Étude de l'élaboration de matériaux composites PVC/Bois à partir de déchets de menuiserie (formulation, caractérisation, durabilité et recyclabilité)

L étude des paramètres d élaboration de composites PVC/bois a permis de montrer que le processus de mise en oeuvre, le taux et le type de fibres de bois influencent plus les propriétés mécaniques du matériau que les traitements de compatibilisation. Un nouvel agent de liaison a été proposé : l acide gallique, polyphénol présent dans plusieurs essences de bois. Il a permis d augmenter nettement les propriétés mécaniques du matériau grâce à une bonne adhésion à l interface fibre/matrice. Le renfort végétal augmente la sensibilité du composite aux rayonnements UV et à l eau provoquant un changement de couleur en surface et une perte des propriétés mécaniques. L ajout de certains pigments a permis de ralentir la dégradation due aux UV et l ajout d acide gallique, celle due à l eau, sans toutefois les supprimer. Il a été démontré enfin que cinq cycles de vieillissement thermo-mécanique ne modifient pas les propriétés mécaniques de ces composites : leur recyclage est possible tel quel.The study of the elaboration of PVC-wood composites showed that the manufacturing process, the wood fibres amount, size and species had more influence on the mechanical properties of the material than any coupling agent previously studied. A new coupling agent was introduced: gallic acid, polyphenol present in some wood species. Its use improved the fibre/matrix interfacial adhesion and the mechanical properties of the material. It was found that the composite weathering resistance was decreased by the wood fibres leading to surface colour change and loss of the mechanical properties (due to water action). The incorporation of some pigments decreased the UV degradation and the addition of gallic acid decreased the degradation by water. But, neither of them stopped the degradation. Five cycles of thermo-mechanical ageing did not modify the mechanical properties of these composites. Thus, it is possible to recycle the PVC/wood composite as it is.TOULOUSE-ENSIACET (315552325) / SudocSudocFranceF

A combined multi-technique in situ approach used to probe the stability of iron molybdate catalysts during redox cycling

A setup combining a number of techniques (WAXS, XANES and UV–Vis) has been used to probe the stability of an iron molybdate catalyst during redox cycling. The catalyst was first reduced under anaerobic methanol/helium conditions, producing formaldehyde and then regenerated using air. Although in this test-case the catalyst and conditions differ from that of a commercial catalyst bed we demonstrate how such a setup can reveal new information on catalyst materials. In particular we observe the formation of two phases during reduction; one which we propose to be an oxygen deficient ‘pseudo-molybdate phase’, the other a molybdenum carbide-like phase, both produced as oxygen is removed from the catalyst. Standard in situ techniques could detect such transient phases, however, the information from multiple techniques, allows us to more accurately identify the nature of these materials and to carry out appropriate complementary ex situ measurements to aid in the analysis. This and similar setups therefore offer a way to more quickly and accurately observe reaction pathways within a catalyst, which may for example, result in the deactivation of the material by different routes to those observed previously. Additionally, the specific combination of these techniques with on-line mass spectrometry, allows us to monitor the activity of the catalyst surface and here observe that different catalytic mechanisms may occur during different stages of the redox process. Therefore this setup should allow for the observation of many novel variations in a catalyst’s reactivity, leading to the improvement of current and development of new materials