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

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

The exposure of polymers to their environments leads to modifications of the macromolecular chemical structure which provokes irreversible changes of their functionnal properties. The main objective of these thesis was to uinderstand the photoaging phenomena from the molecular dimension to the macroscopic level.L'exposition des polymères aux contraintes de leur environnement d'usage provoque une modification de la structure chimique des macromolécules qui se traduit par une évolution irréversible de leurs propriétés fonctionnelles. 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 résultats à de nombreuses autres techniques. Cette méthodologie 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

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

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

L'exposition des polymères aux contraintes de leur environnement d'usage provoque une modification de la structure chimique des macromolécules qui se traduit par une évolution irréversible de leurs propriétés fonctionnelles. 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 re ticulation 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 résultats à de nombreuses autres techniques. Cette méthodologie 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 photovieillissementCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Photodegradation of celluloid used in museum artifacts.

International audienceThe consequences of the photodegradation of celluloid on the modification of the material properties have been analysed. Various techniques were used to follow the accelerated degradation provoked by exposure to light (λ > 300 nm). The objective was to relate the modification of the properties at various levels of investigation, from the molecular properties towards the degradation of the macroscopic properties. The modification of the chemical structure was followed by infrared and UV–visible spectroscopic analyses. Gloss and colour measurements were performed, as well as characterization of surface mechanical properties by microhardness and Atomic Force Microscopy (AFM). The results show that the loss of gloss and the decrease of the mechanical properties are a result of a combination of the progressive loss of plasticizer and chain-scission reactions. These developments were explained in light of the modifications of the chemical structure. Quantitative cross-correlations of the degradation chemistry with performance-critical physical properties were established

Photooxidation of cellulose nitrate: New insights into degradation mechanisms.

International audienceCellulose nitrate (or nitrocellulose) has received considerable interest due to its uses in various applications, such as paints, photographic films and propellants. However, it is considered as one of the primary pollutants in the energetic material industries because it can be degraded to form polluting chemical species. In this work, the UV light degradation of cellulose nitrate films was studied under conditions of artificially accelerated photooxidation. To eliminate the reactivity of nitro groups, the degradation of ethylcellulose was also investigated. Infrared spectroscopy analyses of the chemical modifications caused by the photooxidation of cellulose nitrate films and the resulting formation of volatile products revealed the occurrence of de-nitration and the formation of oxidation photoproducts exhibiting lactone and anhydride functions. The impact of these chemical modifications on the mechanical and thermal properties of cellulose nitrate films includes embrittlement and lower temperatures of ignition when used as a propellant

Impact of photo- and thermooxidative ageing of NBR/PVC blends on the formation of cracks

Photo- and thermal ageing of nitrile butadiene rubber (NBR)/poly(vinyl chloride) (PVC) blends cured with sulfur and a vulcanization agent have been studied. Characterization of the aged NBR/PVC films was performed by using FTIR and UV‒visible spectroscopy, DMTA, Shore A hardness and swelling measurements. The objective was to understand the formation of cracks upon ageing and to put in evidence correlations between the different scales: from chemical structure to functional properties

Influence of functional nanoparticles on the photostability of polymer materials : recent progress and further applications

International audienceThe photochemical behaviour of polymer-nanoparticles/nanocomposites has been studied depending on the geometry of the nanofiller and an overview of the studies reported in the last decade is tentatively given. Depending on their functionality, nanoparticles can impact the durability of the nanocomposite materials under light irradiation. The behaviour to UV-light exposure in presence of oxygen of various types of nanocomposites with clays, LDH and carbon nanotubes has been investigated and recent progress on the influence of functional nanoparticles on the polymer photodegradation is reported. The influence of photocatalytic (ZnO and TiO2) nanoparticles and phosphors on the photooxidation of the polymeric matrix and the durability of the material properties are characterized. From a general point of view, the stabilization strategy of polymer nanocomposites must be adapted depending on the nanofiller

How to reveal latent degradation of coatings provoked by UV-light

International audienceThis paper deals with predictions of the service life of the two main technologies used for automotive clearcoats: acrylic-melamine and acrylic-urethane. This work demonstrates that the UV-light irradiation leads to chain scissions and crosslinking for the unstabilised and stabilised formulations. Mechanisms are proposed to explain the dramatic increase in the values of the mechanical properties for the two technologies as a function of the ageing time. For a determined critical value of the mechanical properties, water acts to reveal the latent damage by leading to the formation of cracks. Moreover, when the polymer reaches a certain level of network densification due to UV-light irradiation, the system cannot accept the stress induced by the water inflation/deflation and cracks will occur. Other solvents were also tested to understand the effects of polarity on the formation of the cracks

The role of hydroperoxides in the chemiluminescence of oxidized polymers reconsidered

International audienceChemiluminescence phenomena often occur on heating oxidized polymers in an inert atmosphere. This light emission is frequently attributed to reactions involving hydroperoxides produced during the oxidation process. The main objective of this study was to check the role played by hydroperoxides in the luminescence of three oxidized polymers: polyoctenamer, an ethylene propylene diene monomer (EPDM), and polypropylene. The hydroperoxides of pre-oxidized polymers (photo-oxidized or hydroperoxidized) were transformed using photolysis or dimethyl sulfide (DMS) treatment. The chemiluminescence of the polymer samples was measured before and after treatment and decomposition of hydroperoxides monitored with IR spectroscopy and thermal analyses. Surprisingly, all the photolysed polymers retained strong luminescence that is not entirely explained by the presence of hydroperoxides. On the contrary, two of the three polymers showed a quenching of luminescence after DMS treatment. Two conclusions can be drawn. First, the results clearly indicate that the luminescence of oxidized polymers does not only depend on the presence of hydroperoxides. The second conclusion concerns the origin of the remaining chemiluminescence after photolysis and the quenching observed after DMS treatment. As photolysis mainly leads to the formation of carbonyl compounds and DMS treatment to the production of alcohols, it is proposed that carbonyl compounds are probably involved in the chemiluminescence of oxidized polymers, especially through associations with remaining hydroperoxides