bluuebunny/crossref_metadata_2025_split huggingface dataset:
A diffusion coefficient model for polymer devolatilization
Authors: Misovich Michael J. , Grulke Eric A. , Blanks Robert F. 
Published: December 2004

AbstractPolymer devolatilizers are in widespread use in the polymer industry for removing solvents and monomers from polymer melts prior to product fabrication. Design equations for describing the solvent flux usually include both the diffusion coefficient of the solvent in the polymer melt and the equilibrium concentration of the solvent at the polymer‐vapor interface. Several models make the as sumption that the solvent diffusivity is constant over the ranges of solvent concentrations and temperatures in the devolatilizer. This is a critical assumption that may be difficult to check without obtaining diffusivity data at the operating temperatures and concentrations of the process equipment. There are three models that can be used for diffusion coefficients in devolatilizer design: the free volume model developed by Duda, Vrentas, and coworkers; a new linear model proposed in this study; and a constant diffusivity model, The linear model is obtained by combining a new correlation for solvent activity coefficients in molten polymers with free volume theory and linearizing the resulting equation. The error between using the complete free volume theory and using the linear model, or alternatively, using a constant diffusion coefficient, is calculated for several solvent‐polymer systems. The linear model is convenient to use for determining the effects of the solvent activity coefficient on the diffusion coefficient. A method is presented for determining whether the complete model, the linear model, or the constant diffusivity model is appropriate for a given devolatilizer design.
A study on poly(vinyl chloride) blends with chlorinated polyethylene and polyethylene
Authors: Xi Xu , Xiande Meng , Keqiang Chen 
Published: December 2004

AbstractBy means of a twin‐roll masticator and Brabender rheometer, the effect of chlorinated polyethylene (CPE) and polyethylene (PE) on the impact strength and processability of poly(vinyl chloride) (PVC) was studied. The experimental results show that CPE can promote the plasticity of PVC and the effect increases with the amount of CPE. Addition of a small amount of PE in PVC/CPE (100/12) makes an impressive improvement in the impact strength of the mixture. The impact strength of PVC/CPE/PE (100/ 12/2.5) at 20°C is 30.0 kJ/m2 higher than that of PVC/CPE (100/12). The dynamic viscoelastic spectra, tensile strength, and elongation test reveal that CPE is incompatible with PVC but may act as a compatibilizer for PVC/PE. The disperse state of the polyblend was studied by differential scanning calorimetry (DSC); it was found that the mixing sequence has an influence on the impact strength of the blend.
Numerical analysis of the temperature profile in the melt conveying section of a single screw extruder: Comparison with experimental data
Authors: Bruker I. , Miaw C. , Hasson A. , Balch G. 
Published: December 2004

AbstractThe prediction and measurement off the developing radial temperature profile in a single‐screw extruder is essential since excessive extrudate temperature and poor temperature uniformity at the die affect the quality of coextrusion and film/sheet extrusion processes. A finite‐difference scheme is used to predict the development of the radial temperature profile in the metering section of a single‐screw extruder for power‐law fluids. A finite‐element analysis of the flow around the screw‐tip transposes this temperature profile onto an on‐line temperature measuring device consisting of 10 thermocouples for a comparison of numerical results with experimental data on polycarbonates.
Uniaxial roll‐drawing of isotactic polypropylene sheet
Authors: Burke P. E. , Weatherly G. C. , Woodhams R. T. 
Published: December 2004

AbstractThe process described as “roll‐drawing” has been applied to commercial extruded sheets of isotactic polypropylene (M̄n = 70,900). Preheated billets were drawn into thin, clear, transparent sheets in a single pass, producing uniaxial orientation of the polymer molecules in the draw direction. At the maximum draw ratio of 20, the ultimate tensile strength and Young's modulus in the draw direction were 0.5 GPa and 20 GPa respectively. The mechanical properties transverse to the draw direction were virtually unchanged. The theory of fiber reinforcement for unidirectional anisotropic plates was applied to interpret the orientation dependence of the stress‐strain behavior of the drawn sheets. From these results, it was estimated that the mechanical properties of biaxially laminated polypropylene sheets equaled the performance of aramid and carbon fiber composites, The roll‐drawing process appears to be economically attractive for the production of ultra‐high modulus crystalline thermoplastics in sheet form having excellent uniaxial or biaxial properties.
Determination of the mode of termination in free‐radical copolymerization
Authors: Chen Chuh‐Yung , Wu Zen‐Zli , Kuo Jen‐Feng 
Published: December 2004

AbstractIn this study the apparent rate constant model was used to determine the mechanism of termination and other rate constants for free radical copolymerizations that are chemically controlled with no penultimate effect. The data required were the number average molecular weight and the conversion obtained at various initial initiator concentrations and monomer compositions, and two rate constants of propagation of the homopolymerizations of its two monomers. The bulk free radical copolymerization of methyl methacrylate (MMA) and styrene(St) at 60°C was studied. Three published literature values of the propagation rate constants k11 and k22. 750, 150; 515, 145; 705, 145, were used for the determination. The unit of the rate constants used was liter/mole/s. The modes of the termination reaction obtained, depending on k11, k22 used, are given as follows:

mole percent Combination in the Termination

(k11, k22)
MMA‐MMA radicals
St‐St radicals
St‐MMA radicals

(750, 150)
17
99
96

(515, 145)
54
99
91

(705, 145)
40
98
87

The modes of termination obtained by the case of k11 = 750 and k22 = 150 are in good agreement with those shown by Bevington, Melville, and Taylor (1).
26‐Year creep and recovery of poly(vinyl chloride) and polyethylene
Authors: Findley William Nichols 
Published: December 2004

AbstractCreep experiments on two thermoplastics at constant values of tensile stress, temperature, and relative humidity previously reported for 132,000 h were continued to about 230,000 h. An equation of the form ϵ = ϵo + ϵ+tn was used to predict the creep, where t is time and ϵo, ϵ+, and n are constants for a given stress. ϵo, ϵ+, and n were determined from the first 1900 h of data and were used to predict the creep to 230,000 h. The subsequent recovery on unloading was predicted using the same equation together with the superposition principle. Also reported are creep and recovery of companion specimens aged for about 98,000 h.
Practical aspects of physicochemical kinetics using thermal techniques
Authors: Khanna Y. P. , Taylor T. J. 
Published: December 2004

AbstractA number of studies on the kinetics of physicochemical processes are described. The methods used are shown to be potentially useful for making time‐temperature predictions and for optimizing process variables. Examples described include (1) the long‐term prediction of the performance of a plasticized polyvinyl chloride and doped polyacetylenes; (2) the polymerization of a monomer and the optimization of time, temperature, and initiator concentration variables; (3) analysis of an order/disorder transition in a thermochromic polymer; (4) the crystallization of polymers and the effect of a nucleating agent; and (5) the crystallization of an amorphous metallic glass. The theoretical background, significance, scope, and limitations of these measurements are also discussed.
The effect of thermal history on the rheology and texture of thermotropic liquid crystalline polymers
Authors: Done D. , Baird D. G. 
Published: December 2004

AbstractThis paper is concerned with the effect of thermal history on the rheology of three liquid crystal copolymers. The polymers were heated to temperatures above their melting points and then cooled down. During the cooling cycle, the dynamic mechanical properties were monitored. It was found that these properties remained unchanged at temperatures as low as 30°C below the normal melting points for two copolyesters of 60 mole percent p‐hydroxybenzoic acid (PHB) and 40 mole percent poly(ethylene terephthalate) (PET) (60‐40 PHB/PET) and 80 mole percent PHB and 20 mole percent PET (80‐20 PHB/PET). For a copolymer of PHB and 2,6‐dihydroxynaphthaic acid, there was a gradual increase in the properties with decreasing temperature. However, at a critical temperature all three systems exhibit a sudden increase In dynamic mechanical properties. The kinetics of solidification were also monitored, and it was found that at temperatures well below the melting point, it took 4 to 6 min before the solidification process impeded flow. Extrusion studies on these materials were also carried out, and it was observed that in this supercooled state, the polymers exhibited significant die swell. The samples also exhibited a fibrous texture and were more oriented than when extruded isothermally above the melting point.
Analysis of epoxy resin curing kinetics using the Avrami theory of phase change
Authors: Pollard M. , Kardos J. L. 
Published: December 2004

AbstractTo przoduce efficiently high quality structural parts from fiber‐reinforced epoxy materials systems, it is necessary to develop detailed process models. One key component in any such model involves the prediction of the cure kinetics, which in turn governs the viscosity, resin flow, void formation, and other important processing parameters. In this study, a series of isothermal and dynamic differential scanning calorimetry experiments was performed using Hercules 3501‐6 and 3502 resins (TGDDM epoxy with DDS curing agent). The hypothesis of a dispersion of growing microgel particles, which become a continuous‐phase solid at the gel point, was used as a basis to apply the Avrami theory of phase change to describe the polymerization kinetics up to the gel point. The extended equations for nonisothermal conditions properly accounted for the temperature effects on the kinetics. Comparison of the theoretical predictions with experimental data suggests that the Avrami theory of phase change may model adequately the cure kinetics of these systems, at least up to the gel point.
A review of recent experimental results concerning the strength and time dependent behavior of fibrous poly(paraphenylene terephthalamide)
Authors: Schwartz Peter 
Published: December 2004

AbstractA review of recent investigations of the strength and stress rupture of single filaments of poly(paraphenylene terephthalamide) (PPTA) is given. The experimental results are presented within an activation energy/power law breakdown framework. The statistics for tensile failure of individual filaments and epoxy impregnated strands and the lifetime of filaments in stress rupture are shown to fit the standard two‐parameter Weibull distribution, as predicted from the model.
Biaxial orientation of polypropylene by hydrostatic solid state extrusion. Part III: Mechanical properties and deformation mechanisms
Authors: Tang H. I. , Hiltner A. , Baer E. 
Published: December 2004

AbstractThe deformation of biaxially oriented polypropylene sheet produced by the BeXor process has been examined in terms of the hierarchical solid state structure described previously. The mechanical properties have been examined over a range of temperatures and strain rates. The anisotropic nature of uniaxial tensile deformation was analyzed from simultaneous measurements of longitudinal extension and lateral contraction in the width and thickness directions, by determining the shape of uniaxially deformed spherulites, and by examining fracture surfaces in the scanning electron microscope (SEM). It was determined that deformation proceeds by elastic extension of the amorphous network and plastic shear deformation of the crystalline regions in the plane of the sheet, and in the thickness dimension, by voiding with induced fibrillation. It is suggested that the property improvements, particularly at low temperatures and high strain rates, which are achieved by the BeXor process, result from changes in the hierarchical structure at the size scale of the crystalline lamellae. Specifically it appears that the small crystalline blocks formed by breakup and recrystallization of lamellae are more easily deformed than the original large coherent lamellae.
A simulation of the effects of high strain energy storage in large plastic structures
Authors: Groshans V. L. , Takemori M. T. 
Published: December 2004

AbstractBrittle failures of large plastic structures observed in the field may have occurred at much higher loads than implied from the fracture surfaces, indeed, as if very ductile failures had occurred. It has been demonstrated that these brittle failures may be a direct result of high energy storage upon impact in large compliant systems. A rubber‐toughened blend of polybutylene terephthalate (PBT) and polycarbonate (PC) was highlighted in this study. Soft steel springs were used in series with compact tension samples to simulate the high energy‐storing capability of large compliant structures, Ductile and stable fractures of compact tension samples of the blend were observed at all of the temperatures tested down through −30°C. With the insertion of springs to simulate large compliant structures, however, unstable failures resulted. At 25°C, initial ductile crack growth was followed by ductile but unstable failure. At −30°C, initial ductile crack growth was followed by brittle unstable failure. These instabilities resulted from the excessive amount of stored energy released by the system during initial crack growth. A higher rubber variant of the PBT/PC blend as well as acrylonitrile‐butadiene‐styrene (ABS) and polycarbonate exhibited similar behavior.
Phenomenological and mathematical analysis of the orientation in biaxially drawn polymeric films
Authors: Jungnickel B.‐J. 
Published: December 2004

AbstractEquations are derived that relate the orientation of “pseudo‐affine” reoriented structural units after a biaxial deformation to the degrees and the directions of the effective drawings. The connection between these drawing parameters and those externally applied is analyzed in detail. It is shown how a comparison of these two sets of drawing parameters allows conclusions regarding the distribution throughout the material of the stresses that cause the deformation, the inhomogeneity of the deformation, and the role of non‐orienting flow during deformation. In particular, the orientation of biaxially drawn poly(ethylene terephthalate) films is investigated, and it is shown what general information can be obtained on the deformation behavior of this material on the basis of these considerations.
Thermodynamic interaction in polybutadiene/solute systems by inverse gas chromatography
Authors: Tseng Hsiao‐Show , Wong Pak‐Choy , Lloyd Douglas R. , Barlow Joel W. 
Published: December 2004

AbstractThe dependence of polymer‐solute interactions on temperature In the range was 66 to 96°C was studied by inverse gas chromatography (IGC). A correlation equation was developed for estimation of the specific retention volume of nonpolar and slightly polar solutes in polybutadiene (PBD). Using equation of state solution theory, thermodynamic interaction was discussed in terms of contact energy and equation of state contributions in polybutadiene/solute systems. It was found that equation of state theory serves better than the Flory‐Huggins theory as a comprehensive model to describe the temperature dependence of thermodynamic interaction.
The rheological characterization of a series of thermotropic liquid crystalline polymers
Authors: Tuttle J. R. , Bartony H. E. , Lenz R. W. 
Published: December 2004

AbstractDynamic rheological experiments were performed on a series of two copolymers and a homopolymer based on units of terephthaloyl chloride and isophthaloyl chloride at 90/10 and 75/25 mole ratios combined with 1,10‐bis(4‐hydroxyphenyl)‐decane. Optical microscopy and wide angle X‐ray diffraction (WAXD) confirmed that all of the polyesters in the present series formed nematic liquid crystals with nematic‐to‐isotropic temperatures in the range of 270 to 320°C with increasing terephthaloyl unit content. Broad nematic‐to‐isotropic transitions observed by differential scanning calorimetry (DSC) were indicative of biphasic regions where the nematic and isotropic phases coexist. The rheological behavior of each polymer was more complex in the nematic phase than in the isotropic phase with shear thinning occurring in the former but Newtonian behavior in the latter. There were also some indications that nematic flow behavior could be induced in these polymers by dynamic oscillatory shear flow above the nematic‐to‐isotropic transition, Ti. A form of hysteresis was observed with the homopolymer in that measurements of the dynamic viscosity, η*, taken with ascending frequency sweeps were higher than those taken with descending frequency sweeps.
Microstructure and mechanical behavior of reinforced reaction injection molded (RRIM) polyurethane
Authors: Kamal M. R. , Singh P. , Samak Q. , Kakarala S. M. 
Published: December 2004

AbstractA study was carried out to characterize the microstructure and distribution of some mechanical properties in reinforced reaction injection molding panels (RRIM). The panels were prepared under a variety of processing conditions. Scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared analysis were employed for microstructure characterization. The following mechanical tests were carried out: dynamic mechanical, tensile, and impact. The results indicate significant relationships between processing conditions, microstructure, and mechanical properties. In particular, the skin/core structure of the panels and the size distribution of bubbles in the matrix have an important effect on the impact properties. Furthermore, the balance between the distributions of cure and crystallinity, which is difficult to define clearly, plays an important role in determining panel behavior.
Estimation of the speed of propagation of intergranular stress waves using a simple elastic contact model
Authors: Stephenson Stuart E. 
Published: December 2004

AbstractA model of a granular bed is used to obtain an estimate of the speed of propagation of intergranular stress waves. In the analysis, a simple elastic contact between neighboring grains is assumed. The model may be extended to include more complex Intergranular interaction mechanisms, but at the expense of such a simple analytical solution as that obtained here. The predicted dependence of compression of a granular bed on compressive load is compared with experimental measurements and is found to describe the relationship very well. The simplified analysis gives a general insight into the dependency of wave speed on bed geometry, indicating for example that while wave speed is independent of grain size, it does depend on the Initial porosity of the bed.
Countercurrent cooling of blown film
Authors: Strater K. F. , Dealy J. M. 
Published: December 2004

AbstractPresently used methods for the external cooling of blown film involve the use of an air ring located at the base of the bubble that blows air upward along the surface of the bubble. The air is heated as it rises, while the film is cooling and moving in the same direction. This is an example of cocurrent heat exchange, and the result is the accumulation of heated air around the upper portion of the bubble, which interferes with the cooling in this region. While rapid initial cooling is required to maintain bubble stability, we have explored the possibility of using countercurrent cooling for the upper region of the bubble. A standard air ring is mounted at the base of the bubble, and a circular shroud surrounds the bubble above this air ring. All the heated air is collected in an upper chamber surrounding the shroud and is exhausted by means of a secondary blower. The proposed scheme was found to increase heat transfer in the upper regions of the bubble and to permit the ducting of all heated air away from the film line.
Tensile creep tests, internal pressure tests, and scanning electron microscopy of electrical conduits of poly(vinyl chloride)
Authors: Johansson Lennart , Törnell Bertil 
Published: December 2004

AbstractElectrical conduits prepared from a mixture of suspension and emulsion poly(vinyl chloride) (PVC) resins were subjected to internal pressure tests at 60°C, covering a wide range of pressures. Some axial tensile creep tests were also carried out at the same temperature. As expected, the ability to withstand internal pressure decreased when the amount of lubricant was increased above the level used in normai commercial production. Fracture surfaces obtained in the two test methods were investigated by scanning electron microscopy. Incompletely melted primary particles or other fragments of resin grains were not observed in any of the fracture surfaces studied in this work. However, a peculiar skinlike structure was found in the fracture surfaces formed at intermediate stress levels in the internal pressure test. This structure was not observed in the fracture surfaces obtained in the notched tensile tests at constant load.
Linear low density polyethylenes and their blends: Part 5 extensional flow of LLDPE blends
Authors: Schlund B. , Utracki L. A. 
Published: December 2004

AbstractThe uniaxial extensional flow at 150°C of two series of blends: I. LLDPE/LLDPE and II. LLDPE/LDPE was examined in full range of concentrations as well as that of accessible in the rheometer strains and strain rates. It was concluded that Series‐I blends containing different LLD‐type polymers are miscible. Their properties can be predicted on the basis of molecular weight and molecular weight distribution. By contrast, excepting low concentration limits, blends of Series‐II are immiscible. Both series show strain hardening, due to higher values of the maximum strain at break. Series‐II seems to be superior (under the test conditions). The stress growth function in shear, computed from the frequency relaxation spectrum, provided a good prediction of the linear viscoelastic component of the stress growth function in uniaxial extension.
Thermal analysis studies on thermoplastic rigid rod molecular composites
Authors: Wiff D. R. , Hwang W‐F. , Chuah H‐H. , Soloski E. J. 
Published: December 2004

AbstractRigid rod molecular composites involve molecular level mixing of two polymers having greatly disparate chain conformations (one rodlike and one flexible coil like). Morphology studies have shown that in such materials the bundle diameter of these rigid rod molecules is less than 5 nm. The rigid rod molecule used is poly(para‐phenylene benzobisthiazole) (PPBT). The thermoplastic flexible polymer matrix is Nylon‐66, DuPont's Zytel 42. Thermal analysis studies on these materials indicate that the expected Tg shifts, as observed for blends of two flexible polymers, and depression of Tm with increased rod molecule composition does not occur.