Preparation Of PVDF Modified Porous Membrane And Its Application

Due to its excellent processability, thermal and chemical stability, polyvinylidene fluoride (PVDF) is widely used in membrane process. The hydrophobicity of PVDF membrane leads to pollution adsorption in oil-water separation and protein separation, hence, hydrophilic modification and antibacterial modification of PVDF membrane become important. In order to obtain excellent PVDF membrane, this paper investigates PVDF membranes with steam/water composite induced phase separation method. Polymethyl methacrylate (PMMA) combined with Polyvinyl pyrrolidone (PVP), and Polyvinyl alcohol (PVA) were added as membrane composition to improve membrane hydrophilic. The silver antimicrobial membrane was modified via silver mirror reaction, and guanidine hydrochloride antimicrobial membrane was modified by adding guanidine hydrochloride. The results on hydrophilic and antibacterial modification of PVDF membrane are as follows:PVDF was used as raw material in orthogonal experiment to prepare membrane via steam/water composite induced phase separation. When the concentration of PVDF was16%, additive of PVP was2%, and the thickness of wet film was0.13mm, PVDF porous membrane had better combination property:the flux was20.17L/m2·h, the rejection of PEG10000was78.3%, and the strength was33.9MPa. These operation conditions could be considered as important reference in membrane hydrophilic and antibacterial modification.Both PMMA/PVP and PVA were added to PVDF casting solution for membrane preparation. The effects of polymer concentration and additive content on PVDF porous membrane performance were studied. The results showed that:at the high melting temperature, PMMA and PVP molecular chain can open and be intertwined, which forms two amphipathic polymer molecules (PMMA/PVP). The two amphipathic polymer molecules were added to PVDF making hydrophilic PVDF/PMMA/PVP mixed membrane, which improves the hydrophilic of PVDF membrane. As the difference of PVDF and PVA solubility is large, they hardly exist in one phase and as a consequence, homogeneous and stable solution exists only with a certain concentration and in a limited time period. Silver particles were deposited onto PVDF membrane surface to enhance antibacterial property. EDS spectrum displays that the weight percentage of silver particles was0.83%, and atomic number percentage of silver particles was0.11%in PVDF antibacterial modification membrane. Flux together with rejection remains nearly unchanged comparing with that of unmodified one, which means silver particles deposited onto the membrane surface did not change the membrane structure while improve the antibacterial performance. Due to the high solubility of guanidine hydrochloride in water, the antimicrobial effect of membrane was not obvious adding guanidine hydrochloride to PVDF casting solution. Moreover, solvation of guanidine hydrochloride induces more pores on membrane surface, higher flux and less rejection.The technology of water soluble polymer complexation-ultrafiltration for copper ions in wastewater treatment process was established, which can be used for water resue and heavy metal recycle from wastewater. The operation conditions are optimized. The sodium polyacrylate (PAAN) had been pretreamented to remove small molecules, the effect of different pH on complexation efficiency and the maximum complexing capacity of PAAN were analyzed, and the effects of running time and volume concentration ratio on membrane flux and separation efficiency respectively were studied.