bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of anhydride curing of isophthalic diglycidyl ester using differential scanning calorimetry
Authors: Khanna Umang , Chanda Manas
Published: April 2003

The cure reaction of a model diglycidyl ester, bis‐(2,3‐epoxypropyl)‐1,3‐benzenedicarbox‐ylate, with hexahydrophthalic anhydride as the curing agent and benzyldimethylamine as the catalyst, was studied by differential scanning calorimetry using an isothermal approach over the temperature range 100–135°C. The results indicate that the cure reaction is au‐tocatalytic in nature and does not follow simple nth‐order kinetics. A semiempirical equation for autocatalytic systems containing two rate constants and two reaction orders, viz., 0.5 and 1.5, provided a good phenomenological description of the cure kinetics up to the point of vitrification. With the inclusion of a diffusion factor into this model, it was, however, possible to predict with precision the cure kinetics over the whole range of conversion covering both pre‐and postvitrification stages and over the entire temperature range of 100–135°C employed for isothermal curing. © 1993 John Wiley & Sons, Inc.
Cyclic voltammetry and conductivity investigations of polyaniline
Authors: Bhadani Suraj N. , Gupta Manoj K. , Gupta Sumanta K. Sen
Published: April 2003

The cyclic voltammograms of polyaniline prepared electrochemically were examined in the range −0.2 to 1.0 V vs. SCE in the presence and absence of aniline in the acqueous solution of HBF4. Cyclic voltammetry studies show that the polymeric film suffers degradation when the potential exceeds +0.85 V, and below this potential, it is quite stable. The redox reaction of the film is reversible. The polymeric film synthesized at low temperature and high acid concentration exhibits higher electronic conductivities. © 1993 John Wiley & Sons, Inc.
Correlation of binder mechanical properties with functionality type and molecular weight distribution for hydroxy‐terminated polybutadienes: 13C‐NMR and SEC studies
Authors: Ramarao M. , Scarish K. J. , Ravindran P. V. , Chandrasekharan G. , Alwan S. , Sastri K. S.
Published: April 2003

Hydroxy‐terminated polybutadiene (HTPB) liquid prepolymers (I‐IX), with closely similar OH values, M̄n, viscosity, and microstructure, were synthesized by H2O2‐initiated free‐radical polymerization of butadiene in an isopropanol–water solvent system. However, binders obtained by curing HTPB polymers showed wide variations in their sol content, cross‐link density, and mechanical properties. These variations were atributed to the differences in functionality‐type distribution (FTD) and molecular weight distribution (MWD) of the polymers. FTD was interpreted in terms of ‐type primary hydroxyls. [V/G] showed excellent linear correlation with the elongation at break (E) of the binders. The polymers exhibited bimodal MWD and this behavior was discussed in relation to two different initiation processes occurring. The high molecular weight fraction (Fh) of the various polymers was determined by reverse‐phase HPLC and showed good correlation with E. The sol content and cross‐link density of the binders also showed good correlation with the parameter V/GFh. The parameters [V/G] and Fh provide acceptance criteria for blending different batches of polymers for propellant formulations. © 1993 John Wiley & Sons, Inc.
Electrostatic and steric stabilization of PVC primary particles
Authors: Kiparissides C. , Moustakis I. , Hamielec A.
Published: April 2003

Problems related to the formation and stability of primary particles in VCM suspension and bulk polymerization were theoretically analyzed, based on the DLVO (Deryaguin‐Landau‐Verway‐Overbeek) and HVO (Hesselink‐Vrij‐Overbeek) theories of stability of colloidal systems. In the absence of secondary stabilizers, PVC primary particles were solely stabilized by negative electric charges, as a result of the presence of HCl formed by a chain transfer reaction of chloride redicals to PVC polymer chains. The dependence of the stability of primary particles on the ionic strength of the medium, temperature, and total particle charge was quantitatively investigated in terms of the stability ratio and the particle coalescence rate constant. The steric stabilization of primary particles, arising from the addition of surfactants or polymers to the monomer phase, was examined, using the HVO theory. It was shown that PMMA improved the stability of primary particles and, thus, could alter the particle agglomeration kinetics. The effects of molar mass and the amount of the absorbed PMMA, as well as the influence of solvent quality on the steric stabilization of primary particles, were also investigated. The experimental results, published on the electrostatic and steric stabilization of PVC primary particles, were in good agreement with the theoretical predictions obtained in this study. © 1993 John Wiley & Sons, Inc.
Formation of polymeric foams from aqueous foams stabilized using a polymerizable surfactant
Authors: Raj W. R. Palani , Sasthav Mohan , Cheung H. Michael
Published: April 2003

Polymerization of foams formed by purging with nitrogen an aqueous precursor system made up of a polymerizable surfactant, a monomer, and a cross‐linking agent yielded stable polymeric foams. The precursor system for foaming contained hydrophobic components (methyl methacrylate as monomer and ethylene glycol dimethacrylate as cross‐linking agent) in water and was stabilized using the polymerizable surfactant potassium acrylamidostearate. The phase‐behavior study for the precursor system was conducted followed by an investigation of the stability of the foams obtained on purging with nitrogen. Sonicating the precursor systems during the process of purging with nitrogen gas followed by polymerization resulted in aqueous foams having a uniform cell size. The aqueous foams were polymerized by a free‐radical mechanism using photoinitiated and thermal techniques to form stable polymeric foams. The morphology and density of the polymeric foams obtained was determined and observed to be significantly dependent on the composition of the aqueous precursor that was foamed. These results indicate the feasibility of synthesizing polymeric foams without using hydrocarbon solvents or blowing agents during polymerization. © 1993 John Wiley & Sons, Inc.
Polyesters containing sulfur. II. Products of reaction of polyesters with elemental sulfur
Authors: Kultys Anna , Podkościelny Wawrzyniec
Published: April 2003

New polyester–sulfur compositions with increased tensile strength were obtained by heating polyesters derived from diphenylmethane‐4,4′‐di(methylthioacetic acid) and ethylene or diethylene glycol with elemental sulfur. The hardness, tensile, thermomechanical, as well as some electrical properties of reaction products were determined. © 1993 John Wiley & Sons, Inc.
Effect of morphology on brittle‐ductile transition of HPDE/CaCO3 blends
Authors: Fu Qiang , Wang Guiheng
Published: April 2003

In this paper, the results of a series of investigations of the effect of morphology on the brittle‐ductile transition for HDPE/CaCO3 blends are summarized: (1) It seems the critical ligament thickness increases with increasing matrix toughness; (2) the interphase adhesion is very important for the toughness of HDPE/CaCO3 blends; (3) small particles are more effective than large ones; (4) CaCO3 particle aggregation will reduce toughening efficiency; (5) uniform CaCO3 particle size is more effective than heterogeneous size for the toughening of HDPE. It is expected that a polymer with higher modulus as well as higher toughness will be obtained by appropriately controlling the morphology of HDPE/CaCO3 blends. © 1993 John Wiley & Sons, Inc.
Synthesis and characterization of homopolymers and copolymers of various acrylates and acrylonitrile
Authors: Joseph Roychen , Devi Surekha , Rakshit Animesh Kumar
Published: April 2003

Various homopolymers and copolymers of methyl acrylate, ethyl acrylate, butyl acrylate, and acrylonitrile in different feed ratios were synthesized. These were characterized by IR, 13C‐NMR, DSC, DTA, and TGA. Spectroscopic characterization helped in differentiating copolymers of different mol ratios. Thermal analysis revealed different degradation patterns for homopolymers and copolymers. The temperature and energy changes associated with various phase transitions were dependent on the chemical composition of homo‐ and copolymers, as expected. © 1993 John Wiley & Sons, Inc.
Preparation of magnetic latex particles by emulsion polymerization of styrene in the presence of a ferrofluid
Authors: Yanase Noriko , Noguchi Hiromichi , Asakura Hideki , Suzuta Tatsuo
Published: April 2003

Magnetic latex particles were prepared by the emulsion polymerization of styrene at 70°C in the presence of a commercial ferrofluid containing surfactant‐stabilized magnetite particles in the aqueous phase or its modification by ultrafiltration, using potassium persulfate as an initiator. The effects of diversified variables such as the amounts of initiator, monomer, and additive (calcium chloride and fluorescent dyes) on the polymerization reaction and particle characteristics were investigated. The general polymerization features were analogous to those of ordinary emulsion polymerizations. Transmission electron microscopy revealed that when the commercial ferrofluid was used the magnetite particles localized in the latex particles and the magnetite content varied from particle to particle and that when the ferrofluid was used after ultrafiltration the magnetite particles were dispersed well in the latex particles. © 1993 John Wiley & Sons, Inc.
Physical properties and structure of unreacted PC/PBT blends
Authors: Sánchez P. , Remiro P. M. , Nazábal J.
Published: April 2003

Unreacted PC/PBT blends have been obtained by melt blending in all the composition ranges. The followed processing method produced partially miscibilized and crystalline blends. The plot of the density of the amorphous part of the blends against its composition indicates that this parameter is more important than the crystallinity level in determining the mechanical properties of the blends. The blends exhibited an overall improvement of mechanical properties with a combination of behaviors that are close to linearity and are synergistic. © 1993 John Wiley & Sons, Inc.
Glucose oxidase immobilization onto a plasma‐induced graft copolymerized polymeric membrane modified by poly(ethylene oxide) as a spacer
Authors: Wang Chee‐Chan , Hsiue Ging Ho
Published: April 2003

Plasma‐induced graft copolymerization of acrylic acid, which was incorporated onto polyethylene (PE) film, was prepared. A bisamino poly(ethylene oxide) (PEO) was immobilized onto the poly(acrylic acid) (PAAc)‐grafted PE membrane to modify the surface properties. The samples were characterized by ESCA. A respective chemical shift of Ar plasma‐treated and control polymeric film was revealed by ESCA. The presence of the grafted PAAc and PEO was also verified. Glucose oxidase (GOD) was immobilized onto this novel grafted polymeric film with and without PEO being used as a spacer. The Michaelis constant, Km, and the maximum reaction velocity, Vmax, were estimated for the free and the immobilized GOD. GOD immobilized onto the polymeric films with and without a spacer obeyed Michaelis kinetics. The Michaelis constant, Km, was larger for the immobilized GOD than for the free one whereas Vmax was smaller for the immobilized GOD. The bioactivity of PEO‐modified PAAc‐grafted PE membrane (PAAc–PEO–GOD) was higher than that of PAAc‐grafted PE membrane (PAAc–GOD). The pH and thermal stabilities of the immobilized GOD without a spacer (PAAc–GOD) were higher than those of the immobilized GOD with a spacer (PAAc–PEO–GOD) and the free form. © 1993 John Wiley & Sons, Inc.
Structure and properties of compatibilized blends of polyamide‐6 and ABS
Authors: Misra A. , Sawhney G. , Kumar R. Ananda
Published: April 2003

Mechanical and Morphological properties of polyamide‐6/ABS blend systems, compatibilized by styrene‐maleic anhydride (SMA) copolymer, have been studied. The strength, modulus, and impact properties improved upon the addition of SMA. Morphological studies, using small angle light scattering, polarizing microscopy, and scanning electron microscopy, showed that SMA acts as a compatibilizer for the above system. © 1993 John Wiley & Sons, Inc.
Structures and mechanisms of formation of poly(acrylic acid)‐iron (II and III) chloride gels in water and hydrogen peroxide
Authors: Lindén Lars‐åke , Rabek Jan F.
Published: April 2003

Poly(acrylic acid) (PAA) can form stable and insoluble gels with FeCl3 in water or in H2O2 (30 wt %). Two carboxylic groups are complexed by the FeCl2+ ion. PAA‐FeCl3 (2 : 1) gels have found practical application in the blocking of microscopic channels in tooth dentin and thereby decrease the fluid permeability and protect against tooth decay. © 1993 John Wiley & Sons, Inc.
Structural analysis and degradation behavior in polyethylene glycol/poly(L‐lactide) copolymers
Authors: Hu David Shiaw‐Guang , Liu Hsin‐Jiant
Published: April 2003

The objective of this research is to investigate the molecular weight, degradation mechanism, and crystalline morphology of polyethylene glycol/poly(L‐lactide) (PEG/PLLA) copolymers during hydrolytic degradation. PEG/PLLA copolymers were prepared from cyclic L‐lactide and polyethylene glycol with molecular weights ranging from 1000 to 6000 Da. The structural analysis was carried out by GPC, DSC, FTIR, 13C‐NMR, and 1H‐NMR. Gel permeation chromatograms also indicate that the hydrolysis causes the change of mass distribution from a unimodal to a bimodal from. An exothermic recrystallization peak and its shoulder portion at the lower temperature range during melting appears immediately following the hydrolytic degradation. This indicates the heterogeneity of the crystals. The data of NMR and FTIR shows that during the initial period (0–200 h) of hydrolysis, there appears to be a formation of hydroxyl end groups connected to PEG blocks and carboxyl end groups connected to polylactide blocks. Due to the hydrophilic ethylene oxide segment in PEG/PLLA copolymers, the rate of hydrolysis is much faster during the first 200 h relative to longer hydrolysis time. It is therefore concluded that the chain scission during the initial period occurs at the ester linkage connecting PEG and PLLA blocks, in addition to ester groups within the PLLA blocks. © 1994 John Wiley & Sons, Inc.
Miscibility studies of polymer blends by viscometry methods
Authors: Lizymol P. P. , Thomas Sabu
Published: April 2003

The intrinsic viscosities of blends of poly(vinyl chloride)/poly(ethylene‐co‐vinyl acetate) (PVC/EVA), poly(vinyl chloride)/poly(styrene‐co‐acrylonitrile) (PVC/SAN), and poly(ethylene‐co‐vinyl acetate)/poly(styrene‐co‐acrylonitrile) (EVA/SAN) have been studied in cyclohexanone as a function of blend composition. In order to predict the compatibility of polymer pairs in solution, the interaction parameter term, Δb, obtained from the modified Krigbaum and Wall theory, and the difference in the intrinsic viscosities of the polymer mixtures and the weight average intrinsic viscosities of the two polymer solutions taken separately are used. © 1994 John Wiley & Sons, Inc.
Physical properties of model graft copolymers and their use as blend compatibilizers
Authors: Peiffer Dennis G. , Rabeony M.
Published: April 2003

The present investigation pertains to the structure–property relationships of highly structured graft copolymers. The specific model graft copolymers are based on an elastomeric backbone, i.e., poly(ethyl acrylate), and monodisperse thermoplastic grafts, i.e., polystyrene. The synthesis of these graft copolymers is based on the free‐radical polymerization of ethyl acrylate and an anionically polymerized polystyrene macromonomer. It is clearly demonstrated that grafts significantly enhance tensile properties. The level of improvement is directly related to the graft level, i.e., number of grafts/chain, and graft molecular weight. In addition, blending these graft copolymers into their respective homopolymer mixture results in a mechanical performance strikingly dependent on the molecular characteristics of the graft copolymer. For example, tensile strength is maximized at a level between one and two grafts per chain. This result parallels observations noted in blend compatibilization using diblock and triblock copolymers. It is also demonstrated that using mutually grafted copolymers produces an interesting variety of compatibilized ternary (or higher) component blends. © 1994 John Wiley & Sons, Inc.
Miscibility and interaction studies on some aqueous polymer blend solutions by ultrasonic and rheological techniques
Authors: Paladhi R. , Singh R. P.
Published: April 2003

The aqueous solutions of poly(ethylene oxide)–polyacrylic acid, poly(vinyl pyrrolidone)–poly(vinyl alcohol), and poly(ethylene oxide)–poly(vinyl alcohol) blends have been studied by ultrasonic, rheological, and viscometric techniques. Extensive investigation over a wide range of concentrations, temperatures, compositions, pH, and shear rates indicate the degree of miscibility, extent of interaction between the polymers, and stoichiometry of the polymer complexes formed by the strong interaction between the polymers in solutions. These investigations indicate the miscibility of poly(ethylene oxide)–polyacrylic acid and poly(ethylene oxide)–poly(vinyl pyrrolidone) blends and the immiscibility of poly(ethylene oxide)–poly(vinyl alcohol) blends in conformity with other reported investigations. © 1994 John Wiley & Sons, Inc.
Studies related to in‐plane flow behavior of elastomer matrix in nonwoven fibrous structures
Authors: Epstein M. , Shishoo R. L.
Published: April 2003

The purpose of the present work has been to produce knowledge as regards the rheological behavior of polymer matrix in nonwoven fibrous reinforcing structures for composites. The results are expected to contribute toward a better understanding of flow mechanisms in fibrous systems in order to develop better techniques for fabricating elastomer‐based composites. Theoretical and experimental analyses have been made of interactions between the structural parameters of the fibrous mats and the flow characteristics of the matrix with systematically varied material and process parameters. In nonwoven mats with fibers laid lengthwise, the flow rate along the fiber direction was found to be significantly higher than the flow rate crosswise to the fiber direction. Nonwoven mats with multidirectionally laid fibers exhibited a practically radial flow front pattern. Nonwoven mats made of coarser fibers showed greater matrix polymer flow rate as compared with finer fibers. The matrix flow distance was proportional to the logarithm of injection time. The decrease of pressure in the mold cavity was linearly proportional to the matrix flow distance. The dependence of permeability on the level of compression of the fibrous structure is in agreement with the results published by other workers. © 1994 John Wiley & Sons, Inc.
Gelation of poly(vinyl alcohol) solutions at low temperatures (20 to −78°C) and properties of gels
Authors: Yamaura Kazuo , Karasawa Koh‐Ichi , Tanigami Tetsuya , Matsuzawa Shuji
Published: April 2003

The flow points of atactic poly(vinyl alcohol) (a‐PVA) gels with H2O/dimethyl sulfoxide (DMSO) = 90/10 (v/v) chilled at 20 to −78°C for 24 h depended on the chilling temperature and were 0–30°C for gels with the initial polymer concentrations (Ci) of 2–5 g/dL, whereas those for H2O/DMSO = 50/50 chilled at 0 to −78°C were independent of the chilling temperature and were 70–75°C. Syneresis occurred after eight cycles of freezing (−24°C) and thawing (20°C) for a‐PVA hydrogels at concentrations above Ci = 4 g/dL and two such cycles for syndiotacticity‐rich PVA (s‐PVA) hydrogels at concentrations above Ci = 1 g/dL. The extent of syneresis per one cycle for s‐PVA hydrogels was higher than that for a‐PVA hydrogels at the initial cycles. In the a‐PVA hydrogels with an initial polymer concentration of ca. 30 g/dL, syneresis was expected not to occur even after 20 cycles. If all the free water in the gels is assumed to have transuded by syneresis after 20 cycles, the residual water is bound water and is estimated to be six water molecules per one vinyl alcohol monomer unit. © 1994 John Wiley & Sons, Inc.
A 13C NMR study of polyflavonoid tannin adhesive intermediates. II. Colloidal state reactions
Authors: Pizzi A. , Stephanou A.
Published: April 2003

Water solutions of 40–50% polyflavonoid tannin extracts appear to be in a colloidal state. This is caused by both the presence of noticeable amounts of hydrocolloid gums as well as the presence of higher molecular mass tannins. 13C NMR analysis appears to confirm that during chemical treatment, reactions occur in these colloidal solutions that would not be likely to occur in noncolloidal solutions as used in model compound experiments. These reactions centre on the role of the organic anhydride used during treatment, and lead to intramicellar direct α‐set attack or to acetylation of the tannin followed by a rapid rearrangement again to an α‐set attack, which is similar to both a Kolbe reaction and a Fries rearrangement. This eventually leads to accelerated cross‐linking of the tannin‐formal‐dehyde adhesive prepared from the chemically modified tannin extract. It appears that such reactions and rearrangements are performance determining in the case of the two lower‐reactivity tannins examined, mimosa and quebracho; have some noticeably positive effects on the higher reactivity pine tannin, and appear instead to have a deleterious effect on the other higher reactivity tannin, namely pecan nut tannin. The reasons for such behaviour are briefly discussed. © 1994 John Wiley & Sons, Inc.
Surface chlorination of polypropylene film by CHCI3 plasma
Authors: Inagaki N. , Tasaka S. , Suzuki Y.
Published: April 2003

Polypropylene films were treated with the CHCI3 plasma, and their chemical composition was analyzed with XPS and ART IR spectroscopy. The CHCI3 plasma irradiation made polypropylene films hydrophilic. The advancing contact angle decreases from 95° for the untreated to about 73° for the CHCI3 plasma‐treated films. In the CHCI3 plasma irradiation, the chlorination occurs, and CCl, CCl2, and CCl3 units are formed in the polypropylene films. Simultaneously with the chlorination, unsaturated units (CC and conjugated CC units) are formed from dehydrogen chlorination of the chlorinated products, but the oxygen incorporation into the films is low. The CHCI3 plasma is preferred in chlorination of polypropylene films to the CCl4 plasma. © 1994 John Wiley & Sons, Inc.
Synthesis and evaluation of acrylate polymers for improving flow properties of waxy crudes
Authors: El‐Gamal I. M. , Ghuiba F. M. , El‐Batanoney M. H. , Gobiel S.
Published: April 2003

N‐Alkyl acrylates and n‐alkyl methacrylates were prepared by esterification of acrylic and methacrylic acids with two long‐chain alcohol blends NAFOL 2022 and NAFOL 1822. The prepared monomers were characterized and polymerized individually. In addition, copolymers of n‐alkyl acrylate‐n‐alkyl methacrylate, and n‐alkyl methacrylate–vinyl acetate and a terpolymer of n‐alkyl acrylate–acrylic acid–vinyl acetate were also synthesized. These polymers were also characterized and then evaluated as flow improvers in Khalda mixtureand Salam Egyptian waxy crudes. The majority of the prepared additives showed good performance in improving the flow properties of the tested crudes. © 1994 John Wiley & Sons, Inc.
LDPE/PP blends modified by peroxide and radiation induced reactions
Authors: Yu D. W. , Xanthos M. , Gogos C. G.
Published: April 2003

LDPE/PP polyblends, modified through either peroxide initiated reactions or irradiation, were characterized in terms of rheological and mechanical properties and microstructure. In the presence of peroxide, or through irradiation LDPE crosslinks, PP degrades. Data were obtained at two peroxide concentration levels (0.1 and 1% by weight) and two radiation doses (30 and 100 kGy). The results show that in peroxide modification, the degradation of PP prevails over the crosslinking of LDPE. However, the effect of irradiation of LDPE (crosslinking) is predominant over that of PP (degradation). The irradiation process tends to yield improved mechanical properties vs. peroxide modification for the PP‐rich blends. In addition, the melt viscosity and elasticity of the irradiated PP‐rich blends are higher than those of the peroxide‐reacted blends at a given level of PP content and frequencies between 10 and 100 rad/s. Attempts were made to relate the shape of the rheological curves and the mechanical properties of the blends to the observed changes in their microstructure. © 1994 John Wiley & Sons, Inc.
Mechanisms of interactive crazing in PC/SAN microlayer composites
Authors: Sung K. , Haderski D. , Hiltner A. , Baer E.
Published: April 2003

Mechanisms are proposed for the two types of interactive crazing that have been observed in PC/SAN microlayer composites when the PC layer thickness is on the micron‐size scale. It is demonstrated that when the PC layer is thin enough the deformation zone that forms at a craze tip can interact with the next‐neighboring SAN layer. By measuring the dimensions of the craze tip in scanning electron micrographs, it was found that the craze‐tip opening does not depend on the SAN layer thickness, i.e., the length of the SAN craze. Consequently, the size and shape of the resulting plastic zone in the PC layer are also independent of layer thickness. The zone that forms in the PC layer consists of a colinear plastic zone together with a pair of micro‐shearbands that grow at an angle of about 45°. When the PC layer is less than 6 μm, the elastic stress concentration from the colinear plastic zone increases the probability of crazing in the neighboring SAN layer with the formation of craze doublets that consist of two aligned crazes in neighboring SAN layers. By taking into consideration the Weibull distribution of crazing, a craze doublet fraction comparable to the 30% observed experimentally was predicted with a stress intensification factor in the range of 1.03–1.05. When the PC layer thickness is less than 1.3 μm, the length of the colinear plastic zone is comparable to the PC layer thickness. Formation of a craze at the point of impingement of the plastic zone on the neighboring SAN layer leads to craze arrays with many aligned crazes in neighboring SAN layers. At higher strains, the micro‐shearbands grow through the PC layers and extend into several adjacent SAN and PC layers. This produces a change in deformation mechanism in the SAN layers at the yield instability, from craze opening to shear yielding. © 1994 John Wiley & Sons, Inc.
Ductility of filled polymers
Authors: Bazhenov S. , Li J. X. , Hiltner A. , Baer E.
Published: April 2003

The ductility of a calcium carbonate‐filled amorphous copolyester PETG in a uniaxial tensite test was examined as a fiction other filler volume fraction. A ductile‐to‐quasibrittle transition occurred as the volume fraction of filler increased. This transition was from propragation of a stable neck through the entire gauge length of the specimen to fracture in the neck without propagation. The draw stress (lower yield stress) did not depend on the filler content and was equal to the draw stress of the unfilled polymer. It was therefore possible to use a simply model to predict the dependence of the fracture strain on the filler volume fraction. It was proposed that when the fracture strain decreases to the draw strain of the polymer the fracture mechanism changes and the fracture strain drops sharply. The critical filler content at which the fracture mode changes is determined primarily by the degree of strain‐hardening of the polymer. © 1994 John Wiley & Sons, Inc.
Studies on cure synergism. I. Effect of safe zinc dithiocarbamates on NR vulcanization accelerated by thiazole‐based accelerators
Authors: Debnath S. C. , Basu D. K.
Published: April 2003

Investigations have been carried out on the effect of several zinc dithiocarbamates in the presence of thiazole‐based accelerators in the vulcanization of natural rubber (NR), keeping in mind the possibility of introducing safe dithiocarbamates derived from safe amines. Mutual activity is observed in all the binary systems studied, the highest being observed in the zinc dibenzyldithiocarbamate‐dibenzothiazyldisulfide (ZBEC–MBTS)‐accelerated system. The effect of zinc diisopropyl dithiophosphate, reportedly a safe rubber additive, which is recognized as an age‐resistant agent for NR, on cure has also been studied. The study reveals that thiuram disulfide and MBT are always formed from the reaction either between zinc dithiocarbamate (ZDC) and MBTS or between ZDC and N‐cyclohexyl‐2‐benzothiazole sulfenamide (CBS). It has been conclusively proved that 2‐mercaptobenzothiazole (MBT) generated from MBTS or CBS reacts with ZDC and produces tetramethyl thinram disulfide (TMTD). The observed mutual activity has been discussed based on the cure and physical data and explained through the results based on HPLC and a reaction mechanism. © 1994 John Wiley & Sons, Inc.
Equilibrium swelling properties of weakly lonizable 2‐hydroxyethyl methacrylate (HEMA)‐based hydrogels
Authors: Baker John P. , Blanch Harvey W. , Prausnitz John M.
Published: April 2003

Hydrogles, sensitive to pH, were prepared by copolymerizing 2‐hydroxyethyl methacrylate (HEMA) with 2‐dimethylaminoethyl methacrylate (DMA). The mole fraction of the DMA monomer present during synthesis was fixed at 0.3, while the volume fraction of total monomer varied from 0.29 (I) to 1.0 (II). Swelling equilibria were measured in citrate of phosphate buffer for pH from 3.0 to 7.6 Swelling of the hydrogels depends on the volume fraction monomer present during synthesis, solution, pH, and identity of the buffer, Hydrogel I reached a four‐fold larger swelling ratio (g swollen hydrogel/g dry hydrogel) in pH 3.0 citrate buffer, as compared to hydrogel II. Experimental results are interpreted on the basis of ideal Donnan equilibria. © 1994 John Wiley & Sons, Inc.
Preparation of poly(vinyl alcohol)‐graft‐N‐isopropylacrylamide copolymer membranes and permeation of solutes through the membranes
Authors: Nonaka Takamasa , Ogata Tomonari , Kurihara Seiji
Published: April 2003

Thermosensitive copolymers were prepared by graft copolymerization of N‐isopropylacrylamide onto poly(vinyl alcohol) in dimethyl sulfoxide (DMSO) using potassium peroxodisulfate as an initiator. The phase transition temperature was measured by differential scanning calorimetry. The copolymers exhibited almost the same transition temperature (about 33°C) as that of poly(N‐isopropylacrylamide) regardless of the composition of the copolymers. The copolymer membranes were obtained by evaporating solvent from the DMSO solution of the graft copolymers and were insolubilized by annealing the membranes at 120°C for 10 h. Permeation of the lithium ion and Methylene Blue through the membranes was investigated at various temperatures. The permeation of solutes was greatly affected by temperature, i.e., the permeation of the solutes could be controlled at temperatures below and above 33°C. © 1994 John Wiley & Sons, Inc.
Study of an aramid surface reactivity: Modification with a cold plasma or an electron beam followed by a postgrafting reaction
Authors: Poncin‐Epaillard Favienne , Chevet Bruno , Brosse Jean‐Claude
Published: April 2003

Different modes of activation are described for a postgrafting reaction of acrylic acid on poly(p‐phenylene terephthalamid) (PPTA)mitrogen plasma or electron‐beam irradiation. Both lead to surface radical formation, and these species are able to initiate grafting. The Functionalization through amino group attachment is characteristic of plasma treatment. Degradation initiated by UV‐visible emission of plasma is noticed, leading to the amide clivage. The surface grafting is more important when the PPTA is irradiated with a cold plasma and if water is used as the solvent. The polymer crystallinity degree reduces the grafting of the electron beam‐irradiated PPTA even with a high radical concentration. © 1994 John Wiley & Sons, Inc.
Preparation of high‐strength and high‐modulus poly(vinyl alcohol) fibers by crosslinking wet spinning/multistep drawing method
Authors: Hwang Kuen‐Shan , Lin Chin‐An , Lin Chung‐Hua
Published: April 2003

This study is mainly focused on the preparation of high‐strength and high‐modulus poly(vinyl alcohol) (PVA) fibers by crosslinking wet spinning and multistep drawing. High strength as well as high modulus can be achieved by introduction of the crosslinks into the oriented chains to reduce entanglement degree and slippage between chains. The relationships between mechanical properties and fine structure of the drawn fibers were examined based on results of measurements of tensile property, thermal property, dynamic viscoelasticity, crystallinity, and orientation. The strength and Young's modulus of the drawn fibers are approximated to 1.82 and 51.76 GPa, respectively. The fiber has a sharp melting peak temperature that appeared at 236.7°C in the differential scanning calorimeter (DSC) curve. Our results indicate the multistep drawing procedure is superior to the conventional one‐step drawing procedure. These excellent mechanical properties can be directly attributed to their high orientation of the amorphous chains. © 1994 John Wiley & Sons, Inc.
Electrical and thermal conductivities of polyethylene composites filled with biaxial oriented short‐cut carbon fibers
Authors: Agari Y. , Ueda A. , Nagai S.
Published: April 2003

Polyethylene composites filled with various types of carbon fiber were prepared for electrical and thermal conductivity measurements. By estimation of the anisotropic parameter (Hermans' parameter), the fibers were confirmed to be significantly biaxially oriented in the composites. The critical volume fractions in the electrical conductivity of these composites for the two oriented directions (X and Y) were equal to each other and smaller than that for a direction (Z) vertical to the above. The electrical anisotropy, i.e., ratio of electrical conductivity of the composite for the Z direction to the X and Y directions varied drastically with increase in filler content. The longer the length of carbon fiber was, the higher became the electrical conductivity of the biaxially oriented carbon fiber composites for all directions. But, the thermal conductivity of the composite was almost unchanged for the Z direction, even if fiber length was sufficiently long. Our equation, previously proposed, proved adaptable to these thermal conductivities. The factors of Cp and Cf in the equation are kept unchanged, in spite of increasing fiber length. © 1994 John Wiley & Sons, Inc.
Cold remote nitrogen plasma polymerization from 1.1.3.3‐tetramethyldisiloxane–oxygen mixture
Authors: Callebert F. , Supiot Ph. , Asfardjani K. , Dessaux O. , Goudmand P. , Dhamelincourt P. , Laureyns J.
Published: April 2003

Cold remote nitrogen plasma (CRNP) selectively reacts with silane‐terminated organosiloxane compounds such as 1.1.3.3‐tetramethyldisiloxane to give polymeric layers. Deposition rate measurements, FT‐IR and Raman spectroscopy were performed. The chemical composition of the deposited film is closely dependent on the reactive gas composition and its flowing conditions. An original effect of dioxygen addition in the nonionic reactive media is pointed out: dioxygen addition leads to a fast and highly hydrocarbonated polymer formation with a nitrogen fixation in a silazane structure. Polymerization is described by a model where SiO· type of radicals are the critical reactant. A global mechanism is proposed involving active species of the CRNP in initiation step of hydrogen abstraction and the nitrogen triplet state molecule N2(A3Σ) in methyl abstraction on Si· type of free radical. Dioxygen adjunction appears to limit the methyl abstraction steps. The efficient direct oxygen reaction on free radicals leads to an increase of the SiO· radical density and, consequently of the average length of the growing polymeric fragments. Nitrogen fixation, involving oxygenated species, is discussed. Under defined conditions, a highly hydrophobic polymeric film is obtained with a volumic mass of 1.34g/cm3 and a deposition rate of about 12 mg/cm2 h corresponding to a growth rate of 200 Å/s. © 1994 John Wiley & Sons, Inc.
Chemical modification of lignocellulosic fibers I. Functionality changes and graftcopolymerization of acrylonitrile onto pineapple leaf fibers; their characterization and behavior
Authors: Samal R. K. , Bhuyan B. L.
Published: April 2003

This paper is an attempt to examine the commercial significance of an agro‐waste “pineapple leaf fiber” (PALF). The quality enhancement of PALF has been tried through chemical modifications. Functionality changes in the above fiber have been done through mercerization, cyanoethylation, oxidation, and graftcopolymerization with acrylonitrile, using cericion as an initiator at varying concentrations of monomer, initiator, and mineral acid at a number of temperatures for various time intervals. The modified fibers have been characterized by FTIR spectroscopy and viscosity measurements. The extent of moisture regain, acid‐alkali solubility, tensile modulus, dye‐uptake ability, and thermal stability of the resulting materials have been tested and compared with the parent fiber. The significance of such chemical modification in the context of better textile performance and reinforcing behavior of the product in FRP has been discussed. © 1994 John Wiley & Sons, Inc.
Transient shear response of liquid crystal‐forming hydroxypropyl cellulose solution in dimethylacetamide. I. Stress growth and relaxation behavior
Authors: Suto Shinichi , Tateyama Shinichiro
Published: April 2003

The stress growth and relaxation behavior of liquid crystalline hydroxypropyl cellulose solutions in dimethylacetamide was characterized by using exponential functions. The parameters evaluated for the stress growth and relaxation processes were compared and the shear history effect on the parameters was determined. The exponential functions proposed were valid for our system. The isotropic solutions had one retardation time and one relaxation time, whereas the liquid crystalline solutions had plural retardation and relaxation times. The concentration dependence of the parameters for the stress growth process was similar to that for the stress relaxation process and to that for the steady‐state shear viscosity. The stress growth and relaxation behavior for the liquid crystalline solutions was originated from the change (deformation or decrease) in liquid crystalline domains. The deformation of liquid crystalline domains with shear seemed to be slower than the recovering of the domains to original shape. The stress growth process was a progressive event, whereas the relaxation process was a sudden event. Stress relaxation behavior for the liquid crystalline solutions was sensitive to the shear history. © 1994 John Wiley & Sons, Inc.
The formation of nodular structures in the top layer of ultrafiltration membranes
Authors: Wienk I. M. , van den Boomgaard Th. , Smolders C. A.
Published: April 2003

The formation of nodular structures in the top layer of ultrafiltration membranes is considered. A critical review of mechanisms described in the literature is given. Flat‐sheet poly(ether sulfone) membranes and hollow‐fiber poly(ether sulfone)/polyvinylpyrrolidone membranes were made by coagulation of a polymer solution in a nonsolvent medium under different circumstances. From these experiments, a number of empirical rules are found to describe the resulting morphology of the top layer. A new mechanism for the formation of a nodular structure is proposed. It is based on the small diffusion coefficient of the polymer molecules compared to the diffusion coefficient of solvent and nonsolvent combined with a high degree of entanglement of the polymer network. For unstable compositions, phase separation will proceed by growth in amplitude of concentration fluctuations. The rapid diffusional exchange of solvent for nonsolvent in the top layer leads to vitrification of the maxima of the concentration fluctuations that form the nodules. Complete disentanglement of the polymer chains between the nodules is not reached, which explains the small pores and the low porosity of ultrafiltration membranes. © 1994 John Wiley & Sons, Inc.
High‐pressure phase behavior in polyethylene/n‐butane binary and polyethylene/n‐butane/CO2 ternary systems
Authors: Xiong Yan , Kiran Erdogan
Published: April 2003

Solubility of polyethylene molecular weight standards (Mw = 2150, 16,400, 108,000, and 420,000 and Mw/Mn = 1.14, 1.16, 1.32, and 2.66, respectively) has been studied in near‐ and supercritical n‐butane and n‐butane/CO2 mixtures at pressures up to 70 MPa. For each polyethylene/solvent system at selected compositions, demixing pressures have been determined using a high‐pressure variable‐volume view‐cell at temperatures up to 200°C. Solutions in pure n‐butane are found to display LCST (lower critical solution temperature)‐type behavior. The behavior of the solutions in n‐butane/CO2 mixtures are observed to change from the LCST to the UCST (upper critical solution temperature) with increasing CO2 content in the binary solvent. Sanchez–Lacombe theory has been used to model these systems. The predictions correctly describe the nature of the phase diagrams for both binary and ternary systems and the calculations are in reasonable agreement with experimental data. © 1994 John Wiley & Sons, Inc.
TSDC and the role of space charge in polyacrylonitrile/methylacrylate copolymer films
Authors: Migahed M. D. , Ishra M. , El‐Khodary A. , Fahmy T.
Published: April 2003

Space charge effects on direct current (DC) conductivity and the thermally stimulated depolarization current (TSDC) in the semicrystalline polyacrylonitrile–methylacrylate [P(AN–MA)] films have been investigated. The conduction was found to be controlled by space charge limited effect. On the other hand, the TSDC studies point to a superposition of dipole orientation and space charge effects. With the aid of the thermal sampling technique, the complex spectrum could be resolved into its elementary processes. Curve fitting has been carried out and peak parameters were determined. Information related to the motion of dipolar groups could be obtained. The compensation effects is observed to be valid and the value of the compensation temperature (Tc = 343 K) greatly differs from the glass transition temperature (Tg = 383 K). From the DC and TSDC studies considerations, the origin of the three conduction regions appearing in the 1n σ vs. 1/T could be explored. © 1994 John Wiley & Sons, Inc.
Chemical modification of poly(styrene‐co‐maleic anhydride) with primary N‐alkylamines by reactive extrusion
Authors: Vermeesch I. , Groeninckx G.
Published: April 2003

Reactive melt‐processing of poly(styrene‐co‐maleic anhydride) (SMA) with primary N‐alkylamines was carried out in one step in a twin‐screw extruder. Ring formation of the imide occurred within the residence time of the extruder, at temperatures exceeding 220°C and with an excess of primary amines. The increasing chain length of grafted amine onto the SMA backbone depressed the glass transition temperature of poly(styrene‐co‐N‐alkylmaleimides) remarkably. © 1994 John Wiley & Sons, Inc.
Electroless reduction and precipitation of gold from acid solution by polypyrrole
Authors: Kang E. T. , Ting Y. P. , Tan K. L.
Published: April 2003

The oxidation of the 25% intrinsically oxidized polypyrrole, containing 25% [N–] and 75% [NH], and the subsequent reprotonation and reduction of the highly intrinsically oxidized polymer in acid gold solution were utilized for the spontaneous and sustained reduction of gold. The X‐ray photoelectron spectroscopic (XPS) results indicate that only elemental gold [or Au (0)] accumulates on the polymer film or powder surfaces. The N1s core‐level spectra of the protonated and deprotonated polypyrrole after metal reduction suggest that the intrinsic structure of the polymer at the polymer/Au interface remains intact, even at [Au]/[N] mol ratios substantially above 1. The process, however, is limited by the decreasing effective surface area of the polymer due to Au coverage. The Au reduction behavior of polypyrrole was also compared to that of polyaniline. © 1994 John Wiley & Sons, Inc.
Water‐sorption properties of poly(ϵ‐lysine): Carboxymethyl cellulose (CMC) dietary complex films
Authors: Ichikawa Tomoko , Mitsumura Yukari , Nakajima Toshinari
Published: April 2003

To investigate the application of supersorbing materials in the food industry, the water sorption of polyion complex films, prepared by solvent‐casting from poly(ϵ‐lysine) (PEL) and carboxymethyl cellulose (CMC), were examined and some physical properties of the hydrogels were studied. Three CMC samples having various degrees of substitution (DS) and molecular weights (MW) were applied to show a variety of water‐sorption behavior and physical properties. The ratio of PEL/CMC was changed from 10/90 to 50/50. Good film swelling in water was achieved when the complex was made from PEL and CMC with a low DS and an appropriate molecular weight, and when the PEL/CMC ratio was low. This indicated that the carboxyl groups in the CMC are not readily dissociated, and that the strength of cationic and anionic interactions affects the film swelling. In line with this view, the addition of electrolytes markedly lowered the film swelling. Nonelectrolytes such as sucrose or urea had no effect. IR and NMR spectra showed that a fraction of the ionic groups in the polyelectrolytes interact. Tensile moduli of complex dry films decreased linearly as the PEL content increased. Compressive moduli of swollen films were affected by neither the degree of swelling nor the molecular weights of CMC. The lower the DS values of CMC, the higher the compressive moduli were. We also examined the relation between the rigidity of polymer component and the ratio of nonfreezable bound water in complex films. On swelling in acetone–water or ethanol–water mixed solvent, expansion–shrinkage transition of the polymer gels occurred at about 20 mol % acetone or ethanol concentrations for every complex film. The overall characterstics of PEL/CMC consisting of a linear polyanionic polypeptide and a chain of cationic rings are reminiscent of polycationic chitosan and polyanionic polyglutamic acid. © 1994 John Wiley & Sons, Inc.
Variables affecting the methylation reactions of cellulose
Authors: Mansour Olfat Y. , Nagaty Ahmed , El‐Zawawy Waleed K.
Published: April 2003

Solubility of methyl cellulose (MC) depends on the degree of substitution (DS), the average degree of polymerization (DP), and the distribution of methoxyl groups. Of these, the DS appears to be the most important. The DS of the MC depends on the conditions of preparation. The conditions studied in this work revealed that the DS of the MC increased as the concentration of sodium hydroxide increased from 10 to 50%. This result is attributed to the increase in the extent of formation of alkali cellulose II as a result of the increase in the alkali concentration and hence the increase of the DS of the MC. Decreasing both the ratio of dimethyl sulfate: cellulose and the liquor ratio increased the DS. High DS was achieved within a period of 2 and 3 h. However, the DS increased as the time increased. The decrease of the DS as the liquor ratio increased may be attributed to the sol–gel transition due to the interaction of the hydrophobic methoxyl groups within the polymer chains. To reveal the effect of the thermal sol–gel transition, the reaction was carried out in nonaqueous medium and the results obtained showed an increase of the DS with the increase of the solvent ratio until a maximum. This result may be contributed to the breakdown of the hydrogen bonding in the presence of solvents that transfer the reaction medium to the sol‐form and hence more methylating reaction takes place. The degree of the solvation of the methyl groups into the solvents also plays a role. © 1994 John Wiley & Sons, Inc.