bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature variation of the photoinduced birefringence of an azo dye doped polymer
Authors: Blanche P.‐A. , Lemaire Ph. C. , Maertens C. , Dubois P. , Jérǒme R. 
Published: April 2004

AbstractThe influence of the temperature on the photoinduced birefringence on an azo dye doped polymer film has been studied. Sample is composed of a polymer matrix PVK (Poly(N‐vinylcarbazole)), doped with 10 weight percent (wt%) of the birefringent molecule DMNPAA (2,5‐dimethyl‐4‐(p‐nitrophenylazo)anisole) and 30 wt% of ECZ (N‐ethylcarbazole) which acts as a plasticizer. Theoretical results can explain the behavior of the amplitude of the photoinduced birefringence versus temperature. Experimental and theoretical results are compared. Holographic recording experiments based on photoinduced birefringence have been carried out. Based on the effect of temperature, we have been able to significantly increase the diffraction efficiency of our sample.
Neutron transmission and quasi‐elastic neutron scattering in polymer hydrogels
Authors: Klepko V. 
Published: April 2004

AbstractInvestigations of hydrogels with high water contents have recently acquired special significance. Hydrogels are crosslinked three‐dimensional networks of water‐soluble macromolecules saturated by water or water solutions of different substances. The interest in examination the fundamental physical properties for such systems is related to their numerious applications. Using neutron transmission and quasi‐elastic neutron scattering (QENS), the mass transfer and self‐diffusion processes of water and water solutions in gelatin and poly(acrylamide) hydrogels were studied. It was shown that the macroscopic liquid flow through network of quasi‐porous polymer gels at relatively low pressure gradients as well as self‐diffusion of water and water solutions in the above systems are adequately described by “effective medium” approach. QENS data were also interpreted using an approach that accounts for the hierarchy of time scales of molecular motions: slow collective motions of liquid molecules contained in Lagrange's clusters and rapid single‐particle motions. The friction and self‐diffusion coefficient data were used to estimate the effective pore sizes of gels at different polymer concentrations as well as the mean Lagrange's cluster sizes.
An optimization approach to practical problems in plasticating single screw extrusion
Authors: Covas J. A. , Cunha A. G. , Oliveira P. 
Published: April 2004

AbstractSetting the extruder operating conditions, or establishing the adequate geometry of the screw, for a given group of specifications, is dealt with as an optimization problem where the solution is searched in a nonconvex space. In practice, this is a conflicting multi‐attribute optimization problem, where various optima may coexist. The methodology developed involves the maximization of an objective function, quantifying the adequacy of the extruder‐die combination response to particular inputs, whose values are computed using an extrusion modeling package developed for this work. Genetic Algorithms (GAs) are used to generate better sets of inputs. In a second stage, multi‐objective optimization through Pareto curves, coupled to GAs, is implemented since, beyond optimization, it also provides a better understanding of the characteristics of the extrusion system under study.
Rod‐Climbing characterization of kaolinite suspended polyisobutylene solutions
Authors: Choi Hyoung J. , Lee Hong J. , Lim Sung T. , Jhon Myung S. 
Published: April 2004

AbstractThe rod‐climbing constants of kaolinite‐suspended polyisobutylene (PIB) solutions are investigated from rod‐climbing experiments. For a low deformation rate, this particle suspended polymer solution can be regarded as a second‐order fluid, and the rod‐climbing constant for such fluids is correlated with the rheological properties of the particle‐suspended polymer solutions. The rod‐climbing constants for kaolinite suspended PIB solutions were found to decrease with temperature and increase with PIB concentration, molecular weight of PIB, solvent viscosity, and particle concentration. The rheological properties were measured using rotational rheometer, and the shear viscosity and the first normal stress difference of the kaolinite suspended PIB solution show the Boger‐fluid characteristics.
Preparation and characterization of anionic collagen: P(VDF/TrFE) composites
Authors: Goissis Gilberto , Piccirilli Luciana , De Guzzi Plepis Ana Maria , Das‐Gupta Dilip K. 
Published: April 2004

AbstractAnionic collagen:P(VDF/TrFE) (75/25) membrane composites were prepared by mixing anionic collagen and P(VDF/TrFE) in aqueous concentrated acetic acid:dimethylsulfoxide solutions and characterized by infrared, electron scanning microscopy, thermal analysis and dielectric properties. The results show that under the appropriate conditions anionic collagen:P(VDF/TrFE) composites, with ratios in the range from 4:1 to 1:4 may be conveniently prepared in the form of membranes, without the loss of tropocollagen secondary structure. As suggested by infrared spectroscopy and thermal analysis, mixing is accompanied by macromolecular interaction conditions anionic collagen and P(VDF/TrFE). Although preliminary, the determined pyroelectric coefficient for the 1:1 composite of 1.89 × 10−4Cm−2K−1, is higher than those determined under the same conditions for native, anionic collagen and P(VDF/TrFE) and of respectively 0.37 × 10−4Cm−2K−1, 1.16 × 10−4Cm−2 K−1 and 17 × 10−6 Cm−2K−1, but comparable to that for PZT (4.2 × 10−4Cm−2K−1) at the same temperature. This increase in pyroelectric coefficient for the 1:1 composite, in respect to anionic collagen membranes, may be a result of a anionic collagen: P(VDF/TrFE) interaction. A model based on hydrogen bonding formation between acidic and alcoholic hydroxyl groups of anionic collagen and the flurine atoms of P(VDF/TrFE) is proposed.
The ferroelectric properties of piezoelectric ceramic/polymer composites for acoustic emission sensors
Authors: Wenger M. P. , Almeida P. L. , Das‐Gupta D. K. , Blanas P. , Shuford R. J. 
Published: April 2004

AbstractTwo different mixed connectivity composites, consisting of a ferroelectric ceramic powder of calcium modified lead titanate (PTCa) dispersed in a polymer matrix, have been fabricated and their ferroelectric properties have been investigated. Hysteresis measurements have been conducted on composites of PTCa with a polar polymer of polyvinylidene trifluoroethylene (P(VDF‐TrFE)) and PTCa with a thermosetting epoxy resin to determine the coercive fields and remanent polarization of the two different composites. The composites show noticeable differences in their behavior during poling along with the values of their piezoelectric coefficients, with the composite of PTCa/P(VDF‐TrFE) showing enhanced piezoelectric activity over that of PTCa/epoxy. This paper reports on the polarization properties and the microstructural nature of the composites.
Electrorheological characterization of semiconducting polyaniline suspension
Authors: Choi Hyoung J. , Lee Jin H. , Cho Min S. , Jhon Myung S. 
Published: April 2004

AbstractElectrorheological (ER) properties of polyaniline suspensions in silicone oil with various experimental conditions were investigated. These suspensions exhibit dramatic changes in their rheological properties which are caused by the formation of particle chain structures induced by an applied electric field. Polyaniline was synthesized by the chemical oxidation of aniline with ammonium peroxysulfate. This study examined the effects of electric field, volume fraction, polymerization temperature and operation temperature on the ER properties of polyaniline suspensions in silicone oil. Rheological measurements were carried out by using a rotational rheometer with a high voltage generator in both controlled shear stress and shear rate modes. Experimental results showed that the ER properties were enhanced by increasing the volume fraction and electric field and were independent of the operating tempertures. The best ER properties were also obtained by using polyaniline particles synthesized at ‐10°C, and these had a conductivity of ˜ 10−10 S/cm.
Effects of dispersing agents on dispersity and mechanical properties of carbon black/PET
Authors: Kim Dae‐Jin , Seo Kwan‐Ho , Hong Ki‐Heon , Kim Sang‐Youl 
Published: April 2004

AbstractThree kinds of dispersing agents, all copolyesters, were synthesized from the polycondensation reaction of dimethyl terephthalate (DMT), dimethyl isophthalate (DMI), sebacic acid (SA), and 1,4‐butandiol (BD). Copolyester from DMT, SA, and BD was designated as PBTS; from DMT, SA, DMI, and BD as PBTIS; and from DMT, DMI, and BD as PBTI. Carbon black masterbatches were prepared by mixing carbon black into the dispersing agents in a Brabender Plasticorder PLE331. Using single screw extruder, masterbatches were compounded with poly(ethylene terephthalate) in 3 wt% concentration and mechanical properties of the compounds were investigated. Gel permeation chromatography data implied that thermal degradation of polymeric dispersing agents was not very significant. Capillary rheometer tests showed that PBTI has the highest viscosity and shear sensitivity of the three dispersing agents. Volume resistivities of each masterbatch were increased as the rotor rpm of the Brabender and mixing time increased. Transmission electron micrographs showed that dispersion of carbon black was enhanced by increasing the melt viscosity of the dispersing agent. The performance and mechanical characteristics of carbon‐black‐filled PET compounds depends directly on the dispersion quality of the carbon black in the masterbatch. Mechanical properties of compounds were improved by increasing dispersion of carbon black and increasing numbers of rigid aromatic groups in the copolyester dispersing agent.
Characterization and evaluation of piezoelectric composite bimorphs forin‐situacoustic emission sensors
Authors: Wenger M. P. , Blanas P. , Shuford R. J. , Das‐Gupta D. K. 
Published: April 2004

AbstractMixed connectivity composites consisting of a ferroelectric ceramic powder of calcium modified lead titanate dispersed in a polymer matrix have been fabricated into piezoelectric bimorph sensors. The piezoelectric, dielectric and electromechanical coupling coefficients of these sensors have been measured and a full characterization of the electromechanical properties are reported. The suitability of these bimorph transducers asin‐situacoustic emission sensors, embedded into glass‐epoxy laminate plate like structures, has been investigated. A comparison of the performance of these sensors to those of previously investigated monomorph sensors fabricated from the same material has been made.
A novel approach to the tailoring of polymers for advanced composites and optical applications, involving the synthesis of liquid crystalline epoxy resins
Authors: Giamberini Marta , Amendola Eugenio , Carfagna Cosimo 
Published: April 2004

AbstractThe authors describe the features of liquid crystalline epoxy resins having both high and low crosslinking densities. These materials seem to be very promising as matrices in advanced composites and in optical and electro‐optical applications because of their peculiar properties. The importance of factors like molecular rigidity, nature of the curing agent, and curing temperature for the development of such properties are analyzed. The authors showed that amines produce thermosets having high Tgs and high fracture toughness. In particular, the enhancement of this last parameter is very promising if a new generation of matrices is to be sought for manufacturing composites. In the case of acids as curing agents, thermosets having lower Tgs and more ordered mesophases can be obtained. In this case, LC elastomers can be prepared that can find applications in the optical industry as waveguides or electro‐optical devices.
Synthesis and characterization of zirconium ionomer dispersions
Authors: Ricardo Nágila M. P. S. , Ricardo Nadja M. P. S. , Holmes Robert , Price Colin 
Published: April 2004

AbstractWater‐based ionomer dispersions were formed by post‐polymerization addition of zirconium species to polymer latices prepared from butyl methacrylate (BMA), butyl acrylate (BA) and acrylic acid (AA) by semicontinuous emulsion polymerization. The mole fraction of AA in the latex particles was kept at 10 mole% in all cases whereas the ratio of BA to BMA was varied. A method was established which allowed zirconium in the form of ammonium zirconium carbonate (AZC) to be successfully introduced into the latices without affecting their colloidal stability. Dynamic light scattering was used to determine average particle size in diluted latices. The structure and properties of cast ionomer films were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), tensile strength and swelling measurements. Fourier transform infrared spectroscopy (FTIR) was used to investigate the nature of the carboxylate bonding.
Thermal stability of poly(methyl methacrylate‐co‐butyl acrylate) and poly(styrene‐co‐butyl acrylate) polymers
Authors: Leskovac Mirela , Kovačević Vera , Flě Dragutin , Hace Drago 
Published: April 2004

AbstractThermal stability of poly(methyl methacrylate‐co‐butyl acrylate) and poly(styrene‐co‐butyl acrylate) modified with a small amount of acrylic acid and/or N‐methylolacrylamide as a crosslinking agent was studied in this work. Programmed thermogravimetric analysis has been used to study the effect of copolymer composition on thermal stability, over a temperature range from 50 to 450°C, under a constant flow of nitrogen. Kinetic parameters of thermal degradation, activation energy, pre‐exponential factor, and reaction order were obtained by using MacCallum‐Tanner's approach. Kinetic data indicate that the thermal degradation of the investigated copolymer systems is the first order reaction, and that the increase of activation energy may be an indication of thermal stability changes in copolymer systems.
Cycle time predictions for the rotational molding process with and without mold/part separation
Authors: Gogos G. , Liu X. , Olson L. G. 
Published: April 2004

AbstractWe present a detailed theoretical heat transfer model for the entire rotational molding process (including heating and cooling stages) and identify the key dimensionless groups affecting the process cycle time. This theoretical model is employed to generate numerical results that are in very good agreement with the experimental data available in the literature. The effects of variations in the dimensionless groups on the cycle time are evaluated. In addition, part shrinkage has been incorporated in the models, and its effect on the process cycle time has been studied extensively.
A factorial design applied to polypropylene functionalization with maleic anhydride
Authors: Nachtigall S. M. B. , Neto R. Baumhardt , Mauler R. S. 
Published: April 2004

AbstractMaleic anhydride functionalized PP was prepared in a melt‐mixer according to a factorial design. Two levels of maleic anhydride concentration (MA), dicumyl peroxide concentration (DCP), reaction time, and temperature were employed. The isolated and interaction effects of these variables on the degree of functionalization and molecular weights were analyzed. The products were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), titration, and torque measures. The reaction time showed no appreciable effect within the studied range (10 to 20 minutes); however, the other three factors showed significant main effects. MA and temperature presented an important interaction effect on the degree of functionalization and molecular weights. The highest degrees of functionalization were found to be related to the smallest molecular weights.
Thermal and mechanical properties of the precursor polymers: Comparison of their properties with poly(amic acid)
Authors: Chang Jin‐Hae , Farris Richard J. 
Published: April 2004

AbstractThe DSC thermograms of P‐PHA show a large endothermic peak at 450–550°C. As the annealing temperature increases from 250°C to 400°C, the endothermic peaks become smaller and then disappear for samples annealed above 450°C. As observed for P‐PHA, the endothermic enthalpy of PHA and PAA became smaller with an increasing annealing temperature. The cyclization onset temperature (T1) of the three precursors increases linearly with an increasing annealing temperature at a constant annealing time (30 min). Otherwise, the initial decomposition onset temperature (T2) was shown to be constant. T2 of P‐PHA, PHA, and PAA were observed in the temperature ranges of 601–603°C, 576–577°C, and 532–534°C, respectively. These TGA results confirm that all of the samples are thermally stable. Increasing the annealing temperature of the three precursor polymers significantly increases the tensile properties of the films. The tensile properties of all annealed precursors were much higher than those of the unannealed films. In contrast, the initial modulus of PAA is improved only slightly when compared with the other two polymers regardless of the heat treatment. The biaxial stresses in the PHA and PAA films were investigated by holographic interferometry. The stresses in the films were 6.85–7.61 MPa for PHA and 27.01–27.70 MPa for PAA.
Transient shear and extensional properties of biodegradable polycaprolactone
Authors: Kapoor Bikram , Bhattacharya M. 
Published: April 2004

AbstractTransient shear and extensional properties of two grades of partially crystalline biodegradable aliphatic polyesters, poly ε caprolactone (PCL), were investigated at three different temperatures. Uniaxial extensional viscosity at a constant strain rate was obtained using the Meissner apparatus. The magnitudes of the stress‐over‐shoot during stress growth experiments were smaller than those typically observed for other polymers. Higher melt temperature and higher strain led to faster relaxation, while the lower molecular weight PCL 767 relaxed faster than the higher molecular weight PCL 787. The relaxation moduli are independent of strain for strain values below 0.1. Transient extensional measurements were conducted at strain rates of 0.01 to 1.0 s−1. At small stresses the extensional viscosity has the threefold value of shear viscosity as predicted by Trouton. There appeared to be no steady state regime for either grade of PCL studied and as a result ηe(ε) could not be determined. The departure from the linear limit is fastest for the highest extensional rate. Extension thickening behavior is observed at Hencky strains ranging from 1.0 to 2.0. PCL 767 displayed greater extension thickening than PCL 787 at the same temperatures. The Wagner integral constitutive equation was found to give an acceptable fit to the stress growth data in shear and extension, with the fit being better for PCL 767 than for PCL 787.
Characterization of the lubricant layer formed at the interface between the extrudate and the die wall during the extrusion of high density polyethylene and fluoroelastomer blends by XPS, SIMS and SEM
Authors: Lo Horace Ho‐Kei , Chan Chi‐Ming , Zhu Shui‐Han 
Published: April 2004

AbstractThe formation of a lubricant layer at the polymer‐metal die interface, when a blend of high density polyethylene (HDPE) and a fluoropolymer processing aid (Dynamar) was extruded through a slit die, was verified and investigated in depth. Blends containing 0.5 and 5 wt% of Dynamar were prepared by a twin‐counter‐rotating‐scew extruder. The viscosity of the blends was measured with a capillary rheometer. A specially made slit die block containing two pieces of insert was used. The inserts which could be taken out from the slit die block at the end of the measurement were separated from the polymer block by acid etching. The polymer block contains the information about the lubricant layer formed between the extrudate and the die wall. X‐ray photoelectron spectroscopic (XPS), secondary ion mass spectrometric (SIMS), and scanning electron microscopic (SEM) analyses of the polymer blocks confirmed the presence of a Dynamar‐rich lubricant layer at the interface between the extrudate and the die‐wall surface. The thickness of the lubricant layer varied from 5 to 15 μm depending on the shear rate and the concentration of the Dynamar in the blend. For the Dynamar concentrations and shear rates considered in this study, the efficiency of the viscosity reduction appears to be independent of the lubricant layer thickness.
A model for the zero shear viscosity
Authors: Locati G. , Pegoraro M. , Nichetti D. 
Published: April 2004

AbstractAn 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

AbstractIn 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

AbstractOwing 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.