bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microphase structure and properties of polyurethane/polyvinyl interstitial composites
Authors: Koberstein Jeffrey T. , Stein Richard S. 
Published: December 2004

AbstractThe morphology of two series of polyurethane/polyvinyl interstitial composites is characterized by scanning electron microscopy, small‐angle light scattering, and small‐angle X‐ray scattering. Thermal and mechanical properties are measured using differential scanning calorimetry and dynamic mechanical analysis. The polyurethane networks examined are microphase separated segmented block copolymers. A variety of linear and network vinylic components are studied including polymethacrylonitrile homopolymer and copolymer, and polyacenaphthalene homopolymer and copolymer. The polyurethane and polyvinyl components phase separate during the in situ polymerization resulting in a three‐phase morphology. Detailed small‐angle X‐ray scattering analysis provides measurements of phase mixing, domain spacings, and diffuse phase boundary thicknesses. A comparison of these parameters for parent polymers and composites reveals only slight differences; indicating that the microdomain structures of the phase‐separated polyurethane networks are preserved in the composite. Appreciable molecular interpenetration of components is not observed. Dynamic mechanical loss measurements for several of the composites demonstrate the presence of loss processes occurring over extremely broad ranges of temperature. The strong mechanical interaction between components observed suggest that the urethane and vinyl phases may be bicontinuous in these materials.
The crystalline morphology of poly(vinylidene fluoride)/poly(methylmethacrylate) blends
Authors: Morra B. S. , Stein R. S. 
Published: December 2004

AbstractPoly(vinylidene fluoride), PVF2, as well as blends of PVF2 with poly(methyl methacrylate), PMMA, develop a variety of crystalline morphologies at low undercoolings. Both the α and γ crystal forms grow from the melt and the former undergoes a solid‐solid phase transition to the latter, though its morphology remains unaltered. Three melting temperatures which decrease with increasing PMMA content are observed. Hoffman‐Weeks analysis shows the equilibrium melting points of the blends to be depressed. Using these equilibrium values, the thermodynamic interaction energy density is calculated to go from −5.40 × 106 to −2.96 × 107 j/m3 as the blend composition goes from 40.1 volume percent to pure PVF2. The band periodicity in the α form spherulites increases with crystallization temperature and PMMA content and it appears to be from a lamellar reorientation process with an apparent activation energy of 322 cal/mole. Electron diffraction patterns taken along the radial direction in a given spherulite reveal lamellar twisting which causes the banded appearance. Light scattering results suggest that the lamellar are formed into rod‐like structures on a local scale but that on a larger scale they develop a disoriented spherulitic morphology.
Performance of gear pumps in polymer processing
Authors: McKelvey James M. 
Published: December 2004

AbstractWithin the past several years considerable interest has developed in the practice of retrofitting plasticating extruders with gear pumps. The primary motivation for this is to reduce surges and fluctuations in the extrusion rate, thereby improving product quality and reducing waste. It is shown that the effectiveness of a gear pump for this purpose is directly related to its volumetric efficiency, which depends upon the pump dimensions, the flow behavior of the polymer, and the operating variables of temperature, pressure differential, and pump speed. Experimental data on three thermoplastic materials using a pump having gear wheels of 36 mm diameter for both leakage and power are reported. These data have been correlated with semi‐empirical equations.
Experimental study and computer simulation of a two‐stage continuous polymerization process for the production of methyl methacrylate
Authors: Carratt G. M. , Shervin C. R. , Soong D. S. 
Published: December 2004

AbstractThe two major problems encountered in industrial liquid‐phase addition polymerization are: the heat released by highly exothermic reactions and the great increase in viscosity with conversion. The high rate or heat generation, coupled with the low thermal diffusivity of the reacting system, often lead to thermal runaway. Even with the process kept under marginal control, large temperature variations broaden the product molecular‐weight distribution. Temperature control is particularly difficult in the Trommsdorff region, where reaction rate rapidly increases as temperature rises and viscosity builds up. A two‐stage process is developed in this work to attack these problems and to achieve continuous operation of poly(methyl methacrylate) bulk polymerization. This process utilizes a continuous stirred‐tank reactor (CSTR) as a first‐stage prepolymerizer and a spray tower as the second‐stage finishing reactor. Use of a CSTR offers good temperature control and product uniformity during the early stages of reaction and eases delivery of the reacting system to the second stage at the desired conversion and molecular‐weight level. Spraying the partially polymerized mixture into the tower as fine droplets prior to the onset of gel effect eliminates the problems of transporting, agitating, and mixing a reacting system with a rapidly increasing viscosity. Heat of reaction is efficiently removed by a countercurrent stream of nitrogen in the tower, in direct contact with the falling droplets. The high surface‐to‐volume ratio of these small droplets facilitates heat transfer, and the problem of heat buildup can be efficiently controlled. Products from the bottom of the tower can then be melt‐processed by conventional methods, such as extrusion. Experiments performed in the laboratory have demonstrated the feasibility of this proposed concept. Process optimization was in no way achieved due to serious space and equipment limitations. The process was thus further examined by computer simulation and model parameter sensitivity study. A practical design was recommended based on the model predictions.
An experimental study on the injection molding of thermosetting polyester resin
Authors: Han Chang Dae , Lem Kwok‐Wai 
Published: December 2004

AbstractAn experimental study was conducted on the injection molding of a thermosetting polyester resin. For the study, a general‐purpose unsaturated polyester resin was used, with benzoyl peroxide as initiator. A differential scanning calorimeter (DSC) was used for studying the curing kinetics, under isothermal curing conditions. A plunger‐type injection‐molding apparatus was constructed, and a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a film the changes in stress birefringence patterns in the mold cavity during the molding operation (i.e., during the isothermal cure, post cure, and subsequent cooling), using a crossed circular polariscope. The injection‐molded specimens were used to determine the distribution of the degree of cure at various positions in the flow direction, and to relate the degree of cure to the dynamic mechanical properties.
A novel hysteresis test for studying crazing and shear yielding in rubber‐toughened polymers
Authors: Bucknall C. B. , Marchetti A. 
Published: December 2004

AbstractTensile, tensile impact, compact tension, and fatigue tests were carried out on ABS (acrylonitrile‐butadiene‐styrene), HIPS (high impact polystyrene), and toughened PMMA (poly(methyl methacrylate)). Dumbbell specimens machined from test pieces were then subjected to sinusoidal tension‐compression cycling at low stress amplitudes. The HIPS specimens produced asymmetrical hysteresis loops characteristic of multiple crazing, whereas PMMA gave more symmetrical, regularly shaped, loops. The behavior of the ABS polymers varied with loading history. It was concluded that the hysteresis test provides a useful additional technique for studying deformation mechanisms, especially under conditions that do not readily permit volumetric measurements.
Binary blends containing a commercial polyarylate
Authors: Eguiazábal J. I. , Calahorra M. E. , Cortázar M. M. , Iruin J. J. 
Published: December 2004

AbstractA commercial polyarylate (PAr), a copolyester of Bisphenol‐A with 50 percent terephthalate‐50 percent isophthalate, has been characterized by means of a combination of gel permeation chromatography and viscometry. It has been studied as first component of a series of polymer blends. The presence of either one glass transition temperature (Tg) or two has been used as a criterion to determine the miscibility of each blend. In some cases, the possible incidence of transesterification reactions has been considered.
Morphology and properties of blends of polypropylene with ethylene‐propylene rubber
Authors: Yang Decai , Zhang Bailan , Yang Yongkuan , Fang Zheng , Sun Guifen , Feng Zhiliu 
Published: December 2004

AbstractGreat attention has been paid to the toughening of isotactic polypropylene (PP) in recent years in order to make full use of this plastic. This paper presents the results of our study on the compatibility of PP with ethylene‐propylene‐diene rubber (EPT), polybutadiene rubber (PB) or styrene‐butadiene rubber (SBR) through characterization of the blends' morphology, and on. the morphology and properties of binary blends of PP with EPT (EPT/PP) and ternary blends of PP, EPT, and polyethylene (PE) (EPT/PE/PP). Morphological structure of solution blends and the great improvement in low‐temperature impact strength and other properties of the mechanical blends have shown the difference among EPT, PB, and SBR in compatibility with PP, the effectiveness of using EPT as PP's toughening agent, and the effect of EPT on EPT/PP blend as both toughening agent and compatibilizer. Addition of EPT to EPT/PP made interesting changes in morphology but no effect on properties was observed.
Common structure, compatibility and complementarity of mathematical models of injection molding
Authors: Grmela Miroslav 
Published: December 2004

AbstractThe hierarchy of mathematical models of injection molding is reviewed. Compatibility of the models of the hierarchy, usefulness of simultaneous applications of models formulated on several different levels of the hierarchy and compatability between physical approximations leading to the formulation of a model, and mathematical approximations used to solve numerically the governing equations of the model are discussed. This review is intended to facilitate the search for a model that is best suited to a given need and to indicate future research.
Permeability of oxygen and water vapor through polyethylene/polyamide films
Authors: Kamal M. R. , Jinnah I. A. , Utracki L. A. 
Published: December 2004

AbstractOxygen and water vapor permeability studies were carried out on binary polyethylene/polyamide immiscible blends incorporating three polyethylene resins (LDPE, LLDPE, and HDsPE), and three polyamide resins (PA‐6, PA‐6,6, and modified PA‐6,6m). It was found that the incorporation of PA into PE reduces the oxygen permeability while water vapor permeability is increased. In the range of 0 to 30 weight percent of PA, the oxygen permeability of PE was reduced by a factor of 2.8 to 3.6. Maximum water vapor permeabilities increased: for HDPE by a factor of about 2.6 to 3.1 and for LDPE and LLDPE blends by about 1.6.
Ultrasonic velocity measurement for the determination of density in polyethylene
Authors: Piché L. 
Published: December 2004

AbstractAn ultrasonic immersion method is presented for the rapid and accurate measurement of longitudinal sound velocity (v) in polyethylene (PE). The method is based solely on the measurement of time delays and can be automated. The samples are the same press‐molded plaques that are prepared for the standard‐density (ρ) determination using a density‐gradient column, Our measurements on a representative group of various types of PE with densities in the range 0.92 to 0.96 g/cm3 show without ambiguity that v is proportional to ρ. The degree of correlation is such that we come to suggest that the acoustic method be used for the characterization of density. We show that the accuracy is good and compares with that of the density‐gradient column and we then conclude on the practical advantages of the ultrasonic method.
Unsaturated polyester based on poly(ethylene glycol)
Authors: Tong S. N. , Chen D. S. , Kwei T. K. 
Published: December 2004

AbstractUnsaturated polyesters were prepared by one‐stage melt condensation of maleic anhydride, phthalic anhydride, propylene glycol, and poly(ethylene glycol)s with different molecular weight, and the properties of their castings from styrenated resins were investigated. Tensile and flexural properties decrease with the increase of molecular weight of poly(ethylene glycol), but impact strength, elongation, and water absorption have an inverse effect. This study improves the understanding of the effect of chain length of poly(ethylene glycol) in unsaturated polyester on the properties of its castings.
Two and three component interpenetrating polymer networks
Authors: Klempner D. , Frisch K. C. , Xiao X. H. , Frisch H. L. 
Published: December 2004

AbstractTwo and three component interpenetrating polymer networks (IPNs) have been prepared from polyurethanes, epoxy resins, and acrylic copolymers using the simultaneous technique (SIN). These materials exhibited a variety of morphologies and properties dependent on the types of polymer, molecular weight of precursors, presence of charge groups, and presence of intentional grafts between the component polymer networks. In general, decreasing molecular weight of prepolymers, presence of intentional grafts, and presence of charge groups of opposite charge resulted in increased homogeneity (interpenetration). In addition, increased homogeneity resulted in enhanced mechanical properties.
Processing of reinforced plastics using multi‐screw compounders
Authors: Eise Kurt , Curry John , Farrell John 
Published: December 2004

AbstractPolymer modification by addition of reinforcing agents represents a popular means of increasing physical property values. The polymer matrix has been forced to accept up to 55 percent by weight of fibrous reinforcement and 80 percent by weight of powdered types in order to meet application requirements. These materials demand sophisticated mixing equipment which must provide extensive intake and conveying capabilities, polymer wetting of reinforcement, and dispersion of reinforcement. This process must also be conducted with controlled shear intensity and excellent temperature and residence time control in order to respect polymer thermal sensitivity and product requirements. The extrusion process is a proven economical method for incorporating reinforcements into polymer resins. Co‐rotating intermeshing twin‐screw extruders are particularly suited for these tasks. Positive conveying, self‐wiping, and shear intensive mixing characteristics provided by the screw mechanism satisfy requirements of reinforcement compounding. This mechanism allows interruption of streamline flow which is needed to disperse both high and low aspect ratio reinforcing agents into a polymer matrix. Mathematical representation of the benefits of twin‐screw extrusion (relative to single‐screw) related to pumping and mixing capability have been developed based on the classical pressure flow continuity equation with proper selection of boundary conditions.
Hydrodynamic analysis of negative flow in a spiral disc extruder
Authors: Krein H. L. , Plumtree A. , Rudin A. 
Published: December 2004

AbstractThe flow of polymer melts in a rotating disc extruder is analyzed with a mathematical model for pressure flow and leakage flow (termed neg ative flow). It is assumed that the material is fully melted and exhibits Newtonian flow behavior under isothermal conditions for each element. Flow is evaluated in successive sections of the flow path and the final expression involves a computer‐assisted numerical solution. Pressure flow, which is negative, is calculated by analyzing the situation in which the pressure gradient causes the extrudable material to flow back across the stationary disc. A simplified geometrical model is developed for numerical solution, assuming incompressible flow. Leakage flow is between the contours of the disc and the engaging interior face of the housing. The flow is also directed opposite to the drag component and is estimated by using parallel plate flow equations.
On the nonlinear response of polymers to periodical sudden loading and unloading
Authors: Brueller O. S. 
Published: December 2004

AbstractIn practice, it happens very often that structural parts made of plastics are submitted to a long term loading which “jumps” periodically between a constant maximal value and a constant minimal one. The knowledge of the material response to such a kind of loading demands very laborious experimental investigations. Since generally the loading takes place in the nonlinear viscoelastic range of the material, an analysis based on linear superposition cannot be applied. In the present paper a computational method is proposed to predict the response of the polymer to a low frequency “jumping” load in the nonlinear viscoelastic range, This method is based on the knowledge of the long term behavior of the material under constant loading conditions, which is approximated by finite exponential series. Both cases, stress‐relaxation‐type and creep‐type loading histories are treated. Examples presented show a very good agreement between theoretical predictions and experimental data.
A computer study of film blowing
Authors: Luo X‐L , Tanner R. I. 
Published: December 2004

AbstractThis paper extends Petrie's work on film‐blowing to cover viscoelastic non‐isothermal flow for both the convected Maxwell and the Leonov models. Good agreement with experimental data is shown for the former. The calculations are highly unstable, however, and it is difficult to obtain convergence with arbitrary values of the film‐blowing parameters. The general effect of viscoelasticity is to stiffen the film and restrain the increase in bubble diameter. There is some difference between bubble shapes generated using the Maxwell and Leonov constitutive models but the temperature variation of properties is seen as the dominant effect, The Leonov model tends not to be stiff enough in its response to the present flow, which is purely extensional and good agreement with experiment was not obtained. For the Maxwell model the relevant mean relaxation time must be used for good agreement between experiment and calculation.
The rubber particle size dependence of crazing in polypropylene
Authors: Jang B. Z. , Uhlmann D. R. , Sande J. B. Vander 
Published: December 2004

AbstractThe tensile crazing and Charpy impact behavior of polypropylene modified with styrene‐butadiene copolymer (SBR) and ethylene‐propylene‐diene monomer (EPDM) was studied. Various rubber particle size distributions were obtained by varying the relative viscosities between rubbery phase and PP matrix. Transmission electron microscopy and computer‐aided image analysis were used to provide particle size information. In general, PP blends with smaller rubber particles are tougher and more ductile than those with larger particles, probably because the former represents a more efficient use of rubbery phase in promoting crazing and/or shear yielding. Samples with average particle diameter D̄ ≥ 0.5 μm were found to exhibit pronounced crazing. Within a given sample, no crazes appeared to develop around individual rubber particles with D < 0.5 μm. The higher the D, the greater the propensity to form crazes. The behavior of samples with D̄ ≪ 0.5 μm appeared to be dominated by shear yielding; very few crazes could be found. That there exists a critical rubber particle size is explained by the requirement that sufficient stress concentration be maintained to a finite radial distance to permit the initiation and growth of a craze, which requires a finite volume. Small particles, inducing smaller stress‐enhanced zones, are therefore not effective in initiating crazes.
Synthesis and rheological study of some maleic acid polyamides
Authors: Jaćović Mihailo S. , Djonlagić Jasna , Macknight William J. , Lenz Robert W. 
Published: December 2004

AbstractThe contributions of the cis and trans configurations of the main chain double bonds to the transition temperatures and rheological properties were determined for four well‐defined polymaleamides, which were prepared by the room temperature ring‐opening, step‐growth polymerization reactions of N,N′‐bisisomaleimide monomers with bifunctional primary diamines. The polymaleamides were glassy solids, which could be thermally isomerized into related polyfumaramides. The glass transition temperatures of the polyfumaramides, as determined by mechanical spectrometry, are systematically and markedly higher than those of the polymaleamides from which they were derived.
Recent studies on interpenetrating polymer networks
Authors: Frisch K. C. , Klempner D. , Xiao H. X. , Cassidy E. , Frisch H. L. 
Published: December 2004

AbstractRecent investigations on interpenetrating polymer networks (IPNs) have included two component IPNs from polyurethanes and poly(methacrylates) and two component IPNs from polyurethanes and epoxies. All the IPNs were prepared by the simultaneous polymerization technique (SIN‐IPNs). Two types of IPNs, polyurethane‐poly(methyl methacrylate) (PU/PMMA) and polyurethane‐poly(methyl methacrylate‐methacrylic acid) (PU/PMMA‐MAA) were prepared. Improved phase miscibility and decreasing extent of phase separation was observed in both types of IPNs with increasing the NCO/OH ratio, decreasing molecular weight of the polyol in the PU and introduction of charge groups. A comparison was made between full‐IPNs, pseudo‐IPNs, graft copolymers and related homopolymers from polyurethanes and epoxies. Increased compatibility in full‐IPNs and graft copolymers was observed by means of DSC, SEM and was also further substantiated by a shift toward single Tgs as determined by dynamic mechanical spectroscopy. The introduction of opposite charge groups in two‐component IPNs from polyurethanes and epoxies led to improved compatibility (no phase separation) and enhanced mechanical properties.
A mathematical model for computer simulation of a direct continuous esterification process between terephthalic acid and ethylene glycol: Part 1. Model development
Authors: Yamada Toshiro , Imamura Yoshio , Makimura Osamu 
Published: December 2004

AbstractA new mathematical model has been developed for the continuous esterification process of terephthalic acid (TPA) and ethlene glycol (EG) with consideration of oligomer characteristics. The liquid weight fraction in the reaction mixture, β, has been selected as a principal parameter in this model. The solubility of TPA in EG and bis β‐hydroxyethyl terephthalate (BHET) has been measured in order to estimate more precisely the concentration of each component. Good agreement has been obtained by plotting the log of solubility data of TPA in EG and BHET against the reciprocal of the absolute temperature with correlation coefficients of 0.998 and 0.989, respectively. The validity of these data has been verified in comparison with other data.