bluuebunny/crossref_metadata_2025_split huggingface dataset:
Starch‐filled ternary polymer composites. I: Dynamic mechanical properties
Authors: Lawrence S. St. , Walia P. S. , Willett J. L. 
Published: April 2004

AbstractThe 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

AbstractIntercalated 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

AbstractMelt 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

AbstractMorphology 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

AbstractWe 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

AbstractThe 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

AbstractIn 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

AbstractThis 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

AbstractThe 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

AbstractRecent 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

AbstractTwin‐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

AbstractPressure 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractBecause 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

AbstractThe 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.