Sustainable starch-based barrier coatings for packaging applications

Starch, as one of the most abundant, sustainable and low-cost commercial biopolymers, has versatile applications in many industries (e.g. food, paper, packaging, construction, etc.). Herein, we reported the synthesis of starch-based polyelectrolyte complexes (SPECs) barrier coatings through a straightforward, industrially scalable shear mixing process. The formation of SPECs was significantly impacted by molecular weight (MW) and charge density of starch polymer chains, resulting in SPECs with different particle sizes, particle morphologies and rheological behaviors. Larger MW and higher charge density contributed to the formation of stiff and entangled starch macromolecular network modulated by different intermolecular interactions, thus leading to a densely packed structure in the coating materials. High MW SPEC coated paperboard exhibited uniform, defect-free surface morphology, improved mechanical properties (18% and 21% increase in tensile strength and Young's modulus, respectively), and excellent barrier performance against water vapor (40% lower than uncoated paperboard), grease (Kit number of 12), and oil penetration (Cobb₆₀: 1.85 g/m²). Such cost-effective, biodegradable and ecologically compatible SPECs barrier materials hold high potential as sustainable alternative coatings for paper and paperboard packaging applications.