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

In Situ Kinetics Study of the Accelerated Aging of Poly(ethylene oxide) Using PhotoDSC

PhotoDSC has been applied to follow the global kinetics of chain scissions resulting from the UV light irradiation or from the thermal degradation of a high molecular weight PEO (4 106 gâmol-1). Infrared spectroscopy, XRD measurements and rheology experiments were performed to evidence the occurrence of chain scissions. Melting energy was used as a tool to quantify the extent of the degradation. It was found that the chain scissions reaction follows a first-order kinetic law for both photo and thermal degradation. The activation energies were found identical in both cases (41 kJ mol-1), whereas the degradation rate was higher in the case of UV irradiation than in the case of thermoageing

Photochemical behaviour of fire-retarded polymers

International audienceThe influence of a non-halogenated intumescent fire retardant on the photooxidation of polypropylene is reported. The photooxidation of polypropylene stabilised with a phenolic antioxidant and two redox antioxidants (HALS), without and with the flame retardant has been studied. The chemical modifications resulting from UV-light exposure with wavelengths above 300 nm in the presence of oxygen were followed by IR and UV-visible spectroscopies. Special attention was given to the influence of each component on the rate of oxidation of the polymeric matrix. The photooxidation of the fire-retarded polymer can be described by two independent phenomena: the photooxidation of the intumescent agent and the photooxidation of the polymer. The results obtained offer new insight in the formulation of stabilised fire-retarded PP for outdoors applications

AFM analysis of CD-R photoageing

International audienceOne of the main parameters controlling durability of optical disks such as CD-R is the stability of the dye layer. Ambient light exposure contributes to degrdn. of the light-sensitive dye used in recordable media. Our study focuses how light irradn. influences the dye layer on a polycarbonate (PC) substrate before and after CD-R engraving. The dye layer surface was characterized by at. force microscopy (AFM) to measure dye degrdn., which, in turn, can be used to assess CD-R readability. For a blank CD-R, pre-groove height is a major degrdn. indicator. For a recorded CD-R, however, pit and land size and depth can be used to show degrdn. For long irradn. times, coded areas completely disappear, leading to the loss of stored informatio

Characterization and photooxidative behaviour of nanocomposites formed with polystyrene and LDHs organo-modified by monomer surfactant.

Editeur ElsevierLayered double hydroxide (LDH) organo-modified by a surface-active monomer, 3-sulfopropyl methacrylate (SPMA) was used as filler for polystyrene (PS). DifFerent nanocomposites SPMA/LDH:PS were prepared by bulk polymerization process using low amount of initiator. The two components, filler and polymer, as well as the degree dispersion of the reactive filler as a function of ils loading in PS were characterized by a combination of several techniques: X-ray diffraction, high resolution t3C CP-MAS NMR, 1-TIR, UV-visible, thermal analysis, SEC and MET. The nanocomposites were submitted to UV-light exposures in the presence of oxygen. The oxidation photoproducts and the rates of oxidation were compared for the varions samples. It was shown that the filler was not modifying the oxidation mechanism of the polymer, but had a slight effect on the oxidation rate

Photodegradation of polymer nanocomposites : interactions with stabilizers.

International audienc

Influence of nanodispersed hydrotalcite on polypropylene photooxidation

International audienceNanocomposites containing hydrotalcite and prepared by melt compounding with polypropylene were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies. The presence of hydrotalcite was shown to change the global rate of photooxidation of polypropylene by reducing the oxidation induction time and increasing the oxidation rate. The differences of the oxidation induction time disappeared after solvent extraction of the antioxidant. They were attributed to a quenching of the antioxidant activity resulting from a migration onto the filler surface induced by the preferential interaction with the polar hydrotalcite. Extracting the antioxidant did not change the oxidation rate at the permanent regime. The increase of the oxidation rate was attributed to transition metal ions, present as impurities in hydrotalcite, which can accelerate the oxidation of the polymer by various mechanisms including a catalysed decomposition of hydroperoxides

Influence of water on the photodegradation of poly(ethylene oxide)

International audienceThe UV-light degradation of polyethylene oxide (PEO) in aqueous solution was investigated operating under long wavelengths (λ > 300 nm) at 20 °C in different pH conditions varying from 2.3 to 12.0 and at two different concentrations. Thermo-oxidation experiments on PEO aqueous solution at 50 °C are also reported and compared to photo-oxidation results. The formation of oxidation products was followed by infrared analysis of deposits obtained by evaporation of aliquots of irradiated polymer solution. Photo-oxidation led to formates and esters but a third product was also identified, formic acid ions formed by partial hydrolysis of formates. The degradation of PEO in water led to the acidification of the aquatic medium. Size exclusion chromatography (SEC) was used to monitor the changes in molar weight and intrinsic viscosity with irradiation time. It was shown that the photo-oxidation produced a dramatic decrease of the average molar weights which is more important in acidic medium. Total organic carbon (TOC) measurements of the aged aqueous solutions showed that the mineralization of PEO could not be achieved in these photo-oxidative conditions

Influence of iron salts on the photooxidation of poly(N-vinylpyrrolidone) in aqueous solution

International audienceThis article reports on the effect of UV-visible radiation (λ ≥ 300 nm) on the degradation of poly(N-vinylpyrrolidone) PVP photoinduced by Fe(III) in aqueous solution and in the presence of oxygen. The formation of oxidation products was followed by infrared analysis of deposits obtained after evaporation of water and by UV-visible analysis of the irradiated polymer solutions. Size exclusion chromatography (SEC) was used for monitoring the variations of molar weight and intrinsic viscosity with irradiation time. Total organic carbon (TOC) measurements were performed with the aim of checking the mineralisation of aqueous solutions. Depending on the concentration of Fe(III), the concentration of PVP and the pH of the solution, we were able to show that the photooxidation of PVP leads to a chain scission and to a cross-linking mechanism, contrary to photooxidation of PVP in the absence of Fe(III) which only involves a mechanism of chain scission. A mechanism of PVP photooxidation until its possible mineralisation is proposed, taking into account the concentration of Fe(III) in the solution

Influence of nanodispersed boehmite on polypropylene photooxidation

International audienceNanocomposites containing pure or organically modified nanoboehmites of different sizes were prepared by melt compounding with polypropylene. The samples were UV light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV–visible spectroscopies. The presence of pristine nanoboehmites was shown to change the rate of oxidation of polypropylene by reducing the oxidation induction period due to the presence of residual processing antioxidant. The differences of the oxidation induction periods between the nanocomposites and the pristine polymer disappear after solvent extraction of the antioxidant. The inefficiency of traditional antioxidant in retarding the photooxidation of polypropylene containing nanodispersed boehmite is proved. Antioxidant migration to the boehmite surface induced by the preferential interaction with the polar filler is proposed as an explanation. The oxidative behaviour of the organically modified boehmites was shown to depend on the type of organic substituent. p-Toluenesulfonate reduces the adsorption of antioxidants while the presence of a long-chain alkyl benzensulfonate increased the oxidation rate by generation of radical initiator