Leo, Mariangela (2011) Polyimide membranes for alcohols dehydration: from basic aspects to separation applications. [Tesi di dottorato] (Unpublished)

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The first part of this work aimed to the determination of the absorption and desorption kinetics of an alcohol (methanol) inside a commercial polyimide (PMDA ODA) and to the identification of the interactions with polymeric network. The understanding of the molecular mechanisms of diffusion can be helpful in designing the chemical structure of future polymers for optimal transport properties. The diffusion of methanol into polyimide films was studied by in situ FTIR spectroscopy, one of the most used techniques for studying and characterizing polymeric materials thanks to some features such as the high sampling rate and the high accuracy, especially appropriate for studying polymer-low molecular weight compounds transport phenomena. FTIR can be usefully used to study real time and ’in situ’ the diffusion phenomenon. Several methods of spectral data analysis were used, among which difference spectroscopy, least-squares curve fitting, 2D correlation spectroscopy. The results gave an insight into the molecular mechanism of diffusion in terms of number and population of penetrant species present in the system and with respect to the nature of the molecular aggregates. The second part of this work was focused on the performance of some ’commercial’ polyimides (similar to those used industrially) and of these new thermally converted hydroxy-containing polyimides as potential condidates for the production of pervaporation and vapor permeation membranes for alchools dehydration. Polybenzoxazoles and polybenzthiazoles synthesized from aromatic polyimides are chemically stable structures that have been shown to have both favorable separation properties and high chemical stability making them an interesting possibility for this separation. The work focused on synthesizing and characterizing a range of such polymers to assess their suitability for ethanol dehydration. Some polyimides (PMDA ODA and its commercial version KAPTON, BPDA ODA and BTDA ODA) and some TR polyimides (obtained from the polyimides ODPA APAF and BPDA HAB) were synthesized and studied as potential membranes for ethanol dehydration. The chemical and thermal stability of the two kinds of polymers was tested: the most aggressive conditions that the membranes would experience were simulated, and the potential hydrolysis of the imide rings was measured. Furthermore, the swelling behaviour of the two materials was analyzed: the swelling and plasticization of the membranes often result in a loss of selectivity. The membranes that showed good stability were tested in a pervaporation system: vapour permeation permeability and selectivity for ethanol and water were obtained for both TR polymers and ’commercial’ polyimides.

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