Low-temperature thermal drying-induced pore expansion effects of cellulosic fibers

Thermal drying makes cellulosic fibers shrink, resulting in pore collapse and degraded fiber performance. However, in this work, the pores of cellulose fibers expanded in the later stage of low-temperature thermal drying by regulating the fiber stacked structure before drying, which was called “low-temperature pore expansion effects”. The results showed a high content of lignin was required because there were no low-temperature pore expansion effects during the drying process of low lignin-containing cellulosic fibers. Three-dimensional fiber stacked structure was also necessary because cellulose fiber materials with two-dimensional stacked structure, such as paper, had no pore expansion effects. The pore expansion effects first strengthened and then weakened with increasing temperature, and the optimum temperature was 60 °C. According to the results, the pore expansion effects included the pore shrinkage period and pore expansion period. Finally, a possible lignin-cellulose phase separation mechanism was proposed to explain this phenomenon. This work reveals the special ultrastructural transformation of cellulosic fibers under low-temperature drying, providing a reference for precise regulation of the properties of dried fibers.