bluuebunny/crossref_metadata_2025_split huggingface dataset:
Network formation during cocure of phenolic resins with vinyl‐ester and epoxy‐amine systems for use in multifunctional composites
Authors: Singh K. P. , Palmese G. R. 
Published: January 2004

AbstractTraditionally, multilayered composites have been manufactured in multiple steps that involve the fabrication of each layer separately and the bonding them together by using adhesives or secondary bonding. More recently, manufacturing techniques have been developed that enable the manufacture of multilayered hybrid composite parts in a single step. In one such technique known as coinjection resin transfer molding (CIRTM), two or more resins are simultaneously injected into a mold filled with a stationary fiber bed. This method not only cuts down manufacturing costs and time, but also offers the potential of cocure of the adjacent thermosetting resins inside the mold, which could aid in the formation of a tougher interphase between the layers and improve long‐term durability. The advantages offered by coinjection are, however, dependent on the successful cocure of the resins involved, and hence, there exists a need to determine compatible resin systems for coinjection. By compatible, it is meant that the resins must cure when in contact with each other, have compatible cure cycles (i.e., cure temperature, cure time, etc.), and result in acceptable physical and mechanical properties. The most commonly used matrix resins are vinyl‐ester resins. The cure of vinyl‐ester resin was found to be severely limited by contact with phenolic resin. This necessitates an impermeable separation layer between phenolic and vinyl‐ester resins in CIRTM manufacture. A possible candidate for this separation layer was epoxy‐amine‐based prepregs or adhesive layers. Thus, the cocure of mixtures of phenolic with epoxy‐amine was studied, and it was found that phenolic resin significantly affects the cure of epoxy‐amines. A model to quantify the effect of phenolic resin on the cure of epoxy‐amines has been proposed. By using this model, the fraction of primary amine consumed by the phenolic can be estimated. It was found that increasing the initial amine concentration in the cocure reaction mixture leads to an increase in the epoxy conversion as well as the Tg of the material. Therefore, it is recommended that, in cocure of epoxy‐amine and phenolic resins, the initial concentration of amine must be greater than the stoichiometric amount to compensate for the loss of amine to the phenolic resin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3107–3119, 2004
The effects of polymer‐nanofiller interactions on the dynamical mechanical properties of PMMA/CaCO3 composites prepared by microemulsion template
Authors: Qiang Xi , Chunfang Zhao , JianZun Yuan , Yuan Cheng Shi 
Published: January 2004

AbstractWe prepared novel poly(methyl methacrylate) (PMMA)/CaCO3 nanocomposites by using reverse micelle as a template. The nanoparticles of CaCO3 were prepared by the reverse microemulsion with functional monomer, methyl methacrylate (MMA) as oily phase, and the PMMA/CaCO3 nanocomposite was obtained via polymerization of MMA monomer. The SEM image showed that the nanoparticles of CaCO3 were dispersed in the polymer matrix. Dynamic mechanical analysis (DMTA) was performed to investigate the interaction between the nanoparticles and the polymer chains. In the low‐temperature ripening process, two tan δ peaks were observed in the nanocomposite, corresponding to the glass transitions of the matrix and the interface layer. In the high‐temperature ripening process, only one tan δ peak was observed, suggesting that the interface layer forms a continuous phase. The nanoparticles behave as a physical crosslinker in the interface layer. Modification of the surface of nanoparticles with polyacrylamide and poly(N,N′‐methylenedisacrylamide) in the nanocomposite did not show an appreciable effect on the interaction of nanoparticles with the matrix. Upon removal of the aqueous phase around the nanoparticles, we obtained surface‐capped nanoparticles by using an improved reverse microemulsion technique. Another PMMA/CaCO3 nanocomposite was also obtained with these modified nanoparticles. DMTA analysis of this nanocomposite demonstrated that the aqueous phase layer around the nanoparticles does not significantly affect the interaction between the nanoparticles and the polymer chains. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2739–2749, 2004
A novel approach for evaluation of polymeric interface materials for chemical sensors using alternate indirect methods
Authors: Dubey Vinita , Saxena Chhaya , Pandey Lokesh Kumar 
Published: January 2004

AbstractThe heart of a chemical sensor based on bulk or surface acoustic wave devices is a polymer‐coated piezoelectric substrate that selectively sorbs and concentrates the target analyte vapors. The development of such sensors often necessitates the screening and evaluation of suitable polymeric interface materials meeting the specified sensitivity and selectivity toward the analytes of interest. The magnitude and dynamics of sorption–desorption of the vapors in the polymer and the extent of polymer–vapor interactions largely determine the performance of a sensor. The standard protocol used for the purpose is rather tedious, involving the generation and calibration of individual analyte vapors, with stringent control on temperature, humidity, and test parameters. This article outlines four different alternative techniques based on mass uptake of the analyte vapors, on its partitioning in polymers, or both, which in combination can determine the characteristics of an interface material used for coating a piezoelectric substrate in acoustic wave‐based chemical sensors. These methods were applied to poly(ethylene maleate), a representative interface material. The analytes ranged from volatile organic chemicals to sarin—a chemical warfare agent—and its simulant, dimethyl methylphosphonate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3428–3432, 2004
Efficient method for recycling poly(ethylene terephthalate) to poly(butylene terephthalate) using transesterification reaction
Authors: Kulkarni Neeta G. , Avadhani C. V. , Sivaram S. 
Published: January 2004

AbstractA method of recycling postconsumer poly(ethylene terephthalate (PET) using transesterification was studied. Shredded flakes of postconsumer PET waste were transesterified with higher diols, such as 1,4‐butanediol, 1,4‐cyclohexane dimethanol, and 1,6‐hexanediol, to yield copolyesters in the presence of Ti(iPrO)4 and Sb2O3 as catalysts. The extent of the formation of undesirable tetrahydrofuran side products was dependent on the molar ratio of PET to1,4‐butanediol and the time of reflux during transesterification. Quantitative insertion of the butylene moiety into PET could be achieved under appropriate reaction conditions. The mechanical properties of PBT obtained by a transesterification reaction of PET with 1,4‐butanediol were comparable to those of virgin PBT (obtained by direct reaction of dimethyl terephathalate with 1,4‐butanediol). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3720–3729, 2004
Cephazoline sodium release from poly(N‐isopropyl acrylamide‐co‐N,N‐dimethylacrylamide) hydrogels
Authors: Escobar J. L. , García D. , Valerino A. , Zaldívar D. , Hernáez E. , Katime Issa 
Published: January 2004

AbstractHydrogels are hydrophilic polymers that swell to an equilibrium volume in the presence of water, preserving their shape. The dynamic swelling behavior of poly(N‐isopropylacrylamide‐co‐N,N‐dimethylacrylamide) [poly(NIPA‐co‐DMA)] copolymers at 37°C was investigated. It was observed that the swelling degree in the copolymers decreases with the N‐isopropylacrylamide content. In addition, the liberation mechanism was found to be Fickian. Diffusion coefficients according to Fick′s law as a function of the N‐isopropylacrylamide concentration and results of the release process are reported. The kinetics of cephazoline sodium release from poly(NIPA‐co‐DMA) hydrogels with different compositions was studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3433–3437, 2004
Preparation and properties of heterocyclically conjugated poly(3‐hexylthiophene)–clay nanocomposite materials
Authors: Yu Yuan‐Hsiang , Jen Chien‐Chih , Huang Hsiu‐Ying , Wu Pei‐Chi , Huang Chao‐Cheng , Yeh Jui‐Ming 
Published: January 2004

AbstractA series of heterocyclically conjugated polymer–clay nanocomposite (PCN) materials that consisted of organic poly(3‐hexylthiophene) (P3HT) and inorganic montmorillonite (MMT) clay platelets were prepared byin situoxidative polymerization with FeCl3as an oxidant. The as‐synthesized PCN materials were characterized by Fourier transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (WAXRD), and transmission electron microscopy (TEM). The effects of the material composition on the anticorrosion, gas barrier, thermal stability, flammability, mechanical strength, and electrical conductivity properties of the P3HT and PCN materials were studied by electrochemical corrosion measurements, gas‐permeability analysis (GPA), thermogrametric analysis (TGA), limiting oxygen index (LOI) measurements, dynamic mechanical analysis (DMA), and a four‐point probe technique, respectively. The molecular weights of extracted and bulk P3HT were determined by gel permeation chromatography (GPC) with THF as an eluant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3438–3446, 2004
Novel V‐shaped negative temperature coefficient of conductivity thermistors and electromagnetic interference shielding effectiveness from butyl rubber–loaded boron carbide ceramic composites
Authors: El‐Tantawy Farid , Dishovsky Nikolay 
Published: January 2004

AbstractThe presentation of a new conductive composite with good effective applications like negative and positive temperature coefficient of conductivity thermistors (i.e., V‐shaped thermistors) and electromagnetic interference shielding effectiveness (EMI) was the aim of this study. The effect of boron carbide (B4C) contents on the vulcanization characteristics and network structure of butyl rubber (IIR) composites were analyzed in detail. The prediction of the type of crosslinks based on the affine and phantom network theory was also analyzed. The influence of the volume fraction of B4C on the dc conductivity and thermoelectric power was investigated. The electrical and dielectric properties of IIR composites were investigated. The results suggest that the conduction occurs by a tunneling mechanism and behaves as a p‐type semiconductor. Isothermal resistance at different temperatures, as a function of B4C content, was displayed. The current–voltage characteristics showed properties of switches, which were explained by coulombic repulsive force. For practical applications, as self‐electrical heating the temperature–time cycles were investigated under certain applied power. It was found that increasing the B4C content increases the thermal stability of the composite. However, the theoretical modeling of the current–voltage characteristic is very useful for planning groups in industrial applications of conducting polymer composites. Furthermore, the endurance test under applied power indicates that the proposed composites could be useful as temperature sensors with good reliability. Specific heat as a function of B4C contents was evaluated by experimental and various energy balance models. Furthermore, the temperature dependency of thermal conductivity and thermal diffusivity were investigated. Finally, the standing wave ratio, reflection coefficient, return loss, and attenuation of IIR/B4C composites were studied in the 1‐ to 4‐GHz frequency range. The resulting values of electromagnetic interference shielding effectiveness were compared with theoretical models. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2756–2770, 2004
Electrical and mechanical properties of expanded graphite‐reinforced high‐density polyethylene
Authors: Zheng Wenge , Lu Xuehong , Wong Shing‐Chung 
Published: January 2004

AbstractHigh‐density polyethylene (HDPE) was reinforced with expanded and untreated graphite in a melt‐compounding process. Viscosity increased upon addition of graphite phase, with the expanded graphite (EG) showing more dramatic rise than the untreated graphite (UG) in viscosity. The increase in viscosity was attributed to the increased surface‐to‐volume ratio for the EG filler after acid treatment. Electrical conductivity also increased from that pertaining to an insulator to one characteristic of a semiconductor. The EG system showed a lower percolation threshold for transition in conductivity compared to that in the UG system. DSC results indicated that the fillers acted as a nucleating agent in inducing the crystallization of HDPE in the composites. However, the overall degree of crystallinity and melting temperature of HDPE decreased with the addition of EG and UG. Mechanical properties improved as a function of filler content but the overall enhancement was not impressive. It was conjectured that the filler–matrix interface was not optimized in the melt‐mixing process. However, the role of EG as a reinforcement phase for both electrical and mechanical properties was unambiguously established. The EG composites demonstrated potentially useful attributes for antistatic, barrier, mechanical, electrical, and cost‐effective applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2781–2788, 2004
Structure and mechanical properties of uniaxially oriented films of syndiotactic polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide) blends
Authors: Dikshit A. K. , Kaito A. 
Published: January 2004

AbstractThe structure and mechanical properties of highly oriented films of a miscible blend of syndiotactic polystyrene and poly(2,6‐dimethylphenylene‐1,4‐oxide) (sPS/PPO) were studied in the composition range of sPS/PPO = 10/0 to 5/5. The oriented films were prepared by stretching the amorphous films of the blends. Wide‐angle X‐ray diffraction and polarized FTIR spectroscopy were used to analyze the amount of mesophase and molecular orientation. Drawing of the amorphous films of sPS and sPS/PPO blend induced a highly oriented mesophase. The mesophase content increases with increasing draw ratio and becomes nearly constant above a draw ratio of 3. Under the same draw ratio, the mesophase content decreases with increasing PPO content. The orientation function in the mesophase is as high as 0.95–0.99 irrespective of the composition and draw ratio. On the other hand, the orientation of molecular chains in the amorphous phase and mesophase increases with increasing draw ratio, and it decreases with increasing PPO content. The drawn films of pure sPS show high strength and high modulus in the drawing direction, but exhibit low strength in the direction perpendicular to the drawing. In the case of sPS/PPO = 7/3 blend, however, the ultimate strength in the perpendicular direction was dramatically improved compared with that of pure sPS and the ultimate strength in the parallel direction was similar to that for the oriented pure sPS. The improved mechanical properties in the sPS/PPO blends were discussed in relation to the structural characteristics of the sPS/PPO blend system. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2789–2797, 2004
Viscoelastic and conductive characteristics of titanium carbide/polyethylene composites in relation to their structural parameters
Authors: Kataoka Mitsuhiro , Masuko Toru 
Published: January 2004

AbstractTitanium carbide (TiC)/polyethylene (PE) composite is a candidate for a positive‐temperature coefficient resistor, which is used for a self‐recoverable element that provides protection from overcurrents in many kinds of electrical devices. In the present study, the PE‐based composites containing various volume fractions (ϕ) of TiC were prepared, after which their viscoelastic characteristics were investigated compared against their electric conductivity as a function of temperature. When the value of ϕ exceeded 0.39, the resistivities of the sample decreased steeply with increasing TiC content. The resistivity of the specimen maintained a constant value of about 0.1 Ωcm in the range of ϕ values > 0.52. Alternatively, the changes in the storage moduli at room temperature with various ϕ values of the samples could be expressed by a modified Kerner equation with the maximum ϕ value of 0.67. Melting behaviors of the samples were also examined and discussed in terms of their morphological features. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3134–3139, 2004
Molecular weight distribution of poly(dimethyl diallyl ammonium chloride): Analysis within the framework of irreversible aggregation models
Authors: G. V. Koslov , Yu A. Malkanduev , G. E. Zaikov 
Published: January 2004

AbstractThe results of the present study have shown that the molecular weight distribution of polydimethyldiallyl ammonium chloride is simulatable and predictable within the framework of the irreversible cluster–cluster aggregation model. The shape and position of a curve of molecular weight distributiion are influenced by a number of factors, for example, by macromolecular coil structure, stochastic contribution of a coil environment to polymerization intensity, and level of coil destruction during polymerization. These factors can be linked by simple relationships to technical characteristics of the polymerization process, which is especially important for fractal applictions of the proposed theoretical model. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3144–3147, 2004
Reaction kinetics modeling and thermal properties of epoxy–amines as measured by modulated‐temperature DSC. II. Network‐forming DGEBA + MDA
Authors: Swier Steven , Van Assche Guy , Van Mele Bruno 
Published: January 2004

AbstractReaction‐induced vitrification takes place in the network‐forming epoxy–amine system diglycidyl ether of bisphenol A (DGEBA) + methylenedianiline (MDA) when the glass‐transition temperature (Tg) rises above the cure temperature (Tcure). This chemorheological transition results in diffusion‐controlled reaction and can be followed simultaneously with the reaction rate in modulated‐temperature DSC (MTDSC). To predict the effect of Tcure and the NH/epoxy molar mixing ratio (r) on the reaction rate in chemically controlled conditions, a mechanistic approach was used based on the nonreversing heat flow and heat capacity MTDSC signals, in which the reaction steps of primary (E1OH = 44 kJ mol−1) and secondary amine (E2OH = 48 kJ mol−1) with the epoxy–hydroxyl complex predominating. The diffusion factor DF as defined by the Rabinowitch approach expresses whether the chemical reaction rate or the diffusion rate determines the overall reaction rate. A model based on the free volume theory together with an Arrhenius temperature dependency was used to calculate the diffusion rate constant in DF as a function of conversion (x) and Tcure. The relation between x, r, and Tg, needed in this model, can be predicted with the Couchman equation. An experimental approximation for DF is the mobility factor DF* obtained from the heat capacity signal at a modulation frequency of 1/60 Hz, normalized for the effect of the reaction heat capacity in the liquid state and the change in Cp in the glassy region with x and Tcure. In this way, an optimized set of diffusion parameters was obtained that, together with the optimized kinetic parameters set, can predict the reaction rate for different cure schedules and for stoichiometric and off‐stoichiometric mixtures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2814–2833, 2004
Modification of acrylonitrile‐butadiene‐styrene terpolymer by graft copolymerization with maleic anhydride in the melt. II. Properties and phase behavior
Authors: Qi Rongrong , Qian Junling , Chen Zhefeng , Jin Xing , Zhou Chixing 
Published: January 2004

AbstractThe graft copolymerization of maleic anhydride (MAH) onto acrylonitrile‐butadiene‐styrene terpolymer (ABS) using dicumyl peroxide and benzoyl peroxide as the binary initiator and styrene as the comonomer in the molten state was described. The properties and phase morphologies of the modified products (ABS‐g‐MAH) were studied. The results indicate that the melt flow index (MFI) of ABS‐g‐MAH increases with the increase of MAH content, the initiator concentration, and the screw speed, whereas the MFI decreases with the increase of temperature. The impact strength and the percentage elongation of ABS‐g‐MAH both decreased and the tensile strength of ABS‐g‐MAH increased slightly as the grafting degree increased. The phase inversion behavior of the modified product was observed by transmission electron microscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2834–2839, 2004
Binder fiber distribution and tensile properties of thermally point bonded cotton‐based nonwovens
Authors: Rong Haoming , Bhat Gajanan S. 
Published: January 2004

AbstractCotton‐based nonwovens are generally produced by carding and then bonding. One of the most important characteristics of nonwoven materials is the uniformity of their structure and properties. However, the carded webs always have irregularities caused by processing and material variables. The binder fiber distribution in carded cotton‐based nonwoven fabrics was analyzed based on the crystallization behavior of one of the components of the binder fibers by DSC. The effects of process parameters, such as bonding temperature and binder fiber component, on the uniformity were discussed in detail in this article. Also, the relationship of binder fiber distribution and the strip tensile property and single‐bond tensile strength were investigated. The results showed that if the binder fibers were not well distributed in the fabric, it would be hard to get the same trend of temperature effect on tensile property for the strip and single‐bond tests. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3148–3155, 2004
Studies of the chemical and pore structures of the carbon aerogels synthesized by gelation and supercritical drying in isopropanol
Authors: Fu Ruowen , Zheng Bo , Liu Jie , Weiss Steve , Ying Jackie Y. , Dresselhaus Mildred S. , Dresselhaus Gene , Satcher Joe , Baumann Theodore 
Published: January 2004

AbstractThe carbon aerogels prepared by a new method through gelation and supercritical drying in isopropanol were characterized by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy, and a surface area analyzer. Their chemical structure, morphology, and pore structure are discussed. We found that all of these carbon aerogel (CA‐IPA) samples have almost the same carbon and oxygen elemental states, as well as similar oxygen‐containing groups. The curve fitting of the C1s XPS spectra of the samples for characterizing oxygen‐containing surface groups can be performed by assuming the peak type to be a Gaussian–Lorentzian Cross Product, but we cannot obtain good results using a Gaussian lineshape. When the mass density of the CA‐IPA decreases, the mesopores and macropores of the samples are found to grow, but the size and the shape of individual carbon nanoparticles in various CA‐IPA samples do not apparently change. The micropore volume of the CA‐IPA samples increases with a decrease in the mass density, while the mesopore volume has a maximum at a certain mass density. The CA‐IPA samples have a very narrow micropore distribution at about 0.5 nm. The mesopore distribution of the CA‐IPA is widened and the average pore size increases as the mass density of the sample decreases. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3060–3067, 2004