bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prevulcanization inhibitor of sulfur‐free thiuram vulcanization
Authors: Ducháček Vratislav 
Published: April 2003

AbstractOn the basis of Mooney scorch measurements at 120°C and of continuous measurements of vulcanization in a Vuremo curemeter at 145°C, sulfenamides which function as inhibitors of the sulfur‐free thiuram vulcanization have been investigated. It was found that the actual prevulcanization inhibitor is 2‐mercaptobenzothiazole. Its formation from sulfenamides is activated by zinc dimethyldithiocarbamate since the vulcanization of rubber by thiuram disulfides in the presence of zinc oxide is always accompanied by the formation of zinc dithiocarbamate. It seems probable that the inhibition effect of 2‐mercaptobenzothiazole is attributable to the formation of a complex with zinc dimethyldithiocarbamate which decreases the reaction rate in the initial steps of the sulfur‐free thiuram vulcanization and thus causes the scorch delay.
Thermal and hydrolytic degradation of poly(1,4‐cyclohexylenedimethylene terephthalate)
Authors: Wampler F. C. , Gregory D. R. 
Published: April 2003

AbstractThe kinetics of simultaneous thermal and hydrolytic degradation of poly(1,4‐cyclohexylenedimethylene terephthalate) (PCHDT) were evaluated by using a 1.5‐in.‐diam. melt extruder (≈20/1 length/diameter ratio) as a reactor. The effects of extrusion temperature (295°‐330°C), residence time (2.6–17.5 min), and moisture content (<0.001% to 0.2%) of the supply polymer on degradation were determined. The rate of degradation was measured in terms of the rate at which inherent viscosity (I.V.) decreased and the rate at which carboxyl endgroup concentration increased. The contributions of both thermal and hydrolytic degradation to the total degradation of PCHDT could be separated because the hydrolysis was rapid enough that it could be considered as occurring prior to thermal degradation. Thus, the hydrolysis merely adjusted the initial properties of the supply polymer, which was then subjected to thermal degradation. Equations were developed from an analysis of the kinetic data based on a random chain scission mechanism. The activation energies for decrease in I.V. and increase in carboxyl endgroup concentration of PCHDT from thermal degradation were determined as 33.5 and 41 kcal/mole, respectively.
Ductile and brittle behavior of amorphous polymers. Relationship with activation energy for glass transition and mechanical fracture
Authors: Aharoni Shaul M. 
Published: April 2003

AbstractAn equation correlating the activation energy for the glass transition with TR, a characteristic reference temperature, the fractional free volume, and the rate of change of the fractional free volume was developed. The resultant activation energies for about 30 polymers are given and favorably compare with the literature. The relationship between the activation energy and the bond‐rupture energy indicates whether a polymer will fail in a ductile or brittle fashion. More accurate results are shown to be dependent on the stress, the stress concentration, molecular orientation, frequency of load application, and temperature. Equations correlating all these with the activation energies are given. These results are in agreement with the molecular domain model. Experimental observations from the literature seem to corroborate the suggestion that the molecular domain model holds in the amorphous solid, too.
Studies on melt spinning. III. Flow instabilities in melt spinning: Melt fracture and draw resonance
Authors: Han Chang Dae , Lamonte Ronald R. , Shah Yatish T. 
Published: April 2003

AbstractAn experimental study has been carried out to investigate threadline instabilities in melt spinning. Two types of melt threadline instabilities, draw resonance and melt fracture, were observed under both isothermal and nonisothermal spinning conditions. Polymers investigated were polypropylene and polystyrene. Draw resonance was observed as an increase of the take‐up speed above a critical value. It was also observed that an increase in take‐up speed reduces the severity of melt fracture, whereas once draw resonance occurs the amplitude and frequency of the pulsing thread diameter increases with the take‐up speed. The phenomenon of draw resonance was investigated by taking motion pictures of the pulsing molten threadline spun vertically downward. Furthermore, a stability analysis was carried out to explain the experimentally observed draw resonance.
Thermal behavior of graft copolymers of cotton cellulose and acrylate monomers
Authors: Varma D. S. , Narasimhan Veena 
Published: April 2003

AbstractCotton cellulose yarn was grafted with methyl acrylate, ethyl acrylate, n‐butyl acrylate, and methyl methacrylate at various percentages of grafting. The effects of concentration of the initiator, concentration of the acid, and of temperature on grafting was studied and the mechanism discussed. The effect of reactivity of the monomer on the percentage graft‐on is pointed out. Thermal behavior of natural and grafted cotton yarn was studied using dynamic thermogravimetry in air at a heating rate of 6°C/min up to a temperature of 500°C. The thermal stabilities of the samples grafted with various acrylate monomers to various percentages of grafting were computed from their primary thermograms by calculating the values of IDT, IPDT, and E*. The results show that the thermal stability increases with increase in graft‐on per cent, and the thermal stabilities of natural cotton and cotton grafted with different monomers are in the order ethyl > methyl > natural cellulose > methyl methacrylate > n‐butyl acrylate.
Fractionation of ethylene–propylene copolymers
Authors: Ogawa Toshio , Tanaka Shoichi , Inaba Tadami 
Published: April 2003

AbstractEthylene–propylene (EP) copolymers were fractionated according to chemical composition, molecular weight, or monomer sequence length, which are fundamental distribution factors. Cloud points of polyethylene (PE), polypropylene (PP), and EP copolymer were determined prior to the fractionation. From the results, it was estimated that xylene–butyl cellosolve and tetralin–ethyl carbitol systems were suitable for the fractionations according to chemical composition and molecular weight, respectively. EP random‐type copolymers were fractionated using a xylene–butyl cellosolve system. Separations according to chemical composition were obtained as expected. Then, the above polymer fractions were further fractionated in a tetralin–ethyl carbitol system. and the dependence on molecular weight was observed fairly well. Furthermore, fractionation according to monomer sequence length was satisfactorily achieved by solvent extraction using ethyl ether, n‐hexane, cyclohexane, and n‐heptane. Therefore, it is concluded that the more detailed characterizations of EP copolymers are made possible by a combination of these techniques.
Friction reduction degradation in dilute poly(ethylene oxide) solutions
Authors: Gold P. I. , Amar P. K. , Swaidan B. E. 
Published: April 2003

AbstractDegradation of friction‐reducing effectiveness of dilute poly(ethylene oxide) solutions subjected to continuous agitation is examined in disk flow. A residual or steady‐state effectiveness is observed which disappears only at a sufficiently high Reynolds number. The onset of friction reduction appears to occur within the transition region and seems to be independent of solution concentration. The onset of degradation also appears to be independent of concentration. Prior shear working is shown to have a significant effect on residual friction‐reducing effectiveness only when the shear working is performed in a more intense shear field than that in which the friction‐reducing effectiveness is evaluated. Degradation of friction‐reducing effectiveness is compared to corresponding changes in viscosity‐average molecular weight. The experimental results are interpreted in terms of a model of the interaction between polymer molecules and the turbulent flow field.
Sorption behavior of mercuric and methylmercuric salts on wool
Authors: Friedman Mendel , Harrison Craig S. , Ward Wilfred H. , Lundgren Harold P. 
Published: April 2003

AbstractSorption by wool of mercuric nitrate, mercuric chloride, and methylmercuric chloride was measured by atomic absorption spectroscopy. Both inorganic mercury compounds are efficiently taken up at low concentrations from acid solution. The rate of binding from the nitrate is appreciably slower than from the chloride. Methylmercuric chloride is bound slowly at low pH, rapidly at pH 6. The extent of its binding is roughly 10% to 20% of that of the inorganic salts. The wool‐bound mercury can be recovered by serial extraction with aqueous citrate or ethylenediaminetetraacetate at pH 6. The residual, firmly bound mercury is roughly equivalent to the sulfhydryl sulfur. Sorption of inorganic mercury compounds at low pH roughly follows a Freundlich isotherm in the concentration range 5×10‐6 to 10−1M. Sorption of methylmercurie chloride at pH 6 follows a roughly parallel isotherm in the range 5×10−6 to 10−3M. These data suggest the potential value of wool and other animal keratins to remove and recover mercury from contaminated water. Wool may also serve as an instructive model for mercury binding and release in the body.
Identification of cis‐4,5‐epoxy‐2‐pentenal from pyrolysis of H3PO4‐treated cellulose
Authors: Lam L. K. M. , Fung D. P. C. , Tsuchiya Y. , Sumi K. 
Published: April 2003

AbstractAn important product, C5H6O2, from the pyrolytic decomposition of phosphoric acid, treated cellulose was isolated and identified as cis‐4,5‐epoxy‐2‐pentenal. NMR, IR UV, and mass‐spectral data of this product were analyzed and discussed. A method for the preparation of cis‐4,5‐epoxy‐2‐pentenal is presented, and a mechanism for its formation is proposed.
The drag reduction of chrysotile asbestos dispersions
Authors: Peyser Paul 
Published: April 2003

AbstractThe drag reduction (DR) of dispersions of Chrysotile asbestos fibers in aqueous solutions of Aerosol OT and in ethylene glycol, and of glass microfibers in water at a pH of 3 were studied as a function of concentration and temperature with a rotating disc apparatus. Only the dispersions of asbestos in aqueous Aerosol OT showed DR comparable to poly(ethylene oxide) WSR 35 (∼500,000 MW), and these dispersions were more fully studied. As was the case with Polyox WSR 35, the asbestos dispersions achieved maximum DR at a concentration of about 200 ppm. They showed no DR temperature dependence at constant Reynolds number at high concentrations but displayed a decreasing DR with increasing temperatures at low concentrations. However, the temperature effect was much smaller for the asbestos dispersions than for Polyox. The asbestos dispersions also showed a much smaller decrease of DR with time at a given disc rotation than was previously measured for poly(ethylene oxide). Electron microscope evidence indicated that less than 10% of the fibers were fully separated, and it is probable that these were the fibers which were primarily active in DR. Hence, if complete separation and dispersion could be accomplished without breaking the fibers, Chrysotile asbestos would be a most potent, not very shear‐degradable DR species.
Diffusive and bulk flow transport in polymers
Authors: Yasuda H. , Peterlin A. 
Published: April 2003

AbstractThe transport properties of polymer membranes in various forms which have a wide variety of practical applications, such as ultrafiltration, dialysis and blood oxygenation, depend upon the structure (homogeneous or heterogeneous) and the transport characteristics of the membrane material. Among many possible driving forces of transport, the pressure gradient and the concentration gradient are considered to be the most general forces encountered in practical use of polymer membranes. The transport of various permeants (gas, dissolved gas, liquid solvent, and solute) through porous and homogeneous (nonporous) polymer membranes under these driving forces is discussed. In the absence of a pressure gradient, the transport of permeants can be described as diffusion, regardless of the permeant phase and the membrane structure. In the presence of a pressure gradient, the transport of permeants may occur by diffusion and/or bulk flow of the permeants, depending upon the membrane structure and the nature of the permeant. In homogeneous membranes, many noninteracting permeants such as gases and nonsolvent vapors permeate by diffusion under applied pressure gradient: however, solvent in homogeneously swollen membranes moves by bulk flow and the diffusion depending on the degree of swelling of the membrane. In heterogeneous membranes under applied pressure, most permeants move by bulk flow.
An experimental study of adsorption of polymers on activated carbon: Butadiene—styrene polymers and poly(methyl methacrylate)
Authors: Sadakne George S. , White James L. 
Published: April 2003

AbstractAn experimental study of the extents and rates of adsorption of several polymers from various solvents onto activated carbon has been carried out. The polymers studied included polystyrene, polybutadiene, butadiene–styrene copolymers and poly(methyl methacrylate). The solvents included toluene, cumene, decalin, 2‐pentanone, and methyl ethyl ketone (MEK). Polystyrene is adsorbed from the different solvents in the order MEK, 2‐pentanone, cumene, toluene, decalin. The adsorption from toluene, decalin, and cumene is in the order polystyrene, polybutadiene butadiene—styrene copolymer. The fact that the copolymer is adsorbed less than either homopolymer is striking. The variation of molecular weight distribution with extent of adsorption has been studied. It was found that low molecular weight polymer was preferentially adsorbed in the early stages of the experiment, but high molecular weight polymer was adsorbed at longer times. The apparent adsorption rate constants have been evaluated for the various systems and resolved into external mass transfer, internal (intraparticle) mass transfer, and adsorption rate constants. The experimental data have been applied to the prediction of the elution of the polymers from chromatographic columns packed with activated carbon.
A model for gel drying
Authors: Shah Y. T. , Porter J. H. 
Published: April 2003

AbstractA theoretical model for drying of a thin gel film is presented. The model is based upon the premise that as solvent is removed from any portion of a gel structure which is permeable by the solvent, the structure shrinks locally to fill the voids left by the solvent. The diffusion coefficient of solvent through the gel film is assumed to be an exponential function of concentration and temperature. The governing equations for the model indicate that for nonisothermal drying, the results of drying and shrinkage rates are functions of 13 independent dimensionless system variables. These results are obtained with the help of a computer solution of the proposed model. The computer results indicate that, except under extreme temperature conditions, the drying and shrinkage rates are most influenced by dimensionless groups M, P, and P̄, defined by eq. (9) of the paper. Furthermore, the drying and shrinkage rates are essentially independent of groups M and P for the values of M and P greater than approximately 100 and 10, respectively. The effect of variable solvent diffusivity on approximate time to achieve the steady‐state drying and shrinkage rates is approximately handled by defining a dimensionless time variable τ in terms of average solvent diffusivity. Finally, some experimental data on drying and shrinkage rates of isothermal drying of lyphogel film under natural convection condition are obtained. These data are found to be in qualitative agreement with similar computer predictions by the proposed model.
Poly(α‐methylstyrene)–poly(dimethylsiloxane) block copolymers
Authors: Noshay Allen , Matzner Markus , Karoly Gabriel , Stampa Guido B. 
Published: April 2003

AbstractBlock copolymers were synthesized by the condensation of dihydroxyl‐terminated poly‐(α‐methylstyrene) oligomers and bisdimethylamino‐terminated poly(dimethylsiloxane) oligomers. Manipulation of block molecular weight produced copolymers ranging in composition from 21% to 73% poly(dimethylsiloxane). Compression moldablity was found to be good. Physical properties were dependent upon siloxane content, varying from high modulus, low elongation to low modulus, high elongation materials. High siloxane‐content compositions exhibited elastomeric properties due to the two‐phase morphology of these systems. Glass transition temperatures were observed as low as −120°C for the poly(dimethylsiloxane) block and as high as + 140°C for the poly(α‐methylstyrene) block. Even higher poly(α‐methylstyrene) transition temperatures may be possible by using higher molecular weight oligomers.
The autoignition of polymers
Authors: Miller Bernard , Martin J. Ronald , Meiser Charles H. 
Published: April 2003

AbstractA consistent and relatively simple method is presented for studying the unpiloted ignition of polymeric materials in contact with hot air. The ignition behavior of a particular polymer as determined by its bulk properties may be characterized by the relationship between sample mass and ignition time at constant area for a series of furnace temperatures. Extrapolation of this linear relationship at a given furnace temperature to zero mass results in an intrinsic ignition time which represents the rate of the ignition process when the time required to heat the sample to its decomposition temperature has been eliminated, i.e., the sample is brought to its decomposition temperature instantaneously. The temperature dependence of this intrinsic ignition time shows an Arrhenius relationship with an apparent activation energy of 8–10 kcal/mole for all but one material investigated. This indicates that the mechanism controlling the kinetics of such an ignition process is a physical one, most likely the diffusion of combustible gaseous products into the heated air surrounding the sample.
A new fiber‐sampling technique for infrared spectroscopy as applied to nylon 6 and poly(ethylene terephthalate)
Authors: Tirpak G. A. , Sibilia J. P. 
Published: April 2003

AbstractA number of techniques have been used in the past for obtaining the infrared spectra of fine fibers. A new technique has been developed which overcomes many of the problems of previous methods. The present technique involves winding a single filament between two salt windows which are separated by a spacer which is the same or slightly greater in thickness than the fibers. This results in a layer of adjacent parallel fibers. Good‐quality polarized infrared spectra were obtained on oriented poly(ethylene terephthalate) and oriented nylon 6 fibers with the new technique. The data demonstrate the high level of “A” conformation orientation present in highly drawn nylon 6 fibers and the existance of chain folds in drawn poly(ethylene terephthalate) fibers. The structural changes which occur during the shrinkage of nylon 6 fibers are also demonstrated.
Dynamic loss energy measurement of tire cord adhesion to rubber
Authors: Murayama Takayuki , Lawton Ernest L. 
Published: April 2003

AbstractThe dynamic loss energy measurements for characterizing adhesion using Vibron DDV‐II have been applied to the tire cord–rubber composite system, and the relationships between these dynamic measurements and static adhesion test (H‐block pull test and strip peeling test) were also investigated. Tested samples were the commercial nylon 66 tire cord and poly(ethylene terephthalate) tire cord with two adhesive systems. The degree of adhesion (adhesion factor) was obtained as the energy dissipation at the tire cord‐to‐rubber interface as measured by dynamic testing. It was shown that energy dissipation is increased at the filament–matrix interface when the composite is subjected to continuous cyclic loading if a condition of poor adhesion exists. The test was based upon the separation of the total energy dissipation in a composite under cyclic loading into a portion associated with viscous properties of the constituent materials and a second portion resulting from the lack of perfect bonding in the interfacial regions. The strip peeling measurement of adhesion exhibited an approximately linear correlation with the dynamic loss energy measurement of adhesion. The dynamic energy loss measurement is suggested as a potential source of information on the rheological characteristics of the interfacial region of bonding.
Gas‐filled polymers. I. Void morphology of polyethylene
Authors: Kolbeck A. G. , Uhlmann D. R. , Calvert P. D. 
Published: April 2003

AbstractMorphologic studies of gas‐filled polyethylene show a characteristic void structure, with an interior region containing distinct gas bubbles surrounded by a surface layer of void‐free polymer. The voids in the bubbled region frequently show an elongated shape with the long dimension oriented parallel to the surface of the specimens. The gas–polymer interface within individual voids is composed of fibrils of the polymer extending into the interior of the void. Studies of the annealing temperatures required to obtain gas bubbles in the material and of the melting range of the ungasified polymer indicate that melting of the crystalline component of polyethylene is required for void formation.
Stress–strain optical study of styrene–butadiene and ethylene–propylene rubbery copolymers
Authors: Durisin J. , Williams H. Leverne 
Published: April 2003

AbstractBirefringence–temperature behavior at constant stress during cooling and heating of styrene–butadiene and ethylene–propylene copolymers between −120°C and +60°C was investigated. Copolymer composition, thermal treatment, and stress levels were shown to have a pronounced effect on the photoelastic properties.
Effect of recrystallization on the solubility of poly(vinylidene chloride)
Authors: Wessling R. A. , Carter D. R. , Ahr D. L. 
Published: April 2003

AbstractA study of the crystallization of poly(vinylidene chloride) from dilute solution in various solvents was carried out. The temperature at which the polymer dissolved was dependent on crystallization history. The minimum solution temperature obtained by recrystallization at high undercooling and redissolving is the preferred parameter for characterizing solvents for poly(vinylidene chloride).
Sur la dégradation thermique du polychlorure de vinyle. VI. Etapes initiales—etude générale préliminaire
Authors: Guyot A. , Bert M. 
Published: April 2003

AbstractA differential conductimetric apparatus allowing the continuous titration of HCl carried by a stream of gas with a limit sensitivity of 40 nanograms is described and applied to study the initial steps of poly(vinyl chloride) thermal degradation. The powdered sample is placed in a quartz cell which may be closed and detached and placed at a chosen time interval in a reflexion diffuse UV spectrometer. The dehydrochlorination process begins just above Tg; the isotherms under argon show, after a variable time, a steady state with a zero order and an activation energy of 22 kcal. For a dehydrochlorination ratio (DR) less than 1000 ppm, the shape of the UV visible spectrum does not depend on the DR, and for the same DR it does not depend on the degradation temperature. A plot of the reflectance ratio versus the DR shows a coloration process in two steps: a rapid step followed by a slower step. The phenomenon, which does not depend on the physical state of the sample, tends to disappear if the amount of polymer is lowered and if the rate of flow of the gas is increased. It suggests that the HCl formed upon the dehydrochlorination process remains partly dissolved in the polymer. Further proof of the dissolution of HCl in the polymer is given, and a through method of titration is proposed. It is suggested that the initial steps of the dehydrochlorination follows an ionic mechanism, and might be partially reversible and diffusion controlled, although the autocatalysis which involves a rather high dehydrochlorination ratio and the presence of a large amount of dissolved HCl might initiate the radical process.