bluuebunny/crossref_metadata_2025 huggingface dataset:
Barrier properties of injection molded blends of liquid crystalline polyesters (Vectra) and high‐density polyethylene
Authors: Flodberg G. , Hedenqvist M. S. , Gedde U. W.
Published: April 2004

Blends of an extrusion‐grade high‐density polyethylene and two liquid crystalline copolyesters (LCP; Vectra A950 and Vectra RD501) were prepared by melt mixing and injection molding, and the morphologies and oxygen permeabilities of the blends were assessed. Scanning electron microscopy revealed that the LCP was present in the blends as mixed oriented bands and small spheres at low LCP contents (4–9 vol%), whereas blends with more than 18 vol% LCP showed LCP lamellae of macroscopic lateral size (mm). Scanning electron microscopy revealed a two‐dimensional continuity of the LCP domains in the disc plane due to radial shear deformation and circumferential stretching of the melt leaving the central gate of the disc‐shaped cavity. The oxygen permeability, diffusivity and solubility decreased with increasing LCP content of the blends. The decrease in permeability with respect to polyethylene was significant (46%–55%) already at 9 vol% LCP. At 27 vol% LCP, the decrease with respect to polyethylene, was 92% for the Vectra A950 blend and 98% for the Vectra RD501 blend. These blends showed a greater decrease in diffusivity (86%–92%) than in solubility (39%–76%) with respect to polyethylene, which showed the very pronounced effect of the LCP lamellae on the geometrical impedance factor. Microvoids were present in all the blends despite the use of a very high injection pressure (180 MPa) but their impact on the oxygen permeability was negligible for the Vectra RD501 blends and relatively small for the Vectra A950 blends.
A method to control the dispersion of carbon black in an immiscible polymer blend
Authors: Feng Jiyun , Chan Chi‐ming , Li Jian‐xiong
Published: April 2004

The dispersion of carbon black (CB) in an immiscible polymer blend of poly‐(methyl methacrylate) (PMMA) and polypropylene (PP) was studied as the viscosity of PMMA increased. It was found that the dispersion of carbon black was strongly influenced by the viscosity of PMMA. The CB was dispersed in the PMMA phase when the viscosities of PMMA and PP are comparable, as predicted by Sumita's model. As the viscosity of PMMA increases, the CB was found to be located at the interface between the PMMA and PP phases. On further increase in the viscosity of PMMA, the CB was found to be dispersed in the PP phase. In addition, the CB dispersion in the PP/PMMA blends can significantly influence the positive temperature coefficient (PTC) intensity of the blends.
Effects of strain and temperature on the electrical properties of carbon black‐filled alternating copolymer of ethylene‐tetrafluoroethylene composites
Authors: Feng Jiyun , Chan Chi‐ming
Published: April 2004

Carbon black (CB)‐filled alternating copolymers of ethylene‐tetrafluoroethylene (ETFE) composites were prepared by the melt‐mixing method. The effects of strain and temperature on the electrical resistivity of the composites were elucidated in detail. Our results indicated that the CB content and CB particle size are the two main factors that influence the electrical resistance of the composites when they are subjected to strain. The large particle size CB‐filled ETFE composites with a low CB content show a significant increase in electrical resistivity as a function of strain. A linear relationship between the logarithm of the electrical resistivity of the composites and strain was observed, indicating that tunneling conduction plays an important role when the composites are subjected to strain. The tensile testing results indicated that the CB‐filled ETFE composites have reasonably good tensile properties.
Investigation of fracture properties of epoxy at low temperatures
Authors: Zhang Z. , Evans D.
Published: April 2004

The work of fracture of a number of epoxide resins has been measured at room temperature, 77K, and 4.2K, using a three‐point‐bending method with deeply notched specimens. Various types of yield behavior were noted, and the results and observations have been used to classify resins as brittle or semi‐flexible at room temperature and to record the presence of plasticity even at lower temperatures. For semi‐flexible resins at room temperature, the geometry dependent elastic/plastic contribution to the work of fracture is discussed. This work indicates how the work of fracture and the glass transition temperatures of the resin may be used to guide developments of resins for low temperature applications and possibly to derive a numerical term as a ‘Cracking Index.’ These results were used to explain the observed thermal shock resistance of these materials. A scanning electron microscope (SEM) and optical microscopy were used to investigate the fracture surfaces associated with the different types of yield and fracture behavior. The fracture surface microstructure has been used to explain the observed mechanical behavior, including the existence of plastic deformation in some resins at 77K. The results are of help in understanding the process of crack initiation, growth, and the crack tip deformation processes in epoxide resins.
Numerical simulation of film casting using an updated lagrangian finite element algorithm
Authors: Smith Spencer , Stolle Dieter
Published: April 2004

This paper presents a new numerical algorithm for 2D nonisothermal time‐stepping simulations of a nonlinear viscoelastic cast film process. A significant contribution of the algorithm is that an updated Lagrangian description of motion is employed, as opposed to the more conventional Eulerian description generally used for continuous polymer processing simulations. Furthermore, use is made of a Perzynatype constitutive equation, which is different from what is usually employed for molten polymers. The constitutive equation accommodates viscoelasticity, extensional thinning/thickening, and strain‐hardening. This new numerical algorithm can find the steady‐state film properties, and it can predict the onset of instability by observing draw resonance. The critical draw ratio is determined from the response problem, which means that the mathematical complications of the more common linear stability analysis are avoided. In terms of the stability of the film, it was observed that stability is decreased by extensional thinning, strain‐hardening, and higher relaxation times, and stability is increased by higher heat transfer coefficients and higher ratios of air‐gap length to die width.
Synthesis and characterization of ethylene vinyl‐acetate/polyaniline blends prepared by emulsion polymerization technique
Authors: Jeevananda T. , Siddaramaiah
Published: April 2004

A series of ethylene vinyl acetate‐polyaniline (98/02, 95/05, 93/07, … … 50/50) (EVA‐PAni) blends were prepared by the emulsion polymerization technique and made into sheets by the compression molding at 150°C. These sheets were characterized by electrical, physico‐mechanical, thermal, X‐ray and morphological studies. All electrical properties of EVA‐(PAni)TSA blends increased with an increase in PAni content. The conductivity, dielectric constant and tan δ values increased from 1.34 × 10−14 to 2.89 × 10−2 S/cm, from 2.113 to 19.845, from 0.094 to 4.789. Tensile strength increased with an increase in PAni content up to 7% and drastically decreased above 15%, while the percentage elongation at break decreased with an increase in PAni content. TGA studies revealed that the thermal stability of PAni improved after blending with EVA. EVA‐PAni blends were found stable up to 110°C. X‐ray diffractograms of EVA‐PAni blend showed an intense peak at 26° (2θ), reflecting the influence of EVA crystallinity. Scanning electron micrographs confirmed the two‐phase morphology of the system.
Development of renewable resource–based cellulose acetate bioplastic: Effect of process engineering on the performance of cellulosic plastics
Authors: Mohanty A. K. , Wibowo A. , Misra M. , Drzal L. T.
Published: April 2004

This paper deals with the development of a cellulose acetate biopolymer. Plasticization of this biopolymer under varying processing conditions to make it a suitable matrix polymer for bio‐composite applications was studied. In particular, cellulose acetate was plasticized with varying concentrations of an eco‐friendly triethyl citrate (TEC) plasticizer, unlike a conventional, petroleum‐derived phthalate plasticizer. Three types of processing were used to fabricate plasticized cellulose acetate parts: compression molding, extrusion followed by compression molding, and extrusion followed by injection molding. The processing mode affected the physicomechanical and thermal properties of the cellulosic plastic. Compression molded samples exhibited the highest impact strength, tending towards the impact strength of a thermoplastic olefin (TPO), while samples that were extruded and then injection molded exhibited the highest tensile strength and modulus values. Increasing the plasticizer content in the cellulosic plastic formulation improved the impact strength and strain to failure while decreasing the tensile strength and modulus values. The coefficient of thermal expansion (CTE) of the cellulose acetate increased with increasing amounts of plasticizer. Plasticized cellulose acetate was found to be processable at 170–180°C, approximately 50°C below the melting point of neat cellulose acetate.
Micromechanical behavior of impact modified poly(ethylene terephthalate)
Authors: Chapleau N. , Ajji A.
Published: April 2004

The micromechanical behavior of poly(ethylene terephthalate), PET, modified with a metallocene polyolefin copolymer (mPE) was investigated. Uniaxial deformation tests were performed using a tensile stage in a scanning electron microscope. This technique allowed the identification of the main deformation mechanisms that are associated with energy dissipation and toughness improvement. The poly(ethylene terephthalate) was blended with 5 wt% mPE by single‐screw extrusion. Films with thicknesses ranging from 200 to 500 μm were produced. Observation of the surfaces of the films during uniaxial deformation revealed the sequence of events leading to the full yielding of the matrix. In the early stages of deformation, the particles deform together with the matrix. As the deformation is increased, cavitation inside the particles occurs and fibrillation at the particle/matrix interface is observed, as well as the onset of shear banding. In order to study the effect of interfacial adhesion of the deformation mechanisms, the PET/mPE blends were compatibilized by grafting with glycidyl methacrylate (GMA). The reduction of the particle size was significant, which is indicative of the efficiency of GMA grafting in this type of blend. In this case, the particles were difficult to detect on the surface. Cavitation and shear banding occurred simultaneously. A similar behavior was observed in the case of oriented blends.
Effect of die temperature on the morphology of microcellular foams
Authors: Han Xiangmin , Koelling Kurt W. , Tomasko David L. , Lee L. James
Published: April 2004

A study on the extrusion of microcellular polystyrene foams at different foaming temperatures was carried out using CO2as the foaming agent. The contraction flow in the extrusion die was simulated with FLUENT computational fluid dynamics code at two temperatures (150°C and 175°C) to predict pressure and temperature profiles in the die. The location of nucleation onset was determined based on the pressure profile and equilibrium solubility. The relative importance of pressure and temperature in determining the nucleation rate was compared using calculations based on classical homogeneous nucleation theory. Experimentally, the effects of die temperature (i.e., the foaming temperature) on the pressure profile in the die, cell size, cell density, and cell morphology were investigated at different screw rotation speeds (10 ∼ 30 rpm). Experimental results were compared with simulations to gain insight into the foaming process. Although the foaming temperature was found to be less significant than the pressure drop or the pressure dropratein deciding the cell size and cell density, it affects the cell morphology dramatically. Open and closed cell structures can be generated by changing the foaming temperature. Microcellular foams of PS (with cell sizes smaller than 10 μm and cell densities greater than 10 cells/cm3) are created experimentally when the die temperature is 160°C, the pressure drop through the die is greater than 16 MPa, and the pressure droprateis higher than 109Pa/sec.
Synthesis and characterization of new aromatic polyimides containing well‐defined conjugation units
Authors: Shin T. J. , Park H. K. , Lee S. W. , Lee B. , Oh W. , Kim J.‐S. , Baek S. , Hwang Y.‐T. , Kim H.‐C. , Ree M.
Published: April 2004

A series of aromatic polyimides composed of well‐defined conjugation units were synthesized form 5,5′‐bis(4‐aminophenyl)‐2,2′‐bifuryl (PFDA) and 2,2′‐bis(furyl) benzidine (FurylBZ) with various dianhydrides. The synthesized polyimides emit blue to green light with a quantum yield of 7.3–14.9%, depending on the polymer backbone. In particular, PFDA‐based polymers exhibit extremely narrow photo‐luminescence. The structure, thermal stability, refractive index and dielectric properties of the polymer films were also determined.
Starch‐filled ternary polymer composites. I: Dynamic mechanical properties
Authors: Lawrence S. St. , Walia P. S. , Willett J. L.
Published: April 2004

The dynamic mechanical properties of starch‐filled blends of polyethylene (PE) and poly(hydroxy ester ether) (PHEE) are strongly dependent on the properties and distribution of the minor component (PHEE). The effect of the minor component on the viscoelastic properties was investigated by modeling the storage modulus. G′, using a step‐wise homogenization process. A comparison of theoretical and experimental data indicates that the morphology changes as the total volume fraction of filler ϕt, increases. At low ϕt, the PHEE encapsulates isolated starch granules. Above ϕt, ∼ 0.2, the PHEE surface coating contributes to the formation of particle clusters. Evidence of particle encapsulation was provided by a microscopic examination of fractured tensile bars. At all filler contents, the decrease in the composite's modulus at the Tg of PHEE is larger than can be accounted for if this material is simply dispersed in the matrix. When the starch granules are clustered, the decrease is also too large to be accounted for by only considering particle encapsulation. The effect of particle clustering must be included in order for the model to correctly describe the temperature dependence of the storage modulus.
Extrusion of polystyrene nanocomposite foams with supercritical CO2
Authors: Han Xiangmin , Zeng Changchun , Lee L. James , Koelling Kurt W. , Tomasko David L.
Published: April 2004

Intercalated and exfoliated polystyrene/nano‐clay composites were prepared by mechanical blending andin situpolymerization respectively. The composites were then foamed by using CO2as the foaming agent in an extrusion foaming process. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. At a screw rotation speed of 10 rpm and a die temperature of 200°C, the addition of a small amount (i.e., 5 wt%) of intercalated nano‐clay greatly reduces cell size from 25.3 to 11.1 μm and increases cell density from 2.7 × 107to 2.8 × 108cells/cm3. Once exfoliated, the nanocomposite exhibits the highest cell density (1.5 × 109cells/cm3) and smallest cell size (4.9 μm) at the same particle concentration. Compared with polystyrene foams, the nanocomposite foams exhibit higher tensile modulus, improved fire retardance, and better barrier property. Combining nanocomposites and the extrusion foaming process provides a new technique for the design and control of cell structure in microcellular foams.
Reactive melt modification of polypropylene with a crosslinkable polyester
Authors: Wan C. , Patel S. H. , Xanthos M.
Published: April 2004

Melt blending of polypropylene (PP) with a low molecular weight (MW) crosslinkable unsaturated polyester (UP) was studied in a batch mixer and a twin‐screw extruder in the presence of peroxide (POX) free radical initiator. Competing degradation and crosslinking reactions of the peroxide with the blend components leading to significant change in their viscosity ratio were studied and controlled during the blending process. Rheological studies show that depending on the process conditions some reacted PP/UP blends have a pronounced suspension behavior due to the presence of the dispersed polyester gel particles in a low MW PP matrix. It is also evident from SEM analysis that the reacted blends have a more uniform and finer morphology than the unreacted ones. The blends are also characterized by FTIR, which strongly suggests the presence of “block” or “graft” PP‐UP structures that may enhance phase interaction and promote compatibility in the reacted PP/UP blends. Such blends are considered as suitable compatibilizers of PP/high MW thermoplastic polyester blends and as modifiers for low density extrusion foaming of similar blends.
Morphology and properties of PBT/nylon 6/EVA‐g‐MAH ternary blends prepared by reactive extrusion
Authors: Kim Seon‐Joon , Kim Dong‐Keun , Cho Won‐Jei , Ha Chang‐Sik
Published: April 2004

Morphology and properties of poly(butylene terephthalate) (PBT)/nylon 6 (PA6)/EVA‐g‐MAH ternary blends were investigated. The blends were prepared in a corotating, intermeshing, twin‐screw extruder. The incorporation of maleic anhyride (MAH) grafted onto ethylene‐vinyl acetate copolymer (EVA) (EVA‐g‐MAH) in the PBT/PA6 binary blends decreased the tensile and flexural strength but increased the impact strength, while the mechanical properties of the PBT/PA6 blends were decreased with increasing PA6 content regardless of the presence or absence of the EVA‐g‐MAH. The morphology studies of the ternary blends showed gross phase separation. The rheological properties of the ternary blends suggested that excessively high reactivity between amine end groups of PA6 and MAH grafted onto EVA makes the compatibility between PBT and PA6 worse, although EVA‐g‐MAH was expected to work as a compatibilizer for PBT/PA6 blends. The degree of reactivity between functional groups in PBT, PA6, and EVA‐g‐MAH was also examined by investigating the effect of blending sequence on the properties of the ternary blends.
Production, properties and impact toughness of die‐drawn toughened polypropylenes
Authors: Mohanraj J. , Chapleau N. , Ajji A. , Duckett R. A. , Ward I. M.
Published: April 2004

We report the solid‐state die‐drawing of polypropylene and blends of polypropylene with a polyethylene elastomer to produce highly oriented products with enhanced mechanical properties. The blends showed an improvement in the drawability compared to the polypropylene homopolymer. The tensile modulus of the polypropylene homopolymer and the blends, along the draw direction, increased with draw ratio. In the transverse direction, the modulus of the homopolymer and the blends decreased with draw ratio as a result of anisotropy along the draw direction. The impact fracture behavior of the isotropic and the oriented samples was evaluated from noteched Charpy tests at 1 m/s over a wide range of temperatures. Linear elastic fracture mechanics were used to characterize the brittle fracture and the J‐integral approach was used to characterize the semi‐brittle and ductile fracture. In the isotropic state, the inclusion of the elastomer phase in the polypropylene matrix increased the toughness and also decreased the brittle‐ductile transition temperature. The oriented sheets, drawn at 110°C to a draw ratio of 4, were tested with the initial notch parallel and perpendicular to the draw direction. When tested with the initial notch parallel to the draw direction, the toughness of the homopolymer and the blends decreased when compared with the isotropic material. The brittle‐ductile transition temperature increased as a result of anisotropy. When tested with the initial notch perpendicular to the draw direction, the blends and the homopolymer showed considerable improvement in toughness compared to the isotropic state. Fracture along this direction is complicated, with subsidiary cracks propagating perpendicular to the main crack direction (which is parallel to the draw direction).
Expansion mechanisms of plastic/wood‐flour composite foams with moisture, dissolved gaseous volatiles, and undissolved gas bubbles
Authors: Rizvi G. M. , Park C. B. , Lin W. S. , Guo G. , Pop‐Iliev R.
Published: April 2004

The large quantity of moisture in wood‐flour may lead to the deterioration of the cell structure of foamed plastic wood‐flour composites in terms of cell size, non‐uniformity, and poor surface quality. Since these anomalies can cause poor mechanical properties of the foamed composites, the removal of the moisture from wood‐flour becomes a critical issue with respect to the improvement of these properties. The wood‐flour in this experimental study was first oven‐dried at different temperatures and then subjected to acetone extraction and thermogravimetric analysis (TGA). The oven‐dried wood‐flour was blended with plastic and then subjected to extrusion foaming. The results obtained from the TGA studies indicate that most volatiles were released from the extractives. Conversely, a comparative experimental study of the foaming behavior of these plastic/wood‐flour composites versus that of undried wood‐flour composites confirms that removal of the adsorbed moisture from wood‐flour results in a better cell morphology. However, it seems that some gaseous emissions released from wood‐flour are soluble in plastic and thereby favorably contribute to the development of the cell morphology. This paper describes the expansion mechanisms of wood‐flour composite foams resulting from the adsorbed moisture and dissolved gaseous emissions as well as resulting from the finely dispersed undissolved gas bubbles released from a chemical blowing agent.
Optimization of blow molded part performance through process simulation
Authors: Gauvin C. , Thibault F. , Laroche D.
Published: April 2004

In this work, a gradient‐based numerical optimization scheme is proposed to determine the optimal process operating conditions to produce a blow molded part by with a given performance. Finite element simulations are used to relate the part performance to the processing conditions. A performance optimization is first performed to find the minimum part thickness distribution that minimizes the part weight while satisfying mechanical performance constraints such as maximum part deflection or maximum stress for an applied load. Then a process optimization finds the optimal operating conditions, e.g. the die gap opening profile, that minimize the part weight while respecting the minimum thickness distribution dictated by the performance optimization. The results show that the optimization scheme minimizes the part weight with minimal constraint violation. The addition of a constraint associated with process stability is proposed.
Three‐dimensional simulation of multi‐material injection molding: Application to gas‐assisted and co‐injection molding
Authors: Ilinca Florin , Hétu Jean‐Françlois
Published: April 2004

This paper presents an overview of the results obtained at the Industrial Materials Institute (IMI) on the numerical simulation of the gas‐assisted injection molding and co‐injection molding. For this work, the IMI's three‐dimensional (3D) finite element flow analysis code was used. Non‐Newtonian, non‐isothermal flow solutions are obtained by solving the momentum, mass and energy equations. Two additional transport equations are solved to track polymer/air and skin/core materials interfaces. Solutions are shown for different thin parts and then for thick three‐dimensional geometries. Different operating conditions are considered and the influence of various processing parameters is analyzed.
Simultaneous biaxial deformation behavior of isotactic polypropylene films
Authors: Capt L. , Rettenberger S. , Münstedt H. , Kamal M. R.
Published: April 2004

The simultaneous biaxial deformation behavior of isotactic polypropylene films was investigated using a novel laboratory film stretcher. A detailed description of the apparatus and its measurement capabilities is presented. The effects of drawing temperature and ratio, strain rate, and deformation modes on the macroscopic equibiaxial deformation and its relation to film dimension uniformity were studied. The strain rate was found to have a large influence on biaxial deformation homogeneity. For temperatures 15°C to 5°C below the melting point, it could be concluded that a homogeneous biaxial deformation was achieved if the Hencky strain rate was higher than 0.1 s−1. Additionally, it was found that the nominal biaxial yield stresses were linearly dependent on temperature in the range under investigation.
Production of barrier films by chaotic mixing of plastics
Authors: Kwon O. , Zumbrunnen D. A.
Published: April 2004

Recent studies have demonstrated that highly multilayered blend morphologies can be formed by chaotic mixing and captured within extrusions of various forms. The number and thickness of internal layers prior to layer breakup and the extent of breakup are controllable via specification of process variables. A variety of derivative morphologies can thereby be obtained. Although methods can be applicable to other blends, the relation of oxygen permeability to various morphologies was specifically investigated in this study for extruded films without drawing consisting of ethylene vinyl alcohol copolymer, low density polyethylene and maleic anhydride modified polyethylene as a compatibilizing agent. Optimal barrier properties were obtained in a novel single phase continuous and mechanically interlocked morphology that was an outcome of stretching and folding characterizing chaotic mixing. Barrier properties were similar to those obtainable in co‐extruded films because of the presence of abundant platelets across the film thickness and crystallinity increases caused by barrier phase refinement.
Behavior of fully filled regions in a non‐intermeshing twin‐screw extruder
Authors: Mudalamane Rajath , Bigio David I. , Tomayko David C. , Meissel Marcel
Published: April 2004

Twin‐screw extruders are operated with sequential filled and partially filled regions in order to perform the required unit processes. Channel fill length, defined as the length of fully filled regions in an extrusion screw, is gaining importance as a design parameter because of its implications on residence time distribution, distributive and dispersive mixing, and also process stability. A detailed study—experimental and theoretical—of the behavior of fill lengths in response to operating conditions (throughput, screw speed) and screw geometry is presented in this paper. Mean residence times were also measured for each geometry and operating condition. The apparatus consisted of a non‐intermeshing counter‐rotating twin‐screw extruder (NITSE) with a transparent (acrylic) barrel, fed with corn syrup (Newtonian at room temperature). Fill length exhibits a nonlinear relationship with specific throughput (Q/N), with the slope increasing monotonously as the throughput Q increases at a given screw speed N. The mean residence time exhibits a strong linear relationship with inverse specific throughput and inverse fill length. A theoretical model was developed to predict the filled length based on pressure‐throughput relationships taken from literature for this system, and the predictions were found to agree very well with experimental observations.
Pressure drop and die surface changes in unplasticized PVC extrusion
Authors: Szarvasy I. , Pittman J. F. T.
Published: April 2004

Pressure drops were measured as a function of time during extrusion of a commercial unplasticized PVC formulation through a specially constructed slit die. For a die with a wire‐eroded surface, the pressure drop per unit length is found to be higher upstream than downstream by about 21% at the start of extrusion, falling to 16% after 130 h, owing to a more pronounced reduction in the pressure gradient upstream. Die surface average roughness, measured mechanically, dropped from an initial value of 2.7 μm to 2.2 μm, independent of position in the die. The lower pressure gradient and the lower sensitivity of pressure drop to decreased surface roughness at the downstream position are believed to indicate a thickening of the slip layer in the flow direction. For a die with a sand‐blasted surface, roughness fell from 1.05 to 0.95 μm over 130 h, appearing to approach a lower bound of 0.5 μm. Atomic force microscopy, and scanning electron microscopy with energy‐dispersive X‐ray spectroscopy was carried out on the surface of inserts removed from the die surface after use. In scans 50, 20 and 10 μm square, the AFM showed roughness on the small scale increasing after use. Raised areas of the surface are smoothed, but covered with parallel striations of approximately 0.5 μm, which, it is believed, are caused by titanium dioxide particles. These raised areas are coated with the lead stabilizer and lubricant. Lower areas remain rough, and trap mineral particles. Very little chlorine is found, indicating that PVC does not adhere to the surface. It is concluded that polishing to below 0.5 μm is unlikely to be worthwhile.
Enhancing slit die performance by optimization of restrictor profiles
Authors: Bates S. J. , Pittman J. F. T. , Sienz J. , Langley D. S.
Published: April 2004

A gradient‐based method is applied to determine optimum profiles of the restrictor (choker bar) required to obtain the best possible flow distribution uniformity in a 1.2 m wide slit die of given design, in a range of applications involving three materials of varying degrees of shear thinning, each at a high and a low flow rate. The kernel of the optimization is a simulation of die performance that takes into account the effects of die body deflection (‘clam shelling’) in a fully coupled flow/deflection analysis. For the most sharply varying restrictor profile, a linear elastic analysis is carried out, which shows that the optimum profile cannot be obtained by bending the bar without exceeding the tool steel yield point. The use of inter‐changeable bars, machined to the optimum profiles computed for various applications, is proposed to extend the operating range of dies. Alternatively, the highly adjustable membrane restrictor technology may be used. The developed software makes it possible to predict whether restrictor adjustment can produce acceptably uniform flow distribution in a given application, using a given die, and shows what restrictor profile should be set up, thereby eliminating or reducing the need for online trial and error adjustment.
Effects of process parameters on the micro molding process
Authors: Zhao J. , Mayes R. H. , Chen Ge , Xie Hong , Chan Poh Sing
Published: April 2004

The trend towards miniaturization has brought about strong demand for increasingly smaller precision‐molded plastic components. In order to control metering accuracy and homogeneity of the very small quantities of melt in the micro molding process, new micro molding machines that use an injection system comprising a screw extruder and a plunger injection unit have been developed. By use of such injection systems, standard plastic granules can be handled by the screw extruder and melt accuracy can be achieved by the electrically driven injection plunger. The objective of this work is to investigate the effects of the process parameters on the micro molding process and part quality. A series of micro gears were molded using a polyoxymethylene resin in a set of statistically designed experiments. Micro component inspection, characterization, and data analysis work was carried out to study the molded gears. It was found that metering size and holding pressure time are the process parameters that have the most significant effects on part quality, and that the process is also significantly affected by the interaction of these two parameters. There is an optimum metering size range in which the hold pressure can act together with the metering size to properly fill micro mold cavities.
Blends of nylon/acrylonitrile butadiene rubber: Effects of blend ratio, dynamic vulcanization and reactive compatibilization on rheology and extrudate morphology
Authors: Kumar C. Radhesh , Nair Sobha V. , George K. E. , Oommen Z. , Thomas Sabu
Published: April 2004

The melt flow behavior of thermoplastic elastomers from nylon and nitrile rubber (NBR) was studied as a function of blend ratio, dynamic crosslinking, compatibilization and temperature. The morphology of the extrudates, i.e., the size, shape and distribution of the domains, was analyzed. Uncompatibilized and compatibilized blends showed pseudoplastic behavior. The viscosity of the blends showed positive deviation from a linear rule of mixtures. Compatibilization using chlorinated polyethylene (CPE) increased the melt viscosity of the blends. The addition of the compatibilizer decreased the domain size of the dispersed phase, followed by an increase after a critical concentration of the compatibilizer, where the interface was saturated. The influence of dynamic vulcanization on the rheological behavior was also studied. The extrudate morphology depended on blend ratio, compatibilization and shear rate.
Poly(L‐lactic acid) composites with flax fibers modified by plasticizer absorption
Authors: Wong Susan , Shanks Robert A. , Hodzic Alma
Published: April 2004

The effect of modified flax fibers by plasticizer absorption in poly(L‐lactic acid) composites was investigated. The plasticizes chosen were triethyl citrate (TEC), tributyl citrate (TBC) and glycerol triacetate (GTA), which were derived from natural sources. Characterization was performed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The morphology was examined from scanning electron microscopy (SEM) and optical microscopy (OM). The results showed that the plasticizer caused a marked increase in the storage modulus of the composites, which could be due to an improvement in the morphology of the matrix and a smoother surface coverage of the fibers by the matrix. The thermal properties were also affected, in which the glass transition temperature (Tg), the crystallization temperature (Tc) and the crystallinity (Xc) were reduced depending on the plasticizer. The citrate esters revealed to be the most effective plasticizers of those tested.
Comparison of vibration and hot‐tool thermoplastic weld morphologies
Authors: Stokes Vijay K.
Published: April 2004

Because of very different heating rates in hot‐tool and vibration welding, and the higher weld pressures used in vibration welding inducing more squeeze flow, the weld zones in these two processes see very different flows and cooling rates, resulting in different morphologies. The weld morphologies of bisphenol‐A polycarbonate (PC) and poly(butylene terephthalate) (PBT) for these two processes are discussed in relation to these differences. The thickness of the heat‐affected zone (HAZ) in hot‐tool welds increases with the melt time; this zone is thicker than in vibration welds. The HAZ thickness in hot‐tool welds increases from the center toward the edges. The HAZ thickness is more uniform in vibration welds. Hot‐tool welds of PC have large numbers of bubbles around the central plane; the bubble size increases from the center to the edges. PC vibration welds do not have bubbles except near the edges. Both hot‐tool and vibration welds of PBT do not have bubbles. The morphology of the HAZ in PBT is very different in hot‐tool and vibration welds. In hot‐tool welds, the resolidified material consists of a sandwich structure in which two thin layers with very small crystallites surround a thicker central layer in which the spherulites are almost as large as in the original molded material. In vibration welds, the HAZ has large crystallinity gradients across the weld zone as well as squeeze‐flow induced distortion of the small spherulites.
Elasticity at large deformations and high strain rates in injection molded polypropylene
Authors: Dijkstra P. T. S. , Gaymans R. J. , Van Dijk D. J. , Huétink J.
Published: April 2004

The deformation behavior of isotactic polypropylene (PP) as a function of strain rate was investigated at 50°C in uniaxial tension. Injection molded dogbone specimens were tested at high strain rates, ε = 10−1 – 102 s−1, and the local deformation in the neck was studied using fast tensile videometry. A strong elastic recoil was observed after fracture in this strain rate range with local elastic strains as high as ϵe = 2.0 – 3.2. The recoil is very fast and takes place within 1 ms. The elastic fraction of the strain at break was found to increase with the local strain rate. The elasticity further depends on strain and temperature. The elastic deformation behavior is part of the known transition from ductile cold drawing behavior to brittle fracture that occurs with strain rate or temperature. The elasticity in PP is thought to be due to a decrease in crystallinity, resulting in a discontinuous crystalline structure comparable to that of thermoplastic elastomers.
Fracture behavior of core‐shell rubber–modified clay‐epoxy nanocomposites
Authors: Gam K. T. , Miyamoto M. , Nishimura R. , Sue H. J.
Published: April 2004

Morphology and fracture mechanisms in two nanoclay‐filled epoxy systems were investigated using both microscopy and spectroscopy tools. Clay exfoliation was achieved using a series of sample preparation steps, and confirmed using wide angle X‐ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Significant improvement in modulus was obtained when clay exfoliation was achieved. Incorporation of core‐shell rubber (CSR) in both caly‐filled epoxy systems leads to greatly enhanced fracture toughness. Optical microscopy and TEM observations of the CSR‐modified nanocomposites suggest that CSR cavitation. shear yielding of the matrix, clay layer delamination. CSR bridging, crack bifurcation. and crack deflection are among the operative toughening mechanisms observed, depending on the nature of the epoxy matrix utilized.
Influence of post‐extrusion parameters on the final morphology of polystyrene/high density polyethylene blends
Authors: Padilla‐Lopez H. , Vázquez M. O. , González‐Núñez R. , Rodrigue D.
Published: April 2004

The deformation of the dispersed phase in polystyrene/high density polyethylene (PS/HDPE) blends produced by ribbon extrusion was studied numerically and experimentally. A mathematical model for the deformation of the dispersed phase in ribbon extrusion processing of polymer blends was developed assuming uniaxial deformation of the ribbon and the equilibrium shapes of the dispersed particles with a pressure balance over a drop. Simulated morphologies as function of the post‐extrusion parameters were obtained and compared with experiments. The analysis of the ribbon extrusion process showed that parameters such as draw ratio (DR) and ribbon‐water contact length (X) significantly influence the ribbon dimensions, the extensional stress, and the stretching force. The results also showed that deformation and coalescence of the dispersed phase in the ribbon extrusion processing of polymer blends increase at higher DR and/or lower X values. The comparison between the model and the experimental morphologies of PS/HDPE produced a good agreement.
Compensating for die swell in the design of profile dies
Authors: Gifford W. A.
Published: April 2004

Because of the effects of die swell, the final shape of an extrudate is often substantially different from that of the exit opening of the die. As a result, the design of profile dies producing complex shapes often involves more than just “balancing” the die but also compensating for the effects of die swell. Typically, a successful design of such dies is achieved only through much “cut and try,” However, with the use of a fully three‐dimensional finite element flow algorithm along with quick mesh generating capabilities, the usual cut and try involved in the design of many profile dies can be greatly reduced, if not eliminated. This paper demonstrates how the effects of die swell can be compensated for in the design of profile dies. For profiles with one plane of symmetry, this includes compensating for the sideways translation of the extrudate as well as the change in shape that the extrudate experiences. Completely asymmetric profiles undergo a “twisting” downstream of the die. This twisting, which appears not to have been reported in the literature (at least for isothermal extrusion), is also accounted for here, along with the change in shape that the extrudate undergoes. The translation or twisting of profiles downstream of a die is often attributed to non‐Newtonian or non‐isothermal effects. Only isothermal Newtonian examples are considered here. These results clearly show that asymmetry of the profile will result in a translation and twisting of the extrudate even in the isothermal Newtonian case.
Preparation of strach‐graft‐polyacrylamide copolymers by reactive extrusion
Authors: Willett J. L. , Finkenstadt V. L.
Published: April 2004

Graft copolymers of starch and polyacrylamide (PAAm) were prepared by reactive extrusion using a co‐rotating twin‐screw extruder and ammonium presulfate initiator. Feed rates were 109 g/min to 325 g/min (all components) at a moisture content of 50%, with screw speeds in the range 100 rpm to 300 rpm. Starch/acrylamide weight ratios ranged from 5:1 to 1.3:1. Conversions of acrylamide to PAAm were generally 80% or greater with residence times of 400 seconds or less. Conversion increased with feed rate, suggesting that reaction efficiency was proportional to the degree of fill in the extruder. Grafting efficiencies were in the range of 50% to 80%. PAAm molecular weight increased with increasing acrylamide content, consistent with free radical polymerization kinetics. Extrusion temperature had no significant impact on acrylamide conversion. Graft frequency, as measured by the number of anhydroglucose units per graft, was essentially constant over the starch: acrylamide ratio and temperature range studied. These results show that reactive extrusion offers the potential for rapid production of starch graft copolymers with unsaturated monomers.
Characterization of fractionated phenolic resins used in photoresists
Authors: Wanat Stanley F. , Rahman M. Dalil
Published: April 2004

Novolak resins fractionated using a liquid/liquid centrifugal fractionation/separation technique were characterized and contrasted to resins fractionated by conventional methods. The new fractionation method resulted in higher yields of resins with comparable or improved functional properties when used in i‐line sensitive (365 nm) photoresist formulations. By characterizing the isolateld resin and the lower molecular weight (Mw) fractions removed during fractionation, a better understanding of the structural differences associated with the fractionation processes could be determined. The potential for improving the fractionation/separation process and for obtaining higher yields and more consistent resists with the resins was identified.
Layered silicate nanocomposites based on various high‐functionality epoxy resins. Part II: The influence of an organoclay on the rheological behavior of epoxy prepolymers
Authors: Becker Ole , Sopade Peter , Bourdonnay Romain , Halley Peter J. , Simon George P.
Published: April 2004

The effect of an organically surface modified layered silicate on the viscosity of various epoxy resins of different structures and different functionalities was investigated. Steady and dynamic shear viscosities of the epoxy resins containing 0–10 Wt% of the organoclay were determined using parallel plate rheology. Viscosity results were compared with those achieved through addition of a commonly used micronsized CaCO3 filler. It was found that changes in viscosities due to the different fillers were of the same order, since the layered silicate was only dispersed on a micron‐sized scale in the monomer (prior to reaction), as indicated by X‐ray diffraction measurements. Flow activation energies at a low frequency were determined and did not show any significant changes due to the addition of organoclay or CaCO3. Comparison between dynamic and steady shear experiments showed good agreement for low layered silicate concentrations below 7.5 wt%, i.e. the Cox‐Merz rule can be applied. Deviations from the Cox‐Merz rule appeared at and above 10 wt%, although such deviations were only slightly above experimental error. Most resin organoclay blends were well predicted by the Power Law model, only concentrations of 10 wt% and above requiring the Herschel‐Buckley (yield stress) model to achieve better fits. Wide‐angle X‐ray measurements have shown that the epoxy resin swells the layered silicate with an increase in the interlayer distance of approximately 15 Å, and that the rheology behavior is due to the lateral, micron‐size of these swollen tactoids.
Melting model for intermeshing counter‐rotating twin‐screw extruders
Authors: Wilczynski Krzysztof , White James L.
Published: April 2004

Previous experimental studies of melting of pellets in an intermeshing counter‐rotating twin‐screw extruder have shown that melting is initiated both between the screws and at the barrel. Models are developed for melting in both those regions. The melting between the screws is initiated by frictional work on the pellets by the calendering stresses between the screws. The melting action at the barrel is induced by a barrel temperature higher than the melting point and propagated by viscous dissipation heating of the melt film produced.
Structure‐property relationships of blends of polycarbonate
Authors: Cheah K. , Cook W. D.
Published: April 2004

Three grades of bisphenol‐A polycarbonate—high molecular weight linear, high molecular weight branched and low molecular weight linear—and their blends have been studied by GPC, DMTA, DSC, rheometry and impact measurements. The molecular weight distribution of the blends agred with that predicted from the component's distributions, indicating that no transesterification reactions had occurred during melt blending. The Tg of the blends varied with blend composition according to the Fox equation and was related to the reciprocal molecular weight predicted by the Flory‐Fox equation. The low shear rate viscosity of the blends agreed with a logarithmic rule of mixtures and showed power‐law dependence on the weight average molecular weight. At higher shear rates, shear thinning was observed. The steady shear viscosity correlated well with the dynamic viscosity, as suggested by the Cox‐Merz relation. The stress relaxation behavior of the melt was very sensitive to the blend composition and molecular weight and correlated well with the real modulus. Temperature studies of the dart impact energy showed that only the low molecular weight polymer underwent a brittle‐duetile transition at ea −30°C and that all the blends were tough at room temperature. The enhanced stress triaxiality inherent in the notched lzod test caused the impact strenght at room temperature to decrease almost linealy with blend composition.