bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mechanism of gelation in the reaction between diisocyanates and polyethylene ethers
Authors: Pearson R. W. 
Published: April 2003

AbstractWhen polyethylene ethers which have been prepared in the presence of alkaline catalysts are reacted with diisocyanates, gelation usually takes place and more isocyanate reacts than is required for complete conversion of hydroxyl groups to urethane. These facts are explained by the rapid reaction, in the presence of basic catalysts, of isocyanate with urethane groups to form allophanate and similar structures. A theory relating the extent of isocyanate reaction at gelation to the initial ratio of hydroxyl to isocyanate group has been developed, and compared with the experimental results. The effect of the addition of sodium hydroxide to neutralized polyethylene ether, and of the addition of sodium to n‐butanol, on the reaction of these compounds with diisocyanates has been examined, and the results support the suggested mechanism.
An empirical concept of flow for polyisobutene systems
Authors: Porter Roger S. , Johnson Julian F. 
Published: April 2003

AbstractViscosities were measured on 11 polyisobutenes with molecular weight of 224 to 71,000. Measurements were made on cetane and tetralin solutions containing 11.2–100 wt.‐% polymer. Tests were made at 80–135°C. and a t shear rates to 8 × lo6 sec.‐l. Low shear capillary and two types of rotational viscometers were used. The data confirm that polyisobutene systems show an abrupt transition in log viscosity—log molecular weight correlations. This transition occurs near 15,000 for MV where M is Viscosity‐average molecular weight and V is polymer volume fraction. Below a product of 15,000, polyisobutene systems exhibit essentially Newtonian flow and an absence of laminar flow shear degradation to stresses above 2 × 105 dynes/cm.2. In this region the viscosity dependence on molecular weight approaches fist order at higher temperatures and lower polymer concentrations. For polyisobutene systems above the transition near 15,000, low shear viscosities uniformly increased aa the 3.4 power of molecular weight. Systems in this range exhibited large and predictable non‐Newtonian effects and frequently showed laminar flow shear degradation at low rates of shear.
Polybenzimidazoles, new thermally stable polymers
Authors: Vogel Herward , Marvel C. S. 
Published: April 2003

AbstractWholly aromatic polybenzimidazoles were synthesized from aromatic tetraamines and difunctional aromatic acids and characterized as new thermally stable polymers. The melt polycondensation of aromatic tetraamines and the diphenyl esters of aromatic dicarboxylic acids was developed as a general procedure of wide applicability. Polybenzimidazoles containing mixed aromatic units in the chain backbone were prepared from 3,3′‐diaminobenzidine, 1,2,4,5‐tetraaminobenzene and a variety of aromatic diphenyl dicarboxylates. Phenyl 3,4‐diaminobenzoate could also be polymerized by melt condensation to give poly‐2,5(6)‐benzimidazole. The polymers were characterized by a high degree of stability, showing great resistance to treatment with hydrolytic media and an ability to withstand continued exposure to elevated temperatures. Most of the polymers were infusible, but some had melting points above about 400°C. Many of the polymers exhibited no change in properties on being heated to 550°C. and showed a weight loss of less than 5% when heated under nitrogen for several hours to 600°C. The polymers were soluble in concentrated sulfuric acid and formic acid, producing stable solutions. Many of the polymers were soluble in dimethyl sulfoxide and some also in dimethylformamide. The inherent viscosities of a number of polymers in 0.5% dimethyl sulfoxide solution ranged from approximately 0.4 to 1.1. The higher polymers could be cast into stiff and tough films from formic acid and dimethyl sulfoxide solutions.
Viscosity and glass temperature relations for polymer‐diluent systems
Authors: Kelley Frank N. , Bueche F. 
Published: April 2003

AbstractExpressions are derived from free volume considerations which predict the concentration dependence of viscosity and glass temperature for polymer‐diluent systems. Experimental data for several systems were examined and general agreement with theory was found over broad ranges of concentration. Particular emphasis is placed on the limited amount of information required for the application of these expressions to describe the viscous properties of polymer‐diluent systems.
Isolation of the precursor of bacterial cellulose
Authors: Khan A. W. , Colvin J. Ross 
Published: April 2003

AbstractA method is described for the isolation of the precursor of cellulose microfibrils from ethanol extracts of active cultures of Acetobacter xylinum. Using the capacity to form cellulose microfibrils for an assay procedure, the method employs column chromatography of chloroform extracts of the residues from the ethanol solutions, on silicic acid and Celite followed by magnesium trisilicate (Magnesol) and Celite. A fraction from the second stage contains only one compound, which is capable of forming typical bacterial cellulose microfibrils in the presence of ultrafiltered supernatant of an active culture. The compound contains glucose, an unknown base, and a fatty acid.
The distribution of polysaccharides in wood fibers
Authors: Meier Hans 
Published: April 2003

AbstractA study was made of polysaccharide distribution in the cell walls of both hardwood fibers and conifer tracheids by means of analysis of fractions obtained through microdissection. Radial sections of about 50 μ in thickness were made through the cambium and the outermost part of the xylem of birch, spruce, and pine woods. In these sections, the successive stages of maturation of the fibers can be distinguished microscopically. Under a polarizing microscope, the optical characteristic of each cell wall layer (M, P, S1, S2, S3) is dependent on the orientation of the cellulose microfibrils in it, and it was therefore possible, with a microdissector, to isolate samples of fibers at different stages of maturation. Samples of about 0.3 mg. of each fiber fraction were hydrolyzed and the sugars present were determined quantitatively. With the use of present knowledge of the chemical composition of the different polysaccharides in wood, the sugar analysis results were converted into polysaccharide contents for each fraction. From these it, was then possible to calcute very roughly the proportions of the different polysaccharides in each cell wall layer. The youngest fibers (M + P fibers) of the three woods studied consist principally of pectic substances (pectic acid, galactan, and arabinan). In birch the S1 layer and the outer part of the S2 layer contain only slightly more cellulose than glucuronoxylan, while the innermost layers of the fiber (around the lumen) contain a large proportion of cellulose. In both sprucc and pine the S1 layers contain about 60% cellulose, between 15 and 20% glucomaiinm, and between 15 and 20% glucuronoarabinoxylan. In the outer part of S2 the cellulose and glucomannan contents increase and the glucuronoarabinoxylan decreases. In the innermost parts of the summer wood tracheids of pine the cellulose content decreases again and the glucurono arabinoxylan content is very high in the S3 layer. In the spring wood tracheids of spruce the composition of the S3 layer cannot be deduced from the present study but there are indications that it is similar to that of summer wood trncheids of pine.
The use of holocellulose to study cellulose supermolecular structure
Authors: Nelson Russell 
Published: April 2003

AbstractHolocelluloses were prepared from slash pine wood at the 17–19, 4‐6, and 0‐2% lignin levels by the chlorite and chlorine–monoethanolamine methods. The products were compared with respect to carbohydrate composition, nitrate degree of polymerization, x‐ray diffraction peak width, x‐ray crystdlinitg index, mercerization resistance, and alkali solubility. Structural differences among holocelluloses at each lignin level were noted. Thest. wvre attributrd to a deperidencc of x‐ray diffraction peak width on delignification conditioris and to small differences in amount of residual lignin. It was determined that alkali‐resistant, heimictrlluloses interfere with mercerization analyses inasmuch as they diminish diffraction pattern resolution. Taking account of such interference, the swelling behavior of the cellulose in whole wood can be estimated from either type of holocellulose. It is necessary, however, to ensure that all of the lignin is removed and that cellulose degradation is not excessive. The effect of stepwise alkaline extraction of hemicelluloses from the holocelluloses containing 0–2% lignin was followed by x‐ray analyses of the extracted residues after each extraction stage. Narrowing of the 002 diffraction peak width was observed and was found to depend on an alkalicellulose interaction and on hemicellulose reinoval. Reinoval of “polyuronides” has less of an effect on peak width than removal of the “cellulosans.” The hemiceliulosic polysaccharides, araboglucuronoxylan, and glucomannan are discussed in regard to molecular structure, probable relationship to the crystalline cellulose, ease of alkaline extraction, and effect of removal on the cellulose supermolecular structure. Narrowing of the 002 peak width, independent of cause, is considered to represent an increase in crystallite width, in development of the crystal lattice, and in packing perfection of the cellulose chains within and on the surfaces of the crystallites. Structure parameters were estimated for native slash pine cellulose, and these were compared with values found for celluloses isolated from the same species by the conventional acid sulfite and prehydrolysis sulfate processes. This comparison enabled approximation of the direction and magnitude of change effected in the native cellulose structure during pulping.
Infrared spectra of cellulose and related polysaccharides
Authors: Higgins H. G. , Stewart C. M. , Harrington K. J. 
Published: April 2003

AbstractA comparison has been made between the infrared spectra of native cellulose and those of various closely related materials differing in each instance from cellulose I in one salient feature. These materials have been compared individually with groups of others, each differing from cellulose in a further salient feature. Considered in conjunction with the spectra of a few formally more distant relatives such as tetrahydropyran and the simple alcohols, these empirical comparisons can contribute to an understanding of the influence on the spectrum of hydrogen bonding, hydroxyl groups (through HD exchange and o‐acylsubstitution), the type of anomeric and positional linkage, attachment at a specific carbon atom, the glycosidic link, and degree of polymerization. The comparative spectroscopy of cellulose, laminarin, amylose, and xylan permits correlation between these glucosans for about a dozen of the major bands or groups of bands in the spectra of the amorphous materials between ca. 3 and 13μ. An examination of the spectra of various crystalline modifications of cellulose lends support to various conclusions drawn by previous workers regarding the relationship between these forms. The effects of deuterating native and regenerated cellulose have been taken into account in considering band assignments. The intensity of the strong band near 8.6 μ (1160 cm.−1) is reduced on deuteration, and it is questioned whether this is consistent with its assignment to stretching in the glycosidic link (on the basis of its strong parallel polarization, etc.). The response to deuteration suggests that the band near 9.0 μ (1120 cm.−1) may be an association band of the type observed in primary and secondary alcohols and that the residual band near 8.9 μ (1120 cm.−1) may be identified with the antisymmetric ring‐stretching vibration. The persistence of the strong bands between 9 and 10 μ (1100–1000 cm.−1) after deuteration, acetylation and, in the case of sugars, freeze drying, supports the conventional assignment to CO stretching, perhaps coupled to CC frequencies. The band near 10.1 μ (990 cm.−1) is eliminated on deuteration or hetero‐geneous acetylation of cellulose. These and other facts suggest that it is connected with a vibration which is restricted in the crystallites. The band a t 11.2 μ (893 cm.−1) in cellulose and other β‐linked glucosans is clearly connected with the C(1) group vibration. In much of this work the samples were examined as dispersions in pressed potassium chloride pellets. In the amorphous state the spectra of the smaller molecules resemble those of the corresponding polymers. It was also observed that freeze‐dried samples, dispersed in potassium chloride, showed a slow reversion to the sharp spectrum characteristic of the crystal.
The effect of crystalline structure on the alkaline degradation of cellulose fibers
Authors: Meller Alexander 
Published: April 2003

AbstractThe resistance of cotton cellulose and of sodium borohydride‐reduced hydrocelluloses to boiling 1% sodium hydroxide solution is decreased by ethylamine treatment. In contrast, hydrocelluloses exhibit a greater resistance to hot dilute alkali after ethylamine treatment. This increased hot alkali stability seems to be associated with the reaction between the reducing end group in the terminal glucose units of the cellulose molecules and the amine. Aqueous hydroxylamine–treated hydrocelluloses also show a slightly increased resistance to hot dilute alkali. The ethylamine treatment apparently induces a change in the physical structure of the fibers, “decrystallization” or conversion of cellulose I to cellulose III, depending on the manner in which the amine is removed from the fibers. The amine treatment results in a lower resistance to boiling dilute alkali. On the other hand, the reaction between the reducing end groups and the amine (possibly a condensation reaction) has an opposite effect on hot alkali stability. The net effect, thus, may depend on the relative magnitudes of the opposing effects and on the rate of change in the physical structure of cellulose that takes place during the hot alkali stability test. With hydrocellulose possessing a large number of reducing groups, the effect on hot alkali stability arising from a chemical reaction between the reducing end groups and anhydrous ethylamine is greater than that caused by the change in physical structure (decrystallization and conversion of cellulose I to cellulose III). With cotton fibers and borohydride‐reduced hydrocelluloses that contain a small number of reducing end groups, the effect of “crystallinity” and crystal structure on hot alkali stability seems to be the greater. Immersion in hot water of amine‐treated celluloses and hydrocelluloses increases their resistance to hot dilute alkali. This increased resistance is probably due to a recrystallization which takes place by the action of hot water.
Kinetics of the acid‐catalyzed degradation of cellulose esters
Authors: Rosenthal Arnold J. 
Published: April 2003

AbstractThe acid‐catalyzed degradation rates of cellulose acetate and cellulose propionate in acetic and propionic acids and anhydrides have been determined by repeated viscosity measurements. Relative degradation rates could be estimated with the aid of a standardized curve that related intrinsic viscosity to extent of degradation under the assumption of pseudozero‐order degradation kinetics. Degradation rates were established as functions of temperature and concentrations of water, sulfuric acid, and aliphatic anhydrides. The most surprising result was that the degradation of cellulose acetate passed through a minimum as a function of acetic anhydride concentration, whereas the degradation rate for cellulose propionate always increased with acetic anhydride or propionic anhydride concentrations. A mechanism is offered in terms of steric interaction between ester groups on the cellulose and various acidic species.
Interaction of cellulose with small molecules. II. Ethylenediamine, ethylene glycol, and tetramethylene sulfone
Authors: Wellisch Eric , Hagan Lamont , Marker Leon , Sweeting Orville J. 
Published: April 2003

AbstractThe interactions of cellulose with highly hygroscopic ethylenediamine and ethylene glycol and with the less hygroscopic tetramethylene sulfone have been determined. The measurements are based on the difference between the equilibrium vapor pressure of films containing known percentages of aqueous softener and the equilibrium vapor pressure of the same aqueous softener not perturbed by the presence of cellulose. The equilibrium moisture content of unsoftened cellulose (α), the equilibrium moisture content of the plasticizing molecule (β), and the equilibrium moisture content of the treated cellulose (γ) were measured as a function of relative humidity and of plasticizer content in the film. From these data relative interaction values expressed as p/p0 ratios (partial pressures of water in softened film and in aqueous softener solutions) or as deviation from additivity, δ = α + β − γ, were calculated. An interpretation of the data in terms of the relative affinities of water for softener and cellulose, arid cellulose for water and softener, is given.
The state of solution of technical viscose
Authors: Treiber Erich 
Published: April 2003

AbstractThe state of solution of a technical viscose is of both theoretical and technical interest. The existing assumptions may be divided into two general theories. These two opposing theories are concerned, to put it simply, with whether cellulose xanthate is more or less molecularly dispersed or is only a dispersion of micelles and bigger aggregates. After a short survey of the more essential and newer contributions a particle spectrum for describing the state of solution of a spinnable viscose is proposed. Furthermore, the assumption is made that about 60% of the cellulose may behave as a molecular dispersion, making possible the determination of molecular weight and other molecular parameters. The frequency distribution of micelles, bigger aggregates, and fiber fragments, derived from a stepwise disintegration process, may follow a Gaussian curve. This hypothetical frequency distribution in our particle spectrum is in agreement with known observations. The microscopic particles, affecting technical operations, can be determined directly by particle counting or indirectly by filterability determinations. After mentioning a new technique for obtaining filter values of unusually high accuracy despite the inhomogeneity of the filter materials, some results of filterability tests combined with gel particle counting are reported.
The sorption of polymers on cellulose
Authors: Luce J. E. , Robertson A. A. 
Published: April 2003

AbstractThe sorption of polyvinyl acetate from solution in organic solvents by cellulose fibers has been investigated and found to resemble the sorption of polymers by other porous sorbents. Differences in the extents of sorption from different solvents have been attributed to competition between solvent and polymer molecules for sorption sites, and have been correlated with the Hildebrand solubility parameter. The sorption properties of cellulose fibers which had been subjected to swelling in organic liquids, to solvent‐replacement procedures, and to freeze drying were examined. The extent of sorption measures the degree of swelling and has been correlated with the properties of the swelling liquid.
Gamma‐ray–induced graft copolymerization of styrene onto cellulose and some chemical properties of the grafted polymer
Authors: Kobayashi Y. 
Published: April 2003

AbstractThe γ‐ray–induced graft copolyinerization of cellulose and styrene by preirradiation was studied. (1) The graft copolymerization of cellulose and styrene was accelerated by immersing the cellulose in H202 solution during γ irradiation. The number of active sites such as hydroperoxides was estimated by the ferrous ion method. There is shown a correlation between the number of active sites and the rate of grafting. (2) The acetylation of the grafted cellulose–styrene polymer was carried out. The progress of the reaction was observed from the weight increase and infrared spectra measurement. The reaction proceeded very rapidly owing to the increased swelling of grafted polymer in the treating bath. (3) The acetylation of the cellulose‐styrene polymer was next carried out under more severe conditions. In this case the ccllulose part of the grafted polymer was degraded by acetolysis and only the polystyrene was extracted from the grafted polymer. The viscosity‐average molecular weight of the extracted polystyrene was estimated by viscometry and the degree of polymerization was calculated as 1.98 × l06. This value was compared with the number of the active sites estimated by the ferrous ion method.
The different crystalline modifications of TiCl3, a catalyst component for the polymerization of α‐olefins. I: α‐, β‐, γ‐TiCl3. II: δ‐TiCl3
Authors: Natta G. , Corradini P. , Allegra G. 
Published: April 2003

AbstractCrystalline TiCl3 is the typical solid component of the catalytic system for the stereo‐specific polymerization of α‐olefins; hence a great interest in the knowledge of its crystal structure arises. Four different crystalline modifications of TiCl3 (α, β, γ and δ) are known to date; three (β, γ, and δ) were first described in our laboratory. A preliminary structural distinction among them can be made in terms of fiber‐shaped (β) and layer (α, γ, and δ) modifications. The crystal structure of the β‐modification can, in fact, be considered as built up by linear macromolecules, while identical bidimensional (planar) macro molecules, packing with different sequences of shifts, between themselves, can originate an α‐, or γ‐, or δ‐TiCl3 crystal. This close structural analogy explains the great similarity in physical and chemical properties of the last three modifications. In the first part of this paper, the most important structural features of α, β, and γ‐modifications are described; in the second, the structure of the most recently discovered δ‐TiCl3 is more deeply analyzed. The presence of diffuse halos instead of sharp reflections in its Debye spectra clearly indicates the presence of a certain structural disorder; mathematical calculations (not fully reported here), based on the alternative assumption of two different statistical models of shift successions between structural layers, have led us to find the most probable succession type. As the possible shifts between adjacent structural layers cannot be different in type, in δ‐TiCl3, from those which take place in the ordered α‐ or γ‐modifications, we can say that, in δ‐TiCl3, the intervention of disorder in shift successions leads to something intermediate (in a statistical sense) between the two stated structures.