bluuebunny/crossref_metadata_2025_split huggingface dataset:
Brittle‐ductile transitions in polyethylene
Authors: O'connell P. A. , Duckett R. A. , Ward I. M. 
Published: April 2004

AbstractThe failure mode of a number of polyethylenes has been studied under predominantly plane strain conditions. Square section samples, notched on all sides, have been tested in tension to failure over a range of crosshead speeds and temperatures. Integration under the subsequent load displacement curve has allowed the total energy, energy to peak load, and energy after peak load to be determined. The data have been analyzed in terms of the ratio of the energy after the peak load to the total energy. The results show that the material can change from brittle to ductile failure as a function of test speed. At a suitable temperature we have observed brittle‐like failure at the highest and lowest test speeds and ductile failure at intermediate speeds. The resulting failure surface features correlate very strongly with the energy ratio analysis—flat smooth surfaces where low energy ratios are seen and large ductile tearing where high ratios are seen. The effect of molecular weight and polydispersity will be shown and possible failure mechanisms discussed.
Time‐temperature superposition principle applicability for blends formed of immiscible polymers
Authors: Macaúbas P. H. P. , Demarquette N. R. 
Published: April 2004

AbstractIn this work, the linear viscoelastic behavior of PP/PS and PP/HDPE blends modified with SEBS and EPDM, respectively, was studied. Small amplitude oscillatory shear measurements were carried out at different temperatures, ranging from 190°C to 240°C. The storage (G') and loss (G") moduli curves obtained were horizontally shifted and curves of angle delta (δ) (δ = atan (G"/G')) as a function of complex shear modulus (G*), known as van Gurp plots, were obtained at several temperatures, to test the applicability of time‐temperature superposition principle (TTS) to these blends. The results showed that successful application of TTS depends on the flow energy of activation and horizontal shift factors of the individual components of the blend, on the interfacial properties of the blend and on the concentration of compatibilizer added to the blend. TTS application failed for PP/PS blend, but held for PP/HDPE blend. Addition of SEBS to PP/PS blends promoted successful TTS application at specific concentrations that corresponded to interfacial saturation of the dispersed phase. Addition of EPDM did not imply sensitive change on TTS application for the PP/HDPE blends.
Influence of ultrasound on the processing and structure of polypropylene during extrusion
Authors: Cao Yurong , Li Huilin 
Published: April 2004

AbstractThe effects of ultrasonic irradiation on extrusion processing and crystallization behavior of polypropylene (PP) are examined. The results show that appropriate irradiation intensity can prominently decrease die pressure and apparent viscosity, increase output, reduce extrudate swell, and improve apparent quality of PP. DSC and WAXD analysis demonstrate that the crystalline structure of PP is changed and the content of the β crystalline increases through ultrasonic vibration. Special effects can be induced by ultrasound, such as strong stress, shatter and vibration, which alter the growth of PP crystals and may favor a special crystal transformation (α → β).
Effects of ABS rubber particles on rheology, melt failure, and thermoforming
Authors: Lee Je Kyun , Scott Chris E. , Virkler Terry L. 
Published: April 2004

AbstractThe rubber particles included in rubber modified polymeric materials such as acrylonitrile‐butadiene‐styrene (ABS) polymer and impact modified polymers play an important role in determining their rheological properties, processing behavior, and mechanical properties. In this study both small strain oscillatory shear viscosity in the frequency range from 10−2 to 102 s−1 and uniaxial elongational viscosity behavior at two elongation rates (

= 0.1 and 1.0 s−1) over the range of temperatures from 140°C to 200°C were measured for commercial ABS polymers with different contents and deformability of rubber particles. The influences of rubber content and deformability on rheological properties such as melt elasticity, elongational viscosity, strain hardening and/or softening, the onset of nonuniform deformation, and thermoforming performance were investigated. The Wagner two‐parameter nonlinear viscoelastic constitutive model was used to describe strain hardening behavior, while the Considère criterion was used to determine the onset point of nonuniform deformation. The part thickness distribution obtained through use of a vacuum snap‐back forming process was simulated to investigate the effects of rheological changes associated with different rubber particles on the thermoforming performance. It was found that ABS polymers with larger contents of hard rubber particles exhibited more melt elasticity, stronger strain hardening, a maximum of biaxial elongational viscosity, onset of nonuniform deformation at later time, and better thermoforming performance. Strain hardening and the Considère criterion provide simple, reliable indicators of the thermoforming performance of ABS polymers.
Functionalizing polymer surfaces by field‐induced migration of copolymer additives—role of shear fields
Authors: Lee Hojun , Archer Lynden A. 
Published: April 2004

AbstractFlow‐induced migration polyethylene‐co‐methacrylic acid (PE‐co‐MA) and polystyrene‐b‐polydimethylsiloxane (PS‐b‐PD MS) copolymer additives in commercial long‐chain branch polyethylene (PE) and narrow‐molecular distribution polystyrene (PS) hosts was investigated in a capillary flow device. Attenuated Total Reflection Fourier Transform Infrared (ATR‐FTIR) spectroscopy and Dynamic Contact Angle (DCA) measurements were used to characterize surface composition of polymer specimen following extrusion through metallic dies with various length‐to‐diameter (L/D) ratios, (1100 ⩽ L/D ⩽ 3000). Results from experiments covering a broad range of shear rates and polymer residence times in the dies are reported. Provided that the polymer residence time in the die is sufficiently long, shear is found to increase the concentrations of low molecular weight copolymer additives on the host polymer's surface. The surface composition of copolymer additive is found to vary strongly with the wall shear rate and die L/D ratio. Decreasing the die diameter at fixed flow rate is found, for example, to be a more effective method for enhancing transport of additive to a polymer's surface than increasing shear rate at fixed diameter. A mechanism based on shear‐induced diffusion is proposed to explain the observed migration.
Melting behavior and crystallization kinetics of sulfonated poly(butylene isophthalate)
Authors: Lotti Nadia , Finelli Lara , Munari Andrea , Siracusa Valentina 
Published: April 2004

AbstractThe melting behavior and the crystallization kinetics of sulfonated poly(butylene isophthalate) random copolymers were investigated by means of differential scanning calorimetry. The multiple endotherms, commonly observed in polyesters, were found to be influenced both by composition and crystallization temperature. By applying the Hoffman‐Weeks method, the equilibrium melting temperatures of the copolymers under investigation were obtained. The presence of a crystal‐amorphous interphase was evidenced and its amount was found to increase as the sulfonated unit content was increased. Isothermal melt crystallization kinetics of the sample containing the lowest amount of sulfonated units was analyzed according to the Avrami treatment. The introduction of such units was found to decrease the overall crystallization rate of poly(butylene isophthalate). Values of Avrami's exponent n close to 3 were obtained, independently of crystallization temperature, in agreement with a crystallization process originating from predetermined nuclei and characterized by three‐dimensional spherulitic growth.
Reactive blending of poly(ethylene terephthalate)(pet)/ poly(ethylene 2,6‐naphthalate)(pen). I: Effect of mixing conditions on chain structure
Authors: Yang Haihua , Ma Jinghong , Li Wengang , Liang Borun , Yu Yihua 
Published: April 2004

AbstractReactive blending of poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6dicarboxylate) with addition of 2,2'‐bis(1,3‐oxazoline) (BOZ) has been studied under various mixing conditions for the different compositions. The transesterification level, the sequence length of both PET and PEN short blocks, and the degree of randomness were estimated using1H NMR. The results indicate that both mixing time and temperature are the primary factors controlling the transesterification, while the chain extender BOZ can significantly accelerate the transesterification between PET and PEN at 275°C. The composition also, to some extent, influences the transerification level as the mixing time is increased. As a consequence of transesterification proceeding, the sequence structures of the reactive blends are also markedly changed, which corresponds to a transfer from an initial block structure to a multiblock structure with higher randomness. The change in the microstructure of the reactive blends has also been analyzed by a Bernoullian statistics model. The effect of the BOZ on the intrinsic viscosity of the reactive blends is discussed.
Comparison of structure development in injection molding of isotactic and syndiotactic polypropylenes
Authors: Choi Dongman , White James L. 
Published: April 2004

AbstractA comparative study of the crystallization and orientation development in injection molding isotactic and syndiotactic polypropylenes was made. The injection molded samples were characterized using wide angle X‐ray diffraction (WAXD) techniques and birefringence. The injection molded isotactic polypropylene samples formed well‐defined sublayers (skin, shear and core zones) and exhibited polymorphic crystal structures of the monoclinic α‐form and the hexagonal β‐form. Considerable amounts of β‐form crystal were formed in the shear and core zones, depending on the injection pressure or on the packing pressure. The isotactic polypropylene samples had relatively high frozen‐in orientations in the skin layer and the shear zone. The injection molded syndiotactic polypropylene exhibited the disordered Form I structure, but it did not appear to crystallize during the mold‐filling stage because of its slow crystallization rate and to develop a distinct shear zone. The core zone orientation was greatly increased by application of high packing pressure. The isotactic polypropylene samples exhibited much higher birefringence than the syndiotactic polypropylene samples at the skin and shear layers, whereas both materials exhibited similar levels of crystalline orientation in these layers.
Thermo‐oxidative stability study of polypropylene composites by using cone calorimetry and thermogravimetry
Authors: Kwak Sung‐bok , Nam Jae‐do 
Published: April 2004

AbstractThe flammability of polypropylene (PP) and recycled PP composite systems was thoroughly investigated by using cone calorimetry and thermogravimetry techniques in order to quantify the effect of brominated and chlorinated fire‐retardant systems. In this study, the efficiency of the fire‐retarding systems was defined from the relation between the amount of fire retardants and the characteristic quantities in cone calorimetry (M‐HRR, THR, and M‐EHC) and the limited oxygen index. The brominated fire retardants showed fire‐retarding capability superior to that of the chlorinated systems, and the recycled polymer was thermo‐oxidatively stabler than the pristine PP systems seemingly because of the fillers and blended polymers. Comparing the degradation behaviors of the composite systems in nitrogen and air environments, the halogen compounds retarded the decomposition rates in both cases, deactivating the reactive radicals of the polymer and restricting the flammable gases from being diffused into the unreacted polymer. Overall, the optimal amounts of fire retardants in different polymeric systems could be evaluated and correlated with several fire indicators in a relatively simple manner.
Structure and mechanical properties of blends of two thermotropic copolyesters
Authors: Vallejo Francisco Javier , Eguiazábal Jose Ignacio , Nazábal Jon , Iribarren Iñaki 
Published: April 2004

AbstractBlends of two thermotropic copolyesters, poly(ethylene terephthalate/p‐hydroxy benzoic acid) (20/80), EB, and poly(p‐hydroxy benzoic acid/2,6‐hydroxy naphthoic acid) (73/27), BN, were obtained in the melt state by direct mixing in an injection machine throughout the full composition range. They comprised an almost pure EB phase and a BN‐rich phase that contained some reacted EB. Important synergisms with most of the values above those of the two pure blend components were found at most compositions in the modulus of elasticity and the tensile strength. The synergisms appeared to be due to the concomitant effect mainly of an orientation of the components higher in the blends than in the pure components, and to a lesser extent, of a blending‐induced specific volume decrease.
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

AbstractIn 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

AbstractThe 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

AbstractOrganosilanes 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

AbstractCarbon 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

AbstractThis 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

AbstractPolypropylene (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

AbstractHigh 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

AbstractA 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).