Wax Coatings for Paper Packaging Applications: Study of the Coating Effect on Surface, Mechanical, and Barrier Properties.

Abstract

The aim of this study was to comprehensively assess the effect of environmentally friendly wax coatings, including beeswax, soywax, TopScreen biowax, and a conventional water-based emulsion wax on paper for food packaging applications. A food-grade paper was bar-coated with a single layer of molten wax on both sides, varying in the coating weight, coating thickness, and wax type. Waxes were thoroughly characterized in terms of their functional groups, thermal properties, degree of crystallinity, and crystal morphology using polarized optical microscopy. Thereafter, wax-coated papers were studied in terms of their morphological, mechanical, and water vapor barrier properties. Moreover, the water and oil contact angles were measured to determine the resistance of wax-coated papers to moisture and grease penetration. Wax coatings represent 10-25% of the weight of the coated paper, with a coating thickness of 5-10 μm. Scanning electron microscopy images showed that waxes penetrated the cellulosic fibers of the paper, thereby effectively reducing its porous structure. Water and oil contact angles of the uncoated paper increased after the wax coating. Among the four waxes, beeswax-coated paper was characterized as having superior capability in improving the water vapor barrier of the uncoated paper (by ∼77%). While the percentage elongation at break (EB %) decreased for all four wax-coated papers, tensile strength (TS) and elastic modulus (E) increased, with beeswax showing the highest percent improvement in TS (by ∼26%) and E (by ∼46%). Our results suggest that paper surface modification through ecofriendly wax coatings can be utilized as an alternative for petroleum-based paper coating materials for food packaging applications.