bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal degradation of EVA and EBA—A comparison. III. Molecular weight changes
Authors: Sultan Bernt‐Åke , Sörvik Erling
Published: April 2003

This is the third in a series of papers in which the thermal degradation of ethylene‐vinyl acetate (EVA) and ethylene‐butyl acrylate (EBA) copolymers are compared. The EBA samples contained 0.8, 1.6, and 5.4 mol % butyl acrylate (BA), respectively, and the EVA samples 1.2 and 6.7 mol % vinyl acetate (VA). The samples were heated in nitrogen in a tubular oven at 285–390°C, for 6–120 min. The molecular weight distribution (MWD), long chain branching, and gel content were analyzed with size exclusion chromatography (SEC). The columns were connected to refractive index, viscometric, and light scattering detectors. EVA gave a pronounced molecular enlargement at all degradation temperatures. In EVA‐6.7, gel was formed at all degradation levels, whereas the low content sample, EVA‐1.2, did not form any visible amount of gel. The strong tendency to molecular enlargement is due to allyl radicals formed after thermal deacetylation and the formation of internal double bonds. These macroradicals will combine or, less frequently, add to double bonds. The EBA copolymers show a more polyethylenelike degradation behavior. At 285°C molecular enlargement dominates, but already at 333°C a net reduction in molecular size is observed. At high temperatures, ester pyrolysis of the BA groups give carboxylic groups and anhydrides. Alkaline treatment will not give any appreciable change in MWD, showing that the anhydride formation is mainly intramolecular. The chain scission increases with the BA content. This is probably due to β‐cleavage of tertiary macroradicals formed in the chain at the acrylate or carboxylic side groups.
Grafting of glycidyl methacrylate onto gelatin
Authors: Sivakumar M. , Radhakrishnan P. Rajalingam Ganga , Kothandaraman H.
Published: April 2003

Gelatin was graft copolymerized with poly(glycidyl methacrylate) using potassium peroxydisulfate in aqueous medium. Effect of temperature, time, initiator, monomer, and backbone concentrations were studied. The percent grafting was found to increase initially and then decrease in all the cases except with variation of monomer concentration. The rate of grafting, grafting efficiency, and percent of grafting were calculated. The grafting results have been discussed in the light of the rate of grafting. Mechanical properties, FT IR spectra, percent swelling, and percent dye uptake were carried out on the graft copolymerization and the results discussed.
Sizes of long‐chain branches in a high‐pressure low‐density polyethylene as a function of molecular weight
Authors: Usami Takao , Gotoh Yukitaka , Takayama Sigeru
Published: April 2003

The mean length and the indices of long‐chain branches (LCBs) of a high‐pressure lowdensity polyethylene (HPLDPE) as a function of molecular weight have been determined for its molecular‐weight‐tractionated parts by the 13C‐NMR analysis and the viscosity measurements. The mean LCB length of the fractions was of the order of 200–300 carbons in length. The size of LCBs increases with increasing molecular weight, but the size of LCBs relative to the overall macromolecular size decreases with increasing molecular weight. The LCB sizes as a function of molecular weight determined for the fractions of one parent HPLDPE are in good agreement with those previously reported for HPLDPE whole polymers.
Mechanism of the reaction involving the formation of dioxane byproduct during the production of poly(ethylene terephthalate)
Authors: Popoola A. V.
Published: April 2003

The formation of certain low molecular weight by‐products during the esterification reaction between ethylene glycol and dimethyl terephthalate was investigated. The result obtained showed that the presence of incorporated diethylene glycol within the polymer led to the formation of low molecular weight side products. An alcoholysis reaction involving the ethylene glycol and the ester was found to show a mechanism that is analogous to that of an ester interchange resulting in the production of the acid and the diethylene glycol precursor of the dioxane by‐product.
Melt rheological behavior of PP–SAN blend
Authors: Maiti S. N. , Agarwal Vanita , Gupta A. K.
Published: April 2003

A study of melt rheology of the blend of styrene‐acrylonitrile (SAN) and polypropylene (PP) in composition range 0–50 wt % SAN content is presented. Measurements are made on a capillary rheometer at temperatures of 210, 230, and 250°C. The data are presented as flow curves and variations of melt viscosity and melt elasticity as functions of shear rate and blend composition. Scanning electron micrographs are presented to illustrate the dispersion and other characteristics of the SAN droplets. Results of melt rheology are interpreted in terms of the role of SAN droplets in the blend.
Short kevlar fiber–thermoplastic polyurethane composite
Authors: Kutty Sunil K. N. , Nando Golok B.
Published: April 2003

Mechanical and dynamic mechanical behavior of short Kevlar fiber‐filled thermoplastic polyurethane (TPU) have been studied with respect to fiber loading and orientation. The strength of the composite is improved at higher fiber content with a minimum at 10 phr of fibers. Storage and loss moduli (E′, E″) are increased and tan δmax is reduced progressively with fiber loading, the effect on moduli being more pronounced at post‐Tg temperatures. Anisotropy in strength is evident beyond 15 phr fiber loading. Impact strength is reduced considerably at all fiber loading irrespective of fiber orientation. Study of the fracture furface by scanning electron microscopy (SEM) shows good correlation between the modes of failure and strength of the composites. SEM study of the extracted fibers shows the existence of a kinking stage through which the fiber undergoes severe breakage during processing.
Copolymerization of styrene with vinyl monomers substituted by nitrile and sulfonyl groups
Authors: Knani Dafna , Kohn David H.
Published: April 2003

Two trisubstituted vinyl monomers, 2‐phenylsulfonyl (crotonitrile) and 2‐phenylsulfonyl (cinnamonitrile) were synthesized and characterized by proton NMR, IR, 13C‐NMR, and mass spectroscopy. Both monomers were copolymerized with styrene by free‐radical initiation. The copolymerization parameters of both systems were determined, and the mutual reactivity of the monomers of the two systems is discussed. The new copolymers were characterized by proton NMR and IR spectroscopy, melting range, Tg, and intrinsic viscosity. The influence of the chemical structures of the two comonomers on these two latter properties of the copolymers is discussed.
Copolymerization of turkish tall oil specimens with indene–coumarone. II. Production and properties of indene–coumarone modified tall oil varnishes
Authors: Üstün Güldem , Cívelekoǧlu Halídun
Published: April 2003

Two varieties of tall oil were copolymerized with indene–coumarone and subsequently esterified with ethylene glycol, glycerol, and pentaerythritol in addition to these esters, Urethanes were also obtained by reacting pentaerythritol esters of copolymers with toluene diisocyanate (TDI). These resultant products were evaluated as varnish vehicles and their film properties were compared with some standard formulation of tall‐oil‐ and vegetable‐oil‐based varnishes. The effect of indene–coumarone content of copolymer on the film properties of final products were additionally studied. Film evaluation showed that these copolymer‐based varnish vehicles could be used in the field of organic surface coating.
Size‐exclusion chromatography of high molecular weight water‐soluble polymers
Authors: Safieddine Abbas M. , Hester Roger D.
Published: April 2003

A preparative‐scale, aqueous size‐exclusion chromatography system was constructed for fractionation of large molecular weight polymers. Calibration of molecular weight to elution volume was accomplished without polymer standards by using an eluent viscosity detector in series with a refractometer. The system was found to have a hydrodynamic size‐separation resolution that ranged from 500 to 3500 Å.
The application of the iosipescu shear test to structural adhesives
Authors: Grabovac I. , Morris C. E. M.
Published: April 2003

The Iosipescu shear test method, adapted for adhesives, was used to evaluate shear stress–strain properties of five epoxy‐based film adhesives. The shear strength of some adhesives, determined by this technique, was found to differ greatly from that determined by either lap shear and/or thick adherend tests. Accurate measurements of the adhesive bond‐line deformation enabled evaluation of the adhesive elastic and plastic properties as well as the calculation of shear modulus. A high‐speed video camera was employed to augment observation on the joint deformation.
FTIR characterization of tropical wood–polymer composites
Authors: Yap M. G. S. , Que Y. T. , Chia L. H. L.
Published: April 2003

Wood–polymer composites (WPC) of Geronggang (Cratoxylon arborescens), a light tropical hardwood, impregnated with methyl methacrylate (MMA), methyl methacrylate‐co‐acrylonitrile (1 : 1; MAN), and styrene‐co‐acrylonitrile (3 : 2; STAN), were prepared by in situ polymerization using gamma radiation or the catalyst–heat treatment. The FTIR spectra of the three types of WPC, with polymer loadings ranging from 10 to 70%, were compared with that of the wood itself and the respective polymers. Characteristic peaks due to CO vibration of MMA, CN stretching of acrylonitrile, and ring stretching and bending of styrene monomers, were prominent in the samples that had higher polymer loadings. For the copolymeric systems, quantitation of the FTIR spectra of these characteristic peaks enabled calculations of incorporated acrylonitrile and styrene monomers in the composites to be made. The FTIR spectra of the residues remaining, after exhaustive extraction to remove homopolymer, showed that graft copolymerization of wood components with acrylonitrile and styrene monomers was possible, but not with MMA. Composites prepared by the two methods, gamma radiation and the catalyst–heat treatment, were shown to be chemically very similar.
In vitro degradation of polylactide and poly(lactide‐co‐glycolide) microspheres
Authors: Zhu Jia‐Huei , Shen Zheng‐Rong , Wu Lan‐Ting , Yang Shi‐Lin
Published: April 2003

Polyactide (PLA) and poly(lactide‐co‐glycolide) (PLGA) were prepared by bulk ring‐opening polymerization of lactide or lactide/glycolide using stannous octoate as initiator. PLA and PLGA microspheres with an average diameter of 65–100 μm were prepared by a solvent evaporation process. An in vitro degradation test of different molecular weight PLA and of different composition PLGA were carried out in pH 7.4 buffer solution at 37°C in the form of microspheres. Quantitatively, the degree of degradation was monitored by gel permeation chromatography (GPC), by measurement of mass loss and determination of lactic/glycolic acid in degradation medium, and qualitatively, by observing the morphological changes of microspheres with a scanning electron microscope (SEM). The decrease in weight average molecular weight (Mw) for PLA with higher molecular weight is faster at the first degradation stage; afterward, the tendency of Mw to decrease for PLA with different molecular weight is almost the same. PLGA degrades much faster than does PLA, and the degradation rate is significantly enhanced with the increase of glycolic acid (GA) content in copolymers.
Synthesis and blend morphology of BA/BC‐type binary graft copolymers composed of polyelectrolyte trunks
Authors: Ishizu Koji , Minematsu Satoru , Fukutomi Takashi
Published: April 2003

Poly(α‐methylstyrene) (PMS) macromonomer having one vinylbenzyl group per polymer chain was prepared by the couplings of living PMS with p‐chloromethylstyrene (CMS). Subsequently, well‐defined poly[acrylic acid (AA)‐g‐α‐methylstyrene (MS)] and poly[4‐vinylpyridine (4VP)‐g‐MS] graft copolymers composed of polyelectrolyte trunks were prepared by radical copolymerization of PMS macromonomer with AA and 4VP monomers, respectively. Binary poly(AA‐g‐MS)/poly(4VP‐g‐MS) or poly[AA · triethyl amine (Et3N) salt‐g‐MS)/poly(4VP‐g‐MS) graft copolymer blend films were cast from a benzene/methanol mixture. The morphological results of binary graft copolymer blends are discussed with respect to three‐phase separated structures.
A kinetic investigation of butyl acrylate polymerization
Authors: Dube M. A. , Rilling K. , Penlidis A.
Published: April 2003

An experimental investigation of the kinetics of the bulk free radical polymerization of butyl acrylate initiated with 2,2′‐azobisisobutyronitrile (AIBN) was conducted at 50° and 60°C using two initiator concentrations. Conversion levels were measured by gravimetry and were independently confirmed using replicate runs. The experiments, conducted in glass ampoules, were performed over the full conversion range. A mathematical model for process simulation purposes was developed. The model was able to predict conversion at the two temperatures and initiator concentrations, thus providing a better understanding of the butyl acrylate homopolymerization kinetics.
Hygroscopic‐aging behavior of pure and NaCl‐filled polyurethane rubber
Authors: Chiu Wen‐Yen , Ding Ding‐Kuo , Chen Chao‐Cheng
Published: April 2003

The aging phenomenon of highly filled rubber in humid environment was investigated. HTPBD was reacted with MDI and mixed with salt at the same time. The mixture was then hot‐pressed for 24 h at 90°C to prepare the sample. The changes in mechanical properties and glass transition temperature of the sample were followed when they were subjected to different humidity at 30°C for 7 days. Furthermore, the effects of humidity on chemical structures were studied with IR.

The results showed that unfilled rubber suffered no changes in mechanical properties after 7 days in environment of high humidity (RH 97). However, for NaCl‐Filled rubber, its strength decreased because of a loss of stiffness of salt after salt deliquesced. The glass transition temperature of unfilled rubber seems not to be affected by various humid conditions, but the Tg of filled rubber decreased slightly. From SEM pictures, we observed that interior holes were left after salt deliquesced. This was the main cause for the reduction in mechanical properties of filled rubber.
Infrared spectra of jute stick bleached with sodium chlorite and hydrogen peroxide
Authors: Roy A. K. , Bag S. C. , Sardar D. , Sen S. K.
Published: April 2003

Jute stick was bleached with sodium chlorite and alkaline hydrogen peroxide solutions. The infrared (IR) spectra of bleached samples and jute stick were analyzed and compared. The bleached samples were characterized by higher absorbance intensity ratios (Av/A2900) of the bands attributed to hemicellulose. Among the bleached samples the chlorite‐bleached sample showed higher intensity for the bands mentioned. The bands attributed to lignin are either absent or very weak in the chlorite‐bleached jute stick as compared to that of peroxide‐bleached jute stick, although some residual lignin was present in the substrate. The 1635 cm−1 band attribute to the vibration of adsorbed water molecules in the noncrystalline regions in cellulose appears as a sharp peak in chlorite‐bleached jute stick and as a shoulder in peroxide‐bleached jute stick. This can be attributed to the difference in the nature of the two bleaching processes.
Modification of natural rubber latex. III. Natural rubber–polystyrene composite latexes synthesized using azobisisobutyronitrile as initiator
Authors: Hourston D. J. , Romaine J.
Published: April 2003

Materials which may be classified as interpenetrating polymer networks have been prepared by the in situ polymerization of styrene in natural rubber latex using azobisisobutyronitrile (AIBN) as the initiator. The resulting materials have been characterized by electron microscopy, Soxhlet extraction coupled with proton nuclear magnetic resonance spectroscopy, dynamic mechanical analysis, and stress‐strain analysis. The styrene polymerizes within the natural rubber latex particles to give a relatively fine phase‐separated morphology with some evidence for a limited degree of segmental mixing. Moreover, it is clear that AIBN, despite what is stated in the literature, does lead to some grafting of polystyrene, and, in addition, causes significant degradation of the natural rubber molecules when the styrene content is low.
Application of a macromolecular Sn (II) complex to the preparation of 99mTc radiopharmaceuticals
Authors: Nakayama Morio , Terahara Takaaki , Wada Masao , Harada Kumiko , Sugii Atsushi , Egawa Hiroaki
Published: April 2003

To develop insoluble Sn2+ complexes for the preparation of 99mTc radiopharmaceuticals, the adsorption of Sn2+ to macroreticular chelating ion exchange resins having various functional groups was investigated. Among them, a resin containing aminophosphonic acid groups showed a high adsorption capacity for Sn2+, which was bound strongly to the resin by chelation. This macromolecular Sn2+ complex was very stable against hydrolysis and oxidation, and could be applied satisfactorily for the reduction of 99mTc.
Competitive primary amine/epoxy and secondary amine/epoxy reactions: Effect on the isothermal time‐to‐vitrify
Authors: Wang Xiaorong , Gillham John K.
Published: April 2003

The effect of temperature on the ratio of the kinetic rate constants, k2/k1, has been investigated using FTIR spectroscopy for the competing reactions of epoxy with secondary amine (k2) and primary amine groups (k1) in a trimethylene glycol di‐p‐aminobenzoate/diglycidyl ether of the bisphenol A system. The ratio of the rate constants increases from 0.16 to 0.33 in the temperature range 100−160°C. The corresponding difference in the activation energies for the competing reactions is about 3.7 kcal/mol. The effect of the ratio on the time‐to‐vitrify contour of the isothermal time–temperature–transformation (TTT) cure diagram is discussed: The effect is more significant at higher curing temperatures.
The effect of sorbed penetrants on the aging of previously dilated glassy polymer powders. IV
Authors: Osborne J. L. , Hopfenberg H. B. , Koros W. J.
Published: April 2003

Uniform, submicron‐diameter polystyrene (PS) and poly(methylmethacrylate) (PMMA) microspheres were dilated by preswelling with pure organic vapors followed by rapid removal of the preswelling penetrant by protracted evacuation of the preswelling chamber to a pressure of 10−3 mm Hg. Aging of the preswollen polymers was carried out both in vacuum and in the presence of various penetrants at sorbed concentrations typically less than 2 wt%. Inferences about relaxations of the polymers were based upon changes in concentrations of the penetrants within the microspheres, at a given temperature and penetrant activity, which result from aging in vacuum or in the presence of penetrant. The kinetics of the relaxations were monitored by probing the expanded glasses with relatively low concentrations of penetrants. In general, the continuous presence of these low concentrations of probe molecules either arrested or retarded the ensuing relaxation as compared with the aging that occurred in vacuum. A series of lower monohydric alcohols, lower n‐alkanes, and some other similar penetrants were used as probes to test explicitly and systematically the effects of size and structure of the penetrant contacting the polymer during aging on the decay of excess sorption capacity of the preswollen glassy polymers. Decay of excess sorption in the presence of penetrant was evident only when molecularly small penetrants with interactive functional groups, alcohols for example, were sorbed into preswollen PMMA. This result suggested that the relaxation occurring in the presence of penetrant involved specific interactions between the penetrants and the carbonyl groups in the PMMA.
The electron beam‐induced cationic polymerization of epoxy resins
Authors: Crivello James V. , Fan Mingxin , Bi Daoshen
Published: April 2003

The rapid, efficient electron beam‐induced cationic polymerization of multifunctional epoxy monomers has been carried out in the presence of diaryliodonium and triarylsulfonium salts. These polymerizations take place at low doses (1–3 Mrad), which make them attractive for commercial applications. The factors that contribute to the high reactivity of these monomers are discussed.
Electrochemical polymerization of acrylonitrile with quaternary salts
Authors: Bhadani Suraj N. , Ansari Qayumuddin , Gupta Sumanta K. Sen
Published: April 2003

The electrochemical polymerization of acrylonitrile was carried out in the solutions of tetrabutylammonium bromide and tetrabutylphosphonium bromide in N,N‐dimethylformamide in a divided electrolytic cell. The formation of polyacrylonitrile of high molecular weight (7.6 × 104) took place in the cathode compartment. The kinetics of the polymerization was investigated for different initial monomer concentrations, current levels, and electrode materials. The polymerization mechanism is anionic.
Bending of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel in electric fields
Authors: Shiga Tohru , Hirose Yoshiharu , Okada Akane , Kurauchi Toshio
Published: April 2003

Bending of poly(vinyl alcohol) hydrogel mixed with poly(sodium acrylate) chains, PVA–PAA gel, under the influence of dc electric fields was studied. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixture of PVA and polyacrylic acid aqueous solutions. The PVA–PAA gel was a hydrogel with the PAA chains, which were entangled with the PVA polymer network and were fixed in the gel. The PVA–PAA gel bent toward the negative electrode in electrolyte solutions under dc electric fields as did the polyelectrolyte gel with negatively charged polyions. The PVA gel, free of PAA, was insensitive to dc electric fields. The deflection of the bending and the bending speed were influenced by the filed intensity, the concentration of the polyion in the gel, and the thickness of the gel. The bending of the PVA–PAA gel was qualitatively explained by a bending theory of polyelectrolyte gel, based upon the change of the osmotic pressure due to the ion concentration difference between the inside and the outside of the gel.
Polyether–polyimide thermoplastic elastomers. I. Synthesis and properties
Authors: Yu Xuehai , Song Chunkang , Li Chi , Cooper Stuart L.
Published: April 2003

A series of polyether–polyimides based on polycondensation of poly(tetramethylene oxide) glycol di‐p‐aminobenzoate with different molecular weights (650, 1000, 2000) and benzenetetracarboxylic acid dianhydride (BTDA) or 3,3′,4,4′‐benzenetetracarboxylic acid anhydride (BPTDA) was synthesized. Infrared spectroscopy (IR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and stress–strain tests were used to follow the imidization process and to study the structure–property relations of this family of polymers. FTIR data showed that the imidization was completed after 6 h at 140°C, which is a much lower temperature than that required for polyimides synthesized from low molecular weight diamines. DSC and DMA results indicated that the block copolymer exhibited a well‐phase‐separated structure and had a broad rubbery plateau from about −70°C to 260°C, which varied with dianhydride type and hard‐segment content. The BTDA series had enhanced mechanical properties compared to the BPTDA series. The excellent tensile properties of the polyether–polyimides suggest that they could be potentially used as heat‐resistant thermoplastic elastomers.
Simulation of microstructure development in injection molding of engineering plastics
Authors: Yu Jeong S. , Wagner Alan H. , Kalyon Dilhan M.
Published: April 2003

Mathematical models were developed to predict the various microstructural properties, including birefringece, residual stress, and density distributions, in the freely quenched compression molded samples as well as in the injection molded samples. To model the birefringence distribution in the injection molded samples, the BKZ type integral constitutive equation was employed to account for the nonisothermal stress relaxation, which takes place during the cooling stage of the molding cycle. The predicted birefringence agreed well with the experimental data near the mold walls. The residual stress distribution was modeled by the existing thermoelastic theory. The residual thermal stress distribution in the freely quenched samples was predicted very well by the model. However, the predicted residual thermal stresses in the injection molded samples were much larger than the measured ones. A phenomenological model to predict the density distribution in injection molded sample is proposed by including the effects of both cooling rate and the pressure on the density development. The predicted results agreed well with the experimental data.
An approach to yielding and toughness in rubber‐modified thermoplastics
Authors: Cigna Giuseppe , Maestrini Claudio , Castellani Leonardo , Lomellini Paolo
Published: April 2003

An interpretation of yielding and fracture of rubber‐toughened polymers is attempted, considering the fracture mechanics behavior of the matrices, with the rubber particles as stress‐intensification sites. The fit of effective tensile yield stresses of composites vs. particle radii defines a stress‐intensity factor KYc for craze yielding much smaller than the classical fracture factor Kc, values are found for polystyrene and poly(styrene‐co‐acrylonitrile)‐based polymers. These factors are considered characteristic for craze initiation and propagation in the matrices, while Kc, in turn, would include also the craze‐crack transformation contribution. KYc appears independent of the rubbery‐phase volume fraction and characteristics, but two different values are found and discussed for poly(styrene‐co‐acrylonitrile)‐based materials in two different particle‐size ranges. A similar treatment on notched specimens' yield stress indicates the presence of a maximum in different radius ranges for polystyrene and poly(styrene‐co‐acrylonitrile) matrices, with higher values than their breakdown stresses. This stress increment is in relation to the minimum particle size inducing and still stabilizing crazes and preventing crack formation. This maximum seems to control the reinforcing extent of the polymer matrix conditioning the Izod fracture initiation energy.
The chemical and physical properties of electrochemically prepared polyaniline hexafluorophosphate (PAPF6)
Authors: Choi Kyung Moon , Kim Keu Hong
Published: April 2003

Polyaniline hexafluorophosphate (PAPF6) was synthesized by electrochemical oxidation from 0.2 M aniline in acetonitrile solution containing 0.1 M TEAPF6 as the supporting electrolyte. From polarographic and cyclic voltammetry results, the values of the half‐wave potential \documentclass{article}\pagestyle{empty}\begin{document}$\left( {{\rm E}{\textstyle{1 \over 2}}} \right)$\end{document} and αn were calculated to be 774 m V and 0.589, respectively. The morphology of the PAPF6 sample was determined from SEM. Thermal analyses for PAPF6 and other polyaniline‐based systems show distinguishable, thermal characteristics depending on the doping methods for the anions. Also, the maximum values (Rmax) of the reaction rates (R) for these polymers were obtained. The electrical conductivity of the PAPF6 pellet was measured at temperatures from −170 to 25°C. From a plot of conductivity vs. 1/T, an activation energy (Ea) of 0.057 eV was obtained. The conduction mechanism in the pressed pellet of PAPF6 is suggested to be hopping conduction. The various ESR‐parameters were obtained from the ESR curve at room temperature.
Column studies on metal ion removal by dyed cellulosic materials
Authors: Shukla S. R. , Skhardande V. D.
Published: April 2003

Cellulosic materials, namely bleached bamboo pulp, jute fibers, and sawdust dyed with a reactive dye of monochlorotriazine type were used in the column studies for removal of different metal ions. The use of an adsorption column makes the process continuous, so that it is economically viable on an industrial scale. After the adsorption of metal ions such as Cu2+, Pb2+, Hg2+, Fe2+, Fe3+, Zn2+ and Ni2+, the adsorbents were successfully regenerated by using dilute acids. These columns were then used repeatedly for adsorption either of the same salt for more than ten times or of different salts in succession. No loss in adsorption power was observed.
Some recent studies on metal/polyaniline schottky devices
Authors: Pandey S. S. , Misra S. C. K. , Malhotra B. D. , Chandra Subhas
Published: April 2003

An attempt has been made to estimate various electronic parameters such as work function, barrier height, and ideality factor through I‐V measurements carried out on metal/polyaniline Schottky junctions. The results of optical studies conducted on chemically synthesized polyaniline used in the fabrication of such Schottky devices have been presented.
Relaxational behavior of CR‐39 polycarbonate used as nuclear track detector
Authors: Vanderschueren J. , Yianakopoulos G. , Niezette J. , Chatry C. , Gasiot J.
Published: April 2003

The relaxational behavior of CR‐39 (poly allyl diglycol carbonate) nuclear track detectors was determined over a large temperature range (−100 to 125°C) including the glassy, glass transition, and ionic conduction regions by means of dynamic mechanical and dielectrical measurements, differential scanning colorimetry, linear coefficient of expansion, and especially thermally stimulated current methods owing to their high sensitivity and resolving power. This investigation was carried out as a first step aimed, on the one hand, at finding possible correlations between dosimetric performances, polymer morphology, and intrinsic or extrinsic relaxations and, on the other hand, at determining the origin of the inconsistent background and response properties, which are still a serious obstacle to the use of this material as a personnel dosimeter in spite of its high sensitivity and wide response range. Six distinct relaxation regions have been evidenced, most of which being to some extent dependent on the sample investigated and its thermal history. From higher to lower temperatures, these various relaxations have been ascribed to charge carrier migration over macroscopic distances (ρ), glass transition (α), nonequilibrium precursor motions of the glass transition (ά), and local mode motions of the diethylene‐glycol dicarbonate links (β), diethylene glycol segments (γ), and carbonate groups (δ). In addition to these intrinsic relaxations, the as‐received samples are also characterized by small‐scale residual stresses that relax out irreversibly at temperatures lower than the glass transition temperature Tg. The systematic study of the influence exercized by the position of a specimen in a given sheet, and, for a given sample, by annealing, thermal cycling, and physical aging on relaxation properties shows that, besides spatially inhomogeneous internal stresses, cross‐linking density, and cluster morphology, marked structural modifications and nonequilibrium processes can occur by heating the polymer above Tg. These phenomena deserve a great deal of consideration because they could be key points for identifying the sources of the troublesome fluctuations of dosimetric response. Relaxation studies thus appear as useful and sensitive tools for a deeper understanding of the performance of CR‐39 polymer as a track recorder.
Preparation of composite membranes via interfacial polyfunctional condensation for gas separation applications
Authors: Chern Yaw‐Terng , Chen Leo‐Wang
Published: April 2003

Composite membranes were prepared by interfacial polycondensation of a water‐soluble diamine (4,4′;‐methylene dianiline [MDA] or ethylene diamine [EDA]) with an organic solvent (hexane)‐soluble 1,2,4,5‐benzenetetra acyl chloride (BTAC) on top of a porous polysulfone (PSF) support. For both the poly(BTAC‐MDA) and poly(BTAC‐EDA) composite film systems, the permselectivity of these films increases only slightly with an increasing number of coatings. The poly(BTAC‐MDA) composite membranes are treated at 135°C in a nitrogen atmosphere for 4 h, and they have a high selectivity [α*(CO2/CH4) = 20.51] and permeability [P̄(CO2) = 44.12 Barrer]. This is due mainly to the great chain stiffness of the formed polyimide, which has high selectivity. The high permeability is due to a porous polysulfone support. The trend of the permeability for this composite film is P̄(CO2) > P̄(O2) > P̄(N2) > P̄(CH4). In poly(BTAC‐EDA) composite membranes, the permeation of different gases decreases in the order of P̄(CO2) > P̄(O2) > P̄(CH4) > P̄(N2). As to the composite films being more permeable to CH4 than to N2, this is probably due to the presence of a considerable quantity of aliphatic chains (–CH2–CH2–) in the poly(BTAC‐EDA) composite film caused by its particularly excellent solubility for methane.
Study on ketalization reaction of polyvinylalcohol by ketones. V. The film properties of polyvinylketals obtained by aliphatic ketones
Authors: Nakamura Naofumi , Suzuki Kimihiro
Published: April 2003

The physical and chemical properties of polyvinylketals (PVKL) prepared from seven aliphatic ketones [acetone, methyl ethyl ketone (MEK), methyl n‐propyl ketone (nPK), methyl i‐propyl ketone (iPK), methyl n‐butyl ketone (nBK), methyl i‐butyl ketone (iBK), methyl t‐butyl ketone (tBK)] were studied. The moisture regain and water vapor permeability of PVKL films decrease in the following order: acetone > MEK > nPK > iPK ≒ nBK > iBK > tBK. The contact angle measurements revealed that this order is determined by the surface free energy of films, which depends upon the kind of the original ketones. PVKL (acetone) with low ketalization degree was not soluble in neutral water and had lower moisture regain than PVA. As shown in X‐ray analysis, the molecular orientation was not random, the crystalline part of PVA remaining. Thus, it becomes clear that behavior of PVKL in water is affected not only by the hydrophobicity of film surface, but also by the crystallinity of PVKL.
Liquid crystal polymer‐based blends: “Universal grade” polymers?
Authors: La Mantia F. P. , Valenza A. , Magagnini P. L.
Published: April 2003

Polymeric materials can be easily processed with different processing operations thanks to suitable rheological properties. Melt flow index, or grade, which is a measure of the fluidity of the polymers, is the most commonly parameter used to characterize the polymers from the point of view of their melt viscosity. Injection molding requires high grade materials, whereas low grade values are best suited for extrusion. Of course, it would be no doubt of interest if single “universal grade” materials could be used for all processing operations. In this paper it is demonstrated that the blends of low grade polymers with small amounts of liquid crystal polymers can be conveniently used for all processing operations. Mechanical and thermal properties of the polymer matrix are in general retained or, in some cases, improved.
Synthetic resins. XIII. Synthesis and characterization of the resins derived from quinacetophenone/substituted benzoic acid/furfuraldehyde
Authors: Burma S. P. N. S. , Lenka S. , Nayak P. L.
Published: April 2003

Some resins have been synthesized by reacting quinacetophenone with substituted benzoic acids and furfuraldehyde in the presence of basic catalysts. The resins have been characterized by IR spectra of the characteristic groups. The number average molecular weights of the resins have been evaluated by the conductance method. The solubility and viscosity behaviors of the resin copolymers have been determined. Cu+2, Ni+2, Co+2, Mn+2, and Mg+2 chelates have been prepared. The resins were shown to be selective ion‐exchange resins for certain metal ions. A batch equilibrium method was used for studying the selectivity of the metal ions. The thermal behavior of the resins has been determined and the values of energy of activation of the resins were computed by using the Freeman–Anderson and Broido methods. The biological assays of some of the resin copolymers were found to be highly sensitive.
Rheology, composition, and peel‐mechanism of block copolymer–tackifier‐based pressure sensitive adhesives
Authors: Nakajima N. , Babrowicz R. , Harrell E. R.
Published: April 2003

Three samples of styrene–isoprene–styrene (S–I–S) block copolymers were chosen; copolymer A had 25% styrene, and copolymers B and C had 14% styrene. Copolymers A and B contained 20% diblock polymer and copolymer C contained 40% diblock polymer. All copolymers were mixed with a terpene type tackifier to make 56% and 48% weight tackifier concentration. These represent our model samples of pressure sensitive adhesives. The determination of tack, room‐temperature peel‐strength, and failure temperature under static shear were performed. The above results have been interpreted with the basic rheological data. The dynamic viscoelastic measurements and tensile stress–strain measurements were used. The effects of tackifier on the rubbery plateau moduli were treated with the Guth–Gold‐type equation. The implications of the deviation from the equation are discussed in terms of the connectivity between polystyrene domains and the stability of the hard domains affected by inclusion of rubber segments.
Differential scanning calorimetric study of the interaction of 2,2′‐dibenzothiazole, sulfur, zinc oxide, and stearic acid in the presence of polyisoprene
Authors: Luyt Adriaan S.
Published: April 2003

The interactions between mixtures of 2,2'‐dibenzothiazole (MBTS), sulfur, ZnO, and stearic acid were studied by DSC in the presence of polyisoprene (IR). In the absence of ZnO, the onset of vulcanization was at a lower temperature than in its presnece, and the crosslink densities were relatively low. ZnO as well as stearic acid did not influence the consumption of MBTS, but the amount of MBT in the sample after vulcanization increased in the presence of ZnO and still more when ZnO and stearic acid were present—the same applied for the crosslink densities. In view of these results, interaction mechanisms are proposed for the different systems.
Morphology and mechanical properties of fibers from blends of a liquid crystalline polymer and poly(ethylene terephthalate)
Authors: Li J. X. , Silverstein M. S. , Hiltner A. , Baer E.
Published: April 2003

The domain morphology and mechanical properties of fibers spun from blends of a thermotropic liquid crystalline polymer, Vectra A‐900, and poly(ethylene terephthalate) (PET) have been studied across the entire composition range. The PET phase was removed by etching to reveal fibrillar LCP domains in the blends of all compositions. The 0.5μm fibril appeared to be the basic structural entity of the LCP domains. A primary effect of composition was the change from discontinuous fibrils when the composition was 35 and 60% by weight LCP to continuous fibrils when the composition was 85 and 96% LCP. This transition had major ramifications on the mechanical properties: the modulus increased abruptly between 60 and 85% LCP, and a change in the fracture mode from brittle fracture to a splitting mode was accompanied by an increase in fracture strength. Different models were required to describe the mechanical properties of the discontinuous and continuous fibril morphologies. Analytic models for short aligned fibers of Nielsen, and Kelly and Tyson were applicable when the LCP fibrils were discontinuous, while modulus and strength of blend fibers with continuous LCP fibrils were discribed by the rule of mixtures.
Ultra‐high modulus isotactic polypropylene. I. The influence of orientation drawing and initial morphology on the structure and properties of oriented samples
Authors: Baranov A. O. , Prut E. V.
Published: April 2003

The influence of a number of factors (temperature–speed regime and the quantity of draw stages, molecular weight of a polymer, etc.) on the deformability of initial isotropic IPP and on mechanical characteristics of highly‐oriented samples, obtained in the process of a two‐stages isothermal orientation drawing, was studied. It was shown that the maximum achievable values of elastic modulus and draw ratio depended not only on the molecular weight of a polymer and the sizes of spherulites, constituting initial IPP, but on the structural organization of inner‐and interspherulite regions. Upon physical aging of initial isotropic films, irreversible structural changes take place, which result in the formation of microvoids while being drawn and in the reduction of mechanical properties of obtained material. An extremal dependence of elastic modulus and draw ratio of maximum drawn IPP samples on draw speed was discovered. A structural model, which is supposed to possesstie molecules with various degrees of tautness in amorphous layers, was proposed. Higher effectiveness of two‐stage drawing in comparison with one‐stage drawing was established. The optimum temperature–speed regime of orientation drawing, which permits the reception of highly oriented, ultra‐high modulus IPP with maximum high mechanical characteristics (elastic modulus ∼ 30–35 GPa and tensile strength ∼ 1,1 GPa), was determined.
Determination of diffusion coefficient of oxygen into polymers by using electron spin resonance spectroscopy. II. Poly(vinyl acetate)
Authors: Kaptan Yilmaz , Pekcan Önder , Güven Olgun
Published: April 2003

Electron spin resonance spectroscopy has been used to follow the kinetics of radical decay during postirradiation oxidation of poly(vinyl acetate). The oxygen uptake of γ‐irradiated spherical poly(vinyl acetate) has been determined from changes in the intensity of the ESR signal. The diffusion coefficient (D) of oxygen determined by this technique showed an inverse relation with dose. The value of the diffusion coefficient of oxygen obtained in this study, after correcting for dose and size effects is 4.5 × 10−8 cm2/s, and is in very good agreement with the literature value of D = 5.1 × 10−8 cm2/s.
Co‐existence of ductile, semi‐ductile, and brittle fractures of polycarbonate
Authors: Chang Feng‐Chih , Chu Line‐Hwa
Published: April 2003

The ductile–brittle transition behavior of polycarbonate and methylmethacrylate–butadiene–styrene (MBS) elastomer modified polycarbonate has been investigated in terms of notch radius and temperature. At−40°C and 21‐mil notch radius, polycarbonate fractures in three possible modes, ductile (25%), semi‐ductile (50%), and brittle (25%). This semiductile mode fracture has never been reported previously with brittle characterization, but to a greater extent in localized shear yielding on the fracture surface and intermediate toughness. A two‐dimensional fracture mode diagram in terms of temperature and notch radius has been constructed to interpret the observed phenomena. This diagram can also predict the existence of other conditions under which the triplet fracture modes may also occur. Another unstable zone has also been identified where the fracture occurs in either ductile mode or brittle mode over a broad temperature range, instead of the narrow temperature range typically observed for polycarbonate. A model based on the excessive precrack strain just below yielding due to the greater notch radius is proposed to explain such observed semi‐ductile mode fracture.
Dielectric analysis of cellulose and its vinylic copolymers
Authors: Flaqué C. , Montserrat S.
Published: April 2003

The real and imaginary parts of the complex dielectric permittivity, ε′ and ε″, for some vinylic copolymers of cellulose [prepared with vinyl acetate (VA) and methyl acrylate (MA) and Ce (IV) ions as initiator ] and for cellulose were measured over a frequency band of 0.1–102 kHz and a temperature range from −40 to 100°C. In vinylic copolymers of cellulose, we observed one dielectric relaxation attributed to the α‐relaxation of the vinylic side chain grafted on cellulose. In cellulose dielectric spectra, this relaxation did not appear, but we detected one relaxation that may correspond to the β‐relaxation. For these vinylic copolymers of cellulose, the ε″ against ε′ plot gives a skewed are that closely resembles that of the Davidson–Cole model, with a broader distribution for high frequencies that shows the overlap of several relaxations in the process considered. Some differences observed between the vinylic copolymers of cellulose may be due to the composition and the length of the vinylic side chains and to the frequency of grafting on the cellulose.
Prostaglandin E1‐immobilized poly(vinyl alcohol)‐blended chitosan membranes: Blood compatibility and permeability properties
Authors: Chandy Thomas , Sharma Chandra P.
Published: April 2003

A series of membranes are prepared by air drying thin films, which were composed of poly(vinyl alcohol) blended with chitosan [a (1 → 4)2‐amino‐2‐deoxy‐β‐D‐glucan] (PVA–Chit) in different ratios. The PVA‐blended chitosan membranes showed improved strength properties and permeability functions for low‐molecular‐weight compounds. Nonthrombogenic PVA–Chit (4 : 6) membranes were derived by immobilizing bioactive molecules like PGE1 on heparin‐modified membranes, via free radical mechanisms, by N2 plasma. This novel membrane demonstrated good permeability properties for small molecules and showed a dramatic reduction in platelet attachment. The prostaglandin E1‐immobilized substrate also indicated an increase in albumin surface attachment and a reduction in fibrinogen binding. This may be one of the parameters for a reduced platelet‐surface attachment, which may also improve the blood compatibility of the substrate. It is also postulated that the total water content of membranes need not be the prime factor governing the permeability of solutes through water‐swollen membranes. However, many other parameters govern the solute permeability, like the amount of solutes dissolved in bound water and the status of water in the polymer matrix.
Chemical and mechanical properties of methyl methacrylate‐grafted wool fiber
Authors: Elangovan V. J. , Saccubai S.
Published: April 2003

Since it has been reported in the literature that polymer‐grafted wool fibers have better acid and alkali resistances and dye uptake, the present study was carried out using KBrO3 and substrates such as Fe (II), Co (II), cysteine, cystine, tyrosine, and urea for graft copolymerization of methyl methacrylate (MMA) onto wool. Acid and alkali resistances, dye uptake, and dry tensile strength of the resulting graft copolymers were studied.
Development of a dilatometer and its application to low‐shrink unsaturated polyester resins
Authors: Kinkelaar Mark , Lee L. James
Published: April 2003

Two dilatometers are presented here that were developed for the use with, but not limited to, low‐shrink unsaturated polyester resins. One of the dilatometers, made from a glass syringe and two aluminum plates, was limited to lower pressures. The other dilatometer, similar in design to the first, was made from a hydraulic cylinder and was capable of pressures to 500 psi. The dilatometers were calibrated and tested by the polymerization of styrene. Several low‐shrink unsaturated polyester resins were cured in the dilatometers and the results of these experiments are given. The interactions of volume change, rheology change, conversion, and microstructure formation were also measured. Finally, the effect of pressure was considered.
Graft copolymerization of methyl methacrylate on stone ground wood using the H2O2Fe2+ method
Authors: Huang Yifang , Zhao Bianan , Zheng Guozhen , He Shujie , Gao Jie
Published: April 2003

Graft copolymerization of methyl methacrylate on stone ground wood (SGW) of masson pine was investigated. The effect of lignin on grafting was carefully examined The phenolic hydroxyl groups of lignin were found to accelerate the decomposition of hydrogen peroxide and graft copolymerization of lignocellulose when minor ferrous ions were added to the system. Nevertheless, the α‐hydroxyl groups of lignin had no great influence on grafting. Also, the graft copolymerization could be initiated with low ferrous ions to the hydrogen peroxide molar ratio, and, additionally, the lignin was observed to be more suitable for grafting than was the hollocellulose.