bluuebunny/crossref_metadata_2025_split huggingface dataset:
Increase of photoluminescence from fullerene‐doped polymers under laser irradiation
Authors: Li G. Z. , Minami N. , Ichio Y. 
Published: April 2004

AbstractPhotoluminescence (PL) from fullerene (C60 and C70)‐doped polymers such as poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(methyl phenyl silane) (PMPS) and poly(phenyl silsesquioxane) (PPSQ) increases gradually under laser irradiation in air (but not in vacuum and in nitrogen) and eventually becomes visible to the naked eye. Concomitantly, the PL peak is broadened and, in most cases, blue‐shifted. No such PL increases are observed for pure C60 films made by vacuum vapor deposition and pure polymer films. Among the polymers used, fullerene‐doped PMMA has the greatest PL increase after several hours of laser irradiation and fullerene‐doped PMPS has the highest rate of PL increase at the initial stage of the laser irradiation. To gain an insight into the mechanism of the PL increase, laser‐irradiated fullerene‐doped PMMA samples were analyzed by UV‐Vis spectrophotometer, FT‐IR, mass spectrometry, GPC and NMR. The results show that the PL increase can be attributed to CH60On‐polymer (or C70On‐polymer) and oxidized fullerene‐polymer adducts formed by some laser‐induced photochemical reactions among fullerenes, oxygen and polymers.
Kinetics of isothermal and non‐isothermal crystallization of poly(butylene terephthalate)/ liquid crystalline polymer blends
Authors: Kalkar A. K. , Deshpande A. A. 
Published: April 2004

AbstractThe melting behavior and isothermal and non‐isothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/thermotropic liquid crystalline polymer (LCP), Vectra A950 (VA) blends were studied by using differential scanning calorimetry. Isothermal crystallization experiments were performed at crystallization temperatures (Tc), of 190, 195, 200 and 205°C from the melt (300°C) and analyzed based on the Avrami equation. The values of the Avrami exponent indicate that the PBT crystallization process in PBT/VA blends is governed by three‐dimensional morphology growth preceded by heterogeneous nucleation. The overall crystallization rate of PBT in the melt blends is enhanced by the presence of VA. However, the degree of PBT crystallinily remains almost the same. The analysis of the melting behavior of these blends indicates that the stability and the reorganization process of PBT crystals in blends are dependent on the blend compositions and the thermal history. The fold surface interfacial energy of PBT in blends is more modified than in pure PBT. Analysis of the crystallization data shows that crystallization occurs in Regime II across the temperature range 190°C‐205°C. A kinetic treatment based on the combination of Avrami and Ozawa equations, known as Liu's approach, describes the non‐isothermal crystallization. It is observed that at a given cooling rate the VA blending increases the overall crystallization rate of PBT.
Thermal behavior of poly(dimethyl itaconate) and poly(di‐n‐butyl itaconate) copolymerized with methyl methacrylate
Authors: Fernández‐Garcia Marta , De La Fuente José Luis , Madruga Enrique López 
Published: April 2004

AbstractThe thermal degradation behavior of random copolymers of dimethyl itaconate and di‐n‐butyl itaconate with methyl methacrylate was studied. The thennal stability of copolymers depends on the structure of the di‐n‐alkyl itaconate comonomer, and on the copolymer composition. The relative thermal stability increases with the methyl methacrylate copolymer molar fraction, following a trend similar to the glass transition temperature variation. The activation energy was obtained by using MacCallum and Tanner's approach. In addition, the thermal degradation of homopolymers was evaluated in inert atmosphere as well as in thermo‐oxidative conditions, presenting different behaviors.
On‐line measurement of polymer orientation using ultrasonic technology
Authors: Edwards Russ , Thomas Charles 
Published: April 2004

AbstractThe propagation velocity of an ultrasonic shear wave can be used to detect anisotropic behavior in the mechanical properties of a solid. Thus, an ultrasonic shear transducer imbedded in an injection mold produces a signal that is sensitive to polymer orientation. This results in a non‐invasive, on‐line technique for monitoring the orientation of polymer in an injection mold cavity during part cooling and solidification. The technique is shown to be quite sensitive for semicrystalline polymers, but much less effective for amorphous polymers. Sensor results are compared to mechanical tests.
Microstructural effects on hot drawing syndiotactic styrene P‐methyl styrene copolymer
Authors: Yan R. J. , Ajji A. , Shinozaki D. M. 
Published: April 2004

AbstractCrystalline syndiotactic styrene/p‐methyl styrene copolymer (SPMS) has been oriented by tensile drawing at various temperatures between the glass transition and crystalline melting point. The microstructural changes resulting from drawing have been studied using differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). WIth increasing draw temperature, both melting temperature and crystalline dimensions of the oriented samples increase. The heat of fusion increases with increasing draw temperature up to ∼200°C. It also increases with draw ratio and draw rate, while the crystalline width increases only with draw ratio. THe amorphous fraction shows a clear glass transition, the temperature of which (Tg) increases with draw ratio. However, Tg decreases somewhat with increasing draw temperature. This is interpreted in terms of the stretching of the randomly coiled amorphous phase molecules.
Numerical simulations of polymer flow in flat spiral dies
Authors: Zatloukal M. , Tzoganakis C. , Perdikoulias J. , Saha P. 
Published: April 2004

AbstractThe flow of a polymer melt through a flat spiral distribution system used in “stacked” type dies was analyzed through three‐dimensional finite element simulations, and predictions of the exit flow variation were compared to experimental measurements. Both isothermal and non‐isothermal simulations were carried out, and the non‐isothermal results were found to be in close agreement with the measured flow variation. It was found that for this particular flat spiral die, viscous dissipation is extremely crucial and may lead to generation of hot spots and to increased flow variation. Finally, the effect of material viscoelasticity on the flow field was simulated by using a CEF constitutive equation. It was shown that neglecting viscoelastic effects due to shear deformation, represented by primary and secondary normal stress coefficients, in the modeling of the flow in the flat spiral dies is a reasonable simplification. On the other hand, extensional behavior should be taken into account for a more suitable description of the leakage flows within this type of die.
Temperature modulated DSC studies of melting and recrystallization in poly (oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK)
Authors: Kampert William G. , Sauer Bryan B. 
Published: April 2004

AbstractThe thermal and crystal morphological properties of amorphous and melt crystallized poly(oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK) were investigated. Two different molecular weights were studied by Temperature Modulated DSC (TMDSC) over a broad range of annealing times and temperatures. The lower molecular weight PEEK under all crystallization conditions was found to exhibit secondary crystal melting in the low endotherm region, followed by melting of primary crystals melting in the low endotherm region, followed by melting of primary crystals superimposed with a large recrystallization contribution. Primary crystal melting broadly overlapped with melting of the recrystallized species and contributed to the broad highest endotherm. Recrystallization contributions and the interpretation of TMDSC were partially confirmed by independent rapid heating rate melting point determinations and variable heating rate DSC. The higher molecular weight PEEK showed many similarities but generally had smaller levels of reorganization above the annealing temperature under most higher temperature crystallization conditions. TMDSC provides excellent resolution of recrystallization and related events compared to standard DSC. The broad and substantial exothermic recrystallization in amorphous samples was also examined, showing that recrystallization continues through the final melting region.
Processing enhancers for rotational molding of polyethylene
Authors: Chaudhary Bharat Indu , Takács Elizabeth , Vlachopoulos John 
Published: April 2004

AbstractRotational molding is a zero shear process used to manufacture hollow plastic parts. One disadvantage of this process is long cycle times, which are significantly affected by the sintering rates of thermoplastic powder. The objective of this work was to evaluate low molecular weight additives as sintering enhancers for polyethylene and to validate the results in rotational molding. The following additives were blended with linear low‐density polyethylene: mineral oil, glycerol monostearate and pentaerythritol monooleate. The additives resulted in decreased melt viscosity and/or elasticity at low shear rate. The reduction in melt elasticity was particularly significant. Sintering studies confirmed that the additives resulted in significantly faster coalescence. In uniaxial rotational molding, the decreased melt viscosity and elasticity obtained with mineral oil were observed to result in much faster densification and bubble removal. Part thickness was uniform and there was no warpage. Adding mineral oil to polyethylene reduced the cycle time in uniaxial rotational molding and the peak impact strength was identical to that obtained without any additive. Biaxial rotational molding experiments confirmed that the use of mineral oil resulted in shorter cycle time without sacrificing peak impact strength.
Crystal structures and orientation development in tubular film extrusion of syndiotactic polypropylene and isotactic polypropylene
Authors: Choi Dongman , White James L. 
Published: April 2004

AbstractThe differences in behavior of isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP) in tubular film extrusion are qualitatively described. The crystalline form and orientation in the films were characterized using wide‐angle X‐ray diffraction (WAXD) patterns, pole‐figure analysis and birefringence. The sPP films had the crystalline form of the disordered Form I and the a‐crystallographic axis was found to be preferentially oriented in the film normal direction (ND) under the conditions of biaxial stresses. High transverse orientations were developed in the sPP films. In the iPP films, the monoclinic crystalline form was found and the b‐crystallographic axis was preferentially oriented in the ND. The birefringence of the films showed trends very similar to the crystalline orientations characterized by WAXD in both iPP and sPP films.
Modeling the viscoelastoplastic behavior of amorphous glassy polymers
Authors: Drozdov Aleksey D. 
Published: April 2004

AbstractConstitutive equations are derived for the viscoelastic and viscoplastic responses of amorphous glassy polymers at isothermal loading with small strains. A polymer is modeled as an ensemble of cooperatively relaxing regions (CRR) that are rearranged at random times as they are thermally agitated. At relatively low stresses, CRRs are bridged by links that ensure that the macro‐strain in a specimen coincides with micro‐strains in relaxing regions. When the average stress exceeds a threshold strength for the links, some of them break, and relaxing domains begin to slide with respect to one another. Rearrangement of CRRs reflects the viscoelastic behavior, whereas sliding of micro‐domains is associated with the viscoplastic response of glassy polymers. Kinetic equations are proposed for the evolution of viscoplastic strains and the strength of an ensemble of links. These equations are verified by comparison with experimental data in tensile relaxation tests and in tensile and compressive tests with constant strain rates. Fair agreement is demonstrated between results of numerical simulation and observations for a polyurethane resin and poly(methyl methacrylate).
Thermal stresses and orientations in acrylic sheet
Authors: McDonagh‐Smith A. , Arnold J. C. , Isaac D. H. 
Published: April 2004

AbstractTwo copolymers of poly(methyl methacrylate) with 3% and 10% ethyl acrylate, respectively, were extruded and calendered, with the same line speed and roll temperatures. The residual stresses and anisotropies, induced by the complex processing deformations and temperature variations, were characterized by monitoring the dimensional changes and sample curvatures resulting from subsequent heat treatments. In both copolymers, two distinct recovery regimes were observed: heat treatments just below Tg caused relaxation of residual thermal stresses and at temperatures above Tg led to recovery of chain extended orientations. It was found that the similar processing conditions induced similar residual thermal stresses in the two copolymers, but the higher viscosity of the 3% EA sheet led to greater residual orientations. Across the width of the sheets, little variations were seen in the thermal stresses, but orientations were lower at the edges. Some curvature changes observed following heat treatment well below Tg, were interpreted as resulting from aging effects.
Anisotropic dielectric properties of polyimides consisting of various molar ratios of meta to para diamine with trifluoromethyl group
Authors: Qu Wen‐Li , Ko Tze‐Man , Vora Rohit H. , Chung Tai‐Shung 
Published: April 2004

AbstractA series of copolyimides based on pyromellitic dianhydride (PMDA) with various molar fractions of 4,4′‐(hexafluoro‐isopropylidene)dianiline (4,4′‐6F) and 3,3′‐(hexafluoro‐isopropylidene)dianiline (3,3′‐6F) were synthesized by a two‐step method. The five different composition copolyimides in the fozrm of {(PMDA+3,3′−6F)m/ (PMDA+4,4′−6F)n were mainly characterized using a dielectric analyzer (DEA) by single surface sensor (in‐plane direction) and thin film parallel plate sensor (out‐of‐plane direction) measurements. DSC, TMA, and XRD were also used to study the structure property. The increasing of molar ratio of para diamine in the copolyimide system up to 35% affected glass transition temperature, coefficient of thermal expansion, in‐plane dielectric constant and out‐of‐plane dielectric constant of copolyimides, correspondingly. The in‐plane dielectric constant was higher than that of the out‐of plane constant for our polyimide films. Anisotropy δε of the dielectric constants was 0.14 for CPI(100/o)a, 0.19 for CPI(85/15)a, 0.11 for CPI(75/25)a, and 0.05 for CPI(65/35)a. The difference in curing history also exhibited an effect on solvent diffusion behavior in our polymer system. Polymers cured at a slower curing rate had smaller CTE than that cured at a faster curing rate, as confirmed by X‐ray diffraction results. Polymers with smaller CTEs had larger dielectric constants at a slower curing rate, and vice versa. The experimental results suggested that CPI(65/35) a with smaller dielectric anisotropy could solve the crosstalk problem and provide equal electrical insulation in microelectronic devices. Therefore, a smaller and faster IC device could, it is hoped, be achieved, with smaller spacing between adjacent metal lines.
Thermal and mechanical properties of a hydroxyl‐functional dendritic hyperbranched polymer and trifunctional epoxy resin blends
Authors: Ratna D. , Simon G. P. 
Published: April 2004

AbstractCuring characteristics of blends of a hydroxyl‐functionalized dendritic hyperbranched polymer (HBP) and a triglycidyl p‐amino phenol (TGAP) epoxy resin have been studied. THe HBP strongly enhances the curing rate owing to the catalytic effect of the hydroxyl groups. THe thermal and dynamic viscoelastic behavior of the blends of various compositions (HBP content 0–20%) have been examined and compared to the neat TGAP matrix. THe glass transition temperature (Tg) gradually decreases with increase in HBP concentration. The blends show a higher impact strength compared to neat TGAP. Scanning electron microscopy analysis indicates a single‐phase morphology.
Coating window for double layer extrusion slot coating of poly (vinyl‐alcohol) solutions
Authors: Lu Shih‐Yuan , Lin Yu‐Ping , Liu Ta‐Jo 
Published: April 2004

AbstractThe expansion of coating windows for low‐viscosity poly(vinyl‐alcohol) (PVA) solutions is achieved via utilization of a higher viscosity PVA solution as the stabilizing carrier layer. It is found that PVA solutions of higher viscosities possess a higher degree of processability than those of lower viscosities, and can serve as a stabilizing carrier layer when coating lower viscosity PVA solutions. The stabilizing effect of the carrier layer enhances with increasing viscosity of the carrier layer, but reaches a saturation state at a high enough viscosity. It is further found that the coating defects occurring at lower maximum coating speeds are dominated by the lower, carrier layer, while those at higher maximum coating speeds are controlled by the upper, carried layer. Consequently, there exists an optimal layer flow rate ratio at which the coating window is the largest. A new type of coating defect, called spreading failure, is observed for coating situations involving a thin and much less viscous upper layer.
Influence of initial sheet temperature on ABS thermoforming
Authors: Lee Je Kyun , Virkler Terry L. , Scott Chris E. 
Published: April 2004

AbstractUnderstanding the effects of material and processing parameters on the thermoforming process is critical to the optimization of processing conditions and the development of better materials for high quality products. In this study we investigated the influence of initial temperature distribution over the sheet on the part thickness distribution of a vacuum snap‐back forming process. The linear viscoelastic properties along with the Wagner two parameter nonlinear viscoelastic constitutive model were utilized for numerical simulation of the thermoforming operation. Simulations of pre‐stretched vacuum thermoforming with a relatively complex mold for a commercial refrigerator liner were conducted. THe effects of temperature distribution over the sheet on the part thickness distribution were determined to examine process sensitivity and optimization. Effects of the temperature distribution on the material rheology and polymer/mold friction coefficient are primarily responsible for the changes in the thickness distribution. We found that even small temperature differences over the sheet greatly influenced bubble shape and pole position during the bubble growth stage and played a critical role in determining the part thickness distribution. These results are discussed in terms of rheological properties of polymers such as elongational viscosity and strain hardening.
Processing of short‐fiber reinforced polypropylene. I. Influence of processing conditions on the morphology of extruded filaments
Authors: Barbosa Silvia E. , Kenny José M. 
Published: April 2004

AbstractAn experimental investigation of the processing of glass fiber reinforced polypropylene is presented. Final fiber orientation distribution, fiber distribution in filament sections, rheological properties, final fiber length distribution and surface morphology were analyzed. This analysis was done taking into account the quantity of fibers and their interactions and flow conditions. The final fiber orientation increased when shear rate increased and fiber concentration decreased. Moreover, inhomogeneities in fiber distribution increased as the concentration of fibers decreased. The density profile showed a significant variation with fiber concentration, but it was not dependent on the shear rate applied. The viscosity showed a linear dependence with shear rate. The average fiber length and the breadth of this distribution decreased with the increasing fiber concentration and extrusion rate. The extruded filament surface showed minor roughness when the shear rate increased or when the fiber concentration decreased. The results of this experimental characterization give useful information to determine the influence of the processing variables on the final properties of short‐fiber reinforced polypropylene and constitutes the first part of a more ambitious project that also includes the development of a modeling strategy of the processing behavior for short‐fiber composites.
Biodegradable drag reducing agents and flocculants based on polysaccharides: Materials and applications
Authors: Singh Ram Prakash , Karmakar G. P. , Rath S. K. , Karmakar N. C. , Pandey S. R. , Tripathy T. , Panda J. , Kanan K. , Jain S. K. , Lan N. T. 
Published: April 2004

AbstractOrganic and inorganic flocculants are used in treatment of water and industrial effluents. Polymeric flocculants, synthetic as well as natural, because of their natural inertness to PH changes, low dosage, and easy handling, have become very popular in industrial effluent treatment. It has been established in the authors' laboratory that by grafting polyacrylamide branches on rigid backbone of polysaccharides, the dangling grafted chains have easy approachability to contaminants in effluents. Thus grafted polysaccharides are very efficient, shear stable and biodegradable flocculants. They also exhibit turbulent drag reducing characteristics. Among grafted guar gum, xanthan gum, carboxymethyl cellulose, and starch, grafted starch performs the best. Starch consists of amylose (a low molecular weight linear polymer) and amylopectin (a high molecular weight, branched polymer). The grafted amylopectin is found to be the best flocculant for various kinds of industrial effluents, providing credibility to the above‐cited model. In the present paper, the details about grafted polysaccharides as turbulent drag reducers and flocculants are given, along with their applications.
Enhanced shielding effectiveness of polymer matrix composite enclosures utilizing constraint‐based optimization
Authors: Mottahed Behzad D. 
Published: April 2004

AbstractMany interrelated factors must be considered in the design of an electronic system. Finding the optimum design condition having been subjected to various design constraints is often not a trivial matter. Utilizing an approach to optimize the design of electronic systems would have many advantages. A design optimization approach allows designers to study and optimize the various design alternatives. To illustrate this approach, in this study the optimum design of electronic enclosures from the viewpoint of electromagnetic shielding effectiveness is considered. An optimization problem has been formulated and the influence of several design variables in the definition of the objective function and constraints set is examined. To solve the problem, a non‐linear optimization solution technique is utilized that allows users to optimize an objective function bound by equality and inequality constraints. A case study is presented to illustrate the utility of this technique in selection of the best composite materials for maximum absorption against radiated energy, a case with application in radar.