bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamics and structure development during high‐speed melt spinning of nylon 6. II. Mathematical modeling
Authors: Patel Rajen M. , Bheda Jayendra H. , Spruiell Joseph E. 
Published: April 2003

AbstractA mathematical model of the melt spinning process that includes crystallization has been used to compute the velocity, diameter, temperature, and birefringence as a function of distance from the spinneret. An improved inversion procedure is described and is shown to give better results for the computed apparent elongational viscosity and heat‐transfer coefficient data. The computed profiles have been compared directly to the experimental profiles determined earlier and reported in Part I of this paper. The results show that the model describes the major features of the melt spinning process. The reasons for the observed differences between experimental profiles and those computed from the model are discussed.
Ionomers: Two formation mechanisms and models
Authors: Han Keling , Williams H. Leverne 
Published: April 2003

AbstractThe FT IR spectra for different degrees of neutralization of ionomers based on poly(ethylene–methacrylic acid) copolymer were obtained. They involve the alkali metal ions (such as lithium, sodium, potassium, rubidium, and cesium), the alkaline earth metal ions (such as magnesium, calcium, strontium, and barium), and the transition metal ions (zinc and copper). Through the analysis of these spectra it can be deduced that there are two formation mechanisms and corresponding models for the ionomers: a cluster–multiplet model and a coordinated complex model. Also, it can be seen that the metal cations play an important role in the structure of an ionomer. By comparing the spectra of the metal ionomers at different temperatures as well as the spectra of the metal ionomers before and after water immersion, the existence of the two formation mechanisms and models can be inferred further.
Shrinkage force studies of oriented polyethylene terephthalate
Authors: Long S. D. , Ward I. M. 
Published: April 2003

AbstractShrinkage force measurements on drawn polyethylene terephthalate fibres have been evaluated in terms of the elastic behaviour of a molecular network. It is shown that for low network deformations the classical theory of Kuhn and Grün describes the stress‐optical behaviour very well. For high deformations, the recent theory of Edwards and Vilgis has been found to give a satisfactory description of the data. It also provides some tentative insights into the structure of the spun yarns.
Influence of continuous stabilization on the physical properties and microstructure of PAN‐based carbon fibers
Authors: Ko Tse‐Hao 
Published: April 2003

AbstractA continuous stabilization and carbonization process was used to prepare polyacrylonitrile (PAN)‐based carbon fibers. The stepwise stabilization of PAN fibers was tried at various temperatures. The effect of stepwise stabilization on the physical properties and microstructure of the final carbon fibers is reported in this article. The fixed temperature in stepwise stabilization is kept below the fusion temperature of PAN precursors to avoid overstabilization of the fibers. The optimum stepwise stabilization process not only increases the amount of ladder polymer in stabilized fiber but also improves the physical and mechanical properties of the resultant carbon fibers. The formation of closed pores from open pores in carbon fiber occurs at 1100°C, but the formation of closed pores occurs at 200°C lower for carbon fiber developed from overstabilized fiber. The effect of continuous stepwise stabilization on the properties of resulting stabilized fibers and the variation in physical properties, element composition, and microstructure of carbon fibers during the carbonization process are also reported in this article.
Molecular weight characterization of poly(acrylamide‐co‐sodium acrylate). I. Viscometry
Authors: Wu X. Y. , Hunkeler D. , Hamielec A. E. , Pelton R. H. , Woods D. R. 
Published: April 2003

AbstractMark–Houwink constants for polyacrylamide and poly(acrylamide‐co‐sodium acrylate) in 0.2M Na2SO4 were measured using eight fractionated samples of polyacrylamide and 26 hydrolyzed polyacrylamide samples. The dependence of K and a on the copolymer compositions was found for the range of acrylate content 6 ∼ 40 mol %. A relationship between intrinsic viscosity and acrylate content in the form of square root law was found. Molecular weights of copolymer samples with various compositions were estimated using viscometry with Mark–Houwink equations established in this work. The molecular weights of narrow MWD copolymer samples could be measured with an error of ±5%, whereas those of broad MWD copolymer samples with an error of ±8%.
Effects of the processing conditions and blending with linear low‐density polyethylene on the properties of low‐density polyethylene films
Authors: Yilmazer Ulku 
Published: April 2003

AbstractEffects of blending low‐density polyethylene (LDPE) with linear low‐density polyethylene (LLDPE) were studied on extrusion blown films. The tensile strength, the tear strength, the elongation at break, as well as haze showed more or less additivity between the properties of LDPE and LLDPE except in the range of 20–40% where synergistic effects were observed. The LLDPE had higher tensile strength and elongation at break than did the LDPE in both test directions, as well as higher tear strength in the transverse direction. The impact energies of the LLDPE and the LDPE were approximately the same, but the tear strength of the LLDPE was lower than that of LDPE in the machine direction. The comparative mechanical properties strongly depend on the processing conditions and structural parameters such as the molecular weight and the molecular weight distribution of both classes of materials. The LLDPE in this study had a higher molecular weight in comparison to the LDPE of the study, as implied from its lower melt flow index (MFI) in comparison to that of the LDPE. The effects of processing conditions such as the blow‐up ratio (BUR) and the draw‐down ratio (DDR) were also studied at 20/80 (LLDPE/LDPE) ratio. Tensile strength, elongation at break, and tear strength in both directions became equalized, and the impact energy decreased as the BUR and the DDR approached each other.
Glass‐fiber‐reinforced polypropylene/EPDM blend. I. Melt rheological properties
Authors: Gupta A. K. , Kumar P. Krishna , Ratnam B. K. 
Published: April 2003

AbstractMelt rheological properties of the blend of isotactic polypropylene (PP) and ethylene propylene diene rubber (EPDM) at varying ratios and of the glass fiber (GF) filled PP and PP/EPDM blend by varying both GF loading and blending ratio of the polyblend matrix are studied. Rheological measurements at 220°C in shear rate range 101−104s−1 were made on a capillary rheometer. Scanning electron micrographs of the extrudates are presented to show the morphology and the alignment of the glass fibers with respect to the flow direction. Variations of pseudoplasticity index, melt viscosity, and melt elasticity with EPDM content in PP/EPDM blend, and with varying GF content at any given composition of the matrix in PP/EPDM/GF ternary system, in the studied range are presented and discussed. Resultes on melt viscosity and melt elasticity show (i) reduced effect of GF at high shear rates on these properties and (ii) upward deviation of melt viscosity versus shear rate curve at low shear rates. A change in flow behavior in presence of GF is observed around a critical shear rate 2 × 103 s−1 and is attributed to the difference of interaction of GF and the dispersed rubber droplets at high and low shear rates. Elastic recovery showed nonequilibrium behavior at low shear rates.
Degradation of polyethylene–starch blends in soil
Authors: Goheen S. M. , Wool R. P. 
Published: April 2003

AbstractBinary polymer films containing different percentages of corn starch and low‐density polyethylene (LDPE) were exposed to soils over a period of 8 months and monitored for starch removal and chemical changes of the matrix using FTIR spectroscopy. A standard curve using the area of the CO stretch band and an empirical second‐degree polynomial to fit the data made it possible to calculate starch concentration over a wide range (0–46% by mass). Starch removal was found to proceed rapidly during the first 40 days and to nearcompletion in very high starch blends (52% and 67% by weight). Starch removal was slower, consisting of mostly surface removal in 29% starch blends. Weight loss data supported spectroscopic data showing similar gross features. Weight loss and spectroscopic data were consistent with percolation theory and suggested that starch removal continues past 240 days. Degradation rates in different soils containing different amounts of organic matter were approximately the same after a period of a few weeks. IR analysis did not show significant chemical changes in the polyethylene matrix after 240 days. However, the matrix did show evidence of swelling, an increase in surface area, and removal of low molecular weight components.
Preparation and characterization of biscyanamide resins containing o‐substituted groups or phenyl–ether linkage
Authors: Suzuki Masao , Nagai Akira , Suzuki Masahiro , Takahashi Akio 
Published: April 2003

AbstractNew biscyanamides containing o‐substituted groups or a phenyl‐ether linkage were synthesized. The curing reaction behaviors of the biscyanamides were investigated. All the prepared biscyanamides began to polymerize as soon as they melted after being put on a heated plate beyond a certain temperature. The cured resins of each biscyanamides were prepared on the optimal conditions. Optimal conditions for cured resins were obtained from the curing reaction behaviors of each biscyanamide by differential scanning calorimetry (DSC). The effect of chemical structures of the biscyanamides on the thermal and mechanical properties of the cured resins such as seen by thermal gravimetric analysis (TGA), density, and flexural strength were studied. The introduction of alkyl groups into the ortho position decreased intermolecular interactions. The introduction of a long phenyl‐ether linkage into the structure gave a broad exothermal peak in the DSC and good workability for the preparation of the cured resins. Moreover, the extension between cross‐linkings improved the flexibility of the cured resins. The cured resins with fluorine‐containing substituent groups also had better thermal stability in the air compared with hydrocarbon group resins.
The influence of pyrolysis on physical properties and microstructure of modified PAN fibers during carbonization
Authors: Ko Tse‐Hao 
Published: April 2003

AbstractModification of polyacrylonitrile (PAN) fibers with potassium permanganate has reduced the time required for stabilization and also improved the mechanical properties of the resulting carbon fibers. In this study, the effect of modification on the physical properties, microstructure, and elemental composition of fibers during the carbonization process was examined for the first time. The resulting carbon fibers developed from modified PAN fibers had a higher density, a greater stacking size (Lc), and a higher preferred orientation than those developed from unmodified PAN fibers. The carbon fibers developed from the modified PAN fibers also showed an improvement in tensile strength from 20 to 40%. These fibers showed a radial structure in the fracture surface and were somewhat different structurally in the cross section than were the carbon fibers developed from the original PAN fibers. A model for the structure of both carbon fibers is presented. The relationship between the formation of closed pores from open pores and the variety of cumulative pore area during the heat‐treatment stage is also discussed.
Preparation of pH sensors by covalent linkage of dye molecules to the surface of polystyrene optical fibers
Authors: Rao B. S. , Puschett J. B. , Matyjaszewski K. 
Published: April 2003

AbstractFunctional Bromothymol Blue dyes containing amino groups in position 3 have been immobilized on the surface of chlorosulfonated polystyrene fibers and characterized by ESCA. Upon laser irradiation, a modified fiber has been used as an antenna fiber in a twisted pair of plastic optical fibers immersed in aqueous solutions having various pH. The light transmitted to the receiving fiber depends on pH values. This device can be used as a pH sensor.
Thermal behavior and reactivities of prepolymers prepared from aromatic biscyanamides and bismaleimide
Authors: Takahashi Akio , Suzuki Masao , Suzuki Masahiro , Wajima Motoyo 
Published: April 2003

AbstractNovel polymers obtained by reaction of aromatic biscyanamide and bismaleimide compounds were investigated. By heating 4,4′‐methylene bis(o‐methylphenylcyanamide) (BMCA) with 4,4′‐methylene bis (phenylmaleimide) (BMI) at 120°C in N,N‐dimethylformamide (DMF), prepolymers were obtained by the conversion of cyanamide to cyanoguanidine and the addition of an imino group on the double bond of maleimide. The prepolymer showed suitable behavior for thermosetting resin used in molding, i.e., it melted temporarily and then polymerized in an isochronal heating process (5°C/min). On heating above 170°C, the prepolymer could polymerize with ring formation of melamine and isomelamine. The cured product had good heat‐resistant properties.
Thermal conductivity of a polyethylene filled with disoriented short‐cut carbon fibers
Authors: Agari Y. , Ueda A. , Nagai S. 
Published: April 2003

AbstractThermal conductivity of polyethylene composites, filled with randomly dispersed and disoriented (oriented at random) carbon fibers with various aspect ratios, were investigated. Orientation of fibers was quantitatively evaluated by Hermans' parameter. In specimens of isotropic composites, i.e., filled with randomly dispersed and disoriented fibers, thermal conductivity increased with an increase in the fiber length. The result is discussed in comparison with electric conductivity of the composites and explained by the contact probability of filled fibers. Further, it was confirmed that our model previously proposed could be adopted to predict thermal conductivity of the isotropic composite filled with carbon fibers. Also, the effect of fiber length of the C2 parameter included in the model is discussed and C2 was found to have a linear relation with the aspect ratio of fibers at a sufficiently large value. In this study, a shape factor of a filler (aspect ratio) could be directly introduced into the equation, which was shown in our previous paper.
Meta‐bromobiphenol epoxy resins: Applications in electronic packaging and printed circuit board
Authors: Wang Chun‐Shan , Berman J. R. , Walker L. L. , Mendoza A. 
Published: April 2003

AbstractNovel 2,2′,6,6′‐tetrabromo‐3,3′,5,5′‐tetramethyl‐4,4′‐biphenol (TBTMBP), and its epoxy derivatives, were synthesized to incorporate the stable meta‐brominated phenol moiety into epoxy resin systems. In electronic encapsulation and laminate applications, epoxy systems derived from TBTMBP have exhibited superior hydrolytic and thermal stability as compared with the conventional ortho‐brominated epoxy resins. These properties have resulted in an extended device life for semiconductors and a highTgwith excellent blister resistance for the printed circuit board, while meeting flame retardancy requirements as well.
Axial compressive strength of carbon fiber with tensile strength distribution
Authors: Miwa Minoru , Tsushima Eiki , Takayasu Jun 
Published: April 2003

AbstractMeasuring the fiber lengths of the broken pieces and estimating the mean tensile strength from the length just before the final fragment length in tension, efforts were made to estimate the axial compressive strengths of carbon fibers when the tensile strength varies with the length. The estimated compressive strength of carbon fibers decreases with increasing temperature. This decrease in compressive strength may be accounted for by a decrease in the radial compressive force owing to a decrease in the residual thermal stress and a decrease in Young's modulus of the resin matrix. There is a linear relationship between the estimated compressive strength and radial compressing force in the temperature range from room temperature to 80°C. The real compressive strength of the fibers, determined by extrapolating this straight line until the radial compressing force is zero, is about 20% higher than the compressive strength estimated by assuming that the tensile strength is uniform. It is approximately 10–50% of tensile strength. A linear relationship between the fiber axial compressive strength and compressive strength of the unidirectional composites is found. The experimental values agree with the values calculated by the rule of mixtures.
Short fiber–elastomer composites. Effects of matrix and fiber level on swelling and mechanical and dynamic properties
Authors: Ibarra Luis , Chamorro Celia 
Published: April 2003

AbstractThe effects of different types of elastomeric matrix (NR, SBR, CR, NBR) and several levels (10, 15, and 20 parts phr) of short fibers on mechanical properties of uncured and cured composites and on swelling behavior of composites in hydrocarbon solvent are studied. The variation of the dynamic properties, E′, E″, and tan δ is determined as a function of deformation amplitude, temperature, and vibration frequency in composite materials subjected to dynamic deformation. The increase of fiber level does not limit the orientation ability of the fibers, which in all materials seemed to be above 70%. The addition of fiber markedly reduces maximum swelling and entails an increase in material stiffness. In addition, the amount of dissipated energy is increased and hence transformable into heat upon fiber incorporation, which can reach up to 16 times the value corresponding to the matrix alone, in addition to an increase with strain amplitude. The effect is most pronounced in the presumed direction of fiber orientation.The marked reduction of elongation at break (up to values of 7–9% of those of unfilled samples) and the shape of stress‐strain curves point to a good fiber‐matrix adhesion. Dynamic glass transition temperature is displaced toward higher values as a consequence of matrix‐fiber interaction, which increases proportionally to fiber level, thus proving a linear relationship between thermal displacement and the number of interactions between the two phases. By the same token, the apparent activation energy of the relaxation process is enhanced for fiber‐containing materials as compared to the fiber‐free. The fiber composites present a less prominent yet broader transition zone.
Grafting of methyl methacrylate onto silk fibers initiated by tri‐n‐butylborane
Authors: Tsukada Masuhiro , Yamamoto Takashi , Nakabayashi Nobuo , Ishikawa Hiroshi , Freddi Giuliano 
Published: April 2003

AbstractStructural characteristics of the methyl methacrylate (MMA)‐grafted silk fibers using tri‐n‐butylborane as an initiator were analyzed by infrared spectroscopy and differential scanning calorimetry (DSC), and their refractive index and tensile properties were measured. Graft polymerization was promoted by FeCl3 pretreatment of the silk. The graft yield reached a maximum by the immersion in 4% FeCl3 solution for 1 min at 25°C. The infrared spectrum of poly(MMA)‐grafted silk fibers showed overlapped absorption bands of silk fibroin with the β structure and of the grafted MMA polymer. A grafted silk fiber with graft yield of more than 140% exhibited two endothermic peaks at 321°C and 396°C on the DSC curve, attributed to the thermal decomposition of silk fibroin and grafted poly(MMA) chain, respectively. Refractive index measurements suggested that the molecular orientation and the crystallinity of the silk fiber decreased with increasing graft yield. Electron photomicrographs showed that silk was coated by grafted PMMA. The tensile strength of the grafted silk decreased rapidly by the grafting even at a lower level.
Effect of particle size on mechanical properties of epoxy resin filled with angular‐shaped silica
Authors: Nakamura Yoshinobu , Yamaguchi Miho , Okubo Masayoshi , Matsumoto Tsunetaka 
Published: April 2003

AbstractEffect of particle size on the mechanical properties of cured epoxy resins has been studied. Resin was filled with angular‐shaped silica particles prepared by crushing fused natural raw quartz. These particles were sorted into six groups having different mean sizes ranging from 2–47 μm. Flexural and compressive moduli of the cured epoxy resin slightly decreased with decrease in the particle size of the silica, whereas tensile modulus slightly increased. Flexural and tensile strengths increased with decrease in particle size. Fractured surfaces were observed using scanning electron microscopy to clarify the initiation point of fracture.
Curing behavior of epoxy resin having hydroxymethyl group
Authors: Ohashi Keiko , Hasegawa Kiichi , Fukuda Akinori , Uede Kazuo 
Published: April 2003

AbstractA new type of epoxy resin having hydroxymethyl group was synthesized. This epoxy resin was mixed with commercial epoxy resin in various ratios. The mixed epoxy resins were cured with a mixture of 4,4′‐diaminodiphenylmethane and m‐phenylenediamine (molar ratio, 6 : 4) as a hardener. Curing behavior of the epoxy resin systems with the hardener was examined by DSC and TG‐DSC, and parameters of cure reaction were obtained. Viscoelastic properties of cured resin were studied by dynamic mechanical analyzer.It was found that the higher the amount of epoxy resin having hydroxymethyl group, the lower the activation energy (Ea) and the higher the rate constant (k) were. It was also found that the higher the amount of the epoxy resin having hydroxymethyl group, the better heat resistance the fully‐cured resin had.These results were explained as follows: Hydroxymethyl group accelerated an epoxideamine reaction. The crosslinking density of the cured resin was increased because in the hydroxymethyl group occurred a condensation reaction above 200°C.
Graft polymerization of vinyl acetate onto silica
Authors: Browne Thomas , Chaimberg Mark , Cohen Yoram 
Published: April 2003

AbstractA method is reported for the surface grafting of polyvinyl acetate (PVAc) onto modified, nonporous silica. The silica surface was modified by silylation with vinyl(triethoxy) silane followed by graft polymerization of vinyl acetate. The graft yield was measured by thermogravimetric analysis and the monomer conversion was monitored by UV spectral analysis. The rate of the graft polymerization and the graft yield were proportional to the initial monomer concentration. Vinyl acetate conversion followed first‐order kinetics and displayed a trend of increasing initial rate with increasing monomer concentration.