bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas permeabilities and permselectivity of photochemically crosslinked polyimides
Authors: Liu Ye , Ding Mengxian , Xu Jiping 
Published: April 2003

AbstractPhotosensitive polyimide BTDA‐3MPDA was modified by UV irradiation. The structure of UV‐irradiated polyimides was investigated by FTIR and gel fraction measurements. The results showed that longer UV exposure time resulted in a higher extent of crosslinking. The gas permeabilities of hydrogen, oxygen and nitrogen through UV‐irradiated polyimides were characterized in a temperature range from 30°C to 90°C. Photocrosslinking resulted in a sharp decline in gas permeability for hydrogen, oxygen, and nitrogen through polyimide in the initial stage of photocrosslinking. Then, as the crosslinked benzophenone percentage amounted to 28–38% for hydrogen, 17–31% for oxygen and 3–28% for nitrogen, the gas permeabilities showed another sharp decline. Gas permselectivity increased significantly with the progress of photocrosslinking, and it can be adjusted in a wide range by controlling the extent of crosslinking. Arrhenius plots of gas permeability for hydrogen and oxygen through UV‐irradiated polyimides are straight lines; for nitrogen, however, change in the slope of the straight line is observed and activation energies for hydrogen and oxygen permeation show abrupt increases when crosslinked benzophenone percentage amounts to about 30%. UV‐irradiated polyimides with simultaneous high gas permeability and permselectivity make them ideal candidate materials for gas separation. © 1995 John Wiley & Sons, Inc.
Morphology control in reaction‐induced phase‐separated polymeric systems
Authors: Kim S. , An J. H. 
Published: April 2003

AbstractIn this article the morphology control of poly(ethyl acrylate)/poly(methyl methacrylate) (PMMA) semi‐interpenetrating polymer networks (IPNs) has been attempted either by changing reaction temperature or by adding the third component at the initial stage of phase separation. The morphological variation was followed via dynamic mechanical behavior and electron microscopy. It was found that raising the polymerization temperature of PMMA or adding linear PMMA to the initial mixture facilitates phase separation during the semi‐IPNs formation process. However, the phase separation was further induced by annealing, which indicates that kinetically controlled morphology was not at its equilibrium state. © 1995 John Wiley & Sons, Inc.
Compatibility in immiscible poly(ether ether ketone)/poly(ether sulfone) blends
Authors: Arzak A. , Eguiazábal J. I. , Nazábal J. 
Published: April 2003

AbstractBoth as‐molded and annealed poly(ether ether ketone) (PEEK)/poly(ether sulfone) (PES) blends have been prepared by direct injection molding. The system has been found to be immiscible at all compositions; however, as a result mainly of the produced morphology, it surprisingly maintains to a very great extent the excellent mechanical performance of both of the pure components. This mechanical response is compared with that of the compression molded blends. The ductility of these blends when quenched appears close to the linear between that of the two components. Leaving aside possible morphological and excess free volume of mixing effects, it is in part attributed to the nature of the blend itself. © 1995 John Wiley & Sons, Inc.
Effect of chemical interaction between surface oxidized carbon black and carboxylated nitrile rubber on dynamic properties
Authors: Bandyopadhyay Sumanda , De P. P. , Tripathy D. K. , De S. K. 
Published: April 2003

AbstractMonsanto rheometric, dynamic mechanical, and solvent swelling studies indicate that functional groups of oxidized carbon black chemically react with carboxylated nitrile rubber (XNBR) when heated at high temperature for prolonged time. The reinforcing ability of the surface oxidized carbon black, measured by failure and hysteresis properties, is higher than the nonoxidized counterpart. © 1995 John Wiley & Sons, Inc.
PET synthesis in the presence of lanthanide catalysts
Authors: Ignatov Vladimir N. , Pilati Francesco , Berti Corrado , Tartari Vittorio , Carraro Claudio , Nadali Giampietro , Fiorini Maurizio , Toselli Maurizio 
Published: April 2003

AbstractSyntheses of poly(ethylene terephthalate), PET, by transesterification of dimethyl terephthalate with ethylene glycol in the presence of well‐known catalysts and various lanthanide compounds were performed. Lanthanide catalysts appeared to be much more efficient in the first stage of the process (transesterification in the presence of an excess of ethylene glycol), and less active in polycondensation. PET produced with lanthanides was found to possess enhanced thermal and hydrolytic stability as compared to PET synthesized with well‐known catalysts and commercial PET. © 1995 John Wiley & Sons, Inc.
Synthesis and characterization of pH‐sensitive and biodegradable hydrogels prepared by γ irradiation using microbial poly(γ‐glutamic acid) and poly(ϵ‐lysine)
Authors: Choi Hyuk Joon , Yang Ryung , Kunioka Masao 
Published: April 2003

AbstractPoly(γ‐glutamic acid) (PGA) and poly(ϵ‐lysine) (PL) solutions were used as components to prepare mixed hydrogels by γ irradiation. A PGA and PL mixed solution was crosslinked to form a hydrogel with specific water content (weight of absorbed water/weight of dry gel) of 10–100 when the 5 wt % solution of mixed polymer was exposed to γ radiation of 87 kGy dosage under N2 atmosphere. The specific water content increased with increasing PGA content of the PGA/PL mixed gel. The influence of pH and salt concentration on equilibrium swelling was studied. A characteristic pH‐sensitive swelling behavior was obtained using compositional changes of PGA and PL in the gel. PGA/PL 50/50 wt % mixed gel swelling in acid (pH < 4.0) and alkaline (pH > 6.0) conditions and was deswelled between pH 4.0 and 6.0 due to the ionic composition changes of the gel network. With an increase in the ratio of PGA to PL, the hydrogels showed increasing sensitivity to salt solutions (NaCl, Na2SO4, and CaCl2). In addition, degradation of PGA/PL gel by protease produced from Aspergillus oryzae was investigated at 40°C and pH 7.0. PL gel was degraded completely within 2 days. An increase in the ratio of PAG in the PGA/PL mixed gel led to a decrease in the degree of degradation as expected. Some subtle degradation changes were found in the 50/50 and 80/20 wt % (PGA/PL) gels that were degraded by only 3.5 and 3.8% by protease, respectively. © 1995 John Wiley & Sons, Inc.
Changes in mechanical behavior during fatigue of semicrystalline thermoplastics
Authors: Lesser Alan J. 
Published: April 2003

AbstractThe tensile fatigue behavior of two engineering thermoplastics (polyacetal and nylon6,6) were studied by measuring changes in the dynamic viscoelastic response together with changes in potential energy density, strain energy density, and irreversible work. The results show that both stress softening and hardening can occur in controlled load cyclic conditions. At high stress levels and/or frequencies, both the polyacetal and nylon6,6 show evidence of thermal softening as characterized by changes in their dynamic viscoelastic properties and decrease in storage modulus with corresponding increases in loss modulus and loss tangent. This effect is supported by observed decreases in the overall crystallinity as measured in DSC experiments. At lower stress levels (the mechanically dominated region), all results indicate that, although fatigue crack propagation (FCP) is one of the mechanisms governing the fatigue life, its contribution is minor and crack initiation time constitutes the majority of the fatigue life. Also, during the initiation stage, both materials become less viscoelastic and more elastic. This phenomenon is evidenced by overall reductions in the loss modulus, loss tangent, and irreversible work densities while the storage modulus is maintained. © 1995 John Wiley & Sons, Inc.
Extraction fractionation of segmented polyurethanes according to composition
Authors: Šimek Lubomír , Bohdanecký Miloslav 
Published: April 2003

AbstractExtraction of solid polyester‐based segmented polyurethanes by chloroform and its mixtures with an increasing amount of N,N‐dimethylformamide is described. Unlike the precipitation in a solvent‐nonsolvent system, where fractionation according to the molecular weight dominates, the extraction can resolve the copolymer into fractions differing in the content of diisocyanate units. © 1995 John Wiley & Sons, Inc.
Modification of waterborne polyurethanes by acrylate incorporations
Authors: Kim Byung Kyu , Lee Jong Cheol 
Published: April 2003

AbstractWaterborne polyurethanes (PUs) were hydrophobically modified using various types of acrylate monomers. PUs having hydroxy ethylacrylate (HEA) terminal groups were first obtained following a prepolymer mixing process. These PU base polymers were then chain extended with acrylate monomers via a radical polymerization mechanism. The effect of the overall composition, base polymer molecular weight, and type of acrylate were studied in terms of water swell and contact angle, as well as mechanical and dynamic mechanical properties of the emulsion cast film. It was found that water resistance, hardness, modulus, and tensile strength of the waterborne PU can be dramatically increased by acrylate incorporation. The reinforcing effect was more pronounced with multifunctional monomers, probably due to the crosslinking effect. © 1995 John Wiley & Sons, Inc.
Toughening of nylon 6 with grafted rubber impact modifiers
Authors: Lu M. , Keskkula H. , Paul D. R. 
Published: April 2003

AbstractRecent work has shown that nylon 6/acrylonitrile–butadiene–styrene (ABS) blends can be made tough by the addition of some polymer additives that are chemically reactive with nylon 6 and physically compatible with the styrene‐acrylonitrile copolymer (SAN) phase of ABS. Imidized acrylic polymers (IA) represent a successful example of such additives that improve the dispersion of ABS in the nylon 6 matrix and render the blends tough. This article examines the possibility of toughening nylon 6 with ethylene/propylene/diene elastomer grafted with SAN copolymer (EPDM‐g‐SAN). This EPDM‐g‐SAN consists of 50% rubber and 50% SAN by weight. However, it was found that the same IA that works well to disperse ABS materials of similar rubber content is not as effective for EPDM‐g‐SAN, primarily because the EPDM forms the continuous phase, not SAN, and, thus, interfaces with nylon 6 during melt blending. Maleated elastomers like maleic anhydride grafted ethylene–propylene copolymer (EPR‐g‐MA) and styrene–(ethylene‐co‐butylene)–styrene triblock copolymer (SEBS‐g‐MA) were more effective for dispersing EPDM‐g‐SAN in the nylon 6 matrix than IA. Various mechanisms that improve the dispersion are discussed. © 1995 John Wiley & Sons, Inc.
Barrier properties of surface sulfonated HDPE films
Authors: Sabne M. B. , Thombre S. M. , Patil A. S. , Patil S. D. , Idage S. B. , Vernekar S. P. 
Published: April 2003

AbstractFilms of high‐density polyethylene (HDPE) have been sulfonated by solid–gas phase reaction using gaseous sulfur trioxide (SO3) of different concentrations in nitrogen. The effect of concentration of SO3 in an SO3 + N2 gas mixture and time of sulfonation on solvent and gas barrier properties of sulfonated HDPE films was studied by determining toluene and oxygen permeability of HDPE films sulfonated with different concentrations of SO3 for different times. The color developed in sulfonated HDPE films during sulfonation could be bleached by aqueous sodium hypochloride solution. The effect of sodium hypochloride solution treatment on oxygen permeability of sulfonated HDPE films was also studied. © 1995 John Wiley & Sons, Inc.
Moisture‐activated, electrically conducting bioadhesive hydrogels as interfaces for bioelectrodes: Effect of film hydration on cutaneous adherence in wet environments
Authors: Woolfson A. D. , Mccafferty D. F. , Mccallion C. R. , Mcadams E. T. , Anderson J. McC. 
Published: April 2003

AbstractThe water contents of bioadhesive polymeric films of poly(methylvinyl ether–maleic anhydride) copolymer, stored at two humidities and at two temperatures, have been determined by continuous gravimetry. The water contents of the films increased under storage conditions of increasing humidity. The bioadhesion of these films was assessed using an in vitro bioadhesive tester previously validated in our laboratory. Water uptake during the bioadhesive test was taken into account and the final water content of films recorded as a “corrected equilibrium water content” (CEWC). A good quality second‐order polynomial relationship between bioadhesion and the CEWC of films stored at both 23 and 35°C was developed using standard curve fitting analyses. A 2 × 2 factorial design experiment revealed that there was a synergistic relationship between temperature and percentage relative humidity with regard to their effect on the bioadhesion of polymeric films, presumably due to their combined effect on film water content. These findings have implications for both the storage and packaging of hydrophilic polymeric films. © 1995 John Wiley & Sons, Inc.
The effect of carbon black on tetramethylthiuram disulfide accelerator sulfur vulcanization of polyisoprene
Authors: McGill W. J. , Shelver S. R. 
Published: April 2003

AbstractPolyisoprene was vulcanized with the tetramethylthiuram disulfide/sulfur/ZnO system in the presence and absence of N330 carbon black. Crosslinking was carried out in a DSC at a programmed heating rate, the reaction stopped at points along the thermal curve, and the system analyzed. Residual curatives and reaction intermediates were determined by HPLC and crosslink densities by swelling in benzene. Combinations of the powdered curatives were also heated with and without carbon black and analyzed. It is shown that the step in the vulcanization sequence, influenced by carbon black, is the formation of tetramethylthiuram polysulfides that act as the active sulfurating agent in vulcanization. Carbon black catalyzes their formation, and to a lesser extent, the formation of accelerator terminated polysulfidic pendent groups on the chain. © 1995 John Wiley & Sons, Inc.
Relationships between the properties of fibers and thermally bonded nonwoven fabrics made of polypropylene
Authors: Andreassen Erik , Myhre Ole Jan , Hinrichsen Einar L. , Braathen Marianne D. , Grøstad Kristin 
Published: April 2003

AbstractTypical polypropylene fibers for use in light nonwoven fabrics were produced in a full scale compact‐spinning line. Molecular weight distribution (MWD), extrusion temperature, draw‐down ratio, and draw ratio were varied. The fibers were thermally bonded (welded) into nonwoven fabrics, at different bonding temperatures, using a pilot calender line. The tensile properties of the fabrics are influenced by the MWD and the processing conditions of the fibers, and the effects of these fiber parameters increase with increasing bonding temperature. The fabric strength increases with increasing Mw/Mn, decreasing draw ratio, and increasing extrusion temperature, while in all these cases the fiber strength generally follows the opposite trend. Furthermore, the fabric strength, as well as the fiber strength, have a maximum as a function of draw‐down ratio. The tensile properties of the fabrics seem to be governed by the bonding properties of the constituent fibers, not the fiber strength per se. Bond characteristics are discussed in terms of skin‐core structures. Some details of the macroscopic fracture mechanisms of fabrics were revealed by scanning electron microscopy and the shape of load‐elongation curves. © 1995 John Wiley & Sons, Inc.
Prediction of service lifetime and performance of a prosthetic thermoplastic
Authors: Chiu C.‐H. , Lautenschlager E. P. , Greener E. H. , Childress D. S. , Healy K. E. 
Published: April 2003

AbstractThe service lifetime and performance for a prosthetic and orthotic thermoplastic, SubortholenTM, was measured using correlations between artificial and natural weathering degradation data of (1) the accumulated carbonyl compound concentration at the polymer surface, (2) changes in thickness of the surface reaction zone, and (3) changes in hardness and tensile properties. An empirical, mathematical relationship between artificial and natural weathering exposures is presented. Results show that the hardness degradation is a useful parameter to estimate the different stages in clinical performance of Subortholen. Corroborating hardness, tensile properties, and weathering exposure time, the service lifetime for Subortholen was determined to be 4–6 years. This finding indicates that the correlation between artificial and natural weathering degradation may provide an effective way to calculate the most appropriate time to replace a worn prosthetic or orthotic device before the device passes into a dangerous stage. © 1995 John Wiley & Sons, Inc.
Differential scanning calorimetry and dynamic mechanical analysis of amine‐modified urea–formaldehyde adhesives
Authors: Ebewele R. O. 
Published: April 2003

AbstractUrea–formaldehyde (UF) resins are susceptible to stress rupture and hydrolytic degradation, particularly under cyclic moisture or warm, humid conditions. Modification of UF resins with flexible di‐ and trifunctional amines reduces this problem. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to study the thermal behavior of modified and unmodified adhesives to identify the physical and morphological factors responsible for the improved performance. A UF resin modified by incorporating urea–capped poly(propyleneoxidetriamine) during resin synthesis exhibited a higher cure rate and greater cure exotherm than the unmodified resin. Resins cured with a hexamethylenediamine hydrochloride curing agent had slower cure rates than those cured with NH4Cl. DMA behavior indicated that modified adhesives were more fully cured and had a more homogeneous crosslink density than unmodified adhesives. DMA behavior changed with storage of specimens at 23°C and 50% relative humidity, after previous heating for approximately 20 min at 105°C to 110°C. The initial changes were postulated to occur because of physical aging (increase in density) and continued cure. These were followed by physical breakdown (microcracking) and possibly cure reversion. © 1995 John Wiley & Sons, Inc.
Flocculation of clay suspensions with water‐insoluble starch grafting acrylamide/sodium allylsulfonated copolymer powder
Authors: Chan Wu‐Chung , Chiang Chen‐Yen 
Published: April 2003

AbstractUse of water‐soluble and ‐insoluble starch grafting acrylamide/sodium allylsulfonated copolymers as flocculants to flocculate the clay suspension was investigated. The composition of acrylamide (AM), sodium allylsulfonated (SAS), and starch (St) repeating units in the water‐soluble and ‐insoluble starch‐grafted copolymer is about 0.718, 0.022, and 0.260 and 0.439, 0.014, and 0.547, respectively. For the water‐soluble starch‐grafted copolymer, the fast initial Ar decreasing rate and the lowest final Ar value occur at pH 2, 80 mg/L water‐soluble starch‐grafted copolymer and 100 mg/L clay suspension. As the suspension contains 1000 mg/L Na+ ion, the flocculating capability would be increased. For the water‐insoluble starch‐grafted copolymer, the initial Ar decreasing rate and the final Ar value are 1.6 times and 0.4 times, respectively, that of the water‐soluble starch‐grafted copolymer at the same test suspension. © 1995 John Wiley & Sons, Inc.
Functionalization of poly(vinyl chloride) through radiation‐induced grafting
Authors: Pande C. S. , Single Sanjay , Gupta N. 
Published: April 2003

AbstractPoly(vinyl chloride) was irradiated in air with γ‐rays. The hydroperoxidized poly(vinyl chloride) when heated with acrylic acid in water was grafted with poly(acrylic acid), thus introducing the elements of glutaric acid on the polymer. Percentage weight gain was investigated as a function of total dose, monomer concentration, and time of reaction. The effect of adding methanol to water as a medium of reaction was studied in terms of percentage weight gain on grafting. © 1995 John Wiley & Sons, Inc.
pH‐responsive gelatin microspheres for oral delivery of anticancer drug methotrexate
Authors: Narayani R. , Rao K. Panduranga 
Published: April 2003

AbstractMultiple unit delivery dosage forms of biodegradable gelatin microspheres containing the anticancer drug methotrexate (GMM) of various mean particle sizes (1–5, 5–10, and 15–20 μm) were prepared by the polymer dispersion technique and were crosslinked with glutaraldehyde. The GMM were coated with biodegradable natural polymers, namely alginate (AGMM) and chitosan (CGMM), which differ in their pH sensitivity, to obtain two different types of pH dependent delivery systems for oral delivery of methotrexate (MTX). The in vitro release profiles of MTX from AGMM and CGMM were determined in simulated gastric medium, intestinal medium, and in media simulating gastrointestinal tract conditions. The effect of the concentration of coating polymer and particle size on the release rate of MTX from both AGMM and CGMM were also studied. Both AGMM and CGMM provided controlled release of MTX following a zero‐order release pattern in gastric and intestinal fluids for prolonged periods of time. The release rate of MTX decreased with an increase in concentration of the coating polymer as well as an increase in particle size of the microspheres. Both AGMM and CGMM showed good potential as pH dependent multiple unit delivery systems for the controlled release of MTX in oral administration. © 1995 John Wiley & Sons, Inc.
Influence of structure of hydroxyl‐terminated maleopimaric acid ester on thermal stability of rigid polyurethane foams
Authors: Zhang Y. , Shang S. , Zhang X. , Wang D. , Hourston D. J. 
Published: April 2003

AbstractA series of hydroxyl‐terminated maleopimaric acid esters (HTMAEs) and rigid polyurethane (PU) foams based on these HTMAEs were synthesized using chemically modified natural gum rosin and its derivative maleopimaric acid as raw materials. Thermal stability of these polyols and their corresponding rigid PU foams was studied by a thermogravimetric method and a dimensional stability measurement. It was shown that the thermal stability of the final foams was strongly dependent on the structure of their corresponding polyols. The thermogravimetric analysis curves of these rosin‐based rigid PU foams displayed two distinct regions of weight loss. It has been shown that at the initial stage of weight loss the process was dominated by polyol component degradation; the second stage was governed by isocyanate component degradation. © 1995 John Wiley & Sons, Inc.