bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of polycarbonate molecular weight on polymer blends of polycarbonate and ABS
Authors: Wu Jiann‐Shing , Shen Shu‐Chen , Chang Feng‐Chih 
Published: April 2003

AbstractThe melt viscosity of polycarbonate/acrylonitrile‐butadiene‐styrene (PC/ABS) blends relative to PC is significantly lower, even lower than that of pure ABS in some compositions. Annealing above theTgof PC coalesces and coarsens phase structure in core and skin regions. Increase in the molecular weight of PC in PC/ABS blends results in low‐temperature fracture toughness improvement but suffers from the disadvantage of higher melt viscosity. The selection of PC in PC/ABS blends must be a compromise between the toughness advantages of higher PC molecular weight and the disadvantage of higher melt viscosity. © 1993 John Wiley & Sons, Inc.
Synthesis and properties of a new AB‐cross‐linked copolymer membrane system
Authors: Kerres J. A. , Strathmann H. 
Published: April 2003

AbstractThe alcohol permeability and permselectivity properties as well as the morphology of membranes made of a newly developed AB‐cross‐linked copolymer system composed of elastomeric and glassy components were investigated. The copolymer was synthesized by a hydrosilylation reaction between poly(styrene‐stat‐isoprenes) (Mn from 40,000 to 100,000 g/mol) with high content in unsaturated side groups (≈ 60% of entire isoprene content) and polyhydrogen polysiloxanes with varying SiH content (0.75 10.7 mol %) and molecular mass, Mn, from 2,500 to 36,000 g/mol. A two‐track approach was taken to determine the morphology of the copolymer system. The first employed the usual polymer characterization methods such as electron microscopy, DSC, IR spectroscopy, the density gradient method, and mechanical measurements. For the second approach, different copolymer permeability models were tested so as to give an insight into the copolymer morphology. As a final step, the permeability and permselectivity properties were correlated with the morphological structure of the copolymer system. It was observed that the respective continuous microphase dominated the copolymer's physical properties, as, e.g., permeability, permselectivity, and mechanical properties. The microphase inversion in the copolymer system was proved by the permeability/permselectivity as well as by the mechanical measurements. © 1993 John Wiley & Sons, Inc.
Dielectric behavior at microwave frequencies of an epoxy resin during crosslinking
Authors: Livi A. , Levita G. , Rolla P. A. 
Published: April 2003

AbstractThe dielectric behavior during the crosslinking process of a low molecular weight liquid diglycidyl ether of bisphenol‐A (DGEBA) and ethylenediamine, as the curing agent, has been investigated at microwave frequencies (0.1–10 GHz) by means of the time domain reflectometry. It was found that both the real and the imaginary part of the dielectric constant, which regularly decreased as the cure reaction proceeded, were mainly affected by the disappearance of specific dipolar species, whose relaxation time did not change significantly. A simple model based on disappearance of dipoles agrees with the experimental data and explains the coincidence between kinetic data obtained by dielectrometry and calorimetry. The microwave dielectric constant can thus be used to directly measure in real time the conversion of the reaction. © 1993 John Wiley & Sons, Inc.
Infrared spectroscopy measurements of residual stresses in polypropylene fibers
Authors: Andreassen Erik , Myhre Ole Jan 
Published: April 2003

AbstractAverage residual stresses in polypropylene fibers, produced in a full‐scale short‐spin line, are estimated from the shift of the IR absorption peak at 975 cm‐1. Linearly polarized incident IR radiation is used to separate between stress components parallel and perpendicular to the fiber axis. For all the fibers in this study, the axial stress component is larger than the average stress perpendicular to the fiber axis. Axial and perpendicular stresses are correlated with draw ratio and polydispersity index. For narrow molecular weight distributions (Mw/Mn < 4–5), the axial stress increases with increasing draw ratio. Average stress perpendicular to the fiber axis decreases with increasing draw ratio for all the molecular weight distributions in this study (Mw/Mn = 3–6). Measurements of residual stresses are consistent with other results characterizing molecular structure and mobility. An expression for estimating the stored deformation energy is discussed. © 1993 John Wiley & Sons, Inc.
Synthesis, rheology, and physical properties of a metathesis polymer
Authors: Asrar J. , Hurlbut J. B. 
Published: April 2003

AbstractThis paper describes the synthesis, physical properties, and the impact modification of poly(N‐phenylnorbornene dicarboximide) (PNDI). Impact modification is carried out both by physical blending with acrylonitrile‐butadiene rubber (Hycar®) and by in situ metathesis polymerization of the monomer with the rubber. Better success is achieved by in situ metathesis polymerization. A copolymer, poly(N‐phenylnorbornene dicarboximide) ‐ co‐poly(norbornene nitrile) containing Hycar rubber (PNDI/PNN/Hycar), is prepared with a good balance of high‐heat impact and flexural properties. The melt viscoelastic behavior of PNDI/PNN/Hycar is evaluated and the energy of activation for viscous flow (Ea) was found to be 42 kcal/mol. © 1993 John Wiley & Sons, Inc.
Synthesis and characterization of acrylic‐based superabsorbents
Authors: Askari F. , Nafisi S. , Omidian H. , Hashemi S. A. 
Published: April 2003

AbstractThis paper is devoted to the synthesis and characterization of superabsorbent polymers based on acrylic acid. These hydrogels were prepared by carrying the inverse suspension polymerization in an aromatic hydrocarbon. The dispersion is stabilized by the mixture of micromolecular and macromolecular emulsifiers. To obtain high swelling and appropriate absorption kinetics, parameters such as initial monomer and cross‐linker concentration, range of neutralization, monomer addition rate, temperature, initiating system, stabilizing system, and nature of the organic phase were studied but not reviewed here. Thus, based on these topics a basic formula is obtained to display the effect of some structural parameters on behaviour of superabsorbents utilized. © 1993 John Wiley & Sons, Inc.
Ring‐opening polymerization of tetrahydrofuran with rare earth‐contained catalysts
Authors: Li Fengfu , Jin Yingtai , Pei Fengkui , Wang Fosong 
Published: April 2003

AbstractRare earth trifluoroacetates, Ln(CF3CO2)3 (Ln=thirteen rare earth elements), combined with RnAlH3−n (R=methyl, octyl, n=3; R=ethyl, i‐Butyl, n=2,3) were used as catalysts for the polymerization of tetrahydrofuran (THF). The activity increased by adding propylene oxide (PO), as a promoter, to the polymerization system, producing high molecular weight polytetrahydrofuran (PTHF). The effects of Ln, PO/Ln, and Al/Ln, and others on the polymerization of THF were also studied. © 1993 John Wiley & Sons, Inc.
Preparation of a polyelectrolyte complex gel from chitosan and κ‐carrageenan and its pH‐sensitive swelling
Authors: Sakiyama Takaharu , Chu Chia‐Hong , Fujii Tomoyuki , Yano Toshimasa 
Published: April 2003

AbstractA polyelectrolyte complex gel was prepared by mixing chitosan and k‐carrageenan solutions in the presence of NaCl. To study the effect of ambient pH on the swelling behavior, the diameter of the cylindrical gel(4 mm x 8 mm) immersed in aqueous NaOH, KOH, or HCl solution was measured. In the range of pH 10–12, the diameter increased with time, and the gel reached swelling equilibrium within 6 days. In an NaOH solution of pH 10.5, the maximum swelling occurred, and the volume of the gel at equilibrium was 10.2 times as large as the initial one. At pH below 9 and at pH 13, no swelling was observed. Thus, the swelling of the complex gel prepared in this study was sensitive to a rather narrow range of pH. The swelling equilibrium in the presence of NaCl was also investigated at various pH. © 1993 John Wiley & Sons, Inc.
Highly crosslinked polymer particles by dispersion polymerization
Authors: Hattori M. , Sudol E. D. , El‐Aasser M. S. 
Published: April 2003

AbstractMonodisperse poly(divinylbenzene) and poly(styrene‐co‐divinylbenzene) particles were prepared in the 0.4−3 μm size range by dispersion polymerization in methanol and methanol/co‐solvent mixtures. The effects of polymerization parameters, such as the crosslinking monomer concentration, the co‐solvent, and the presence of oxygen were studied. For good colloidal stability, it was necessary to use a relatively large fraction of crosslinking monomer. The initial presence of oxygen was also found to play an important role in determining the colloidal stability during the polymerization. Although the exact mechanism is not certain, it is considered likely that the oxygen promotes the grafting of poly(divinylbenzene) to the polyvinylpyrrolidone (PVP) stabilizer molecules. The growing particles were investigated by electron microscopy. Precipitation of small particles onto the nucleated particles was determined to be the primary mechanism of particle growth. © 1993 John Wiley & Sons, Inc.
A comparative C13 NMR study of polyflavonoid tannin extracts for phenolic polycondensates
Authors: Pizzi A. , Stephanou A. 
Published: April 2003

AbstractAssignment of C13 NMR bands to important sites of polymeric flavonoid tannin extracts produced industrially for production of tannin–formaldehyde resins is reported. Five different tannin extracts were studied. The C13 NMR bands' position and relative intensities allowed us to qualitatively explain comparative differences in the five tannins' structural features and properties that are of importance for tannin adhesives applications. The five tannins could be divided into two classes (1) mimosa and quebracho tannins and (2) pecan nut, pine, and gambier tannins. Properties of relevance that varied considerably among the five tannins and that could be detected by 13C NMR were: the relative proportions of fisetinidin/robinetinidin units in relation to catechin/gallocatechin units; differences in number average degree of polymerization; the extent of open heterocycle forms present; branching; and relative proportion of pyrogallol versus catechol B‐rings in the flavonoid repeating units. © 1993 John Wiley & Sons, Inc.
Ion sorption by polyamide with consideration of ionic interaction and other physical interactions
Authors: Yang Yiqi , Li Shiqi , Lan Tian 
Published: April 2003

AbstractA modified Donnan model is discussed with consideration of physical interactions in the ion sorption by polyamide as a function of the influence of ions in the system. Lyotropic numbers and the salt effect on water‐structure changes are considered to describe their influence on the physical interactions between the sorbate and the sorbent. It is found that some electrolytes, such as sulfates and phosphates, can increase the sorption of some negatively charged ions (e.g., acid dyes) on positively charged polyamide it salt concentration is high (e.g., > 0.5 M), after the initial decrease of ion sorption at a low salt concentration range. This result is difficult to explain by the model that treats all interactions other than ionic interaction as a constant. The modified Donnan model explains both the decrease and increase of ion sorption with increasing salt concentration quantitatively. © 1994 John Wiley & Sons, Inc.
Heat sealing of semicrystalline polymer films. II. Effect of melting distribution on heat‐sealing behavior of polyolefins
Authors: Stehling Ferdinand C. , Meka Prasadarao 
Published: April 2003

AbstractHeat sealing of films, i. e., formation of a joint between two films by placing them fleetingly between heated platens, was experimentally investigated for a variety of semicrystalline polyolefins, especially various polyethlenes, to determine how sealing temperature affected seal strength measured at room temperature. Seal strength as a function of sealing temperature, SS(T), is closely related to the melting distribution of the polymer determined by DSC measurements, i. e., to the fraction of amorphous phase as a function of temperature, fa(T). Seal initiation temperature, the temperature at which a specific, low level of seal strength of polyethylene films is achieved, corresponds to the temperature at which the fraction of amorphous phase equals 77±3%. At higher temperatures, SS(T) increases approximately as fa(T) increases. At the final melting point of the polymer, i.e., when fa(T) =1, seal strength reaches an approximately constant value termed the plateau seal strength. The magnitude of the plateau seal strength is determined by the yield stress of the polymer film. Thus, the heat‐sealing curve, SS(T), for a polyethylene can be semiquantitatively predicted from the melting distribution and yield stress of the polymer. © 1994 John Wiley & Sons, Inc.
Surface modification of polyethersulfone hollow‐fiber membranes by γ‐ray irradiation
Authors: Mok S. , Worsfold D. J. , Fouda A. , Matsuura T. 
Published: April 2003

AbstractThe fouling of ultrafiltration membrane is often caused by gel formation on the membrane surface. This gel layer arises due to concentration polarization or macromolecular adsorption on the membrane surface. The gel layer affects both the hydraulic permeability and the rejection properties of the membrane. In this report, the adsorption of porcine albumin and the concentration polarization effect on modified and unmodified polyethersulfone (PES) hollow‐fiber membrane is studied. PES ultrafiltration hollow‐fiber membranes were modified by the grafting of polyethylene glycol (PEG) polymer on the internal surface using γ‐ray irradiation method. The modified hollow fibers were less susceptible to fouling than were the unmodified fiber. The performance of both modified and unmodified hollow fibers was tested as a function of feed flow rates and protein concentrations. © 1994 John Wiley & Sons, Inc.
Interchain crosslinking between NBR and polyacrylic rubber and effect on (i) processibility and blend‐morphology
Authors: Tripathy A. R. , Das C. K. 
Published: April 2003

AbstractFlow behaviour of NBR and polyacrylic rubber blends have been studied throughout the entire composition ranges. The effect of preheating of the blends is also studied in order to understand the interchain crosslinking. Viscosity, extrudate swell, power law indices, have been studied as a function of shear rate and blend ratio. The shearing accompanied by blend ratio has a predominent effect on the rheological behaviour of the preheated blends due to microgel formation. From the rheological behaviour it appears that there is a phase inversion at around 50% of NBR, however, preheating does not change this trend. © 1994 John Wiley & Sons, Inc.
Computer simulation of crystallization kinetics in fiber‐reinforced composites
Authors: Krause Th. , Kalinka G. , Auer C. , Hinrichsen G. 
Published: April 2003

AbstractA computer simulation model was developed to investigate spherulitic growth in polymers of infinite and plate‐limited volume as well as in fibre‐reinforced polymer composite systems. Parameters like thermal nucleation rate and athermal nucleation density, plate distance, and fibre content were varied. The simulation crystallization process was evaluated following Avrami's method in the case of infinite volume and by stepwise approximation by Avrami functions in the case of limited volume. In addition, the simulation method allows the visualization of the growing entities at any phase of crystallization. Therefore the geometry of growing entities can be easily compared with the corresponding crystallization exponent. A good agreement between the crystallization exponent and the growth geometry was found.Depending on nucleation mode, “infinite” systems yield Avrami exponents of 3 and 4. In plate‐limited volume, a transcrystallization effect was observed in case of high athermal nucleation density on plate surface and large plate distances. This particular skin effect decreases the three‐dimensional growth to a one‐dimensional needle‐shaped one. Small plate distance changes the spherical to a disk‐like growth, resulting in crystallization exponents of 2 or 3, depending on nucleation mode. The crystallization behaviour of fibrereinforced composite systems is more complex. Low fibre content or large fibre distance and high athermal nucleation density on the fibre surface induce the formation of transcrystalline zones. The three‐dimensional growth of the spheres at the beginning is restricted by their neighbours, so that their geometry changes to a pyramidical one. They grow with a front normal to the fibre surface and the crystallization exponent is shifted in between 2.0 and 2.6 depending on nucleation density. High fibre content leads to a growth along the triangular channels between three adjacent fibres; the corresponding exponent amounts to 1.6. © 1994 John Wiley & Sons, Inc.
Separation of water/ethanol mixture through poly(acrylonitrile‐co‐acrylic acid)/poly(ethylene oxide) membranes by pervaporation
Authors: Jo Won Ho , Kim Hyo Jin , Kang Yong Soo 
Published: April 2003

AbstractThe separation of water/ethanol mixtures was investigated by poly(acrylonitrile‐co‐acrylic acid) and by poly(acrylonitrile‐co‐acrylic acid)/poly(ethylene oxide) blend membranes. The flux increased with the content of acrylic acid in copolymers and the selectivity remained constant. The marked increase of the selectivity was observed for blend membranes of a certain blend ratio, suggesting that the two polymers are partially miscible. Poly(ethylene oxide) in blends was thought to act as a plasticizer as well as a preferentially water absorbing and diffusing component. © 1994 John Wiley & Sons, Inc.
Studies of water‐soluble oligomers formed in emulsion copolymerization
Authors: Wang Shou‐Ting , Poehlein Gary W. 
Published: April 2003

AbstractA polymer chain transfer agent was synthesized by the reaction between poly(vinylbenzyl chloride) latex particles and 2‐aminoethanethiol in a basic environment. In subsequent emulsion polymerization reactions, low molecular weight species were formed when waterborn oligomeric radicals diffused to the surface of these seed particles. These low molecular weight oligomers were separated by membrane filtration and their composition and molecular weight weight were analyzed by FTIR and mass spectroscopy. The measured composition results were compared with those that were calculated from the copolymerization equation. The molecular weights were compared with earlier experimental results that were obtained by isolation of oligomers formed when a water‐soluble inhibitor was added to a reacting emulsion.Three seeded emulsion copolymerization systems, that is, styrene–acrylic acid, styrenemethacrylic acid, and styrene–methyl methacrylate, were investigated. The distribution of monomer in the water phase and in the copolymer particles was analyzed. The results show that the oligomer compositions for different copolymerization systems can be approximated reasonable well by the copolymerization equation, using the reactivity ratios obtained from bulk copolymerization. The length of the oligomer radicals formed depends on their composition and the properties of the polymer particles, such as surface charge, composition, size, and concentration. © 1994 John Wiley & Sons, Inc.
Temperature‐responsive characteristics of N‐isopropylacrylamide‐grafted polymer films prepared by photografting
Authors: Kubota Hitoshi , Nagaoka Noriyasu , Katakai Ryoichi , Yoshida Masaru , Omichi Hideki , Hata Yasuo 
Published: April 2003

AbstractPhotografting of N‐isopropylacrylamide (NIPAAm) on ethylene–vinyl alcohol copolymer films (thickness = 15,20, and 25 μm) and low‐and high‐density polyethylene films (thickness = 30 μm) was carried out at 60°C in a water medium. Xanthone was used as a photoinitiator by coating it on the film samples. The resultant NIPAAm‐grafted films exhibited a temperature‐responsive character, which was evaluated by measuring a dimensional change of the grafted films. The grafted films swelled and shrank in water at temperatures lower and higher than around 30°C, respectively. The character was found to be reversible between 0 and 50°C. It was observed that the extent of the character is largely influenced by film thickness, location of NIPAAm‐grafted chains, and crystallinity of film substrate. © 1994 John Wiley & Sons, Inc.
Effects of thermal and mechanical fatigue on flexural strength of G40‐600/PMR‐15 cross‐ply laminates
Authors: Roberts Gary D. , Ho Barry Ping Hsiao , Wallace John F. 
Published: April 2003

AbstractThe effects of thermal and mechanical fatigue on the flexural strength of G40‐600/PMR‐15 cross‐ply laminates with ply orientations of (02, 902)2sand (902, 02)2sare examined. The relative improtance of shear and tensile stresses is examined by varying the span‐to‐depth ratios of flexural test specimens from 8 to 45 Acoustic emission singals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine speciments for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, for regardless of ply orientation, span‐to‐depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0° ply of specimens with high span‐to‐depth ratios. Because of the complex failure modes, the flexural test results represent the “apparent” strengths rather than the true flexural or shear strenghts for these cross‐ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strins during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32–260°C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (‒85 to 85°C, 500 cycles). Mechanical cycling (0–50% of the flexural strength, 100 cycles) has a similar effect, except that acoustic events are reduced only at strains less than the maximum strain applied during flexural fatigue. © 1994 John Wiley & Sons, Inc.This article is a US Government work and, as such, is in the public domain in the United States of America.
Preparation and characterization of cryogenic adhesives. I. Glycidyl‐terminated polyurethane resins
Authors: Chen Der‐Shyang , Ma Chen‐Chi M. , Hsia Hung‐Chung , Wang Wang‐Nang , Lin Shiaw‐Ruey 
Published: April 2003

AbstractGlycidol has been introduced into isocyanate‐terminated polyurethane to form glycidyl‐terminated polyurethane resin. A series of glycidyl‐terminated polyurethanes, based on PTMEG, PPG, and polyester soft segments, having different molecular weights were synthesized and their adhesion properties on aluminum were evaluated. The effect of the soft‐segment structure, soft‐segment length, and temperature on adhesion were examined. It was found that the resin showed superior adhesion at cryogenic temperatures. The results coincide with the phenomenon observed in dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). In addition, the modified system also offered some distinct advantages over the commercial polyurethane adhesives, e.g., good storage stability and room‐temperature curing. © 1994 John Wiley & Sons, Inc.