bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aromatic poly(1,4‐phenylene‐1,3,4‐oxadiazole) fibers by dry jet‐wet spinning
Authors: Jones R. S. , Soehngen J. W. 
Published: April 2003

AbstractFibers of poly(1,4‐phenylene‐1,3,4‐oxadiazole) have been prepared by dry jet‐wet spinning sulfuric acid solutions of the polymer. Polymer was prepared by polymerizing terephthalic acid and hydrazine dihydrochloride in 30% fuming sulfuric acid and directly spinning the resulting solution. Dry jet‐wet spinning allows greater flexibility in conditions than does wet spinning in that spinneret temperature and coagulation bath temperature are independent of one another. Therefore, coagulation may be at temperatures well below those needed at the spinneret to maintain a flowing, extrudable solution. Another common advantage of dry jet‐wet spinning is application of draw to the extruded fiber before coagulation, but in this system, drawing the fiber before coagulation was shown to be a disadvantage. Fiber properties were maximized by spinning with a spinneret temperature of 58–73°C into a coagulation bath at 3–4°C and with an air gap of 1/4 in. Water as a coagulation medium allowed operation at speeds up to 40 m/min, while with 50% sulfuric acid less than half that speed was reached. Application of draw ratios of 3/1 on the coagulated but still swollen fiber combined with high‐temperature treatments at low draw ratios (1.05/l) gave maximum fiber properties–tenacity 6 g/denier, elongation 20–25%, and modulus 200–240 g/denier.
Effect of temperature gradients on cure and stress gradients in thick thermoset castings
Authors: Pusatcioglu S. Y. , Hassler J. C. , Fricke A. L. , McGee H. A. 
Published: April 2003

AbstractThe temperature gradient developed during casting of an unsaturated polyester for which the kinetics of reaction and the heat capacities, thermal conductivities, and densities were known from earlier work was measured experimentally as a function of time in a thick casting and compared with predicted values calculated from a mathematical model. Agreement was excellent. The castings were sectioned and the sections were examined by birefringence. These examinations show good agreement between the temperature gradient developed during cure and the residual stress gradient. This work demonstrates that the extent of cure as a function of position can be predicted from heat transfer calculations if the reaction kinetics and thermal properties are known and that the residual stress gradient is dependent upon the temperature gradient developed.
Effect of crystalline structure on the infrared spectra of γ‐irradiated cotton cellulose
Authors: Moharram M. A. , Hakeem Nagwa Abdel 
Published: April 2003

AbstractThe effect of crystalline modifications on the infrared spectra of γ‐irradiated cotton cellulose is presented. The crystalline modifications were brought about by treating cotton material with an aqueous solution of NaOH of various concentrations. The infrared spectra of the irradiated samples indicate an absorption band corresponding to the absorption of CO groups. It was found that the intensity and frequency of this band depend on the crystalline structure. Thus, it appears at 1735 cm−1 in the spectrum of cellulose I and at 1610 cm−1 in the spectrum of cellulose II.
The use of acetylene glow discharge for improving adhesive bonding of polymeric films
Authors: Moshonov Aharon , Avny Yair 
Published: April 2003

AbstractCoating of polyethylene (PE), poly(vinyl fluoride) (PVF), poly(tetrafluoroethylene) (PTFE), and poly(vinyl chloride) (PVC) films with flow discharge‐polymerized acetylene was investigated. The influence of glow discharge experimental conditions on the nature of the coated layer, the films' wettability, surface roughness, and adhesive joint strength was determined. It was found that coating of these films with plasma‐polymerized acetylene led to the formation of a rough, crosslinked, irremovable layer with an improved wettability. The presence of the plasma‐polymerized acetylene on the film surface lead to a large improvement in the adhesive joint strength of these films with epoxy adhesive. Best results were obtained with films coated at a low acetylene flow rate. Increase in glow discharge power and treatment time lead to a further improvement.
Membranes prepared from keratin–polyacrylonitrile graft copolymers
Authors: Schaller Johann , Miyamoto Takeaki , Shimamura Kaoru , Inagaki Hiroshi 
Published: April 2003

AbstractGraft copolymerization of acrylonitrile onto a soluble wool keratin derivative was studied with the reduced and carboxymethylated low‐sulfur protein fraction from wool. Copolymerization was carried out under a variety of conditions with a redox system of (NH4)2S2O8–Na2SO3 in 60% (w/w) aqueous ZnCl2 solution at 10°C. Monomer conversions higher than 90% were obtained by the stepwise addition of initiator. The graft products were successfully separated into grafted copolymer and homopolyacrylonitrile (PAN) by fractional precipitation or solvent extraction with DMF. Grafted PAN were isolated by acid hydrolysis of the keratin backbone. Characterization of grafted and homo‐PAN was carried out by IR spectroscopy, amino acid endgroup analysis, and viscometry. On the basis of the results, effects of polymerization conditions on grafting parameters were discussed. Membranes were prepared from 60% aqueous ZnCl2 solution by using ice‐cold water as the regenerating medium. All the membranes formed from the graft products were transparent. Observation by scanning electron microscopy showed that the surface consisted of rather spherical keratin domains regularly distributed in the PAN matrix. Selective hydrolysis of the keratin domains allowed a new type of porous PAN membrane to be obtained, with the inner walls of the pores being charged with amino acid residues attached to PAN chains as the endgroup.
Copolyester studies. VI. Melt spinning and mechanical properties of tetramethylene terephthalate–poly(tetramethylene oxide) random block copolymers
Authors: Boussias C. M. , Peters R. H. , Still R. H. 
Published: April 2003

AbstractFibers were prepared from tetramethylene terephthalate–polytetrahydrofuran (PTHF) random block copolymers, containing the latter in the range of molecular weights 1000–5000 with up to 30% by weight incorporation, using a conventional melt spinning technique. The spinnability of the copolymer and the mechanical properties of these undrawn fibers were evaluated. The changes in mechanical properties brought about by the incorporation of PTHF groups in 4GT units were related to the PTHF block size and content in the copolymer. X‐ray diffraction data are also discussed briefly in terms of the structural differences.
The influence of thermal history on internal stress distributions in sheets of PMMA and polycarbonate
Authors: Saffell J. R. , Windle A. H. 
Published: April 2003

AbstractThe through‐thickness birefringent patterns (nx – nz) of PMMA and polycarbonate (PC) are measured as a function of thickness, cooling rate, and annealing time. A method is demonstrated for separating the elastic stress from the residual birefringence. The residual birefringence is explained as the residual orientation induced when cooling through the galss transition. The shape of the elastic (tempering) stress distribution is apparently independent of the cooling rate and annealing time, the choice of polymer, and the sheet thickness. The magnitude of the tempering stres is dependent on cooling rate but nearly independent of choice of polymer and sheet thickness. The decays of both the tempering stress and the residual orientation are measured as a function of annealing time at 120°C for polycarbonate. The measured birefringence decays only slightly; however, the elastic tempering stress reverts, on annealing, to permanent (anelastic) orientational strain. The tempering stress at the sheet surface is not an adequate criterion for defining toughness in polycarbonate.
Interaction of lead and chromium with chitin and chitosan
Authors: Eiden Catherine A. , Jewell Carolyn A. , Wightman J. P. 
Published: April 2003

AbstractThe interaction of the natural marine polymer chitin and its deacetylated derivative chitosan with lead and chromium has been investigated. The uptake of lead and chromium was determined from changes in concentration as measured by atomic absorption spectroscopy. A significant uptake of Pb(II) on both chitosan and chitin was observed. However, the uptake of Pb(II) on chitin was approximately 21% of that on chitosan. The number of Natoms in chitin and chitosan and per number of Pb(II) ions sorbed was 115 and 29, respectively. The number density of flakes observed in the scanning electron microscope and characterized by an intense Pb signal in energy dispersive analysis of x rays (EDAX) was greater on the surface of chitosan [containing 1.7 × 10−4 mole Pb(II)/g chitosan] than chitin [containing 3.5 × 10−5 mole Pb(II)/g chitin] after equilibration with Pb(II) solution. The bonding state of lead on chitosan as determined by electron spectroscopy for chemical analysis (ESCA) is similar to the bonding of lead in PbO based on the Pb 4f7/2 binding energy. A significant shift in the O 1s binding energy from 532.2 to 531.4 eV was observed for chitosen after equilibration with Pb(II) solution. The caculated values of the N/Pb ratio from ESCA spectra were 0.5 and 11, for chitosan and chitin, respectively. A significant uptake of Cr(III) on chitosan was observed and a significant increase in the pH of solutions of Cr(III) on equilibration with chitosan occurred. A high number density of nodules characterized by an intense Cr signal in EDAX was observed in chitosan [containing 2.5 mole Cr(III)/g chitosan] after equilibration with Cr(III) solution. The calculated values of the N/Cr ratio from ESCA spectra was 18 for chitosan.
Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride
Authors: Acierno D. , La Mantia F. P. , Polizzotti G. , Russo S. , Titomanlio G. 
Published: April 2003

AbstractNylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x‐ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high‐modulus fibers after subsequent crystallization. Also, the possibility of restoring some crystallinity in the material has been proven.
Hydraulic permeability of open‐cell hydrophilic polyurethane foams
Authors: Sefton Michael V. , Lusher Harris M. 
Published: April 2003

AbstractThe hydraulic permeabilities of open‐cell hydrophilic polyurethane (Hypol) foams have been measured at steady state over a preassure gradient range of 102–104dyn/cm3. These permeabilites were sensitive to the relative amounts of prepolymer, water, and surfactant, and to the mode of preparation, Furthermore, the noted sample‐to‐sample variations suggested that mixing effects were also significant. Intertial losses, and energy losses associated with the pushing aside of loose foam struts were apparent at high, low, and very low gradients, respectively. Over the gradient range investigated, compression of the foam was considered to be a monor factor in accounting for the decreased permeability at higher gradients. The viscous loss term or Darcian permeability was correlated with cell size using the Carman–Kozeney equation indicating that the major determinant of hydraulic permeability was pore size rather than porosity. The fiber drag model of flow through porous media was also used to account for the permeability in terms of strut diameter rather than cell size.
Dynamic mechanical analysis and image analysis characterization of crimped yarns
Authors: Felty D. C. , Murayama T. 
Published: April 2003

AbstractThe Quantimet image analysis system and dynamic mechanical analysis have been applied to characterization of crimped yarns. The image analysis system is useful for obtaining accurate measurements of crimps per inch, uncrimped versus crimped length, crimp wavelength, and crimp amplitude. In addition, the dynamic tensile mechanical properties of fibers and the dynamic compression mechanical properties of the fiber masses were examined. These analyses identify the relationships between crimp parameters and loss tangents for the first time. The loss tangents of fiber masses increase with increasing crimp frequency. The higher loss tangents of crimped yarns in the glassy region quantify both the internal friction of constituent fibers and the external fiber to fiber friction separately.
Structural time dependency in the rheological behavior of molten polymers
Authors: Dealy J. M. , Tsang Wm. K.‐;W. 
Published: April 2003

AbstractIn order to elucidate the role of reentanglement processes in the rheology of molten polymers, we have used the interrupted shear test and the reduction‐;in‐;shear‐;rate test to study a linear and a branched polyethylene at 170°C. A cone‐;plate rheometer was used, and shear rates were thus limited to values below 1 sec−1. For both polymers, the characteristic time for reentanglement was found to be significantly greater than the time scales associated with the relaxation of shear and normal stresses after cessation of steady shear. This observation has important implications for the modelling of melt flow in plastics processes and the evaluation of constitutive equations.
Metal smoke retarders for poly(vinyl chloride)
Authors: Kroenke William J. 
Published: April 2003

AbstractThis article provides an overview of smoke‐;retarding rigid PVC using metal compounds. It shows that a large variety of metals from throughout the Periodic Table can form compounds which are smoke retarders for PVC. These metals act to change the thermal degradation pattern of the PVC and promote the formation of char. Most of the active metals are transition metals, although many of the post‐;transition metals and a few of the pretransition metals also are active. The activity of metal smoke retarders primarily is determined by the choice of metal and the environment surrounding the metal ion. Since most of the effective smoke retarders are transition metal compounds, the ability to undergo redox reactions may be important. The initial oxidation state, however, appears to be relatively unimportant. Particle and dispersion characteristics are secondary factors. Increasing the concentration of a smoke retarder can increase, decrease, or have no effect on its effectiveness. It is impossible to predict the influence of a tin stabilizer on a metal smoke retarder, but for many smoke retarders there is little effect. Transition metal compounds are the most effective metal smoke retarders. Smoke‐;reducing synergisms result when molybdenum trioxide is combined with certain compounds of copper, iron, and tin.
Water transport mechanisms through asymmetric membranes
Authors: Cerrella E. G. , Massaldi H. A. 
Published: April 2003

AbstractPermeability coefficients and activation energy values for the transport of water through asymmetric cellulose acetate membranes were determined in order to establish the mechanism of the process when different driving forces are applied. A stirred Lucite cell with controlled temperature was used to measure the membrane transport properties under hydraulic and osmotic pressure differences and also in the presence of a tracer concentration gradient across the membrane. The experimental results based on the temperature dependence of water flow show that the controlling step for water transport is diffusion with net flux in the dense zone of the membrane under hydraulic or osmotic pressure gradients. When a tracer concentration gradient is used, equimolar diffusion of water in the thicker, porous zone of the membrane is the controlling mechanism. A mass transport model based on the composed structure of the membrane is presented to provide a general framework for treating the particular cases. Finally, the difference in the controlling barriers, in agreement with a previous work by Hays,18 is shown to account for the much higher absolute values of osmotic than tracer water permeabilities determined here and frequently reported in the literature.
On the mechanism of the mercerization of cellulose in wood
Authors: Revol J.‐F. , Goring D. A. I. 
Published: April 2003

AbstractWhen spruce wood was treated with 20% aqueous NaOH, only partial conversion of cellulose I to cellulose II took place. In contrast, complete conversion occurred when a low yield kraft pulp from the same wood was mercerized. This difference in behavior is interpreted in terms of restricted swelling of the wood in the mercerizing alkali; this treatment preserves some memory of meridional order. Differences in polarity of the molecules in cellulose I and cellulose II are also considered as a possible reason for the difficulty in mercerizing the cellulose in wood.
Adsorption characteristics of polyacrylamide and sulfonate‐containing polyacrylamide copolymers on sodium kaolinite
Authors: Hollander Agnes F. , Somasundaran P. , Gryte Carl C. 
Published: April 2003

AbstractPolyacrylamide and its copolymer containing 6.8 mole % 2‐acrylamido‐2‐methylpropane sulfonic acid were prepared by an irradiation‐initiated precipitation polymerization technique. The polymer was characterized by intrinsic viscosity under conditions similar to those used during adsorption measurements. Hydrolytic degradation of the polyacrylamide was found to be negligible under conditions used. The adsorption substrate, sodium kaolinite, was prepared by extensive ion exchange treatment. Equilibrium adsorption of the polymers on the sodium kaolinite was made as a function of polymer concentration, solution pH, ionic strength, and temperature.
Hydroxypropylcellulose, a thermotropic liquid crystal: Characteristics and structure development in continuous extrusion and melt spinning
Authors: Shimamura Kaoru , White James L. , Fellers John F. 
Published: April 2003

AbstractHot‐stage polarized light microscopy suggests that bulk hydroxypropylcellulose (Hercules Klucel E) is a cholesteric liquid crystal. Rheological measurements indicate this system exhibits shear viscosities similar to those of polyolefin melts except that it has a yield value comparable to suspensions. Birefringent characteristics were observed in shear flow between glass slides. No relaxation of birefringence is observed following flow. Extruded filaments (without applied take‐up tensions) show high levels of birefringence and significant orientations from WAXS measurements. These have skin‐core structure with highly oriented outer layers which are caused by the flow patterns in the reservior and die preceding the extrudate. In the case of melt‐spun filaments, where tensile elongation occurs, a highly oriented structure of uniform cross section is found.
Penetration of p‐xylylene vapor into small channels prior to polymerization
Authors: Broer D. J. , Luijks W. 
Published: April 2003

AbstractThe penetration of p‐xylylene gas into small rectangular channels has been studied by measuring the thickness of the formed poly(p‐xylylene) films as a function of penetration distance. The experimental values are related to the theoretical penetration curves under various process conditions. At low monomer and residual gas pressures, meeting the Knudsen conditions for wall‐to‐wall collisions of the monomer, a molecular flow model is valid which shows large penetration distances and a gradual decrease in film thickness. At increasing monomer pressures and corresponding deposition rates the molecular flow at the entrance is disturbed in favor of a more viscous type of flow. Consequently an accumulation of poly(p‐xylylene) has been observed in the first part of the channel. At increasing residual gas pressures the penetration can be described by a mass transfer model. Under our process conditions however, its ideal penetration characteristics could not be realized due to a visccus flow transition at the entrance of the channel. Polymerization of chloro‐p‐xylylene at low residual gas pressures showed a molecular flow controlled penetration, also at high deposition rates. Owing to its higher reactivity the penetration is less favorable than for p‐xylylene.
Modeling of poly(ethylene terephthalate) reactors. I. A semibatch ester interchange reactor
Authors: Ravindranath K. , Mashelkar R. A. 
Published: April 2003

AbstractA comprehensive model for a semibatch ester interchange reactor has been developed with a view to investigate the effect of various process and operational variables on the DMT conversion rate as well as the by‐product formation. The influence of important variables such as EG‐to‐DMT ratio, catalyst concentration, and operational variables such as temperature and pressure has been considered. Definite conclusions concerning the choice of the desirable range of process and operational variables to maximize productivity and minimize by‐product formation have been reached.
Chlorinated atactic polypropylene as a plasticizer for poly(vinyl chloride)
Authors: Sharma Y. N. , Satish S. , Bhardwaj I. S. 
Published: April 2003

AbstractAtactic polypropylene, a byproduct obtained in the manufacture of isotactic polypropylene, has been chlorinated under various reaction conditions. The chlorination reaction is reasonably fast so as to give a product of 53‐43% chlorine content in 3 h. The chlorinated product has been incorporated in poly(viny1 chloride) formulations with a view to study its plasticizing activity. Generally this type of compound acts only as a secondary plasticizer; hence it has been used in combination with di(2‐ethylhexyl)phthdate, a primary plasticizer. Different proportions of these two plasticizers have been added to poly(vinyl chloride) resin to obtain a series of formulations. These compounds were evaluated, and it appears that the addition of chlorinated atactic polypropylene (APPC) helps in easy processing and increases the throughput. The increasing concentration of APPC showed an upward trend in die head pressure and torque indicating an increase in melt viscosity. The results of physical properties evaluation show that APPC acts as a reinforcing agent and also imparts permanence to the plasticizers.