Full title: Production of High Solid Nanocellulose by Enzyme-Aided Fibrillation Coupled with Mild Mechanical Treatment
Jaakko Pere, Tekla Tammelin, Piritta Niemi, Martina Lille, Tommi Virtanen, Paavo A. Penttilä, Patrik Ahvenainen, and Stina Grönqvist
Conclusions of the work: This work introduces a novel nanocellulose grade produced via enzymatic action under gentle mechanical mixing. The nanocellulose product and the corresponding process are designated as high-consistency enzymatic fibrillation of cellulose, abbreviated as HefCel. We hypothesize that the fiber–fiber friction at low water content generates shear forces that in combination with the processive action of CBH induce surface fibrillation via a peeling-type of reaction. Through the peeling-type of action, a pastelike fibril network is formed with a high yield (∼85%). The dimensions and size distribution of the fibrils based on high-resolution microscopy imaging suggest that the HefCel grade falls into a nanocellulose category of microfibrillated cellulose or cellulose microfibrils (CMFs). SEM and AFM imaging of the lateral width of the fibrils is typically between 15 and 20 nm. The intriguing finding is related to the finest fraction of HefCel, whose size and rodlike shape resemble the cellulose crystallites. Extensive morphological characterization by solid-state NMR and X-ray diffraction reveals that synergetic actions of CBH and EG enzymes induce peeling-type of reactions to take place on the fiber surface and that the crystallinity index is slightly increased as fibrillation proceeds due to partial hydrolysis of less-ordered cellulose and xylan caused by the xylanase side activity. Our approach to producing nanocellulose at a high solid content in a much less energy-intensive manner puts forward the sustainable production of nanocellulose for novel application areas beyond textiles, packaging, and papermaking.
Keywords: Nanocellulose, Nanofibers, Organic polymers, Pulp, Cellulose
Reprinted with permission from ACS Sustainable Chem. Eng. 2020, 8, 51, 18853–18863. Copyright 2020 American Chemical Society.
