Polyolefins–biofibre composites: A new way for an industrial production

International audienc

The study of temperature and radiation induced degradation of cable polymers: A comparison between the mechanical properties of industrial and neat EPDM

AbstractThe mechanical properties of industrial and neat Ethylene Propylene Diene Monomer (EPDM) polymers, aged under γ-irradiation at different temperatures, are studied. The focus is given to the dose rate effects in polymer insulation materials, so the ageing is performed in the wide range of dose rates, doses and temperatures. Industrial EPDM samples are extracted from the cables in use in Belgian Nuclear Power Plants (NPP), and the neat EPDM samples are produced in the laboratory. The mechanical tests of non-aged and aged polymers are performed, and the methodology of estimating the polymer life time is discussed. The ultimate tensile stress and elongation at break are found to be strongly affected by both irradiation condition and temperature. The ultimate tensile stress clearly exhibits the dose rate effect observed through the shift of the crossover between cross-linking to chain scission process as a function of the dose. This crossover shifts to high dose for large dose rates, while the opposite is observed by increasing the temperature. Dose rate effect is less evident in the elongation at break data, probably because both cross-linking and chain scission affect the elongation at break in the same way, by decreasing it. In comparison to industrial EPDM aged under the same conditions, the cross-linking to chain scission crossover appears at lower dose in neat polymer and the elongation at break decreases faster by increasing the dose. In addition, the elongation at break experimental results can be modeled by changing single parameter, namely pre-exponential factor of the irradiation rate constant. This confirms that both aging processes, cross-linking and chain scission affect the elongation at break in a similar way, by deteriorating network structure responsible for polymer elastic properties. Irradiation rate constant is found to follow the square root dependence for industrial EPDM, while the linear dependence is observed for the neat EPDM. This indicates the existence of different degradation processes in these two polymers

The correlation between elongation at break and thermal decomposition of aged EPDM cable polymer

The effect of simultaneous thermal and gamma irradiation ageing on the mechanical and physicochemical properties of industrial EPDM was investigated. Accelerated ageing, covering a wide range of dose rates, doses and temperatures, was preformed in stagnant air on EPDM polymer samples extracted from the cables in use in the Belgian nuclear power plants. The mechanical properties, ultimate tensile stress and elongation at break, are found to exhibit the strong dependence on the dose, ageing temperature and dose rate. The thermal decomposition of aged polymer is observed to be the dose dependent when thermogravimetry test is performed under air atmosphere. No dose dependence is observed when thermal decomposition is performed under nitrogen atmosphere. The thermal decomposition rates are found to fully mimic the reduction of elongation at break for all dose rates and ageing temperatures. This effect is argued to be the result of thermal and radiation mediated oxidation degradation process

Foaming in CO2 sc medium as an efficient way to produce electromagnetic interference shielding materials

This communication reports on the preparation of novel nanocomposites foams that are efficient broadband microwave absorbers.7 Multiwalled carbon nanotubes (MWNT) are first successfully dispersed into polymer matrix by melt-blending as confirmed by TEM microscopy and rheology. Then foaming of these nanocomposites8 occurs under supercritical CO2 conditions by a two-step process.9 This physical foaming constitutes a green alternative to classical foaming agents.10 Well-defined microcellular foams11 were obtained with cell size around 10-50 μm and cellular density around 108 cells per cm3, the morphology of the foam was determined by SEM microscopy. The impact of several criteria on the morphology of the foam will be discussed. The EMI shielding efficiency of these materials are then evaluated and compared to the non-foamed nanocomposites. Finally, we will discuss about the design of the foam that is essential to optimize the performances of the EMI absorber

Influence of homogenization and drying on the thermal stability of microfibrillated cellulose

Homogenization has been used to release microfibrils from cellulose fibres to produce microfibrillated cellulose (MFC) Oven drying, atomization or freeze-drying were used to dry MFC Morphological differences were observed linked to the compaction of the system and the formation of microfibril agglomerates Thermal stability of the dried MFC, checked by TGA, decreased after homogenization and drying Char level at the end of the pyrolysis was higher than for cellulose fibres Derivative TGA (dTGA) showed a shoulder around 250 degrees C for the dried MFC Volatile degradation product detection by FTIR spectroscopy (FTIR) coupled to TGA and DSC showed that the shoulder corresponds to expected dehydration reactions of the cellulose Increasing the contacts between microfibril(s) (bundles) and agglomerates of the freeze-dried MFC by compression promoted dehydration reactions Homogenization and drying modified the thermal properties of the MFC No significant influence of freeze-drying kinetics on the thermal behaviour of the MFC was observed (C) 2009 Elsevier Ltd All rights reserved

Multifunctional architectured materials for electromagnetic absorption

A sandwich structure involving a honeycomb core filled with a carbon nanotube-reinforced polymer foam and glass fiber-reinforced composite face sheets has been developed in order to combine high electromagnetic absorption and high mechanical performance. The large electromagnetic absorption is attained by simultaneously minimizing the reflection and transmission, which, in terms of effective material properties, requires a low dielectric constant and a conductivity around 1 S m−1. The sandwich offers also high stiffness versus density performance

Properties of poly(D,L-lactide)-based nanocomposites

International audienc

Polypropylene nanocomposites based on aqueous eemulsions and unmodified Montmorillonite elaborated by reactive extrusion

International audienc