bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modified cellulose acetate prepared from acetic anhydride reacted with cellulose dissolved in a chloral–dimethylformamide mixture
Authors: Clermont L. P. , Manery N. 
Published: April 2003

AbstractA bleached sulfite pulp (85.0% α‐cellulose) was dissolved in dimethylformamide containing anhydrous chloral and pyridine as catalyst. The clear cellulose solution was then reacted with acetic anhydride under various conditions. The reaction products contained both acetyl groups and chlorine in amounts varying from 20% to 38%. Curves of reaction rates with respect to chlorine and acetyl groups under various conditions of temperature and reactant ratios were similar in appearance, and all the products contained approximately 2 moles of acetyl groups per mole of chloral. Yields varied from 180% after treatment at room temperature (25°C) for 1 hr to 250% after 4 hr. The products could be hydrolyzed in acid with some difficulty but very easily in dilute alkali. The products had low flammability and hygroscopicity. Films cast form acetone solutions had higher permittivity and lower a.c. conductivity than similar films made from cellulose diacetate.
Effect of aerosil on the course of thiuram accelerated sulfur vulcanization
Authors: Ducháček Vratislav , Brajko Vladimír 
Published: April 2003

AbstractTetramethylthiuram disulfide (TMTD)‐accelerated sulfur vulcanization of natural rubber has been investigated at temperatures from 100°C to 145°C. Continuous measurements in a Vuremo curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. The cure curves as well as their linearized forms (dependences of the logarithm of the extent of vulcanization on the cure time) clearly show that at lower cure temperatures the course of the vulcanization differs significantly from the first‐order rate law. These digressions have been removed by the addition of a highly dispersed silica gel, Aerosil, which simultaneously speeds up the course of the vulcanization up to the value corresponding to the rate of zinc dimethyldithiocarbamate (ZnDMDC)‐accelerated sulfur vulcanization. These results are in accordance with our recent theory supposing that ZnDMDC is the actual accelerator in TMTD‐accelerated sulfur systems. In the presence of Aerosil, the formation of ZnDMDC from TMTD is catalyzed via dispersed silica gel. Support for this view derives from the temperature dependences of vulcanization reactions. The activation energies of TMTD‐accelerated sulfur vulcanizations in the absence (31 kcal/mole) and in the presence of Aerosil (23.5 kcal/mole) correspond exactly to the values calculated from the rate constants of the thiuram decrease in TMTD‐accelerated vulcanization (30 kcal/mole) and from the rate constants of crosslinking in the dithiocarbamate‐accelerated sulfur vulcanization (23 kcal/mole), respectively.
Viscosity of bead suspensions in polymeric solutions
Authors: Nicodemo L. , Nicolais L. 
Published: April 2003

AbstractViscosity measurements made by a cone‐plate viscometer on polyisobutylene in decalin solutions at different concentrations and their corresponding glass bead suspensions with filler loadings up to 40% by volume are reported. The range of shear rate $ \dot \gamma $ investigated is between 0.1 and 1000 sec−1. The solutions show shear‐thinning behavior, and the relative viscosity ηr of the slurries generally decreases with increasing shear rate. The results indicate two different types of mechanism, respectively at high and low shear rates. At low $ \dot \gamma $, the relative viscosity can be correlated extending relations already well known for suspensions in Newtonian liquids which are based on the mechanism of aggregate disruption. The behavior at high $ \dot \gamma $ values is believed to be due to the influence of the filler on the flow properties of macromolecules, in particular on relaxation time. Through a shifting procedure, an increase in relaxation time which depends on filler content and not on polymer concentration is shown.
Ethylene copolymers of N‐substituted acrylamides
Authors: Mortimer George A. 
Published: April 2003

AbstractEthylene copolymers containing even small amounts of certain N‐alkylacrylamides show some unusual properties: transparency while semicrystalline, preservation of stiffiness during reduction in crystallinity, and an unusual melt flow‐versus‐solution viscosity relationship. These properties are due to hydrogen bonding between macromolecules. By proper choice of the N‐alkyl group, copolymers containing more than 95% ethylene were made which were stiff, tough, and transparent.
Determination of internal energy contribution to the thermoelasticity of natural rubber during compression by use of a thermomechanical analyzer
Authors: Hwo Chiu‐Hsiung , Bell James P. , Johnson Julian F. 
Published: April 2003

AbstractA method for measuring the internal energy change of elastomers under compression is demonstrated using a conventional thermomechanical analyzer. The method is rapid and convenient and has a major advantage in that only a very small sample is required. Results are reported for natural rubber cured with two different crosslinking agents. The results are compared with previous work on similar materials in tension and torsion.
An experimental study of the relationship between rheological properties and spinnability in the dry spinning of cellulose acetate–acetone solutions
Authors: Griswold Phillip D. , Cuculo John A. 
Published: April 2003

AbstractThe elastic and viscous properties of five cellulose acetate–acetone solutions, varying from 19.9% to 28.6% solids concentration, are independently determined at 60°C by capillary rheometry techniques. The viscous flow behavior of the solutions is determined over four decades of shear rate. The Bagley analysis is used to determine the entrance pressure drop and the true shear stress at various shear rates. A plot of the entrance pressure drop at the maximum experimental shear rate versus solution concentration undergoes a rapid increase in slope at 24.0% solids concentration, the significance of which is discussed with respect to the development of an elastically deformable chain entanglement network. The die swell behavior of the solutions at 60°C is determined on a commercial‐type dry‐spinning apparatus. When the die swell ratio is plotted versus volumetric flow rate, all five solutions are found to possess a characteristic curve with a distinct maximum. Photographs illustrating the variation of die swell with volumetric flow rate are shown. Die swell measurements are also shown to correlate well with entrance pressure drop measurements. The degree of spinnability of each cellulose acetate–acetone solution at 60°C is found by determining first godet speed at which one or more threads break abruptly. Spinnability is found to go through a maximum at 24.0% solids concentration. The rheological measurements and spinnability results are discussed through the aid of a single rheological parameter incorporating both elastic and viscous solution responses.
Hydrolysis mechanism of crosslinks formed between hydroxymethylated 2‐substituted 4,6‐diamino‐s‐triazines and cotton
Authors: Tashiro Tatsuo 
Published: April 2003

AbstractHydrolysis resistance and mechanism of reaction products of hydroxymethylated 2‐substituted (X) 4,6‐diamino‐s‐triazines (MXT) with cotton fabrics has been studied. Finishing reagents used were MXT having the following substituents: X = CH3O (MMT), (CH3)2CHO (MIPT), CH3 (MAG), C2H5NH (MEM), HOC2H4NH (MHEM), and (HOC2H4)2N (MBHEM). For comparison, trimethylolmelamine (TMM), dimethylolurea (DMU), dimethylolethyleneurea (DMEU), and dimethylol‐ethyltriazone (DMET) were used. Hydrolysis was carried out in buffer and NaOH solutions of various pH's for 30 min at 80°C. The order of hydrolysis resistance of crosslinked reagents was determined from the nitrogen contents retained. It was as follows: pH 1, MROT < MRNT < MRT; pH ≧ 2, MROT > MRT > MRNT; pH ≦ 13, MROT > MRNT; pH 14, MROT < MRT < MRNT, where MROT is hydroxymethylated 2‐alkoxy (MMT, MIPT), MRT is hydroxymethylated 2‐alkyl (MAG), and MRNT is hydroxymethylated 2‐alkylamino‐4,6‐diamino‐s‐triazine (MEM, MHEM, MBHEM). This fact can be explained in terms of the basicity constant (pKb) of crosslinked MXT with cotton (approximately pKb) of 2‐substituted 4,6‐diamino‐s‐triazine (XT). The hydrolysis rates of crosslinked MMT, MAG, and MEM were determined at pH 2. The activation energies were 21.8 for MMT, 20.9 for MAG, and 21.0 kcal/mole for MEM.
Fissure sealants
Authors: Keizer S. , Arends J. 
Published: April 2003

AbstractThe adhesive bonding of a fast‐setting system consisting of three different monomers to etched human enamel surfaces was investigated. Combinations of MMA, methacrylic acid, and adducts of glycidyl methacrylate andp‐substituted phenols have been employed. Best results were obtained with hydrogen ort‐butyl‐substituted phenols. It is shown that a well‐chosen three‐component system has the advantage of a very low initial viscosity and fast setup times over two‐component systems. Various compositions of three‐component systems were studied. The maximum bond strength between enamel surfaces and the polymer was 80 kg/cm2. Setup times as well as in vivo setup times are reported.
Compositional analysis of the styrene–isobutylene copolymer
Authors: Forrette John E. , Rozek Adele L. 
Published: April 2003

AbstractAnalysis for composition of the styrene–isobutylene copolymer has been accomplished by independent techniques which include carbon‐hydrogen analysis and infrared and NMR spectroscopy. The use of blends of homopolymers presents difficulties in establishing true absorptivities for the solution of two‐component systems, and appropriate corrections were applied to enable use of IR as an analytical technique. Carbonhydrogen elemental analysis and NMR spectroscopy were used to verify the IR results.
Rheological phenomena in polymerization reactors: Rheological properties and flow patterns around agitators in polystyrene–styrene solutions
Authors: Ide Yoshiaki , White James L. 
Published: April 2003

AbstractThe rheological properties (viscosity and principal normal stress difference) of poly‐styrene–styrene solutions at concentrations of 15, 20, 30, 35, 43, 50 and 57 wt‐% have been measured at 60°C. The flow patterns around a sphere, disc, turbine, and screw propellers in such solutions have also been determined. The second‐order fluid theory of viscoelastic fluids containing parameters determined from our rheological measurements has been used to predict the flow patterns about the sphere. The observed flow patterns are in good agreement with the theoretical predictions based upon externally measured rheological properties. The implications of this study of this behavior of batch and CSTR polymerization reactors are discussed.
Plasticity in peeling
Authors: Duke A. J. 
Published: April 2003

AbstractContrary to classical theory, a high proportion of bond failures by peeling involve progressive plastic adherend flexural yield. Such yield occurs with adherend thicknesses below a critical value, Tc, which is shown calculable by combining elastic peel mechanics with plastic bending criteria. The geometry of such “peel with yield,” and thence the moment‐controlled peel forces, can be accounted for only if the adhesive is also recognized as behaving essentially plastically. Subsequent plastic adherend unbending is important with highly extensible adhesives. The geometry of “legging” peel in such cases is best described by fully plastic mechanics. These are derived and shown to account for literature data on dependencies of peel force upon peel rate and adhesive thickness. “Stick‐slip” peel phenomena are indicated to be controlled by recurring interacting plastic–elastic transitions, in both adhesive and adherend: adhesive strain rate is critical in such phenomena. Four regimes of peel behavior can therefore apply as adherend thickness (T) increases, with peel forces proportional respectively to T0, T2/3, T3/2 (above Tc) and finally controlled by moment limitations due to joint configurational constraints (“cleavage”).
A study of interfacial polycondensation in a continuous reaction system
Authors: Griskey Richard G. , Hundia S. R. , Siskovic Nandor 
Published: April 2003

AbstractA study was made of the interfacial polycondensation of nylon 6–10 in a continuous reaction system since no previous detailed work of this type was reported in the literature. An experimental stirred‐flow reactor was used to determine both yield and intrinsic viscosity (molecular weight) as functions of reactant ratio (sebacoyl chloride/hexamethylenediamine) and Reynolds number. It was found that mass transfer was the controlling factor in the reaction system. The yield as a function of Reynolds number correlated directly with the behavior of mass transfer coefficient. In addition, reactant ratio effects on yield were shown to relate to change in organic phase volume. Intrinsic viscosity was a maximum in the same reactant ratio range as for batch and continuous cascade systems studied earlier. Intrinsic viscosity behavior was also shown to relate to mass transfer. The jD data for the reactor systems were also determined. These values were shown to correlate if normalized for reactant ratio.
The depolymerization of low molecular weight poly(chloroacetaldehydes)
Authors: McCain G. H. , Sanders J. M. 
Published: April 2003

AbstractStability of low molecular weight (D.P. < 300) polychloral has been found to be a function of the amine used as the polymerization initiator. The polymer produced with diethylamine unzips much more rapidly than that made with triethylamine. This investigation also showed that ester endcaps provide little protection from amine‐induced depolymerization. The amine‐initiated copolymer of chloral and dichloroacetaldehyde behaves anomalously in that it is unstable in the presence of normally inert organic solvents. Mechanisms are proposed to account for these observations.
Formation of 2,4‐dinitrophenylhydrazones in polyethylene film treated with chromic acid mixture
Authors: Kato Koichiro 
Published: April 2003

Abstract2,4‐Dinitrophenylhydrazones formed by the reaction of 2,4‐dinitrophenylhydrazine with carbonyl groups were formed in polyethylene film oxidized with chromic acid mixture. The changes in amount of the hydrazones formed in the films were inferred by comparing the absorptions in the ultraviolet spectra and compared with changes in wettability with water of the films. In the early stage of treatment with chromic acid mixture, the hydrazone amount increased and the contact angle of water decreased. After the early stage of the treatment, the hydrazone amount decreased slightly and increased again thereafter, and the contact angle of water seemed to increased slightly and decreased again thereafter. The hydrazone amount increased with increase in time of the reaction between 2,4‐dinitrophenylhydrazine and oxidized polyethylene film. For temperatures of treatment with chromic acid mixture above about 45°C, the hydrazone amount increased with rise in the treatment temperature and rate of the increase increased with rise in the treatment temperature, and the contact angle of water decreased with rise in the treatment temperature, and the rate of the decrease seemed to increased with rise in the treatment temperature.
Entropy and melt fracture
Authors: Balmer R. T. 
Published: April 2003

AbstractThe onset of a well‐known flow instability commonly called “melt fracture” has remained one of the fundamental unsolved problems of polymer rheology. This work attempts to explain this phenomenon via a criterion based upon limitations to configurational entropy as dicated by the second law of thermodynamics. It is shown that the molecular orientation resulting from a sustained stress‐deformation rate field may be sufficient to affect the entropy balance of the system to the point of violation of the second law. The flow field then spontaneously changes, producing the condition called melt fracture, in a manner such as to prevent the violation of this law. Other theories on the mechanism of melt fracture are discussed in the context of the above criterion.
Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. III. Structural changes occurring in low‐density polyethylene at oxygen contents below 1.2%
Authors: Holmström Arne , Sörvik Erling 
Published: April 2003

AbstractSamples of low‐density polyethylene, free from additives, were kept at temperatures between 284° and 355°C under nitrogen containing 1.16% oxygen or less. Changes in molecular weight distribution (MWD) and degree of long‐chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). Both chain scission and molecular enlargement occur simultaneously. Chain scission accounts for the formation of low molecular weight material and volatiles. Molecular enlargement reactions cause an increase in LCB and ultimately the formation of insoluble material. At lower temperatures (284°C) an increase in the high molecular weight end of the MWD is observed. The amount of olefinic unsaturation, carbonyl, and ether groups increase with degradation. Conjugated systems are formed. The formation of thin discolored and insoluble surface layers indicate that the attack of oxygen is diffusion controlled. The DSC thermograms undergo large changes at 3333° and 355°C, increasing with time and oxygen content. A reaction scheme for the thermo‐oxidative degradation of polyethylene is discussed. Both inter‐ and intramolecular hydrogen abstractions by peroxy radicals are suggested to occur. Thus, the formation of trans‐vinylene and ether groups results from intramolecular abstraction, while internal carbonyl groups are formed by intermolecular abstraction. Chain scission will be accomplished by both routes and together with “back‐biting” is suggested to account for the formation of volatiles. The formation of conjugated sequences causing discoloration is correlated with the formation of trans‐vinylene groups. Because of the restricted accessability of oxygen under our conditions, the reactions discussed previously for pure thermal degradation1 are also considered to be important. The molecular enlargement observed is thus proposed to be mainly due to the combination of alkyl radicals even when oxygen is present.
Gamma ray‐induced graft copolymerization of acrylamide and acrylic acid to nylon 6 fabric
Authors: Trivedi I. M. , Mehta P. C. , Rao K. N. , Rao M. H. 
Published: April 2003

AbstractKinetics of radiation‐induced grafting of acrylamide (Aam) and acrylic acid (Aa) to nylon 6 fabric were investigated employing a mutual radiation technique. Copper sulfate was used as the radical scavenger to reduce homopolymer formation. Formic acid was used for swelling, and its effect on grafting was studied. Maximum amount of grafting was doubled when formic acid was used for swelling nylon prior to, but not during, irradiation. The rate of grafting was not significantly affected if it was carried out in an atmosphere of air instead of nitrogen. The effect of monomer concentration, dose rate, and total dose on grafting has been studied. Rate of grafting was significantly higher when lower dose rates and monomer concentrations were used. Saturation grafting was proportional to monomer concentration up to 2.1M. Initial rate of grafting was proportional to monomer concentration. The rate of grafting of Aam was proportional to the dose rate to the power 0.25–1.0. A synergestic effect was noticed during grafting with mixtures of Aam and Aa (80:20; 20:80). Grafted fabrics showed considerable increase in moisture regain. Dyeability and tensile properties of the grafted fabrics were not significantly affected by grafting. Aa‐grafted fabrics did not melt up to 320°C, whereas untreated nylon melts at 215°C.
Physicochemical characterization of some fully aromatic polyamides
Authors: Gan L. H. , Blais P. , Carlsson D. J. , Suprunchuk T. , Wiles D. M. 
Published: April 2003

AbstractThe characterization of eight fully aromatic polyamides are described with the procedures required to yield film‐ and fiber‐forming materials. Solutions of these aromatic polyamides in dimethylacetamide were characterized by NMR and the effects of dissolved lithium chloride on these spectra investigated. The NMR resonances for specific protons in these polymers are assigned. The IR spectra of thin films and fibers of these polyamides are also reported, together with glass transition temperatures as measured by differential scanning calorimetry (DSC). The value of NMR and IR to identify specific polyamide homopolymers and copolymers is discussed.
Kinetics of vinyl chloride and vinyl acetate emulsion polymerization
Authors: Friis N. , Hamielec A. E. 
Published: April 2003

AbstractThe kinetics of vinyl chloride and vinyl acetate emulsion polymerization are reexamined. The validity of Ugelstad's model for systems with high desorption rate is confirmed by simulating conversion histories for both systems at different initiator concentrations and particle numbers. On the basis of the model, it is shown that at ordinary initiation rates, termination reactions are unimportant with respect to molecular weight development in both systems, and as a consequence, molecular weight development is independent of number and size distribution of polymer particles and of initiator and emulsifier level. Based on this conclusion, it is shown that in accordance with experimental facts, the molecular weight distribution obtained in vinyl chloride emulsion polymerization is the most probable distribution, and it is concluded that the number of long‐chain branch points per repetition unit is less than 2 × 10−4 at high conversions. In vinyl acetate emulsion polymerization, an almost logarithmic normal distribution is obtained. The distribution is strongly broadened by branching reactions with the number of long‐chain branch points increasing rapidly with monomer conversion. The increase of Mn with increasing conversion is due to terminal double‐bond polymerization, while the increase in Mw is due mainly to transfer to polymer.
Analysis of cotton fiber maturity. I. x‐ray study of phase transformation in various cottons
Authors: Kulshreshtha A. K. , Chudasama V. P. , Dweltz N. E. 
Published: April 2003

AbstractAn x‐ray diffraction technique is described for the determination of the extent of conversion of cellulose I to cellulose II lattice in partly mercerized cottons. This technique has been applied to obtain the degree of phase transformation, after subjecting various cottons to swelling in 12% (w/w) NaOH at 65% R.H. and 27°C. For the various cottons studied, a direct relationship is found to exist between fiber maturity and the untransformed cellulose after swelling.
Flow‐induced crystallization from solution: The relative effects of extension and shearing flow fields
Authors: McHugh Anthony J. 
Published: April 2003

AbstractCalculations have been performed to evaluate the relative effects of extensional and shearing flow fields on both the chain elongation and crystal nucleation rate enhancement for polyethylene crystallizing from xylene solutions. Rheological behavior was evaluated by means of the elastic dumbbell model modified for nonlinear effects at high elongations, and nucleation rate effects were considered from an essentially phenomenological view point. Molecular weight effects were also incorporated explicitly in the computations. Results show that chain elongation and nucleation rate enhancement is far greater for extensional than for shearing flows. Semiquantitative comparisons with experimental results reported in the literature for various aspects of the flow induced process, including the important fractionation effects, are discussed. Modification of the dumbbell model to account for shear rate effects on the intrinsic viscosity is also discussed.