bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of crystallinity on gas transprt in polymeric films
Authors: Horas Jorge A. , Rizzotto Marcos G.
Published: April 2004

We developed a model to describe the diffusion of gases through partially crystalline polymers. Diffusion is negligible in the crystalline fraction and occurs mainly in the amorphous region; however, crystallinity affects chain stiffness in the amorphous fraction. In our model this effect is taken into account in the activation energy calculation. The semicrystalline polymer in which diffusion takes place is treated as a heterogeneous medium in the framework of effective medium theories. An effective diffusion coefficient is obtained that takes into account the influence of both the presence of crystallites and the distribution of chain separations. We compare the results of two effective medium models and thus determine their respective applicability ranges.
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

The 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

The 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

The 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

Toughening 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 () from the strong maximum in the diffraction scan using Bragg's equation. The half‐width () of the maximum was used to qualitatively describe the distribution of . An increase in  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

In 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

A 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

Polymer 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

Suspensions 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

Water 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

Several 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

A 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

Polyimide 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

A 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

Mixing 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

A 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

Rubber 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

The 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

A 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

Electrical 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.
Deformation behavior of a polyvinyl chloride (PVC) tube by mandrel drawing
Authors: Ulas I.
Published: April 2004

Biaxial mechanical properties of products produced by drawing over an expanding mandrel are found to be closely associated with the imposed axial and hoop draw ratio. The paper assists the understanding of the deformation behavior and related mechanical improvements in a processed polyvinyl chloride (PVC) tube and shows that behavior is controlled by the polymer network structure. The effect of post‐mandrel bath cooling on product straightness, spring‐back, and thickness distribution was investigated, and it was shown that bath cooling greatly improves the quality and integrity of the product.
Coarsening in molten quiescent polymer blends: The role of the initial morphology
Authors: Willemse R. C. , Ramaker E. J. J. , Van Dam J. , De Boer A. Posthuma
Published: April 2004

Coarsening of the phase dimensions in polymer blends under quiescent conditions is studied in blends of different morphologies; the dependence of the rate and extent of coarsening on the initial morphology is demonstrated. In blends with a droplet/matrix structure, coarsening via coalescence is found only above the percolation threshold for spherical particles (16 vol%). The rate of coalescence in the droplet/matrix structure is shown to obey the theory of Fortelny and Zivny for coalescence of droplets in quiescent media, and no constant level of the phase dimensions is reached. Below a volume fraction of 0.16 limited coarsening is found only for fibrillar and co‐continuous morphologies. This coarsening is in fact the result of a restructuring because retraction and breakup occur, leading to a droplet/matrix morphology in which the droplet diameter is approximately twice the diameter of the original fiber. Breakup and retraction are completed in a short time relative to coalescence. At higher volume fractions in co‐continuous structures (>30 vol%), these structures do not break up, and coarsening is found to take place by retraction only. No constant level of the phase dimensions is reached in the latter case.
Morphology and mechanical performance of pregenerated and “in‐situ” PP/vectra B composites
Authors: Vallejo F. J. , Eguiazábal J. I. , Nazábal J.
Published: April 2004

Polypropylene/Vectra B blends were obtained at different LCP contents and barrel temperatures by an extrusion‐injection process. The wide barrel injection temperature range chosen, from 200 to 300°C, gave rise to blends in which the pregenerated extruded morphology was preserved, partially preserved, or lost. The blends processed at 260 and 300°C showed the usual morphology and properties of “in‐situ” composites. The blends injected at 240°C showed the worst properties because of their partially melted and agglomerated morphology. A barrel temperature of 200°C (80°C below the melt temperature of Vectra B) was needed to maintain the pregenerated fibers. These pregenerated composites, without post‐extrusion drawing, showed smaller modulus of elasticity and tensile strength than those of the “in‐situ” composites, but an increased notched impact strength as a consequence of their less perfectly oriented but more homogeneous morphology.
DC conductivity and dielectric response in amorphous polycarbonate of Bisphenol‐A
Authors: Santos S. , Cedeño A. , Gómez C.
Published: April 2004

We report the dielectric response measurements of amorphous polycarbonate of Bisphenol‐A at room temperature in the frequency range from 12 to 105 Hz. The data is analyzed within the graphical representation of Wei and Sridhar. Such an approach has allowed us to estimate the DC conductivity value of the order of 5 × 10−11 S/m in good agreement with the direct DC measurements.
A study of rheological behavior of a polypyrrole modified UHMWPE gel using a parallel plate rheometer
Authors: Chiu Hsien‐Tang , Wang Jyh‐Horng
Published: April 2004

Polypyrrole powder was added to a 6% UHMWPE decalin solution as an interfacial modifier. Rheological properties and dynamic viscoelastic properties, including shear viscosity, shear storage modulus (G′), and shear loss modulus (G″), were measured with a parallel plate rheometer using rotation and oscillation modes. The results show that these properties increase with the PPy content. In addition, the gelation temperature decreased with increasing PPy content. This suggests that the presence of PPy enhanced the entanglement network in the solution, which is similar to the role of filler in rubber.
Monodisperse poly(p‐chloromethylstyrene) microbeads by dispersion polymerization
Authors: Bahar T. , Tuncel A.
Published: April 2004

In this study, an alternative dispersion polymerization method for the para isomer of chloromethylstyrene was proposed. Highly monodisperse poly(p‐chloro‐methylstyrene) (PCMS) particles in the size range of 1.67–3.75 μm were obtained. The monodispersity and the isolation yield of PCMS particles were significantly improved relative to the methods available in the literature. Azobisisobutyronitrile and polyacrylic acid were selected as the initiator and the steric stabilizer, respectively, in the dispersion medium composed of ethanol and methoxyethanol. The results indicated that the particle size increased with increasing initiator concentration. An increase in the stabilizer concentration led to a decrease in the particle size. The methoxyethanol/ethanol ratio was found as one of the most important parameters controlling the average size and the size distribution. Contrary to the tendencies noted in the literature, the particle size decreased with increasing polymerization temperature.
Polymer‐dispersed liquid‐crystal polymers (PDLCPs). Morphology of the LCP droplets
Authors: Magagnini Pierluigi , Paci Massimo , Poli Giovanna , Tonti Maria Silvia , Narducci Piero
Published: April 2004

“Synthetic blends” of a flexible polymer forming the matrix and a liquid‐crystalline polymer (LCP) forming the dispersed phase have been prepared by transesterification of PET with a mixture of sebacic acid (S), 4,4′‐diacetoxybiphenyl (B) and 4‐acetoxybenzoic acid (H) in the mole ratio 1:1:2. A change of the synthesis conditions causes marked variations of the chemical composition and the morphology of the phases. The SEM investigation of the inner morphology of the LCP droplets of blends consisting of two phases with fairly different aromatic content has shown that the LCP macromolecules are aligned tangentially at the matrix surface boundary, and that the nematic director configuration is toroidal. When the two phases have closer chemical composition, and are therefore supposed to possess improved mutual compatibility, a perpendicular anchoring of the LCP fibrils to the matrix cavity surface, and an axial configuration of the nematic director, are observed. The expected effect of the nematic configuration of the LCP droplets on their ability to deform into fibrils under appropriate flow conditions is preliminarily discussed.
Control of orientation in liquid crystalline epoxies via magnetic field processing
Authors: Lincoln Derek M. , Douglas Elliot P.
Published: April 2004

We demonstrate control over the orientation of the 4,4′‐bis(2,3‐epoxypropoxy)‐α‐methylstilbene (EPAMS)/sulfanilamide (SAA) epoxy system. A statistical experimental design was generated and analyzed to determine the effects of the time in the magnetic field, field strength, and the amount of B‐staging. A regression model with a coefficient of determination, R2, of 0.8577 was calculated to predict the orientation parameter for the input variables. An optimization study was also conducted to check the prediction of the orientation parameters by the model. The model can predict the experimentally measured orientation in regions where the model predicts physically realistic values for the orientation.
Reactive compatibilization of polypropylene and polymide‐6,6 with carboxylated and maleated polypropylene
Authors: Manning Steven C. , Moore Robert B.
Published: April 2004

Blends of polypropylene and polyamide‐6,6 have compatibilized with polypropylene that was carboxylated through a reactive extrusion process with an asymmetric functional peroxide. The compatibilized blends demonstrated a finely dispersed minor phase as shown by SEM. Because of the enhanced dispersion, additions of the carboxylated polypropylene to the blends resulted in a change in the crystallization nucleation mechanism of the PA‐6,6 minor phase from heterogeneous to homogeneous in nature. A linear increase in the impact strength and significant enhancement in the tensile properties of the blends was observed with incorporations of the compatibilizer up to 30% of the matrix phase. In addition, the compatibilizing efficiency of the carboxylated polypropylene was compared to the of maleic anhydride functionalized polypropylene. When compared on an equivalent basis (total concentration of carboxylate or anhydride functionality added to the blend), the carboxylated polypropylene demonstrated a slightly better compatibiliziling efficiency than that of the anhydride functionalized polypropylene. The higher compatibilizing efficiency of the carboxylated polypropylene was attributed to a higher grafting efficiency of the carboxylation procedure as compared to the anhydride functionalization procedure.
Numerical modeling of injection/compression molding for center‐gated disk: Part II. Effect of compression stage
Authors: Kim I. H. , Park S. J. , Chung S. T. , Kwon T. H.
Published: April 2004

In the accompanying paper, Part I, we have presented a physical modeling and the associated numerical analysis of the injection molding process with a compressible viscoelastic fluid model. In Part II, effects of the compression stage in the injection/compression molding process are presented. Numerical results showed that the injection/compression molding process reduced birefringence as compared with the injection molding process. In this respect, the injection/compression molding process seems to be more suitable for manufacturing precise optical products of good optical quality than the injection molding process. Effects of the packing stage on the birefringence distribution in the injection/compression molding process were found to be similar to those in the injection molding process. Our numerical results show that the birefringence becomes smaller as the melt temperature gets higher and the closing velocity of the mold gets smaller with the flow rate and the mold temperature affecting the birefringence insignificantly. As far as the density distribution is concerned, the flow rate, melt temperature, and mold closing velocity have insignificant effects on the density distribution in comparison with the mold temperature.
Influence of compatibilization and viscosity ratio on the barrier and impact properties of blends of a modified polyamide‐6 and polyethylene
Authors: Yeh Jen‐Taut , Jyan Chau‐Fae , Yang Shun‐Syu , Chou Shen
Published: April 2004

Nylon 6 was grafted with a zinc‐neutralized ethylene/acrylic acid copolymer (CP) to produce four different modified polyamides (MPA) with varying CP content. These were mixed with four polyethylenes with different viscosities and the blends were blow‐molded into bottles. The clearest MPA lamina was developed for blends with an optimum ratio of the viscosities of MPA and PE (VRoptimum), and bottles with the clearest lamina exhibited the best xylene permeation resistance, impact strength and the highest melting temperature (Tm). The value of VRoptimum increased with increasing CP content. A maximum improvement in barrier properties of MPA was found as the CP content reached about 15 wt%. The CP content of the MPA, however, only slightly affected the impact strength and xylene permeation resistance of the bottles.
Synthesis and solution properties of poly(acrylamide‐styrene) block copolymers with high hydrophobic content
Authors: Shaikh Sohel , Ali Sk. Asrof , Hamad Esam Z. , Abu‐Sharkh Basel F.
Published: April 2004

Hydrophobically associating block copolymers of polyacrylamide/styrene with a high hydrophobe content were synthesized using micellar copolymerization under various conditions of surfactant and initiator concentrations with the objective of determining the conditions that produce optimum solution properties for enhanced oil recovery. Solubilities, aqueous solution viscosities and interfacial properties with air and oil of the copolymers were investigated. The influence of salt on the solution properties was also studied. Nature of hydrophobic sites and onset of hydrophobic association were studied by measuring the fluorescence of pyrene in polymer solutions. Optimum solution properties were obtained for copolymers synthesized under conditions of high surfactant and initiator concentrations. The copolymers displayed substantial thickening properties at low concentrations with enhanced thickening in the presence of salt. The interfacial tensions of the aqueous solutions with n‐decane and air were also reduced. Interfacial properties were slightly sensitive to salt concentration. The copolymer solutions showed shear and temperature thinning behaviors typical of polymer solutions.
Numerical simulation of wire‐coating: The influence of temperature boundary conditions
Authors: Wapperom Peter , Hassager Ole
Published: April 2004

A finite element program has been used to analyze the wire‐coating process of an MDPE melt. The melt is modeled by a nonisothermal Carreau model. The emphasis is on predicting an accurate temperature field. Therefore, it is necessary to include the heat conduction in the metal parts. A comparison is made with the results of a simulation that models the heat conduction in the metal head by means of a Biot boundary condition. The influence of the wire velocity, inlet temperature and power‐law index will be examined.
Rheokinetical behavior of melamine‐formaldehyde resins
Authors: Hagstrand P.‐O. , Klason C. , Svensson L. , Lundmark S.
Published: April 2004

The effects of cure temperature and amount of catalyst on the rheokinetical behavior of a melamine‐formaldehyde (MF) thermosetting system is investigated using a dynamic mechanical technique similar in nature to Torsion Impregnated Cloth Analysis (TICA) and Torsional Braid Analysis (TBA). The proposed name of the used technique is Torsional Substrate Analysis (TSA). Isothermal cures of the resin are carried out from 115°C to 160°C for varying amounts of catalyst. Each TSA measurement exposes several transitions. First, a glass‐to‐liquid transition during the heatup procedure is seen, indicated by sharp peaks of the loss shear modulus, G″, and loss tangent, tanδ. Later, vitrification is seen, indicated by a second G″ maximum. Finally, a completion of shift to a diffusion controlled cure reaction occurs, shown as a storage shear modulus, G′, plateau. The rheokinetical data is used to construct Time‐Temperature‐Transformation (TTT) cure diagrams, for each level of catalyst. High pressure differential scanning calorimetry (HPDSC) measurements are carried out in order to estimate the fractional conversion of samples that have been cured isothermally for times corresponding to a second tanδ maximum, the second G″ maximum, and the G′ plateau. The fractional conversion is determined by the residual entalphy technique. The HPDSC measurements do not give a clear answer whether the second tanδ maximum corresponds to gelation or not. It is therefore likely that TSA, like similar techniques, is not capable to detect gelation. A glass transition temperature of 130°C and 150°C is found to correspond to a fractional conversion of 0.65 and ∼0.80, respectively. Preliminary measurements suggest that the maximum glass transition temperature, Tg ∞, of the investigated MF resin is at least 180°C.
Vacuum forming of thermoplastic foam
Authors: Akkerman Remko , Pronk Ruud
Published: April 2004

The process of thermoforming of foam sheet is analyzed using both finite element modeling and experiments. A simple constitutive model for finite tensile deformations of closed cellular material around its glass transition temperature is proposed, starting from well‐known results from Gibson and Ashby (1988). The model is implemented in a finite element code and applied in isothermal vacuum forming simulations. The distributions of thickness and in plane strains are in adequate accordance to the experimental results.
Supercritical carbon dioxide assisted blending of polystyrene and poly(methyl methyacrylate)
Authors: Elkovitch Mark D. , Tomasko David L. , Lee L. James
Published: April 2004

A method for blending polystyrene and poly(methyl methacrylate), (PMMA), with the addition of supercritical carbon dioxide has been investigated. The first series of blends was a PMMA and polystyrene with similar melt viscosities. The second series of blends was a PMMA and polystyrene with a viscosity ratio (ηPMMA/ηpolystyrene) of about 20. The results show that a reduction in the size of the minor or dispersed phase is achieved when supercritical carbon dioxide is added to the blend system. A high‐pressure mixing vessel was used to prepare the blends under pressure with carbon dioxide for batch blending. The solubilities of CO2 in PMMA and polystyrene, measured in the high‐pressure mixing vessel at 200°C and 13.78 MPa (2000 psi) was 5.8 and 3.6 wt%, respectively. A single screw extruder was used to study the effects of carbon dioxide on the viscosity of polymer melts. The melt viscosity of PMMA was reduced by up to 70% with approximately 0.4 wt% CO2. The melt viscosity of polystyrene was reduced by up to 56% with a CO2 content of 0.3 wt%. A twin screw extruder was used to study the effects of injecting carbon dioxide in a continuous compounding operation.
An improved kinetic model for the peroxide initiated modification of polyethylene
Authors: Pedernera Marisa N. , Sarmoria Claudia , Vallés Enrique M. , Brandolin Adriana
Published: April 2004

We propose a generalized kinetic model for the peroxide initiated modification of polyethylene. It takes into account not only combination reactions but also transfer to polymer and scission. The model describes the length of the polymer chain and the concentration of vinyl groups simultaneously. Any number of vinyl groups per molecule is allowed. The resulting infinite system of mass balance equations is solved using a double moment technique. The model calculates number, weight and z‐average molecular weights and the average concentration of vinyl groups as functions of time. The kinetic constants and the initiation efficiency were estimated through a nonlinear regression using experimental data. The relevance of each one of the reactions included in the mechanism was assessed. By means of the model we studied the influence of temperature and initial peroxide concentration on the modified polymer properties. It follows well the observed experimental trends and gives good estimates of both average molecular weights and average vinyl content, within experimental error.
Crystallinity and microstructure in injection moldings of isotactic polypropylenes. Part 1: A new approach to modeling and model parameters
Authors: Guo X. , Isayev A. I. , Guo L.
Published: April 2004

The present study is an attempt to formulate a new approach to the modeling of the injection moldings of semicrystalline polymers. A phenomenological approach is employed to develop the qualitative description of crystallization phenomena under nonisothermal flow occurring in various polymer processing operations. The unified crystallization model, which is suitable to describe the multilayer microstructure arising in the injection moldings of semicrystalline polymers, is proposed. The “competing mechanisms” of crystallization in terms of the induction time indices for introducing various microstructure layers are utilized to quantitatively distinguish between the highly oriented skin layer and spherulitic core in the moldings. The application of the equations of continuity, momentum and energy, along with the rheological model, the equation of state and the unified crystallization model, to the injection molding process leads to the modeling of crystallinity and microstructure development in the moldings. The material parameters to be used in the modeling of the crystallinity and microstructure development in the injection moldings of isotactic polypropylenes (i‐PP's) with various molecular weights are determined. The melt viscosity as a function of shear rate and temperature is measured and fitted to the modified Cross model. Quiescent crystallization kinetics, including the induction time and the heat release due to crystallization, is characterized using differential scanning calorimetry. The spherulite growth rate of i‐PP's under isothermal and nonisothermal quiescent crystallization conditions is measured by optical microscopy. The molecular deformation factor during the induction period of shear‐in‐duced crystallization is obtained from the extrusion‐quenching and extrusion‐relaxation‐quenching experiments with a slit die. The variation of the induction time with shear rate obtained by Lagasse and Maxwell from the shearing‐crystallization experiments is used to determine the shear enhancement coefficient of crystallization.
Crystallinity and microstructure in injection moldings of isotactic polypropylenes. Part II: Simulation and experiment
Authors: Guo X. , Isayev A. I. , Demiray M.
Published: April 2004

The injection moldings of isotactic polypropylenes with various molecular weights were simulated using finite difference method. In the simulations, the unified crystallization model proposed in our previous paper was applied. The prediction of crystallinity and microstructure development in the moldings was based upon the crystallization kinetics and the “competing mechanisms” for introducing various microstructure layers in the moldings. Extensive injection molding experiments were carried out. The pressure traces during the molding experiments were recorded. The crystallinity distribution in the moldings was determined using differential scanning calorimetry. The measurements on the microstructure embedded in the moldings were performed, including the thickness of the highly oriented skin layer and the gapwise distribution of the spherulite sizes. The measured data for the crystallinity and microstructure in the moldings were compared with the simulated results. The effects of molecular weight and processing conditions on the development of crystallinity and microstructure in the moldings were elucidated. Theoretical predictions were found to be in a good agreement with experimental measurements.
Attempts to enhance the properties of EPON 830‐4,4′‐methylene bis cyclohexylamine epoxy resin systems by exposing them to 0.1290 to 0.8810 Tesla magnetic fields while thermally curing them
Authors: Gerzeski Roger
Published: April 2004

This effort determined if enhancements to the properties of fully cured EPON 830‐4,4′‐Methylene Bis Cyclohexylamine epoxy resin systems (ERSs) could be induced by thermally curing them, while also simultaneously exposing them to economically generated magnetic fields (MFs). Stoichiometric mixes were cured for 5 hours at 121°C while being exposed to MFs between 0.1290 and 0.8810 Tesla. Exposed and control specimens were simultaneously cast from the same mix in each run. The resulting specimens were mechanically and thermally tested to find any property differences. This effort determined that under these conditions there were no modifications to the properties of MF exposed, fully thermally cured, ERSs relative to their controls.