Mohamed Baba

Ageing of EPDM—2. Role of hydroperoxides in photo- and thermo-oxidation

The first stages of photo- and thermo-oxidation of ethylene-propylene-diene monomer (EPDM) based on 5-ethylidene-2-norbornene (ENB) were studied and compared with the photolysis and thermolysis of hydroperoxidized EPDM (EPDM-OOH), which were described in our first paper. Nitric oxide derivatizations of oxidized EPDM revealed an unexpectedly strong contribution of secondary hydroperoxides while sulfur tetrafluoride and ammonia treatments showed the presence of saturated and unsaturated carboxylic acids and ketones. Saturation reactions of the residual ENB double bond are more efficient in thermal oxidation, as they were in thermolysis of EPDM-OOH. Photo-oxidation and thermal oxidation of EPDM (ENB) are compared with those of EPDM-OOH, EPDM based on dicyclopentadiene (DCPD) and EPDM based on 1,4-hexadiene (HD). The inductive effect of hydroperoxide as well as the lower stability of ENB sites compared with DCPD and HD are revealed.

Effect of ZnO nanofillers treated with triethoxy caprylylsilane on the isothermal and non-isothermal crystallization of poly(lactic acid)

The crystallization of PLA-silane surface-treated ZnO nanocomposites was investigated by DSC and compared to that of neat PLA. Several modes of crystallization were considered: isothermal and non-isothermal cold crystallization and also isothermal and non-isothermal melt crystallization. The kinetics of cold crystallization were studied using different methods, namely the Avrami and Ozawa-Flynn-Wall models, to calculate activation energies and kinetic constants. In contrast to what is typically observed when the foreign particles are added in a polymer matrix, the silane surface-treated ZnO delayed the crystallization of PLA and made it more difficult to start. The nucleation activity of the ZnO nanoparticles, ϕ, was calculated and found to be greater than 1 (ϕ = 1.7). This indicated that ZnO played an anti-nucleating role in the crystallization of PLA nanocomposites. This effect has been linked mainly to the interactions between the silane groups onto the surface of nanoparticles and PLA macromolecules. These interactions which reduce the mobility of polymer chains have been evidenced by rheological experiments.

Multiscale characterization of hierarchically organized porous hybrid materials

In this work, monolithic hybrid materials exhibiting both meso- and macropores of controlled size have been prepared using the hydrolysis–condensation of modified silicon alkoxide in the presence of a surfactant. These materials have been thoroughly characterized using gas sorption, mercury intrusion porosimetry, small angle X-ray scattering and electronic microscopies both in scanning and transmission modes. Using these hierarchically porous samples, it has been possible to demonstrate for the very first time that the thermoporosimetry (TPM) technique, based on the measurement of transitions of confined liquids, is indeed valid over a very wide pore size range (from few nm up to several hundred nm) to characterize the porosity in solids. This first experimental evidence is a major breakthrough because it offers a unique technique covering the whole range from mesopores to macropores, filling the known gap from standard techniques. This unique combination of smart design of hierarchically porous materials and advanced calorimetric characterization of porous solids has also brought the first true calibration data for TPM on such a large size scale.

Evaluation of crosslinking in elastomers using thermoporometry, densimetry and diffential scanning calorimetry analysis

Abstract The classical methods available for evaluating the degree of crosslinking in elastomers are stress-strain and swelling measurements. In this study, we have adopted a new analytical approach based on thermoporometry, densimetry and DSC for comparing the crosslinking density in elastomers. Crosslinking by chemical reaction or by photo-oxidation has been studied on polymer samples Ethylene-Propylene-Diene rubber (EPDM) and PolyButadiene (PB). Analysis has been done separately for soluble and insoluble fractions. The soluble fraction has been studied by densimetry and the insoluble fraction by thermoporometry and measurement of decomposition of dicumyl peroxide (DCP). The results of both these studies are complementary to each other. The DSC thermal curves of both EPDM and PB are identical in nature, but the density of the photo-oxidized EPDM samples shows a marked increase contrary to that found in PB.

FTIR and DSC studies of the thermal and photochemical stability of Balanites aegyptiaca oil (Toogga oil).

The oil extracted from the bean of Balanites aegyptiaca was characterized, and its photochemical and thermal stabilization were evaluated. The chemical composition was determined using gas chromatography (GC), revealing that the oil is very rich in unsaturated fatty acids (72% omega-6 and omega-9). The photochemical stability was assessed by subjecting it to artificially accelerated photo-aging and then examining the changes using infrared spectroscopy. The thermal stability was studied at six different temperatures ranging from 130 to 200°C and monitored in situ by differential scanning calorimetry (DSC). The kinetic parameters (EA and k) describing the thermal degradation of this oil were calculated. It has been shown that the antioxidants present in the oil delay the oxidation process (induction period). The degradation of the Toogga oil was compared with that of oleic and linoleic fatty acids. In addition, the degradation of the Toogga oil extracted with hexane was compared to that of the neat oil.