G. Boiteux

Rheological and electrical properties of EVA copolymer filled with bamboo charcoal

The electrical and rheological properties of an ethylene vinyl acetate (EVA) copolymer filled with bamboo charcoal were investigated. The composites were prepared by melt process in an internal batch mixer. Size distribution analysis showed that d(50) and d(90) values of the bamboo charcoal particles are 12.7 and 40 μm, respectively, with a mean diameter of 22 μm. Scanning electron microscopy proved that the particles of bamboo charcoal present a rectangular shape. The electrical percolation threshold was observed at 0.18 volume fraction (35 wt%) of bamboo. Beyond the percolation threshold, a considerable increase in electrical properties was observed up to a limit value of 10-2 S/m. The rheological percolation was studied from different rheological models. As a result, the rheological percolation threshold was observed at 0.3 volume fraction (50 wt%) of bamboo charcoal contents. So, the electrical percolation occurs before the rheological percolation. This is principally due to the filler’s characteristics such as the specific surface area, the aspect ratio, and the surface properties. Finally, the bamboo charcoal confers high electrical properties to the EVA composite without inducing strong changes in its viscoelastic properties.

Microdielectric analysis of the polymerization of an epoxy-amine system

Abstract Microdielectrometry is used to detect in real time critical events such as gelation or vitrification during the curing of epoxy resins (DGEBA-DDS). These new results are compared with that given by classical methods of investigation (insoluble fractions, dynamic mechanical analysis, viscosimetry). The efficiency of the electrical technique allows one to detect chemical phenomena with parameters sensitive to the modification of the epoxy system during the network formation.

Interfacial polarization in composite materials with spherical fillers: characteristic frequencies and scaling laws

The dielectric properties of composite materials consisting of a host matrix filled with spherical particles are investigated as a function of frequency by means of numerical calculations. Two different cases are analyzed: (a) composites with a conductive matrix and insulating fillers and (b) composites with an insulating matrix and conductive fillers. In both situations, dielectric dispersions due to interfacial polarization effects are observed in the dielectric spectra. In the present contribution, the characteristic frequencies of interfacial polarization effects are systematically analyzed in dependence on the volume fraction of the spherical fillers and on the conductivity values of the composite phases. The resulting scaling laws are discussed in detail.

Molecular Relaxations in Hybrid Organic–Inorganic Materials Prepared by a Sol–Gel Process

Organic–inorganic hybrid materials based on alkoxy-silane-terminated macromonomers synthesised from a hydroxy-terminated hydrogenated polybutadiene, H-PBD, have been investigated. Different morphologies of the hybrid materials are obtained according to the conditions of the synthesis and to the non compatibility between the organic and the inorganic components. n n n nIn order to establish the relationships between the structure and the properties of the organic–inorganic (O/I) materials, infrared, small-angle X ray scattering, transmission electron microscopy, dynamical mechanical spectroscopy and dielectric measurements have been performed. This paper focuses especially on the analysis of the dielectrical relaxations in a large range of frequencies and temperatures compared with the dynamic mechanical one to propose a model of morphology of the final O/I materials. It is found in particular that a distinct interfacial region between the organic-rich phase and the silicate clusters is developed in the case of the low acid-to-alkoxide ratio for hybrids (based on γ-amino propyl triethoxysilane) (i.e. for the long periods of gelation).

Use of in-situ dielectric sensing for intelligent processing and health monitoring

Frequency dependent dielectric measurements (FDEMS) provide a sensitive, automated in situ sensor for intelligent processing and an in situ means for monitoring durability, that is degradation of polymers during use. FDEMS in situ sensors can be designed and calibrated to monitor changes in processing properties during fabrication and changes in mechanical or electrical service life properties of polymer materials during use. With a proper understanding of the type of polymer and the use environment, the sensor output can be related to changes in modulus, maximum load and elongation at break. The FDEMS technique has advantages over other monitoring techniques: nondestructive; accuracy/reproductivity; sensitivity; in situ capability; remote sensing; automated.

Structural Peculiarities of Ion-Conductive Organic-Inorganic Polymer Composites Based on Aliphatic Epoxy Resin and Salt of Lithium Perchlorate

The article is concerned with hybrid amorphous polymers synthesized basing on epoxy oligomer of diglycide aliphatic ester of polyethylene glycol that was cured by polyethylene polyamine and lithium perchlorate salt. Structural peculiarities of organic-inorganic polymer composites were studied by differential scanning calorimetry, wide-angle X-ray spectra, infrared spectroscopic, scanning electron microscopy, elemental analysis, and transmission and reflective optical microscopy. On the one hand, the results showed that the introduction of LiClO4 salt into epoxy polymer leads to formation of the coordinative metal-polymer complexes of donor-acceptor type between central Li+ ion and ligand. On the other hand, the appearance of amorphous microinclusions, probably of inorganic nature, was also found.

Relaxation processes in hybrid organic-inorganic polymer nanosystems polymerized in situ

The relaxation processes of hybrid organic-inorganic polymer nanosystems (OIS) synthesized by joint polymerization of organic and inorganic components were studied using methods of differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and broadband dielectric relaxation spectroscopy (DRS). The organic component was a mixture of two products: high-molecular-weight macrodiisocyanate (MDI) with low reactivity and low-molecular-weight isocyanate-containing modifier poly(isocyanate) (PIC) with high reactivity. Sodium silicate (SS) was used as inorganic component. The structures of the OIS obtained were in the form of hybrids with covalently connected building blocks and interpenetrating networks: weakly cross-linked network MDI/SS and highly cross-linked network PIC/SS. Depending on the MDI/PIC ratio, one of the networks was prevailing and created a continuous structure with domains of second network.PACS61.25.hk; 82.35.Lr; 64.70.pj

Electrophysical behavior of ion-conductive organic-inorganic polymer system based on aliphatic epoxy resin and salt of lithium perchlorate

In the present work, ion-conductive hybrid organic-inorganic polymers based on epoxy oligomer of diglycide aliphatic ester of polyethylene glycol (DEG) and lithium perchlorate (LiClO4) were synthesized. The effect of LiClO4 content on the electrophysical properties of epoxy polymers has been studied by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The effect of LiClO4 content on the structure has been studied by wide-angle X-ray scattering (WAXS). It was found that LiClO4 impacts on the structure of the synthesized hybrid epoxy polymers, probably, by formation of coordinative complexes {ether oxygen-lithium cations-ether oxygen} as evidenced from a significant increase in their glass transition temperatures with increasing LiClO4 concentration and WAXS studies. The presence of ether oxygen in DEG macromolecules provides a transfer mechanism of the lithium cations with the ether oxygen similar to polyethylene oxide (PEO). Thus, the obtained hybrid polymers have high values of ionic conductivity σ (approximately 10−3 S/cm) and permittivity ϵ (6u2009×u2009105) at elevated temperatures (200°С). On the other hand, DEG has higher heat resistance compared to PEO that makes these systems perspective as solid polymer electrolytes able to operate at high temperature.PACS81.07.Pr; 62.23.St; 66.30.hk

In-situ electrical analysis in view of monitoring the processing of thermoplastics

In the last recent years, electrical techniques like microdielectrometry have presented an attracting and increasing interest for continuous monitoring, in a nondestructive way, of the advancement of the reaction of thermoset resins under cure. We think that the use of electrical analysis for in situ monitoring of chemical reactions can be extended to get information on thermoplastic and the physical phenomena such sa crystallization or study of residence time distribution in processing machines such as extruders.

Préparation, caracterisations, études diélectriques de quelques poly-vinylbenzylalkylcarbonates

Resume Cinq vinylalkylbenzylcarbonates ont ete prepares en trois etapes a partir du chloromethylstyrene puis polymerises. Les proprietes dielectriques de ces polymeres montrent que les permittivites les plus elevees sont obtenues lorsque le radical alkyl est peu volumineux.