bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymorphic behavior of nylon 6/saponite and nylon 6/montmorillonite nanocomposites
Authors: Wu Tzong‐Ming , Chen Erh‐Chiang , Liao Chien‐Shiun 
Published: April 2004

AbstractX‐ray diffraction methods and DSC thermal analysis have been used to investigate the structural change of nylon 6/clay nanocomposites. Nylon 6/clay has prepared by the intercalation of ε‐caprolactam and then exfoliaton of the layered saponite or montmorillonite by subsequent polymerization. Both X‐ray diffraction data and DSC results indicate the presence of polymorphism in nylon 6 and in nylon 6/clay nanocomposites. This polymorphic behavior is dependent on the cooling rate of nylon 6/clay nanocomposites from melt and the content of saponite or montmorillonite in nylon 6/clay nanocomposites. The quenching from the melt induces the crystallization into the γ crystalline form. The addition of clay increases the crystallization rate of the α crystalline form at lower saponite content and promotes the heterophase nucleation of γ crystalline form at higher saponite or montmorillonite content. The effect of thermal treatment on the crystalline structure of nylon 6/clay nanocomposites in the range between Tg and Tm is also discussed.
Shear stress nucleation in microcellular foaming process
Authors: Chen Lee , Wang Xiang , Straff Rich , Blizard Kent 
Published: April 2004

AbstractThe effect of shear stress on the foaming process has been studied using the Foaming Process Simulator developed previously. The polymer samples were saturated with gas in the test chamber. A rotor was used to apply shear stress to the polymer samples. Foams were obtained by releasing the pressure quickly. Polystyrene, filled and unfilled, was used as the material. The cell density was analyzed with a scanning electron microscope. It was found that the cell density was significantly increased by introducing shear stress. The higher the shear stress, the more significant the effect. A cell stretch model has been developed to explain the cell nucleation enhancement with shear stress. The nucleation sites are stretched under the shear stress. The stretched nuclei are much easier to expand for cell formation owing to their larger surface areas and non‐spherical shapes. The model prediction shows the same tendency of the effect of shear stress observed in the experiment. The key issue with shear stress nucleation is the transformation of mechanical shear energy into surface energy.
“In‐situ” monitoring of the non‐isothermal crystallization of polymers by dielectric spectroscopy
Authors: Gonnet J‐M. , Guillet J. , Sirakov I. , Fulchiron R. , Seytre G. 
Published: April 2004

AbstractIn recent years, experimental techniques based on microdielectrometry have attracted increasing interest for continuous monitoring, in a nondestructive way, of the advancement of the reaction of thermoset resins under cure. The extension of this technique for “in‐situ” monitoring of the crystallization of thermoplastics has been carried out. A correlation between the evolution of the dielectric parameters of the material and its viscoelastic properties was done. A dynamic rheometer equipped with a dielectric cell and an instrumented slit die was designed. The crystallization process is depicted by a conductivity drop and by the occurrence of a maximum in the real permittivity. The decrease of the specific conductivity results from a modification of the conductive paths, whereas the increase of the permittivity is due to an interfacial polarization phenomenon (so‐called Maxwell Wagner Sillars effect) between the amorphous phase and the growing crystalline entities. The sudden variation of the dielectric response is envisioned as a means for following the progression of the crystallization front within a mold. The description of the crystallization with Nakamura's model allowed the modeling of the crystallization inside a mold. The evolution of the temperature profile and of the crystallinity rate is modeled by a classical finite difference method. Dielectric measurements performed at controlled cooling rate experiments are in good agreement with the numerical simulation results and confirm the usefulness of dielectric measurements for “In‐situ” monitoring of the crystallization process of a polymer inside a mold.
In‐line monitoring of the injection molding process by dielectric spectroscopy
Authors: Gonnet Jean‐Marc , Guillet Jacques , Raveyre Claude , Assezat Gilles , Fulchiron Rene , Seytre Gerard 
Published: April 2004

AbstractIn recent years, electrical techniques like microdielectrometry have increasingly been utilized for their ability to continuously monitor, in a nondestructive way, the advancement of the reaction of thermoset resins under cure. This paper discusses an extension of this technique for the “in‐situ” monitoring of the crystallization of thermoplastics applied during an injection molding process. Electric sensors were positioned at the walls of the mold cavity so that an analysis of the volume dielectric properties of material during the filling, the post‐filling, and the cooling steps could be carried out. Poly(vinylidene fluoride) was chosen for this study. A correlation between the evolution of the dielectric parameters and the succession of the steps in this process was undertaken. The dielectric response was sufficiently sensitive to identify the steps of the closing of the mold, filling, post‐filling, cooling, and ejection of the part. In addition, information concerning the crystallization phenomenon near the wall or in the middle of the sample was collected. The gradual filling of the cavity of the mold was also identified by dielectric measurements. The temperature dependence of dielectric properties of the sample was beneficial in evaluating the increase of the temperature of the mold with the succession of injection cycles. The influence of the packing pressure has been clearly identified and confirms the usefulness of the dielectric method as a probe for detecting the shrinkage of the part during the optimization phase of the machine parameters. The dielectric method detailed herein provides a new non‐invasive technique and could be applied to a closed‐loop control of the injection molding process.
Relating De Mattia cut growth to network structure of crosslinked elastomers
Authors: Tse M. F. , McElrath K. O. , Wang H.‐C. 
Published: April 2004

AbstractDe Mattia cut growth, an important fatigue test, of a number of crosslinked elastomers based on terpolymers of isobutylene, p‐methylstyrene, and p‐bromomethylstyrene brominated isobutylene paramethylstyrene copolymers (BIMS), butadiene rubber (BR), and blends of BR and natural rubber (NR) has been studied. In these compounds the carbon black level and the cure state are varied. We attempt to relate this fatigue performance to bulk mechanical properties (strain at break, εb, and strain energy density, U) and network structural parameters (contour length, Lc, and root‐mean‐square end‐to‐end distance, 〈r〉, of network molecular chains).
Synthesis and properties of new soluble poly(amide‐imide‐imide)s
Authors: Yang Chin‐Ping , Chen Ruei‐Shin , Wei Chi‐Shu 
Published: April 2004

AbstractA new‐type tetraimide‐dicarboxylic acid (I) was synthesized starting from the ring‐opening addition of p‐aminobenzoic acid (p‐ABA), 4,4'‐oxydiphthalic anhydride (ODPA), and 4,4'‐methylenedianiline (MDA) at a 2:2:1 molar ratio in N‐methyl‐2‐pyrrolidone (NMP), followed by cyclodehydration to the diacid I. A series of poly(amide‐imide‐imide)s (IIIa‐i) with inherent viscosities of 0.78–1.45 dL/g was prepared by triphenyl phosphite‐activated polycondensation from the tetraimide‐diacid I with various aromatic diamines (IIa‐i) in a medium consisting of NMP, pyridine, and calcium chloride. Most of the polymers were readily soluble in a variety of organic solvents such as NMP, N,N‐dimethyl acetamide, dimethyl sulfoxide, and even in less polar m‐cresol. Compared with those of the corresponding poly(amideimide)s IVa‐i, the solubilities of poly(amide‐imide‐imide)s IIIa‐i were greatly improved. Polymers IIIa‐h afforded tough, transparent, and flexible films, which had tensile strengths ranging from 87 to 107 MPa, elongations at break from 9% to 14%, and initial moduli from 2.0 to 2.4 GPa. The glass transition temperatures of polymers were recorded at 270°C–309°C. They had 10% weight loss at temperatures in the range of 540°C–570°C and left more than 52% residue even at 800°C in nitrogen.
Barrier and mechanical properties of montmorillonite/polyesteramide nanocomposites
Authors: Krook M. , Albertsson A.‐C. , Gedde U. W. , Hedenqvist M. S. 
Published: April 2004

AbstractThe barrier and mechanical properties of biodegradable melt‐mixed polyesteramide/octadecylamine‐treated montmorillonite clay (filler) have been studied. Extruded films containing 5 and 13 wt% filler were prepared by melt‐mixing. Samples compression molded after extrusion was also studied. Oxygen and water transmission rates were measured. X‐ray diffraction was used to assess the periodic distance of the clay layers and transmission electron microscopy was used to assess the composite morphology. An increase of the periodic distance from 23.7 Å for pure filler to 32–36 Å for the processed composites was observed. This suggested that the collapsed stacks of clay particle of the first order X‐ray reflection became intercalated upon extrusion. A decrease in the intensity with increasing rotation speed was observed, which suggested that higher shear rates promoted delamination, especially in composites with higher filler content. Transmission electron microscopy indicated that a sizable portion of the clay stacks were delaminated into smaller aggregates, containing generally one to three clay sheets. Density measurements indicated that shear‐induced voids were formed in the nanocomposite, and these were, according to transmission electron microscopy, almost exclusively located between the clay sheets. The presence of voids limited the improvement in barrier properties with increasing filler content. However, the very large improvement in stiffness and strength with filler content indicated that these properties were unaffected by these voids.
Deformation and energy absorption characteristics of microcellular ethylene‐octene copolymer vulcanizates
Authors: Nayak N. C. , Tripathy D. K. 
Published: April 2004

AbstractCompressive stress‐strain properties of unfilled, CaCO3, silica and aluminum silicate filled closed‐cell microcellular ethylene‐octene co‐polymer vulcanizates were studied with variation of blowing agent loading (density). With decrease in density, the compressive stress‐strain curves for microcellular vulcanizates behave differently from those of the solid vulcanizates. The stress‐strain properties are found to be strain rate dependent. The log‐log plots of relative compressive moduli versus relative density of the microcellular vulcanizates show a fairly linear correlation. The energy absorption behavior was also studied from the stress‐strain properties. The efficiency, E, and Ideality parameter, I, were evaluated. These parameters were plotted against stress to find the maximum efficiency and maximum ideality region, which will make these materials suitable for cushioning and packaging applications. The cushioning factor, C, for microcellular vulcanizates has also been evaluated for various systems.
Compatibilizers for thermotropic liquid crystalline polymer/polyethylene blends prepared by reactive mixing
Authors: Son Younggon , Weiss R. A. 
Published: April 2004

AbstractThis paper describes the effects of composition and processing conditions on the efficiency of the compatibilizer prepared from a thermotropic liquid crystalline polymer (TLCP) and the sodium salt of a poly(ethylene‐co‐r‐acrylic acid) ionomer (EAA‐Na) in TLCP/low‐density polyethylene (LDPE) blends and TLCP/high‐density polyethylene (HDPE) blends. The TLCP‐ionomer graft copolymer formed by a melt acidolysis reaction effectively reduced the interfacial tension between TLCP and polyethylene, which improved impact strength and toughness of the compatibilized blends. Higher processing temperatures for the reactive extrusion produced a more efficient compatibilizer, presumably due to increased graft‐copolymer formation, but the reaction temperature had little effect on the impact strength of compatibilized blends for temperatures above 300°C. The addition of the compatibilizer to TLCP/LDPE blends significantly increased the melt viscosity due to increased interfacial adhesion. The TLCP/EAA‐Na ratio used to prepare the compatibilizer had little effect on the performance of the compatibilizer. Although the compatibilizer can be prepared in situ by blending and extruding a ternary blend of TLCP/EAA‐Na/polyethylene, pre‐reacting the compatibilizer resulted in blends with improved toughness and elongation.
Mechanical properties of thermoplastic polyurethanes containing aliphatic polycarbonate soft segments with different chemical structures
Authors: Tanaka Hideho , Kunimura Masaru 
Published: April 2004

AbstractMechanical properties of linear thermoplastic polyurethanes (TPUs) prepared by polyaddition reaction using a polycarbonate diol (PCD), 1,4‐butanediol (a chain extender) and 4,4'‐diphenylmethane diissocyanate were investigated. Chemical composition among these three components was kept constant. Primary attention was directed to how chain length of an alkylene group in the PCD affected the mechanical properties of the resultant TPU. To clarify this effect, the PCDs were synthesized using 1,6‐hexanediol and 1,12‐dodecanediol. In addition, the TPUs from copolycarbonate diols containing these two components were also produced, and then extensively examined and further compared to the ones from the corresponding blended PCDs. From a practical point of view, weatherability and solubility in a polar solvent were also evaluated.
Morphological and mechanical properties of polypropylene [PP]/poly(ethylene vinyl acetate) [EVA] blends. II: Polypropylene‐(ethylene‐propylene) heterophasic copolymer [PP‐EP]/EVA systems
Authors: Ramírez‐Vargas E. , Medellín‐Rodríguez F. J. , Navarro‐Rodríguez D. , Avila‐Orta C. A. , Solís‐Rosales S. G. , Lin J. S. 
Published: April 2004

AbstractMorphological characteristics and mechanical properties of PP‐EP/EVA blends were studied and compared to those of PP/EVA previously reported. For the PPEP/EVA blends, interfacial interactions in amorphous zones, which were associated with shifts in Tg, were well defined compared to those of PP/EVA blends, although the nature of crystalline zones was similar for both systems. At EVA concentrations up to 20%, the elongation at break and impact strength slightly increased in both systems. However, PP‐EP/EVA displayed higher values of these properties compared with PP/EVA. At high EVA concentrations (above 20%), the indicated properties were enhanced in both polymeric systems, and the same proportional behavior was maintained. The decrease in tensile strength of PP‐EP/EVA was not as marked as in PP/EVA with the addition of EVA, and it remained below PP/EVA at high EVA concentrations. The improvement in properties of PP‐EP/EVA was attributed to favorable interactions between the ethylene groups contained in both copolymers. These interactions rendered a high degree of compatibility between the PP‐EP and EVA components.
Ethylene copolymers as sintering enhancers and impact modifiers for rotational molding of polyethylene
Authors: Chaudhary Bharat Indu , Takács Elizabeth , Vlachopoulos John 
Published: April 2004

AbstractThe objective of this work was to evaluate the effect of blending minor amounts of ethylene styrene Interpolymer or ethylene vinyl acetate (EVA) with polyethylene on cycle times and impact strength in rotational molding. The blends sintered significantly faster than polyethylene. The sintering rates were primarily influenced by the melting points of the minor blend components, and not by differences in melt viscosity and/or elasticity at low shear rate. Blending Interpolymer or EVA with polyethylene resulted in improved environmental stress crack resistance and decreased flexural modulus. In rotational molding, blending Interpolymer or EVA with polyethylene generally resulted in faster bubble removal, more uniform thickness and shorter cycle times. Ductile failure was generally observed at the peak mean failure energy (MFE). The blend containing Interpolymer yielded significantly increased MFE, possibly because the Interpolymer was compatible with polyethylene and was very well dispersed.
Plane‐stress fracture behavior of syndiotactic polypropylenes of various crystallinity as assessed by the essential work of fracture method
Authors: Karger‐kocsis J. , Bárány T. 
Published: April 2004

AbstractThe fracture behavior of 1‐mm‐thick syndiotactic polypropylene (sPP) sheets of various crystallinity (owing the various stereo‐ and regioregularity) was studied by the essential work of fracture (EWF) concept. The specific work of fracture parameters were determined on tensile‐loaded deeply double‐edge notched (DDEN‐T) specimens at various deformation rates (v = 1, 10 and 100 mm/min) at ambient temperature. As the DDEN‐T specimens showed full ligament yielding prior to subsequent necking, the energy partitioning method was adopted for data reduction. The specific essential work of fracture slightly increased as a function of crystallinity. Its yielding‐related constituent increased with both crystallinity and deformation rate similarly to that of the yield strength and E‐modulus. The specific plastic work parameters were less sensitive to crystallinity and deformation rate. The strain‐induced crystalline phase transition from helical toward all‐trans conformation was accompanied by voiding and crazing.
Mixed matrix membrane materials with glassy polymers. Part 1
Authors: Mahajan Rajiv , Koros William J. 
Published: April 2004

AbstractMixed matrix materials comprising molecular sieve entities embedded in a polymer matrix can economically increase membrane permselectivity, thereby addressing a key challenge hindering the widespread use of membrane‐based gas separations. Prior work has clarified the importance of proper selection of the dispersed sieve phase and the continuous matrix phase based on their intrinsic transport properties. Proper material selection for the two components, while necessary, is not sufficient since the interfacial contact zone appears to be equally important to achieve optimum transport properties. Specifically, it was found that chemical coupling of the sieve to the polymer can lead to better macroscopic adhesion but to even poorer transport properties than in the absence of the adhesion promoter. This counterintuitive behavior may be attributed to a nanometric region of disturbed packing at the polymer sieve interphase. The poor properties are believed to result from “leakage” of gas molecules along this nanometric interface. The Maxwell model was modified to take into account these complexities and to provide a first order quantification of the nanometric interphase. The analysis indicates that optimization of the transport properties of the interfacial region is key to the formation of ideal mixed matrix materials. This approach is used in the second part of this paper to form successful mixed matrix membrane materials.
Mixed matrix membrane materials with glassy polymers. Part 2
Authors: Mahajan Rajiv , Koros William J. 
Published: April 2004

AbstractAnalysis presented in Part 1 of this paper indicated the importance of optimization of the transport properties of the interfacial region to achieve ideal mixed matrix materials. This insight is used in this paper to guide mixed matrix material formation with more conventional gas separation polymers. Conventional gas separation materials are rigid, and, as seen earlier, lead to the formation of an undesirable interphase under conventional casting techniques. We show in this study that if flexibility can be maintained during membrane formation with a polymer that interacts favorably with the sieve, successful mixed matrix materials result, even with rigid polymeric materials. Flexibility during membrane formation can be achieved by formation of films at temperatures close to the glass transition temperature of the polymer. Moreover, combination of chemical coupling and flexibility during membrane formation produces even more significant improvements in membrane performance. This approach leads to the formation of mixed matrix material with transport properties exceeding the upper bound currently achieved by conventional membrane materials. Another approach to form successful mixed matrix materials involves tailoring the interface by use of integral chemical linkages that are intrinsically part of the chain backbone. Such linkages appear to tighten the interface sufficiently to prevent “nonselective leakage” along the interface. This approach is demonstrated by directly bonding a reactive polymer onto the sieve surface under proper processing conditions.
Lithium ion transport through nonaqueous perfluoroionomeric membranes
Authors: Sachan Sunil , Ray Cameron A. , Perusich Stephen A. 
Published: April 2004

AbstractThe transport properties of lithiated perfluorinated ionomers imbibed with nonaqueous solvents and solvent mixtures were studied. Polymeric ion‐exchange membranes have potential use in the next generation single‐ion secondary lithium polymer batteries, where the lithiated form of the membrane is used as a polymer electrolyte. The novelty of the approach for lithium battery applications lies in the advantage offered by a transference number of unity, no additional salt (e.g., LiPF6) is needed, and the excellent physical and chemical stability of the fluoropolymers. Ion‐exchange membranes were converted to the Li+ salt form and analyzed for total conversion using FT‐IR. Nonaqueous solvents and solvent mixtures were imbibed into the membranes in a glove box, and the uptake was measured over time. A four‐point probe was used to determine the ionic conductivity based on impedance measurements performed over a frequency range of 10 to 35,000 Hz. Conductivities exceeding 10−4 S/cm with transference numbers of unity were achieved making these ionomeric membranes potentially useful in rechargeable lithium polymer batteries.
Strategies for achieving ultra low‐density polypropylene foams
Authors: Naguib Hani E. , Park Chul B. , Panzer U. , Reichelt Norbert 
Published: April 2004

AbstractThe volume expansion behavior of low‐density polypropylene foams in extrusion is investigated in this paper. Since escape of blowing agent from the foam would cause the foam to contract, and to have low expansion, efforts were made to prevent gas loss during foaming. The basic strategies to the promotion of a large volume expansion ratio are: to use a branched material for preventing cell coalescence; to use a long‐chain blowing agent with low diffusivity; to lower the melt temperature for decreasing gas loss during expansion; and to optimize the processing conditions in the die for avoiding too‐rapid crystallization. Use of a branched polypropylene resin was required to achieve large volume expansion because prevention of cell coalescence will retard gas loss from the extruded foam to the environment. The foam morphologies of linear and branched polypropylene materials at various processing temperatures were studied using a single‐screw tandem foam extrusion system and their volume expansion behaviors were compared. Ultra lowdensity, fine‐celled polypropylene foams with very high expansion ratio up to 90 fold were successfully produced from the branched polypropylene resins.