Short-term thermal drying-induced pore expansion effects of cellulosic fibers and its applications

In this work, a short-term thermal drying procedure of cellulosic fibers was designed to present pore expansion and increase via lignin-cellulose phase separation. The applicability of this procedure was studied by using four never-dried cellulosic fibers with different lignin contents and tree species (poplar, eucalyptus, bamboo) as raw materials. This procedure significantly improved the properties of high lignin containing fibers, especially pore parameters and water retention capacity. When heated at 150 °C, the increased yields of fiber properties reached 38% (specific surface area), 26.8% (pore volume), 30.5% (average pore size), and 29.4% (water retention value), respectively. Based on its most critical change, this phenomenon was called “thermal drying-induced pore expansion effects”. Key factors for pore expansion effects were temperature, time, lignin content, and the stacked structure (i.e., fiber arrangement structure). Pore expansion effects could be used to enhance pore related applications, such as lignocellulosic enzymatic hydrolysis and papermaking. Pore expansion effects under heating at 105 °C for 10 min increased enzymatic digestibility at 6 h by 11%. After the same treatment, the water absorption and bursting index of papers made of the treated fibers were increased by 9.09% and 40%, respectively. The pore expansion effect proposed in this study expands the drying research of cellulosic fibers and provides a reference for using drying to enhance biomass conversion and improve the properties of cellulose materials.