bluuebunny/crossref_metadata_2025 huggingface dataset:
A model for the zero shear viscosity
Authors: Locati G. , Pegoraro M. , Nichetti D.
Published: April 2004

An empirical equation for the number of entanglements per molecule has been proposed, which applies over all the molecular weight range. On this ground a simple equation for the zero shear viscosity of monodisperse polymer melts, η0, has been worked out that appears able to properly take into account the sharp transition of viscosity between the monomeric and the entanglement regimes. The molecular parameters appearing in the new viscosity equation are: the monomeric molecular weight m0, the monomeric friction factor ζ0, the molecular weight M, the average molecular weight between entanglements Me, and the entanglement friction factor ζe3.4. This last parameter was evaluated for a number of monodisperse polymers.
Rheological and mechanical properties of recycled polypropylene
Authors: Incarnato Loredana , Scarfato Paola , Acierno Domenico
Published: April 2004

In order to verify the possibility of manufacturing good quality articles by recycled polypropylene (PP), a study on the effect of many recycling operations on the rheological and mechanical properties of PP was conducted. The amount of degradation occurring during the reprocessing was estimated in the melt state by means of rheological measurements and the results obtained were correlated with the weight average molecular weight Mw and the molecular weight distribution MWD. Since the properties in the solid state are strictly dependent upon the molecular structure parameters and the morphology, mechanical properties were checked on films produced from virgin and recycled PP with a cast technology. Moreover, in order to estimate the effect of film composition and of the number of reprocessings on the final properties of the manufactured articles, blend films having different percentages of PP recycled several times and virgin PP were prepared.
Thermally conductive EMC (epoxy molding compound) for microelectronic encapsulation
Authors: Kim Wonho , Bae Jong‐Woo , Choi Il‐Dong , Kim Yong‐Seog
Published: April 2004

Owing to the trend of faster and denser circuit design, the dielectric properties of packaging materials for semi‐conductors will have greater influence on performance and reliability. Also, as chips become more densely packaged, thermal dissipation becomes a critical reliability issue. Consequently, four important properties for manufacturing semi‐conductor packaging are: low values of dielectric constants, high values of thermal conductivity, relatively low values of thermal expansion coefficients, and low cost. Thus, in this study, AlN (Aluminum Nitride) was selected as the filler for an epoxy matrix to achieve increased performance of an EMC. As a result, the thermal conductivity of an EMC filled with 70 vol% of AlN increased as much as 7–8 times compared with the EMC filled with a crystalline silica (vol. 70%). When more than 60 vol% of AlN was added to the EMC, the dielectric constants and thermal expansion coefficient decreased rapidly.
Advances in calculating thermally induced stresses in nonlinear viscoelastic materials
Authors: Schmachtenberg E. , Schoeche N.
Published: April 2004

Temperature change can build up tensile stresses into thermoplastic materials, if their thermal expansion is hindered. This paper describes how to calculate those stresses. Because thermoplastic materials are time dependent with respect to temperature and strain, a nonlinear viscoelastic material model is necessary for the prediction of thermal stresses. This paper presents a numerical model that is able to predict thermally induced stresses in dependency on the load history. The calibration as well as the numerical procedures are described. The model is evaluated with a semicrystalline high density polyethylene (HDPE). Finally, a simulation of a screwed joint reveals the importance of this modeling for a more effective use of thermoplastics in the future.
Thermal analysis characterization of fiberglass epoxy prepreg used to join composite pipes
Authors: Mensah Patrick F. , Stubblefield Michael A. , Pang Su‐Seng , Wingard Doug
Published: April 2004

Thermal characterization of a fiberglass/epoxy prepreg fabric used as the bonding material to join composite‐to‐composite pipes by curing has been investigated. The prepreg material and composite pipes have temperature dependent thermal properties. Thus the resulting boundary value equations are nonlinear and analytical solutions cannot be easily obtained. Finite difference modeling (FDM) and numerical computational techniques were used to solve the one‐dimensional heat conduction with chemical kinetics in the thermosetting material. Temperature distributions and degree of cure within the composite pipe joint are predicted. A Differential Scanning Calorimeter (DSC) in both isothermal and dynamic modes was used to characterize the curing kinetic properties of the prepreg. The result of this characterization is necessary for optimizing the curing process to produce a superior heat activated coupled joint. In addition, to assess the effects of induced thermal stress in the joint, the temperature profile is needed. The methodology employed in this analysis compares favorably with data from experimentation.
Anhydride chain ends functionalization of poly(ethylene terephthalate)
Authors: Sclavons M. , Carlier V. , Legras R.
Published: April 2004

This paper aims at the end‐capping of poly(ethylene terephthalate) (PET) chainends in order to introduce anhydride moieties on this polymer. An acid chloride reactive carrier of anhydride was chosen because it selectively reacts by alkoxy‐dehalogenation with the hydroxyl chain ends of PET. This type of functionalization has already been described and claimed (1–3) on various polymers. However, in the present paper, a solid‐liquid synthesis is reported for the first time: The reaction was performed on solid PET powder swollen in a solvent of the trimellitic anhydride chloride. This new reaction method prevents the polymer from degrading. This point is supported by parallel studies of similar reactions performed in the melt and in solution.
Influence of molecular structure on the rheological and processing behavior of polyethylene resins
Authors: Kazatchkov I. B. , Hatzikiriakos S. G. , Bohnet N. , Goyal S. K.
Published: April 2004

The rheological and processing behavior (melt fracture performance) of linear lowdensity polyethylenes (LLDPEs) is studied as a function of both the weight average molecular weight (Mw) and its distribution (MWD). A number of LLDPE resins having different molecular characteristics were tested, with essentially one characteristic (Mw or MWD) changing at a time. The first series of resins consisted of nine samples having a wide range of polydispersities (3.3–12.7) and nearly constant Mw and short chain branching. The second series had six resins with varying Mw (51,000–110,000) but fixed MWD (about 4). The influence of Mw and MWD on the viscosity profiles, linear viscoelastic moduli as expressed by means of a discrete spectrum of relaxation times, extrudate swell, and melt fracture behavior for these resins is reported. Correlations between the molecular characteristics of the resins and their rheological and processing behavior are also reported. It is found that for a given molecular weight, the optimum melt fracture performance is obtained at a specific polydispersity value, and it is characterized by a minimum relaxation time for the resin defined in terms of recoverable shear.
Shear viscosity of nylon 6 melts reinforced with microfibrous calcium silicate hydrate
Authors: Tanaka Hideho , Watanabe Kunio
Published: April 2004

Steady shear viscosity of nylon 6 melts reinforced with xonotlite, microfibrous calcium silicate hydrate (6CaO · 6SiO2 · H2O), is investigated. The highly filled nylon 6 melt tends to exhibit a yield value, resulting in remarkable viscosity increase particularly at low shear rates. Addition of the xonotlite significantly increases activation energy of viscous flow of the nylon 6 melt, leading the viscosity to be strongly temperature dependent. Comparisons with the melts filled with glass fibers and wollastonite are made. Flow‐induced orientation becomes more important at low volume fractions. Shortening of the xonotlite during shear flow measurement can also be observed.
Optical and acoustical investigation for plastic deformation of isotactic polypropylene/ethylene‐1‐hexene copolymer blends
Authors: Yamaguchi Masayuki , Nitta Koh‐Hei
Published: April 2004

The effects of morphology on mechanism of plastic deformation are investigated for binary blends of isotactic polypropylene and rubbery ethylene‐1‐hexene copolymers. In this work, plastic deformation developed during elongation is investigated by measuring light transmittance, electron microscopy, and ultrasonic propagation in the temperature region between 298 K and 353 K. It is found that the compatible blends hardly show stress‐whitening at any temperature, whereas the incompatible blends show distinct stress‐whitening below 333 K. Furthermore, microscopic defects such as microvoids and crystalline defects are found to be precursors for crazing which are origin of the stress‐whitening.
Polybenzimidazole nanofiber produced by electrospinning
Authors: Kim Jong‐Sang , Reneker Darrell H.
Published: April 2004

Nanofibers of aromatic heterocyclic PBI (poly(2,2′(m‐phenylene)‐5,5′ bibenzimidazole)) polymer were made by an electrospinning process. The diameter of the fibers was around 300 nanometers. A liquid jet of a polymer solution, formed when electrical force overcame surface tension, stretched and dried as the solvent evaporated. The resulting electrically charged nanofibers were attracted to and collected on a rotating cylinder covered with aluminum foil that was electrically grounded. The fibers were collected in non‐woven sheets about 20 centimeters wide and 100 centimeters long, with a compressed thickness of a few tens of microns. The mass per unit area of the nonwoven sheets was 15 to 50 g/m2. The nonwoven fabric of PBI nanofibers was treated with sulfuric acid, and then washed, dried and heated to improve its strength. Optical microscopy showed that electrospun PBI nanofibers fibers were birefringent. Other morphological features of these fibers were observed with scanning electron microscopy, transmission electron microscopy and atomic force microscopy.
Drawing of high density polyethylene tube: Effect of different cooling conditions
Authors: Ulas I.
Published: April 2004

A method of producing biaxially oriented high density polyethylene tube is described where some of the deformation parameters may be controlled by a post mandrel cooling bath application. Experimental results show that dimensional stability of the drawn products primarily depend on uniform temperature distribution around the tube circumference. This research gives a clear understanding of the post mandrel deformation process and shows that natural cooling conditions may lead to inhomogeneous products having properties significantly different from water cooled products.
Solvent‐free generation of poly(vinyl acetals) directly from poly(vinyl acetate)
Authors: O'Neill Mark L. , Newman Deborah , Beckman Eric J. , Wilkinson Steve P.
Published: April 2004

The simultaneous methanolysis and butryalization of poly(vinyl acetate) was conducted via the reaction of methanol and butyraldehyde with polyvinyl acetate under batch conditions at temperatures from 70°C to 90°C at the vapor pressure of the reactants. It was found that use of an acid catalyst allowed for the methanolysis to be the rate limiting step of a simultaneous methanolysis‐butyralization reaction, minimizing the buildup of alcohol repeat units in the polymer during the reaction. As such, use of an excess of aldehyde was counterproductive in that it served to dilute both the methanol and the acetate groups in the polymer phase, lowering the overall rate of the reaction. With 20% stoichiometric excesses of methanol and butyraldehyde, it was possible to produce poly(vinyl butyral) directly from poly(vinyl acetate) with very low residual acetate and overall conversions equivalent to commerical samples. Further, carbon dioxide was evaluated as a reversible plasticizer for polyvinyl acetate during methanolysis. Results at various pressures were consistent with the expectation that the presence of CO2 would lower the reaction rate, primarily because of dilution of reactants in the CO2‐swollen polymer phase. Finally, it was shown that the simultaneous reaction procedure can be used to generate polyvinyl acetals from a variety of aldehydes.
Reinforcement of polyamide 6 with thermotropic liquid crystalline polymer
Authors: Kurokawa M. , Nagai S.
Published: April 2004

The in‐situ composites of polyamide 6 (PA 6)/liquid crystalline polymer (LCP) were investigated from the standpoint of fibrillation of LCP to develop a new high performance gear material for heavy load use that is superior to conventional plastic gears made of polyacetal (POM). LCP used was a wholly aromatic copolyester. PA 6 was chosen as the matrix polymer because of its excellent fatigue resistance. Extrusion of PA 6 added with LCP from 10 to 30 vol% was carried out at a temperature between 260 and 290°C by a twin screw extruder and take‐up equipment. Insitu fibrillation of LCP droplets, which were dispersed in PA 6 matrix, took place during the process. Injection molding of the composites was followed at a temperature below the softening point of LCP fibrils so as to keep the fibrils as extruded. Key factors for fibrillation of LCP were found as follows: (1) control of stress relaxation of LCP when the melt passes through the die‐head, (2) the optimum temperature of nent, (3) the optimum LCP content, and (4) addition of a small amount of 3rd component. A gear made of in‐situ composite of PA 6/LCP (30 vol%) added with 2‐functional epoxy resin (2.5 phr) was found to bear a load about 1.2 times heavier than a POM gear.
Influence of molecular parameters on material processability in extrusion processes
Authors: Nichetti D. , Manas‐Zloczower I.
Published: April 2004

A viscosity model showing a direct correlation between molecular weight distributions and shear thinning behavior of polymeric melts was used in 3D numerical simulations of an extrusion process. The equipment analyzed was a single screw extruder with an annular die attached. The material of choice in the simulations was polystyrene in a range of molecular weights and degrees of polydispersity. The influence of material parameters (molecular weight and polydispersity) on the system operating point, power consumption and residence time distribution was analyzed. The results were generalized and a window of processing conditions for resins with different properties was analyzed. The effect of blending homologous polymers with different molecular parameters on material processability was also presented. The model can be extended to other materials and various processing equipment.
A new method for estimating the cellular structure of plastic foams based on dielectric anisotropy
Authors: Nagata Shinichi , Koyama Kiyohito
Published: April 2004

The characterization of the cellular structure of plastic foams has long been of importance to investigate their physical properties. We have been developing an instrument that measures the orientation of seat materials based on their dielectric anisotropy. It is demonstrated by electromagnetic theory that composite materials with an island‐sea structure show a macroscopic anisotropy of dielectric constant because of the shape of islands, even if both the islands and sea are dielectrically isotropic themselves. The orientation based on the dielectric anisotropy caused by the shape of cells was investigated for the polystyrene by using our microwave cavity resonator method. From this data, a better manufacturing condition to minimize the thermal shrinkage was derived. The manufacturing condition was taken as extrusion rate, foaming temperature and die gap. The shape of cells of polystyrene foams was estimated using the derived equations, which express the maximum and minimum dielectric constant of whole composite materials as a function of the eccentricity of their ellipsoidal islands and the volume fraction and the dielectric constant of each materials in the islands‐sea structure.
Polypropylene reactor blends: Composition evaluation by analytical TREF
Authors: Zacur R. , Goizueta G. , Capiati N.
Published: April 2004

The molecular structure of a polypropylene (PP) blend, of the type referred to commercially as “impact polypropylene copolymer” (IPC), was studied and a procedure to determine its main component composition developed. The constituent species of the whole IPC, PP and ethylene‐propylene copolymers (EPC), were separated by step elution analytical Temperature‐Rising Elution Fractionation (TREF). The corresponding fraction compositions were calculated as percent areas of the fractogram. Since the EPC elution signal overlaps that of the homopolymer, an independent determination of pure PP fractions has to be performed in order to subtract its effect from the IPC profile. Thermal and molecular analysis of the recovered fractions by Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC), and spectroscopic analysis by FTIR and 13C‐NMR supported the necessary assumptions for a good estimation of the composition.
One‐line measurement of the residence time distribution in screw extruders
Authors: Hu Guo‐Hua , Kadri Ilham , Picot Claude
Published: April 2004

A fluorescence monitoring device was constructed to measure in real time the residence time distribution (RTD) function in screw extruders. Its centerpiece was an optical fiber probe capable of transmitting optical excitation energy to the processed flow stream and detecting the subsequent fluorescence emission. The source of fluorescence emission was an anthracene‐bearing substance that was injected to the flow stream as a pulse (tracer) in very small amounts. This device was validated against an off‐line ultraviolet spectrophotometer and self‐checked as well. In addition to its great sensitivity to fluorescence emission and ease of implementation on an extrusion line, this device could be used to monitor in real time subtle variations of an extrusion operation. The influence of the nature of anthracene‐bearing compounds on the measured distribution and the effects of processing parameters on the RTD function were also investigated.
Thermal analysis of vectra B950 liquid crystal polymer
Authors: Chung Tai‐Shung , Cheng Min , Pallathadka P. K. , Goh Suat Hong
Published: April 2004

The melting and crystallization behavior of Vectratm B950, a random liquid crystalline copoly(ester amide), was studied by differential scanning calorimetry (DSC). Nonisothermal experiments showed the existence of some interesting and peculiar transition behavior, which may depend on the crystallization conditions (cooling rate). In isothermal experiments, both the thermal and crystallization behavior have been studied as functions of annealing temperature and annealing time. Different thermal behaviors were observed, indicating the possibility of multiple states of mesophase aggregation In addition, the thermal decomposition of Vectra B950 was also studied by TGA‐FTIR in both nitrogen and air environments. A single‐stage decomposition process was found when heating in nitrogen atmosphere, and the decomposition is due to the easter linkage rupture. A double‐stage decomposition process was found when heating in air, and the decompositions are mainly due to the ester linkage rupture for the first decomposition step and the oxidative reaction for the second decomposition step. Annealing slightly changes the decomposition composition occuring in the early stage of thermal degradation.
Influence of the additive type and modification on the properties of blends of polyamide‐6 with poly(styrene‐co‐maleic anhydride)
Authors: Kelnar I. , Fortelný I. , Stephan M. , Jakisch L.
Published: April 2004

Addition of rigid poly(styrene‐co‐maleic anhydride) (SMA) to a polyamide‐6 (PA‐6) matrix leads to a system with increased stiffness and unchanged toughness as a consequence of absorption of deformational energy by the plastic deformation of brittle inclusions together with the matrix. The range of properties of both components, where this effect occurs, was studied. In addition to the use of various PA‐6 and SMA types, PA‐6 was also modified with epoxy resin, as well as SMA with liquid rubber bearing amino groups. Owing to the crosslinking ability of both modifiers, the influence of the changed deformability of blend components was demonstrated. Simultaneous influencing of rheological properties and reduction of the amount of reactive groups usable for the in situ compatibilizer formation make it possible to vary the size of dispersed SMA particles and the interfacial adhesion. Thus, a more comprehensive insight into the behavior of ductile‐brittle blends is gained. As SMA and modifiers have negative effect on the PA‐6 crystallinity, comparison of the obtained data with model calculations is difficult.
Morphology development of in situ compatibilized semicrystalline polymer blends in a co‐rotating twin‐screw extruder
Authors: Cartier Hervé , Hu Guo‐Hua
Published: April 2004

This paper concerns the morphology development of in situ compatibilized semicrystalline polymer blends in a co‐rotating, intermeshing twin‐screw extruder, using polypropylene (PP) and polyamide 6 (PA‐6) blends as model systems. The morphology of in situ compatibilized blends develops much faster that of mechanical ones. The size of the dispersed phase (PA‐6) undergoes a 104 fold reduction from a few millimeters to sub‐micron during its phase transition from solid pellets to a viscoelastic fluid. The final morphology is reached as soon as the phase transition is completed, which usually requires only a small fraction of the screw length in a co‐rotating twin screw extruder. Screw profiles and processing conditions (screw speed, throughput and barrel temperature) control the PA‐6's melting location and/or rate, but do not have significant impact on the ultimate morphology and mechanical properties of in situ compatibilized blends. The finding that morphology of PP/PA‐6 reactive blend develops rapidly makes it possible to produce compatibilized PP/PA‐6 blends by the so‐called one‐step reactive extrusion. It integrates the traditionally separated free radical grafting of maleic anhydride onto PP and the compatibilization of PP/PA‐6 into a single extrusion step.
Coalescence in blends of thermoplastic polyurethane with polyolefins
Authors: Wallheinke Katrin , Pötschke Petra , Macosko Christopher W. , Stutz Herbert
Published: April 2004

The coalescence behavior of immiscible blends was determined by annealing the melt without shear. The kinetics and the mechanism of coalescence were observed for blends of thermoplastic polyurethane (TPU) and polyolefins. Two different types of measurements were used to observe coalescence in quiescent melt at the processing temperature. On the one hand, the blend granules were annealed in bulk. The resulting particle sizes were determined by light microscopy and by SEM on particles separated from the blend. On the other hand, thin samples were annealed on a hot stage. Coalescence was observed in situ by light microscopy or static laser light scattering. It was found that the higher viscosity and elasticity ratios between polyethylene and TPU lead to a more pronounced coarsening of the morphology of 80/20 blends than in TPU/polypropylene. It has been shown that the process of reshaping coalescence is one mechanism of coalescence that occurs in quiescent melt. Another mechanism that was directly observed is a “domino effect” where one coalescence process causes the next one.
Modeling of structured polyblend flow in a laminar shear field
Authors: Bousmina M. , Palierne J. F. , Utracki L. A.
Published: April 2004

A new model is proposed for describing the negative deviating behavior, NBD, of polymer blends. The model was derived for a telescopic flow of two Newtonian liquids, flowing through a capillary at vanishing Reynolds numbers. The stress field was considered continuous along the radial position, while the velocity field, due to the slippage, was assumed to be discontinuous at each interface between the two adjacent polymeric layers. A special case of an interphase with its own characteristics, thickness and viscosity, was also considered. The model derived here is applicable for Newtonian fluids or for generalized Newtonian fluids (non‐Newtonian) but at constant stress and for morphologies where the phases are structured in oriented layer in the direction of flow or for sheared sandwiches. The capability of the model for describing the NDB behavior was shown on some experimental data of the literature. The main future of the results is that the interlayer slip is caused by the interfacial lubrication due to low viscosity of the narrow interphase. The proposed model was compared with Heitmiller's and Lin's models. Some inconsistencies of Lin's approach have been indicated.
Flow induced deformation of dual‐phase continuity in polymer blends and alloys. Part I
Authors: Lyngaae‐Jørgensen J. , Rasmussen K. Lunde , Chtcherbakova E. A. , Utracki L. A.
Published: April 2004

A hypothesis for formation of bi‐continuous phase structures in immiscible polymer blends is proposed. It is based on the observation that a critical volume fraction φcr for the dual continuity of phases may be calculated considering the geometry of the dispersed phase. The knowledge of the form of discrete domains at the volume fractions φ < φcr and the probability that two close neighbor domains will form a strongly fused connection are sufficient to calculate φcr. Furthermore, it can be predicted that φcr should increase with stabilization of the interface. A comparative study showed that an addition of block copolymer may narrow the volume fraction range where bi‐continuous phase structures are formed. Both annealing in the molten state and shearing history influence the measured φcr for the formation of bi‐continuous phase structure in amorphous immiscible polymer blends.
Extensional flow of polymeric dispersions
Authors: Bourry D. , Khayat R. E. , Utracki L. A. , Godbille F. , Picot J. , Luciani A.
Published: April 2004

A 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

An 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

Modified 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

High‐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

Polypropylene‐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

Electroactive 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

A 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

In 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

Poly(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

Poly(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

The 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

Plastic 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

A 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

The 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

The 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.