bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture behavior of core‐shell rubber–modified clay‐epoxy nanocomposites
Authors: Gam K. T. , Miyamoto M. , Nishimura R. , Sue H. J. 
Published: April 2004

AbstractMorphology and fracture mechanisms in two nanoclay‐filled epoxy systems were investigated using both microscopy and spectroscopy tools. Clay exfoliation was achieved using a series of sample preparation steps, and confirmed using wide angle X‐ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Significant improvement in modulus was obtained when clay exfoliation was achieved. Incorporation of core‐shell rubber (CSR) in both caly‐filled epoxy systems leads to greatly enhanced fracture toughness. Optical microscopy and TEM observations of the CSR‐modified nanocomposites suggest that CSR cavitation. shear yielding of the matrix, clay layer delamination. CSR bridging, crack bifurcation. and crack deflection are among the operative toughening mechanisms observed, depending on the nature of the epoxy matrix utilized.
Influence of post‐extrusion parameters on the final morphology of polystyrene/high density polyethylene blends
Authors: Padilla‐Lopez H. , Vázquez M. O. , González‐Núñez R. , Rodrigue D. 
Published: April 2004

AbstractThe deformation of the dispersed phase in polystyrene/high density polyethylene (PS/HDPE) blends produced by ribbon extrusion was studied numerically and experimentally. A mathematical model for the deformation of the dispersed phase in ribbon extrusion processing of polymer blends was developed assuming uniaxial deformation of the ribbon and the equilibrium shapes of the dispersed particles with a pressure balance over a drop. Simulated morphologies as function of the post‐extrusion parameters were obtained and compared with experiments. The analysis of the ribbon extrusion process showed that parameters such as draw ratio (DR) and ribbon‐water contact length (X) significantly influence the ribbon dimensions, the extensional stress, and the stretching force. The results also showed that deformation and coalescence of the dispersed phase in the ribbon extrusion processing of polymer blends increase at higher DR and/or lower X values. The comparison between the model and the experimental morphologies of PS/HDPE produced a good agreement.
Compensating for die swell in the design of profile dies
Authors: Gifford W. A. 
Published: April 2004

AbstractBecause of the effects of die swell, the final shape of an extrudate is often substantially different from that of the exit opening of the die. As a result, the design of profile dies producing complex shapes often involves more than just “balancing” the die but also compensating for the effects of die swell. Typically, a successful design of such dies is achieved only through much “cut and try,” However, with the use of a fully three‐dimensional finite element flow algorithm along with quick mesh generating capabilities, the usual cut and try involved in the design of many profile dies can be greatly reduced, if not eliminated. This paper demonstrates how the effects of die swell can be compensated for in the design of profile dies. For profiles with one plane of symmetry, this includes compensating for the sideways translation of the extrudate as well as the change in shape that the extrudate experiences. Completely asymmetric profiles undergo a “twisting” downstream of the die. This twisting, which appears not to have been reported in the literature (at least for isothermal extrusion), is also accounted for here, along with the change in shape that the extrudate undergoes. The translation or twisting of profiles downstream of a die is often attributed to non‐Newtonian or non‐isothermal effects. Only isothermal Newtonian examples are considered here. These results clearly show that asymmetry of the profile will result in a translation and twisting of the extrudate even in the isothermal Newtonian case.
Preparation of strach‐graft‐polyacrylamide copolymers by reactive extrusion
Authors: Willett J. L. , Finkenstadt V. L. 
Published: April 2004

AbstractGraft copolymers of starch and polyacrylamide (PAAm) were prepared by reactive extrusion using a co‐rotating twin‐screw extruder and ammonium presulfate initiator. Feed rates were 109 g/min to 325 g/min (all components) at a moisture content of 50%, with screw speeds in the range 100 rpm to 300 rpm. Starch/acrylamide weight ratios ranged from 5:1 to 1.3:1. Conversions of acrylamide to PAAm were generally 80% or greater with residence times of 400 seconds or less. Conversion increased with feed rate, suggesting that reaction efficiency was proportional to the degree of fill in the extruder. Grafting efficiencies were in the range of 50% to 80%. PAAm molecular weight increased with increasing acrylamide content, consistent with free radical polymerization kinetics. Extrusion temperature had no significant impact on acrylamide conversion. Graft frequency, as measured by the number of anhydroglucose units per graft, was essentially constant over the starch: acrylamide ratio and temperature range studied. These results show that reactive extrusion offers the potential for rapid production of starch graft copolymers with unsaturated monomers.
Characterization of fractionated phenolic resins used in photoresists
Authors: Wanat Stanley F. , Rahman M. Dalil 
Published: April 2004

AbstractNovolak resins fractionated using a liquid/liquid centrifugal fractionation/separation technique were characterized and contrasted to resins fractionated by conventional methods. The new fractionation method resulted in higher yields of resins with comparable or improved functional properties when used in i‐line sensitive (365 nm) photoresist formulations. By characterizing the isolateld resin and the lower molecular weight (Mw) fractions removed during fractionation, a better understanding of the structural differences associated with the fractionation processes could be determined. The potential for improving the fractionation/separation process and for obtaining higher yields and more consistent resists with the resins was identified.
Layered silicate nanocomposites based on various high‐functionality epoxy resins. Part II: The influence of an organoclay on the rheological behavior of epoxy prepolymers
Authors: Becker Ole , Sopade Peter , Bourdonnay Romain , Halley Peter J. , Simon George P. 
Published: April 2004

AbstractThe effect of an organically surface modified layered silicate on the viscosity of various epoxy resins of different structures and different functionalities was investigated. Steady and dynamic shear viscosities of the epoxy resins containing 0–10 Wt% of the organoclay were determined using parallel plate rheology. Viscosity results were compared with those achieved through addition of a commonly used micronsized CaCO3 filler. It was found that changes in viscosities due to the different fillers were of the same order, since the layered silicate was only dispersed on a micron‐sized scale in the monomer (prior to reaction), as indicated by X‐ray diffraction measurements. Flow activation energies at a low frequency were determined and did not show any significant changes due to the addition of organoclay or CaCO3. Comparison between dynamic and steady shear experiments showed good agreement for low layered silicate concentrations below 7.5 wt%, i.e. the Cox‐Merz rule can be applied. Deviations from the Cox‐Merz rule appeared at and above 10 wt%, although such deviations were only slightly above experimental error. Most resin organoclay blends were well predicted by the Power Law model, only concentrations of 10 wt% and above requiring the Herschel‐Buckley (yield stress) model to achieve better fits. Wide‐angle X‐ray measurements have shown that the epoxy resin swells the layered silicate with an increase in the interlayer distance of approximately 15 Å, and that the rheology behavior is due to the lateral, micron‐size of these swollen tactoids.
Melting model for intermeshing counter‐rotating twin‐screw extruders
Authors: Wilczynski Krzysztof , White James L. 
Published: April 2004

AbstractPrevious experimental studies of melting of pellets in an intermeshing counter‐rotating twin‐screw extruder have shown that melting is initiated both between the screws and at the barrel. Models are developed for melting in both those regions. The melting between the screws is initiated by frictional work on the pellets by the calendering stresses between the screws. The melting action at the barrel is induced by a barrel temperature higher than the melting point and propagated by viscous dissipation heating of the melt film produced.
Structure‐property relationships of blends of polycarbonate
Authors: Cheah K. , Cook W. D. 
Published: April 2004

AbstractThree grades of bisphenol‐A polycarbonate—high molecular weight linear, high molecular weight branched and low molecular weight linear—and their blends have been studied by GPC, DMTA, DSC, rheometry and impact measurements. The molecular weight distribution of the blends agred with that predicted from the component's distributions, indicating that no transesterification reactions had occurred during melt blending. The Tg of the blends varied with blend composition according to the Fox equation and was related to the reciprocal molecular weight predicted by the Flory‐Fox equation. The low shear rate viscosity of the blends agreed with a logarithmic rule of mixtures and showed power‐law dependence on the weight average molecular weight. At higher shear rates, shear thinning was observed. The steady shear viscosity correlated well with the dynamic viscosity, as suggested by the Cox‐Merz relation. The stress relaxation behavior of the melt was very sensitive to the blend composition and molecular weight and correlated well with the real modulus. Temperature studies of the dart impact energy showed that only the low molecular weight polymer underwent a brittle‐duetile transition at ea −30°C and that all the blends were tough at room temperature. The enhanced stress triaxiality inherent in the notched lzod test caused the impact strenght at room temperature to decrease almost linealy with blend composition.
Relationship between segment structures and elastic properties of segmented poly(urethane‐urea) elastic fibers
Authors: Yoshihara Nori , Ishihara Hideaki , Yamada Toshiro 
Published: April 2004

AbstractStudies on segmented poly(urethane‐urea) (SPUU) elastic fibers having various segment structures were done in terms of elastic recovery and stress‐strain relationship (S‐S). Three kinds of segment structures were used: 1) the same composition having different sequences of segment units, 2) the same length of soft segments having different molecular weights of polyol, and 3) different segment structures having almost the same stress at 350% elongation. The SPUU elastic fibers having higher sequence numbers of both soft and hard segment units, that is, greater block structures, show better elastic recovery properties, especially delayed elastic recovery. The SPUU elastic fibers showing better elastic recovery take an optimum value for the number‐average molecular weight (Mn) of soft segments jointed with urethane bonds. Here the optimum Mn depends on the molecular weight of polytetramethyleneglycol (PTMG) as a starting material. The hysteresis loss in S‐S for the pre‐elongation decreases with an increase of Mn of PTMG. The SPUU elastic fibers having greater block structures show lower stress with lower 2C1 and 2C1 + 2C2 of Mooney‐Rivilin plot constants for elastic fibers having the same composition. This indicates a lower density of crosslinks for finite deformation. An increase of the urea bonds or the molar ratio of urea bond to urethane bond raises the stress. It is found that the polymerization process, as well as composition, is important for design structures of SPUU elastic fibers.
A rheological and morphological model for blends of flexible and rigid macromolecules
Authors: Edwards Brian J. , Williams Karen L. 
Published: April 2004

AbstractA model is developed that describes the complicated rheology and morphology of thermoplastic polymers blended with relatively small amounts of liquid‐crystalline polymers (LCPs). Such blends typically display properties superior to, but more complicated than, those of ordinary thermoplastic polymers. Viscosity predictions are obtained with this model that exhibit the wide range of behavior that is observed experimentally in these blended materials for both shear and elongational flows. For example, the viscosity‐composition curve can display a minimum at low compositions of LCP, and the addition of an LCP to a thermoplastic polymer can result in a reduction in the shear viscosity but an increase in the elongational viscosity. Corresponding morphological descriptions are also obtained for the internal microstructure of the blends that provide information about the underlying causes of the complicated rheological behavior.
Melt strength and extensibility of talc‐filled polypropylene
Authors: McInerney L. F. , Kao N. , Bhattacharya S. N. 
Published: April 2004

AbstractPolypropylene homopolymer melts containing up to 50 percent by weight of talc filler (24 vol%) were tested on a Gottfert Rheotens melt strength testing unit. Melt strength and drawability parameters were measured from these tests to evaluate changes in the extensional behavior of the melt induced by filler addition. It was found that the melt strength of the polypropylene was decreased for talc additions of less than 40 wt% (17.5 vol%) under all test conditions. Addition of 50 wt% talc improved the melt strength under all testing conditions. Drawability, defined as the stretch ratio at strand break, decreased with increased filler loading. The melt strength of all materials was found to decrease with increased temperature within the range 180°C to 210°C. The melt strength of all melts showed dependence on the test extrusion rate, and this dependence was well described by an exponential relationship. Highest dependencies were seen for the unfilled and 50 wt% talc‐filled polymer. While it was found that addition of 50 wt% talc provided improvement in melt strength, high melt strength alone was a poor indicator of the melt processability, as drawability was also regarded as an important consideration.
Methyl methacrylate modification of polyolefin in a batch mixer and a twin‐screw extruder experiment and kinetic model
Authors: Cha Jaehyug , White James L. 
Published: April 2004

AbstractFree radical grafting with methyl methacrylate onto molten polypropylene was investigated in both an internal mixer and a modular co‐rotating twin‐screw extruder. There has been little open literature on melt free radical grafting copolymerization of methyl methacrylate. There is also little information on the evolution of grafting reaction with respect to reaction time in an internal mixer and along the screw axes with methyl methacrylate. The influence of residence time on the degree of grafting in an internal mixer and a twin‐screw extruder was studied through measuring reaction yields with respect to reaction time in a mixer and evolution of reaction yield along the screw axis. The degree of grafting increased with initial monomer and peroxide concentration. The grafting reactions with three different peroxides were also investigated. The grafting levels were similar to maleic anhydride and suggested that only an individual methyl methacrylate unit be grafted. The melt viscosity was dramatically reduced with addition of peroxide. A kinetic scheme of our reaction system for methyl methacrylate was proposed and compared with the experimental results.
Rheology and extrusion of medical‐grade thermoplastic polyurethane
Authors: Lu Guangyu , Kalyon Dilhan M. , Yilgör Iskender , Yilgör Emel 
Published: April 2004

AbstractThe selection of operating conditions and geometry for the processing of thermoplastic polyurethane, TPU, is a complicated task. This complication arises from the relatively high melting temperature of the crystalline hard blocks and the oxidative and thermal degradation and crosslinking that occur at temperatures that are relatively close to the melting temperature of the TPU. This article documents the rheology, extrusion, and structure development of a medical‐grade TPU. The medical application requires that the additives commonly utilized in the development of polymeric resins, i.e., stabilizers, antioxidants, and lubricant, should be minimized; the TPU of this study contains no additives. At temperatures 10–20°C lower than the melting temperature of the TPU, the morphology of the hard blocks continues to evolve to generate a reversible increase in elasticity and shear viscosity of the TPU with increasing time. At temperatures greater than the melting temperature, the TPU undergoes degradation and crosslinking reactions, which give rise to a permanent increase in the elasticity and the shear viscosity of the TPU. The ramifications of the degradation and crosslinking at temperatures greater than 200°C and morphology modification upon the continuing evolution of the hard blocks at temperatures less than 200°C on the rheology and processing were investigated.
Quantitative determination of short‐chain branching content and distribution in commercial polyethylenes by thermally fractionated differential scanning calorimetry
Authors: Zhang Mingqian , Wanke Sieghard E. 
Published: April 2004

AbstractA method for rapid quantitative analysis of the content and distribution of short chain branching (SCB) for α‐olefin/ethylene copolymers based on thermally fractionated DSC is presented. Eight commercial polyethylenes, four made with conventional Ziegler‐Natta catalysts and four made with metallocene catalysts, were analyzed by differential scanning calorimetry (DSC), after having been thermally segregated by successive nucleation annealing (SNA). The polyethylenes were also analyzed by temperature rising elution fractionation (TREF) and carbon‐13 nuclear magnetic resonance (13C‐NMR). The SNA‐DSC procedure segregates polyethylenes according to methylene sequence lengths (MSL). The relationship between DSC melting temperature and SCB content was obtained by calibration with linear hydrocarbons; TREF results were not used in the SNA‐DSC calibration. Deconvolution of the SNA‐DSC endotherms yielded estimates of the average SCB contents and SCB distributions. The SCB contents obtained from the SNA‐DSC for linear low density polyethylenes agreed very well with the SCB contents obtained by 13C‐NMR and TREF, and the SCB distributions measured by SNA‐DSC were very similar to those obtained by TREF. The SCB contents obtained by SNA‐DSC for ultra‐low density polyethylenes, made with metallocene catalysts, were about 20% lower than the values obtained by 13C‐NMR; the values obtained by TREF were even lower.
Crystallization of poly(butylene terephthalate)
Authors: di Lorenzo M. L. , Righetti M. C. 
Published: April 2004

AbstractThis article provides a thorough analysis of the crystallization process of poly(butylene terephthalate) (PBT). Isothermal crystal growth rates have been experimentally measured between 459 and 491 K, and analyzed according to the Hoffman and Lauritzen theory. A II–III regime transition occurs at 484 K, accompanied by a change in crystal morphology. By means of a non‐linear fitting procedure, precise values of the nucleation constant Kg were obtained. The lateral surface free energy σ was calculated and, from this, the α parameter of the Thomas‐Staveley expression was obtained.
Preparation and characterization of polystyrene‐based magnetic nanocomposites. Thermal, mechanical and magnetic properties
Authors: López Daniel , Cendoya Ione , Torres Francesc , Tejada Javier , Mijangos Carmen 
Published: April 2004

AbstractIn this paper we report results on both material preparation and characterization of a polystyrene‐based magnetic nanocomposite material. CoFe204 mineralized sulfonated polystyrene was prepared by in‐situ precipitation and oxidation of Co+2 and Fe+2 within a sulfonated polystyrene resin. The magnetic oxide particles of nanometer size were characterized by wide angle X‐ray diffraction (WAXD). Polystyrene‐based composite films were obtained by dispersion of the finely milled mineralized resin in a polystyrene matrix from the melt state (compositions ranging from 0 to 50 wt% of mineralized resin). The thermal and mechanical properties of the nanocomposite films were determined by TGA, DSC, and stress‐strain testing. The magnetic characterization of the samples was also performed. No significant changes in thermal stability, glass transition temperature or mechanical properties of the polystyrene matrix occur as a consequence of the content in mineralized resin. These results show that the filler acts as aninert diluent for the polymer matrix. On the other hand, the magnetic characterization of the samples reveals the presence of nanoparticles with diameters ranging from 3 to 8 nm, showing, at room temperature, coercive field values of around 800 Oe and saturation magnetization between 120 and 420 emu/g. The combination of these properties suggests the use of these systems in the preparation of magnetic recording materials with high recording density.
Chemorheology of model filled rubber compounds during curing
Authors: Cai Jianfen J. , Salovey Ronald 
Published: April 2004

AbstractThe rheological behavior and crosslinking kinetics of model filled rubber compounds during curing were investigated. The effect of chemical composition of monodisperse size particles, prepared by emulsifier‐free emulsion polymerization, on dynamic moduli and gelation time of the filled compounds was studied. All filled systems showed much shorter gelation times than the pure matrix in the order PSVP < PS < PMMA ≪ Pure Matrix. The dynamic moduli during curing increased with increasing interactions between particles and matrix. Physical crosslinking, due to either particle clustering or a network of filler particles with an adsorbed polymer layer, made a significant contribution to the overall crosslink density and the gelation of rubber compounds. As a result, the dynamic mechanical properties and curing kinetics of the rubber compounds varied with the chemical nature of the filler particles.
Role of coupling microscopic and macroscopic phenomena during the crystallization of semicrystalline polymers
Authors: Prabiiu N. , Schultz J. , Advani S. G. , Jacob K. I. 
Published: April 2004

AbstractIn this work a microscopic cell model of crystallization incorporating solute rejection is coupled with the macroscopic heat transfer using a finite element procedure to study the evolution of crystallinity. The role of coupling is analyzed using two contrasting polymers, polyethylene and polystyrene. Simulations of the solidification were carried out using both the coupled and the uncoupled formulations to elucidate the effect of coupling. Both polymeric systems considered were affected by this coupling on the evolution of the crystallinity; however, the initial solute content has more effect on the slower crystallizing system. An incremental stress model is also applied to predict the residual stresses generated during the crystallization of the two polymeric systems. It was found that the predicted residual stresses are significantly affected by coupling. Good agreement with experimental results was observed for crystallization half‐time results from the coupled solution by incorporating solute segregation effects for high undercooling, but the deviation was more significant at lower undercooling. For the slow‐crystallizing polymer, fair agreement was observed irrespective of the degree of undercooling. The results show that the solute segregation has only a secondary influence on these systems, especially compared to the effect of undercooling.