Direct determination of the degree of fibrillation of wood pulps by distribution analysis of pixel-resolved optical retardation.

We propose a new methodology for direct evaluation of the degree of fibrillation of fibrillating pulp suspensions through the pixel-resolved retardation distribution. Through simple normalization by just injecting a pulp suspension with a certain concentration into a quartz flow channel with a constant cross-sectional shape, the degree of fibrillation (i.e., the degree of bundling of cellulose molecular chains) can be directly mapped by the retardation gradation, reflecting locally high retardation (pulp fibers), smaller retardation (balloons on fibrillating pulps), and much smaller retardation close to water (dispersed nanofibers). Both the average retardation and standard deviation are found to be the direct indicators of the degree of fibrillation. We envision that the proposed methodology will become the future standard for determining the degree of fibrillation by the retardation distribution, and it will pave the way for more precise control of pulp fibrillation and more sophisticated applications of cellulose nanofiber suspensions.