Hydrogels with Enhanced Mechanical Properties from Starch-Rich Food Waste: Optimization by Response Surface Methodology

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, <i>N</i>,<i>N</i>'-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.