Optimized Synthesis of Lignosulphonate-gpoly (acrylic acid-co-acrylamide) Superabsorbent Hydrogel Based on the Taguchi Method

Amethod for inclusion of lignosulphonate into superabsorbent hydrogels by graftcopolymerization of partially neutralized acrylic acid and acrylamide ontolignosulphonate was developed. The Taguchi method, a robust experimentaldesign, was employed for the optimization of synthetic conditions for the hydrogelsbased on water absorbency. The Taguchi L16 (4^5) orthogonal array was selected forexperimental design. Concentrations of cross-linker N,N -methylene-bisacrylamide(CNMBA), initiator potassium persulphate (CKPS) and magnesium lignosulphonate(CMgLS), neutralization degree of acrylic acid (NAA) and molar ratio of acrylamide toacrylic acid (RAM/AA) were chosen as five factors. From the analysis of variance of thetest results, the optimal conditions were obtained as follows: CNMBA 7.5×10^-4 mol/L,CKPS 4.0×10^-3 mol/L, CMgLS 2.5 g/L, NAA 60 and RAM/AA 1:1. The confirmed maximumwater absorbency of the optimized final hydrogel is found to be 1156 g/g. The hydrogelalso shows high physiological saline absorbency (122 g/g) and high Pb^2+ adsorptioncapacity (332 mg/g). FTIR analysis confirmed the graft copolymerization oflignosulphonate with acrylic acid and acrylamide. SEM Photograph showed a hydrogelof porous sponge structure with increased surface area. The thermogravimetricanalysis indicated the hydrogel has good thermal stability with initial decompositiontemperature of about 320°C and maximum decomposition temperature of about 360°C.