Polysulfone based poly(methyl methacrylate) dual layer hollow fiber membrane incorporated with activated carbon for uremic toxins removal

Abstract

Daily and nocturnal hemodialysis practices require a portable dialysis machine. To foster the development of portable dialysis machine, an innovative technology to regenerate dialysate is needed. Hence, the objective of this study is to develop a highly selective polysulfone/poly(methyl methacrylate) (PSf/PMMA) dual layer hollow fiber (DLHF) membrane incorporated with activated carbon (AC) for collective removal of uremic toxins. In the first phase of the study, the urea adsorption capacity of PMMA was enhanced by a surface modification process using 5 %v/v aqueous (3-aminopropyl)triethoxysilane solution. The silane coating on the surface of PMMA particle was observed using transmission electron microscopy and the identification of silicon and nitrogen elements by the energy-dispersive X-ray spectroscopy has confirmed the successful modification of PMMA. A comprehensive adsorption study of urea was then conducted on the PMMA, whereby the isotherm, kinetic and thermodynamic of the adsorption process were determined. Modified PMMA showed urea adsorption capacity of 57 mg/g, which was higher than the unmodified PMMA (23 mg/g) due to the increased number of active adsorption sites. The urea adsorption onto PMMA surface was found as a non-spontaneous physical process that follows Freundlich isotherm model and Lagergren’s pseudo-second-order kinetic model. In the second phase of the study, DLHF membranes consisting of PSf inner layer and PSf/PMMA outer layer were fabricated via a single-step co-extrusion technique using a triple orifice spinneret. The effect of PSf/PMMA composition (PSf:PMMA; 18:2, 15:5, 12:8, 10:10 and 8:12) on physical compatibility, molecular sieving properties and urea removal performance of the DLHF membranes were investigated. In conditions where the composition of PMMA is lesser than PSf, there was no sign of delamination between the two membrane layers. Results showed that the DLHF membrane exhibited urea adsorption capacity from 5.5 to 27.6 mg/g. In ultrafiltration adsorption experiment, the membrane with PSf/PMMA composition of 12:8 demonstrated significant urea removal of 39.2% and showed desired sieving properties towards large solute (lysozyme). In the third phase of the study, AC particles were incorporated in the inner layer of the DLHF membrane, where the effect of AC loading (0, 3, 5, 7 and 9 wt%) on the co-adsorptive urea and creatinine removal performance was investigated. The DLHF membrane with the highest AC loading (9 wt%) displayed the highest maximum adsorption capacity of creatinine of 86.2 mg/g. Besides, the membrane demonstrated the highest flux of 16.4 Lm-2h-1 and rejection of 35.3% and 73.3% for urea and creatinine, respectively. In the final phase of the study, the long-term stability of the optimized PSf/PMMA/AC DLHF membrane in continuous operation was evaluated. The membrane was tested for 3 cycles of 6-hour operation, whereby in each cycle, the membrane experienced different extents of reduction in flux and solute rejection. The membrane showed promising reusability with a high overall solute rejection recovery rate of 86% and 73% in the second and third cycles, respectively. The PSf/PMMA/AC DLHF membrane was successfully fabricated and showed collective removal of uremic toxins via the combined process of adsorption and filtration, hence becoming a potential candidate for dialysate regeneration.