bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the chemical reactivity of cotton cellulose in xanthogenation
Authors: Amine Abou‐State M. , Ali Abdel Fattah H. , Mostafa Naglaa Y. S. 
Published: April 2003

AbstractHydrochloric acid prehydrolysis of cotton cellulose resulted in a less accessible fine strucuture, higher crystallinity and lower reactivity in xanthogenation than sulphuric acid prehydrolysis. The reactivity was improved only when the duration of the hydrochloric acid treatment was reduced to 1 h. Hydrochloric acid prehydrolysis‐soda‐anthraquinone pulping raised the yield of α‐cellulose and improved greatly the affinities towards water and alkali, and resulted in much better reactivity in xanthogenation. The optimum quinone concentration was 0.2%. A comparison between the most reactive pulps obtained by sulphuric acid prehydrolysis‐soda‐anthraquinone pulping and hydrochloric acid prehydrolysis‐soda‐anthraquinone pulping indicated that hydrochloric acid allowed a great reduction in the duration of both prehydrolysis and pulping. Both acids resulted in the same α‐cellulose and the same degree of polymerization, but hydrochloric acid led to higher yield, higher crystallinity, more open and accessible fine structure, and much better reactivity in xanthogenation. However, in absence of anthraquinone, hydrochloric acid prehydrolysis resulted in a less accessible fine structure and lower reactivity in xanthogenation.
Effect of gamma radiation on low density polyethylene
Authors: Mukherjee A. K. , Tyagi P. K. , Gupta B. D. 
Published: April 2003

AbstractLow density monofilaments of polyethylene with varying draw ratios were subjected to high energy radiation using Co60 gamma radiation source. It was found that the tensile strength is sharply improved with the increasing dose up to 20 Mrd beyond which a sharp decrease in tenacity and initial modulus was observed. The swelling behaviour also decreased with the increased in dose of irradiation. However, density showed an increasing trend. The shrinkage behaviour of all the filaments was found to increase with increasing dose and draw ratios. The results have been explained in terms of continuous increase in crosslink density with the increasing dose of irradiation along with loss of crystallinity, which appears to be more severe in the latter stages of exposure. The samples exhibited memory effect after redrawing at 100°C and cooling under tension followed by further heating at 110°C under relaxed condition. The shrinkage was still much higher but independent of draw ratio.
Acrylic copolymers with controlled properties
Authors: Sândescu F. , Simionescu C. I. 
Published: April 2003

AbstractA method of the control of copolymer endgroups in a solution‐suspension copolymerization process was elaborated. The method is based on the utilisation of an initiating system containing three components: S2O2‐8 /HSO‐3 /Fe2+, their ratio and the ratio S2O2‐8 /comonomer mixture being optimized. In this way it is possible to control the content of endgroups of the copolymer, the saturation value, the M̄n values and polydispersity, without using comonomers with polar groups –SO3H or –OSO3H. Due to their conformational peculiarities and their packing manner in concentrated solutions, the macromolecular chains with a high endgroup content behave much better during the solving and spinning processes.Thus, an increase of the content of copolymer endgroups favours not only the tinctorial properties, but also the spinnability of the spinning dopes obtained from the respective copolymers.The proposed method for the copolymer endgroup control is more economical than the utilization of the comonomers with polar groups.
Preparation and characterization of some polyesterurethanes and polyesterurethane‐ureas based on 1,3‐bis(carboxymethoxy)benzene
Authors: Shaaban Abd‐El‐Fattah Fadel , El‐Safty Maher Abd‐El‐Rahman , Moustafa Hamed Yosef , Messiha Nagi Naguib 
Published: April 2003

AbstractHydroxy terminated polyesters were prepared by a melt condensation technique using 1,3‐bis(carboxymethoxy)benzene and various diols. They were characterized by hydroxy number, acid number, and intrinsic viscosity measurements. The polyesters were reacted with excess toluene‐2,4‐diisocyanate to yield isocyanate terminated prepolymers which were subsequently reacted with diols or benzidine. These polymers were characterized by IR and 1H‐NMR spectra, viscosity measurements, and thermogravimetric analysis.
Chlorocarboxylation of polyethylene, IV. Radical scavenging action of maleic anhydride
Authors: Joshi Shashikant G. , Kulkarni Bhaskar D. 
Published: April 2003

AbstractRadical scavenging action of maleic anhydride (MA) is observed during chlorocarboxylation of polyethylene (PE) (CCPE). Reduction in the rate of chlorination is observed in the presence of MA in the CCPE process as compared to the rate of chlorination of PE (CPE) alone. Reduction in the rate of chlorination is due to the competitive nature of CCPE process and the radical scavenging action of MA. Radical scavenging action arises as a result of the formation of MA excimers of very short half life and their interactions with solvent. Other reactions responsible for scavenging action may also exist and are discussed.The kinetics of the scavenging process is studied by considering number of sites (N̄0Cl), (N̄Cl + N̄MA) occupied during CPE and CCPE processes, respectively. The temperature dependence of the apparent rate constant kSCV is investigated and reveals that activation energy and pre‐exponential factor are of the order of 10.3 kcal/mol and 9.1 s‐1, respectively.
Particle size distribution of polypropylene produced in continuous polymerisation
Authors: Carson Ian G. 
Published: April 2003

AbstractA theoretical relationship has been developed between the particle size of polyolefin powders and that of the Ziegler‐Natta catalyst from which they are derived. This has been extended to examine how the yield on catalyst and the residence time distribution in a continuous stirred tank reactor affect the particle size distribution. Experimental confirmation of these relationships has been obtained using TiCl3 catalyst of near‐spherical morphology prepared by low‐temperature reduction of titanium tetrachloride with triethyl aluminium in solution.
Automatic polymerization reactor with on‐line data measurement and reactor control
Authors: Budde Uwe , Reichert Karl‐Heinz 
Published: April 2003

AbstractAn automatic polymerization reactor has been developed for on‐line measurement of conversion, viscosity, and molecular weight distribution of homogeneous free radical polymerization.For on‐line measurements during polymerization a fraction of the reaction mixture is pumped as bypass through a densimeter and a viscometer. In time intervals of 15 min samples are taken, diluted semi‐automatically, and then injected into a high performance gel permeation chromatography for determination of the molecular weight distribution of the polymers. A microcomputer collects these data, calculates the conversion of reaction and the output data for different control units.Methyl methacrylate is polymerized batch‐wise in solution with ethyl acetate as solvent and dicyclohexyl peroxydicarbonate as initiator. Semi‐batch polymerizations with constant reaction rate are performed by feeding initiator which is controlled by open‐loop and closed‐loop control.
Die elektrochemische Polymerisation. Ein interessantes Prinzip zur Synthese von elektrisch leitfähigen Polymeren
Authors: Naarmann Herbert 
Published: April 2003

AbstractIn einem kontinuierlichen Prozeß werden organische Polymerfilme — mit intrinsischer elektrischer Leitfähigkeit — durch anodische Oxidation direkt aus den Monomeren hergestellt.Die Arbeit beschreibt die Synthese, die Variationsbreite des Verfahrens sowie wesentliche Eigenschaften der neuen Polymeren.Im Gegensatz zu den klassischen Kunststoffen, die nach radikalischen oder ionischen Polymerisationen oder auch durch Polyadditions‐ oder ‐kondensationsverfahren gewonnen werden, stellt die elektrochemische Oxidation, z.B. von Pyrrol zu „Polypyrrol”︁, ein neues Polymerisationsprinzip dar. Aber nicht nur das Syntheseprinzip, auch die Eigenschaften des neuen Polymeren sind ungewöhnlich.
Polymerization of diallyl dimethyl ammonium chloride in inverse emulsion. I. Kinetics and mechanism
Authors: Huang P. C. , Reichert K.‐H. 
Published: April 2003

AbstractAn aqueous solution of diallyl dimethyl ammonium chloride was dispersed in an isoparaffinic liquid. A mixture of sodium di‐2‐ethyl‐hexyl sulfosuccinate and sorbitan monooleate was used as emulsifier. The polymerization was initiated by an oil soluble azo initiator and conducted in a stirred tank reactor at constant temperature. The initial rate of polymerization can be expressed as following in the region studied:

A kinetic model is presented by which the rate of polymerization can be calculated up to high conversions by considering gel effect and initiator decomposition. Based on experimental results the loci of polymerization are assumed to be the micelles and latex particles. The polymerization mechanism is conform to the Smith‐Ewart mechanism. The influences of ion strength and partition equilibria on the rate of polymerization were studied and are considered to be the causes of the 3rd order with respect to the monomer concentration.
Bruchmechanische Zähigkeitscharakterisierung polymerer Werkstoffe vom elastischen bis zum plastischen Deformationsbereich
Authors: Könnecke Klaus 
Published: April 2003

AbstractDie vergleichende Zähigkeitsbeurteilung von Materialien, die einen sehr weiten Zähigkeitsbereich überspannen, erfordert eine Meßmethode, die vom spröden, überwiegend elastischen bis hin zum duktilen, vollplastischen Deformationsverhalten ohne Bruch der Probekörper brauchbare Ergebnisse liefert. In dieser Arbeit wird bestätigt, daß mit der Bestimmung des bruchmechanisch definierten Parameters „J‐Integral”︁ ein hierfür geeignetes Verfahren zur Verfügung steht.Insbesondere wird deutlich gemacht, daß über die bereits mehrfach für langsame Deformationen beschriebene Anwendung hinaus diese Methode auch für hohe Verformungsgeschwindigkeiten eingesetzt werden kann. Damit eröffnet sich eine neue Möglichkeit zur vollständigen bruchmechanischen Charakterisierung des Deformationsverhaltens von Polymeren unter Schlagbeanspruchung.Anhand einer Reihe von Werkstoffen auf PP‐Basis mit sehr unterschiedlichen Zähigkeitseigenschaften wird die in der Praxis erreichbare Aussagefähigkeit der Methode gezeigt.
Die wichtigsten polymerphysikalischen Aspekte des Polycarbonats
Authors: Morbitzer L. , Grigo U. 
Published: April 2003

AbstractDie sich ausweitenden Einsatzbereiche des PolycarbonatsPolycarbonat auf Basis von Bisphenol A (im Text als BPA‐PC oder einfach als PC bezeichnet)
. (PC) machen es notwendig, das Verständnis für die physikalischen Grundlagen auch in die mehr anwendungsorientierten Bereiche hineinzutragen. Der vorliegende Artikel macht den Versuch, die wichtigsten polymerphysikalischen Aspekte, auf denen eine Vielzahl von technologischen Eigenschaften beruht, in Form einer Übersicht darzustellen. Behandelt werden: Deformationsmechanismen, dynamisch‐mechanisches Relaxationsverhalten, Spannungs‐Dehnungsverhalten, Zäh/Spröd‐Übergang, Einfluß der Probendicke, physikalische Alterung, Orientierungsverhalten, Spannungsrißbildung in Medien.
Einfluß der chemischen Struktur auf die mechanischen Eigenschaften von modifizierten Polycarbonaten
Authors: Weymans G. , Berg K. , Morbitzer L. , Grigo U. 
Published: April 2003

AbstractAusgehend von den bisher erarbeiteten Vorstellungen über die Festkörperstruktur des Bisphenol‐A‐Polycarbonats wird die Auswirkung einer chemischen Substitution des Bisphenols auf die thermischen, mechanischen und mechanisch‐dynamischen Eigenschaften diskutiert. Innerhalb der Substanzklasse der Polycarbonate zeigt sich dabei hinsichtlich der beobachteten mechanischen Phänomene ein erheblicher Einfluß der chemischen Struktur. Vor allen Polycarbonaten ist das Bisphenol‐A‐Polycarbonat besonders hinsichtlich seiner Tieftemperatur‐Eigenschaften ausgezeichnet. Der Spröd/Zäh‐Übergang als Funktion der Temperatur korreliert mit der Hochtemperaturflanke des mechanischen Nebenrelaxationsgebietes. Eine die experimentell beobachteten Phänomene vollständig charakterisierende Theorie muß als wesentlichen Parameter die konformative Beweglichkeit der Polycarbonat‐Ketten berücksichtigen.
Effect of vulcanization temperature on the cure characteristics and vulcanizate properties of natural rubber and styrene‐butadiene rubber
Authors: Kurian T. , George K. E. , Francis D. J. 
Published: April 2003

AbstractGum compounds of natural rubber (NR) and styrene‐butadiene rubber (SBR) are vulcanized at different temperatures and the cure characteristics and vulcanizate properties are compared. The optimum cure time at a particular vulcanization temperature could be expressed empirically in terms of that temperature using an exponential relation. The crosslink density of the vulcanizates is found to decrease with an increase in the vulcanization temperature. For a given compound there is a particular vulcanization temperature which gives the best compromise of properties for specific applications.
Graft copolymerization of methyl methacrylate on poly(vinyl chloride)
Authors: Ghosh Premamoy , Bhattacharyya Arabinda Shekhar , Maitra Somnath 
Published: April 2003

AbstractChemical modification of poly(vinyl chloride), PVC, by an amine renders the polymer more reactive towards graft copolymerization with a vinyl monomer. The graft copolymerization of methyl methacrylate (MMA) on PVC modified by treatment with n‐butylamine (n‐BA) was started thermally at 30° using benzoyl peroxide (Bz2O2) as initiator and under photoactivation at 40° using benzophenone (BP) as photo sensitizer. The gross polymer products from selected experiments were fractionally separated into the constituent polymeric entities viz., poly(methyl methacrylate), PMMA (homopolymer), PVC‐g‐PMMA (graft copolymer), and unreacted (aminated) PVC following a method of fractional precipitation. The separated fractions were characterized by IR spectroscopy and thermogravimetry. The mechanisms of graft copolymerization for the two different systems have been discussed. In each case, grafting efficiencies of the order of 30–70% and graft copolymers having compositions given as PMMA/PVC (w/w) equal to 2–3 were readily obtained.
GPC estimation of molecular mass distribution of addition polymers from bisphenol‐a‐diglycidyl ether and amines
Authors: Szesztay Márta , László‐Hedvig Zsuzsanna , Tüdős Ferenc , Hörhold Hans Heinrich , Klee Joachim 
Published: April 2003

AbstractThermally polymerized samples of linear addition polymers of bisphenol‐A‐diglycidyl ether (DGEBA) and the following three different amines (A): benzylamine (BA), p‐chloroaniline (PCA), and cyclohexylamine (CHA) were chromatographed by gelpermeation chromatography (GPC) using THF as eluent. The solvation effect of hydroxyl groups by THF has been taken into consideration when calibrating the system and interpreting the chromatograms. The comparison of the chromatograms suggests that the polymer with CHA is cyclized already in the range of small molecular masses (including dimers) and in an early stage of reaction. The comparison of average molecular masses of the samples as measured with independent methods—vapour pressure osmometry (VPO) and GPC—shows that the cyclization of the polymers with BA and PCA takes place to a lower extent, the latter polymer being less capable of cyclization.
Synthèse de Copolymères Greffés Poly(ethylène‐g‐Méthacrylate de méthyle) et leur Influence sur les Propriétés Mécaniques des Alliages de Polyéthylène avec le Polychlorure de Vinyle
Authors: Boutevin Bernard , Piétrasanta Yves , Sarraf Tarek 
Published: April 2003

AbstractLes copolymères greffés P(E‐g‐MMA) sont préparés par réaction du méthacrylate de méthyle (MMA) en masse sur le polyéthylène basse densité ozonisé. La masse moyenne des greffons de PMMA variable suivant la température et le temps de réaction est de 7700 et 21400. Ces copolymères sont testés comme émulsifiants de mélanges de PE et de PVC dont les propriétés mécaniques, la contrainte à la rupture σR, l'allongement à la rupture εR% et le module d'élasticité E sont mesurées avant et après l'addition de 5% en poids de copolymère. Pour le mélange PE‐PVC 50‐50 σR passe de 0,60 à 1,10 kg/mm2, la variation de εR est plus complexe. La visualisation, au microscope électronique à balayage, des fractographies de ces divers mélanges, montre une diminution d'au moins un facteur 10 de la taille des phases après addition de copolymère et confirme bien le rôle d'émulsifiant d'émulsifiant de ceux‐ci permettant d'obtenir ainsi de nouveaux alliages PE‐PVC dont les propriétés sont comparées avec celles d'alliages préparés par d'autres auteurs avec d'autres émulsifiants.
Surface sulphonated highly crosslinked styrene‐divinylbenzene copolymers
Authors: Kolarz Boz̊ena N. , Trochimczuk Andrzej , Wojaczyńska Maria 
Published: April 2003

AbstractA series of surface sulphonated macroporous styrene‐divinylbenzene (S‐DVB) copolymers containing various amounts of —SO3H groups was obtained. Porous structure, surface hydrophilicity and polarity, and sorption properties of these copolymers as well as those of starting S‐DVB resin towards some substances which are present in blood were determined. The sorption degree becomes the smaller the higher is the surface polarity. The partially sulphonated copolymers may find an application in hemoperfusion.
Thermal chlorination of atactic polypropylene
Authors: Mukherjee A. K. , Patri M. 
Published: April 2003

AbstractChlorination of atactic polypropylene (APP) was thermally initiated and carried out in carbon tetrachloride (CCl4) solution. It was found that with the increase in dilution, there is an increase in the extent of chlorination, as measured in terms of % weight‐gain. The reason for this behaviour has been ascribed to a greater degree of opening up and mobility of APP chains thus increasing the accessibility of the replaceable sites to chlorine. The order of the reaction with respect to APP concentration was found to be 0.84, the overall activation energy (Er) being 5.29 kcal/mol. Increase in flow rate leads to an increase in the extent of chlorination and was found to be increasing linearly with a flow rate up to 1 l/h beyond which it levels off. IR spectroscopy and 13C‐NMR studies indicate the chlorination occurring in all the three types of replaceable H‐atoms in APP. The mechanism appears to be initial substitution of tertiary H‐atom by free chlorine radical followed subsequently by replacement of secondary and primary H‐atoms via either progressive substitution or elimination‐addition mechanism.
Effect of blending techniques on the curing of elastomer blends
Authors: Joseph R. , George K. E. , Samad E. A. A. , Francis D. J. 
Published: April 2003

AbstractCompounding of styrene‐butadiene copolymer/polybutadiene, natural rubber/ethylene‐propylene‐diene terpolymer and natural rubber/butadiene‐acrylonitrile copolymer blends was done in three different ways and their curing behaviour and the tensile properties of the vulcanizates are compared.
Adsorption of phenols on carbonaceous adsorbents produced from phenol‐formaldehyde‐resin mixed with olive stones
Authors: Simitzis Johannis , Sfyrakis Johannis 
Published: April 2003

AbstractMixtures of phenol‐formaldehyde‐resin and pressed olive stones in a weight ratio of 20/80 were cured as small cylinders and then pyrolyzed. Some samples were also activated by steam. For these specimens and for two commercial activated carbons of laboratory or industrial uses the specific surface area, the structure, the adsorption properties, and the adsorption capacity were determined. The results indicate that the carbonaceous material produced by activation has greater values for the examined properties in comparison to the only pyrolyzed and the two commercial activated carbons, respectively. It was found that the Freundlich‐equation is valid for the adsorption of 4‐nitrophenol on all carbonaceous materials examined. The produced carbonaceous materials have different kinds of pores than the commercial activated carbons. The experimental results are explained with regard to the molecular dimensions of the adsorptive substances and the polarization effect of the substituents of the benzene ring.
Modification of starch by graft copolymerisation with methyl methacrylate
Authors: Egboh S. H. O. , Jinadu B. 
Published: April 2003

AbstractMethyl methacrylate (MMA) was grafted onto starch using ceric ammonium nitrate as initiator. The graft copolymers were isolated by selective solvent extraction in a Soxhlet apparatus. The effects of reaction time, initiator concentration, temperature, monomer, and acid concentrations on the graft yields were investigated. A preliminary kinetic study of the graft copolymerisation reactions shows that they follow the conventional kinetic behaviour of free radical polymerisation.
Thermoplastic blends of physically crosslinked multiblock copolymers and copolymers with uniform grafts
Authors: Xie Hongquan Q. , Li Shirong R. 
Published: April 2003

AbstractTwo multiblock copolymers of styrene and propylene oxide and four acrylate copolymers with uniform polystyrene grafts were prepared and blended. The blends are melt processable and their properties varied from thermoplastic elastomers to toughened plastics. The relationship between mechanical properties and composition of the thermoplastic blends indicated that all the blends exhibited a synergism, which is probably due to the increase of miscibility between the components caused by the same physical crosslinks — the glassy domains aggregated from both the polystyrene grafts and polystyrene blocks. The synergistic effect seemed more evident when two different graft copolymers were blended together than when one multiblock copolymer was blended with one graft copolymer. In all cases a maximum tensile strength appeared at the blend with 90 wt.‐% of the component, possessing higher tensile strength and ultimate elongation.
Differential technique in thermally stimulated depolarization current measurements
Authors: Topić Mladen 
Published: April 2003

AbstractTwo modes of differential technique in thermally stimulated depolarization current (TSDC) measurements were applied on novolac phenol‐formaldehyde (NPF) resin in the temperature range which covered the dipolar α peak and the detrapping ρ peak. The first mode, already described in literature, was carried out with one polarized and one unpolarized sample connected serially. The comparison between the usual and differential run allowed one to discuss the mechanism of the charge release and the interference of the local electric fields with the depolarization processes. The other mode, proposed for the first time in the present work, was performed with two parallelly connected samples polarized oppositely. The dipolar peaks were cancelled while the detrapping peaks appeared as a difference. By performing the polarization with partial opposition it was possible to modulate the magnitude of the peaks. The proposed technique can be used as a method for distinguishing between dipolar and space charge peaks and for increasing the resolution in TSDC curves. The problem of extraction of the background currents of different origins by various differential methods is discussed.