bluuebunny/crossref_metadata_2025 huggingface dataset:
Blends of a bottle‐grade polyethylene terephthalate copolymer with a liquid crystalline polymer. Part II: Thermal and transport properties
Authors: Da Silva L. B. , Marinelli A. L. , Bretas R. E. S. , Rúvolo‐filho A.
Published: April 2004

In this work the thermal and transport properties of dichloromethane in blends of a bottle‐grade polyethylene terephthalate copolymer, PET, and a liquid crystalline polymer, LCP, were measured. Thermal characterizations of the blends were made by modulated differential scanning calorimetry and dynamic mechanical thermal analyses. An approximated LCP “bulk orientation” was also calculated by wide angle X‐ray diffraction. The morphology was analyzed by scanning electron microscopy. The resulting sorption curves of pure PET, and the B20, B40 and B60 blends were sigmoid type curves, while the sorption curve of the B80 blend was a two‐stage type curve. The diffusion coefficients of the B20 and B40 blends were found to be the lowest of all the blends. These low diffusivities were attributed to the occurrence of strong long‐range and short‐range interactions between the PET and the LCP in the B20 and B40 blends, and also to the perfection of the PET crystals in the B20 blend.
Formation of a polyetheramide triblock copolymer by reactive extrusion; process and properties
Authors: Lee Byung H. , White James L.
Published: April 2004

The synthesis of polyetheramide, containing poly(tetramethylene ether) (PTMEG) as the soft segment phase and polylactams as the hard phase was carried out in a Leistritz modular intermeshing counter‐rotating twin‐screw extruder in a one‐step, solvent‐free process. No by‐product such as carbon dioxide or H2O is formed during the reaction procedure. Isocyanate‐terminated telechelic PTMEG was premixed with caprolactam, and these were fed into the twin‐screw extruder to form the polyetheramide triblock copolymer. This triblock copolymer has not been previously polymerized in a twin‐screw extruder or continuous mixer. Subsequent to polymerization, the copolymer and PA6 homopolymer were also melt‐spun into fibers. Molecular weights and molecular weight distributions were determined by GPC on trifluroacetylated samples. Thermal, rheological, mechanical, and structural properties were investigated. It appears that phase separation (arising from immiscibility between the polyether segment and the polyamide segment as the reaction proceeds) did not hinder the chemical reaction between the two reactants because of the intense mixing in the twin‐screw extruder. The new triblock copolymer should have application as a rubber‐toughened thermoplastic or thermoplastic elastomer depending upon the elastomer content.
Thermoplastic polyurethanes (TPUs) with grafted organosilane moieties: A new way of improving thermomechanical behavior
Authors: Dassin Stéphane , Dumon Michel , Mechin Françoise , Pascault Jean‐pierre
Published: April 2004

Organosilanes were grafted on thermoplastic polyurethanes (TPUs) using an internal mixer or reactive extrusion. The reaction described here proceeds in two stages, with the help of a diisocyanate as a coupling agent to create allophanate junctions between TPU chains and an aminosilane. Such materials could then be crosslinked by a hydrolytic condensation mechanism, resulting in increased thermomechanical properties. The starting TPU was at first carefully characterized. Using the plastograph, the different stages (reactions between TPU and diisocyanate, isocyanate‐grafted TPU and aminosilane, but also between TPU and aminosilane alone) were then studied separately, together with the influence of several essential parameters (time, temperature, rotating speed, etc.). Optimal conditions for a well‐controlled grafting process were defined, and the different ways of crosslinking the TPU chains were compared.
Effect of crosslinking on the positive temperature coefficient stability of carbon black‐filled HDPE/ethylene‐ethylacrylate copolymer blend system
Authors: Lee Gun Joo , Han Moon Gyu , Chung Su Chul , Suh Kyung Doh , Im Seung Soon
Published: April 2004

Carbon black‐filled high‐density polyethylene (HDPE)/ethylene ethylacrylate copolymer (EEA) blends were prepared and the effect of crosslinking of the blends on the positive temperature coefficient (PTC) stability was investigated. By irradiation and silane‐crosslinking methods, crosslinked composites with various degrees of crosslinking were obtained. Crosslinking of the matrix polymer led to the disappearance of the negative temperature coefficient (NTC) phenomenon. Also, the PTC intensity increased with an increasing degree of crosslinking. The PTC stability of silane‐crosslinked samples was notably improved at heat cycles of 140°C. This was sufficiently improved by both the silane‐ and radiation‐crosslinking methods when they were treated at 85°C. Therefore, the limiting temperature of self‐regulating heat is about 85°C. Both radiation‐ and silane‐crosslinked samples are thought to be of use to the industry.
High performance films: Review of new materials and trends
Authors: Friedman Michael , Walsh Gerard
Published: April 2004

This paper reviews some modern aspects and trends in the development of high performance polymer materials and processing technologies providing fabrication of advanced film and film structures. Changes in understanding of technical requirements and properties, along with novel approaches in creating high performance films of various thermoplastic materials, are discussed. The most important groups of polymer materials being used in high performance applications are described.
Polypropylene/Clay nanocomposites: Effect of compatibilizer on the thermal, crystallization and dynamic mechanical behavior
Authors: Hambir Sangeeta , Bulakh Neelima , Jog J. P.
Published: April 2004

Polypropylene (PP)/clay nanocomposites are prepared using different grades of PP, compatibilizers, and organically modified clays. The melt intercalation of the PP is carried out in presence of a compatibilizer. The nanocomposites are characterized using various techniques for the structure and properties. X‐ray diffraction results indicate well‐defined structures. Thermogravimetric analysis indicates improved thermal stability of PP/clay nanocomposites. Isothermal crystallization studies carried out using differential scanning calorimeter illustrate enhanced crystallization of PP in all the nanocomposites. Optical microscopic study demonstrates that the nanocomposites can be crystallized at higher temperatures, exhibiting well‐defined birefringent structures. The dynamic mechanical analysis reveals higher storage moduli over a temperature range of −400C to 1200C for nanocomposites, and the extent of increase in the storage modulus is dependent on the type of compatibilizer used.
High performance epoxy‐layered silicate nanocomposites
Authors: Kornmann X. , Berglund L. A. , Thomann R. , Mulhaupt R. , Finter J.
Published: April 2004

High performance epoxy‐layered silicate nanocomposites based on tetra‐glycidyl4,4'‐diamino‐dipheny1 methane (TGDDM) resin cured with 4,4'‐diaminodipheny1 sulfone (DDS) have been successfully synthesized. Fluorohectorites modified by means of interlayer cation exchange of sodium cations for protonated dihydro‐imidazolines and octadecylamine were used. Fluorohectorite exchanged with 1‐methy12‐norsteary1‐3‐stearinoacid‐amidoethy1‐dihydro‐imidazolinium ions was immiscible with the epoxy matrix. In contrast, fluorohectorites exchanged with hydroxyethy1‐dihydro‐imidazolinium (HEODI) and riciny1‐dihydro‐imidazolinium ions (RDI) favored the formation of a nanocomposite structure. This is most likely due to the presence of ‐OH groups in their molecular structure, which has a catalytic effect on the polymerization occurring between the silicate layers. The diffusion of epoxy and curing agent molecules between the silicate layers is also promoted. Microscopy observations revealed that the dispersion of the silicate aggregates on a microscale was proportional to the degree of separation of the silicate layers on a nanoscale. Decreased apparent glass transition temperature was observed in all the nanocomposites. Finally, mechanical property studies showed that epoxy‐layered silicate nanocomposite formation could simultaneously improve fracture toughness and Young's modulus, without adversely affecting tensile strength.
Polymerization compounding: Epoxy‐montmorillonite nanocomposites
Authors: Feng Wei , Ait‐kadi Abdellatif , Riedl Bernard
Published: April 2004

A strategy to design intercalated montmorillonite nanocomposites has been explored. A commercial organoclay, 1.34 TCN (Nanocor Inc.), with bis(2‐hydroxylethy1) methy1 tallow ammonium, was modified by tolylene 2,4‐diisocyanate (TDI) and bisphenol A (BA). Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) results of unmodified and modified 1.34 TCN (1.34‐TDI‐BA) indicate that TDI and BA have reacted with hydroxy1 groups on the surface of 1.34 TCN and hydroxy1 groups in the interlayer of 1.34 TCN. Using a classical two‐stage cure process with diamine as curing agent, intercalated epoxy nanocomposites were prepared for both types of organoclays. XRD and TEM results showed that the basal spacing of clay in nanocomposites was 3.68 and 4.42 nm for 1.34 TCN and 1.34‐TDI‐BA, respectively. Dynamic mechanical analysis (DMA) was performed on both modified and unmodified organoclay composites. Modified organoclay composites were found to have enhanced storage moduli, particularly at temperatures higher than the glass transition, Tg, of the matrix. Glass transition temperatures extracted from linear viscoelastic data are found to be slightly higher for modified organoclay nanocomposites, indicating enhanced interactions between the modified organoclay and the epoxy matrix. These results were also confirmed by independent measurements of Tg using differential scanning calorimetry (DSC).
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

Polymer 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

A 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

Moisture 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

The 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

It 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

Nanocomposites 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

The 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

Light 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

The 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

Two 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

Blends 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

Blends 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

Blends 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

The 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

The 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

A 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

A 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.
Influence of additives on the crystallization kinetics of semicrystalline polymers. II: Selective polymer‐additive interaction in poly(vinylidene difluoride)—poly(methylmethacrylate) blends
Authors: Pillin Isabelle , Pimbert Sylvie , Levesque Guy
Published: April 2004

The influence of pigments and mineral fillers on the crystallization kinetics of poly(vinylidene fluoride) (PVDF) in its blends with poly(methyl methacrylate) (PMMA) was studied by Differential Scanning Calorimetry and Optical Microscopy. The introduction of organic pigments or mineral fillers into PVDF results in a more or less significant increase in non‐isothermal crystallization temperatures, depending on the additives used. In PVDF, the pigment nucleation activity is quite different from that previously found in poly(butylene terephthalate) (PBT). Attractive interactions between PVDF and additive surfaces are particularly important parameters. The competition between pigments and talc lead to the observation that some pigments are able to inhibit the nucleating power of this mineral in PVDF, probably through specific attractive interactions. In PVDF‐PMMA blends, selective interactions between polymers and additives were observed, depending on their chemical structures. Highly chlorinated pigments present a strong attraction for PMMA and then lose an important part of their nucleating power towards PVDF. On the other hand, a pigment containing carbonyl groups becomes the most active nucleating agent, illustrating the presence of strong interactions between such compounds and the PVDF C‐H bonds.
Influence of the processing conditions on a two‐phase reactive blend system: EVA/PP thermoplastic vulcanizate
Authors: Joubert Catherine , Cassagnau Philippe , Michel Alain , Choplin Lionel
Published: April 2004

The elaboration of a TPV based on copolymer of ethylene and vinyl acetate (EVA) and polypropylene (PP) as thermoplastic phase was investigated in a batch mixer. The crosslinking reaction is carried out through a transesterification reaction between ester groups of EVA and alcoxysilane groups of the crosslinker agent tetrapropoxyorthosilicate (TPOS). The main advantage of this crosslinking reaction is that it can be well controlled and suitable for different processing conditions. The aim of the present study is to get a better understanding of the dispersion mechanism and of the phase inversion of the EVA major phase during its dynamic vulcanization into the PP minor phase. It was proved that the initial viscosity ratio, λ = ηpp/ηEVA, between EVA and PP plays an important part in the morphology development of the reactive blend. The viscosity ratio must be close to the critical ratio expressed by Utracki's model of phase inversion mechanism. Furthermore, the influence of different processing parameters on the variation of the morphology and on the mechanical properties of the ultimate TPV was investigated. The main conclusion of this study is that the characteristic time of crosslinking must be of the same order than the time of mixing. Indeed, better mechanical properties are obtained when a progressive phase inversion occurred and when it is controlled by rheological aspects and transient morphology equilibrium of the two phases and not by the mechanical fragmentation of the crosslinked EVA. For example, in our experimental conditions (concerning the amounts of catalyst and crosslinker reagents), high shear rates can be avoided (\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma} $\end{document} < 80 s−1) as the self‐heating of the blend under shear considerably increases (ΔT ≈ 50°C for \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma} $\end{document} = 225 s−1), leading to faster kinetics and consequently to a phase inversion controlled by the fragmentation of the crosslinked EVA phase.
Numerical prediction of residual stresses and birefringence in injection/compression molded center‐gated disk. Part I: Basic modeling and results for injection molding
Authors: Lee Young Bok , Kwon Tai Hun , Yoon Kyunghwan
Published: April 2004

The present study attempted to numerically predict both the flow‐induced and thermally‐induced residual stresses and birefringence in injection or injection/compression molded center‐gated disks. A numerical analysis system has been developed to simulate the entire process based on a physical modeling including a nonlinear viscoelastic fluid model, stress‐optical law, a linear viscoelastic solid model, free volume theory for density relaxation phenomena and a photoviscoelasticity and so on. Part I presents physical modeling and typical numerical analysis results of residual stresses and birefringence in the injection molded center‐gated disk. Typical distribution of thermal residual stresses indicates a tensile stress in the core and a compressive stress near the surface. However, depending on the processing condition and material properties, the residual stress sometimes becomes tensile on the surface, especially when fast cooling takes place near the mold surface, preventing the shrinkage from occurring. The birefringence distribution shows a double‐hump profile across the thickness with nonzero value at the center: the nonzero birefringence is found to be thermally induced, the outer peak due to the shear flow and subsequent stress relaxation during the filling stage and the inner peak due to the additional shear flow and stress relaxation during the packing stage. The combination of the flow‐induced and thermally‐induced birefringence makes the shape of predicted birefringence distribution quite similar to the experimental one.
Numerical prediction of residual stresses and birefringence in injection/compression molded center‐gated disk. Part II: Effects of processing conditions
Authors: Lee Young Bok , Kwon Tai Hun , Yoon Kyunghwan
Published: April 2004

The accompanying paper, Part I, has presented the physical modeling and basic numerical analysis results of the entire injection molding process, in particular with regard to both flow‐induced and thermally‐induced residual stress and birefringence in an injection molded center‐gated disk. The present paper, Part II, investigates the effects of various processing conditions of injection/compression molding process on the residual stress and birefringence. The birefringence is significantly affected by injection melt temperature, packing pressure and packing time. However, the thermally‐induced birefringence in the core region is insignificantly affected by most of the processing conditions. On the other hand, packing pressure, packing time and mold wall temperature affect the thermally‐induced residual stress rather significantly in the shell layer, but insignificantly in the core region. The residual stress in the shell layer is usually compressive, but could be tensile if the packing time is long, packing pressure is large, and the mold temperature is low. The lateral constraint type turns out to play an important role in determining the residual stress in the shell layer. Injection/compression molding has been found to reduce flow‐induced birefringence in comparison with the conventional injection molding process. In particular, mold closing velocity and initial opening thickness for the compression stage of injection/compression molding have significant effects on the flow‐induced birefringence, but not on the thermal residual stress and the thermally‐induced birefringence.
Crystalline forms in melt‐crystallized syndiotactic polystyrene/clay nanocomposites
Authors: Wu Tzong‐Ming , Hsu Sung‐Fu , Wu Jeng‐Yue
Published: April 2004

X‐ray diffraction methods and polarized optical microscopy have been used to investigate the structural change of syndiotactic polystyrene/clay nanocomposites. The nanocomposite has prepared by mixing an sPS polymer solution with organically modified montmorillonite. Both X‐ray diffraction and transmission electron microscopy results indicate that most of the swellable silicate layers are exfoliated and randomly dispersed into the sPS matrix. The X‐ray diffraction data also show the presence of polymorphism in sPS/clay nanocomposites, which is strongly dependent on the thermal history of the nanocomposites from the melt and on the content of clay. In this study, the effect of premelting temperatures and crystallization temperatures of sPS and sPS/clay nanocomposites on their crystalline phases is discussed.
Carboxyl terminated polyamide 12 chain extension by reactive extrusion using a dioxazoline coupling agent. Part II: Effects of extrusion conditions
Authors: Chalamet Yvan , Taha Mohamed , Berzin Françoise , Vergnes Bruno
Published: April 2004

Condensation reactions between a carboxyl terminated polyamide 12 and a dioxazoline carried out by reactive extrusion have been characterized in the first part of this study. In the present paper, we focus on the influence of extrusion conditions on reaction progress. Influences of screw profile, screw speed, barrel temperature and feed rate have been established. The use of a flow computation software permitted confirmation of the importance of thermal and mechanical degradations in the condensation process.
Bulk polymerization of methyl methacrylate in crosslinked NBR: The effect of the nature of boundary conditions on phase morphology and dynamic behavior of the final IPN
Authors: Omaraee I. Amiri , Mohammadi N.
Published: April 2004

The influence of the nature of confining walls on morphology development during bulk polymerization of methyl methacrylate in a poly(acrylonitrile‐ran‐butadiene) network was investigated by dynamic mechanical analysis and light and scanning electron microscopy. Some samples polymerized while confined by metallic walls showed broad damping properties between the Tg of the components and, consequently, a microheterogeneous morphology. On the other hand, the same compositions, polymerized while confined by glass walls, showed clear separation into a macroscopic three‐layer structure of poly(methyl methacrylate) film between NBR layers. This suggests that phase separation of polymeric systems under symmetric boundary conditions also depends on the nature of the boundaries.
Macroscopic observation of healing process in stress‐whitened polypropylene under hydrostatic pressure
Authors: Lee Jong Keun , Kim Jong Hyun , Chu H.‐C. , Pae Kook D.
Published: April 2004

Stress‐whitening and its healing phenomena in polypropylene under tensile load superposed on hydrostatic pressure up to 89.7 MPa have been investigated. Tensile samples of polypropylene were first cold‐drawn beyond the yielding at atmospheric pressure to develop stress‐whitening, and the stress‐whitened samples were further drawn under various intensities of hydrostatic pressure (P = 7.6 − 89.7 MPa). As a result of the experiment, morphological changes in stress‐whitening occurred in the necked gauge sections (RI and RII) and in the shoulders of the neck (RIII). The macroscopic observations were made by optical microscopy on the entire specimen and on the sliced sections. The stress‐whitening in the RI region was found to be either partially or nearly completely healed depending on the level of hydrostatic pressure at which the specimens were drawn. The cross sections of polypropylene specimens exhibited two concentric ring structures upon stress‐whitening. The stress‐whitened core region is surrounded by clear shell region. The size and degree of healing of stress‐whitening in the core region were affected by the applied hydrostatic pressure.
Rheokinetics of linear polymerization. A literature review
Authors: Cioffi M. , Ganzeveld K. J. , Hoffmann A. C. , Janssen L. P. B. M.
Published: April 2004

The dramatic increase of viscosity is a fundamental problem when designing a polymerization process. Since a thorough understanding of rheokinetics—the study of the coupled rheological changes and chemical kinetics in the reaction mixture—especially at high degrees of conversion, is still missing, industrial polymerization processes are often designed on basis of trial and error procedures and operate in far‐from‐optimal conditions. Even at laboratory scale the measurement of the viscosity of systems rapidly changing with time is troublesome and predicting quantitatively the increase of viscosity is not an easy task. The non‐Newtonian character of polymeric systems makes rheokinetics an even more challenging field, and more interesting as well. In this review article the difficulties encountered by the research community, the results obtained so far and the problems still to be faced are discussed.
The influence of alkyl end‐groups on the miscibility of hyperbranched polymers with polyolefins
Authors: Sendijarevic Ibrahim , McHugh Anthony J. , Orlicki Joshua A. , Moore Jeffrey S.
Published: April 2004

Polyetherimide (PEI) hyperbranched polymers (HBPs) with alkyl terminated endgroups were blended with linear low density polyethylenes (LLDPEs) and extruded as thin films. The effects of length and concentration of the alkyl groups on the miscibility of the extruded films were examined using confocal and scanning electron microscopy (SEM). Surface properties of the blends were further characterized using contact angle measurements in de‐ionized water. Results indicate that migration of PEI HBPs to the film surfaces is predominantly driven by the surface energy differences of HBPs and polyolefins. Moreover, the addition of PEI HBPs to LLDPEs has a negligible effect on the processing properties of LLDPEs.
Effect of the compatibilizer on the physical properties of biaxially deformed in situ composites
Authors: Seo Yongsok , Kim Jinho , Kim Hyong‐Jun
Published: April 2004

The effect of a compatibilizer (poly(ester imide), PEsI) on the biaxial deformation of a thermotropic liquid crystalline polymer (TLCP, poly(ester amide)) in a poly(ether imide) and the properties of biaxially deformed in situ composites were studied. The compatibilizer improved dispersion of the TLCP and the adhesion between TLCP and the matrix. The properties of blown films were affected by the amount of the compatibilizer used. The morphology evidently shows that ca. 0.6 wt% PEsI provides the best morphology when 10 wt% VB phase is included. The mechanical properties, especially in the hoop direction, were significantly improved for the compatibilized films compared to uncompatibilized one. The impact strength of a compatibilized blend film with 0.6 wt% PEsI was almost twice that of an uncompatibilized blend film.