bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure of porous cellulose acetate membranes and a method for improving their performance in reverse osmosis
Authors: Kopeček J. , Sourirajan S. 
Published: April 2003

AbstractExperimental data support the hypothesis that the surface layer of the asymmetric Loeb‐Sourirajan type porous cellulose acetate membranes has a heterogeneous microporous structure. A general method is proposed for improving the performance of the above membranes in reverse osmosis, by which product rates are increased without decreasing solute separation. The method consists in pumping pure water past the back side of the membrane under just enough pressure for a sufficiently prolonged period of time; after such pretreatment, the membrane is used in the reverse osmosis experiments in the normal manner with the surface layer facing the feed solution. Back‐pressure treatment at 400 psig for 85 hr on preshrunk and normally pressure‐treated membranes increases the product rate by over 20% without decreasing solute separation in reverse osmosis experiments at 600 psig with the use of 0.5 wt‐% NaCl–H2O feed solutions; with a different sequence of back‐pressure treatment, similar results have been obtained in reverse osmosis experiments at 1500 psig also. The compaction effect of a normal membrane and that of a back pressure treated membrane are the same during continuous reverse osmosis operation under 600 psig; the effects of back‐pressure treatment on a normal membrane and a compacted membrane are also the same. The pure water permeability data obtained in cyclic experiments show that the smaller pores on the surface layer are opened more than the bigger ones during the back side operation. The probable structural changes taking place in the film during back‐pressure treatment are discussed.
Chemically crosslinked high‐density polyethylene
Authors: Narkis Moshe , Miltz Joseph 
Published: April 2003

AbstractChemical crosslinking of high‐density polyethylene was studied. The amount of gel produced by a given peroxide concentration depends on the molecular weight of the polymer. More scission reactions, during the crosslinking process, occur in low‐density than in high‐density polyethylene crosslinked with Varox and Luperox 130 peroxides. The rheological behavior of partially crosslinked polyethylene is useful and convenient for quality control, for characterization, and for studies on the various mechanisms associated with the crosslinking process.
Sulfonium polymers derived from Ar‐vinylbenzyl chloride. I. Exploratory study of the preparation and properties of the monomers and polymers
Authors: Hatch Melvin J. , Meyer Fred J. , Lloyd Winston D. 
Published: April 2003

AbstractAlthough sulfonium salts are well known, polymeric sulfonium salts seldom have been mentioned in the chemical literature. This paper describes exploratory work in the preparation of various sulfonium monomers and polymers from ar‐vinylbenzyl chlorides (ortho and para isomers). These chlorides—particularly the para isomer—reacted readily with 2,2′‐thiodiethanol and water to yield the corresponding ar‐vinylbenzyl sulfonium chloride monomers in aqueous solution.
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The odorless, reactive monomer mixture polymerized readily with persulfate or hydroperoxide catalysts; however, polymerization could be inhibited with cupric salts. Copolymerization with trimethyl(ar‐vinylbenzyl)ammonium chloride was random. In copolymerization with acrylamide or acrylonitrile, the sulfonium monomer was more reactive. Analogous sulfonium monomers were made by reaction of ar‐vinylbenzyl chlorides with various sulfides. In general, all the sulfonium monomers yielded homopolymers which were fairly stable in aqueous solution in the absence of strongly nucleophilic agents which would attack the sulfonium groups. However, when dried at room temperature the polymers would crosslink; and when heated, the polymers became hydrophobic also. Scrambling of the sulfonium group substituents during drying, and nucleophilic displacement reactions by chloride ion during heating were likely explanations. The high cationic charge on the polymers made them substantive to cellulose fibers. This property, when coupled with high nucleophilic reactivity of the sulfonium groups with the carboxylate sites of the pulp or other anionic counterious during drying and heating, made the polymers very effective as beater additives for imparting wet strength to paper.
Embrittlement and stress cracking of polyethylene by fuming nitric acid
Authors: Hinton T. , Keller A. 
Published: April 2003

AbstractOxidative embrittlement and stress cracking of high‐density polyethylene has been studied by using fuming nitric acid at 60°C as the oxidative agent. Oxidative stress cracking was found to be insensitive to changes in molecular weight in contrast to environmental stress cracking in a surface‐active medium. The oxidative attack was found to be influenced by the surface crystalline texture of the polyethylene. Oriented polyethylene showed an increased resistance to oxidative embrittlement and stress cracking, the mode of failure being dependent upon the prior annealing treatment.
Correction of instrument spreading in gel‐permeation chromatography
Authors: Tung L. H. 
Published: April 2003

AbstractPresent methods of correcting instrument spreading (resolution correction) in GPC are either too cumbersome to use or inaccurate when the correction is large. Two new methods which are both accurate and simple to use are presented in this work. The first method using the technique of Fourier analysis is more general and can be used to correct non‐Gaussian instrument spreading. The second method using a fourth‐degree polynomial requires a Gaussian instrument spreading function. The instrument spreading function may vary with respect to the elution volume in both methods.
Disorder in cellulosic fibers
Authors: Viswanathan A. , Venkatakrishnan V. 
Published: April 2003

AbstractRuland's concept of an isotropic disorder function is applied to estimate the disorder parameter and the degree of crystallinity in a few cellulosic fibers: two cottons, native ramie, and a high‐tenacity rayon. The results indicate an increase in disorder without any change in crystallinity on mercerization of native celluloses. On hydrolysis, with or without a pretreatment of mercerization, the samples exhibit a higher crystallinity, disorder remaining the same as for native celluloses. A ball‐milled sample of “amorphous” cellulose is still found to be fairly crystalline with the lowest disorder. On being wetted in water and oven‐dried, a distorted form of cellulose II with higher crystallinity and disorder was obtained. The polynosic fiber, Tufcel, has low values for the degree of crystallinity, disorder parameter, as well as crystallite dimension. A strong dependence of the degree of crystallinity on the crystallite size, particularly the lateral, is observed.
Attachment of amino groups to polymer surfaces by radiofrequency plasmas
Authors: Hollahan J. R. , Stafford B. B. , Falb R. D. , Payne S. T. 
Published: April 2003

AbstractLow temperature gaseous plasmas of ammonia or nitrogen–hydrogen mixtures contain NH2 groups, or precursors thereof, formed in the plasma, which experimental evidence strongly suggests, can add to various polymer surfaces. The plasmas were established in the 0.3–1.5 torr range by radiofrequency (13.56 MHz) electrodeless excitation at powers ranging from 50 to 500 W. Samples of polypropylene, poly(vinyl chloride), polytetrafluorethylene, polycarbonate, polyurethane, and poly(methl methacrylate) were investigated. All these polymers added amino groups to varying degrees of amino site densities depending on the choice of plasma parameters and the reactivity of the polymer itself. In every instance the polymer was rendered more wettable, although no quantitative wettability measurements were made. Following the plasma treatment, degrees of amino attachment to the polymer were followed radiometrically and reported in terms of “heparin thicknesses” resulting from ionic heparin 35S attachment to quaternary sites produced from the amino groups. Two implications of such a surface modification are to adhesion and blood compatible materials preparation.
Spin orientation during acrylic fiber formation by wet‐spinning
Authors: Paul D. R. 
Published: April 2003

AbstractThe molecular orientation acquired during fiber formation of acrylic fibers by wetspinning has been studied. Orientation was detected by measurements of sonic modulus which were converted into an orientation factor. The orientation correlates very well with the ratio of take‐up velocity to the freely extreuded velocity. Several mechanisms for the origin of spin orientation are discussed.
Efficiency of nucleating additives in polypropylene
Authors: Rybnikář F. 
Published: April 2003

AbstractInvestigation of the nucleating ability of selected nucleating agents in various commercial types of isolactic polypropylene revealed that the efficiency of individual additives is not equal for all types of polypropylene. As to the nucleation mechanism, it can be supposed that in most cases the added nucleating agents act mainly secondarily, activating the heterogeneities originally present in the polymer.
Study of the reaction of resorcinol, formaldehyde, and ammonia
Authors: Van Gils G. E. 
Published: April 2003

AbstractLatex dip adhesives for nylon and rayon tire cords are prepared by reacting resorcinol and formaldehyde in aqueous solution in the presence of a catalyst for a specified time and then adding a butadience–styrene–vinylpyridine latex. Ammonia improves the stability of the latex and increases the adhesion of rubber to cord. However, a white precipitate forms if ammonia is added before the resorcinol and formaldehyde have reacted sufficiently. This paper is study of the nature of this precipitate and the conditions for its formation. By measuring the heat of reaction of formaldehyde and ammonia and, subsequently, of mixtures of formaldehyde and resorcinol to which varying amounts of ammonia were added, information on the reaction mechanism has been obtained. Ammonia reacts rapidly with formaldehyde to form an unstable intermediate, presumably trimethylolamine, which then reacts further with resorcinol to form trisdihydroxybenzylamine. This compound is also very reactive and condenses withmore ammonia and formaldehyde to give a polymer of low solubility, the composition depending on the amounts of ammonia and formaldehyde available for reaction. Elemental analyses support this concept. Primary and secondary amines react in a maner similar to ammonia.
Isothermal pyrolysis of cellulose: Kinetics and gas chromatographic mass spectrometric analysis of the degradation products
Authors: Lipska Anne E. , Wodley Frank A. 
Published: April 2003

AbstractUntreated and fire‐retardant‐treated white α‐cellulose samples were isothermally pyrolyzed in a fluidized bath in a nitrogen environment at 298–360°C. Results were reported in terms of volatilization (based on weight loss‐time measurements) and the degradation products (based on gas chromatographic–mass spectrometric analysis). The findings products (based on gas chromatographic–mass spectrometric analysis). The findings on untreated cellulose indicate that: (1) pyrolysis occurs in three distinct phases in the temperature range 276–360°C; (2) there is a single activation energy of 42 kcal/mole over this temperature range; (3) the initial rapid weight loss is not due to the desoprtion of water, but primarily to decomposition of the cellulose; molecules: (4) there is little difference in either the quality or relative quantity of the volatiles generated during the three different phases of pyrolysis. The findings on treated cellulose show that the fire retardant, KHCO3, does not markedly change the types of degradation products having molecular weights below about 110, althought it does change their relative concentrations. Furthermore, the rate of product generation and the quantity of residual char are increased.
Studies on selenium–organic polymer interfaces
Authors: Chiang Y. S. , Ing S. W. 
Published: April 2003

AbstractInterfaces of evaporated viterous selenium and various organic polymeric resins of both the thermosetting and thermoplastic type have been studied by ultra‐thin sectioning and transmission electron microscopy techniques. Epoxy, phenoxy, polyamide, butadien–styrene copolymer, vinyl‐toluene–butadiene copolymer, resins as well as polyethylene are among those organic polymers studied. Interfaces prepared by vaccum evaporation of selenium onto the various substrates and under varying processing conditions were examined. Intermixing and interdiffusion of the inorganic and organic polymers in the interfacial region were observed in certain cases when selenium was evaporated onto incompletely curved epoxy or lower viscosity polymers. These occurrences were found to contribute significantly to the mechanical strength of the assembly. Electrical properties of certain specific systems have also been investigated.
Liquid‐induced crystallization of poly(ethylene terephthalate)
Authors: Lawton E. L. , Cates D. M. 
Published: April 2003

AbstractAmorphous unoriented poly(ethylene terephthalate) was crystallized at 25°C by various organic liquids. The crystalliznity induced in the amorphous polymer was measured by differential scanning calorimetry and infrared spectroscopy. The ability of liquids to interact with and induced crystallinity in the amorphous polymer was classified on the basis of their solubility parameters. Measurements of the density of liquid‐crystallized 0.8‐mil films of poly(ethylene terephthalate) indicated the presence of extensive internal voids in the semicrystalline polymer matrix. Comparison of differential scanning calorimetric thermograms and infared spectra of heat‐crystalized and liquid‐crystallized polymer indicated significant differences in the polymer morphologies induced by the two crystallization processes.
Greffages mecanochimiques sur le polychlorure de vinyle. I. Polyméarisations amorcéaes par le malaxage
Authors: Guyot Alain , Michel Alain 
Published: April 2003

AbstractThe grafting of methyl methacrylate and of methacrylic esters on poly(vinyl chloride) by mechanicochemical synthesis can be performed in the Brabender Plastograph. These monomers possess sufficient intermolecular plasticizing power to bring the poly(vinyl chloride)‐monomer system into the viscoelastic state required for the formation of free radicals by homolytic scission of polymeric chains. Nevertheless several other monomers (among them the styrene) have interstructural plasticizing ability and can be grafted by mechanicochemical synthesis by addition of an intermolecular plasticizer or a monomer of the first class (methyl methacrylate). Also, except for basic monomers, the monomers stabilize poly(Vinyl chloride) during the mastication, probably because they act as free‐radical scavengers.
Greffages mecanochimiques sur le polychlorure de vinyle. II. Éatude des copolymègres grefféas
Authors: Michel Alain , Galin Monique , Guyot Alain 
Published: April 2003

AbstractThe copolymers obtained by mastication of poly(vinyl chloride) (PVC) in presence of methyl methacrylate and styrene monomers, and their fractions, were studied by using infrared spectroscopy, NMR, and flash pyrolysis. The degree of alternation between vinyl chloride and methyl methacrylate or styrene units is very low, and the copolymers are heterogeneous in composition. The results suggest that the mastication medium involves three kinds of domains: the inner part of the elementary grains of PVC is very slightly penetrated by the monomers. The polymerization initiated by the polymeric free radicals created by the rupture of bonds, begins in the surface layers of the grains and cause the formation of a true copolymer which accounts for 5–10% of the material. Light radicals arising from transfer reaction migrate into the third external domain which consists practically entirely of pure monomers and initiate polymerization.
Greffages mecanochimiques sur le polychlorure de vinyle. III. Stabilitéa thermique des polymègeres modifiéas
Authors: Michel Alain , Bert Michel , Guyot Alain 
Published: April 2003

AbstractThe mastication of poly(vinyl chloride) (PVC) in presence of monomers causes important changes of the thermal stability of the polymer when the last one possesses a basic character (e.g., 2‐vinylpyridine). The dehydrochlorination rate is greatly increased, even if the monomer is present in only small amounts. In the most cases (styrene, acrylic ester) a better thermal stability is observed with respect to the acceleration of the dehydrochlorination, which is retarded or even suppressed. Infrared spectroscopy and differential thermal analysis show that the improved stability is due to an improved crystalline organization. When mastication causes the polymerization of the monomer (methyl methacrylate), degradation of the PVC part and depolymerization of the rafted part are observed simultaneously; this fact supports a radical mechanism for the thermal degradation of the PVC.
Tensile behavior of glass fiber‐reinforced acetal polymer
Authors: Hardy G. F. , Wagner H. L. 
Published: April 2003

AbstractThe tensile stress‐strain behavior of glass fiber‐reinforced polyacetal resin was investigated for various fiber concentrations, fiber length distributions, and finishing agents. The polyacetal fiber blends change considerably in strength and elongation at break when treated with ammonium chloride, but otherwise similar specimens still follow a common stress‐strain curve to a point shortly before failure. As the mean fiber length decreases, the modulus and tensile strength fall, but the elongation at break remains almost unchanged. The observed tensile behavior is discussed in terms of a simplified model, which assigns the fibers to two categories: a fraction α parallel to the applied load, and the remainder distributed in a plane perpendicular to the load axis. By fitting this model to the stress‐strain curves, two other constants of each system are derived: a length‐dependent efficiency factor β for parallel fibers, whose magnitude agrees with the predictions of Rosen and his co‐workers, and a factor γ which expresses the constraint of the matrix resin by the “transverse” fibers. The behavior of γ is consistent with Tsai's theory of the transverse modulus of laminates, if a reasonable amount of fiber–fiber contact is assumed. In terms of this model, possible interpretations of the behavior under repeated loading and the mechanism of tensile failure are presented.
Thermal properties of an epoxide resin cured with bicyclo Diels‐Alder anhydride adducts
Authors: Fleming Gerald J. 
Published: April 2003

AbstractThe thermal properties of polymers derived from resorcinol diglycidyl ether cured with several bicyclo Diels‐Alder anhydride adducts have been investigated. Increased char yields and decreased rates of weight loss were observed for these systems as compared to polymers cured by Diels–Alder adducts from acyclic dienes. This is explained on the basis of a reverse Diels‐Alder reaction which these bicyclo adducts undergo at lower temperatures than do adducts from acyclic dienes.
Influence of elastic effects on capillary flow of molten polymers
Authors: McLuckie Colin , Rogers Morris G. 
Published: April 2003

AbstractCapillary viscometer measurements for a number of polyethylenes and polystyrenes reveal deviations from linearity in plots of applied pressure versus capillary length to diameter ratio, at constant rates of shear, resulting in apparently negative end corrections. This is contrary to previous physical considerations. Some polymers obey Hooke's law in shear permitting the separation of the end correction into two components. A Couette correction, dependent upon the capillary dimensions, is constant for any given polymer, shear rate, and temperature; an elastic shear strain correction, dependent upon the transit time through the capillary, may be determined by post‐extrusion measurements. Determination of these two correction leads to linear plots of pressure versus capillary length to diameter ratio and enables flow curves to be calculated independent of the capillary dimensions and the swell properties of the polymer.
Young's modulus and secondary mechanical dispersions in polypromellitimide
Authors: Butta Enzo , De Petris Silvano , Pasquini Mario 
Published: April 2003

AbstractDynamic mechanical properties were determined in polypyromellitimide at acoustic frequencies over a wide temperature range (80–750°K). Two distinct secondary relaxation effects were found: one (β′) at lower temperature, characterized by a loss maximum at 250°K, and another (β) at higher temperatures with a loss maximum at 400°K. The lower temperature peak is shifted towards higher temperature with increasing frequency following an Arrhenius‐type equation (apparent activation energy: 15 kcal/mole); the relaxation strength increases with water content and becomes practically zero when samples dried under vacuum at 200°C are examined. The β′ relaxation process is thus attributed to the presence of adsorbed water molecules. The higher‐temperature (β) dispersion, which persists even after dehydration, on the basis of some results obtained for other polymers containing p‐oxylphenylene rings in the backbone, is tentatively attributed to torsional oscillations of aromatic rings along the chain.
Adhesion of metals to polymers. I. Study of interfaces modified by inductive heating
Authors: Raff R. A. V. , Sharan A. M. 
Published: April 2003

AbstractThe objective of the work reported in this paper is to explain theoretically the observations made in an earlier study that castings of an epoxide resin reinforced by electrically conductive inserts, after having been postcured by inductive heating, had strength properties superior to those achieved by a purely thermal postcure. A search of the literature on adhesion suggested that among the theories presented, those dealing with electrical double layer formation, interdiffusion, and mixed polymer grafting on the insert–polymer interface deserve to be considered. Experiments were then planned in such a manner as to permit a choice between these theories. Epoxide resin specimens reinforced with various metals (pure silver, silver with an oxide layer, pure copper, copper with an oxide layer, aluminum, and stainless steel) were prepared. They were then either postcured in a heated oven, or postcured in an induction furnace for various lengths of time. Bonding strength was determined by a knife‐edge method, and the exposed insert and resin surfaces were tested for electrical potential and surface wettability (angle‐of‐contact). Most strikingly, the curves obtained with increasing induction heating times for bonding strength, electrical potential, and wettability were all sinusoidal in shape, and their maxima and minima generally were found to coincide. For oven‐postcured specimens, bonding between different metal inserts and an epoxide resin is explained by double electrical layer formation (insert positive, resin negative), with bonding strength increasing as the stability of the oxide forming the surface layer of the metal decreases. Metals with no oxide surface layer thus have the highest bonding strengths. For inductively postcured specimens, bonding is effected by both electrical double layer formation and mixed polymer grafting through the oxygen atoms in the metal surfaces, with the more stable metal oxide giving the stronger bonding in grafting. Where the insert does not carry an oxygen surface layer, bonding takes place through electrical forces only. Alternating build‐up and internal discharge of electrical double layers are the direct cause of the sinusoidal shape of the electrical potential curves and the indirect cause of the comparable shape of the wettability curves. Their combination results in the observed periodicity of the breaking load curves.