bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of a compatibilizer on the structural development of a thermotropic liquid crystalline polymer/polystyrene blend
Authors: Seo Yongsok , Kim Hyong‐Jun , Kim Youngjun , Rhee Hee Woo
Published: April 2004

A fine fibril structure of a thermotropic liquid crystalline polymer (TLCP, a poly(ester amide)) can be developed in a shear flow field of a thermoplastic matrix (polystyrene, PS). Addition of a third component, a poly(styrene‐co‐maleic anhydride) (SMA), that interacts with the thermotropic liquid crystalline polymer facilitates the structural development of the TLCP phase by acting at the interface. Moreover, it brings about good adhesion at the interface and enables the dispersed liquid crystalline polymer phase to be deformed in shear flow without strong elongation even though the viscosity of the matrix is much lower than that of the liquid crystalline polymer. The mechanical properties were substantially improved because of both the good adhesion at the interface and fibril generation, which were ascribed to the SMA interaction. These results have important implications in that they provide a means to produce strong and tough in‐situ composites when the viscosity of the matrix polymer is lower than that of the dispersed liquid crystalline polymer which is immiscible with the matrix polymer. Morphological observations determined the significance of the third component (SMA) in immiscible polymer blends, and an optimum amount of SMA exists for best mechanical performance.
Miscibility evolution of polycarbonate/polystyrene blends during compounding
Authors: Chuai C. Z. , Almdal K. , Johannsen I. , Lyngaae‐Jørgensen J.
Published: April 2004

The miscibility evolution of polycarbonate/polystyrene (PC/PS) blends during the compounding process in three blending methods of industrial relevance, namely melt blending, remelt blending in a twin‐screw extruder and third melt blending in an injection molding machine, was investigated by measuring their glass transition temperatures (Tg) and their specific heat increment (ΔCp). Differential scanning calorimetry (DSC) was used to examine nine blend compositions. Shifts in glass transition temperature (Tg) of the two phases in melt‐mixed PC/PS blends suggest partial miscibility of one polymer in the other. The observed solubility strongly depends on blend composition and blending method. The Tg measurements showed maximum mutual solubility around 50/50 composition. The miscibility of PC/PS blended after the third stage (melt injection molding) was higher than that after the first stages (melt extrusion) and the second stages (remelt extrusion).
High speed imaging of drop formation from low viscosity liquids and polymer melts in spinning disk atomization
Authors: Senuma Yoshinori , Hilborn Jöuns G.
Published: April 2004

An investigation of drop formation in a recently developed spinning disk atomization (SDA) technique is presented. In‐situ observations of drop formation at the disk rim, using a high speed imaging installation, are made. Atomizations covering two orders of magnitude in flow rate show that ligaments can also form at low flow rates. Sequences of pictures indicate that drops undergo a rotary motion as they detach from a ligament. In the direct drop regime, oscillating motions dominate. The effect of teeth shape at the disk rim on the resulting drops is compared. The effect on drop size and size distribution is found to decrease with increasing rotation rate and corresponding images are studied. Experiments with liquid viscosities ranging from 1 to 120 mPas reveal a fundamental difference in drop breakup, but a negligible change in drop size. Likewise, only a small effect of liquid density is detected. The surface tension's influence on the liquid spreading at the disk rim is described and the subsequent drop formation is qualitatively analyzed.
Tensile modulus of polymer nanocomposites
Authors: Ji Xiang Ling , Jing Jiao Kai , Jiang Wei , Jiang Bing Zheng
Published: April 2004

Based on Takayanagi's two‐phase model, a three‐phase model including the matrix, interfacial region, and fillers is proposed to calculate the tensile modulus of polymer nanocomposites (Ec). In this model, fillers (sphere‐, cylinder‐ or plateshape) are randomly distributed in a matrix. If the particulate size is in the range of nanometers, the interfacial region will play an important role in the modulus of the composites. Important system parameters include the dispersed particle size (t), shape, thickness of the interfacial region (τ), particulate‐to‐matrix modulus ratio (Ed/Em), and a parameter (k) describing a linear gradient change in modulus between the matrix and the surface of particle on the modulus of nanocomposites (Ec). The effects of these parameters are discussed using theoretical calculation and nylon 6/montmorillonite nanocomposite experiments. The former three factors exhibit dominant influence on Ec. At a fixed volume fraction of the dispersed phase, smaller particles provide an increasing modulus for the resulting composite, as compared to the larger one because the interfacial region greatly affects Ec. Moreover, since the size of fillers is in the scale of micrometers, the influence of interfacial region is neglected and the deduced equation is reduced to Takayanagi's model. The curves predicted by the three‐phase model are in good agreement with experimental results. The percolation concept and theory are also applied to analyze and interpret the experimental results.
Studies of spinodal decomposition in a ternary polymer‐solvent‐nonsolvent system
Authors: Saxena Rahul , Caneba Gerard T.
Published: April 2004

Much of the work in modeling and computer simulation of spinodal decomposition has been done for binary systems. This work attempts to carry out the analysis of spinodal decomposition in ternary polymer‐solvent‐nonsolvent systems, where the solvent is the monomer used to produce the polymer and the nonsolvent is the major component. Various experimental methods are used to determine values of the parameters of the ternary version of the Cahn‐Hilliard equation of spinodal decomposition, such as cloudpoint experiments, time‐resolved light scattering in the ternary system, and morphological development of polymer membranes formed during the early stages spinodal decomposition. The combination of these experimental methods and computer simulation work shows the validity of the assumptions made in characterizing spinodal decomposition in ternary polymer systems of interest.
Mechanical performance of starch based bioactive composite biomaterials molded with preferred orientation
Authors: Sousa R. A. , Mano J. F. , Reis R. L. , Cunha A. M. , Bevis M. J.
Published: April 2004

Composites of blends of starch with ethylene vinyl alcohol copolymer (SEVA‐C) filled with 10, 30 and 50% by weight (wt.) of hydroxyapatite (HA–the major inorganic constituent of human bone) were produced by twin‐screw extrusion (TSE) compounding. These composites were molded into tensile test bars using two molding techniques: (i) conventional injection molding and (ii) shear controlled orientation in injection molding (SCORIM). The bars produced were mechanically characterized by means of tensile testing and dynamical mechanical analysis (DMA). The structure of the moldings was assessed by wide‐angle X‐ray diffraction (WAXD) and the failure surfaces of the moldings analyzed by scanning electron microscopy (SEM). The enhancement of stiffness observed with HA reinforcement results partially from the stiffening effect of the blend associated with the decrease in plasticizer content during the compounding stage. SCORIM was able to further increase the stiffness of SEVA‐C/HA composites, allowing a maximum improvement of 12% for 30% wt. HA as compared to conventional molding. DMA results showed that the reinforcement of SEVA‐C causes the broadening of the relaxation peak of the polymer, suggesting a structural change within the starch fraction that may be related with thermal degradation of the polymer. The addition of HA particles reduces the preferred orientation exhibited by the SEVA‐C matrix, which is believed to limit the maximum mechanical performance that can be attained. Nevertheless, composites based on a biodegradable matrix with modulus above 7 GPa (in the bounds of the lower limit for human cortical bone) could be successfully produced.
Strain‐rate and temperature effects on the deformation of polypropylene and its simulation under monotonic compression and bending
Authors: Ohashi F. , Hiroe T. , Fujiwara K. , Matsuo H.
Published: April 2004

Monotonic compressive loading and bending tests are conducted for solid polypropylene (PP) under constant or time‐varying strain‐rates and temperatures of 10, 25, 40°C. The observed compressive stress‐strain responses under constant conditions have revealed that the inelastic deformation behavior is remarkably dependent on loading rates and temperatures of normal use. The examination of such inelastic behavior has indicated that the strain‐rate effects correspond with the temperature effects based on the concept of time‐temperature equivalence. The viscoplastic constitutive theory based on overstress (VBO) has successfully reproduced the experimental responses with stress‐jumping phenomena using the equivalent time. Four‐point bending tests are performed under monotonic loading and holding for PP beams at three different temperatures. The observed deformation behavior has shown that the Bernoulli‐Euler hypothesis is valid. The VBO model and beam bending theory has generated the basic equations for PP beams, showing an analogy with the uniaxial one. In the numerical analysis, the equations are transformed into nonlinear ordinary differential equations with use of Gaussian quadrature for the spatial integrals. The comparison of numerical and experimental results has suggested some modifications for actually loaded moment taking the effect of deflection and friction into consideration. Finally, the numerical calculation has simulated the experimental time‐histories of curvatures fairly well.
Haze of polyethylene films—effects of material parameters and clarifying agents
Authors: Andreassen Erik , Larsen Åge , Nord‐Varhaug Katrin , Skar Merete , Øysæd Harry
Published: April 2004

Effects of material parameters on the haze of blown films were analyzed. Four linearlow‐density polyethylenes (two metallocene grades and two Ziegler‐Natta grades) were studied in combination with three additives (two sorbitol‐based clarifying agents and a low‐molecular‐weight long‐chain branched polyethylene). One of the sorbitol‐based additives reduced the haze of both the metallocene materials in this study, but did not have any positive effect on the two Ziegler‐Natta materials. The variation in haze among the four base materials was directly related to the root‐mean‐square surface roughness (σ). When considering all 16 material/additive combinations, the link between haze and surface topography was not a simple σ‐haze relationship, but the haze was correlated with the average distance between adjacent surface profile peaks, the average slope, and the power spectral density at high lateral frequencies. Both of the mechanisms referred to in the literature, extrusion‐induced haze and crystallization‐induced haze, were probably active for the films in this study.
Polymorphic behavior of nylon 6/saponite and nylon 6/montmorillonite nanocomposites
Authors: Wu Tzong‐Ming , Chen Erh‐Chiang , Liao Chien‐Shiun
Published: April 2004

X‐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

The 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

In 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

In 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

De 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

A 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

The 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

Compressive 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

This 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

Mechanical 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

Morphological 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

The 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

The 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

Mixed 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

Analysis 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

The 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

The 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.
Brittle‐ductile transitions in polyethylene
Authors: O'connell P. A. , Duckett R. A. , Ward I. M.
Published: April 2004

The 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

In 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

The 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

The 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

Flow‐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

The 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

Reactive 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

A 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

The 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

Blends 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.