9 / 2021-05-13 19:52:18

Distribution analysis of cellulose nanofibrils in paper handsheets: Dye-labeled Method

cellulose nanofibrils,distribition,dye-labeled CNF

It is known that the fibrillated surface in refined pulps facilitated the binding of fiber and CNFs. The distribution of CNFs in different papers is important way to analyze the mechanism of CNFs strengthening paper. Due to the nanoscale and the same chemical structure to cellulosic fibers, it is difficult to directly observe the distribution of CNFs in paper sheets. Although the current detection methods such as UV-Vis spectroscopy and confocal laser scanning microscopy could provide high precision information, the CNFs labeling methods are time-consuming and require high-quality sample preparation. Herein, dye-labeled CNFs were introduced to analyze the distribution of CNFs in paper handsheets. The dye was successfully loaded on CNFs through hydrogen bonding with an environmentally friendly method. Dye-labeled CNFs were mixed with four types of pulps with different beating degrees to form paper handsheets. The colorimetric value was used to describe the distribution of marked CNFs in the paper. The results showed that with the beating degree increasing, the colorimetric values of wire side and felt side were different among the four types of paper, which indicated that distributions of CNFs in the Z-direction of papers were not uniform. This phenomenon was attributed to the fact that the primary and the outer layers of secondary walls in the unbeaten fibers were hardly broken, and the surfaces of fibers were smooth. Therefore, the colloidal adsorption of fibers with CNFs or CNFs flocs was weak. CNFs were evenly distributed in paper handsheets when the fibers were fibrillated properly and formed stable networks with CNFs by hydrogen bonding. However, excessive beating weakened the bridging ability of fibers, resulting in some unbridged fine fibers and dye-labeled CNFs near the net diverting into white water. The fine components that settle behind gradually accumulated on the felt side through mechanical interception. For the four types of pulps, the morphology of fibers obviously affected the CNFs distribution in the Z-direction of the paper handsheets. Therefore, the uniformity of CNFs distribution was largely influenced by the type and the beating degree of pulps. The study demonstrated that the dye-labeled CNFs methods is an effective way to analyze the distribution of CNFs in paper-based materials.