UV cured polysulfone based membranes for ultrafiltration

Membrane technology has acquired significant importance in a variety of applications such as water treatment, health sector and food industry. Nevertheless there is a growing demand of more functional and stable membranes. This thesis is focused on improving solvent stability of polysulfone based membranes without compromising the flux properties. Polysulfone (PSF) is a widely used membrane material for ultrafiltration process because PSF can be easily fabricated into highly porous structure via non–solvent induced phase separation (NIPS). Such a structure is imperative for ultrafiltration process as efficiency of filtration largely depends upon the size of pores and overall porosity of membrane. Generally membranes made of pristine PSF have good chemical and mechanical stability but get dissolved in many of organic solvents. Though previous attempts somehow attained solvent stability but membrane structure was deteriorated and so does the transport property. In order to increase the solvent stability, an approach based on UV induced acrylic functionalization of PSF is described in this thesis. A two-steps method of membrane fabrication, involving NIPS and UV curing, was established. At first the acrylic functionality was introduced on the backbone of polysulfone chain through synthesis of methacrylated polysulfone (PSF–DM) macro-monomer. The thin films of PSF-DM containing phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide (BAPO) photoinitiator cast on the glass plates were subjected to UV curing and NIPS processes to prepare the membranes. The reverse process i.e. NIPS followed by UV curing was also applied. The developed membranes were thoroughly characterized and the flux properties were evaluated in a dead–end filtration apparatus. The solvent stability was good in DMSO and acetone. Regardless of sequence of operations the average flux values were in the range of tight ultrafiltration. The sequence UV–NIPS resulted into more uniform and structurally stable membranes. The next approach was based on incorporating acrylic functionality in a way that a diacrylate monomer was added into pristine PSF solution in DMF and the membranes were fabricated following the previously established method i.e. UV curing followed by NIPS. For this purpose two structurally different di-acrylates, Bisphenol A ethoxylate diacrylate (BEDA) and Poly (ethylene glycol) diacrylate (PEGDA) were incorporated and in order to study the effect of concentration, different amounts of acrylic resins were investigated. The acrylic double bond conversions were studied through FTIR and ATR–FTIR. The viscoelastic properties were analyzed via dynamic mechanical thermal analysis (DMTA) and morphological properties were studied through field emission scanning electron microscopy (FESEM). The solvent stability was analyzed by immersing the membranes cutouts in a number of solvents for 120 hrs at room temperature. The flux properties were evaluated in a pressurized stirred cell apparatus and the rejection of 27 nm polystyrene particles was also collected. Almost all the formulations came up with excellent solvent stability in DMF, DMSO, THF, Acetone, Toluene and Ethyl Acetate. The 10 % BEDA functionalized PSF membrane exhibited the best flux properties, i.e. very close to that of pristine PSF, along with good rejection (>90 %) of 27 nm polystyrene particles. The UV cured acrylic functionalized PSF membranes were further applied to specific contaminant removal. The previously developed best UF membranes were coated with polydopamine (PDA) in order to combine the rejection of ultrafiltration membrane with the adsorption of contaminant by PDA layer. As BEDA cross-linked membranes were developed through UV curing followed by NIPS so the strategy of PDA coating was coupled with NIPS either as a separate action next to NIPS or in a more facile and advantageous one–step method where NIPS and PDA coating occurred at the same time. In order to study the increased adsorptive behavior of PDA coated membranes, methylene blue (MB) was taken as a model contaminant. The removal of MB was investigated both in batch and continuous filtration. The Zwitterionic behavior of PDA was effectively exploited and the coated membranes released MB in acidic condition thus regenerated for next adsorption. The cyclic stability of several adsorption and desorption cycles was studied. Above stated all three works discussed the development of UV cured membranes through NIPS In recent years, electrospun nano-fibrous membranes (ENMs’) have been employed as successful replacement of phase separation membranes because of high porosity thus much lower mass transfer resistance. We designed a reactive electrospinning setup where electrospinning was coupled with online UV irradiation. The same BEDA functionalized PSF formulation was taken as feed solution. All the parameters of electospinning and UV curing were thoroughly investigated, optimized and correlated so the optimum curing of acrylic monomer and production of nano fibers take place simultaneously. The electrospun mats were also prepared via offline curing method and compared with the counterparts. All the UV cured mats were fully characterized and solvent stability was assessed in the same way as reported before.