bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymer sorbents for phosphorus esters: II. Hydrogen bond driven sorption in fluoro‐carbinol substituted polystyrene
Authors: Barlow J. W. , Cassidy P. E. , Lloyd D. R. , You C‐J. , Chang Y. , Wong P. C. , Noriyan J.
Published: December 2004

A series of copolymers containing styrene and a fluorocarbinol substituted styrene, vinyl benzyl hexafluorodimethyl carbinol, were prepared by substitution of hexafluoroacetone on polystyrene followed by hydrolysis, and by copolymerization of styrene and substituted styrene monomers. Sorption of dimethyl methyl phosphonate, DMMP, vapor in the copolymers was examined at 135°C by the piezoelectric sorption method and at 135 to 165°C by Inverse Gas Chromatography, IGC, and the results were analyzed by the Flory‐Huggins equation. Both methods yield similar negative values of the Flory‐Huggins Chi parameter at 135°C, and the Chi values are observed to become increasingly negative to −4.9 as the percent substitution of the aromatic rings In the copolymer is increased to 54 mole percent. A simplified thermodynamic analysis, based on experimental studies of the hydrogen bond formed between DMMP and hexafluoro‐isopropanol, an analog of the fluoro‐carbinol, through infrared spectroscopy and calorimetry at ambient conditions, is shown to predict the Chi dependency on copolymer composition observed at 135°C to within the accuracy of the experimental observations, however, the analysis predicts a decrease in Chi with increasing temperature that is too high relative to values observed by IGC at temperatures greater than 135°C.
Effect of segmental diffusion on irreversible, step growth polymerizations of ARB monomers
Authors: Kumar Anil , Saksena Kamal , Foryt John P. , Gupta Santosh K.
Published: December 2004

The role of segmental diffusion in step‐growth polymerizations has been studied using a simple, phenomenological theory. Theoretical results have been generated to study the effect of the parameters, several of which can be estimated from experiments on non‐reacting systems. The values of the parameters have been selected in this study in such a manner that segmental‐diffusional limitations are encountered quite early during polymerization. This facilitates detailed parametric sensitivity studies. Thereafter, the model is used to predict behavior of trains of reactors, and more appropriate values are used for the parameters. Segmental‐diffusional limitations are then limited to final stages of polymerization (as indeed they are in industrial practice).
The calorimetric and mechanical properties of virgin and recycled poly(ethylene terephthalate) from beverage bottles
Authors: Müller A. J. , Feijoo J. L. , Alvarez M. E. , Febles A. C.
Published: December 2004

In the present work, fusion behavior, crystallinity, and mechanical properties of beverage bottle poly(ethylene terephthalate) (PET) was compared with those of the virgin material. Viscosimetry measurements, differential scanning calorimetric studies, impact and tensile determinations were made in both materials. The lower Mv of bottle PET revealed that a thermomechanical degradation occurred during processing. Although bottles possess a considerable degree of crystallinity (≈30 percent), the crystallites are so small that they don't scatter light and, therefore, bottles are transparent. Virgin PET exhibited a brittle behavior while bottle PET exhibited a ductile one. This is a consequence of the difference In crystallinity between both materials (greater for virgin PET because of its original higher crystallinity content), although they were molded under the same conditions. Such difference was attributable to a “crystalline memory” effect having its origin in the orientation of the material during Injection molding at low temperature (250°C). Injection‐molded PET specimens showed a strong, crystalline memory, capable of crystallization during very fast quenchings.
Determining viscosity temperature behavior of four amorphous thermoplastics using a parallel plate technique
Authors: Macho E. , Alegría A. , Colmenero J.
Published: December 2004

The temperature dependence of the Newtonian viscosity, ηo(T), of four structurally related amorphous thermoplastics (polyarylate, polysulfone, polycarbonate, and phenoxy) was measured in the temperature region between Tg and (Tg + 100 K) by means of a parallel plate technique. This offers a simple and quick alternate mode of measurement to traditional techniques. Values of ηo(T) measured, as well as some data obtained from literature and corresponding to the T > (Tg + 100 K) range, were fitted to Vogel‐Fulcher expressions. Fractional free volume at Tg was evaluated from Vogel‐Fulcher parameters. The values obtained are similar for all polymers studied, and they are greater than those normally observed for other amorphous polymeric systems that are structurally simpler. From the results obtained we can conclude that the rheological behavior and, hence, the chain “stiffness” of polyarylate, polysulfone, and polycarbonate, at the temperature range of industrial processing, are very similar. However, phenoxy, which contains a greater number of nonaromatic flexible structures in its chain, has a different behavior with a lower activation energy for viscous flow in the same range of temperature.
Measurement and correlation of mutual diffusion coefficients for molten polystyrene‐hydrocarbon systems
Authors: Iwai Yoshio , Kohno Masafiide , Akiyama Takayuki , Arai Yasuhiko
Published: December 2004

The mutual diffusion coefficients for three molten polystyrene(PS)‐hydrocarbon systems—PS‐in‐xylene, PS‐n‐octane, and PS‐n‐nonane—were measured by using a sorption apparatus with quartz spring in the temperature region from 130 to 175°C and for mass fraction of hydrocarbon ranging from 0 to 0.15. The mutual diffusion coefficients were correlated with good agreement by the freevolume theory.
A miscible nylon blend with poly(2‐vinyl pyridine)
Authors: Skrovanek Daniel J. , Coleman Michael M.
Published: December 2004

Polymer blends of an amorphous polyamide with poly(2vinyl pyridine) (P2VP) are presented. Differential scanning calorimetry results suggest that the system exists as a single phase material as evidenced by a single glass transition temperature. However, as illustrated by light scattering studies, this miscible binary mixture possesses a relatively low, lower critical solution temperature (LCST). Fourier transform infrared (FTIR) spectroscopic investigations indicate that the interactions occur in the blend between the NH group of the polyamide and the N: atom of P2VP and that the strength of the Interactions between the components is nearly identical to that occurring in the self‐association of the pure amorphous polyamide. Additionally, by monitoring the concentration of “free” carbonyl groups, a quantitative measure of the number of interactions occurring in the blend is obtained.
Biaxial orientation of polypropylene by hydrostatic solid state extrusion. Part II: Morphology and properties
Authors: Pan S. J. , Tang H. I. , Hiltner A. , Baer E.
Published: December 2004

Changes in the lamellar structure of polypropylene during biaxial orientation by hydrostatic extrusion have been examined. Examination of etched surfaces in the transmission electron microscope has revealed that up to a draw ratio of about 1.5 × 1.5 the primary mechanism is lamellar rotation into the plane of orientation, At higher draw ratios breakup of the lamellae is observed with formation of a granular structure. Thermal measurements suggest that localized melting and recrystallization may accompany the process of lamellar breakup. These morphological observations confirm the previous interpretation of SAXS and permit a more detailed model of the hierarchical structure to be proposed. Stress strain measurements show a gradual change from sharp necking to uniform deformation as the draw ratio is increased. On the other hand, the structural change at a draw ratio of about 1.5 × 1.5 Is accompanied by a large increase in the tensile impact strength.
Loss of 2‐tertiary‐butyl‐4‐methoxy phenol (BHA) from high‐density polyethylene film
Authors: Han J. K. , Miltz J. , Harte B. R. , Giacin J. R. , Gray J. I.
Published: December 2004

The rate of loss of the antioxidant 2‐tertiary‐butyl‐4‐methoxy phenol (BHA) from high‐density polyethylene (HDPE) was determined using high pressure liquid chromatography (HPLC). The rate of loss was found to follow a first‐order expression. Almost all of the antioxidant was lost (>95 percent) within 1 day at 50°C, within 3 days at 40°C, and within 7 days at 30°C. The controlling parameter for mass transfer of the antioxidant was found to be volatilization rather than diffusion.
Surface spectroscopic studies of poly(methyl methacrylate) (PMMA) and modified PMMA surfaces
Authors: Salvati Lawrence , Hook Thomas J. , Gardella Joseph A. , Chin Roland L.
Published: December 2004

Multitechnique surface characterization of plasma and chemically modified poly(methyl methacrylate) (PMMA) is reported using Low Energy Ion Scattering Spectrometry (LEIS or ISS) and angular‐dependent X‐Ray Photoelectron Spectroscopy (XPS or ESCA). A complete picture of the depth, extent, and mechanism of modifications developed. ISS yields results, which especially complement ESCA because of the sensitivity to functional group arrangement due to shadowing and shielding of atoms in the topmost layer.
Shelf life of phenolic resole resins
Authors: Gupta Manoj K. , Hindersinn Raymond R.
Published: December 2004

Viscosity, number‐average and weight‐average molecular weights (measured by gel permeation chromatography), and carbon‐13 nuclear magnetic resonance (NMR) were used to monitor the changes in phenolic resoles as a function of time and pH. It was observed that phenolic resoles with pH around 5 are more stable, as indicated by the lowest increase in viscosity and molecular weight. Carbon‐13 NMR spectroscopic studies also suggest that the concentration of methylol groups is higher for resoles with pH around 5 and, thereby, indicate a slower reaction.
Elastic contact stress analysis of semi‐crystalline polymers under normal and tangential loading
Authors: Youn Jae R. , Su Ching‐Lo
Published: December 2004

Stress distribution in a polymeric subsurface under the asperity contact is investigated assuming the well known Hertzian contact stress distribution. Elastic stress analyses for three different materials are performed using a finite element method: (1) isotropic elastic solid, (2) isotropic elastic solid with a soft layer, and (3) isotropic elastic solid with a hard layer. Highly linear polymers as high density polyethylene (HDPE), poly(tetrafluoroethylene) (PTFE), and polyoxymethylene (POM) which transfer thin wear films are modeled as the elastic solid with a soft layer. Gammaray irradiated highly linear polymers and the other ordinary semi‐crystalline polymers which transfer massive lumpy wear debris are considered as the elastic solid without any heterogeneous surface layer. Helium plasma treated polymers are modeled as the elastic solid with a hard layer. Octahedral shear stress and equivalent strain contours in the subsurface are obtained for each case. The octahedral shear stress and equivalent strain distributions are examined to explain various wear behaviors of semicrystalline polymers based on the Mises yield criterion and the delamination theory of wear.
Influence of materials and structure on performance of a football helmet
Authors: Vetter L. , Vanderby R. , Broutman L. J.
Published: December 2004

A nonlinear finite element model for the static analysis of football helmets is developed as a first step in a methodology for the mathematical modeling of helmets. Polycarbonate and acrylonitrile‐butadiene‐styrene are considered as the shell material for the helmet. Such a methodology can be used to predict helmet response to loading and impact and can be incorporated in a computer program studying injuries caused by helmeted head collisions in football. Numerical results in terms of force‐deflection curves, maximum stresses, and work of deformation are given. The influence of the polymeric material forming the helmet shell on energy absorption is studied. The effect of the internal padding material and suspension system is also considered.
Fracture toughness and crack instability in tough polymers under plane strain conditions
Authors: Lee L. H. , Mandell J. F. , McGarry F. J.
Published: December 2004

The plane strain fracture toughness and fracture mechanisms of several tough engineering plastics have been studied and compared with poly(methyl methacrylate) (PMMA), a relatively brittle polymer. The tough polymers all are observed to form a multiple craze zone at the crack tip, which is shown to be the primary source of plane strain fracture toughness in these materials. The multiple craze zone is retained during slow crack growth but is metastable, and at a critical stress intensity and associated crack velocity, the system passes through a transition to a greatly accelerated single craze mode of unstable propagation.
Modification of butadiene‐acrylonitrile rubber/poly(vinyl chloride) blend using natural rubber, styrene‐butadiene rubber, and polybutadiene rubber
Authors: George K. E. , Joseph Rani , Francis D. Joseph , Thomas K. T.
Published: December 2004

Natural rubber, styrene‐butadiene rubber, and polybutadiene rubber were used to replace part of the butadiene‐acrylonitrile rubber in a 70/30 butadiene‐acrylonitrile rubber/poly(vinyl chloride) blend. Such replacement up to 15% of the total weight of the blend improved the mechanical properties, while decreasing the cost of the blend. Styrenebutadiene rubber could replace butadiene‐acrylonitrile rubber up to 30% of the total weight of the blend without deterioration in the mechanical properties.
Ductile tearing instability in some engineering thermoplastic blends
Authors: Dekkers M. E. J. , Hobbs S. Y.
Published: December 2004

The stability of ductile crack growth in two engineering thermoplastic blends is examined. The blends are a poly(phenylene oxide)/nylon 6,6 blend and a poly(butylene terephthalate)/polycarbonate blend. Fracture tests were performed with single‐edge notched specimens in tension and three‐point bending over a wide range of test speeds. Both larger radius notches and longer specimens were found to promote ductile tearing instability. This behavior is attributed to the higher driving force for crack growth produced by increased elastic energy storage before crack initiation. Over a certain range of test speeds, these factors lead to a novel effect of notch sharpness on toughness; a sharp notch gives rise to a higher fracture energy than does a blunt notch. The results are discussed in terms of the tearing modulus concept developed by Paris and co‐workers.
Space‐time distribution in filling a mold
Authors: Manas‐Zloczower I. , Blake J. W. , Macosko C. W.
Published: December 2004

The residence time of a fluid particle in mold filling is total time spent in the mold. Displaying curves of constant residence time in the mold gives the space‐time distribution during the filling process. A simple method to calculate space‐time distributions is presented. Applications to mold filling in reaction injection molding (RIM) are illustrated.
Adiabatic reactive viscometry for polyurethane reaction injection molding
Authors: Blake J. W. , Yang W. P. , Anderson R. D. , Macosko C. W.
Published: December 2004

Adiabatic reactive rheometry involves the simultaneous measurement of viscosity and temperature changes during adiabatic polymerization. Using the adiabatic reactor method to relate temperature to fractional conversion results in a useful rheokinetic tool ideally suited for fastreacting reaction injection molding (RIM) systems for which the mold‐filling step is nearly adiabatic. In this work, a small laboratory RIM machine is used to mix the reactants and deliver them to a constant stress rheometer retrofitted with a wide‐gap Couette geometry and two thermocouples. Measurements on two polyurethane systems are reported. A simple cross‐linking system is used to verify the adiabatic rheokinetic method through comparison to a known gel conversion. Subsequent measurements on a phase‐separating RIM system show that increases in catalyst level, hard segment content, and initial reactant temperature result in a decreased gel time and an increased gel conversion. The viscosity rise profiles aid our understanding of the onset and development of phase separation. They are also essential for mold‐filling models and establishing moldability criteria for these RIM systems.
Analysis of reaction injection molding process of polyurethane‐unsaturated polyester blends. Part II: Mechanical properties
Authors: Kim J. H. , Kim S. C.
Published: December 2004

The mechanical properties of polyurethane‐unsaturated polyester interpenetrating polymer networks (IPNs) that were prepared by reaction injection molding (RIM) process were measured with variations In composition, cross‐link density, and relative reaction rate. From dynamic mechanical analysis (DMA), it was found that the two component polymers had a good compatibility over the whole composition range. The tensile strengths of the blends were greater than those of the pure components and had a maximum value at 50/50 composition. The modulus of elasticity and surface hardness decreased and the impact strength increased as the polyurethane content was increased, but the changes were not high at low polyurethane content, below 50%. For higher cross‐link density, the compatibility was enhanced and the mechanical properties were improved. When the reaction rates of the components were different, some extent of phase separation was found in DMA and the properties were affected adversely.
Concentration, temperature and deformation effects in concentrated polymer solutions with volatile solvents
Authors: Foster R. W. , Lindt J. T.
Published: December 2004

A novel high pressure polymer solution viscometer has been experimentally evaluated using the polystyrene/ethylbenzene system. The polymer solutions range in concentration from 60 weight percent polystyrene to the pure melt. The overall temperature range is 132°C to 240°C. The shear rates range from roughly 5 s−1 to 2000 s−1. It has been concluded that the present method is useful in determining the shear dependent behavior of these volatile solutions, The shear dependent nature of this system is consistent with accepted non‐Newtonian viscosity theory.
Structure‐property relationships for thermoplastic block terpolymers containing poly(styrene‐p‐tert‐butylstyrene) copolymer end segments
Authors: Chen John C. , Fetters Lewis J.
Published: December 2004

Terpolymers containing polybutadiene as a central segment and diblock or random copolymer terminal units of equimolar amounts of styrene and p‐tert‐butylstyrene have been synthesized and evaluated. The structure property relationships were examined by a combination of transmission electron microscopy (morphology), dynamic viscoelasticity measurements, and melt rheological evaluations. The presence of p‐tert‐butylstyrene was found to lead, under certain circumstances, to thermoplastic elastomers exhibiting good phase separation and mechanical properties at ambient temperature along with Newtonian melt viscosities at low shear rates at elevated temperatures. This latter behavior is in contrast with that exhibited by conventional poly(styrene‐diene‐styrene) triblock copolymers.
Cure kinetics of an epoxide/anhydride/amine resin system: A fractional‐life method approach
Authors: Lee Sung‐Nung , Yuo Wu‐Bin
Published: December 2004

A fractional‐life method coupled with dynamic differential scanning calorimetry (DSC) scan was employed to study the kinetics of the isothermal polymerization of the DGEBA (diglycidyl ether bisphenol A)/HHPA (hexahydrophthalic anhydride)/BDMA (benzyl dimethyl amine) resin system. This method avoids the problem of uncertainty in the total heat evolution in the isothermal DSC scan, The reaction orders obtained for this epoxy resin vary from 1.05 to 1.44 in the temperature range 118–135°C and are believed to be more accurate than those determined in previous studies.
An approach for estimating the permeation of phosphonofluoridates into a high polymer matrix part 1. Development of the approach
Authors: Mangaraj D. , Pfau J. P. , Luttinger M. , Block F. , Magee W. S.
Published: December 2004

An approach has been developed to estimate the solubility and diffusivity of toxic phosphonofluoridates in high molecular weight polymeric matrices based upon experimentation with nontoxic simulants. This approach is based on Gee's relation for estimating solubility (equilibrium swelling) from knowledge of the solubility parameters for the polymer and the simulant liquids concerned and on Van Krevelen's relation between diffusivity and activation energy of diffusion. The latter is interpolated from a standard plot of activation energy of diffusion against penetrant molar volume. Equilibrium swelling values and diffusivities for toxic alkyl phosphonofluoridates in styrene‐butadiene rubber (SBR) and low density polyethylene (LDPE) were estimated from results of swelling measurements (as a function of time and at three different temperatures) involving the two polymers and a series of nontoxic liquids, similar to the toxic alkyl phosphonofluoridates.
Nonisothermal flow of a generalized power‐law fluid in converging sections for rubber extrusion
Authors: Kakouris A. P. , Freakley P. K. , Harrison M. C.
Published: December 2004

A method for predicting pressure drop and temperature distribution in convergent sections is proposed. The generalized power‐law rheological equation of state is used. Only the shear component of the converging flow is considered in order to estimate its contribution to total flow in such sections. A finite‐difference scheme was used to simulate the flow. The method was applied to an ethylenepropylene terpolymer compound using different angles of approach for which the pressure drop and the extrudate temperature had been measured experimentally. Comparison with theoretically predicted data showed excellent agreement for small angles, while for large angles the inclusion of extensional effects was found to be necessary. The contribution of viscous dissipation effects was found to be negligible for the converging sections tested.
Catalyst fragmentation during propylene polymerization: Part I. The effects of grain size and structure
Authors: Ferrero Monica A. , Chiovetta Mario G.
Published: December 2004

Fragmentation of support/catalyst particles during propylene polymerization in the gas phase is analyzed via a mathematical model including energy and mass transfer with chemical reaction processes. The rupture phenomenon is considered specifically by the model, and evaluated as it proceeds in time, Two different regions are recognized in the polymerizing particle at fragmentation time: an inner core resembling the original solid support/catalyst structure, and an external set of layers where most of the polymerization occurs. Model predictions concerning the effects of fragmentation on polymerization are discussed. The influence of different degrees of fragmentation on thermal runaways and monomer availability at active sites located inside the support/catalyst/polymer complex is shown. Monomer concentration profiles inside the growing particles are explained in terms of the combined fragmentation‐polymerization interaction. Results show a strong influence of catalyst structure on critical phenomena during early polymerization stages, and suggest the possibility of controlling critical parameters via the definition of fragment structure at catalyst preparation time.
Blends of polycarbonate and poly(hexamethylene sebacate): II. Effect of molecular weight on compatibility
Authors: Shih K. S. , Beatty C. L.
Published: December 2004

Blends of polycarbonate (PC) and poly(hexamethylene sebacate) (HMS) with two different molecular weights were prepared and their thermal properties were studied via differential scanning calorimetry. It was found that the high molecular weight PC (HPC) and high molecular weight HMS (HHMS) were partially miscible as evidenced by the decrease in glass transition temperature of HPC in the blends. This partial miscibility is attributed to the interaction of the carbonyl dipole of the ester group and the highly polarizable aromatic carbonate structure. When the low molecular weight PC or HMS was used, the compatibility was enhanced because of the increased entropic contribution to the Gibbs free energy of mixing. In all the blends prepared, the PC crystallized as a result of the plasticizing effect of HMS. Bisphenol‐A diphenyl carbonate (dimer) was synthesized and used as the dimeric model of PC. This material was found to be an excellent diluent for HPC. A single glass transition was found in the HPC/dimer system and the temperature was dependent on the composition. The Couchman's equation was found to fit very well the glass transition temperature versus composition relationship for this system. A single glass transition was also found in the HHMS/dimer system. The melting point depression analysis was performed and resulted in a very low heat of fusion for the 100% crystalline HHMS. It may suggest that the dimer and HHMS are not completely miscible in the amorphous region.
Structure‐property relationships in polyamide/acrylonitrile‐butadiene‐styrene (ABS) blends
Authors: Howe David V. , Wolkowicz Michael D.
Published: December 2004

The structures and physical properties of four blends of poly(acrylonitrile‐co‐styrene‐g‐butadiene) (ABS) materials with polycaprolactam (PA6) have been characterized. The blends were separated into components by selective solvent extraction and were found to contain different structures: Blend A contained no PA6 grafts. Blend B contained PA6 grafted onto both soluble and insoluble ABS. Blend C contained PA6 grafted onto soluble poly(styrene‐co‐acrylonitrile) (p‐SAN). In Blend D, PA6 was grafted onto both the insoluble ABS and the p‐SAN phases. Transmission electron microscopy showed different morphologies in the blends. Blend A had a co‐continuous, somewhat laminar structure, while Blend D consisted of an ABS phase dispersed in a PA6 continuum. Blends B and C had intermediate structures. All four blends, however, had very similar rheological and physical properties despite the variation in structure.
The effect of viscosity ratio on the morphology of polypropylene/polycarbonate blends during processing
Authors: Favis B. D. , Chalifoux J. P.
Published: December 2004

The size of the minor phase in an immiscible polymer blend can have a significant effect on properties such as the impact strength. Few studies, however, have quantitatively considered the parameters controlling the size of the dispersed phase. In this paper, light and scanning electron microscopy have been used to examine the size of the minor phase in polypropylene/polycarbonate blends after melt processing. The size was examined as a function of both the viscosity ratio (p) and the torque ratio (TR). The viscosity ratio is studied in the regions of p > 1 and p < 1. p has a marked effect on the morphology of the dispersed phase with the phase size increasing by a factor of 3 to 4 times from p = 4.5 to p = 17.3. Reduction in the size of the minor phase was achieved below p = 1 with the minimum particle size occurring at p ≃ 0.15. The results for these systems indicate the presence of upper and lower limits of p beyond which deformation becomes difficult. This is shown to be similar in some respects to the behavior of Newtonian fluids in shear flow, although the upper limit extends beyond that observed in the Newtonian fluid studies.
Phase behavior studies of the system polystyrene‐polybutadiene‐chloroform. II. Modification of the Flory‐Huggins theory
Authors: Tseng H.‐S. , Lloyd D. R. , Ward T. C.
Published: December 2004

Phase behavior of polymer‐polymer‐solvent systems can be determined using gel permeation chromatography. This technique enables one to generate the binodal curve and tie lines relating coexisting phases, to locate the critical point and, through the use of an appropriate solution theory, to calculate interaction parameters. Previous studies of the incompatible polystyrene‐polybutadiene‐chloroform system indicated that the classical Flory‐Huggins theory yields an anomalous behavior of negative interaction parameters. Probable causes are specific interactions due to the polar nature of chloroform plus failure to account for the concentration dependence of the polystyrene‐chloroform interaction. A modified version of the Flory‐Huggins theory incorporating concentration dependence of polymer‐solvent interaction was used to reevaluate the polystyrene‐polybutadiene‐chloroform system. This approach yields positive interaction parameters for the incompatible system polystyrene and polybutadiene.
Reaction‐induced crystallization kinetics during the anionic polymerization of ϵ‐caprolactam
Authors: Lee Kwang Hee , Kim Sung Chul
Published: December 2004

The kinetics of crystallization during anioiiic polymerization of ϵ‐caprolactam was studied by the adiabatic temperature rise method, A new kinetic model for the non‐isothermal crystallization was derived and the possibility of its application was Investigated. By evaluating the parameters in the model for the given adiabatic system, the crystallization behavior during the; polymerization process was analyzed. The experimental and calculated temperature rise showed a very good agreement, which indicated that the model equation was appropriate to describe the non‐isothermal reaction‐induced crystallization kinetics in this study. The melting temperature of the reaction mixture increased steadily due to the change of the crystal structure with conversion. The equilibrium crystallinity was higher when the crystallization started in the presence of unreacted monomer than when the crystallization occurred after polymerization was completed. At lower conversion, the reaction mixture was less viscous, a condition that made transport to the liquid‐crystal interlace easier, and thus the activation energy for transport decreased. On the other hand, the increasing mobility resulted in difficulty in forming stable nuclei arid the free energy of nucleation increased.
Relationship between electron sensitivity and chemical structures of polymers as electron beam (EB) resists. V: Polyamides containing sulfur groups as positive eb resists
Authors: Oguchi Kiyoshi , Ygneyama Sachiko , Sanul Kohei , Ogata Naoya , Takahashi Yoichi , Nakada Tomihiro
Published: December 2004

Polyamidethioethers were synthesized and evaluated as positive electron beam (EB) resists, The polyamidethioethers decomposed easily with EB exposure. At high doses (indicating low sensitivity), crosslinking reactions occurred for polyamidethioethers having C‐S bonds produced by Michael addition, but the other polyamidethioethers did not crosslink. The C‐S bonds produced by Michael addition may influence crosslinking rather than decomposition. The sensitivity of oxidized polyamidethioether was higher than that of the nonoxidized polymer with no change in resolution. The oxidized polyamidethioether had a high sensitivity and a high resolution, and is adaptable as a positive EB resist.
Computation of the gel effect in multifunctional self‐polymerization in the presence of intramolecular reactions
Authors: Kumar A, , Khandelwal P. K.
Published: December 2004

Intramolecular reactions in the step‐growth polymerization of multifunctional monomer, RAf, were modeled. The rate constant for this step was taken from the Monte Carlo studies of Plate and Noah. Species Pvn, with v Intramolecular bonds and chain length n, was defined, and differential equations governing their molecular weight distribution (MWD) in hatch reactors were written. An algorithm of computation valid up to the gel point was developed, and the process of gelation was studied under the variation of the rate constant parameters of the intramolecular reaction step. It was found that the larger the molecule, the greater is its tendency to form intramolecular bonds. We devised a mathematical method to find the conversion of A groups on Pon species. Whenever this reaches a critical value {= l/(f−1)}, conditions for gelation are generated and molecules of infinite structure begin to form. In the presence of intramolecular reactions, the tendency to form a network is reduced because larger molecules undergo cyclization and there is consequently a shift in the gel point, which has been computed in this work.
Latent skin in asymmetric loeb‐type hollow fiber membrane
Authors: Castellari Carlo , Francesconi Romolo , Ottani Stefano , Comelli Fabio , Pezzin Giovanni
Published: December 2004

A computer simulation model for the latent skin growth inside a hollow fiber polymeric membrane Is developed. The evaporation step is studied using a solvent evaporation Law and a concentration‐dependent diffusion coefficient, both derived from data. The solvent concentration profiles inside the fiber are obtained as a function of the evaporation time for different sets of the parameters governing the internal diffusion and the surface evaporation of the solvent. The computer model enables estimation of the role of the parameters in the growth of the asymmetric latent skin.
Rheological properties of thermotropic liquid crystalline aromatic copolyesters
Authors: Zhou Zhenglong , Wu Xiuge , Wang Meirong
Published: December 2004

A series of thermotropic liquid crystalline polyesters based on p‐acetoxybenzoic acid, naphthalene dicarboxylic acid, hydroquinone diacetate, and poly(ethylene terephthalate) were prepared via melt polycondensation. The anisotropic melts were studied by means of thermal optical testing, differential scanning calorimetry, scanning electron microscopy. X‐ray diffraction, and rheological methods. It was found that the copolyesters in the mesomorphic state exhibit drastic shear‐thinning and the experimental results indicate that the non‐Newtonian Indexnis in the range of 0.17 to 0.50, the flow‐activation energies ΔEηare 297.1 to 182.0 KJ/mol over the shear rate of 10 to 1000 S−1at temperature 225 to 270°C; and the mesomorphic copolymers are readily oriented during processing, resulting in highly oriented as‐spun fibers.
Influence of the processing conditions on morphology and deformation behavior of poly(butylene terephthalate) (PBT)
Authors: Ludwig H.‐J. , Eyerer P.
Published: December 2004

This paper discusses the effect of varying cooling rates during crystallization on the spherulitic structure of poly(butalene terephthalate). Light microscopy, transmission electron microscopy, and differential scanning calorimetry were used to examine specimens. The mechanical properties of the polymers studied were examined by a variety of methods.
The effect of processing conditions on the microstructure of embossed polyethylene films
Authors: Kamal M. R. , Haber A. , Li Song
Published: December 2004

Film embossing is a mechanical process in which a flat film is transformed into an embossed product. During the process, thermal and stress fields are applied Lo the polymer, causing changes in the microstructure and physical dimensions of the material. The engineering analysis of the process requires the study of various aspects relating to the characterization of the microstructure before and after embossing, A variety of techniques were employed to characterize the properties and microstructure of the embossed film in relation to: crystallinity, orientation, mechanical properties, and dimensions of the embossed films. The thermal treatment of the polymer film was shown to be the most significant factor in the process. By controlling the thermal treatment of the film, it is possible to manipulate the properties and dimensions of the embossed film. The important aspects: influencing thermal treatment include the radiation heater temperature, preheat roll temperature, line velocity, and film thickness. The initial film orientation and embossing pressure have a minor effect on the final properties of the embossed film. The main effect of the embossing pressure is on the bulk thickness of the embossed film.
Production of controlled‐rheology polypropylene resins by peroxide promoted degradation during extrusion
Authors: Tzoganakis C. , Vlachopoulos J. , Hamielec A. E.
Published: December 2004

Results of experimental and modeling studies of the peroxide promoted degradation of polypropylene (PP) are presented. Experiments were carried out, in glass ampoules and in a plasticating extruder. The initiator, 2.5‐dimethyl‐2,5‐bis(tert‐butylperoxy)hexane was used as a radical generator. The extruder used had a 38 mm diameter and 24:1 L/D single‐screw. In these experiments, the effect of peroxide concentration and screw speed on the molecular weight distribution (MWD) of the polypropylene resin was studied. Samples collected from the experimental runs were analyzed for melt flow index (MFI), flow curve, extrudate swell, and MWD. The measured data are presented and correlations among various parameters are considered. Generally, it can be concluded that controlled‐rheology (CR) resins with lower molecular weight, narrower MWD, and reduced viscosity and elasticity, can be produced, A kinetic model for the peroxide Initiated degradation of PP is proposed. Simulations based on this model are compared with experimental data for the production of CR resins. The experimental data were obtained from three sources: (i) industry, (ii) literature, and (iii) present experimental work. The comparison was done in terms of average molecular weights of the resin. Agreement between model predictions and experimental results is quite satisfactory suggesting that this model should find use in commercial practice.
Effects of mechanical drawing on the structure and properties of peek
Authors: Lee Lidia H. , Vanselow Janice J. , Schneider Nathaniel S.
Published: December 2004

This study examines the effects of crystallinity and temperature on the mechanical properties of PEEK. Crystallinity in PEEK Increases with annealing temperature up to a maximum of 28 percent with a melting point at 335°C. A minor melting peak also occurs about 10°C above the annealing temperature. In cold drawing the samples exhibited a yield stress and necking followed by homogeneous drawing. The yield stress increases with crystallinity, but there is no change in the modulus. The extension in the necking process also increases with crystallinity, however there is only a slight increase in extension‐to‐break since necking is compensated by the final amount of homogeneous drawing. The yield stress of PEEK when drawn at Tg (145°C) is significantly lower than at room temperature indicating a reduction in mechanical properties at temperatures approaching Tg. After mechanical drawing the minor melting peak disappears and on heating the material undergoes cold crystallization near the onset of Tg. There is evidence that this minor crystalline component might contribute to the yield stress changes with annealing history. Cold drawing induces crystallization of amorphous PEEK but decreases crystallinity and generates microscopic voids in crystalline PEEK, The various effects of crystallinity on mechanical properties could be important in determining the stress response of PEEK as the matrix in composites.
Concurrent enthalpy recovery and curing phenomena in epoxy encapsulating materials for semiconductor applications
Authors: Belton Daniel J. , Molter Michael
Published: December 2004

Post mold thermal processing of epoxy encapsulated semiconductor devices is accomplished in order to optimize the properties of the encapsulating material. Traditionally, such processes were believed to alter solely the state of cure in such systems. We have examined the effects of aging at temperatures close to, but below the molding temperature via dynamic mechanical spectroscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry as a function of molding temperature. The large property changes observed during aging for samples molded at the lowest temperatures studied were attributed to physical aging phenomena in the presence of low levels of chemical reaction. As the molding temperature was increased chemical aging, phenomena began to precede the volume recovery associated with physical aging, and the overall property shift was altered. It is the intent of this paper to examine in detail the microstructural basis for such observations, as well as the time dependence of the overall property shifts.
Preparation of crosslinked membranes with controlled pore size distribution
Authors: Fujita Sharon M. , Soane David S.
Published: December 2004

A technique has been developed to prepare crosslinked, porous/asymmetric membranes from poly(styrene‐co‐divinylbenzene). Mixtures of styrene monomer, divinylbenzene, benzoin (a photo‐initiator), and some dead polystyrene are dissolved in a cosolvent and cast on a flat, transparent substrate. The coating is then irradiated with a UV lamp and subsequently phase separated by exposure to a nonsolvent bath. Pores are generated by phase separation induced by nonsolvent ingression. Crosslinking is achieved via the photo‐initiated incorporation of divinylbenzene with styrene, while the membrane morphology evolves. A mechanism for the formation of crosslinked membranes prepared by this technique has been proposed. Experimental results systematically examine the effects of crosslinking and nonsolvent/solvent combinations on pore size and overall membrane structure. Temperature and solvent treatments on the finished membrane structure are also studied.
Effect of heat aging on the properties of a nylon 6,6/poly(phenylene oxide) blend
Authors: Laverty J. J.
Published: December 2004

Accelerated aging of an Initial formulation of a nylon 6,6/poly(phenylene oxide) (PA/PPO) blend resulted in a significant loss in impact strength after a relatively short aging period. Fourier transform infrared (FTIR) spectroscopy showed considerable surface oxidation in air‐aged samples. Scanning electron micrographs (SEM) of fracture surfaces showed evidence of embrittlement (glassy skin formation). This brittle skin apparently influenced crack propagation throughout the entire cross section of the test specimens. It was determined by nuclear magnetic resonance (NMR) analysis that the PPO phase of the blend contained a poly(styrene‐butadiene) copolymer, probably added as an impact modifier. The susceptibility of the polybutadiene to oxidation, especially at elevated temperature, is believed to have caused the oxidation and surface embrittlement. However, the surface oxidation also resulted in a large loss in molecular weight of the nylon phase (m‐cresol‐soluble portion) and considerable cross‐linking of the PPO phase (chloroform‐soluble portion). Samples aged in inert atmosphere showed no skin formation nor loss in impact properties, thus confirming that oxidative degradation caused the embrittlement.
Computer aided applications to injection molding: Transfinite/finite element thermal/stress response formulations
Authors: Tamma K. K. , Dowler B. L. , Railkar S. B.
Published: December 2004

The paper describes two different computational approaches for simulating the effects due to temperature variations and therein the associated thermally induced stresses and warpage with emphasis on computer aided engineering applications to ‘plastic’ components. One approach is the conventional finite element approach, and the other is termed as the transfinite element approach. The development of unified thermal/stress formulations for each of the aforementioned approaches is described for applications to injection molded plastic parts. Results of both computational formulations are in excellent agreement for predicting the thermal response and unified thermal/stress response and agree qualitatively with previous studies. For this study, it is found that the transfinite element formulations are computationally more efficient although the conventional formulations can still be effectively used. Both formulations are capable of serving as powerful computational tools to help part designers to predict the thermal/stress responses accurately and effectively. The unified concepts and approaches offer potential for extension to more complex geometries and for combined heat transfer and stress problems.
Experimental and theoretical study of the injection molding of thermoplastic materials
Authors: Agassant J. F. , Alles H. , Philipon S. , Vincent M.
Published: December 2004

Most of the commercially available computation programs for injection molding use restrictive assumptions which lead to simple mechanical and thermal equations. These computations are generally sufficient to predict the flow distribution in the mold but the pressure and temperature distributions are not precise. Our aim was first to model very accurately the filling stage of several molds of elementary geometries. For this purpose, a two‐dimensional model has been built which solves at each time step the finite difference forms of the continuity, momentum, and energy equations. A refined grid is used near the mold walls to take into account the great temperature gradients. These models have been validated by comparing the pressure field with experimental measurements. The precision of the model is better than 15 percent for several mold geometries and several injection conditions. In a second step, molds of complex geometries have been analyzed by assembling elementary geometries. The flow distribution at the branching between several geometries has been studied with special attention. These computations have been compared with short shots and pressure measurements in a four rectangular cavities tool and in a box shaped cavity tool. Experimental and theoretical results are in good agreement.
Creep induced buckling of plastic materials
Authors: Cohen A. , Arends C. B.
Published: December 2004

In this work, creep induced buckling was studied for a number of thermoplastic materials. The effect was observed by monitoring top displacements of thermoplastic bars as a function of time under static loading conditions. The recorded times to failure were averaged and correlated with the applied loads. The experiments, conducted for different materials, established an exponential dependence between the critical time and the load. The evolution of the buckling eigenvalues was modeled numerically. The simulations of eccentric columns behavior under compressive loads were coupled with the eigenvalue analyses. The correlation of the time‐load predictions obtained from the numerical simulations followed the experimental results within acceptable limits. The observed phenomenon of creep induced buckling was explained by damage accumulation leading to an effective reduction of the load carrying capability.
Cost effective, high‐technology civil transports
Authors: Swihart John M.
Published: December 2004

This paper discusses the cost of high technology and its benefits to commercial air transportation. The manufacturer's dilemma today is that, while one could pay a 16 percent price premium to obtain a 10 percent reduction in fuel cost in the late 1970s, in 1985 that price premium has diminished to only 2‐1/2 percent to achieve a 10 percent fuel saving. Consequently, we must obtain the benefits of high technology at an extremely low cost. Four areas are discussed in some depth: Aerodynamics, including the effects of computational fluid dynamics, wing design, and laminar flow; structures, including the effects of new materials, both metallic and nonmetallic, and the automated tools necessary to build the nonmetallic structure; avionics, including both fly‐by‐wire and fly‐by‐light, and the improvements due to high‐speed digital computers as well as flat panel flight deck displays; and propulsion systems, including the effects of high‐bypass ratio, high‐pressure ratio turbofan engines, and single and counter rotation turbopropellers. The final result is an integration of these four areas of technology into a composition transport aircraft and the resulting performance.