Role of Lignin in Hot-Pressing of Paper: Insights from Molecular Simulations and Experiments

Improving the mechanical properties of wood and paper is crucial for enhancing their performance in structural and packaging applications. A particularly effective method for increasing strength is hot-pressing, where lignin softening has been proposed as a key mechanism underlying improved fiber bonding. In this study, we investigated the deformation behavior of Norway spruce lignin across temperatures of approximately 25-300 °C and moisture contents of 0-25 wt % using molecular dynamics simulations and paper hot-pressing experiments. We simulated key mechanical paper properties, including Young's modulus, glass transition temperature, and the diffusivity of water and lignin chains. Experimental results showed a pronounced increase in wet strength above 175 °C, which correlated with lignin softening and enhanced fiber-fiber bonding in the simulations. Our findings highlight the ability of molecular simulations to elucidate the mechanisms of lignin-driven bonding and provide a foundation for optimizing the use of lignin-rich materials in various applications.