Review : Auto-oxidation of aliphatic polyamides

The literature on oxidation kinetics of polyamides and model compounds has been reviewed in order to try to extract suitable information for non-empirical kinetic modeling. Polyamide characteristics are systematically compared to polyolefin ones, these latter being more extensively studied. From kinetic analysis point of view, it is shown that oxidation attacks predominantly a amino methylenes of which C eH bond is considerably weaker than the other methylenes. As a result, propagation by H abstraction is considerably faster in polyamides than in polyethylene for instance. Termination by radical combination is also very fast. Another cause of PA oxidizability is the instability of a amino hydroperoxides linked to the inductive effect of nitrogen. This instability is responsible for many key features of oxidation kinetics especially the absence of induction period. The main stable oxidation products are imides resulting from disproportionation processes meanwhile chain scissions resulting from rearrangements of a amino alkyls by b-scission are also significant process although their yield appears lower than in polyolefins

Molecular and macromolecular structure changes in polyamide 11 during thermal oxidation

The present article reports a study of thermal oxidation of unstabilized polyamide 11 films at several temperatures (90–165 °C) under atmospheric pressure and under various oxygen pressures (up to 1.6 MPa) at 110 °C. The chemical structure changes are monitored by IR spectroscopy (carbonyl groups) and UV–visible spectrophotometry (yellowing). Molar mass changes are determined by size exclusion chromatography (SEC). By investigating the influence of oxygen pressure it is clearly shown that reactions involving P° radicals other than O2 addition cannot be neglected under atmospheric pressure. Under the conditions of this study limited to relatively low oxidation levels, IR and UV measurements indicate that carbonyl groups and chromophores responsible for yellowing have the same relative yield whatever the temperature and oxygen pressure. SEC measurements highlight the significant predominance of random chain scissions over crosslinking events. Crosslinking only appears after an induction time, presumably because it involves reactions between primary oxidation products. The ratio of carbonyl groups over chain scissions is about 7.5 at low conversion and about 2.5 at high conversion, showing that α amino alkoxy radicals are mainly transformed into imides without chain scission

Investigation of polyamide 11 embrittlement during oxidative degradation

Embrittlement processes occurring during thermal oxidation are investigated for stabilized and unstabilized polyamide 11 samples differing by their thicknesses and initial molar masses. Tensile tests were carried out in the temperature range between room temperature and 110 °C in order to investigate the influence of mechanical testing temperature on the embrittlement coordinates. In the same time, molar mass and crystalline morphology are monitored by size exclusion chromatography (SEC) and DSC/SAXS measurements respectively. The experimental results point out the existence of a critical molar mass for ductile-brittle transition M′c about 10 kg mol−1, independent of sample initial molar mass or stabilization, but depending on tensile testing temperature. However, even if oxidation chain scissions are shown to be clearly responsible for the loss of mechanical properties at failure, the structure-property relationships governing ductile-brittle transition require a mixed criterion involving molar mass and crystalline morphology, especially the interlamellar distance. For this purpose, specific molar mass – crystalline morphology relationships are investigate

Quantification of hindered phenols in polyamide 11 during thermal aging

Polyamide 11 films stabilized by Irganox® 1098, Irganox® 1010 or Irganox® 245 were subjected to thermal oxidation at 110°C. The residual phenol content was assessed by comparing three analytical methods:high performance liquid chromatography (HPLC), determination of the Oxidation Induction Time (OIT)and Onset Oxidation Temperature (OOT) by thermal analyses. Both OIT and OOT are reliable for virgin PA11 after a relevant calibration by HPLC measurement. In the case of oxidized samples, OOT measurements have the benefits of being more easily interpretable than OIT and less time-consuming than HPLC measurements.CIFR

Quantitative determination of interfacial copolymers from co-extruded films

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Raman spectroscopy and chemometrics for quantitative analysis of complex flows in an industrial transesterification process

International audienceA method based on Raman spectroscopy has been used for determination of ester acrylate mixture composition from an industrial production of acrylic monomers. Five molecules of the industrial mixture have been studied: main components and an impurity. Experiments were carried out with an immersion probe on the spectral range of 100-3425cm(-1). Usually, monitoring a complex industrial flow by spectroscopic analysis requires a lot of samples in order to have a representative prediction model. Here only 60 samples from the process were necessary to build the model. The statistics was then artificially increased by synthetically increasing the number of samples. A qualitative study by principal component analysis was at first done, and then a partial least squares method was performed to assess the feasibility of quantitative measurements in such transesterification process. Internal and external validations methods have been used and their results show a RMSEP below 1% of samples predicted concentration ranges. The repeatability and reproducibility of Raman measurements are also discussed