bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conformation of polylysine and polyglutamic acid adsorbed on the charged mercury/water interface
Authors: Pavlovic O. , Miller I. R. 
Published: June 2010

AbstractInformation on the structure of adsorbed monolayers of polypeptides is obtained from differential capacitance values measured in the presence of the adsorbing polypeptides and supporting electrolyte. The uncharged polylysine (pH>11) is strongly adsorbed and fails to desorb even from highly polarized mercury surfaces, thus no desorption peaks can be determined. The capacity values decrease with increasing polylysine concentration until a limiting saturation capacity curve is reached at a bulk concentration which decreases with the square root of the age of the mercury drop. The area per lysine residue on a saturated surface, calculated from the diffusion controlled adsorption kinetics, is 38Å2, irrespective of polarization. At lower pH values, when the charge on the polylysine increases gradually, a desorption peak appears at positive polarization, while at negative polarization a hump caused by reorientation of the polypeptide in the surface is observed. The surface confor‐mation reflects also the concentration of the polypeptide in the bulk. The area per lysine residue in the saturated surface layer adsorbed from very dilute solution at pH's 1.3–7 was calculated to be 22Å2.Polyglutamic acid (PGA) at low degrees of ionization (pH 4.6) produces a region of low capacities around the zero charge potential. It is desorbed from either a positively or a negatively charged mercury surface, giving rise to anodic and cathodic desorption peaks at +0.1 and −1.4 volts, respectively, relative to NCE. Completely ionized polyglutamic acid (pH 10.4) raises the differential capacity around the zero charge region and is expelled from the surface at higher negative polarization. The area per residue of fully ionized PGA was found from the adsorption kinetics to be 45Å2, corresponding to a spread out molecule with the residues in the trans position. At pH 4.6, when PGA is only about 20% ionized, the area per residue is 34Å2 at positively charged surfaces. This area decreases gradually with increasing negative polarization of the surface, to values between 13Å2 (40° C) and 18Å2 (0.9° C). These values are in accord with a helical conformation prevailing in the surface.
Adsorption of polymers at the solution‐solid interface. IV. Styrene‐methyl methacrylate copolymers on silica
Authors: Herd Jacqueline M. , Hopkins A. J. , Howard G. J. 
Published: June 2010

AbstractA series of random and block copolymers of styrene and methylmethacrylate has been prepared and characterized and the adsorption behavior on silica found from several solvents, in particular, from benzene and trichloroethylene. Specific adsorption measure‐ments have been supplemented by infrared determinations of bound fractions. Relatively few methacrylate groups are necessary to bind the copolymers to the silica surface. Little variation in specific adsorption is found over a wide range of copolymer composition and within this range the fraction of bound groups (of both structures) is approximately constant. Only rather small differences in adsorption behavior are shown by the random and block copolymer structures.
Tracer study of kinetics and mechanism of hydrolytically induced interfacial failure
Authors: Schrader M. E. , Block A. 
Published: June 2010

AbstractAnalysis of the kinetics of hydrolytic desorption of chemisorbed C‐14 labelled polymeric APS (gamma‐aminopropyltriethoxysilane, a coupling agent for glass reinforced epoxy resins) from flat silica or borosilicate surfaces, indicated that the polymer probably consisted of short chains each chemisorbed at one end to the surface with little or no cross‐linking. A method was developed to determine from kinetic data whether or not more than one type of bond is severed during the desorption process. Application of the method to these results indicated that more than one type of linkage was being hydrolyzed in the desorption of APS.Glass‐epoxy adhesive joints were prepared from glass containing various amounts of APS chemisorbed to the surface. In one set of experiments, the amounts were varied through aqueous extraction of increments of the originally deposited material. In a second set, the amounts were varied by adsorption from very dilute solution. The lifetimes of the adhesive joints were measured under static load in hot water. It was found that the maximum lifetime is not dependent on the thickness of the chemisorbed layer, but that it is dependent on the lateral surface concentration of the chemisorbed polymeric units. Examination of the debonded joints for radioactivity indicated that failure resulted from hydrolysis of siloxane bonds in the coupling agent structure.
Viscoelastic behavior of polymers undergoing crosslinking reactions
Authors: Moacanin J. , Aklonis J. J. 
Published: June 2010

AbstractPreviously a method was developed for predicting the viscoelastic response of polymers undergoing scission reactions. These results are now extended to include crosslinking reactions. As for scission, at any given time the character of the network chains is determined by the instantaneous crosslink density. For scission all chains were assumed to carry the same stress; for crosslinking, however, the stress is distributed between the “new” and “old” chains. Equations for calculating the creep response of a system which experiences a step increase in crosslink density are derived.
Die swell and recoverable shear strain in polyethylene extrusion
Authors: Mendelson R. A. , Finger F. L. , Bagley E. B. 
Published: June 2010

AbstractThe present paper treats die swell as unretarded recovery of elastic strain imparted during flow into and through the die. Three mechanistic models are developed. All three models treat the material as an elastic solid for the purpose of elucidating die swell, and two models utilize rubber‐like elasticity theory. Equations relating swelling ratio, recoverable shear strain (SR), axial normal stress, shear stress, and shear modulus are derived for the three models. While the forms of the results differ somewhat from model to model, the numerical results are quite similar. Experimental die swell data were obtained for four high density polyethylene resins in several large L/D capillaries using an Instron Capillary Rheometer. A procedure for obtaining equilibrium, or strain‐free, values of the swelling ratio by annealing the extrudates above the melting point is discussed. Values of SR and normal stress were calculated and compared to corresponding quantities obtained directly from measurements using a cone‐and‐plate Weissenberg Rheogoniometer. Excellent agreement between results from the widely divergent methods of measurement was obtained.
Oxidative reactions of cellulose initiated by free radicals
Authors: Arthur Jett C. , Hinojosa Oscar 
Published: June 2010

AbstractOxidative reactions in cellulose are commonly initiated by thermal, ultraviolet, and high‐energy radiations and by chemical oxidation. Long‐lived free radicals, formed in cellulose on the localization of energy from thermal, ultraviolet, and high‐energy radiations, and short‐lived free radicals, formed in cellulose by oxidation, e.g., by ceric ion or redox reactions, were investigated by electron spin resonance spectroscopy. Dehydrogenation and oxidative depolymerization reactions of cellulose are indicated. The physical, chemical, and morphological effects of these free‐radical initiated reactions on cellulose are summarized. The formation of free radicals in cellulose also increases the chemical reactivity of cellulose, particularly for chain copolymerization reactions with vinyl monomers. Preparation of cellulose‐poly(vinyl) copolymers, using free‐radical initiation, yields paper, film, wood, and textile products with new physical and chemical properties.
The distribution of aqueous solutions within wood
Authors: Fengel D. 
Published: June 2010

AbstractOne of the basic reactions during pulping processes is the penetration of wood chips by the delignifying solution. For the study of the distribution of fluids within the cell walls, dry and green samples of pine wood (Pinus sylvestris L.) were treated with aqueous solutions of staining compounds, only by dipping‐in (diffusion), under vacuum, and under pressure. Best penetration was achieved by vacuum treatment in dry wood and by pressure treatment in green wood. The studies made by electron microscopy and by electron probe microanalyzer showed that the staining material is not equally distributed in the cell wall. In all samples the compound middle lamella is intensively stained. In some places there is a high concentration of staining material in the secondary wall 1 (S1), in other places there is a high concentration in a zone of the secondary wall 2 (S2) adjoined to the secondary wall 1. In most cases the tertiary wall (S3) and the adjoined part of the S2 is stained more intensively than the residual S2. Also the tori of the bordered pits are penetrated by the staining substance. The connection between the passage and the distribution of fluids within the cell wall and the ultrastructure of the cell wall is discussed.
Twisting energy of holocellulose fibers
Authors: Mark R. E. , Thorpe J. L. , Angello A. J. , Perkins R. W. , Gillis P. P. 
Published: June 2010

AbstractFreely drying fibers exhibit collapse and twist behavior that is only infrequently observed in the formation of a paper web. Anisotropic fiber shrinkage models are employed that enable calculation of the twisting energy of a freely drying fiber as well as the reverse case (dry to wet). The twisting energy appears to be highly significant in relation to the fiber and bond energies associated with paper strength. Some experimental results with southern pine fibers have been obtained using specially designed testing devices.
Graft copolymerization of ethyl acrylate with γ‐irradiated cotton cellulose I and II
Authors: Nakamura Yoshio , Hinojosa Oscar , Arthur Jett C. 
Published: June 2010

AbstractThe graft copolymerization of ethyl acrylate from methanol‐water solutions with γ‐irradiated cotton cellulose I and II was investigated by electron spin resonsance spectroscopy and by the formation of cellulose‐poly(ethyl acrylate) copolymer. The rate and extent of graft copolymerization reactions in these heterogeneous systems were dependent on conditions of storage of the irradiated celluloses prior to reaction, the composition of the methanol‐water solutions, reaction time, agitation during the reaction, and cellulose crystal lattice type. Agitation of the heterogeneous system during reaction decreased both the rate and extent of copolymerization. From water the extent of copolymerization of ethyl acrylate with irradiated collulose I was greater than with cellulose II; from methanol the extent of copolymerization with irradiated cellulose II was greater than with cellulose I. From methanol(40 vol‐%)‐water(60 vol‐%) maximum extent of copolymerization occurred with both irradiated celluloses; however, the extent of copolymerization was less with irradiated cellulose II than with cellulose I. The extent of copolymerization was directly related to the initial concentration of free radicals in the irradiated cellulose. However, a fraction of the radicals, about 10% of the maximum concentration in cellulose obtained at a dosage of 5.2 × 1019 eV/g, was apparently in the highly ordered regions of the cellulosic structure. These radicals were not scavenged and did not initiate copolymerization reactions.
Grafting of cellulose and derivatives by means of diazonium salts
Authors: Simionescu Cristofor I. , Dumitriu Severian 
Published: June 2010

AbstractNew amino aromatic esters and ethers of cellulose were synthetized. Then grafting processes were performed on these derivatives by using acrylic, methacrylic and N‐vinyl pyrolidone monomers. Finally, chemical structure and physicomechanical properties were determined. Industrial experiments proved the utility of this grafting method.
The effect of vinyl monomer grafting on the water sorption kinetics and equilibria in cellulose
Authors: Lepoutre P. F. , Hopfenberg H. B. , Stannett V. 
Published: June 2010

AbstractWood pulp cellulose was grafted with styrene and a number of other vinyl monomers using the mutual radiation technique. The effects of the level of grafting, type of monomer, and the grafting conditions on the water sorption equilibria and kinetics were determined. Styrene was studied in considerable detail. Styrene grafting reduced the equilibrium water content but water diffusivities increased as a consequence of styrene grafting. Conversely, the grafting of polar monomers such as acrylonitrile, ethyl acrylate, and acrylic acid led to somewhat higher water regains but to decreased diffusion constants.The swelling conditions used during the mutual grafting process with styrene significantly affected the grafting rates and the properties of the resulting grafts. For example, the equilibrium water contents at the same level of grafting, was a function not only of percent graft but also of the specific swelling conditions. These moisture regains were inversely related to the density of the grafted fibers. These results are discussed in terms of the conformation of the grafted side chains which is determined by the various grafting conditions.
Hydrodynamically induced crystallization of polymers from solution. V. Tensile properties of fibrillar polyethylene crystals
Authors: Pennings A. J. , Schouteten C. J. H. , Kiel A. M. 
Published: June 2010

AbstractA study has been made on the tensile properties of mats of fibrillar polyethylene crystals grown at various temperatures from stirred xylene solutions in a Couette‐type instrument. The stress‐strain behavior of fibrillar crystals precipitated above 100°C was found to be essentially Hookean, and the maximum values determined for Young's modulus and tensile strength at break amounted to 27 × 104 kg/cm2 and 10 × 103 kg/cm2, respectively. The elongation at break for these high temperature fibers was 6%. Stress‐strain diagrams for fibrillar polyethylene crystals grown at temperatures below 100°C were curved and the elongations at break amounted to roughly 12%. Both the Young's modulus and the tensile strength were found to increase strongly with the crystallization temperature; this trend is attributed mainly to the decrease in the amount of lamellar overgrowth and the improvement in orientation.Microscopic examinations have shown that the mats can be regarded as assemblies of macrofibers having diameters in the micron range. Homogeneous fracturing is found in samples with extensive lamellar overgrowth, whereas carefully washed samples fractured into fibrils. Electron micrographs reveal that the elementary fibrils (the shish‐kebabs) develop brittle fractures and that the lamellar overgrowth is capable of transmitting stresses normal and parallel to the backbones. Digestion of the fibrillar crystal material with fuming nitric acid causes a decrease in tensile strength and elongation at break, but the Young's modulus remains approximately unaltered.
The influence of supermolecular structure on the strength and deformation characteristics of linear polyethylene
Authors: Marichin V. A. , Miasnikova L. P. , Sutchkov V. A. , Tuchvatullina M. Sh. , Novak I. I. 
Published: June 2010

AbstractThe influence of supermolecular structure on the mechanical properties of linear polyethylene has been studied. The change in film structure has been realized by means of variation of isothermal crystallization conditions. The films obtained had either lamellar structure, or consisted of spherulites. It has been shown that the tensile strength of unoriented films with small spherulite structure is twice as great as that of films with well developed lamellae. This mechanical difference remained after 20‐fold drawing of the specimens at high‐temperature (102°C) for short times. The study of the structure of oriented films showed that in all the cases the transverse size of microfibrils remained constant. However, with the help of infrared spectroscopy it has been found that the amorphous phase orientation here was different, while the degree of elongation was the same.
Morphological changes during the melting of bulk‐crystallized polymers
Authors: Fulcher K. U. , Brown D. S. , Wetton R. E. 
Published: June 2010

AbstractThe melting behavior of some bulk‐crystallized, high molecular weight polymers has been studied in relation to morphology. Small‐angle x‐ray scattering results from two polymers, polytetramethylene oxide and polyethylene, are presented and discussed.Theoretical correlation functions have been calculated from models based on randomly oriented regions of alternating crystalline and amorphous layers, and have been compared with experimental correlation functions obtained from desmeared x‐ray scattering data. With this approach it has been possible to study changes in the thickness and widths of distributions of both crystalline and amorphous regions, over the temperature range from the crystallization temperature to the melting point.Evidence has been obtained in favor of a “surface melting” mechanism in which fusion occurs by the progressive transfer of chain segments from the “fold surfaces” of the crystalline lamellae to the amorphous or melt‐like phase. This involves the progressive thinning of each lamella towards its center.
Morphology of the fracture surface layer of poly (methyl methacrylate) and the fracture mechanism
Authors: Lednicky F. , Pelzbauer Z. 
Published: June 2010

AbstractOptical and electron microscopic methods were used to investigate the morphology and optical properties of the fracture surface layer of poly (methyl methacrylate). A new method developed by us made it possible to evaluate, from interference phenomena, the optical thickness of the layer which in the proximity of the secondary fracture center always exhibited a minimum and attained maximum values (1.1‐1.6 μm) at the boundaries of the conic fracture formation. After mutual correlation, the local refractive index of the surface layer was calculated and found to be 1.31 to 1.35. Although the macromolecular chains are oriented in crazes, no chain orientation in the fracture surface layer was detected. The lower refractive index of the surface layer is therefore interpreted in terms of material dilution of about 35% by volume of small holes. When the sample is subjected to thermal treatment, the profile of the optical thickness of the fracture surface layer remains unaltered, only the interference colors gradually disappear. This fact is attributed to a change in the reflectivity on the upper or lower boundary of the surface layer caused by local changes in the material density. The replica electron micrographs of the fracture surfaces showed pits in the foci of the conic markings which had various shapes and diameters about 1 μm. Using the facts established about the geometry and morphology of the fracture surface layer, a mechanism for the initiation and propagation of fracture has been suggested.
Calculation of minimum potential energy of folds and kinks in polyethylene crystals
Authors: Petraccone V. , Allegra G. , Corradini P. 
Published: June 2010

AbstractWe have performed calculations of potential energy minima for the possible conformations of folds and kinks in a polyethylene crystal. Unlike previous work, the calculations take into account the possibility of coupled variations of internal rotation angles as well as of bond angles in the search for energy minima.The conformations of minimum energy found by us for tight folds in the 200 and 110 planes of polyethylene structure have energies of the order of 3 and 4 kcal/mole, respectively, less by a factor of say 2.5 than the figures obtained by previous authors, even when the earlier results were recalculated with our “softer” energy functions. Possible conformations for a “Reneker kink” have also been calculated; their energy turned out to be of the order of 7 kcal/mole.In all cases, a wide variety of geometrical models is almost isoenergetic in the neighborhood of the conformations studied.
Entropy of mixing of polymer and solvent as derived from the free‐volume concept
Authors: Dayantis Jean 
Published: June 2010

AbstractA theory is proposed for the entropy of mixing of polymer and solvent. The theory is an extension of Hildebrand's derivation of the Flory‐Huggins combinatorial entropy of mixing by use of free‐volume concepts. The noncombinatorial (or equation of state) entropy of mixing originates, according to the proposed theory in the different free volume fractions which characterize ordinary simple solvents and high polymers. Two parameters are introduced: a parameter ρ, which is the ratio of the free volume fractions in the polymer and in the solvent, and a parameter c, which describes the external degrees of freedom of the polymer segments and is equivalent to Prigogine's parameter c. The noncombinatorial entropy of mixing, as derived from the present theory is equivalent (but not identical) to that derived from the newer theory of Flory et al. Concomitantly, the agreement with experiment of the calculated interaction parameter × for the athermal system polyisobutylene‐cyclohexane is about the same as that obtained from the theory of Flory et al.
Influence sur la viscosite intrinsèque d'un copolymère de son mode de dissolution dans un mélange binaire solvant‐non‐solvant
Authors: Vial J. 
Published: June 2010

AbstractThere are two ways of dissolving a polymer in a binary mixture of a solvent and a nonsolvent: direct dissolution or dissolution in the solvent followed by dilution with the nonsolvent. The two methods have been applied to two types of vinylacetochloride copolymers, one containing 6% by weight of hydrolyzed groups, with a series of solvents diluted with polar nonsolvents (butyl alcohol, acetronitrile). The thermodynamic quality of the resulting solutions has been evaluated by intrinsic viscosity measurements. The addition of butyl alcohol to a moderately good solvent greatly improves the solvent power, particularly if solution is effected directly in the mixture. This does not happen with the nonhydroxylated polymer for which results are identical regardless of the mode of dissolution. These phenomena are also observed in some cases with both polymers when acetonitrile is used. None of the above phenomena occurs with a very good solvent regardless of the mode of dissolution.
Polymeric UV absorbers of the 2‐hydroxybenzophenone type. II. On the mechanism of the polymerization of 2‐hydroxy‐4‐(2,3‐epoxypropoxy) benzophenone with phthalic anhydride
Authors: Lustoň J. , Schubertová N. , Maňásek Z. 
Published: June 2010

AbstractSimultaneously with the preparation of 2‐hydroxybenzophenone light stabilizers with a reduced extractability from polypropylene, the mechanism of the propagation reaction of 2‐hydroxy‐4‐(2,3‐epoxypropoxy) benzophenone with phthalic anhydride was studied under different concentrations and temperature conditions, with tert‐amines, potassium benzoate, and potassium hydroxide being used as catalysts. If the polymerization of epoxide with anhydride is performed in melt at 125°C, an alternating copolymer is formed whether an equimolar ratio or a molar excess of anhydride with respect to epoxide has been used. Provided epoxide is present in molar excess with respect to anhydride in the reaction system, some changes in ultraviolet absorption spectra are observed in comparison with the spectra of alternating copolymers which indicate that some undesirable reactions of the orthophenolic groups of benzophenone occur simultaneously with the catalyzed polyaddition reaction, and that the polymeric stabilizer is impaired.