bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of the pyrolysis of cellulose in the temperature range 250–300°C.
Authors: Lipska Anne E. , Parker William J. 
Published: April 2003

AbstractSamples of α‐cellulose, containing 0.11–0.14% ash, were isothermally pyrolyzed in a fluidized bath in a nitrogen environment at 250–298°C. Results were reported in terms of volatilization (based on weight‐loss measurements) and decomposition (in term of glucosan loss). The findings show three distinct stages of pyrolysis: (1) an initial period of rapid decomposition and weight loss; (2) a range in which both the volatilization and decomposition are of zero order; (3) a region in which the volatilization follows a first‐order rate, leaving a char deposit which does not undergo further pyrolysis. The degree of decomposition and volatilization occurring during the zero‐order phase increases with increasing temperature. A single activation energy of 42 kcal./mole describes both the decomposition and volatilization rates in the zero‐order phase over the entire 250–298°C. range.
Low‐temperature thermal expansivities of polyethylene, polypropylene, mixtures of polyethylene and polypropylene, and polystyrene
Authors: Zakin Jacques L. , Simha Robert , Hershey Harry C. 
Published: April 2003

AbstractLength‐temperature measurements on a series of polymer blends over the whole range of composition from pure polyethylene to pure polypropylene and one set of determinations on a 50:50 copolymer and on polystyrene are evaluated. The total crystallinity of the samples did not exceed 54%. The experimental procedure utilized a linear variable differential transformer without the use of a confining fluid, and the temperature ranged from about +20 to –185°C. A least‐square numerical differentiation procedure based on moving arcs is applied to yield directly the coefficients of thermal expansion as a function of temperature. The linear voltage differential transformer (LVDT) technique can detect transitions in which the change in thermal expansion coefficients is less than 10−5°C.−1. In polypropylene as well as the blends, the principal glass transition is clearly seen in the range observed by others, namely at about –9 to –14°C. Its location varies only slightly with composition at polyethylene contents less than 88 mole‐%. For polyethylene the transition region broadens noticeably. The results are suggestive of two transitions for 0 > T > –40°C. A second transition region is observed for either pure component around –126°C. Its location varies some what with composition. However, our results do not indicate the appearance of an additional transition region characteristic of the mixture. The copolymer exhibits a major transition at –61°C. in good agreement with earlier workers. The thermal expansion decreases again around –150°C. In general our observations concerning transitions below Tg are consistent with dynamic results.
Dielectric relaxations in poly(vinyl alcohol)
Authors: Shida Ken‐Ichi , Wada Yasaku 
Published: April 2003

AbstractDielectric constant and loss of poly(vinyl alcohol) films of different stereoregularity and crystallinity are measured at frequencies from 30 cps to 3 Mcps in the temperature range from −50 to 25°C. The relaxation strength of local mode relaxation is higher for atactic and syndiotactic samples than for isotactic samples when compared at zero crystallinity. This behavior is reasonably explained in terms of interchain hydrogen bonds in the former and intrachain hydrogen bonds in the latter. Dielectric constant and loss of the crystal aggregate of atactic poly(vinyl alcohol) are measured at temperatures from −50 to 140°C. The relaxation strength of the crystalline relaxation is in good agreement with the theory in which the relaxation is attributed to torsional vibration of crystalline chains. The weak loss peak at low temperatures which almost agrees with the local mode relaxation of bulk samples in the frequency‐temperature position is ascribed to the surface disorder of single crystals.
Cure of epoxy resins with aromatic amines: High heat‐distortion studies
Authors: Illman J. C. 
Published: April 2003

AbstractCastings having unexpectedly high heat‐distortion temperatures result when certain treated resins of the EPON EPON is a registered trademark of the Shell Oil Company.
828 type and about 75% of the stoichiometric amount of m‐phenylenediamine, are postcured for 10–20 hr. at 175–200°C. The improvement in heat‐distortion temperature is about 100°C., to values as high as 250°C. A recrystallized resin has given the highest values. Other glycidyl ethers of polyphenols have shown this phenomenon to a lesser degree, but other amine curing agents, including isomers and substitution products of m‐phenylenediamine, have not. Some evidence of a new curing reaction has been developed, by NMR and pyrolysis studies of model compounds, which supports the postulate that the m‐phenylenediamine is alkylated with a fifth epoxy group during the postcure, presumably at a ring carbon, resulting in greater crosslinking.
Rheological behavior of some acrylic fibers dissolved and spun in the ZnCl2 system
Authors: Tzentis L. S. 
Published: April 2003

AbstractConcentrated solutions of Acrilan 16 and 1656, Creslan 58 and 61, Orlon 42, and several experimental acrylic copolymers were prepared by dissolution of the staple fibers in 60% ZnCl2. The solutions were investigated rheologically. It was shown that a 3.5‐power relationship between the log of the Newtonian viscosity and the log of the molecular weight held for these solutions. Their elastic behavior as exhibited by the Barus effect was shown to be a function of shear stress and independent of molecular weight or composition. The ZnCl2 solutions of the acrylic fibers were spun under a harsh and a mild condition of coagulation. On physical and beinding properties of the fibers, mild coagulation has an effect similar to an increase in the content of the minor component of the copolymer. The loop properties and shrinkage of Turbo‐stretched fibers are shown to be mainly functions of their composition.
Strength of epoxy polymers. I. Effect of chemical structure and environmental conditions
Authors: Kwei T. K. 
Published: April 2003

AbstractThe breaking times of two crosslinked epoxy polymers under constant stresses were found to decrease at high temperature and humidity. The effect of humidity is, in terms of Bueche's theory, to increase the jump frequency of the polymer segments and to reduce the number of polymer units in cooperative motion in a jump process. When two epoxy polymers with different segment mobilities are compared at a given temperature, the stress‐breaking time relationship shifts toward longer times for the polymer with the higher transition temperature. The relation is also applicable in the presence of absorbed water molecules.
Detection of polymer transitions by measurement of thermal properties
Authors: Steere Robin C. 
Published: April 2003

AbstractThermal diffusivity, thermal conductivity, and specific heat per unit volume were measured for the following polymers: poly(ethylene terephthalate), polytetrafluoroethylene, polycarbonate, polypropylene, and three poly(vinyl chloride) samples plasticized to different levels. First‐ and second‐order transitions can be identified and located by the following features in the thermal property‐temperature curves: discontinuities, sharp inflections, broad inflections, sharp maxima, broad maxima, and change in linear slope. The results for poly(vinyl chloride) indicate the possibility of the use of plasticizer to control the thermal insulation properties of polymers, both for steady‐state and unsteady‐state conduction.
Studies with thin membranes. II. Measurement of membrane potentials and evaluation of membrane fixed charge density
Authors: Lakshminarayanaiah N. 
Published: April 2003

AbstractMembranes prepared from 5% Parlodion solution have been characterized. These and other membranes prepared from 0.38, 0.5, 1.0, 2.0, and 3.0% Parlodion solutions and already characterized, have been used severally to estimate the number of anionic sites present in them by two different methods. The potentiometric method, which is indirect, gave values of X̄P which were higher than X̄T, the values obtained by a direct isotopic method. The order was reversed for well‐characterized ion‐exchange membranes. These discrepancies were attributed to the shortcomings of the Teorell, Meyer, and Sievers theory of membrane potentials from which the potentiometric method was derived.
Mechanisms of oxidative degradation. II. Effect of metallic salts and metal deactivators on the oxidation of polybutadiene
Authors: Lee Lieng‐huang , Stacy C. L. , Engel R. G. 
Published: April 2003

AbstractThe metal‐catalyzed oxidation of polybutadiene is further discussed. The mild catalytic effect of stearic acid on the oxidation was shown due to the synergism of the acid and a stearate. The synergism was also found for the mixture of two different stearates. The results of the preliminary study on the stabilization are given. For both iron and copper stearates, zinc diethyldithiocarbamate (ZDC) was found to be the best metal deactivator, and the chelated mixture behaved as an oxidation inhibitor. Tetramethylthiuram disulfide (TMT), phenyl‐β‐naphthylamine, and oxamide were less effective.
Prediction of mechanical behavior of plastics undergoing decomposition from the combined effects of environmental exposure and stress
Authors: Goldfein S. 
Published: April 2003

AbstractA study was made to determine whether the behavior of plastics undergoing breakdown from the effects of stress, elevated temperatures, and chemical attack could be predicted by means of a mechanical‐chemical equation of state. Five systems were studied, the first four of which were tested for retention of strength at room temperature after environmental exposure: (a) glass‐reinforced polyester laminate exposed to an alkaline medium at elevated temperatures; (b) cellulose laminate exposed to elevated temperatures, resulting in oxidative degradation; (c) paper‐phenolic laminate exposed to elevated temperatures, resulting in further crosslinking followed by oxidative degradation; (d) heat‐resistant glass fiber polyester resin laminate exposed to very high degradative temperatures; and (e) same material and treatment as (d) except that the specimens were under stress during the exposure (stress rupture). It is concluded that the effects of the various environments on the mechanical properties of the plastics under study can be predicted accurately by use of a parameter of the equation of state representing a second‐order chemical reaction.
Degrees of heterogeneity of distribution of formaldehyde crosslinks in cotton cellulose
Authors: Rowland Stanley P. , Rollins Mary L. , Degruy Ines V. 
Published: April 2003

AbstractThe distribution of formaldehyde crosslinks in cotton cellulose has been followed by electron micrographic analyses of fiber cross‐sections and by kinetic analyses of rates of reactions of formaldehyde with cotton. Rapid and slow phases of the crosslinking reactions are indicated to extents which vary with the specific processes of reaction. A wide range in heterogeneity of distribution of crosslinks is found among the compositions investigated, the most heterogeneous distribution appearing in a high concentration of crosslinks in peripheral regions of the fiber. It is evident that additional substantial differences among the formaldehyde‐crosslinked cottons are due to different extents of reaction of agent per accessible hydroxyl group.
Swelling characteristics of gel fractions of formaldehyde‐modified cotton celluloses
Authors: Stark Samuel M. , Rowland Stanley P. 
Published: April 2003

AbstractA method for assessing extent of swelling of the gel fraction of formaldehyde‐modified cottons, employing cupriethylenediamine hydroxide as the swelling agent, is described. Substantial differences in apparent specific volumes of swollen gel fractions are observed for cottons crosslinked by different processes to the same level of agent. The apparent crosslink density measured by the swelling of gel fraction increases with formaldehyde content of the cotton; at 0.20% formaldehyde the order of increasing crosslink density in the various processes of reaction is as follows: nonaqueous system (forms D and D′) < aqueous system (forms W and W′) <swelling system (form F) < vapor system (form V) < bake‐cure system (form C).
Measurement of the limiting viscosity with a rotating sphere viscometer
Authors: Hermes R. A. 
Published: April 2003

AbstractThe rotating sphere viscometer is found to be a superior method of measuring the viscosity at zero shear rate of moderately viscous non‐Newtonian fluids. The effects of inertia and container walls are studied experimentally. The shear stress‐shear rate relationship is found to be linear at the low shear rates studied; thus yielding the limiting viscosity. This measured value of the limiting viscosity can be used in empirical models that are applicable over a wide range.
Alkylbenzene‐Maleic anhydride photoadducts as dianhydrides for epoxies and polyimides
Authors: Bradshaw J. S. , Stevens M. P. 
Published: April 2003

AbstractDianhydrides from ethylbenzene, cumene, and branched C5‐C6 alkylbenzene‐maleic anhydride photoadducts have a surprisingly high solubility in epoxy resins. Dianhydrides from benzene, toluene, and n‐C10‐C13 alkylbenzene adducts, which are homologs of the above, were not soluble. Epoxies cured with the ethylbenzene and cumene dianhydride adducts had higher heat distortion temperatures and flexural strengths than epoxies cured with two commerical monoanhydrides. High‐melting polyimides were also obtained with these two new dianhydrides.
Mechanisms for initiating thermal degradation of certain anhydride‐cured epoxides
Authors: Fleming Gerald J. 
Published: April 2003

AbstractThe mechanisms initiating the unusual thermal degradation of epoxy resins cured with methylbicyclo [2.2.1] hept‐5‐ene‐2, 3‐dicarboxylic anhydride were investigated. Two mechanisms were elucidated, each assuming greater importance than the other depending upon the severity of the thermal environment. One is an internal acid‐initiated mechanism operating from 240 to 350°C. under slow heating rates. The other is a reverse Diels‐Alder reaction which operates above 350°C., usually under instantaneous pyrolysis conditions such as encountered in ablation. These two mechanisms, working simultaneously, promote further crosslinking of the resin system giving rise to a greater amount of carbonaceous residue than would otherwise be expected.
Properties of linear elastomeric polyurethanes
Authors: Cooper Stuart L. , Tobolsky Arthur V. 
Published: April 2003

AbstractThe viscoelastic properties of some polyester‐urethanes are compared with the properties of other polymers. The behavior observed is anomalous in that these polyurethanes exhibit an unusually high value of modulus well above their Tg, unaccounted for by either crosslinking or crystallinity. Various experiments including incorporation of plasticizes of widely varying chemical composition have suggested interpretation of the system as a block copolymer, each block having its own Tg. Each of the two types of blocks seems to associate with similar blocks from other molecules.
Emulsion polymerization of ethylene. IV. Effect of recipe and polymerization conditions on polymer properties
Authors: Mantell Gerald J. , Stryker Harry K. , Helin Arthur F. , Jamieson Donald R. , Wright Charles H. 
Published: April 2003

AbstractSome Physical, chemical, and solution properties of polyethylene prepared by emulsion polymerization are described and compared with those of conventional high‐pressure polymer. The emulsion polymers contain an unusually large amount of low molecular weight material for the solution viscosities they exhibit. It is this low molecular weight material that contributes to the characteristic low elongation of the emulsion polymer, as well as to its wide distribution of molecular weights. The effect of changes in recipe and in conditions of polymerization on these properties is discussed. It is shown that some of the emulsifier present during polymerization becomes part of the polymer chain.
Polymerization of methyl methacrylate under ultrasonic irradiation. Part II. Polymerization in toluene–dimethyl sulfoxide mixed solvent
Authors: Osawa Zenjiro 
Published: April 2003

AbstractPolymerization of methyl methacrylate with Grignard reagents in mixed solvent of toluene and dimethyl sulfoxide (DMSO) under ultrasonic irradiation was carried out, and the effects of ultrasonic irradiation in connection with the mixed solvent on the stereoregularity and the properties of the polymers obtained were studied. The yield of polymers decreases with increasing concentration of DMSO in the solvent, and both yield and intrinsic viscosity of the polymers produced than ultrasonic irradiation are lower than those of polymers produced without it. A marked change in the configurational structure, namely, decrease in isotactic structure, is observed at a DMSO: toluene volume ratio of 5:95 in the series without ultrasonic irradiation, while a higher concentration of DMSO 15% by volume is required to obtain similar results in the series with ultrasonic irradiation.
Cooperative unfolding of α‐keratin
Authors: Feughelman M. 
Published: April 2003

AbstractThe unfolding of the α‐helices of the microfibrils in α‐keratin fibers such as wool proceeds in a cooperative manner. When a wool fiber is extended in water, the load‐extension curve obtained indicates on the basis of relationships derived from rate process theory, that the number of α‐helical residues n that unfold simultaneously is at least 50. This is probably an underestimation, as fiber diameter variability severely reduced any estimate of the value of n. Other experimental evidence is also indicated that support the existence of considerable mechanical cooperation between α‐helical components.
Behavior of fibers in cumulative extension cycling
Authors: Hearle J. W. S. , Plonsker H. R. 
Published: April 2003

AbstractThe cumulative extension cycling behavior is a combination of the effects of elastic recovery, viscoelasticity, and fatigue. The purpose of this research was to examine the elastic recovery aspects of the behavior. A model behavior idealized to include only elastic recovery was assumed and a computer program written to simulate cumulative extension cycling behavior based upon this idealized model. Tests were performed with an apparatus which removed the sample's slack after each cycle. A comparison of the experimental and computed results yielded an improved understanding of the elastic recovery aspects of the cumulative extension cycling behavior.
Propagation of vinyl polymers on clay surfaces. II. Polymerization of monomers initiated by free radicals attached to clay
Authors: Dekking Henri G. G. 
Published: April 2003

AbstractThe adduct of Kaolin and 2,2′‐azobisisobutyramidine hydrochloride has been used to initiate the polymerization of methyl methacrylate, styrene, styrene‐butadiene, vinyl acetate, chloroprene, acrylamide, and acrylonitrile. Both extractable and nonextractable polymers are obtained. The adduct of bentonite and 2,2′‐azobisisobutyramidine hydrochloride will initiate the polymerization of methyl methacrylate, acrylamide, vinyl acetate, 4‐vinylpridine, and styrene. Both extractable and nonextractable polymers are formed. When the bentonite or the hectorite adducts are more than 99% decomposed prior to the addition of methyl methacrylate, essentially no extractable polymer is formed, but an increased quantity of nonextractable polymer is produced. This is probably due to an increased accessibility of the monomer to the clay's interior surface and a decrease in the rate of chain termination. As is the case of the kaolin adduct, the clay surface of bentonite appears to accelerate the chain growth considerably.
Structural characterization of natural and vulcanized rubber by ozonolysis
Authors: Chakravarty Shom Nath , Sircar Anil K. 
Published: April 2003

AbstractA quantitative characterization of natural rubber, both as the raw polymer, and unaccelerated vulcanized samples containing different proportions of sulfur and ranging from soft to hard rubber, is reported. A value of 86% of the chains of natural rubber could be accounted for against 37% as reported by Harries assuming that levulinic acid is the sole degradation product. About 5% of the chain is present as a 3,4 structure which gives rise to formic acid in the degraded product. A small amount of sulfuric acid is present in the degradation product from the vulcanized samples, which decreases with the increases in the percentage of sulfur in the stock as well as the cure time. A chromatographic technique for the separation of levulinic, acetic, and formic acid in the presence of sulfuric acid is reported. It is observed that the total amount of carbon main chain escaping sulfuration decreases and the amount of insoluble fraction increases with increasing proportion of sulfur in the stock.
Copolymerization of unsaturated polyester with styrene in inverted emulsion
Authors: Horie Kazuyuki , Mita Itaru , Kambe Hirotaro 
Published: April 2003

AbstractCopolymerization of unsaturated polyester with styrene in water‐in‐oil (W/O) type emulsion was carried out with the use of various basic compounds as emulsifiers. It was found that a stable, gellike W/O type emulsion of unsaturated polyester resin is formed only when pKa's of the bases are above 6 and their concentrations are higher than some critical value. In these conditions, water can be dispersed in emulsion up to 900% to the resin. By polymerization, the stable W/O type emulsion is transformed to a white solid copolymer which is dry to the touch and which contains 90–95% of initially added water. It was confirmed that the basic compounds react with the carboxylic group of the polyester to form at the water‐resin interface polyester salts, which act as true emulsifying agents. The stabilization mechanism of the emulsion at various concentrations of the polyester salt was investigated, mainly by microscopic observations, and an interpretation of the critical value of emulsifier concentration is proposed.
Alkylaluminum–Lewis base complexes as initiators of vinyl polymerization
Authors: Breslow David S. , Christman Donald L. , Espy Herbert H. , Lukach Carl A. 
Published: April 2003

AbstractComplexes of aluminum alkyls with Lewis bases catalyze the polymerization of vinyl chloride. Triethylaluminum is most effective, but other compounds of type R3Al, R2AlCl, R2AlH, and LiAIR4 are operable. Dialkylmagnesiums are active, but Grignard reagents, as well as a number of other metal alkyls are inactive. Among Lewis bases, tetrahydrofuran (THF) and tetrahydropyran give the best yields of poly(vinyl chloride). Oxygen bases, such as ethers and esters, are more effective than nitrogen bases, e.g., tertiary amines. Cyclic compounds are better than acyclic ones. The polymerization occurs in a variety of hydrocarbon, chlorinated hydrocarbon, or ether solvents, but especially well in CCl4. Radical polymerization is probably initiated through the reaction R3Al:Base + CCl4 → R2AlCl: Base + R + Cl3C., to form trichloromethyl radical.
Curing of resole‐type phenol–formaldehyde resin
Authors: Katović Zvonimir 
Published: April 2003

AbstractThe process of resole‐type phenol–formaldehyde resins was studied by differential thermal analysis and infrared spectroscopy. It was shown that in neutral media the first reactions that occur are those between free phenol present in the resin and monosubstituted methylol phenol with free reactive positions on the benzene ring. The formation of methylene linkages is followed immediately by the condensation of methylol groups to give dibenzyl ether linkages. These are subsequently destroyed at about 210°C. It is believed that the entire curing process is governed by a free‐radical mechanism. It is also shown that oxidation of the resin occurs slowly at room temperature and humidity.