Synthesis, characterization, and application of biodegradable superabsorbent gels based on carboxymethyl chitosan-modified sodium lignosulfonate

Abstract

In this study, a novel three-dimensional bio-based superabsorbent hydrogel, SL-P(AA-AMPS)/CMCS, was synthesized via freeze-drying using sodium lignosulfonate (SL) with rigid phenylpropane structures as the bio-based framework, carboxymethyl chitosan (CMCS) enriched with hydrophilic groups (–OH, –COOH, and –NH₂) as the hydrophilic modifier, and acrylic acid (AA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as monomers. Polymerization was initiated by ammonium persulfate (AP) and crosslinked with N,N’-methylenebisacrylamide (MB). The hydrogel’s structure, morphology, and absorption properties were systematically characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Results revealed a uniform porous structure with an average pore size of 5.8 μm. Absorption capacities in deionized water and 0.9 % NaCl solution reached 1132.9 g/g and 127.9 g/g, respectively, surpassing commercial diaper fillers (273.3 g/g and 61.5 g/g) and feminine hygiene products (223.5 g/g and 45.8 g/g). Under pressurized conditions (2068 Pa), absorption values remained high at 125.7 g/g (deionized water) and 24.0 g/g (0.9 % NaCl solution). The hydrogel exhibited exceptional water retention, retaining 88.8 % and 85.8 % of absorbed water after 8 h at 40 °C and 60 °C, respectively. Swelling kinetics followed a pseudo-first-order model (R² > 0.99), achieving equilibrium within 600 s (deionized water) and 60 s (0.9 % NaCl solution). Biodegradation tests demonstrated a 47.5 % degradation rate in soil after 28 days, significantly exceeding that of non-bio-based P(AA-AMPS) (3.7 %). Application tests highlighted superior absorption capacities for artificial urine (82.4 g/g) and blood (179.2 g/g), outperforming conventional hydrogels by 3.3- and 7-fold, respectively.