Improvement in fouling release properties of ultrafiltation PVDF membranes

PVDF membranes are commonly used for water and wastewater applications, however partly due to their highly hydrophobic nature they are prone to fouling. One approach to mitigate fouling is to alter the membrane via surface modification. Under optimum conditions of membrane fabrication, in-situ membrane surface modification may be  achieved as a result of the spontaneous migration of hydrophilic/low surface energy component to the membrane upper surface; so-called surface segregation (see image). Non-polar low surface energy polymers, such as polysiloxane, could render the surface with a permanent fouling release ability. However, they cannot spontaneously segregate onto the polymer-water interface during phase separation due to the unfavourable solution thermodynamics. While some hydrophilic polymers such as polyethylene glycol (PEG) may improve the surface hydrophilicity and inhibit the adsorption and deposition of foulant onto surface, their low compatibility with the membrane matrix and consequent depletion during filtration process is considered as drawback.

In this study, commercial SiO2 nanoparticles were chemically functionalized by silane coupling agents, which were then specifically decorated with either non-polar hydrophobic PDMS chains or PEG molecules on their surface. We have shown that flux recovery ratio (FRR) of the membrane modified by blending 0.5 wt.% SiO2-COOH-PEG was at least 20% higher than control membrane after fouling and cleaning. With addition of surface functionalized SiO2 the value of DRr, which represents degree of flux decline due to reversible fouling, reached 38%; more than 50% of total degree of flux decline (DRt) value. In comparison, reversible fouling only accounted for around one sixth and one third of the total fouling for the control membrane and membrane with 2 wt.% unmodified SiO2.