Innovative fluorinated membranes for water and organic solvent treatment application

Abstract

The aim of this thesis was to study the use of different types of fluoropolymer in order to prepare membranes for chemical and pharmaceutical applications. In fact, the potential use of fluoropolymeric membranes respect to other materials, at industrial levels, has several advantages such as high mechanical strength, high efficiency and stability. However, the unique properties of these materials such as excellent chemical and thermal strength make them extremely versatile but at the same time very difficult to process. As example, Ethylene-Chlorotrifluoroethylene (ECTFE) is insoluble in common organic solvents, and it can only be processed at high temperature, depending on the solvent used. In this work, three types of fluoropolymers have been studied, such as low-melting ECTFE (Halar®LMP-ECTFE), poly(vinylidene fluoride) (PVDF grade 1015) and perfluoropolyether (PFPEs) (Fluorolink®AD1700 and Fluorolink®MD700). Moreover, low-toxic solvents for humans and the environment have been appropriately selected and used for first time for solubilising the fluoropolymers of interest. -The Halar®LMP-ECTFE polymer was studied and characterized in terms of solubility parameters, compared with the standard Halar® ECTFE 901 polymer. In fact, this new grade of Halar® shows comparable properties with standard Halar® (hydrophobicity and mechanical properties), but lower crystallinity and lower melting point. Porous membranes and dense film were produced by thermally induced phase separation (TIPs). Two solvents, Diethyl Adipate (DEA) and Dibutyl Itaconate (DBI), never tested before, were selected. The chemical stability of the dense film was evaluated over time (192h) by swelling tests with aggressive organic solvents. Porous Halar®LMP-ECTFE membranes have been tested for organic solvents ultra- (UF) and nano-filtration (NF), such as methanol, ethanol and dimethylformamide. The results show that Halar®LMP ECTFE membranes are promising candidates to be used in separation processes under harsh conditions, such as chemicals production, purification and processing of food, nutraceuticals products and solvents recycling. - The influence of three different solvents in the membrane formation, using PVDF 1015 as polymer, was studied. Plasticizers from to Citroflex family, such as acetyl tributylcitrate (ATBC), acetyl triethylcitrate (ATEC) and triethylcitrate (TEC) have been selected and used. In particular ATEC and TEC as solvents, were used for the first time. Membranes were produced by thermally induced phase separation (TIPs) technique. The flat sheet membranes produced have been tested in microfiltration process (MF). These membranes can be used in several industrial applications such as sterilisation and clarification of pharmaceuticals or applied to separate contaminants from the water. - Perfluoropolyethers (PFPE) (Fluorolink®AD100 and Fluorolink®MD700) studied are new types of PFPE, UV cross-linkable. These PFPE photo-reticulated, have been used for coating commercial hydrophilic membrane, such as polyamide (PA) and polyethersulfone (PES) membranes. The aim of this work was to produce hydrophilic/hydrophobic coated membranes, keeping the morphology of the started membrane, unchanged. The study focused on morphological analysis, and on the influence of coating on the support membrane. The membranes produced, hydrophilic/hydrophobic, were characterized and the coating resistance was evaluated over time by direct contact with several chemical agents. The membranes were then tested, in membrane distillation process for direct contact (DCMD), using both deionized water and 0.6M saline. The results show that these coated membranes can be applied to desalination of seawater and wastewater treatment.