bluuebunny/crossref_metadata_2025 huggingface dataset:
Dimensionless groups for the description of sorption equilibria in dyeing with anionic dyes. I. Inorganic co‐ion exclusion
Authors: Mcgregor Ralph , Iijima Toshiro
Published: April 2003

The equations of a general Donnan Model have been simplified and used to describe the equilibrium sorption of anionic dyes by fibers containing acidic and basic groups. By examining simple situations, the dependence of the sorption behavior on specific dimensionless groups of variables has been clarified. This approach emphasizes common features of different ionic dyeing systems, it can be applied in graphical methods of data analysis, and it has potential applications in process control.
The glass transition temperature (Tg) as an index of chemical conversion for a high‐Tg amine/epoxy system: Chemical and diffusion‐controlled reaction kinetics
Authors: Wisanrakkit G. , Gillham J. K.
Published: April 2003

The glass transition temperature (Tg) is used as a parameter to monitor the isothermal cure of a tetrafunctional aromatic diamine and a difunctional aromatic epoxy system. There is a one‐to‐one relationship between Tg and conversion that is independent of cure temperature, Tcure. Prior to vitrification (Tg = Tcure), the reaction is only kinetically controlled; after vitrification, the reaction becomes diffusion‐controlled. Time‐temperature shifts of Tg vs. In (time) data at different cure temperatures to form a master curve for the kinetically controlled reaction at an arbitrary reference temperature yield a single Arrhenius activation energy (15.2 kcal/mole). The master curve and the reaction activation energy are used in calculating iso‐Tg contours prior to vitrification and also the vitrification contour in the time‐temperature‐transformation (TTT) isothermal cure diagram for the system. The chemical kinetics of the reaction is satisfactorily described by an autocatalyzed reaction mechanism. The overall rate constant of the reaction in both kinetically and diffusion‐controlled regimes is modeled by a combination, in parallel, of the chemical rate constant and the diffusion rate constant. The chemical rate constant has the usual Arrhenius form, whereas the diffusion rate constant is assumed to be given by a modified form of the WLF equation. Results suggest that both primary and secondary amino hydrogens are equally reactive. A theoretical model for calculating Tg as a function of conversion is presented for a network‐forming system with one bond‐forming reaction.
Radiopaque polymers based on acrylated phosphonate esters derived from polyols
Authors: Cabasso Israel , Smid Johannes , Sahni Suresh K.
Published: April 2003

A number of miscible metal salt–polymer systems of acrylated phosphonates derived from various polyols such as glycerol, D‐mannitol, D‐sorbitol, pentaerythritol, and dipentaerythritol are described. The salt–monomer systems could be polymerized radically to form homogeneous transparent glassy polymers. Incorporation of heavy metal salts in polymers imparts radiopacity on otherwise radiolucent materials rendering them useful for X‐ray imaging. The polymer–salt systems have been characterized with the aid of infrared spectroscopy and thermal and radiographic analyses. In these salt–polymer systems, salts are bonded to the polymers predominantly through the phosphoryl's oxygen. The results indicate that about 11 wt % of uranyl nitrate hexahydrate and 12.5 wt % of bismuth bromide impart a radiopacity equivalent to that of aluminum. The glass transition temperatures (Tg) of the salt‐containing polymers are substantially higher than the salt‐free polymers. TheTgvalues seem to depend on the chemical nature of the polymers, concentration of metal salts, and the extent of crosslinking induced through chelation. The analysis indicated complete solubility in the polymer matrices. No melting point endotherms of free salt crystals were detected. Some preliminary adhesion measurements revealed that acrylated phosphonates are excellent adhesion promoters for hard tissues.
Protease immobilization onto porous chitosan beads
Authors: Hayashi Toshio , Ikada Yoshito
Published: April 2003

Water‐insoluble proteases were prepared by immobilizing papain, ficin, and bromelain onto the surface of porous chitosan beads with any length of spacer by covalently fixation. The activity of the immobilized proteases was found to be still high toward small ester substrate, N‐benzyl‐L‐arginine ethyl ester (BAEE), but rather low toward casein, a high‐molecular‐weight substrate. The relative activity of the immobilized proteases with spacer gave an almost constant value for the substrate hydrolysis within the surface concentration region studied. The values of the Michaelis constant Km and the maximum reaction velocity Vm for free and immobilized proteases on the porous chitosan beads are estimated. The apparent Km values were larger for immobilized proteases than for the free ones, while Vm values were smaller for the immobilized proteases. The pH, thermal, and storage stability of the immobilized proteases were higher than those of the free ones. The initial enzymatic activity of the immobilized protease maintained almost unchanged without any elimination and inactivation of proteases, when the batch enzyme reaction was performed repeatedly, indicating the excellent durability.
Chemical modification of poly(substituted‐acetylene). V. Alkylsilylation of poly(1‐trimethylsilyl‐1‐propyne) and improved liquid separating property at pervaporation
Authors: Nagase Yu , Takamura Yuriko , Matsui Kiyohide
Published: April 2003

In order to improve the separation characteristic at pervaporation, the introduction of several kinds of trialkylsilyl groups into poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) was achieved via metalation of PTMSP followed by treating with trialkylchlorosilanes to afford trialkylsilylated PTMSP. Ratio of TMSP monomer unit and trialkylsilylated unit, x/y, was in the range of 95/5 to 80/20. All the chemically modified PTMSP membranes showed ethanol permselectivity at pervaporation of aqueous ethanol solution. Introduction of appropriate length of alkyl groups (methyl, ethyl, propyl, butyl, hexyl, octyl, and decyl groups) into PTMSP effectively enhanced the selectivity. However, excess introduction of octyl and decyl groups or introduction of dodecyl and octadecyl groups caused decrease of selectivity, of which the value was smaller than that of PTMSP membrane. Furthermore, acetone, acetonitrile, dioxane, and isopropanol were efficiently separated from their aqueous solutions at pervaporation through trimethylsilylated PTMSP membrane.
Fracture toughness of particle filled fiber reinforced polyester composites
Authors: Dharmarajan N. , Vipulanandan C.
Published: April 2003

Fracture behavior of polyester composite systems, polyester mortar and glass fiber reinforced polyester mortar, was investigated in mode I fracture using single edge notched beams with varying notch depth. The beams were loaded in four‐point bending. Influence of polymer content on the flexural and fracture behavior of polyester composites at room temperature was studied using a uniform Ottawa 20–30 sand. The polymer content was varied between 10 and 18% of the total weight of the composite. The flexural strength of the polyester mortar systems increase with increase in polymer content while the flexural modulus goes through a maximum. The critical stress intensity factor (KIC) for the optimum polyester mortar (14%) was determined by two methods including a method based on crack mouth opening displacement. TheKICfor polyester mortar is linearly related to the flexural strength. Polyester mortar (18%) reinforced with 4% glass fibers was also investigated, and crack growth resistance curve (KR) was developed with crack extension (Δa). A model has been proposed to represent the fracture toughness with change in crack length,KR‐ Δarelationship, of fiber reinforced polyester composite.
Kinetic model for short‐cycle bulk styrene polymerization through bifunctional initiators
Authors: Villalobos M. A. , Hamielec A. E. , Wood P. E.
Published: April 2003

A model describing the kinetics of bulk styrene polymerization through bifunctional initiators has been developed. The diffusion‐controlled propagation and termination reactions at high monomer conversions are modeled with the free volume theory for polymer solutions. Three different commercially available bifunctional initiators were experimentally evaluated for a wide range of polymerization conditions to study the effect of the reaction rate on the molecular weight and molecular weight distribution. The model predictions for the same polymerization conditions show excellent agreement with the experimental data, for the whole range of conversions, for both reaction rate and molecular weight distribution development, under all the conditions tested. It is demonstrated throughout this study that high molecular weights, very high reaction rates, and narrow molecular weight distributions can be achieved simultaneously by using bifunctional initiators. A comparison between monofunctionally initiated systems with the bifunctionally initiated ones shows that short‐cycle reactions with reductions in polymerization time of up to 75% may be achieved with the bifunctional initiators for a wider range of conditions without significantly affecting the molecular weight and molecular weight distribution of the final product.
New method for the preparation of thick conducting polymer composites
Authors: Ruckenstein Eli , Park Jun Seo
Published: April 2003

A highly porous and absorbable crosslinked polystyrene, prepared by the concentrated emulsion polymerization method, was used as host polymer for the preparation of conducting, large objects, polymer composites. The composites, whose conductivity can be as high as 0.80 S/cm, were prepared by (i) imbibing the host polymer with a pyrrole (or oxidant) solution, (ii) partially drying the imbibed host polymer, and (iii) imbibing again with an oxidant (or pyrrole) solution for polymerization to take place. The electrical conductivity of the composite and the penetration of polypyrrole in the host polymer are influenced by the polymerization conditions (i.e., the concentrations of oxidant and pyrrole and the nature of the solvents used for the oxidant and pyrrole), the order in which the two imbibing solutions are introduced, and the drying time used after the first imbibation. The mechanical properties of the host polymer are improved with the incorporation of polypyrrole. Scanning electron micrographs of the composites indicate that the polypyrrole coats uniformly as a film the inside of the porous host polymer.
Thermal, mechanical, and fracture properties of copolyureas formed by reaction injection molding: Effects of hard segment structure
Authors: Ryan Anthony J. , Bergstromcu Todd B. , Willkomm Wayne R. , Macosko Christopher W.
Published: April 2003

A series of copolyureas containing 50% by weight hard segment have been formed by RIM. The hard segment structure was systematically varied to investigate the effects of urea group density, hard segment crosslinking, relative reaction rates, and to compare the properties of aromatic and aliphatic hard segment materials. In each case the soft segment was based on a 2000 molecular weight polyether diamine. The RIM materials formed ranged from flexible elastomers to brittle plastics depending on composition and were characterized by SAXS, DSC, DMA, tensile stress–strain and fracture mechanics studies. SAXS, DSC, and DMA showed that microphase separation had occurred to give materials with a non‐equilibrium morphology. DMA and tensile stress–strain studies showed the small strain properties to be very sensitive to the volume fraction of glassy material whereas the ultimate properties were dependent on chemical structure of the hard segment. Fracture properties were determined using the single‐edge notch technique. In most cases ductile failure occurred with Gc > 2.5 kJ m−2 and the fracture surfaces showed gross yielding and tearing. In the case of the copolyurea with the highest urea group content, brittle fracture occurred with Gc = 0.06 kJ m−2.
Styrene–butadiene rubber/lead oxide composites as gamma radiation shields
Authors: Abdel‐Aziz M. M. , Badran A. S. , Abdel‐Hakem A. A. , Helaly F. M. , Moustafa A. B.
Published: April 2003

Composites of styrene–butadiene rubber were prepared with three different types of lead oxide, namely, monolead oxide (PbO), lead dioxide (PbO2), and red lead oxide (Pb3O4). Concentrations of Pb3O4 ranging between 17 and 88 wt % were utilized, whereas 87 wt % was used for PbO and PbO2. The prepared composites were investigated for their gamma radiation shielding properties. Moreover, physical and mechanical properties, and electrical conductivity were measured for both the unirradiated and irradiated composites. The highest value obtained for the linear absorption coefficient was 0.424 cm−1 for 88% Pb3O4.
Thermal conductivities of composites in several types of dispersion systems
Authors: Agari Y. , Ueda A. , Nagai S.
Published: April 2003

We measured thermal conductivities as well as electric conductivities of some composites in several types of dispersion systems. The dispersion state, that is, the ease in forming conductive chains in these composites, was estimated by the characteristic electric conductivities and compared with the thermal conductivities. Thus, it became clear that thermal conductivity of a composite was significantly affected by the dispersion state in the composite. Further, it was confirmed that the predictive model proposed in the previous report was adaptable to the thermal conductivity of the composites in several types of dispersion systems. It was made clear that the dispersion state of a composite affected the values C1 and C2 in the previous model.
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

A 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

The 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

Shrinkage 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

A 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

Mark–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

Effects 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

Melt 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

Binary 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

New 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

Modification 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

Functional 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

Novel 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

Thermal 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

Novel 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

Measuring 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

The 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

Structural 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

Effect 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

A 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

A 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.
Synthesis and polymerization of some iodine‐containing monomers for biomedical applications
Authors: Jayakrishnan A. , Thanoo B. Chithambara
Published: April 2003

Triiodophenol and iothalamic acid (5‐acetamido‐2,4,6‐triio‐N‐methyl isophthalamic acid) were converted to their acrylic derivatives by esterfication with methacryloyl chloride and 2‐hydroxyethyl methacrylate (HEMA), respectively. The monomers due to presence of heavy iodine atoms were expected to be radiopaque in nature. The monomers were characterized using TLC, IR, and 1H‐NMR spectroscopy. Both monomers were highly resistant to homopolymerization and copolymerization with other acrylic monomers such as methyl methacrylate (MMA) or HEMA by initiators such as 2,2′‐azobis isobutyronitriie (AIBN) or benzoyl peroxide (BPO) yielding only polymers of low molecular weight. The polymers obtained were charactrized by gel permeation chromatography (GPC) and differential thermal analysis (DTA). The resistance to polymerization is presumably due to the presence of bulky iodine atoms in the monomers sterically hindering the propagation step. The decomposition temperatures of the homopolymers and copolymers were close to 300°. Copolymers of HEMA with both radiopaque monomers incorporated to the extent of 25 wt % in the feed, however, produced polymers with good radiopacity. Copolymers with HEMA were also prepared in the form of microspheres by a solvent evaporation method with the aim of using them as particles in therapeutic embolization. While the polymer based on triiodophenol was found to cause extensive blood haemolysis in in vitro tests, polymer based on iothalamic acid was found to be nonhemolytic in character suggesting that copolymers based on iothalamic acid would be suitable for implantation in the living tissue.
Longitudinal variation in the stress–strain properties of wool fibers
Authors: Dunn Linda A. , Weatherall Ian L.
Published: April 2003

In order to obtain information on possible end‐to‐end differences in the physical properties of wool caused by weathering of the more exposed portions, a comparison has been made of the stress–strain characteristics of the tip and root halves of fibers taken from the midback region of sheep reared outdoors over a 6‐month summer to winter period. The results were further compared with the tip and root halves of fibers taken from animals reared indoors under conditions of essentially continuous darkness. When 11 features of the stress–strain curves were compared, it was found that for the outdoor wools the tip halves had lower initial moduli, higher yield strains, and lower yield moduli than the root halves. In contrast, the dark grown wools showed no end‐to‐end differences. The greater ease of extension of the tip halves of outdoor wools may be attributed to light‐induced diminution in the levels of crosslinking within the keratin structure. The results show that normal environmental influences caused end‐to‐end differences and that longitudinal variations in physical properties may be a typical characteristic of all field grown wools at the time of harvesting.
Mechanisms of antioxidant action: Photoantioxidant activity of polymer‐bound hindered amines. II. Bis acrylates
Authors: Al‐Malaika S. , Ibrahim A. Q. , Rao M. J. , Scott G.
Published: April 2003

1‐Acryloyl‐4‐acryloyloxy‐2,2,6,6‐tetramethylpiperidine (AATP) has been covalently attached to polypropylene under conditions of reactive processing to give substantial concentrations of essentially 100% grafted antioxidant (AATP‐B). Solution of the concentrates showed that at high concentration of grafted antioxidant some homopolymerized AATP was present and the polymer undergoes transient cross‐linking during processing. Concentrates of bound AATP (AATB‐B) when used as conventional additives for polypropylene are very effective photoantioxidants due to conversion to the related polymer‐bound nitroxyl radicals by photosensitized oxidation. A typical commercial hindered phenol, Irganox 1076, when used at low concentration in combination with ‐B also acts as a photosensitizer for nitroxyl formation. Unlike low molar mass‐hindered piperidinoxyl, polymer‐bound nitroxyls are effective thermal antioxidants that synergize very effectively with low concentrations of Irganox 1076.
The curing mechanism and properties of bismaleimide–biscyanamide resin
Authors: Suzuki Masao , Nagai Akira , Suzuki Masahiro , Takahashi Akio
Published: April 2003

Thermoset networks consisting of N, N‐bismaleimidediphenylmethane (BMI) and bis [4‐(4‐cyanamide‐3‐methylphenyl)] methane (BCMM) were investigated with the aim of correlating macroscopic behavior and structure as network composition was varied. The glass transition temperatures of these cured resins obtained from the dynamic mechanical data and thermal expansion data had a distinct minimum at the 50/50 molar ratio of BMI/BCMM. Also, at this molar ratio, the decomposition temperature at a 5% weight loss in helium atmosphere for cured resins was the lowest. These results provided a rough idea of the thermoset network structure.
Peroxide‐initiated grafting of acrylamide on to polyethylene surfaces
Authors: Kildal K. , Olafsen K. , Stori A.
Published: April 2003

Acrylamide has been grafted onto the surface of a polyethlene film with the aid of a peroxide initiator (tert‐butyl peroxyneodecanoate). The peroxide was first swollen into the film from cyclohexane solution; the film was then dried under reduced pressure at room temperature. Excess initiator, adsorbed on the surface, was washed off with acetone. The grafting reaction was carried out by placing the film in a boiling solution of the monomer in water. After grafting, the film was extracted with water to remove monomers and homopolymer. The grafted films were characterized by infrared spectroscopy, X‐ray photoelectron spectroscopy (XPS), gravimetric measurements, and contact angle measurements. The graft yield was found to increase with reaction time up to about 5–15 min and thereafter level off. The presence of air was found to retard the grafting reaction. Increase in monomer concentration gave an almost continuous increase in graft yield, but high concentrations were not necessary to cover the surface of the film with polyacrylamide. This grafting has been found to function, but the process requires further development to reduce the total grafting time before it can be used commercially.
Stress relaxation studies on wool fibers
Authors: Gupta V. B. , Rao D. Rama
Published: April 2003

Stress relaxation studies were made on single fibers of Lincoln, Chokla, and Merino wool in water in the temperature range 2–80°C. Differences in the viscoelasticity of the three wool types were related to differences in their fine structure and morphology. Of the three wools, Merino fibers have the lowest crystalline content and the poorest fibril orientation and packing. This results in greater viscoelastic effects in this wool. Stress relaxation studies have been made in the Hookean, yield, and postyield regions, and the molecular mechanisms of stress relaxation have been discussed.
The color of absorbing scattering fibers having skin‐core structure
Authors: Sokkar T. Z. N. , Kabeel M. A. , Ramadan W. A.
Published: April 2003

A treatment of the color of fabrics is proposed that is an extension of the Allen and Goldfinger approach to the prediction of the color of absorbing scattering substrates. Here, a model of isotropic cylindrical fibers of a skin–core structure in a parallel array is assumed. Using the proposed model, the spectral reflectance curves of ring dye and uniform dye samples are calculated. Their tristimulas values and the color difference between them are calculated to study the effect of ring distribution of dye in the fiber on color of fabric. Refractive indices of undyed and dyed polyester fibers are measured using the Pluta polarizing interference microscope. Illustration are given by microinterferograms.
Dimensionless groups for the sorption of dye and other ions by polymers. II. Hydrochloric acid, C.I. acid blue 25, and polyamides with an excess of basic groups
Authors: McGregor Ralph , Iijima Toshiro
Published: April 2003

The equations of a generalized Donnan model have been used in dimensionless form to describe and analyze the sorption of hydrochloric acid and of C.I. Acid Blue 25 by polyamide fibers containing an excess of basic groups. The method is applicable to a wide variety of ionic sorption systems, and removes some of the restrictions of earlier treatments of the problem. Acid–base reactions, ion exchange processes, electrolyte sorption, and both ion binding and zwitterion formation have been considered.
Impact toughening of polypropylene by ethylene vinyl acetate copolymer
Authors: Gupta A. K. , Ratnam B. K. , Srinivasan K. R.
Published: April 2003

In this article we studied the potential of ethylene vinyl acetate copolymer (EVA) as an impact modifier for isotactic polypropylene (PP). PP/EVA blend in the range 0–40 wt % EVA content is studied by using three grades of EVA containing 9, 12, and 19 wt % VA. Izod impact strength measurements were made at temperatures ranging from liquid nitrogen temperature to 60°C to explore the impact‐toughening effect as a function of blending ratio both at low and above ambient temperatures. The results are compared with various reported blends of PP with other elastomers. Morphological studies through scanning electron microscopy on etched impact‐fractured surfaces are carried out and a correlation of morphology and impact properties at various blending ratios is presented. Finally, a mathematical analysis of the data is performed in terms of second‐degree polynomial to express impact strength as a simultaneous function of two variables, and an equation is proposed that shows the best fit with the experimental data. Relevant contour diagrams, based on the proposed equation, for optimization of properties are also presented.
Thermal properties of wool‐g‐poly(methyl methacrylate) copolymers
Authors: Elangovan V. J. , Saccubai S.
Published: April 2003

The thermal properties of wool fibers can be improved by graft copolymerization with vinyl monomers. Using TGA, DTG, and DSC techniques, the thermal behavior of methyl methacrylate grafted wool fibers was studied. Graft copolymerization was carried out using KBrO3 and substrates such as Fe(II), Co(II), cysteine, cystine, tyrosine, and urea. Of all the systems studied the grafted fibers which involve Fe(II), Co(II), and cystine gave improvement in the thermal stability.
Improvements of the physical properties of fibroin membranes with sodium alginate
Authors: Liang Chuan Xin , Hirabayashi Kiyoshi
Published: April 2003

The effects of sodium alginate on the physical properties of fibroin membranes, such as rupture elongation, rupture strength, water absorption, and thermal properties, were investigated. The experimental results showed the β‐form crystal and β‐form molecular conformation increased due to the increase of intermolecular hydrogen bonds, such as CO‐‐‐HN and CO‐‐‐HO. The kind of intermolecular interaction and β‐form molecular conformation of polymer blends were clarified by 13C–NMR and infrared spectroscopy. The increase in β‐form crystal was examined by X‐ray analysis. Further, membranes were characterized by thermogravimetric analysis (TGA) and by determining their water contents and tensile properties.