Roles of lignin in conversion of poplar via pyrolysis, hydrothermal carbonization, and activation - Chao Li; Yunyu Guo; Yahan Zhang; Yuewen Shao; Tao Wei; Shu Zhang; Obid Tursunov; Baoqiang Lv; Jianhong Zhu; Xun Hu (Fuel, 2026)