Study On The Preparation, Microstructure Control And Modification Of PSF/SMA Blend Membrane By Thermally Induced Phase Separation

Polysulfone（PSF）has received growing attention in membrane fabrication,for the treatment of water and wastewater due to its good physical-chemical properties upon blending with other polymers.However,serious membrane fouling would reduce water flux and deteriorate the water quality.Herein,the aim of this study is to enhance the permeability and antifouling performance of PSF membrane by blend modification of poly（styrene-co-maleic anhydride）（SMA）polymers and surface dip-coating using trimesoyl chloride（TMC）/β-Cyclodextrin（β-CD）.Firstly,Schneier theory or thermodynamics calculation and molecular-dynamic（MD）simulations were employed to investigate the compatibility of PSF/SMA blend system.Molecular dynamics simulations were achieved using the condensed phase-optimized molecular-potentials for atomistic-simulation studies（COMPASS force field）with atomic based electrostatic.The PSF/SMA blend compatibility facets and thermodynamic Gibb’s free energy over across ranges of PSF/SMA blend compositions were estimated.In doing so,the Flory-Huggins chi-interaction parameter of mixing（χ）and solubility-parameters（δ）were computed at 298 K.Results showed that the blend system was miscible using the interaction chi parameter of Flory-Huggins at a temperature above400K.At higher time-step,mesoscopic simulations for PSF/SMA reached equilibrium and computed free energy,mixing energy indicated the stability of PSF/SMA polymer blend.The results of this part of this dissertation relate to the Flory Huggins theory enthalpy of mixing for binary blend polymers（PSF and SMA）.Furthermore,the kinetic phase of the miscibility or immiscibility of the PSF/SMA blending system was studied by using differential scanning calorimetry（DSC）technique.It was found that a single glass transition temperature（Tg）in the blend polymers was observed,which is in the range within the Tg of individual polymers.That is to say,DSC analysis is in consistent with MD simulations and thermodynamic calculations.The MD simulation provides a powerful,accurate computational tool in the estimation of polymer compatibilities.PSF/PSMA blend microporous membranes were prepared by the thermally-induced phase separation（TIPS）method using nontoxic dipropylene glycol-dibenzoate（DPGDB）as a diluent to dissolve the mixture of polymers.The effect of SMA content on the membrane structure and properties were explored in terms of morphologies,water contact angle,permeation performance,antifouling,and mechanical stability.The results showed that the pore structures of the membrane were gradually changed from uniform sponge-like to the network structure and cellular structure with an increase of SMA content from 0 to 5 wt.%in the casting solution.The porosity decreased from 83.5%to73.5%when SMA content in the casting solution increased to 1 wt.%.Then the porosity slightly increased to 79.6%with the increase of SMA content to 5 wt.%.In particular,the average pore size continuously increased from 68 nm to 88 nm with the increase of SMA content from 1 wt.%to 5 wt.%.Importantly,the contact angle of PSF/SMA blend membranes declined from 86.2°to 61.1°with the addition of SMA from 1 to 5 wt.%.It implied that the hydrophilicity of the PSF/SMA membrane was improved.The highest pure water flux of 565 L m^-2 hr^-1 was obtained from the membrane（S4）with SMA content of 4 wt.%,which was 11 times larger than that of pristine PSF membrane（S0）.However,the bovine serum albumin（BSA）rejection（84%）obtained from membrane S4was lower than that of S0（95%）.The fouling recovery of the PSF/SMA blend membrane with SMA content of 3 wt.%was up to 94%,much higher than that of the pristine PSF membrane（81%）.In summary,this study provides a simple technique to fabricate the microporous organic-membrane with improved hydrophilicity trend and separation performance.Moreover,the PSF/SMA blend membranes with high performance in terms of pure water flux and BSA rejection were selected as supporting membranes for surface modification by dip coating withβ–CD and TMC to form tight UF membranes.The effects ofβ–CD on the separation performance,structure,and morphology of the flat sheet PSF/SMA membranes were examined.The tight UF membranes were characterized and then tested for the removal of BSA and Congo red（CR）from water.Results indicated that the top layer thickness increased from 8μm to 18μm with an increase in the concentration ofβ-CD from 2 wt.%to 8 wt.%in aqueous volume.Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy（ATR-FTIR）and X-Ray Photoelectron Spectroscopy（XPS）were used to confirm the successful deposition of the TMC andβ-CD on the surface of PSF/SMA supporting membrane.Atomic Force Microscopy（AFM）revealed that the roughness of membranes increased with an increase inβ-CD concentration.Importantly,the contact angle of PSF/SMA blend membranes declined from 79.8°to55.9°with the addition ofβ-CD,implying that the hydrophilicity of the tight-UF PSF/SMA membranes improved.The pure water flux（PWF）of 40 L m^-2 hr^-1 was achieved after the blend membrane coated with 8 wt.%β-CD.However,the highest PWF of 127 L m^-2 hr^-1 observed on the uncoated PSF/SMA UF membrane with 3 wt.%SMA.Additionally,the highest BSA rejection（94%）was recorded from PSF/SMA with the coating layer containing 8 wt.%ofβ-CD concentration.Furthermore,the maximum CR dye rejection（96%）was achieved by the tight UF membrane whenβ-CD concentration was 8 wt.%.In conclusion,this work presents the development of permeable-antifouling PSF/SMA blend membranes by TIPS method and the surface modification to fabricate a novel tight UF membranes for use in water treatment and dye removal in textile effluent industries.