Development of quality evaluation method for cellulose fibrils

Highly fibrillated cellulose, including cellulose micro or nanofibrils (CMFs or CNFs), has been extensively investigated. However, its morphological properties defined as the degree of fibrillation vary over time according to the fiber sources and preparation methods. In this study, a facile method for evaluating the degree of fibrillation was developed using a conventional Canadian standard freeness (CSF) tester and the obtained values were called drainage volumes (DVs). The standard screen used in the CSF test is used to retain fibers and fibril, but the screens in the DV test to fractionate the fibrils by their size. Two DVs of the highly fibrillated cellulose were obtained using two special mesh size screens in the DV test. The differences between two DVs were found to have a linear relationship with the degree of fibrillation and the average fibril width of the highly fibrillated cellulose. They also exhibited a linear relationship with the crystallinity, degree of polymerization and the mechanical properties of the fibril-based sheets. Two commercial CNFs produced by paper mills with different wood sources were evaluated using the developed method. Their DV differences enabled the estimation of their degree of fibrillation, with which the average fibril widths and physical and mechanical properties were predicted and they were found to be well matched.