Preventing Water-Induced Mechanical Deterioration of Cardboard by a Sequential Polymer Treatment

Paperboards and corrugated cardboard are some of the most used products in packaging today. Because of their geometry, i.e., undulations, they are mechanically robust and can sustain a significant amount of weight. However, exposure to water or humidity is highly destructive toward cardboard mechanical properties. Water-soaked corrugated cardboard can easily collapse with irreversible shape distortions. Various treatments have been developed to render cardboard hydrophobic including wax layers and nanoparticle treatments. However, not all hydrophobic cardboard mechanical properties can necessarily withstand water immersion or high humidity. In this work, we utilize hydrolysis-resistant polyester-based thermoplastic polyurethane (TPU) to prevent mechanical deterioration of water-immersed and humidity-exposed cardboard. TPU-treated wet cardboard featured enhanced Young modulus, tensile stress, and elongation at break by 226%, 727%, and 116%, respectively, compared to plain cardboard. Results outperformed a similar treatment with a hydrophobic silicone resin indicating that a hydrophobic polymer is not essential for preventing mechanical deterioration of cardboard against water. The sequential treatment by these two polymers was also very effective in the wet case with 276% enhancement in Young's modulus and 950% boost in tensile stress. The role of silicone resin in the sequential treatment was to form durable and stable hydrophobic surface properties on the cardboard.