bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological properties of fumed silica filled Bis‐GMA dispersions
Authors: Kim Sangwoo , Jang Jyongsik , Kim Ohyoung 
Published: April 2004

AbstractThe rheological properties of Bis‐GMA dispersions filled with fumed silica were investigated to optimize the manufacturing process and mechanical properties by using a Rheometrics Mechanical Spectrometer (RMS). Steady and dynamic measurements on the RMS were carried out to obtain shear viscosity and dynamic mechanical properties. The effect of several factors on the rheological properties of fumed silica dispersions was also examined. The factors were a concentration of a silane coupling agent (γ‐MPS), the methods of surface treatment of fillers, silica content, diluent concentration, shear rate, and operating temperatur. From these studies, it was observed that shear viscosity showed an asymptotic phenomenon at a higher concentration than a uniform multi‐layer coverage concentration of γ‐MPS. The silane coupling agent had a significant role in the reduction of tan δ, resulting from a decrease of loss modulus, while fillers decreased tan δ by increasing the storage modulus. In cases where the silica content and diluent concentration increased simultaneously, the Barcol hardness of Bis‐GMA/silica composites was increased, but there was no change in the viscosity of dispersions and diametral tensile strength of those composites.
Comparison of oxidation induction time measurements with values derived from oxidation induction temperature measurements for EPDM and XLPE polymers
Authors: Mason L. R. , Reynolds A. B. 
Published: April 2004

AbstractOxidative stability and retained operational utility of polymers used as insulation for electrical cables, such as ethylene propylene diene monomer (EPDM) and crosslinked polyethylene (XLPE), may be assessed by oxidation induction time (OIT) analysis. OIT is measured directly with a differential scanning calorimeter. Using a simplified kinetics model, Gimzewski demonstrated that it is possible to calculate the OIT from measured values of oxidation induction temperature and the activation energy for petroleum lubricants. In the present research, directly measured OITs are compared with OITs calculated from measured oxidation induction temperatures and activation energies for EPDM and XLPE cable insulation. Good agreement between the two methods was demonstrated for these materials.
Prediction of equilibrium polymer blend morphology in dispersed two‐phase flow and comparison with experiment
Authors: Han Chang Dae , Sun Junsuo , Chuang Hsiao‐ken , Lee Je Kyun 
Published: April 2004

AbstractA theory is developed to predict equilibrium polymer blend morphology in dispersed two‐phase flow in terms of the viscosity ratio and blend ratio of the constituent components. We formulated a system of equations for the ‘One‐Cell Model,’ describing the situation where a spherical droplet of one liquid is dispersed in another liquid, by first considering a pair of Newtonian liquids and then a pair of truncated power‐law fluids. The question posed was: which of the two liquids, A or B, will form a droplet dispersed in another liquid? Finite element method was employed to calculate the rate of the energy dissipated per unit volume when a unit cell, having either Morphology I or Morphology II, was subjected to steady‐state simple shear flow, where Morphology I has a droplet of liquid A dispersed in the matrix phase of liquid B and Morphology II has a droplet of liquid B dispersed in the matrix phase of liquid A. We used a criterion that the morphology that requires a lower rate of the energy dissipated per unit volume in dispersed two‐phase flow is an equilibrium polymer blend morphology. In so doing, we determined the blend composition, at which a matrix inversion takes place, in terms of the viscosity ratio of the constituent components. Theoretically predicted blend morphologies compared favorably with experimental results.
Rheological and mechanical relaxation behavior of a thermally crosslinkable poly(ethylene terephthalate)
Authors: Mather Patrick T. , Romo‐uribe A. 
Published: April 2004

AbstractA novel terephthalic acid derivative based on benzocyclobutene, XTA, has been used as a comonomer in the preparation of thermally crosslinkable poly(ethylene terephthalate) copolymers. We have examined the rheological properties of a series of such polymers containing varying monomer percentages of the XTA comonomer: 0, 1, 5, 10, and 20. Incorporation of XTA into PET is found to cause dramatic changes in the temperature and time dependence of the rheological material functions, all indicating that the rate of crosslinking between chains in the melt increases as the XTA percentage is increased. The impact of thermal crosslinking on mechanical properties is also examined using dynamic mechanical analysis (DMA) on samples molded at a selected crosslinking temperature for times yielding varying levels of crosslinking extent. DMA results show that the activation energy of the β mechanical relaxation increases significantly, indicating the importance of torsional mobility of the aromatic ring of PET.
Processing and characterization of microcellular foamed high‐density polythylene/isotactic polypropylene blends
Authors: Doroudiani Saeed , Park Chul B. , Kortschot Mark T. 
Published: April 2004

AbstractIn this paper, a study on the batch processing and characterization of microcellular foamed high‐density polyethylene (HDPE/iPP) blends is reported. A microcellular plastic is a foamed polymer with a cell density greater than 109 cells/cm3 and fully grown cells smaller than 10 µm. Recent studies have shown that the morphology and crystallinity of semicrystalline polymers have a great influence on the solubility and diffusivity of the blowing agent and on the cellular structure of the resulting foam in microcellular batch processing. In this research, blends of HDPE and iPP were used to produce materials with variety of crystalline and phase morphologies to enhance the subsequent microcellular foaming. It was possible to produce much finer and more uniform foams with the blends than with neat HDPE and iPP. Moreover, the mechanical properties and in particular the impact strength of the blends were significantly improved by foaming.
Photochemical modification of polymers—photocrosslinking, surface photografting, and lamination
Authors: Rånby Bengt 
Published: April 2004

AbstractThe molecular mechanism, the kinetics and the process development of photocrosslinking of diene elastomers, of high density and low density polyethylenes, and of new linear and dendritic unsaturated polyesters using UV‐irradiation are described. New methods for modification of various polymers by surface photografting are presented, the effects on adhesion and adsorption, and the mechanism of the reactions related to the shortlived high energy states of aromatic ketones as initiators are presented and discussed. The development of surface photografting as a new method for UV‐initiated lamination of various polymer films and sheets is described, the molecular mechanism and the kinetics of the reactions are discussed, and the mechanical and barrier properties of the laminates are presented.
Crosslinking of polybutadiene rubber without any vulcanization agent
Authors: Bellander Martin , Stenberg Bengt , Persson Sture 
Published: April 2004

AbstractPolybutadiene rubber with 10% vinyl unsaturation has been crosslinked without the addition of any vulcanization chemicals. The crosslinks have been created through treatment at high temperature (240–250°C) and elevated pressure (<293 MPa) in a plunger type mold. The treatment time needed to achieve a crosslinked material is of the order of a few minutes and the reaction rate is shown to be dependent upon the temperature as well as upon the pressure applied. As a result of the severe treatment, some degradation reactions may be expected but careful FTIR analysis shows no increased oxidation. There is some consumption of the vinyl unsaturation, to an amount comparable to the number of crosslinks formed. The presence of carbon black increases the measured crosslink density, as expected, but at higher pressures the amount of extra network material, because of the carbon black, is much larger than at lower pressures, suggesting that the carbon black plays a critical role in the network formation process. The stress relaxation properties in compression of the rubber material were investigated and found to be comparable to those of a peroxide vulcanizate.
Assessment of development and relaxation of orientation in a sheared thermotropic liquid crystalline copolyester
Authors: Wiberg G. , Hillborg H. , Gedde U. W. 
Published: April 2004

AbstractShear‐induced chain orientation and relaxation of chain orientation in a thermotropic liquid‐crystalline poly(4‐hydroxybenzoic acid (73mol%)‐co‐2‐hydroxy‐6‐naphthoic acid (27 mol%)) (Vectra A950) were studied by means of transmitted light intensity through crossed polarizers in a shear cell. Shear rates ranged between 4 and 1000 s−1 and the level of chain orientation increased with increasing shear rate and increasing temperature. Overall, the times for relaxation were very short. The longest relaxation times (˜21s) were obtained at the lowest shear temperatures and at intermediate shear rates. At high shear rates, the relaxation times were generally short (˜2s) and independent of temperature. The rapid relaxation of orientation after high rate shearing (100–1000 s−1) indicates that shear‐induced crystallization is inhibited under these conditions. A certain degree of chain orientation was still present although the relaxation as judged by the transmitted light intensity was complete. Signs of recrystallization were observed if the samples were not preheated to 320°C prior to shearing. By simultanecous shearing and cooling, high degrees of orientation were achieved (f ˜ 0.7) as revealed by X‐ray diffraction and infrared dichroism. Infrared spectroscopy showed that annealing of oriented samples at 250°C led to an increase in thermal stability of the orientation with annealing time.
Poly(styrene‐g‐ethylene oxide) copolymers as interfacial agents in immiscible polymer blends
Authors: Kvist L. , Bertilsson H. , Meuller P. 
Published: April 2004

AbstractA poly(styrene‐g‐ethylene oxide) copolymer with an average of 100 styrene units between the graft points is studied with respect to its interfacial activity in binary incompatible mixtures of polymers having different degrees of miscibility toward the graft copolymer components. The interfacial properties were studied by scanning electron microscopy, dynamic mechanical spectroscopy, and differential scanning calorimetry. The data obtained are compared with previously published data from a graft copolymer with the same composition but with shorter PEO branches and only 20 styrene units between them. In spite of their structure, the two graft copolymers could reduce the size of the dispersed phase in the case of athermal mixing. With a negative heat of mixing between only one graft component and the blend, the short branch graft had no effect, while the longer branch graft caused a reduction of the size of the dispersed phase. With a negative heat of mixing for the graft branches as well as for the backbone a strong compatibilizing effect was found for both types of graft copolymers. The results show that even very short parts of the backbone of a graft copolymer can contribute to compatibilization in a polymer blend, especially when the backbone has a negative heat of mixing with one of the blend components.
Multi‐layer modeling of diffusion of water in acrylamide‐grafted aliphatic polyesters
Authors: Hedenqvist M. S. , Ohrlander M. , Palmgren R. , Albertsson A.‐C. 
Published: April 2004

AbstractA new mass transfer model for layered structures, based on an implicit multi‐step integration algorithm including concentration dependent diffusivities, has been developed and applied to systems of water diffusing in electron beam pre‐irradiated, acrylamide‐grafted aliphatic polyesters (poly(ϵ‐caprolactone) and poly(1, 5‐dioxepan‐2‐one)). The much higher water solubility and water diffusivity in the amorphous crosslinked poly(1, 5‐dioxepan‐2‐one) than in the semicrystalline poly(ϵ‐caprolactone) is explained as being due to the fact that crystals are more effective crosslinks than the chemical crosslinks. Water solubility in the grafted layer is a function of the concentration of polyacrylamide, but it is believed to be limited by compressive swelling‐induced stresses. The zero concentration water diffusivity in the graft layer passes through a maximum, whereas the graft‐layer density passes through a minimum with increasing acrylamide concentration. It is suggested that this is because the accessible free volume for the penetrating water molecule is increased in the initial stages of grafting because the matrix polymer chains are separated by growing acrylamide graft chains. At later stages, the accessible free volume decreases because additional polyacrylamide chains are growing adjacent to the already existing ones and thus fill up empty spaces.
Nanocomposites based on montmorillonite and unsaturated polyester
Authors: Kornmann X. , Berglund L. A. , Sterte J. , Giannelis E. P. 
Published: April 2004

AbstractThe concept of nanoscale reinforcement provides opportunity for synthesis of new polymer materials with unique properties. Montmorilonite (MMT) was derived from bentonite, purified, activated by sodium ions and mixed with reacting unsaturated polyester (UP). X‐ray and transmission electron microscopy data were in support of the formation of a partially delaminated nanocomposite material. At an MMT content of only 1.5 vol%, the fracture energy,GQ, of the nanocomposite was doubled, 138 J/m2as compared with 70 J/m2for the pure UP.
The crystalline phase transformation of poly(vinylidene fluoride)/poly(vinyl fluoride) blend films
Authors: Kim Bong Shik , Lee Jae Yeon , Porter Roger S. 
Published: April 2004

AbstractPoly(vinylidene fluoride) (PVDF), poly(vinyl fluoride) (PVF), and their blends were prepared by solution casting, followed by quenching in ice water after melting to obtain an α‐crystalline phase. The films were drawn by solid state extrusion at two different drawing temperatures, 50°C and 110°C. The crystalline phases were analyzed by DSC and FTIR. In the undrawn films, the content of β‐crystalline phase in the blend of PVDF/PVF 88.5/11.5 was higher than in the PVDF homopolymer, but it was lower than in the PVDF film with a draw ratio higher than 4. The α‐crystalline phase in PVDF/PVF blends was mostly transformed into the β‐crystalline phase beyond a draw ratio of 4, regardless of the draw temperature and PVF content. The α‐crystalline phase of PVDF systematically transformed into the β‐crystalline phase with increasing draw ratio. The crystallinity of PVDF/PVF blend films drawn at 110°C was higher than those drawn at 50°C. In the drawn blend films, characteristic IR bands of the α form were shifted to those of the β form and completely changed into those of β form at draw ratio of 4, regardless of the draw temperature and PVF content.
Residence time distributions and basic studies of flow and melting in a modular buss kneader
Authors: Lyu Min‐Young , White James L. 
Published: April 2004

AbstractExperimental studies of residence time distribution, fill factor, temperature, and melting profiles of thermoplastic resins are presented. Residence time distributions were determined as a function of throughput and screw speed. The melting of polypropylene and low density polyethylene in the entrance region was investigated. Fill factor and temperature profiles are reported.
New models for rotational molding of plastics
Authors: Gogos G. , Olson L. G. , Liu X. , Pasham V. R. 
Published: April 2004

AbstractWe present a detailed theoretical model of the rotational molding process, and identify the key dimensionaless groups affecting the process cycle time. This theoretical model is employed to create differential and lumped parameter numerical models, as well as a simple closed form estimate for the time required for complete powder deposition. Both numerical models give results that are in very good agreement with experimental data available in the literature. The closed form solution gives good predictions over a wide range of processing parameters. In addition, the effects of variations in the dimensionaless groups on processing time are evaluated.
Experimental study and numerical simulation of the injection stretch/blow molding process
Authors: Schmidt F. M. , Agassant J. F. , Bellet M. 
Published: April 2004

AbstractThe injection stretch/blow molding process of PET bottles is a complex process, in which the performance of the bottles depends on various processing parameters. Experimental work has been conducted on a properly instrumented stretch/blow molding machine in order to characterize these processing parameters. The objective being a better understanding of the pressure evolution, preform free inflation has been processed and compared with a simple thermodynamic model. In addition, a numerical model for the thermomechanical simulation of the stretch/blow molding process has been developed. At each time step, mechanical and temperature balance equations are solved separately on the current deformed configuration. Then, the geometry is updated. The dynamic equilibrium and the Oldroyd B constitutive equations are solved separately using an iterative procedure based on a fixed‐point method. The heat transfer equation is discretized using the Galerkin method and approximated by a Crank‐Nicholson's scheme over the time increment. Successful free blowing simulations as well as stretch/blow molding simulations have been performed and compared with experiments.
Environmental stress cracking resistance of blends of high‐density polyethylene with other polyethylenes
Authors: Schellenberg J. , Fienhold G. 
Published: April 2004

AbstractA special modified tensile creep test was used to investigate the stress cracking behavior of various high‐density polyethylenes (HDPE). Blends of HDPE with other HDPEs, with linear low‐density polyethylene (LLDPE), and specifically with various slightly long‐chain branched linear low‐density polyethylenes (HBPE) were tested for their failure times. Whereas HDPE blends, including higher‐molecular‐weight HDPE components, yield only a minor improvement in stress cracking resistance, a considerable improvement was produced when an LLDPE weight fraction of 0.3 or more was used. Adding HBPE also improves the environmental stress cracking resistance. Environmental stress cracking resistance improves with increasing HBPE content, and, for a constant HBPE concentration, it increases with increasing octene content of the HBPE. Adding HBPE with a low octene content, however, results in reduced failure times of the blend compared with HDPE blends that exhibit relatively good environmental stress cracking behavior. The results are explained in terms of the tie‐molecule density.
Ethylene vinyl alcohol copolymer/high density polyethylene blends compatibilized through functionalization
Authors: Park Seong Ho , Lee Gun Joo , Im Seung Soon , Suh Kyung Do 
Published: April 2004

AbstractIn order to evaluate the compatibilizing effects of isocyanate (NCO) functional groups on ethylene vinyl alcohol copolymer/high density polyethylene (EVOH/HDPE) blends, HDPE grafted with 2‐hydroxyethyl methacrylate‐isophorone diisocyanate (HDEP‐g‐HI) was prepared and blended with EVOH. The grafting was confirmed by infrared spectra, and the grafting ratio was 4.9% from elementary analysis. From the morphologies of EVOH/HDPE‐g‐HI blends, it was found that an improved adhesion between the two components and finer dispersions were produced as a result of chemical reactions occurring during the melt blending. The depression of melting temperature of EVOH in the 10/90 EVOH/HDPE‐g‐HI blend indirectly indicated increased miscibility. The tensile strength of the EVOH/HDPE‐g‐HI blend was much higher than that of the EVOH/HDPE blend having no adhesion at each composition, and a dramatic increase in the impact strength was produced at the 90/10 EVOH/HDPE‐g‐HI blend composing of the fine HDPE‐g‐HI dispersions.
Evaluation of rheological properties of non‐newtonian fluids in internal mixers: An alternative method based on the power law model
Authors: Mallette J. Guillen , Soberanis R. Rios 
Published: April 2004

AbstractA new method was developed to evaluate rheological properties of polymer melts such as shear stress, shear rate, apparent viscosity and other rheological parameters in internal mixers. It is based on the classical power law model where the power law index n is directly evaluated from a set of data containing speed S, torque M, and the consistency index m is indirectly determined by an empirical relation. The method is based on a model with only one geometrical parameter (α), which involves a chamber radius R2 and an equivalent radius Re. It is assumed that the measuring head consists of two adjacent sets of coaxial cylinders. This method has advantages over previously reported models that use two parameters and do not propose a straightforward method to evaluate m. The pseudoplastic nature of the polymer melt decreases as the rate of loss of structural points, i.e., molecular entanglements and network junctions, increases, which produces greater mobility of the melt. A relationship between α and C(n) is found, which is simpler than other models previously reported. These results further demonstrate the feasibility of evaluating rheological properties of polymer melts in internal mixers.
Structural rearrangements during yielding of glassy polymers
Authors: Kontou E. , Spathis G. 
Published: April 2004

AbstractThe tensile yield and post yield behavior of polycarbonate (PC) are examined by means of a new experimental device, based on a noncontact measurement of the deformation. This method has the advantage of a detailed measurement of the deformation along the gauge length, which leads to the construction of the true stress‐strain curves of the material tested. Especially in the case of nonuniform deformation, where neck initiation and neck propagation occurs, the correct description of the intrinsic response of the material requires true stress‐strain plots. A viscoplastic model based on the fundamental assumptions of Eyring is used to describe the yield and post‐yield behavior of PC. The strain softening is attributed to a relaxation mechanism that was introduced in previous treatments, and this effect is supported by DSC tests. The theoretical results are compared with the results obtained by an elasto‐plastic model, developed elsewhere, and it is shown that the material follows a viscoplastic path in this deformation procedure.