Role of Lignin in Hot-Pressing of Paper: Insights from Molecular Simulations and Experiments
Patric Elf, Amanda Mattsson, Antti Paajanen, Jukka A. Ketoja, Gunilla Pettersson, José Luis Sanchez-Salvador, Ángeles Blanco, Carlos Negro, Per Engstrand, Mikael S. Hedenqvist, Fritjof Nilsson
Abstract
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.