bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modification of natural rubber tubes for biomaterials I. Radiation‐induced grafting of N,N‐dimethyl acrylamide onto natural rubber tubes
Authors: Razzak Mirzan T. , Otsuhata Kasushige , Tabata Yoneho , Ohashi F. , Takeuchi A. 
Published: April 2003

AbstractRadiation‐induced simultaneous grafting of N,N‐dimethyl‐acrylamide (DMAA) onto natural rubber (NR) tubes has been studied to improve blood compatibility of the NR tubes. Concerning grafting of DMAA onto NR tubes, it was found that the grafting proceeds effectively in the presence of carbon tetrachloride (CCl4) as a solvent. The degree of grafting was found to be saturated at about 26 wt%, but a higher degree of grafting can be obtained by either “so called two‐step grafting” or “putting a standing time for a while before irradiation.” The initial grafting rate was proportional to 0.85 power of dose rate. The apparent activation energy of the graft‐copolymerization was 7.42 kcal/mol. Evaluation of blood compatibility of DMAA‐grafted NR tubes has been carried out by ex vivo test. According to the results, significant improvement of blood compatibility was obtained for the samples in which degree of grafting is higher than 30 wt%.
Sample overloading effects in polymer characterization by field‐flow fractionation
Authors: Caldwell Karin D. , Brimhall Steven L. , Gao Yushu , Giddings J. Calvin 
Published: April 2003

AbstractThere are two subtechniques of field‐flow fractionation (FFF), thermal FFF and flow FFF, that have been successfully employed for polymer fractionation and characterization. These techniques are primarily analytical in nature, yielding accurate polymer characteristics from small sample loads (∼ 10 μg or less, depending on detection sensitivity). In this study the effects of increasing sample size are examined. Modest increases in load are found to result in shifts toward higher retention volumes. These modest loads also result in some broadening of the sample peaks without a major loss of peak symmetry. Excessive loading, by contrast, appears to give rise both to skewed peaks and to new artifact peaks at higher levels of retention. These observations are discussed in terms of the concentration dependence of various properties (viscosity, diffusivity, thermal diffusivity) which influence polymer transport through the FFF channel. The results are used to indicate upper limits to suitable sample concentrations.
Thermotropic polyester carbonates. III. Thermotropic polyester carbonates as self‐reinforced plastics
Authors: Lai Y.‐C. , Debona B. T. , Prevorsek D. C. 
Published: April 2003

AbstractThermotropic polyester carbonates derived from t‐butylhydroquinone, methylhydroquinone, diphenyl terephthalate, and diphenyl carbonate in the molar ratio of 50 : 50 : 55 : 45; 50 : 50 : 57.5 : 5 : 42.5 and 50 : 50 : 60 : 40 can be injection molded successfully from temperatures 10°C below melting to 30–40°C above melting. Normally the best molding temperatures are 10–20°C above melting. If the molding conditions are controlled properly, tensile strengths as high as 1.8 × 104 psi, tensile moduli as high as 7.4 × 105 psi, and flex moduli as high as 1.1 × 106 psi can be obtained.
Polymerization in gel‐like emulsions
Authors: Ruckenstein Eli , Kim Kyu‐Jun 
Published: April 2003

AbstractPolymerization of styrene in gel‐like emulsions (concentrated emulsions which have a volume fraction of monomer greater than 0.74), by using sodium dodecylsulfate as emulsifier and small amounts of water, was carried out with an oil‐soluble initiator, AIBN. Both higher conversions and higher molecular weights of the polymer were obtained as compared to the polymerization in bulk. The higher “rigidity” of the monomer in the interior of the cells of the gel is responsible for the increased rate of polymerization and molecular weight. The polymer particles thus obtained have diameters in the range of 0.1 to 0.3 μm, depending upon the conditions of preparation of the gel. The effects of the concentration of the initiator, the concentration of surfactant, the monomer volume fraction, termperature, and ionic strength of the aqueous solution have been investigated.
Study on rough‐surface biaxially oriented polypropylene film. VI. Roughening by laminated cast sheet
Authors: Fujiyama Mitsuyoshi , Kawamura Yoshimasa , Wakino Tetsuo , Okamoto Tomomi 
Published: April 2003

AbstractWhen the roughening of biaxially oriented polypropylene film (BOP) is performed by forming β crystals in a monolayer cast sheet, occasionally voids are formed in the BOP. In order to prevent this and to roughen both sides of the BOP, rough‐surface BOPs were obtained by casting two‐resin, three‐layer sheets consisting of two surface layers with a high‐melt flow index (MFI) polypropylene (PP) and a core layer with a low‐MFI PP, by stretching the cast sheets five times in the machine direction (MD) with a roll‐type stretching machine, and by stretching the MD‐stretched sheets 10 times in the transverse direction (TD) with a pantograph‐type stretching machine. Comparatively large spherulites were observed in the surface layers of the cast sheets and structural differences between the surface layers and core layer were recognized. Both sides of the cast sheets could be roughened. The influence of processing conditions on the roughness state of BOP was generally similar to that in the case of monolayer cast sheet.
Thermal degradation of poly(aryl‐ether–ether‐ketone) (PEEK): A differential scanning calorimetry study
Authors: Day M. , Suprunchuk T. , Cooney J. D. , Wiles D. M. 
Published: April 2003

AbstractDifferential scanning calorimetry (DSC) has been used to study the crystallization kinetics and thermal characteristics of poly(aryl‐ether–ether‐ketone) (PEEK) samples heated under a variety of conditions. Samples were heated in nitrogen and air at temperatures between 380 and 420°C for times up to 120 min. The results indicate that as the holding time and temperature of the melt increased, the amount of recrystallizable material decreased, especially when heated in air. Isothermal crystallization kinetics confirmed the presence of a two‐stage crystal nucleation and growth process with Avrami exponents of the order of about 2.4 and 1.5 for the first and second processes, respectively. Analysis of the primary crystallization process using the Avrami equation revealed that PEEK samples heated above the melt temperature in air crystallized at a much slower rate than samples heated in nitrogen.
Organotin polymers. XII. Azeotropy in binary and ternary copolymerization reactions of di(tri‐n‐butyltin) itaconate with acrylic acid esters, styrene, and acrylonitrile
Authors: Shaaban A. F. , Mahmoud A. A. , Messiha N. N. 
Published: April 2003

AbstractBinary and ternary copolymerizations of di(tri‐n‐butyltin) itaconate (TBTI) with methyl acrylate (MA), ethyl acrylate (EA), n‐butyl acrylate (BA), styrene (ST), and acrylonitrile (AN) were carried out in solution at 70°C in the presence of a free‐radical initiator. Experimental terpolymerization data agreed well with calculations based on the Alfrey–Goldfinger equation. The determination of unitary, binary, and ternary azeotropies of the various systems studied was easily handled by a computer. Ternary azeotropic compositions for TBTI–MA–AN and TBTI–EA–AN systems were 37 : 48 : 15 and 9 : 80 : 11 mol %, respectively. Also, “Pseudo‐azeotropic” regions were identified where the deviation between feed and polymer compositions is very small.
Mechanism of accelerated photofading of thioether anthraquinone dyes in styrene butadiene resins
Authors: Paine Anthony J. , Winnik Françoise M. , Bocking Victor 
Published: April 2003

AbstractMany anthraquinone dyes fade in visible light up to 100 times faster in styrene butadiene copolymers than in polyester resins or polystyrene. A mechanistic investigation of the photofading of 1,5‐dihydroxy‐2,6‐diisobutyl‐4‐thiophenylanthraquinone has established that the dye sensitizes formation of singlet oxygen, a very reactive species, which attacks the double bonds in the styrene butadiene, resulting in extensive chain cleavage and peroxide formation. The major process is the oxidation of the polymer, and the dye fading is a minor process whereby the dye is apparently attacked by polymeric peroxides. The mechanism appears to be general for anthraquinone dyes, especially those with thioether, amino, hydroxy, or double‐bond functionality. Unfortunately the fading is unaffected by most anticxidant stabilizers: the best result achieved was a doubling of half‐life with 1 wt% Spinuvex A‐36. This is still insufficient to give colored styrene butadiene copolymer resins the intrinsic dye stability available in other polymers, rendering styrene butadiene unsuitable for applications requiring high photostability of anthraquinone dyes.
Optimizing poly(chloro‐p‐xylylene) or parylene C synthesis
Authors: Sharma Ashok K. , Hahn Allen W. , Nichols Michael F. 
Published: April 2003

AbstractCurrent interest for implantable insulating biomaterials has resurrected a class of polymers synthesized from p‐xylylene and its derivative dimers. Important kinetic aspects for the synthesis of the polymer are derived from measurements of chamber pressure and total weight of film deposition. Reduction of peak chamber pressure during polymer deposition was found to improve film quality, uniformity of deposit, adhesion, and transparency. A low‐cost reactor design is proposed which simplifies the deposition characterization steps needed for producing high quality films.
Far infrared birefringence versus other orientational measurements of high‐pressure injection‐molded high‐density polyethylene
Authors: Boldizar Antal , Jacobsson Stellan , Hård Sverker 
Published: April 2003

AbstractFar infrared (FIR) birefringence is a new tool for measuring orientation in semicrystalline polymers. In this work FIR birefringence of high‐pressure injection‐molded high‐density polyethylene (HDPE) was compared with wide‐angle X‐ray scattering (WAXS) and shrinkage for the first time. An indirect measure of orientation was obtained by differential thermal analysis (DTA). The content of high‐temperature melting crystals was found to increase with increasing orientation. A high correlation was found between FIR birefringence and the other orientational measurements. Contrary to the other orientational methods used, FIR birefringence does not saturate with highly oriented samples. It is furthermore faster, nondestructive, and can be used for probing fairly thick samples.
Effect of fillers on electrical properties of epoxy composites
Authors: Sastry S. Sreehari , Satyanandam G. , Raj T. F. Sundar , Vasanthakumari R. 
Published: April 2003

AbstractThe effect of fillers such as glass, ferrite, and carbon on the dielectric properties of epoxide resin along with conductivity has been studied as a function of frequency (1–100 kHz) and temperature (30–200°C). The glass transition temperature is not much affected by the presence of the fillers. The observed higher values of dielectric permittivity and loss in the case of filled polymers are attributed to Maxwell–Wagner–Sillars polarization.
Enhanced compatibility of SAN and PC in their blends exposed to extremely high shear field
Authors: Takahashi Hideroh , Matsuoka Takaaki , Ohta Takashi , Fukumori Kenzo , Kurauchi Toshio , Kamigaito Osami 
Published: April 2003

AbstractOriginally incompatible blends of SAN 30% and PC 70% were extruded with extremely high shear rate up to 107 s−1 as a typical example of the blends. The materials were examined with a scanning electron microscope (SEM), a pulsed NMR, etc. The molecular weight of the blends was also measured with gel permeation chromatography. The blends are of binary systems microscopically in the first run of extruding, in which the minor constituent is present as small spherical particles in the major constituent. The apparent volume fraction of the spherical minor constituent estimated from the microscopic photographs decreases with the shear rate. The fraction is decreased also with the repeated runs. SEM observation reveals that dimple fracture of microsize takes place on SAN sphere dispersed in PC matrix. And at the bottom of the dimple, a small particle, which would be composed of PC, is present. From these, SAN in the blend is thought to be partly ductile even at the temperature of liquid nitrogen. At the fifth run, the blend appears uniform or structureless. Dynamic loss tangent gives two peaks corresponding to that of SAN and that possibly attributed to PC. The latter shifts to lower temperatures with the number of extruding run. These show that some of SAN is mixed with PC in a compatible form. The pulsed NMR analysis supports the conclusion. Furthermore, the analysis suggests that some of SAN is mixed in PC. This result shows the compatibility of SAN with PC is enhanced in extremely high shear rate processing.
Impact fracture behavior of continuous glass fiber‐reinforced nylon 6
Authors: Otaigbe J. U. , Harland W. G. 
Published: April 2003

AbstractThe impact fracture toughness of nylon 6/continuous glass fiber composites at four levels of fiber content has been studied. The composites were produced by anionically polymerizing caprolactam within a glass mat using a vacuum injection technique. Application of linear elastic fracture mechanics to characterize the impact fracture toughness of the composites, using an energy approach (GIC), has been found to be applicable provided that a correction is made for the size of the damage zone. The concept of Jc, fracture energy per unit ligament area, has also been applied to the composites and agreement between GIC and Jc has been found to be reasonably satisfactory. The ratio of crack propagation energy to the total energy absorbed (ductility index) has also been calculated. The ductility index was found to be close to one for the composites, indicating that additional energy is involved in propagating the fracturing cracks probably due to fiber debonding and/or crack blunting and fiber pullout. Fractographic examination of the impact fracture surface confirmed the presence of these features.
Solubility properties of poly(1,1‐difluoroethylene) in dipolar aprotic solvents
Authors: Galin J. C. , Lutringer G. , Galin M. 
Published: April 2003

AbstractA screening study of the solubility of poly(1,1‐difluoroethylene) (PVF2, M̄w = 2 × 105) at room temperature in a wide variety of dipolar aprotic species has facilitated the discovery of a series of new solvents (N‐methyloxazolidone, cyclic‐substituted ureas) and rationalization of the data in a two‐dimensional solubility map involving their dipole moment, μ, and their hydrogenx‐bond‐accepting (HBA) power β (Taft solvatochromic parameter). This map may be used as a predictive tool for the research of new functional classes of solvents, such as N‐substituted mixed amideester of phosphoric acid or N‐substituted sulfurous diamides. The variations of the intrinsic viscosity of the polymer with solvent polarity may be quantitatively analyzed using a linear multiparametric correlation which emphasizes the two opposite contributions of cavitation effects (Hildebrand solubility parameter δ) and of polymer–solvent interactions (β) on the coil expansion: [η] (dL.g−1) = 0.792 ‐ 1.2 × 10−3δ2(J.cm−3) + 1.59 β. Finally, 1,3‐dimethyl‐2‐oxo‐hexahydropyrimidine (N,N′‐dimethylpropylene urea) leads to the highest value of the refractive index increment (dn/dc = −0.065 mL.g−1 at λ = 632 nm), and thus appears as the best solvent for light‐scattering measurements.
Quick determination of dielectric anisotropy of paper sheets by means of microwaves
Authors: Osaki Shigeyoshi 
Published: April 2003

AbstractThis paper deals with a new type of method for determining the complex dielectric constant at microwave frequencies in about 30 s. This method determines the dielectric anisotropy and refractive index for optically opaque paper sheets. The dielectric anisotropy ascribable to the local motions of cellulose molecules is supported by electron microscopic observations and mechanical anisotropy. The angular dependence of the complex dielectric constant gives the degree of molecular orientation and the distribution of cellulose molecules in paper sheets. The direction of the average orientation of molecular chains can be inferred from the anisotropic data. It is also suggested that the cellulose molecules should be oriented on an average in the direction of long axis of pulp fibers. The accumulation of data for complex dielectric constant and refractive index at microwave frequencies gives an important chart for manufacturing the functional paper corresponding to needs.
Measurements of residence time distribution for the peroxide degradation of polypropylene in a single‐screw plasticating extruder
Authors: Tzoganakis C. , Tang Y. , Vlachopoulos J. , Hamielec A. E. 
Published: April 2003

AbstractMeasurements of the residence time distribution (RTD) in a single‐screw plasticating extruder were carried out during experimental studies of the peroxide‐initiated controlled chemical degradation of polypropylene (PP). A radioactive tracer method was employed, and the effect of screw speed, temperature, and reaction on the RTD was examined. An increase of the peroxide concentration resulted in a broader distribution whereas an increase of the extrusion temperature was found to result in a narrower distribution. Use of low screw speeds simply increased the time delay through the extruder without affecting considerably the breadth of distribution. Results obtained from the present experiments were compared with several theoretical models.
Influence of coupling agents and treatments on the mechanical properties of cellulose fiber–polystyrene composites
Authors: Maldas D. , Kokta B. V. , Daneault C. 
Published: April 2003

AbstractWood fibers of aspen in the form of chemithermomechanical pulp (CTMP) and Tembec 6816 have been used as reinforcing fillers in different varieties of polystyrene. The tensile strength, elongation, and energy at maximum point, as well as tensile modulus at 0.1% strain is reported. Also revealed is the optimum condition of compression molding. The influence of different coupling agents, such as poly[methylene(polyphenyl isocyanate)], silanes (A‐172, A‐174, A‐1100), and grating on the mechanical properties of composites is discussed. The extent of increase in mechanical properties depends on the weight percentage of fibers, the concentration of coupling agents, and the grafting level (add‐on %). Coating followed by an isocyanate treatment appears to be the best treatment. In addition, the isocyanate treatment and grafting are superior to the silane treatment. Experimental results are explained on the basis of possible interactions among cellulose fiber‐coupling agent‐polymer in the interfacial area.
Polymerization reactor: The influence of “gel effect” in batch and continuous solution polymerization of methyl methacrylate
Authors: Maschio G. , Moutier C. 
Published: April 2003

AbstractThis article describes the influence of gel effect in the free radical polymerization of methyl methacrylate. A mathematical model has been developed which tries to predict the performance of batch and continuous polymerization reactors under dynamic and steady‐state conditions. The influence of diffusion phenomena on the process kinetics (gel effect) is very important. The autoacceleration in the polymerization rate of the batch reactor and the mulitple steady state for the continuous stirred tank reactor (CSTR) are connected with the attainment of critical conditions in the system. Such a model is useful for the design of the reactor and the choice of the control system.
Photodegradation of rigid PVC formulations. I. Wavelength sensitivity to light‐induced yellowing by monochromatic light
Authors: Andrady Anthony L. , Torikai Ayako , Fueki Kenji 
Published: April 2003

AbstractLight‐induced yellowing of extruded rigid poly(vinyl chloride) formulations containing 0, 2.5, and 5 phr of titanium dioxide under exposure to monochromatic light was studied. Both photoyellowing and photobleaching were observed as wavelength‐dependent phenomena in the range of 280–500 nm. Action spectra for yellowing of the different compounds were similar. In the case of the formulation with no titanium dioxide, significant color changes were observed on the back surface of the sample, indicating transmission of the longer wavelength light through the 1‐mm thickness of the sample.
Kinetics and mechanism of emulsion copolymerization. IV. Kinetic modeling of emulsion copolymerization of styrene and methyl methacrylate
Authors: Nomura Mamoru , Horie Ichiro , Kubo Masayuki , Fujita Kazumi 
Published: April 2003

AbstractBased on the micellar nucleation theory, a mathematical kinetic model for an unseeded emulsion copolymerization system is developed, where the radicals with and without electric charge are discriminated from each other in view of the role in the particle nucleation process. In order to demonstrate the validity and utility of this kinetic model, the experiments of the unseeded emulsion copolymerization of styrene (ST) and methyl methacrylate (MMA) are carried out varying the initial initiator (potassium persulfate) and emulsifier (sodium lauryl sulfate) concentrations and the monomer composition in the initial monomer feed, and various kinetic features observed are compared with the model predictions. It is concluded from this comparison that in this system, almost all the polymer particles are generated by the charged radicals stemming from the initiator, and further that this mathematical kinetic model can provide a satisfactory explanation of the various kinetic features observed.
A facile method for the study of slow physical and chemical processes in polymeric systems
Authors: Lundgren Roger , Sandén Roland , Albertsson Ann‐Christine 
Published: April 2003

AbstractA method is described for continuously following a long‐duration process in a complex polymeric system by isothermal calorimetry. Computerized models for slow physical or chemical processes have been applied to calorimetric runs under different conditions and these have given information in the form of thermodynamic and kinetic data. The method also gives a means of determining the relationship between molecular weight and functionality for one of the polymers used, the order of reaction, and the degree of conversion before the start of the measurements. An example is given of a kinetic study of the reaction of hydroxyl‐terminated polybutadiene with two different diisocyanates. The temperature dependence of the formation of urethanes, the rate constants, and the degree of conversion before the start of the measurements were determined as well as the heat of reaction for the formation of urethanes using hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) as curing agents. The results have been compared with other kinetic studies of these systems.
Influence of hydrostatic pressure on the electrical properties of unvulcanized FEF‐loaded SBR
Authors: Nasr G. M. , Amin M. , Osman H. M. , Badawy M. M. 
Published: April 2003

AbstractStyrene butadience rubber (SBR‐1502) loaded with different concentrations of FEF carbon black was tested to find out the effect of pressure on its electrical properties during vulcanization. Using the thermodynamically calculated values of the pressure coefficient (K), the thermoelastic coefficient (L = ∂T/∂P) was also estimated and compared with that obtained by other workers. The thermoelastic coefficient was found to be strongly dependent on the carbon black concentration.