Effect of plasticizers on AFM features, functional properties and mechanical properties of guar gum-neem gum composites for packaging applications

Five guar gum-neem gum biofilms plasticized with glycerol and PVA were prepared. The two polymers were crosslinked by thermal protocol using GA or MBA crosslinkers. Two ratios of ZnO were incorporated in order to enhance the antimicrobial properties of the prepared biofilms. The morphology of some membranes was verified through SEM while the topographic features of the five membranes were verified through the AFM. The AFM finding compared were with the original samples (with no plasticizers) in order to investigate the effect of plasticizing materials on the consistency and evenness of the membranes. Functional testing revealed clear effects of plasticization: water vapor transmission rate (WVTR) and water solubility (WS) increased, while water holding capacity (WHC) decreased slightly (e.g., from \~33% in GG2-NG1-GA to \~30% in P-GG2-NG1-GA). Crosslinking chemistry also played a role, with MBA-crosslinked films showing lower WS and WVTR than GA-crosslinked ones, reflecting denser network formation. The incorporation of ZnO reduced WS but raised WVTR, suggesting filler–matrix interactions that improved water resistance while modifying diffusion pathways. Mechanical testing highlighted strong differences: P-GG4-NG1-GA displayed the best balance of strength and ductility (ultimate ≈ 13 MPa, break strain ≈ 128%), whereas MBA + ZnO films were less extensible (ultimate ≈ 5 MPa, break strain ≈ 30%). Overall, the addition of glycerol and PVA effectively regulated deformation, preserved flexibility, and produced workable biofilms with tunable barrier and mechanical properties. These findings confirm the potential of plasticized GG–NG–ZnO composites as biodegradable films for sustainable packaging and related applications.