Effects of CELF Pretreatment Severity on Lignin Structure and the Lignin-Based Polyurethane Properties Authors Yun-Yan Wang, Priya Sengupta, Brent Scheidemantle, Yunqiao Pu, Charles E. Wyman, Charles M. Cai, and Arthur J. Ragauskas Journal-Book Frontiers in Energy Research Year 2020