Mechanical and Sustained-Release Properties of Crosslinked Poly(vinyl alcohol)/Sodium Humate Composite Membranes

Humic acid, as a natural macromolecular aggregate rich in functional groups, offers abundant modification sites and tunable chemical functionality, making it a promising building block for three-dimensional network construction. In this study, glutaraldehyde (GA) was employed as a crosslinking agent to incorporate sodium humate (NaHA, sodium salt of humic acid from alkaline treatment) into a polyvinyl alcohol (PVA) matrix, yielding composite membranes with enhanced structural stability and performance. The results demonstrate that NaHA effectively modulates the crosslinked network, and the physical and mechanical characteristics can be readily tailored by varying the PVA/NaHA/GA ratio. Compared with pristine PVA/GA hydrogel, the inclusion of NaHA significantly influences the mechanical response, with optimal comprehensive performance achieved at a NaHA content of 7.5 wt%, corresponding to a tensile strength of 60.4 MPa and an elongation at break of 74.2%. Furthermore, the cumulative release of NaHA after two days reached 64.4%, confirming that NaHA supramolecular aggregates were stably entrapped within the PVA/GA crosslinked matrix. The release kinetics were well described by the Korsmeyer-Peppas model. Overall, the covalent crosslinking of PVA with GA, together with hydrogen-bonding associations and physical entrapment mediated by NaHA, constructed a composite membrane network. This network exhibited tunable dry-state mechanical properties and sustained NaHA release, supporting its further evaluation as a prospective candidate for agricultural mulching films.