Plasma-assisted surface engineering for value added in starch bioplastics: A study on enhanced surface properties and natural dye immobilization

This study examines the enhancement of starch-based bioplastic sheets for immobilizing natural dyes (ND) using plasma processes. The effects of poly(vinyl alcohol) (PVA) as a binder for ND were also assessed. Starch substrates were treated with air plasma, air plus 1,7-octadiene (OD) plasma, and air plus 2-methy-2-oxazoline (Ox) plasma before immobilizing curcumin and telang NDs, followed by an OD overcoating. Surface morphology, wettability, chemical composition, tensile strength, and surface charge were analyzed. Results showed improved wettability and dye immobilization, particularly for telang with a PVA binder and plasma treatment. OD overcoating prevented dye leaching. Air plasma reduced, while OD plasma maintained the starch's negative charge. XPS analysis indicated increased oxygen and nitrogen presence after air plasma and enhanced aliphatic carbon from OD overcoating. Tensile strength was largely unaffected, but elongation at break was reduced, especially after air and OD plasma treatment.