Effect of Ce⁴⁺ pretreatment on swelling properties of cellulosic superabsorbents

Cellulosic superabsorbents are prepared by pretreating the wood pulp (WP) with Ce⁴⁺ initiator, followed by the graft copolymerization of acrylamide (AM) monomer onto Ce⁴⁺-pretreated WP (Ce⁴⁺ WP) in acidic medium and in the presence of N, N(-methylenebisacrylamide (MBAM) cross-linker. The rate of AM copolymerization of Ce⁴⁺ WP is significantly faster than that of the untreated WP. The obtained polyAM (PAM)-grafted cellulosic copolymers (PAM-g-Ce⁴⁺ WP copolymers) are alkaline-hydrolyzed to produce the water-absorbents. As PAM grafting yield increases, the absorbency increases rapidly and reaches the maximum value at a yield of 210-240%. The maximum water and saline absorbencies are around 2500 and 50 gg^-1, respectively. The optimum feed concentration of Ce⁴⁺ pretreatment on the maximum water and saline absorbencies is 5.0 × 10^-3 molL^-1. The water and saline absorbencies of the PAM-g-Ce⁴⁺ WP water-absorbents are remarkably higher in comparison with that of the untreated WP (with a similar grafting yield) due to uniform PAM-grafting onto Ce⁴⁺ WP specimen. In addition, as the amount of cross-linker increases, the grafting yield is not changed whereas the water and saline absorbencies are remarkably decreased.