bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas sorption and transport in poly(phenylene oxide) and comparisons with other glassy polymers
Authors: Toi K. , Morel G. , Paul D. R.
Published: April 2003

The sorption and transport of several gases in poly(phenylene oxide) were measured at 35°C, and the results have been analyzed in terms of the dual sorption/mobility models which have been successfully employed for this purpose for other glassy polymers. Both the extent of sorption and rate of permeation of gases are quite large for poly(phenylene oxide) compared to other glassy polymers with rigid chain backbones. It is shown that the high extent of sorption is owing to the high glass transition temperature of this polymer, but this is not a significant factor in its high permeability to gases. The latter stems from large diffusion coefficients. It is shown that the capacity of the Langmuir mode of sorption inherent to glassy polymers is related to the value of the glass transition temperature in a general way for a wide variety of polymers. Observations about the diffusion coefficients for numerous gas–polymer pairs are discussed.
Glass‐transition behavior of particle composites modeled on the concept of interphase
Authors: Theocaris P. S. , Spathis G. D.
Published: April 2003

The thermomechanical behavior of particle composites was investigated in their transition region. In particular, the value of the glass‐transition temperature Tg, which constitutes an upper limit for the structurally important glassy region, was examined. According to experimental evidence existing in the literature the introduction of a reinforcing filler in a polymeric matrix causes Tg of the latter to increase, unless mechanical imperfections counterbalance the reinforcing effect or even produce a Tg for the composite which is lower than that of the matrix. Based on mechanical theories, valid for the mechanical moduli of viscoelastic particle composites, a model was introduced that explains why the glass transition of composite materials may be reduced in some cases, whereas it may be increased in others. The concept of interphase between inclusions and matrix was used for the development of the model. Interphase is assumed to be a region, which is created between the matrix material and the filler particles, both considered as homogeneous and isotropic, whose thermomechanical properties and volume fraction may be determined from the overall thermomechanical behavior of the composite.
Stress‐induced chemiluminescence from nylon 66 fibers
Authors: George G. A. , Egglestone G. T. , Riddell S. Z.
Published: April 2003

The emission of visible light during the tensile deformation of medium‐ and high‐tenacity nylon 66 yarns in air has been studied at strain rates of 0.63–200%/min and at temperatures of 20–110°C. Emission is observed only in an oxidative atmosphere and increases with temperature according to an Arrhenius relation. The activition energy decreases with applied stress. The intensity at any temperature can be described by the sum of a component linear with stress and another exponential in stress above ∼60% of the ultimate strength. These results and the measured spectral distribution suggest that light emission arises from bimolecular termination of alkyl peroxy macroradicals. The chemiluminescence growth curves indicate that the applied stress increases the oxidation rate of the fiber due to internal and external frictional heating while, at high strains, stress‐induced main‐chain scission occurs up to fiber failure. The growth curve is sensitive to the load history of the fiber. The chemiluminescence decay curves are a sensitive probe of radical reactions such as cage termination and stabilizer scavenging in the amorphous region of the polymer.
Yields and composition of sirups resulting from the flash pyrolysis of cellulosic materials using radiant energy
Authors: De Jenga Chine I. , Antal Michael Jerry , Jones Maitland
Published: April 2003

Cellulosic materials have been flash pyrolyzed using concentrated solar energy. The sirups obtained were composed mainly of levoglucosan. Radiant flash pyrolysis has thus been identified as a potentially attractive means of selectively degrading biomass material into good yields of relatively few products. The techniques and equipment employed to determine the composition of the pyrolyzates are described.
Epoxy‐resin‐cured carboxylated nitrile rubber
Authors: Chakraborty Sunity K. , De Sadhan K.
Published: April 2003

Curing of carboxylated nitrile rubber (XNBR) with epoxy resin in presence of different fillers has been studied. It was observed that 7.5 phr of resin give a compromise combination of properties in FEF black (N 550)‐filled vulcanizates at 40 phr loading. Further studies at different loadings of black, reinforcing silica and clay were done at 7.5 phr resin. Technical properties at different filler loadings have been determined. Polymer‐filler interaction involving FEF black, silica, and clay was examined by a Kraus plot and the equation of Lorenz and Parks. Silica and carbon black give a similar type of reinforcement, but clay shows nonreinforcing characteristics. In the case of carbon black–XNBR system, polymer‐filler attachment is similar to that existing in carbon black–natural rubber system. In the case of silica, reaction of the silanol group with the epoxide group of the epoxy resin and the carboxyl group of the base polymer may be responsible for the polymer‐filler attachment. Scanning electron microscopy (SEM) studies of the fracture surfaces corroborate the findings on technical properties and polymer‐filler interaction.
Grafting of methyl methacrylate onto collagen initiated by tributylborane
Authors: Kojima Kuniharu , Iguchi Shuichi , Kajima Yoshihiro , Yoshikuni Masako
Published: April 2003

The graft copolymerization of methyl methacrylate onto collagen initiated by tributylborane was investigated in aqueous medium. The total conversion, percentage of grafting and efficiency of grafting increased with increasing collagen content. The optimum conditions on the percentage of grafting and efficiency of grafting were determined by varying initiator concentration, monomer concentration, and polymerization temperature. The grafting onto denaturated collagen was also studied. It has been suggested that the grafting onto collagen proceeds by a radical mechanism via a complex of TBB and hydrated collagen.
Preparation of high‐modulus and high‐strength isotactic polypropylene fiber by zone‐annealing method
Authors: Kunugi Toshio , Ito Taihei , Hashimoto Minoru , Ooishi Masashi
Published: April 2003

The zone‐annealing method was utilized to prepare a high‐modulus and high‐strength fiber from isotactic polypropylene. The dynamic storage modulus at room temperature of the fiber obtained reached 21 times; 1010 dyn/cm2, which corresponded to 51% of the crystal modulus along the molecular chains, 41.2 × 1010 dyn/cm2. The relationships between mechanical properties and superstructure were investigated based on results of measurements of orientation, crystallinity, tensile properties, and dynamic viscoelasticity. It was found that the excellent mechanical properties were directly attributed to the large number of tie molecules and to the high orientation of the amorphous chains. Further, the characteristics of this method were discussed compared with the results obtained by other investigators.
Polycaprolactone degradation by mixed and pure cultures of bacteria and a yeast
Authors: Benedict Christine V. , Cameron J. A. , Huang Samuel J.
Published: April 2003

The degradability of three high molecular weight polycaprolactones (M̄w = 35,000, 18,600, and 7,130) and one low molecular weight polycaprolactone diol(M̄w = 2060) by mixed and pure cultures of microorganisms was assayed. A yeast, Cryptococcus laurentii, a gram‐negative rod, Acinetobacter calcoaceticus var. lwoffi, and a gram‐positive coryneform rod were used in the pure culture assays. The analysis of degradation by gel permation chromatography (GPC) allowed for quantitation independent of the growth of the organisms or the addition of supplementary growth factors. GPC analysis showed that the degradation effected by pure cultures was often enhanced when alternate carbon sources were present. This was not the case for mixed cultures. Mixed cultures. Mixed cultures completely metabolized polymer breakdown products while in some cases pure cultures did not.
Dielectric loss behavior of cross‐linked polyethylene and analog materials
Authors: Jang Y. T. , Phillips P. J.
Published: April 2003

The dielectric loss behavior of crosslinked polyethylene has been determined over the frequency range 10–5 kHz and over the temperature range −150 to 100°C. Major loss effects occur at the lower temperatures and are caused by libration of the organic byproducts of the crosslinking agent, dicumyl peroxide. Analog materials prepared from linear low density polyethylene by blending in of either acetophenone or 2‐phenyl‐2‐propanol confirm the hypothesis. The effects of concentration of by products and of orientation of the polymer have been studied. Activation energy analyses suggest that room temperature losses will occur in the microwave region. The behavior is significantly affected by curing with steam, typical loss peaks being an order of magnitude lower than for dry cured specimens. A new loss region appears close to but below, 0°C.
Polypropylene/nylon 6 blends: Phase distribution morphology, rheological measurements, and structure development in melt spinning
Authors: Liang Bo‐Run , White James L. , Spruiell Joseph E. , Goswami Bhuvenesh C.
Published: April 2003

A series of polypropylene (PP)/nylon 6 (N6) blends of composition 75/25, 50/50, and 25/75 have been prepared in a screw extruder combined with a Koch static mixer. The phase morphology was observed with a scanning electron microscope. The influence of heating in the reservoir of a rheometer followed by subsequent extrusion through a capillary on the phase morphology was investigated. Phase size growth as a function of time was observed under quiescent and mild deformation rate conditions. The discrete phase size was observed to decrease with increasing extrusion rate through dies. The shear viscosity and principal normal stress difference of the blends were measured as a function of composition. The crystalline orientation of both polypropylene and nylon 6 in blend melt spun fibers was characterized by wide angle X‐ray diffraction and interpreted in terms of Hermans–Stein orientation factors. The orientation increases with drawdown ratio. The orientation factors for the polypropylene phase vary with spinline stress in a manner independent of composition and identical to that for pure polypropylene. Extracting melt spun blend fibers with formic acid has produced small‐diameter polypropylene minifilaments with diameters of the order of microns.
Determination of number‐average and weight‐average molecular weights of polymer sample from diffusion and sedimentation velocity measurements in theta solvent
Authors: Okabe Masaru , Matsuda Hideomi
Published: April 2003

Several methods to determine number‐average molecular weight Mn and weight‐average molecular weight Mw, of a polymer sample are proposed from diffusion and sedimentation velocity measurements at the θ point. According to these methods, Mn and Mw are determined from the diffusion constant vs. molecular weight relationship, and also from the equations of Svedberg and Flory–Mandelkern, using the 2nd‐order and the –2nd‐order diffusion constants. These methods have been applied to four samples of polydisperse polystyrene in the θ solvent, cyclohexane at 35°C. It was experimentally ascertained that Mn and Mw of each sample determined by the present methods were in good agreement with the results of column fractionation, light scattering, and calculated values from molecular weight distribution curve within experimental errors. It is concluded that the present methods are useful for determining Mn and Mw, since the reliabilities of Mn and Mw values, which are fundamental quantities of polymer characterization, can be raised by comparing the experimental data observed by conventional methods such as osmotic pressure, light scattering, and the Archibald method with those observed by the present methods.
Time–temperature–transformation (TTT) cure diagram: Modeling the cure behavior of thermosets
Authors: Enns John B. , Gillham John K.
Published: April 2003

The times to gelation and to vitrification for the isothermal cure of an amine‐cured epoxy (Epon 828/PACM‐20) have been measured on macroscopic and molecular levels by dynamic mechanical spectrometry (torsional braid analysis and Rheometrics dynamic spectrometer), infrared spectroscopy, and gel fraction experiments. The relationships between the extents of conversion at gelation and at vitrification and the isothermal cure temperature form the basis of a theoretical model of the time–temperature–transformation (TTT) cure diagram, in which the times to gelation and to vitrification during isothermal cure versus temperature are predicted. The model demonstrates that the “S” shape of the vitrification curve depends on the reaction kinetics, as well as on the physical parameters of the system, i.e., the glass transition temperatures of the uncured resin (Tg0), the fully cured resin (Tg∞), and the gel (gelTg). The bulk viscosity of a reactive system prior to gelation and/or vitrification is also described.
Solid‐state polymerization of poly(ethylene terephthalate)
Authors: Chang Shuya , Sheu Ming‐Fa , Chen Shu‐May
Published: April 2003

Solid ‐state polymerization of poly(ethylene terephthalate) (PET) is carried out by heating the low molecular weight prepolymer at temperatures below its melting point but above its glass transition temperature. Postcondensation occurs and the condensation byproducts can be removed by applying vacuum or inert gas. Polymers obtained usually have high molecular weight, low carboxyl and acetaldehyde content, and can be used for beverage bottle or industrial yarns. Polyesters for textile purposes are manufactured by a melt process. Chemical reactions involved in the solid state polymerization are transesterification, esterification, as well as the diffusion of byproducts. Overall reaction rate was governed by the molecular weight, carboxyl content of prepolymer, crystallinity, particle size, reaction temperature, and time. Prepolymer for solid state polymerization should have intrinsic viscosity 0.4 dL/g or more, density 1.38 g/mL, and minimum dimension 3 mm or less. The reaction temperature could be 200–250°C. When textile grade PET is used as prepolymer, crystallization at 180–190°C for 1–2 h increases the density to 1.38 g/mL. Polymerization at 240–245°C for 3–5 h can raise the intrinsic viscosity to 0.72 dL/g and carboxyl content less than 20 meq/kg. Appropriate reaction conditions are subject to the properties of prepolymers and the design of reactors. Reactor used for solid state polymerization could be vacuum dryer type or stationary bed. The former is suitable for a small capacity and is run batchwise. The latter is a continuous process and is economically feasible for large ‐scale production.
Hydrolytic degradation of cured urea–formaldehyde resin
Authors: Dutkiewicz Jacek
Published: April 2003

The degradation of cured urea–formaldehyde (UF) resin in aqueous suspension was investigated by gravimetric analysis of the changes in the content of nonextractable low‐molecular components. In acid conditions (pH 4.0) at 47°C the consecutive processes of post‐curing and of polymer break‐down (activation energy 90 kJ/mol) are detectable whereas at 80°C and 97°C only the formation of the extractable hydrolysates is observed. The degraded polymer contains less carbonyl groups than does the original resin substrate as shown by means of infrared (IR) analysis. In contrast to the results of the tests carried out in acid conditions, in neutral and basic aqueous media the hydrolytic decomposition of UF macromolecular network is less significant. During the hydrolysis of UF polymer at 30°C–45°C the concentration of formaldehyde released from the resin to the aqueous phase increases initially (2 days) at a relatively high rate both at acid and alkaline pH. Then its growth slows down but is still detectable in acid conditions, whereas in basic medium no further liberation of HCHO is observed.
Semi‐ and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. III. Polyurethane–poly(methyl acrylate) semi‐2‐interpenetrating polymer networks
Authors: Hourston D. J. , Zia Y.
Published: April 2003

Two series of semi‐2‐IPNs based on a polyurethane and a poly(methyl acrylate) crosslinked with divinyl benzene were prepared and investigated using dynamic mechanical analysis, sonic velocity measurements, and electron microscopy. In the one series, the level of crosslinking was varied to give ultratight networks. In the other, the composition was altered, but the amount of the crosslinking agent used was kept constant. For the first series, it was concluded that the degree of crosslinking had a significant influence on the morphology and properties by controlling the amount of enforced mixing. The dynamic mechanical data for the second series fitted the Davies modulus–composition equation, indicating that both phases are continuous.
Engineering plastics from lignin. III. Structure property relationships in solution cast polyurethane films
Authors: Saraf Vasudev P. , Glasser Wolfgang G.
Published: April 2003

Lignin‐based polyurethane films were synthesized by solution casting from hydroxypropyl lignin derivatives and either an aliphatic or an aromatic isocyanate. Two lignins, kraft and steam explosion lignin, and two diisocyanates, hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI), were chosen for the study. It was found necessary to use stoichiometric excess diisocyanate in the synthesis of the thermosetting polyurethanes. This part of the series addresses the effect of synthesis variables on film properties. The study examines the effect of lignin type, of diisocyanate type, and of composition in terms of NCO to OH stoichiometry on thermal and mechanical properties. Stoichiometric NCO‐excess was found to cause a more significant increase in the glass transition temperature of TDI‐based films than of films made with HDI. The films swelled less with increasing NCO/OH ratio. Use of aliphatic diisocyanate (HDI) resulted in films with lower moduli as compared to aromatic diisocyanate (TDI). Kraft‐lignin‐based polyurethanes had slightly inferior strength characteristics (Young's modulus and tensile strength) in comparison with those derived from steam explosion lignin. Variation in the NCO/OH stoichiometry had no noticeable effect on modulus or tensile strength, but did significantly influence glass transition temperature, swelling, and strain at break. It is observed that the properties of these thermosetting polyurethanes are very sensitive to their composition. The study illustrates that materials of satisfactory performance characteristics can be engineered by proper selection of synthesis variables and modification of network architecture.
Effects of catalyst on the electrical properties of silicone rubber
Authors: Yokoyama T. , Kinjo N. , Mukai J.
Published: April 2003

Electrical properties, such as dissipation factor and electric conductivity, were studied for silicone rubber sheets. The specimens were prepared by the reaction of α,ω‐dihydroxypolysiloxane with ethoxysilane, using dibutyltin dilaurate as a catalyst, at a relative humidity of about 100% at various temperatures and for various reaction times. It was found that the electrical properties were a function of the vulcanizing conditions; i.e., the further the vulcanization proceeded, the higher the dissipation factor and the electric conductivity. A reaction describing deterioration in electrical properties was then considered. Infrared spectroscopic studies on dibutyltin dilaurate showed that the dibutyltin dilaurates were partly hydrolyzed to lauric acid and dibutyltin dihydroxide. It was concluded that electrical property deteriorations, which were caused by changes in the vulcanizing conditions, were due to dibutyltin dilaurate hydrolysis. However, since the decomposed products were finally oxidized at elevated temperatures in an oxygen atmosphere, with a subsequent change to electrically inactive compounds, the initial electrical properties were recovered.
Transformation of liquid to amorphous solid: The time to vitrify for styrene polymerization
Authors: Aronhime M. T. , Gillham J. K.
Published: April 2003

A model is presented for the calculation of the time to vitrify vs. temperature for isothermal polymerization by the chain growth mechanism. The model is based on the glass transition temperature (Tg) rising from its initial value to the reaction temperature. The relationships between Tg and the volume fraction of polymer and monomer, the volume fraction of polymer and the extent of reaction, and the extent of reaction and time are also required. In a plot of temperature vs. time the vitrification curve is generally S‐shaped; the time passes through a maximum just above the glass transition temperature. The model applies to linear polymerization in which monomer and high molecular weight polymer are the dominant species, i.e., to chain reactions. In this communication the model is applied to the bulk polymerization of styrene by the free radical mechanism.
Radiant flash pyrolysis of biomass using a xenon flashtube
Authors: Hopkins Mark Willard , Antal Michael Jerry , Kay Jack G.
Published: April 2003

Biomass materials, including lignin, redwood, corn cob, Calotropis Procera, Leucaena wood, Kraft paper, newsprint, cow manure, D‐glucose, and D‐cellobiose, were pyrolyzed in vacuum by the visible radiant flux emitted from a Xenon flashtube. The flux density exceeded 8 kW/cm2 during the 1 ms flash. Sirup yields were low (avg 25%), while the gas yield was high (avg 32%). The gaseous products were composed primarily of CO and CO2. The high relative yields of CO establish the existence of a high temperature fragmentation pathway active during the flash pyrolysis of all biomass materials.
A relaxation model for property changes during the cure reaction of filled and unfilled silicone elastomers
Authors: Hsich H. S.‐Y. , Yanyo L. C. , Ambrose R. J.
Published: April 2003

A generalized kinetic model of cure, which is described by a distribution relaxation function, is used to predict physical and mechanical properties of silicone elastomers during isothermal and nonisothermal cure reactions. The model can also predict the effect of filler and cure behavior of filled elastomers. The structural relaxation times of the molecular state of uncured and cured elastomers is also discussed.
Microstructure of biaxially drawn ultrahigh molecular weight polyethylene
Authors: Kaito Akira , Nakayama Kazuo , Kanetsuna Hisaaki
Published: April 2003

The microstructure of ultrahigh molecular weight polyethylene (UHMW‐PE) sheets biaxially drawn in the molten state was investigated by means of wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering (SAXS), differential scanning calorimetry (DSC), and electron microscopy. The crystallographic c‐axis tended to be oriented in the sheet plane by the biaxial drawing in the molten state. The microstructure of the biaxially drawn UHMW‐PE was shown to depend upon molecular weight of UHMW‐PE. The biaxially drawn sheet of higher molecular weight (Mv = 2,700,000) showed a fibrous structure, while the lower molecular weight sample (Mv 700,000) had a lamellar structure. The result of DSC measurements suggested that a small number of nucleating extended chain crystals was produced by biaxial melt drawing of the UHMW‐PE sheet with higher molecular weight.
Development of a new composite material from waste polymers, natural fiber, and mineral fillers
Authors: Ramirez Amando Padilla , Solis Antonio Sánchez
Published: April 2003

This work describes a panel made from waste polyethylene, henequen fibers, and mineral fillers. The physical and mechanical properties of the product were determined and compared with the properties of commercial panels. The new material has good mechanical properties and high environmental resistance. Its thermal insulating capacity is about 10 times better than that of asbestos–cement panels. The adhesion grade between fibers and polymer was investigated.
Hydrolysis of cotton fibers by cellulase enzyme
Authors: Paralikar K. M. , Bhatawdekar S. P.
Published: April 2003

Cotton cellulose has been subjected to continuous and repeated enzymatic hydrolysis for different periods. It has been observed that the length of hydrocellulose particles obtained on repeated enzyme action is reduced to about 300–500 Å as compared to 900–3000 Å obtained on prolonged enzyme treatment. Corresponding changes in moisture regain, crystallinity of the hydrolysates, and weight loss brought out by the hydrolysis are also discussed.
Size exclusion chromatography of polyelectrolytes in dimethylformamide
Authors: Scheuing D. R.
Published: April 2003

A study of the size exclusion chromatographic behavior of styrene–methacrylic acid and epoxyacrylic polymers has been made. These polymers exhibit strong “ion‐exclusion” effects in DMF, similar to that found for water‐soluble polyelectrolytes such as sodium polystyrene sulfonate. The addition of lithium bromide, at a concentration of 0.1M, overcomes ion exclusion on a set of silicabased, “deactivated” duPont SEC columns. Calibration of both the duPont columns and a set of styrene–divinyl benzene based columns (μ‐Styragel) is complicated by absorption of polystyrene standards in DMF and DMF/salt mobile phases. The absorption of monomeric solutes on the duPont columns in DMF/salt mobile phases is different from that of their corresponding polymers.
Dielectric properties of cellulose acylates
Authors: Morooka Toshiro , Norimoto Misato , Yamada Tadashi , Shiraishi Nobuo
Published: April 2003

Thirteen kinds of cellulose acylates from the acetate to stearate were prepared by trifluoro acetic anhydride–fatty acid esterification, and their dielectric constant and loss were measured over wide temperature and frequency ranges. Two types of relaxation process (αd and βd) were recognized for all the acylates and an additional relaxation process (γd) was detected for the acylates with side chain length longer than that of the butyrate. These αd to γd processes were attributed to the micro‐Brownian motion of the main chain (αd), the motion of oxycarbonyl group of the side chain (βd) and the motion initiated by minimum three methylene groups in addition to the oxycarbonyl group (γd), respectively. In the transition map for the βd process, inflection points were observed, and the temperature at the inflection point could be regarded as a freezing point of the micro‐Brownian motion of the acyl side chain. In the temperature region above the inflection point, plots in transition map for all the acylates were found to be on the same straight line.
Design of polymer membrane with permselectivity for water–ethanol mixture. II. Preparation of crosslinked poly(methyl acrylate) membrane with diethylene triamine and its permselectivity
Authors: Itoh Toshiaki , Toya Hideki , Ishihara Kazuhiko , Shinohara Isao
Published: April 2003

In order to permeate water from a water–ethanol mixture by pervaporation on the basis of the difference in solubility between two components toward a polymer membrane, polymer membrane having polar group, poly(methyl acrylate) (PMA) membrane crosslinked with diethylene triamine (DETA) was prepared. The permselectivity of the membrane was investigated with attention to the feed composition of water–ethanol mixture and the effect of introduction of DETA into the membrane. It is found that water was permeated through PMA–DETA crosslinked membrane preferentially in all ranges of feed composition, the highest permselectivity being observed at 25% ethanol aqueous solution. Moreover, the pervaporation rate of water was found to depend on the ratio of DETA introduction into the membrane. When the ratio of introduction into the membrane was 0.144, water was permeated through the membrane from 25% ethanol aqueous solution at a rate of 1.26 × 10−1 g m/m2 h. These results can be explained by high diffusivity of the membrane due to the low glass transition temperature of PMA and permeation of water through polar DETA moiety in the membrane.
Correlation of solubility in polydimethylsiloxane and polyisobutylene systems
Authors: Tseng Hsiao‐Show , Lloyd Douglas R. , Ward T. C.
Published: April 2003

Solubility data of organic probes in polydimethylsiloxane (PDMS) and polyisobutylene (PIB) obtained by inverse gas chromatography (IGC) were collected from the literature and analyzed. Applying the principle of corresponding states, empirical correlations were derived and presented for the estimation of solubilities of nonpolar and slightly polar probe molecules in these polymers. Estimation of other thermodynamic properties, such as activity coefficient of the solute, Henry's law constant, Flory–Huggins interaction parameter, and heat of solution through the use of these correlation equations, was demonstrated.
Mercerization of cellulose. II. Alkali–cellulose intermediates and a possible mercerization mechanism
Authors: Okano T. , Sarko A.
Published: April 2003

Continued study of the five crystalline Na–celluloses, previously shown to occur as intermediates during the mercerization of cellulose and exhibiting two types of crystallographic fiber repeats, further indicates that they fall into three classes based on their unit cells and NaOH contents. In one class are Na–celluloses I and III, both containing up to 34% NaOH; in the second class are Na–celluloses IIA and IIB, marked by ca.15 Å fiber repeat and containing up to 65% NaOH; and in the third class is Na–cellulose IV which is likely to be a hydrated form of cellulose II. Na–cellulose I was found to be the common first alkali–cellulose structure produced in the NaOH treatment of both cellulose I and cellulose II. Further study of this conversion step suggested a mercerization mechanism in which the alkali begins the conversion of cellulose to Na–cellulose I in the amorphous parts of the fiber. The conversion of the parallel‐chain cellulose I structure to an antiparallel one is likely to occur already in this first step.
No2–initiated polymerization of acrylamide in dimethylsulfoxide
Authors: Mishra Mahendra Kumar , Bhadani Suraj N.
Published: April 2003

NO2‐initiated polymerization of acrylamide in dimethylsulfoxide was carried out. The dependence of monomer, initiator concentrations, and temperature on polymer yield and initial rate of polymerization was studied. The overall activation energy of polymerization was calculated to be about 15 kcal mol−1. The copolymerization of acrylamide with methyl methacrylate was also studied. The kinetic mechanism of polymerization was proposed.
Percolation conductivity in Nafion membranes
Authors: Wódzki Romuald , Narębska Anna , Nioch Wojciech Kwaś
Published: April 2003

This article deals with the method of determination of a threshold volume fraction of the conductive phase within perfluorosulfonic acid ionomer Nafion. Experiments have been performed with the commercial Nafion‐120 and Nafion‐427 membranes equilibrated with concentrated sodium chloride and sodium hydroxide solutions at 353 K. It has been stated that the insulator‐to‐conductor transition in membranes occurs at the critical volume fraction of the conductive phase (Vc) equal to 0.1. The same Vc has been estimated for a geometrical cluster‐network model. Lower than the theoretical Vc for a classical dense‐packed‐hard‐sphere model (Vc = 0.15), the volume fraction for the membranes is caused mainly by channels connecting the ionic clusters. The critical exponent t has been calculated for both membranes and found to be equal to 1.6 for Nafion‐120 and 1.5 for Nafion‐427. Both these constants correspond to those theoretically predicted for 3D systems. The ratios of sodium ion mobility in the internal membrane solution to its mobility in the equilibrating NaCl or NaOH solutions (u+/u+) are below unity, and they are dependent on the nature and concentration of the electrolyte.
Tensile properties of carbon fibers from acrylic fibers stabilized under isothermal conditions
Authors: Takaku A. , Hashimoto T. , Miyoshi T.
Published: April 2003

A series of carbon fibers were prepared from the acrylic fibers thermally stabilized in air under various temperature–time conditions, and the relation between the extent of stabilization and the tensile properties of carbon fibers was investigated. The density of stabilized fibers was adopted as a measure of the extent of stabilization. The tensile modulus of carbon fibers changed dependently on stabilization temperature. However, the variation of the tensile modulus of carbon fibers with the density of stabilized fibers was small if stabilization temperature was constant. In the relation between the tensile strength of carbon fibers and the density of stabilized fibers, a feature depending on stabilization temperature was not evident, and the tensile strength of carbon fibers showed a maximum in the density range from about 1.34 to 1.39 g/cm3 of stabilized fibers.
The tensile behavior of polycarbonate and polycarbonate–glass bead composites
Authors: Dekkers M. E. J. , Heikens D.
Published: April 2003

The tensile behavior at 20°C of unfilled polycarbonate and polycarbonate–glass bead composites (90/10 vol %) has been investigated by tensile testing with simultaneous volume change measurements. Both the effect of the bead size and the degree of interfacial adhesion on the tensile behavior of the composites has been studied. A simple model has been applied to obtain quantitative information on the separate contributions of several possible deformation mechanisms to the total deformation. For unfilled polycarbonate and the polycarbonate–glass bead composites with excellent interfacial adhesion, shear deformation is found to be the only significant non‐Hookean deformation mechanism. By means of strain recovery experiments it is shown that the shear deformation is highly elastic in character. For the composites with poor interfacial adhesion, besides shear deformation also dewetting cavitation contributes to the non‐Hookean deformation. The differences in tensile behavior between the composites with excellent and poor interfacial adhesion are explained by the different mechanisms for shear band formation at excellently and poorly adhering glass beads.
Active transport and selective transport of alkali metal ions through polyelectrolyte complex membranes consisting of the three materials [2‐(diethylamino)ethyl]dextran hydrochloride, sodium carboxymethyldextran, and sulfate of poly(vinyl alcohol)
Authors: Kikuchi Yasuo , Kubota Naoji
Published: April 2003

Active and selective transport of alkali metal ions through the polyelectrolyte complex membranes consisting of [2‐(diethylamino)ethyl]dextran hydrochloride, sodium carboxymethyldextran, and sulfate of poly(vinyl alcohol) have been investigated for the first time. The transport behavior was much affected by the hydrogen ion concentration. The driving force for the active transport of alkali metal ions was considered to be the hydrogen ion concentration. It was suggested that both the appropriate changes of chemical and physical properties of polyelectrolyte complex membrane and the affinity of the carrier fixed to the membrane for alkali metal ions controlled the active transport and selectivity through the membranes.
Mechanical, thermal, and electric properties of polyurethaneimide elastomers
Authors: Masiulanis Bogumiła , Zielin̂ski Ryszard
Published: April 2003

Linear polyurethaneimide elastomers (PUI) were obtained from polyether‐ or polyester‐diols, diphenylmethane diisocyanate or bitolylene diisocyanate and pyromellitic acid dianhydride. It was found that these polymers have considerably better mechanical properties than typical linear polyurethanes (PU). The elastic modulus and stress at break increase with contents of the hard polyimide segments. The softening temperatures and thermal stability of the PUI at 500°C were higher than the ones of PU with similar hard segment contents. Electric properties of PUI were close to the ones of conventional PU. It was shown that cellular PUI had considerably lower dielectric constant. Tg's of the soft segments PUI were less than Tg's corresponding to PU. It is connected with greater phase separation of the hard imide segments from the soft polyether– or polyester–urethane matrix.
The conduction mechanism of polymer–filler particles
Authors: Miyauchi Shin'nosuke , Togashi Eiki
Published: April 2003

In this paper, the electrical properties and the conductive mechanism of polymer‐filler particles are discussed using polymer‐grafted carbon black. Resistors with resistivities in the range of ca. 10–108 Ω cm were made, and the resistance–temperature relationship was measured between 77 and 298° K. In this temperature range, the resistance decreased with an increase of temperature, suggesting that the electrical conduction is thermally activated. The resistance as a function of field strength was measured by a pulse method. The resistor was a resistivity of ca. 104 Ω cm showed field dependence, and the change of resistance was reversible. It was found that the resistance was independent of temperature at high field strength, and tunneling conduction is predominant. On the basis of these facts, theoretical equations were derived and compared with the experimental values.
Bonding in cotton fiber from formaldehyde‐free crosslinks
Authors: Frick J. G.
Published: April 2003

Cotton fabric was crosslinked with five agents, three of which were prepared form formaldehyde and two of which were formaldehyde‐free. The formaldehyde‐free agents produced less bonding between layers in the laminated microstructure of the cotton fiber. One agent, 4,5‐dihydroxy‐1,3‐dimethyl‐2‐imidazolidinone, gave no evidence of any interlayer bonding. All five agents gave the same relationship between wrinkle recovery angle and molar substitution on the cotton up to moderate recovery angles, but only agents based on formaldehyde gave higher wrinkle recovery angles with additional reaction. Intralayer crosslinking did not reduce absorptivity, as shown by moisture regain and dye receptivity, but did restrict swelling in cupriethylenediamine hydroxide to the same extent as combined interlayer and intralayer crosslinking. The decrease in extensibility of treated fabric with increasing wrinkle recovery angle was the same with all agents. These results indicate the regions of the fiber that are important for each of these properties.
Mechanical degradation of PVC films monitored by photoacoustic spectroscopy
Authors: Abu‐Zeid M. E. , Nofal E. E. , Tahseen L. A. , Abdul‐Rasoul F. A.
Published: April 2003

PVC films were subjected to mechanical degradation at room and elevated temperatures and monitored by photoacoustic spectroscopy. Broken bonds in the main PVC chain result in the formation of “mechano‐radicals,” which in turn yield a zipper reaction and the formation of submicrocracks in the PVC samples. The mechanistic schemes based on the formation of the mechano‐radicals are introduced and are successfully supported by the experimental results.
The effect of cobalt complex addition on the cure and properties of an epoxy matrix resin
Authors: Stoakley D. M. , St. Clair A. K.
Published: April 2003

The effects of adding various cobalt complexes to a tetraglycidyl methylene dianiline‐based epoxy resin were determined. The addition of cobalt(III) acetylacetonate was found to alter the epoxy cure and improve the flexural strength and fracture toughness of the cured resin. These effects were not duplicated by the addition of various other cobalt complexes.
Surface modification of cellulose fibers III. Durability of cellulose–polyester composites under environmental aging
Authors: Zadorecki Pawel , Flodin Per
Published: April 2003

The effects of improved interfacial adhesion on the environmental aging behavior of cellulose–polyester composites were studied. The reduction in maximum water content of the composites upon immersion in water which occurs for surface‐treated fibers is explained by the restrictions from fiber/matrix network. Whitening of the specimens based on the untreated fibers, or on fibers treated but not covalently bonded to the matrix, was found to be due to the formation of debonding cracks. Such cracks were formed on drying the materials. When the fiber and the matrix are covalently bonded, the matrix follows the fiber during shrinking, and thus no cracks are formed.
Vanadium‐cyclohexanone–initiated graft copolymerization of methyl methacrylate onto jute fibers
Authors: Mohanty A. K. , Singh B. C. , Mishra M.
Published: April 2003

Graft copolymerization of methyl methacrylate (MMA) was carried out on jute fibers using a V5+ ‐cyclohexanone redox initiator system. The effect of the concentration of acid, monomer, and V5+ on graft yield have been studied. In order to obtain optimum conditions of grafting, the effects of temperature, acid, reaction medium, solvent, and some inorganic salts on graft yield have been investigated. The most remarkable features of the investigation include the proposition of a mechanism and derivation of rate expression for the grafting process. More than 100% grafting could be achieved with the present system.
Control of solute permeability based on pH‐induced reversible conformational change in block copolypeptide membrane
Authors: Minoura Norihiko , Aiba Sei‐Ichi , Fujiwara Yukihiko
Published: April 2003

An ABBA‐type block copolypeptide membrane composed of L‐glutamic acid (A) and L‐leucine (B) was prepared, and a solute permeability of the membrane was studied. According to the observation of electron microscope, the membrane had the phase‐separated morphology that the domains consisting of poly(L‐glutamic acid) blocks are emebedded in a continuous matrix of the poly(L‐leucine) phase. The reversible conformational change of the poly(L‐glutamic acid) from α‐helix to random coil induced by changing the pH of the external medium was presumed to occur in the domains on the basis of the results of infrared absorption spectra. In the pH dependence of the diffusion coefficients of KCl, NaCl, and LiCl in the membrane, a considerable decrease was found at about pH 4, and thought to result from the conformational transition. In an acidic medium, the permeability of KCl, NaCl, and NiCl was higher then that of glucose, but this order was reversed in higher pHs. These results indicate that the poly(L‐glutamic acid) domains in the membrane function as channels for solute transport.
Plasma polymerized membranes and gas permeability. II
Authors: Sakata Jiro , Yamamoto Minoru , Hirai Masana
Published: April 2003

Thin films were deposited onto porous substrates by plasma polymerization using three kinds of organosilicic compounds, tetramethylsilane (TMS), hexamethyldisiloxane (M2), and octamethylcyclotetrasiloxane (D4). Those composite membranes showed different characteristics of gas permeability. When D4 was plasma‐deposited onto a porous substrate, the composites membrane showed the highest oxygen permeability and the lowest oxygen‐to‐nitrogen permeability ratio. The composite membrane prepared from TMS showed the permeability characteristics opposite to the membrane obtained from D4. Infrared spectrum of the polymer from D4 resembles that of dimethylpolysiloxane. The plasma polymers from TMS and M2 showed different profiles in SiO absorption bands in the range 1100–1000 cm‐1 or in absorption bands of SiCH3 groups in the range 850–750 cm‐1 from respective monomers. X‐ray photoelectron spectroscopic observation indicated that all the plasma polymers contained more than two species of Si atom with different oxidation states. The greater part of Si atoms in plasma polymers took the same oxidation states in corresponding monomer. The gas permeability characteristics were closely related to the oxidation states of Si atom in the plasma polymers.
Effect of molecular weight on high‐speed melt spinning of nylon 6
Authors: Koyama Kiyohito , Suryadevara Jogendra , Spuriell Joseph E.
Published: April 2003

An extensive experimental study of the structure and properties developed in as‐spun nylon 6 filaments is reported. Five polymers representing different molecular weights in the range 25,000–73,000 g/mol (viscosity average) were studied. These polymers were melt spun over a range of spinning speeds using an air drag type of drawdown device. Maximum take‐up velocities achieved were in the neighborhood of 4000 m/min. The structure and properties of the as‐spun filaments were characterized using density, DSC, WAXS, SAXS, birefringence, and tensile tests. The structural characteristics and properties of the filaments are strongly dependent on molecular weight. Generally, higher molecular weight leads to higher modulus and filament tenacity and lower elongation to break in the as‐spun filaments. The structural changes with molecular weight are rather complicated; the complications are explained in terms of changes of crystallization rate and attainable crystallinity.
Effect of time‐temperature path of cure on the water absorption of high Tg epoxy resins
Authors: Aronhime M. T. , Peng X. , Gillham J. K. , Small R. D.
Published: April 2003

The effect of different time—temperature paths of cure on the water absorption of high Tg epoxy resins has been investigated. The resins were cured isothermally for different times, with the following results: as extent of cure increased, the glass transition temperature (Tg) increased, the room temperature (RT) modulus decreased, the RT density decreased, the RT diffusion coefficient appeared to decrease, and the RT water absorption increased. The decrease in RT density is related to an increase in free volume, which controls the amount of water absorbed. A qualitative model accounts for the increase in RT free volume with increasing cure. The model is based on a restricted decrease of free volume on cure due to the rigid molecular segments in the cured resin systems. The sorption isotherms can be characterized by the dual mode theory at low activities but at high activities the sorption is complicated by penetrant clustering. A thermodynamic approach, independent of the absorption model, can correlate sorption data at different temperatures. The diglycidyl resin was also cured for extended times at three temperatures, in an effort to achieve full cure at each temperature. For these, the higher the cure temperature, the lower the RT density, which could result from the lower initial density of materials cured at higher temperatures. The equilibrium water absorption increased with increasing cure temperature, consistent with the decrease in RT density. The systems studied were a diglycidyl ether of bisphenol A cured with an aromatic tetrafunctional diamine, trimethylene glycol di‐p‐aminobenzoate (Tg∞ = 156°C), and a triglycidyl ether of tris(hydroxyphenyl)methane cured with the same amine (Tg∞ = 268°C).
Preparation and reactions of polymers having 1‐aroyl‐2‐(3‐pyridyl)ethylenes as photosensitive groups
Authors: Watanabe Shoji , Ichimura Kunihiro , Suda Yoshio
Published: April 2003

The reactions of 1‐aroyl‐2‐(3‐pyridyl)ethylenes (APE) with polychloromethylstyrene (PCMS) yield polymeric systems which undergo rapid crosslinking upon short exposure to ultraviolet (UV) light. The photochemical reaction of polymers as well as model compounds was followed by the measurement of UV absorption of APE and the analysis of extinction coefficient difference (ED) diagrams.1