Investigating the Usability of Alkali Lignin as an Additive in Polysulfone Ultrafiltration Membranes

Abstract

The effects of natural and synthetic polymer additives on the properties of ultrafiltration membranes were studied. The use of NaOH to remove the residual additive remaining in the membranes during coagulation was also investigated, as was the effect of NaOH post-treatment relative to membrane performance. To evaluate the residual additives present, ATR-FTIR was used. Contact-angle analysis and water-absorption experiments were used to examine the hydrophilic properties of the prepared membranes. Membranes modified with lignin (Lig) were found to absorb more water (94% water uptake) than other membranes. In general, the contact angles were found to be low for membranes treated with NaOH. Membrane permeability was greatest in lignin_polysulfone (Lig_PSf), followed by polyvinylpyrrolidone_polysulfone (PVP_PSf), and with polyethylene glycol_polysulfone (PEG_PSf) the least permeable, similar to the trend observed in water uptake. A ‘Robeson plot’ analogue showed that Lig_PSf membranes had high separation factors regardless of the size of the solute being rejected. This study indicates the feasibility of using cheap, readily available additives to increase the performance of membranes.

Keywords

• Additive
• Lignin
• Biopolymers
• Polysulfone
• Synthetic polymers