Characterization of acid-modified polyvinyl alcohol and its application to barrier-coated paper for eco-friendly food packaging

Polyvinyl alcohol(PVA) can be used as a barrier film against gases such as oxygen because of its dense thin-film structure formed by hydrogen bonding; however, its poor water/moisture resistance and low water vapor barrier properties limit its application in food packaging. Herein, oxalic acid-modified PVA(POA) was prepared and crosslinked with Ca2+ to develop a PVA coating solution with improved water resistance for application on paper-based food packaging materials. The crosslinking reaction to improve the water resistance of conventional PVA requires a long reaction time, and preparing a coating solution with crosslinked PVA is virtually impossible. However, the newly developed PVA coating solution may be suitable for the paper-coating industry because crosslinking proceeds simultaneously with drying after coating. Furthermore, in eco-friendly processes using water as a solvent, multilayer-coating is not possible with conventional PVA, whereas the developed coating is resistant to water-soluble processes through crosslinking and can be stacked on top of each other. The Ca2+-crosslinked POA layer exhibited excellent oxygen and water vapor barrier properties through an additional acrylic emulsion coating resulting in OTR and WVTR of 0.13 mL/m2·day and 0.82 g/m2·day. To evaluate recyclability of the coated paper, alkali dissociation and recyclability tests were conducted, and the results showed a repulpability rate of 99.7%, indicating that the paper pulp can be recycled. Biodegradability tests under lab-scale simulated industrial composting conditions showed 91.8% biodegradability, confirming eco-friendliness of the coated paper. Those multifunctional properties of the developed multicoated paper make it excellent additions to paper packaging, particularly for food packaging applications.