bluuebunny/crossref_metadata_2025 huggingface dataset:
Calendering analysis without the lubrication approximation
Authors: Mitsoulis E. , Vlachopoulos J. , Mirza F. A.
Published: December 2004

A general‐purpose finite‐element program has been used to simulate the flow of Newtonian, power‐law, and viscoelastic fluids in calendering. The analysis is fully two‐dimensional and does not make use of the lubrication approximation. Isothermal and nonisothermal calendering is studied and the results are compared with predictions from the lubrication approximation. The free surface is determined and circulatory flow patterns are predicted in the melt bank. Detailed calculations have been performed for a rigid poly(vinyl chloride) (PVC) resin that exhibits slip at the wall using rheological data for the melt and machine parameters. The results include determination of the shape and location of the free surface, vortex patterns, temperature and pressure distributions, and predictions of roll‐separating force, torque, and power consumption. Comparisons are made with experimental data available in the literature.
A method of computation of the pressure effect on melt viscosity
Authors: Utracki L. A.
Published: December 2004

Simha's equation of state provides the relation between reduced pressure, temperature, and volume (P̃, T̃, and Ṽ, respectively) and the occupied site fraction, y = y (P̃, T̃). The latter theoretical parameter combines the P and T effects on the occupied and unoccupied (“free volume”) part of the model liquid. It can be computed for each liquid once the thermodynamic reducing parameters are known. Empirical correlation between published zero shear viscosity data, η = η (P, T), and y indicates that for n‐paraffins and molten polymers η is a single parameter function: η = η (y). The mathematical form of this dependence was explicitly given for n‐paraffins. However, for polymers the correlation depends on molecular weight, molecular weight distribution, branching, composition, etc. In Practical terms, η = η (y) should be determined for each polymer by measuring the temperature dependence of η in as wide a range of T as possible. Then pressure effect on η can be determined from η = η(y) plot, knowing the y = y(P̃, T̃) relation.
A simple, accurate model for viscosities of polymer blends
Authors: Carley James F.
Published: December 2004

The accurate but complex McAllister model for the melt viscosities (η) of binary polymer blends has been greatly simplified by dropping the terms involving only mole fraction and molecular weight, by switching from mole fraction to mass fraction, and by making the model explicit in dynamic, rather than kinematic, viscosity. The simpler Lecyar model was tested side‐by‐side with the McAllister in five binary systems and at seven levels of shear rate from 5 to 500 s−1 in each system. For the 35 pairs of curves fitted, the rms standard error of estimate was 0.0945 (In η), for the Lecyar model versus 0.0911 for the McAllister; the difference corresponds to only 0.4 percent additional error in the blend viscosity. Comparison of results in two systems, reported by Carley and Crossan (12) with those of other workers, indicate that the differences among what appear to be comparable, self‐consistent data sets are much greater than the within‐set errors of rheometric measurement and model fitting.
Properties of elongational flow injection‐molded polyethylene. Part 1: Influence of mold geometry
Authors: Bayer R. K. , Zachmann H. G. , Calleja F. J. Baltá , Umbach H.
Published: December 2004

Injection molding of polyethylene was carried out using molds that introduce axial elongational flow during the filling process, As compared with conventional injection‐molding methods, the present technique yields polyethylene materials having higher mechanical strengths (σ ≈ 150 MPa). The σ‐value of the moldings can be systematically monitored by adequately varying the elongational flow through modification of the mold geometry. Geometrical features of the volume containing the melt before injection as well as geometry of the die, the extruder, and the inlet influence the overall elongational flow, and thus, the mechanical strength of the moldings.
Microstructural diagnosis of block copolymer nonlinear mechanical properties. III: Cycling tensile tests
Authors: Diamant Joram , Williams Michael C.
Published: December 2004

The same three styrene‐butadiene‐styrene copolymers discussed in the companion paper (this issue) were tested by cycling in uniaxial tension/retraction, with large magnitude (to 600% in some cases) and different sequences and rates. The behavior of “set”, at the end of each retraction, is examined in detail and invoked to explain several other features of the stress‐strain curves. Time scales for structural recovery determined in the companion paper are found to assist this interpretation. Quantitative modeling of the isostructure retraction curves is accomplished in terms of the Mooney‐Rivlin strain function, modified to employ a strain variable amplified by the volume of broken glassy “filler”. Values of the two Mooney moduli G1 and G2 are used to infer various features of the microstructure.
Some theoretical results of swelling in fiber or particle filled polymers
Authors: Wu Wen‐Li , Prahinski John R.
Published: December 2004

The problem of inhomogeneous swelling of polymers around particles or fibers is treated analytically within the context of Gaussian statistics for polymer chains and the Flory‐Huggins approximation for the interaction between polymer and solvent. The resulting differential equation for the displacement field around the inclusions is quite simple; it contains a homogeneous part and a nonlinear part. The nonlinear part of the differential equation is preceded by a parameter n(1 − 2χ), where n is the molecular weight between crosslinks and χ is the Flory‐Huggins interaction parameter. Accordingly, the displacement field for the case of theta solvent, i.e. χ equals 0.5, can be solved exactly. In good solvents, the problem can be treated as a perturbation of the theta solvent condition. The amount of deviation from the theta solvent solution is obtained through a numerical technique and the results are tabulated as a function of n(1 − 2χ).
Dielectric analysis of the cure of thermosetting epoxy/amine systems
Authors: Bidstrup Sue Ann , Sheppard Norman F. , Senturia Stephen D.
Published: December 2004

A low molecular weight epoxy resin is cured isothermally with an aromatic amine hardener, and the dielectric properties are measured as a function of the frequency, reaction time, and cure temperature. At specific stages in the cure, small samples from the reacting mixture are quenched and subsequently analyzed for the glass transition temperature and epoxy group conversion by differential scanning calorimetry. In this manner, the change In dielectric properties can be directly correlated with the network structure. The ionic conductivity is modeled as a function of the cure temperature and the cure‐dependent glass transition temperature using a Williams‐Landel‐Ferry (WLF) relation. Combining this WLF relation with the DiBenedetto equation, a comprehensive model relating conductivity with the extent of reaction and cure temperature has been developed.
Dielectric determination of cure state during non‐isothermal cure
Authors: Day David R.
Published: December 2004

As a result of increased interest from industry in using dielectric cure monitoring, a need has arisen for simplifying frequency, cure, and temperature dependent data so that control decisions can be readily made. Techniques utilizing data covering several decades of frequency now exist for separating ionic conduction levels from dipole and electrode polarization responses. Ionic conduction levels are particularly useful since they can be correlated to both viscosity and extent of cure. In addition to being a function of extent of cure, dielectric properties are also influenced by temperature. This dependence often makes the dielectric response more difficult to interpret. This paper investigates two methods for overcoming the temperature dependence of the dielectric response during nonisothermal cure. The first method utilizes recent WLF modeling techniques and extends them with the end result of extracting Tg in real time during cure. The second technique involves measuring the temperature dependence of uncured and cured material. Utilizing the correlation between log ionic conductivity and extent of cure, which has been noted by previous researchers, the normalized conductivity can be converted to a cure index. Several examples including epoxy, polyurethane, and a UV cured photoresist are presented, showing data before normalization and after both Tg and cure index determination.
Model reference adaptive control of a continuous polymerization reactor under periodic operation
Authors: Eliçabe G. E. , Meira G. R.
Published: December 2004

This work proposes a cascade model reference adaptive algorithm to control a continuous polymerization reactor, which is operated under forced oscillations of its feeds. The objective is to produce a polymer with desired average values of the average chain length, of the average polydispersity and of the average polymer production; in spite of the fact that some of the model parameters may be unknown and/or may vary slowly with time. This objective is achieved by imposing the first two moments of the number chain length distribution (NCLD) to follow predetermined periodic trajectories. The proposed control scheme is an extension of that by Eliçabe, et al., when the number of independent controls is less than the number of system states. Computer simulations have shown the feasibility of the proposed technique, provided continuous state measurements are available.
Structure and orientation development in biaxial stretching of ultrahigh molecular weight polyethylene gel films
Authors: Kyu Thein , Fujita Kenichi , Cho Myung H.
Published: December 2004

Ultrahigh molecular weight polyethylene (UHMWPE) gel films were prepared by gelation crystallization from decalin solutions. According to wide‐ and small‐angle X‐ray scattering (WAXD and SAXS) studies, single crystal mat texture with crystal c‐axis oriented normal to film surface generally develops. However, randomly oriented structure can also develop if an external force is applied to gel films during gelation crystallization. Both textures invariably yield high drawability in uniaxial mode with outstanding modulus and strength. Biaxial films, typically 5 × 5, 6 × 6, 8 × 8, and 10 × 10 times the original dimensions, were prepared at 130°C–135°C in a biaxial stretcher. Optical microscopic Investigations reveal the development of interwoven fibrillar structure in all specimens. WAXD and SAXS studies show that lamellar structure transforms to fibrillar texture during biaxial stretching. Crystal orientation is characterized by WAXD pole figure and infrared dichroic methods. Mechanical studies suggest that tensile modulus and strength appear uniform. In comparison with uniaxial deformation, significant improvement in the lateral strength is seen in the biaxially stretched films.
Effect of molecular weight distribution on the rheological and mechanical properties of polypropylene
Authors: Tzoganakis C. , Vlachopoulos J. , Hamielec A. E. , Shinozaki D. M.
Published: December 2004

The effect of molecular weight distribution on the Theological and mechanical properties of a series of polypropylenes is evaluated. The polypropylenes tested were produced by controlled chemical degradation in a single‐screw plasticating extruder. Measured properties include shear, extensional and intrinsic viscosity, melt flow index, extrudate swell, melting and crystallization temperatures, impact strength, flexural modulus, and tensile stress.
Nonisothermal crystallization kinetics of poly(etheretherketone) (PEEK)
Authors: Choe Chul Rim , Lee Kwang Hee
Published: December 2004

Analysis of the crystallization kinetics of poly(etheretherketone) (PEEK) was achieved with dynamic differential scanning calorimetry results. A new kinetic model for the nonisothermal crystallization was derived and the possibility of its application was investigated. By evaluating the parameters in the model, the crystallization behavior of PEEK was analyzed. The experimental and predicted crystallinity change showed good agreement, which indicated that the model equation was appropriate to describe the nonisothermal crystallization kinetics of PEEK. As the melt temperature was increased the number of heterogeneous nuclei decreased, hence the crystallization was delayed.
Hydrolysis of 1,4‐cyclohexanedimethanol‐based copolyester
Authors: Golovoy A.
Published: December 2004

The solid state hydrolysis of a copolyester based on a mixture of 1,4‐cyclohexanedimethanol and ethylene glycol condensed with terephthalic acid was studied at 100°C and 57 to 96 kPa water vapor partial pressure (55% to 95% relative humidity). The equilibrium water sorption in weight percent (C∞) was found to be

where P is the water vapor partial pressure in kPa. For specimens 0.32‐cm thick, it took about 24 h to reach 0.9C∞. The intrinsic viscosity (IV) was measured and used to calculate the relative change in molecular weight (M̄w) from the relationship IV ∝︁ (M̄w)0.7. The decrease in molecular weight was linear with time, and the rate of decrease was found to be proportional to C∞; the empirical correlation is

where the rate constant, k, is in day−1. A decrease of 50% in M̄w was observed after 22 days at 95% relative humidity.
Applications of polymeric materials for condensing heat exchangers
Authors: Bigg D. M. , Stickford G. H. , Talbert S. G.
Published: December 2004

Manufacturers have begun to investigate the use of plastic materials for use in condensing heat exchangers attached to high‐efficiency gas‐fired furnaces. However, a number of technical problems have slowed the use of polymers in this application. While a low thermal conductivity relative to metals is one limitation, a more significant problem relates to the unknown performance of polymers in the harsh chemical environment of a condensing heat exchanger. Recent years have seen some major developments in the use of coatings and plastics for hightemperature service in heat exchangers. In these studies, commercially available acid‐resistant and heat‐resistant polymers were tested, primarily as protective coatings on metal heat exchanger elements, in both experimental‐ and prototypecondensing heat exchangers. These studies indicated that the effectiveness of polymers as coatings was sensitive to the presence of pinholes, and thus, the coating thicknesses had to exceed 0.25 mm to insure adequate protection. The use of a covering, rather than a coating, was found to be one method of insuring pinhole‐free coatings. In this study several all‐plastic heat exchanger elements were found to perform satisfactorily as heat exchanger elements in a gas‐fired condensing heat exchanger. This investigation identified several promising polymeric materials that survived 10,000 cycles in a highly acidic condensing heat exchanger. The polymers that successfully survived this evaluation included fluorinated ethylene propylene, poly(phenylene sulfide), polysulfone, poly(ether imide), and poly(tetrafiuoroethylene).
Optical fiber coatings: High modulus coatings for fibers with a low microbending sensitivity
Authors: Bouten P. C. P. , Broer D. J. , Jochem C. M. G. , Meeuwsen T. P. M.
Published: December 2004

An important function of an optical fiber coating is to prevent optical losses due to microbending induced by lateral forces on the fiber. To protect the fiber over a wide temperature range the modulus of the primary and the secondary coating should be low and high, respectively, and temperature independent. However, selecting the most appropriate organic coating materials introduces a new source of optical losses. Since the linear thermal expansion coefficients of silica and the organic coatings differ by about two orders of magnitude, thermal, fluctuations will cause axial stresses. Cooling may then induce bending or buckling of the glass fiber in the soft primary coating, resulting in increased transmission losses. This effect is especially pronounced when a high‐modulus secondary coating is selected with a glass transition temperature above 80°C. For this type of coating the difference in radial shrinkage between the buffer and the top coating during cooling from the curing temperature becomes important. The influence of primary coating thickness is discussed.
A novel process for the formation of poly(p‐phenylene terephthalamide) film from liquid crystalline solutions
Authors: Fujita Tadahiro , Fujiwara Takashi , Sato Eiji , Nagasawa Keisaku , Amano Toshihiko
Published: December 2004

A novel process for the formation of biaxially balanced films of poly(p‐phenylene terephthalamide) was developed. The liquid crystalline sulphuric acid solution is extruded through a slit die on a flat plate. The optically anisotropic to isotropic transition is generated by controlling the temperature and/or the water content in sulphuric acid before coagulation. The wet gel films are dried while holding their width and length constant. The films thus produced are transparent and biaxially oriented. Young's modulus of 12 GPa, tensile strength of 450 MPa, and elongation at break of 25% were obtained in the plane of the film. Such films which possess high dimensional and thermal stabilities are expected to be useful for new practical uses under severe conditions.
The importance of axial misalignment on the long term strength of polyethylene pipe butt fusion joints
Authors: Bowman Jeremy , Parmar Ravindra
Published: December 2004

The importance of axial misalignment at polyethylene pipe butt fusion joints has been assessed by undertaking elevated temperature lifetime tests. Both medium and high density polyethylene pipes were fusion joined to give aligned and controlled misaligned butt joints. These were tested under either a constant or fluctuating internal pressure loading using conditions that induced failure by slow, stable crck growth. It was observed that the lifetime of a butt joined system depends upon both the internal pressure or pressure range applied and the level of misalignment at the butt fusion joint. Increasing either the internal pressure (range) or the misalignment reduced system performance. These two variables of misalignment and internal pressure (range) may be incorporated into a single parameter, the amplified axial stress (or stress range) at the butt joint. This amplified or butt joint axial stress (or stress range) may be derived by considering the additional bending stresses introduced at the butt joint by virtue of misalignment combined with the axial stress loading.
The effects of flow on miscibility in a blend of polystyrene and poly(vinyl methyl ether)
Authors: Katsaros J. D. , Malone M. F. , Winter H. H.
Published: December 2004

Shear and extensional flows can have a significant effect on the miscibility for a blend of polystyrene with poly(vinyl methyl ether). The cloud point temperature in a planar stagnation flow is elevated by as much as 12 K; the magnitude depends on the extension rate, the strain, and the blend composition. Flow‐induced miscibility is also observed in the shear flow between parallel plates which has been used to test smaller samples and to prepare solid samples for further characterization. At lower temperatures, as much as 30 K below the coexistence temperature, flow‐induced phase separation occurs in both shear flow and extensional flows. The stress, rather than deformation rate, appears to be the most important parameter in flow‐induced phase separation.
Monitoring the cure of an epoxy‐anhydride resin
Authors: Zukas Walter X.
Published: December 2004

The cure of an epoxy‐anhydride resin system used in pultrusion was characterized to develop an understanding of the cure behavior and to determine potential process controls parameters. Isothermal cures of neat resin formulations were monitored by differential scanning calorimetry (DSC), torsional braid analysis (TBA), and microdielectrometry (MDE). The processing conditions define a time/ temperature region in which monitoring would be applicable. Both DSC and MDE were found to yield useful information in this region, however, the events typically monitored by TBA either did not occur or occurred too quickly to be monitored. Significant ionic conductivity was observed in the fully cured resins at temperatures above the glass transition temperature and could possibly be used as a control parameter. This study revealed an apparent change in reaction mechanism with increasing cure temperature. DSC showed a change in activation energy with extent of reaction and a decrease in heat of reaction at the higher isothermal cure temperatures. The formation of a different network structure was indicated by a decreasing glass transition temperature of the cured resin with increasing cure temperature by both DSC and TBA.
The optical properties of a polyetherimide
Authors: Philipp H. R. , Le Grand D. G. , Cole H. S. , Liu Y. S.
Published: December 2004

The optical properties of polyetherimide resin as described by the complex index of refraction, N = n ‐ ik, are derived by Kramers‐Kronig analysis of experimental absorption and reflectance data obtained in the range 40 μm ≥ λ ≥105 nm. Potential uses of this polymer as a printed circuit board material and as a packaging medium for microelectronic circuitry and the relevance of optical data in laser‐assisted processing schemes used in these and other applications are briefly discussed.
Monitoring the quality of mix of polymer melts with particulate fillers using fluorescence spectroscopy
Authors: Bur Anthony J. , Shibata John , Trout Todd K. , Wang Francis W. , Thomas Charles L.
Published: December 2004

Fluorescence spectroscopy has been employed to monitor the mixing of polymer melts with filler material. The polymer melts were low molecular weight polybutadiene and PBAN, a terpolymer consisting of 85% butadiene, 11% acrylonitrile, 4% acrylic acid, and the filler material was aluminum oxide. To carry out the fluorescence observations, a dopant chromophore was mixed into the polymer melt at very low concentrations, 10−4 to 10−6 molar or 11 to 0.11 ppm by weight. The mixing experiments were carried out using a small laboratory mixer which had glass walls for viewing the fluorescence spectra from the dopant chromophore. Fluctuations in fluorescence intensity were observed to decrease as a function of mixing time indicating that the spatial distribution of the fluorescent chromophores was becoming more uniform. Concerning the mixing of polymer melt and filler, we hypothesize that uniform mixing of ingredients is achieved when fluorescence intensity as a function of time is constant. In order to obtain quantitative support for this hypothesis, we used a fluorescence microscope to measure fluorescence intensity and optical transmittance from microscopic regions of well‐mixed and poorly mixed specimens.
Studies on blends of polyethylene terephthalate with bisphenol‐a‐polycarbonate and polypropylene
Authors: Halder R. S. , Deopura B. L. , Misra A.
Published: December 2004

Moldability and mechanical properties of polyethylene terephthalate (PET) under normal molding conditions were found to improve significantly when it was blended with bisphenol‐A‐polycarbonate (PC) and polypropylene (PP) to form ternary polymer blend systems. DSC results of these blends revealed that the PET and PC components formed a miscible blend while PP being incompatible with them, formed a separate phase. PP was also found to form a sleeve around the PET‐PC miscible phase and, thereby, showed a skin‐core type of morphology. Variations of mechanical properties with varying amounts of PP was measured keeping the ratio of PET and PC constant. Tensile and flexural properties of the blends decrease with the amount of PP. Notched impact strength increases up to a certain level of PP and then decreases, while the unnotched values decrease gradually. The effect of annealing on the mechanical properties of these blends have been discussed on the basis of the increased crystallinity of some of the components.
Grafting of a liquid crystal polymer on carbon fibers
Authors: Bhama Satya , Stupp Samuel I.
Published: December 2004

Covalent grafting of mesogenic chains on carbon fiber surfaces was attempted as part of a study on composite materials containing liquid crystal polymer matrices. Grafting in these composite systems is viewed not only as a mechanism to achieve interfacial bonding but also as an approach to modify the interphase physical structure. The synthetic approach to grafting involved the in‐situ polymerization of monomers in the presence of functionalized fibers in order to grow chains covalently attached to the fibers. The chemical mechanism may be viewed as the “transesterification of car boxy lated fibers” with acetylated monomers. The monomers used were pimelic acid, p‐acetoxybenzoic acid and diacetoxy hydroquinone which are known to yield upon condensation a chemically aperiodic nematic polymer. Evidence for grafting was obtained from X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis on fibers retrieved from composite samples. Interestingly, SEM micrographs of fractured composite specimens containing the mesogen‐grafted fibers reveal excellent wetting and interfacial bonding of a liquid crystalline matrix on the carbon surfaces. Based on theoretical considerations for end‐adsorbed macromolecules and the nematogenic nature of the grafted chains we infer that dense layers of adsorbed polymer may form at the interfaces studied. From a materials point of view the in situ growth of liquid crystal polymer chains on fibers may offer mechanisms to control composite properties through both bonding and molecular orientation in interfacial regions.
Crystallization of isotactic (D,L) poly(propylene oxide) in the presence of fine‐particle silica. I: Radial growth rates of spherulites
Authors: Kennedy M. A. , Brown G. R. , St‐pierre L. E.
Published: December 2004

The effect of added silica on the spherulite radial growth rates of isotactic poly(propylene oxide) (i‐PPrO) has been investigated by optical photomicroscopy. Two different i‐PPrO samples were used of different molecular weights and isotacticity, 87 and 100% as determined by 13C NMR. The addition of fine particle silica, an effective nucleating agent, depresses the spherulite growth rates throughout the entire temperature range, but the effect is more dramatic for the i‐PPrO of lower isotacticity. For a given sample, the retardation increases as the quantity of filler increases. The growth rate‐temperature behavior is analyzed in terms of the classical Hoffman‐Lauritzen equation, modified to take into account the polymer‐filler interaction.
Dimensional stability and property gradients in thick sheet molding compound (SMC) sections
Authors: Kau H. T. , Petrusha L. A.
Published: December 2004

The dimensional stability of sample cylinders cured with sheet molding compound pastes was investigated. A significant amount of dimensional change was found for these samples when they were annealed. Furthermore, the amount of change varied with location from the center to the wall along the radial direction of the sample cylinder to form a strain gradient. A series of experiments were then carried out to determine property gradients along the same direction in search of the source of the dimensional instability. It was found that the sample also had a gradient in cure and a gradient in dynamic mechanical properties. But these gradients are not in full agreement. In particular, the gradient of cure appears to be opposite to the direction of the strain gradient, while the gradient of the dynamic mechanical properties coincides with it. These results, therefore, suggest that the dimensional stability may be predominantly governed by the viscoelastic behavior of the material.
Analysis of the birefringence distributions in compact discs of polycarbonate
Authors: Wimberger‐Friedl R.
Published: December 2004

The birefringence distributions in injection‐molded Compact Discs (CD) are determined in radial and tangential cross‐sections and interpreted in terms of the process. The influence of processing conditions is discussed in several examples. It is shown that despite the high birefringence level the retardation of a beam of normal incidence is almost zero due to several compensation mechanisms. One optical axis is almost perpendicular to the surface. The medium, however, is biaxial with the preferential directions depending on the distance from the surface and the radial position. In contrast to a parallel beam, zero retardation cannot be achieved with a convergent beam in injection‐molded polycarbonate disks for that reason.
Crystallization and structure‐mechanical property relations in poly(aryl ether ether ketone) [PEEK]
Authors: Medellin‐Rodriguez F. J. , Phillips P. J.
Published: December 2004

In the development of advanced composite materials, the mechanical behavior of the matrix is of critical importance. The next generation of composite materials will be based on high modulus tough matrices, of which poly(aryl ether ether ketone) [hereinafter, referred to as PEEK] is one of the first crystalline thermoplastics to receive serious attention. As in all crystalline polymers, the matrix is itself a composite material whose properties depend significantly on the crystalline morphology developed during processing. In this contribution, the current understanding of crystallization in PEEK and its influence on mechanical properties is reviewed. Problems yet to be resolved are highlighted.
Rheological properties of multicomponent polymer systems undergoing melting or softening during compounding
Authors: Shih C.‐K. , Tynan D. G. , Denelsbeck D. A.
Published: December 2004

The rheological characteristics of a number of polymer blends, including amorphous and semi‐crystalline plastic matrices, during melting or softening, are analyzed with a batch mixer. The physical changes accompanying the phase transitions taking place as the slat‐and‐pepper blends are heated and mixed in the region of their component melt transition temperatures are monitored visually through a transparent window with video recordings. The torque of mixing and the mixture temperature are also recorded continuously. The strong effects of additives such as filler or lower melting resin as well as rotor speed, degree of fill, and ram pressure were observed.
Curing of unsaturated polyester resins: Effect of surface treatment of particulates
Authors: Shieh Jiunn‐Jye , Hsu Tzu‐Chien J.
Published: December 2004

The effect of surface treatment of particulates on the curing kinetics of unsaturated polyester resin has been investigated using a differential scanning calorimeter. Two coupling agents, γ‐methacryloxy propyltrimethoxy silane (γ‐MPS) and phenyltriethoxy silane (PTS), were employed. The former reacted with the resin; the latter did not. A kinetic model of free radical addition polymerization was used. A correction factor was used to represent the effective free radical concentration in order to account for the formation of charge transfer complex between the glass beads and the free radicals in the resin. The results indicate that (1) the resin with treated particulates showed generally faster reaction rate and conversion than the resin with untreated particulates; (2) no obvious difference on the curing kinetics was observed between these two coupling agents; the primary role of coupling agent is to inhibit the influence of particulates on the curing kinetics of the resin by effective surface coverage; and (3) a minimum aqueous concentration of 0.05 wt% was suggested for surface treatment of particulates; the reaction rate of the resin was slightly improved when the concentration of the coupling agent was 0.01 wt%; this might possibly be due to insufficient coverage of the particulate surface.
Dynamics of a continuous stirred tank reactor for styrene polymerization initiated by a binary initiator mixture. II: Effect of viscosity dependent heat transfer coefficient
Authors: Kim Kee Jeong , Choi Kyu Yong , Alexander James C.
Published: December 2004

The dynamic behavior of the solution polymerization of styrene in a continuous stirred tank reactor is analyzed with a mixture of tert‐butyl perbenzoate and benzoyl peroxide as an initiator system. In the modeling of the reactor, a viscosity dependent reactor wall heat transfer coefficient is used to account for the changing heat transfer efficiency as monomer conversion and polymer molecular weight increase. The steady state and bifurcation behaviors have been investigated with the reactor residence time, initiator feed composition, initiator concentration, feed solvent volume fraction, and coolant temperature as bifurcation parameters. Unlike the reactors with constant heat transfer coefficient, the present system exhibits relatively simple steady state and dynamic bifurcation behaviors. Oscillatory behavior is observed only when the solvent volume fraction in the feed exceeds 0.2. The dynamic simulation of the reactor also indicates that a feedback temperature controller may fail to maintain the reactor temperature when the heat transfer coefficient changes as a result of process disturbances.
Catalysis and kinetics of cyclotrimerization of cyanate ester resin systems
Authors: Osei‐Owusu A. , Martin G. C. , Gotro J. T.
Published: December 2004

The kinetics of cyclotrimerization and the thermal stability of bisphenol Abased cyanate ester resin systems were determined using Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. The bisphenol A dicyanate was cured with 4 phr nonylphenol and with the octoates of zinc and manganese, and cobalt acetylacetonate at concentrations ranging from 0 to 750 ppm metal. An empirical rate law was used to predict the cyanate concentration profiles. The observed reaction rate showed a first‐order dependenće on the initial metal concentration and a second‐order dependence on the cyanate concentration in the kinetically controlled regime. For the uncatalyzed systems, the kinetics was described by a second‐order autocatalytic model. The thermal stability of the network was found to be dependent on the catalyst concentration for the zinc catalysts. For the samples cured with manganese, no effect of concentration on the thermal stability was observed.
Applications of flow simulation in reactive processing for cases in which the filling stage can be decoupled from heat transfer and chemical reaction
Authors: Castro J. M.
Published: December 2004

Flow simulation to predict the position of the flow front during SMC and IMC compression molding, RIM, SRIM, and RTM, is very useful in obtaining better molded parts. We have derived criteria to determine when the filling stage for these processes can be decoupled and simulated without regard to heat transfer and chemical reaction. We discuss why a Generalized Hele‐Shaw model can be used to predict the flow front. Examples are given of the use of flow simulation in designing and locating SMC charges so as to reduce or eliminate knit lines, in locating IMC injection ports so as to avoid trapping air, in locating RIM injection gates to avoid trapping air and minimize knit‐lines, and in locating vents to avoid trapping air in RTM or SRIM molding.
Morphological responses in thermally conditioned linear low density polyethylene
Authors: El‐Kindi Mohammed , Schreiber Henry P.
Published: December 2004

An octene‐modified linear low density polyethylene has been used to examine the mechanisms involved during thermal annealing. Annealing temperatures ranged from 60 to 100°C. Annealing results in crystallinity increments and these respond to two concurrent effects. One involves the segregation from crystalline regions of low molecular weight moieties in the polymer's molecular weight distribution; the other is lamellar thickening, leading to the formation of more highly perfected crystalline domains. In the present polymer, the two effects were found to be in balance at annealing temperatures near 80°C leading to the optimum distribution of crystalline regions in the amorphous portions of the polymer. The effect of thermal conditioning on mechanical properties of the polymer was illustrated in terms of the initial modulus and the polymer's yield strength. The twin mechanisms of molecular fractionation and lamellar thickening were found to influence both of the mechanical property parameters.
Influence of reprocessing on the mechanical properties of a commercial polysulfone/polycarbonate blend
Authors: Sánchez P. , Remiro P. M. , Nazábal J.
Published: December 2004

Commercial polysulfone/polycarbonate (PSU/PC) polymer blends were reprocessed up to five times to determine the influence that reprocessing has on their structure and physical properties. All the high strain properties, mainly ductility, significantly decreased under harsh processing conditions, such as five cycles at 320°C. The results of reprocessing the blends at 320°C have been compared with results at a lower temperature and also with those of the separate components with the aim of clarifying the origin of the degradation. These results plus Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis, and melt flow index measurements (MFI) indicate that the presence of the two polymers together clearly decreases the resistance to degradation of each component. Moreover, degradation under the stated conditions is mainly thermal and does not change the chemical nature of the blends. However, a clear decrease in molecular weight was observed both by viscosimetry and MFI measurements as was a shift to higher temperatures of the low temperature secondary transition of both PC and PSU. Both molecular weight and secondary transition changes usually deteriorate mechanical properties but not in the degree observed here. This probably means that the fine and difficult‐to‐observe structure of the blend has also changed.
The influence of intracomplex compounds of copper and cadmium on the properties of epoxy amine systems
Authors: Kurnoskin A. V.
Published: December 2004

The influence of intracomplex metal compounds, namely, copper salicylate and cadmium anthranilate on the properties of diglycidyl bis‐phenol A ether (DGEBA) hardened with diethylene triamine and triethylene tetramine has been investigated. The dependence of hardenability of the amines modified with the salts on the content of the salts has been determined. The saturation of the amines with salts has been shown to result in formation of hardeners affording good stability of compositions. The above fact can be attributed to the blocking of the amino nitrogen atoms by the metals and neutralization of the hydrogen atoms with the anions. The properties of metal‐containing polymers has been studied; increases of their strength indices and heat stability in comparison with the initial aliphatic amines have been established.
Anisotropy in mechanical and dynamic properties of composites based on carbon fiber filled thermoplastic elastomeric blends of natural rubber and high density polyethylene
Authors: Roy D. , Bhowmick Anil K. , De S. K.
Published: December 2004

The effects of short carbon fibers on static and dynamic properties of thermoplastic elastomeric blends of natural rubber (NR) and high density polyethylene (HDPE) have been studied. Both mechanical and dynamic properties are dependent on fiber concentration. The fiber aspect ratio ranges from 20 to 30. Adhesion between fiber and matrix is evident from the SEM photomicrographs of the failed composites and from variation of relative damping properties. Fiber orientation occurring during processing causes anisotropy in the physical properties. In composites with longitudinally oriented fibers, tensile failure occurs by both fiber pullout and breakage, while in composites with transversely oriented fibers, matrix failure dominates. The incorporation of fibers into the matrix lowers the tan δmax value, but no change in glass transition temperature is observed.
An investigation of brittle failure in ductile, notch‐sensitive thermoplastics
Authors: Nimmer Ronald P. , Woods Joseph T.
Published: December 2004

Brittle failure, a significant design issue for plastic components subject to impact loads, is especially catastrophic when the material is normally ductile. Such behavior is not adequately understood relative to the micromechanisms, controlling parameters, and design consequences in plastics. Previous work has identified the process of crazing as being relevant to these failures in thermoplastics. The relationship between crazes generated through mechanical loading and subsequent brittle failure of amorphous thermoplastics is discussed and the hypothesis that the craze event is a necessary but insufficient condition for brittle failure is employed. Emphasis is focused upon the engineering prediction of craze formation and its use as a conservative brittle failure criteria for defining geometric details to prevent brittle failure. First, a series of experiments using one geometry is applied to study the concept of crazing as a precursor to brittle fracture in the two amorphous polymers polycarbonate and polyetherimide. Second, three‐dimensional finite element analyses are used to assess the effects of changes in geometric detail upon the continuum stress state and eventual failure of the specimen for these two materials.
Scanning tunneling microscopy studies of single‐molecule single‐crystals
Authors: Bu Haishan , Chen Erqiang , Yao Junen , Xu Shengyong , Kuang Yalei
Published: December 2004

The study of single‐molecule single‐crystals of isotactic polystyrene was carried out by scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). It was shown that STM provided more information than TEM. By means of STM, the single‐molecule single‐crystals were found even in the case of aggregation. Regular strips were also found on the top surface of single‐molecule single‐crystals. This seems to imply regular adjacent folding.
Thermal properties of poly(vinyl cyclohexane)
Authors: Grebowicz J. S.
Published: December 2004

Isotactic poly(vinyl cyclohexane) (PVCH) was studied by thermal analysis. The deduced equilibrium melting point, T, is 405°C (678 K). The heat of fusion, Δ H was found to be 50.82 J/g (5.60 kJ/mol) and Δ Cp at Tg, is 0.273 J/(gK) [30.1 J/(molK)]. The glass transition temperature, Tg, of the amorphous PVCH is 80°C (353 K). In semicrystalline samples, Tg increases up to 165°C (438 K) for crystallinities > 40%. Beside crystalline and flexible amorphous, a rigid amorphous phase is postulated in the semicrystalline polymer.
Thermal characterization of high performance PBI and 6F polymers and their alloys
Authors: Jaffe Michael , Haider M. Ishaq , Menczel Joseph , Rafalko Joseph
Published: December 2004

The effectiveness of thermal analysis as a technique for screening polymeric candidates for high temperature composite application is described. DSC, DMA, and TGA were employed to measure glass transition temperature, characterize blend phase morphology, and assess thermo‐oxidative stability. The materials studied were polybenzimidazole (PBI), polyimide copolymer (6FCoPI), and blends of PBI with Ultem 1000™ and 6FCoPI. The potential of misinterpretation of thermal analysis as the primary screening tool was also demonstrated. It was shown that if thermal analysis was used with insufficient understanding of the chemistry and physics of the materials under investigation, highly misleading conclusions may be derived.
Crystallite elastic constants and macroscopic moduli of isotropic semicrystalline polyethylenes
Authors: Janzen Jay
Published: December 2004

Available literature data, augmented with a few mild and plausible assumptions, have been used to derive an estimated empirical compliance matrix for orthorhombic crystalline polyethylene at ambient conditions. Compared with this representation of experimental observations, reported theoretical compliance surfaces, derived from molecular mechanics, are shown to be in quantitative disagreement, although qualitatively their shapes are not dissimilar.

It is further shown that if an accurate theoretical determination were to be available, it would yield an ability to translate (in surprisingly few, and rather simple, theoretical steps) directly from interatomic forces, acting over nanometer lengths, into realistic, crystallinity‐dependent, estimates of macroscopic moduli of isotropic semicrystalline polyethylenes.
Thermal analysis of poly(phenylene sulfide). II: Non‐isothermal crystallization
Authors: Collins George L. , Menczel Joseph D.
Published: December 2004

The non‐isothermal crystallization of Fortron poly(phenylene sulfide), PPS, was examined to better understand its behavior during injection molding. The nonisothermal Avrami formalism was applied to this system, but this method was found to be questionable because of the sometimes severe curvature that appears in the plots of the transformed data. A method of ranking crystallization rates at low cooling rates by plotting the peak in the crystallization exotherm versus the cube root of cooling rate has been considered and shown to have limitations at the higher cooling rates of interest. The growth rate expression developed by J. D. Hoffman for polymer crystallization of chain folded lamella in three dimensions has been used to simulate crystallization exotherms. It was found that this could only fit the data at low cooling rates. At high cooling rates it was necessary to use a growth rate expression developed by Calvert and Ulhmann for polymer crystallization without chain folding. When this is used to describe a two dimensional growth geometry, close agreement in the positions of high cooling rate exotherms could be obtained. The implication is that a change in crystallization mechanism is possible as the conditions go from low to high cooling rates.
Thermogravimetric kinetics of polymer degradation: Science or fiction?
Authors: Schneider Hans Adam
Published: December 2004

Weight changes in thermogravimetry are dependent on the volatility of the degradation products. Thus, molecular weight determinations (or related studies) must fist be undertaken to prove whether or not nonvolatile chain fragments will be removed only at high temperatures. In this case both thermal stability and kinetic studies by thermogravimetry are senseless. But even if volatile products are formed, the kinetic parameters will depend on the conversion degrees because of the kinetic chain character of the polymer degradation. Changes in reaction mechanism aggravate the situation; it is thus problematic to define in such conditions reliable kinetic parameters. Values calculated from a single TG curve are valid for specific conditions only, but of no sense from the general kinetic view.
Thermal properties, phase transitions, and morphology of a conjugated polymer
Authors: Cheng Stephen Z. D. , Wu Xiao Xin , Zhang Anqiu , Meador Michael A.
Published: December 2004

A highly conjugated polymer was synthesized from α,α′‐dibromo‐p‐xylene, 1,4‐bis(2‐hydroxy‐benzoyl)benzene, and benzyl bromide via a modified Williamson ether synthesis under phase transfer conditions. Based on thermal analysis, polarized light microscopy, electron diffraction, and wide angle X‐ray diffraction experiments, the heat capacities in the solid and liquid states have been determined. The glass transition temperature is at 358 K with a heat capacity increase of 164 J/(K mol). Two different ordered crystal forms with different crystal unit cells were observed. The more ordered crystal shows a low transition temperature and the less ordered one a high transition temperature. This is mainly due to the effect of entropy change. These crystals exhibit various crystal morphologies with different birefringences. Transition kinetics are expressed by an Avrami equation. Two crystals show different Avrami exponents with crystallization temperature, which corrspond to the morphological change. Competition between crystal growths is also discussed.