bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and characterization of hydrogels obtained by grafting of acrylonitrile onto cassava starch by ceric ion initiation
Authors: Vera‐Pacheco M. , Vázquez‐Torres H. , Canché‐Escamilla G. 
Published: April 2003

AbstractGraft starch‐polyacrylonitrile copolymers have been obtained from cassava starch (yucca starch or tapioca), which was pre‐heated at 65 and 95°C for different lengths of time. The copolymerization was carried out by using ceric ion as initiator at different concentrations (2.0 to 8.0 mmol/L) and also varying both the length of time of copolymerization and the ratio of monomer to starch. The composition, or grafting parameters, of all the obtained copolymers was determined by weight difference after they were extracted with dimethylformamide and hydrolyzed with an acidic solution. Samples of these copolymers were also hydrolyzed with an aqueous solution of potasium bydroxide to produce the corresponding hydrogels, and its absorbency in water was determined. © 1993 John Wiley & Sons, Inc.
Chemical composition and physical properties of Gonometa rufobrunnae silk
Authors: Freddi G. , Bianchi Svilokos A. , Ishikawa H. , Tsukada M. 
Published: April 2003

AbstractChemical composition and physical properties of silk fibers from Gonometa rufobrunnae, a silkworm belonging to the family Lasiocampidae (order Lepidoptera, class Insecta) have been studied. G. rufobrunnae silk fibroin contains a large amount of glycine and alanine, as well as hydroxyl, acidic, and basic amino acids. The gly/ala ratio is 1.5, similar to that of Bombyx mori silk fibroin. The ratio between polar and nonpolar amino acids is higher than that of either domestic (family Bombycidae) or wild (family Saturniidae) silk fibroins. The sericin is characterized by a large amount of hydroxyl amino acids, mainly serine. The infrared spectrum of G. rufobrunnae silk fibroin showed characteristic absorptions at 1630, 1530, and 700 cm−1 attributed to the β structure and at 1650 and 1540 cm−1 due to the random‐coil conformation. The birefringence and isotropic refractive index values were 0.027 and 1.559, respectively. The differential scanning calorimetry (DSC) curve showed two minor endothermic peaks at 222 and 288°C, together with a major endothermic peak at 344°C, attributed to the decomposition of the fibroin with β conformation. The fibers exhibited a maximum contraction peak (4.3%) at about 230°C. The dynamic storage modulus (E′) exhibited an abrupt drop at 190°C, while the loss modulus (E″) curve increased above 185°C with a sharp slope. The surface of degummed G. rufobrunnae silk fibers was very smooth. The shape of the cross section was triangular, round, or roundish shaped. Some fibers were very flat, showing a ribbonlike shape. © 1993 John Wiley & Sons, Inc.
Polyethylene toughened by CaCO3 particle: Brittle‐ductile transition of CaCO3‐toughened HDPE
Authors: Fu Qiang , Wang Guiheng , Shen Jiusi 
Published: April 2003

AbstractThe dependencies of the notched Izod impact toughness of HDPE / CaCO3 blends on CaCO3 particle concentration and particle size are analyzed. It was found that the notched Izod impact strength (S) of HDPE / CaCO3 blends depends discontinuously on CaCO3 particle concentration. A brittle‐ductile transition occurs when the CaCO3 volume fraction (Vf) increases to a critical value (Vηf). Furthermore, a brittle‐ductile transition master curve can be constructed by taking the matrix ligament thickness (L) into account as a parameter instead of Vf. The results show that the critical matrix ligament thickness (Lc) is a single parameter for the transition and Lc = 5.2μm for HDPE / CaCO3 blends. The impact strength, however, varies considerably with CaCO3 particle size, which shows that CaCO3 particle size is another dominating parametor for the toughness of HDPE / CaCO3 blends. © 1993 John Wiley & Sons, Inc.
Activation of wood surface by corona treatment to improve adhesive bonding
Authors: Sakata Isao , Morita Mitsuhiro , Tsuruta Natsuhi , Morita Kenzo 
Published: April 2003

AbstractOxidative activation of resinous wood surfaces by a corona treatment to improve adhesive bonding was studied. It was found that the wettability of the veneers, including hardwoods, softwoods, and tropical woods increased with an increase in the degree of treatment, and the gluability increased rapidly after the initial mild treatment. To elucidate the nature of any chemical change occurring on the wood surface, the dyeing examination of the wood and its components with Schiff's reagent was made, and the results showed a higher dyeing ability for corona‐treated samples compared to untreated ones, indicating that aldehyde groups increased by the corona treatment. The treatment affected the alcohol‐benzene extractives, and oxidized them to produce aldehyde groups. Especially, the neutral fraction in the extractives was significantly affected. On the other hand, negligible chemical effects of the treatment on the surface modification of the wood's main components were seen. Both the untreated and corona‐treated samples adsorbed basic dye to the same extent of coloration. Thus, no measurable carboxyl groups increased on the surface of the samples. It seems that an increase in the wettability of corona‐treated wood veneers resulted mainly from the oxidation of the high hydrophobic surface layer of neutral fraction substances in the extractives, and from the reduction in their hydrophobicity. © 1993 John Wiley & Sons, Inc.
Permeability and diffusion of gases in segmented polyurethanes: Structure–properties relations
Authors: Galland G. , Lam T. M. 
Published: April 2003

AbstractTo determine the structure‐transport properties relations, we synthetized segmented polyether polyurethane with increasing rigidity. The formulation is based on poly(tetramethylene oxide diol) (PTMO) of different molecular weights, diphenylmethane aiisocyanate (MDI), and butanediol (BD). The synthesis is effectuated in bulk. The phaseseparation degree of the soft segments is determined by ΔCp measurements. The volume fractions and compositions of soft and hard phases are calculated with the help of Tg values. The polyurethanes studied correspond to three types of morphology: soft‐phase matrix, phase‐inversion, and hard‐phase matrix. The best phase segregation is observed in the phase‐inversion region. The time‐lag method is used for determining the permeability, diffusion, and solubility coefficients of gases (He, O2, N2, CO2, Freon 11) in polyurethane at different temperatures. Activation energies of permeation and diffusion and dissolution energy are calculated. The most important factor in diffusion is the chain mobility in the soft phase, which is represented with a good approximation by M̄n, the molecular weight of soft segments. The phase‐inversion region where the ratio surface/volume is minimum gave the lowest solubility coefficient. Freon 11 presents a particular interaction with polyurethane; polyurethane membranes are broken when immerged in Freon 11, except the one which has the morphology of the inversion region. © 1993 John Wiley & Sons, Inc.
Infrared identification of carboxylic acids formed in polymer photooxidation
Authors: Wilhelm Catherine , Gardette Jean‐Luc 
Published: April 2003

AbstractSeveral low molecular weight carboxylic acids with different substitutions were introduced into various polymer matrices: polypropylene, polystyrene, poly(butylene terephthalate), MDI‐based polyurethane, and poly(vinyl chloride). These acids were then submitted to chemical treatments by sulfur tetrafluoride and ammonia. Derivatization reactions by SF4 and NH3 gave, respectively, acyl fluorides and carboxylate ions. The wavenumbers corresponding to the v̄co maxima of the carboxylic acids, acyl fluorides, and carboxylate ions were determined. For each one of these species, noticeable shifts were recorded that depended on the nature of the substitutents as well as on the nature of the polymer matrix. In addition, samples of the chosen polymers were exposed to photoaging. Photooxidized samples were reacted with SF4 and NH3. Their IR characteristics were determined before and after the treatments. Comparison with the results obtained with the molecular acids permitted us to specify the chemical structure of the acids formed by photooxidation and then to determine the oxidation sites on the macromolecular chains of the different polymers. © 1994 John Wiley & Sons, Inc.
Experimental investigation on high conversion free‐radical polymerization of behenyl acrylate
Authors: Baruah Shashi D. , Laskar Narayan C. , Subrahmanyam Bulusu 
Published: April 2003

AbstractAn experimental investigation on the kinetics of free‐radical polymerization of behenyl (a mixture of 14.8% n‐octadecyl, 15.1% n‐docosyl) acrylate initiated with benzoyl peroxide was conducted at 70°C using a HAAKE rotational viscometer. Molecular weight measurements and differential scanning calorimetric studies of the samples are also described and the results are compared with those obtained by batch reactions conducted under a nitrogen atmosphere. A high monomer order of 1.61±0.11 and a low initiator order of 0.35±0.04 was obtained. The role played by the long methylene chain in behenyl acrylate is also discussed. © 1994 John Wiley & Sons, Inc.
Sorption/desorption properties of ethanol, toluene, and xylene in poly(dimethylsiloxane) membranes
Authors: Sun Yi‐Ming , Chen Jack 
Published: April 2003

AbstractSorption/desorption kinetics and sorption equilibria have been determined for ethanol, toluene, and xylene vapors in a poly(dimethylsiloxane) membrane containing about 32 wt % silica resin at 25°C. Dependence of diffusion coefficient on vapor activity and sorption isotherms have been compared to identify the transport mechanisms of those penetrants in the PDMS membrane. The analysis of Zimm–Lundberg clustering functions showed that all three penetrants had a tendency to form clusters and ethanol molecules might be immobilized by the residual silanol groups within the silica resin in the membrane. The diffusion coefficient of toluene was roughly constant and that of xylene slightly decreased as increasing the vapor activity due to the competing effects of penetrant clustering and solvent swelling of polymer. The diffusion coefficient of ethanol versus activity exhibited a maximum due to the effects of ethanol immobilization and cluster formation. The freevolume effect by solvent swelling to diffusion was obscured by either penetrant clustering or immobilization for the three penetrant–polymer systems. © 1994 John Wiley & Sons, Inc.
Stress relaxation in short sisal‐fiber‐reinforced natural rubber composites
Authors: Varghese Siby , Kuriakose Baby , Thomas Sabu 
Published: April 2003

AbstractStress relaxation behavior of chemically treated short sisal fiber‐reinforced natural rubber composite was studied. The effect of bonding agent, strain level, fiber loading, fiber orientation, and temperature has been studied in detail. The existence of a single relaxation pattern in the unfilled stock and a two‐stage relaxation mechanism for the fiber‐filled composite is reported. The relaxation process is influenced by the bonding agent, which indicated that the process involved fiber‐rubber interface. The rate of stress relaxation increased with fiber loading, whereas it decreased with aging. © 1994 John Wiley & Sons, Inc.
Crystalline structure of polyacrylonitrile–iodine complex
Authors: Kim Hong Sung , Cho Hyun Hok 
Published: April 2003

AbstractThe existence of structural order is found in the polyacrylonitrile (PAN)‐iodine complex obtained by immersing PAN film in an aqueous solution of I2/KI. We provide an interpretation for the key features of this structural order and for the structural change of PAN by iodine sorbing. The observed diffractions suggest that iodine penetrates into the crystalline phase of PAN at relatively low iodine concentrations and are intercalated between PAN molecular cylinders in the form of polyiodine columns that are composed mainly of I (most likely the I2/I complex). Pseudohexagonal crystals of PAN are expanded uniaxially by replacement of PAN molecular cylinders by the polyiodine columns. The intercalated polyiodine column layers are arrayed parallel with PAN chain layers in the crystalline phase. The results led to a proposal of an intercalation model for the crystalline structure of the PAN–iodine complex. The crystalline structures are expected to exist with two different types of the polyiodine layers. The crystalline transition between these structures occurs by thermal mobility of PAN chains. © 1994 John Wiley & Sons, Inc.
Hydrolysis of polycaprolactone fibers by lipase: Effects of draw ratio on enzymatic degradation
Authors: Mochizuki Masatsugu , Hirano Madoka , Kanmuri Yoshihiro , Kudo Kazushige , Tokiwa Yutaka 
Published: April 2003

AbstractUsing polycaprolactone (PCL) fibers drawn with various draw ratios, the effects of draw ratio on enzymatic degradation were studied in order to understand the influence of fine structure on biodegradation. Degradability of PCL fibers as monitored by total organic carbon (TOC) formation or weight loss decreased with increase in draw ratio due to higher crystalline content. There were some distinct features of degradation behavior among the fibers, because the fibers underwent significant change in molecular organization of the polymer, such as crystallinity and orientation, during drawing processes. From scanning electron microscopy (SEM) photographs showing that the enzyme preferentially attacked amorphous or less ordered regions rather than crystalline or more ordered regions of the fiber, spherulites were observed in the undrawn fiber, and on the other hand, fibrillar stripes along the fiber axis were observed in the drawn fibers, which suggest that the spherulites in the undrawn fiber were extended to be broken, and fibril structures were formed during the drawing processes. These SEM photographs suggest that there are differences of crystal structures in addition to crystallinity among the fibers with different draw ratio, which significantly affects the enzymatic degradation behavior of the fibers. The diameter of the fibers became gradually slim, macroscopically uniform, as enzymatic degradation proceeded although it was dependent on draw ratio. It is evident that the degradation proceeded in the crystalline regions as well as the amorphous regions. © 1995 John Wiley & Sons, Inc.
The fracture behavior of phenolphthalein polyether–ether ketone at elevated temperature for long terms
Authors: Yang Yuming , He Tianbai , Yu Fusheng 
Published: April 2003

AbstractThe fracture behavior of phenolphthalein polyether–ether ketone (PEK‐C) affected by physical aging at 200°C was studied by tensile experiments, scanning electron microscopy, and differential scanning calorimetry observations. The ductile–brittle fracture transition (DBT) caused by physical aging can be considered as a competition between fracture mechanisms of crazing and shear yielding. The aging time required for the DBT is found to be around 400 h, based on the morphological studies and tensile experiments. The shear yielding component of the mechanical deformation could erase the aging effect, thus a deaging phenomenon occurs. We found that the deaging phenomenon has an intrinsic relationship with the extent of aging in the specimen and as a result of the fracture behavior. © 1995 John Wiley & Sons, Inc.
Structure of some styrene–divinylbenzene copolymers
Authors: Wojaczyñska M. , Kolarz B. N. 
Published: April 2003

AbstractStructures of copolymers of styrene and divinylbenzene (50% crosslinking degree) prepared in suspension polymerization in the presence of mixtures of nonsol (heptane or decane) and sol (toluene or tetralin) diluents were investigated. The studies showed that the diluents enriched with nonsol solvents resulted in an increase of pore volumes and posities for the prepared copolymers. The sol diluents affected mainly the gel regions of the polymer matrices. Isotropic swelling of the matrices prepared in the presence of toluene is the opposite of the effect observed for tetralin family copolymers. The virtual difference of both kind of matrices was demonstrated in the sorption of phenol. The tetralin family copolymers were characterized by a prolonged time for column breakthrough. © 1995 John Wiley & Sons, Inc.
Diffusion hindrance vs. wood‐induced catalytic activation of MUF adhesive polycondensation
Authors: Pizzi A. , Panamgama L. A. 
Published: April 2003

AbstractThe reaction of hardening of melamine–urea–formaldehyde (MUF) adhesive resins in the presence of wood and cellulose was confirmed to have a lower energy of activation than the MUF adhesive alone, both in the presence or absence of ammonium chloride hardener, thus both in mildly acid and mildly alkaline environments. DSC exotherms showed that during hardening of melamine to melamine, melamine to urea, and urea to urea crosslinks through methylene bridges occur. Only the earliest reaction, mainly melamine to melamine crosslinking, presents a decrease in energy of activation which can be assigned to catalytic activation by the cellulosic substrate. The other types of crosslinking reactions (i) appear not to occur due to the more favorable and rapid melamine to melamine reaction which precedes them at lower temperature or (ii) do not present catalytic activation by the substrate but rather hindrance by it or (iii) variation of their energy of activation appears to be due to increased diffusion hindrance by the substrate caused by the increasing molecular weight of the resin while hardening. This because the Kissinger equation plots of the resin alone are in the main linear, for all the exotherms, indicating that in hardening of the resin alone diffusion problems appear to be limited. © 1995 John Wiley & Sons, Inc.
A new approach to chemical characterization of polymer surfaces
Authors: Lloyd Thomas B. , Ferretti Kathleen E. , Lagow Joyce 
Published: April 2003

AbstractThe “three‐liquid” contact angle procedure of Good et al. was applied to polymer films of varying Lewis acidic and basic nature to test the procedure. Surface energy parameters with the units of mJ/m2 are determined for the surfaces. These are γLWs (Lifshitz‐van der Waals or apolar), γ+s (acidic), and γ−s (basic). Very little has yet been published on this new method, and this study found it to be promising. More research on the procedure is warranted. The study included films of basic polymethylmethacrylate (PMMA), and predominately acidic chlorinated polyvinylchloride (CPVC) and polyvinylfluoride (PVF) as well as the series: polyethylene (PE) and PE copolymerized with 1.8% and 7.0% acrylic acid. In some of the experiments receding contact angles were measured, and the surface energy parameters determined in order to cast more light on the mechanism of contact angle hysteresis. © 1995 John Wiley & Sons, Inc.
The radial distribution function in planetary nebulae
Authors: Phillips J.P. 
Published: April 2003

AbstractWe have investigated the variation of planetary nebula number densities as a function of nebular radius, taking account of uncertainties arising from interstellar extinction. We find that the trend is composed of two components: one (a “spike” component) located at radii R < 0.035 pc, and the other (a “plateau” component) extending to larger radii. The plateau component appears to follow a Gaussian fall‐off law with scale radius R0 = 0.28 pc. It is shown that this latter trend is not consistent with the assumption that larger shells are optically thin and density bounded. Rather, it seems likely thatmany of the larger sources have appreciable Lyman continuum optical depths and are ionization bounded. The deduced variation in N(R) then suggests that the velocities of the ionization fronts increase with radius. The nature of the spike component is less easy to fathom, and this may arise as a result of sharply lower ionization front velocities at radii R < 0.035 pc, or through contraction of the shells following a down‐turn in central star luminosities.
The total‐to‐selective extinction ratio determined from near IR photometry of OB stars
Authors: Wegner W. 
Published: April 2003

AbstractThe paper presents an extensive list of the total to selective extinction ratios R calculated from the infrared magnitudes of 597 O and B stars using the extrapolation method. The IR magnitudes of these stars were taken from the literature. The IR colour excesses are determined with the aid of “artificial standards” – Wegner (1994). The individual and mean values of total to selective extinction ratios R differ in most cases from the average value R= 3.10 ±0.05 – Wegner (1993) in different OB associations. The relation between total to selective extinction ratios R determined in this paper and those calculated using the “method of variable extinction” and the Cardelli et al. (1989) formulae is discussed. The R values presented in this paper can be used to determine individual absolute magnitudes of reddened OB stars with known trigonometric parallaxes.
An oscillating model suggestion for 63 Her
Authors: Kiziloğlu N. , Kirbiyik H. , Civelek R. 
Published: April 2003

AbstractAn attempt has been made towards explaining the observed frequencies in 63 Her. The evolution of rotating stars of 1.96, 1.98, 2.00, 2.05 and 2.10 M⊙ have been studied up to a point where stellar parameters match the observed luminosity and effective temperature of 63 Her. Radial and nonradial adiabatic oscillation frequencies were obtained in low harmonic degrees ( l = 0,1,2,3 ). One radial and three nonradial frequency values that match with the observed values were found for the model of mass 2.00 M⊙.
The integral Newton's and MacLaurin's theorems in tensor form
Authors: Caimmi R. 
Published: April 2003

Abstract The current paper deals with the investigation of the gravitational potential of heterogeneous ellipsoids and its extension to the tensor potential, since little attention has been given to this point in the last century. In this view, both integral Newton's and integral MacLaurin's theorems are formulated in tensor form. The generalization is extended to heterogeneous homeoids and focaloidally striated ellipsoids, respectively. A discontinuity in the tensor potential is found across a homogeneous, infinitely thin focaloid, which vanishes in the spherical limit. The potential‐energy tensors related to focaloidally striated ellipsoids are expressed in integral form, depending on the density profile. All the results are particularized to the spherical limit, for which both Newton's and MacLaurin's theorems hold. With the aim of illustrating the procedure, an explicit calculation of the potential‐energy tensors is outlined in the special case of homogeneous, spherical configurations. Finally, an application is made to the Coma cluster of galaxies.
Groups of symmetries in the two‐body problem associated to Einstein's PN field
Authors: Mioc V. 
Published: April 2003

AbstractThe two‐body problem associated to a spherical post‐Newtonian (PN) field with Einsteinian parameterization is revisited from the single standpoint of symmetries. The corresponding vector fields, in Hamiltonian and standard polar coordinates, or in collision‐blow‐up and infinity‐blow‐upMcGehee‐type coordinates, present symmetries that form diffeomorphic commutative groups endowed with a Boolean structure. The existence of such symmetries is of much help in understanding characteristics of the global flow, or in finding symmetric periodic orbits in more complex problems depending on a small parameter.