bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deformation and fracture characterization of inelastic composite materials using potentials
Authors: Schapery R. A. 
Published: December 2004

AbstractAn approach using strain energy‐like potentials to characterize deformation and fracture of inelastic, nonlinear composite materials is described. The inelasticity may be due to various causes, including microcracking, microslipping, and rate processes responsible for fading memory (viscoelasticity). The concept of work potentials is introduced first, and then arguments are given for their existence for inelastic materials. Emphasis in the paper is on elastic composite materials with changing or constant states of distributed damage. Experimental results on polymeric composites are subsequently presented to illustrate this approach to deformation and fracture characterization. Finally, extension to viscoelastic behavior is discussed.
Volume change and the nonlinearly thermo‐viscoelastic constitution of polymers
Authors: Knauss W. G. , Emri I. 
Published: December 2004

AbstractThe time‐dependent behavior of linearly viscoelastic materials is known to be very sensitive to changes in temperature and in solvent (water) concentration. Following an investigation by the authors of this sensitivity in terms of the associated small volume changes, a nonlinearly viscoelastic model of constitutive behavior was formulated earlier in terms of the free volume concept and evaluated in terms of experiments on poly(vinyl acetate). Following a brief presentation of the earlier results these concepts are expanded and refined in the present paper to deal with transient deformation histories under pressure. In this connection, model computations explore the effect of simultaneous pressurization and straining. In addition the effect of “ageing” the polymer under pressures of various magnitudes and for different lengths of time are investigated. It becomes clear that the yield phenomenon depends sensitively on pressure and on the ageing time. In addition, the volume change under transient thermal histories in the glass transition range is explored, largely in terms of Kovacs' experimental data and attendant computations. These considerations are presented from a unified point of view of nonlinear thermoviscoelastic constitutive behavior, principally with phenomenological material description in mind. These computations provide guidance to the design of experiments for the proper determination of the relevant material functions and seem to indicate a need for the reevaluation of certain experimental procedures in the time histories of thermal material characterization.
The nonlinear viscoelastic characterization of graphite/epoxy composites
Authors: Dillard D. A. , Straight M. R. , Brinson H. F. 
Published: December 2004

AbstractFiber reinforced plastics offer many structural advantages for a variety of designs. Before these material systems can achieve more widespread usage, however, some of the unanswered questions regarding the long‐term behavior and durability of these materials must be answered. Nonlinear compliance data is presented for T300/934 and T300/5208 graphite/epoxy composites. Several nonlinear viscoelastic techniques are compared for modeling the response. Comments for applying nonlinear models to orthotropic materials are given. A procedure for predicting long term laminate response from short term unidirectional data is reviewed.
Multiaxial nonlinear viscoelasticity of solid polymers
Authors: Buckley C. P. 
Published: December 2004

AbstractA scheme is presented for characterizing multiaxial nonlinear viscoelasticity of solid polymers in a manner suitable for application to the prediction of deformation of polymeric parts. The basis of the scheme is the systematic exploitation of simplifications resulting from: (1) restrictions on the class of stress histories considered, (2) material symmetry (e.g., isotropy), and (3) the nature of viscoelastic nonlinearity in any given material. Several classes of stress history are considered. In the special case of inplane response of an isotropic material to a two‐dimensional proportional loading history, it is shown that the nonlinearity can be expressed through the dependences of compressibility B and shear compliance J on two invariants of the stress history: I1 and I2′, which separately characterize the magnitudes of hydrostatic and deviatoric components of the stress tensor. When this approach is applied to the description of biaxial creep and recovery of isotropic polypropylene, it is found that for strains up to 0.012, B is independent of I1 and I2′, while J is linearly related to I1 and I2′. These results are used to predict axial strain and hoop strain in the wall of a pressurized pipe, and the predictions compared with those obtained with three approximate procedures.
Flow distribution in spiral mandrel dies
Authors: Rauwendaal Chris 
Published: December 2004

AbstractAn analysis of flow of a power law fluid in a spiral mandrel die is presented. The analysis is applied to study the effect of various die design parameters on the flow distribution at the end of the spiral mandrel section. Three variables that have a very strong effect on the flow distribution are the number of grooves, the initial clearance, and the groove helix angle. The distribution is improved by increasing the number of grooves, by using a non‐zero initial clearance, and a relatively small helix angle. Two more variables that have a significant effect on the flow distribution are the taper angle and the initial groove depth. The optimum taper angle was found to be between 1 and 3 degrees. The distribution uniformity improves with the initial groove depth, while the pressure drop reduces at the same time.
Effects of mixing on morphology, rheology, and mechanical properties of blends of ultra‐high molecular weight polyethylene with linear low‐density polyethylene
Authors: Vadhar Parimal , Kyu Thein 
Published: December 2004

AbstractVarious blends of ultra‐high molecular weight polyethylene (UHMWPE) with linear low‐density polyethylene (LLDPE) were prepared in an internal (Banbury type) mixer, a static mixer, and by solvent blending. Two mixing techniques, namely simultaneous and sequential loading methods, were employed with the internal mixer. In the former case, the two polymer components were simultaneously loaded at 180°C and mixed. The latter method allowed the UHMWPE component to diffuse at 250°C and cooled it down to 180°C, then the LLDPE component was added subsequently and mixed. Rheological and mechanical properties of these blends are profoundly affected by the mixing techniques used. Rheological results shows yield characteristics of UHMWPE/LLDPE blends, in particular in blends of high UHMWPE contents. Tensile properties of sequentially loaded blends vary more or less linearly with blend compositions. However, negative or positive deviations are seen in the simultaneously prepared blends. Differential scanning calorimetry (DSC) studies indicate that co‐crystallization takes place between UHMWPE and LLDPE components in sequentially mixed blends. DSC and small‐angle light scattering (SALS) studies show that separate crystallization takes place in simultaneously blended compounds as a result of poor mixing. It seems that the sequential loading method provides more homogeneous compounds than those of simultaneous blending.
Influence of casting and curing conditions on gas sorption and transport in polyimide films
Authors: O'Brien K. C. , Koros W. J. , Husk G. R. 
Published: December 2004

AbstractCarbon dioxide and methane gas permeabilities, solubilities and diffusivities for poly [N, N′‐(phenoxyphenyl)‐pyromellitimide] films synthesized in our laboratory are contrasted with values measured for a chemically identical commercial polyimide film, Kapton H. The synthesized samples exhibited greater permeabilities, solubilities, and diffusivitles than those of the commercial sample. At the same time, the higher carbon dioxide permeability is associated with only a moderate reduction in permselectivity for the CO2/CH4 system. The increased sorption and transport coefficients for the synthesized sample are attributed to a lower degree of aggregation and orientation of this film as compared to the Kapton H sample.
Polymers based on divalent metal salts of mono(hydroxyethyl) phthalate—a review
Authors: Matsuda Hideaki 
Published: December 2004

AbstractDivalent metal salts of mono(hydroxyethyl) phthalate are useful starting materials for synthesis of ionic polymers into which metal is firmly incorporated. This article surveys a series of polymers that have been synthesized by using metal salts. The salts can react with compounds having functional groups capable of reacting with hydroxyl groups. By polyaddition reactions of the salt‐diol with diisocyanates in dimethylformamide, metal‐containing polyurethanes, polyurethane‐ureas, and isocyanurate‐type crosslinked polyurethanes are obtained. In polycondensation reactions of the salt‐diols with anhydrides, some systems give unsaturated polyesters soluble in styrene. Meanwhile, polyaddition reactions of systems of the salt‐anhydride‐epoxide give metal‐containing polyesters containing ionic links in the main chain. The metal carboxylate groups of the salts catalyze the reactions in this case. The reactions have offered a commercially favorable synthetic route. Through the proper selection of components, various types of metal‐containing unsaturated polyesters, cured resins, and cured rubbers are obtained. The effect of introducing metal on their physical and other properties results, and, in addition, generally Mg is more effective than Ca in improving the properties of the polymers.
Formation of dispersed phase in incompatible polymer blends: Interfacial and rheological effects
Authors: Wu Souheng 
Published: December 2004

AbstractThe formation of dispersed phase in blends of incompatible polymers during melt extrusion with a co‐rotating twin screw extruder was studied, using nylon and polyester as the matrix and ethylene‐propylene rubbers as the dispersed phase. A master curve is obtained, i.e., Gηmα/γ = 4p±0.84, where G is the shear rate, γ the particle diameter, η the interfacial tension, ηm the matrix viscosity, ηd the dispersed‐drop viscosity, and p = ηd/ηm. The plus (+) sign applies for p > 1, and the minus (−) sign for p < 1. Thus, the dispersed‐drop size is directly proportional to the interfacial tension and the ±0.84 power of viscosity ratio. The dispersed drops are the smaller, when the interfacial tension is the lower and the viscosity ratio is the closer to unity. The interfacial tension is largely controlled by the polarities of the two phases, and can be varied over several orders of magnitude by using appropriate dispersants.
Phase transitions during shear flow of two‐phase polymer blends. I. Theory. Transition to “Homogeneous” melt state
Authors: Lyngaae‐Jørgenson J. , Søndergaard K. 
Published: December 2004

AbstractA hypothesis for critical conditions for a transition from a two‐phase system to a homogeneous state during simple shear flow is advanced. It is predicted that at sufficiently high shear stress a homogeneous state is the stable steady state structure.
Phase transitions during shear flow of two phase polymer blends. II. Styrene‐acrylonitrile/poly(methylmethacrylate) transition to “Homogeneous” melt state
Authors: Lyngaae‐Jørgensen J. , Søndergaard K. 
Published: December 2004

AbstractAn advanced hypothesis derived in Part I (this issue) is tested with selected model blends. Blends of copolymers of styrene and acrylonitrile (SAN) and poly(methylmethacrylate), (PMMA) were studied because they are both amorphous, thermally stable, have large density differences, are easy to cut (in an ultramicrotome) and because comprehensive studies have been reported In the literature on this system. The melt viscosity of the blends were studied using a Rheometrics Mechanical Spectrometer and an Instron capillary rheometer. Light scattering measurements were performed during flow in order to measure the critical transition stress. The phase structure of quenched samples was studied by transmission electron microscopy on ultramicrotome cuts. It was shown that an Interpenetrating co‐continuous structure develops when flow is stopped, if a homogeneous phase Is formed during flow. Melt fracture limits the applicability of this approach to nearly compatible blends.
Linear low density polyethylenes and their blends: Part 2. Shear flow of LLDPE's
Authors: Utracki L. A. , Schlund B. 
Published: December 2004

AbstractThe steady state and dynamic shear behavior of eleven commercial linear low density polyethylenes (LLDPE) and one low density polyethylene (LDPE) resin were measured in capillary and parallel plate geometries at T = 150 to 230°C. The extrudate swell and the Bagley correction were determined. A large pressure effect on capillary flow of narrow molecular weight distribution LLDPE was observed and a new corrective procedure was proposed. After the correction the steady state viscosity was found to be equal to the dynamic (not complex) viscosity: η(\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}) = η'(ω = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}). A newly proposed four parameter relation between η and the deformation rate was found to provide a simple means for computation of the zero shear viscosity, ηo, and the primary relaxation time. Both these parameters showed a high degree of correlation. The expected relation: ηo ∝︁ Mw3.4 was observed for low molecular weight samples with low polydispersity. The LLDPE activation energy of flow, Eσ=29.9 ± 1.8 kJ/mole, was determined.
A study on poly(vinyl chloride) blends with chlorinated polyethylene and acrylic resin
Authors: Xi Xu , Liwu Zhang , Huilin Li 
Published: December 2004

AbstractThe compatibility, morphology, fusion behavior, and mechanical properties of blends of poly(vinyl chloride) (PVC), acrylic resin (ACR), and chlorinated polyethylene (CPE) (100/0–30/0–20) were studied. The experimental results show that the compatibility of the polyblend increases with the amount of ACR added. The blends composed of PVC/ACR/CPE (100/3–25/10–15) are fairly compatible. So far as impact strength is concerned, partially compatible blends are preferred.
Interrelationship between the crystallization behavior, injection molding conditions, and morphology of poly(ethylene terephthalate)/poly(methyl methacrylate) alloys
Authors: Nadkarni V. M. , Jog J. P. 
Published: December 2004

AbstractThe thermal and isothermal crystallization behavior of PET/PMMA (poly(ethylene terephthalate)/poly(methyl methacrylate)) alloys was investigated. The crystallization of PET is accelerated significantly by alloying with PMMA. As a result, crystalline specimens could be injection molded with the alloy at low mold temperatures of 19°, 55° and 90°C., whereas a mold temperature of about 130°C is normally required for crystallinity to develop in the virgin PET grade. The impact strength of the alloy specimens increased significantly with decreasing mold temperature despite a comparable degree of crystallinity. The increase in impact strength is correlated to the reduction in the crystallite size and broadening of the crystal size distribution with decreasing mold temperature.
Melt rheology of polyarylate/polybutylene terephthalate blends
Authors: Ausín A. , Eguiazabal I. , Munñoz M. E. , Peña J. J. , Santamaría A. 
Published: December 2004

AbstractThe viscosity, the activation energy of flow, and the exchange reactions of bisphenol A 50/50 isophthalic/terephthalic acid and poly(butylene terephthalate) blends are studied by means of an extrusion capillary rheometer, covering a range of 10 s−1 to 300 s−1 shear rate and 280°C to 300°C temperature. The results are interpreted in terms of compatibility and free volume additivity. The decrease in viscosity with time is explained as a result of transesterification rather than degradation.
Spectroscopic study of poly(ethylene terephthalate)/poly(amide‐6,6) blends
Authors: Pillon L. Z. , Utracki L. A. , Pillon D. W. 
Published: December 2004

AbstractFourier transform infrared (FT‐IR) studies of poly(ethylene terephthalate) (PET)/poly/(amide‐6,6) (PA) blends are presented. The blends were prepared in the molten state and in solution with trifluoroacetic acid (TFA) as the solvent. The PET/PA blend is a complex system containing, two crystallizable polymers with the ability to interact chemically. Some of the blends were prepared in the molten state in the presence of a catalytic amount of p‐toluenesulfonic acid (TsOH) to undergo the ester‐amide interchange reaction. Nuclear magnetic resonance (NMR) and FT‐IR have proven to be excellent techniques with which to study these blends. 1HNMR was used to follow the ester‐amide interchange reaction and FT‐IR to detect the presence of hydrogen bonding. FT‐IR studies showed the lack of hydrogen bonding in all the blends prepared in the molten state and its presence in the blends prepared in solution.
Dynamic mechanical behavior of continuous multilayer composites
Authors: Gregory Bryan , Hiltner Anne , Baer Eric , Im J. 
Published: December 2004

AbstractThe dispersion processes in multilayer laminate composites of styrene acrylonitrile (SAN) and polycarbonate (PC) were studied utilizing the torsion pendulum. A third damping peak with a log decrement intensity of approximately one was observed at a temperature intermediate to the damping peaks corresponding to the Tg's of the two constituent phases. Variations of numerous material and experimental parameters such as composition ratio, orientation, thermal history, thermal cycling, number of layers, and layer thickness, as well as overall changes in the composition of the phases had no effect on the observance of a third peak. Only the disruption of the continuous layer structure effectively eliminated this novel transition. The origin of this transition was explained by assuming appropriate temperature dependencies for the controlling viscoelastic parameters in such a continuous layer composite.
Minimum end time policies for batchwise radical chain polymerization. Part VI: The initiator addition policies for copolymerization with constant copolymer composition control
Authors: Chen Show‐An , Lee Song‐Tai 
Published: December 2004

AbstractFor batchwise radical chain solution copolymerization, the minimum end time problem with constant copolymer composition control is studied by considering the initiator concentration (or feed rate) and temperature as two control variables. During copolymerization, the more rapidly depleting monomer is continuously fed to the reactor to maintain the comonomer ratio constant. The volume variation due to contraction during copolymerization, in addition to monomer and solvent feeding, is also considered. It is found that the optimal initiator addition policy is to make the rate of initiation (2fkdIV) constant. The volume factor V is for taking account of volume variation. For the isothermal case, the number of moles of initiator in the reactor should remain constant. Experimental verification for acrylonitrile and styrene isothermal copolymerization with the proposed stepwise feeding of the more rapidly depleting monomer to simulate the optimal continuous monomer feeding policy shows that the present method is applicable.
Material selection considerations for gas separation processes
Authors: Koros W. J. , Story B. J. , Jordan S. M. , O'Brien K. , Husk G. R. 
Published: December 2004

AbstractAdvantages and disadvantages associated with common membrane types used in gas separation operations are reviewed. Comparisons between dense‐walled and several different types of asymmetric structures are made. In addition to overall membrane structure, the molecular natures of different membrane material types are treated. Tradeoffs between the use of rubbery and glassy polymers are considered first, followed by a treatment of the optimization of glassy membrane permeability and permselectivity properties. Material optimization principles are defined in terms of the basic thermodynamic solution and kinetic transport properties of polymers, and applications of these principles are illustrated for a modified poly(phenylene oxide) and a homologous series of polyimides derived from pyromellitic dianhydride.
The glass transition of compatible blends
Authors: Couchman P. R. 
Published: December 2004

AbstractIn a thermodynamic model of the glass transition, general but circular relations for the compositional variation of the glass‐transition temperature, Tg, can be derived from the entropy, the volume, and the enthalpy. The circumstances necessary for each of these to reduce to predictive relations are stated. Of these relations, that derived from the entropy should be the most general because of the expected rather wide applicability of the random mixing assumption, with which it is associated. The entropic theory is used to account for several aspects of the compositional variation of Tg, including problems not of solutions per se.
Properties and morphology of some injection‐molded polycarbonate‐styrene acrylonitrile copolymer blends
Authors: Skochdopole R. E. , Finch C. R. , Marshall J. 
Published: December 2004

AbstractA series of blends was prepared with broad concentration ranges of polycarbonate (PC) and styrene‐acrylonitrile copolymers (SAN) containing 5.5 and 30 weight percent acrylonitrile (AN). These blends were then injection molded, and their properties were measured and correlated with the morphologies of the blends (as determined by transmission electron microscopy). The toughness properties were shown to be discontinuous and very sensitive to composition of the continuous phase in the blends. The dart impact toughness remained high up to 30–40 weight percent SAN and dropped rapidly above this SAN concentration. The notched Izod toughness fell off rapidly at 10 weight percent SAN and greater. The strength and modulus had a more linear dependence on composition. Results of studies of the Tg by differential scanning calorimetry (DSC) show the presence of two phases over the entire concentration and a small solubility of each phase in the other. The heat distortion temperature under load (DTUL) of the blends approximated a linear additivity curve for the components. As expected, the blends had much better clarity where the refractive indexes more nearly match (in the case of the 5.5 percent AN copolymer).
Polymer sorbents for phosphorus esters: I. Selection of polymers by analog calorimetry
Authors: Chang Y. , Noriyan J. , Lloyd D. R. , Barlow J. W. 
Published: December 2004

AbstractHeats of mixing of a variety of solvents with dimethyl methyl phosphonate, DMMP, are presented. A qualitative correlation between the exothermicity of the heat of mixing of DMMP with a particular solvent and sorption of DMMP by polymers containing structural units analogous to the solvent is observed. By this approach, polymers containing acidic hydroxyl functionality, such as phenol‐formaldehyde condensation products and poly(styrene‐co‐vinyl benzyl hexafluorodimethyl carbinol), were identified as good sorbents for DMMP. Sorption isotherms, measured for these materials by the piezoelectric method, show enhanced sorption at low vapor activity and 135°C compared to polystyrene and poly(vinyl chloride) which lack these acidic sites and whose solvent analogs mix more endothermically with DMMP.