Enhanced PVDF membrane antifouling performance via surface modification by functional polymers

• Main Author: Zhao, Guili
• Other Authors: Chen Wei Ning, William
• Format: Theses and Dissertations
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Chemical engineering::Polymers and polymer manufacture; DRNTU::Engineering::Environmental engineering::Water treatment; DRNTU::Engineering::Materials::Functional materials; DRNTU::Engineering::Materials::Material testing and characterization
• Online Access: http://hdl.handle.net/10356/69492
• Institution: Nanyang Technological University

In the past several decades, membrane technology is widely used in separation process in various fields. In particular, membrane bioreactors (MBRs) as an application of membrane technology has attracted increasing attention from the researchers worldwide. However, there still exists many obstacles in membrane widespread application and the major challenge is membrane fouling. Recently, antifouling membrane fabrication by functional polymers is regarded as a promising and effective strategy to inhibit membrane fouling. Thus, this research work mainly focuses on poly(vinylidene fluoride) (PVDF) membrane modification by thermosensitive polymer PNIPAAm [poly(N-isopropylacrylamide)] and its copolymer with other functional polymers. Meanwhile, the objective of this thesis is to investigate the application potential of antifouling membrane prepared and to provide a feasible and effective strategy to achieve better antifouling performance for wide application, thereby providing a meaningful reference for future study. Firstly, functional polymer PNIPAAm was successfully bonded onto PVDF membrane via surface-initiated atom transfer radical polymerization (ATRP). The hydrophilicity of PVDF membrane was dramatically enhanced due to the incorporation of PNIPAAm chains. The microfiltration experiments indicated that PNIPAAm modified membrane exhibited a flux recovery ratio (FRR) as high as 91.59%. In addition, bacteria adhesion test revealed that the attachment of Escherichia coli on the modified membrane was reduced by 75% compared to the original membrane. Hence, the fouling tests demonstrated that PNIPAAm modified membrane exhibited obvious thermosensitive property and good antifouling ability compared with pure PVDF membrane. In order to further improve not only fouling resistance but also fouling release property of membrane, three types of modified membrane were well designed by grafting PNIPAAm, PHEMA [poly(hydroxyethyl methacrylate)] and P(HEMA-co-NIPAAm) respectively. Minimum protein adsorption and bacterial adhesion were both obtained on PVDF-g-P(HEMA-co-NIPAAm) membrane, with reduction by 44% and 71% respectively compared to the pristine membrane. The filtration testing indicated that the copolymer modified membrane exhibited high resistance to protein fouling and the foulant on the surface was removed easily by washing, suggesting easy-cleaning capacity. The biofouling on the membrane surface was analyzed using Gram-negative E. coli and Gram-positive Staphylococcus epidermidis. According to biofilm study using E. coli and S. epidermidis, it is inferred that microorganism species played an essential role in the formation and structure of biofilm as the species influenced the bacterial adhesion each other owing to their characteristics. Besides, the modified membrane exhibited higher fouling resistance during filtration and higher flux recovery after hydraulic cleaning compared with the original membrane for long-term use. Furthermore, for thermosensitive PVDF-g-P(HEMA-co-NIPAAm) membrane prepared in this thesis, water cleaning with temperature control provide an auxiliary and feasible strategy to promote the fouling release and to enhance the efficiency of fouling removal except for classical cleaning methods for wastewater treatment. This thesis was one of the limited studies to achieve higher antifouling property focusing on not only fouling resistance but also fouling release for PVDF membrane via grafting functional polymers P(HEMA-co-NIPAAm). This research study provided a feasible and effective strategy of antifouling membrane preparation which can be also used for other types of the membrane in wide range of applications.