Photoageing at λ>300 nm (SEPAP, WOM, Xenotest), natural ageing (Bandol) and thermal ageing (100 and 150°C) were performed on ethylene–propylene–diene monomer (EPDM) rubber designed for automotive ...applications. The thermal ageing study was concentrated on a formulation designed for engine applications (peroxide crosslinked) and photoageing concerned a formulation for outdoor applications (sulfur vulcanized). Analyses were based both on infrared spectroscopy (surface analysis and profile by successive abrasion) and on physical properties analysis (dynamic mechanical thermal analysis (DMTA) and tensile tests). Both methods were complementary to describe the two competitive phenomena involved in ageing of elastomers (oxidation and crosslinking).
The thermal ageing at 100°C of vulcanized acrylonitrile-butadiene copolymer (NBR) is described. Analysis was based both on infrared spectroscopy (surface analysis) and on physical properties analysis ...(tensile and microhardness tests). Both methods appear to be complementary to describe the two competitive phenomena (oxidation and crosslinking) involved in the elastomer ageing. It is emphasised that the mechanical behaviour of aged NBR is different in comparison with chloroprene rubber.
Proton relaxation times in the rotating frame, as obtained from the decay of nuclear magnetization locked along a radio frequency field B 1, have been measured in a series of cross-linked natural ...rubber materials. These decays are monoexponential and the relevant time constants, T 1 ρ , can be monitored as a function of the radio frequency field strength B 1 . At any B 1 value, they appear to be correlated in a very sensitive way to the cross-link density. A novel interpretation of the T 1 ρ dependence upon B 1 is presented. It is based on a theory describing the evolution of a two spin 1/2 system coupled by dipolar interaction in the presence of a spin-locking field. The measured rotating-frame relaxation rate is shown to be equal to the sum of the motionally related 1/T 1 ρ and a term arising from the radio frequency field inhomogeneity. Both terms are proportional to the square of the dipolar interaction (the second moment in the present case where a distribution of dipolar interactions exists). Concerning changes of cross-link density, T 1 ρ measurements provide therefore a more direct information than transverse relaxation measurements (also performed in this study), the composite nature of the latter decay curves making their interpretation less straightforward. As a complement to the present relaxation study, we show the correlation of the self-diffusion coefficient of a solvent imbedded in the material with rubber T 1 ρ values.
The presence of large amounts of carbon black in number of industrial applications of rubbers makes their analytical study by infrared spectroscopy difficult, particularly their chemical evolution ...upon ageing . The present paper reports the use of a Horizontal Attenuated Total Reflectance accessory equipped with a germanium crystal. HATR (Ge) /FTIR analysis of both thermal-and photo-oxidations of EPDM, CR and NBR were first validated by conventional transmission spectroscopy in the absence of carbon black. Then, HATR (Ge) was used with fully formulated rubbers with the aim of studying their long term behaviour. Influence of temperature, UV exposure, carbon black or stress as well as the oxidation profile across the materials or the identification of carboxylic acids/carboxylates groups have been examined.
Reversed-phase liquid chromatography of thiuram monosulphide and disulphides (e.g. thiram, disulfiram) was performed using UV or mass spectrometry detection. Mixed thiuram formation was studied as a ...function of pH, and methanol/water ratio in the sample solvent. Conditions allowing a largely decreasing exchange reaction rate were based on the use of a 85/15 methanol/water pH 2.5 as sample solvent in vials with septum.
The thermal and photo-oxidation of various formulations of polychloroprene have been studied. The ATR-FTIR technique has been especially used. The first step in oxidation is an allylic hydrogen ...abstraction leading to different radicals. Some hydroperoxides are formed and then decomposed into alcohols, ketones, acid chlorides and acids. The influence of crosslinking and carbon black on the oxidative degradation is also reported.
Dessert grapes: gustatory merits of new varieties Alavoine Mornas, F. (Centre National du Machinisme Agricole du Genie Rural des Eaux et des Forets, Aix en Provence (France)); Cardinet, C; Vidaud, J ...
Infos,
(Jul-Aou 1993)
93
Journal Article
