bluuebunny/crossref_metadata_2025 huggingface dataset:
An experimental study of morphology and rheology of ternary Pglass‐PS‐LDPE hybrids
Authors: Guschl Peter C. , Otaigbe Joshua U.
Published: April 2004

Ternary blends of low‐density polyethylene (LDPE), polystyrene (PS), and a lowTgtin‐based phosphate glass (Pglass) were prepared at compositions ranging from 0–50 vol% Pglass in which either LDPE or PS was the continuous matrix phase. Differential scanning calorimetry was used to investigate the phase behavior of the pure components, PS‐LDPE blends and binary Pglass‐polymer hybrids. Interesting steady‐shear and transient rheology was observed for the hybrids. In particular, the steady shear viscosity curves for the hybrids of ϕPglass≤ 30% exhibited unusual, four‐region flow behavior, similar to that of liquid crystalline polymers. Two Newtonian plateaus at low (\documentclass{article}\pagestyle{empty}\begin{document}${\rm \dot \gamma }$\end{document}≤ 0.1 s−1) and moderate (0.4 ≤\documentclass{article}\pagestyle{empty}\begin{document}${\rm \dot \gamma }$\end{document}≤ s−1) shear rates connected by two distinct shear‐thinning regimes were apparent. This observed rheology is ascribed to a unique composite morphology of these multi‐component systems. Rheological data on the binary Pglass‐polymer systems suggest that the presence of the Pglass within both PS and LDSE contributes significantly to this unusual behavior, perhaps because of the interfacial behavior between the phases. Micrographs obtained via scanning electron microscopy reveal preferential placement of the Pglass phase dispersed within the PS‐phase and surrounding the LDPE phase. Optical shearing data confirmed the evolution of this microstructure under specific shear conditions.
Study on the phase behavior of EVA/PS blends during in situ polymerization
Authors: Cheng Shih‐Kai , Wang Cheng‐Chien , Chen Chuh‐Yung
Published: April 2004

A triangular phase diagram of the polystyrene/styrene/ethylene vinyl‐acetate (PS/SM/EVA) system is established to account for the phase change during polymerization of SM. The phase behaviors for EVA and PS domains in the SM polymerization system are also studied by an optical microscope (OM) and a photometer. Both EVA and PS dissolve in SM quite easily, but PS and EVA are immiscible. Hence, the exclusion of PS from the EVA phase domain results during the polymerization. That is, the polymer solution will be phase‐separated at the initial stage of polymerization. Additionally, EVA phase inversion occurs as the conversion of SM increases to 15%, at which the volume ratio of EVA/PS is approximately unity. Monitoring the light transmittance level of EVA/PS/SM solution during polymerization, the EVA phase proves to have been completely inverted to the dispersed phase when the SM conversion reaches 20%.
Probe segregation and Tg determination of a supported ultra‐thin polystyrene film studied by X‐ray and neutron reflectivity, and SIMS
Authors: White Chris , Wu Wen‐Li , Pu Yuxie , Rafailovich M. , Sokolov J.
Published: April 2004

Selective deuteration combined with X‐ray and neutron reflectivity has been used to determine the extent of probe segregation to an interface in ultra‐thin polymer films as a function of the number of thermal cycles. The extent of probe segregation to the interface was also investigated using Secondary Ion Mass Spectroscopy (SIMS). Significant probe segregation was not evident in these studies. X‐ray reflectivity has also been employed to measure the coefficient of thermal expansion of ultra‐thin polystyrene films supported on quartz. The glass transition temperature determined with this method is equivalent to that measured for bulk polystyrene films.
TOF‐SIMS study of injection‐molded polystyrene
Authors: Pisciotti Francesco , Lausmaa Jukka , Boldizar Antal , Rigdahl Mikael
Published: April 2004

The purpose of this study was to provide experimental evidence of the separation of the polymer components at different scales during conventional processing. This was achieved by characterizing the surface and the bulk (cross section) of moldings manufactured with a high‐flow grade and a low‐flow grade of commercial polystyrene by the time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) analytical technique. Owing to the geometric constraints of the mold used, a weld was also obtained. Different surface spectra were observed for the two molded polystyrenes. The surface of the high‐flow grade moldings showed the spectral features of low‐molar polyolefin (paraffin) contaminants, whereas the bulk was dominated by polystyrene. Spectra from both the surface and the bulk of the low‐flow grade moldings were characteristic of polystyrene. Mold‐filling effects on the surface composition were observed in the flow front region of molded short‐shots of the low‐flow grade. The spectral changes indicated the abundance, in the surface, of the high end of the molar‐mass distribution of the material during the mold filling process. Two‐dimensional maps of the secondary ions from the low‐flow grade also showed an occasional alkali contamination, preferentially along the notch of the weld.
Preparation and properties of polyethylene‐clay hybrids
Authors: Kato M. , Okamoto H. , Hasegawa N. , Tsukigase A. , Usuki A.
Published: April 2004

Polyethylene‐clay hybrids have been prepared successfully by melt compounding with maleic anhydride grafted polyethylene (MA‐g‐PE), organophilic clay and polyethylene. In these polyethylene‐clay hybrids, the silicate layers of the clay were exfoliated and dispersed to the monolayers. The hybrids exhibit higher tensile yield strengths and tensile moduli than those of polyethylene matrices and those of polyethylene‐inorganic clay composites. When the 5‐wt% clays were loaded, the tensile yield strength and the tensile modulus of the hybrid were, respectively, 1.4 and 1.8 times higher than those of the polyethylene/MA‐g‐PE mixture. The gas permeability of that clay hybrid decreased 30% compared with polyethylene/MA‐g‐PE mixture.
Continuous extrusion of microcellular polycarbonate
Authors: Gendron Richard , Daigneault Louis E.
Published: April 2004

Extruded microcellular foams have been obtained from mixtures of polycarbonate (PC) and n‐pentane. Cell diameters were in the range of 2 to 5 μm and the foam densities varied between 400 and 700 kg/m3. Although two types of PC have been investigated, one linear and one branched, the presence of side branchings did not modify the extruded foam characteristics. Use of carbon dioxide as the blowing agent was also attempted, and cell sizes below 10 μm have been successfully obtained. One prerequisite for microcellular foaming was believed to consist in a concentration of the blowing agent close to its limit of solubility as that defined under the actual processing conditions of pressure and temperature. This hypothesis was validated from the observation of extrusion of regular PC foams (intermediate to low densities and cell sizes ranging between 100 μm and 1 mm) using moderate concentrations of blowing agents, and from solubility and viscosity measurements on similar polymer/blowing agent systems.
Effects of die geometry on cell nucleation of PS foams blown with CO2
Authors: Xu Xiang , Park Chul B. , Xu Donglai , Pop‐Iliev Remon
Published: April 2004

This paper investigates the effect of varying the geometry of the die on the cell nucleation behavior of extruded PS foams blown with CO2. Three interchangeable groups of carefully calibrated filamentary dies have been used in the experimental study. The dies were deliberately designed to have either different pressure drop rates while having identical die pressures and flow rates, or different die pressures while having identical pressure drop rates and flow rates. The experimental results revealed that the geometry of the die governs the cell density of extruded PS foams, especially because of its significant effect on the pressure drop rate across the die. However, the effect of the die back pressure on the cell density was found to be marginal, whereas its effect on the cell morphology was found to be predominant. In addition, regardless of die geometry, the CO2content proved to be a very sensitive parameter with respect to the cell nucleation behavior of extruded PS foams. On the other hand, the cell density was slightly improved by an increase of the tale content, especially at reduced concentrations of CO2.
Rheological effects of polyethylenes in film blowing
Authors: Fang Yunli , Carreau Pierre J. , Lafleur Pierre G.
Published: April 2004

The aim of this work is to correlate the rheological properties and processability of various polyethylenes during the film‐blowing process. The effect of rheology on the kinematics and dynamics of film blowing for five different polyethylene resins has been extensively studied using a fully instrumented laboratory unit. The complex viscosity, shear viscosity, uniaxial elongational viscosity, and non‐uniform biaxial elongational viscosity, as well as the strain rates and stresses during film blowing, have been determined and correlated to the bubble stability.G′ versusG″ plots were found to be virtually independent of temperature for all polymers investigated. The more elastic polymers (largerG′ values) were found to be more stable in film blowing. Also, the more stable polymer melts were found to be those possessing larger elongational properties.
Hyperbranched polymers in cationic photopolymerization of epoxy systems
Authors: Sangermano M. , Malucelli G. , Bongiovanni R. , Priola A. , Harden A. , Rehnberg N.
Published: April 2004

Mixtures of epoxy resins in the presence of epoxy hyperbranched polymers (HBP), in the range of 5–15 wt%, were investigated in the cationic photocuring process. No significant differences in rate of polymerization or final epoxy groups conversion were observed. At low concentration, HBP acts as plasticizer and causes a decrease of the glass transition temperature of the epoxy matrix and of the E′ value. At higher concentration (about 15 wt%), two Tg values are evident, indicating a biphasic structure of the system. The SEM analysis of the fracture surface of the samples confirms a particulate structure with separate HBP domains interconnected to the epoxy matrix. In all the samples investigated, a clear increase of the impact resistance was observed, resulting either from the plasticization effect or from the particulate structure induced by the presence of the HBP resin.
Tribological behavior of pure and graphite‐filled polyimides under atmospheric conditions
Authors: Samyn P. , De Baets P. , Schoukens G. , Hendrickx B.
Published: April 2004

As the use of common engineering plastics in tribological systems is limited to low sliding velocities and low loads because of creep and insufficient temperature resistance, there is increasing interest in application of high‐performance polymers such as polyimides, characterized by their ability to maintain favorable mechanical properties up to their melting point. However, for practical design, tribotesting remains necessary for determination of the material's performance under a given contact situation. In this article, two commercially available polyimides are tested at relatively high sliding velocities and contact pressures under atmospheric conditions of temperature and humidity. A consistent overview of tendencies in friction and wear for pure polyimides as a function of applied normal loads and sliding velocities is given. Addition of 15% by weight graphite powder as internal solid lubricant strongly influences friction and wear. Its behavior is compared with pure polyimide grades and differences are discussed in relation with experimental measured bulk‐temperatures. A linear temperature law is derived as a function of pv‐levels and a steady‐state condition is found at different temperature levels, in accordance with thermal conductivity of the polymer bulks. In case of graphite additives, a steady state in temperature coincides with the regime condition of wear rate.
Enhanced apparent payne effect in a gum vulcanizate at low temperature approaching glass transition
Authors: Pan Xiao‐Dong , Kelley Edward D.
Published: April 2004

For a vuleanized elastomer compound containing no filler, variation of dynamic moduli with strain was examined in the transition zone approaching glass transition at 0.1, 1, 10, and 15 Hz. In the complete absence of filler‐filler/filler‐polymer interactions, the nonlinearity in dynamic moduli becomes enhanced upon approaching glass transition regardless of testing frequency. Under the test protocol employed, the extraordinary nonlinearity at 10 Hz and 15 Hz is shown to be associated with a spectacular shear‐heating event. At 10 Hz and −19°C, a pronounced yielding‐like peak in the in‐phase stress component emerges at small strain (< 2%) during testing of increasing strain. However, the corresponding temperature rise here is only about 0.4°C. Interestingly, at or above 0°C, no such peak in the in‐phase stress component emerges for compounds filled with reinforcing filler above the percolation threshold. Discussion is also made relating the observations to the sliding friction of rubber materials.
Experiments on the induction welding of thermoplastics
Authors: Stokes Vijay K.
Published: April 2004

In induction welding of thermoplastics, induction heating of a gasket, made of a ferromagnetic‐powder‐filled bonding material and placed at the interface of thermoplastic parts to be joined, is used to melt the interface; subsequent solidification of the melt results in a weld. Tensile tests on induction butt‐welds of polycarbonate (PC), poly(butylene terephthalate) (PBT), and polypropylene (PP) are used to characterize achievable weld strengths, and microscopy is used to correlate weld strength with the morphology of failure surfaces. In PC, PBT, and PP relative weld strengths as high as 48%, 43%, and 55% of the respective strengths of PC, PBT, and PP have been demonstrated. Relative weld strengths on the order of 20% have been demonstrated in PC‐to‐PBT welds.
Prediction of flow patterns in the polyurethane foaming process by numerical simulation considering foam expansion
Authors: Mitani Tetsuo , Hamada Hiroyuki
Published: April 2004

We present a foam flow model for flow pattern prediction in the polyurethane foaming process that considers the flow caused by foam expansion due to bubble generation. The flow pattern in the cavity is calculated by taking into account the initial volume shape and the rate of foam expansion of a poured reaction mixture. The validity of the model is investigated by applying it to the Hele‐Shaw formulation, which assumes that the cavity is very thin compared to its width. The predicted flow patterns generally agree closely with experimental results measured in panel‐type molds. A three‐dimensional simulation is further developed based on the Stokes flow. The numerical formulation is performed by the control volume based‐finite element method with an equal‐order velocity‐pressure formulation that does not exhibit spurious pressure modes. The flow patterns predicted by the three‐dimensional simulation agree very closely with the experimental results. In particular, it clearly expresses the edge effect, in which the flow slows down at the edge, which is ignored in the Hele‐Shaw formulation. This numerical simulation is suitable for rapid determination of the pouring position, volume of the mixture, and the air vent position.
Tensile mechanical behavior of linear high‐density polyethylenes modified with organic peroxide
Authors: Pérez Claudio J. , Cassano Guillermo A. , Vallés Enrique M. , Quinzani Lidia M. , Failla Marcelo D.
Published: April 2004

The molecular structure of several high‐density polyethylenes of different molecular weights and vinyl contents was modified without altering their thermoplastic character using an organic peroxide. Chain linking was the main chemical event that occurred during the modification process. Samples of these polymers were crystallized from the melt, generating materials with different morphologies. Two crystallization procedures were followed: slow cooling and quenching. The density and crystallinity of the polymers were found to be slightly dependent on the molecular structures generated by the modification process. Tensile tests were performed at room temperature to evaluate the mechanical behavior of the polymers. The mechanical response of some of the slowly cooled samples changed from brittle to ductile when increasing concentrations of peroxide were added to the formulation. All the quenched samples displayed ductile behavior. The elastic modulus and yield stress were found to increase linearly with the crystallinity of the polymers independently of the molecular structure generated by the modification process. The molecular weight of the modified polymers appears to be the main structural property that influences the draw ratio after break and the ultimate tensile stress of the samples. The draw ratio diminishes, while the ultimate tensile stress increases with the molecular weight of the polymers, irrespective of the evolution of other molecular parameters.
Super‐toughness in compatibilized poly(butylene terephthalate)/poly(ethylene‐octene) copolymer blends
Authors: Aróstegui A. , Nazábal J.
Published: April 2004

Poly(butylene terephthalate) (PBT)/poly(ethylene‐octene) (PEO) blends containing 1.0 wt% epoxy and from 0 to 30 wt% PEO were obtained by extrusion and injection molding. The blends were composed of two pure amorphous phases. The observed torque increases showed that epoxy reacted with PBT, leading to a fine and homogeneous morphology up to 15 wt% PEO content, which appeared larger and more heterogeneous at higher PEO contents. Toughness values fifteen‐fold those of pure PBT were obtained with only 13 wt% PEO. The tensile properties, including ductility, decreased with increasing PEO content, indicating that the adhesion level necessary for high ductility is higher than that necessary for super‐toughness. The inter‐particle distance (τ) was the main parameter that controlled toughness. The comparison of the results of this work with those of the same PBT/PEO blends with two different compatibilizers provides additional strong evidence of the adhesion at the interphase as the main parameter that controls the critical τ in these modified thermoplastic/rubber blends.
Measurements of the thermal conductivity and thermal diffusivity of polymers
Authors: Zhang Xing , Fujii Motoo
Published: April 2004

In this paper, the thermal conductivity and thermal diffusivity of nine polymers were measured by using the transient short‐hot‐wire method. The corresponding specific heat was measured with a commercial Differential Scanning Calorimeter (DSC). The effects of temperature on the thermal conductivity, thermal diffusivity, and the product of density and specific heat are further discussed. The results show that the transient short‐hot‐wire method can be used to measure the thermal conductivity, thermal diffusivity, and the product of density and specific heat of polymers within uncertainties of 3%, 6%, and 9%, respectively.
Spinning and drawing properties of ultrahigh‐molecular‐weight polyethylene fibers prepared at varying concentrations and temperatures
Authors: Jian Tao , Shyu Wei‐De , Lin Yue‐Tang , Chen Kan‐Nan , Yeh Jen‐Taut
Published: April 2004

The concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed.
Effect of wall slip on blown film thickness distribution
Authors: Higuchi Hiroyuki , Sato Mikio , Koyama Kiyohito
Published: April 2004

One of the most important materials for blown film is high‐density polyethylene (HDPE) with wide molecular weight distribution. First, we computed a wall stress at the entrance of a spiral groove in a particular die during blown film processing on a particular condition, to which a similar condition is widely utilized in a film works. The computed value is about 170 kPa, while the HDPE melt slips at die wall at stresses above approximately 50 kPa. The stress of 170 kPa is sufficiently large for the slip occurrence of the melt. Then, we investigated the effects of wall slip and melt visosity on film thickness distribution in the circumferential direction; the distribution tends to decrease with decreasing wall slip and melt viscosity. This tendency is explained by considering flow distribution in a spiral mandrel die and polymer melt flow characteristics.
Water‐assisted injection molding of thermoplastic materials: Effects of processing parameters
Authors: Liu Shih‐jung , Chen Yen‐show
Published: April 2004

The objective of this study was to experimentally investigate the effects of various processing parameters on the water‐assisted injection molding of thermoplastic materials. Experiments were carried out on a lab‐developed water‐assisted injection molding system, which included a water pump, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. Two types of water injection pins designs were proposed to mold the parts. After molding, the lengths of water penetration in molded parts were measured. The effects of different processing parameters on the lengths of water penetration were determined. It was found that the shrinkage rate and the viscosity of the polymeric materials, and the void shapes of the hollowed cores mainly determined the water‐penetration lengths in molded products. In addition, a comparison has been made between the parts molded by water assisted injection molding and gas‐assisted injection molding. It was found that water‐assisted injection molded parts exhibit less uniform void sizes along the water channel. The cycle time for water‐assisted injection molded parts was shorter than that of conventional injection molded parts and gas‐assisted injection molded parts.
A study of residence time distribution in co‐rotating twin‐screw extruders. Part I: Theoretical modeling
Authors: Poulesquen A. , Vergnes B.
Published: April 2004

A theoretical model to determine the residence time distribution (RTD) in a co‐rotating twin‐screw extruder is proposed. The method consists of coupling a continuum mechanics approach with a chemical engineering one and allows us to obtain the RTD without any adjustable parameter. The process parameters are obtained using Ludovic® twin‐screw modeling software, and ideal reactors are chosen to depict the screw profile. The influence of screw speed, feed rate and viscosity on RTD are described on a fictive screw profile. The predictions of the model are in qualitative agreement with literature data. The key point of this procedure is obviously the correct association between an ideal reactor and a screw element.
Generalized slit flow of an ellis fluid
Authors: Steller Ryszard T.
Published: April 2004

Isothermal, steady‐state and fully developed flows of Ellis fluids in planar and annular slits are discussed. The flow equations derived for Ellis fluids describe also the flows of Newtonian and power law fluids as specific cases. The most important flows resulting from thp general theory, i.e., the pressure flows in flat and annular slits for stationary channel walls and at transverse and longitudinal movements of a wall, are analyzed in detail. Numerical verification of the results leads to the conclusion that the planar and annular flows of Ellis and power law fluids are qualitatively similar The quantitative differences resulting from the slit curvature and the type of constitutive equation are relatively large only for flows of strongly non‐New‐tonian liquids.
The effect of wall slip on the performance of fiat extrusion dies
Authors: Gifford W. A.
Published: April 2004

Flat extrusion dies are commonly used in a wide variety of film. Sheet and coating applications. Although flal dies can be designed to produce an exit flow distribution that is very uniform across most of the width, there will usually be a region along each side where it drops gradually to zero. This often requires trimming the edges of the film or sheet downstream in order to meet product specifications. It is commonly believed that treating the land area of the die with coatings that promote a small amount of wall slip will reduce the size of this edge effect and therefore improve die performance. This analysis shows that slip over the entire land region of the die will adversely affect die performance. Better performance is possible but only if the sides of the land are treated.
Rheological effects of the incorporation of chlorinated polyethylene compatibilizers in a HDPE/PVC blend
Authors: Zárraga A. , Muñtoz M. E. , Peña J. J. , Santamaría A.
Published: April 2004

Small‐amplitude oscillatory measurements, creep and recoil experiments, capillary extrusion flow and shrinkage measurements have been performed to elucidate the effect of block and random chlorinated polyethylene (CPE) on the rheological properties of a ternary high density polyethylene (HDPE)/ poly(vinyl chloride) (PVC)/CPE system. It is observed that the storage modulus, the complex viscosity and the steady stale viscosity at low shear rates decrease when a small amount of CPE is incorporated to 50/50 (wt.) HDPE/PVC binary blend. However, at high shear rates, in experiments performed in extrusion flow, the trend is reversed, and the incorporation of CPE to the binary blend increases viscosity. The high melt elasticity of HOPE is severely reduced when this polymer is mixed with PVC, but when CPE is included as a third component, elastic recovery is considerably increased. All these rheological results, which are independent of type (block or random) of CPE used, are explained considering the morphological changes produced by CPE and during extrusion flow.
Crystallization characteristics of polyoxymethylene with attapulgite as nucleating agent
Authors: Xu Wei‐Bing , He Ping‐Sheng
Published: April 2004

The nucleation of polyoxymethylene (POM) crystallization using attapulgite was studied using differential scanning calorimetry, polarized light microscopy, wideangle X‐ray diffration and mechanical testing. Two isothermal crystallization kinetic equations were employed to describe the crystallization of virgin POM and POM containing attapulgite as a nucleating agent. The addition of attapulgite decreased the spherulitic size of POM, and interfacial free energies per unit area perpendicular to the molecular chain direction ρe, accelerated the crystallization growth rate and enhanced the impact toughness of POM, but no change occurred for the hexagonal system of POM. The addition of attapulgite up to its saturation concentration in POM increased the number of effective nuclei by three orders of magnitude. A high concentration of attapulgite caused agglomeration of the agent and lowered the number of effective nuclei.
Grafting of poly(vinyl chloride) and polypropylene with styrene in a supercritical CO2 solvent medium: Synthesis and characterization
Authors: Trivedi Akshay H. , Kwak Soonjong , Lee Sunggyu
Published: April 2004

Graft copolymerization of styrene onto poly(vinyl chloride) (PVC) and polypropylene (PP) was carried out in a supercritical CO2 medium using AIBN as a free radical initiator. The supercritical CO2 medium served as a reaction medium in addition to being a solvent for the styrene monomer and the free radical initiator. The reaction temperature and pressure were kept above the critical points of the solvent‐monomer mixture to form a homogeneous single‐phase medium. The resulting graft copolymers were characterized using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) techniques. The weight percent of grafting was determined using IR absorbance ratio technique. TGA results showed that the thermal stabilily of grafted copolymer of PVC was better than that of PVC, while grafted copolymer of PP had poorer thermal stability than PP. DSC results showed that glass transition temperatures (Tg's) of the grafted copolymers were higher than those of the starting polymers PVC and PP. The presence of polystyrene attached to the backbone polymer was confirmed by 1H NMR and 13C NMR analyses.
Effects of CO2 on crystallization kinetics of polypropylene
Authors: Takada Mitsuko , Tanigaki Masataka , Ohshima Masahiro
Published: April 2004

When CO2 dissolves into a polypropylene (PP), its crystallization kinetics changes These changes were studied, in the expectation that the information would reflect on the behavior of other semicrystalline polyolefins. The isothermal crystallizatior rate of the PP‐CO2 solutions was measured using a high‐pressure differential scanning calorimeter (DSC), which performed calorlmetric measurements while keeping the polymer in contact with pressurized CO2. Although the measured crystallizatior rate followed the Avrami equation, the value of the crystallization kinetic constant was different from that measured for PP crystallized in air under atmospheric pressure. The dissolved CO2 decreased the overall crystallization rate of PP within the nucleation dominated temperature region. This suggests that the dissolved CO2 decreases the melting and the glass transition temperatures and prevents formation of critical size nuclei.
Transparency of polymer blends
Authors: Maruhashi Yoshitsugu , Iida Setsuko
Published: April 2004

Polymer blending is useful for improving physical properties. Blends of transparent polymers are generally hazy. However, transparency is required in many products such as packages (especially PET bottles). The miscible blends, PET (polyethylene terephthalate)/PBT (polybuthylene terephthalate), maintain transparency in almost all cases regardless of the blending ratio, whereas the immiscible blends, PET/MxNYLON (MXD6 nylon, i.e. polymethaxylirene adipamide) and PET/PMAI (polymethacril imide, i.e. N‐methyl dimethyl glutarimide) become hazy as the blending ratio increases. The reason for this haze is the number and size of the dispersed particles. Differences in the refractive indices of various polymers also have a large influence on haze. Stretching makes even the transparent blends hazy in the case of PET/MxNYLON. One reason for this phenomenon is that stretching increases the size of the dispersed particles in the sheet plane. A second reason is that the difference in the anisotropic refractive indices of the matrix and the dispersed phase is increased by stretching. These effects are very consistent with light scattering theory.
Computer simulation of stress‐induced crystallization in injection molded thermoplastics
Authors: Guo Jianxin , Narh Kwabena A.
Published: April 2004

Injection molding of semicrystalline plastics was simulated with the proposed stress‐induced crystallization model. A pseudo‐concentration method was used to track the melt front advancement. Stress relaxation was considered using the WFL model. Simulations were carried out under different processing conditions to investigate the effect of processing parameters on the crystallinity of the final part. The simulation results reproduced most of the experimental results in the literature. Comparison is made between the slow‐crystallizing polymer (PET) and fast‐crystallizing polymer (PP) to demonstrate the effect of stress on the crystallization kinetics during the injection molding process for materials with different crystallization properties. The results show that for fast‐crystallizing plastics, stress has little effect on the final crystallinity in the injection molded parts.
Processing and properties of polymeric nano‐composites
Authors: Wang Hua , Zeng Changchun , Elkovitch Mark , Lee L. James , Koelling Kurt W.
Published: April 2004

Polymeric nano‐composites are prepared by melt intercalation in this study. Nano‐clay is mixed with either a polymer or a polymer blend by twin‐screw extrusion. The clay‐spacing in the composites is measured by X‐ray diffraction (XRD). The morphology of the composites and its development during the extrusion process are observed by scanning electron microscopy (SEM). Melt viscosity and mechanical properties of the composites and the blends are also measured. It is found that the clay spacing in the composites is influenced greatly by the type of polymer used. The addition of the nano‐clay can greatly increase the viscosity of the polymer when there is a strong interaction between the polymer and the nano‐clay. It can also change the morphology and morphology development of nylon 6/PP blends. The mechanical test shows that the presence of 5–10 wt.% nano‐clay largely increases the elastic modulus of the composites and blends, while significantly decreases the impact strength. The water absorption of nylon 6 is decreased with the presence of nano‐clay. The effect of nano‐clay on polymers and polymer blends is also compared with Kaolin clay under the same experimental conditions.
Propylene polymerization in a semibatch reactor. Analysis of soluble metallocene catalyst behavior through reactor modeling
Authors: Belelli P. G. , Ferreira M. L. , Lacunza M. H. , Damiani D. E. , Brandolin A.
Published: April 2004

We study the process involved in metallocene activation and further propylene polymerization. In this paper, we begin by analyzing the behavior of soluble metallocene in propylene polymerization before advancing to the study of the heterogeneous polymerization. Experimental data obtained in a semibatch laboratory polymerization reactor using ethylenbisindenylzirconium dichloride (EtInd2ZrCl2)/ methylaluminoxane (MAO) are combined with a mathermatical model providing useful information such as number of active sites and their activation patterns. We present a mathematical model for the reactor that predicts not only reactor productivity but also the molecular properties of the product. We apply the model to soluble systems in order to find the optimal parameters for the catalyst itself and in the presence of different types of additives such as aluminum chloride (AlCl3) and ethyl benzoate (E.B.).
Microlayer coextrusion as a route to innovative blend structures
Authors: Jarus D. , Hiltner A. , Baer E.
Published: April 2004

Nanolayer and microlayer coextrusion is a method for combining two or three polymers as hundreds or thousands of alternating layers with individual layers as thin as tens of nanometers. The possibility for utilizing microlayer coextrusion as a tool for creating microplatelets of high aspect ration was explored. Polypropylene (PP) was combined with polyamide‐66 (PA66) in microlayers. A high volume fraction of PA66 microplatelets dispersed in PP was achieved by injection molding the microlayered materials at a temperature intermediate between the melting points of the two constituents. The difference in melting temperatures provided a broad processing window of about 60°C in which the PP layers melted to form the matrix whereas the PA66 layers remained in the solid state as dispersed microplatelets of high aspect ration. The resulting material had significantly improved oxygen barrier properties. An enhancement of 4–5 times over the barrier of the conventional melt blend resulted from increased tortuosity of the diffusion pathway.
Melt rheology of poly(lactic acid): Consequences of blending chain architectures
Authors: Lehermeier Hans J. , Dorgan John R.
Published: April 2004

The rheology of blends of linear and branched poly(lactic acid) (PLA) architectures is comprehensively investigated. Measurement of the melt rheological properties of PLA is complicated by degradation effects but the addition of 0.35 wt% tris(nonylphenyl) phosphite (TNPP) provides excellent stabilization over a range of temperatures. Master curves of dynamic viscosity constructed using time‐temperature superposition show significant dispersion for unstabilized samples; this behavior is accompanied by a loss of molecular weight. TNPP stabilized samples show excellent superposition throughout the entire frequency range and minimal loss in molecular weight. For the linear architecture, the Cox‐Merz rule is valid for a large range of shear rates and frequencies. The branched architecture deviates from the Cox‐Merz equality and blends show intermediate behavior. Both the zero shear viscosity and the elasticity (as measured by the recoverable shear compliance) Increase with increasing branched content. The viscosities of both the unstabilized samples and the TNPP stabilized samples roughly obey a log additivity mixing rule. The recoverable shear compliance is monotonic in blend composition and a mixing rule for this property is also presented. For the linear chain, the compliance is independent of temperature but this behavior is apparently lost for the branched and blended materials. Tensile and thermal properties of the blends are also measured and found to be roughly equal within the statistical error of the experiments. The results suggest that excellent control over rheological behavior of PLA is possible through blending chain architectures without compromising mechanical properties.
Structure and physical properties of biaxially stretched polyethylene terephthalate sheets under different heat‐set and stretch conditions
Authors: Maruhashi Yoshitsugu
Published: April 2004

The thermal shrinkage of heat‐set polyethylene terephthalate (PET) sheets at 85°C after stretching at low speed and low temperature was similar to that for sheets stretched at high speed and high temperature if the crystallinities of these sheets were the same. However, differences between other physical properties, such as yield strength, were observed, which may be due to differences in the amorphous phase. The sheets stretched at the higher temperature and higher speeds may have different structures in the molecular segments in the amorphous phase, more relaxed than in the sheets prepared at the lower speed and temperature.
Direct measurement of permeabilities at high pressures
Authors: Wiff D. R. , Roach J. F.
Published: April 2004

A new procedure for measuring the peermeability of a high pressure gas (10.34 MPa) through a polymeric material has been developed. The procedure employs a vacuum system on the low‐pressure side of the material. Although it gives a pressure difference of seven orders of magnitude during testing, the real purpose of the vacuum system is to allow the permeability measurements to be made rapidly for a small amount of transported material. The permeability of several commercial polymers to either natural gas or helium has been measured and is reported.
Effect of processing variables on the linear viscoelastic properties of SBS‐oil blends
Authors: Navarro F. J. , Martínez‐Boza F. J. , Partal P. , Gallegos C. , Muñoz M. E. , Areizaga J. , Areizaga J. , Santamaría A.
Published: April 2004

Block copolymers, especially styrene‐butadiene‐styrene three‐block copolymers (SBS), are recognized as especially effective asphalt modifiers because of their thermoplastic elastomeric properties. The concentration of copolymer, its ability to swell by the maltenic oils, and the processing variables are essential in the development of a three‐dimensional network in the polymer‐rich phase that enhances the vis‐coelastic properties of these modified binders. This swollen polymer phase may influence the mechanical properties of the modified bitumens and synthetic binders. This paper deals with the influences that processing variables exert on the linear viscoelastic properties of oil/SBS mixtures in a wide range of temperatures. From the experimental results obtained we may conclude that most of the oil/SBS blends studied are highly structured thermoplastic gels above a critical SBS concentration that depends upon temperature, time of processing and surrounding atmosphere.
Interfacial crosslinking and diffusion via extensional rheometry
Authors: Saito Takushi , Macosko Christopher W.
Published: April 2004

When a coextruded multilayer sheet is pulled in a uniaxial extensional rheometer the interfacial area per unit volume increases, amplifying interfacial effects. To investigate interfacial reaction, a pair of functional and miscible polyethylenes were co‐extruded into multilayer sheets (256 layers). One polyethylene contained 8 wt% glycidyl methacrylate comonomer the other 4 wt% anhydride grafts. The extensional force to pull the molten multilayer sheet was measured via a rotating clamp extensional rheometer (RME, Rheometric Scientific). Owing to the reaction in the interfacial region before and during the extension, the measured extensional force increased dramatically. The interfacial stress was extracted and correlated to the extent of interfacial crosslinking. The rate of interfacial crosslinking was found to exceed the rate of area generation at extension rates < 0.01 s−1. By annealing samples and then stretching them, the growth rate of the interlayer was determined, and a diffusion coefficient estimated.
Characterization of the cure‐state of DGEBA‐DDS epoxy using ultrasonic, dynamic mechanical, and thermal probes
Authors: White S. R. , Mather P. T. , Smith M. J.
Published: April 2004

Three experimental techniques were used to characterize the cure state of an epoxy resin system of DGEBA epoxide and DDS diamine curing agent. Samples were prepared from non‐stoichiometric monomer mixtures designed so as to simulate various stages of cure of a stoichiometrically prepared epoxy. Such an approach allows for variable temperature characterization of specimens without concern for ongoing chemical reactions that would cloud interpretation of results. Additional experiments were performed on stoichiometric samples that were isothermally cured. Differential scanning calorimetry (DSC) was used to measure the heat of reaction and glass transition temperature. Dynamic mechanical analysis (DMA) was used to measure complex modulus, while ultrasonic cure monitoring (UCM) was used to measure longitudinal velocity throughout cure. DSC analysis was found to be insensitive to changes occurring at the latter stage of polymer network development, especially after vitrification. DMA characterization, however, was found to be quite sensitive to the rubbery modulus (and as such, the cure state), but is limited to cure states above gelation. Only the UCM technique was robust enough to accommodate all cure states while providing highly sensitive measurements of mechanical property development.
Synthesis and characterization of ozonized polyethylene
Authors: Boutevin B. , Robin J. J. , Torres N. , Casteil J.
Published: April 2004

Polyolefins (LDPE and HDPE) can be ozonized with ozone/air gas flow to create peroxide and hydroperoxide groups on polymers. These reactive groups can be used to initiate radical polymerization of vinylic monomers and produce graft copolymers. In this study, the optimization of the experimental conditions and the explanation of the phenomena occurring during the ozonization of polyolefins in a fluidized bed have been studied. The most reproducible methods for placing peroxide and hydroperoxide groups onto polyolefins are the iodometric method and indirect titration by thiol. This work shows that it is necessary to control the temperature of the fluidized bed to avoid the acceleration of the reaction and the degradation of the polymers. Then, we studied the effect of different parameters such as the crystallinity and the granulometry of polymers, the time of ozonization and the effect of the load of the reactor on the quality of ozonization. Infrared spectroscopy and steric exclusion chromatography were used to characterize the ozonized polymers. We show that double bonds of PE, particularly vinyl groups, are very reactive to ozone and that ozonized HDPE leads essentially to the formation of hydroperoxide groups, whereas ozonized LDPE leads to the formation of peroxide groups.
Polyimides from isomeric biphenyltetracarboxylic dianhydrides and the effects of chemical structure on solubility
Authors: Tong Y. J. , Liu S. L. , Guan H. M. , Ding M. X.
Published: April 2004

A series of homopolyimides and copolyimides was synthesized by the solution condensation of biphenyltetracarboxylic dianhydride (BPDA) isomers and various diamines followed by chemical imidization. These polyimides had intermediate to high molecular weights with inherent viscosities of 0.34–1.01 dL/g for homopolyimides and 0.48–1.02 dL/g for copolyimides. Thermogravimetric analysis indicated that the aromatic polyimides were stable up to 500°C, and the 5% weight loss temperatures were recorded in the range of 506–597°C in an air atmosphere and in the range of 517–601°C in a nitrogen atmosphere, depending on the diamines used. The glass transition temperatures of aromatic homopolyimides were above 271°C, while the glass transition temperatures of the copolyimides increased with an increase in the 2, 2′, 3, 3′‐BPDA‐component. The effects of the chemical structure of the polymer chain on the solubility were investigated. It was found that the solubility of BPDA‐based polyimides could be improved by the introduction of flexible units, nonlinear and non‐coplanar units, and copolymerization. The polyimides with nonlinear and non‐coplanar units derived from 2, 2′, 3, 3′‐BPDA appeared to have prominently enhanced solubility in polar aprotic solvents and polychlorocarbons when compared with the homopolyimide derived from 3, 3′, 4, 4′‐BPDA.