bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of molecular networks and thermally activated processes in the deformation behavior of polymers
Authors: Ward I. M. 
Published: May 2005

AbstractThe 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

AbstractSome 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

AbstractThe 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

AbstractThe 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

AbstractPaper 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

AbstractA 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

AbstractA 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

AbstractStress‐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

AbstractWe 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

AbstractA 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

AbstractIntegral 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

AbstractCopoly(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

AbstractPolycaprolactone 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

AbstractA 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

AbstractAs 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

AbstractPolymer 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

AbstractWe 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

AbstractAn 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

AbstractThe 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

AbstractBased 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

AbstractChawla, 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

AbstractThe 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.