bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extensional flow of polymeric dispersions
Authors: Bourry D. , Khayat R. E. , Utracki L. A. , Godbille F. , Picot J. , Luciani A. 
Published: April 2004

AbstractA general‐purpose extensional flow mixer, EFM, was recently introduced. To improve the understanding of its performance and potentials, several fundamental studies were initiated. These can be divided into two groups: (i) studies of the model drop deformation and breakup, and (ii) studies of the flow through EFM. Experimental, theoretical, and numerical methods (finite or boundary element methods, FEM or BEM, respectively) have been employed. The paper summarizes these efforts. The experimental study of flow of Newtonian and viscoelastic drops through a slit showed a difference in deformability. Initially, the former are reluctant to deform, but then deformaiton is rapid, whereas the viscoelastic drops initially deform readily, but then the deformation slows down. The slit flow does not flatten drops with diameters at least ten‐fold smaller than the slit gap. A comparison of the experimental data with the BEM 2‐D simulation showed that BEM provides good description of deformability. The effects of shear and elongation stress, the viscosity ratio, the drop diameter to channel gap ratio, the initial drop position, the interfacial tension coefficient, and elasticity of the dispersed phase were examined using the BEM. Simulation of flow through EFM was carried out using either FEM or Binding's theory. Both methods are suitable for computing the pressure losses and the stress fields. Analysis of flow lines can be used for optimization of the mixer's geometry.
Innovative TPV two‐phase polymers: Formulation, morphology formation, property profiles and processing characteristics
Authors: Fritz H. G. , Bölz U. , Cai Q. 
Published: April 2004

AbstractAn innovative TPV two‐phase polymeric system is described. The new TPV is composed of a polypropylene (PP) matrix in which a metallocene‐type ethylene/octene copolymer (EO) is dispersed. The EO‐copolymers are grafted with vinyl organosilanes, then blended with PP, hydrolyzed and water‐crosslinked in a co‐rotating, intermeshing twin‐screw extruder. The resulting TPV‐grades are easy to process into articles showing an attractive range of properties. The advantages are due to blend composition and crosslinking concept. The new TPV's can be‐processed without pre‐drying. Molding are characterized by excellent surface quality and absence of odor as a result of the innovative use of the EO elastomer and the modified crosslinking concept. They can easily be colored to any desirableshade. The reduced cost of ingredients is another advantage of the newly developed thermoplastic elastomers. High ultimate strength (σR) and elongation‐at‐break (εR) values as well as a broad spectrum of different Shore A grades open up many new fields of application. The main focus has been on the automotive applications not least because of very low fogging rates.
Micro‐morphology of modified and nonmodified blends of polypropylene with linear low density polyethylene
Authors: Scer F. , Rasoul F. , Kosior E. 
Published: April 2004

AbstractModified and nonmodified blends of linear low‐density polyethylene (PE) and polypropylene (PP) form separated phases of crystalline PP and PE. They form spherulitic crystals in the core, but highly oriented nonspherulitic phases at the skin of injection molded test bars. The dimension of the spherulites decreases with increasing PE content within the blends. Crystallization behavior of both crystalline phases is influenced by the other phase. The crystallization temperature of PP is increased in the presence of the compatibilizer. Transmission electron micrographs of blends modified by poly(styrene‐block‐ethylene/butylene) (SEBS) and stained by OsO4 showed co‐continuous lamellar structure of the blends with a polypropylene phase containing the majority of the modifier. Smaller portions of the modifier can be found on the surface of the two olefinic phases as dispersed spheres, with an average diameter of 50–90 nm. The lamellar structure is independent of the spherulitic structure, and interpenetrates the spherulites. The conclusion of this study is that this block copolymer, while improving the physical properties of the blends, is not a true compatibilizer of the system according to the conventional terminology of physical chemistry.
Relationship of fracture behavior and morphology in polyolefin blends
Authors: Niebergall U. , Bohse J. , Schürmann B. L. , Seidler S. , Grellmann W. 
Published: April 2004

AbstractHigh‐density polyethylene (HDPE) and isotactic polypropylene (PP) were mixed either with a stabilizer or with a stabilizer and a compatibilizer in different mixing ratios. The structure and properties of these blends were analyzed by methods such as torsion pendulum measurements, mechanical short time experiments, electron microscopy, and fracture mechanical toughness tests. The results display a strongly increased impact strength in the HDPE/PP blend with compatibilizer within a specific mixing region. The deformation behavior and the mechanism leading to the increased impact strength of the blends were investigated in tensile tests by acoustic emission analysis and scanning electron microscopy: Increased fibrilation and strong strain was registered in the blend with compatibilizer. The impact strength was modeled, using experimentally measured properties such as energy release rate, matrix and inclusion volumes, the impact strength of each component. The inclusion volume that causes plastic deformation was chosen as an additional parameter. The calculated results are in good agreement with the experimental ones.
Performance of talc/ethylene‐octene copolymer/polypropylene blends
Authors: Huneault Michel A. , Godfroy Patrice G. , Lafleur Pierre G. 
Published: April 2004

AbstractPolypropylene‐based compounds are increasingly attractive because of low cost, processability, and good balance of properties. In recent years, metallocene ethylene‐octene copolymers have started displacing EPR and EPDM as an impact modifier for PP. This study examines the effect of compounding conditions and composition on the properties of talc/ethylene‐octene copolymer/PP compounds. The mechanical properties of the compounds were not significantly affected by the mixing conditions on a laboratory twin screw extruder. The use of 30 wt% of talc provided a twofold increase in tensile modulus compared with pure PP. Impact resistance of filled and unfilled compounds was found to increase rapidly once the copolymer concentration reached around 20 wt% based on the polymer phase. Modulus and tensile strength decreased linearly with copolymer concentration. Four different commercial maleic anhydride‐grafted PPs were tested as interfacial modifiers. In the best cases, a slight tensile strength increase was observed when using between 2 and 10 wt% of modified PP.
Mixed connectivity composite material characterization for electroactive sensors
Authors: Wenger M. P. , Das‐Gupta D. K. 
Published: April 2004

AbstractElectroactive composites consisting of a ferroelectric ceramic in a polymer matrix have gained much interest as compliant electromechanical or pyroelectric sensors. Of the various theoretical models developed to understand the dielectric and electroactive properties of composites, the majority are based on a cube of unit dimensions representing the matrix with fractional inclusions representing the ceramic. Composite properties are dictated by the choice of constituent materials along with the intra‐ and inter‐connectivity of the separate phases. A ceramic powder randomly dispersed in a polymer matrix is referred to as having 0‐3 connectivity, i.e. the ceramic phase possesses no intra‐connectivity throughout the composite in thex,y, andzdirections, whereas the polymer possesses full intraconnectivity in these directions. For thin composite films, where the ceramic grain size is comparable to the film thickness, or for composites with high ceramic volume content, the degree of ceramic connectivity throughout the composite thickness will be enhanced over thick or low ceramic content composites, thus implying an amount of 1‐3 connectivity within the composite. In order to investigate the properties of such composites, a cube model has been applied that deals with mixed 0‐3 and 1‐3 connectivity composites. This paper reports on the experimental and theoretical characterization of two different mixed connectivity composites, one with a polar polymer matrix and another with a nonpolar matrix.
Modification of a Ziegler‐Natta catalyst with a metallocene catalyst and its olefin polymerization behavior
Authors: Ahn Tae Oan , Hong Sung Chul , Huh Wan Soo , Lee Young‐Chul , Lee Dong‐Ho 
Published: April 2004

AbstractA Ziegler‐Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl4 catalyst supported on MgCl2 (MgCl2‐Ti) with a rac‐ethylenebis(indenyl)zirconium dichloride (rac‐Et(Ind)2ZrCl2, EIZ) catalyst, the obtained catalyst showed relatively low activity but produced high isotactic polypropylene. These results suggest that the EIZ catalyst might block a non‐isospecific site and modify a Ti‐active site to form highly isospecific sites. To combine two catalysts in olefin polymerization by catalyst transitioning methods, the sequential addition of catalysts and a co‐catalyst was tried. It was found that an alkylaluminum like triethylaluminum (TEA) can act as a deactivation agent for a metallocene catalyst. In ethylene polymerization, catalyst transitioning was accomplished with the sequential addition of bis(cyclopentadienyl)zirconium dichloride (Cp2ZrCl2)/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiCl4/VOCl3, Ti‐V) catalyst. Using this method, it was possible to control the molecular weight distribution (MWD) of polyethylene in a bimodal pattern. In the presence of hydrogen, polyethylene with a very broad MWD was obtained due to a different hydrogen effect on the Cp2ZrCl2 and Ti‐V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning.
Influence of triblock copolymer interfacial modifiers on fracture behavior of polystyrene/ethylene‐propylene rubber blends
Authors: Odje Stephen , Vu‐Khanh Toan , Cigana Patrick , Favis Basil D. 
Published: April 2004

AbstractIn a previous study, two triblock copolymers of styrene/ethylene‐butylene/styrene (SEBS), of different molecular weights, were used to compatibilize a blend of 80 vol% polystyrene (PS) and 20% ethylene‐propylene rubber (EPR). The emulsification curve, which relates the average minor phase particle diameter to the concentration of interfacial agent added, was used to quantify the effect of the interfacial agents on the blend morphology. Links between morphology, interface, and properties were established by combining the emulsification curve with a fracture mechanics approach. The aim of this work is to foster the understanding of the effects of these two triblock copolymers on the fracture behavior of the blend over various loading rates and temperatures. The focus is on the brittle‐ductile transition in fracture behavior, which is a critical condition for the application of these materials. It has been found that adding an interfacial agent lowers the temperature at brittle‐ductile transition. However, this effect is much more pronounced for the copolymer with a lower molecular weight. The time‐temperature dependence of fracture performance of the blend is also affected by the interface and morphology. When loading rate increases, the shift of the temperature at brittle‐ductile transition is less significant for the blend with an interfacial agent having a lower molecular weight. The effect of loading rate and temperature on the brittle‐ductile transition in fracture performance of the blends is controlled by an energy activation process. Adding the interfacial agents results in a plasticizing effect of the polystyrene matrix and a reduction in the energy barrier controlling the fracture process. With the addition of interfacial agent, the yield stress slightly increases at low concentration, attains a maximum value, and then decreases. The increase in yield stress confirms the coupling role of the copolymer and is in agreement with the observed emulsification curves. The reduction of yield stress and increase in ultimate strain with the copolymer concentration demonstrate the plasticizing effect of the interfacial agent. The result of stress relaxation tests also confirms the above effects of the interfacial agent.
Plasticizing polylactide—the effect of different plasticizers on the mechanical properties
Authors: Jacobsen S. , Fritz H. G. 
Published: April 2004

AbstractPoly(lactide) (PLA), a biodegradable aliphatic polyester with excellent property profiles for different polymer applications, will play a major role in future markets for biodegradable polymers from renewable resources. PLA is a very brittle and stiff polymer with a glass transition temperature of around 58°C. The mechanical properties of PLA are comparable to those of polystyrene, with an elasticity modulus of 3500 MPa, a maximum tensile strength of 50 MPa, and an elongation at break of 4%. To introduce PLA into other applications requiring other mechanical property profiles, especially higher flexibility and higher impact resistance, it is necessary to use plasticizers. In this study the influence of several biocompatible plasticizer systems on the mechanical properties of PLA is determined. Poly(ethylene glycol), glucosemonoesters and partial fatty acid esters are introduced at 2.5, 5, and 10 wt% into polylactide. The mechanical properties, such as impact strength and the stress‐strain‐interrelationship of tensile tests, show changes, which are discussed.
Polylactide (PLA)—a new way of production
Authors: Jacobsen S. , Fritz H. G. , Degée Ph. , Dubois Ph. , Jérôme R. 
Published: April 2004

AbstractPoly(lactide) (PLA), a biodegradable aliphatic polyester with excellent properties for different polymer applications, has been used mostly in the biomedical field, mainly because of its high price, resulting from expensive polymerization and purification techniques. Although this polymer can play a major role in future markets for biodegradable polymers, the current high price has to be reduced significantly to at least $4 US/kg. Therefore, this paper aims to partially review the polymerization techniques traditionally used in PLA synthesis and to propose new developments that enable us to produce these polymers by an innovative process for just a portion of the costs traditionally charged, using reactive extrusion techniques in a closely intermeshing co‐rotating twin screw extruder. This paper gives an overview of attainable mechanical properties and future markets.
Variation in dielectric properties of an epoxy‐novolac molding compound during dynamic cure
Authors: Hsieh T. H. , Ho K. S. 
Published: April 2004

AbstractThe variation in dielectric characteristics of an epoxy‐novolac molding compound during dynamic cure was studied by means of dielectrometry (DE). Dielectric parameters such as permittivity (ϵ′), loss factor (ϵ″), and dissipation (tan δ) were observed to depend on various factors including temperature, frequency, the extent of cure (α, measured previously by using differential scanning calorimetry, DSC), as well as contributions from ionic conductivity (σ) and electrode polarization. The characteristic relaxation time (τ) and the relaxed permittivity (ϵr), suggested in the literature as possible parameters for cure monitoring purposes, was found difficult to determine because of interfernce from ionic conduction and electrode polarization. In comparison, σ could be measured throughout the entire cure process and was observed to depend only on temperature and α. In combination with our previous DSC results, an empirical function relating α to temperature and α was constructed. Our analysis also indicated that the strong maximum in the ϵ′ and the ϵ″ curves during the course of dynamic cure was a direct result of the α‐and the temperature‐dependence of σ; the strong maximum of ϵ″ is directly related neither to gelation nor to vitrification.
Biodegradability of poly(vinyl alcohol)
Authors: López O. Betty Lucy , Sierra G. Ligia , Mejía G. Amanda Inés 
Published: April 2004

AbstractPlastic waste increases at a rate of several tons per year and the time required for their biodegradation is often unknown. ThePhanerochaete chysosporiumfungus oxidizes a wide variety of toxic organic compounds to nontoxic compounds or CO2and H2O. The biodegradability of the poly(vinyl alcohol) (PVOH) caused by this fungus was analyzed by gel permeation chromatography (GPC) with differential refractive index (Δn) and ultraviolet (UV) detectors. During the GPC analyses, the PVOH is in contact with the components of the culture medium. These components can interact with the stationary phase and also with the polymer producing erroneous results in the molecular weight determination. Therefore, we compare results using differnt mobile phases. A phosphate‐acetate buffer of pH 7.4 was found to be appropriate mobile phase to follow the degree of degradation of the PVOH by the change in the average molecular weight determined by GPC in this culture medium. UV detection enabled us to identify structural changes associated with transformations of the carbonyl groups, mainly to enolized β‐diketones groups. Infrared absorption (FTIR) confirmed these changes and also showed important modifications in the C‐O stretching region probably due‐to apertures of cyclic ether groups or transformations of the OH groups by oxidation reactions.
The effect of TLCP melt structure on the bulk viscosity of high molecular mass polyethylene
Authors: Chan C. K. , Whitehouse C. , Gao P. 
Published: April 2004

AbstractA thermotropic liquid crystalline polyester (TLCP), denoted as TCLP3 and based on hydroxybenzoic acid, hydroquinone and sebacic acid, was used as a processing aid in the extrusion of high molecular mass polyethylene (HMMPE). This TLCP is in the nematic phase at 179.6–182°C. Capillary rheometry experiments were carried out at two processing temperatures: 190°C and 230°C. At 190°C TLCP3 is predominantly nematic and at 230°C it is predominantly isotropic. It is an effective processing aid for HMMPE, particularly at 190°C, with viscosity reductions in excess of 90% with a 1 wt% TLCP3/HMMPE blend. The rheological characteristics of the blends have been linked to the optical textures of the TLCP3 using hot‐stage optical microscopy. From the experimental observations speculations are made about the mechanisms of viscosity reduction. Initial viscosity reductions are caused by TLCP3 structure effects (fibrillation and phase change), giving rise to fibrillation‐induced molecular orientation in the neighboring HMMPE phase. This is only effective when nematic structures are present. Above a critical wall shear stress value the lubrication effect due to TLCP3 migration is dominant.
Effects of injection molding–induced morphology on the work of fracture parameters in rubber‐toughened polypropylenes
Authors: Karger‐Kocsis J. , Mouzakis D. E. 
Published: April 2004

AbstractThe effects of the injection‐molding induced skin‐core morphology on the fracture behavior of rubber‐toughened polypropylene (RTPP) systems were studied by employing the essential work of fracture (EWF) method. RTPP with 31 wt% ethylene/propylene rubber (EPR) showed no skin‐core structure after molding and the EWF approach worked well in this case. In contrast, RTPP with 10 wt% EPR exhibited a pronounced skin‐core morphology: EPR deplection and enrichment was observed in the skin and core region, respectively. This morphology caused necking instead of crack growth in deeply double edge‐notched (DDENT) specimens under tensile loading along the filling direction (MFD). The necking process not only was accompanied by a large scatter but also yielded highly unrealistic specific essential work of fracture (we) values. This skin‐core structure was also the reason for an anistropic EWF response of this system observed by loading the specimens both in longitudinal (L) and transverse (T) directions to the MFD. The failure sequence and its characteristics were studied by light microscopy (LM) and infared thermography (IT). It was concluded that the EWF approach cannot be applied for RTPP with a prominent skin‐core structure. Since yielding preceded the limited crack growth prior to necking in the loading directin for the DDEN‐T specimen of RTPP with 10 wt% EPR, the yielding‐related specific essential work (we,y) was used for toughness comparison. In case of RTPP with 31 wt% EPR, where yielding was less pronounced prior to the crack growth, the work of fracture until the maximum load was assigned to the yielding‐related work of fracture (wf,y) used for computing we,y. The latter value seems to be closely matched to the plane‐strain essential work of fracture value.
Precipitation‐redissolution liquid chromatography of styrene‐ethyl acrylate copolymers
Authors: Chiantore Oscar , Simonelli Alessandra 
Published: April 2004

AbstractThe technique of Precipitation‐Redissolution Liquid Chromatography (PRLC) has been applied for fractionation of styrene‐ethyl acrylate copolymers in the whole composition range, from one homopolymer to the other. Two different polar types of column packings were used, pure silica and CN modified silica. Samples dissolved in tetrahydrofuran were injected in the columns where a nonsolvent mixture is used as chromatographic mobile phase. Polymers precipitate in the columns, and their elution is obtained by applying a gradient of eluent with increasing polarity and solvent power. The different copolymers, and the homopolymers, could be separated as a function of acrylate unit content. The best gradient conditions were obtained with a compromise between resolution, efficiency and analysis time. It was found that the polarity of the packing influences the separation in term of retention and peak resolution. This means that a composite mechanism is involved, with adsorption effects adding to the precipitation in favoring the fractionation according to the sample polarity.
Influence of crystallinity on gas transprt in polymeric films
Authors: Horas Jorge A. , Rizzotto Marcos G. 
Published: April 2004

AbstractWe developed a model to describe the diffusion of gases through partially crystalline polymers. Diffusion is negligible in the crystalline fraction and occurs mainly in the amorphous region; however, crystallinity affects chain stiffness in the amorphous fraction. In our model this effect is taken into account in the activation energy calculation. The semicrystalline polymer in which diffusion takes place is treated as a heterogeneous medium in the framework of effective medium theories. An effective diffusion coefficient is obtained that takes into account the influence of both the presence of crystallites and the distribution of chain separations. We compare the results of two effective medium models and thus determine their respective applicability ranges.