bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sorption of water by nylon 66 and kevlar 29. Equilibria and kinetics
Authors: Auerbach I. , Carnicom M. L. 
Published: April 2003

AbstractThe sorption of water by nylon 66 and Kevlar 29 fabrics was studied over a range of 20–98% relative humidities at 27°C. Equilibrium and rate relationships were developed from the data in this study and from nylon 66 and nylon 6 data of other studies involving fiber and film. The ratio of sorbed moisture to amide concentration is, on average and at high relative humidities, one water molecule per amide unit. The nylon equilibrium data show that there exist threshold relative humidities above and below which sorption properties differ. One threshold is correlated with the glass transition. Another is identified in the glassy state of nylon 6 in which moisture is tightly bound. The equilibrium constant values are highest and the moisture is most tightly bound at very low humidities, and the values are lowest in the plastic region at high humidities. NMR, DSC, and mechanical property data from others are correlated with the sorption discontinuities observed in this study. Rate data indicate that sorption is a diffusion‐controlled process.
Interactions in the system isotactic polypropylene–calcite
Authors: Rybnikář František 
Published: April 2003

AbstractInteraction in the system isotactic polypropylene–calcite was investigated using X‐ray diffraction and transmission electron microscopy. Calcite acts as a weak nucleation agent for polypropylene crystallization and its activity could be increased or decreased by a suitable surface treatment. Investigation of the morphology on the polypropylene–calcite interface using calcite single crystals disclosed the tendency of polypropylene for epitaxial crystallization along preferred substrate crystallographic directions. This tendency was analogous to polymer crystallization on other ionic crystals.
Quinone–amine polymers. V. Syntheses and solubilities of several diamine–p‐benzoquinone oligomers (PAQ)
Authors: Nithianandam V. S. , Kaleem K. , Chertok F. , Erhan S. 
Published: April 2003

AbstractSeveral diamine–p‐benzoquinone polymer/oligomers were synthesized to find those that exhibited superior properties, in addition to being able to displace water from wet, rusty steel surfaces. Unfortunately, many of these were found to be insoluble in most commonly used solvents and a few to be insoluble in all 34 solvents used in polymer solubility studies. The reason for this low solubility is believed to be the extremely regular structure of the polymers.
Pyrolysis of melamine–formaldehyde and urea–formaldehyde resins
Authors: Hirata Toshimi , Kawamoto Sumire , Okuro Akio 
Published: April 2003

AbstractPyrolysis of melamine–formaldehyde and urea–formaldehyde resins in helium and air was investigated by means of TG and gravimetry with isothermal heating, as well as elemental and HCN analyses. Weight loss curves suggest three kinds of reactions involved in the pyrolysis, namely, initiation reactions, reactions splitting off volatile fragments, and reactions forming stabilized structures. In TG, in both helium and air atmospheres, the active weight loss of the melamine resin was completed in two steps, and that of the urea resin was completed in one step, which, however, consisted of a few small successive steps. The isothermal heating weight losses progressed through a few stages of first‐ and zeroth‐order reactions. Arrhenius parameters were obtained for the weight losses in TG and with isothermal heating. The residue from the melamine resin is rich in carbon and nitrogen, and poor in oxygen and hydrogen, while that from the urea resin is rich in carbon, and poor in nitrogen, oxygen, and hydrogen. The effects of temperature on HCN yield changed, depending on the amount of air fed. The melamine resin evolved much more HCN than the urea resin because of the more stable C—N linkages in the resin.
Vinylic graft copolymers of cellulose. II. Thermal degradation of cellulose and its vinylic copolymers and blends by differential scanning calorimetry
Authors: Flaqué C. , Montserrat S. 
Published: April 2003

AbstractCotton cellulose with different % NaOH treatments (mercerized), graft copolymers of cellulose prepared with vinyl acetate (VA) and methyl acrylate (MA) and Ce (IV) ions as initiator, and some blends of cellulose–copolymer PVA–PMA were submitted to differential scanning calorimetry (DSC) analysis in nitrogen atmosphere. Two aspects were considered: (a) moisture loss of celluloses with different % NaOH treatments, which showed differences attributed to structural changes in the amorphous region of cellulose‐I and cellulose‐II; (b) thermal degradation analysis of celluloses, their copolymers, and their blends. Experimental results show that thermal stability of celluloses decreases when % NaOH in mercerization increases. For cellulosic vinylic copolymers, the thermal stability increases with the grafting frequency (GF). The blends of cellulose–copolymer PVA–PMA were found to have lower thermal stability than the cellulosic copolymers and the cellulose alone, which was attributed to the acetic acid eliminated in the thermal decomposition of PVA–PMA. The present results seem to be in agreement with the thermal degradation mechanism of cellulose proposed by Patel et al. and provide useful confirmation that the free OH group content is a very important factor in the thermal stability of cellulose.
Distribution of higher‐order structures in injection moldings of particulate‐filled polypropylenes
Authors: Fujiyama Mitsuyoshi , Wakino Tetsuo 
Published: April 2003

AbstractFlexural test specimens were injection‐molded from polypropylenes filled with flaky talc or spherical calcium carbonate at levels of 0‐40 wt % under cylinder temperatures of 200‐320°C. Distributions in the flow direction of higher‐order structures such as thickness of skin layer, a*‐axis‐oriented component fraction [A*], and crystalline orientation functions and distributions in the thickness direction of higher‐order structures such as crystallinity, β‐crystal content, [A*], and crystalline orientation functions were studied. These higher‐order structures are inhomogeneous in the flow and thickness directions also for injection moldings of particulate‐filled polypropylenes, which strongly influences the product properties such as mechanical and thermal properties. Molecular orientation process in injection molding was theoretically analyzed from a viewpoint of growth of recoverable shear strain at the gate and its relaxation in the cavity, which could considerably well explain the influences of particulate filling and cylinder temperature on not only the mean values but also the changes in the flow and thickness directions, of the quantities such as thickness of the skin layer and crystalline orientation functions, which express the degree of molecular orientation.
Relationship between interchain spacing of amorphous polymers and blend miscibility as determined by wide‐angle X‐ray scattering
Authors: Halasa A. F. , Wathen G. D. , Hsu W. L. , Matrana B. A. , Massie J. M. 
Published: April 2003

AbstractThe average molecular interchain spacing (〈R〉) in Angstroms for amorphous polymers was calculated from the strong maximum in the wide‐angle X‐ray scattering (WAXS) diffraction scan using established equations. The half‐width (HW) of the maximum was used to qualitatively describe the distribution of 〈R〉. 〈R〉 and HW for immiscible blends corresponded to the weighted average of 〈R〉 and HW of the homopolymers in the blend. 〈R〉 for a miscible blend (natural rubber and high‐vinyl PBd) was much larger than the weighted average of 〈R〉 of the component homopolymers, indicating that a new amorphous molecular structure had developed. The larger 〈R〉 for the miscible blend indicates that the molecular chains are spread further apart, resulting in an increase in free volume to accommodate the new packing order. The single Tg of this blend was lower than predicated by the Gordon‐Taylor equation.
Aqueous dispersion of polyurethanes from H12MDI, PTAd/PPG, and DMPA: Particle size of dispersion and physical properties of emulsion cast films
Authors: Kim Byung Kyu , Kim Tae Kyoon 
Published: April 2003

AbstractAqueous dispersions of ionic/nonionic polyurethane (PU) were prepared from hydrogenated diphenylemthane diisocyanate (H12MDI), poly(tetramethylene adipate) glycol (PTAd), polypropylene glycol (PPG), monofunctional ethylene‐propylene oxide ether, and dimethylol propionic acid (DMPA). The effects of DMPA, PTAd/PPG ratio, and the average molecular weight of PPG on the state of dispersion, mechanical, and viscoelastic properties of the emulsion cast films were determined using Authosizer, Instron, and Rheovibron.
Electrical conductivity of plasma‐treated poly(p‐phenylene sulfide) doped with iodine
Authors: Tu D. M. , Zhuang G. P. , Kao K. C. 
Published: April 2003

AbstractPlasma treatment of poly(p‐phenylene sulfide) (PPS) doped with I2 is found to increase both the electrical conductivity and the stability of the material. The average conductivity of plasma‐treated samples reaches an apparently saturated value of 1.7 × 10−3s cm−1, which is about six orders of magnitude higher than that of the same material without plasma treatment, and this conductivity remains practically unchanged under exposure to ambient environment for 10 days. Infrared and secondary ion mass spectra of the samples before and after plasma treatment suggest that the charge‐transfer complexes are formed in PPS doped with I2 after plasma treatment. This is also consistent with the temperature dependence of conductivity results which show that the activation energy for electrical conduction decreases from 2.0 eV for pure PPS to 0.2 eV for plasma‐treated I2‐doped PPS. Using isothermal potential and current decay techniques, we have also measured the trap density distribution. Plasma treatment, on the one hand, does create more traps in PPS, but, on the other hand, it enhances conductivity. The mechanism of electrical conduction is briefly discussed.
Polystyrene crosslinked with oligomeric and polymeric poly(dimethyl siloxane) derivatives. Thermal and dynamic mechanical studies
Authors: Tenhu Heikki , Heino Eeva‐Leena 
Published: April 2003

AbstractStyrene has been copolymerized with various bifunctional poly(dimethyl siloxane) cross‐linkers having molar masses in the range 200–35,000. Calorimetric and rheological measurements show that the crosslinkers change Tg, Tll, and Texo, as well as melt viscosity and elasticity of polystyrene. These changes are strongly dependent on the molar mass of the crosslinker. Increasing the length of the siloxane crosslinker lowers Tg and melt viscosity, if the molar mass of the crosslinker is in a range 200–2000. Copolymerizing styrene with a bifunctional poly(dimethyl siloxane) having molar mass near 35,000 leads to a phase‐separated polymer where polystyrene phase largely retains its original properties.
Crystallization of linear polyethylene from melt in isothermal compression
Authors: Kowalewski T. , Galeski A. 
Published: April 2003

AbstractCrystallization and primary nucleation of linear polyethylene has been studied by means of a custom‐made miniature pressure apparatus. It has been shown that during isothermal compression of linear polyethylene melt at a constant rate crystallization occurs. In the range of fastest conversion rates the crystallization assumes isobaric character. The level of pressure at which the crystallization occurs increases with the increase of the crystal‐lization temperature and/or with the increase of the compression rate. The crystallization has a spherulitic character up to the highest pressure achieved in the apparatus (approx. 600 MPa). Surprisingly, there are no dependencies of average spherulite size, degree of crystallinity, and lamellae thickness on the pressure and the temperature of crystallization during melt compression, but there is a strong relation to the compression rate. Below 250 MPa and above 300 MPa the crystallization proceeds under pressure, ensuring a constant undercooling. The undercooling for the pressure above 300 MPa is approximately 10°C lower than that for the pressure below 250 MPa. For the pressure 250–300 MPa a change in a primary nucleation and spherulite crystallization has been observed that is connected with the transformation from orthorhombic to pseudohexagonal symmetry of crystals. No noticeable effect of molecular weight of linear polyethylene on crystallization during iso‐thermal melt compression has been observed.
Solid state NMR investigation of cationic polymerized epoxy resins
Authors: Egger N. , Schmidt‐Rohr K. , Blümich B. , Domke W.‐D. , Stapp B. 
Published: April 2003

AbstractCationic UV‐polymerized resins, based on cycloaliphatic epoxides with aryl sulfonium salts as photoinitiators and polypropylene glycols of variable length as flexibilizers, have been investigated with respect to the network‐forming reactions and the morphology of the resulting polymers. The combination of UV‐curing and thermal postcure makes the chemical process complex and dependent on many variables, such as photoinitiator, exposure time, reaction temperature, and polyol components. Structure and curing of the epoxide were investigated by 13C CPMAS NMR. Morphology and domain sizes were studied by spin diffusion experiments using the novel “dipolar filter” technique for selective magnetization of mobile components.
Ultraviolet‐radiation induced graft‐copolymerization of hydroxyethyl methacrylate onto cotton cellulose
Authors: Shukla S. R. , Athalye A. R. 
Published: April 2003

AbstractTwo‐hydroxyethyl methacrylate was grafted onto cotton cellulose using photoinitiation technique in the presence of the photoinitiator benzoin ethyl ether. Various parameters of the graft‐copolymerization reaction, namely time, temperature, initiator, and monomer concentrations, were optimized using the grafting bath containing 10% methanol/acetone to dissolve the photoinitiator. The cotton sample, preswollen in sodium hydroxide, was subjected to grafting under optimized conditions. The preswollen samples showed higher graft add‐on values at the equivalent monomer concentration. The moisture regain initially decreased at lower graft add‐on levels and increased marginally with higher graft add‐on. This behavior of the grafted substrate with respect to moisture regain has been explained.
Processes of wood delignification and cellulose mercerization under conditions of shear deformations
Authors: Enikolopian N. S. , Balashova E. A. , Sakhonenko L. S. , Rogovina S. Z. 
Published: April 2003

AbstractThe development of high‐yielding and environmentally safe procedures of processing wood and cellulose constitutes a topical problem at present. To facilitate delignification of wood and mercerization of cellulose, a method was proposed, its principle of action based on the use of shear deformations combined with pressure. It is shown that under the conditions of plastic flow the fibrous high‐yield semifinished product produced from birch wood features, due to its specific structure, shows better physicomechanical properties. It is established that under the conditions of high pressure and shear deformations, when cellulose interacts with hard alkali, alkaline cellulose is produced, which is proved by X‐ray analysis data. The depth of wood delignification and cellulose mercerization processes under the conditions of plastic flow does not depend on temperature, i.e., these processes are inactive.
Radiation‐absorbing hydrogel–melanin blends for ocular devices
Authors: Chirila Traian V. , Cooper Richard L. , Constable Ian J. , Horne Robert 
Published: April 2003

AbstractHydrophilic polymers and copolymers of 2‐hydroxyethyl methacrylate, with low or high crosslinking density, were synthesized and then treated in aqueous medium with epinephrine (adrenaline) at neutral or acid pH, at room temperature, and in the presence of oxygen and light. During this treatment, a melanin is formed and uniformly dispersed in polymers. The resulting slightly colored hydrogels display radiation‐absorbing properties in the ultraviolet and visible regions of the natural spectrum. This enhances significantly their value as materials for ocular devices (contact lenses, intraocular lenses) that should protect the retina of the patients without their natural lens from potential damage induced by ultraviolet and visible (violet and blue) radiation. The incorporation of common ultraviolet absorbers led to transmittances similar to that of the natural human lens, i.e., 30% or less at 450 nm, 40% or less at 500 nm, and no more than 50% at 700 nm. The two‐phase morphology of the melanized hydrogels, as investigated by TEM, revealed a very fine structure comprising melanin domains of 1 to 12 nm in size. Although no proof for a network interpenetration could be provided, it is believed that the novel blends are true sequential interpenetrating polymer networks.
Heat transfer from moving fibers in melt spinning process
Authors: Chung B. T. F. , Iyer V. 
Published: April 2003

AbstractThe purpose of this study is to develop a steady‐state thermal model for melt spinning of polyester fiber by incorporating the radial heat conduction inside the fiber and the combined effect of radiation and convection at the boundary. The governing equations are obtained from the energy, mass, and momentum balances coupling with the rheological properties of the fibers. The effects of drag, surface tension, gravity, and inertia force are also taken into consideration in the analysis. The velocity profile, temperature profile, and the variation of cross‐sectional area of the filament along the axial direction are solved by employing a finite‐difference scheme.
Modification of polyethylene by unsaturated compounds
Authors: Vijayalakshmi N. S. , Murthy R. A. N. 
Published: April 2003

AbstractPolyethylene was reacted with maleic anhydride and N‐phenylmaleimide in solution. The effect of modification on its physico–chemical properties, such as mechanical, oxygen gas transmission, water vapor transmission, and grease resistance properties, was studied.
Controlled release of riboflavin and insulin through crosslinked poly(vinyl alcohol)/chitosan blend membrane
Authors: Kim Jin Hong , Kim Ju Young , Lee Young Moo , Kim Kea Yong 
Published: April 2003

AbstractThe permeation of riboflavin and insulin through poly(vinyl alcohol) (PVA) and chitosan blend membrane was conducted. The permeability coefficients of both solutes through the crosslinked PVA and chitosan blend membrane were in the order of 10−6−10−7 cm3 cm/cm2s and showed a pH dependence. The pH‐dependent permeation behavior was discussed in terms of water content and water structure inside of the swollen membrane. Riboflavin and insulin were presumed to permeate through the free water region in the swollen blend membrane. The DSC thermograms of these membranes indicated that the content of free water and the amount of freezing bound water increased with the water content in the membrane. The greater permeation rate of solutes in acidic solution rather than in neutral solution was due to an increase in both water content and the amount of free water and freezing bound water.
Crystallization of fiber‐reinforced poly(phenylene sulfide) composites. I. Experimental studies of crystallization rates and morphology
Authors: Desio Glenn P. , Rebenfeld Ludwig 
Published: April 2003

AbstractThe isothermal crystallization from the melt of unreinforced poly(phenylene sulfide) (PPS) and of model carbon, aramid, and glass‐fiber‐reinforced PPS composites was studied by differential scanning calorimetry and optical microscopy. Crystallization was studied as a function of temperature, and the fiber contents in the composites were varied over a wide range. The results indicate that the influence of fibers on PPS crystallization is not only fiber specific, but also strongly dependent on the surface treatment (size). In general, fiber‐reinforced systems crystallized faster than unreinforced (PPS), and the degree of crystallinity was less under comparable crystallization conditions. It was also observed that the rate of crystallization was enhanced in those systems which exhibited transcrystallinity in thin PPS film/single fiber composites as compared to those systems which did not exhibit transcrystallinity. Furthermore, the degree of crystallinity showed a nonlinear crystallization temperature dependence for those systems that exhibited transcrystallinity.
Structural features of native cellulose gels and films from their susceptibility to enzymic attack
Authors: Beltrame Pier Luigi , Paglia Ernestina Dubini , Seves Alberto , Pellizzoni Elisabetta , Romanò Maria 
Published: April 2003

AbstractThe reaction of enzymic hydrolysis has been used as a probe to evidence the different structural features of bacterial native cellulose gels and films synthesized from different carbon sources. The gels were found to be more hydrolyzable than were the films, both in terms of reaction extent and of initial reaction rate, by factors increasing with temperature. For instance, a cellulose gel synthesized from glucose showed at 50°C a hydrolysis yield twice as much as that of the corresponding film, thus revealing, in the former case, a higher level of substrate accessibility and enzyme penetrability. It has been suggested that the increase of gel accessibility with temperature can be associated with a corresponding lowering of the amount of structured water close to the polymer chains in the gel. The significant decrease of susceptibility to enzymic attack observed in going from the cellulose film obtained from glucose to that obtained from xylose has been related to the markedly lower value of specific surface area estimated in the latter case. Likely, in the film obtained from xylose, densely packed microfibrils occur that are scarcely accessible to enzyme. In some cases, the reaction progress has been followed by SEM analysis. Microcrystalline cellulose has been also considered for comparison.
Single‐Phase blends of polycarbonate and poly(phenyl methacrylate)
Authors: Kyu Thein , Park Dongkyu , Cho Wookap 
Published: April 2003

AbstractMiscibility studies on blends of polycarbonate (PC) and poly(phenyl methacrylate) (PPMA) were undertaken by means of differential scanning calorimetry (DSC), dynamic mechanical, and dielectric relaxation methods. PC and PPMA were mixed by dissolving in tetrahydrofuran (THE) and subsequently coprecipitated in methanol. DSC studies showed a single glass transition (Tg) that shifts systematically with composition. These Tgs are reproducible in repeated DSC heating cycles, suggesting true miscibility of the pair. The dry PC and PPMA pellets were melt mixed in a Mini‐Mixer/Molder. The extrudates were compression molded. These melt‐mixed PC/PPMA blends exhibited glass like transparency and also showed a single Tg in the DSC scans. The true miscibility of PC and PPMA was further confirmed by dynamic mechnaical and dielectric relaxation methods. The net birefringence has been reduced substantially because of the opposite sign of the itrinsic birefringence of PC and PPMA molecules. At the 12/88 PC/PPMA, the birefringence remains zero at all draw ratios, indicating the achievement of birefringence free polymer alloys.
Polyanhydride microspheres. IV. Morphology and characterization of systems made by spray drying
Authors: Mathiowitz Edith , Bernstein Howard , Giannos Steve , Dor Phillip , Turek Tom , Langer Robert 
Published: April 2003

AbstractThe morphology of bioerodible polyanhydride microspheres produced by spray drying is described. Microspheres prepared from a variety of homo‐ and copolymers were studied and characterized using X‐ray powder diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Crystalline polymers, such as poly(sebacic anhydride) (P(SA)) and poly(fumaric acid) (P(FA)), yielded microspheres with a crenelated and porous surface, as judged by SEM. Polymers, with lower crystallinity, such as copolymers of carboxyphenoxypropane and sebacic acid P(CPP‐SA), yielded microspheres with a smooth external surface. Polymer crystallinity decreased after spray drying, for both blank and drug loaded microspheres.