Crosslinked polyvinyl alcohol with boric acid and its application for high barrier packaging coatings

The development of high-barrier paper is currently a major challenge in packaging science. Among polymer coating materials, polyvinyl alcohol (PVA) has been the most commonly used polymer for high barrier purposes. However, PVA has poor water-resistance, which is attributable to the abundant hydroxyl groups in its structure; thus, this limits its application in the packaging industry. With this concern, the introduction of boric acid (BA) as a crosslinker along with hydrochloric acid (HCl) as a crosslinking trigger into the PVA matrix could result in a crosslinked structure in the matrix, which might improve the barrier and water-resistance properties. This study evaluates the chemical, mechanical, and barrier properties of papers coated PVA/BA/HCl. To optimize the concentration of BA and HCl, the PVA coatings were first characterized in the form of the film while optimal coatings were coated on paper using the solution casting method. High barrier paper and crosslinked PVA coatings were characterized to identify the effect of crosslinking density on the properties of paper coated PVA/BA/HCl using Nuclear magnetic resonance (NMR), X-ray diffraction (XRD), differential scanning calorimetry(DSC), Field emission scanning electron microscope (FESEM), Water contact angle, Water vapor transmission rate (WVTR) and Oxygen transmission rate (OTR) and water-resistance test. DSC and XRD results showed a reduction in the crystallinity of PVA film with increasing the concertation of HCl. OTR, WVTR, water-resistance results revealed that the incorporation of optimal concentration of BA and HCl led to a remarkable enhancement of barrier properties of paper coated PVA/BA/HCl. Therefore, results highlighted that the paper coated PVA/BA/HCl could be an eco-friendly alternative to conventional high barrier packaging for use in the food and cosmetics industries.