Êtes-vous un étudiant de l'EPFL à la recherche d'un projet de semestre?

Travaillez avec nous sur des projets en science des données et en visualisation, et déployez votre projet sous forme d'application sur GraphSearch.

Découvrez-en plus sur les applications Graph.

Graph
Search

fr|en

Se Connecter

Concept

Solution polymerization

Résumé

Solution polymerization is a method of industrial polymerization. In this procedure, a monomer is dissolved in a non-reactive solvent that contains a catalyst or initiator. The reaction results in a polymer which is also soluble in the chosen solvent. Heat released by the reaction is absorbed by the solvent, reducing the reaction rate. Moreover, the viscosity of the reaction mixture is reduced, preventing autoacceleration at high monomer concentrations. A decrease in viscosity of the reaction mixture by dilution also aids heat transfer, one of the major issues connected with polymer production, since most polymerizations are exothermic reactions. Once the desired conversion is reached, excess solvent must be removed to obtain the pure polymer. Accordingly, solution polymerization is primarily used in applications where the presence of a solvent is desired anyway, as is the case for varnish and adhesives. Another application of polymer solutions includes the manufacture of fibers by w

Source officielle

https://en.wikipedia.org/wiki/Solution_polymerization

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (16)

Chargement

Afficher plus

Publications associées

Chargement

Personnes associées (2)

Personnes associées

Chargement

Unités associées (1)

Unités associées

Chargement

Concepts associés (4)

Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomer, and surfactant. The most common type of emulsion polymerization is an oil

La polymérisation (par voie) radicalaire est un processus de polymérisation en chaîne qui, comme son nom l'indique, fait intervenir comme espèce active des radicaux. Elle fait intervenir des réactions

An acrylate polymer (also known as acrylic or polyacrylate) is any of a group of polymers prepared from acrylate monomers. These plastics are noted for their transparency, resistance to breakage, an

Afficher plus

Concepts associés

Chargement

Cours associés (2)

Cours associés

Chargement

Séances de cours associées (4)

Séances de cours associées

Chargement

Publications associées (16)

Efficiency of SPIONs functionalized with polyethylene glycol bis (amine) for heavy metal removal

Heinrich Hofmann, Yongyuth Wanna

Hybrid magnetic nanoparticles based on poly(methylmethacrylate) (PMMA) and super-paramagnetic iron oxide nanopaticles (SPIONs) with selective surface modification has been developed for heavy metal removal by applying external magnetic fields. The nanoparticles were prepared by the emulsion polymerization technique in an aqueous suspension of SPIONs. The hydrolysis of carboxyl functional group was then applied for grafting polyethylene glycol bis(amine)(PEG-bis(amine)) onto the PMMA-coated SPIONs. The morphology, the chemical structure and the magnetic properties of the grafted nano particles were investigated. The efficiency of the hybrid nanoparticles for heavy metal removal were conducted on Pb(II), Hg(II), Cu(II) and Co(II) in aqueous solutions. The metal concentration in the solutions after separation by the hybrid nanoparticles was determined by inductively coupled plasma optical emission spectrometer (ICP-OES). The results show the heavy metal uptake ratios of 0.08, 0.04, 0.03, and 0.01 mM per gramme of the grafted SPIONs for Pb(II), Hg(II), Cu(II), and Cu(II), respectively. A competitive removal of Cu(II), Pb(II), Co(II) and Hg(II) ions in mixed metal salt solutions has also been studied. The heavy metal removal efficiency of the hybrid nanoparitcles was found to depend on the cation radius, in accordance with capture of metal ions by the amine group. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier2016

Chargement

, ,

Bitumen is a complex viscoelastic material used as a binder in applications ranging from road paving to waterproof membranes for roofing [1]. In such applications, bitumen is often blended with a polymer in order to improve its elasticity. The resulting polymer modified bitumens (PMBs) also generally show improvements in thermal and fatigue cracking resistance, and temperature susceptibility [2, 3]. A wide range of polymers have been used in PMBs, including thermoplastic elastomers, thermoplastics and thermosets [1], but among the most successful are styrene-butadiene-styrene (SBS) block copolymers, in which the polystyrene blocks provide cohesive strength and the rubbery polybutadiene blocks provide elasticity [3]. Because SBS is relatively expensive, the possibility of mixing bitumen with other polymers remains of interest [2-4] and metallocene-catalyzed linear low density polyethylenes (m-LLDPE) have recently been discussed as a possible alternative, combining low cost and elasticity with improved storage stability compared with conventional polyolefins [5, 6]. In the present study, PE/octene and PE/butene based m-LLDPE copolymers with different melt flow indices, glass transition temperatures, melting temperatures and degrees of crystallinity have been used to modify a roofing grade gel bitumen. The morphology, the thermal behaviour and the viscoelastic properties of the PMBs have been studied in the composition range 5 to 50 wt% m-LLDPE. In the case of the butenebased copolymer, fluorescence microscopy indicated a continuous m-LLDPE-rich phase matrix containing discrete asphaltene-rich domains at all polymer contents, although at 5 wt% of the octene-based copolymer; the continuous phase remained asphaltene-rich, and there was some evidence for phase inversion, the discrete m-LLDPE-rich domains containing additional asphaltene-rich domains. It follows that the melt rheological response of the PMBs was dominated by the m-LLDPE, but the excellent flow characteristics of this latter resulted in relatively modest increases in shear viscosity compared to those obtained with equivalent concentrations of SBS. Significant swelling by the maltene-rich components of bitumen led to a decrease of the melting point of both types of m-LLDPE, although the degree of crystallinity relative to the polymer content increased somewhat at low m-LLDPE concentrations. Time temperature superposition was used to provide an indication of the dynamic viscoelastic response in shear over a wide range of frequencies. The pure bitumen exhibited liquid-like behaviour over the entire temperature and frequency range investigated, the loss modulus, G’’, generally being significantly higher than the storage modulus, G’. However, whereas blending with the relatively crystalline octene-based m- LLDPE resulted in more elastic behaviour (G’ greater than G’’) the less crystalline butene-based m-LLDPE showed a crossover in G’ and G’’ for all the concentrations investigated. The crossover frequency was found to shift towards lower frequencies as the m-LLDPE content increased, suggesting it to be possible to fine tune the viscoelastic response, depending on the required end-properties. In view of the relative stability of the PMB microstructures referred to above, these results confirm the promise of m-LLDPE as additives to gel bitumen, and suggest there to be considerable flexibility in the range of m-LLDPE contents that may be envisaged, without compromising processing requirements. The consequences for applicative properties will be discussed.

2010

Chargement

Functionally graded polymer nanocomposites using magnetic fields

Tommaso Nardi

Functionally Graded Materials (FGM) are a class of materials in which the composition and the properties gradually change over the volume. The present PhD project aims to generate a full understanding of a novel synthetic strategy for polymeric FGMs based on the magnetophoretic motion of magnetic nanofillers in a polymer matrix under the application of an external magnetic field gradient. Due to its high rate, costâeffectiveness and lowâtoxicity, UV polymerization was considered as the first curing option for the magnetic nanocomposites. The curability problem deriving from the presence of opaque particles was tackled by studying two different systems based on the same hyperbranched acrylated polymer matrix (HBP): one containing bare Fe3O4 nanoparticles whereas the other loaded with Fe3O4@SiO2 coreâshell nanoparticles. The employment of Fe3O4@SiO2 NPs for the synthesis of magnetic polymeric films showed to be effective towards the inclusion of 10âtimes higher particle volume fractions compared to formulations including bare Fe3O4. By adding Fe3O4@SiO2 nanoparticles to the UVâcurable matrix, the motion of the magnetic responsive filler was induced upon the application of magnetic field gradients generated by permanent magnets. The process was speeded up through the employment of a simple setâup composed of two block magnets in repulsion configuration and through the functionalization of the particle surfaces with an acrylated silane. From the experimental analysis of the photocuring process, the residual stresses arising during the photopolymerization of functionally graded composite coatings based on the UVâcurable HBP matrix and Fe3O4@SiO2 nanoparticles were evaluated with a Finite Element Method approach. These coatings were able to consistently decrease the residual stresses at the coatingâsubstrate interface compared to those encountered either in composites with homogeneous compositions or in the pure polymer, provided that reinforcing fillers were concentrated at the coatingâsubstrate interface. If instead nanoparticles were concentrated at the free surface, graded nanocomposite coatings could reduce by as much as 40% the interfacial stress arising from thermal variations, as demonstrated through numerical simulations. Nanoindentation tests were carried out on the surface of polymer nanocomposites exhibiting either graded or homogeneous distributions of Fe3O4@SiO2 nanoparticles in the UVâcurable matrix. It was experimentally shown how only at relatively small indentation depths, large increases in modulus and hardnesswere obtained for graded composites with respect to their homogeneous counterparts. Through a Material Point Method approach, experimental nanoindentation tests were successfully simulated. Finally, nanocomposite systems based on epoxy matrices were considered. In particular, composites with gradients in permittivity were synthesized through the application of a magnetic field to suspensions of highâpermittivity Fe3O4@TiO2 particles in an epoxy resin. The application of the magnetic force not only induced the movement of the particles, but also caused their alignment in high aspect ratio structures, resulting in rather steep permittivity gradients. Numerical simulations clarified how the asâsynthesized materials, employed as insulators, have the potential to efficiently reduce the electric field stress at the electrodeâinsulator interface and have intrinsic durability advantages over their homogeneous counterparts.

EPFL2015

Chargement

Afficher plus

Functionally graded polymer nanocomposites using magnetic fields

Tommaso Nardi

EPFL2015

, ,

2010