Isolation of nanocellulose from spruce bark
The interest in the forest industry as a bio-based sustainable resource for renewable materials, chemicals and fuels has increased over the past decade. A main waste product in this sector is the tree bark, which is nowadays mainly used in combustion or applications such as mulch for the garden. 1.5 million tons are generated in Sweden yearly. In this work, value added products are isolated from the bark of Norway spruce such as nanocellulose. Economic but environmentally advantageous methods of separation and extraction were investigated to isolate the non-cellulosic compounds without affecting the cellulose. Subcritical water extraction was used to extract the hemicelluloses and pectic material, followed by peracetic acid delignification of the bark fibers. The delignified bark fibers were converted in a solvent-free reaction to cellulose oxalate. The chemical compositions and properties, such as thermal degradation and crystallinity of the fibers after the individual steps have been evaluated. The thermal degradation of the cellulose oxalate was found to start around 171°C which is in the range of the cellulose oxalate prepared from wood pulp. From sonication of aqueous suspensions, it was possible to isolate nanocellulose in good yield. The morphological properties of the nanocellulose will be investigated and compared to the results obtained for nanocellulose from wood. The cellulose oxalate is expected to have good reinforcing properties for the preparation of composites and the nanocellulose isolated can be used to prepare thin films or additives in different applications.