bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combinatorial methods for polymer materials science: Phase behavior of nanocomposite blend films
Authors: Karim Alamgir , Amis Eric , Yurekli Koray , Krishnamoorti Ramanan , Meredith Carson 
Published: April 2004

AbstractPolymer materials are often mixed with inorganic materials in the bulk to enhance properties, including mechanical, electrical, thermal, and physical. Such property enhancements are induced not only by the physical presence of the filler but also significantly by the interaction of the polymer with the filler via altering the local properties of the polymer material. In this regard, recently layered silicate nanocomposites have been shown to be effective in modifying the polymer properties because of their high surface area of contact between the polymer and the high aspect ratio nanoparticle. Potential property enhancements should also occur in polymer nanocomposite thin films owing to nanoparticle orientation from film confinement effects. In this paper we investigate the effect of layered silicate nanoparticles on the phase behavior of a classic polymer blend using small angle neutron scattering and compare those results to phase diagrams obtained by high throughput combinatorial methods.
Manipulating the microstructure and rheology in polymer‐organoclay composites
Authors: Gelfer Michael , Avila‐orta Carlos , Liu Lizhi , Yang Ling , Chu Benjamin , Hsiao Benjamin S. , Song Hyun H. , Si Mayu , Rafailovich Miriam , Tsou Andy H. 
Published: April 2004

AbstractA series of nanocomposites prepared by melt‐blending of cloisite‐based organoclays with poly(ethylene‐vinylacetate) (EVA) and neutralized poly (ethylene‐methacrylic acid) (EMA) copolymers were investigated via DSC, small‐angle X‐ray scattering (SAXS), and rheological techniques. SAXS results indicated partial clay exfoliation in all samples. In both EMA and EVA systems, the nominal melting temperature Tm and bulk crystallinity are not significantly affected by the presence of organoclays, suggesting that clay particles are predominantly confined in the amorphous phase. In rheological measurements (above Tm), the EVA‐clay system demonstrated a solid‐like rheological behavior under the small‐strain oscillatory shear, yet it was able to yield and flow under a steady shear, which is the characteristic of physical crosslinking. In contrast, the EMA‐clay system exhibited a melt‐like rheological behavior, where the influence of organoclay on the thermorheological behavior of the EMA composite was quite minimal. We propose that the carbonyl groups of vinylacetate in EVA interact with the clay surface, resulting in a strong physically crosslinking like interaction in the melt. On the other hand, the interaction between EMA and clay is weak because of repulsion between carboxyl anions and negatively charged clay surface.
Moisture diffusion through vinyl ester nanocomposites made with montmorillonite clay
Authors: Shah Apoorva P. , Gupta Rakesh K. , Gangarao Hota V. S. , Powell Clois E. 
Published: April 2004

AbstractMoisture diffusion was studied through vinyl ester samples containing up to 5 wt% of organically treated montmorillonite. Two different kinds of clay surface treatment were employed to make the clay compatible with DerakaneTM 411‐350 vinyl ester resin. The nanocomposites were characterized using differential scanning calorimetry (DSC), mechanical property measurements, X‐ray diffraction (XRD) and transmission electron microscopy (TEM). TEM pictures showed that the clay platelets were either exfoliated or intercalated, and the two different surface treatments resulted in different dispersion characteristics. All the samples were post cured, and the diffusivity of moisture was measured by soaking the samples in 25°C water and noting the increase in weight with increasing time of immersion. It was found that water diffusivity decreased with increasing clay content, and it was reduced to half its value in the neat resin when the clay content was only 1 wt% regardless of the nature of clay surface treatment. However, the equilibrium moisture content, the glass transition temperature, and the elastic modulus all increased with increasing amounts of clay.
The effect of pressure and clay on the crystallization behavior and kinetics of polyamide‐6 in nanocomposites
Authors: Kamal M. R. , Borse N. K. , Garcia‐Rejon A. 
Published: April 2004

AbstractThe crystallization kinetics of polyamide‐6 (PA‐6) and its nanocomposite (PNC) with 2% clay were studied, using a pressure dilatometer (50 MPa to 200 MPa) to follow the volume changes associated with the crystallization process. Isobaric experiments were carried out to evaluate the effect of pressure and clay on melting temperature (Tm) and crystallization temperature (Ta) of PA‐6. The melting temperatures of PA‐6 in the PNC were very close to those of PA‐6 alone at comparable pressures, but the crystallization temperatures in the PNC were lower than those of PA‐6 alone. The materials exhibited two crystallization zones in isothermal/isobaric experiments. The initial zone involved both the γ‐form and the α‐form of PA‐6, while in the latter zone the γ‐form was dominant. The Avrami equation was used to fit the isothermal/isobaric crystallization data. The Avrami exponent n was between 1.0 and 3.2 for the γ‐form of unfilled PA‐6, between 0.9 and 2.6 for the γ‐form in PNC and for the γ‐form of PA‐6 alone, n was between 1.0 and 2.1 and in PNC between 1.2 and 2.6. The Avrami rate constants (K) for PA‐6 and PNC depend on the experimental crystallization temperature as well as pressure. The rate of crystallization under similar conditions was higher for PNC. Infrared studies on compression molded PA‐6 and PNC samples, cooled from melt at different rates, confirm the formation of the γ‐form in the initial stages of crystallization, as well as its transformation into the α‐form at later stages. In the case of PNC, the γ‐form stabilized when the sample was quenched from melt.
Impact and wear resistance of polymer nanocomposites at low filler content
Authors: Wetzel Bernd , Haupert Frank , Friedrich Klaus , Zhang Ming Qiu , Rong Min Zhi 
Published: April 2004

AbstractIt is well known that inorganic filler particles enhance the mechanical and tribological properties of polymers. The stiffness, toughness, and wear performance of the composites are extensively determined by the size, shape, volume content, and especially the dispersion homogeneity of the particles. In the present study, various amounts of micro‐ and nano‐scale particles (titanium dioxide TiO2, 200–400 nm, calcium silicate CaSiO3, 4–15 μm) were introduced into an epoxy polymer matrix for its reinforcement. The influence of these particles on the impact strength, dynamic mechanical thermal properties, and block‐on‐ring wear behavior was investigated. Using only the nano‐particles, the results demonstrate the best improvement in stiffness, impact strength, and wear resistance of the epoxy at a nano‐particle content of 4 vol% TiO2. Therefore, this nanocomposite was used to act as a matrix for the CaSiO3 micro‐particles, in the hope of finding synergistic effects between the micro‐ and the nano‐particles. Results show, in fact, a further improvement of wear resistance and stiffness, whereas the impact strength suffers. Geometrical properties of the particles, the homogeneous dispersion state, energy dissipating fracture mechanisms, and a transition of wear mechanisms mostly contribute to the increase in performance.
Biodegradable polyester layered silicate nanocomposites based on poly(ϵ‐caprolactone)
Authors: Pantoustier Nadège , Lepoittevin Bénédicte , Alexandre Michaël , Dubois Philippe , Kubies Dana , Calberg Cédric , Jérôme Robert 
Published: April 2004

AbstractNanocomposites based on biodegradable poly(ϵ‐caprolactone) (PCL) and layered silicates (montmorillonite, MMT) were prepared either by melt interaction with PCL or by in situ ring‐opening polymerization of ϵ‐caprolactone as promoted by the so‐called coordination‐insertion mechanism. Both non‐modified clays (Na+ ‐MMT) and silicates modified by various alkylammonium cations were studied. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. Even at a filler content as low as 3 wt% of inorganic layered silicate, the PCL‐layered silicate nanocomposites exhibited improved mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as a result of a charring effect. It was shown that the formation of PCL‐based nanocomposites depended not only on the nature of the ammonium cation and related functionality but also on the selected synthetic route, melt intercalation vs. in situ intercalative polymerization. Interestingly enough, when the intercalative polymerization of ϵ‐caprolactone was carried out in the presence of MMT organo‐modified with ammonium cations bearing hydroxyl functions, nanocomposites with much improved mechanical properties were recovered. Those hybrid polyester layered silicate nanocomposites were characterized by a covalent bonding between the polyester chains and the clay organo‐surface as a result of the polymerization mechanism, which was actually initiated from the surface hydroxyl functions adequately activated by selected tin (II) or tin (IV) catalysts.
Effect of marangoni stresses on the deformation and coalescence in compatibilized immiscible polymer blends
Authors: Van Puyvelde Peter , Velankar Sachin , Mewis Jan , Moldenaers Paula , Leuven K. U. 
Published: April 2004

AbstractThe effect of physical compatibilization on the deformation and coalescence of droplets in immiscible polymer blends is discussed. Evidence is provided for the existence of concentration gradients in block copolymers along the interface during deformation. This causes complex changes in droplet shapes during deformation and relaxation. These concentration gradients also result in Marangoni stresses, which stabilize the droplets against deformation and breakup. Coalescence experiments have been performed, varying both the compatibilizer concentration and the shear rate. Existing coalescence models have been evaluated. An empirical extension of Chesters' partially mobile interface model is presented, that treats the effects of Marangoni stresses on the coalescence process as a higher effective viscosity ratio.
Online light scattering measurements: A method to assess morphology development of polymer blends in a twin‐screw extruder
Authors: Schlatter G. , Serra C. , Bouquey M. , Muller R. , Terrisse J. 
Published: April 2004

AbstractLight scattering has proved itself an efficient technique to determine particle diameters in heterogeneous dilute dispersions in the micrometer range. Extrusion of polymer blends is expected to give rise to very small particles, typically in the range from hundreds of nanometers to tens of micrometers. A light scattering device developed in our laboratory has been used to study the morphology of polymer blends obtained in a twin‐screw extruder. The main advantage of this technique is the immediate response obtained without any surface or interface modification that can occur during the sample preparation by using more conventional techniques like electron microscopy. To show the possible applications of this light scattering device, preliminary tests have been carried out. First, we present a comparison between experimental measurements and theoretical results for dilute systems. Second, we have investigated the effect of shear flow on the droplet deformation. Finally, we have studied the variations of the light scattering pattern for a reactive blend.
Monitoring the evolution of the properties of PA‐6/EPM‐g‐MA blends in a twin‐screw extruder
Authors: Machado A. V. , Covas J. A. , Van Duin M. 
Published: April 2004

AbstractThe evolution of the properties of PA‐6/EPM‐g‐MA blends are investigated along a twin‐screw extruder in terms of chemical conversion, morphology development, and rheology evolution. Despite the interfacial structure of the various blends with different composition being distinct, an important decrease of the MA content at the first kneading zone from 0.5 to approximately 0.1 wt.% MA and only a slight decrease further downstream is generally observed. In all cases in‐situ compatibilization reactions occur in the melting zone within a few seconds. The relative differences in morphology can be directly explained by differences in blend composition. Although the morphology development along the extruder of the various blends as monitored by electron microscopy seems to follow a pattern similar to that of chemical conversion, their viscoelastic response shows a more gradual evolution.
Effect of styrene‐butadiene triblock copolymer structure on its compatibilization efficiency in PS/PB and PS/PP blends
Authors: Horák Z. , Hlavatá D. , Fortelný I. , Lednický F. 
Published: April 2004

AbstractTwo styrene‐butadiene triblock copolymers differing in the length of their styrene blocks (40S‐60B‐40S and 10S‐60B‐10S) were used as compatibilizers for PS/PB (4/1) and PS/PP (4/1) blends. The supramolecular structure of the copolymers determined by small‐angle X‐ray scattering (SAXS), morphology of the blends using transmission electron microscopy (TEM), and their tensile impact strength were chosen as criteria of the compatibilization efficiency of the copolymers used. Different mechanisms of compatibilization for “symmetrical” system (PS/PB/SBS) and “asymmetrical” system (PS/PP/SBS) were proved. While for the PS/PB blend, the 40S‐60B‐40S copolymer proved to be a good compatibilizer, for the PS/PP blend, surprisingly, the 10S‐60B‐10S copolymer is more efficient.
Thermal and morphological evaluation of very low density polyethylene/high density polyethylene blends
Authors: Arnal Maria Luisa , Cañizales Edgar , Müller Alejandro J. 
Published: April 2004

AbstractBlends of very low density polyethylene (VLDPE) and high density polyethylene (HDPE) were prepared by melt extrusion. These blends exhibit a tendency to phase segregate when they are slow cooled from the melt. If they are cooled at increasingly faster rates, a finite population of co‐crystals can be isolated from the rest of the phase segregated material, indicating that this system is probably miscible in the melt but phase separates during cooling. Transmission electron microscopy observations are consistent with the blend melt miscibility since inter‐lamellar mixing was clearly appreciated in the samples examined. Other effects arising from interactions between the polymers were the nucleation of VLDPE rich phase by HDPE rich phase, and a melting point depression of HDPE rich phase caused by a dilution effect exerted by molten VLDPE rich phase. After a successive self‐nucleation and annealing thermal fractionation procedure is applied to the blends, phase separation dominates the behavior, although some small fraction of co‐crystals was still present.
A lithium ionomer of poly(ethylene‐co‐methacrylic acid) copolymer as compatibilizer for blends of poly(ethylene terephthalate) and high density polyethylene
Authors: Retolaza A. , Eguiazábal J. I. , Nazábal J. 
Published: April 2004

AbstractBlends of 75/25 poly(ethylene terephthalate) (PET)/high density polyethylene (HDPE) containing poly(ethylene‐co‐methacrylic acid) partially neutralized with lithium (PEMA‐Li) were obtained by direct injection molding in an attempt (i) to ameliorate the poor performance of the binary blend and (ii) to find the best compatibilizer content. The presence of PEMA‐Li caused a nucleation effect on PET, and a decrease in the crystalline content of HDPE. The compatibilizing effect of PEMA‐Li was due to the combined effects of interaction at the interface and chemical reactions. The ternary blends showed a complex morphology, with two dispersed HDPE and PEMA‐Li phases that contained a small internal dispersed phase, probably of PET. The compatibilizing effect of PEMA‐Li was clearly shown by means of an impressive increase in the ductility and to a minor extent in the impact strength. The highest property improvement (ductility increase 1450%) appeared upon the addition of 45% PEMA‐Li with respect to the HDPE phase, but taking into account the recycling interest, the ternary blend with the addition of roughly 22.5% PEMA‐Li appears to be the most attractive.
Linear viscoelastic and transient behavior of polypropylene and ethylene vinyl acetate blends: An evaluation of the linear Palierne and a nonlinear viscoelastic model for dispersive mixtures
Authors: Tyagi Sandeep , Ghosh Anup K. , Montanari P. , Peters G. W. M. , Meijer H. E. H. 
Published: April 2004

AbstractBlends of polypropylene/ethylene vinyl acetate (PP/EVA) have been investigated for linear and transient characteristics. The emulsion model developed by Palierne in 1990 is used to characterize the linear viscoelastic properties of the blends. PP/EVA blends with the viscosity ratio of 0.26 and different compositions, such as 90/10, 80/20 and 70/30 wt% PP/EVA have been studied. It was found that the Palierne Model predicts well the linear behavior of all the compositions studied. At low frequencies, some deviation in dynamic moduli was found in case of the 70/30 composition. Structural changes are studied during transient shear flow (step‐up) experiments. A nonlinear rheological model for blends, developed by Peters, Hansen and Meijer (PHM model), is used to describe these transient rheological data. Overshoots and undershoots observed in the experimental data are compared to numerical results obtained with PHM model and explained on the basis of the deformation of the dispersed phase. A modification of the model is proposed in order to get a better description of the behavior of the viscoelastic blend. Predictions of the morphological evolution of the blends under stepwise increase in shear rate experiments were calculated from the modified model and are found to describe the break‐up phenomenon under moderately high shear flow.
Steady and transient flow of a non‐Newtonian chemically reactive fluid in a twin‐screw extruder
Authors: Zhu W. , Jaluria Y. 
Published: April 2004

AbstractThe flow of chemically reactive non‐Newtonian materials, such as bio‐polymers and acrylates, in a fully intermeshing, co‐rotating twin‐screw extruder is numerically investigated. A detailed study of the system transient behavior is carried out. The main transient aspects, including response time, variation of system variables, and instability of operation, are studied for both single‐ and twin‐screw extruders, since single‐screw extruder modeling closely approximates the region away from the intermeshing zone in a twin‐screw extruder. The effect of a time‐dependent variation in the boundary conditions is studied. The coupling due to conduction heat transfer in the screw barrel is found to be very important and is taken into account for single‐screw extruders. In the absence of this conjugate coupling, the response time is much shorter. Several other interesting trends are obtained with respect to the dependence of the transient response on the materials and operating conditions. Steady state results are obtained at large time. The calculated velocity distributions in the screw channel are compared with experimental results in the literature for steady state flow and good agreement has been obtained. The calculated results for transient transport agree with the few experimental observations available on this system. Chemical reaction, leading to chemical conversion of the material, is also considered and the resulting effects on the flow and transport determined. These results will be useful in the design, control and optimization of polymer extrusion processes.
Melting behavior, crystallization kinetics and morphology of random copolyesters of poly(2‐hydroxyethoxybenzoate) with ε‐caprolactone
Authors: Finelli Lara , Siracusa Valentina , Lotti Nadia , Munari Andrea 
Published: April 2004

AbstractThe melting behavior after isothermal crystallization and the crystallization kinetics of random poly(2‐hydroxyethoxybenzoate/ε‐caprolactone) copolymers rich in 2hydroxyethoxybenzoate units were investigated by means of differential scanning calorimetry and hot‐stage optical microscopy. The observed multiple endotherms, which are commonly displayed by polyesters, were found to be influenced both by crystallization temperature and composition. By applying the Hoffman‐Weeks method to the melting temperatures of isothermally crystallized samples, the equilibrium melting temperatures of the copolymers were obtained. Furthermore, isothemal crystallization kinetics was analyzed according to the Avrami treatment. Values of the exponent n close to 3 were obtained, independently of crystallization temperature and composition, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three‐dimensional spherulitic growth. Space‐filling banded spherulites were observed by hot‐stage optical polarizing microscopy at all the crystallization temperatures explored, the band spacing being affected by both crystallization temperature and composition. As expected, the introduction of ε‐caprolactone comonomeric units in the polymer chain of PHEBA was found to decrease its crystallization rate.
Sequential injection molding of thermoplastic polymers. Analysis of processing parameters for optimal bonding conditions
Authors: Carella A. R. , Alonso C. , Merino J. C. , Pastor J. M. 
Published: April 2004

AbstractA systematic approach was used to study the effect of the process variables that control bonding of the injected melt to the previously injected parts, in sequential injection molding of thermoplastic polymers. Three polymer pairs were sequentially injected in a mold with the same geometry, in a range of mold and injected melt temperatures, and packing pressure conditions. Standard Peel Tests were conducted on injected samples to measure the resulting bonding strength. The analysis of the experimental results allows the quantification of the relative importance of the processing parameters involved. A direct correlation is found between the calculated interface temperature and the packing pressure needed for bonding. A generalized procedure is proposed to establish the processing conditions, which allow polymerpolymer bonding to be optimized.
Development of a two‐stage, dual‐Arrhenius rheology model for a high‐performance phenylethynyl‐terminated poly(etherimide)
Authors: Bullions Todd A. , McGrath J. E. , Loos A. C. 
Published: April 2004

AbstractA two‐stage, dual‐Arrhenius rheology model was successfully utilized to model the isothermal complex viscosity of a phenylethynyl‐terminated poly(etherimide) as a function of time and temperature over the experimental temperature range of 325°C to 350°C. Union of the dual‐Arrhenius model with a previously developed combination reaction kinetics model provided a chemoviscosity model giving viscosity as a function of degree of cure. A two‐stage, versus a single, dual‐Arrhenius model was used to accommodate a transition in the reaction process from chain growth to branching and network forming that was found to onset around a degree of cure of 0.37. The reduction in chain mobility brought on by branching and networking was quantified by the almost order of magnitude increase in the apparent activation energy for initial viscosity from the chain growth stage to the networking stage. The calculated apparent activation energies for gelation for the first and second stages, 2.14 × 105 J/mol and 2.05 × 105 J/mol, respectively, agree well with results presented elsewhere from differential scanning calorimetry measurements. The experimental procedures followed to obtain the rheological data and the construction of the model from these data are described; the predictions of the model are compared with experimental results.