bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of curing reaction of epoxide catalyzed by tertiary amine
Authors: Han J. L. , Hsieh K. H. , Chiu W. Y. 
Published: April 2003

AbstractThe kinetic study of the curing reaction of epoxide catalyzed by tertiary amine was carried out through thermal analysis of the reaction by differential scanning calorimetry (DSC). Using infrared spectroscopy (IR) and neutron magnetic reasonance (NMR) analysis, a reaction mechanism for this reaction was proposed. The reaction proceeded to anionic polymerization. An autocatalytic reaction was induced at high concentration of the tertiary amine catalyst. © 1993 John Wiley & Sons, Inc.
Structure and thermal properties of polyether polyurethaneurea elastomers
Authors: Lee Ho Kyung , Ko Sohk Won 
Published: April 2003

AbstractThree series of polyether polyurethaneurea (PEUU) elastomers based on poly(tetramethylene glycol) (PTMG, MW = 1000 or 2000), 4,4′‐diphenylmethane diisocyanate (MDI), and three kinds of diamine chain extenders, i.e., 4,4′‐diaminodiphenylmethane (DAM), m‐phenylenediamine (MPD), and p‐phenylenediamine (PPD) were synthesized in dimethylformamide or DMF–LiCl solvent by the prepolymer method. The degree of phase separation was higher in the samples with PTMG‐2000 than in those with PTMG‐1000. Three‐dimensional hydrogen bonding between hard segments led to strong hard‐domain cohesion, but solubilized soft segment and the remaining LiCl within hard domains interfered with microstructural ordering of hard segments. According to the TG/DTA analyses, as‐cast PEUU elastomers showed two‐stage degradation behavior at a heating rate of 20°C/min in a nitrogen atmosphere. Initial degradation temperature was closely related with both hard‐segment content and microstructural ordering, i.e., most of the hard segments were degraded in the first stage and samples with less ordered hard segments degraded at a lower temperatures. © 1993 John Wiley & Sons, Inc.
Carboxylated nitrile rubber as a reactive compatibilizer for immiscible blends of poly(vinyl chloride) and epoxidized natural rubber
Authors: Ramesh P. , De S. K. 
Published: April 2003

AbstractBlends of poly(vinyl chloride) (PVC) and epoxidized natural rubber (ENR) were prepared by melt‐blending and studied using a Monsanto rheometer, infrared spectrophotometer, and dynamic mechanical analyzer. The PVC/ENR blends were found to be self‐crosslinkable, but immiscible at 25/75, 50/50, and 75/25 blend ratios. However, addition of a third reactive polymer, such as carboxylated nitrile rubber (XNBR), can make the ternary blend miscible. The quantity of XNBR required to make the binary blend miscible depends on the blend ratio of the binary PVC/ENR blend and increases as the binary blend ratio changes through 25:75 to 50:50 to 75:25. © 1993 John Wiley & Sons, Inc.
Curing of epoxy resins with dicyandiamide and urones
Authors: Güthner Thomas , Hammer Benedikt 
Published: April 2003

AbstractThe curing of epoxy resins using dicyandiamide (DICY) and combinations of DICY with several uron accelerators as curing agents is investigated. DSC, FTIR, mechanical, and sorption measurements indicate complex multistage curing processes. There is no evidence that the curing reaction is catalyzed by DICY. The optimum stoichiometry is determined as 7 epoxy units per 1 molecule DICY. Contour plots for curing reactions with DICY in presence of Fenuron 3c or TDI‐uron 3d give some information for optimizing technical formulations. © 1993 John Wiley & Sons, Inc.
Structural analysis of methacrylamide‐grafted silk fibers
Authors: Tsukada Masuhiro , Freddi Giuliano , Ishiguro Yosio , Shiozaki Hideki 
Published: April 2003

AbstractThe structural changes and the thermal behavior of silk fibers grafted with methacrylamide (MAA) were investigated as a function of the weight gain. The refractive index parallel to the fiber axis decreased with increasing weight gain, whereas that perpendicular remained almost unchanged. Accordingly, birefringence decreased with a steeper slope in the weight gain range 0–80%, suggesting a lower degree of average molecular orientation. Only small changes in the isotropic refractive index were detected, suggesting that the crystallinity of the fibers remained essentially unaffected by MAA grafting, as confirmed by the X‐ray diffraction data. The molecular orientation in the crystalline regions remained unchanged in the weight gain range 0–60%, then sharply decreased. The strength and the initial tensile resistance of grafted silk fibers decreased both in the dry and wet states, while elongation at break increased in the dry state and remained almost constant in the wet state. The results of the thermal behavior, investigated by differential scanning calorimetry, thermomechanical and thermogravimetric analysis, and dynamic mechanical measurements, were consistent with an increased thermal stability conferred on silk fibers by MAA grafting. The cross‐sectional area of MAA‐grafted silk fibers increased. Moreover, ion‐etched cross sections of the grafted silk fiber showed the presence of fibrils with a diameter larger than that of the untreated control. © 1993 John Wiley & Sons, Inc.
A simple method for determining water‐induced gelling times of isocyanate prepolymers
Authors: Braatz James A. 
Published: April 2003

AbstractA spectral assay has been developed that permits reliable determination of polymer gelling times. Water‐soluble, isocyanate‐containing polyether prepolymers initiate chain extension on contact with water and after some period of time form a semisolid hydrogel matrix. Techniques based on visual observations used to determine the end point for this process generally produce erratic results. By following scattered transmittance of visible light by an aqueous solution of prepolymer during the gelation process, it is possible to obtain a more objective determination of the gelation time. It was empirically demonstrated that the minimum of the first derivative of the scattered transmittance versus time spectrum correlated with the observed gel time over a wide time scale. © 1993 John Wiley & Sons, Inc.
Application of the kinetic composite methodology to autocatalytic‐type thermoset prepreg cures
Authors: Nam Jae‐Do , Seferis James C. 
Published: April 2003

AbstractUsing a commercial epoxy/carbon fiber prepreg as a model system, cure kinetics of an autocatalytic‐type reaction were analyzed by a general form of conversion‐dependent function first proposed for degradation kinetics of polymers and composites. The characteristic feature of conversion‐dependent function was determined using a reduced‐plot method where the temperature‐dependent reaction rate constant was analytically separated from the isothermal data. Assuming two elementary reaction mechanisms that were expressed by the nth order and autocatalytic kinetic models, they were combined with a composite methodology capable of predicting overall kinetic behavior. The activation energies were determined and favorably compared for both isothermal and dynamic‐heating differential scanning calorimetry experiments in the temperature region for standard epoxy cures at 177°C (350°F). Finally, the proposed model equation demonstrated excellent predictive capability and broad applicability in describing various types of thermoset polymer cure for both isothermal and dynamic heating conditions. © 1993 John Wiley & Sons, Inc.
Thermal degradation study of poly(vinyl chloride): Kinetic analysis of thermogravimetric data
Authors: Jiménez A. , Berenguer V. , López J. , Sánchez A. 
Published: April 2003

AbstractThe thermal degradation of a poly(vinyl chloride) (PVC) resin was studied using a non‐isothermal thermogravimetric technique. Kinetic parameters such as activation energies, reaction orders, and preexponential factors are calculated using integral and differential methods reported in the literature. Advantages and disadvantages of these methods are discussed in order to characterize PVC. © 1993 John Wiley & Sons, Inc.
The kinetics of the polymerization reaction of toluene diisocyanate with HTPB prepolymer
Authors: Kothandaraman H. , Nasar A. Sultan 
Published: April 2003

AbstractThe uncatalysed and catalysed polymerization of a hydroxyl‐terminated polybutadiene with toluene diisocyanate has been studied in toluene solution at four different temperatures. The rate constants (k1, k2) and the activation parameters (Ea1, Ea2, ΔS1‡, ΔS2‡) for the isocyanate groups in the 4 and 2 positions were calculated. It was found that the catalysts enhance the reactivity of the 2 position isocyanate group rather than the 4 position isocyanate group. It was also found that diethylcyclohexylamine has higher selectivity than dibutyltin dilaurate to enhance the reactivity of the isocyanate group in the 2 position. The effect of solvent has also been studied. The reactivity decreased in the following order; benzene = toluene > chlorobenzene > dioxane > nitrobenzene. © 1993 John Wiley & Sons, Inc.
Biodegradation of radiolabeled cellulose acetate and cellulose propionate
Authors: Komarek Ronald J. , Gardner Robert M. , Buchanan Charles M. , Gedon Steven 
Published: April 2003

AbstractBiodegradation of cellulose acetate and cellulose propionate was conclusively established with a naturally derived mixed microbial culture derived from activated sludge and 14C labeled cellulose esters. Radiolabeled cellulose esters were synthesized with either [1‐14C]‐acetate or [1‐14C]‐propionate and back hydrolyzed to the desired degree of substitution (DS) ranging from 1.77 to 2.64. Biodegradation was measured in an in vitro aerobic culture system that was designed to capture 14CO2 produced by the aerobic microbial metabolism of the cellulose esters. Microorganisms were able to extensively degrade cellulose [1‐14C]‐acetate (CA) with DS ranging from 1.85 to 2.57 over periods of 14–31 days. More than 80% of the original 14C‐polymeric carbon was biodegraded to 14CO2 for CA substrates with a DS of 1.85. CA polymers with a DS of 2.07 and 2.57 yielded over 60% conversion to 14CO2. The amount of biodegradation that was observed with cellulose [1‐14C]‐propionate with DS of 2.11, 2.44, and 2.64 were lower than the corresponding acetyl ester and ranged from 0.09 to 1.1%. However, cellulose [1‐14C]‐propionate with a DS of 1.77 and 1.84 underwent very rapid degradation in the mixed culture system, with 70 to over 80% conversion of labeled polymeric carbon metabolized to 14CO2 in 29 days. The high level of microbial utilization of carbon from both cellulose esters and its conversion to CO2 confirms the biodegradability of these polymers and the potential they have for total mineralization in natural microbiologically active environments. © 1993 John Wiley & Sons, Inc.
Effects of particle shape and size distributions on the electrical and magnetic properties of nickel/polyethylene composites
Authors: Göktürk Halit S. , Fiske Thomas J. , Kalyon Dilhan M. 
Published: April 2003

AbstractElectrical and magnetic properties of composite materials prepared by incorporating various nickel‐based fillers of different shapes into polyethylene were investigated. The fillers used were nickel powders, nickel filamentary powders, nickel flakes, and nickel‐coated graphite fibers. The particle‐size distributions of the fillers were determined both before and after the processing of the composite samples. A wide range of filler volume fractions were used. In some cases, the volume fraction approached the maximum packing fraction of the solid phase to significantly exceed the percolation threshold. The composite samples were characterized in terms of their volume resistivity, dielectric constant, and magnetic permeability values. Filler particles of asymmetric shapes were very effective in terms of altering the electrical properties of the composite samples. At the highest loading levels of the nickel fillers, the volume resistivity values of the composites decreased by more than 17 orders of magnitude. At such high filler concentrations, the dielectric constant values of the composite samples increased considerably, to values that were greater than 1000. The permeability values of the samples increased linearly with the volume fraction of the nickel filler and were insensitive to the shape of the fillers. The highest relative permeability value measured was 5.8 for composites with 67% by volume of nickel powder. © 1993 John Wiley & Sons, Inc.
Thermal behavior and morphology of rubber‐modified epoxies
Authors: Kim Woo Nyon , Park Chan Eon , Burns Charles M. 
Published: April 2003

AbstractRubber‐modified epoxies of tetraglycidyl‐4,4′‐diaminodiphenyl methane and a carboxylterminated copolymer of butadiene–acrylonitrile (CTBN) have been investigated by differential scanning calorimetry, scanning electron microscopy, and micrograph image analysis. Bisphenol‐A (BPA) was used to produce chain‐extended resins by reaction with the epoxy‐terminated rubber. Diaminodiphenyl sulfone was used as a hardener. Partially cured resins were prepared with different amounts of added CTBN and cured in an oven for different cure times at 448 K. From the measured heat of reaction of the samples, a fast curing reaction was observed when BPA was present in the resin formulation. In the study of the morphology, the average size of the domains was seen to increase with the CTBN content. These CTBN‐rich domains appear to include substantial amounts of epoxy material, as indicated by the measured glass transition temperature of the CTBN‐rich phase. The size of domains was observed to range mostly from 0.1 to 5 μm in diameter and to show a slightly bimodal distribution, with modes around 1 μm and 3–4 μm when 15 and 20 phr CTBN was added. © 1993 John Wiley & Sons, Inc.
New use of size exclusion chromatography in kinetics of mechanical degradation of polymers in solution
Authors: Florea Mircea 
Published: April 2003

AbstractA new method to investigate the mechanical degradation of polymers in solution is described that uses size exclusion chromatograms of the initial polymer and of the degraded sample. The incipient parts of these chromatograms are analyzed to obtain kinetic data about degradation at the level of infinitesimal fractions. The procedure is based on the fact that mechanical degradation of the polymers is a first‐order reaction and macromolecules are cleaved mostly in their central region. The rate constant and the variation in the rate constant with molecular weight are determined in a single experiment, avoiding additional fractionation steps. Moreover, the slope of the size exclusion chromatographic calibration curve is derived, opening new ways to determine polydispersities or even to make rapid calibration for unknown polymers. To verify the method, the rate constant and the molecular weight dependence of the rate constant were determined for the sonic degradation of polystyrene in toluene. The rate constant is found to vary with the square of the molecular weight, and its value is in good agreement with results reported using much more laborious methods. © 1993 John Wiley & Sons, Inc.
Reactive processing of rubber–plastic blends: Role of chemical compatibilizer
Authors: Bhowmick Anil K. , Chiba Tsuneu , Inoue Takashi 
Published: April 2003

AbstractThe present investigation was aimed at understanding the role of chemical compatibilizers like carboxy‐terminated nitrile rubber, amine‐terminated nitrile rubber, liquid carboxylated nitrile rubber, etc. in the reactive processing of a dynamically vulcanized 50 : 50 nylon/ HNBR blend. The interfacial parameters for a bilayer specimen of nylon and rubber and structure parameters during the processing were determined. The interfacial thickness (λ) increased from 48 to 70–80 nm and the interfacial tension (γ∞) decreased from 0.240 to 0.209–0.198 mN/m, depending on the nature and concentration of the compatibilizer. There was, however, an optimum level of the compatibilizer beyond which the thickness did not change significantly. For the ionomeric compatibilizer, λ decreased after the optimum concentration. The increase in λ is ascribed to the formation of a graft copolymer of nylon and rubber and the compatibilization reactions. Structure parameters were dependent upon the sequence of mixing of the compatibilizer. If the compatibilizer and the cross‐linker were added in the rubber and the mixture was then added to nylon, the mean radius of the dispersed particle was smaller over the range of mixing times. The compatibilizers also reduced the particle size at the early stage of mixing due to reduced interfacial tension. In general, the particle size decreased with mixing time, attained a minimum, and then increased. The volume fraction of the interface was also very large for compatibilized systems. The particles were larger, however, when the compatibilizer was first mixed in nylon. SEM studies indicated that the compatibilizer in the latter case was not acting as a surfactant. © 1993 John Wiley & Sons, Inc.
Electrooptical properties of poly(diisopropyl fumarate‐co‐styrene)/cyanobiphenyl‐type liquid crystal composite films
Authors: Choi C. H. , Kim B. K. , Kikuchi H. , Kajiyama T. , Amaya N. , Murata Y. 
Published: April 2003

AbstractComposite films composed of poly(diisopropyl fumarate‐co‐styrene) (PFS) and nematictype liquid crystal (E8) (40/60 by weight) were prepared by solvent casting in chloroform at room temperature. Scanning electron microscopy measurement showed that a liquid crystal phase is continuously embedded in a spongy‐like PFS martrix. Optical responses of the composite films under the conditions of an externally imposed ac electric field (60–240 Vp‐p,10–1000 Hz), temperature (290–355 K), and a film thickness (8–16 μm), were determined using an He–Ne laser (wavelength 632.8 nm). The results obtained indicated that, under the conditions imposed, the output can be continuously controlled, and the response time is only of several milliseconds or less. In addition, the response to temperature sweep, heating and cooling, was reversible with only a delay, and it was interpreted in terms of the rigidity and thermal stability of the matrix polymer. © 1993 John Wiley & Sons, Inc.
The characterization of short chain branching in polyethylene using fourier transform infrared spectroscopy
Authors: Blitz Jonathan P. , McFaddin Douglas C. 
Published: April 2003

AbstractThe characterization of short chain branching in polyethylene using transmission FTIR spectroscopy is investigated. Traditional methodologies, using the methyl deformation band for qualitative and quantitative analyses, have recognized shortcomings. The methyl and methylene rocking bands, which are more characteristic of short chain branch type, were found to be more useful. Methyl, ethyl, butyl, isobutyl, and hexyl branches are qualitatively and quantitatively characterized in LLDPE copolymers by FTIR spectroscopy. Methyl branches were characterized by an absorbance at 935 cm−1, ethyl branches at 770 cm−1, butyl branches at 893 cm−1, isobutyl branches at 920 cm−1, and hexyl branches at 888 cm−1. Fourier self‐deconvolution was used to resolve overlapping bands for ethyl, butyl, and isobutyl branches. Using calibrations derived for LLDPE copolymers from 13C NMR data, FTIR spectroscopy was also used to characterize LLDPE terpolymers and LDPE resins. The FTIR and NMR data are in qualitative and quantitative agreement. In some cases correction were made to the FTIR results using data obtained from the methyl deformation band. The FTIR technique is less costly and faster than NMR spectroscopy. © 1994 John Wiley & Sons, Inc.
The properties of polyurethanes with mixed chain extenders and mixed soft segments
Authors: Ahn Tae Oan , Jung Soon‐Uk , Jeong Han Mo , Lee Sang Won 
Published: April 2003

AbstractSeries of polyurethaneurea elastomers were prepared from 4,4′‐diphenylmethane diisocyanate, poly(teuramethylene ether) glycol and poly(hexamethylene carbonate) glycol for mixed soft segments, and 1,4‐butanediol and isophoronediamine for mixed chain extenders. Characteristics of the copolymers related with compositions were examined. FT‐IR spectra showed that most of the urea carbonyl groups associated in hydrogen bonding, while urethane carbonyls only partially did so. Thermal and mechanical properties were investigated through differential scanning calorimetry and tensile testing. These thermal and mechanical properties are discussed from the viewpoint of microphase domain separation of hard and soft segments. © 1994 John Wiley & Sons, Inc.
Plasma modification of cellulose fibers: Effects on some polymer composite properties
Authors: Felix Johan , Gatenholm Paul , Schreiber H. P. 
Published: April 2003

AbstractCellulose fibers have been surface‐modified by selected cold, microwave plasma treatments. Inverse gas chromatographic (IGC), XPS, and SEM analyses showed surface treatment to be incomplete, but, nevertheless, effective in controllably altering the acid/base interaction balance of fiber surfaces. Surface‐modified fibers were used in composites with polystyrene (PS), chlorinated polyethylene (CPE), and polypropylene (PP) as, respectively, basic, acidic, and neutral matrices. Favorable acid/base interactions led to enhanced mechanical properties and increased glass transition temperatures of composites. Acid/base interaction appears to be an important, though not the sole consideration, in the design of superior systems using cellulose fibers as reinforcing agents. As expected, in the case of PP composites, acid/base considerations proved to be irrelevant. © 1994 John Wiley & Sons, Inc.
Changes in the fine structure of silk fibroin fibers following gamma irradiation
Authors: Tsukada Masuhiro , Freddi Guiliano , Minoura Norihiko 
Published: April 2003

AbstractThe physicochemical changes of silk fibers irradiated with γ‐rays was studied in relation to the amount of absorbed does in the range 0–21 Mrad. The yellowing index (b/L) suddenly increased at low dose for both raw and degummed silk fibers. An equilibrium value was attained from 10 Mrad upward. The tensile properties were significantly affected by exposure to γ‐rays. Both strength and elongation at break decreased at almost the same rate and extent, attaining a final value that was one‐half of the untreated control. The birefringence and isotropic refractive index of exposed silk fibers decreased, the effect being larger in the low dose range, suggesting a decrease of crystallinity and molecular orientation. X‐ray diffraction curves, however, demonstrated that the crystalline structure remained unchanged even after exposure of the highest γ‐ray dose. The thermal behavior evaluated by DSC and TMA measurements showed that the γ‐irradiation induced a slight decrease of thermal stability in irradiated silk fibers, this effect being detectable only at 21 Mrad of the absorbed dose. The dynamic viscoelastic behavior suggested that the thermal movement of the fibroin molecules in the amorphous and crystalline regions increased with increasing absorbed dose, attributing to the physicochemical modifications induced by the ionizing radiations. © 1994 John Wiley & Sons, Inc.
Preparation of flame‐retardant polyethylene foam of open‐cell type by radiation grafting of vinyl phosphonate oligomer
Authors: Kaji Kanako , Yoshizawa Iwao , Kohara Choji , Komal Kuniaki , Hatada Motoyoshi 
Published: April 2003

AbstractFlame‐retardant polyethylene foam was successfully obtained by grafting a vinyl phosphonate oligomer onto polyethylene foam of an open‐cell type using a simultaneous radiation grafting technique. The foam was impregnated with the oligomer and irradiated in a nitrogen atmosphere with an electron beam. The grafted foam thus obtained was found to pass the three most severe flammability tests that have to be cleared when the foam is to be used for materials where high flame‐retardant property is required. No hydrogen cyanide was detected in burning exhaust gas of the grafted foam. © 1994 John Wiley & Sons, Inc.