bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of atmosphere on radiation‐induced crosslinking of polyethylene. Part IV. Sensitizing effect of nitrous oxide and xenon
Authors: Okada Yoichi 
Published: April 2003

AbstractLow density polyethylene film was irradiated with gamma‐rays from Co60 in atmospheres of nitrous oxide and xenon. A plot of solubility (S + S1/2) against reciprocal of irradiation dose gives a nearly straight line in each case. The probability of crosslinking increases by 44% in N2O as compared with vacuum irradiation, and increases by 10% in Xe. On the other hand, the probability of main‐chain scission is scarcely affected by these gases. Therefore the increase in gel fraction due to these gases is not due to the protection against main‐chain scission, but is caused mainly by the sensitization against crosslinking. Furthermore, the formation of trans vinylene unsaturation is also sensitized by these gases.
Curing relations of hexakis(methoxymethyl)melamine and its combinations with acrylic polymers
Authors: Saxon Robert , Lestienne Firmin C. 
Published: April 2003

AbstractThe curing of hexakis(methoxymethyl)melamine (HMM) alone and in blends with functionally substituted acrylic polymers was monitored by means of torsional braid analysis, infrared spectroscopy, weight change, and analysis of the volatile by‐products. HMM alone, when heated with a strong acid catalyst, forms thermoset condensation polymers which evidently have the same methylene‐bridged structure as conventional melamine‐formaldehyde resins; the major elimination product is methylal. When HMM is blended with an acrylic polymer containing methacrylic acid units, the acrylic chains are crosslinked by elimination of methanol and formation of methylene ester linkages between the acid groups and the melamine. The crosslinking reaction proceeds with or without strong acid catalysis and is many times faster than the self‐condensation of HMM. Acrylic polymers containing primary hydroxyl groups (derived from 2‐hydroxyethyl methacrylate) also undergo acid‐catalyzed reaction with HMM, and at a rate so much faster than analogous carboxylated polymers, that storage stability of the catalyzed resin becomes a serious problem. If a weaker catalyst, such as phthalic anhydride, is used, the curing reaction is very much slower. In order to develop the maximum number of new linkages, according to any of the experimental criteria, all of these systems must be heated for longer times, or at higher temperatures, than are customarily used in thermosetting resin technology. Thus the known utility and durability of such acrylic/melamine resins are achieved with only a fraction of the total number of crosslinks which are potentially capable of formation.
Unsymmetrical diisocyanates. II
Authors: Case L. C. 
Published: April 2003

AbstractIt has long been known that certain aromatic diisocyanates exhibit unequal reactivities of the two isocyanate groups. However, the degree of unsymmetry of reactivity in the previously known diisocyanates is limited. In this research, a number of structurally unsymmetrical diisocyanates were screened for unsymmetry of reactivity by reacting the diisocyanate with excess isoamyl alcohol in chlorobenzene solvent. The reaction was followed by observing the decrease of infrared absorption of the solution at 4.5 μ. A number of diisocyanates were found to have desirably high degrees of unsymmetry in reactivity. These diisocyanates, and the ratio of apparent half‐lives of reaction for the two isocyanate groups are: 2,6‐diethyl‐p‐phenylenediisocyanate, 100; 2,6‐dimethyl‐p‐phenylenediisocyanate, 80; 2‐bromo, 6‐methyl‐p‐phenylenediisocyanate, 50; 2,6‐dichloro‐p‐phenylenediisocyanate, 30; and 3,5‐diethyl‐4‐4′‐diisocyanato‐diphenylmethane (DEMDI), 49.
Thermal expansion of photomechanical materials
Authors: Colao Angelo , Becker Herbert 
Published: April 2003

AbstractA quartz thermal expansion apparatus was developed to measure the thermal expansion of photomechanical plastics. Three different methods of motion measurement correlated with a maximum error of ±1% for three different models of Hysol 4290 epoxy. The thermal expansion of a 30% plasticized epoxy was determined and was found to exhibit essentially the same characteristics as the 4290 epoxy except for a shift in the temperature scale.
Unsymmetrical diisocyanates. III. The kinetics of reactions of DEMDI
Authors: Case L. C. , Li K. W. 
Published: April 2003

AbstractIn the previous investigation it was found that 3,5‐diethyl‐4,4'‐diisocyanatodiphenylmethane (DEMDI) exhibits a marked asymmetry in the reaction with isoamyl alcohol. Since DEMDI is potentially rather cheap, and since the unsymmetrical nature of the diisocyanate is quite advantageous in certain urethane formulations, the reactions of this diisocyanate with a series of model compounds were investigated. The model compounds were chosen so as to represent the important classes of functional groups commonly reacted with diisocyanates in the preparation of polyurethanes. The compounds used were isoamyl alcohol, 2‐octanol, water, 2,6‐diethylaniline, 1‐n‐butyl‐3‐phenylurea, and 1‐(4‐n‐butylphenyl)‐3‐(methylphenyl)‐urea. The reactions were conducted in dry diglyme solvent. The extent of reaction of the isocyanate groups was followed by reaction with excess di‐n‐butylamine and back‐titration with hydrochloric acid. Tetramethyl‐1,3‐butanediamine and dibutyltin dilaurate were used as catalysts in some runs. The results show that DEMDI has a desirably high asymmetry of reaction with alcohols or water at low temperatures. Catalysis with dibutyl dilaurate markedly increases this asymmetry. An increase in temperature generally decreases the asymmetry of DEMDI reactions, so that elevated temperatures should be avoided in prepolymer formation. The dibutyltin dilaurate is a more effective catalyst than the diamine for all of the reactions studied. The diamines are very poor catalysts for urea reactions, whereas the tin compound is quite effective.
Effects of mechanical action on the electron paramagnetic resonance of wool and silk
Authors: Windle J. J. , Wiersema A. K. 
Published: April 2003

AbstractWool fibers and cloth damaged by mechanical action such as abrading and grinding show strong EPR signals. Silk fibers after grinding also show strong EPR signals. Both wool and silk ground in a dry nitrogen atmosphere exhibit a doublet spectrum attributed to a ·CH radical on the polypeptide chain. In wool, a complex curve centered at g = 2.025 is observed. It is attributed to a CH2S· radical resulting from the rupture of the disulfide bond in the cystine residue. These radicals are stable for many months in a nitrogen atmosphere or vacuum. In dry oxygen the spectrum of the ·CH radical is transformed within a few hours from a double into a single, narrow curve, whereas the spectrum characteristic of the cystine radical disappers more slowly. In the presence of water vapor both radical species are rapidly destroyed and their spectra disappear. The mechanisms for the production of free radicals by mechanical action are believed to be direct chain rupture or localized pyrolysis, coupled with migration to specific radical traps in the protein.
Hydration and density of collagen and gelatin
Authors: Fels I. Gordon 
Published: April 2003

AbstractThe water sorption by adult and embryonic native and insoluble collagen was investigated, along with that of calfskin gelatin. Greater sorption was obtainable with the collagen fractions than with gelatin, but the technique could not distinguish the fractions themselves. The suggestion is made that the greater sorption by collagen over gelatin and differences in apparent wettability between the adult and embryonic insoluble collagen might be explained by the formation of helical grooves with aging. Density measurements of the collagen fractions indicate that collagen becomes more crystalline with aging. This also applied to the insoluble collagen. These results are consistent with the view that differences in collagen solubility are due to differences in molecular ordering. The density of the insoluble collagens and gelatin passes through a maximum at 3–4% sorbed water. The phenomenon is explained on the basis of water bridges comprised of a single water molecule double hydrogen bonded to closely aligned chains. A discussion is presented in this connection. A calculation based on the density yields a molecular volume of 4.32 × 10−19 cm.3 For tropocollagen. This is in agreement with the molecular dimensions and consistent with the idea that collagen is formed from an aggregation of the monomer.
Polymers as fibers
Authors: Tippetts E. A. , Zimmerman J. 
Published: April 2003

AbstractThe relation between polymer and fiber structure and fiber properties is discussed. The specific effects of intermolecular forces, chain stiffness, monomer unit regularity, crystallinity, crosslinking, orientation, molecular weight, and chemical composition on the important fiber properties of melting point, modulus, elasticity, or recovery from strain, tensile strength, moisture adsorption, and dyeability are discussed in some detail. An example is given to illustrate the role of today's sophisticated engineering in further controlling and modifying fiber properties.
Gas permeability apparatus for films and sheets
Authors: Huldy H. J. 
Published: April 2003

AbstractAn apparatus for measuring the gas permeability of films and sheet material has been developed at the Central Laboratory TNO, Delft (The Netherlands). The apparatus consists of a high vacuum unit, connected to six film holders of a new design and construction. The pressure of the gas which permeates through the film in a constant volume, is measured with the aid of McLeod manometers. The apparatus was developed for rapid, accurate measurements of materials of very low permeability, but it is also suitable for films of high permeability, but it is also suitable for films of high permeability. The range of permeabilities to be measured is between 10−7 and 10−13 cm.3 (S.T.P.)‐film thickness/cm.2‐sec.‐cm. Hg. The measuring time for the 10−13 range is about 6 hr. (for plastic laminated with aluminum) and for the 10−7 range is about 15 min. (for polyethylene). Measurements can be executed simultaneously on six heads and easily at various temperatures and relative humidities. The apparatus is suitable both for research purposes and for routine measurements in industry.
Effect of agitation and molecular weight on polymer adsorption and deflocculation
Authors: Jankovics L. 
Published: April 2003

AbstractThe rates of adsorption of PAM's were measured on calcium phosphate at various intensities of agitation. Vigorous mechanical stirring promotes the adsorption by degrading the floccules, thus providing new surfaces available for further adsorption of polymers. The rising parts of the rate curves correspond to the breaking up of flocs or “deflocculation” by the applied mechanical stirring. The flat portions of the curves in the high stirring time range indicate complete redispersion; no further surfaces are available for the adsorption of polymer flocculants. The effect of the intensity of agitation upon adsorption was investigated. Increasing the number of revolutions of the stirrer causes the adsorption curves to rise more sharply. This suggests that the deflocculation also becomes more rapid. At equimolar initial concentrations the rates of adsorption and deflocculation decrease with increasing molecular weight.
Dipolar solvents in polyurethane foams
Authors: Kuryla William C. 
Published: April 2003

AbstractA number of catalytic solvents have been discovered for the polyurethane foaming process. These solvents include N,N‐dimethylformamide (DMF), dimethyl sulfoxide (DMSO), formamide, and a number of others. The catalytic effectiveness of a given solvent appears to be dependent on its dipole moment, water solubility, and the size or bulkiness of the groups which are attached to the carbonyl carbon or sulfur atom of the amides and sulfoxides, respectively. Steric effects play a very important role in controlling the catalytic efficiency of these solvents. A mechanism is proposed for the catalytic action of these solvents in the polyurethane reaction.
A note on the conductivity and modulus of carbon black‐loaded rubbers
Authors: Payne A. R. 
Published: April 2003

AbstractElectrical conductivity and dynamic shear modulus measurements were made simultaneously on carbon black‐filled natural rubbers. G′ the in‐phase shear modulus, and the electrical conductivity, C, were shown to vary in an approximately similar way as the amplitude of dynamic oscillation was increased. Both G′ and C altered sigmoidally from a high value at low amplitudes of oscillation to very much reduced values at high amplitudes of oscillation. Recovery curves for conductivity were shown to be parallel with respect to the logarithm of the time (in minutes), even though the initial deforming amplitudes varied widely.
Degradation and stabilization of polyacetal copolymers
Authors: Berardinelli F. M. , Dolce T. J. , Walling Cheves 
Published: April 2003

AbstractAcetal copolymers prepared from trioxane and ethylene oxide consist of polyoxymethylene segments with oxyethylene units distributed in the chain. These oxyethylene units profoundly affect the thermal and chemical behavior of the polymer. The presence of the oxyethylene units renders the copolymer amenable to thermal or base hydrolytic treatment which results in a final product with stable endgroups. The copolymers so obtained are significantly more stable, thermally and chemically, than acetylated polyoxymethylene homopolymer.
Continuous measurement of polymerization rates over the entire conversion range with a recording dilatometer
Authors: Rubens L. C. , Skochdopole R. E. 
Published: April 2003

AbstractA new type dilatometer has been described which will automatically record the volume changes which occur during the entire course of polymerization reactions. Experiments have shown that the weight per cent polymer in a monomer solution is more accurately described as a function of additive densities of monomer and polymer than of additive volumes of monomer and polymer. The operation of the dilatometer, the relation of the observed volume changes to monomer conversion to polymer, and the possible errors involved in these type measurements have been discussed. The apparatus has been used to obtain rate curves for the polymerization of both linear and crosslinked vinyl monomer compositions over the entire course of polymerization, despite the early formation of a firm crosslinked gel structure in the latter case.
Mechanical properties of highly filled elastomers. II. Relationship between filler characteristics, thermal expansion, and bulk moduli
Authors: Van Der Wal C. W. , Bree H. W. , Schwarzl F. R. 
Published: April 2003

AbstractModel substances were prepared of a polyurethane rubber filled with different amounts of various fractions of sodium chloride. Eight filler fractions were used of sizes in the range of 1–480 μm. The amount of filler was varied between 0 and 50 vol.‐%. An experimental method is described by which thermal expansion and bulk modulus of an isotropic material may be simultaneously determined as functions of temperature. The materials were investigated for thermal expansion and bulk modulus. All filled and unfilled samples show a glass–rubber transition, at which temperature the thermal expansion coefficient increases considerably and the bulk modulus decreases sharply. These temperatures do not depend on amount or size of filler. The values of the bulk moduli and the thermal expansion coefficients are independent of filler size, but depend considerably on the volume fraction of filler. These values may be predicted by means of a simple macroscopic theory (Fröhlich‐Sack‐Van der Poel,) describing the bulk modulus, the thermal expansion, and the density of the composite material in terms of the corresponding properties of the components and of their relative amounts.
Effect of dispersion on the dynamic properties of filler‐loaded rubbers
Authors: Payne A. R. 
Published: April 2003

AbstractA study has been made of the effect of increased time of mixing carbon black in rubber on the dynamic properties of the carbon black‐rubber vulcanizates. Increased time of mixing reduces the dynamic modulus and dynamic viscosity as well as the phase angle at moderate amplitudes of oscillation. The changes in dynamic properties with mixing time are shown to be associated with the dispersion of the carbon black.
Interfacial polycondensation of nylon 610 in continuous cascade systems
Authors: Kispert Robert C. , Griskey Richard G. 
Published: April 2003

AbstractThe interfacial polycondensation of nylon 610 in unstirred, continuous, cascade systems has been studied. It was found that yields increased with increased reactant flow rates. The increase was shown to result from improved mass transport due to the change from molecular diffusion at low flow rates to eddy diffusion at high flow rates. The effect of improved mass transfer was also shown in the behavior of plots of polymer intrinsic viscosity versus sebacoyl chloride concentration.
Stress softening in natural rubber vulcanizates. Part II. Stress softening effects in pure gum and filler loaded rubbers
Authors: Harwood J. A. C. , Mullins L. , Payne A. R. 
Published: April 2003

AbstractConsiderable stress softening (Mullins effect) occurs in both gum and filler loaded vulcanizates of natural rubber and SBR. When compared at the same stress, the extent of softening is similar in both gum and filled vulcanizates. The stress softening is shown to be mainly due to changes in the rubber phase in the filled vulcanizate, and related to that of the gum vulcanizate by the use of the strain‐amplification factor discussed in Part I of this series.
Oxidative stress relaxation of natural rubber vulcanizates at high strains
Authors: Bell C. L. M. 
Published: April 2003

AbstractThe effect of high strain on the oxidative stress relaxation of several natural rubber vulcanizates has been investigated. In the case of peroxide and CBS accelerated vulcanizates, the rate of stress relaxation increases with increasing strain, and this increase appears to be due to an increase in the rate of oxidation of the network. TMTD and MBT vulcanizates showed marked premature failure at high strains and no oxidative stress relaxation measurement could be made. It was found that the tensile strength of a TMTD vulcanizate was at least 20% higher in vacuum than in oxygen, due, it is believed, to stress‐induced oxidative degradation at the tip of surface flaws in the rubber.
The influence of structure and processing conditions on engineering mechanical properties in bulk crystallized isotactic polypropylene
Authors: Reinshagen J. H. , Dunlap R. W. 
Published: April 2003

AbstractA study of the influence of processing conditions and structure on engineering mechanical properties was conducted in bulk isotactic polypropylene. The influence of one processing parameter, undercooling, defined so as to account for both pressure and temperature effects, was particularly studied.Improved mechanical properties were found with increased undercooling. At low undercoolings, brittle failure without yield occurred, presumably the result of a sparsity of intercrystalline links under these conditions. As undercooling was increased, failure occurred after yielding as failure stress elevated dramatically, apparently because of greater link density. A modest improvement in yield stress with increased undercooling was attributed to the increasingly crosshatched lamellar structure produced at higher undercoolings, a structural trend confirmed by electron microscopy.Spherulite size, varied by altering melt history (melt temperature and time at melt temperature) at constant undercooling, was found to have no effect on engineering yield stress. This result indicates that apparent yield stress–spherulite size effects found by several earlier investigators were probably caused by structural variations other than spherulite size.
Hyperfiltration membranes prepared by radiochemical grafting of styrene onto poly(tetrafluoroethylene). Influence of the size and shape of emulsion particles used to obtain the PTFE film
Authors: Munari S. , Vigo F. , Nicchia M. , Canepa P. 
Published: April 2003

AbstractThe hyperfiltration performances of membranes obtained from PTFE films sintered with different granulometric distribution emulsions were studied. It has been possible to show that: (1) large spherical particles lead to high flux, poor rejection membranes, and vice versa for small spherical particles; (2) the particle shape affects the membrane properties. “Stick” shaped particles lead to better rejection properties than the spherical and “fibrillar” ones. An attempt was also made to utilize a PTFE/PMMA porous support to make asymmetric membranes.
Effect of orientation of two‐dimensional filler on dynamic mechanical properties of cured epoxy resin
Authors: Iisaka Katsuyoshi , Shibayama Kyoichi 
Published: April 2003

AbstractDynamic mechanical properties of cured epoxy resin filled with mica flake, as two‐dimensional filler, were investigated over the temperature range from room temperature to 200°C. Two series of composite specimens were examined. One is series RM, containing ill‐oriented mica flakes, and another is RMB, containing mica flakes oriented in the direction parallel to the specimen surface. Both tensile and shear moduli for RMB series were determined by dynamic mechanical experiments. The tensile modulus for RMB series was always higher than that for RM series over the whole temperature range. The shear modulus for RMB series was low, compared with that of the tensile modulus in the rubbery state. The behavior of the modulus reinforcement, observed both in the glassy and rubbery states, was compared with recently proposed theories of Wu and Padawer and Beecher. In the glassy state, the tensile modulus of RM series follows Wu's theory, while that of the RMB series agrees with Padawer and Beecher's theory. In the rubbery state, the tensile modulus of each series cannot be well explained by either theory. It was proposed that the tensile stress applied to the specimen was converted to shear stress in a thin resinous layer sandwiched by two mica flakes. The modulus behavior of the RMB series can be fully explained by this model.
Improvement of the impact strength of a blend of poly(vinyl chloride) with copolyester thermoplastic elastomer by heat treatment
Authors: Nishi T. , Kwei T. K. 
Published: April 2003

AbstractDynamic mechanical properties and impact strength of a blend of poly(vinyl chloride) with a copolyester thermoplastic elastomer were studied. The microscopic structure of the blend was dependent on the thermal history of the specimen. By an appropriate heat treatment, the blend underwent phase separation with an attendant severalfold increase in room‐temperature impact strength. The mechanism of energy dissipation involves both crazing and shear flow processes.