bluuebunny/crossref_metadata_2025_split huggingface dataset:
The precision of dynamic oscillatory measurements
Authors: Bafna Sudhir S. 
Published: April 2004

AbstractThis paper examines the precision of complex viscosity measurements in the constant stress and constant strain modes. A Bohlin Controlled Stress Melt Rheometer was used to make the measurements, which cover a stress range of 400 to 3227 Pa and a frequency range of 0.01 to 30 hertz. In principle, oscillation in the linear region should give the same values regardless of how it is done. In reality, various measurement modes exhibit different precision. A wide range of parameters encompassing three decades in complex viscosity and over three decades in frequency are considered. Contrasting frequency dependence, i.e., shear‐thinning and Newtonian plateau, are also considered. Constant stress measurements are found to provide improved precision at lower frequencies, while constant strain measurements provide improved precision at higher frequencies. This is significant because low frequency data are often used to estimate the zero‐shear viscosity, which correlates with the weight‐average molecular weight. The “between‐sample” and “within‐sample” components of the total variation are examined separately for poly(dimethyl siloxane) and polyethylene. To do this for polyethylene, a new technique (moving range average) had to be used. Initial attempts at modeling are discussed. The discussion is limited to isotropic polymeric melts. This paper provides guidance in determining the most appropriate way to perform oscillation.
Compatibilizing effect of natural rubber‐g‐poly(methyl methacrylate) in heterogeneous natural rubber/poly(methyl methacrylate) blends
Authors: Oommen Zachariah , Gopinathan Nair M. R. , Thomas Sabu 
Published: April 2004

AbstractThe morphology and properties of heterogeneous poly(methyl methacrylate)/natural rubber blends have been modified by the addition of a graft copolymer of natural rubber and poly(methyl methacrylate) (NR‐g‐PMMA). The morphology has been studied as a function of copolymer concentration. A sharp decrease in the dispersed domain size was observed by the addition of a few per cent of the copolymer followed by leveling off at higher concentrations. The compatibilizer increases the interfacial adhesion by the formation of micro‐bridges with the matrix. The effects of homopolymer molecular weights, processing conditions, and mode of addition on the morphology of the dispersed phase have been investigated. The experimental results are compared with the theoretical predictions of Noolandi and Hong. Attempts have been made to explain the conformation of the graft copolymer at the interface. The changes in mechanical properties of the blends as a result of the addition of the compatibilizer were related to the morphology of the blends.
Henry constants in polymer solutions with the van der waals equation of state
Authors: Bithas Sotiris G. , Kalospiros Nikolaos S. , Kontogeorgis Georgios M. , Tassios Dimitrios 
Published: April 2004

AbstractThe simple der Waals equation of state, as extended to polymer systems, is applied to the correlation and prediction of Henry constants in polymer solutions comprising five polymers and many nonpolar and polar solvents, including supercritical gases. The correlation achieved with one adjustable parameter is satisfactory, with typical errors within the experimental uncertainty and comparable to those with the more complex Perturbed Hard Chain Theory‐based equations of state with the same number of adjustable parameters. A predictive scheme for calculating Henry constants is also presented, which is a corresponding‐states correlation for a dimensionless Henry constant defined based on the van der Waals equation of state. Satisfactory results—often close to the ones from the one‐parameter correlation—are obtained for all systems investigated in this work. Compared with literature models that have been applied to the prediction of Henry constants in polymers, this scheme is simpler and applicable to supercritical gas‐containing systems.
Elastomer‐toughened poly(phenylene sulfide)
Authors: Masamoto Junzo , Kubo Kimihiro 
Published: April 2004

AbstractFor use as electrical and electronics parts, or automobile and mechanical parts, toughened poly(phenylene sulfide) (PPS) is desired. For these applications, our investigation centered on improving the toughness of PPS and developing elastomer‐toughened PPS and elastomer‐toughened compounds of PPS. Using chemically treated PPS and an olefinic elastomer with a functional group, we developed elastomer‐toughened PPS using a reactive processing method. In the PPS matrix, the elastomer is finely dispersed. While the notched Izod impact strength of the original PPS is about 1 kg · cm/cm. clastomer‐toughened PPS has a notched impact strength around 50 kg · cm/cm. The notched fracture surface of elastomer‐toughened PPS is observed using a scanning electron microscope. We concluded that the mechanism for the toughening is attributed to energy dissipation by matrix yield.
Extrusion blow molding of microcomposites based on thermotropic liquid crystalline polymers and polypropylene
Authors: Handlos A. A. , Baird D. G. 
Published: April 2004

AbstractThis work is concerned with the extrusion blow molding of bottles from pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The TLCPs used are HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties observed for in situ composites in which the TLCP fibrils are generated in elongational flow fields that occur in polymer processing operations and to determine if TLCP reinforced bottles could be produced by extrusion blow molding of microcomposites. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors considered include the effect of TLCP concentration and in situ composite strand properties on the mechanical properties and anisotropy of bottles made from microcomposites. Specifically, strands having three different draw ratios are used to produce bottles at 10 and 20 wt% TLCP. Increasing the in situ composite strand modulus is shown to cause an increase in both the machine and transverse direction moduli of the composite bottles. The mechanical properties of the bottles increase with increasing TLCP composition. Finally, the machine and transverse direction properties are not balanced in the composite bottles produced in this study (degrees of anisotropy ranging from 1.5 to 1.8). The mechanical anisotropy is probably the result of a low blow up ratio (2) in the bottles and the TLCP fibers being oriented primarily in the machine direction due to the shear flow in the die.
Swell and distortions of high‐density polyethylene extruded through capillary dies
Authors: Eggen Svein , Hinrichsen Einar L. 
Published: April 2004

AbstractThe effect of varying the die entrance angle and the die length on extrudate swell and on the onset of extrudate distortion in capillary extrusion has been studied. Using theory from the literature, we have analyzed the contribution to the total pressure drop from the elongational and shear deformation in the entrance region, and from the capillary pressure drop in the land region of the die. From the contribution of the elongational deformation, we obtained an estimate for the elongational viscosity of the polymer. The same analysis was used to study the influence of the die geometry on the stick‐slip instability. It is found that the elongational component at the inlet region mainly influences the extrudate distortions. The onset of the stick‐slip instability occurs within 10% at a wall stress τw of 0.3MPa, where τw is calculated from expressions assuming fully developed flow. The variation around this average value is systematic with changes in die geometry, and the observed variations are probably due to the non‐homogeneous pressure field in the die. We also propose a model for predicting extrudate swell. Input to the model are material parameters obtainable from oscillatoric measurements of the loss and storage modulus and residence times calculated from the geometry of the die. The swell model includes a fitting parameter that sets the overall scale of the swell.
A cell model to describe the spherulitic growth in semicrystalline polymers
Authors: Bénard André , Advani Suresh G. 
Published: April 2004

AbstractThe evolution of the spherulitic morphology, commonly encountered during the solidification of semicrystalline materials, is modeled by taking into account the transport of the solute (the noncrystallizing species) and the crystallization kinetics. In this paper, a microscopic cell model is presented that incorporates the influence of these phenomena. The growth of the spherulite in the cell is represented by defining three concentric zones within the unit cell: a liquid zone, a dendritic zone, and a solid zone. The governing equations that describe the process are solved simultaneously with an integral method and a time‐stepping scheme to obtain a description of the growth of a spherulite within the cell. Five dimensionless parameters are identified that affect the cooling profile and the microstructure. Also, the concentration profiles of the noncrystallizing species, the cooling history of the spherulite, and the evolution of the grain envelope and the dendritic zone are calculated during the solidification process. These results are obtained for boundary conditions of prescribed heat flow, prescribed cooling rate, and isothermal crystallization. The development of a significant interdendritic region is observed under prescribed heat flow, along with the rise in temperature associated with the self‐heating of the polymer due to the latent heat. No interdendritic region developed with the prescribed cooling rate, and a much smaller one appeared under isothermal conditions. The solid fraction, in the last case, also reached a plateau below unity due to the choice of cooling conditions. These results are consistent with experimental observations.
Diffusion of moisture in poly(p‐phenylene terephthalamide) film: Analysis by the adsorption‐controlled diffusion equation
Authors: Fukuda Mitsuhiro 
Published: April 2004

AbstractDiffusion of moisture in poly(p‐phenylene terephthalamide) films was observed using a gravimetric method at various vapor pressures at 25°C. The equilibrium moisture regain was 4.9% (g/g) and 4.2% (g/g) at 65% relative humidity for the 16‐μm and 50‐μm thick film, respectively. These values are slightly larger than regular Kevlar or Kevlar 49 that have the same chemical structure of poly(p‐phenylene terephthalamide) (PPTA). The sorption and desorption curves were satisfactorily analyzed by the adsorption‐controlled diffusion equation assuming reversible bimolecular kinetics. These results strongly indicate that the interaction between the water molecules and amide groups of polymer plays an important role in the diffusion process and has much effect on the shape of sorption/desorption curves. The diffusion coefficients for the films were in the order from 10−‐11 to 10−‐10 cm2/s, which were also larger than those for Kevlar fibers of 10−‐12 cm2/s. The higher moisture diffusivity in the film reflects sparser molecular packing and existence of interstitial microvoids due to the lower molecular orientation in the noncrystalline region in the PPTA film than in the fiber (Kevlar).
Epoxidation reaction of trimethylolpropane with epichlorohydrin: Kinetic study of chlorohydrin formation
Authors: Quintela Arturo Lopez , Pellin Mercedes Pazos , Abuin Senen Paz 
Published: April 2004

AbstractThe kinetics of the reaction between trimethylolpropane (TMP) and epichlorohydrin (ECH) were studied. A mechanism is proposed which involves the synthesis of chlorohydrins, a previous stage which then leads to epoxy resin formation. From this mechanism a set of three coupled non‐linear differential equations, (each equation corresponds to each chlorohydrin) was derived and numerical solutions were obtained using a Monte‐Carlo method. The concentrations of chlorohydrins determined by this method (41.7, 35.7, and 22.5%) compare well with the experimental GPC results (42.7, 34.7, and 22.6%). The corresponding rate constants for the formation of the chlorohydrins were obtained.
Liquid crystalline polymer blends with stabilized viscosity
Authors: Wei K. H. , Kiss G. 
Published: April 2004

AbstractThe rheology of blends of thermotropic liquid crystalline copolyester co(hydroxybenzoate‐isophthalate‐hydroquinone) (HIQ) and polyetherimide were studied at different temperatures. As a result of the anisotropic‐to‐isotropic transition, the viscosity of the biphasic HIQ was found to be able to compensate that of the host polyetherimide at proper composition when the temperature increased or decreased in the capillary rheometer study. The 33% HIQ blend had almost stabilized viscosity between 350 and 370°C, whereas the 15% HIQ blend did not have stabilized viscosity. For the nonisothermal spiral molding trial, the 33% HIQ blend stabilized at a mean length of 21 inches (53 cm) with a standard deviation of 2.1 inch (5.3 cm) when the melt temperature increased by 30 Celsius degrees from 340 to 370°C.
Injection molding of PC/PBT/LCP ternary in situ composite
Authors: Xu Qianwei , Leng Yang , Mai Yiu‐Wing 
Published: April 2004

AbstractA liquid crystalline polymer (LCP), Vectra B950, reinforced polycarbonate (PC) 60 wt%/polybutylene terephthalate (PBT) 40 wt% blend was studied using the injection molding process. Morphology and mechanical properties of ternary in situ LCP composites were investigated and compared with binary polycarbonate/Vectra B950 LCP composites. Good in situ fibrillation of LCP was observed in the direct injection‐molded LCP composites. Preliminary results of this work indicate that addition of PBT improves skin‐core distribution of LCP microfibrils in the matrix and also enhances adhesion between the matrix and Vectra B950, which contains terephthalic acid. The PC/PBT/LCP ternary system also exhibits lower viscosity than the PC/PBT blend and pure LCP. In a ternary system with 30 wt% of Vectra B950, tensile modulus and strength increase approximately threefold and twofold, respectively. The rule of mixtures (ROM) for continuous reinforcement can accurately represent the strengthening effects for the ternary LCP in situ composites. Generally, LCP reduces the ductility and impact strength of the thermoplastic blends; however, the relative loss is less in the ternary system than in the binary system.
Note: Micromechanical testing of toughness in nylon 6/PDMS block copolymers and blends
Authors: Mukai U. , Argon Ali S. , Cohen R. E. 
Published: April 2004

AbstractSmall specimens of nylon 6/PDMS compositions were screened for relative levels of toughness using a micromechanical testing device. Measurements were made of the total crack length emanating from pre‐cut notches in a specially designed specimen. At room temperature, cracks propagated readily in nylon 6 homopolymer and somewhat more slowly in a composition containing 4 wt% PDMS; at 10 and 28 wt% PDMS the cracks were blunted in a diffuse whitened zone and did not propagate through the specimens. At −40°C, the 10 wt% blend appeared to be as tough as the 4 wt% blend at room temperature.
Estimates for process conditions during the ultrasonic welding of thermoplastics
Authors: Nonhof C. J. , Luiten G. A. 
Published: April 2004

AbstractOrder of magnitude estimates are presented for processes that play a role in ultrasonic welding. The fact that the sonotrode may not always be in contact with the product being welded, which results in the sonotrode repeatedly hammering the product, is accounted for in this study. The calculations do not use estimates for loss or storage modulus of plastics at 20 kHz around the glass or melting point for amorphous or semicrystalline polymers respectively. The flow of molten polymer in the weld zone is shown to be a laminar viscous squeeze flow driven by the welding pressure. An energy balance is used to show that the heat generated by the internal damping is, in part, used in heating cold material and is squeezed out into weld flash. The theoretical findings are correlated with existing practical pointers on ultrasonic welding in series and mass production in industry.
Optimization of hot plate welding for series and mass production
Authors: Nonhof C. J. 
Published: April 2004

AbstractA single optimal parameter setting for hot plate welding is not possible because of the large number of plastics and fillers, different types of parts, and different demands on joints. Results of a program aimed at finding an optimization procedure are presented. It is shown that one of the procedures proposed in the past is not always valid. After considering alternative approaches, the general method of a statistical process optimization is shown to be best. A complete factorial experimental design with welding machine parameters is employed.
Moldable thermoplastic elastomers: Electrical worker gloves and sleeves
Authors: Bigg D. M. 
Published: April 2004

AbstractA series of blends of styrene‐isoprene‐styrene block copolymers and ultralow density polyethylenes were evaluated for mechanical and electrical properties. A number of these blends were found to be suitable for use as moldable gloves for electrical workers. The mechanical properties exceeded those required of natural rubber solvent dipped gloves. The electrical properties were also found to satisfactorily meet the required levels of voltage and current resistance. Of particular importance were the blends in which the SIS component comprised the matrix phase. These blends exhibited low values of hardness, which made the resulting material highly flexible and compliant. The addition of polyethylene to the SIS elastomer reduced the surface tack to an acceptable level, without negatively affecting the other key properties of the elastomer. Good interfacial compatibility was found at low levels of each component in the other.
Transport in a twin‐screw extruder for the processing of polymers
Authors: Chiruvella Raman V. , Jaluria Y. , Karwe M. V. , Sernas V. 
Published: April 2004

AbstractThe fluid flow and heat transfer in polymer extrusion in a twin‐screw extruder was studied numerically by using the finite volume method. In the mathematical model, the coordinate system is fixed to the screw so that it is held stationary and the barrel is moved to simplify the complicated geometry. The screw channel of a twin‐screw extruder is approximated as two regions: translation and intermeshing. The flow in the translation region is similar to that in a shallow single screw extruder and is treated by the numerical methods given in the literature. In the nip or intermeshing region, strong mixing effects are expected, along with the diffusion of energy and momentum. The full governing equations are solved in this region to determine the velocity components in all the three coordinate directions. The energy equation is coupled with the equations of motion through viscosity, since the viscosity of the polymeric, non‐Newtonian, fluids considered here is dependent upon the shear rate and temperature. There is no clear physical demarcation between the nip region and the translation region. Therefore, a domain matching was employed at an arbitrary location that was varied numerically to ensure that the results were independent of this location. The variation of pressure and bulk temperature along the helical channel of the twin‐screw extruder is obtained, along with the shear rate. An experimental investigation of the velocity profiles in the translation region of a self‐wiping twin‐screw extruder, which is often used in practical applications, was carried out using a Laser Doppler Anemometer. The numerically predicted velocity profiles are compared with those from the experiments, yielding fairly close agreement.
Throughput calculation with considerations of leakage flow on injection molding plasticizing units
Authors: Potente H. , Effen N. , Liu J. 
Published: April 2004

AbstractThe metering time or melt throughput frequently dictates the cost efficiency of the injection molding process, which means that as accurate as possible an advance calculation must be guaranteed. In the past, leakage flow via the screw flights was neglected in pressure/throughput calculations for plasticizing units on injection molding machines. This paper presents equations for the melt throughput calculation of isothermal/non‐isothermal Power Law fluid in multi‐zone screws when considering the leakage flow over the screw flights. The concluding comparison of experimental and calculated throughputs shows a good level of agreement.
Generation of fibrillar morphology in blends of block copolyetheresteramide and liquid crystal polyester
Authors: Champagne M. F. , Dumoulin M. M. , Utracki L. A. , Szabo J. P. 
Published: April 2004

AbstractPolymer blends comprising liquid crystal polymers, LCP, as a minor component can be formed into fibrillar‐type morphology. This morphology enables the generation of improved mechanical properties in the draw direction, in a manner comparable to unidirectional composites: In this paper, the results obtained for blends of a polyetheresteramide block copolymer, PEBA, with a liquid crystalline copolyester are presented. Films prepared using a single‐screw extruder were melt drawn on calendering rolls. The blends' storage modulus increased with draw ratio, λ, reaching a maximum value for λ = 3–4. The storage modulus of blends containing 30 wt% LCP, and drawn to λ = 4 to 12, was found to increase nearly 50‐fold in comparison to neat PEBA (from 18 MPa to almost 1 GPa). The blends' morphology was characterized by dissolving the PEBA matrix, followed by gravimetric and microscopic analysis of the LCP phase. As expected, the average fiber diameter decreased as a function of λ−0.5. The fiber content as a function of λ followed a trend parallel to that of the modulus. Longitudinal and transverse moduli followed the Halpin‐Tsai predictions for unidirectional composites. Properties of compression molded specimens prepared from these blends compared favorably with glass fiber composites.
Contribution of polyalkyl(meth)acrylates to the design of PVC melt viscosity
Authors: Vankan R. , Fayt R. , Jérôme R. , Teyssié Ph. 
Published: April 2004

AbstractThe shear viscosity of poly(vinylchloride) (PVC) at 200°C can be decreased by at least one order of magnitude by the addition of as little as 5 wt% poly n‐alkyl‐(meth)acrylates (PMA) of a much lower dynamic viscosity than PVC. For this effect to be observed, the polymeric additive must be immiscible with PVC at 200°C. The average size of the dispersed phases is observed in the range of 0.5 to 5 μm; size fluctuation in this domain has no significant effect. When these conditions are met, there is a linear increase in the shear viscosity ratio ηblend/ηPVC from 0.2 to 1.0 with increasing logarithmic values of the dynamic viscosity ratio of the additive over PVC [(log(η/η)) from −4 to −1].
Diffusivity of a drug preservative in bromobutyl rubber
Authors: Hoyt Michelle A. , Balik C. M. 
Published: April 2004

AbstractSorption of phenylethyl alcohol (a model drug preservative) by bromobutyl rubber (a polymer used in drug packaging) is characterized by relatively low apparent diffusivities at room temperature (D ≈︁ 10−10 cm2/s) and a high solubility that leads to considerable swelling of the polymer. The sorption curves for thin samples exhibit non‐Fickian anomalies, which are normally observed only in glassy polymers, including two‐stage sorption and sorption overshoot. The desorption curves were much more Fickian. The swelling kinetics were very slow, and true equilibrium was not reached in the time frame of most of the experiments, which ranged up to 78 days. This produced lower apparent diffusivities and higher activation energies for sorption compared to desorption.