bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of the kinetic parameters of the thermal oxidative degradation of styrene/butadiene copolymers
Authors: Grgurić T. H. , Rek V. , Hace D. , Gomzi Z. , Jelćić Ž. 
Published: April 2004

AbstractThe intensity of the thermal oxidation has been followed through kinetic parameters. In styrene/butadiene copolymers, soft polybutadiene phase (PB) and hard polystyrene phase (PS) have different sensibilities to thermal degradation. The thermal oxidative stability of high‐impact polystyrene (PS‐HI), styrene/butadiene/styrene block copolymers (SBS), and PS‐HI + SBS blends were investigated by isothermal DSC analysis. The kinetic parameters of the thermal oxidative degradative process: the reaction rate constants, the reaction orders and the activation energies have been determined. The total area under the exothermic curve was used to calculate the isothermal heats of degradation. The conversion (α) and the rate of the thermal oxidative degradation (dα/dt) have been derivated. The experimental data have been tested with a kinetic model for autocatalytic reactions: dα/dt = k αm (1 − α)n. Activation energies have been determined from the Arrhenius equation and the order of the thermal oxidative stability evaluated. The extent of agreement of the experimental data with the autocatalytic model is discussed.
Effects of gamma‐irradiation on mechanical characteristics of recycled polyethylene blends
Authors: Suarez João Carlos Miguez , Mano Eloisa Biasotto , Bonelli Claudia Maria Chagas 
Published: April 2004

AbstractThe recycling of polymeric materials has gained increasing attention in the world because of economic and environmental considerations. Therefore, blends of low cost plastics such as polyolefins, Polystyrene, and poly(vinyl chloride) present in polymeric waste are of particular interest. Among the different methods for recovering plastic residues, a two‐step process, developed by two of the authors, permits the production of materials with controllable composition and homogeneous characteristics. The paper discusses the behavior of recycled 75/25 blends of low density polyethylene (LDPE) and high density polyethylene (HDPE) after exposure to various does of gamma‐irradiation (10–2000 kGy) in the presence of oxygen. Mechanical testing, differential scanning calorimetry, gel permeation chromatography, and infrared spectroscopy have been used to investigate the effects of gamma‐irradiation on the polymer material. Mechanical strength was found to increase with irradiation doses up to 100 kGy, followed by a small decrease and a tendency to stabilization at higher doses. The degradation process is discussed.
Surface characterization and adsorption abilities of cellulose fibers
Authors: Stana‐Kleinschek Karin , Strnad Simona , Ribitsch Volker 
Published: April 2004

AbstractThe adsorption abilites of cotton cellulose fibers are very often modified by alkaline treatments in form of alkaline purification or mercerization using high concentration of NaOH. We tried to determine the correlation between morphological modifications and the adsorption abilities of cotton fibers using several methods: the analysis of microscope images of fibers by image processing and the analysis of the electrokinetic surface properties which express the adsorption behavior of fibers.The longitudinal images and cross‐sections of native and modified cotton fibers were analyzed and the parameters: form factor, wall thickness, cross‐section area, fiber diameter, lumen area were calculated using image processing. The adsorption behavior of native and NaOH modified polymers was investigated by the determination of electrokinetic properties. The zeta potential (ζ) was calculated from streaming potential measurements as a function of pH and surfactant concentration in the liquid phase. The results indicate that only a correct combination between the morphological modifications and electrokinetic behavior of fibers leads to a desirable adsorption mechanism which causes a specific adsorption of components of the liquid phase.
Characterization of liquid carboxy terminated copolymer of butadiene acrylonitrile modified epoxy resin
Authors: Nigam Vineeta , Setua Dipak K. , Mathur Gyanesh N. 
Published: April 2004

AbstractToughening of epoxy cresol novolac resin (ECN) by carboxy terminated acrylonitrile‐co‐butadiene (CTBN) liquid functional rubber have been studied. Wide angle X‐ray scattering (WAXS) has been utilized to evaluate average molecular interchain spacing (<R>) from the strong maximum in the diffraction scan using Bragg's equation. The half‐width (<HW>) of the maximum was used to qualitatively describe the distribution of <R>. An increase in <R> value signifies formation of a separate packing order as well as increase in the free volume. Fourier transform infrared spectroscopy (FTIR) studies convincingly establish that the interaction between oxirane group of epoxy and carboxyl group of CTBN are responsible for characteristic peak shifts in the blends compared to individual polymers. Physicomechanical properties of the blends e.g., the tensile, flexural and impact strengths showed an optimum concentration of CTBN (10 wt%) into ECN, which can offer maximum toughening. Cross sections of the composite specimens failed during impact testing have been critically studied through scanning electron microscopy (SEM) to gain insight into the mechanism of toughening and phase morphology.
Study of the mechanical, thermal, and thermodegradative properties of virgin PP with recycled and non‐recycled HDPE
Authors: Albano C. , Sanchez G. 
Published: April 2004

AbstractIn order to show the significance of plastic recycling, a study of the properties of blends of PP with non‐recycled and recycled high density polyethylene (HDPE) is made. The results of the Young's modulus for polypropylene (PP)/non‐recycled and recycled HDPE blends present a slight synergism, although no significant dependence of this property on the compound was observed. The values of elongation at break and impact strength reflect the incompatibility of the blends. In thermal studies of the blends, the values of fusion enthalpy are below the values of the components. The results of the thermodegradative studies show that activation energies (Ea) obtained are lower, in the case of the blends, than the Ea corresponding to pure polymers. In PP/recycled HDPE blends, activation energy, at 5% to 20% concentration, is maintained and falls abruptly with an increase in the concentration of the recycled material. Based upon the facts previously exposed, it is possible to recycle the recycled HDPE up to 20% concentration, in PP blends. The addition of the compatibilizer at 5% represents the optimal concentration for improving the final properties of the finished product.
Prediction of the tensile impact behavior of injection molded samples from quasi‐static data
Authors: Viana J. C. , Cunha A. M. , Billon N. 
Published: April 2004

AbstractA methodology for predicting the mechanical behavior of injection molded semi‐crystalline thermoplastics, within a wide range of strain rates and temperatures, is proposed in this work. This method is based on data obtained at isothermal low velocity tensile tests and on a phenomenological constitutive equation that describes the stress as a function of independent and multiplicative terms of the strain, strain rate and temperature. The effect of the processing conditions on the coefficients of this equation is considered by evaluating their dependence on thermo‐mechanical indices, calculated from melt flow simulations. Using a finite element code that has this equation built‐in, it is possible to predict the mechanical behavior of samples injected with different molding conditions. The extrapolation of the impact properties requires the consideration of the dependence of the material consistency on the strain rate, which is affected by the sample skin‐core structure. So, any constitutive equation used to describe the mechanical behavior of the injection molded samples must consider the distinct contributions of the main microstructural layers.
Effect of temperature gradient on polymer migration
Authors: Choi Hyoung J. , Cho Min S. , Kim Chul A. , Jhon Myung S. 
Published: April 2004

AbstractPolymer migration in a flow field is a well‐known phenomenon, and it has been verified that the sources of such phenomena are nonhomogeneity of the flow field, concentration effects, and hydrodynamic interactions between the polymer molecules and walls. In this study, we investigate the temperature gradient effect on polymer dynamics due to an imposed flow field. The diffusion equation and concentration profile of the polymer molecules induced by a temperature gradient using a two‐bead dumbbell model are obtained from the Fokker‐Planck equation. From the concentration equation constructed for a dilute solution in a general flow geometry, we find that there are significant effects on the polymer migration not only due to the nonhomogeneity of the flow field, but also due to temperature gradients.
Electrorheological properties of poly(aniline‐co‐o‐ethoxyaniline) suspensions
Authors: Kim Ji W. , Choi Hyoung J. , To Kiwing 
Published: April 2004

AbstractSuspensions of copolyaniline containing ethoxy group, namely poly(aniline‐co‐o‐ethoxyaniline), in silicone oil have been investigated as one of many potential candidates for dry‐base electrorheological (ER) fluid systems. The copolyanilines were synthesized by a chemical oxidation of aniline and o‐ethoxyaniline with various molar ratios in an acidic media, and the characteristics of these polymers were examined by using several techniques. By using FT‐IR, SEM, and a particle size analyzer, we studied chemical structure, particle size, and the particle size distribution of the copolymer, respectively. A Physica rheometer equipped with a high voltage generator was also adopted to measure the rheological properties of ER fluids using the copolyaniline. Controlled shear stress mode was used for the shear rate sweep measurement, and the copolyaniline synthesized in this study was found to give a typical ER behavior, that is, shear stresses increase with increasing electric fields and volume fractions.
Water diffusion in unsaturated polyester films. Effect of plasticization on the glass transition
Authors: Marais S. , Metayer M. , Labbe M. , Legras M. T. , Saiter J. M. 
Published: April 2004

AbstractWater diffusion through Unsaturated Polyester Resin (UPR) is investigated. From differential scanning calorimetry, we observe that the plasticization effect due to water sorption leads to large variations of Tg and is a reversible phenomenon. The transport of water through the polymer is characterized with a new instrument developed in our laboratory which shows that the water transport deviates from Fickian behavior. It is found that the diffusion coefficient is not a constant and experimental data are in good agreement with D = DoeγC where γ is a plasticization coefficient.
Newspaper‐reinforced plastic composite laminates: Mechanical and water uptake characteristics
Authors: Yadav P. , Nema A. , Varghese S. , Nema S. K. 
Published: April 2004

AbstractSeveral useful composite materials have been developed with natural fiber and plastic matrices, and their commercial viability has been established in terms of adding value to abundant and cheap natural resources. The Macromolecular Research Centre, Jabalpur, India, has recently developed composite from waste newspaper reinforced with plastic material using a prepreg technique wherein the matrix resin consists of resol type phenolic resin (PR) and bifunctional epoxy resin (EP) condensate. Laminates of newspaper and PR‐EP condensate were prepared by hot press molding, and the newspaper weight fraction in these composites was varied from 0.30 to 0.65. The mechanical properties of five selected newspaper (PR‐EP) condensate composites are reported for parameters such as ultimate tensile strength, elongation, tensile modulus, flexural strength and modulus, and heat deflection temperature (HDT). The water uptake behavior of these composites was examined by constructing water absorption isotherms, and the water diffusion coefficient and water absorption (24 h soak test) were determined. The specific tensile and flexural strengths and modulus properties of newspaper‐(PR‐EP) condensate composites are found comparable with one prepared elsewhere from recyclable newspaper‐reinforced polypropylene thermoplastics.
Mechanical characterization of carbon fiber reinforced phenolic resol and epoxy condensate plastic
Authors: Varghese S. , Yadav P. , Jain S. , Ghuratia S. , Nema S. K. 
Published: April 2004

AbstractA matrix resin for carbon fiber reinforced composite was developed that consisted of resol type phenolic and difunctional epoxy resin (PR‐EP) condensate or adduct. Carbon fiber reinforced composite with fiber volume fraction of 0.6 was prepared with PR‐EP matrix containing 0, 50, 100, 150, and 175 parts of epoxy resin per hundred parts of phenolic resin (php), especially a synthesized resol type. One‐shot and prepreg techniques have been adopted and the study of loss of volatiles has indicated the superiority in terms of favorable processability of prepreg technique over the other. FTIR spectroscopic analysis confirmed the PR‐EP adduct formation at the prepreg preparation stage. The improvement in properties such as tensile strength and elongation at break was observed in resin matrices with epoxy and phenolic resin; however, the flexural strength and modulus remained more or less unaltered. The prepreg technique of composite preparation has resulted in substantial improvement in mechanical properties and the same was attributed to the formation of PR‐EP adduct and low volatiles during cure. Composites of carbon fiber reinforced PR‐EP matrix developed here are likely to meet the requirement of aerospace structures in view of the realization of a wide spectrum of properties.
Physicochemical characterization of alloy of polyimide with varying degree of crosslinking through diisocyanates
Authors: Rajani S. , Jain S. , Verma M. M. , Dubey M. , Nema S. K. 
Published: April 2004

AbstractPolyimide alloys are prepared by blending the crosslinked and uncrosslinked polyamic acid components and followed by thermal imidization. The blend components can be synthesized by the reaction of polyamic acid with the varying concentration of crosslinker [here methylene bis (4‐phenyl isocyanate or MDI)] from 1.54 × 10−2 mol/L (i.e. hypothetically calculated critical crosslinker concentration or CCC) to 1.54 × 10−6 mol/L. This communication discusses the synthesis and characterization of polyimide (PI) blends and alloys prepared by varying degrees of crosslinking introduced via isocyanate‐amic acid reaction. The polyimides were prepared by thermally imidizing the polyamic acid blends at different curing temperatures from 50°C to 350°C. The degree of imidization and residual solvent content for blends having varying mole fractions of crosslinked (or branched) and uncrosslinked components and two extreme conditions and at specified temperature‐time profiles have been studied. The resultant PI‐MDI blends have exhibited synergism on mechanical properties. The improvement in mechanical properties, however, was significantly higher at the lower imidization temperature (i.e. 50°C to 150°C). The feasibility of preparing polyimide alloys with synergistic combinations of crosslinked and uncrosslinked polyimide components was inferred.
Molecular structure evolution in peroxide‐initiated crosslinking of an ethylene vinyl acetate copolymer and a metallocene polyolefin elastomer
Authors: Tai Horng‐Jer 
Published: April 2004

AbstractA combination of molecular theories and chemical reaction kinetics was employed to study the molecular structure evolution in the ethylene vinyl acetate and dicumyl peroxide, EVA/DCP, and metallocene polyolefin elastomer, m‐POE/DCP crosslinking systems. Premixed EVA/DCP and m‐POE/DCP compounds were cured at different temperatures and their gel contents were then measured. The values of crosslinking efficiency were evaluated and were then applied in the theoretical prediction of molecular evolution in a crosslinking process. The molecular weight distributions, gel time, relationships among gel content, degree of conversion, crosslinking density and processing time can all be predicted effectively. Information involving molecular structure evolution provides insights to practical process synthesis and material design.
Analysis of mixing during melt‐melt blending in twin screw extruders using reactive polymer tracers
Authors: Shearer Gifford , Tzoganakis Costas 
Published: April 2004

AbstractMixing during melt‐melt blending of segregated polypropylene melt streams in a co‐rotating twin screw extruder was experimentally investigated. The mixing limited reaction between two polymer reactive tracers, which are terminally functionalized polyolefin oligomers, was used to determine the mixing performance of a kneading block section. The selected functional groups were succinic anhydride and a primary amine, and Fourier‐Transform Infrared Spectrometry (FT‐IR) was used to determine the anhydride conversion. In the absence of interfacial tension, the reaction conversion was directly related to the amount of interfacial area generated. Experiments were completed to study the effects of operating conditions, kneading block design, and polymer material properties. The screw speed effect was observed to be non‐linear because of competing contributions from shear rate, residence time, channel fill, and viscous heating. The mixing performance of kneading blocks backed by a reverse conveying element was observed to follow the trend of: forward > reverse > neutral. For each kneading block design, the mixing performance decreased with an increase in polymer viscosity.
Effect of IR transparency of the top polymer layer on low thermal IR emittance paint coatings
Authors: Ma Chen‐Chi M. , Ho Wen‐Dar 
Published: April 2004

AbstractA two‐layer model was developed to accurately represent low thermal IR emittance paint coatings. The coatings were formed by mixing aluminum flakes with polymeric binders. Because of the different densities of these two components, a two‐layer structure was constructed with a pure polymeric layer on top and an in‐homogeneous layer underneath. The absorption properties of the top polymeric layer hinder the IR reflectance of the coating. This two‐layer model was used to quantitatively determine how IR transparency of the top polymer layer influences the reflectance of the coating. The bottom layer was considered to be a substrate with a specific diffuse reflectance, and the ray tracing method was used to calculate the reflectance of this polymer‐coated, diffusing substrate system. The reflectance of the coating with a low absorption coefficient (0.01 μm−1) top polymer (3 μm thick) was reduced 50% compared with when a high absorption coefficient (0.1 μm−1) top polymer was used. Measurements of coatings of chlorinated rubber and alkyd rubber on a diffuse gold substrate confirmed the reliability of the model predictions.
Damping enhancement of rubber dampers for high speed compact disk players
Authors: Chang Seung Hwan , Choi Jin Kyung , Lee Dai Gil , Kim Hyun Surk 
Published: April 2004

AbstractRubber dampers are widely used to dissipate vibrations generated in machines and electronic equipments due to the excellent damping capacity of rubber. However, the effectiveness of the rubber damper is often limited because of the dependency of its damping characteristics on temperature and frequency. In this study, the damping and stiffness characteristics of the rubber damper for compact and digital video disk players were enhanced by inserting a solid core into the rubber damper with interference tolerance fit. The damping characteristics of the coreinserted rubber damper were investigated experimentally and numerically with respect to the interference tolerance, core roughness, rubber stiffness and damping and environmental temperature. From the experimental and numerical investigations, it was found that the core was effective both for the damping and stiffness enhancement of the damper. Using the results of the experimental and numerical investigations, the optimum design method for the core‐inserted rubber damper was suggested.
Viscoelastic properties and transitions during thermal and UV cure of a methacrylate resin
Authors: Lange Jakob 
Published: April 2004

AbstractThe solidification behavior of a dimethacrylate system during UV and thermal cure at temperatures from the Tg of the monomer (T) to above the ultimate Tg of the polymer (T) is investigated using torsional dynamic mechanical analysis. Gelation and vitrification times are quantified using several criteria for the transitions, and the data are presented as a function of cure temperature in TTT diagrams. The influence of cure method and temperature on the mechanical properties, degree of conversion, and gel content of the cured samples is discussed. The results show that gelation occurs before or at the same time as vitrification at all temperatures, including T. With UV cure, gelation generally occurred within seconds, whereas the properties continued to develop for minutes or hours afterwards. The method of cure was found to influence the properties of the cured material. When prepared above T, the UV cured material had a higher Tg, a higher crosslink density, and a higher degree of conversion than the thermally cured material.
Effects of viscosity ratio and compatibilizers on the morphology and mechanical properties of polycarbonate/acrylonitrile‐butadiene‐styrene blends
Authors: Yang Kumin , Lee Shi‐Ho , Oh Jong‐Man 
Published: April 2004

AbstractA comprehensive experimental study was carried out to investigate the effects of (1) viscosity ratio, (2) temperature on the viscosity ratio, (3) extruder screw location, and (4) compatibilizers on the morphology of bisphenol‐A‐polycarbonate/acrylonitrile‐butadiene‐styrene (PC/ABS). Blends were prepared by utilizing a co‐rotating twin screw extruder and in‐situ morphology obtained via the screw pullout technique. A plot of the PC/ABS viscosity ratio, ηPC/ηABS, versus the shear rate showed a gradual rise in the curve up to a critical shear rate and thereafter displayed asymptotic character. Contrary to premise, ηPC/ηABS decreased with increasing temperature. This was elucidated by the melt viscosity of PC being thermally more sensitive than ABS over the temperature range investigated. As expected, the plot of the average domain size versus the viscosity ratio gave a concave up curve with a minimum when the viscosity ratio was close to unity. The morphology evolution along the screw of a twin screw extruder was examined. When sections of the kneading block were examined, the minor phase domains gradually showed reduction in size toward the extruder die, and the samllest domain was realized at the end of the block, namely, the flow impeding left‐handed screw element. Polymethylmethacrylate (PMMA) exhibited the greatest ABS domain size reduction, and annealed samples showed that it suppressed coalescence.
Conductive polymer blends filled with carbon black: Positive temperature coefficient behavior
Authors: Yu Gang , Zhang Ming Qiu , Zeng Han Min , Hou Yan Hui , Zhang Hai Bo 
Published: April 2004

AbstractElectrical conductivity and positive temperature coefficient (PTC) behavior of carbon black (CB) filled incompatible polyblends of ethylene‐vinyl acetate copolymer/low density polyethylene (EVA/LDPE) were investigated. In comparison with single polymer systems, more possibilities for tailoring composite performance were brought about with the employment of polymer blends as matrix resins in conductive composites. Based on the concepts of double percolation and two‐step percolation, PTC‐type composites with balanced performance, improved processability, and reproducibility can be made. Thermodynamical and kinetic factors including interfacial energy, melt viscosity, blending ratio, melt mixing time, sequence of blending as well as CB concentration were shown to be closely related to the ultimate properties obtained.