bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of the molecular weight distribution of cellulose on calibrated gel columns
Authors: Almin Karl Erik , Eriksson Karl‐erik , Pettersson Bo A. 
Published: April 2003

AbstractCMC samples obtained by gel filtration on a preparative scale were used to calibrate an agarose column. The relation between molecular weight and the peak elution volume for monodisperse samples were calculated as well as the relation between band broadening and the peak elution volume. In the calculations of the molecular weight distribution curves of the studied CMC samples, consideration was given to the variable band broadening by proper transformations of the experimental data, thus making it possible to obtain numerical solutions free from oscillations. The method admits a rapid determination of the molecular weight distribution of cellulose and related materials.
Thermomechanical and thermogravimetric analyses of systematic series of polyimides
Authors: Gillham J. K. , Hallock K. D. , Stadnicki S. J. 
Published: April 2003

AbstractTwelve polyimides which differ systematically in chemical structure were investigated in nitrogen through the temperature range −190° rlhar2; 500°C by torsional braid analysis. The degradative regions were also examined in nitrogen by thermogravimetric analysis. Relationships between chemical structure/thermal history, processibility, thermomechanical behavior, and weight loss are discussed. A logical thermal program for converting the precursor polyamic acid solutions to solid polyimides was developed. High‐temperature, thermally induced chemical reactions could be regulated so as to preferentially freeze out longer‐range relaxations and extend the glass state behavior to well above its original load‐limiting Tg. Materials made from more flexible molecules had lower glass transitions, softened more through the Tg, and had simpler damping spectra and lower thermal stability than materials made from more rigid molecules. A commercially available polyimide film and polyimide‐forming varnish of undisclosed structures were examined by torsional pendulum and torsional braid analyses, respectively. The thermomechanical spectra of the film and cured varnish were similar to the spectra of one structural type of polyimide.
Thermo‐oxidative and photo‐oxidative aging of polypropylene under simultaneous tensile stress
Authors: Czerný Jiří 
Published: April 2003

AbstractThe effect of uniaxial tensile stress at constant load in the range of 0 to 6.86 MN/m2 upon the behavior of stabilized and unstabilized types of isotactic polypropylene was investigated in the course of thermo‐oxidative aging at 80° to 130°C and of photo‐oxidative aging in the Xenotest 450 apparatus at 45° and relative humidity of 65%. From kinetic evaluation of the temperature dependence of weight changes of unstabilized polypropylene during thermo‐oxidative aging, it was found that the weight losses of unstressed and tension‐stressed specimens obey the kinetic equations for a reaction of the first order. The degradation of stressed specimens, however, proceeds at a considerably higher rate as compared with the unstressed state and is marked by a decrease in apparent activation energy as well as by an increased rate of crack development. The cracks develop in the direction perpendicular to the tensile stress and have the shape of hollow funnels widening outward. The tensile stressing of stabilized types of polypropylene in thermo‐oxidative and photo‐oxidative environments causes an accelerated embrittlement of the polymer, manifested particularly by a marked decrease of elongation at break. This accelerated embrittlement goes on under the action of tensile stresses exceeding the so‐called safe stress, i.e., the stress below which no acceleration of aging (as measured by the relative decrease in the elongation at break of the stressed and unstressed specimens), can be detected. The values of this safe tensile stress decrease with the temperature and lie well below the tensile strength of the polymer. In the range of tensile stresses exceeding the safe stress, the dependence of the logarithm of time of a 50% decrease of the elongation at break on the applied tensile stress was found to be linear. The findings are in agreement with Zhurkov's kinetic concept of mechanical deterioration of polymers, where the effect of the applied mechanical stress is superimposed on the thermal fluctuation and leads to the scission of chemical bonds and to the formation of cracks in the polymer.
Some observations on the mechanism of action of retarders in rubber vulcanization. A new class of retarder
Authors: Ballard D. G. H. , Myatt J. , Richter J. F. P. 
Published: April 2003

AbstractAttempts have been made to demonstrate the involvement of free radicals in the benzthiazolesulfenamide‐accelerated vulcanization of natural rubber. Free radicals were only detected by ESR in reaction mixtures containing the retarder N‐nitrosodiphenylamine (NDPA). In addition, NDPA was the only compound found, from the vulcanization accelerator and retarders tested, to affect the free‐radical polymerization of methyl methacrylate. A purely ionic mechanism for sulfur vulcanization of natural rubber accelerated by benzthiazolesulfenamide derivatives has therefore been assumed and used to help in the design of new vulcanization retarders. A new class of retarder has been discovered, consisting of hydrocarbylthio derivatives of trisalkylsulfonyl methane. These retarders are believed to be the first vulcanization retarders to act by cleavage of a carbon–sulfur bond.
Study of structure and thermal properties of polypropylene and chlorinated polypropylene by infrared spectroscopy and differential scanning calorimetry
Authors: Sakai Kazuyuki , Sobue Hiroshi 
Published: April 2003

AbstractThe infrared spectra of chlorinated polypropylene (CPP) are interpreted and tentative assignments of C—Cl stretching vibration of CPP are proposed. Recently, infrared spectrophotometry has been applied as a useful tool for the investigation of polymer transitions. The solid‐state transition in isotactic polypropylene (IPP) was studied by infrared method in the range of −50° to 30°C; and from the temperature dependence of the peak absorbance, transition at ‐10°C was detected. This temperature of ‐10°C agrees well with the Tg2 detected by other methods. From these results, it is presumed that Tg2 is attributed to a motion (thermal expansion) of IPP segments in either crystalline and amorphous region. The thermal transition of chlorinated isotactic polypropylene (CIPP) was also examined with differential scanning calorimetry and infrared method, and two thermal transitions were observed. A higher transition (TH) has a minimum at a degree of chlorination of about 39 wt‐%; and a lower transition (TL) changes linearly with increasing degree of chlorination. Infrared results indicate that TH may be associated with a motion (thermal expansion) in chlorinated segments, and TL may be associated with a motion in unchlorinated segments. These results of infrared studies also suggest that CIPP may have a block structure.
Correlations between chemical structure, stress‐induced crystallization, and deformation behavior of polyurethane elastomers
Authors: Morbitzer L. , Hespe H. 
Published: April 2003

AbstractThe deformation behavior of polyurethane elastomers depends strongly on physical interactions.In this paper the stress‐induced crystallization of the polyester or polyether segments in investigated in several polyurethane elastomer systems having different chemical structure for the soft segments. The correlation between the tensile properties (hysteresis loss, extension set, modulus) and the stress‐induced crystallization is discussed.
Stabilization of unsaturated elastomers with phenolic antioxidants
Authors: Patel A. R. , Dibattista A. D. , Klemchuk P. P. 
Published: April 2003

AbstractAn investigation of the thermo‐oxidative stabilization of ethylene–propylene–diene monomer (EPDM), polybutadiene, and emulsion styrene–butadiene rubbers (SBR) with a large number of variously substituted phenolic antioxidants disclosed a limited number of specific antioxidants to be remarkably effective as processing and storage stabilizers for the unsaturated elastomers. The most effective antioxidants of this investigation promise to provide better stabilization of unvulcanized rubbers than currently achievable with present stabilizers. Stabilizer performance in EPDM was assessed by both carbonyl absorbance and gel content measurement after oven aging at 100° and 150°C. Gel measurement after oven aging was found most useful for the other two elastomers. In all instances, good correlation was found between onset of gel formation and onset of color development. The specificity of stabilizer performance is interpreted in terms of functionality, compatibility, stability, and volatility.
Salt effect on gel permeation chromatography of partially charged polymers
Authors: Coppola Gerolamo , Fabbri Piero , Pallesi Bice , Bianchi Umberto 
Published: April 2003

AbstractThe effect of the addition of 0.1M LiBr to dimethylformamide (DMF) solutions of charged and uncharged polymers has been studied by GPC and [η] measurements. LiBr has a salting‐out effect on polyacrylonitrile (with (PAN‐S) and without (PAN) sulfonate sulfur), polystyrene (PS), and poly(vinyl acetate) (PVAc), which is seen by a decrease in [η] and an increase in the GPC retention time. The increase in retention time is, however, abnormally high for charged polymers. Association in PAN and PAN‐S solutions in DMF can explain the experimental observations.
Graft copolymers of starch with mixtures of acrylamide and the nitric acid salt of dimethylaminoethyl methacrylate
Authors: Fanta George F. , Burr Robert C. , Doane W. M. , Russell C. R. 
Published: April 2003

AbstractMixtures of acrylamide and the nitric acid salt of dimethylaminoethyl methacrylate (DMAEMA·HNO3) have been graft polymerized onto unmodified wheat starch with ferrous ammonium sulfate–hydrogen peroxide initiation. Graft polymerizations were carried out with both unswollen starch granules and granules that had been swollen by heating in water to 60°C. Ungrafted synthetic polymers were removed from graft copolymers by cold‐water extraction and were characterized by their M̄n and DMAEMA·HNO3 content. Graft copolymers were characterized with respect to per cent add‐on, M̄n and DMAEMA·HNO3 content of grafted polymer, and grafting frequency. Ungrafted synthetic polymers contained a mole percentage of DMAEMA·HNO3 equal to or greater than that present in the initial monomer mixtures; whereas in most grafted polymers the mole‐% DMAEMA·HNO3 in the grafted branches was less than that in the starting monomers. At all monomer ratios examined, polymer grafted to swollen starch granules contained a higher percentage of DMAEMA·HNO3 then polymer grafted to unswollen starch. The influence of starch granule swelling on the molecular weight and frequency of grafted branches was correlated with the composition of the initial monomer mixture. It was determined that the effect of granule swelling on graft copolymer structure would be minimal when 25–30 mole‐% DMAEMA·HNO3 was used. In an acetonitrile–water solvent system, reactions with 20 and 50 mole‐% DMAEMA·HNO3 produced graft copolymers with less DMAEMA·HNO3 in grafted branches than corresponding graft polymerizations run in water. The flocculation of 3% aqueous suspensions of diatomaceous silica was examined with selected starch graft copolymers.
Molecular sieves as drying agents for the monomer in the radiation‐induced ionic polymerization of liquid vinyl monomers
Authors: Stannett V. T. , Du Plessis T. A. , Goineau A. M. 
Published: April 2003

AbstractThe factors which influence the drying of liquid vinyl monomers with molecular sieves are discussed. It is found that the best results are obtained by drying the monomer for at least 12 hr at −15°C on molecular sieves that received no pretreatment at elevated temperatures. Although the prepolymerization that takes place on the molecular sieves during the drying can be quite extensive, the excellent reproducibility that can be achieved by using this method makes it a promising drying technique.
Imidazole catalysis in carbamate and polyurethane formation
Authors: Jerussi Robert A. , Orlando Charles M. 
Published: April 2003

AbstractPolyurethanes have been prepared from the reactions of the diimidazole and ditriazole adducts of 2,4‐toluene diisocyanate and ethylene glycol or polyols. Suitable formulations have been developed from these components which are useful in preparing polyurethane coatings and foams. Imidazole was established as an effective catalyst for the reactions of the diphenol adduct of 2,4‐toluene diisocyanate with polyols. Imidazolecatalyzed polyurethane formation from the phenol‐blocked diisocyanate occurs readily between 100° and 140°C. A mechanism for the catalytic activity of imidazole in these reactions is proposed.
Modifications of the weissenberg rheogoniometer for measurement of transient rheological properties of molten polyethylene under shear. Comparison with tensile data
Authors: Meissner Joachim 
Published: April 2003

AbstractImprovements to the Weissenberg rheogoniometer are necessary in order to measure the transient rheological properties of polymer melts correctly. The improvements reported concern the mechanical design, a new heating system, a new normal force measuring system, and additional equipment for the relaxation test. Reliable short‐time results require sufficiently stiff torque and normal force springs, and a small radius and relatively large angles of the cone‐and‐plate gap. The behavior of the LDPE melt under test is “linear viscoelastic,” if shear rate or total shear are small: The relaxation modulus, the stress growth at the onset of constant shear rate, the stress relaxation after cessation of steady shear flow, and, in addition, dynamic shear data (from an oscillation viscometer) all show consistent results when correlated by means of formulae from the theory of linear viscoelasticity. Shearing in the nonlinear range with constant shear rate leads to pronounced maxima of the shear stress p12 and of the first normal stress difference p11 − p22 which occur at constant total shear, almost independent of shear rate. Comparison of shear and tensile data (from extensional rheometer) confirms the Trouton relation in the linear‐viscoelastic case. In the nonlinear case, there is a “work softening” in shear and a “work hardening” in extension.
On the initiation of melt fracture
Authors: McIntire L. V. 
Published: April 2003

AbstractThe importance of (τ11 − τ22)/τ12 (sometimes called the Weissenberg number) in determining the onset of melt fracture is examined using classical linearized hydrodynamic stability analysis. The constitutive relation used is that proposed by Bird and Carreau. It is shown that simple shearing flow of a viscoelastic fluid becomes unstable at a critical value of the Weissenberg number. Implications with regard to polymer processing are discussed.
Ultraviolet irradiation of poly(alkyl acrylates) and poly(alkyl methacrylates)
Authors: Morimoto Kazuyuki , Suzuki Soji 
Published: April 2003

AbstractAcrylic and methacrylic homopolymers containing different side groups were irradiated with ultraviolet light in the presence of air. The changes of molecular weight distributions of the irradiated polymers were analyzed by means of gel permeation chromatography (GPC), and the rates of chain scission and crosslinking were estimated. As the result of this study, it was found that chain scission takes place more easily in polyalkyl methacrylates than in polyalkyl acrylates.
The formation of polyimides from anhydrides and isocyanates
Authors: Carleton Peter S. , Farrissey William J. , Rose James S. 
Published: April 2003

AbstractThe addition of water to the reaction of isocyanates with carboxylic acid anhydrides has been observed to increase markedly the rate of formation of the corresponding imide. This effect has been observed with both monofunctional and difunctional reagents as well as in different solvents. Evidence is presented which suggests that water hydrolyzes the isocyanate either to the corresponding urea or amine.
Spectroscopic investigation of cellulose degraded celluloses, and their phenylhydrazine derivatives in relation to assessment of degradation
Authors: Blair H. S. , Cromie R. 
Published: April 2003

AbstractThe ultraviolet absorption spectra of Cadoxen solutions of hydrocellulose and hydrocellulose phenylosazones are described. With solutions of hydrocellulose no simple relationship between D.P. and absorbance was found. Solutions of hydrocellulose phenylosazone in Cadoxen show well‐defined maxima at 277 nm and 390 nm and do not change over 1 hr when oxygen is excluded. The absorbance of the phenylosazone at 390 nm may be used to determine the D.P. of the hydrocellulose samples.
High‐temperature elastomers: Glass transition–structure correlations for two systematic series of linear poly(carborane–siloxane)s. I
Authors: Roller M. B. , Gillham J. K. 
Published: April 2003

AbstractNine linear poly(carborane–siloxane) high‐temperature elastomers which differ systematically in chemical structure were investigated by torsional braid analysis. The structural variations include two different carborane cage structures in the polymer chain (CB10H10C and CB5H5C) and the stepwise increase in the number of Si(CH3)2O linkages associated with each cage in the repeat unit. Poly(dimethylsiloxane) was studied as the compositional limit of both series. The dynamic mechanical relaxations (at about 1 cps) of the materials are reported. These include the melting points of the semicrystalline polymers and the glass transitions and secondary transitions of all the polymers. The glass transition temperatures in each series were systematized using the well‐known copolymer composition‐versus‐glass transition temperature relationship 1/Tg = W1/Tg1 + W2/Tg2.
High‐temperature elastomers: Glass transition–structure correlations for two systematic series of linear poly(carborane–siloxane)s. II. Incompatibility
Authors: Roller M. B. , Gillham J. K. 
Published: April 2003

AbstractPreviously reported results related glass transition temperature to structure in two systematic series of poly(carborane–siloxane)s using a well‐known copolymer composition–glass transition relationship 1/Tg = W1/Tg1 + W2/Tg2. The relationship was originally proposed to apply not only to copolymers, but also to diluent systems. Accordingly, mixtures of polymers within each series were prepared and the thermomechanical spectra were determined by the technique of torsional braid analysis. The binary mixtures included poly(dimethylsiloxane) with polymers in both series and a mixture of two CB10H10C siloxane polymers. In all cases, the thermomechanical spectra revealed only those transition regions characteristic of the individual components. This type of behavior is indicative of phase separation of incompatible polymeric species.
Dynamic mechanical properties of nonstoichiometric, amine‐cured epoxy resin
Authors: Hirai T. , Kline D. E. 
Published: April 2003

AbstractThe dynamic mechanical properties of epoxy resins cured with nonstoichiometric amounts [37%–103% of stoichiometric composition (SC)] of diethylenetriamine at room temperature have been measured in the temperature range 85° to 300°K and correlated to structures of cured resins. The dynamic mechanical behavior changed above and below 62.5% of SC, at which network structures are formed. The intensities of γ‐ and β‐peaks, ∼150° and ∼250°K, respectively, depend upon the concentration of DETA used. The processes of the γ‐ and β‐peaks are discussed.
Improvement of porous cellulose acetate reverse osmosis membranes by change of casting conditions
Authors: Pageau Lucien , Sourirajan S. 
Published: April 2003

AbstractThe effects of temperature of casting solution in the range −10° to 15°C, that of casting atmosphere in the range 10° to 30°C, relative humidity of casting atmosphere in the range 35% to 75%, and solvent evaporation period in the range 0.5 to 3 min were studied on shrinkage temperatures, solute separations, and product rates of Loeb‐Sourirajan‐type cellulose acetate membranes in reverse osmosis experiments. The composition of casting solution used was as follows: cellulose acetate, 17; acetone, 69.2; magnesium perchlorate, 1.45; and water, 12.35 wt‐%. Best performance was obtained with membranes cast under the following conditions: temperature of casting solution, 10°C; temperature of casting atmosphere, 30°C; relative humidity of casting atmosphere, 65%; and solvent evaporation period, 1 min. For a 90% level of solute separation, the productivities of the above type of membranes were 22.9, 61.4, and 64.5 gallons/day‐ft2 at 250, 600, and 1500 psig using 3500 ppm NaCl–H2O, 5000 ppm NaCl–H2O, and 28395 ppm NaCl–H2O feed solutions, respectively. In all cases, the feed flow rates corresponded to a mass transfer coefficient of 45 × 10−4 cm/sec on the high‐pressure side of the membrane. The general specifications of the above type of membranes are given for the operating pressures of 250, 600, and 1500 psig. The effects of the above casting condition variables on the surface pore structure during film formation are discussed.
Fibers from aromatic copolyamides of limited order
Authors: Preston J. , Smith R. W. , Sun S. M. 
Published: April 2003

AbstractFibers were spun from six different, wholly aromatic copolyamides of limited order. Tensile properties of the fibers were obtained at standard conditions and, for selected fibers, at elevated temperatures and after heat‐aging at 300°C in air. The dry‐heat shrinkage determined up to 400°C on selected fibers was relatively low; zero‐strength temperatures ranged from 375°C to 495°C. Resistance to numerous chemical reagents was determined for one of the fibers and found to be comparable to that of the fibers from other wholly aromatic polyamides. Resistance to ultraviolet light appeared to be of the same order as that of unstabilized nylon 66.
Thermal analysis of irradiated poly(vinyl chloride)
Authors: Salovey R. , Badger R. G. 
Published: April 2003

AbstractThe thermal decomposition and resultant disposal of waste poly(vinyl chloride) (PVC) is facilitated by preliminary exposure to ionizing radiation, such as energetic electrons, in an oxygen atmosphere. The results of isothermal and temperature‐programmed thermogravimetry, differential thermal analysis, and effluent gas analysis in nitrogen and in oxygen indicate that the major effect of irradiation is to render PVC increasingly susceptible to oxidation. The presence of oxygen during heating enhances the decomposition. Crystalline order in PVC is destroyed by irradiation.
Studies on melt spinning. II. Analysis of the deformation and heat transfer processes
Authors: Lamonte Ronald R. , Han Chang Dae 
Published: April 2003

AbstractA generalized, empirical equation is proposed which takes into account the dependence of elongational viscosity on both elongation rate and temperature. From this, a mathematical model for simulating the melt spinning process has been developed. The model has been tested against experimentally observed velocity profiles in fibers of polystyrene and high‐density polyethylene spun into an isothermal chamber. It has been found that predicted velocity profiles agree well with experimentally observed ones. The mathematical model has been used to predict velocity and temperature profiles in fibers spun into a cooling medium. The simultaneous solution of momentum and energy balance equations by means of a numerical integration scheme has generated important information such as distributions of force components involved in spinning and distributions of the total rate of heat transfer along the spinning way.