bluuebunny/crossref_metadata_2025 huggingface dataset:
Three‐dimensional nonisothermal mold filling simulations in resin transfer molding
Authors: Young Wen‐Bin
Published: May 2005

The manufacture of polymer composites through the process of resin transfer molding (RTM) involves the impregnation of the reactive polymer resing into a mold with preplaced fibrous reinforcements. Determination of RTM processing conditions requires the understanding of various parameters, such as material properties, mold geometry, and mold filling conditions. Modeling of the entire RTM process provides a tool for analyzing the relationship of the important parameters. This study developed a nonisothermal 3‐D computer simulation model for the mold filling process of RTM based on the control volume finite element method. The model will be able to simulate mold filing in molds with complicated 3‐D geometry. Results of some numerical studies in RTM show the applications of the proposed model.
Probing morphology and toughening mechanisms of high performance composities using transmission electron microscopy
Authors: Garcia‐Meitin E. I. , Sue H.‐J.
Published: May 2005

The usefulness of the transmission electron microscopy (TEM) technique in probing the morphology and toughening mechanisms of high performance composite systems is demonstrated. TEM provides an effective study of both the morphology and fracture behavior of graphite fiber reinforced epoxy and for cyanate composite systems. The failure process in these composites can be under stood. The TEM technique introduced here is found to be valuable for both fundamental and developmental research in improving both physical and mechanical properties of high performance composites. The present work focuses on demonstrating how a composite can be successfully prepared for TEM investigations. Experimental procedures concerning identification and isolation of the crack tip damage zoen, followed by cutting, trimming, staining, and thin section of the composite sample are detailed.
Fracture and acoustic emission characteristics of glass fiber reinforced plastics panels for hot water
Authors: Morii Tohru , Tanimoto Toshio , Hamada Hiroyuki , Maekawa Zen‐Ichiro , Hirano Takahiro , Kiyosumi Kenji
Published: May 2005

This study deals with the fracture process and acoustic emission (AE) characteristics of a randomly oriented E‐glass fiber mat reinforcement with a crosslinked polyester. These panels were evaluated after they were immersed in hot water. The fiber volume content of the panel was 19%. Glass fiber reinforced plastics (GFRP) panels wer immersed in water at 81°C. Bending and AE monitoring tests were Performed and after bending, the cross‐section of the specimen was observed by an optical microscope and SEM. The influence of degradation, due to water immersion, on the changes of fracture process of GFRP is discussed. The dominant fracture mode of the virgin specimen was matrix cracks, whereas that of the immersed specimen was debondings at the fiber bundle/matrix and fiber/matrix interfaces. This change was caused by reduction of the bonding strength at the interface. The scale of fracture can be estimated by both AE amplitude and AE energy and this estimation method was used to estimate the fracture mode changes of GFRP panels immersed in hot water.
Estimation of the resin flow permeability of fiber tow preforms using the self‐consistent method
Authors: Cai Zhong , Berdichevsky Alexander L.
Published: May 2005

This paper presents a model using the self‐consistent method for estimating the resin flow permeability of fiber tow preforms. The permeable resin is assumed to be a Newtonian fluid, such as an uncured and low viscosity epoxy resin. Permeability in both longitudinal and transverse directions is considered. In the discussion, a basic cell insertion is constructed to include a representative fiber tow surrounded with fluid. The insertion is placed into a homogeneous medium with an unknown permeability. Stokes flow is applied to the fluid region, and Darcy flow is considered at the tow region and in the outside homogeneous medium. Boundary and interface conditions as well as consistent conditions, including the total amount of the flow and the dissipation energy, are applied accordingly. Permeability is solved from these considerations. The prediction expresions using parameters of average fiber volume fraction, tow volume fraction, and tow size are derived. The results show that the main flow paths are the openings or gaps between neighboring tows in both longitudinal and transverse directions. The observation provides a scientific base for the simplification of the problem treatment.
Applications of a fiber orientation prediction algorithm for compression molded parts with multiple charges
Authors: Reifschneider L. G. , Akay H. U.
Published: May 2005

An application of a finite element simulation of mold filling and predication of fiber orientation in fiber filled compression molded parts is presented. Three‐dimensional thin‐walled geometries are considered. Following a simulation of the filling process, a set of transort equations are solved to predict the locally planar orientation of short fiber composites. The final orientation states throughout the part provide the necessary information to obtain a locally orthotropic mechanical model of the composite. A sheet molding compound part with a multiple charge pattern is used to illustrate the generality of the algorithms developed for compression flow, fiber orientation, and property predications. Derivations of the orthotropic mechanical properties obtained from the fiber orientation results are outlined.
Interpretation of 3‐D permeability measurements for RTM modeling
Authors: Woerdeman Dara L. , Phelan Frederick R. , Parnas Richard S.
Published: May 2005

The resin transfer molding (RTM) technique often utilizes reinforcement with a complex fiber architecture. Several parameters, including the permeability tensor, are necessary to characterize the flow behavior in these intricate fibrous porous media. In this paper, a general procedure for extracting three‐dimensional permeability tensors from data is presented. A general procedure is warranted if the permeability tensor lies out of the material plane. An approximate solution to Darcy's law was employed to relate the components of the permeability tensor to experimental measurements. The procedure requires inverting six nonlinear equations with a robust binary search algorithm. The accuracy of the approximate solution to Darcy's law was checked and found to be in close agreement with a nearly exact solution to Darcy's law obtained by finite element methods.
Investigation of the microcracking behavior of bismaleimide composites during thermal aging
Authors: Burcham Loyd J. , Eduljee Rushad F. , Gillespie John W.
Published: May 2005

Samples of 16‐ply, quasi‐isotropic bismaleimide composites were aged in convection ovens at 150°C, 177°C, and 204°C for up to 16,000 hours. As a measure of degradation, transverse microcrack density was characterized as a function of time, temperature, and ply depth. Times required to reach onset and saturation crack density were delayed on the tool side of the laminate, for lower temperatures, and for deeper ply depths. Saturation crack densities ranged from 35 cracks/cm to 46 cracks/cm, depending on ply depth. Master curves were constructed for each ply level to express all time‐temperature data for that ply as a single reference curve. A mass transfer analysis further suggests that diffusion is the controlling mechanism in the degradation process. Finally, a prediction of the degradation behavior in the 120,000‐h lifetime of the HSCT aircraft for a sustained temperature of 150°C indicates that ∼13 plies will have reached initiation in a quasi‐isotropic laminate.
Environmental effect on stress relaxation in polyester‐fiberglass composite
Authors: Gutman E. M. , Soncino R.
Published: May 2005

Environmental behavior of reinforced polyester was studied by stress relaxation. Relaxation failure of polyester matrix and fiberglass degradation appear dramatically at short time after exposure to acid and alkali electrolytes. The relaxation spectrum is thus influenced by environmental action. Indeed, the stress relaxation modulus is a sensitive characterization of environmental effects.
Determination of the packing density of solid polymer chains. Determination of the specific surface area of polymers by sorption of nitrogen vapor
Authors: Tsilipotkina M. V. , Tager A. A. , Petrov B. S. , Pustobaeva G.
Published: May 2005

The sorption of nitrogen vapors on polyethylene, polytetrafluoroethylene, saran, polyvinylalcohol, polyvinylacetate, polystyrene, cellulose and ethylcellulose at the nitrogen boiling point has been investigated. It has been shown that polyethylene, polytetrafluoroethylene, saran, polyvinylalcohol and polyvinylacetate are non‐porous sorbents with dense packing of the macromolecules. It has been shown that the specific surface area of cellulose, ethylcellulose and the total pore volume of polystyrene calculated from nitrogen vapor sorption is less than the corresponding value determined from the sorption of organic substances. Nitrogen vapor sorption at the nitrogen boiling point cannot be used for estimating the porosity of loosely packed polymers.
Some observations on the morphology and fracture characteristics of knit lines
Authors: Hobbs S. Y.
Published: May 2005

The morphology of isotactic polypropylene in molded plaques containing a knit line is described in detail. The effects of mold temperature and flow on the size and orientation of spherulitic and transcrystalline regions are discussed. Deformation at the weld line under uniaxial tensile stress is analyzed by optical microscopy.
The mechanical properties of oriented discontinuous fiber‐reinforced thermoplastics. I. Unidirectional fiber orientation
Authors: Blumentritt Bruce F. , Vu Ban T. , Cooper Stuart L.
Published: May 2005

The mechanical properties of a series of thermoplastics reinforced with unidirectionally oriented short fibers are reported. Both organic and inorganic fiber reinforcements were used in fiber volume fractions of 0.10 to 0.50. A number of these composites were found to have excellent strength and stiffness properties combined with good toughness and low density. The dependence of composite properties on the properties of the constituent materials is discussed. Fiber efficiency factors for strength and modulus are presented and models for predicting composite mechanical behavior are reviewed.
Glass transitions of topologically interpenetrating polymer networks
Authors: Frisch H. L. , Frisch K. C. , Klempner D.
Published: May 2005

Two component topologically‐interpenetrating polymer networks were made of the SIN type (simultaneous interpenetrating network) composed of two polyurethanes (a polyether‐based and a polyester‐based) in combination with an epoxy resin, a polyacrylate and two unsaturated polyesters. The linear polymers and/or prepolymers were combined in solution and in bulk together with the necessary crosslinking agents and catalysts. Films were cast and chains extended and crosslinked in situ. All of the IPN's exhibited one glass transition (Tg) intermediate in temperature to the Tg's of the component networks, and as sharp as the Tg's of the components. This suggests that phase separation may not occur and thus some chain entanglement (interpenetration) of the two networks is involved. The observed Tg's are always several degrees lower than the arithmetic means of the component Tg's. A theory based on interpenetration is developed to account for this.
End corrections in the capillary flow of polystyrene melts
Authors: Hyun Kun Sup
Published: May 2005

The origin of the discrepancy between the Bagley method and the modified method suggested by Han in obtaining the end correction data is traced to the effect of a deviatoric stress contribution in the pressure measurement at the capillary wall. The end correction factors for polystyrene melt were obtained by the Bagley method. The effects of temperature, die entry angle, contraction ratio or reservoir diameter‐to‐die diameter ratio are discussed.
Effect of molecular weight on rate of enthalpy relaxation of poly (methyl methacrylate) and its oligomers
Authors: Yoshida Hirohisa , Kobayashi Yasuji
Published: May 2005

The enthalpy relaxation process of methyl methacrylate oligomers and poly (methyl methacrylate) was analyzed by use of the excess enthalpy (ΔHt), which was obtained from a differential scanning calorimetric measurement. The apparent relaxation time (τ½) was estimated by the assumption of the single relaxation time response. The Tg of oligomers increased with an increase of molecular weight, and approached a constant value above 1 × 104. The apparent relaxation time showed a similar molecular‐weight dependency as Tg, and approached a constant value above 1 × 104. It was expected that the molecular motion which caused the enthalpy relaxation was based on the segmental motion of main chains.
A breakthrough to the plasma deposited dry‐developable e‐beam resist
Authors: Hattori Shuzo , Morita Shinzo , Yamada Masao , Tamano Junji , Ieda Masayuki
Published: May 2005

This paper presents the preliminary results of efforts to improve dry processed electron beam resist materials using plasma polymerization coating technology. Three approaches investigated were chemical susceptibility modification, the use of multilayer resist structures, and the effect of grafting reactions.
The role of molecular networks and thermally activated processes in the deformation behavior of polymers
Authors: Ward I. M.
Published: May 2005

The deformation behavior of three polymers, polyethylene terephthalate (PET), polymethylmethacrylate (PMMA), and linear polyethylene (LPE) is considered in terms of two key factors, the stretching of a molecular network and the influence of thermally activated processes. In PET the observation of a natural draw ratio leads to studies of shrinkage, shrinkage force, and optical birefringence to define the nature of the network. The network is further exemplified by measurements of the molecular reorientation in deformation bands, spectroscopic studies of molecular orientation in drawing, and the concept of a true stress‐strain curve. Yield and plastic deformation are also to be considered as thermally activated processes, but it appears that a major part of the flow stress is associated with the stretching of the molecular network. In PMMA the concept of a true stress strain curve also appears to be valuable, but the possibility of network breakdown during deformation has to be admitted as an extra complexity. In LPE the concept of a molecular network embracing both crystalline and non‐crystalline material is helpful in understanding the drawing behavior. There is also direct evidence for the existence of a network from measurements of shrinkage and shrinkage force, and the existence of a true‐stress strain curve. However, the dominant contribution to the flow stress now appears to come from thermally activated processes, with a key contribution from a small activation volume process which is tentatively associated with slip in the crystalline regions.
Behavior and properties of shear bands
Authors: Li J. C. M.
Published: May 2005

Some recent observations on shear bands in polymers are reviewed. These include intrinsic properties such as the mechanism of formation, the intersection of shear bands, the rate of propagation with and without obstacles, recovery of shear strain by annealing, and the stored energy in shear bands. Mechanical responses include the shear yielding criteria, reverse shear behavior and the Bauschinger effect, and the fracture of and at shear bands. Environmental effects include methanol transport in shear bands and in deformed poly(methvl methacrylate) in the region of mixed Fickian and case II behavior and methanol crazing of a shear banded material.
Deformation modes and fatigue behavior in styrene‐acrylonitrile and acrylonitrile‐butadiene‐styrene copolymers
Authors: Sauer J. A. , Chen C. C.
Published: May 2005

The performance of styrene‐acrylonitrile copolymers under alternating stresses has been examined. Information has been obtained concerning the influence of acrylonitrile content and of molecular weight on thermal effects due to hysteresis, on cyclic lifetime to craze initiation, on average cycles to fracture, and on fatigue fracture surface morphology. The influence of an elastomeric second phase has been determined by comparing fatigue performance under comparable conditions of both styrene‐acrylonitrile (SAN) and acrylonitrile‐butadiene‐styrene (ABS). The stress concentrating effects of the rubber particles cause earlier initiation of fatigue‐induced damage and lower fatigue fracture resistance. The fatigue‐induced specimen temperature rise is greater in ABS than SAN and it increases linearly with test frequency and as the square of the stress amplitude. The fracture surface morphology of ABS, which differs from that of unmodified SAN and also from that of rubber modified polystyrene, is discussed.
Thermal conductivity and thermal expansion behavior of glass fiber‐reinforced rigid polyurethane foam
Authors: Morimoto Kiyotake , Suzuki Toshio , Yosomiya Ryutoku
Published: May 2005

The thermal conductivities and the thermal expansion curves of glass fiber‐reinforced rigid polyurethane foams with various fiber lengths, various fiber volume fractions and various matrix densities were determined experimentally. Additionally the thermal expansion coefficients of these materials at room temperature were examined in terms of the interaction between fiber and matrix. The thermal expansion properties were analyzed successfully with the analogous treatment which is applied to the mechanical tensile behavior.
Evaluation of paper properties of thermomechanical pulp modified by ozonation and grafting with thermoplastic polymers
Authors: Kokta Bohuslav V. , Araneda Lisandro , Daneault Claude
Published: May 2005

Paper properties of the thermochemical pulp modified by ozonation and grafting with styrene, acrylamide or their mixtures have been studied. Paper sheets, prepared by hot pressing from ozonated and grafted pulps showed improvement in: wet breaking length; dry breaking length; burst and dimensional stability.
An investigation of optical clarity and crystalline orientation in polyethylene tubular film
Authors: Ashizawa Hiroshi , Spruiell Joseph E. , White James L.
Published: May 2005

A study of the crystalline orientation, light transmission, and surface roughness of polyethylene tubular film prepared in our laboratories is presented. The present studies were primarily carried out on low‐density (LDPE) and linear‐low‐density (LLDPE) polyethylene films. The optical properties of a few films of high‐density polyethylene (HDPE) prepared for a previous study of morphology were characterized for comparison to the LDPE and LLDPE films. Wide angle X‐ray diffraction and birefringence were used to characterize orientation. Both the LDPE and LLDPE films exhibited crystalline texture in which the b‐axes tended to be perpendicular to the film surface and the a‐axes had some tendency to align with the machine direction. The c‐axes tended to be concentrated in the plane of the film with nearly equal biaxial orientation with respect to the machine and transverse directions. Little variation in the crystalline orientation was found with changes of process conditions in the range studied. Birefringence results indicate that the amorphous regions developed an orientation in which the chains tend to be normal to the film surface. The majority of light scattering from these films and a series of HDPE films was from the surface and not from the film interior. The transmission coefficient for the surface contribution was found to be a monotonic decreasing function of the standard deviation of the surface height obtained from surface profiles measured by profilometer. The surface asperites were largest for the HDPE and smallest for the LDPE samples. The intensity of both the surface and interior contributions to the scattering increased with increasing frostline height, i.e., a slower cooling rate. As draw‐down ratio and blow‐up ratio increase the scattering contribution from the film interior decreases but the contribution from the surface increases somewhat. These effects are discussed in terms of the changes in crystalline morphology and surface roughness produced by flow defects generated during extrusion.
A Wide‐angle X‐ray diffraction method of determining chopped fiber orientation in composites with application to extrusion through dies
Authors: Menendez Hernan , White James L.
Published: May 2005

A method of determining fiber orientation in composites using wide‐angle X‐ray diffraction (WAXS) is described. Oriented crystalline fibers are suspended in an amorphous polymer matrix. The WAXS reflects characteristics of the fiber are used to determine the mean orientation and orientation distribution of the crystallographic axes representing the polymer chain relative to preferred axes located in the test specimen. The chain direction crystallographic axis is taken as representing the fiber axis, and the orientation of this axis to represent the orientation of the fibers. Experimental studies were carried out using Kevlar (poly(p‐phenylene terephthalamide)) fibers suspended at a 20 volume percent loading in a polymethyl methacrylate matrix. The Kevlar fibers had Hermans orientation factors of 0.92. Specific attention is given to how through circular dies. We have examined both extrudates and the material frozen‐in when the composite in the reservoir and die is cooled to room temperature. Fiber orientation factors, corresponding to Hermans orientation factors, 0.3 to 0.38 were obtained for the extrudates. Orientation factors for fibers within the die is about 0.45. Specially prepared completely oriented samples had orientation factors of 0.93, which closely corresponds to the orientation of the fiber.
Environmental testing of a glass‐fiber‐reinforced thermoplastic
Authors: Lhymn C. , Schultz J. M.
Published: May 2005

Stress‐corrosion data for poly(ethylene terephthalate) reinforced with short glass fibers are provided under various environments and the microscopic observations are compared with the lifetime data. It is concluded that the lifetime behavior coincides with the microstructural features; this aspect is quantified by the statistical analysis.
Molecular dynamics of physical aging in the glassy state
Authors: Simha Robert , Curro John G. , Robertson Richard E.
Published: May 2005

We review first recent results concerning the relation between the relaxation of extensive thermodynamic and of viscoelastic functions. In the underlying theory a central role is assigned to a particular excess‐free volume function h. It was originally introduced in a theory of the equilibrium melt. The time dependence of h can then be derived from volume (or enthalpy) recovery data and serves to predict other quantities, such as mean‐square density fluctuations and viscoelastic‐temperature shift factors during the aging process. Next the physical basis and results of two kinetic theories of volume relaxation are summarized. In both approaches the h‐function is employed as an expression of the molecular dynamics in the drive to equilibrium. The first describes a gradual elimination of free‐volume gradients through a diffusion process, characterized by a diffusion parameter, varying with the local free volume in accord with a Doolittle relation. The second, a stochastic theory, derives expressions for the matrix of transition rates between different free‐volume states, the resulting spectrum of retardation times, and the size distribution of free volume in the relaxing system. Satisfactory agreement between observed and predicted volume recovery of poly(vinyl acetate) ensues. In the limit of an infinitesimal temperature jump, both theories yield a Williams‐Watts correlation function as an approximate interpolation expression. The exponent β, however, varies in time with a constant value of approximately 0.60 over a limited time interval.
A simple test method for the response of materials to large bending deformations
Authors: Charrier J.‐M. , Gent A. N.
Published: May 2005

A simple test device is described for subjecting bars to large bending deformations and simultaneously monitoring the bending moment. Examples are given of the elastic bending of a bar of a natural rubber vulcanizate and of the maximum bending moment that molded bars of polyethylene and polypropylene can withstand before the fully‐plastic state is attained.
Evidence of dual mobility in sulfur dioxide‐polyarylate system: An integral sorption analysis
Authors: Ranade G. R. , Chandler R. , Plank C. A. , Laukhuf W. L. S.
Published: May 2005

Integral sorption/desorption measurements were carried out for the sulfur dioxide‐glassy polyarylate polymer system at 25°C, 40°C, 55°C, and 63°C. The transport of sulfur dioxide in the glassy polyarylate polymer was governed by Fickian diffusion. The effective diffusion coefficient of sulfur dioxide increased with increasing penetrant concentration. The concentration dependence of the effective diffusion coefficient is explained on the basis of the partial‐immobilization model developed by Paul and Koros. The mobility of the molecules sorbed in the Langmuir mode is shown to be significantly lower than the mobility of the molecules in Henry's law dissolution mode. The predictions of permeability values as a function of upstream gas pressure are presented. The equilibrium sorption isotherms for this system are well represented by the dualmode sorption model. The eltergetics and the temperature dependence of the dual‐mode parameters are also discussed.
Synthesis and properties of copoly(carbonate imides)
Authors: Maudgal Shubha , Pratt J. R. , Wakelyn N. T. , St. Clair T. L.
Published: May 2005

Copoly(carbonate imides) with varying amounts of carbonate in the backbone were prepared by reacting 4,4′‐diaminodiphenyl carbonate and 4,4′‐diaminodiphenyl ether with benzophenonetetracarboxylic acid dianhydride in dimethylacetamide at room temperature. Homopolymers of the two diamines as well as of 3,4′‐ and 3,3′‐diaminodiphenyl carbonate were prepared in a similar procedure and their properties compared with those of the copolymers.
γ‐Radiation effects on chemical degradation of polycaprolactone
Authors: Sibony‐Chaouat S. , Narkis M. , Siegmann A. , Shkolnik S.
Published: May 2005

Polycaprolactone samples were vacuum irradiated and subsequently immersed in aqueous methylamine solution, pH 10, and saline water solutions, Weight loss, solution viscosity, thermal analysis, tensile properties, and scanning electron microscopy were used to study the effects of immersion time and radiation. Irradiation accelerates all studied degradative and damaging processes taking place during exposure to the various environments. Degradation mechanisms in unirradiated and irradiated materials are discussed.
Water in epoxy resins Part II. Diffusion mechanism
Authors: Wong T. C. , Broutman L. J.
Published: May 2005

A model is proposed for the diffusion mechanism of water in glassy epoxy resins. The polymer network is assumed to consist of two regions in which water molecules possess different mobilities. By considering the distribution of water molecules among these regions it is possible to describe the concentration dependency of the diffusion coefficient in the sorption and resorption processes. The diffusion coefficient becomes constant when the sorption temperature is close to the effective glass transition temperature of the epoxy‐water binary mixture. An explanation of this effect is also provided by the model.
Fatigue behavior of acetal homopolymer
Authors: Connolly R. , Gauvin R. , Chalifoux J. P.
Published: May 2005

As an engineering thermoplastic acetal homopolymer is often used in the manufacture of parts subjected to fatigue. This article presents the results of flexural fatigue tests on acetal Delrin 550 under different environmental conditions, namely ambient air, forced‐air ventilation at ambient temperature, or oil kept at a constant temperature at 40°C. The fatigue tests were performed on specimens cut from extruded sheets at a constant frequency of 30 Hz. Surface temperatures of the test specimens were measured either optically or electrically, depending on the environment. The test results show that both acetal stress and surface temperature of specimen, which are somehow related, vary considerably from one type of environment to another. However, results show that the fatigue life of the specimen is mainly governed by the amplitude of the initial stress and is almost independent of the environment, Another subject examined was the effect of oil on acetal's mechanical properties. It was found that prolonged contact with oil produced slight variations in tensile properties, but no significant effect on fatigue, life.
Compatibilization of thermosetting‐thermoplastic polymer blends
Authors: Jayabalan M. , Balakrishnan T.
Published: May 2005

Polymer blends of thermosetting and thermoplastic polymers were developed by properly mixing them in the presence of compatibilizers. Two compatibilizers that are structurally and chemically similar to thermosetting and thermoplastic polymers and a compatibilizer that does not have such similarity were synthesized. Polymer blends of phenol formaldehydepoly(methyl methacrylate) and phenol formaldehyde‐polystyrene were prepared by using the compatibilizers, poly(phenol formal dehyde‐s‐triazine‐methyl methacrylate), P(PF‐g‐MMA), poly(phenol formaldehyde‐s‐triazine‐styrene), P(PF‐g‐S), and poly (cinnamaldehyde‐co‐oxy propylene oxy isophthaloyl‐cooxy propylene oxy fumaroyl), P(C‐g‐E). The effects of molecular weight and quantity of the copolymer on the compatibility of the polymer were examined. The optimum compatibility which leads to superior tensile properties of the present blends was observed with P(PF‐g‐MMA) and P(PF‐g‐S) copolymers. The superior properties were also found to occur only in the range of the optimum molecular weight and quantity of the copolymer present in the blend. The polymer blends were analyzed by differential scanning calorimetry (DSC) and Electron Microscopy. DSC scans of P(PF‐g‐MMA) and P(PF‐g‐S) copolymer blends showed a single Tg whereas the scans of P(Cg‐E) copolymer blends showed an additional Tg for unblended thermoplastic fractions. The electron microscopy studies also revealed good compatibility in P(PF‐g‐MMA) and P(PF‐g‐S) copolymer blends in which the unblended thermoplastic fractions are negligibly less. The UV‐vacuum and heat resistance of the P(PF‐g‐MMA) and P(PF‐g‐S) copolymer blends were found to be good.
Calculated stresses in dual coated optical fibers
Authors: Suhir E.
Published: May 2005

We examine several practically important problems, related to the mechanical behavior of dual coated optical fibers: low temperature microbending, evaluation of spring constant due to coating layers, strength of the end portions of fibers clamped in terminal fixtures, and prediction of stresses caused by the misalignment of the openings in the frame and in the terminal fixture. The developed formulas are simple, easy‐to‐use, and clearly indicate the role of the major factors affecting the mechanical behavior of the fibers. The obtained results can be of help in physical design of dual coated fibers and optical interconnections.
Experimental modeling of solvent‐casting thin polymer films
Authors: Powers G. W. , Collier J. R.
Published: May 2005

An apparatus was designed and assembled to study the solvent removal from solution‐cast thin polymer films. The computer interfacing of a thermogravimetric analyzer, spectrophotometer, electronic flowmeters, and control valves for the apparatus enabled the preprogramming of the carrier gas velocity, carrier gas solvent content, and temperature profiles to simulate the environment experienced in large parallel flow industrial driers. The apparatus has also been designed and operated to enable the visual observation of the drying film with an optical microscope. Initial experimental studies conducted with the apparatus involved the effect of temperature on solvent removal. The results indicate that high dryer gas temperatures can apparently cause skinning of the film surface resulting in slower solvent removal rates. The skin formation can be suppressed by higher solvent concentration in the carrier gas. The visual observations revealed the formation of standing waves in the film surface during drying at high gas velocities (>2OO cm/min). The wave formation at least partially overcomes the effect of skinning by increasing the surface area of the film, and may be the manifestation of flow instabilities involving circulation within the film.
Liquid crystal polymer‐carbon fiber composites. Molecular orientation
Authors: Bhama Satya , Stupp Samuel I.
Published: May 2005

The objective of this work has been to study composite systems in which carbon fibers are dispersed in a liquid crystal polymer matrix. The fundamental point of interest here has been the interfacial response that fiber surfaces can potentially induce in self‐ordering polymers. The matrix material used was a thermotropic liquid crystal polyester synthesized in our laboratory from the monomers p‐acetoxybenzoic acid, diacetoxyhydroquinone, and pimelic acid. The aromatic‐aliphatic polymer was characterized by NMR as a chemically disordered polymer of the three structural units which exhibits a nematic phase at temperatures above 150°C. Breadline proton NMR above the solid to liquid crystal transition was used to measure the rate of magnetic alignment of molecules in the matrix and polarized optical microscopy was used to analyze interfacial zones in composite samples. Fiber surfaces were found to influence the orientation and orientational dynamics of a liquid crystal polymer matrix. This was revealed by enhanced rates of magnetic orientation in the polymer melt when carbon fibers are dispersed in the medium. Fiber surfaces were also found to stabilize nematic ordering of the polymer as the melt was heated towards complete isotropization. The phenomena discovered here may originate in the development of zones around fibers with a common molecular orientation anchored by the carbon surface.
Dynamic behavior of continuous vinyl chloride bulk and suspension polymerization reactors. A simple model analysis
Authors: Pinto J. C.
Published: May 2005

Based on previous works, a simple model is built to simulate the vinyl chloride monomer (VCM) polymerization in continuous suspension and bulk reactors. The branches of steady‐state solutions are computed and their dynamic behavior is analyzed. It is observed that these systems present multiple steady‐state solutions for some ranges of parameter values and that non‐adiabatic reactors can also present ISOLAs. These reactors can also experience self‐sustained oscillations in a very wide region of operation conditions.
Multiloop control of a polymerization reactor
Authors: Prasad P. R. , Deshpande P. B. , Kwalik K. M. , Schork F. J. , Leffew K. W.
Published: May 2005

Chawla, et al. (2) recently described a new SISO control algorithm called the Conservative Model Based Control (CMBC). In this paper, we assess the feasibility of implementing CMBC as a multiloop controller on a simulated reactor used for the polymerization of methyl methacrylate. Both servo and regulatory behavior of the controller are studied. Despite the non‐linearities and coupling between the two controlled variables, the easy‐to‐implement CMBC algorithm has been shown to give good control performance.
Calorimetric and microwave dielectric monitoring of epoxy resin cure
Authors: Carrozzino Simona , Levita Giovanni , Rolla Pierangelo , Tombari Elpidio
Published: May 2005

The cure process of a BADGE (diglycidyl ether of bisphenol‐A) resin (Epon 828) and ethylenediamine has been investigated by means of calorimetry and dielectrometry in the microwave region (107–1010 Hz) in the temperature range 50 to 70°C. Kinetic data from calorimetry were analyzed in detail. An overall kinetic order of 2.5 has been obtained. The time domain reflectometry (TDR) has been used to characterize pure components and their mixtures. Cure monitoring was carried out with both TDR and a cavity method at fixed frequency (9.5 × 109 Hz). A very good agreement was obtained between the reaction rate as measured by calorimetry and the rate of decrease of dielectric constants up to very high conversion. This was explained by admitting that the rates of disappearance of dielectric dipoles and of reactive species coincided.
AC and DC dielectric properties of some polypropylene/calcium carbonate composites
Authors: Bánhegyi György , Karasz Frank E. , Petrović Zoran
Published: May 2005

AC dielectric properties and thermally stimulated polarization (TSP) and depolarization (TSD) currents were studied in a series of CaCO3‐filled polypropylene composites. The filler content (0 to 50 weight percent) and the average particle size (3.0 to 16.1 μm) at constant filler content (30 weight percent) were varied in separate groups of samples. In a third group of samples the filler (20 to 40 weight percent) was surface treated with stearates. The AC dielectric behavior of composites containing untreated fillers is largely determined by a small amount of adsorbed water. Upon heating, the dielectric properties show maxima (increasing with decreasing frequency) which disappear on cooling. In the case of stearate‐treated fillers the dielectric loss level is higher, the dispersion and loss curves on heating reflect a combination of dipolar and protonic processes with water desorption. In the dry state the onset of an audio frequency relaxation process is observed in the pre‐melting zone. The thermally stimulated currents of the composites containing treated and untreated fillers are also different. In the case of the untreated fillers the TSP curves show maxima indicating water desorption which are increasingly intense and roughly exponential with filler content. The high temperature conductivity and the intensity of the pre‐melting depolarization peak pass through a minimum as a function of filler content. Above 20 weight percent filler content the activation energy of high temperature conductivity decreases. In the case of the surface treated samples, the thermally stimulated response is different for “wet” and dried samples. The dry samples exhibit a relaxation between the amorphous and crystalline transitions of the matrix polymer which is probably due to interfacial relaxation caused by the enhanced surface conductivity of the stearate‐treated fillers.
Component interactions and properties of crosslinked vinyl systems
Authors: Schreiber H. P. , Degrendele C. , Bataille P.
Published: May 2005

Compositions based on poly(vinylchloride) (PVC) containing diisodecyl phthalate (DIDP) or trioctyl trimellitate (TOTM) plasticizers and, in several cases, also containing chlorinated polyethylene (CPE) as property modifier were cross‐linked by γ irradiation, using a trifunctional acrylic cross‐linking agent. Cross‐linking effectiveness was analyzed by solvent swelling data, and the effects of irradiation up to dosages of about 10 Mrad on the mechanical properties of the systems were recorded. The interaction potential of components used in these systems was determined by recently developed methods of inverse gas chromatography (IGC). These classify PVC and CPE as electron acceptors and the plasticizers as donors. Expectedly, increased moduli and decreased elongational properties follow exposure to γ‐rays. The plasticizers reduce the effectiveness of cross‐linking, the magnitude of the reduction being related to the degree of acid‐base interaction between PVC and plasticizing fluids. Interference with cross‐linking mechanisms thus is a function of the solvent power of the plasticizers. CPE competes with PVC for plasticizer so that for given quantities of DIDP or TOTM, the fraction available to solubilize the host polymer is reduced. In compounds with CPE, therefore, the cross‐linking effectiveness of irradiation is raised, consistent with the acid‐base balance of Interactions, as given by the IGC results. Twin yield points have been observed in the stress‐strain curves of compounds containing CPE. It is postulated that distinct, interpenetrating cross‐link networks are formed when these polymers are subjected to γ irradiation.
Rheology of polycarbonate/linear low density polyethylene blends
Authors: Utracki L. A. , Sammut P.
Published: May 2005

The flow behavior of linear low density polyethylene blended with polycarbonate (LLDPE/PC) was studied at 245°C using an Instron Capillary Rheometer and a Rheometrics Mechanical Spectrometer. The capillary measurements were repeated several times for each crosshead speed and capillary. The averaged values were corrected for shear heating as well as the pressure, entrance‐exit, and power‐law fluid effects. In spite of the utmost care, blend results were erratic with a standard deviation of 25 to 35 percent. Analysis of the capillary data suggested a telescopic flow with the lower viscosity component of the blend migrating toward the capillary wall. The experimental difficulties resulted from the flow and time induced variations of blend morphology. By contrast, the dynamic shear test results were found to be rapid and reproducible with a standard deviation for the complex viscosity of blends not exceeding four percent. The shear moduli of blends indicated the presence of an apparent (time dependent) yield stress, originating from interaction between domains of the dispersed phase. At frequencies exceeding a critical value, shear coalescence of the dispersed phase was observed near the rim of the rheometer plates.
Dynamic mechanical properties of VAMAS polycarbonate/polyethylene blends
Authors: Wippler C.
Published: May 2005

As part of the Versailles Project on Advanced Materials and Standards Technical Working Party on Polymer Blends, the dynamic mechanical properties of polycarbonate/linear low density polyethylene (PC/LLDPE) blends were measured. Ten laboratories participated in the round robin tests. As a whole, the inter‐laboratory agreement of data is good, particularly when results are obtained using the same apparatus (especially a Rheovibrom DDV‐III EA). The results clearly show the nonmiscibility of the parent components. The influence of frequency is also obvious but difficult to characterize because of the narrowness of the frequency range explored. The Takayanagi model applies very well for the calculation of the storage moduli as a function of composition and morphology. The most specific result is probably that of the processing orientation effect: There is no visible influence of flow orientation on dynamic tensile moduli of the parent polymers, but there is a significant difference in the moduli measured in the direction of extrusion and in the transverse direction for the blends at temperatures above 0°C. The difference is greatest for the high PE‐concentration blend.
Criteria for selecting cure cycles in autoclave processing of graphite/epoxy composites
Authors: Williams R. J. J. , Benavente M. A. , Ruseckaite R. A. , Churio M. S. , Hack H. G.
Published: May 2005

Room temperature mechanical properties, such as flexural strength and impact resistance, of epoxies and graphite/epoxy composites go through a maximum as a function of epoxy conversion. For tetraglycidyl 4,4′‐diaminodiphenylmethane (TGDDM)‐4,4′‐diamlnodiphenylsulfone (DDS) formulations, the recommended cure cycle prescribes a maximum temperature close to 177°C. The maximum extent of reaction that may be obtained at this temperature is determined from the vitrification curve. At this maximum conversion, balanced mechanical and physical properties are attained in the partially cured specimen. However, if the standard cycle is used to cure thick parts, the maximum temperature inside the sample increases beyond 177°C. This leads to a complete conversion in most of the part and a consequent impairment of resulting physical and mechanical properties. It is shown how numerical solutions of differential energy and mass balances may be used to propose alternative cure cycles such that the maximum conversion at every point remains bounded by the vitrification curve. An illustration for a particular thickness is provided.
Flow‐drawing of poly(ethylene terephthalate)
Authors: Gupta V. B. , Sett S. K. , Venkataraman A.
Published: May 2005

The drawing characteristics of poly(ethylene terephthalate) (PET) yarns spun at 1000 and 3000 m/min and film cast at 10 m/min have been studied as functions of drawing temperature up to 200°C and drawing rate up to 50 min−1. The fiber spun at 1000 m/min and the film had very low degrees of pre‐orientation and flow‐drawing occurred 20 to 30°C above their respective glass transition temperatures, for which the drawing tension dropped to almost zero and the resulting drawn samples were found to be amorphous and isotropic. In these samples, flow‐drawing could be prevented if they were drawn at relatively low temperatures or high strain rates. The partially‐oriented yarn spun at 3000 m/min, which had higher pre‐orientation, did not exhibit flow‐drawing under the conditions used. Flow‐drawing apparently occurs due to molecular relaxation processes, which predominate if the drawing temperatures are high, the strain rates are low, and the PET precursor has a low degree of orientation.
A process for making microcellular thermoplastic parts
Authors: Kumar Vipin , Suh Nam P.
Published: May 2005

A novel process to produce microcellular thermoplastic parts is described. This is achieved by integrating the deformation process in the foaming cycle in such a way that the cell nucleation and growth processes are effectively uncoupled from deformation. The nitrogen‐polystyrene system is studied and the relationships between the essential process parameters are established. It is experimentally shown that the pressures associated with deformation do not reduce the number of bubbles nucleated. The process synthesized is demonstrated by making a microcellular polystyrene container.
Mechanical behavior related to the phase morphology of PC/SAN polymer blends
Authors: Quintens D. , Groeninckx G. , Guest M. , Aerts L.
Published: May 2005

The phase morphology of intensively melt mixed and injection moulded bisphenol‐A polycarbonate (PC)/styrene‐acrylonitrile copolymer (SAN) blends changes on annealing above the glass‐transition temperature (Tg) of both components. For the selected PC and SAN resins, the phase morphology of the 60/40 PC/SAN blend changes from a fine dispersion of the PC phase in a SAN matrix to a coarse co‐continuous phase network, whereas a co‐continuous 70/30 PC/SAN blend changes to a dispersion of SAN domains in a PC matrix. The effect of the blend morphology on dynamic mechanical properties and ambient tensile stress‐strain properties have been studied thoroughly. An increase of the storage modulus between Tg(SAN) and Tg(PC) is observed with increasing coarsening of the phase structure until a continuous PC matrix is formed. The coarsening of the phase structure of the blends gives rise to a transition from ductile to brittle fracture. The loss in ductility is related to a decrease in relative amount of interface and a transition in the type of dispersion.
Devolatilization of polymer melts: Machine geometry and scale factors
Authors: Biesenberger J. A. , Dey S. K. , Brizzolara J.
Published: May 2005

This study was aimed at comparing vented extruder geometries and identifying scale‐up parameters for melt devolatilization. Data are presented comparing single‐ and corotating twin‐screw extruders for devolatilization of methyl methacrylate from poly(methyl methacrylate), and parameters are identified which characterize dynamic similarity for potential use in design and scale‐up. These parameters include conventional process variables such as temperature, throughput, screw RPM, and degree of fill.