. A similar behavior is observed for the ratio between the slip and whole average fluid velocities. The analysis is validated using experimental data obtained during the continuous extrusion of linear low‐density polyethylene melts under strong slip conditions in a brass die.
Properties of polytetrafluoroethylene (PTFE) paste extrudates
Authors: Ariawan Alfonsius B. , Ebnesajjad Sina , Hatzikiriakos Savvas G.
Published: April 2004

In this work, we have studied the effects of extrusion die design, resin molecular structure, and lubricant concentration on the properties of PTFE paste extrudates by performing macroscopic extrusion pressure measurements, Raman spectroscopy, differential scanning calorimetry and mechanical testing on the extrudates. Five resins of different molecular structures were tested. We have found that a balance between fibril quantity and quality (in terms of fibril orientation and continuousness) is necessary to ensure acceptable products, as illustrated through the effects of the operating variables on the extrudate tensile strength. The number of fibrils formed during extrusion can be increased by extruding the paste through a die of larger reduction ratio or by decreasing the lubricant content in the paste, thereby increasing the extrusion pressure. However, excessive pressure will cause fibril breakage. By using a die of larger entrance angle, the extent of fibrillation is also increased, although the quality of the fibrils is somewhat compromised. Increasing the die aspect (L/D) ratio does not increase the extent of fibrillation. However, it increases the degree of fibril orientation and ensures smoother extrudate. Finally, we have found that extrudates obtained using a paste of higher molecular weight are mechanically superior.
Estimation of Weibull parameters for the flexural strength of PMMA‐based bone cements
Authors: Riccardi Carmen C. , Vallo Claudia I.
Published: April 2004

The wide scatter of data observed in the strength of bone cements based on poly(methyl methacrylate) (PMMA) can be described properly by the two‐parameter Weibull function. However, the statistical character of the distribution leads to an uncertainty in the parameters evaluated from a limited number of experiments. This study is concerned with the analysis of the methods of estimation as well as sample size on the estimates of the Weibull parameters. The maximum likelihood method, moments method, and linear regression method were studied. Monte Carlo simulations were carried out in order to assess the influence of the number of specimens tested on the Weibull parameters calculated by the different methods. The number of specimens tested displayed a large influence upon the calculated Weibull modulus. By applying weighing factors to the linear regression method, the standard deviation of Weibull parameters decreased significantly. As a compromise between minimizing both the dispersion of the evaluation method and the experimental effort, the use is suggested of the linear regression method with a minimum number of 20 specimens in a nonweighted analysis and 10 in a weighted analysis.
The formulation of powder coatings using solid state shear extrusion
Authors: Wojcik B. , Teymour F. , Arastoopour H. , Mostovoy S.
Published: April 2004

The feasibility of producing homogeneous powder coating formulations without melting is investigated using Solid State Shear Extrusion (SSSE). A detailed comparison between conventional melt extrusion and SSSE processing conditions of identical formulations is accomplished by following the behavior and degree of polymerization during curing. Commercially available polyester and epoxide powder coating premix formulations were processed by SSSE using a Brabender® laboratory‐scale twin‐screw extruder and further pulverized in a ball mill. Calculations based on particle size before and after comminution in single batch ball mill studies indicate a reduction in energy requirements for SSSE during pulverization. Metal coupons were coated with dry pulverized formulations using an electrostatic fluidized bed coating system. The dynamics of curing were followed for a series of bake time exposures. The sol was separated from the gel using Soxhlet methods and characterized by gel permeation chromatography (GPC). A comparison of experimentally determined gel points and gelation dynamics showed general agreement between both processing methods. The critical yield stress, determined from preliminary mechanical testing of modified thick adherend specimens crack‐line‐loaded in compression, was also determined. Results showed the SSSE process to be equivalent to melt extrusion.