Thermo-mechanical analysis of dental silicone polymers

Soft lining materials are used to replace the inner surface of a conventional complete denture, especially for weak elderly patients, with delicate health who cannot tolerate the hard acrylic denture base. Most of these patients have fragile supporting mucosa, excessive residual ridge resorption, particularly on the mandibular arch. The application of a soft liner to the mandibular denture allows absorbing impact forces during mastication and relieving oral mucosa. Actually, the silicone rubbers constitute the main family of commercialised soft lining materials. This study was conducted to understand the relationships between the mechanical properties and the physical structure of polysiloxanes. For this purpose, a series of polysiloxanes of various chemical compositions have been investigated. The evolution of their physical structure as a function of temperature has been followed by differential scanning calorimetry (DSC). In order to facilitate comparisons, the mechanical modulus has been analysed upon the same heating rate using dynamic mechanical analysis (DMA). Polysiloxanes actually commercialised as soft denture liners are three-dimensional networks: the flexibility of chains allows a crystalline organisation in an amorphous phase leading to the low value of the shear modulus. The dynamic mechanical analysis shows that they are used in the rubbery state. So, polysiloxanes have steady mechanical properties during physiological utilisation

Dielectric relaxations in PEEK by combined dynamic dielectric spectroscopy and thermally stimulated current

The molecular dynamics of a quenched poly (ether ether ketone) (PEEK) was studied over a broad frequency range from 10-3 to 106 Hz by combining dynamic dielectric spectroscopy (DDS) and thermo-stimulated current (TSC) analysis. The dielectric relaxation losses e00 KK has been determined from the real part e0 T(x) thanks to Kramers–Kronig transform. In this way, conduction and relaxation processes can be analyzed independently. Two secondary dipolar relaxations, the c and the b modes, corresponding to non-cooperative localized molecular mobility have been pointed out. The main a relaxation appeared close to the glass transition temperature as determined by DSC; it has been attributed to the delocalized cooperative mobility of the free amorphous phase. The relaxation times of dielectric relaxations determined with TSC at low frequency converge with relaxation times extracted from DDS at high frequency. This correlation emphasized continuity of mobility kinetics between vitreous and liquid state. The dielectric spectroscopy exhibits the ac relaxation, near 443 K, which has been associated with the rigid amorphous phase confined by crystallites. This present experiment demonstrates coherence of the dynamics of the PEEK heterogeneous amorphous phase between glassy and liquid state and significantly improve the knowledge of molecular/dynamic structure relationships

Effect of electronic irradiations on electrical properties of a high-performance space-used thermoplastic polymer

International audiencePolymer materials used in satellite manufacturing are exposed to diverse environmental constraints. Since they are electrical insulator, electronic radiations can induce electrostatic discharge phenomena which can damage satellite electronic systems. Moreover, these charging issues are potentially amplified by radiation induced physico-chemical ageing. Thus, it is essential to investigate these modifications to anticipate the material behaviour once in orbit. PolyEtherEtherKetone (PEEK) being used recently in space industry for structural applications, it is necessary to study its behaviour regarding electronic radiations. This work aims to analyse the effects of experimental electronic irradiations on electrical properties of PEEK samples. In this context, semi-crystalline PEEK films were irradiated under high vacuum and at ambient temperature by a mono-energetic electron beam. Analysis of the electric and charge transport behaviours showed evolutions induced by radiative ageing. Especially, a DC conductivity decrease was observed which has been associated with more numerous charge traps

PAEK / piezoelectric particles nanocomposites for interactive structures

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Electrical Conductivity of a Space-Used Silicone Elastomer: Evolution Under Electron Irradiation

International audienceThe electrical conductivity of a space-used commercial silicone adhesive has been measured and its temperature dependence evidenced. It was shown to obey an Arrhenius law with an activation energy of 0.4 eV, associated with an electron-hopping transport. In parallel, this material was deprived from its fillers in the laboratory, and the dc conductivity of the resulting polysiloxane matrix was shown to obey the same Arrhenius law as the filled material. When exposed to high-energy electrons, the dc conductivity of both materials decreases, probably due to a predominant chain cross-linking process. For the highest experimental ionizing dose, the dc conductivity of this commercial silicone elastomer fell from 6×10^−13 down to 2×10^−16  S.m^−1.Consequently, the associated electrostatic discharge triggering risk in space applications moved from safe to critical

New Insights in the Production of Simulated Moon Agglutinates: The Use of Natural Zeolite-Bearing Rocks

Two natural zeolite-bearing rocks (one containing clinoptilolite and the other chabazite, phillipsite, and analcime) were Fe-exchanged and thermally treated in a reducing atmosphere at 750 °C for 2 h. Two nanocomposites, formed by the dispersion of Fe nanoparticles in a ceramic matrix, were obtained. The prepared lunar dust simulants also contain Na+, K+, Ca2+, and Mg2+ and other mineral phases originally present in the starting materials. The samples were fully characterized by different techniques such as atomic absorption spectrometry, X-ray powder diffraction, followed by Rietveld analysis, transmission electron microscopy, N2 adsorption/desorption analysis at 77 K, measurements of grain size distribution, magnetic property measurements, broad-band dielectric spectroscopy, and DC conductivity measurements. The results of this characterization showed that the obtained metal-ceramic nanocomposites exhibit a chemical and mineralogical composition and electrical and magnetic properties similar to real moon dust and, thus, appear valid moon dust simulants

New Insights in the Production of Simulated Moon Agglutinates: The Use of Natural Zeolite-Bearing Rocks

Two natural zeolite-bearing rocks (one containing clinoptilolite and the other chabazite, phillipsite, and analcime) were Fe-exchanged and thermally treated in a reducing atmosphere at 750 \ub0C for 2 h. Two nanocomposites, formed by the dispersion of Fe nanoparticles in a ceramic matrix, were obtained. The prepared lunar dust simulants also contain Na+, K+, Ca2+, and Mg2+ and other mineral phases originally present in the starting materials. The samples were fully characterized by different techniques such as atomic absorption spectrometry, X-ray powder diffraction, followed by Rietveld analysis, transmission electron microscopy, N2 adsorption/desorption analysis at 77 K, measurements of grain size distribution, magnetic property measurements, broad-band dielectric spectroscopy, and DC conductivity measurements. The results of this characterization showed that the obtained metal-ceramic nanocomposites exhibit a chemical and mineralogical composition and electrical and magnetic properties similar to real moon dust and, thus, appear valid moon dust simulants