Sustainable co-production of fibers and biochemicals from softwood bark: methanol pre-extraction and soda cooking

Burning wood bark at pulp mills generates biogenic CO 2 emissions, affecting also the aquatic organisms via wastewater treatment plant. With the limited nature of forest resources and the increasing energy self-sufficiency of mills, developing new ways of valorizing bark is imperative. The quality of bark-origin fiber is considerably better than its counterpart xylem, but bark contains more chemically reactive components. Efficient valorization of wood bark is currently hampered by lack of tailored methods of cooking and biochemicals recovery. This study aims to recover fibers and biochemicals from bark and assess their fiber's mechanical properties. Methanol pre-extraction is designed to recover 8 w /w% extractives in their unreacted form prior to cooking. Compared with bark and its resulting pulp, methanol pre-extraction reduced extractive concentrations by 66% and 75%, respectively. Surface of fiber made from post-extracted bark is clearly cleaner than that of the reference ones. Under same H-factor, the 28 w /w% pulp yield of the bark obtained with soda cooking was similar to kraft cooking. To our knowledge, effective delignification using soda is for the first time discovered. Paper sheet made from unrefined bark pulp provides 20 times higher inter-fiber bonding and 2 times higher tensile strength than sheet made from counterpart wood pulp. Valorizing these unique fibers, biochemicals, and other bark components instead of burning them for energy could create economic value for the forest industry while utilizing 200 million cubic meters of bark currently wasted globally. This approach could provide a carbon-negative alternative to synthetic textiles and fossil-based chemicals.