bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrophilic gels based on copolymers of 2‐hydroxyethyl methacrylate with methacrylamide and acrylamide
Authors: Dušek K. , Janáček J. 
Published: April 2003

AbstractCopolymerization of 2‐hydroxyethyl methacrylate with methacrylamide or acrylamide and a crosslinking agent in the presence of water or other diluents yielded transparent hydrogels with a varying degree of swelling and varying sorption properties. The equilibrium degree of swelling increases with increasing content of amide groups and exhibits a maximum at ca. 60 wt‐% methacrylamide. The temperature dependence of swelling at 25–50°C changes from negative to positive with growing content of methacrylamide in the copolymer. The effect of the introduction of the amide groups can be interpreted by a weakening of the extent of hydrophobic interactions and by an increase in the role played by the hydrogen bonds. At the same time, the swelling‐in effect of the salting‐in anions decreases and the sensitivity to the sorption of metal cations increases. The increasing content of methacrylamide is reflected in an increase in the modulus, tensile strength, and elongation‐at‐break in gels swollen to the same degree. In gels swollen in water to equilibrium, the positive effect of methacrylamide units is compensated for by the negative effect of the increasing degree of swelling, so that the mechanical properties of these gels do not depend too much on the composition of the copolymer. The increasing content of acrylamide in the copolymer strongly raises the degree of swelling, which is reflected in poorer mechanical properties compared to poly(2‐hydroxyethyl methacrylate).
Experiments with soap‐free polymerization of styrene in the presence of alcohols
Authors: Homola A. M. , Inoue M. , Robertson A. A. 
Published: April 2003

AbstractPolystyrene latexes have been synthesized by a method based on that Kotera et al.4 The polymerization rates and yields have been improved by the addition of an alcohol (methanol) to the reactants. The effects of varying the methanol content and other process variables on the polymerization and on the properties of the latex are reported.
Time lag and permeation rate in liquid/liquid dialysis
Authors: Lee Cheng H. 
Published: April 2003

AbstractTime lag and permeation rate in liquid/liquid dialysis in general are found different from those in pervaporation. Theoretical treatments of time lag in liquid/liquid dialysis indicate that time lag, in certain cases, may be correlated to the “relaxation time” of the membrane, defined as the time required for the membrane to relax, or as the change of the permeation flux of diffusable species from initial flux to steady state due to the long time required for the dialysis solvent to reach steady state in the membrane. The permeation of dichlorobenzene in a Teflon‐FEP membrane for both the operations of liquid/liquid dialysis and pervaporation was measured as an example. It was found that the time lag in liquid/liquid dialysis is much longer than that calculated from a diffusion constant calculated from pervaporation. Permeation rate and activation energy are also different in both operations.
A comparison of methods for assessing the degree of interaction between plasticizers and poly(vinyl chloride)
Authors: Bigg D. C. H. 
Published: April 2003

AbstractThe Hildebrand solubility parameter δ, the Flory‐Huggins interaction parameter χ, dilute‐solution viscosities, apparent melting temperatures, and the equilibrium swelling of poly(vinyl chloride) (PVC) granules in plasticizer are compared as methods for assessing the degree of PVC–plasticizer interaction. Results from the empirical methods agree well with each other, but not with δ or χ. A quantitative activity parameter α, derived from χ, correlates well with all results other than δ values. A relative order of plasticizer solvent power has been established for nine plasticizers of widely differing structures and activities.
Préparation et etude de copolymères triséquencés isoprène et méthacrylate de méthyle
Authors: Guyon‐Gellin J. M. , Golé J. , Pascault J. P. 
Published: April 2003

AbstractA convenient method is described for the synthesis of ABA triblock copolymers having a high vinyl polyisoprene as center block and poly(methyl methacrylate) as end blocks. Dynamic mechanical properties of these copolymers as a function of temperature are compared for different compositions (100%, 85%, 70%, 60%, 50%, and 30% of rubber) using solvent‐casting methods. Since the morphology is dependent on the method of preparation of the samples, five solvents of different solubility parameters were tested for the same copolymer (i.e., 70% polyisoprene by weight) to show their influence on mechanical behavior.
Thermoplastic urethane elastomers. III. Effects of variations in isocyanate structure
Authors: Seefried C. G. , Koleske J. V. , Critchfield F. E. 
Published: April 2003

AbstractThe dynamic mechanical properties of thermoplastic urethane elastomers have been compared for materials based on different diisocyanate structures, either 4,4′‐diphenylmethane diisocyanate (MDI) or an isomeric ratio of tolylene diisocyanate (TDI). Two comparable series of polymers were prepared with a polycaprolactone diol as the soft segment and varying concentrations of hard segments based on the respective diisocyanates and 1,4‐butanediol. Over the composition range studied, the polymer glass transition temperatures increased for the TDI‐based polyurethanes, but remained relatively constant for the series containing MDI. Differences in the degree of macroscopic order within the hard segments, due to variations in the symmetry of the diisocyanate structures, are suggested as an explanation of these dynamic mechanical properties.
A method for the dynamic measurement of diffusivities of gases in polymers
Authors: Felder R. M. , Spence R. D. , Ferrell J. K. 
Published: April 2003

AbstractA method is presented for determining the diffusivity of a gas in a polymer from the response to a step concentration change in a continuous‐flow permeation chamber. The outlined procedure has several advantages over techniques currently in use: it requires simple numerical integration rather than curve fitting; it utilizes the complete response, rather than a portion of the response which falls within the region of validity of a short‐time asympotic solution of the diffusion equation; and it is applicable both to flat membranes and cylindrical tubes. An illustration of the method is provided by the measurement of the diffusivity of sulfur dioxide in a PTFE tube at several temperatures.
Quantitative explanation of the mechanism of corrosion of poly(tetrafluoroethylene) caused by active alkali metals
Authors: Jansta J. , Dousek F. P. , Řiha J. 
Published: April 2003

AbstractThe known method of surface treatment of poly(tetrafluoroethylene) (Teflon) by alkali metals was studied quantitatively. It was shown that the reaction proceeds by an electrochemical mechanism in solid phase. The alkali metal acts as anode and Teflon as a cathodic active material of a typical galvanic corrosion cell. A relation describing the rate of the penetration of this reaction into the depth of Teflon was derived.
Mono‐ and diquaternary ammonium cellulose cottons prepared in nonaqueous media
Authors: Perrier Dorothy M. , Benerito Ruth R. 
Published: April 2003

AbstractMono‐ and diquaternary ammonium cellulose anion exchangers in fabric form were prepared in nonaqueous media by reacting diethylaminoethyl (DEAE)‐cotton with an alkyl halide, RX, or a dihaloalkane, X(CH2)nX, respectively. The alkyl group was varied from CH3 to C18H35, and n varied from 5 to 10 in the dihaloalkanes. Electron emission spectroscopy for chemical analyses (ESCA) showed that approximately 70% of the amino groups in the original DEAE‐cotton were free amines. ESCA data showed that highest degree of quaternization of the free amine groups was obtained with CH3I but that diiodo and dibromo pentanes and decanes were also effective. Diquaternary ammonium cellulose exchangers of high nitrogen content had high wet and conditioned wrinkle recoveries, whereas the monoquaternary ammonium cellulose exchangers showed no improvement in wet or conditioned wrinkle recoveries. The monoquaternaries, like unmodified cottons and DEAE‐cottons, were soluble in cupriethylenediamine hydroxide (cuene), and cross sections of their fibers expanded when subjected to layer expansion techniques. All diquaternaries were insoluble in cuene, and their cross sections did not layer.
A new method for the measurement of dynamic shear mechanical properties of materials with a rheovibron viscoelastometer
Authors: Murayama Takayuki 
Published: April 2003

AbstractThe Rheovibron viscoelastometer is useful for obtaining dynamic tensile mechanical properties of films and fibers over a wide temperature range. Numerous studies of dynamic tensile mechanical properties have been made in the temperature range of −160°C to 250°C in an atmosphere at 0% relative humidity. However, no studies exist which show the measurement of dynamic shear mechanical properties of materials using the Vibron instrument. A new shear grip and procedure was developed for measuring dynamic mechanical properties of material in the shear mode using the Rheovibron instrument. The dynamic shear properties on a polyurethane elastomer and polyester film are presented. This technique will be useful in studies on the dynamic shear characterization of materials in conjunction with end use performance.
Ultrasonic properties of phenolic and poly(phenylquinoxaline) polymers
Authors: Hartmann Bruce 
Published: April 2003

AbstractLongitudinal and shear sound speeds and absorptions were measured for a phenolic polymer and a poly(phenylquinoxaline) (PPQ) polymer, from room temperature to 70°C, at a frequency of 1.8 MHz. Phenolic specimens were cured at a maximum temperature of either 120°C, 135°C, or 180°C. The specimens varied in density from 1.217 to 1.229 g/cm3 with no correlation to curing temperature. Longitudinal sound speed in phenolic was found to depend only on density (or specific volume) and not directly on temperature or degree of crosslinking. Sound speeds and elastic constants, in phenolic, are not sensitive to cure temperature but sound a bsorption is: the higher the cure temperature, the lower the absorption. Hence ultrasonic absorption is a possible way to monitor or measure degree of crosslinking. Sound absorption is higher in phenolic than in PPQ, contrary to what is expected for a polymer with high sound speed. This high absorption indicates an additional mechanism of absorption in phenolic not found in PPQ. Also, the sound absorption increases with temperature in phenolic but is constant in PPQ. The Gruneisen parameter of phenolic appears high and that of PPQ about right when compared with other polymers. All of these results suggest there is a molecular transition in phenolic, but not PPQ. Further evidence for a transition comes from specific volume measurements as a function of temperature. The exact temperature of the transition and the molecular process responsible cannot, however, be determined from the measurements reported here.
Studies on blown film extrusion. I. Experimental determination of elongational viscosity
Authors: Han Chang Dae , Park Jong Yoo 
Published: April 2003

AbstractBlown‐film extrusion experiments were carried out to investigate the elongational flow behavior of viscoelastic polymer melts at different melt temperatures. Materials chosen for study were high‐density polyethylene, lowdensity polyethylene, and polypropylene. In the study, isothermal blown‐film extrusion experiments were carried out in which the molten blown film traveled upward through a heated chamber of about 13 in. in length maintained at the same temperature as the melt. Axial tension was measured at the take‐up roller, the axial profiles of bubble diameter were determined by a photographic technique, and, from the samples collected, the variation in the film thickness along the axial direction was found. These measurements were used later to determine the elongational viscosity, using the force balance equations. It was found, in the experiment, that a careful control of the pressure difference across the thin film permitted one to maintain the bubble diameter constant, and, therefore, depending on the choice of the extrusion conditions, either a uniaxial or biaxial elongational flow was made possible. The experimental results show that, depending on the materials, elongation rate, and melt temperature tested, the elongational viscosity may decrease or increase with elongation rate, and may also stay constant independent of elongation rate. It was observed that the data of elongational viscosity obtained under uniaxial stretching in blown film extrusion is consistent with the data of elongational viscosity obtained earlier by use of the melt‐spinning operation.
Studies on blown film extrusion. II. Analysis of the deformation and heat transfer processes
Authors: Han Chang Dae , Park Jong Yoo 
Published: April 2003

AbstractHaving investigated the elongational flow behavior of polymer melts (part I of this series), we have carried out both theoretical and experimental studies in order to better understand the deformation and heat transfer processes involved in blown film extrusion. For the experimental study, nonisothermal experiments were carried out, using high‐density and low‐density polyethylenes. Measurements were taken of the axial tension, bubble diameter, and film thickness at a series of extrusion conditions (i.e., flow rate, pressure difference across the film, and take‐up speed). For the theoretical study, an analysis was carried out to simulate the blown‐film extrusion process, by setting up the force‐ and energy‐balance equations on the blown bubble moving upward. The approach taken in the theoretical study may be considered as an extension of the earlier work by Pearson and Petrie who considered the isothermal operation of Newtonian fluids. In the present study, However, we have considered the nonisothermal operation of power law fluids, whose rheological parameters were determined by an independent experimental study an described in part I of this series. Four highly nonlinear differential equations were solved numerically with the aid of the CDC 360 digital computer, using the fourth‐order Runge‐Kutta method. The mathematical model predicts the bubble shape, temperature profile, and film thickness as a function of the distance along the machine axis. Comparison is made of the experimentally observed bubble shapes with the theoretically predicted ones, showing a reasonable agreement.
Studies on blown film extrusion. III. Bubble instability
Authors: Han Chang Dae , Park Jong Yoo 
Published: April 2003

AbstractAn experimental study has been carried out to investigate flow instabilities in blown film extrusion. Two types of flow instabilities were observed, depending on whether a bubble was under uniaxial or biaxial stretching. Under biaxial stretching, the phenomenon of a surface wave‐type instability was observed, yielding wavy bubble shapes which very much resembled water waves at the free surface. Under uniaxial stretching, another type of instability, frequently referred to as draw resonance, was observed. It was also observed that, once draw resonance occurs, the amplitude and frequency of bubble diameter pulsing increased with stretch ratio. Quantitative information was obtained from a series of motion pictures taken of bubble diameter in both types of flow instability. It was observed further that an increase in extrusion melt temperature enhanced the severity of bubble instability.
Gelation of dilute collagen solutions by ultraviolet light
Authors: Hamed Gary , Rodriguez Ferdinand 
Published: April 2003

AbstractDilute collagen and collagen–polymer solutions were irradiated at 4°C with UV light (254 nm) under a nitrogen atmosphere. The collagen had been recovered from native tissue by a process of simultaneous acid solubilization together with proctase treatment to remove telopeptides. In the range of concentrations studied (0.1% to 0.9% collagen), gelation occurs after a few minutes, and the dynamic mechanical properties are followed thereafter using a freely oscillating torsion pendulum. During the irradiation, crosslinking and scission reactions compete. Initially crosslinking reactions dominate and the storage modulus increases. However, with extensive irradiation, scission reactions become important, and the storage modulus passes through a maximum and finally decreases. Furthermore, the time for incipient gelation decreases with concentration and the maximum storage modulus increases with concentration to the 2.5 power for collagen solutions. As an example, the maximum storage modulus for a 0.5% solution is 1.1×104 dynes/cm2. The modulus–dose behavior can be reduced to a single relationship in which the ratio of modulus to maximum modulus is a function of dose divided by dose to reach the maximum modulus.
The mechanism of corona and ultraviolet light‐induced self‐adhesion of poly(ethylene terephthalate) film
Authors: Owens D. K. 
Published: April 2003

AbstractThe ability of corona treatment to render polyethylene film self‐adherent has been previously reported and the mechanism explained. A similar effect has now been found with corona‐treated poly(ethylene terephthalate) film which adheres strongly to itself when joined under conditions of heat and pressure that give no adhesion with untreated film. Poly(ethylene terephthalate) films irradiated with short‐wave UV light also become self‐adherent. The behavior of the adhesive joints in both cases is the same as that reported for corona‐treated polythylene film in that the joint strength is zero in the presence of hydrogen‐bonding liquids, but recovers completely if the joint is allowed to dry undisturbed. Chemical and physical tests have shown that the adhesive bond is a hydrogen bond between the hydrogens of phenol groups created by corona or UV irradiation in one surface with carboxyl carbonyl groups in the other surface. Thin‐layer chromatography of surface extracts from corona‐ and UV‐treated films has shown the products of treatment to be practically identical for both types of treatment, supporting the conclusion that the mechanism of corona treatment resembles that of greatly accelerated photo‐oxidation.
Oxidative degradation of polyolefins. I. Thermal oxidative degradation of atactic polypropylene in solution
Authors: Niki Etsuo , Shiono Takeo , Ido Teruyoshi , Kamiya Yoshio 
Published: April 2003

AbstractAtactic polypropylene was oxidized in solution with radical initiator in the absence and presence of metal catalyst to considerably high conversion over the temperature range of 70° to 125°C, and oxidation products and the change in molecular weight distribution were measured. The unoxidized polypropylene had no ultraviolet absorption at 253.7 nm, whereas the oxidized polypropylene showed distinct absorption over a wide range of molecular weights. It was found that oxygen was incorporated into the polymer chain as hydroperoxide, acid, carbonyl, and hydroxy groups. Much of the absorbed oxygen was found to be involved in smaller fraction of low molecular weight products. Although the average molecular weight of the oxidized polypropylene decreased significantly, the formation of low‐boiling products was quite small.
Fracture properties of rigid polyurethane foams
Authors: Anderton G. E. 
Published: April 2003

AbstractThe fracture behavior of rigid polyurethane foams has been investigated and is shown to obey the Griffith criterion for fracture in so far as the predicted behavior of tensile strength on the size of artificially introduced cracks is concerned. The energy for crack propagation (fracture surface energy) has been measured as 91.4J/m2. From this result, the intrinsic flaw size of the material is calculated. This value was found to be within the range of cell dimensions of the material.
Cuticular hydrocarbons and wax esters of the ectoparasitoid Habrobracon hebetor: Ontogenetic, reproductive, and nutritional effects
Authors: Howard Ralph W. , Baker James E. 
Published: April 2003

AbstractHydrocarbon and wax ester components of cuticular lipids of the braconid parasitoid Habrobracon hebetor Say reared at 25°C on larvae of a pyralid moth have been identified by GC‐MS and analyzed with respect to adult age, mating status, and diet. The hydrocarbons range in carbon number from C21 to C45 and consist of a homologous series of n‐alkanes, 11‐, 13‐, and 15‐methyl alkanes, 13,17‐dimethyl alkanes, and Z‐5, Z‐7, and Z‐9‐alkenes. The wax esters found in the cuticular lipid fraction are a series of homologous compounds with the acid portion being short chain, unbranched, even carbon number acids from C8 to C20 (predominately C8 to C16). The alcohol portions of the esters are secondary alcohols with carbon number from C22 to C25 (predominately C23 and C25) with the hydroxyl function located at C6, C7, C8, and C9. Gender, age, and nutritional states were significant factors for variation in several of the individual esters, but mating status did not affect wax ester composition. Ontogenetic examinations indicated that prepupal, and early pupal cuticular lipids contain only hydrocarbons. Low levels of wax esters are detectable in late stage pupae, and somewhat greater quantities of wax esters are present on newly eclosed adults. When pharate adults emerge from the cocoon, however, their cuticular lipids consist of approximately equal amounts of hydrocarbons and wax esters, and 6d post emergence from the cocoon, wax esters are the predominant lipid component. Arch. Insect Biochem. Physiol. 53:1–18, 2003. Published 2003 Wiley‐Liss, Inc.†
Proteolytic gut activities in the rice water weevil, Lissorhoptrus brevirostris Suffrian (Coleoptera: Curculionidae)
Authors: Hernández Carlos A. , Pujol Merardo , Alfonso‐Rubí Julio , Armas Raúl , Coll Yamilet , Pérez Maylin , González Annerys , Ruiz Marisa , Castañera Pedro , Ortego Félix 
Published: April 2003

AbstractDigestive endoprotease activities of the rice water weevil, Lissorhoptrus brevirostris Suffrian (Coleoptera: Curculionidae), were characterized based on the ability of gut extracts to hydrolyze specific synthetic substrates, optimal pH, and hydrolysis sensitivity to protease inhibitors. Larvae of this species were found to use a complex proteolytic system that includes cathepsin D‐, cathepsin B‐, trypsin‐, and chymotrypsin‐like activities. Trypsin‐like activity was evenly distributed among the anterior, middle, and posterior portions of the gut, whereas cathepsin B– and cathepsin D–like activities were mainly located in the anterior and middle sections, and the chymotrypsin‐like activity was highest in the middle and posterior sections. Gelatin‐containing native‐PAGE gels indicated the presence of several aspartyl, cysteine, and serine protease forms and confirmed the spatial organization of the proteolytic digestive process. Arch. Insect Biochem. Physiol. 53:19–29, 2003. © 2003 Wiley‐Liss, Inc.