Photooxidation of Polypropylene/Montmorillonite Nanocomposites. 2. Interactions with Antioxidants.

2005 American Chemical SocietyThe influence of stabilizing additives on the photooxidation of polypropylene/montmorillonite (PP/ MMt) nanocomposites exposed to UV light was studied. Two différent stabilizers were used, a phenolic antioxidant and a redox antioxidant. A significant reduction in the induction period of oxidation was observed in the presence of MMt. This is believed to arise from interactions between the additives and the nanoclay. The interactions could involve the adsorption of additives onto the clay, the degradation of the alkylammonium cations exchanged in MMt, and the catalytic effect of iron impurities of the organomontmorillonite. Iron could catalyze the decomposition of the primary hydroperoxides formed by photooxidation of PP, which would in turn accelerate the additive consumption and decrease the length of the period before the permanent regime of oxidation is reached

Photophysical processes and photochemical reactions involved in poly (N-vinylcarbazole) and in copolymers with carbazole units.

LPMM UMR CNRS-UBP 6505 Université Blaise Pascal Clermont-Ferrand (63) et StateUniversity of Moldova Kishinev (Moldavie).This paper is devoted to the analysis of the photochemical behaviour of copolymers with carbazole units exposed to long-wavelength radiation. These copolymers are constitued of two types of carbazolylethyl methracrylate units (CEM) with octyl methacrylate moieties (OMA). The exposure of copolymers and PVK to UV light results in dramatic modifications of the physical and photophysical properties of the polymer. These modifications can be correlated with modifications of the chemical structure of the matrix. The photoageing of copolymers and PVK has been analysed by fluorescence, ESR, UV-vis and infrared spectroscopies. The effects of crosslinking and chain scissions were determined by gel fraction measurements and size exclusion chromotography

Du vieillissement naturel à la stabilité des dispositifs médicaux : étude du mécanisme d'évolution chimique du matériau

International audienceRESUME-Cet article traite de la dégradation d'un matériau polymère, le polyuréthane. Il compare les approches qui sont développées pour analyser sa détérioration différents environnements d'usage. L'étude du vieillissement à la lumière de ce matériau montre que celui-ci se dégrade selon un mécanisme chimique qui met en jeu des réactions de coupure des macromolécules et la formation de produits d'oxydation dont certains sont volatils. L'étude de la biostabilité a été réalisée en se basant sur la norme de test des dispositifs médicaux. L'étude a été effectuée avec des solutions de peroxyde d'hydrogène à 37°C ou 70°C, avec ou sans agitation, avec un suivi expérimental de la dégradation du matériau similaire à celui développé lors des études de vieillissement à la lumière. L'influence des différents paramètres est examinée et comparée aux données de la littérature qui concernent des tests effectués in-vivo

Etude des conséquences de l'evolution de la structure chimique sur la variation des propriétés physiques de polymères soumis à un vieillissement photochimique

L'objectif majeur de cette thèse était de passer dans la compréhension des phénomènes de photovieillissement, du niveau moléculaire au niveau macroscopique. Pour ce faire, trois polymères dont le vieillissement est gouverné par des réactions de réticulation et / ou de coupures de chaîne, ont été étudiés. Nous avons principalement développé l'utilisation de la microscopie à force atomique en effectuant des nanoindentations tant à la surface que dans l'épaisseur du matériau irradié et comparé les resultats à de nombreuses autres techniques. Cette mèthodologie nous a permis de progresser dans la connaissance des relations qui existent entre modification de la structure chimique et variation des propriétés physiques de polymères sous l'impact du photovieillissement.CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Polystyrene photooxidation. 2. A pseudo wavelength effect

International audienceThe photoproducts formed in polystyrene photooxidized by exposure to long wavelengths (lambda greater-than-or-equal-to 300 nm) or short wavelength (lambda = 253.7 nm) absorbing in the IR range were identified and reported in the preceding paper. It was shown that, despite some differences in the distribution of oxidation photoproducts, the same products were obtained. The present paper reports on complementary experiments carried out at a different temperature and on microspectrophotometric determination of the photoproduct profiles. The apparent differences resulting from the short- or long-wavelength irradiation are attributed to the diffusion of the low molecular weight photoproducts. A general mechanism accounting for the photooxidation of the polystyrene at short or long wavelengths is given

Polystyrene photooxidation. 1. Identification of the IR-absorbing photoproducts formed at short and long wavelengths

International audiencePolystyrene films were exposed to radiation of long wavelength (lambda greater-than-or-equal-to 300 nm) and short wavelength (lambda = 253.7 nm) under atmospheric oxygen. Changes in the FTIR spectra of the photooxidized samples were followed, along with several postirradiation treatments including chemical derivatization reactions and HPLC analysis of the low molecular weight fragments that were obtained after extraction by methanol. The absorption maxima which were found in the carbonyl and hydroxyl regions of the infrared were assigned, and the corresponding photoproducts were identified

Fourier transform infrared and Fourier transform Raman analysis of styrenic polymers

International audiencePoly(styrene-acrylonitrile) (SAN) and acrylonitrile-[ethylene-propylene diene monomer (EPDM)]-styrene (AES) films were exposed to long-wavelength radiations (A > 300 nm) in the presence of atmospheric oxygen. Fourier transform infrared (b-T-IR) and Fourier transform Raman (FT-Raman) spectroscopy were used to follow the chemical evolution of the polymer. The different photoproducts formed were identified by coupling FT-IR analysis to chemical derivatization reactions. The contribution of styrene, acrylonitrile and EPDM to the general mechanism of degradation was determined, showing that the presence of EPDM enhanced the chemical evolution of the other components, compared to the homopolymers polyacrylonitrile and polystyrene, both studied previously. The distribution of the photoproducts profile within thick samples was also determined

Mechanism of thermolysis, thermooxidation and photooxidation of polyacrylonitrile

International audiencePolyacrylonitrile (PAN) films were exposed to radiations of long wavelengths (λ ≥ 300 nm) and of short wavelength (λ = 254 nm) under atmospheric oxygen. Changes in the Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectra were followed and compared to those obtained during the thermolysis and the thermooxidation of PAN films at 150°C. The products formed in these four conditions of degradation were identified by coupling FTIR and UV-Vis analysis to chemical derivatisation reactions and physical treatments. An analysis of the gas phase has also been done. A general mechanism accounting for thermolysis, thermooxidation and photooxidation is proposed

Mechanism of poly(styrene-co-acrylonitrile) photooxidation

International audiencePoly(styrene-co-acrylonitrile) (SAN) films were exposed to long wavelength radiation (λ ≥ 300 nm) and to short wavelength radiation (λ = 254 nm) in the presence of atmospheric oxygen. Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopies were used to follow the chemical changes in the polymer. The different photoproducts formed were identified by coupling FTIR and UV-Vis analysis to chemical derivatisation reactions or physical treatments such as thermolysis and photolysis. A mechanism accounting for the photooxidation of SAN is then proposed. This mechanism involves both the styrene and the acrylonitrile units. Moreover, the products responsible for the discoloration occurring during SAN photooxidation are shown to result from styrene oxidation

Synthèse, caractérisation et durabilité de systèmes photostructurables destinés à l'holographie

Le but de cette étude est d'obtenir de nouveaux matériaux polymères photostucturables pour l'enregistrement holographique. La première partie de ce travail a été consacrée à la synthèse radicalaire de copolymères carbazoliques à base d'unités carbazolylméthacylates espacées par des groupements octylméthacrylates, puis à leur purification et enfin à leur caractérisation. Une analyse approfondie de leur comportement photochimique a été menée à des longueurs d'onde d'irradiation supérieures à 300 nm représentatives du vieillissement naturel. Une étude des mécanismes photochimiques mis en jeu sous irradiation laser à 405 nm (longueur d'onde utilisée pour l'enregistrement holographique) a ensuite été réalisée avec des copolymères dopés avec de l'iodoforme. Enfin, la faisabilité des enregistrements holographiques a pu être démontrée sous irradiation laser à 480 et 532 nm en dopant les copolymères avec de la trinitrofluorénoneCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF