bluuebunny/crossref_metadata_2025 huggingface dataset:
Crazing and acoustic emission in poly(methyl methacrylate)/acetone and polystyrene/methanol systems
Authors: Jakus Karl , Ritter John E. , Larsen Clifford A.
Published: December 2004

Craze initiation and growth in the poly(methyl methacrylate)/acetone and polystyrene/methanol systems was studied using photographic and acoustic emission techniques. The poly(methyl methacrylate) system was the only one that produced detectable acoustic emission; however, it was found that craze initiation occurs predominantly in the first half of a sample's lifetime while acoustic emission is detected predominantly in the second half. The detected acoustic emission in the poly(methyl methacrylate) system is believed to be due to the rupture of craze fibrils. Craze initiation in both polymer systems was found to be dependent on stress and time with higher stresses initiating more crazes at earlier times. Although the craze growth rate in both systems exhibited extreme variability, the average growth rate tended to increase with craze size and applied stress. In the poly(methyl methacrylate) system, craze velocity was independent of time but in the polystyrene system it decreased with time. None of the existing craze growth theories were capable of explaining these results.
Kinetic treatments of glass transition phenomena and viscoelastic properties of glasses
Authors: Aklonis J. J.
Published: December 2004

Phenomenological treatments of viscoelasticity and recent models proposed to explain the kinetic aspects of glass transition phenomena are shown to be based on the same underlying physical considerations. This realization suggests the possible unification of these two areas by a single model. This possibility is explored for the simple case of a glass subjected to a single temperature jump followed by a stress relaxation experiment. Presently, sufficient data on any single chemical system to support a critical test of the viability of this model does not exist. Nevertheless, data from several sources on various materials indicate that the qualitative aspects of viscoelastic behavior of glasses at temperatures well below Tg are in accord with the predictions of the unified model.
Fourier transform infrared characterization of conformational changes in amorphous poly(ethylene terephthalate) during volume recovery
Authors: Moore R. S. , O'loane J. K. , Shearer J. C.
Published: December 2004

Samples of melt‐quenched, amorphous poly(ethylene terephthalate), APET, annealed for up to four successive 30‐min intervals at 50°C, were analyzed by Fourier transform IR (FTIR) spectroscopy at room temperature. Results confirm earlier observations that the fraction of the gauche conformation of the ethylene glycol moiety increases upon annealing. This suggests a change toward a more random structure during the concomitant process of volume recovery. Spectra obtained after annealing for times to and beyond the onset of embrittlement, as judged from mechanical response, indicated that several distinct changes in band intensities occur during this time interval. Spectroscopic results for times longer than that required for embrittlement suggest an increase in motions associated with in‐plane vibrations located in and near the aromatic portions of the chains, as well as a decrease in out‐of‐plane vibrations. The overall results suggest that this method has potential for evaluating fast as well as slow recovery processes.
Characterization of glassy state relaxations by low pressure carbon dioxide sorption in poly(methyl methacrylate)
Authors: Fechter J. M. H. , Hopfenberg H. B. , Koros W. J.
Published: December 2004

Poly(methyl methacrylate) (PMMA) microspheres were swollen in methanol vapor, the swelling penetrant was quickly evacuated, and the subsequent relaxation of the polymer under vacuum was monitored by determination of the rate of settling of rapidly measured low pressure pseudoequilibrium CO2 sorption isotherms. The decrease in CO2 sorption capacity occurred very rapidly at short times, but the final stages of consolidation were protracted. In all cases, the microspheres were under vacuum between isotherm determinations. A single relaxation time is not sufficient to describe the relaxation processes characterized by the time‐dependent sorption measurements. The sorption relaxation curves are similar in shape to volume relaxation curves for glassy polymers following imposition of a large pressure or temperature step change. The observed similarity between the sorption relaxation curves and classical volume relaxation curves is consistent with the notion that the excess sorption capacity introduced by methanol preswelling results from excess unrelaxed volume introduced into the glass by the quickly removed alcohol. As the excess volume relaxes, the excess sorption capacity decreases. One can, therefore, monitor the subtle process of consolidation using CO2 as a probe of the excess volume introduced by the swelling perturbation. Subatmospheric pressure CO2 sorption isotherms measured between 20 and 40°C for two different diameter microsphere samples (5436 Å and 1453 Å) for pressures up to 700 mm Hg were concave to the pressure axis. Such general isotherm shapes can be described by a two‐term expression consisting of a Henry's law term and a Langmuir term. The Langmuir term, which arises due to unrelaxed volume in the nonequilibrium glass, is responsible for the observed concavity in the sorption isotherm. Annealing the sample, increasing the temperature of the sorption experiment closer to the Tg of the PMMA or permitting the preswollen sample to relax tends to reduce the concavity of the isotherm relative to the corresponding case for sorption in the preswollen sample measured at 25°C. This trend is presumably a consequence of the reduction in unrelaxed volume in the glass which attends either annealing, approaching the glass transition temperature of the polymer, or consolidation of excess volume following exposure to a swelling penetrant.
Non equilibrium annealing behavior of poly(vinyl acetate)
Authors: Bair H. E. , Johnson G. E. , Anderson E. W. , Matsuoka S.
Published: December 2004

The water absorbed by poly(vinyl acetate), PVAc, at 23°C was found in two states. The first, which can account for up to 4 weight percent, was bound to the polymer. The second was in a freezable or clustered form. The latter type of water had no effect on PVAc's glass temperature, whereas, the former kind plasticized Tg. In annealing studies, the enthalpic and dielectric response of PVAc when held at a fixed temperature increment, ΔT, below Tg, was observed to be independent of the amount of bound water. The time dependence of the shift in the dielectric relaxation spectrum and the recovery of the enthalpy towards its equilibrium value as PVAc approached its equilibrium glassy state from a lower temperature as compared to a higher temperature was initially slower. This delayed response to expansion was of the order of the polymer's average relaxation time at the lower temperature. A model was proposed to explain this asymmetric behavior based upon changes in the polymer's free volume as well as its occupied volume.
Sub‐Tg annealing studies of UV‐cured poly(urethane) acrylate coatings on optical fibers: A correlation of annealing behavior with microbending loss
Authors: Levy Nicole
Published: December 2004

Three types of UV‐curable acrylate network systems were coated on optical fibers and studied calorimetrically. It was found that an endothermic transition of ΔH ∼2‐14 cal/g is superimposed on the glass transition of these coatings. This transition is present in the fiber coatings, but not in sheet form. The time‐dependence of sub‐Tg annealing of these crosslinked coatings (following rapid quenching from a temperature above the end temperature of the endotherm) was found to correlate with a mechanical‐optical property of the coated fibers; namely, the contribution of the coating to the microbending loss of the optical fiber.
The curing of unsaturated polyester resins in adiabatic reactors and heated molds
Authors: Rojas Alfredo J. , Borrajo Julio , Williams Roberto J. J.
Published: December 2004

The influence of several process parameters on the curing of multipurpose unsaturated polyesters with styrene, in heated molds, is discussed. The polymerization kinetics was studied in a quasi‐adiabatic reactor taking into account corrections for heat losses. The following expression resulted: dx/dt = k′[I](1 − x)3 exp(−16.6/RT), where x is the conversion of unsaturated bonds and [I] is the initial initiator concentration (benzoyl peroxide); cobalt octoate was used as an accelerator. Specimens were cured in two kinds of heated molds (one jacketed and the other electrically heated), and temperature profiles recorded. The temperature increase at the midplane showed a maximum when plotted as a function of the reaction rate (Arrhenius preexponential factor), in agreement with previous theoretical predictions. The temperature increase was enhanced for a thermally initiated reaction.
A theoretical analysis of non‐isothermal flow in wire‐coating co‐extrusion dies
Authors: Basu Santanu
Published: December 2004

A theoretical study of non‐isothermal superimposed flow of two polymer melts in wire coating co‐extrusion dies has been carried out. Numerical methods have been employed to solve the coupled momentum‐ and energy‐balance equations. Various combinations of three polymers—namely, high density polyethylene (HDPE), polystyrene (PS) and low density polyethylene (LDPE) have been studied and least squares curve fitted quadratic polynomials have been used for constitutive equations for all three polymers in non‐Newtonian high shear rate regions. A multitude of thermal and mechanical boundary conditions can be treated by this algorithm. It was found that temperature and velocity profiles in the die depend significantly on the arrangement of the polymers. Maximum temperature rise has been noted to increase sharply with wire velocity but it can be reduced by increasing the die radius. When the thickness of the outer layer is increased from zero, the shear stress at the wall undergoes a dramatic change (if the viscosities of the polymers are different) at small values of the flow rate ratio and it reaches an asymptotic value at large values of flow rate ratio. It was also found that viscosity ratio at the interface can be reduced by changing the initial temperatures of the liquids. It was observed in some cases that large errors in the calculation of rheological and thermal variables for this problem can be made if temperature rise due to viscous dissipation is not considered.
Optimal thermal design of compression molds for chopped‐fiber composites
Authors: Barone M. R. , Caulk D. A.
Published: December 2004

Because heat is convected by the motion of material in the cavity of a compression mold, the time‐averaged heating load on the cavity surface is nonuniform. In rapid production of large, thin parts, this can lead to large variations in cavity surface temperature when the mold is heated by the usual uniform distribution of heating lines. In this paper, a new method is developed for optimizing the mold heating design so that this nonuniform heating requirement can be satisfied with a minimum variation in cavity surface temperature. Oil heating is considered specifically, but the method can also be used for stream or electric heat. The optimal position and power supply for each heating line in the mold is determined by combining mathematical programming techniques with an analysis of the steady temperature field in the mold. The nonuniform heating load on the cavity surface is represented by a time‐averaged steady heat transfer coefficient calculated from the transient temperature distribution in a polyester sheet molding compound as it fills the mold cavity. The design method is applied to an example mold for a large flat panel. At a one‐minute cycle, the optimal heating design dramatically reduces nonuniformity in cavity surface temperature compared with a conventional distribution of heating lines. The optimal design is remarkably simple, uses only conventional equipment, and involves only half the customary number of heating lines. Nevertheless, it still has sufficient flexibility to adjust for changes in cycle time without sacrificing uniformity in cavity surface temperature.
Non‐equilibrium processes in poly(vinyl chloride) glasses vitrified at elevated pressures
Authors: Prest W. M. , O'Reilly J. M. , Roberts F. J. , Mosher R. A.
Published: December 2004

The conformational and enthalpic changes that occur in poly(vinyl chloride) (PVC) glasses that have been vitrified from the melt under pressure have been examined by Fourier transform infrared spectroscopy and quantitative differential scanning calorimetry. It is shown that these pressures freeze in the high energy states that are characteristic of the vitrification temperature and increase the apparent glass transition temperature of the polymer. In addition, pressures in excess of the vitrification pressure, cause intermolecular effects that can be relaxed out below Tg. Both of these processes create characteristic endothermic and exothermic changes in the apparent heat capacity of the glass that appear over a period of time and are sensitive functions of the glass formation processes as well as the subsequent annealing history. The endothermic events are interpreted as the stress perturbed volumetric relaxation process white the exotherms are associated withh the release of the frozen in stresses.
New model of curing process kinetics of diurethane crosslinked natural rubber
Authors: Jurkowski B. , Kubis J. , Jȩdraszak A.
Published: December 2004

A new model for the curing kinetics of diurethane crosslinked natural rubber is elaborated. On the basis of rheometric data, calculation of rate constants of both formation and degradation of the following bond types: urea‐urea, urethane‐urethane, and urea‐urethane, was enabled and thermal activation energies of these processes were determined. Activation energy values for formation of the bonds above are: 61.5 kJ/ mole, 187.6 kJ/mole, and 28.9 kJ/mole, respectively. For degradation, activation energies are: 293.9 kJ/mole, 195.5 kJ/mole, and 163.3 kJ/mole, respectively. An algorithm for carrying out of these calculations on a computer was developed.
Charpy impact fracture testing—a precise measure of ductile‐brittle transition in a filled polymeric system
Authors: Cahill R. W.
Published: December 2004

The fracture toughness of a filled nitrile rubber/phenolic polymeric system was assessed by means of ductile‐to‐brittle transition temperature (DBTT) as measured by the Charpy impact method to search for sampling location dependencies of toughness in structures. This investigation established the relationship between the Charpy DBTT and exposure to selected relative humidity (RH) for the filled polymer from the three lots. Charpy fracture tests of specimens subjected to a low RH environment (15 percent) had higher DBTTs than their counterparts exposed to a high RH condition (70 to 75 percent). Charpy specimens of this material exhibited a 9 to 22°F change in DBTT which depended upon the manufacturer and the conditioning period for a corresponding change of 60 percent RH. The change in DBTT with relative humidity was found to be reversible; initial fracture behavior could be restored to samples from the low RH (15 percent) station by equilibrating at a high RH (75 percent) level.
Processing and commercial application of polymer blends
Authors: Shaw M. T.
Published: December 2004

The number of commercial blends has skyrocketed in the past several years and the trend toward blending—in preference to the creation of new polymer structures—has been firmly established. This paper analyzes the reasons for this growth; the types of commercial products, their manufacturer, and their applications; the patent situation; and possible future directions of the industry.
The influence of impingement mixing on striation thickness distribution and properties in fast polyurethane polymerization
Authors: Kolodziej Paul , Macosko Christopher W. , Ranz William E.
Published: December 2004

Impingement mixing in a polyether polyol/butanediol/MDI, thermoplastic urethane system was evaluated using measurements of striation thickness distribution, adiabatic temperature rise, and molecular weight. Adiabatic temperature rise was less sensitive to mixing quality for this system than for the crosslinking ones previously studied. The average of the distribution of striation thickness as measured by optical microscopy on the resultant polymer decreased with increasing nozzle Reynolds numbers, Re. Molecular weight increased and its polydispersity decreased with increasing Re. Morphological data indicate better phase separation in the poorly mixed samples. These results are consistent with relatively slow diffusion for the polyol and thus the preferential formation of unattached hard segments at lower Re.
Failure modes in piezoelectric poly(vinylidene fluoride)
Authors: Kolbeck A. G.
Published: December 2004

This article describes a number of potential failure mechanisms for piezoelectric poly(vinylidene fluoride) (PVDF), including decay of piezoelectric properties, film shrinkage at elevated temperatures, electrode erosion due to water, curling and fibrillation of the highly oriented PVDF films, and abrasion or impact damage. Piezoelectric aging and shrinkage are found to be strongly correlated; neither process occurs below 60°C, and both show logarithmic time dependences above that temperature. Thus, shrinkage and piezoelectric aging likely both result from similar mechanisms associated with micro‐structural annealing effects at elevated temperatures. The degradation of piezoelectric response observed when PVDF films are exposed to moisture is found to be due primarily to water‐induced erosion of the vapor‐deposited aluminum electrodes rather than to enhanced piezoelectric decay. Observations of mechanical damage suggest that the susceptibility of PVDF films may be partially due to imperfections introduced during the manufacturing process. One conclusion of this study is that biaxial PVDF offers advantages over uniaxial film, including reduced shrinkage and piezoelectric decay, superior resistance to curling and fibrillation, and lower susceptibility to formation of pinholes and other localized defects.
Modeling of poly(ethylene terephthalate) reactors: 6. A continuous process for final stages of polycondensation
Authors: Ravindranath K. , Mashelkar R. A.
Published: December 2004

A mathematical model of a continuous polycondensation reactor used in the finishing stages is developed. This axial dispersion model predicts the directions in which mixing, and other process and operational variables, will influence the progress of polycondensation. The available pilot plant data have been compared with the model predictions. In view of the neglect of the side reactions in our model, the comparison is only approximate but appears reasonable. The analysis developed is used to highlight certain critical design considerations.
Mechanistic studies of adhesion promotion by γ‐aminopropyl triethoxy silane in α‐Al2O3/polyethylene joint
Authors: Sung N. H. , Kaul A. , Chin I. , Sung C. S. P.
Published: December 2004

In order to understand the mechanism of adhesion promotion by organo silane in joints where its chemical reaction with a polymer matrix may be negligible, we studied the role of γ‐aminopropyl triethoxy silane (γ‐APS) in α‐Al2O3/ polyethylene joints. When adsorbed or deposited on α‐A12O3/ and moderately dried, γ‐APS forms a multimolecular film that is not fully cured. Drying at elevated temperatures for an extended time leads to further curing, resulting in a glassy silane film with a Tg around 108°C, while prolonged dry may cause some degradation. Joint strength is markedly improved by the application of a γ‐APS film with a maximum peel strength of 2.3 kg/cm when the silane is applied from a 2 percent aqueous solution. Drying the silane at an elevated temperature prior to joint formation reduces joint strength and also changes the failure mode from cohesive failure through the polyethylene to a mixed mode. Evidence of interdiffusion between γ‐APS film and polyethylene at a temperature (149°C) that is above the melting point of polyethylene and the Tg of the silane film was obtained by measuring the Si concentration profile across the interface of the laminate of polyethylene/γ‐APS/polyethylene. Diffusion constants in the order of 10−12 cm2/s were obtained, with a teridency toward reduced diffusion as a consequence of extensive drying. DSC results indicate at least partial miscibility of the silane polymer in the amorphous region of polyethylene. It is proposed that the interdiffusion between γ‐APS silane film and polyethylene is an important mechanism for adhesion promotion of the joints investigated in this study.
A criterion for craze formation
Authors: Juska T. , Harrison I. R.
Published: December 2004

A general criterion for craze formation is presented. Crazes are deformation zones that are common to both glassy and semicrystalline polymers. Crazes are composed primarily of fibrils. This paper attempts to describe the process that transforms unoriented glassy and semicrystalline polymeric solids into a fibrous state. The criterion for crazing discussed is a local phase transition. The transition occurs at the draw temperature. Unoriented solid‐phase macromolecules, at local high‐stress regions, undergo a transition to the elastomeric phase. Rapid extension and accompanying resolidification produce the fibrous morphology of craze fibrils. Cavitation of the deforming rubber phase ocurs because the local length increase is riot compensated for by an overall area decrease. Craze formation in glassy polymers has long been suspected to involve a local solid‐to‐rubber phase change. To relate crazes in glassy and semicrystalline polymers, one can assume that a solid‐to‐rubber phase change is required to produce craze fibrils in semicrystalline polymers. The transient melt phase would undergo rapid elongation, causing the formation of extended chain crystallites. These subsequently nucleate the remaining melt, which then crystallizes epitaxially as lamellae. Crystallization during flow would, therefore, be the mechanism of fiber formation.
Characterization of plastics in fire
Authors: Paul K. T.
Published: December 2004

Fire is a complex process in which temperature and oxygen concentration vary considerably. The methods of characterizing the flammability of plastics materials advocated in this paper use simple test procedures in a series of different fire environments; i.e., at different temperatures and oxygen concentrations. The limits of both flaming and smouldering combustion, flame spread, and burning define the burning behavior of materials as dynamic multivariable parameters and not as single‐point data characteristics of the majority of current fire tests. The feasibility studies were based on modified oxygen index (ASTM D2863, NES 715) and Setchkin furnaces (ASTM D1929). The burning behavior of plastics may also be directly affected by their softening and viscosity characteristics, and this has been explored with relation to suspended ceilings and stacking chairs. The techniques used showed major differences between materials that may not always be seen in standard single‐point tests but which have been correlated with full‐scale ad hoc tests; e.g., room and corner tests, and actual product tests.
Quantitative determination of the vinylacetate content in ethylene vinyl‐acetate copolymers—a critical review
Authors: Koopmans R. J. , van der Linden R. , Vansant E. F.
Published: December 2004

The various methods for the determination of the vinylacetate (VA) content in any ethylene vinylacetate copolymer are examined critically. Each available method is described briefly, together with its relative accuracy. All methods give comparable results and are equally valid, but IR spectrometry can be considered the most flexible and accurate VA content measuring technique.
Flow, pressure distributions, and internal forces in stacked‐disc filters
Authors: Body Max L.
Published: December 2004

A mathematical model is described for isothermal flow of Newtonian liquids through stacked‐disc filters. Dimension‐less flow rates, velocities through filter media, pressure distributions, and internal forces are shown as functions of resistance ratios and reduced dimensions. The distribution of velocities through the media is a strong function of the ratios of the resistances to flow through the gaps between discs and through the spaces inside the discs to the resistance to flow through the filter media. Internal forces compress the discs and can, in exceptional cases, impair the media and open up leakage passages.
Mathematical modeling of the blow‐molding process
Authors: Ryan M. E. , Dutta A.
Published: December 2004

A mathematical simulation of the blow‐molding cycle has been developed by combining general conservation principles along with appropriate constitutive relations for the material. A model of the parison formation stage has been devised by considering the competing effects due to swell and drawdown. A more rigorous numerical analysis of parison formation is also discussed. A theoretical treatment of parison inflation is described for both inelastic and viscoelastic materials by assuming uniform radial growth, Comparisons are made with experimental data for all phases of the molding cycle. The mathematical model is in reasonable quantitative agreement with experimental results and is capable of elucidating the influence of material properties and process conditions on the dynamics and performance of the blow‐molding process.
13C NMR characterization of intermolecular interactions for polymers. Part 3. Solvent effect on the blend compatibility of poly(vinyl methyl ether) and polystyrene
Authors: Djordjevic M. B. , Porter Roger S.
Published: December 2004

The solvent has an influence on the homogeneity of the poly(vinyl methyl ether)‐polystyrene, PVME‐PS blends Prepared by drying cosolutions. This influence has been analyzed in terms of the competition among polymer‐polymer and polymer‐solvent interactions. Model solutions have been prepared in which intermoleeular interactions correspond to the interactions in this blend and in some of the cosolutions. These interactions in the model solutions have been detected and identified by applying Rummens' method. The 13C NMR spectra have been determined for PVME and for styrene oligomer dissolved in n‐alkanes, cyclohexane, diethyl ether, isopropyl methyl ether, diisopropyl ether, and chloroform, and for PVME dissolved in benzene, toluene, and cumene. The chemical shifts have been plotted against the parameter g2 = [(n22 − 1)/(n22 + 1)]2, where n2 is the refractive index of the solvent. If the structural segment represented by certain carbon and some solvent has an interaction that is stronger than dispersive, the chemical shift for this carbon will deviate from the line formed by its shifts in n‐alkane solutions, these deviations indicate characters and intensities of the intermoleeular interactions. Results indicate that cyclohexane exhibits weak interactions with both of the polymers and does not interfere with their mutual interaction, leading to a compatible blend. Results also suggest that benzene and toluene interact in the PVME in the same manner as PS. This leads to a gradual increase of the number of polymer‐polymer interactions as the concentration of the polymers is increased by solvent removal, resulting in a compatible blend. Chloroform apparently interacts more strongly with PVME than with PS but interacts strongly enough with both to restrict interaction among the two polymers. As the concentration of polymers in the cosolution is increased, PS forms a separate phase. This leads to an inhomogeneous blend when the solvent is evaporated.
Compatibilization of the polystyrene/poly(ethyl acrylate) and polystyrene/polysoprene systems through ionic interactions
Authors: Eisenberg A. , Smith P. , Zhou Z.‐L.
Published: December 2004

Interactions between anions on one polymer chain with cations on another can lead to compatibilization of otherwise incompatible materials. Thus, if 5 mol% of ∼SO3H groups are attached to polystyrene, and 5 mol% of vinyl pyridine is copolymerized with ethyl acrylate, proton transfer occurs upon mixing, and the pairwise attractive interactions between the resultant ions compatibilize the blend. The same has been observed for the styrene‐vinyl pyridine and sulfonated polyisoprene polymer pair. Dynamic mechanical and optical properties are used as a measure of compatibilization.
Computer simulation of injection mold filling for viscoelastic melts with fountain flow
Authors: Kamal M. R. , Chu E. , Lafleur P. G. , Ryan M. E.
Published: December 2004

The ultimate properties of a molded article arc directly related In the microstructure of the article and are consequently influenced by the thermomechanical history experienced by the melt during processing. The mold filling behavior of thermopalastic polymer melts has been analyzed quantitatively by means of a computer simulation. The mathematical model is based on the equations of continuity, motion, and energy, along with appropriate constitutive relations and relevant initial and boundary conditions. The governing system of equations is solved numerically by means of a Marker‐and‐Cell computational scheme. One to the significant implications for microstructure development, the fountain effect at the advancing free surface is explicitly taken into consideration in the simulation. The model yields data on filling time and melt front position as well as velocity, temperature, pressure, and shear stress distributions within the mold cavity. The rearrangement of the velocity and temperature profiles in the vicinity of the melt front are considered in detail. Experimental studies have also been undertaken in order to verify the predictions of the computer Simulation.
Effects of stoichiometric mixing ratio on epoxy cure—a dielectric analysis
Authors: Day David R.
Published: December 2004

Variation of molar mix ratio of the Epon 828/Diamino‐diphenyl sulfone (DDS) system was found to have significant influences on pre‐cure and post‐cure properties. Microdielectrometry showed that dielectric constant varies from about 9 to above 30 depending on DDS content before cure. Times to the 10 kHz loss peak during cures at 177°C were found to decrease with increasing DDS content. Above a ratio of 2/1 and below 1/2, due to the low molecular weight of the reaction products, loss peaks did not occur. Ionic conduction was shown to have a strong correlation with calorimetric kinetic cure data. The influence of both excess amine and excess DDS was to produce cured material with high ionic conduction levels indicative of loose networks. Deviations from ideal stoichiometry as small as 1.1/1 produced noticable differences in the finally cured network.
The polymerization of a phenolformaldehyde resin in a porous glasswool composite
Authors: Järvelä Pentti K. , Törmälä Pertti , Purola Jaakko , Järvelä Pirkko
Published: December 2004

The polymerization of the phenolformaldehyde matrix material of porous glass fiber composites is of vital importance in the production of the composite; it also has an, essential effect on the strength properties of the composite, which correlate directly with the degree of polymerization. With a certain material combination, the optimal strength properties can be obtained by a suitable thermal treatment, which depends on the kinetics of the polymerization process. In this study we found that the highest strength values of the composite are obtained by making the polymerization (curing) rapid at a very high temperature using resins with a high degree of polymerization and a high dry matter content. As regards the structure of the composite, the factors that affect the polymerization process arc density, resin content, and thickness. The results obtained with this kind of a composite are valid within a density region of 600 to 1500 kg/m3. At lower densities, the polymerization process changes, since thermal convection plays a greater role, and at higher densities the insulating effect of porosity begins to decrease.
Chemorheology of an amine‐cured epoxy resin
Authors: Tajima Yuji A. , Crozier Donald G.
Published: December 2004

The objective of a chemoviscosity model of a thermosetting resin is to describe the change of viscosity for a temperature‐time program. A model is most advantageously developed by starting with a viscosity‐temperature relationship and then relating the parameters of this equation to the rate of polymerization. Thus, the chemoviscosity is related directly to the polymerization kinetics of the thermosetting resin and, thereby, to its chemical composition. Viscosity‐temperature relationships based on free‐volume theory such as the Williams‐Landel‐Ferry equation and the Vogel equation appear to fit the chemoviscosity of an amine‐cured epoxy resin more precisely than relation ships based on resin flow as an activated process.
Causes of edge beads in cast films
Authors: Dobroth T. , Erwin Lewis
Published: December 2004

Cast polymer films are extruded through a uniform thin slit onto a quench roll. Between the die and the quench roll, thick edges called edge beads form, which have to be trimmed from the film, and are often scrapped. The relation between edge beads and neck‐in is shown. Three causes of edge beads are discussed: surface tension, die swell, and an edge stress effect. Surface tension and die swell effects can be important in low viscosity and elastic materials respectively. The predominant cause of edge beads is an edge stress effect which occurs because the film is stretched between the die and the roll. The edge elongates in uniaxial stress while the center material elongates in plane strain.
Flow induced fiber orientation in an expanding channel tubing dies
Authors: Doshi S. R. , Dealy J. M. , Charrier J.‐M.
Published: December 2004

In the application of plastic pipes for fluid transport and for the protection of underground electrical cables, it is desirable to improve mechanical properties, particularly in the hoop direction. The use of orientable reinforcing particles such as chopped glass fibers could make possible such an improvement if the orientation of the fibers could be controlled. While conventional pipe extrusion dies tend to promote axial fiber orientation, the use of an expanding channel die has been proposed to produce a preferential hoop orientation of fibers. In this paper, a theoretical model of the flow of a fiber suspension through an expanding channel die that predicts the fiber orientation distribution at the die exit is described. The effects of Theological properties and die geometry on the final fiber orientation distribution are predicted. The results of an experimental study of fiber orientation in pipe extruded using an expanding channel die are shown to be in agreement with the theoretical predictions.
A mechanistic kinetic model for the initiated anionic polymerization ofϵ‐caprolactam
Authors: Cimini R. A. , Sundberg D. C.
Published: December 2004

The preparation of Nylon‐6 via the initiated anionic polymerization of EE‐caprolactam is characterized by rapid reaction rates displaying marked auto‐acceleration. A mechanistic approach has been taken to analyze the kinetics of this system and has resulted in the postulation that the auto‐acceleration is directly linked to a polymer chain degradation reaction. This reaction is significant even in the early stages of the polymerization and in many cases becomes the dominant mechanism for the production of reactive end groups, thereby controlling the overall reaction rate. A kinetic model is presented which is capable of differentiating between polymerizations carried out with different levels and ratios of catalyst and initiator, and contains but two rate constants—one for the propagation reaction and one for the degradation reaction. Predictions of the model are compared to experimental rate data derived from using both mono‐and difunctional initiators and close agreement is found.
Effects of water absorption on physical properties and degree of molecular orientation of poly (ethylene terephthalate)
Authors: Jabarin Saleh A. , Lofgren Elizabeth A.
Published: December 2004

Poly(ethylene terephthalate) (PET) is known to be a hygroscopic thermoplastic, which absorbs moisture from its environment at a rapid rate. The water absorption characteristics of PET as a function of relative humidity, exposure time, temperature, thickness, and molecular weight are reported here. Results indicate that absorbed moisture has significant influences on the physical properties of PET, leading to large decreases in the glass transition temperature, crystallization temperature, and degree of molecular orientation.
Mechanisms for variations in electrical properties of silicone rubber vulcanized by the condensation reaction
Authors: Yokoyama T. , Kinjo N. , Wakashima Y.
Published: December 2004

The electrical conductivity and the dissipation factor of silicone rubber vulcanized by the condensation reaction of α,ω‐dihydroxypolysiloxane with ethoxysilane, using dibutyltin dilaurate as a catalyst, were studied. Rubber specimens, with different amounts of catalyst, were prepared using various vulcanization times and then heat treated in dry or wet atmospheres containing oxygen and nitrogen. The electrical properties of these specimens were measured at 20 to 200°C in dry air. The amounts of residual catalysts and unreacted ethoxy groups were analyzed by colorimetric and gas chromatographic methods. Factors influencing the specimen electrical properties were discussed in terms of preparation conditions and amount of residual compounds.
Wire coating extrusion–an approximate solution
Authors: Tiu Carlos
Published: December 2004

An approximation method is proposed to predict the Mow rate‐pressure drop relation for isothermal laminar flow of any time‐independent fluid in wire coating extrusion. A geometric parameter method proposed earlier is used in predict the pressure‐driven flow in the annulus. The method is demonstrated for Newtonian, power law, and Ellis fluids. The accuracy of the method is shown by comparing the predictions with the theoretical and experimental results of Han and Rao. An expression for wire coating thickness is also given.
Study of polymer powder and melt rheology using a constant pressure, non‐isothermal rheometer
Authors: Lee Biing‐Lin
Published: December 2004

A rheological analysis is proposed on a non‐conventional, constant pressure, non‐isothermal rheometer. The test usually starts with a polymer powder and ends with melt extrudate. The volume‐ (or displacement of plunger) temperature curve of the test is analyzed according to the following model: (1) at a temperature below the glass transition temperature, the test is related to the packing and/or compaction of powders, and also the compressive deformation of powders; (2) as the temperature is raised to where polymer flow begins, the test is analyzed according to melt viscous flow. The activation energy of flow of a polymer may also be estimated using this rheometer. Comparison and correlation of data using other techniques (e.g. torsional pendulum dynamic measurement, capillary rheometer, Rheometric dynamic spectrometer) will also be discussed.
Analysis of transient sorption and permeation in heterogeneous media
Authors: Kang Yong‐Soo , Meldon Jerry H. , Sung Nak‐Ho
Published: December 2004

Experimental data on hexane vapor sorption in phase‐segregated polybutadiene/polystyrene blends are reported, which exhibit seemingly non‐Fickian characteristics that previous workers with styrene/butadiene copolymer attributed to a diffuse interphase. These data, plus results derived from a model of sorption in heterogeneous media containing a slowly permeable dispersed phase, indicate that the mere presence of two phases with different diffusion time constants is a sufficient condition for apparently non‐Fickian overall behavior. Consequently, definitive morphological inferences cannot be drawn from such observations. In addition, results of modeling the corresponding permeation process are analogous to those obtained in an earlier study of permeation with immobilizing chemical reaction.
Creep and recovery behavior of a linear high density polyethylene and an ethylene‐hexene copolymer in the region of small uniaxial deformations
Authors: Crissman J. M.
Published: December 2004

The results of creep and recovery experiments are reported for two types of polyethylene—one a linear high density homopolymer, and the other an ethylene‐hexene copolymer. Data were obtained at temperatures in the range 23°C to 57°C and creep times of 10 s to 4.33 × 105 s. In order to approximate constant true stress conditions, all of the experiments were carried out at the same value of applied stress (4 MPa) and the change in strain during creep was in all cases less than 2 percent. Comparison of these results with the results from earlier work on an ultra high molecular weight polyethylene shows that there is a great similarity in the behavior of all three materials, and the behavior of all three can be described quite well by a one‐dimensional equation consisting of two terms—one a hereditary term and the other a plasticity term. It is further shown that to a very good approximation the idea of time‐temperature superposition can be applied to the description of the hereditary term.
Temperature changes in poly(methyl methacrylate) and high‐density polyethylene during rapid compressive deformation
Authors: Rodriguez E. L. , Filisko F. E.
Published: December 2004

The adiabatic temperature changes for poly(methyl methacrylate) (PMMA) and high‐density polyethylene are reported as the result of rapid compressive stress applications at different temperatures. A specially‐modified Instron capillary rheometer was used in the experiments. Results were examined by determining the experimental thermoelastic coefficients (δT/δ). These were compared with the predicted coefficients from the equation (δT/δ) = ∝LTo/ρCp. Good agreement was found for ambient temperature, and deviations were found for higher temperatures. High‐density polyethylene showed higher temperature changes than PMMA, the causes for which are also discussed.
Integral sorption with induced crystallization
Authors: Durning C. J. , Rebenfeld L. , Russel W. B.
Published: December 2004

We studied the integral sorption of saturated, organic vapors in amorphous films of poly (ethylene terephthalate) (PET) using a spring balance apparatus. The penetrants employed (methylene chloride [MeCl2] and N. N. dimethyl formamide [DMF]) induce substantial crystallization of the polymer during sorption. The experimental data (mass of vapor absorbed versus exposure time) do not obey Fick's law for diffusion but reflect the influence of time dependent polymer swelling and crystallization. The data show that polymer swelling controls the penetrant transport in thin films, while molecular diffusion in the highly swollen semi‐crystalline polymer controls in thick films. Small activation energies were found for transport in thin films suggesting that ductile deformation controls the swelling in PET. A mathematical model developed previously explains the important features of the experiments.
A molded deep‐UV portable conformable masking system
Authors: Lin B. J. , Chao V. W. , Petrillo K. E. , Yang B. J. L.
Published: December 2004

A second‐generation capped deep‐UV portable conformable masking system Is described. Two major improvements of this system are; (1) The replacement of the PMMA bottom layer with the PMMA‐MA‐MAN terpolymer which has a higher thermal stability and a higher deep‐UV sensitivity. (2) The application of the mold hardening process to eliminate the “wings” protruding from the novolac‐terpolymer interface, to facilitate a better choice of developers for the bottom layer, and to provide a better refractive index match between the novolac image lines.
Radiation‐induced reactions of ring‐substituted polystyrenes analyzed by radiolysis of low molecular‐weight model compounds
Authors: Tanigaki Katsumi , Tateishi Kazuo , Ohnishi Yoshitake
Published: December 2004

Radiation‐induced reactions of polystyrene derivatives have been studied by the radiolysis of ring‐substituted isopropylbenzene derivatives, i. e., 4‐amino. 4‐hydroxy, 4‐methoxy, 4‐methyl, 4‐chloromethyl, 4‐chloro, and 4‐acetyl derivatives. Low‐temperature ESR analyses measured at 77 K indicate that. In general, the a‐position is the most sensitive site to radiation and that thus a‐radicals are produced through a‐hydrogen removal. However, among these derivatives, the amino, acetyl, chloromethyl, and. chloro derivatives undergo different reactions from the other derivatives. A phCOCH3 cleavage from the‐ acetyl derivative and NH cleavage from the amino derivative occur, and chlorine removal takes place from the chloro‐methyl and chloro derivatives. Final products detected by gas chromatography‐mass spectrometry indicate not only that radiation‐induced free radical recombination occurs. but also that if chlorine is produced by radiation, hydrogen abstraction by radiation‐induced chlorine takes place prior to the free radical recombination. The susceptibility of each derivative to hydrogen abstraction by radiation‐induced active chlorine increases, as the electron‐donation of ring‐substituents is increased. Based on the clarified reaction mechanism, the design of polystyrene derivatives as resist materials is discussed and two new types of resist systems are described. One is a new chloromethylstyrene based blend resist, which is formulated from poly(4‐meth‐oxystyrene) and poly(4‐chloromethylstyrene). The other is a new non‐swelling alkaline developable negative resist, which is formulated from poly(4‐hydroxystyrene) and a chlorine‐releasing compound.
Optimal developer selection for negative acting resists
Authors: Novembre A. E. , Masakowski L. M. , Hartney M. A.
Published: December 2004

A methodology for determining the optimal single component developer/rinse pair for a negative acting resist is described. This method is applicable to any resist basing its negative action on crosslinking and development in organic based solvents. Within the method, initial developer/rinse candidates are identified by utilizing the Hansen 3‐dimensional solubility parameter model. This model provides a thermodynamic solubility picture of the resist, and determines those developers which will only minimally contribute towards swelling of defined features. Developer/rinse pairs are subsequently evaluated for acceptable resist dissolution kinetics, and compatibility with existing spray development processes. The optimum developer/rinse pair will only minimally effect changes in temperature which result in a minimum sensitivity to relative humidity variations. The use of this method is illustrated by choosing an optimal developer/rinse system for a chlorine containing, styrene based negative acting resist. The overall electron beam lithographic performance of this resist is shown to be improved with respect to a previously used 2‐component ketone based developer.
Phase decomposition phenomena in polystyrene/(polyvinylmethylether)
Authors: Han C. C. , Okada M. , Muroga Y. , Bauer B. J. , Tran‐Cong Q.
Published: December 2004

This paper reports studies on polystyrene/poly‐(vinylmethylether) blends to elucidate phase decomposition phenomena. Small angle neutron scattering (SANS) and temperature jump light scattering (TJLS) techniques were used to study both static and kinetic properties. The SANS methods were used to characterize the blends with respect to phase diagram, the Flory‐Huggins interaction parameter, and the critical fluctuation length as a function of temperature. From the TJLS experiments, we have demonstrated the possibility of two kinds of phase decomposition mechanisms which should lead to distinct morphology and material properties.