bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prediction of flow patterns in the polyurethane foaming process by numerical simulation considering foam expansion
Authors: Mitani Tetsuo , Hamada Hiroyuki 
Published: April 2004

AbstractWe present a foam flow model for flow pattern prediction in the polyurethane foaming process that considers the flow caused by foam expansion due to bubble generation. The flow pattern in the cavity is calculated by taking into account the initial volume shape and the rate of foam expansion of a poured reaction mixture. The validity of the model is investigated by applying it to the Hele‐Shaw formulation, which assumes that the cavity is very thin compared to its width. The predicted flow patterns generally agree closely with experimental results measured in panel‐type molds. A three‐dimensional simulation is further developed based on the Stokes flow. The numerical formulation is performed by the control volume based‐finite element method with an equal‐order velocity‐pressure formulation that does not exhibit spurious pressure modes. The flow patterns predicted by the three‐dimensional simulation agree very closely with the experimental results. In particular, it clearly expresses the edge effect, in which the flow slows down at the edge, which is ignored in the Hele‐Shaw formulation. This numerical simulation is suitable for rapid determination of the pouring position, volume of the mixture, and the air vent position.
Tensile mechanical behavior of linear high‐density polyethylenes modified with organic peroxide
Authors: Pérez Claudio J. , Cassano Guillermo A. , Vallés Enrique M. , Quinzani Lidia M. , Failla Marcelo D. 
Published: April 2004

AbstractThe molecular structure of several high‐density polyethylenes of different molecular weights and vinyl contents was modified without altering their thermoplastic character using an organic peroxide. Chain linking was the main chemical event that occurred during the modification process. Samples of these polymers were crystallized from the melt, generating materials with different morphologies. Two crystallization procedures were followed: slow cooling and quenching. The density and crystallinity of the polymers were found to be slightly dependent on the molecular structures generated by the modification process. Tensile tests were performed at room temperature to evaluate the mechanical behavior of the polymers. The mechanical response of some of the slowly cooled samples changed from brittle to ductile when increasing concentrations of peroxide were added to the formulation. All the quenched samples displayed ductile behavior. The elastic modulus and yield stress were found to increase linearly with the crystallinity of the polymers independently of the molecular structure generated by the modification process. The molecular weight of the modified polymers appears to be the main structural property that influences the draw ratio after break and the ultimate tensile stress of the samples. The draw ratio diminishes, while the ultimate tensile stress increases with the molecular weight of the polymers, irrespective of the evolution of other molecular parameters.
Super‐toughness in compatibilized poly(butylene terephthalate)/poly(ethylene‐octene) copolymer blends
Authors: Aróstegui A. , Nazábal J. 
Published: April 2004

AbstractPoly(butylene terephthalate) (PBT)/poly(ethylene‐octene) (PEO) blends containing 1.0 wt% epoxy and from 0 to 30 wt% PEO were obtained by extrusion and injection molding. The blends were composed of two pure amorphous phases. The observed torque increases showed that epoxy reacted with PBT, leading to a fine and homogeneous morphology up to 15 wt% PEO content, which appeared larger and more heterogeneous at higher PEO contents. Toughness values fifteen‐fold those of pure PBT were obtained with only 13 wt% PEO. The tensile properties, including ductility, decreased with increasing PEO content, indicating that the adhesion level necessary for high ductility is higher than that necessary for super‐toughness. The inter‐particle distance (τ) was the main parameter that controlled toughness. The comparison of the results of this work with those of the same PBT/PEO blends with two different compatibilizers provides additional strong evidence of the adhesion at the interphase as the main parameter that controls the critical τ in these modified thermoplastic/rubber blends.
Measurements of the thermal conductivity and thermal diffusivity of polymers
Authors: Zhang Xing , Fujii Motoo 
Published: April 2004

AbstractIn this paper, the thermal conductivity and thermal diffusivity of nine polymers were measured by using the transient short‐hot‐wire method. The corresponding specific heat was measured with a commercial Differential Scanning Calorimeter (DSC). The effects of temperature on the thermal conductivity, thermal diffusivity, and the product of density and specific heat are further discussed. The results show that the transient short‐hot‐wire method can be used to measure the thermal conductivity, thermal diffusivity, and the product of density and specific heat of polymers within uncertainties of 3%, 6%, and 9%, respectively.
Spinning and drawing properties of ultrahigh‐molecular‐weight polyethylene fibers prepared at varying concentrations and temperatures
Authors: Jian Tao , Shyu Wei‐De , Lin Yue‐Tang , Chen Kan‐Nan , Yeh Jen‐Taut 
Published: April 2004

AbstractThe concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed.
Effect of wall slip on blown film thickness distribution
Authors: Higuchi Hiroyuki , Sato Mikio , Koyama Kiyohito 
Published: April 2004

AbstractOne of the most important materials for blown film is high‐density polyethylene (HDPE) with wide molecular weight distribution. First, we computed a wall stress at the entrance of a spiral groove in a particular die during blown film processing on a particular condition, to which a similar condition is widely utilized in a film works. The computed value is about 170 kPa, while the HDPE melt slips at die wall at stresses above approximately 50 kPa. The stress of 170 kPa is sufficiently large for the slip occurrence of the melt. Then, we investigated the effects of wall slip and melt visosity on film thickness distribution in the circumferential direction; the distribution tends to decrease with decreasing wall slip and melt viscosity. This tendency is explained by considering flow distribution in a spiral mandrel die and polymer melt flow characteristics.
Water‐assisted injection molding of thermoplastic materials: Effects of processing parameters
Authors: Liu Shih‐jung , Chen Yen‐show 
Published: April 2004

AbstractThe objective of this study was to experimentally investigate the effects of various processing parameters on the water‐assisted injection molding of thermoplastic materials. Experiments were carried out on a lab‐developed water‐assisted injection molding system, which included a water pump, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. Two types of water injection pins designs were proposed to mold the parts. After molding, the lengths of water penetration in molded parts were measured. The effects of different processing parameters on the lengths of water penetration were determined. It was found that the shrinkage rate and the viscosity of the polymeric materials, and the void shapes of the hollowed cores mainly determined the water‐penetration lengths in molded products. In addition, a comparison has been made between the parts molded by water assisted injection molding and gas‐assisted injection molding. It was found that water‐assisted injection molded parts exhibit less uniform void sizes along the water channel. The cycle time for water‐assisted injection molded parts was shorter than that of conventional injection molded parts and gas‐assisted injection molded parts.
A study of residence time distribution in co‐rotating twin‐screw extruders. Part I: Theoretical modeling
Authors: Poulesquen A. , Vergnes B. 
Published: April 2004

AbstractA theoretical model to determine the residence time distribution (RTD) in a co‐rotating twin‐screw extruder is proposed. The method consists of coupling a continuum mechanics approach with a chemical engineering one and allows us to obtain the RTD without any adjustable parameter. The process parameters are obtained using Ludovic® twin‐screw modeling software, and ideal reactors are chosen to depict the screw profile. The influence of screw speed, feed rate and viscosity on RTD are described on a fictive screw profile. The predictions of the model are in qualitative agreement with literature data. The key point of this procedure is obviously the correct association between an ideal reactor and a screw element.
Generalized slit flow of an ellis fluid
Authors: Steller Ryszard T. 
Published: April 2004

AbstractIsothermal, steady‐state and fully developed flows of Ellis fluids in planar and annular slits are discussed. The flow equations derived for Ellis fluids describe also the flows of Newtonian and power law fluids as specific cases. The most important flows resulting from thp general theory, i.e., the pressure flows in flat and annular slits for stationary channel walls and at transverse and longitudinal movements of a wall, are analyzed in detail. Numerical verification of the results leads to the conclusion that the planar and annular flows of Ellis and power law fluids are qualitatively similar The quantitative differences resulting from the slit curvature and the type of constitutive equation are relatively large only for flows of strongly non‐New‐tonian liquids.
The effect of wall slip on the performance of fiat extrusion dies
Authors: Gifford W. A. 
Published: April 2004

AbstractFlat extrusion dies are commonly used in a wide variety of film. Sheet and coating applications. Although flal dies can be designed to produce an exit flow distribution that is very uniform across most of the width, there will usually be a region along each side where it drops gradually to zero. This often requires trimming the edges of the film or sheet downstream in order to meet product specifications. It is commonly believed that treating the land area of the die with coatings that promote a small amount of wall slip will reduce the size of this edge effect and therefore improve die performance. This analysis shows that slip over the entire land region of the die will adversely affect die performance. Better performance is possible but only if the sides of the land are treated.
Rheological effects of the incorporation of chlorinated polyethylene compatibilizers in a HDPE/PVC blend
Authors: Zárraga A. , Muñtoz M. E. , Peña J. J. , Santamaría A. 
Published: April 2004

AbstractSmall‐amplitude oscillatory measurements, creep and recoil experiments, capillary extrusion flow and shrinkage measurements have been performed to elucidate the effect of block and random chlorinated polyethylene (CPE) on the rheological properties of a ternary high density polyethylene (HDPE)/ poly(vinyl chloride) (PVC)/CPE system. It is observed that the storage modulus, the complex viscosity and the steady stale viscosity at low shear rates decrease when a small amount of CPE is incorporated to 50/50 (wt.) HDPE/PVC binary blend. However, at high shear rates, in experiments performed in extrusion flow, the trend is reversed, and the incorporation of CPE to the binary blend increases viscosity. The high melt elasticity of HOPE is severely reduced when this polymer is mixed with PVC, but when CPE is included as a third component, elastic recovery is considerably increased. All these rheological results, which are independent of type (block or random) of CPE used, are explained considering the morphological changes produced by CPE and during extrusion flow.
Crystallization characteristics of polyoxymethylene with attapulgite as nucleating agent
Authors: Xu Wei‐Bing , He Ping‐Sheng 
Published: April 2004

AbstractThe nucleation of polyoxymethylene (POM) crystallization using attapulgite was studied using differential scanning calorimetry, polarized light microscopy, wideangle X‐ray diffration and mechanical testing. Two isothermal crystallization kinetic equations were employed to describe the crystallization of virgin POM and POM containing attapulgite as a nucleating agent. The addition of attapulgite decreased the spherulitic size of POM, and interfacial free energies per unit area perpendicular to the molecular chain direction ρe, accelerated the crystallization growth rate and enhanced the impact toughness of POM, but no change occurred for the hexagonal system of POM. The addition of attapulgite up to its saturation concentration in POM increased the number of effective nuclei by three orders of magnitude. A high concentration of attapulgite caused agglomeration of the agent and lowered the number of effective nuclei.
Grafting of poly(vinyl chloride) and polypropylene with styrene in a supercritical CO2 solvent medium: Synthesis and characterization
Authors: Trivedi Akshay H. , Kwak Soonjong , Lee Sunggyu 
Published: April 2004

AbstractGraft copolymerization of styrene onto poly(vinyl chloride) (PVC) and polypropylene (PP) was carried out in a supercritical CO2 medium using AIBN as a free radical initiator. The supercritical CO2 medium served as a reaction medium in addition to being a solvent for the styrene monomer and the free radical initiator. The reaction temperature and pressure were kept above the critical points of the solvent‐monomer mixture to form a homogeneous single‐phase medium. The resulting graft copolymers were characterized using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) techniques. The weight percent of grafting was determined using IR absorbance ratio technique. TGA results showed that the thermal stabilily of grafted copolymer of PVC was better than that of PVC, while grafted copolymer of PP had poorer thermal stability than PP. DSC results showed that glass transition temperatures (Tg's) of the grafted copolymers were higher than those of the starting polymers PVC and PP. The presence of polystyrene attached to the backbone polymer was confirmed by 1H NMR and 13C NMR analyses.
Effects of CO2 on crystallization kinetics of polypropylene
Authors: Takada Mitsuko , Tanigaki Masataka , Ohshima Masahiro 
Published: April 2004

AbstractWhen CO2 dissolves into a polypropylene (PP), its crystallization kinetics changes These changes were studied, in the expectation that the information would reflect on the behavior of other semicrystalline polyolefins. The isothermal crystallizatior rate of the PP‐CO2 solutions was measured using a high‐pressure differential scanning calorimeter (DSC), which performed calorlmetric measurements while keeping the polymer in contact with pressurized CO2. Although the measured crystallizatior rate followed the Avrami equation, the value of the crystallization kinetic constant was different from that measured for PP crystallized in air under atmospheric pressure. The dissolved CO2 decreased the overall crystallization rate of PP within the nucleation dominated temperature region. This suggests that the dissolved CO2 decreases the melting and the glass transition temperatures and prevents formation of critical size nuclei.
Transparency of polymer blends
Authors: Maruhashi Yoshitsugu , Iida Setsuko 
Published: April 2004

AbstractPolymer blending is useful for improving physical properties. Blends of transparent polymers are generally hazy. However, transparency is required in many products such as packages (especially PET bottles). The miscible blends, PET (polyethylene terephthalate)/PBT (polybuthylene terephthalate), maintain transparency in almost all cases regardless of the blending ratio, whereas the immiscible blends, PET/MxNYLON (MXD6 nylon, i.e. polymethaxylirene adipamide) and PET/PMAI (polymethacril imide, i.e. N‐methyl dimethyl glutarimide) become hazy as the blending ratio increases. The reason for this haze is the number and size of the dispersed particles. Differences in the refractive indices of various polymers also have a large influence on haze. Stretching makes even the transparent blends hazy in the case of PET/MxNYLON. One reason for this phenomenon is that stretching increases the size of the dispersed particles in the sheet plane. A second reason is that the difference in the anisotropic refractive indices of the matrix and the dispersed phase is increased by stretching. These effects are very consistent with light scattering theory.
Computer simulation of stress‐induced crystallization in injection molded thermoplastics
Authors: Guo Jianxin , Narh Kwabena A. 
Published: April 2004

AbstractInjection molding of semicrystalline plastics was simulated with the proposed stress‐induced crystallization model. A pseudo‐concentration method was used to track the melt front advancement. Stress relaxation was considered using the WFL model. Simulations were carried out under different processing conditions to investigate the effect of processing parameters on the crystallinity of the final part. The simulation results reproduced most of the experimental results in the literature. Comparison is made between the slow‐crystallizing polymer (PET) and fast‐crystallizing polymer (PP) to demonstrate the effect of stress on the crystallization kinetics during the injection molding process for materials with different crystallization properties. The results show that for fast‐crystallizing plastics, stress has little effect on the final crystallinity in the injection molded parts.
Processing and properties of polymeric nano‐composites
Authors: Wang Hua , Zeng Changchun , Elkovitch Mark , Lee L. James , Koelling Kurt W. 
Published: April 2004

AbstractPolymeric nano‐composites are prepared by melt intercalation in this study. Nano‐clay is mixed with either a polymer or a polymer blend by twin‐screw extrusion. The clay‐spacing in the composites is measured by X‐ray diffraction (XRD). The morphology of the composites and its development during the extrusion process are observed by scanning electron microscopy (SEM). Melt viscosity and mechanical properties of the composites and the blends are also measured. It is found that the clay spacing in the composites is influenced greatly by the type of polymer used. The addition of the nano‐clay can greatly increase the viscosity of the polymer when there is a strong interaction between the polymer and the nano‐clay. It can also change the morphology and morphology development of nylon 6/PP blends. The mechanical test shows that the presence of 5–10 wt.% nano‐clay largely increases the elastic modulus of the composites and blends, while significantly decreases the impact strength. The water absorption of nylon 6 is decreased with the presence of nano‐clay. The effect of nano‐clay on polymers and polymer blends is also compared with Kaolin clay under the same experimental conditions.
Propylene polymerization in a semibatch reactor. Analysis of soluble metallocene catalyst behavior through reactor modeling
Authors: Belelli P. G. , Ferreira M. L. , Lacunza M. H. , Damiani D. E. , Brandolin A. 
Published: April 2004

AbstractWe study the process involved in metallocene activation and further propylene polymerization. In this paper, we begin by analyzing the behavior of soluble metallocene in propylene polymerization before advancing to the study of the heterogeneous polymerization. Experimental data obtained in a semibatch laboratory polymerization reactor using ethylenbisindenylzirconium dichloride (EtInd2ZrCl2)/ methylaluminoxane (MAO) are combined with a mathermatical model providing useful information such as number of active sites and their activation patterns. We present a mathematical model for the reactor that predicts not only reactor productivity but also the molecular properties of the product. We apply the model to soluble systems in order to find the optimal parameters for the catalyst itself and in the presence of different types of additives such as aluminum chloride (AlCl3) and ethyl benzoate (E.B.).
Microlayer coextrusion as a route to innovative blend structures
Authors: Jarus D. , Hiltner A. , Baer E. 
Published: April 2004

AbstractNanolayer and microlayer coextrusion is a method for combining two or three polymers as hundreds or thousands of alternating layers with individual layers as thin as tens of nanometers. The possibility for utilizing microlayer coextrusion as a tool for creating microplatelets of high aspect ration was explored. Polypropylene (PP) was combined with polyamide‐66 (PA66) in microlayers. A high volume fraction of PA66 microplatelets dispersed in PP was achieved by injection molding the microlayered materials at a temperature intermediate between the melting points of the two constituents. The difference in melting temperatures provided a broad processing window of about 60°C in which the PP layers melted to form the matrix whereas the PA66 layers remained in the solid state as dispersed microplatelets of high aspect ration. The resulting material had significantly improved oxygen barrier properties. An enhancement of 4–5 times over the barrier of the conventional melt blend resulted from increased tortuosity of the diffusion pathway.