Polymer Blends (polymer + blend)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Polymer Blends

  • immiscible polymer blend

  • Terms modified by Polymer Blends

  • polymer blend system

  • Selected Abstracts

    Effect of Organic Modification on the Compatibilization Efficiency of Clay in an Immiscible Polymer Blend

    Suprakas Sinha Ray
    Abstract Summary: This communication describes the effect of organic modifier miscibility with the matrices, and the effect of the initial interlayer spacing of the organoclay, on the overall morphology and properties of an immiscible polycarbonate/poly(methyl methacrylate) blend. By varying the organic-modifier-specific interactions with the blend matrices at the same time as changing the initial interlayer spacing of the organoclay, different levels of compatibilization were revealed. The evidence for the interfacial compatibilization of the organoclay was assessed by scanning electron microscopy observations and was supported by differential scanning calorimetry analyses. The effect on the level of clay exfoliation was also examined. Differential scanning calorimetry scans of virgin, montmorillonite, and various organically modified montmorillonite-compatibilized 40PC/60PMMA blends [source]

    Scanning Kelvin Probe Microscopy on Bulk Heterojunction Polymer Blends

    Klára Maturová
    Abstract Here, correlated AFM and scanning Kelvin probe microscopy measurements with sub-100,nm resolution on the phase-separated active layer of polymer-fullerene (MDMO-PPV:PCBM) bulk heterojunction solar cells in the dark and under illumination are described. Using numerical modeling a fully quantitative explanation for the contrast and shifts of the surface potential in dark and light is provided. Under illumination an excess of photogenerated electrons is present in both the donor and acceptor phases. From the time evolution of the surface potential after switching off the light the contributions of free and trapped electrons can be identified. Based on these measurements the relative 3D energy level shifts of the sample are calculated. Moreover, by comparing devices with fine and coarse phase separation, it is found that the inferior performance of the latter devices is, at least partially, due to poor electron transport. [source]

    Generation of Compositional-Gradient Structures in Biodegradable, Immiscible, Polymer Blends by Intermolecular Hydrogen-Bonding Interactions,

    B. Hexig
    Abstract A biodegradable, immiscible poly(butylenes adipate- co -butylenes terephthalate) [P(BA- co -BT)]/poly(ethylene oxide) (PEO) polymer blend film with compositional gradient in the film-thickness direction has been successfully prepared in the presence of a low-molecular-weight compound 4,4,-thiodiphenal (TDP), which is used as a miscibility-enhancing agent. The miscibilities of the P(BA- co -BT)/PEO/TDP ternary blend films and the P(BA- co -BT)/PEO/TDP gradient film were investigated by differential scanning calorimetry (DSC). The compositional gradient structure of the P(BA- co -BT)/PEO/TDP (46/46/8 w/w/w) film has been confirmed by microscopic mapping measurement of Fourier-transform infrared spectra and dynamic mechanical thermal analysis. We have developed a new strategy for generating gradient-phase structures in immiscible polymer-blend systems by homogenization, i.e., adding a third agent that can enhance the miscibility of the two immiscible polymers through simultaneous formation of hydrogen bonds with two component polymers. [source]

    Semiconductive Polymer Blends: Correlating Structure with Transport Properties at the Nanoscale (Adv. Mater.

    ADVANCED MATERIALS, Issue 7 2004
    To view the original paper click http://dx.doi.org/10.1002/adma.200305747 [source]

    Quantitative Analysis of Dielectric Constants from EFM Images of Multicomponent Polymer Blends

    Andrey V. Krayev
    Abstract Summary: A simple quantitative model for the analysis of EFM images of three- or more-component polymer blends is applied to determine the dielectric constants of the blend constituents. The value of the dielectric constant of PIPA calculated from the EFM images of POMA-PIPA-APP blend is determined in good agreement with the literature value. [source]

    Rheology and Physical Characteristics of Synthetic Biodegradable Aliphatic Polymer Blends Dispersed with MWNTs

    Seung Woo Ko
    Abstract PLA/PBAT blends and PLA/PBAT/MWNT nanocomposite systems were prepared via a melt mixing process to examine their thermal and rheological properties. To compare the polymer blend/MWNT nanocomposite with a pure polymer/MWNT nanocomposite, PLA/MWNT, PBAT/MWNT, and PLA/PBAT/MWNT nanocomposite systems were prepared. TEM and SEM were used to observe that one phase has better affinity with the MWNT, while the MWNT was found to increase both the thermal properties of the PLA/PBAT blends and rheological properties of the PLA/PBAT/MWNT nanocomposite with distinct shear-thinning behavior due to the addition of the MWNT. An increase in the storage (G,) and loss (G,) moduli for the PLA/PBT/MWNT nanocomposite was also observed. [source]

    Electromagnetic Interference (EMI) Shielding Effectiveness of PP/PS Polymer Blends Containing High Structure Carbon Black

    Mohammed H. Al-Saleh

    Nanocellular Foams of PS/PMMA Polymer Blends

    Tetsuo Otsuka
    Abstract A nanocellular PS/PMMA polymer blend foam was prepared, where bubble nucleation was localized in the PMMA domains. The blend, which contains dispersed nanoscale PMMA islands, was prepared by polymerizing MMA monomers in a PS matrix to form highly dispersed PMMA domains in the PS matrix by diffusion mixing. The resulting blend was foamed with CO2 at room temperature. A higher depressurization rate at lower foaming temperature made the bubble diameter smaller and the bubble density larger, and a higher PS composition in the blend resulted in a larger bubble density. A void with 40,50 nm in average diameter and a pore density of 8.5,×,1014 cm,3 was obtained as for the finest nanocellular foams. [source]

    Effect of Chain-Length Dependence of Interaction Parameter on Spinodals for Polydisperse Polymer Blends

    Xiyan Du
    Abstract Summary: The chain-length dependence of the Flory-Huggins (FH) interaction parameter is introduced into the FH lattice theory for polydisperse polymer-blend systems. The spinodals are calculated for the model polymer blends with different chain lengths and distributions. It is found that all the related variables, rn, rw, rz, and chain-length distribution, have effects on the spinodals for polydisperse polymer blends. The spinodals at different chain lengths. [source]

    Morphology in Immiscible Polymer Blends During Solidification of an Amorphous Dispersed Phase under Shearing

    Yves Deyrail
    Abstract Solidification under shear of dispersed polycarbonate (PC) fibers in copolymer polyethylene-methyl acrylate matrix (EMA) was investigated using a hot optical shear device. First, the deformation of PC droplets and its modeling under isothermal conditions were studied for comprehension purposes. Overall agreement with literature models was found and the main influence of the viscosity ratio has been stressed. Second, the morphology control through dynamic quenching was experimented. It consists of solidifying the amorphous PC dispersed phase under shear flow. Break-up times of PC fibers were taken into account. Shear rate and quenching-time balance was demonstrated. Thus, during dynamic solidification, a fibrillar morphology could be obtained through rapid quenching. Long quenching times allow nodular morphology, whose size depends on the shear rate used. PC rods can be obtained by adjusting the shear rate during dynamic quenching. La solidification sous cisaillement du polycarbonate (PC) dispersé dans une matrice copolymère éthylène-acétate de vinyle (EMA) a été suivie à l'aide d'un microscope et d'une platine de cisaillement chauffante. Dans un premier temps la déformation isotherme de billes de PC pour différentes températures a été étudiée, ainsi que sa modélisation. Une bonne corrélation avec les modèles issus de la littérature a été obtenue. L'importance du rapport des viscosités a été ainsi soulignée. Dans un second temps le contrôle de la morphologie par le procédé de « refroidissement dynamique » a été expérimenté. Celui-ci consiste à solidifier le PC sous cisaillement pendant le refroidissement. Les temps de rupture des fibres de PC ont été considérés et l'importance du couple gradient de cisaillement-temps de refroidissement sur le contrôle de la morphologie a été mis en évidence. Pendant la solidification, un refroidissement rapide permet d'obtenir une morphologie fibrillaire. [source]

    Drop Deformation and Breakup Mechanisms in Viscoelastic Model Fluid Systems and Polymer Blends

    Frej Mighri
    Abstract This paper reviews the dispersion mechanisms in viscoelastic systems under relatively high shear rate conditions. In particular, two non-Newtonian deformation and breakup mechanisms were revealed by flow visualization in a transparent Couette shearing setup. The first one is the dispersed droplet elongation perpendicular to the flow direction. This was observed only for viscoelastic drops and had been associated to normal force buildup in the droplet. The second deformation/breakup mechanism was observed in very high viscosity ratio polymer systems. It consists in erosion at the drop surface. Clouds of very small ribbons and sheets were developed around the drop then stretched and finally broken into very small droplets, rapidly distributed in the matrix. Cet article examine les mécanismes de dispersion dans les mélanges viscoélastiques à des taux de cisaillement relativement élevés. Deux nouveaux mécanismes de déformation et de rupture de gouttes viscoélastiques ont été révélés en utilisant un montage de visualisation transparent de type Couette. Le premier mécanisme est l'orientation de l'axe principal de la goutte perpendiculairement à la direction de l'écoulement, phénomène qui n'a été observé que pour des gouttes viscoélastiques. Ce phénomène a été relié au développement de forces normales (élasticité) à l'intérieur de la goutte. Le second mécanisme de déformation/rupture a été observé avec des systèmes de polymères fondus possédant des rapports de viscosité élevés. Il consistait en une érosion de la surface de la goutte générant ainsi un nuage de gouttelettes et de minces feuillets autour de la goutte principale. Ces derniers s'étiraient suite à l'écoulement de la matrice et finissaient par être brisés en gouttelettes très fines rapidement dispersées dans la matrice. [source]

    Excited-State Dynamics of a Hemicyanine Dye in Polymer Blends

    CHEMPHYSCHEM, Issue 4 2010
    Ah-Young Jee
    The twisting motion of trans -4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (4-DASPI) is studied in rigid environments. The elastic modulus of the medium is found to play a key role in the molecular rotor dynamics. The picture shows the isomerization rate constant of 4-DASPI as a function of the Young modulus of polystyrene/1-octene copolymer (PS/EOC) blends. [source]

    Kinetic analysis of thermo-oxidative degradation of PEEK/thermotropic liquid crystalline polymer blends

    M. Naffakh
    The thermal degradation behavior of blends of poly(aryl ether ether ketone), PEEK, with a thermotropic liquid crystalline polymer (TLCP), Vectra®, were investigated in an oxidative atmosphere, using thermogravimetric analysis under dynamic conditions. The theoretical weight loss curves of the blends were compared with the experimental curves in order to explain the effect of blending on the thermal stability of the pure polymers. The thermo-oxidative degradation of PEEK/Vectra® blends of different compositions takes place in various steps and the characteristic degradation temperatures and the kinetic parameters such as activation energy are strongly influenced by blending. Polymer blends based on this TLCP polymer had not been previously studied from kinetic viewpoint. POLYM. ENG. SCI. 46:129,138, 2006. © 2005 Society of Plastics Engineers [source]

    Relationship between cell morphology and impact strength of microcellular foamed high-density polyethylene/polypropylene blends

    Pornchai Rachtanapun
    Polymer blends, such as those resulting from recycling postconsumer plastics, often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher-value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell-population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Pure HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins because of the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well-developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. The cell morphology had a strong relationship with the impact strength of foamed samples. Improvement in impact strength was associated with well-developed microcellular morphology. Polym. Eng. Sci. 44:1551,1560, 2004. © 2004 Society of Plastics Engineers. [source]

    Charge Transfer Excitons in Polymer/Fullerene Blends: The Role of Morphology and Polymer Chain Conformation

    Markus Hallermann
    Abstract Here, it is shown how carrier recombination through charge transfer excitons between conjugated polymers and fullerene molecules is mainly controlled by the intrachain conformation of the polymer, and to a limited extent by the mesoscopic morphology of the blend. This experimental result is obtained by combining near-infrared photoluminescence spectroscopy and transmission electron microscopy, which are sensitive to charge transfer exciton emission and morphology, respectively. The photoluminescence intensity of the charge transfer exciton is correlated to the degree of intrachain order of the polymer, highlighting an important aspect for understanding and limiting carrier recombination in organic photovoltaics. [source]

    Ultrathin, Organic, Semiconductor/Polymer Blends by Scanning Corona-Discharge Coating for High-Performance Organic Thin-Film Transistors

    Hee Joon Jung
    Abstract A new thin-film coating process, scanning corona-discharge coating (SCDC), to fabricate ultrathin tri-isopropylsilylethynyl pentacene (TIPS-PEN)/amorphous-polymer blend layers suitable for high-performance, bottom-gate, organic thin-film transistors (OTFTs) is described. The method is based on utilizing the electrodynamic flow of gas molecules that are corona-discharged at a sharp metallic tip under a high voltage and subsequently directed towards a bottom electrode. With the static movement of the bottom electrode, on which a blend solution of TIPS-PEN and an amorphous polymer is deposited, SCDC provides an efficient route to produce uniform blend films with thicknesses of less than one hundred nanometers, in which the TIPS-PEN and the amorphous polymer are vertically phase-separated into a bilayered structure with a single-crystalline nature of the TIPS-PEN. A bottom-gate field-effect transistor with a blend layer of TIPS-PEN/polystyrene (PS) (90/10 wt%) operated at ambient conditions, for example, indeed exhibits a highly reliable device performance with a field-effect mobility of approximately 0.23 cm2 V,1 s,1: two orders of magnitude greater than that of a spin-coated blend film. SCDC also turns out to be applicable to other amorphous polymers, such as poly(, -methyl styrene) and poly(methyl methacrylate) and, readily combined with the conventional transfer-printing technique, gives rise to micropatterned arrays of TIPS-PEN/polymer films. [source]

    Inkjet-Printed Single-Droplet Organic Transistors Based on Semiconductor Nanowires Embedded in Insulating Polymers

    Jung Ah Lim
    Fabrication of organic field-effect transistors (OFETs) using a high-throughput printing process has garnered tremendous interest for realizing low-cost and large-area flexible electronic devices. Printing of organic semiconductors for active layer of transistor is one of the most critical steps for achieving this goal. The charge carrier transport behavior in this layer, dictated by the crystalline microstructure and molecular orientations of the organic semiconductor, determines the transistor performance. Here, it is demonstrated that an inkjet-printed single-droplet of a semiconducting/insulating polymer blend holds substantial promise as a means for implementing direct-write fabrication of organic transistors. Control of the solubility of the semiconducting component in a blend solution can yield an inkjet-printed single-droplet blend film characterized by a semiconductor nanowire network embedded in an insulating polymer matrix. The inkjet-printed blend films having this unique structure provide effective pathways for charge carrier transport through semiconductor nanowires, as well as significantly improve the on-off current ratio and the environmental stability of the printed transistors. [source]

    A New Supramolecular Route for Using Rod-Coil Block Copolymers in Photovoltaic Applications

    ADVANCED MATERIALS, Issue 6 2010
    Nicolas Sary
    A new polymer blend formed by poly(3-hexylthiophene)-poly(4-vinylpyridine) (P3HT- P4VP) block copolymers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is reported. The P4VP and PCBM are mixed together by weak supramolecular interactions, and the resulting materials exhibit microphase separated morphologies of electron-donor and electron-acceptor rich domains. The properties of the blend, used in photovoltaic devices as active layers, are also discussed. [source]

    In-line analysis of the influence of monomeric and oligomeric hindered amine on the hydrolysis of polycarbonate in a PC/ABS blend

    Vipin V. Rajan
    Abstract The polycarbonate/polyacrylonitrile butadiene styrene (PC/ABS) blends lose mechanical properties when exposed to outdoor conditions. This is due to the ultraviolet (UV) induced photo-oxidation of the PC phase and the polybutadiene portion of the ABS. It is known that ABS can be stabilised against terrestrial light by the use of hindered amine in combination with a UV absorber. However, such hindered amine cannot be used when PC is present in a multi component polymer blend. The hydrolysis of PC is accelerated when a small amount of hindered amine light stabilisers (HALS) is incorporated in the resin and is exposed to elevated temperature. In this article the effect of monomeric and oligomeric hindered amine on the hydrolysis of PC during the compounding of PC/ABS blend in a twin screw extruder at 240°C is observed by means of in-line UV-vis spectroscopy. Tinuvin 765 was used as monomeric hindered amine and Tinuvin 622 as oligomeric hindered amine. The molecular weight of the compounded sample was determined by gel permeation chromatography (GPC) and the rheological properties were observed using an online viscometer. It was found that the extent of hydrolysis induced by the oligomeric hindered amine is less compared to monomeric amine. It was also observed that polymeric hindered amine imparts better dispersion of the ABS phase into the polymer blend. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    The totally miscible in ternary hydrogen-bonded polymer blend of poly(vinyl phenol)/phenoxy/phenolic

    Shiao-Wei KuoArticle first published online: 28 MAY 200
    Abstract The individual binary polymer blends of phenolic/phenoxy, phenolic/poly(vinyl phenol) (PVPh), and phenoxy/PVPh have specific interaction through intermolecular hydrogen bonding of hydroxyl,hydroxyl group to form homogeneous miscible phase. In addition, the miscibility and hydrogen bonding behaviors of ternary hydrogen bond blends of phenolic/phenoxy/PVPh were investigated by using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy, and optical microscopy. According to the DSC analysis, every composition of the ternary blend shows single glass transition temperature (Tg), indicating that this ternary hydrogen-bonded blend is totally miscible. The interassociation equilibrium constant between each binary blend was calculated from the appropriate model compounds. The interassociation equilibrium constant (KA) of each individually binary blend is higher than any self-association equilibrium constant (KB), resulting in the hydroxyl group tending to form interassociation hydrogen bond. Photographs of optical microscopy show this ternary blend possess lower critical solution temperature (LCST) phase diagram. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

    Drug,polymer interaction and its significance on the physical stability of nifedipine amorphous dispersion in microparticles of an ammonio methacrylate copolymer and ethylcellulose binary blend

    Jingjun Huang
    Abstract Using spectroscopic and thermal analysis, this study investigated drug,polymer interaction and its significance on the physical stability of drug amorphous dispersion in microparticles of an ammonio polymethacrylate copolymer (Eudragit RL®) (RL) and ethylcellulose (EC) binary blend (RL/EC,=,2:1 w/w) prepared for use in controlled release of poorly water-soluble drugs. Solid dispersion of the model drug, nifedipine in the microparticles could be described as an ideal amorphous mixture for drug loadings up to 11% w/w. The antiplasticizing effect of the polymer blend was indicated by a significant increase in the glass transition point from ,50°C for the amorphous nifedipine to ,115°C for its solid solution. Moreover, shifts in infrared vibration wavenumber of nifedipine carbonyl and amine groups suggested that the hydrogen bonds (H-bonds) originally formed among nifedipine molecules were broken and replaced by those formed between nifedipine and polymers in the microparticles. Further infrared analysis on nifedipine amorphous dispersions with a single polymer, namely RL or EC, confirmed the proposed hydrogen-bonding interactions; and their stability study results suggested that both antiplasticizing effects and hydrogen bonding of EC and RL with nifedipine might be responsible for the physical stability of the microparticles of nifedipine amorphous dispersion with a RL/EC binary blend. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:251,262, 2008 [source]

    Direct characterization of phase behavior and compatibility in PET/HDPE polymer blends by confocal Raman mapping

    Shuangyan Huan
    Abstract Morphology, chemical distribution and domain size in poly(ethylene terephthalate)/high-density poly(ethylene) (PET/HDPE) polymer blends of various ratios prepared with and without maleic anhydride have been analyzed with confocal Raman mapping and SEM. The ratioimage method introduced here allows us to obtain enhanced chemical images with higher contrast and reliability. Compatibility numbers (Nc) are calculated to evaluate the compatibility of the blends. The incompatible polymer blends show heterogeneous distribution with phase separation behavior, while the semicompatible blends prepared with maleic anhydride show much smaller subphase distributions with less distinct interphases. After the blending modification by maleic anhydride of only 0.5%, the viscosity status and dispersibility between PET and HDPE could be substantially improved, and the interactions that exist between the two phases have also been proved by ATR-FT-IR results. High-spatial-resolution confocal Raman mapping coupled with the ratioimage method provides a very attractive way to characterize the compatibility and phase behavior of the polymer blend through different blending methodologies. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Electrospun, Biofunctionalized Fibers as Tailored in vitro Substrates for Keratinocyte Cell Culture

    Dirk Grafahrend
    Abstract Cell adhesion preventing fiber surfaces were tailored differently with bioactive peptides (a fibronectin fragment (GRGDS), a collagen IV fragment (GEFYFDLRLKGDK) and a combination of both) to provide an artificial extracellular matrix as a substrate for HaCaT keratinocyte cell culture. Therefore, a polymer blend containing a six-arm star-shaped statistical copolymer of ethylene oxide and propylene oxide in the ratio 80:20 (NCO- sP[EO- co -PO]) and poly-[D,L -(lactide- co -glycolide)] (PLGA) was electrospun. The resulting fibers were biofunctionalized and investigated as in vitro substrates using the HaCaT kerationcyte cell line. Appropriate surface chemistry on these electrospun fibers proved to prevent adhesion of keratinocytes, while additional immobilization of certain peptide sequences induced cell adhesion. These specific fibers enable investigation of immobilized active molecules and the subsequent cellular response to the scaffold. HaCaT keratinocytes were found to selectively adhere to those fibers modified with either collagen IV segment GEFYFDLRLKGDK or a mixture of the two peptide sequences GEFYFDLRLKGDK and GRGDS (1:1). However, the synergistic effects of both (the fibronectin fragment and the collagen IV fragment) seem to significantly increase the numbers of adherent keratinocytes. [source]

    Enhanced Stereocomplex Formation of Poly(L -lactic acid) and Poly(D -lactic acid) in the Presence of Stereoblock Poly(lactic acid)

    Kazuki Fukushima
    Abstract Stereoblock poly(lactic acid) (sb-PLA) is incorporated into a 1:1 polymer blend system of poly(L -lactic acid) (PLLA) and poly(D -lactic acid) (PDLA) that has a high molecular weight to study its addition effect on the stereocomplex (sc) formation of PLLA and PDLA. The ternary polymer blend films are first prepared by casting polymer solutions of sb-PLA, PLLA, and PDLA with different compositions. Upon increasing the content of sb-PLA in the blend films the sc crystallization is driven to a higher degree, while the formation of homo-chiral (hc) crystals is decreased. Lowering the molecular weight of the incorporated sb-PLA effectively increases the sc formation. Consequently, it is revealed that sb-PLA can work as a compatibilizer to improve the poor sc formation in the polymer blend of PLLA and PDLA. [source]

    Liquid-liquid equilibria of binary polymer blends: molecular thermodynamic approach

    Bong Ho Chang
    Abstract We extended and simplified the modified double-lattice model to binary polymer blend systems. The model has two model parameters, C, and C,. Those are not adjustable parameters but universal functions. In comparison with Ryu et al.'s simulation data for symmetric polymer blend with various chain lengths (r1 = r2 = 8, 20, 50, 100), C, is determined. Our results show that C, is negligible for symmetric polymer blend systems. The proposed model describes very well phase behaviors of weakly interacting polymer blend systems. [source]

    DGEBA monomer as a solvent for syndiotactic polystyrene

    Jaap Schut
    Abstract Syndiotactic polystyrene (sPS) has to be processed at high temperatures (i.e. >290°C due to its melting point of 270°C), which approaches its degradation temperature. We aim to facilitate the processing of sPS by lowering its melt temperature and viscosity with a curable epoxy/amine model system as reactive solvent, which will result in a thermoplastic-thermoset polymer blend. As a first step we therefore investigated the melting behaviour of sPS in epoxy monomer, established its phase diagram, and investigated the crystalline form of sPS in these mixtures. DGEBA epoxy monomer is found to be a solvent for syndiotactic polystyrene at temperatures above 220°C. The DGEBA-sPS phase diagram was established by means of DSC, on the basis of crystallization and melting peaks. The form of the curve in the phase diagram indicates that DGEBA is a poor solvent for sPS. In WAXS studies of blends only the , crystalline form was detected, not the , form, thus no sPS-DGEBA polymer-solvent compounds (clathrates) were detected. However, DGEBA can still serve as a monomer for improved processing as it depresses the crystallization temperature by 20 to 60 K upon addition of 20 to 90 wt% DGEBA respectively, while a 16 to 45 K melting peak depression can be observed by adding 20 to 90 wt% DGEBA. [source]

    Composites formed by glass fibers and PS-modified epoxy matrix.

    POLYMER COMPOSITES, Issue 6 2010
    Influence of the glass fibers surface on the morphologies, mechanical properties of the interphases generated
    In this work, the influence of the nature of the reinforcement surface on the interfacial morphologies developed in E-glass fibers/polystyrene (PS)-modified epoxy composites has been studied. Different surface modifications of the fibers were considered. In a complementary way, morphological analysis and nanoindentation measurements were carried out using atomic force microscopy to subsequently correlate the interfacial structure with the morphologies observed. In every composite, reaction-induced phase separation happened with a morphology composed of PS-rich domains immersed in an epoxy-rich phase. However, depending on the surface modification of the glass fibers, different distributions of PS-rich domains at the interfaces were obtained. The results were interpreted in terms of a gradual phase separation process because of stoichiometric gradients from the glass fibers surface to the matrix bulk caused by specific segregation of one of the components of the reactive epoxy mixture to the fibers occurs. It was concluded that specific and controlled reinforcement modification allows obtaining tailored interfaces formed by a polymer blend and a reinforcement in which the morphology can be previously selected. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source]

    Formation of a fibrillar morphology of crosslinked epoxy in a polystyrene continuous phase by reactive extrusion

    Françoise Fenouillot
    An immiscible polymer blend where the dispersed phase is fibrillar was prepared by in situ crosslinking of the minor phase. A model polystyrene/epoxy-amine blend was selected on the basis of rheological (achievement of the fibrillar structure) and reactivity (fast crosslinking) criteria. The system was a polystyrene/diglycidyl ether of bisphenol A (DGEBA)-aminoethyl piperazine (AEP) blend. At the temperature of extrusion, 180°C, the DGEBA is immiscible in PS and heterogeneous material is obtained. The elongational flow imposed by drawing the extrudate at the die exit permitted controlled generation of a fibrillar morphology of the dispersed epoxy phase, with a fiber diameter of 1 ,m and an aspect ratio greater than 100. It was shown that when the amine comonomer was injected into the extruder, its reactivity with DGEBA at high temperature was high enough to ensure partial crosslinking of the epoxy. The fibrils were formed even though the gel point of the epoxy phase was exceeded. However, above a certain critical insoluble fraction that we estimated to be between 45% and 70%, a coarsening of the structure appeared, caused by the decreasing deformability of the domains and their coalescence. Finally, for our system, the crosslinking of the dispersed phase up to 90% of insoluble fraction did not totally stabilize the morphology after the second processing step (injection molding). Polym. Eng. Sci. 44:625,637, 2004. © 2004 Society of Plastics Engineers. [source]

    Reactive extrusion of recycled bottle waste material

    R. Hettema
    The objective of this study is to investigate the effect of reactive processing of commingled bottle waste polymer in an extruder. A variety of peroxides and monomers were tested to assess their influence on the final mechanical properties of the product. The reactive extruded polymer blends were prepared in two types of extruders: a co-rotating twin-screw extruder and a Buss co-Kneader single-screw extruder. Blends were analyzed for mechanical and thermal properties. The effectiveness of the different monomers and peroxides was evaluated in terms of improvement in impact properties. It has been found that the toughness of the polymer blend is improved by reactive processing. Depending on the amount and type of reactants, the impact strength can be improved by 220%, with a slight reduction in the modulus compared to an unmodified physical blend. The most suitable monomers were n-butylmethacrylate (BMA), t-butylamino ethylmethacrylate (TBAEMA) and a combination of styrene/maleic anhydride (ST/MAH). The peroxide should have a short half-lifetime compared to the average residence time in the extruder. The most effective monomers have a high initial reactivity and low rate of evaporation at the processing conditions used. Changes in processing conditions in the extruder influence the reaction conditions and therefore the final properties of the blend. Results were interpreted in terms of residence time, melting profile and peroxide concentration. [source]

    Organic Light-Emitting Diodes Based on Poly(9,9-dioctylfluorene- co -bithiophene) (F8T2)

    Peter A. Levermore
    Abstract A study of the optical properties of poly(9,9-dioctylfluorene- co -bithiophene) (F8T2) is reported, identifying this polymer as one that possesses a desirable combination of charge transport and light emission properties. The optical and morphological properties of a series of polymer blends with F8T2 dispersed in poly(9,9-dioctylfluorene) (PFO) are described and almost pure-green emission from light emitting diodes (LEDs) based thereon is demonstrated. High luminance green electroluminescence from LEDs using only a thin film of F8T2 for emission is also reported. The latter demonstration for a polymer previously primarily of interest for effective charge transport constitutes an important step in the development of emissive materials for applications where a union of efficient light emission and effective charge transport is required. [source]