The Modification of Polyethersulfone Membranes with Polyacrylic Acid

A method for obtaining ultrafiltration membranes based on polyethersulfone (PES), which react to a change in pH of the feed solution is proposed. The method consists in using aqueous solutions of polyacrylic acid (PAA) as the coagulation bath (CB). The introduction of 0.1–1.5% PAA to the CB leads to an increase in the pure water flux of the membranes from 50 up to 108–288 L m −2 h −1 depending on pH and a decrease in the surface roughness of the selective layer. The modified membranes possess enhanced hydrophilicity (a decrease in the water contact angle is 27°–33° in comparison with the control sample) and manifest pH-sensitivity and pH-reversibility. Using the example of fractionation of process waters in thermomechanical pulp mills in order to isolate hemicellulose so that the modified membranes provide higher flux (22.3–29.4 L m −2 h −1 at 1 atm) in comparison with the initial membrane (11.2 L m −2 h −1 at 1 atm) at close selectivity indices and are characterized by enhanced resistance to fouling. The irreversible flux decline ratio (DR ir ) of the membranes decreases from 76.0 down to 2.0–17.9% as a result of the modification with PAA, and the value of the flux recovery ratio (FRR) of the membranes after ultrafiltration increases from 24 up to 82–98%.