bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of positive photosensitive polyimide precursors
Authors: Kubota Shigeru , Yamawaki Youko , Moriwaki Toshimoto , Eto Shohei
Published: December 2004

This paper is concerned with the study of the positive photosensitive polyimide precursors, and deals with monomer synthesis, polymerization, and characterization. The polymers were prepared from diamines and diaeid chlorides whieh were derived from the reactant with biphenyltetracarboxilic dianhydride and o‐nitrobenzyl alcohol. The molecular weights of the polymer were controlled by adjusting the monomer stoichiometry. The photoreaction of the polymers was confirmed from the change in IR spectra between the film exposed and unexposed to UV light from a HgXe lamp. The exposed areas of the film dissolved in alkaline solution, forming the positive tones. There was a marked difference in sensitivity between the polymers having different molecular weights. Their sensitivities decrease as their molecular weights increase. Further, there was a difference in the thermal behavior. Imidization temperature was shifted to a high temperature side and thermal stabilities increased with an increase in molecular weight.
Photochemical image enhancement for 0.5 μm g‐line lithography
Authors: Sheats James R.
Published: December 2004

Materials and processing are described that provide 0.5 μm resolution with between 1 and 2 μm total depth of focus using a 436 nm stepper with 0.42 N.A., using the previously described PIE process (SPIE 631, 171 (1986)); 0.4 μm lines, spaces, and line/space gratings were reproduced. The chemistry is based on the photobleaching of anthracene derivatives in the presence of oxygen, followed by a deep‐UV pattern transfer exposure under nitrogen. Although resolution and process control are quite good, the exposure time of 1.2 s is somewhat long due to the limited oxygen permeability of the chosen polymer; in addition the strong unbleachable absorbance of the deep‐UV resist limits the usable thickness to ∼500 nm. Materials have been identified that promise to overcome both limitations, yielding thicknesses of 1 μm or more and exposure times less than 500 ms. Application to 365 and 248 nm imaging is also possible.
An experimental study of distributive mixing in fully intermeshing, co‐rotating twin screw extruders
Authors: Kalyon Dilhan M. , Sangani Harish N.
Published: December 2004

Co‐rotating twin screw extruders are widely used for various mixing and reactive extrusion tasks in polymer processing operations. In this study, the prevailing mixing mechanisms of various screw elements employed in co‐rotating twin screw extrusion process, including regular flighted, and reverse and forward kneading disc elements, were experimentally investigated. A direct goodness of mixing technique based on pigmented thermoplastic elastomers and computerized image analysis was used. The results were elucidated in conjunction with mixing indices suitable for image analysis and the continuous mixing process. Significant differences in the distributive mixing characteristics of various screw elements were revealed.
Shear‐Induced orientation in liquid crystalline polymers
Authors: Kenig S.
Published: December 2004

The orientation development characteristics in shear flow of wholly aromatic thermotropic liquid crystalline polymers were studied. Based on the analysis of shear flow in a capillary followed by elongational flow, an experimental setup has been proposed to determine the shear‐induced orientation. Experimental results have indicated that shear‐induced orientation depends on total shear strain. However, orientation enhancement due to shear flow is much less effective compared with orientation buildup in the case of elongational flow. Thermotropic liquid crystalline polymers that exhibited higher orientability in elongational flow exhibited also higher orientability in shear flow. Finally, to obtain high, shear orientation in processing of thermotropics, special care should be exercised in the design of dies and molds and in optimizing processing conditions, so that high shear rates and/or long shearing times should prevail.
How coating/polymer properties affect fiber/cable performance
Authors: Skutnik Bolesh J.
Published: December 2004

The selection of the coatings/polymers used to fabricate optical fibers has been shown to be very important in determining their optical, mechanical, and connectorization performance. Material properties such as refractive index, optical transmission, and thermal coefficient of linear expansion are critical for coatings functioning as cladding materials. Coating adhesion to the glass surface, water absorption and water vapor permeation, as well as the ability to passivate the glass surface, have strong affects on the strength and fatigue behavior of fibers. Hard, thin, adhesive primary coatings are beneficial in making connectorization easier and more reliable.

Many of the preferred properties for the fiber coating are different from those preferred for electrical wire, not only because light must be transmitted rather than electricity, but also because of the brittle nature of the silica substrate and the coupling between physical displacements and light transmission within the guiding material (microbend effects).

The selection of cable materials is quite similar to that employed in the electrical wire and cable field. Much more attention must be given to cable design than for the latter. Designs/applications requiring tight jacketed or filled cables put special constraints on the selection of materials for the optical cables, which are more restrictive than for electrical cables.
The effect of temperature dependent materials properties on fiber optic cable design
Authors: Grant Susan C. , Zimmermann Bernd D. , Coupe Kelly L.
Published: December 2004

Young's Modulus and the thermal expansion coefficient are material parameters used to predict the low temperature contraction of a fiber optic cable. In the past, room temperature values for these properties were used to estimate this contraction. In this paper, these properties have been determined as functions of temperature. Using these properties, the overall expansion coefficient of the cable was determined as a function of temperature. This overall coefficient was integrated from room temperature to the low operating temperature of the cable to predict the contraction of the cable. In this way, the temperature variations in the materials properties were incorporated into the design, resulting in a more accurate determination of the low temperature contraction of fiber optic cable.
Plastic molded single and ribbon type optical fiber connectors
Authors: Inada K. , Yokosuka H.
Published: December 2004

Two types of precisely molded fiber optic connectors have been developed. They are a cylindrical ferrule connector for a single fiber and a five‐fiber array connector for a tape fiber. The connectors are made by using a transfer molding technique with a silica‐filled thermosetting epoxy resin. The resin has low pressure and high melt‐flow characteristics, high dimensional accuracy, and high stability. The single fiber connector consists of a pair of plastic molded ferrules, a slitted alignment sleeve, and a plate spring. A fiber is inserted into a ferrule capillary and is fixed with adhesive. Then the fiber end face positioned in the center of the ferrule is polished to have a mirror surface. The five‐fiber connector consists of a couple of precisely molded ferrules, two alignment pins, and a plate spring. The five‐fiber ribbon is inserted into fiber receiving capillaries, of the ferrule, and fixed with adhesive. The fiber end faces on the ferrule mating face are polished to have a mirror face. In order to realize a low‐loss connection, the alignment pin holes and five‐fiber positioning capillaries on the ferrule mating face must be molded precisely. Various kinds of reliability tests on the connectors were conducted. All the results obtained proved that the connectors have entirely satisfactory properties for practical use. The connectors are now widely used in an optical fiber subscriber network.
Materials for nonlinear optics‐orientationally ordered polymer films
Authors: Sohn J. E. , Singer K. D. , Kuzyk M. G. , Holland W. R. , Katz H. E. , Dirk C. W. , Schilling M. L.
Published: December 2004

Emerging guided‐wave integrated optical technologies require suitable active devices and optical interconnects. Certain organic molecular materials possess the required optical nonlinearities for application in active devices. Glassy polymers, such as poly(methyl methacrylate), have been used to fabricate high optical quality passive structures. For application in integrated optics, requirements include high optical quality (low scattering and absorption losses), low dielectric constant, and suitable fabrication techniques.

We describe the preparation and optical properties of a new material, class, poled polymer glasses, which combines the attractive properties of the optical nonlinearities of organic molecules and the optical quality of polymer glasses. These materials are formed by incorporating organic compounds possessing large optical nonlinearities into a host material lacking long‐range order. The orientational order is imparted to the composite system by applying a strong electric field at a temperature above the glass transition temperature, where molecular motion is enhanced, thereby aligning the optically nonlinear dopant molecules. By cooling the material through the phase transition with the field still applied, the orientational order is frozen in, and the composite material possesses second‐order nonlinear optical properties.
Effect of temperature and shear rate on polyisoimide solution viscosity
Authors: Levinson William , Czornyj George , Capo Donald , McMahon Jeffrey
Published: December 2004

The following models describe the effect of temperature and shear rate on the viscosity of polyisoimide solutions.

Data was obtained for 20, 30, and 40% polyisoimide solutions in 20:80 tetrahydrofuran/diglyme and for a 30% solution in N‐methyl‐pyrrolidone at temperatures of 25°, 35°, 55°, and 75°C. The measurements were taken on a Brookfield cone and plate viscometer at shear rates ranging from 9.59 to 383.4 reciprocal seconds. Experimental data fits model (1) reasonably well. In some cases, model (2) provides a better fit. This model accounts for temperature dependencies in the power law shear‐thinning exponent.

The coefficients β depend on the material lot that is being tested even though the lot molecular weights are very close. Slight differences in acid functional group concentrations for this particular material are a possible explanation.
On the slip phenomenon of polymeric solutions through capillaries
Authors: De Vargas L. , Manero O.
Published: December 2004

The slip phenomenon through capillaries has been analyzed experimentally using solutions of polyacrylamide and xanthan gum. These polymeric solutions present macromolecules with different conformations in flow. Attention was given to the influence of molecular conformation of those polymeric solutions upon the slip velocity. Considerable variations on the slip velocity were observed when the ionic strength of the xanthan solution was increased and also when the material of the capillaries was changed. Measured magnitudes were much larger in the xanthan solutions than those observed in the polyacrylamide solution.
Effects of physical aging on dynamic mechanical and transient properties of polyetheretherketone
Authors: Wang S. F. , Ogale A. A.
Published: December 2004

The effects of physical aging on dynamic mechanical and transient stress‐relaxation properties of a high performance thermoplastic, polyetheretherketone (PEEK), are reported in this study. The aging effects are shown to be physical effects (and not chemical degradation) by establishing thermoreversibility of the aging process. The unique aspect of the present study is the simultaneous investigation of both dynamic and transient properties in the same mode of loading, namely, in shear. The influence of continuous dynamic deformation on the aging process is also reported. The results for the aging rate, obtained from dynamic and transient testing under shear load, agree with one another and verify the equivalence of dynamic and transient viscoelastic properties. However, these results differ significantly from the aging rate results reported in an earlier study for tensile loading. A possible explanation for the difference has been proposed in terms of the volume change that accompanies tensile creep deformation.
Modeling the chemorheology of thermosetting resins during processing
Authors: Martin G. C. , Tungare A. V. , Gotro J. T.
Published: December 2004

The curing conditions determine the rheological changes in the resin during the lamination of prepregs into multilayered circuit boards. In order to specify the optimum curing conditions during lamination, it is necessary to understand the rheology of the resin as it cures. In this study, the chemorheological behavior of two commercial epoxy resins and one cyanate‐based resin was characterized using an engineering model for the resin viscosity. A linear regression technique was used to evaluate the model parameters from the conditions at the minimum viscosity obtained during resin cures at constant heating rates. The technique was extended to predict the minimum viscosities reached by the resins when subjected to temperature conditions commonly encountered during lamination. The utility of the technique for specifying the curing conditions necessary to have a desired resin flow during lamination and for selecting resin systems for lamination based upon chemorheology has been demonstrated.
An experimental study of the dynamics of the curing process of sheet molding compound (SMC) paste
Authors: Kau Hua‐Tie
Published: December 2004

The dynamic curing behavior of sheet molding compound (SMC) has been investigated by using a cylindrical cure reactor. Both thermal and mechanical responses were determined for R‐25 SMC paste. The responses from this material were analyzed to determine the chemical and physical transformations that occur during the SMC molding process. The thermal response was obtained from a thermocouple placed along the centerline of the paste sample in the cure reactor. The thermal history at this location shows distinctive stages associated with heat transfer and crosslinking reactions during the cure cycle. The R‐25 paste has a precure time of 160 seconds, a reaction time of 25 seconds, and a temperature rise of 134°C. The mechanical response describes the volume change and the pressure of the paste. The displacement curve shows volume changes due to thermal expansion, cure shrinkage, and thermal contraction during the course of a cure cycle. We found a less than 1% shrinkage during the reaction of the R‐25 paste. The pressure response of the paste was found to parallel the volume transformation, although it also is strongly influenced by mechanical interactions between the press and the paste.
Repairability of plastic automobile bumpers by hot gas welding
Authors: Atkinson J. R. , Turner B. E.
Published: December 2004

Problems associated with the repair of fractured plastic car bumpers by traditional hot gas welding have been identified. In particular, interfacial cracks arising due to contraction stresses, weld pores, root notches, and voids in filler rods have been observed. These result in welds with inferior mechanical properties. Even so the impact properties and strength of plastic bumpers which were fractured and have been repaired by hot gas welding are likely to be acceptable for the purposes that the bumpers are intended. We have considered three materials: a polycarbonate/polyester blend, poly(butylene terephthalate), and an ethylene‐propylene‐diene rubber. Improvements in weld strength and interfacial bonding arise if a heated roller immediately following the welding torch is used to consolidate and compress the molten plastic. Porosity is reduced if the hot gas can escape easily from beneath the weld.
Synthesis and physical behavior of siloxane modified polyimides
Authors: Arnold C. A. , Summers J. D. , McGrath J. E.
Published: December 2004

A variety of thermoplastic fully imidized poly(imide siloxane) segmented copolymers with useful thermal and mechanical properties have been prepared. Other interesting properties described are the materials' hydrophobic character, surface domination, UV stability, and atomic oxygen plasma resistance.
Characterization and cold compaction of polyether‐etherketone powders
Authors: Reilly J. J. , Kamel I. L.
Published: December 2004

This study deals with the characterization and cold compaction of polyetheretherketone (PEEK) powders. Four different types of PEEK powders which are commercially available from Imperial Chemical Industries (ICI) were characterized for density, crystallinity, particle size, particle size distribution, and particle morphology. Fine and coarse size powders of a low viscosity grade (150PF and 150P) and similar powders of a high viscosity grade (450PF and 450P) were processed. Compaction was successful at room temperature using the 150 grade powders but not with the 450 grade powders. Compressibility curves were obtained at room temperature for the 150 grade powders and their post‐compaction viscoelastic recoveries were measured. The coarse and fine size 150 grade powders reached relative plateau densities of 95.8% and 95.1%, respectively, when compacted at pressures exceeding 300 MPa. These high densification values at room temperature were associated with minimal post‐compaction viscoelastic recoveries and as‐compacted strengths as high as 8.9 MPa. A modified densification parameter (DP*) was developed based on the plastic deformation of the crystalline regions alone. This new dimensionless parameter, DP*, demonstrated a better fit of all the compaction data. The transverse rupture strength and the green density data are presented and explained in terms of this DP*.
Structure‐property relationships in rubber‐toughened epoxies
Authors: Hwang J.‐F. , Manson J. A. , Hertzberg R. W. , Miller G. A. , Sperling L. H.
Published: December 2004

Epoxies toughened with two reactive liquid rubbers, an epoxy‐terminated butadiene acrylonitrile rubber (ETBN) and an amino‐terminated butadiene acrylonitrile rubber (ATBN), were prepared and studied in terms of their structure property relationships. A two‐phase structure was formed, consisting of spherical rubber particles dispersed in an epoxy matrix. A broad distribution of rubber particles was observed in all the materials with most of the particles ranging in size from 1 to 4 μm, but some particles exceeding 20 μm were also found. Impact strength, plane strain fracture toughness (KIC), and fracture energy (GIC) were increased, while Young's modulus and yield strength decreased slightly with increasing rubber content and volume fraction of the dispersed phase. Both GIC and KIC were found to increase with increasing apparent molecular weight between crosslinks and decreasing yield strength. The increased size of the plastic zone at the crack tip associated with decreasing yield strength could be the cause of the increased toughness. An ATBN‐toughened system containing the greatest amount of epoxy sub‐inclusion in the rubbery phase demonstrated the best fracture toughness in this series. In the present systems, rubber‐enhanced shear deformation of the matrix is considered to be the major toughening mechanism. Curing conditions and the miscibility between the liquid rubber and the epoxy resin determine the phase morphology of the resulting two‐phase systems. Kerner's equation successfully describes the modulus dependence on volume fraction for the two‐phase epoxy materials.
Biaxially oriented films prepared from poly(vinyl chloride)/poly(methyl methacrylate co imide) blends
Authors: Kotnis Mahesh A. , Spruiell Joseph E.
Published: December 2004

A study was conducted of blends of poly(vinyl chloride) (PVC) with a poly(methyl methacrylate co imide). The latter polymer was found to be miscible in PVC and to raise the glass transition temperature of the blend. Blends of all compositions could be oriented, but the processing temperature increased in proportion with Tg. For a given blend composition, orientation increased with increasing stretch ratio and strain rate and with decreasing stretch temperature. Increasing copolyimide content and increasing orientation generally lead to improved mechanical properties, though the blends containing high levels of copolyimide exhibited low ductilities.
Craze dissemination during fatigue fracture in polystyrene
Authors: Botsis J. , Gregory B. L.
Published: December 2004

Results of studies on fatigue fracture in polystyrene are reported. Experiments were carried out on tension‐tension single edge notched specimens, 0.25 mm thick. Macroscopic studies involved the propagation of the crack and its associated active zone (or the so‐called process zone) evolution. Microscopic studies consisted of fracture surface examination and quantitative characterization of the crazing distribution along the trailing edge and within the active zone. The width and length of the active zone increased monotonically during the quasi‐static phase of crack layer growth. The crack growth kinetics followed an S‐shaped curve. Analysis of crazing distribution showed that; (i) the distribution of crazing along the trailing edge of the active zone is related by a scaling parameter, (ii) the average crazing density along the trailing edge as well as within the active zone is constant, (iii) the specific energy of crazing evaluated here compares well with previously reported data. The results of this work support the form of self similarity of damage evolution adopted by the crack layer model, and that the specific energy of damage is a material constant.
Statistical model for predicting the strength of solid‐filled rubbers
Authors: Chen U. D. , So H.
Published: December 2004

The tensile strength of solid‐filled rubbers is predicted by the statistical model proposed in this paper, by which the maximum area fraction of the solid filler in a representative cube is calculated. The minimum net cross‐section area of the rubber matrix is thus obtained, and this is used to calculate the reduction in strength of the compound in comparison to that of the unfilled rubber. The prediction is then tested by experiments using hydroxyl‐terminated polybutadiene (HTPB) filled with glass spheres. After curing, tensile specimens were cut from sheets and exposed to humidity‐controlled environments so as to debond the filler particles from the rubber matrix, and were tested in tension. The experimental results were found consistent with the predictions.
Statistical procedure to identify sources of extrusion line variation
Authors: Stevenson J. F.
Published: December 2004

A statistical procedure is proposed to identify sources of variation in the operation of complex extrusion lines. This approach involves separating multichannel extrusion line data, as necessary, into appropriate time scales; identifying significant cross correlations among various pairs of channels; and then comparing the pattern of the observed cross correlations with those expected for possible sources of variation. This procedure is able to detect unsuspected relationships among processing variables and to provide a rational basis for upgrading extrusion line performance. The pattern generation and comparison methodology could also be useful for expert systems. To illustrate the procedure, 11 channels of data from a dual extrusion line with metered feed were collected and analyzed. Since two sources of variation on different time scales were evident, the data were divided into long‐term and short‐term components using statistical methods. Cross correlation functions among pairs of variables were used to estimate offset times and identify variables that were significantly correlated. To be considered significant, the extremum in the cross correlation function had to occur at a realistic time offset and have an absolute value exceeding a prescribed threshold. The observed cross correlations between pairs of short‐term and of long‐term components were compared with the expected correlation patterns for typical process disturbances. By this procedure, the cause of the short‐term trends was identified as surging primarily in the larger extruder; a particular long‐term trend was attributed to a property change in the feed material to the smaller extruder. This analysis formed the basis for a novel process control device to minimize the consequences of short‐term variation in extruder output.
Strength and bonding mechanisms in vibration‐welded polycarbonate to polyetherimide joints
Authors: Stokes V. K. , Hobbs S. Y.
Published: December 2004

Under the right conditions, high strengths are shown to be achievable in vibration welded polycarbonate to polyetherimide Joints. While welding of thermoplastic interfaces of the same material can be understood in terms of interchain diffusion at elevated temperatures, this mechanism is severely limited in the case of dissimilar materials. Scanning electron microscopy is used to show that part of the bond strength in such dissimilar materials results from mechanical interlocking of the two polymers, which is caused by viscous mixing. The effects of the weld parameters on the weld morphology are considered in detail.
Microspheres and microcapsules: A survey of manufacturing techniques. Part 1: Suspension cross‐linking
Authors: Arshady R.
Published: December 2004

A methodological survey of preparation of microspheres and microcapsules by suspension cross‐linking is presented. Thus, basic features of suspension cross‐linking, i.e., the formation of small droplets of a polymer solution (or melt) in an immiscible liquid followed by hardening of these droplets by covalent cross‐linking, are discussed. Typical microspherical and microcapsular products manufactured by suspension cross‐linking of naturally occurring and preformed synthetic polymers, including agarose and cellulose beads, albumin microspheres and microcapsules, polystyrene beads and epoxy resin microcapsules, are described. Manufacturing parameters controlling microsphere/microcapsule characteristics are also briefly outlined.
3‐D structure‐property relationships in rolltruded polymers. Part II: Anisotropic yielding and deformation in triaxially oriented polymers
Authors: Sun D. C. , Berg E. M. , Magill J. H.
Published: December 2004

Rolltrusion, a single step solid state deformation process, has been successfully applied to isotactic poly(propylene), iPP, to produce unique 3‐D properties. Mechanical property enhancement not only occurs in the principal draw direction, but also in the transverse directions. A systematic series of standard (ASTM) tensile and compressive experiments were made on well oriented materials supporting this claim. Tensile testing was also performed on dumb‐bell shaped specimens cut at various angles to the main deformation direction. A variety of observations were made during testing. Deformation bands, anisotropic yielding, and ductile‐to‐brittle behavior were observed. These results are presented along with a morphological model that has been developed to account for the behavior of these unique triaxially oriented polymers.
Viscous dissipation effect on solidification of a liquid onto a tube wall
Authors: Ahmadian M. Taghi , Burmeister Louis C.
Published: December 2004

The effect of viscous dissipation on solidification onto the inner surface of a straight circular tube of a liquid flowing laminarly with a specified volumetric rate is analytically determined. Steady conditions and a constant tube wall temperature below the solidification temperature of the liquid are assumed. Solutions for the thickness of the solidified shell and for the pressure drop are obtained. The pressure gradient versus volumetric flow rate curve exhibits a minimum, suggesting that it might be possible to design runners for injection molding machines to have a minimum pressure drop if the volumetric flow rate is specified.
Optimization of injection molding design. Part I: Gate location optimization
Authors: Pandelidis Ioannis , Zou Qin
Published: December 2004

The placement of a gate in an injection mold is one of the most important variables of the total mold design. The quality of the molded part is greatly affected by the gate location, because it influences the manner in which the plastic flows into the mold cavity. Some defects, such as weldline and overpack, can be effectively controlled only by the gate location. Therefore, the product quality can be greatly improved by determining the optimum gate location. In this paper, we develop a general methodology for gate location optimization. We first quantify quality in terms of flow simulation outputs. We can thus assess detrimental effects such as warpage and dimensional instability as a function of the independent variable, which is in this case the gate location. Next we develop methods to search for the optimum gate location. The search method introduced in this paper is a method that combines a deterministic hill climbing search with a stochastic annealing search method. The method is appropriately called simulated annealing and hill climbing (SANHIL). The criteria used for evaluation during the search process are a function of the flow simulation outputs. We demonstrate the success of the method for a complex industrial mold. The approach is applicable to any complex mold geometry and any plastic.
An accelerated method for establishing the long term performance of polyethylene gas pipe materials
Authors: Popelar C. H. , Kenner V. H. , Wooster J. P.
Published: December 2004

It was demonstrated in a previous investigation that both horizontal and vertical shifting is required to produce master curves for the relaxation moduli from elevated temperature data for polyethylene gas pipe materials. In this study, the shift functions obtained from these stress relaxation tests are applied to an assortment of elevated temperature time‐dependent failure data for a variety of medium and high density polyethylenes. In all cases the data are successfully shifted to produce coherent master curves within the intrinsic scatter of the original data sets. The implication is that these horizontal and vertical shift functions are, for all practical purposes, universal for polyethylene gas pipe materials. This finding provides the basis for interpreting elevated temperature test data for polyethylene pipe materials so that a substantial savings in cost and time may be achieved in assessing the performance, structural integrity, and life expectancy of piping systems made from these materials.
Optimal temperature profiles for methylmethacrylate polymerization in the presence of end point constraints
Authors: Vaid Nitin R. , Gupta Santosh K.
Published: December 2004

Optimal temperature histories have been obtained for methylmethacrylate polymerization using a kinetic model incorporating gel and glass effects. The minimum end time problem has been studied, with end point constraints on monomer conversion and the number average chain length, μn. The optimization algorithm used is efficient and easy to use. It is found that the optimal temperature histories obtained when the desired chain length lies beyond the maxima in the μn vs. time plot differ qualitatively and significantly from those obtained when the desired μn lies before the maxima.
Flow visualization of the influence of compatibilizing agents on the mixing of elastomer blends and the effect on phase morphology
Authors: Setua Dipak K. , White James L.
Published: December 2004

The effect of several different potential compatibilizing agents on the rate of mixing and phase morphologies of immiscible blends of ethylene propylene (EPM) and acrylonitrile‐butadiene (NBR) copolymers of varying nitrile content is described. Flow visualization investigations using an internal mixer with glass windows have been used to show that these agents increase the rate of homogenization of EPM‐NBR blends. A scanning electron microscopy (SEM) study on the morphology of the EPM‐NBR blends shows that the choice of a suitable compatibilizing agent results in a final dispersion of NBR particles inside the EPM phase with an average size even as low as 0.5 to 1 μm. Chlorinated polyethylene (CM) has been found to be the most effective in increasing mixing rate and reducing the scales of morphology. However, for NBRs with low acrylonitrile concentration, chlorosulfonated polyethylene (CSM), polychloroprene (CR), hydrogenated nitrile (HNBR), arid polybutadiene (BR) were also found to act as suitable compatibilizing agents.
Rheological characterization of fast‐reacting thermosets through spiral flow experiments
Authors: González U. F. , Shen S. F. , Cohen Claude
Published: December 2004

The standard spiral flow test is normally used to assess the “moldability” of thermosetting materials. It is proposed that such tests can be modified and analyzed to yield rheological information as from a viscometer. Specifically, a “parameter‐identification” scheme is developed to determine the constants in a viscosity model by minimizing the difference between the outcome of spiral flow tests and the results of numerical simulations of these tests. The proposed scheme is particularly applicable to fast‐reacting thermosets for which typical viscometers cannot be used. Successful application of the scheme is demonstrated for a particular encapsulating epoxy material, where constants are obtained for a modified WLF equation viscosity model. These constants are used to predict the outcome of spiral flow experiments not involved in the minimization procedure. A favorable comparison between experiment and simulation occurs at most operating conditions. The method requires no elaborate equipment or delicate instrumentation.
Simulation of polymer flow through a coat‐hanger die: A comparison of two numerical approaches
Authors: Arpin Benoit , Lafleur Pierre G. , Vergnes Bruno
Published: December 2004

Coat‐hanger dies are commonly used for the extrusion of plastic sheets and films. To describe the flow of a molten polymer through a coat‐hanger die, a two‐dimensional approach is necessary. Moreover, the thermal effects, which play an important role in the flow distribution, have to be taken into account. In this paper, two numerical models for the simulation of coat‐hanger dies are described and compared. These models differ mainly in the simplifying assumptions used and in the treatment of the thermal problem. The simulations obtained with the two models were compared with each other and with experimental data. The discrepancies between the two models can be explained by the different theoretical treatments.
Compressional behavior of inked open‐cell foams
Authors: Phillips J. C. , Auslander J.
Published: December 2004

The mechanical behavior of various classes of inked and non‐inked (dry) open‐cell foam rollers has been investigated from stress/strain measurements in compression. Hysteresis, creep, and recovery in dynamic loading were used to differentiate the rollers as to their utility in printing applications. Creep, ϵc(t), and recovery, ϵr(t), were determined in a compression mode from force measurements and strain decay, ϵ(t), i.e., Δϵc(t) = ϵ0 – ϵ(t) [ϵ0 = ϵ(t = 0)] or ϵc(t) = 2ϵ0 – ϵ(t). The creep function, Δϵc(t), represents the plastic strain, ϵpl(t = th), and is uniquely defined from the recovery function, Δϵc(t) = ϵr(t = th), where th is the hold or contact time. The recovery results for a polyurethane ester (PUE) and acrylonitrile/butadiene (AB) rollers (dry/ink), poly(vinylidene fluoride) film (PVF2) (air/vapor) and low‐density polyethylene film (LDPE) (air/vapor) were found to fit a master curve of the form Fr(θ) = EXP[‐Kr(th)θ] = [ϵr(t) – ϵ∞(th)]/[ϵ0(t = O) – ϵ∞(th)] at a reduced time of Kr(th)θ {θ = t/th and Kr(th) = k′r(th)th = C0/(th)α−1 (where C0 depends on the material's “dry” or “wet” state, α is a function of the type of material, and ϵ∞ is the permanent set). These empirical results are consistent with the observed decreases in print intensity during transfer to a paper substrate and weight changes of the roller, i.e., creep and recovery are important in the printing characteristics of a given roller material. Other factors of importance in the overall transfer and print quality, but of longer‐term considerations, are diffusion processes within the polymer and the nature of the polymer (e.g., porosity, chemical constitution, surface and interfacial tensions).
Characterization of thermotropic liquid crystalline polyester/polysulfone blends
Authors: Golovoy A. , Kozlowski M. , Narkis M.
Published: December 2004

The morphology, rheology, and mechanical properties of blends of polysulfone (PSF) with up to 65% of a wholly aromatic liquid crystalline polymer (LCP) were investigated. In injection molded specimens a skin‐core morphology was observed with the LCP minor phase oriented in the skin and globular in the core. Scanning electron microscopy of fractured surfaces showed sharp phase boundaries, suggesting low interfacial adhesion. The neat PSF and blends with low amounts of LCP exhibited a low shear Newtonian plateau not observed in the blends with high LCP levels. The addition of LCP to PSF resulted in an increase in stiffness, a small increase in tensile strength, and a significant improvement in processability.
Negative synergism of crosslinking agent and antioxidant in polyethylene
Authors: Fang Zhengping , Xu Chengwei , Shao Guoming , Lu Qianyi
Published: December 2004

The melt flow index and oxidation induction period of low‐density polyethylene crosslinked with dicumyl peroxide (DCP) in the presence of tetrakis (methylene β‐3, 5‐di‐butyl‐4‐hydroxypheny1)‐propionate methane (Antioxidant 1010) were determined. The results suggest that there is a negative synergism between this crosslinking agent and antioxindant. Part of the antioxidant terminated the chain propagation by trapping radicals, and thus reduced the efficiency of crosslinking. The antioxidant efficiency was also reduced owing to meaningless consumption.
The effect of the length of the short chain branch on the impact properties of linear low density polyethylene
Authors: Liu T. M. , Baker W. E.
Published: December 2004

The ability to evaluate various mechanical test parameters of polymers using an instrumented impact tester is reviewed. The nature of the short chain branching (SCB) in a series of linear low density polyethylenes (LLDPE) was characterized and related to several impact test parameters for these materials. The impact strength, ductility, and impact fatigue life were observed to increase with increasing branch length. This was attributed, in fact, to an increase in the number of interlamellar tie molecules as the SCB length increased. With an increase in the SCB length the SCB distribution became broader; the number of chains rich in short chain branches increased. This component acts somewhat like the rubber particles in a rubber‐toughened blend which gives rise to the concept of a “one copolymer blend”.
Determining the components of mixing energy when preparing rubber compounds in instrumented internal mixers
Authors: Leblanc Jean L. , Lionnet Roger
Published: December 2004

An experimental procedure has been developed to assess the various components of the mixing energy when preparing carbon black filled rubber compounds. A microprocessor based instrument developed for laboratory mixers allows the measurement and recording of all the relevant parameters of the operation, which are stored on diskette, loaded in a Lotus 123 spreadsheet, and further processed with the appropriate macro‐programs. Using compounds based either on ethylene‐propylene rubber, EPDM, or natural rubber, NR, and constant level of different carbon blacks, experiments were made using single pass mixing procedures, typical of factory processes. The position of the ram during the process has been identified as an important parameter of the process, and a method to correct the actual mixing energy by the effective batch volume has consequently been developed. With this correction and the data treatment described, it is possible to split the overall mixing energy into its various components, i.e., the energy to masticate the rubber alone, the energy to fragment and disperse the filler, and the extra mastication energy due to the presence of the filler. The energy to fragment and disperse various types of carbon black is dependent on the structure and the particle size of the filler considered. Depending on the compounding formulation, 65 to 80% of the total mixing energy is associated with the mastication of the pure gum, 15 to 20% accounts for the extra mastication energy due to the presence of the filler, and 5 to 15% is needed to fragment and disperse the filler.
Blends of a chlorinated poly(vinyl chloride) compound and a thermotropic liquid crystalline copolyester: Mechanical properties of squeezed flow films
Authors: Lee Biing‐Lin
Published: December 2004

The mechanical properties of squeezed flow films were measured on blends of a chlorinated poly(vinyl chloride) (CPVC) compound and a thermotropic liquid crystalline copolyester of p‐hydroxybenzoic acid/poly(ethylene terephthalate) (60/40), hereafter referred to as LCC. CPVC is immiscible with LCC. The most serious and unique problem of liquid crystalline polymers is their tendency to fibrillate when fabricated into films and injection molded parts, primarily because of a high degree of mechanical anisotropy. It has been found that the mechanical anisotropy of LCC and blends could be lessened using nonisothermal squeezing equibiaxial extension flow. The maximum tensile properties of LCC are achieved when processed in the vicinity of 260°C. For blends of CPVC containing LCC, the mechanical properties are dependent on the processing temperature and compositions. Blends with no more than 20 wt% of LCC exhibit significant increases in tensile properties. This is due to the possibility of frozen‐in macroscopic biaxial orientation of LCC in the blends during the nonisothermal squeezing flow. Within the range of processable temperatures, the reinforcement of CPVC due to the incorporation of LCC can be achieved at a temperature below the optimum processing temperature of LCC, although the thermal history of blends never reaches that temperature.
Modeling the uniaxial rate and temperature dependent behavior of amorphous and semicrystalline polymers
Authors: Amoedo J. , Lee D.
Published: December 2004

Strain rate and temperature dependent constitutive equations are proposed for polymer materials based on existing isotropic formulations of viscoplasticity. The proposed formulations are capable of simulating some of the important features of deformation behavior of amorphous and semicrystalline polymers. The materials model is based on the assumption that the evolution of flow stress is dependent on the rate of deformation, temperature, and an appropriate set of internal variables. The proposed theory is capable of modeling yielding, strain softening, and the orientation hardening exhibited by amorphous polymers. It is also possible to model the initial viscoplastic and subsequent nonlinear hardening behavior shown by semicrystalline polymers at large strains. Uniaxial tensile tests with uniform and hourglass specimens are made at temperatures ranging from 23 to 100°C and under various crosshead speeds. Both amorphous polycarbonate and semicrystalline polypropylene sheet materials are tested to characterize the stress and strain behavior of these materials and to determine their appropriate material constants. Load relaxation experiments are also conducted to obtain the necessary material constants describing the rate and temperature dependent flow stress behavior of polypropylene. Simulation results compare favorably against experimental data for these polymer materials.
Thermal analysis of poly(phenylene sulfide) polymers. I: Thermal characterization of PPS polymers of different molecular weights
Authors: Menczel Joseph D. , Collins George L.
Published: December 2004

Thermal properties of Fortron®

®Registered trademark of Hoechst Celanese Corporation.

poly(phenylene sulfide) (PPS) polymers of different molecular weights were studied by DSC. Crystallization studies revealed that the ability of these polymers to crystallize decreases with increasing molecular weight. The Avrami equation poorly describes the isothermal crystallization of PPS. Lamellar crystallization was observed for the lowest molecular weight sample. For the other, higher molecular weight polymers the Avrami exponent is always between 2 and 3, suggesting development of distorted spherulites with heterogeneous nucleation. The temperature dependence of the solid and melt heat capacities have been determined. The solid specific heat capacity did not exhibit a molecular weight dependence. The heat capacity increase at the glass transition, Tg, has been calculated to be 28.1 J°C−1 mole−1. The equilibrium melting point of PPS has been estimated to be 348.5°C using the Hoffman–Weeks method. The Tg of PPS increases with molecular weight. The Tg of the highest molecular weight evaluated is 92.5°C. A DMA relaxation peak corresponding to the onset of the phenylene ring rotation occurs at −92°C. Only the highest molecular weight could be quenched to a completely amorphous state.
Methods of studying macromolecular entanglements
Authors: Qian Baojun , Hu Panpan , He Jianmin , Zhao J. X. , Wu Chengxun
Published: December 2004

Macromolecular entanglements in polyacrylonitrile (PAN) and polyacrylonitrile copolymer (PAC) fibers have been systematically studied by the methods of swelling thermal analysis, i.e., swelling differential scanning calorimetry (SDSC), swelling shrinking stress (SSS), swelling shrinkage (SS), and terminal swelling modulus (TSM). When a PAC fiber sample was immersed in a swelling agent, e.g., 80% aqueous dimethylformamide (DMF) and subjected to a programmed heating, the fiber swells, with the dissociable intermolecular couplings gradually broken until finally the fiber was completely dissolved. If this process was done in a DSC analyzer, a small endothermic peak appears on the latter part of the SDSC thermogram. This represents the disentanglement energy of the entangled bonds in the sample. If done in a thermomechanical analyzer, the SSS, SS, and TSM, measured just before incipient dissolution, i.e., the point that intermolecular couplings were broken and only the entangled loopings junctions were left, should reflect the number of the entanglement loops. Thus, the long argued problem whether an entanglement is topological, or due to loci of chain coupling, or is of dual nature may be experimentally elucidated. By using these methods, problems were detailed concerning entanglements, such as the different textural changes of PAC fiber during ambient storage to below 0°C, the effects of heating at 125°C for various times on the PAC fiber texture, and the textural characteristics of gel‐spun PAN fibers with different molecular weight and different draw ratios.
Molecular weight dependent of the crystallization kinetics of poly(vinylidene fluoride)
Authors: Roussel Sophie , McElroy Kathy Lynn , Judovits Lawrence H.
Published: December 2004

Samples of poly(vinylidene fluoride) with weight average molecular weights between 100,000 to 500,000 were analyzed using differential scanning calorimetry to study the influence of molecular weight on crystallization. Isothermal crystallization from the melt was investigated between 140 and 145°C. Crystallization rates were analyzed in terms of the Avrami equation. Avrami exponents between 3 and 11 were observed depending upon the microstructure, molecular weight, and cooling rate. The midrange molecular weight samples were found to crystallize slower than the high and low molecular weight materials.