bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractIt 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

AbstractOptimal 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

AbstractThe 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

AbstractThe 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

AbstractCoat‐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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractAn 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

AbstractThe 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

AbstractStrain 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

AbstractThermal 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

AbstractMacromolecular 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

AbstractSamples 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.
Miscibility of polyamide‐6 and polystyrene functionalized with sulfonic acid groups
Authors: Molnár Attila , Eisenberg Adi 
Published: December 2004

AbstractPolyamide‐6 (PA‐6) and sulfonated polystyrene (SPS) interact strongly in solution. Thus, solution blends of PA‐6 and SPS (sulfonation levels from 0 to 12.3 mol%) in m‐cresol form clear, hazy, or gelled solutions–depending on the ratio of amide (A) to sulfonic acid (S) groups (A/S). NMR studies show that the S groups interact with the nitrogen of the amides, most probably through the transfer of the sulfonic acid protons. During melt blending, the addition of SPS to the PA‐6 leads to a torque rise because of strong interactions. The glass transition temperatures of the components in the melt blended samples shift towards each other as the sulfonation level of the SPS increases, indicating enhanced miscibility. The analysis of the extracted PA‐6 from thee blends, however, shows that it is degraded at processing temperatures (250°C), owing to some residual water and the catalytic activity of the sulfonic acid groups. The extent of the PA‐6 degradation is inversely related to the A/S ratio. Each sulfonic acid group causes between one and two chain scissions of the PA‐6. In blends with high A/S ratios, the degradation of the PA‐6 is minimal; yet considerable dispersion of the SPS can be achieved, as evidenced by scanning electron micrographs of the fracture surfaces.
Experimental investigation of the drag flow assumption in extruder analysis
Authors: Campbell G. A. , Sweeney P. A. , Felton J. N. 
Published: December 2004

AbstractA new screw pump or extruder has been constructed with the goal of testing the drag flow analysis currently used in the evaluation of polymeric extruders. The new device has been constructed in a manner that allows the barrel, screw helix, and screw core to be rotated independently or in pairs. The experimental results of the flow produced for rotation of the barrel agree well with the theory. However, the flow produced by rotation of the screw elements does not agree with the predictions of the currently accepted theory. The experimental results indicate that the primary element that produced fluid propulsion when the screw is rotated is the screw helix. A new qualitative theory is proposed that is in agreement with the data.
Analysis of isothermal two‐layer blown film coextrusion
Authors: Yoon K.‐S. , Park C.‐W. 
Published: December 2004

AbstractThe mechanics of a bicomponent two‐layer blown film coextrusion is studied theoretically. As a first step for the modeling of this complex process, we adopt a simple system in which the flow is assumed to be isothermal and the two layers are a Newtonian and an upper‐convected Maxwell fluid (UCM), respectively. The two fluids are chosen to investigate the relative influence of viscous and viscoelastic forces on the flow mechanics of the process. For a given total flow rate, blow‐up ratio, freeze‐line height, and film gage, the radius and the melt thickness profiles of the blown film are determined numerically for various values of the flow rate ratio of the two fluids. When the relaxation time of the UCM layer is small, the flow mechanics including the shape of the bubble (or the radius profile) is not much different from that of a Newtonian single‐layer flow. With increasing relaxation time, the viscoelasticity effect of the UCM layer becomes more and more pronounced and eventually dominates the bubble dynamics even though its layer thickness may be smaller than that of the Newtonian layer.
Properties of a thermotropic liquid crystalline polymer blended with different thermoplastics
Authors: Chapleau Nathalie , Carreau Pierre J. , Peleteiro Carmen , Lavoie Paul‐André , Malik Tariq M. 
Published: December 2004

AbstractThermal, rheological, morphological, and mechanical properties of a thermotropic liquid crystalline polymer, TLCP (copolyester Vectra A‐950 from Hoechst), blended with a polycarbonate (PC), a polyethylene glycol terephthalate (PETG), and a blend of PC and PETG (20/80) are presented and discussed. Important supercooling effects are observed for the TLCP. For the blends the glass transition temperature of the matrix is shown to decrease slightly, suggesting partial miscibility of the components. A finer dispersion is observed for the TLCP/PC blends, at least for TLCP concentrations lower than 20%, for which the mechanical properties are quite good. For higher TLCP concentrations, as well as for the other two matrices, the mechanical properties follow more or less the mixing rule, and the morphology of the blends suggests poor adhesion. We were unable to obtain fibrillar structures by extruding the blends through a capillary rheometer; in the TLCP/PC blends, the TLCP domains were too small, and for the other blends the extrudates had not enough melt strength.