Optimisation des propriétés barrières de membranes nanocomposites à base de caoutchouc nitrile contre les solvants organiques

Abstract

The barrier properties of the polymers can be significantly altered by the inclusion of impermeable lamellar nanoclays. The improvement of these properties is governed by the extent of the lamellar dispersion as well as by their orientation in the polymeric matrix. The present thesis consists in developing nanocomposite materials based on nitrile rubber, loaded with lamellar nanoclays, to optimize barrier properties. The adopted approach is divided into three stages. In a first step, the synthesis of nanocomposites was achieved using three different protocols found in the literature. The resistance against solvents was evaluated by a gravimetric technique based on mass uptake experiments and the obtained results showed an obvious effect of processing parameters. Analyses carried out by two X-ray diffraction techniques combined with microscopic observations led to the conclusion that obtained improvements result from the intercalation of the lamellar nanoclays. Given these considerations, the effort was focused on optimizing the delamination of the nanoclay platelets while ensuring their orientation along lateral directions of the membrane. The adopted method consisted in applying chemical modifications on the structure of the rubbery matrix as well as on the surface of the nanoclay lamellae in order to improve the affinity between the two. On the one hand, a maleic anhydride monomer having a high polarity was grafted onto the macromolecular chain of nitrile rubber and, on the other hand, nanoclays with organic functionalizations have been used. As a processing method, extrusion was retained to ensure a maximum of orientation. Spectroscopic analyzes validated the maleic anhydride grafting and thermogravimetric tests confirmed the stability of the organic surfactants on the nanoclays during processing. Microscopic analyses have shown a substantial increase in the presence of individual lamellae which confirms the delamination of nanoclay stacks. In addition, intercalation state seemed to be more pronounced. The results reflected an excellent correlation between the diffraction analysis and the microscopic observation. Furthermore, a statistical study conducted through a dispersive energy analysis showed the chemical modification effect on the improvement of the nanoclays homogeneity in the matrix. Besides, the orientation was evaluated by a three-dimensional approach applied to small angle diffraction stereograms. The results revealed a privileged alignment according to the direction of the extrusion. After achieving the synthesis of a nanocomposite with an optimized morphology, the barrier properties of solvents were tested. Molecular transport occurring during the liquid penetration process was studied based on Fick's laws. The absorption of the solvent in the grafted nanocomposite was significantly lower compared to a conventional nanocomposite. The kinetic parameters of mass transfer were also evaluated. The grafted nanocomposite exhibited a significant reduction in the diffusivity of the solvent through its structure, as well as a decrease in its permeation coefficient. With some exceptions, these observations were validated for three different solvents and at four temperatures ranging from 23 to 70 °C. It has been shown that all mass transfer parameters were exacerbated by the increase in temperature. However, an opposite effect was observed with increasing the molecular size of the penetrant.

Date	5 Jun 2019
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Stéphane Hallé (Supervisor) & Ludwig Vinches (Co-supervisor)