bluuebunny/crossref_metadata_2025_split huggingface dataset:
Production of hydroxyl‐terminated liquid natural rubber—mechanism of photochemical depolymerization and hydroxylation
Authors: Ravindran T. , Nayar M. R. Gopinathan , Francis D. Joseph 
Published: April 2003

AbstractPhotochemical degradation of natural rubber yielded hydroxyl‐terminated liquid natural rubber (HTNR) when carried out in solution in presence of H2O2. Ultraviolet radiation from a medium pressure mercury vapor lamp and sunlight were found to be almost equally effective in bringing about the depolymerization and hydroxylation of natural rubber. The variations in the composition of the reagents and exposure time on the extent of depolymerization was conducted, and a suitable procedure for the large scale preparation of HTNR was described. A probable mechanism leading to the formation of HTNR as well as the side products is discussed based on the analytical data.
The three stages in degradation of polymers—polyethylene as a model substance
Authors: Albertsson Ann‐Christine , Karlsson Sigbritt 
Published: April 2003

AbstractData 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

AbstractThe 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

AbstractNew 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

AbstractIn 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

AbstractThe 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

AbstractSulfonated 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractIn 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractSemicrystalline 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

AbstractAmidoxime 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

AbstractGraphite‐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

AbstractThe 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

AbstractModification 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.