Preparation and characterization of polyvinyl alcohol/sodium lignosulfonate/black rice anthocyanin extract agricultural film for monitoring soil pH

This study focuses on the formulation of polyvinyl alcohol (PVA)-based films with pH-sensitive properties and ultraviolet (UV) resistance by incorporating sodium lignosulfonate (LS) and varying concentrations of black rice anthocyanin extract (BRE) into PVA matrix. The films were characterized through Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), tensile test, water vapor permeability (WVP), and ultra-violet-visible (UV-vis) spectroscopy. The results indicated that BRE and LS effectively formed strong hydrogen bonds with PVA, leading to reduced film crystallinity, improved mechanical properties, and lowered WVP as the BRE content increased. The addition of LS and BRE improved the UV resistance of the films, and BRE imparted films with excellent pH-sensitive properties. Among the film variants, the PVA/LS/BRE film containing 1 wt% BRE exhibited excellent mechanical performance, boasting an elongation at a break of 360.66 % and a strength of 35.68 MPa. Additionally, soil pH visualization holds significant potential within agriculture. In this study, the PVA/LS/BRE film containing 2 wt% BRE exhibited minimum UV transparency (0.9 %) and displayed the most distinct color response across varying pH environments. Therefore, the PVA/LS/BRE film containing 2 wt% BRE excelled in both UV resistance and pH sensitivity, positioning it as the most suitable material for the development of agricultural films integrated with soil pH monitoring capabilities.