bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shear modification of polymers
Authors: Rudin Alfred , Schreiber Henry P. 
Published: December 2004

AbstractTime dependence of recovery from shear history effects in polymer liquids can be used advantageously to modify the properties of macromolecules. The net result of shearing is a reduction in elasticity and possibly in viscosity of the polymer fluid. The material may be processed subsequently in a transient, less elastic, and less viscous state if the diffusion‐related rate of recovery of a more fully entangled equilibrium state is not too rapid. Shear‐induced changes in entanglement density are manifested in variations in die swell, die entrance pressure losses, normal stresses, melt strength, flow defects such as melt fracture and sharkskin surfaces, haze of extruded films, application properties of coatings liquids and, other properties. Evidence for shear‐modification effects is reviewed in this article. The polymer species that are most amenable to this treatment are identified in general terms; shear modification processes that have been used are summarized. Methods for augmenting the efficiency of mechanical shear modification include addition of plasticizers, fillers, and incompletely miscible polymers. The expedient mentioned last can be particularly effective. Assessments of the degree of shear modification are reviewed and applications to coatings mixtures are also summarized. The time‐dependent behavior of the type reviewed in this article limits the success of theoretical approaches, as in the application of constitutive equations to describe polymer‐liquid behavior. Attempts to relate Newtonian viscosities and other rheological parameters to polymer characteristics are similarly hindered when shear history effects are not taken into account.
Pressure dependence of newtonian viscosity
Authors: Utracki L. A. 
Published: December 2004

AbstractRecently, a new method of generalization of the zero shear viscosity of liquids has been proposed. The method utilizes a modified Doolittle formula and the temperature‐dependent volume, as expressed by the corresponding states theory of liquids. Furthermore, the glass‐transition temperature has been employed as the scaling parameter. The proposed treatment allowed prediction of the correlation between: (i) viscosity, η, and temperature, T, (ii) η and the molecular weight of polymer, (iii) η and concentration, and (iv) the combined effect of these variables. At present, the method is extended to the pressure, P, effect. Furthermore, by substituting the free volume fraction in the Doolittle formula by the theoretical “hole fraction,” a master‐relation is proposed that provides means for predicting η = h(T, P) dependence.
Heat transfer and microstructure in extrusion blowmolding
Authors: Kamal Musa R. , Kalyon Dilhan 
Published: December 2004

AbstractExperimental measurements were made to determine the contact temperature and the rate of heat transfer between the mold and the polymer during the cooling stage of the extrusion blowmolding process. The experimental data were compared to the results of a finite difference computer simulation of the heat transfer problem, allowing for the variation of the properties of the polymer in the solid and molten states. Good agreement was obtained between experimental and calculated results. Heat transfer results were subsequently employed to explain observed differences in the microstructure of the blowmolded articles, particularly in relation to the distributions of crystallinity and birefringence. Finally, it was demonstrated that much faster cooling rates and more uniform molded articles can be obtained by employing rapid internal cooling, as in the case of water injection into subzero air inside the inflated parison.
The hydrolytic stability of glass fiber reinforced poly(butylene terephthalate), poly(ethylene terephthalate) and polycarbonate
Authors: Kelleher P. G. , Wentz R. P. , Hellman M. Y. , Gilbert E. H. 
Published: December 2004

AbstractThe hydrolytic stability of glass fiber reinforced poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET) and polycarbonate (PC) was studied. The activation energies in kcal/mole for hydrolysis are 26 for PBT and 23 for PET. Both PBT and PET contain 30 percent glass fiber reinforcement. The hydrolysis rates for a series of experimental PC's containing 10, 30 and 40 percent glass were obtained from GPC data. These increase with glass concentration but are lower than that of the unreinforced PC. Melt flow rate changes are a good measure of the hydrolytic degradation of PET. However, in the time scale of these experiments, the tensile properties of glass reinforced PBT and PC do not correlate well with M̄w changes, unlike unreinforced PBT and PC polymers. Consequently, to compare these three glass fiber reinforced polymers, estimates of failure time must be based on changes in tensile strength rather than melt flow rate.
Distribution of striation thickness from impingement mixers in reaction injection molding
Authors: Baldyga J. , Bourne J. R. 
Published: December 2004

AbstractThe striation thickness distribution developed in an impingment T‐mixer is predicted using the statistical theory of turbulent diffusion. The predicted distribution is independent of the mixing nozzle Reynolds number, in agreement with some experiments, and is primarily a function of the mixing head geometry, the ratio of the reagent flow rates and the residence time distribution of the flow in the mixing head. Mixing is described as the result of fluid deformation in the intertial subrange of turbulent flow. The relationship of deformation to time and energy dissipation rate ϵ is examined. In the impingement T‐mixer ϵ is related to the kinetic energies of the streams entering and leaving the head. (There are no surface tension effects and pressure is relatively uniform in the mixing head, so that the kinetic energy is dissipated by viscous forces.) The distribution of residence times of fluid elements in the T‐mixer is responsible for varying degrees of deformation and hence a distribution of striation thickness. This residence time distribution does not seem to have been studied and the flow pattern was thus modeled as perfect macromixing, having an exponential distribution. The procedure developed in this paper to calculate the distribution of striation thickness allows reasonable estimates of its parameters from fluid mechanical information and showed good agreement with experimental values, without having to fit any quantities. This new approach to striation thickness distribution is worth further evaluation.
Effects of axial stretching on the resistivity of carbon black filled silicone rubber
Authors: Kost J. , Narkis M. , Foux A. 
Published: December 2004

AbstractThe resistance and resistivity of Ketjenblack EC/silicone rubber compounds were studied as function of strain in constant strain rate experiments. Both strain and rate of strain affect the electrical resistivity of the compounds. Such effects are carbon black concentration dependent. Ketjenblack EC, a low structure black, is shown to behave differently than other blacks of high structure in the electrical resistivity‐strain experiments. The resistivity in the straining experiments is determined by the transient distribution of the conductive particle array.
Melt rheology of polymer blends the morphology feedback
Authors: Plochocki A. P. 
Published: December 2004

AbstractParticular rheology compositions (PRC) so far observed for blends of polyolefins are confirmed with composition dependence of melt elasticity and viscosity functions for polypropylene/rubbers and blends of other commercial polymers. Particular morphology at PRC was indirectly ascertained from the composition dependence of specific volume, vT–compositions for which the maximum vT observed are those of minimum viscoelasticity. Direct evidence from scanning electron microscopy (SEM) indicates that the disperse morphology undergoes distinct change at PRC: from uniform into bimodal, with coarser core. Rubber rich mixtures display stratified texture confirming that the melt elasticity ratio (Van Oene's) criterion for disperse/stratified morphology transition is valid in case of polypropylene/rubber blends. For a set of polymers of given melt elasticity ratios and at a composition ratio, static and rotational distributive mixers generate polyblends differing significantly in the melt rheology—morphology interaction.
NMR characterization of intermolecular interactions for polymers, IV. Intermolecular interactions of low molecular weight analogues for compatible blends of polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Djordjevic Miomir B. , Porter Roger S. 
Published: December 2004

AbstractThe intermolecular interaction, IMI, leading to the compatibility of polystyrene, PS, and poly (2,6‐dimethyl‐1,4‐phenylene oxide), PPO, has been identified by analyzing the IMI of the model compounds of low molecular weight; cumene, styrene oligomer, 2,6‐dimethyl phenol, and its trimer. The IMI has been detected and identified applying Rummens' method for the analysis of the solvent‐induced changes in NMR chemical shifts. The results indicate that the driving force in the formation of the compatible blend of PS and PPO is the π‐hydrogen bond between the electrodeficient methyl groups in PPO and π‐orbitals in PS. There were no indications that n‐hydrogen bonds are formed between ring hydrogens of PS and the oxygen in PPO.
Stress‐relaxation crazing of polymers — an energy criterion
Authors: Brueller O. S. 
Published: December 2004

AbstractOne of the most important signs of failure, easily observable in transparent and translucent polymers, is the appearance of visible crazes. The observation of first crazes is relatively simple in uniaxial long‐term experiments (such as creep and stress‐relaxation). An energy‐related crazing criterion has allowed good predictions of the appearance of first visible crazes under uniaxial creep loading conditions. The results have shown that in spite of the different applied stresses and different corresponding crazing times, the specific dissipated energy at crazing was the same. The objective of the present work was to investigate if this criterion, based on the constancy of the specific dissipated energy, is valid also for uniaxial stress‐relaxation. The good agreement between theoretical predictions and experimental results confirms this assumption.
The apparent rate constant model for kinetics of radical chain copolymerization: Chemical‐controlled process
Authors: Kuo Jen‐Feng , Chen Chuh‐Yung , Chen Chun‐Wen , Pan Ting‐Chung 
Published: December 2004

AbstractIn this article the kinetics of chemical‐controlled radical‐chain copolymerization have been reduced to pseudohomopolymerization kinetics by introducing the apparent rate constants, The methods for the determinations of the values of the apparent rate constants, mode of termination, and the methods for the calculation of molecular weights and distributions are proposed. The data required for these determinations and calculations are simply obtained by the usual steady‐state method. According to the traditional kinetics along with the definitions of the apparent rate constants, these apparent rate constants as functions of traditional rate constants, monomer compositions, and copolymer compositions are derived. Further utilizing the theoretical expressions obtained, we show that the apparent rate constants are the general rate constants for both radical chain homo‐ and copolymerizations. The bulk radical copolymerizations of methyl methacrylate and styrene at various monomer feed compositions at 60°C are used to test the proposed model. The empirical apparent rate constants obtained are described well, by the following expressions,

and

and the mode of termination on the combination termination is

where K and K denote the apparent rate constants of propagation and termination, respectively. The term f1(= 1 − f2) stands for the mole fraction of styrene in the monomer solution fed. F1 is the copolymer composition produced at f1. β is the mode of termination.
Modeling of polyethylene terephthalate reactors: 7. MWD considerations
Authors: Ravindkanath K. , Mashelkar R. A. 
Published: December 2004

AbstractA mathematical model has been developed to compute the molecular weight distribution (MWD) in the polyethylene terephthalate (PET) manufacturing process. Unlike the previous efforts, this model takes into account the influence of side reactions and various interchange reactions on MWD. The process of blending of molten polyester chips has also been simulated with a view to calculate the equilibrium MWD as well as the time required to reach the equilibrium MWD. The1 significance of the results has been discussed in terms of industrial operations involving PET polymerization and PET blending.
Theoretical investigations on some rigid‐rod polymers used as high‐performance materials
Authors: Welsh William J. , Bhaumik Dharmajyoti , Jaffe Hans H. , Mark James E. 
Published: December 2004

AbstractThis review focuses on a new type of para‐catenated aromatic polymer being used in the preparation of high‐performance films and fibers of exceptional strength, thermal stability, and environmental resistance, including inertness to essentially all common solvents. Polymers of this type include cis and transpoly(p‐phenylene benzobisoxazole) (PBO), and the cis and trans forms of the corresponding poly(p‐phenylene benzobis‐thiazole)(PBT). The purpose of this paper is to summarize the authors' theoretical work on the structures, conformational energies, intermolecular interactions, and electronic properties of PBO and PBT chains, including the protonated forms known to exist in strong acids. The emphasis is on how such studies provide a molecular understanding of the unusual properties and processing characteristics of this new class of materials.
Linear‐low‐density polyethylene melt rheology: Extensibility and extrusion defects
Authors: Constantin D. 
Published: December 2004

AbstractThis paper investigates three aspects of linear‐low‐density polyethylene (LLDPE) rheological properties: shear viscosity variations with shear rate and temperature, tensile behavior determined with an extensiometer, and extrusion defects. The differences in shear viscosity variation with shear rate and temperature between LLDPE and LDPE (low‐density polyethylene) are shown. These differences, attributed to wider molecular weight distribution and to long chain branching (LCB) in LDPE, involve different extrusion behaviors. The lack of LCB in LLDPE can be demonstrated by comparison of the measured Newtonian viscosity with the value of the same parameter calculated from molecular weight distribution and composition law of Newtonian viscosities. The lack of LCB leads to good melt extensibility, which is shown by tensile properties of polyethylene melts determined with a non‐isothermal extensiometer. The melt fracture phenomenon is studied because it promotes surface defects on bubbles in film application. Extrudate distortions are examined at the laboratory extruder outlet. This test shows differences between LLDPE and LDPE, but also between some LLDPE samples.
The influence of high storage humidity on some properties of solid propellants
Authors: Harniv Israel , Rigbi Zvi 
Published: December 2004

AbstractThe absorption of water vapor by propellants based on hydroxy‐terminated polybutadiene and an isocyanate from atmospheres of increasing relative humidities, and the swelling index of the propellant which had absorbed various proportions of water, were measured in an attempt to establish the extent of hydrolytic damage. The method was found incapable of assessing such damage, but it was shown that there was no measurable absorption of vapor below 92 percent relative humidity (RH). The MEK/polymer and toluene/polymer interaction parameters were determined.
Gas chromatographic determination of the interaction parameter of poly(ethylene oxide)/poly(methyl methacrylate) blends
Authors: Elorza J. M. , Fdz‐Berridi M. J. , Iruin J. J. , Guzman G. M. 
Published: December 2004

AbstractInverse gas chromatography (IGC) has been used to investigate thermodynamic miscibility of a molten poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blend. Toluene, benzene, and chloroform have been employed as probes in pure and mixed stationary phases of these polymers. Experimental measurements have been taken over a narrow range of temperatures because of the high PMMA glass transition temperature as well as the degradation of the PEO. The interaction parameter χ23 determined at 150°C is slightly negative and dependent on the interacting probe, as has been also noted in previous chromatographic studies on polymer‐polymer miscibility. The last section is devoted to a model calculation, using Flory's equation of state theory. Different χ23‐concentration curves have been simulated, with the interaction energy parameter X23 as an adjustable parameter.
Chain scission and mechanical degradation of polystyrene
Authors: Fordyce P. , Devries K. L. , Fanconi B. M. 
Published: December 2004

AbstractThe extent of molecular degradation of amorphous polystyrene when subjected to mechanical grinding at cryogenic temperature has been investigated using electron spin resonance, infrared spectroscopy, and viscometry. Essentially identical concentrations of chain ruptures in the degraded samples were found from infrared spectroscopic determinations of molecular end group concentrations and by the changes in the viscosity‐average molecular weights. The chain‐scission concentration was from two to four times the free‐radical concentrations, indicating that free‐radical‐propagation reactions play a much less dominant role in the degree of molecular damage associated with mechanically induced chain scission in glassy polymers. In addition, experiments were carried out as a function of molecular weight and these indicated a virtual independent behavior with molecular weight.
High‐temperature electrical conductivity and thermal decomposition of Sylgard® 184 and mixtures containing hollow microspherical fillers
Authors: Johnson R. T. , Biefeld R. M. , Sayre J. A. 
Published: December 2004

AbstractThe high‐temperature electrical conductivity and thermal decomposition characteristics of Sylgard® 184 with and without hollow microspheres of glass, silica, and ceramic have been determined to 600 to 700°C in air and nitrogen environments. The materials are silicone‐based dielectrics and are used as electronic encapsulants. Results show that a peak in the conductivity temperature dependence at ∼300°C results principally from volatilization of [Si(CH3)2O]n with some evolution of water, that oxygen accelerates decomposition, and that the microspheres may help form a network of interconnected conductive pathways in the residual material. There is a good correlation between thermal stability and temperature‐dependent electrical properties.
Mechanical compatibilization of immiscible blends
Authors: Barlow J. W. , Paul D. R. 
Published: December 2004

AbstractThe mechanical properties of a variety of immiscible binary blends, with and without third component polymeric compatibilizers, are reviewed and qualitatively related to the degree of adhesion between blend components as determined by lap shear testing. Generally, blends comprised of components which adhere well, one to the other, show improved ductility relative to blends of components which do not adhere, Similarly, polymeric compatibilizers are found to be more effective for improving the properties of a binary blend system if they adhere well to both primary components of the immiscible mixture. These results suggest that adhesion between phases in the mixture strongly influences the ultimate properties of the blend. Some evidence is presented which suggests that components which adhere well are partially miscible.
Polypropylene based polymer blends: Fields of application and new trends
Authors: Galli P. , Danesi S. , Simonazzi T. 
Published: December 2004

AbstractThe new industrial strategy in the polymer field requires the transformation of plastic “commodities” into “specialties”. From this point of view, polypropylene (PP) plays an important role both for its intrinsic properties such as high melting temperature, low density, high chemical inertness and for its capability to be produced with different morphological and molecular structures, to be modified with the addition of other polymers or mineral fillers and to be grafted with functional groups. The present range of special and reinforced polypropylene grades includes: elastomer‐modified PP, elastomer‐modified filled PP, glass fiber‐reinforced PP, filled PP, esthetic filled PP, flame‐retardant PP, and thermoplastic elastomers. New trends for significantly improving this family of polymers involve impact resistance, processability, durability, dimensional stability, elasticity, and surface properties. A positive answer to this complex emerging demand will put, as indicated, in this work, “special and reinforced polypropylene grades” in a position to successfully compete with technopolymers in some important, rapidly growing application sectors.
Roll fusing of toner particles on rough papers in the xerographic process
Authors: Kuo Youti 
Published: December 2004

AbstractThis paper deals with squashing of toner particles in a variety of paper topographies in the roll fusing of toner images in xerographic machines. The model developed can be used for predicting the mean spreading ratio of toner particles related to fix level with given rheological properties and fusing temperature and pressure.The deformation of toner particles is solved with respect to the asperity pressure encountered in the contact between the roll and the paper surfaces. Various contact situations are considered, among them: toners on smooth papers, on tops of paper asperities, and at valleys of a paper surface. In addition to rheological properties and fusing conditions, toner spreadings also depend on toner size, paper roughness, and the rubber modulus of the fuser roll.Based on an integration algorithm, statistical averages of toner spreadings can be computed in terms of distribution functions of toner and paper asperity height. Comparisons of theoretical predictions with measurements show good agreement over a broad range of data.
Heat transfer in injection molding of crystallizable polymers
Authors: Kamal M. R. , Lafleur P. G. 
Published: December 2004

AbstractA model is proposed for the treatment of heat transfer with crystallization during plastics processing in general, and injection molding in particular. The model incorporates experimentally determined crystallization kinetics parameters. It permits the calculation of the distribution of both temperature and crystallinity in the molding. Theoretical predictions are in good agreement with experimental measurements in both injection molding and a prototype apparatus.
Compatibilization of polyester/polyamide blends via catalytic ester‐amide interchange reaction
Authors: Pillon L. Z. , Utracki L. A. 
Published: December 2004

AbstractIn a series of publications we reported on melt rheology, morphology, and mechanical properties of the poly(ethylene terephthalate)/poly(amide‐6,6) blends (PET/PA). The non‐oriented samples had poor interphase bonding resulting in low impact and tensile strengths. To improve these properties the ester‐amide interchange reaction was carried out in solution and in melt. In the latter case a Brabender Plastograph was used in the mixing chamber or twin‐screw extruder configurations with p‐toluenesulfonic acid as a catalyst. The interchange reaction was followed by 400 MHz proton and 13C nuclear magnetic resonance spectroscopy.