bluuebunny/crossref_metadata_2025 huggingface dataset:
The three stages in degradation of polymers—polyethylene as a model substance
Authors: Albertsson Ann‐Christine , Karlsson Sigbritt
Published: April 2003

Data relating to the degradative conversion of 14C present in low density polyethylene (LDPE) film to respiratory 14CO2 during a 10‐year aerated cultivation with soil are presented. The degradation was performed with two sets of LDPE samples, one without additive (PE) and the other containing UV sensitizer (NDPE). Samples were exposed to UV irradiation for 0, 7, 26, and 42 days. The degradation is characterized by three stages: (I) a constant degradation rate, (II) a parabolic decline in the rate of degradation, and (III) a subsequent final increase in the rate of degradation. The first step (I) is probably dependent on the environment. The material changes rapidly until some kind of equilibrium with the environment has been achieved. CO2 is evolved, oxygen uptake is rapid, and a rapid change in mechanical properties is also observed. The second step (II) is characterized by low oxygen uptake, a low evolution of CO2 and slow changes in the mechanical properties, crystallinity, and molecular weight. The changes in mechanical properties are not necessarily synchronous with the decrease in molecular weight. Step III, finally, is a rapid deterioration of the structure. The degradation rate increases again, and all the mechanical properties are more or less lost due to the final collapse of the structure. For an inert material such as PE, 10 years is a short time, so that only small indications of step III and a coming mineralization point can be observed. The changes are more evident for NDPE. The use of degradable materials, for example polypropiolactone, however, means that it is possible during a 2‐year period to study all three stages. An understanding of the mechanisms in each step will give a better base for lifetime predictions.
O2 and N2 gas permselectivity of alternating copoly(vinylidene cyanide–vinyl acetate)
Authors: Hachisuka Hisao , Kito Hitoshi , Tsujita Yoshiharu , Takizawa Akira , Kinoshita Takatoshi
Published: April 2003

The sorption and permeation of oxygen and nitrogen in and through alternating copoly(vinylidene cyanide–vinyl acetate) [copoly(VDCN–VAc)] (Tg = 176°C) membranes annealed for different periods just below Tg, 160°C, were investigated over the pressure range from 100 to 1000 cmHg. The dual‐mode sorption and mobility models were used to analyze the results. A sub‐Tg annealing of copoly(VDCN–VAc) caused a slight decrease in the amount of sorption in the membranes. This decrease in the amount of oxygen and nitrogen sorption can be attributed to a decrease in the Langmuir sorption capacity term, C′H, with increasing sub‐Tg annealing period. The densification of copoly(VDCN–VAc) membranes caused simultaneously by the annealing remarkably reduced diffusion coefficients for both gases. The reduction in diffusion coefficients of Langmuir mode, DH, for both gases was found to be larger than that of Henry's law mode, DD. Furthermore, permselectivity of oxygen to nitrogen, the ratio of permeability coefficient of oxygen to nitrogen (PO2/PN2), reached to 11.8 for the copoly(VDCN–VAc) annealed for 30 h. Evidently the reduction of DH and DD for nitrogen with increasing annealing period was much larger than that for oxygen.
Linear polythioesters. XIV. Products of interfacial polycondensation isomeric di(mercaptomethyl) trimethylbenzenes with some aliphatic acid dichlorides
Authors: Podkościelny Wawrzyniec , Szubińska Stanisława
Published: April 2003

New polythioesters by interfacial polycondensation of 4,6‐di(mercaptomethyl)‐1,2,3,‐trimethylbenzene, 3,5‐di(mercaptomethyl)‐1,2,4,‐trimethylbenzene and 2,4‐di(mercaptomethyl)‐1,3,5‐trimethylbenzene with adipoyl and sebacoyl chlorides were obtained. Process of polycondensation was carried out under the same condition as established earlier as an optimal for synthesis of polythioester from 2,5‐di(mercaptomethyl)‐1,4‐dimethylbenzene and sebacoyl chloride. The conditions of polycondensation process were as follows: the organic phase benzene/hexane (1:1), ratio of aqueous to organic phase 1:1, the presence of 100% excess of NaOH as hydrogen chloride acceptor, temperature of reaction 15°C, little excess of acid dichloride with addition time 8.5 min. The structure of all polythioesters was determined by elementary analysis, infrared spectra, and X‐ray analysis. Initial decomposition and initial intensive decomposition temperature were defined by the curves of thermogravimetric analysis. The molecular weights for these polymers were determined by gel chromatography.
Decrease in the etch rate of polymers in the oxygen afterglow with increasing gas flow rate
Authors: Lerner N. R. , Wydeven T.
Published: April 2003

In this paper we report the variation of the etch rate of polymers in the afterglow of a radio frequency discharge in oxygen as a function of total flow rate in the range 2–10 cm3 (STP)/min. The measurements were made at ambient temperature with the O(3P) concentration held essentially constant. We report results on three polymers: cis‐polybutadiene, a polybutadiene with 33% 1,2 double bonds, and a polybutadiene with 40% 1,2 double bonds. We have observed that the etch rate of these polymers decreases significantly with increasing flow rate, strongly suggesting that the vapor‐phase products of polymer degradation contribute to the degradation process.
Characterization of nonderivatized cellulose by gel permeation chromatography
Authors: Schwald Wolfgang , Bobleter Ortwin
Published: April 2003

The development of a gel permeation chromatography (GPC) system for the analysis of nonderivatized cellulose in the DP range of technical cellulose products is reported. In contrast to traditional GPC, where cellulose derivatives have to be prepared, in this work the cellulose solvent cadoxen was applied for the determination of the molecular weight distribution using a special analysis system. Nuclear magnetic resonance studies of cadoxen solutions indicated no complex formation between cadoxen and cellulose. Therefore, to avoid precipitation of cellulose from the prepared solution, cadoxen was also used as eluent in the chromatographic system. For this reason a stationary phase had to be found which is stable under the given strong alkaline conditions. The utilization of Fractogel TSK as column material resulted in the separation of dissolved cellulose showing a DPv between 400 and 2000 with good reproducibility. The application of very sensitive detectors together with a GPC program allows the characterization of unknown cellulose samples of different origin within a few hours.
Sulfonated latex particle as acid catalysts for the continuous inversion of sucrose
Authors: Kim J. H. , El‐Aasser M. S. , Klein A. , Vanderhoff J. W.
Published: April 2003

Sulfonated polystyrene latex particles were used as acid catalysts in the continuous inversion of sucrose at 50–70°C. The particles (surface charge 168 μeq/g) were confined in a stirred reactor with a semipermeable membrane; sucrose solution was pumped in, and product solution was pumped out. The catalytic activity of the particles was unchanged after 20 days continuous use. Variation of particle size (0.13 and 0.42 μm) and stirring rate showed that internal and external mass transfer was not a controlling factor. The kinetics were pseudo‐first‐order; the rate constant at 70°C was 2.30/N min as compared with 0.07/N min for macroporous sulfonated ion‐exchange resin; the apparent activation energy was 111 kJ/mol as compared with 121 kJ/mol for the homogeneous acid‐catalyzed reaction. The faster rate was attributed to the very great surface area, high charge density, and lack of internal diffusional resistance of the latex particles. The proposed mechanism comprised adsorption of sucrose on the particle surface, followed by inversion and desorption of product.
On‐line studies and computer simulation of the melt spinning of nylon‐66 filaments
Authors: Zieminski Kenneth F. , Spruiell Joseph E.
Published: April 2003

A mathematical model was developed to describe the high‐speed melt‐spinning behavior crystallizable polymers. This model included the effects of acceleration, gravity, and air friction on the kinematics of the process; temperature and molecular orientation on the crystallization kinetics of the polymer; and temperature, molecular weight, and crystallinity on the elongational viscosity of the material. Experimental on‐line diameter, birefringence, and temperature profiles were obtained for a 12,000 Mn nylon‐66 at 2.5 g/min spun at take‐up speeds ranging from 2800 to 6600 m/min. These profiles were qualitatively and reasonably quantitatively in agreement with the predicted profiles. They indicated that orientation induced crystallization occurs at spinning speeds greater than 4000 m/min. The experimental diameter and birefringence profiles were compared to those predicted by the model using Avrami indices of 3, 2, and 1. There was a small increase in the crystalline index at the lower speeds with decreasing index. The effect of the strain hardening was more significant at the higher speeds, this being shown by decreasing the exponent in the relationship for the crystallinity on the elongational viscosity. The model developed in this study indicates that high spinning speeds provide the high stress environment that increases the molecular orientation within the fiber. It is this higher molecular orientation that is the driving force for rapid crystallization on the spinline. This rapid crystallization causes a strain hardening, preventing any further drawdown in the fiber diameter and an abrupt rise in the birefringence. This behavior closely corresponds to the observed spinline profiles.
The effect of composition on the properties of nylon 612 copolymers
Authors: Garner David P. , Fasulo Paula D.
Published: April 2003

The series of nylon 612 copolymers was synthesized from caprolactam (C) and laurolactam (L) at 145°C. The 50/50 C/L molar ratio copolymer was found to have the minimum melting temperature (Tm ) for the series. The glass transition temperatures (Tg 's) of the copolymers were affected by the crystallinity of the copolymers. The Tg was at a minimum for the 50/50 copolymer for crystalline samples. However, for amorphous samples there was a decrease in Tg with increasing L content. Percent crystallinity was determined by differential scanning calorimetry and X‐ray techniques. It was found that the degree of crystallinity was at a minimum for copolymers of 70/30 to 40/60 C/L ratios. Coefficients of linear thermal expansion (CLTE) were obtained for the copolymers at 10°C intervals from 20 to 70°C for dry and from 20 to 50°C for samples conditioned at 50% relative humidity and 50°C. The dry samples gave lower initial values, but had a greater temperature dependence than the conditioned samples. As expected, the CLTE was found to be lowest for samples exhibiting the highest crystallinity. The tensile strengths and moduli decreased rapidly with increasing L up to the 70/30 C/L ratio after which they remained relatively constant. Elongations reached maximums between 70/30 and 40/60 C/L ratios. An inverse relationship was found between crystallinity and impact strength.
Mechanical properties of polypivalolactone: Effects of thermal history and solvent exposure
Authors: Paul Charles W.
Published: April 2003

The mechanical properties and solvent resistance of polypivalolactone (PPL) were determined as part of our study of PPL composites. High elongation (30%) films were obtained when moldings were cooled slowly and annealed for 15 min at 200°C prior to testing. The ductility fell when samples were held at 71°C for 2 weeks either dry or more so when exposed to water. Molecular weight degradation is believed to be responsible. This conditioning, however, raised the modulus of the sample by up to 32% in the vicinity of the conditioning temperature. It is speculated that this is due to densification in some of the stressed amorphous regions. The high crystallinity of PPL makes it insoluble in all common organic solvents. However, it swells and softens considerably when immersed in methylene chloride or methyl ethyl ketone.
High temperature laminating resins based on maleimido end‐capped pyromellitimide
Authors: Mikroyannidis John A. , Melissaris Anastasios P.
Published: April 2003

A novel class of bismaleimides, biscitraconimides, and bisdichloromaleimides chain‐extended by pyromellitimide was prepared and characterized by infrared and proton nuclear magnetic resonance spectroscopy. These polymer precursors were prepared by reacting maleic/citraconic/dichloromaleic anhydride (1 mol) with an equimolar amount of a diamine and subsequently with pyromellitic dianhydride (0.5 mol). The tetraamic acid formed was cyclodehydrated by chemical or thermal means. The curing behavior of polymer precursors was investigated by differential thermal analysis. Bismaleimide was thermally polymerized at a relatively higher temperature than the corresponding biscitraconimide and at lower temperature than bisdichloromaleimide. The curing temperature of monomers fluctuated between 209 and 318°C. Dynamic thermogravimetric analysis of the cured aromatic resins showed that they were approximately stable up to 370°C both in nitrogen and air. Their char yield was 53–63% at 800°C under anaerobic conditions. The relative thermal stability of the cured resins, with respect the diamine utilized for imidization, was of the order p‐phenylenediamine > 4‐aminophenyl ether > 4,4′‐diaminodiphenylmethane > 4,4′‐diaminodiphenylsulfone > hexamethylenediamine. In addition, the thermal and thermooxidative stability of polymers was ascertained by isothermal gravimetric analysis.
Study on rough‐surface biaxially oriented polypropylene film. V. Analysis and control of roughness
Authors: Fujiyama Mitsuyoshi , Kawamura Yoshimasa , Wakino Tetsuo , Okamoto Tomomi
Published: April 2003

In the previous papers, the roughening of biaxially oriented polypropylene film (BOP) by utilizing β‐form crystals in a successively stretching tenter method has been studied, and BOPs with various roughness have been obtained. In the present paper, the results obtained in the previous studies have been summarized. The roughness can quantitatively be represented by average roughness Ra (depth of roughness) and roughness period L (density of roughness). Ra and L can largely be changed by changing machine direction (MD)‐stretching temperature and the melt flow index (MFI) of base polypropylene (PP), respectively. Furthermore, a BOP with a low roughness period (high density of roughness) can be obtained by adding crystal nucleators to the base PP.
A novel method for crosslinking polyetheretherketone
Authors: Thompson S. A. , Farris R. J.
Published: April 2003

A novel method for crosslinking polyetheretherketone via imine formation at carbonyl groups is presented. In polyetheretherketone these Schiff bases form short, stiff crosslink junctions which are stable up to 630°C. Dynamic mechanical and thermal properties of polyetheretherketone and imine crosslinked polyetheretherketone are reviewed. A large reduction in the temperature sensitivity of the material stiffness has been achieved. Increases in the glass transition temperature from 143°C to greater than 280°C have been obtained.
Pervaporation separation of ethanol–water mixtures using ionically crosslinked blended polyacrylic acid (PAA)–nylon 6 membranes
Authors: Xu Y. F. , Huang R. Y. M.
Published: April 2003

The pervaporation separation of ethanol–water mixtures was carried out through a series of ionically crosslinked polyacrylic acid (PAA)–Nylon 6‐blended membranes crosslinked to varying degrees in aluminum nitrate solution. The polyacrylic acid (PAA)–Nylon 6 membranes were cast from homogeneous PAA–Nylon 6 mixtures to various thicknesses and then crosslinked. Optimum pervaporation results were obtained from crosslinked blends containing 75 wt% Nylon 6 and 25 wt% PAA. These membranes have separation factors (water/ethanol) of 35–40 at flux rates of 120–160 g/m2 h. The optimum crosslinking time was found to be approximately 35 h to yield membranes with the best separation and flux rates at 25 wt% PAA content.
Chain transfer constants of mercaptans in the emulsion polymerization of styrene
Authors: Dietrich B. K. , Pryor W. A. , Wu S. J.
Published: April 2003

The chain transfer reaction and overall consumption of three mercaptans (n‐decyl mercaptan. n‐dodecyl mercaptan, and tert‐dodecyl mercaptan) were studied in batch and semibatch seeded emulsion polymerizations of styrene. Seventy to ninety‐five percent of the mercaptans reacted by chain transfer. The apparent chain transfer constants of mercaptans in the batch process decreased with increasing carbon chain length of the mercaptans. This tendency is connected with the analogous difference of the distribution coefficients of these mercaptans between the water phase and monomer droplets. The values of the chain transfer constant are independent of the amount of mercaptans used and reaction temperatures from 60°C to 90°C. The chain transfer constant of tert‐dodecyl mercaptan had the same value in both the batch and semibatch processes. This indicates that varying the concentrations of initiator and monomer had negligible effects on the chain transfer reaction.
Processing of polyurethane–polyester interpenetrating polymer network (IPN)
Authors: Hsu T. Jeffrey , Lee L. James
Published: April 2003

The kinetics and heat transfer during the curing of a polyurethane–polyester interpenetrating polymer network (IPN) were investigated experimentally and theoretically. A model based on the additivity rule of constituent ingredients was used to predict the IPNs reaction kinetics and heat transfer. Compared with the adiabatic temperature rise measured during reaction injection molding and the temperature profiles measured during a casting process, the model prediction is close to the experimental data. Deviations of model prediction from experimental results were found in the comparison of reaction rate profiles measured by differential scanning calorimetry. This suggests that reaction interactions may exist in the polymerization system.
Investigation of crystalline changes in LaRC‐TPI powders
Authors: Hou T. H. , Wakelyn N. T. , St. Clair T. L.
Published: April 2003

Semicrystalline LaRC‐TPI is known to be capable of recrystallizing to higher melting crystalline forms upon initial melting. The behavior of these different crystalline forms has not been studied before. The present study uses techniques of differential scanning calorimetry and X‐ray diffractometry to investigate thes crystalline structural changes during recrystallization of this material. Semicrystalline LaRC‐TPIs synthesized from three different laboratories are included in this work.
Effect of water content of hydrophilic amidoxime polymer on adsorption rate of uranium from seawater
Authors: Hirotsu Takahiro , Katoh Shunsaku , Sugasaka Kazuhiko , Takai Nobuharu , Senō Manabu , Itagaki Takaharu
Published: April 2003

Amidoxime polymers crosslinked with tetraethylene glycol dimethacrylate (40 wt%) and with differing water contents were prepared by poly(acrylonitrile) treatment in various quantities of toluene with hydroxylamine. Adsorption rates of uranium on the amidoxime polymers from seawater were examined in relation to their porosity. The amidoxime polymer prepared from poly(acrylonitrile) in an increasing quantity of toluene exhibits a significantly increasing water content. On the basis of mercury intrusion measurements, the increasing water content was revealed to be predominantly owing to the enhancement of porosity. The adsorption rate of uranium from seawater increased steadily with an increase of porosity, suggesting the dependence of the adsorption rate on a diffusion process of uranium into the pore domain.
High‐performance composites from polyimide matrix resins that utilize a cross linking reaction of biphenylene end‐caps with acetylene units in the main chain
Authors: Stoessel Steve , Takeichi Tsutomu , Stille J. K. , Alston William B.
Published: April 2003

Graphite‐reinforced composites were prepared with oligomeric polyimides having biphenylene end‐caps and acetylene linkages in the polymer chain. The oligomers were crosslinked by the reaction of the biphenylenes with the diphenyl acetylenes to form 9,10‐diphenylphenanthrene units. The resulting composites had good mechanical properties. Thermal oxidative aging studies show that the unidirectional graphite fiber composites maintained good mechanical properties up to 1200 h at 316°C.
Tensile properties and morphology of the dynamically cured EPDM and PP/HDPE ternary blends
Authors: Ha Chang Sik , Kim Sung Chul
Published: April 2003

The tensile properties and morphology of the polyolefin ternary blends of ethylenepropylene–diene terpolymer (EPDM), polypropylene and high density polyethylene were studied. Blends were prepared in a laboratory internal mixer where EPDM was cured in the presence of PP and HDPE under shear with dicumyl peroxide (DCP). For comparison, blends were also prepared from EPDM which was dynamically cured alone and blended with PP and HDPE later (cure–blend). The effect of DCP concentration, intensity of the shear mixing, and rubber/plastics composition was studied. The tensile strength and modulus increased with increasing DCP concentration in the blends of EPDM‐rich compositions but decreased with increasing DCP concentration in blends of PP‐rich compositions. In the morphological analysis by scanning electron microscopy (SEM), the small amount of EPDM acted as a compatibilizer to HDPE and PP. It was also revealed that the dynamic curing process could reduce the domain size of the crosslinked EPDM phase. When the EPDM forms the matrix, the phase separation effect becomes dominant between the EPDM matrix and PP or HDPE domain due to the crosslinking in the matrix.
Improvement of various properties of fiber surfaces containing crosslinked polyethylene glycols
Authors: Vigo Tyrone L. , Bruno Joseph S.
Published: April 2003

Modification of a variety of fabric and fibrous surfaces was achieved by insolubilization thereon of crosslinked polythylene glycols (called POLYTHERM) to impart several useful properties: thermal storage and release, improved resiliency and resistance to oily soiling, static charge, pilling, wear life, and marked increases in hydrophilicity among them. Moreover, these improved properties were durable because up to 70% of the crosslinked polyol was retained after 50 launderings. Such modification was achieved by using average molecular weights of the polyols ranging from 600 to 20,000 by crosslinking with polyfunctional methylolamides (such as DMDHEU) in the presence of acid catalysts by a conventional pad‐dry‐cure textile finishing procedure. The role of crosslink density of the polyol in determining textile properties was determined by evaluation of films derived from crosslinking the polyols and comparison of selected properties.
Crosslinking of polypropylene–polyethylene blends by peroxide and the effect of pentaerythritol tetrallyl ether
Authors: Borsig Eberhard , Fiedlerová Agnesa , Rychlá Lyda , Lazár Milan , Rätzsch Manfred , Haudel Gottfried
Published: April 2003

Crosslinking of polypropylene–polyethylene (PP‐PE) blends involving 10, 20, 30, 40, 50, 60, 70, 80, and 90% of PP with dicumylperoxide (DCP) or tert‐butyl perbenzoate (TBPB) and in the presence of coagent pentaerythritol tetrallyl ether (PETA) was investigated at 180°C. It was found that at lower concentrations of peroxide alone (e.g., 2.5% of DCP) only PE component is crosslinked in all compositions of PP‐PE blends. In the crosslinking of PP‐PE 50:50 with 4% of TBPB, insoluble gel was obtained, which contained 13% PP and 87% PE. If 2% PETA was also used, the portion of PP in gel increased to 39%; the total yield of gel in PP‐PE blend increased from 50 to 70%. The lower crosslinking efficiency of coagent PETA in the PP‐PE blends compared with PP alone is associated with better solubility of the coagent in the PE phase in contrast to the PP phase. The coagent does not particularly raise the crosslinking efficiency of peroxide in PE, but increases it in the PP phase. A remarkable decrease in melting temperature and temperature of crystallization of both polymer components depending on peroxide concentration was found by calorimetric measurements.
Bulk functionalization of ethylene–propylene copolymers. II. Influence of the initiator concentration and of the copolymer composition and chain microstructure on the reaction kinetics
Authors: Greco Roberto , Maglio Giovanni , Musto Pellegrino , Scarinzi Gennaro
Published: April 2003

The effect of the dicumylperoxide (DCPO) concentration on the kinetics of the bulk functionalization of an ethylene‐propylene copolymer (EPR) has been studied. It has been found that, enhancing the DCPO initial concentration in the reaction mixture, results in both increased initial reaction rate and grafting process efficiency. DCPO content also affects degradation, which always accompanies the grafting reaction. At high DCPO content, products with a high degree of grafting and intrinsic viscosity close to that of the parent copolymer can be obtained. Furthermore, the influence of the EPR composition and chain microstructure on the functionalization as well as on the degradation processes has been investigated. By increasing the C2 content in EPRs prepared by using vanadium‐based conventional catalysts, obtains faster functionalization kinetics and a less pronounced degradation of the products. At fixed experimental conditions, the highest grafting degrees have been obtained by using EPRs prepared by high‐yield titanium catalysts and characterized as a block‐like microstructure. The experimental results have been interpreted on the basis of a proposed reaction mechanism.
Anionic polymerization of styrene: Integration with styrene monomer production
Authors: Priddy Duane B. , Pirc Michael
Published: April 2003

Anionic polymerization and ethylbenzene dehydrogenation were carried out in the laboratory using continuous reactor designs and conditions typical of current commerical processes. The dehydrogenator was operated at 43–55% conversion with continuous distillation of the ethylbenzene/styrene mixture to remove byproducts that would interfere with the subsequent anionic polymerization. The anionic polymerization was carried out using a reactor of the CSTR type which operated at > 99% conversion of styrene. The volatiles were recovered from the polymer syrup and recycled back to the dehydrogenator. During 4 months of continuous operation the integrated process showed no detrimental buildup of impurities which affected the anionic polymerization or dehydrogenation. The polystyrene produced had excellent color, clarity, thermal stability, and polydispersity (Mw/Mn = 2.1–2.4). The ability to control weight average molecular weight was within a range of 20,000 using an on‐line GPC in concert with a colorimeter.
Thermal stability characteristics of some resins from chemically modified PVC
Authors: Moitra Subrata , Biswas Mukul
Published: April 2003

PVC has been modified by chlorine displacement reaction with m‐aminophenol, bisphenol A, and phenophthalein. Sulfonation of these condensates yields bifunctional weak acid resins which do not exhibit SO3H ionogenic group. Reaction of PVC with presulfonated bisphenol A, phenolphthalein, and phenol yields strong acid resins. Thermal stability characteristics of these various resins have been determined and the results indicate that such modifications improve the overall thermal stability of PVC.
A re‐evaluation of heat transfer associated with drawing of polymers
Authors: Chung B. T. F. , Liu F.
Published: April 2003

The temperature rise due to heat generation associated with drawing of polymer is re‐evaluated and rederived starting from the first law of thermodynamics. The errors of both formulations and sample calculations made in a previous investigation were corrected. The predicted efficiency or the fraction of mechanical work converted into heat during necking based on the present formulations is found to be reasonable.
Anomalous behavior of cured epoxy resins: Density at room temperature versus time and temperature of cure
Authors: Pang K. P. , Gillham J. K.
Published: April 2003

The room temperature density (ρRT) of a difunctional aromatic epoxy resin cured with a tetrafunctional aromatic amine passes through a maximum value in the vicinity of gelation with increasing conversion. For a given cooling rate cure resutls in a unique value of ρRT for each conversion as long as the material does not vitrify on cure. The occurrence of vitrification during cure eliminates the one‐to‐one relationship because of the nonequilibrium nature of the glass transition region and of the glassy state. In the glass transition region there is competition between physical aging which increases the density and chemical aging which, after gelation, decreases ρRT. After gelation, prolonged isothermal cure and physical aging to well beyond vitrification result in limiting values of ρRT which decrease with increasing temperature of cure. The maximum in the ρRT vs. conversion relationship is discussed in terms of the effects of shrinkage due to cure, the corresponding nonlinear increase in the glass transition temperature with increasing conversion after gelation, and longer relaxation times in the glass transition region with increasing crosslink density. Other factors which affect room temperature density are discussed.
Prediction of the concentration dependence of diffusion coefficients of polymers in solution
Authors: Qian J. W. , Rudin Alfred
Published: April 2003

The hydrodynamic volumes of solvated polymers shrink with increasing concentrations in solution until a concentration (cx) is reached at which the effective dimensions are those of a Theta solvent. A simple model (Ref. 7) can be used to calculate the volume fraction of solvated polymer coils as a function of concentration. From this, the concentration dependence of diffusion coefficients can be estimated (Ref. 5). Calculated data are in very good agreement with experimental values except for some lower molecular weight polymers in poor solvents.
Estimation of reactivity ratios of N‐methacryloloxyphthalimide copolymers by1H NMR
Authors: Shaaban A. F. , Khalil A. A. , Messiha N. N.
Published: April 2003

Copolymerization of N‐methacryloyloxyphthalimide (NMP) with methyl acrylate (MA), methyl methacrylate (MMA), and acrylonitrile (AN) was carried out in dimethylformamide using azobisisobutyronitrile (AIBN) as an initiator at 60°C. The estimation of the copolymer compositions were carried by 1H nuclear magnetic resonance (NMR) spectroscopy. The monomer reactivity ratios for NMP‐MA, NMP‐MMA, and NMP‐AN systems were found to be r1 = 1.223, r2 = 0.208, r1 = 1.441, r2 = 0.704, r1 = 1.496 and r2 = 0.228, respectively, by Kelen–Tüdős method. Also, the Q and e values for NMP monomer was found to be Q = 0.90 and e = 0.01, respectively.
Permselectivities through artificial membranes at a non‐steady state
Authors: Higuchi Akon , Nakagawa Tsutomu
Published: April 2003

Non‐steady‐state flux ratios of oxygen to nitrogen in a poly(dimethyl siloxane) membrane are theoretically investigated as a function of time. Concentration profiles of oxygen and nitrogen are found to decay to a negligible concentration with an increase of the distance from membrane surface and it is observed that oxygen penetrates deeper than nitrogen in the membrane at the non‐steady state. Differences of concentration profiles of oxygen and nitrogen lead to enormously high selectivity for oxygen at the non‐steady state. The flux and selectives are studied under the condition that the upstream pressure is pulsating to keep the non‐steady state continuously as suggested by Paul[Ind. Eng. Chem. Proc. Des. Dev., 10, 375 (1971)]. Model calculations are also performed for the concentration of uranium 235 from natural uranium. The flux ratio of uranium 235 to uranium 238 in the non‐steady state is calculated to be 1.144 at time/L2 = 800 s/cm2 (L = membrane thickness), which is higher than the value, 1.00429, at a steady state.
Thermodynamic study of polymer–solvent systems by reversed‐flow gas chromatography
Authors: Agathonos Pericles , Karaiskakis George
Published: April 2003

Reversed‐flow gas chromatography, a new method for studying heterogeneous catalysis, diffusion, adsorption, evaporation, and other related phenomena, is now applied to the determination of activity of the solvent in a polymer–solvent system in the whole range of polymer concentration, as well as for the calculation of excess partial molar thermodynamic functions of mixing. The systems used were polystyrene in cyclohexane, polyvinylacetate in cyclohexanone and polyvinylpyrrolidone in methanol. In the first system, which was studied in detail, weight fraction activity coefficients (a1/w1) at several temperatures (333.8–348.1 K) and various polymer concentrations (0.020–0.131 g/g) were determined. From the latter parameters weight fraction activity coefficients at infinite dilution (a1/w1)∞ were computed. Flory–Huggins interaction parameters x and solubility parameters δ2 were also determined. Finally, the thermodynamic parameters found by the present method are compared with those determined by other techniques or calculated theoretically.
Studies on the thermal properties of PVC : Polystyrene alloy
Authors: Eboatu A. N. , Olojo D. O. , Momoh M.
Published: April 2003

The effect of composition on the thermal properties of poly(vinyl chloride) (PVC)–polystyrene (PSt) alloy was investigated. Using the DSC, it was observed that the glass transition temperature (Tg) and melting point (Tm) as well as the enthalpic change at melting (ΔH) were altered with respect to their theoretical values. An attempt is made to explain these facts.
Miscible blends from plasticized poly(vinyl chloride) and epoxidized natural rubber
Authors: Varughese K. T. , De P. P. , Sanyal S. K. , De S. K.
Published: April 2003

Miscible blends from plasticized poly(vinyl chloride), and epoxidized natural rubber having 50 mol% epoxidation level were prepared in a Brabender Plasticorder by the melt‐mixing technique. Changes in Brabender torque and temperature, density, dynamic mechanical properties, and differential scanning calorimetry of the samples were examined as a function of blend composition. The plasticized poly(vinyl chloride)/epoxidized natural rubber blends behaved as a compatible system at all composition ranges as evident from their single glass‐rubber transition temperature (Tg) obtained from dynamic mechanical analysis as well as from differential scanning calorimetry. Profound changes in the nature of the glass‐rubber transition were noted with respect to blend composition. The Tg‐width values of blends lie between those of plasticized poly(vinyl chloride) and epoxidized natural rubber.
A new inductive detection for the magnetoviscometer
Authors: Hermann W. , Sobczak R.
Published: April 2003

For a new magnetoviscometer with an inhomogeneous magnetic field to move iron spheres similar to the Stokes experiment, a nonoptical detection was developed. As a measuring principle the change of the impedance of a coil, penetrated by the sphere is used. The measuring principle is the change of impedance of an induction coil wrapped around the cell by the sphere. The measuring block, consisting of heating elements, detection coils, and a measuring cell is quite simple and therefore well suited for measuring under pressure. Since the proper cells are simply brass cylinders closed by a screw, they can be thrown away after the experiment (e.g., for network‐building polymers). Examples for said measurements are given.
Mathematical modeling of emulsion copolymerization reactors
Authors: Richards John R. , Congalidis John P. , Gilbert Robert G.
Published: April 2003

This article presents the physical mechanism and the mathematical structure of a comprehensive dynamic emulsion polymerization model (EPM). EPM combines the theory of coagulative nucleation of homogeneously nucleated precursors with detailed species material and energy balances to calculate the time evolution of the concentration, size, and colloidal characteristics of latex particles; the monomer conversions; the copolymer composition; and molecular weight in an emulsion system. The capabilities of EPM are demonstrated by comparisons of its predictions with experimental data from the literature covering styrene and styrene/methyl methacrylate polymerizations. EPM can successfully simulate continuous and batch reactors over a wide range of initiator and added surfactant concentrations.
Radiation grafting of α,β,β‐trifluorostyrene onto poly(ethylene–tetrafluoroethylene) film by preirradiation method. I. Effects of preirradiation dose, monomer concentration, reaction temperature, and film thickness
Authors: Momose Takashi , Yoshioka Hiroko , Ishigaki Isao , Okamoto Jiro
Published: April 2003

Preirradiation grafting of α,β,β‐trifluorostyrene onto poly(ethylene–tetrafluoroethylene) film was studied. The trapped radicals formed upon irradiation were able to induce graft polymerization under appropriate conditions. The influences of the grafting conditions were analyzed kinetically. The grafting rate dependency on the preirradiation dose was found to be of order 0.3, and the monomer concentrations, 1.0. The overall activation energies for this grafting were calculated to be 6.2 × 104 and 9.3 × 103 J/mol below and above 50°C. The grafting rate was found to be independent of the film thickness, which ranged from 25 to 100 μm.
Turbulent drag effectiveness and shear stability of xanthan‐gum‐based graft copolymers
Authors: Ungeheuer S. , Bewersdorff H.‐W. , Singh R. P.
Published: April 2003

A number of graft copolymers of xanthan gum and polyacrylamide have been synthesized by grafting acrylamide onto xanthan gum using the ceric‐ion‐initiated solution polymerization technique. The effects of various synthesis parameters such as amount of catalyst, reaction time, and ratio of xanthan and acrylamide on drag reduction effectiveness of the graft copolymers have been studied. The scaling up of grafting reaction has been accomplished in 40‐L reactor. The drag reduction effectiveness of the graft copolymers is investigated over a wide range of concentrations and Reynolds numbers. It is shown that the maximum drag reduction obtainable in xanthan gum solutions above 300 ppm can be obtained in solutions of graft copolymers at concentrations of 100–150 ppm. The grafting also improves the shear stability at higher Reynolds numbers. The shear stability of the graft copolymers at constant wall stress has been found to be superior to polyacrylamide and the mixtures of polyacrylamide and xanthan gum. In general, the shear stability of graft copolymers and polyacrylamide is shown to increase with concentration. The drag reduction characteristics and shear stability have been discussed in terms of structural features of the graft copolymers. The drag reduction characteristics of the graft copolymers are found to be similar to those of flexible polymers.
Preparation of glycidyl celluloses from completely allylated methylcellulose and tri‐O‐allylcellulose
Authors: Kondo Tetsuo , Ishizu Atsushi , Nakano Junzo
Published: April 2003

Glycidyl celluloses were prepared from completely allylated methylcellulose and tri‐O‐allylcellulose with m‐chloroperbenzoic acid in homogeneous chloroform solutions. The degrees of substitution (DS) by epoxy groups were 0.60 and 1.33 for the products prepared from allylated methylcellulose and tri‐O‐allylcellulose, respectively. They were soluble in not only many organic solvents, but also methanol‐water mixtures [more than 70% (v/v)]. These products were characterized by infrared spectroscopy (IR), 13C‐NMR spectroscopy, and gel permeation chromatography (GPC).
Phenoxy resin: Characterization, solution properties, and inverse gas chromatography investigation of its potential miscibility with other polymers
Authors: Iribarren J. I. , Iriarte M. , Uriarte C. , Iruin J. J.
Published: April 2003

A commercial sample of a copolymer of bisphenol‐A and epichlorohydrin (Phenoxy) has been carefully fractionated in a dioxane/methanol mixture. Mark‐Houwink constants in THF and the molecular weight distribution of the raw material have been obtained on the basis of the universal calibration procedure. Conformational magnitudes such as the characteristic ratio C∞ or the steric factor σ have been determined from viscometric data at 63°C in a good (dioxane) and a θ‐solvent (1,2‐dichloroethane). Inverse gas chromatography was used to study phenoxy miscibility with a variety of polymers. Using different probes as model compounds, the partial molar enthalpy of mixing ΔH at infinite dilution has been determined. Results were correlated with the reported miscibility of phenoxy with polyesters, polyethers, and polyoxides. A linear multiparametric correlation of ΔH with polarizabilities, dipole moments, and hydrogen bond accepting powers provides for a comprehensive analysis of other miscible systems.
Synthesis of 6‐ and 7‐oxo poly(vinyl ester)s and their evaluation
Authors: Shantha K. L. , Pratap G. , Rao V. S. Bhaskar
Published: April 2003

Long chain vinyl esters of 6‐ and 7‐oxoaliphatic acids are synthesized as intermediate monomers for the preparation of poly 6‐oxo and 7‐oxo vinyl esters. These comblike polymers have wide applications as fluidity improvers. Detailed characterization of all the intermediates is done by IR, PMR, and MS for the first time. Their evaluation is done on high waxy Bombay high crude.
Characterization of substituted phenol–formaldehyde resins using solid‐state carbon‐13 NMR
Authors: Sinha Brijnaresh R. , Blum Frank D. , O'Connor Daniel
Published: April 2003

Crosslinked substituted phenol–formaldehyde resins were synthesized from cashew nut shell liquid, 3‐n‐pentadecylphenol and phenol with formaldehyde. The resulting resins were crosslinked and investigated using carbon‐13 NMR in the solid state using cross‐polarization, magic angle spinning, and dipolar decoupling. Comparisons were made between the spectra of pure phenol–formaldehyde resins and it was shown possible to distinguish between the resins. It was also shown that the proton‐dephased spectrum gave better spectral resolution for the substituted compounds. In addition, the solids carbon‐13 technique verified that the degradation of the substituted phenolic resins occurs first with the degradation of the side chain in agreement with suggestions from earlier work.
Shear rate dependence of the viscosity of cellulose nitrate solutions in the dilute concentration regime revisited
Authors: Marx‐Figini M. , Gonzalez F. Rex
Published: April 2003

A detailed rheological study of cellulose nitrate in ethylacetate had been carried out in the dilute concentration (c) regime, covering a degree of polymerization (DP) range between 300 < DPη < 7000 and shear rates (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}) between 100 s−1 < \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} < 2000 s−1. The results show a strong dependence of the transition Newtonian to non‐Newtonian behavior on the three variables \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}, DP, and c, similar to that found recently on solutions of synthetic polymers. Emphasis has been put on the critical concentrations corresponding to the standard shear rate 1000 s−1 to correspond to the standard conditions (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} ≅ 1000 s−1; 0.3 < [η] · c < 0.6; DS = 2.90 ± 0.02) proposed for the determination of the intrinsic viscosity [η] of cellulose nitrates. It is shown that solutions with concentrations adjusted according to the above given conditions still exhibit Newtonian behavior, up to the highest range of DP. It follows, therefore, that applying the standard conditions, an extrapolation to \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} = 0 as has been proposed often for the intrinsic viscosity determination of cellulose nitrate is not advisable and results in considerable error. Considering the relationship between [η] and DP, the present results indicate that the decrease of the exponent (a) from a = 1.0 to a = 0.76, taking place above a DP ≅ 1000, is not a consequence of the applied shear rate but rather of the molecular properties of the solutes themselves.
Graft copolymerization of poly(butyl methacrylate) onto wool in the presence of air and nitrogen atmosphere. II
Authors: Shukla J. S. , Tiwari S. C.
Published: April 2003

Poly(butyl methacrylate) (PBMA) was grafted onto wool in the presence of air and nitrogen atmosphere using potassium bromate and thioaceticacid (TAA) as redox initiating system, under different reaction conditions. The percentage grafting and percentage efficiency have been determined as a function of various reaction variables and the results have been compared. The graftcopolymer was characterized by scanning electron micrograph, thermogravimetry, and molecular weight.
The strain rate dependency of fracture in polyethylene: Fracture initiation
Authors: Barry D. B. , Delatycki O.
Published: April 2003

The dependency of fracture on the rate of strain of a range of polyethylene samples was measured in three point flexural tests at 23°C. The range of strain rates from 10−1 to 10−7 reciprocal seconds was examined. The J integrals at the initiation of the cracks were determined. This enabled the interrelationship between fracture initiation and the test rate to be established. The dependency follows a power law relation. The values of the exponents in the power law equations, derived from experiment, were found to be higher than the values calculated using established criteria for crack initiation. The difference is postulated to be due to the strengthening of the fibrils ahead of the crack because of the orientation of the fibrils in that region.
Surface characterization of hydrophilic functional polymer latex particles
Authors: Tamai H. , Hasegawa M. , Suzawa T.
Published: April 2003

Surface characteristics of styrene/acrylamide/acrylic acid copolymer and styrene/2‐hydroxyethyl methacrylate/acrylic acid copolymer latexes prepared without emulsifier using potassium persulfate as initiator and their colloidal stabilities were investigated. The negative ζ‐potentials decreased with increasing the amount of acrylamide and 2‐hydroxyethyl methacrylate copolymerized. In spite of the increase in surface charge density, the negative ζ‐potentials decreased through the maximum with increasing pH. The colloidal stabilities for NaCl concentration were remarkably enhanced with increasing both pH and the amount of acrylamide and 2‐hydroxyethylmethacrylate. These results suggest that the contration and expansion of water‐soluble polymer layer surrounding the particles play an important role in the surface properties.
Benzoyl‐peroxide‐initiated graft copolymerization of poly(ethylene terephthalate) fibers with acrylamide
Authors: Saçak M. , Pulat E.
Published: April 2003

In this study the grafting of acrylamide onto poly(ethylene terephthalate) fibers with the help of benzoyl peroxide and the effects of the temperature and the concentrations of initiator and monomer were investigated. Some of the experiments were repeated several times in order to check the reproducibility. The optimum temperature for grafting was found to be 75°C. The graft yield was observed to increase with the monomer concentrations examined. The graft yield increased up to the benzoyl peroxide concentration approximately 0.05 g/50 mL, and then passed a plateau, before showing a decrease. The fiber diameter, intrinsic viscosity, and the moisture regain increased while the fiber density decreased with the graft yield.