Enhancing soil water retention and plant growth with thermal crosslinked silk sericin-based hydrogel

In this study, a simple and clean crosslinking method was evaluated as a novel strategy to improve the structural stability of sericin-based hydrogels for soil water retention. The hydrogels were prepared by casting a polymer mixture of silk sericin (SS), carboxymethylcellulose (CMC), and polyvinyl alcohol (PVA). The films (HF) were heated at 90 °C for 4 h to obtain a thermally crosslinked hydrogel (HFT). The HFT was evaluated using Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM). The changes in water absorption, gel fraction, and swelling behavior after crosslinking were also analyzed. The biodegradability of the HFT and its performance as a soil conditioner were evaluated through burial tests and in vivo assays using Chilli plants (Capsicum annuum), respectively. According to the results, the thermal crosslinking of HF is the result of the formation of microcrystals in the SS and PVA fractions, as well as the development of a dense network of H-bonds. Both mechanisms promoted the formation of a more stable pore structure in the HFT, which proved to be potentially biodegradable and suitable for improving soil water retention and supporting plant growth. Regarding HFT biodegradability, rapid weight loss was noted during the first 14 days of the soil burial test. On the other hand, HFT improved the availability of soil water and nutrients, favoring leaf growth and likely chlorophyll production.