Adding Value to Spruce Bark by the Isolation of Nanocellulose in a Biorefinery Concept
Barbara Rietzler, Monica Ek
Abstract
It is shown that the isolation of nanocellulose in a biorefinery approach adds value to the bark and its components. The utilization of a chlorine-free delignification and the preparation of cellulose oxalate in a solvent-free process are an economic and environmentally advantageous way of applying the biorefinery concept and to use the bark in a sustainable way. The properties of cellulose oxalate from delignified bark were determined, and the morphological structure of the isolated nanocellulose was characterized. The chemical composition and thermal properties were monitored during the extraction and separation steps, and it was possible to prepare cellulose oxalate in a yield of 82% with a degree of substitution of 0.3 and surface charge of 1.53 mmol g–1. The isolated nanocellulose was found to be a mixture of rodlike nanocrystals and nanofibrils. Initial thermal analysis of the isolated nanocellulose shows promising properties. The results show that the bark is a potential inexpensive source of high-value nanocellulose that can be isolated in high yield, for use in cosmetics or as reinforcement in nanocomposites. Since the isolated nanocellulose contains two different morphological types, it can be used where the properties of both cellulose nanocrystals and cellulose nanofibrils are required.