bluuebunny/crossref_metadata_2025_split huggingface dataset:
The degradation of high impact polystyrene with and without starch in concentrated activated sludge
Authors: Jasso G. C. F. , González‐Ortiz L. J. , Contreras J. R. , Mendizábal M. E. , Mora G. J. 
Published: April 2004

AbstractDisposal of plastic solid waste is primarily accomplished by landfilling, degradation, and recycling. Degradation is highly justified in some applications. In this work, high impact polystyrene blended with starch (16–32% weight) in a “V” mixer is degraded in concentrated activated sludge for 12 weeks. Samples of 0.75 mm thickness were obtained in ribbon geometry by single screw extrusion. Mechanical degradation was determined by stress‐strain tests. Gel permeation chromatography measurements established changes towards lower polymer molecular weights. Scanning electron microscopy examination showed the presence of microorganisms in the polymer samples, as well as changes in polymer morphology in areas near holes produced in samples. Results demonstrate the utility of concentrated activated sludge in polymer degradation and the effectiveness of starch inclusion as a filler to accelerate the structural molecular changes.
A study of sub‐Tg heat flow transition of cured epoxy resin
Authors: Chen Xiangxu , Li Shanjun 
Published: April 2004

AbstractThe physical aging behavior of fully and partially cured epoxy resins based on diglycidyl ether of bisphenol A(DGEBA) has been investigated by differential scanning calorimetry (DSC). A sub‐Tg heat flow transition (Tg1) could not be attributed to the phase separation or dynamic mechanical relaxation, as reported in the literature. In both fully and partially cured epoxy resins, it occurs only when the cooling rate is higher than that having the lowest Tg in the DSC scan. Therefore, it could be attributed to the motion of the internal stress‐relaxed molecular chain.
Thermomechanical studies on newly developed copolyester thin films. Part II: Thermal and intrinsic stress
Authors: Shi Frank F. , Economy James 
Published: April 2004

AbstractThermal stresses were determined by a wafer bending technique for a newly developed family of all‐aromatic and aromatic/aliphatic copolyester thermosetting films prepared by spin coating. The intrinsic stresses of the films were also estimated for T > Tg (glass transition temperature). The effects of chemical structure and film processing conditions on thermal stresses are discussed. Thermal stresses varied with temperature and processing conditions, and the variations were dependent upon the chemical structures and Tg of the copolyester films. The Tg's of different copolyesters were also estimated from thermal stress‐temperature curves.
Kinetics of polyesterification of adipic acid with 1,3‐butanediol
Authors: Bacaloglu Radu , Fisch Michael , Biesiada Keith 
Published: April 2004

AbstractThe kinetics of non‐catalyzed, acid catalyzed and alkyltin catalyzed polyesterification of adipic acid with 1, 3‐butanediol as a model for polymeric ester synthesis was followed at 180°C and 215°C by monitoring of carboxyl, hydroxyl, and water content of the reaction system. The rate constants of the three processes were calculated using a simulation method. The process is kinetically controlled during the first 4–10 h (down to AV ≅ 20 mg KOH/g, conversion 95%) and then thermodynamically controlled by elimination of water from the system. Methyltin derivatives, especially trichloride, are more active catalysts but dibutyltin oxide can be used with good results. The model study suggests that addition of the catalyst at the beginning of the process and applying a vacuum (pressure 60 Torr) will reduce the reaction time in half, compared with adding catalyst at AV ≅ 20 mg KOH/g and using no vacuum.
Theoretical analysis of the thermally induced delamination of polymeric coatings in double‐coated optical fibers
Authors: Shiue Sham‐Tsong 
Published: April 2004

AbstractTo maintain its mechanical strength, the glass fiber of optical fibers is coated by polymeric materials during the fabrication process, However, when the thermally induced shear stress at the interface of the glass fiber and primary coating is larger that its adhesive stress, the adhesive bond between the glass fiber and primary coating will be broken. When the polymeric coatings are delaminated from the glass fiber, the optical fiber will lose its mechanical strength. In this article, the thermally induced delamination of polymeric coatings in double‐coated optical fibers is investigated. To minimize the coating's delamination, the thermally induced shear stress at the interface of the glass fiber and primary coating should be reduced. The method to minimize such a shear stress is to select suitable polymeric coatings as follows: The thickness and Poissòn's ratio of the primary coating should be increased, but the Young's modulus of the primary coating and the thickness, Young's modulus, and thermal expansion coefficient of the secondary coating should be decreased. Finally, the optimal design of commercialized double‐coated optical fibers to minimize the thermally induced coating's delamination is also discussed.
The effect of surface tension on extrudate swell from square and rectangular channels
Authors: Gifford W. A. 
Published: April 2004

AbstractThe effect of surface tension on extrudate swell of a Newtonian fluid from square and rectangular channels is presented. Surface tension decreases extrudate cross‐sections in all cases examined. The influence on the shapes of final extrudate profiles is found to be greater for channels with higher aspect ratios. Surface tension has the greatest influence on the swell of the longer side of the extrudate while that of the shorter side is virtually unaffected. The effect of the capillary number can be significant and in certain cases should be considered in the design of extrusion dies.
Free volume, mobility, and structural relaxations in poly(ethylene oxide)/poly(methyl methacrylate) blends
Authors: Wästlund C. , Schmidt M. , Schantz S. , Maurer F. H. J. 
Published: April 2004

AbstractTime‐dependent structural relaxations in a melt‐mixed 38/62 vol% poly(ethylene oxide)/atactic poly(methyl methacrylate) blend were studied using several techniques: differential scanning calorimetry, pressure‐volume‐temperature analysis, positron annihilation lifetime spectroscopy, dynamic mechanical analysis, and solid‐state nuclear magnetic resonance. The internal volume (free volume hole size) and the external volume (specific volume) of the blend are found to decrease with aging time. The time scale of the volume changes is the same, suggesting that internal and external volumes can be calculated from each other. Increasing mobility of poly(ethylene oxide), composition fluctuations, and shifting glass transition temperatures are observed upon aging. Phase separation in terms of spinodal decomposition below an upper critical solution temperature occurs within minutes and results in two amorphous phases of different composition. Subsequent crystallization then causes further structural changes.
Barium sulfate–filled blends of polypropylene and poly(styrene‐co‐acrylonitrile)—dynamic mechanical melt state properties and interlayer effects
Authors: Hammer Claes O. , Maurer Frans H. J. 
Published: April 2004

AbstractDifferent microstructures were obtained as a result of the chemical character of the polymer phases in barium sulfate–filled blends of polypropylene (PP) and poly(styrene‐co‐acrylonitrile) (SAN). The microstructure was controlled with the aid of low molecular mass maleic anhydride–grafted polypropylene (PP‐g‐MAH), which seems to form an interlayer around the filler particles resulting in controlling of the polymer phase in which the filler is occluded. The variation of the properties as a function of the concentration of PP‐g‐MAH with different amounts of grafted maleic anhydride and the average filler size was found to be due to a change of the microstructure. A low molecular weight PP‐g‐MAH interlayer around the filler particles occluded in the PP phase, dilution of the filler when occluded in the PP matrix phase of low viscosity as compared with SAN and filler network formation were found to be of importance for the dynamic mechanical properties. A theoretical model, the interlayer model, was used to simulate the dynamic mechanical properties of the filled blends.
Process studies in precision injection molding. II: Morphology and precision in liquid crystal polymers
Authors: Liu C. , Manzione L. T. 
Published: April 2004

AbstractPrecision injection molding is an important technology for improving productivity and lowering costs in fields such as electronics, photonics, and medical plastics by allowing the substitution of molded plastics for more expensive metal and ceramic parts. The work in this phase of the program examines correlations between morphology and precision of injection molded liquid crystal polymers. The materials were poly(benzoate naphthoate) polymers with several different filler packages including glass fibers and minerals. These materials show a distinct skin/core morphology in which the relative amounts of skin and core vary with process parameters. The precision of the parts is affected by this ratio of skin to core.
Shear and extensional flow of a thermotropic liquid crystalline polymer
Authors: Pickles A. P. , Gibson A. G. 
Published: April 2004

AbstractThe flow of a thermotropic liquid crystalline polymer (unfilled and glass fiber filled) was studied using a capillary rheometer and an instrumented injection molding machine. Despite different thermal histories, the techniques gave similar results. From 330 to 350°C, viscosity was independent of temperature. At 340°C, where most measurements were carried out, pronounced shear‐thinning occurred and the shear flow curves were nonlinear, the power law exponent decreasing from 0.51 at a shear rate of 10 s−1 to 0.35 at 104 s−1. A previously reported model was used to derive elongational flow curves from die entry pressure data. Because of the nonlinearity of the flow curves, quadratic log‐stress vs. log‐strain rate plots were needed to model behavior over the strain rate region studied. The elongational flow curves were similar in shape to the shear flow curves, with an effective Trouton ratio of 30. Despite orientation and structure present in the melt, the extensional viscosities and Trouton ratios were within the range found with normal thermoplastic melts. The results suggest that extensional flow may be inhomogeneous, the flowing units possibly being partially ordered domains.
Extrusion of polypropylene. Part I: Melt rheology
Authors: Brandao J. , Spieth E. , Lekakou C. 
Published: April 2004

AbstractThis paper considers the rheology of extruded polypropylene regarding melt flow index, shear viscosity, and die swell. Two grades of polypropylene are studied with differences in the molecular weight and rheology. An Instron capillary rheometer is used for the measurement of viscosity and die swell. A range of shear rates and temperatures is covered in these measurements. Die swell is also measured in polypropylene extruded through a commercial single screw extruder where the effect of varying conditions of cooling and annealing on die swell are tested. A detailed theoretical analysis is carried out for the die swell. Analytical expressions are employed for the description of viscosity and die swell with empirical constants which are determined from the experimental data.
Polymerization of styrene in a continuous filled tubular reactor
Authors: Yoon Won Jung , Choi Kyu Yong 
Published: April 2004

AbstractFree radical solution polymerization of styrene has been studied using a binary mixture of symmetrical bifunctional initiators in a filled tubular reactor packed with static mixers. Owing to intensive radial mixing induced by the static mixers, a near plug flow pattern was obtained in the reactor with some axial dispersion effect. The axial mass dispersion coefficient was determined from the residence time distribution experiment and a dynamic axial dispersion model has been developed and solved to investigate steady state and transient behavior of the filled tubular reactor. With a solvent volume fraction of 0.3, the monomer conversion up to 70% was obtained without fouling problems in the temperature range 90 to 120°C. The experimental filled tubular reactor was operated under various reaction conditions and a reasonably good agreement between the model and the experimental data was obtained without using any adjustable parameters.
Suspension polymerization of unsaturated polyester oligomers
Authors: Natov M. , Vassileva St. , Abood L. 
Published: April 2004

AbstractA study has been made of an unsaturated polyester resin prepared from maleic anhydride, phthalic anhydride and 1,2‐propene glycol. The resin is transformed by alkalization with ammonia into a water‐soluble emulsion, which was polymerized with initiators and accelerators. It was found that water acts as an inert diluent in the emulsion. By measuring the temperature of the reaction mass during polymerization, the actual conversion has been estimated. The latter is lower than literature values. A correction of the method of A. Rojas et al. for the determination of the actual conversion is proposed, and the polymerization heat is thus determined. A value of 478 J/g is obtained, which is higher than reported. The apparent order of the polymerization reaction has also been determined; it changes from 5 to 18 with reaction progress.
Evaluation of data on the kinetics of isothermal polymer crystallization
Authors: Lambrigger Markus 
Published: April 2004

AbstractThe kinetic crystallization model of Avrami is generally accepted as a starting point for the analysis of isothermal polymer crystallization. However, in most cases, the experimental situation is complicated by an incubation time prior to isothermal crystallization, so that the Avrami equation must be modified. Moreover, the experimental data are often limited in number and restricted to an intermediate crystallinity range. Furthermore, data of isothermal crystallization experiments performed at different temperatures, cannot be evaluated together by using an evaluation procedure being based on the Avrami equation. An iterative procedure and a crystallization‐temperature independent Avrami master curve, which overcome these problems if the Avrami index n is bigger than one, are displayed in this work.
Mechanical behavior of injection molded β‐crystalline phase polypropylene
Authors: Tjong S. C. , Shen J. S. , Li R. K. Y. 
Published: April 2004

AbstractHigh purity and a large amount of β‐modification can be produced in polypropylene (PP) by adding a bicomponent β‐nucleator consisting of equal amounts of pimelic acid and calcium stearate. Wide angle X‐ray diffraction (WAXD), scanning electron microscopy (SEM), static tensile tests, Izod impact tests, and instrumented drop weight impact testing were used to characterize the structure, morphology, and mechanical behavior of the β‐phase PP. The WAXD patterns show that the relative content of the β‐phase (K value) in the skin layer of the injection molded specimen is 0.54, whereas the K value in the core section is 0.92. SEM observations reveal that the β‐spherulite exhibits a sheaf‐like structure and there are no clear boundaries between the spherulites. Static tensile tests indicate that the elongation at break of pure PP is enhanced by the addition of a β‐nucleator. The impact and drop weight tests also indicate that the impact resistance of PP is improved by adding the β‐nucleating agent. The improvement in impact toughness is associated with the formation of microcrazes within the PP.
The fracture toughness of thin polymeric films
Authors: Klemann Bruce M. , DeVilbiss Tad 
Published: April 2004

AbstractA fracture test using the single edge notch (SEN) geometry was developed for thin polymeric films. The SEN specimens were videotaped while they were stressed to fracture within an Instron tensile testing machine operating at a constant crosshead speed. Critical stress intensity factors for fracture instability and for the initiation of crack growth, along with the corresponding fracture energies, were obtained using a residual stress analysis. The method is applicable to brittle films and films of moderate ductility. Critical stress intensity factors ranging from 0.12 to 4.03 MPa√m were determined for thin films under plane stress conditions. Results of the test are presented for poly(di‐n‐hexylsilane), Kapton polyimide, polystyrene, and Trycite biaxially oriented polystyrene film. Validation of the test and interpretation of the results are also discussed.
Studies of polymerization of acrylic monomers using luminescence probes and differential scanning calorimetry
Authors: Serrano Berna , Levenfeld Belén , Bravo Julio , Baselga Juan 
Published: April 2004

AbstractA fiber optic system has been designed to couple calorimeter and fluorimeter equipment for in situ monitoring of polymerization reactions by both techniques simultaneously. Two acrylic monomers (cyclohexyl methacrylate, CHM, and 2‐ethylhexyl acrylate, EHA) were studied at different temperatures. Pyrene (Py) was employed at a low concentration (≤10−4 mol/L) as a fluorescence probe. The emission spectrum of pyrene shows a broad band peaking at 390 nm, whose intensity grows with polymerization progress. A correlation with conversion degree could be established by collecting fluorescence intensity through the optical fiber at different polymerization times. For the more flexible polymer formed, poly(ethylhexyl acrylate) (PEHA), Py emission sharply increases only when high conversions are reached and continues increasing for a long time after the limiting conversion is attained. For CHM polymerizations, S‐shaped curves are found. Isochronal plots of intensity vs. scaled conversion allow elaboration of master curves for the peak emission. Data at 50°C for CHM cannot be fitted to the master curve, and this is explained in terms of vitrification.
How does “phase transformation toughening” work in semicrystalline polymers?
Authors: Karger‐Kocsis József 
Published: April 2004

AbstractThe possibility of phase transformation toughening is demonstrated by the example of the β‐modification of isotactic polypropylene (β‐iPP), which undergoes βα‐transformation (i.e., from hexagonal to monoclinic) during mechanical loading. The resulting α‐iPP exhibits a higher crystalline density than the initial β‐modification. That, along with the exothermic character of the βα‐recrystallization, is responsible for the improvement in toughness that occurs. The occurrence of this βα‐transformation is evidenced by differential scanning calorimetry (DSC). Toughness of the α‐ and β‐iPP is studied and compared with the “essential work of fracture” concept by using static‐loaded deeply double‐edge‐notched tensile (DDEN‐T) specimens. The main effect of the βα‐transformation is a large increase in the specific plastic work consumed in the necked zone. Light microscopic (LM) and infrared thermographic (IT) pictures reveal that the plastic zone becomes larger and its shape more circular when βα‐transformation takes place. It is suggested that the principle of mechanical stress‐induced phase transformation from a less toward a more dense crystalline state may be a universal tool for toughness upgrading in semicrystalline polymers.
Flexibility of epoxy coatings part 1: Determination of molecular weight of network chains
Authors: Kojima Shunji 
Published: April 2004

AbstractThe chemistry of network formation for an epoxy/phenolic coating determines structure of baked film. The theory of partitioning of components between sol and gel proposed by Flory was applied to determine the crosslink density and the molecular weight of the network chains, Mc. This procedure appears useful to eliminate the problems in the determination procedure of Mc by equilibrium swelling.
Flexibility of epoxy coatings. Part 2: The relationship with the degree of cure
Authors: Kojima Shunji , Watanabe Yoshiki 
Published: April 2004

AbstractThe flexibility of epoxy coating films, crosslinked by a phenolic resin, has been evaluated. The network structures of these films were estimated by the method proposed in the companion paper. The coating films with a higher molecular weight of network chain, Mc, showed more flexibility. This was achieved by the use of an epoxy resin with higher molecular weight or an epoxy resin with a lower content of lower molecular weight components and by control of cure.
Melt viscosity of calcium‐carbonate‐filled low density polyethylene: Influence of matrix‐filler and particle‐particle interactions
Authors: Bomal Y. , Godard P. 
Published: April 2004

AbstractThe melt viscosity of filled polymers depends on the filler particle packing. It is shown that the maximum particle packing for a low density polyethylene, filled with calcium carbonate, depends strongly on the filler surface treatment. This packing can be evaluated from melt viscosity measurements using the Quemada model. From contact angle measurements and using the Lee unified adhesion theory, it has been demonstrated that the maximum packing depends on particle‐particle and matrix‐filler interactions. The competition between both types of interaction leads to different organizations of particles in the composite.
Analysis of polymer membrane formation through spinodal decomposition. Part 4: Computer simulation of early‐stage coarsening
Authors: Caneba Gerard T. , Saxena Rahul 
Published: April 2004

AbstractIn a previous work, an early‐stage coarsening mechanism was proposed, whereby continued growth of structure (via spinodal decomposition) in a polymer‐solvent system will occur because some of the polymer‐rich domains are being depleted. Such a mechanism was explained based on the situation wherein portions of the solvent‐rich domains have already reached their binodal composition while the polymer‐rich domains are still on their way to their corresponding binodal composition. In this work. we have simulated the nonlinear version of the Cahn‐Hilliard theory to verify this phenomenon. Moreover, we have observed that the depleted polymer‐rich domains seem to be uniformly distributed in space. Finally, as a validation of the proposed mechanism, we did not observe this uniform depletion of the domains when portions of the solvent‐rich and polymer‐rich domains reach their respective binodal compositions almost simultaneously.