bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melt rheology of poly(lactic acid): Consequences of blending chain architectures
Authors: Lehermeier Hans J. , Dorgan John R. 
Published: April 2004

AbstractThe rheology of blends of linear and branched poly(lactic acid) (PLA) architectures is comprehensively investigated. Measurement of the melt rheological properties of PLA is complicated by degradation effects but the addition of 0.35 wt% tris(nonylphenyl) phosphite (TNPP) provides excellent stabilization over a range of temperatures. Master curves of dynamic viscosity constructed using time‐temperature superposition show significant dispersion for unstabilized samples; this behavior is accompanied by a loss of molecular weight. TNPP stabilized samples show excellent superposition throughout the entire frequency range and minimal loss in molecular weight. For the linear architecture, the Cox‐Merz rule is valid for a large range of shear rates and frequencies. The branched architecture deviates from the Cox‐Merz equality and blends show intermediate behavior. Both the zero shear viscosity and the elasticity (as measured by the recoverable shear compliance) Increase with increasing branched content. The viscosities of both the unstabilized samples and the TNPP stabilized samples roughly obey a log additivity mixing rule. The recoverable shear compliance is monotonic in blend composition and a mixing rule for this property is also presented. For the linear chain, the compliance is independent of temperature but this behavior is apparently lost for the branched and blended materials. Tensile and thermal properties of the blends are also measured and found to be roughly equal within the statistical error of the experiments. The results suggest that excellent control over rheological behavior of PLA is possible through blending chain architectures without compromising mechanical properties.
Structure and physical properties of biaxially stretched polyethylene terephthalate sheets under different heat‐set and stretch conditions
Authors: Maruhashi Yoshitsugu 
Published: April 2004

AbstractThe thermal shrinkage of heat‐set polyethylene terephthalate (PET) sheets at 85°C after stretching at low speed and low temperature was similar to that for sheets stretched at high speed and high temperature if the crystallinities of these sheets were the same. However, differences between other physical properties, such as yield strength, were observed, which may be due to differences in the amorphous phase. The sheets stretched at the higher temperature and higher speeds may have different structures in the molecular segments in the amorphous phase, more relaxed than in the sheets prepared at the lower speed and temperature.
Direct measurement of permeabilities at high pressures
Authors: Wiff D. R. , Roach J. F. 
Published: April 2004

AbstractA new procedure for measuring the peermeability of a high pressure gas (10.34 MPa) through a polymeric material has been developed. The procedure employs a vacuum system on the low‐pressure side of the material. Although it gives a pressure difference of seven orders of magnitude during testing, the real purpose of the vacuum system is to allow the permeability measurements to be made rapidly for a small amount of transported material. The permeability of several commercial polymers to either natural gas or helium has been measured and is reported.
Effect of processing variables on the linear viscoelastic properties of SBS‐oil blends
Authors: Navarro F. J. , Martínez‐Boza F. J. , Partal P. , Gallegos C. , Muñoz M. E. , Areizaga J. , Areizaga J. , Santamaría A. 
Published: April 2004

AbstractBlock copolymers, especially styrene‐butadiene‐styrene three‐block copolymers (SBS), are recognized as especially effective asphalt modifiers because of their thermoplastic elastomeric properties. The concentration of copolymer, its ability to swell by the maltenic oils, and the processing variables are essential in the development of a three‐dimensional network in the polymer‐rich phase that enhances the vis‐coelastic properties of these modified binders. This swollen polymer phase may influence the mechanical properties of the modified bitumens and synthetic binders. This paper deals with the influences that processing variables exert on the linear viscoelastic properties of oil/SBS mixtures in a wide range of temperatures. From the experimental results obtained we may conclude that most of the oil/SBS blends studied are highly structured thermoplastic gels above a critical SBS concentration that depends upon temperature, time of processing and surrounding atmosphere.
Interfacial crosslinking and diffusion via extensional rheometry
Authors: Saito Takushi , Macosko Christopher W. 
Published: April 2004

AbstractWhen a coextruded multilayer sheet is pulled in a uniaxial extensional rheometer the interfacial area per unit volume increases, amplifying interfacial effects. To investigate interfacial reaction, a pair of functional and miscible polyethylenes were co‐extruded into multilayer sheets (256 layers). One polyethylene contained 8 wt% glycidyl methacrylate comonomer the other 4 wt% anhydride grafts. The extensional force to pull the molten multilayer sheet was measured via a rotating clamp extensional rheometer (RME, Rheometric Scientific). Owing to the reaction in the interfacial region before and during the extension, the measured extensional force increased dramatically. The interfacial stress was extracted and correlated to the extent of interfacial crosslinking. The rate of interfacial crosslinking was found to exceed the rate of area generation at extension rates < 0.01 s−1. By annealing samples and then stretching them, the growth rate of the interlayer was determined, and a diffusion coefficient estimated.
Characterization of the cure‐state of DGEBA‐DDS epoxy using ultrasonic, dynamic mechanical, and thermal probes
Authors: White S. R. , Mather P. T. , Smith M. J. 
Published: April 2004

AbstractThree experimental techniques were used to characterize the cure state of an epoxy resin system of DGEBA epoxide and DDS diamine curing agent. Samples were prepared from non‐stoichiometric monomer mixtures designed so as to simulate various stages of cure of a stoichiometrically prepared epoxy. Such an approach allows for variable temperature characterization of specimens without concern for ongoing chemical reactions that would cloud interpretation of results. Additional experiments were performed on stoichiometric samples that were isothermally cured. Differential scanning calorimetry (DSC) was used to measure the heat of reaction and glass transition temperature. Dynamic mechanical analysis (DMA) was used to measure complex modulus, while ultrasonic cure monitoring (UCM) was used to measure longitudinal velocity throughout cure. DSC analysis was found to be insensitive to changes occurring at the latter stage of polymer network development, especially after vitrification. DMA characterization, however, was found to be quite sensitive to the rubbery modulus (and as such, the cure state), but is limited to cure states above gelation. Only the UCM technique was robust enough to accommodate all cure states while providing highly sensitive measurements of mechanical property development.
Synthesis and characterization of ozonized polyethylene
Authors: Boutevin B. , Robin J. J. , Torres N. , Casteil J. 
Published: April 2004

AbstractPolyolefins (LDPE and HDPE) can be ozonized with ozone/air gas flow to create peroxide and hydroperoxide groups on polymers. These reactive groups can be used to initiate radical polymerization of vinylic monomers and produce graft copolymers. In this study, the optimization of the experimental conditions and the explanation of the phenomena occurring during the ozonization of polyolefins in a fluidized bed have been studied. The most reproducible methods for placing peroxide and hydroperoxide groups onto polyolefins are the iodometric method and indirect titration by thiol. This work shows that it is necessary to control the temperature of the fluidized bed to avoid the acceleration of the reaction and the degradation of the polymers. Then, we studied the effect of different parameters such as the crystallinity and the granulometry of polymers, the time of ozonization and the effect of the load of the reactor on the quality of ozonization. Infrared spectroscopy and steric exclusion chromatography were used to characterize the ozonized polymers. We show that double bonds of PE, particularly vinyl groups, are very reactive to ozone and that ozonized HDPE leads essentially to the formation of hydroperoxide groups, whereas ozonized LDPE leads to the formation of peroxide groups.
Polyimides from isomeric biphenyltetracarboxylic dianhydrides and the effects of chemical structure on solubility
Authors: Tong Y. J. , Liu S. L. , Guan H. M. , Ding M. X. 
Published: April 2004

AbstractA series of homopolyimides and copolyimides was synthesized by the solution condensation of biphenyltetracarboxylic dianhydride (BPDA) isomers and various diamines followed by chemical imidization. These polyimides had intermediate to high molecular weights with inherent viscosities of 0.34–1.01 dL/g for homopolyimides and 0.48–1.02 dL/g for copolyimides. Thermogravimetric analysis indicated that the aromatic polyimides were stable up to 500°C, and the 5% weight loss temperatures were recorded in the range of 506–597°C in an air atmosphere and in the range of 517–601°C in a nitrogen atmosphere, depending on the diamines used. The glass transition temperatures of aromatic homopolyimides were above 271°C, while the glass transition temperatures of the copolyimides increased with an increase in the 2, 2′, 3, 3′‐BPDA‐component. The effects of the chemical structure of the polymer chain on the solubility were investigated. It was found that the solubility of BPDA‐based polyimides could be improved by the introduction of flexible units, nonlinear and non‐coplanar units, and copolymerization. The polyimides with nonlinear and non‐coplanar units derived from 2, 2′, 3, 3′‐BPDA appeared to have prominently enhanced solubility in polar aprotic solvents and polychlorocarbons when compared with the homopolyimide derived from 3, 3′, 4, 4′‐BPDA.
Morphology and rheology relationships of epoxy/core‐shell particle blends
Authors: Nguyen‐Thuc Boi Huyen , Maazouz Abderrahim 
Published: April 2004

AbstractThe morphological and rheological behaviors of toughened epoxy resins modified with core‐shell rubber particles (CSR) were studied. These rubber particles were based on a poly (butadiene‐co‐styrene) core and a crosslinked poly (methyl methacrylate) shell. The effect of functionalized groups was performed on two types of CSR particles: first, those containing carboxyl‐functionalized groups (CSf), and second, particles containing no carboxyl‐functionalized groups (CSnf) in the PMMA‐shell. For these blends, the correlations between the morphology, particle dispersion state and their rheological behaviors before curing were investigated. Preliminary work using TEM micrographs indicated that the blends modified with CSf and CSnf exhibited the same particle size but differed with respect to the dispersion state. Rheological behavior of these blends was assessed in steady shear flow and dynamic viscoelastic experiments. Yield viscosity near‐zero shear rate occurred in the DGEBA/CSf blend presenting non‐Newtonian behavior at the particle volume fraction of 20% vol. The rheological behavior was clearly related to the state of particle dispersion and analyzed taking into account interactions between the particles‐particles and the particles‐matrix. The Williams‐Landel‐Ferry (WLF) shift procedure was used to construct modulus master curves G′ and G″ from the elastic solid state to molten polymers. A secondary plateau existed at low frequencies and was related to the presence of interactions leading to a physical network‐type structure. The deviation between theoretical G′ (Paleirne's model) and experimental G′ values was evaluated and exhibited high elasticity at the terminal zone, which correlated well with available literature.
Prediction of the creep of heterogeneous polymer blends: Rubber‐toughened polypropylene/poly(styrene‐co‐acrylonitrile)
Authors: Kolaříak Jan , Fambri Luca , Pegoretti Alessandro , Penati Amabile , Goberti Paolo 
Published: April 2004

AbstractA previously proposed predictive format for elastic, storage and loss moduli is extended for the time‐dependent compliance Db(t) of polymer blends. The format employs a two‐parameter equivalent box model (EBM) and the data on the phase continuity of components in blends obtained by using modified general equations of the percolation theory. As input data, the compliances D1(t) and D2(t) and the critical volume fractions V1cr and V2cr (delimiting the interval of phase co‐continuity in blends) of components are sufficient. To describe the effect of time on D1(t), D2(t) and Db(t) within the linear stress‐strain region, a routinely used empirical equation was found suitable. Applicability of the proposed format is demonstrated on rubbertoughened polypropylene/poly(styrene‐co‐acrylonitrile) blends consisting of components with markedly different viscoelastic properties. The proposed predictive format fits fairly well the creep behavior of blends over the interval 0.1‐10,000 minutes.
An optical device to measure in‐line residence time distribution curves during extrusion
Authors: Mélo Tomás Jeferson A. , Canevarolo Sebastião V. 
Published: April 2004

AbstractThis paper proposes a setup for in‐line measurement of residence time distribution (RTD) curves during extrusion. The detection system is composed of a slit die with transparent borosilicate glass windows fixed at the extruder exit, an optical arrangement with an incandescent light microbulb with fixed luminescence, and a Light Dependent Resistor (LDR) photocell of CdS. As the tracer passes through the light path, the reduction in the transmitted light intensity is followed by changes in the voltage induced by the photocell to an electric circuit. The signal is collected by an external interface and sent to a computer. Software acquires the data, does all calculations, and presents all curves and calculated variables to the monitor. The validation of the system was done by checking for data reproducibility and linearity with tracer concentration. The response of the LDR sensor with respect to the concentration of the tracer was calibrated using a set of slight dark film, obtaining a logarithmic relationship. Thus the signal enhances any disturbance, if present, particularly in the tail‐region of the curves. Measurements were taken from a Werner‐Pfleiderer ZSK 30 twin‐screw extruder equipped with K‐Tron gravimetric feeders operating with various screw speeds, feeding rates and screw configurations. In this last case, the presence of kneading elements was taken into account.
Measurement of the residual mechanical properties of crazed polycarbonate. I: Qualitative analysis
Authors: Clay Stephen B. , Kander Ronald G. 
Published: April 2004

AbstractA new technique to quantify the bulk craze density of transparent plates was used to characterize the craze growth behavior of polycarbonate at various stress levels. The craze growth rates were found to exponentially increase with an increase in stress, obeying the Eyring equation for thermally activated processes in the presence of an applied stress. The residual mechanical properties of crazed polycarbonate were then correlated to the crazing stress, relative craze density and strain rate. The results show that increasing the bulk craze density does not affect the yield stress but decreases both the failure stress and ductility of polycarbonate. Also, a crazing stress of 40 MPa was found to cause a much larger degree of degradation of failure properties than a crazing stress of 45 MPa. Correlating the crazing stress to the craze microstructure revealed that fewer, larger crazes form at the lower crazing stress. Therefore, flaw size has a greater effect on the failure properties of polycarbonate than flaw quantity.
Flow behavior of stratified viscoelastic laminar flow at junctions with different angles
Authors: Yamaguchi Hiroshi , Yamamoto Hideaki 
Published: April 2004

AbstractDetailed study was carried out in order to investigate flow phenomena occurring at the junction of two incoming stratified flow layers with junction angles. Various combinations of fluids with Newtonian and non‐Newtonian rheological characteristics were tested in a relatively high‐speed stratification where the inertia of flow cannot be neglected. The flow characteristics at the junctions were classified into six main flow modes, which were arranged in mode maps by use of generalized Reynolds numbers and viscous ratios. From the resultant mode maps it was found that a mutual relation of inertial and viscous effects is essential for the determination of flow modes in the stratified flows.
Simulation of non‐isothermal melt densification of polyethylene in rotational molding
Authors: Bellehumeur C. T. , Tiang J. S. 
Published: April 2004

AbstractRotational molding involves powder mixing, heating and melting of powder particles to form a homogeneous polymer melt, as well as cooling and solidification. The densification of a loose powder compact into a homogeneous melt occurs over a wide range of conditions as the material passes from a solid state into a melt state. The numerical simulation of the non‐isothermal melt densification in the rotational molding process is presented in this work. The simulation combines heat transfer, polymer sintering and bubble dissolution models, and is based on an idealized packing arrangement of powder particles. The predictions are in general agreement with experimental observations presented in the literature for the rotational molding of polyethylenes. The simulation allows for systematic and quantitative studies on the effect of molding conditions and material properties on the molding cycle and molded part density. Results indicate that the densification process is primarily affected by the powder characteristics, which are accounted for in terms of the particle size and the particle packing arrangement. The material rheological properties become increasingly important as the powder characteristics lessen in quality. The simulation demonstrated that while certain combinations of processing conditions help reduce the molding cycle, they have a detrimental effect on the densification process.
Modeling of a Buss‐Kneader as a polymerization reactor for acrylates. Part I: Model validation
Authors: Troelstra E. J. , Van Lune J. , Van Dierendonck L. L. , Janssen L. P. B. M. , Renken A. 
Published: April 2004

AbstractThe Buss‐Kneader is generally known as a compounding device. Although a reasonable number of papers have been published on extruders as polymerization reactors, only little is known about the behavior of the Buss‐Kneader when used as a polymerization reactor. Its good mixing properties in the radial and axial directions make it a suitable reactor for exothermal polymerization reactions. This paper describes experiments with the co‐polymerization of n‐butyl acrylate and hydroxyethyl methacrylate in a Buss‐Kneader. For model calculations the Buss‐Kneader was treated as a plug flow reactor with axial dispersion. Experimental results on axial temperature profile, monomer conversion and molecular weight are compared with model calculations. Model parameters are based on independently measured data on the heat transfer coefficient, axial dispersion and polymerization kinetics.
Phase separation and gelation of epoxy resin/hyperbranched polymer blends
Authors: Mezzenga Raffaele , Luciani Andrè , Månson Jan‐Anders E. 
Published: April 2004

AbstractThe structural buildup during reticulation of thermoset systems containing reactive modifiers can strongly influence the final properties of such blends. This was studied by considering the rheological behavior during cure of an epoxy/amine thermoset system blended with reactive dendritic hyperbranched polymers (HBPs). Depending on the chemical structure of the HBP used in the blend, a phase separation could be observed. The onset and offset of the phase separation process could be detected by observing the evolution of the viscoelastic properties. The phase separation onsets obtained by rheological measurements were compared with the values obtained by traditional cloud point observations. Good agreement between the two techniques was observed. Hyperbranched polymers that did not phase separate during the curing process were used to study gelation phenomena and its dependence on the reactivity and functionality of the HBP. The gelation of the homogeneous blend system using the Flory‐Stockmayer theory was also modeled. This highlighted the influence of both functionality and reactivity of the components, and the appearance of co‐operative polymerization mechanisms in homogeneous blends.
Effect of polymer matrix on the rheology of hydroxyapatite‐filled polyethylene composites
Authors: Joseph R. , McGregor W. J. , Martyn M. T. , Tanner K. E. , Coates P. D. , Bonfield W. 
Published: April 2004

AbstractThe effect of matrix polymer and filler content on the rheological behavior of hydroxyapatite‐filled injection molding grade high‐density polyethylene (HDPE) has been studied. Studies of the flow curves revealed that the matrix and the composite exhibit three distinct regions in the flow curve, namely, a pseudoplastic region at low to moderate shear rates, a plateau and a second pseudoplastic region at high shear rates. The shear stress corresponding to the plateau (τc) is dependent on both the filler concentration and the melt temperature. Addition of HA in the HDPE matrix increases the value of τc and decreases compressibility of the melt. An increase in temperature also raises the value of τc. From the nature of flow curves it is concluded that the matrix polymer largely decides the rheology of the composite.
Extrusion blow molding of long fiber reinforced polyolefins
Authors: Garcia‐Rejon A. , Meddad A. , Turcott E. , Carmel M. 
Published: April 2004

AbstractA 58% (by weight) long glass fiber reinforced (LGF)‐HDPE master batch was blended with a typical blow molding HDPE grade. HDPE composites having between 5% and 20% (by weight) long fiber content were extruded at different processing conditions (extrusion speed, die gap, hang time). The parison swell (diameter and thickness) decreased with increasing fiber content. Although the HDPE exhibited significant shear rate dependence, the LGF/HDPE composites were shear rate insensitive. Both the diameter and weight swell results also indicated very different sagging behavior. The LGF/HDPE parisons did sag as a solid‐body (equal speed at different axial locations) governed by the orientation caused by the flow in the die. Samples taken from blown bottles showed that fiber lengths decreased to 1‐3 mm, from the original 11 mm fiber length fed to the extruder. No significant difference in fiber length distribution was found when samples for different regions of the bottle were analyzed. SEM micrographs corroborate the absence of fiber segregation and clustering or the occurrence of fiber bundles (homogeneous spatial fiber distribution) as well as a preferential fiber orientation with the direction of flow. The blowing step did not change the orientation of the fibers. Five‐percent (5%) and 10% LGF/HDPE composites could be blown with very slight variations to the neat HDPE inflation conditions. However, 20% LGF/HDPE composites could not be consistently inflated. Problems related to blowouts and incomplete weldlines were the major source of problems.