To achieve optimal recovery and value-added utilisation of cellulose in peanut shells, the cellulose in peanut shells was first extracted using the sodium hydroxide-sodium chlorite method. Then, cellulose hydrogel was prepared by graft copolymerisation using N, N’-methylenebisacrylamide as the cross-linking agent, sodium persulfate as the initiator, and acrylic acid as the monomer. Orthogonal optimisation experiments were designed to obtain optimal process parameters for hydrogel preparation with the cellulose dosage of 0.40 g, initiator dosage of 0.20 g, polymerisation temperature of 70°C, cross-linking agent of 0.25 g, and monomer dosage of 3.0 mL. The effect of initiator dosage on hydrogel synthesis was the most significant, followed by monomer dosage and reaction temperature. Characterisation using X-ray diffraction analysis and scanning electron microscopy revealed that the hydrogel was amorphous and exhibited a distinct three-dimensional double network structure. Hydrogel swelling kinetic analysis showed that the hydrogel swelling process was divided into three stages, and fitted the Schott secondary swelling kinetic model. The prepared hydrogel had a good adsorption effect on methylene blue; the adsorption of methylene blue by the hydrogel was 1.259 mg/g at 25°C when the initial concentration of methylene blue was 5 mg/L. The adsorption kinetics of the hydrogel fit the pseudo-first-order kinetic model, pseudo-second-order kinetic model, Eovich model and particle diffusion model. The best fitting effect was obtained with the pseudo-second-order kinetic model. The adsorption isotherm analysis of methylene blue on hydrogel showed that the adsorption process was consistent with Langmuir and Freundlich models. The correlation coefficient of the Freundlich isotherm model was higher, indicating that the adsorption of methylene blue on hydrogel was mainly chemisorption.

In this study, hydrogels were prepared from municipal sludge to recycle and realize the value-added utilization of the carbon components in this abundant waste material. The carbon sources were extracted from the municipal sludge using synthesised nano CaO2 as an oxidant, and the carbon sources were graft copolymerised with acrylic acid monomer using N, N′-methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator. The factors influencing the hydrogel preparation were investigated by single-factor experiments. Based on the results of the single-factor experiments, a hydrogel with a swelling ratio of up to 19768.4% at 12 h was prepared with an oxidant dosage of 0.20 g, a monomer dosage of 5.8 g, a neutralisation degree of the monomer of 70%, an initiator dosage of 0.15 g, and a crosslinking agent dosage of 0.15 g. The hydrogel preparation conditions were optimized using the response surface method, and the interactions between the different reaction conditions were analysed to obtain the best preparation conditions. X-ray diffraction results showed that hydrogels were amorphous in structure. Scanning electron microscopy images showed that the SiO2 particles from the sludge acted as crosslinking points between different layers of hydrogel chains. The crosslinking polymerisation and crosslinking agent worked together to form hydrogels with an inorganic-organic double network structure, and this structure was highly stretchable, resulting in hydrogels with good swelling properties.

Food waste starch (FWS) is abundant, inexpensive, and biodegradable, making it an ideal feedstock for resource valorization. In this study, FWS was employed to fabricate an eco-friendly starch-based hydrogel via free radical grafting and cross-linking polymerization, with compressive strength selected as the primary performance indicator. Single-factor experiments combined with response surface methodology were used to optimize the feedstock-to-liquid ratio, reaction temperature, and formulation, where acrylamide (AM) served as the monomer, N,N′-methylenebisacrylamide (MBA) as the cross-linker, and sodium persulfate (SPS) as the initiator. Under the optimal conditions (feedstock-to-liquid ratio 1:5, reaction temperature 69.395 °C, AM 5.6 g, MBA 0.014 g, SPS 0.561 g), the hydrogel exhibited a compressive strength of 5.15 MPa. Mechanical testing revealed a compressive modulus of 3.12 MPa, tensile strength of 0.03 MPa, and elongation at break of 1005.30%. In low-frequency cyclic compression testing (LFCTC), pronounced energy dissipation occurred in the first cycle, while subsequent curves largely overlapped, indicating excellent structural stability and shape recovery under repeated loading. Fourier transform infrared spectroscopy (FTIR) confirmed the successful grafting of AM onto starch chains, X-ray diffraction (XRD) showed disruption of the semicrystalline structure into an amorphous matrix, and scanning electron microscopy (SEM) revealed a dense and continuous three-dimensional network. These results demonstrate that starch-rich food waste can be converted through a simple and controllable chemical route into functional hydrogels with both strength and ductility, opening a promising pathway for its high-value utilization.