bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of critical fiber length for glass fiber‐reinforced thermosetting resins
Authors: Ohsawa Tadashi , Nakayama Akira , Miwa Minoru , Hasegawa Akira
Published: April 2003

In discontinuous fiber‐reinforced composites, the critical fiber length plays an essential role in determining the mechanical properties. A method was devised to accurately determine the critical fiber length and the temperature dependence of the critical fiber length was studied for glass fiberepoxy and glass fiber‐unsaturated polyester resin composites. If a continuous glass fiber is embedded in the matrix and the system is subjected to a tensile strain greater than the fiber ultimate tensile strain, the fiber breaks into many pieces. If the average length of these broken pieces (l̄) is measured, the critical fiber length (lc) is expressed as lc = 4/3l̄. The critical fiber length greatly increases with increasing temperature and the apparent shear strength at the interface, calculated from the critical fiber length, decreases linearly with increasing temperature.
Graft copolymerization of 2‐methyl‐5‐vinyl pyridine to poly(ethylene terephthalate) fibres using a post‐radiation technique
Authors: Hebeish A. , Shalaby S. E. , Bayazeed A. M.
Published: April 2003

Radiation‐induced grafting of 2‐methyl‐5‐vinyl pyridine (MVP) to poly(ethylene terephthalate) fibers (PET) was investigated under a variety of conditions employing a post‐radiation technique. Over a range of a total dose of 1–10 Mrad, increasing the total dose from 1 up to 3 Mrad was accompanied by a significant enhancement in the extent and rate of grafting. Further increase in the total dose caused a decrease. The same situation was encountered with respect to MVP concentration (5%–10%) and polymerization temperature (75°–90°C). A MVP concentration of 8% and a temperature of 85°C constituted the optimal. Addition of copper sulfate at a concentration of 0.05 mmole/l. offset grafting. The effect of the said parameters on homopolymerization occurring during grafting was also investigated.
Physicochemical properties of kevlar 49 fiber
Authors: Penn Lynn , Larsen Fred
Published: April 2003

The high‐strength, high‐modulus Kevlar 49 fiber is widely used today because of its superior properties. In this paper, we discuss the fundamental physicochemical nature of the commercial fiber. It is an extended chain polymer, poly(p‐phenylene terephthalamide), which is highly crystalline. Extensive analysis shows that the material composition is quite consistent from lot to lot and is low in impurities. The fiber absorbs water reversibly; the extent of absorption is related to the ash content. The well‐known interaction of the fiber with ultraviolet light is illustrated with spectra, and the thermal stability of the fiber is demonstrated with various thermal analysis techniques.
Applicability of the two‐dimensional approach to polymer miscibility in pure and mixed organic liquids
Authors: Chen Show‐An , Lai Wen‐Jen
Published: April 2003

Previously it was proposed that the solvent power of a pure or mixed organic liquid for a given polymer can be characterized by two parameters δh and χH. Using these two parameters, a two‐dimensional (2D) solubility diagram can be constructed to predict solubility or insolubility. In the investigation only the polymers, poly(methyl methacrylate), polystyrene, and poly(vinyl acetate), were used to demonstrate the applicability of the 2D method. In this note, applicability of the 2D method to the 33 polymers investigated in Hansen's works is presented.
Radiation‐Induced graft copolymerization of methyl methacrylate on natural and modified wool. II. Sorption behavior
Authors: Varma D. S. , Sadhir R. K.
Published: April 2003

The water vapor sorption‐desorption isotherms of graft copolymers of methyl methacrylate with natural and chemically modified wool (i.e., oxidized, reduced, methylated, and crosslinked) has been investigated. As a result of graft copolymerization a reduction in water absorption was observed. The results have also been analysed in the light of Hailwood–Horrobin equations.
Effect of short thermal treatment on cotton degradation
Authors: Hebeish A. , El‐Aref A. T. , El‐Alfi E. A. , El‐Rafie M. H.
Published: April 2003

Cotton fabric was subjected to thermal treatment for durations ranging from 0.5 to 5 min at a temperature range of 160°C. In comparison with the untreated cotton, the copper number (measure of the aldehyde content) decreased after heating cotton for up to 3 min at 160°, 180°, and 190°C but increased when heating was prolonged to 5 min. Thermal treatment at 200°C or above caused an appreciable increase in the copper number. The carboxyl content increased with time of heating, attained a maximum, and then fell down to reach values which in some cases were lower than that of untreated cotton. Thermal treatment at 180°C caused a substantial reduction in the D. P.; this reduction increased with time of treatment. At the other temperatures there was no significant decrease in D. P. when cotton was heated up to 3 min. The D. P. decreased in these cases only when the thermal treatment was conducted for 5 min. The tensile strength remained practically unimpaired after thermal treatment of the cotton for up to 2 min, regardless of the temperature used within the range studied. A loss in tensile strength of ca. 9% and 13% was observed with fabrics treated for 5 min at 160° and 180°C, respectively. This contrasts with a loss of ca. 4% at 190°C, 7% at 200°C, and 8% at 220°C. The highest dye exhaustion was obtained on cotton which was thermally treated at 180°C prior to dyeing, while the lowest dye exhaustion was obtained on cotton heated at 220°C. Thermal treatment at 160°C left the susceptibility of cotton toward the dyestuff practically unaltered.
The dielectric behavior of natural resin shellac
Authors: Goswami Dipendra Nath
Published: April 2003

The Cole‐Cole method has been applied for an analysis of the dielectric relaxation data of the natural resin shellac, obtained by Bhattacharya in the temperature range 20–110°C. Three relaxation processes were observed for temperatures 20–60°C. At 70°C, two relaxation processes were noticed, whereas only one was observed by Bhattacharya between 20 and 110°C. The relaxations at 80°C and above represented typical Cole‐Cole type. The variation of the static dielectric constant with temperature revealed three distinct slopes, which indicated different phases of the resin during its thermal transition from solid to liquid state. Two “transformation points,” around 40 and 70°C were noted, i.e., the glass transition temperature and melting point of the resin, respectively. Significant changes in static dielectric constant, dielectric increment, relaxation time, and Cole‐Cole distribution parameter were observed during a rise of temperature from 80 to 110°C. The results of the present study indicate that some rearrangement in the teriary disposition of the resin molecules takes place during the rise of temperature from 20 to 110°C.
Removal of trace quantities of nickel from solution
Authors: Randall J. M. , Randall V. G. , McDonald G. M. , Young R. N. , Masri M. S.
Published: April 2003

Chitosan, which is produced from the natural polymer chitin, is a much more efficient scavenger of nickel ion than other natural ion exchange materials tested. An industrial waste containing about 7 ppm Ni2+ and 10,000 ppm Na+ was reduced to less than 0.1 ppm Ni2+ by contact in a packed column of chitosan. Capacity of the chitosan substrate under these conditions was a little more than 1 meq/g. The substrate can be regenerated by contact with buffered NH4Cl at pH 10. The high sodium content of the nickel waste did not prevent sorption of Ni2+, but it apparently produced an interference with atomic absorption spectrophotometer analyses, giving a spurious reading of 0.8 ppm Ni2+ when the major nickel line at 232 nm was used for analysis.
Gel permeation chromatography in the study of the molecular weight distribution vinyl chloride–vinyl acetate copolymer. III. Influence of the incompatibility of polymers and some problems of interpretation of experimental data
Authors: Janča J. , Pokorný S. , Kolínský M.
Published: April 2003

The influence of incompatibility in the ternary systems gel–polymer–solvent and polymer–polymer–solvent on the results of gel permeation chromatography of the copolymer vinyl chloride–vinyl acetate was investigated. The measurements were performed on styrene–divinylbenzene gels and on porous silica gels. Detection in GPC was made using a differential refractometer together with a UV detector, which permitted evaluation of the extent of interactions of the polymer components in the mixture. Some aspects of the GPC data are discussed for the application of universal calibration, the validity of which for the copolymer vinyl chloride–vinyl acetate has been proved.
Controlled release of drugs from hydrogel matrices
Authors: Hosaka Shuntaro , Ozawa Hitoshi , Tanzawa Hiroshi
Published: April 2003

A series of polymers with wide ranges of water absorptivity were prepared and utilized as matrices for the controlled release of drugs. The drugs were introduced into the matrices by use of an appropriate organic solvent. Release rates of erythromycin and erythromycin estolate from hydrogel were analyzed kinetically and found to conform to Higuchi's equation, that is, Mt = A(2DtCsC0)1/2, where Mt is the accumulated amount of released drug at time t, A is the surface area, D is the diffusion coefficient, Cs is the solubility of drug in the hydrogel matrix, and Co is the initial drug content of the preparation in the swollen state. The relationship between the water content of hydrogel and the diffusion coefficient of erythromycin in hydrogel is expressed by the equation D = 3.03 × 10−10 W3.03 (cm2/sec), where W is the water content (%). The release rate of drug can be controlled quantitatively by adjustment of the water content of the hydrogel matrix. A guide to the design for the preparation is suggested.
The radiation‐induced emulsion copolymerization of vinyl chloride with vinyl acetate in an engineering flow system
Authors: Tsai J. T. , Stahel E. P. , Stannett V. T.
Published: April 2003

A flow reactor system was used to study the radiation‐induced emulsion copolymerization of vinyl chloride with vinyl acetate. The emulsion was recirculated from a stirred vessel through transfer lines to a tubular reactor located within a high‐intensity Co‐60 source. The effects of physical chemical variables such as soap concentration, phase ratio, reaction temperature and residence time distribution on the molecular weight properties were investigated. The rate of copolymerization was found to be proportional to the 0.17 power of the soap concentration. Variation of the monomer‐water ratio produced no significant change in rate. The rate increased with an increase in temperature over the range 5–50°C, while the average molecular weights of the copolymer increased with decreasing polymerization temperature. The molecular weight distribution in this engineering system was found to be essentially similar to those produced in a batch system.
New acetylene‐terminated phenylquinoxaline oligomers
Authors: Hedberg F. L. , Arnold F. E.
Published: April 2003

A series of new acetylene‐terminated phenylquinoxaline oligomers and diacetylene compounds have been prepared utilizing 4‐(3‐ethynylphenoxy)benzil. The amorphous materials with molecular weights from 500 to 1460 exhibited softening in the 25–160°C range with a strong polymerization exotherm reaching a maximum at 270–290°C. The addition nonvolatile cure provides materials which show excellent thermoxidative stability and processability for high‐temperature matrix and adhesive resins.
Temperature dependence of the brittleness of cellulose fibers and of chemically modified cellulose fibers
Authors: Zeronian S. H. , Ellison M. S.
Published: April 2003

The temperature dependence of the brittleness of cellulose fibers was studied by the breaking twist angle method. The selected fibers were purified ramie cells, the same cells after fibrous acetylation to form the triacetate, annealed acetylated ramie cells, and mercerized ramie cells. Water acts as a plasticizer to reduce the brittleness of ramie and of mercerized ramie cells but does not appear to affect the brittleness of ramie cells after acetylation. The brittleness of ramie cells is reduced by similar amounts by fibrous acetylation and by mercerization. The brittleness of acetylated ramie cells is increased by annealing, which induces additional crystallization in the cells. The brittleness of ramie and acetylated ramie before and after annealing varied as the test temperature was progressively increased in the range 100–200°C. The effect of temperature on the brittleness of the fibers is interpreted in terms of the relaxation transitions previously determined on the same types of fibers, and in terms of the supramolecular structure of the fibers.
Influence of the ratio of styrene and acrylonitrile in crosslinked polymeric binders for use in high‐temperature polymer concrete composites
Authors: Zeldin A. , Kukacka L. E. , Carciello N.
Published: April 2003

The feasibility of using a monomer composition based on a styrene–acrylonitrile copolymer as a binder in high‐strength and chemically resistant polymer concrete was demonstrated earlier. From this work it is clear that properties of the polymer concrete composite are dependent on the styrene/acrylonitrile ratio. This paper deals with the study of the effect of the styrene/acrylonitrile ratio in styrene–acrylonitrile–acrylamide–trimethylolpropane trimethacrylate monomer formulations on the thermomechanical properties of polymer concrete composites.
Polyether‐based thermoplastic polyurethanes. I. Effect of the hard‐segment content
Authors: Zdrahala R. J. , Gerkin R. M. , Hager S. L. , Critchfield F. E.
Published: April 2003

A series of Polyether‐based thermoplastic polyurethanes, varying in hard‐segment content between 20 and 80 wt. %, was prepared using an (oxypropylene‐oxyethylene) diol of Mn = 2000 as the soft segment and 4,4′‐diphenylmethane diisocyanate extended with 1,4‐butanediol as the hard segment. Physical‐mechanical, dynamic‐mechanical, and specific heat (DSC) data are used to elucidate the mechanical and morphological behavior of these materials. The polyurethanes varied from soft elastomeric (continuous soft phase) to high‐modulus plastic (continuous hard phase) and showed changes in their tensile properties at about 60% hard‐segment content, possibly due to phase inversion.
Polymer effect in electrochromic behavior of oligomeric viologens
Authors: Sato Hirotsugu , Tamamura Toshiaki
Published: April 2003

A series of oligomeric viologens were synthesized in order to investigate the polymer effect in electrochromic behavior of viologen compounds. These materials have a lower first‐step reduction potential and a higher second‐step reduction potential compared with monomeric viologens. As a result, they have wider potential separation, where stable viologene radical salts are produced. Spectroscopic analysis suggests that stable monomeric viologen radical salts do not exist in water, but there is some intramolecular interaction between viologen radicals of the oligomers. This intramolecular interaction is responsible for the reduction behavior and the stability of radical films of oligomeric viologens.
Surface modification of polyethylene by radiation‐induced grafting for adhesive bonding. V. Comparison with other surface treatments
Authors: Yamakawa Shinzo , Yamamoto Fumio
Published: April 2003

Helium gas plasma treatment of low‐density polyethylene (LDPE) yields much lower peel strength than oxidative treatment using chromic acid and oxygen gas plasma. The practical adhesion, the bondability retention, and the bond durability of oxidatively treated LDPE sheets, bonded with epoxy adhesives, have been compared with those of partially hydrolyzed LDPE–methyl acrylate surface grafts. The oxidized surfaces easily lose the bondability by light rubbing with tissue paper, solvent extraction, heat aging, and artifical weathering, whereas the grafted surfaces retain the bondability. The bondability loss is due to removal of the oxidized layer, and the bondability retention is due to retention of the surface homopolymer layer. Conventional antioxidants stabilize the grafted but not the oxidized surfaces against thermal oxidative degradation. The grafted LDPE joints have much higher bond durability in humid environments than those of the oxidized LDPE joints. The dry and wet peel strengths of oxidized LDPE joints are greatly improved by application of primers consisting of a base epoxy resin and organic solvents. An adhesion mechanism involving penetration of epoxy adhesives into the oxidized layers and subsequent reinforcement of the layers by curing of the penetrated epoxy is proposed.
Reinforcement of acrylonitrile copolymer by polymer blending
Authors: Lawton E. L. , Murayama T. , Holland V. F. , Felty D. C.
Published: April 2003

Blends of an acrylonitrile copolymer and a reinforcing polymer were formed by polymerization of the second component in a concentrated solution of the first component. The second component, polyureas or polycarbodiimides, precipitated as an intimate dispersion of particulate domains in the liquid medium. Film or fiber formation by coagulation of the solution containing the second component as particulate matter resulted in a distinct two‐phase blend. Reinforcement of the acrylonitrile copolymer was evidenced by significant increases in dry and wet moduli above the glass transition temperature of the polyacrylic component. The blends were characterized with dynamic mechanical testing and optical and electron microscopy. The blends exhibited two glass transitions corresponding to those of the individual components. The phase domains were evident over the compositional range examined. The method of blending is illustrative of effective reinforcement by interpenetration of phases in the absence of compatibility of the components at the macromolecular level.
Experimental investigations of the influence of molecular weight distribution on melt spinning and extrudate swell characteristics of polypropylene
Authors: Minoshima Wataru , White James L. , Spruiell Joseph E.
Published: April 2003

An experimental study of the influence of molecular weight distribution on the melt spinning and extrudate swell of a series of polypropylenes of varying molecular weight and distribution is reported. Emphasis is given to effects of variations of molecular weight distribution. Narrowing the molecular distribution increases the slope of the elongational viscosity–elongation rate curve, stabilizes the spinline relative to both random disturbances and draw resonance, and decreases both instantaneous and delayed extrudate swell. These results are interpreted in terms of viscoelastic fluid mechanics and earlier experimental studies by the authors of the influence of molecular weight distribution on rheological properties. The influences of these rheological factors on spinline structure development is discussed.
Aromatic poly(1,4‐phenylene‐1,3,4‐oxadiazole) fibers by dry jet‐wet spinning
Authors: Jones R. S. , Soehngen J. W.
Published: April 2003

Fibers of poly(1,4‐phenylene‐1,3,4‐oxadiazole) have been prepared by dry jet‐wet spinning sulfuric acid solutions of the polymer. Polymer was prepared by polymerizing terephthalic acid and hydrazine dihydrochloride in 30% fuming sulfuric acid and directly spinning the resulting solution. Dry jet‐wet spinning allows greater flexibility in conditions than does wet spinning in that spinneret temperature and coagulation bath temperature are independent of one another. Therefore, coagulation may be at temperatures well below those needed at the spinneret to maintain a flowing, extrudable solution. Another common advantage of dry jet‐wet spinning is application of draw to the extruded fiber before coagulation, but in this system, drawing the fiber before coagulation was shown to be a disadvantage. Fiber properties were maximized by spinning with a spinneret temperature of 58–73°C into a coagulation bath at 3–4°C and with an air gap of 1/4 in. Water as a coagulation medium allowed operation at speeds up to 40 m/min, while with 50% sulfuric acid less than half that speed was reached. Application of draw ratios of 3/1 on the coagulated but still swollen fiber combined with high‐temperature treatments at low draw ratios (1.05/l) gave maximum fiber properties–tenacity 6 g/denier, elongation 20–25%, and modulus 200–240 g/denier.
Effect of temperature gradients on cure and stress gradients in thick thermoset castings
Authors: Pusatcioglu S. Y. , Hassler J. C. , Fricke A. L. , McGee H. A.
Published: April 2003

The temperature gradient developed during casting of an unsaturated polyester for which the kinetics of reaction and the heat capacities, thermal conductivities, and densities were known from earlier work was measured experimentally as a function of time in a thick casting and compared with predicted values calculated from a mathematical model. Agreement was excellent. The castings were sectioned and the sections were examined by birefringence. These examinations show good agreement between the temperature gradient developed during cure and the residual stress gradient. This work demonstrates that the extent of cure as a function of position can be predicted from heat transfer calculations if the reaction kinetics and thermal properties are known and that the residual stress gradient is dependent upon the temperature gradient developed.
Effect of crystalline structure on the infrared spectra of γ‐irradiated cotton cellulose
Authors: Moharram M. A. , Hakeem Nagwa Abdel
Published: April 2003

The effect of crystalline modifications on the infrared spectra of γ‐irradiated cotton cellulose is presented. The crystalline modifications were brought about by treating cotton material with an aqueous solution of NaOH of various concentrations. The infrared spectra of the irradiated samples indicate an absorption band corresponding to the absorption of CO groups. It was found that the intensity and frequency of this band depend on the crystalline structure. Thus, it appears at 1735 cm−1 in the spectrum of cellulose I and at 1610 cm−1 in the spectrum of cellulose II.
The use of acetylene glow discharge for improving adhesive bonding of polymeric films
Authors: Moshonov Aharon , Avny Yair
Published: April 2003

Coating of polyethylene (PE), poly(vinyl fluoride) (PVF), poly(tetrafluoroethylene) (PTFE), and poly(vinyl chloride) (PVC) films with flow discharge‐polymerized acetylene was investigated. The influence of glow discharge experimental conditions on the nature of the coated layer, the films' wettability, surface roughness, and adhesive joint strength was determined. It was found that coating of these films with plasma‐polymerized acetylene led to the formation of a rough, crosslinked, irremovable layer with an improved wettability. The presence of the plasma‐polymerized acetylene on the film surface lead to a large improvement in the adhesive joint strength of these films with epoxy adhesive. Best results were obtained with films coated at a low acetylene flow rate. Increase in glow discharge power and treatment time lead to a further improvement.
Membranes prepared from keratin–polyacrylonitrile graft copolymers
Authors: Schaller Johann , Miyamoto Takeaki , Shimamura Kaoru , Inagaki Hiroshi
Published: April 2003

Graft copolymerization of acrylonitrile onto a soluble wool keratin derivative was studied with the reduced and carboxymethylated low‐sulfur protein fraction from wool. Copolymerization was carried out under a variety of conditions with a redox system of (NH4)2S2O8–Na2SO3 in 60% (w/w) aqueous ZnCl2 solution at 10°C. Monomer conversions higher than 90% were obtained by the stepwise addition of initiator. The graft products were successfully separated into grafted copolymer and homopolyacrylonitrile (PAN) by fractional precipitation or solvent extraction with DMF. Grafted PAN were isolated by acid hydrolysis of the keratin backbone. Characterization of grafted and homo‐PAN was carried out by IR spectroscopy, amino acid endgroup analysis, and viscometry. On the basis of the results, effects of polymerization conditions on grafting parameters were discussed. Membranes were prepared from 60% aqueous ZnCl2 solution by using ice‐cold water as the regenerating medium. All the membranes formed from the graft products were transparent. Observation by scanning electron microscopy showed that the surface consisted of rather spherical keratin domains regularly distributed in the PAN matrix. Selective hydrolysis of the keratin domains allowed a new type of porous PAN membrane to be obtained, with the inner walls of the pores being charged with amino acid residues attached to PAN chains as the endgroup.
Copolyester studies. VI. Melt spinning and mechanical properties of tetramethylene terephthalate–poly(tetramethylene oxide) random block copolymers
Authors: Boussias C. M. , Peters R. H. , Still R. H.
Published: April 2003

Fibers were prepared from tetramethylene terephthalate–polytetrahydrofuran (PTHF) random block copolymers, containing the latter in the range of molecular weights 1000–5000 with up to 30% by weight incorporation, using a conventional melt spinning technique. The spinnability of the copolymer and the mechanical properties of these undrawn fibers were evaluated. The changes in mechanical properties brought about by the incorporation of PTHF groups in 4GT units were related to the PTHF block size and content in the copolymer. X‐ray diffraction data are also discussed briefly in terms of the structural differences.
The influence of thermal history on internal stress distributions in sheets of PMMA and polycarbonate
Authors: Saffell J. R. , Windle A. H.
Published: April 2003

The through‐thickness birefringent patterns (nx – nz) of PMMA and polycarbonate (PC) are measured as a function of thickness, cooling rate, and annealing time. A method is demonstrated for separating the elastic stress from the residual birefringence. The residual birefringence is explained as the residual orientation induced when cooling through the galss transition. The shape of the elastic (tempering) stress distribution is apparently independent of the cooling rate and annealing time, the choice of polymer, and the sheet thickness. The magnitude of the tempering stres is dependent on cooling rate but nearly independent of choice of polymer and sheet thickness. The decays of both the tempering stress and the residual orientation are measured as a function of annealing time at 120°C for polycarbonate. The measured birefringence decays only slightly; however, the elastic tempering stress reverts, on annealing, to permanent (anelastic) orientational strain. The tempering stress at the sheet surface is not an adequate criterion for defining toughness in polycarbonate.
Interaction of lead and chromium with chitin and chitosan
Authors: Eiden Catherine A. , Jewell Carolyn A. , Wightman J. P.
Published: April 2003

The interaction of the natural marine polymer chitin and its deacetylated derivative chitosan with lead and chromium has been investigated. The uptake of lead and chromium was determined from changes in concentration as measured by atomic absorption spectroscopy. A significant uptake of Pb(II) on both chitosan and chitin was observed. However, the uptake of Pb(II) on chitin was approximately 21% of that on chitosan. The number of Natoms in chitin and chitosan and per number of Pb(II) ions sorbed was 115 and 29, respectively. The number density of flakes observed in the scanning electron microscope and characterized by an intense Pb signal in energy dispersive analysis of x rays (EDAX) was greater on the surface of chitosan [containing 1.7 × 10−4 mole Pb(II)/g chitosan] than chitin [containing 3.5 × 10−5 mole Pb(II)/g chitin] after equilibration with Pb(II) solution. The bonding state of lead on chitosan as determined by electron spectroscopy for chemical analysis (ESCA) is similar to the bonding of lead in PbO based on the Pb 4f7/2 binding energy. A significant shift in the O 1s binding energy from 532.2 to 531.4 eV was observed for chitosen after equilibration with Pb(II) solution. The caculated values of the N/Pb ratio from ESCA spectra were 0.5 and 11, for chitosan and chitin, respectively. A significant uptake of Cr(III) on chitosan was observed and a significant increase in the pH of solutions of Cr(III) on equilibration with chitosan occurred. A high number density of nodules characterized by an intense Cr signal in EDAX was observed in chitosan [containing 2.5 mole Cr(III)/g chitosan] after equilibration with Cr(III) solution. The calculated values of the N/Cr ratio from ESCA spectra was 18 for chitosan.
Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride
Authors: Acierno D. , La Mantia F. P. , Polizzotti G. , Russo S. , Titomanlio G.
Published: April 2003

Nylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x‐ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high‐modulus fibers after subsequent crystallization. Also, the possibility of restoring some crystallinity in the material has been proven.
Hydraulic permeability of open‐cell hydrophilic polyurethane foams
Authors: Sefton Michael V. , Lusher Harris M.
Published: April 2003

The hydraulic permeabilities of open‐cell hydrophilic polyurethane (Hypol) foams have been measured at steady state over a preassure gradient range of 102–104dyn/cm3. These permeabilites were sensitive to the relative amounts of prepolymer, water, and surfactant, and to the mode of preparation, Furthermore, the noted sample‐to‐sample variations suggested that mixing effects were also significant. Intertial losses, and energy losses associated with the pushing aside of loose foam struts were apparent at high, low, and very low gradients, respectively. Over the gradient range investigated, compression of the foam was considered to be a monor factor in accounting for the decreased permeability at higher gradients. The viscous loss term or Darcian permeability was correlated with cell size using the Carman–Kozeney equation indicating that the major determinant of hydraulic permeability was pore size rather than porosity. The fiber drag model of flow through porous media was also used to account for the permeability in terms of strut diameter rather than cell size.
Dynamic mechanical analysis and image analysis characterization of crimped yarns
Authors: Felty D. C. , Murayama T.
Published: April 2003

The Quantimet image analysis system and dynamic mechanical analysis have been applied to characterization of crimped yarns. The image analysis system is useful for obtaining accurate measurements of crimps per inch, uncrimped versus crimped length, crimp wavelength, and crimp amplitude. In addition, the dynamic tensile mechanical properties of fibers and the dynamic compression mechanical properties of the fiber masses were examined. These analyses identify the relationships between crimp parameters and loss tangents for the first time. The loss tangents of fiber masses increase with increasing crimp frequency. The higher loss tangents of crimped yarns in the glassy region quantify both the internal friction of constituent fibers and the external fiber to fiber friction separately.
Structural time dependency in the rheological behavior of molten polymers
Authors: Dealy J. M. , Tsang Wm. K.‐;W.
Published: April 2003

In order to elucidate the role of reentanglement processes in the rheology of molten polymers, we have used the interrupted shear test and the reduction‐;in‐;shear‐;rate test to study a linear and a branched polyethylene at 170°C. A cone‐;plate rheometer was used, and shear rates were thus limited to values below 1 sec−1. For both polymers, the characteristic time for reentanglement was found to be significantly greater than the time scales associated with the relaxation of shear and normal stresses after cessation of steady shear. This observation has important implications for the modelling of melt flow in plastics processes and the evaluation of constitutive equations.
Metal smoke retarders for poly(vinyl chloride)
Authors: Kroenke William J.
Published: April 2003

This article provides an overview of smoke‐;retarding rigid PVC using metal compounds. It shows that a large variety of metals from throughout the Periodic Table can form compounds which are smoke retarders for PVC. These metals act to change the thermal degradation pattern of the PVC and promote the formation of char. Most of the active metals are transition metals, although many of the post‐;transition metals and a few of the pretransition metals also are active. The activity of metal smoke retarders primarily is determined by the choice of metal and the environment surrounding the metal ion. Since most of the effective smoke retarders are transition metal compounds, the ability to undergo redox reactions may be important. The initial oxidation state, however, appears to be relatively unimportant. Particle and dispersion characteristics are secondary factors. Increasing the concentration of a smoke retarder can increase, decrease, or have no effect on its effectiveness. It is impossible to predict the influence of a tin stabilizer on a metal smoke retarder, but for many smoke retarders there is little effect. Transition metal compounds are the most effective metal smoke retarders. Smoke‐;reducing synergisms result when molybdenum trioxide is combined with certain compounds of copper, iron, and tin.
Water transport mechanisms through asymmetric membranes
Authors: Cerrella E. G. , Massaldi H. A.
Published: April 2003

Permeability coefficients and activation energy values for the transport of water through asymmetric cellulose acetate membranes were determined in order to establish the mechanism of the process when different driving forces are applied. A stirred Lucite cell with controlled temperature was used to measure the membrane transport properties under hydraulic and osmotic pressure differences and also in the presence of a tracer concentration gradient across the membrane. The experimental results based on the temperature dependence of water flow show that the controlling step for water transport is diffusion with net flux in the dense zone of the membrane under hydraulic or osmotic pressure gradients. When a tracer concentration gradient is used, equimolar diffusion of water in the thicker, porous zone of the membrane is the controlling mechanism. A mass transport model based on the composed structure of the membrane is presented to provide a general framework for treating the particular cases. Finally, the difference in the controlling barriers, in agreement with a previous work by Hays,18 is shown to account for the much higher absolute values of osmotic than tracer water permeabilities determined here and frequently reported in the literature.
On the mechanism of the mercerization of cellulose in wood
Authors: Revol J.‐F. , Goring D. A. I.
Published: April 2003

When spruce wood was treated with 20% aqueous NaOH, only partial conversion of cellulose I to cellulose II took place. In contrast, complete conversion occurred when a low yield kraft pulp from the same wood was mercerized. This difference in behavior is interpreted in terms of restricted swelling of the wood in the mercerizing alkali; this treatment preserves some memory of meridional order. Differences in polarity of the molecules in cellulose I and cellulose II are also considered as a possible reason for the difficulty in mercerizing the cellulose in wood.
Adsorption characteristics of polyacrylamide and sulfonate‐containing polyacrylamide copolymers on sodium kaolinite
Authors: Hollander Agnes F. , Somasundaran P. , Gryte Carl C.
Published: April 2003

Polyacrylamide and its copolymer containing 6.8 mole % 2‐acrylamido‐2‐methylpropane sulfonic acid were prepared by an irradiation‐initiated precipitation polymerization technique. The polymer was characterized by intrinsic viscosity under conditions similar to those used during adsorption measurements. Hydrolytic degradation of the polyacrylamide was found to be negligible under conditions used. The adsorption substrate, sodium kaolinite, was prepared by extensive ion exchange treatment. Equilibrium adsorption of the polymers on the sodium kaolinite was made as a function of polymer concentration, solution pH, ionic strength, and temperature.
Hydroxypropylcellulose, a thermotropic liquid crystal: Characteristics and structure development in continuous extrusion and melt spinning
Authors: Shimamura Kaoru , White James L. , Fellers John F.
Published: April 2003

Hot‐stage polarized light microscopy suggests that bulk hydroxypropylcellulose (Hercules Klucel E) is a cholesteric liquid crystal. Rheological measurements indicate this system exhibits shear viscosities similar to those of polyolefin melts except that it has a yield value comparable to suspensions. Birefringent characteristics were observed in shear flow between glass slides. No relaxation of birefringence is observed following flow. Extruded filaments (without applied take‐up tensions) show high levels of birefringence and significant orientations from WAXS measurements. These have skin‐core structure with highly oriented outer layers which are caused by the flow patterns in the reservior and die preceding the extrudate. In the case of melt‐spun filaments, where tensile elongation occurs, a highly oriented structure of uniform cross section is found.
Penetration of p‐xylylene vapor into small channels prior to polymerization
Authors: Broer D. J. , Luijks W.
Published: April 2003

The penetration of p‐xylylene gas into small rectangular channels has been studied by measuring the thickness of the formed poly(p‐xylylene) films as a function of penetration distance. The experimental values are related to the theoretical penetration curves under various process conditions. At low monomer and residual gas pressures, meeting the Knudsen conditions for wall‐to‐wall collisions of the monomer, a molecular flow model is valid which shows large penetration distances and a gradual decrease in film thickness. At increasing monomer pressures and corresponding deposition rates the molecular flow at the entrance is disturbed in favor of a more viscous type of flow. Consequently an accumulation of poly(p‐xylylene) has been observed in the first part of the channel. At increasing residual gas pressures the penetration can be described by a mass transfer model. Under our process conditions however, its ideal penetration characteristics could not be realized due to a visccus flow transition at the entrance of the channel. Polymerization of chloro‐p‐xylylene at low residual gas pressures showed a molecular flow controlled penetration, also at high deposition rates. Owing to its higher reactivity the penetration is less favorable than for p‐xylylene.
Modeling of poly(ethylene terephthalate) reactors. I. A semibatch ester interchange reactor
Authors: Ravindranath K. , Mashelkar R. A.
Published: April 2003

A comprehensive model for a semibatch ester interchange reactor has been developed with a view to investigate the effect of various process and operational variables on the DMT conversion rate as well as the by‐product formation. The influence of important variables such as EG‐to‐DMT ratio, catalyst concentration, and operational variables such as temperature and pressure has been considered. Definite conclusions concerning the choice of the desirable range of process and operational variables to maximize productivity and minimize by‐product formation have been reached.
Chlorinated atactic polypropylene as a plasticizer for poly(vinyl chloride)
Authors: Sharma Y. N. , Satish S. , Bhardwaj I. S.
Published: April 2003

Atactic polypropylene, a byproduct obtained in the manufacture of isotactic polypropylene, has been chlorinated under various reaction conditions. The chlorination reaction is reasonably fast so as to give a product of 53‐43% chlorine content in 3 h. The chlorinated product has been incorporated in poly(viny1 chloride) formulations with a view to study its plasticizing activity. Generally this type of compound acts only as a secondary plasticizer; hence it has been used in combination with di(2‐ethylhexyl)phthdate, a primary plasticizer. Different proportions of these two plasticizers have been added to poly(vinyl chloride) resin to obtain a series of formulations. These compounds were evaluated, and it appears that the addition of chlorinated atactic polypropylene (APPC) helps in easy processing and increases the throughput. The increasing concentration of APPC showed an upward trend in die head pressure and torque indicating an increase in melt viscosity. The results of physical properties evaluation show that APPC acts as a reinforcing agent and also imparts permanence to the plasticizers.
Separation of liquid mixtures by using polymer membranes. III. Grafted poly(vinyl alcohol) membranes in vacuum permeation and dialysis
Authors: Shantora V. , Huang R. Y. M.
Published: April 2003

A series of poly(vinyl alcohol) membranes were modifed by radiation‐induced graft copolymerization with acrylic acid and methacrylic acid monomers. These grafted poly(vinyl alcohol) membranes were then tested for their separation and permeability characteristics in vacuum permeation and dialysis experiments. The permselectivity of the membranes toward methanol and water was studied on a vacuum permeation apparatus at 30, 40, and 50°C. The permeation process was found to be a temperature‐activated process. The logarithm of the permeation rate varied linearly with the reciprocal of the absolute temperature. The permeability of the grafted membranes was found to increase with the degree of grafting, with no appreciable selectivity toward water in binary mixtures. The acrylic acid‐grafted membranes generally showed greater improvement in permeability than the methacylic‐grafted membranes. The permeability of the grafted membranes toward methanol, sodium chloride, urea, creatinine, and uric acid was studied in a dialyzer. In all cases, the grafted membranes showed an improved permeability toward these solutes over the commercial poly(vinyl alcohol) membranes. The dialysis results were then compared with those obtained for dialysis‐grade cellophane membranes. For the case of sodium chloride, urea, and methanol, the permeability of the grafted membranes was comparable to that of cellophane. A comparison of commercial and grafted poly(vinyl alcohol) membranes in their permeability toward ionic solutes exhibited somewhat anomalous behavior in that the permeability of the commercial membranes was higher than that of the grafted membranes. This related to the ionic nature of the modified membrane. The permeability coefficients determined in the dialysis experiments were found to be directly related to the degree of hydration of the grafted membrane. This behavior was attributed to changes in the size and shape of voids within the membrane structure.
Analysis of the impurities in industrial ε‐caprolactam. Hypothesis of formation
Authors: Jodra L. G. , Romero A. , García‐Ochoa F. , Aracil J.
Published: April 2003

Analysis of an industrial ε‐caprolactam by gas–liquid chromatography has been carried out using different stationary phases and operating conditions. The impurities in the ε‐caprolactam are identified and hypotheses about their formation are presented. In some cases the presence either in cyclohexane or cyclohexanone of the possible impurity‐producing compounds is shown.
Solution spinning of a semirigid chain polymer forming ultrahigh modulus fibers
Authors: Valenti B. , Alfonso G. C. , Ciferri A. , Giordani P. , Marrucci G.
Published: April 2003

Single filaments of the polyterephthalamide of p‐aminobenzylhydrazide (X‐500) were prepared by spinning X‐500 solutions in dimethyl sulfoxide (DMSO) using water as a coagulating agent. The polymer is known for its ability to develop ultrahigh modulus fibers and for having a semirigid chain conformation with a persistence length of ∼50 Å in DMSO. In the latter solvent, molecular rigidity appears to be just below that required for spontaneous formation of a nematic phase. The orientation of the fibers was performed in three different stages: during coagulation (I), in the washing bath following coagulation (II), and during postspinning treatments (III). Corresponding mechanical properties were determined. The results indicate that high elastic modulus (15 GPa) already appears during step I at very moderate pulloff ratios. Therefore, considerable orientation had already occurred in the flowing solution. Further increase of fiber orientation yields a large increase of modulus (from 22 to 67 GPa) during solid‐state deformation (step III). The orientation of the flowing solution was monitored by viscosity and birefringence measurements. The results are discussed in terms of orientation due to elongational and shear flow and, possibly, a flow‐induced transition to a nematic phase in the concentrated solution in which chain entanglement is shown to occur.
The formation and structure of suspension‐polymerized styrene–divinylbenzene copolymers
Authors: Howard G. J. , Midgley C. A.
Published: April 2003

Porous polymers were prepared by suspension copolymerization of styrene/divinylbenzene in various ratios together with various quantities of diluents, both solvating and nonsolvating. Parallel bulk polymerizations were made to detect the onset of gelation and phase separation. The dry polymeric beads were examined by a range of techniques: apparent densities; mercury porosimetry; nitrogen sorption/desorption isotherms, vapor sorption, equilibrium swelling, and electron microscopy. The properties of the porous polymers are discussed in terms of phase separation during polymerization consequent on either an unfavorable polymer–solvent interaction or a microsyneresis.
Mechanical properties of borate crosslinked poly(vinyl alcohol) gels
Authors: Cheng A. T. Y. , Rodriguez F.
Published: April 2003

Boric acid does not introduce crosslinks in poly(vinyl alcohol) solutions, but gelation does occur in the presence of cations. In this experimental study, the dynamic mechanical properties of these gels were determined using test‐tube torsion pendulums and an air‐bearing torsion pendulum. The modulus at a fixed concentration of polymer and boric acid increases with increasing sodium ion concentration up to the point where the atom ratio of sodium to boron reaches 1. Higher sodium concentrations do not increase the modulus. The log decrement, on the other hand, decreases with increasing sodium concentration continuously without reaching a plateau at the equal atom ratio. Log decrements as low as 0.02 can be measured. The storage modulus depends on the logarithm of borate concentration and on the 4.7 power of poly(vinyl alcohol) concentration. Only a very small portion of the borates in solution take part in effective crosslinks. The activation energy for breaking individual bonds in a function of temperature and the cation to boron ratios. At a fixed cation concentration, this activation energy is more negative with increasing amount of boron ions due to a transformation of monomeric crosslinks into polymeric crosslinks, so that the storage modulus which measures crosslink density decreases as a temperature rises.